MXPA95005308A - Molding apparatus by sopl - Google Patents

Abstract

The object of the invention is to achieve an economical manufacture of a preform transport mechanism, of simple construction, for a blow molding apparatus, for the biaxial stretching of the hollow molded parts, such as PET bottles, from the preforms . The molding apparatus is provided with a linear transport line for transporting the preforms (P), and the transport line comprises: a beam (81), on which are supported a plurality of transport members (82), a mechanism of transport (83), and a lifting mechanism (84) for the beam. The transport members (82) that are on the beam, move repeatedly back and forth at a constant speed pace, by means of the mechanisms. A preform holding / releasing mechanism (85) is actuated in synchronism with the movement, so that while the respective transport members (82) are made to advance from backward positions, the preforms are delivered to the respective transport members (82). As the preforms P can be transported along the transport line, only by the movement of the beam (81), which supports thereon the plurality of transport members (82), back and forth to a constant step,

Description

r MOLDING APPARATUS BY BLOWING TECHNICAL FIELD The invention relates to a blow molding apparatus 5, suitable for the molding of PET bottles and the like. More particularly, the invention relates to an improvement in the carrying mechanism of the preform of a blow molding apparatus. The invention also relates to a heating control system, which is used in a blow molding apparatus for radiation heating of the preforms, up to a temperature suitable for blow molding.

BACKGROUND OF THE INVENTION A hollow molded part, such as for example a PET bottle, is molded by heating a cylindrical preform extrusion, molded from a thermoplastic resin in order to have an opening in a The end and a closed bottom in the other, and then the preform is biaxially stretched until it has cooled to a suitable molding temperature. The blow molding apparatus that is used is constructed in order to carry out these processes on the preforms, as These are carried along a conveyor line, at a constant speed of passage. A blow molding apparatus of this type is disclosed in JP-B 1-17855. The apparatus shown by this publication has: a preform carrier line, closed on four sides; and shaped block carrying units, placed on this line, which are fed successively at a constant passing speed. The carrier units are equipped with transport members to immobilize the preforms by insertion into their openings, and the preforms are carried by the conveyor units, with the carrier members inserted therein. Each conveyor unit receives a preform, in a preform loading unit, passing through a heating section and a stretch molding section, and delivers the molded parts to a withdrawal section, and then returns, being already empty , to the loading section of preforms. Circular conveyor lines are also used. The prior art transport system for blow molding apparatus includes the so-called closed conveyor line, which has a large number of preform transporting members, placed at a constant pitch, and the preform transporting members are fed successively to a constant step. Each preform carrying member carries a preform through a heating section and a stretch molding section, located along the conveyor line, and then returns to the preform loading section, being already empty, after having passed through the stretch molding section and delivering the molded parts to the removal section. In addition, the conveyor members can be rotated in the heating section to provide uniform heating of the preforms, by radiant heat coming from a single direction. In case of using this type of closed conveyor line, the conveyor members have to return to their initial position being completely empty, after the removal of the molded part. This is not an efficient operation, since there is a proportional loss of operation. In addition, as conveyor members traveling on the line need to be equipped additionally with rotating systems to rotate the preforms, their systems are complicated. In addition, fasteners are required to hold the preforms constantly to the carrying members traveling on the line. On the other hand, in the prior art, the conveyor members move, and the supply of molding air, etc., is carried out in relation to the preforms held by the conveyor member, in the molding and stretching section. Therefore, it is necessary to provide the conveyor members with systems for blowing air. Conveyor member systems also tend to increase complexity at this point. On the other hand, the heating of the preforms in the blow molding apparatuses of the prior art, is carried out in general by placing the radiant heating element of an infrared heater, or the like, along the conveyor line of the preform, and heating the preforms transported uniformly, from the side, as they revolve around their axes. Since radiant heating from the outside causes the outer surface of the preform to heat up faster than the internal surface, its temperatures change, as shown by the curves Al (external surface temperature) and A2 (surface temperature) internal), from figure 10. As can be seen from these curves, the heating increases the temperature of the external surface at a higher temperature. As the stretch ratio of the inner surface is greater, the temperature of the inner surface has to be made higher to ensure molding and stretching. After heating, the preform is allowed to stand for cooling, until the difference in temperatures between the inner and outer surfaces is reversed, after which the molding and stretching is carried out. As the external surface is heated in this way more rapidly during the radiant heating of the preform, there is a risk, in spite of the fact that the heating is carried out properly, that the outer surface can be degraded by overheating before the inner surface has reached a properly hot state. Overheating the preform also increases the time it takes for the preform to cool, until the temperature of the inner surface is higher than that of the outer surface, which is the temperature state suitable for molding and stretching. An increase in the cooling time is not desirable because the efficiency of the molding line decreases. Furthermore, the molding and stretching of a PET bottle or the like, from a preform, requires that the amount of stretching be different in different portions of the preform, depending on the shape of the molded product. As a result, the molded part can be formed with thin and thick local portions. It is therefore necessary to properly regulate the temperature state of the preform during the molding and stretching operation.

EXPOSITION OF THE INVENTION In view of the foregoing points, an object of this invention is to propose a blow molding apparatus, equipped with a conveyor system having a simple structure and which can be manufactured at low cost. Another object of the invention is to propose a blow molding apparatus equipped with a heating system, which allows radiant heating of the preforms, without overheating the external surface thereof. Another object of the invention is to propose a blow molding apparatus, equipped with a temperature regulation system, which allows the preforms to reach a state of temperature suitable for molding, in a short time after radiant heating. Another object of the invention is to propose a blow molding apparatus that optimizes the molding and stretching operation of the preforms, by carrying out a suitable heating thereof. To achieve the above objectives, the blow molding apparatus of this invention comprises: preform heating means for radiant heating of cylindrical preforms having an opening at one end and a closed bottom at the other end; molding and stretching means for biaxial molding and stretching of the heated preforms so as to form hollow moldings in a prescribed manner; and preform conveying means for intermittently conveying the preforms, through the heating means to the molding and stretching means, at a prescribed speed of passage. The conveying means are constituted in order to include: a linear member extending in the conveying direction of the preform; several preform carrying members supported by the linear member, which are placed at regular intervals in the transport direction of the preform, and which are equipped with a conveyor system having a simple structure and which can be manufactured economically. Another object of the invention is to propose a blow molding apparatus, equipped with a heating system and allowing radiant heating of the preforms, without overheating the external surface thereof. Another object of the invention is to propose a blow molding apparatus, equipped with a temperature regulation system, which allows the preforms to reach a state of temperature suitable for molding after a short time after radiant heating. Another object of the invention is to propose a blow molding apparatus that maximizes the efficiency of the molding and stretching of the preforms, carrying out a suitable heating thereof. To achieve the above objectives, the blow molding apparatus of this invention comprises: a preform heating means, for the radiant heating of cylindrical preforms having an opening at one end and a closed bottom at the other end; a molding and stretching means for biaxially stretching the molded parts of the heated preforms in order to form hollow molded parts in a pre-established manner; and a preform transport means for intermittently transporting the preforms, through the heating means and the molding and stretching means, at a prescribed speed of passage. The heating means is constructed in order to include: a linear member extending in the transport direction of the preforms; various preform carrying members supported by the linear member, and placed at regular intervals in the conveying direction of the preform, and which are capable of being inserted into the openings of the preforms; and a mechanism adapted to move the linear member to a retracted position in a backward step, causing it to descend from its initial position to a lowered position where the conveyor members are out of contact with the preforms, and moving it from its retracted downward position in an opposite direction, towards the direction of transport, and then raising it to then move it forward from the retracted position to the initial position; and a clamping / releasing mechanism, adapted to hold the preforms while the transport members supported by the linear member are moving from the initial position to the retracted position, and to release and deliver the preforms to the transporting member, upon arrival to the retracted position. With this configuration, the feeding operation of the conveyor members supported by the linear member, consists simply of moving them forward and backward in the transport direction, to a degree corresponding to a feeding step. In addition, since it is enough that the preform holding / releasing mechanism holds / releases the preforms in a fixed position, the conveyor means is simple and economical in its manufacture.

The clamping / releasing mechanism can be replaced in order to have a pair of clamping plates, left and right, placed in the transport direction, and preform clamping sections that are formed at intervals in the transport direction, equal to intervals of the transport members, when the clamping plates close to each other, and which fasten the preforms during the closing of the clamping plates, and release the preforms during the opening of the clamping plates. In this case, the preforms are transported by the transport members and simultaneously can be held by the closing of the pair of clamping plates, and the preforms can simultaneously be delivered to the transport members by the opening of the clamping plates. Instead of using a pair of clamping plates of the aforementioned type, it is also possible to adopt a configuration comprising: several groups of rollers placed at intervals, in the transport direction, equal to the intervals of the transport members; and a roller movement mechanism, for moving the rollers of the individual groups: in close proximity to each other for holding the preforms, and moving away, for releasing them. For the heating means of the invention, it is possible to adopt one of the type comprising thermal sources placed along a conveyor line of preforms of the conveyor means, one of the sources of radiant heat is placed in a position corresponding to all stop position of the preform. When the heating means of this configuration is used, the preforms are transported at a constant pitch and heated radially in the stop or lift positions. In other words, it heat intermittently. In comparison with the case of continuous radiant heating, the increase in the temperature of the external surface of the preform is suppressed, and the difference between the temperatures of the internal and external surfaces is less. He overheating of the outer surface of the preforms can therefore be avoided. In addition, the cooling time at a temperature suitable for molding is shortened. / ', A heating medium can be used near infrared heater, or similar. In this case, it suffices that the filament serving as the heating element has spiral sections, in the stopping positions of the preform, and that it extends straight in the remaining positions. It is preferred to provide a preform rotating means for rotating the preforms carried by the preform transport means around their axes, and causing the preform rotating means to rotate the preforms in order to vary the orientation of the portion. of external peripheral surface, towards the heating source, between adjacent stop positions. As this causes the radially heated portion of the outer peripheral surface of the preform to change in a progressive manner, it allows uniform radiant heating of the entire outer peripheral surface of the preform. This invention comprises an air cooling means for cooling the preforms, after radiant heating, by blowing air thereon, the air cooling medium cools to each preform at a point at the time subsequent to that in which its temperature has passed a peak value. By rapidly decreasing the temperature of the outer surface of the preform in this way, it is possible to establish in a short time after heating, a state of temperature at which the temperature of the internal surface is higher, namely an adequate temperature state for molding. For this, it is preferred to cool the preform by blowing air thereon, in the axial direction of the preform. By this it is possible to cool the preforms uniformly and with good efficiency. On the other hand, the invention is characterized in that it allows the molding and stretching operation to be carried out adequately in the molding and stretching medium.; and in that a temperature adjusting means capable of adjusting the heating temperature of the preform is placed on the transport line, immediately in front of the molding and stretching means. For example, a means is provided that uniforms the temperature in order to adjust the preforms to a temperature distribution suitable for the stretch and molding temperature, by blowing air over the entire preform, this air containing a humidity and a temperature adjusted to a prescribed interval. With this, the preforms can be adjusted precisely to the optimum temperature necessary for the stretching and molding operation, immediately before reaching it. In addition, in order to allow the adjustment of the degree of stretching and the like, in different portions of the preforms, it is preferred to provide a temperature-changing imparting means that imparts a temperature change in local portions of the preforms, by blowing air locally in the preforms. preforms, this air containing a humidity and a temperature adjusted to a prescribed range, this after having adjusted the preforms to a uniform temperature. Instead of blowing air locally on the preforms, it is possible to impart a change of temperature, putting them in contact with a temperature conducting part, adjusted to a prescribed temperature. As this makes it possible to adjust the degree of stretching in different portions of the preforms, during molding and stretching, it has the advantage of allowing different portions to acquire an ideal thickness after the mold.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side view showing the structure of a blow molding apparatus, which is a first embodiment of the invention. Figure 2 is a cross-sectional view of the apparatus of Figure 1. Figure 3 is a partial plan view showing a pair of clamping plates constituting a preform clamping / releasing mechanism, of the apparatus of Figure 1 Figure 4 is a set of diagrams explaining the transport operation of the apparatus of Figure 1, wherein (A) is an explanatory diagram showing the movement of the transport members; and (B) and (C) are explanatory diagrams showing the operation of the preform clamping / releasing mechanism. Fig. 5 is a time diagram showing the operation of the apparatus of Fig. 1. Fig. 6 is a vertical sectional view of the heating system, in a heating section downstream of the apparatus of Fig. 1. Fig. 7 is a plan view, schematically illustrating the heating system in the heating station downstream of the apparatus of Figure 1. Fig. 8 is a plan view, schematically illustrating the relationship between the rotation of the preform and the heating position, in the heating station downstream of the apparatus of Fig. 1. Fig. 9 is an explanatory diagram of a preform cooling system, in the heating station downstream of the apparatus of figure l. Figure 10 is a set of graphs showing the change in the temperatures of the internal and external surfaces, during the heating of the preform, where (A) is a graph comparing the change of temperatures in the case of continuous radiant heating, and the change in temperature in the case of intermittent radiant heating; (B) is a graph comparing the change in temperature after continuous radiant heating, between the case of natural cooling and the case of cooling with air blowing; and (C) is a graph comparing the change in temperature between the case of continuous radiant heating and the case of intermittent radiant heating, together with cooling by air blowing. Figure 11 is a set of diagrams showing another example of an intermittent heating system in the downstream heating station of the apparatus of Figure: wherein (A) is a schematic sectional view showing the state of the heating radiant, and (B) is a schematic sectional view showing the state of the radiant heating protection. Fig. 12 is a side view of an essential portion of a molding and stretching machine of the apparatus of Fig. 1. Fig. 13 is a front view of an essential portion of the molding and stretching machine of the apparatus of Fig. 1 Figure 14 is a schematic side view showing the structure of a blow molding apparatus, which is a second embodiment of the invention. Fig. 15 is a schematic cross-sectional view of the apparatus of Fig. 14. Fig. 16 is a partial plan view, showing a pair of holding plates of a clamping / releasing mechanism of the apparatus of Fig. 14.

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the invention will be explained in relation to the drawings.

FIRST MODALITY Figures 1 and 2 show the overall structure of a blow molding apparatus, to which the present invention is applied. The blow molding apparatus l of this embodiment serves for the blow molding of PET bottles, namely preforms P resulting from the molding and stretching of cylindrical shapes having an opening at one end and a closed bottom at the other (in the form of test tube), to form containers B for soft drinks or the like. As shown in Figure 1, apparatus 1 of this mode, receives two preforms Pl, P2 at a time, from a preform loading station 2, on the left side of the figure, and after molding them, delivers the resulting containers Bl, B2 from a container removal station 3 , to the next processing station (not shown). A linear conveyor line is formed between the charging station 2 and the withdrawal station 3. A heating station 5 in upstream, a heating station 6 in downstream, and a molding and stretching machine 7, are placed in order , along the transport direction of the conveyor line. The preforms P carried along the transport line are heated to a prescribed temperature in the upstream station 5, and then the temperature of their surfaces is allowed to cool, after passing through these stations. Subsequently they are reheated in a transport line 61, laterally and upstream, of the heating station 6 downstream, and subsequently cooled to a suitable temperature to pass to molding and stretching in a lateral transport line 62 and downstream. Subsequently, they pass to the operation of molding and stretching in the molding and stretching machine 7 in order to form the containers B. The transport mechanism for carrying the preforms P along the transport line, is constituted by a first transport station 8 for carrying the preforms P, received in the loading station 2, towards the entrance of the molding and stretching machine 7; a second transport section 9 for receiving the preforms P from the first transport station 8, and molding them in the molding and stretching machine 7; and a third transport section 11 for transporting the formed containers B towards the removal station 3. The structure of the first transport section 8 will be explained in relation to figures 1 and 2. The first transport section 8 is constituted basically of a beam 81, positioned along the transport line; several transport members 82 mounted on the upper surface of the beam 81; a transport mechanism 83 for moving beam 81 forward and backward in the transport direction; a lifting mechanism 84 for raising and lowering the beam 81; and a clamping / releasing mechanism 85 positioned along the transport line. The transport members 82 are mounted on the upper surface of the beam 81, and spaced at regular spaces L. Each transport member 82 has a rod 821, rotatably supported relative to the beam 81; a transport surface 822 formed at the upper end of the rod 821; and an insertion rod 823 extending vertically from the center of the transport surface 822. The transport mechanism 83 of the beam has a support section 831 to support the beam 81, and the support section 831 is supported by the lifting mechanism 84, by rollers 832, so that it can move forward and backward in the transport direction. In addition, one end of the beam support section 831 is connected through a hinge (not shown) with a hinge 833 for forward and backward oscillation in the transport direction. The beam support section 831 can be moved forward and backward relative to the transport direction, at a constant pitch, by oscillating the joint 833. In this embodiment, it can be moved at a constant feed pitch of 2L. The lifting mechanism 84 is constituted with the aforementioned beam support section 831, and a vertical guide 841 supporting the support section 831, by the rollers 832 in order to move in a vertical direction with respect to a frame A of the apparatus . The beam support section 831 is configured to be raised and lowered at a constant distance by means of the hinge 841. This mode is configured in order to drive the beam movement and the lifting operations, by means of the energy supplied to the beam. through 4 a joint, coming from a common source of energy. As this articulation can have any of the various configurations and the related technology is well known among experts in this field, the particularities thereof will be omitted in this specification. In this embodiment, the lower end of the rod 821 of each conveyor member 82 is connected through a pulley-band mechanism 824, with a motor 825 attached to the beam support section 831. The rod 821 is rotated about its axis by the action of this motor. As shown in Figures 2 and 3, the clamping / releasing mechanism 81 of this embodiment is equipped with a pair of clamping plates 851, 852, placed on each of the left and right sides, in relation to the direction Of transport. The holding plates 851, 852 are configured to be laterally symmetrical and to be supported on the frame IA of the apparatus, which will move laterally. As will be understood from FIG. 3, the inner edges of the holding plates 851, 852 are formed at a constant pitch L, with semicircular depressions 853, 854, which coincide with the outer diameter of the open end portion of the plates. preforms P. When the clamping plates are put together, the left and right semicircular depressions, therefore, form a circular preform clamping section. The opening and closing of the holding plates 851, 852 is also carried out through an articulation or the like, by the same energy source 80 that is used for the beam 81.

Preform Feed Operation The movement operation of the preform P in the first transport section 8 of this embodiment will be explained in relation to figures 4 and 5. Let us assume that a transport member 82 on beam 81 is in the initial position 82A shown in Figure 4 (A), on the upstream side in the transport direction A. At that time, the pair of holding plates, right and left, 851, 852, of the holding mechanism / release 85, are closed so as to hold a preform P (point in time TO in figure 5), as shown in figure 4 (B). From this state, the lifting mechanism 84 first descends to the conveyor member 82 to a second position 82B (point in time TI in Figure 5). As a result, the insertion rod 823 of the conveyor member 82 is withdrawn from the opening of the preform 3, thus bringing the conveyor member 82 out of contact with the preform P. Then, the transport mechanism 83 retracts the beam 81 in the direction in upstream, in a 2L grade.

As a result, the transport member 82 reaches a third retracted position 82C (point in time T2 in Figure 5). The lifting mechanism 84 then raises the beam 81 to bring the transport member 82 to a retracted position 82D. The retracted position 92D, at this time is a position of the transport member 82 upstream of the initial position 82A to a degree of two steps. As the clamping / holding mechanism holds a preform P in this position, the elevation of the beam 81 causes the insertion rod 823 of the conveyor member 82 to be inserted into the opening of the preform P, whereby the preform P remains supported on the transport surface 822 of the transport member (point in time T3 in figure 5). Then, as shown in Figure 4 (C), the holding plates 851, 852 of the clamping / release mechanism 85, open (point in time T4 in Figure 5). As a result, the preform P is supported only by the transport member 82. The transport mechanism 83 then advances the transport member 82 back to the initial position 82A (point in time T5 in Figure 5). Since the rod 821 of the transport member 82 rotates constantly at this time, the preform P supported in this manner also rotates constantly as it is transported. The clamping plates 851, 852 of the clamping / releasing mechanism 85 are subsequently closed in order to establish the clamping state of the preform P (point T6 in time in Figure 5). In this way, in this embodiment the transport members 82 that move integrally with the beam 81 feed the preforms P at a constant rate of passage, once every 2L. During the feeding of the preforms P supported on the transport members 82, these rotate by means of rotation using the motor 825. However, they do not rotate to stop positions where they are held by the pair of clamping plates 851, 852 As shown in Figure 5, the fed preforms are molded in the molding and stretching machine 7, after each transport operation (between points at time T7 and T8). as the molding and stretching machine 7 of this mode carries out the same molding operations as the machines of general use, no further explanation will be given regarding its structure or operation. Subsequently, cycles identical to the previous ones are carried out for the transport and molding of the preforms. In this embodiment, the second transport section 9 for receiving the preforms T from the transport section 8 of the previous structure, and sending them to the molding and stretching machine 7, has basically the same configuration as in the first section of transport 8. As shown in Figure 1, the second transport section 9, is equipped, however, with a single pair of transport members 91, 92, whose separation interval L in the retracted positions 91A, 92A, differs from its separation interval L2, in the molding and stretching machine. To make the feeding step different in this way, just use a cam-link mechanism and adjust them to set different steps. Alternatively, it is possible to establish the different feed passages, so as to compress and forcibly release several transport members that are slidable through the compression spring means. The transport members of the second transport section 9, have the same configuration as those of the first transport section 8, with the exception of the points where a single pair of transport members are provided, and in which they have different steps of transport. feeding and do not need to be equipped with rotating mechanisms. On the other hand, the third transport section 11 also has basically the same configuration as the first transport section 8, and is equipped with a single pair of transport members 111, 112, moving them at the same passage, and removes the molded containers Bl , B2 of the molding and stretching machine 7, two at a time, and delivers them to the next processing station (not shown). This transport section is the same as the first transport section 8, with the exception of the fact that its feed passage is different and that it is not equipped with a mechanism for rotating the molded part. (Heating control of the preform) Next, the heating control system of the preform P will be explained, downstream of the heating station 6 of the apparatus of this mode. Figure 6 shows the sectional configuration of the heating station 6 downstream, on the downstream side of the transport line 61. As shown in this figure, several near infrared heaters 68, arranged in a single vertical row at regular intervals, they extend along one side of the transport line in the transport direction. As shown in Figure 7, the filament 69 sealed in the seal tube 68A of each infrared heater 68 is formed in order to have spiral sections 691, the substantial sources of heat, at prescribed intervals in the longitudinal direction . In this embodiment, each of the spiral sections 691 constitutes the substantial heat sources of the filament 69, and is located on the side of one of the semicircular depressions 853, 854 of the holding plates 851, 852. The clamping sections of preforms formed by the meeting of the semicircular depressions 853, 854 of the holding plates 851, 852, are stopping positions of the preforms P fed intermittently. Therefore, and as schematically illustrated in Figure 8, the preforms P are heated by radiant heat from the spiral sections 691 of the filaments 69, while they stop because they are held by the semicircular depressions 853, 854 of the holding plates 851, 852. While they are being fed, they are rotating due to the effect of the transport members 82. At the moment when the preforms P are rotating during the movement between the stop positions Al, A2, A3. .., move, however, through regions where the filaments 69 do not have spiral sections 691, ie, along sections where the filaments are straight. Therefore, they hardly receive radiant heat. Thus, in this embodiment, a heating means capable of intermittently heating the preforms P, is constituted by the use of near infrared heaters 68, each consisting of a filament 69 formed, at prescribed intervals, with sections in spiral 691. If the same portion of external lateral surface of a preform P were to be oriented towards the filaments, each time the preform stops, only this portion will heat up. In this embodiment, the preforms P are rotated, therefore, so that a different portion of the outer lateral surface PO thereof is oriented towards the spiral sections 691, in each stop position A 1, A2, A3 .... For example, assuming that the external side surface PO of each preform P is divided into equiangular portions P1-P8, as shown in Figure 8, the portion Pl of the external lateral surface PO of the preform P , it is oriented towards the spiral sections 691 of the filaments 69, in the first stop position Al on the transport line. As a result, the radiant heating of the preform P is centered on a region of its outer lateral surface PO, corresponding to the portion of P8 to P2. Then, while the same preform P is being transported to the stop position A2 on the transport line, it is rotated several times by the transport member 82 and the portion P8 of the external lateral surface PO of the preform P is placed in orientation towards the spiral sections 691 of the filaments 69, in the stop position A2. As a result, the radiant heating of the preform P is centered on the region of the external lateral surface PO, between P7 and Pl. The different portions of the outer lateral surface PO of the preform P, are therefore placed in orientation towards the spiral sections 691 of the filaments 69, in the stop positions A3, A4 ... During the passage through the heating station 6 downstream, the surfaces of the external side PO of the preforms P, are subjected to thus to intermittent or discontinuous radiant heating, by means of the near infrared heaters 68, whereby its entire outer periphery is uniformly heated. On the other hand, the lateral transport line 62 downstream, in the heating station 6 downstream, is adapted with a cooling system to cool the radially heated preforms P. As shown in Figure 9, the cooling system of this mode is equipped with a fan 65 installed directly above the transport line. The air stream coming from the fan 65 is directed towards the preform P from flows, immediately above and along and outside thereof, and passes outwards. In this embodiment, the cooling action of the fan is adjusted so that it starts at the point in time after the temperature of the radially heated preform P has passed the peak value. The heated condition of the preforms P in the heating station 6 downstream of this embodiment will be explained in relation to Figure 6 (C). The curves Al and A2 in Figure 10 (C) represent the temperature changes on the external surface and the internal surface of a preform P, when the preform P is continuously heated by radiant heat and cooled naturally. The difference in temperatures between the internal and external surfaces of the preform, when the heating temperature reaches its peak temperature, in this case is defined as? (Al - A2). In contrast, in this embodiment, the temperatures of the surfaces, internal and external, of the preform P, rise step by step, since the radiant heating is carried out intermittently. Specifically, the surface temperatures, internal and external, follow the curves D2, DI. As can be observed from these curves, the peak values of the surface temperatures, internal and external, are lower than in the case of continuous heating. In addition, the degree to which the peak values are decreased is greater for the external surface temperature. Due to this, the difference in temperature of the internal-external surfaces,? (D1 - D2) is smaller than that which is had in the case of continuous radiant heating. In order to heat the internal surface to the desired temperature, the outer surface is heated to a considerably higher temperature. In this modality, as the difference between the temperatures of the surfaces, internal and external, can be narrowed, the temperature of the external surface at the moment in which the internal surface has risen to the required temperature, can be kept lower than in the technique previous. The intermittent radiant heating of this mode therefore makes it impossible to avoid the damage caused by the degradation, which is due to excessive heating of the external surface. In addition, since the difference in surface temperatures, internal and external, (D1 - D2), is lower than in the case of continuous radiant heating, a temperature state suitable for the temperature can be achieved with a short cooling period. molding, where the temperature of the internal surface is higher than the temperature of the external surface. As the efficiency of the molding line increases with a shorter cooling period, the productivity therefore rises.

In this embodiment, the preform P is cooled by the blowing of air thereon, from the fan 65, at a point after the temperatures of the surfaces, internal and external, have passed their peak values (indicated by an arrow). in the figure). As this blowing of air rapidly reduces the temperature of the outer surface, a state of temperature suitable for molding can be reached in a short time. It is to be observed in particular in this embodiment that the air is blown on the preform in an axial direction to it, directly from above, which allows the cooling of the preform to be carried out uniformly around its entire periphery and with good efficiency. Figure 10 (A) shows the curves B2, Bl of temperature change on the external surface, in the case of intermittent radiant heating without cooling, with a cooling fan, together with the temperature change curves A2, Al, in the case of continuous radiant heating. In Figure 10 (B) shows the curves C2, Cl of temperature change on the internal and external surfaces, in the case of continuous radiant heating, followed by cooling with a cooling fan, together with the change curves of A2, Al temperature in the case of continuous radiant heating.

As can be seen from these graphs, even when only intermittent radiant heating is adopted, the merit of being able to avoid excessive heating of the external surface in the preform is nevertheless obtained. Furthermore, when only cooling with a fan is adopted, the merit of being able to establish an adequate temperature state by molding in a short time, is nevertheless obtained in spite of everything. In the above embodiment, it is also possible to carry out intermittent radiant heating in the upstream heating station, 5. Another example of the temperature control system. Figure 11 shows another example of the heating control system installed in the line of transport 61 from the side upstream, from the heating station 6 downstream. In this example, several near infrared heaters 163 are arranged in a single vertical row, at regular intervals, extended along a single side of the line. transport, in the direction of transport. A sealing blade 164 is positioned between the near infrared heaters 163 and the preforms P carried on the transport line. The sealing blade 164 is moved in a vertical direction by a drive mechanism (not shown). In this example, the sealing blade 64 is raised, as shown in (A), and the radiant heating is carried out when the preforms P are held by the clamping / releasing mechanism 85 and not. they are spinning As shown in Figure 11 (B), the sealing blade 64 is lowered and the radiant heating is blocked when the preforms P are being transported by the conveyor member 82 while they are rotating. In this way, the sealing blade 64 moves up and down in association with the transport operation of the preform P, to heat, intermittently or discontinuously, the preforms P with the radiant heat coming from the infrared heaters 163 near. The same effect as in the case of the intermittent heating shown in Figure 7, is also obtained when the heating control system of the previous configuration is adopted.

Structure of the molding and stretching machine An example of the configuration of the molding and stretching machine 7 will be explained below in relation to Figures 12 and 13. Figure 12 is a side view showing a portion of the molding machine and stretching, which focuses on a top of the blow molds, and Figure 13 is a front view thereof. As shown in these figures, in the molding and stretching machine 7 of this invention, the blow molds 90 for the molding and stretching preforms P to give the containers Bl, B2 with the desired shape, each include separate sections mold 91, 92, defining a prescribed side container shape, and a lower mold section 93 defining the bottom shape of the container. As this blow mold 9 has the same structure as the prior art, it will not be described in more detail, it will only be mentioned that the separate mold sections 91, 92, are opened laterally by a mold opening mechanism 95, at the time of the demolding. The lower section 93 of the mold is provided with a cylinder 101, pneumatic or hydraulic by means of a cam 102. The cylinder and the cam 102 constitute a mold closing mechanism 100 for pressing the lower section 93 of the mold at the time of molding. The mold closing mechanism 100 is positioned such that at the time of demolding, the cylinder 101 functions to raise the cam 102 and pull the lower section 93 of the mold upwardly to a prescribed height. In this embodiment, two guide arrows 110 extend perpendicular to the transport direction of the preforms P, and the containers Bl, B2 between a pair of frames IB and an upper portion of the molding and stretching machine 7. The sliders 121 are mounted on the guide arrows 110 to form a horizontal sliding mechanism 120, for removal of the lower mold section 93, from its described position, by the horizontal movement of the sliders 121. A frame 130 is supported on the sliders 121 of the horizontal sliding mechanism 120. The frame 130 is provided with a fixed plate 131 oriented horizontally, and the cylinder 101 is fixed at the center of the upper surface of the fixed plate 131, with the cam 102 directed downwards. A support plate 103 for the lower mold section is attached to the lower end portion of the cam 102, and the pair of lower mold sections 93 are fixed on the support plate 103 of lower mold section, oriented towards down. The guides 105 are provided in the upper part of the fixed plate 131, in association with the rods 104, extending upwardly from the support plate 103 of the lower mold section. Stoppers 109 are provided between the fixed plate 131 and a movable plate 106, horizontally fixed on the upper end portions of the rods 104, to define a lower limit position of the movable plate 106.

In addition, stops 109 are provided between the movable plate 106 and an upper plate 137 of the frame 130, to define the upper limit position of the movable plate 106. When the adjustment of the molding and stretching machine 7 configured in this way, it goes to When changing, the cylinder 101 of the mold closing mechanism 100 is first operated to remove the lower mold sections 93 from their adjustment positions during molding. Then, in the horizontal sliding mechanism 120, the sliders 121 move horizontally on the guide arrows 110 towards the position indicated by the imaginary line 121 in Figure 3, thus moving the entire frame 130 horizontally in the perpendicular direction, towards the conveying direction of the preforms 3. As a result, the lower mold sections 93 are removed together with the frame 130 and the mold closing mechanism 100, to positions where they can be easily changed. Since the space above the divided mold sections 91, 92 is thus completely open, the operation of changing the divided mold sections 91, 92 is simple. The time required to change the setting is decreased as a consequence.

Second embodiment Figures 14 to 16 show the overall structure of another embodiment of the blow molding apparatus of the present invention. The basic structure of the blow molding apparatus of this embodiment is the same as that of the first embodiment. The corresponding portions will be explained, as a consequence, using the same reference numbers. Figures 14 and 15 show the overall structure of the blow molding apparatus of this embodiment. The blow molding apparatus 1000 of this embodiment is also used for the blow molding of PET bottles, namely preforms M for molding and stretching in the form of a test tube, to form mold containers B for sodas or the like. As shown in Figure 14, the apparatus 1000 of this embodiment receives two preforms Pl and P2 at the same time, starting from a station 2 for loading preforms, on the left side of the figure, and after molding them, delivers the resulting containers Bl, B2 from a container removal station 3 to the next processing station (not shown),. A linear transport line is formed between the charging station 2 and the withdrawal station 3. A heating station 5 in upstream, a heating station 6 in downstream and a molding and stretching machine 7, are placed in order , along the transport direction of the transport line. The preforms P carried along the transport line are heated to a prescribed temperature in the upstream station 5, and then their surfaces are cooled, subsequently as they pass through these stations. Then, they are reheated to a suitable temperature for molding and stretching, and the surfaces thereof are again cooled in the downstream heating station 6. Then, they undergo the molding and stretching operation in the molding and stretching machine 7, to form the containers B. The transport mechanism for transporting the preforms P along the transport line is constituted by: first transport section 8 for transporting the preforms P received in the loading station 2, towards the entrance of the molding and stretching machine 7; a second transport section 9 for receiving the preforms P from the first transport station 8, and molding them in the molding and stretching machine 7; and a third transport section 11 for transporting the formed containers B towards the removal station 3. The structure of the first transport section 8 will be explained in relation to Figures 14 and 15. The first transport section 8 is basically constituted from a beam 81, positioned along the transport line, several transport members 82 mounted on the upper surface of the beam 81; a transport mechanism 83 for moving beam 81 forward and backward in the transport direction; a lifting mechanism 84 for raising and lowering the beam 81; and several clamping / releasing mechanism 85, placed along the transport line. The transport members 82 are mounted on the upper surface of the beam 81, and spaced at regular spaces L. Each transport member 82 has a rod 821 supported to be rotatable relative to the beam 81; a transport surface 822 formed at the upper end of the rod 821; and an insertion rod 823 extending vertically from the center of the transport surface 822. The transport mechanism 83 of the beam has a support section 831 to support the beam 8, and the transport section 831 it is supported by the lifting mechanism 84, by rollers 832 in order to be able to move forward and backward in the transport direction, by the beam lifting mechanism 84. In addition, one end of the beam support section 831 is connected by a hinge (not shown) with a hinge 833 to oscillate back and forth, in the transport direction. The beam support section 831 can be moved forward and backward relative to the transport direction, at a constant pitch, by oscillating the hinge 833. In this mode, it can be moved at a constant feed pitch of 2L. The lifting mechanism 84 is constituted by the aforementioned beam support section 831 and a vertical guide 841, which supports the beam support section 831 through the rollers 832, in order to be movable in a vertical direction with respect to the frame of the appliance. The beam support section 831 is configured to be raised and lowered at a constant distance by means of the link 841. This mode is configured to carry the beam motion and the lifting operations by means of the energy supplied through the beam. an articulation, from a common source of energy. Since this joint can have any of various configurations, and the related technology is well known to those skilled in the art, the particularities thereof will be omitted in this specification. In this embodiment, the lower end of the rod 821 of the transport member 82 is connected through a pulley and a band 824, with a motor 825 attached to the support section 831. The rod 821 is rotated about its axis through this engine. As shown in Figure 15, in a position corresponding to that of each transport member 82, a clamping / releasing mechanism 85 is placed, equipped with four rollers 1851, 1852, 1853 and 1854, whose centers are on a circle, whose center coincides with the axis of the transport member 82. Each of the rollers 851, 852 on one side, is attached to be movable in a direction perpendicular to the direction of transport. In addition, the roller 1851 is a drive roller connected through a belt and pulley mechanism 855, with a motor 856. The motor 856 is supported to move integrally with the rollers 1851, 1852. The other rollers 1853, 1854, are joined similarly to be movable in a direction perpendicular to the transport direction. As illustrated, in this embodiment, the rollers on the opposite sides are adjusted in order to establish a clamping state of a preform P between them when they are close to each other. The roller 1851 is rotated in this state, and therefore the preform P is clamped between the rollers and can be rotated about its axis. Obviously, the rotational speed of the rollers approximately coincides with the speed at which the preform P rotates about its axis, due to the rotation of the conveyor member 82. In this embodiment, the opening and closing operation of the left and right rollers , it is also carried out through an articulation or the like, by means of the same energy source 80 that is used for the beam 81. The movement operation of the preform P in the first transport section 8 of this mode will be explained in relation to Figure 16. Let us assume that a transport member 82 on the beam 81 is in the initial position 82A on the water side. up in the transport direction A. At this time, the roller group of the clamping / releasing mechanism is closed, as shown in Figure 16 (B), so as to hold a preform P. From this state , the lifting mechanism 84 first decreases the transport member 82 to a second position 82B. The preform P is held by the clamping / releasing mechanism 85 and maintained in a rotational state. As a result of this level decrease, the insertion rod 823 of the conveyor member 82 is withdrawn from the opening of the preform P. Next, the transport mechanism 83 retracts the beam 81 in the upstream direction, in a 2L grade. As a result, the transport member 82 reaches a third retracted position 82C. The lifting mechanism 84 then elevates the beam 81 to carry the transport member 82 to a retracted position 82D. The retracted position 82D at this time is a position of the transport member 82 upstream of the initial position 82A in a two-step degree. Since the clamping / releasing mechanism holds a preform P in this position, the elevation of the beam 81 causes the insertion rod 823 of the conveyor member 82 to be inserted into the opening of the preform P, whereby the The preform P is supported on the transport surface 822 of the conveyor member. Then, and as shown in Figure 16 (C), the group of rollers constituted by three or more rollers per block (in this mode there are four) of the clamping / releasing mechanism 85, open to the left and to the right. As a result, the preform P is only supported by the transport member 82. The transport mechanism 83 then advances the transport member 82 back to the initial position 82A. Since the rod 821 of the transport member 82 rotates constantly at this time, the preform P supported in this way also rotates constantly as it is transported. The roller group of the clamping / releasing mechanism 85 is thus closed, in order to establish the clamped state of the preform P. Therefore, in this embodiment, the transport members 82 that move integrally with the beam 81, feed the preforms P once each step 2L constant speed. The fed preforms are molded in the molding and stretching machine 7, after each transport operation. Since the molding and stretching machine 7 of this embodiment carries out the same molding operation as the machines of general use, no further explanation of its structure or operation will be given. Cycles identical to the previous ones are repeated for the feeding and molding of preforms. In this embodiment, the second transport section 9 for receiving the preforms P from the first transport section 8 of the previous structure, and delivering them to the molding and stretching machine 7, is configured in a manner similar to the first section of 8. As shown in Figure 14, the second transport section 9 is, however, equipped with a single pair of transport members 91, 92 whose separation interval L in the retracted positions 91A, 92A, differs from its separation interval L2 in the molding and stretching machine. To make the feeding step different in this mode, just use a cam-link mechanism and adjust them to set different steps. Alternatingly, it is possible to establish different feeding steps, for example by compressing and forcingly releasing several conveyor members which are slidable through the means of compression springs. The transport members of the second transport section 9 have the same configuration as those of the first transport section 8., except that a single pair of transport members is provided and that they have different feeding steps and are not equipped by rotation mechanisms. On the other hand, the third transport section 11 is basically the same as the first transport section 8, and is equipped with a single pair of transport members 111, 112, moving them at the same passage, and removes the molded containers Bl, B2 from the molding and stretching machine 7, two at a time, delivering them to the next processing station (not shown). This transport section is equal to the first transport section 8, with the exception of the fact that its feeding passage is different and that it is not equipped with a rotation mechanism for molding. In the transport mechanism of the blow molding apparatus 100, configured in accordance with this embodiment, the feeding of the preforms is achieved by repeatedly moving the multiplicity of transport members 82 supported by the beam 81, frd and backward, and towards up and down. Therefore, the transport mechanism is simpler and more economical in its manufacture than the prior art transport mechanism, configured to move the transport members along the transport line. The preforms are rotated by the transport members during transport, since the transport members themselves rotate, as a result of the clamping / releasing mechanism of the roller group, while the transport members are moving towards the retracted position . As a result, the preforms are in a state of continuous rotation as they are transported through the heating stations 5 and 6. The preforms can therefore be heated uniformly. This mode uses cam-link mechanisms to energize the beam lifting mechanism, the beam movement mechanism and the clamping / releasing mechanism, from the same power source. Therefore, the apparatus is also beneficial since it is configured in a compact form. In addition, since the second and third clamping sections used to feed the preforms and the molds at different steps are also energized by the same energy source, a further reduction in the size of the apparatus is possible. In the transport mechanism of this mode, the transport members 82 simply move back and forth, and up and down, in a fixed location. It is therefore easy to implement a configuration in which some of the transport members do not rotate, and the preforms that are carried by these transport members do not rotate. Therefore, if for example, only one or some of the transport members 82 of the downstream heating section 6 are placed immediately above the molding and stretching machine 7, without turning, it is impossible to heat or cool locally only a desired portion of the preforms P carried through this region. By imparting a temperature change in a preform in this way, immediately before the molding and stretching operation, it becomes impossible to control the amount of stretching in different portions during molding and drawing, and therefore adjusting the thickness of the molded piece. This advantageously makes it possible to avoid problems such as an excessive thickening of the portions, where the degree of stretching is great. As a mechanism for locally heating and / or cooling the preforms, an air blowing mechanism, adjusted to a prescribed temperature range, on a desired portion can be adopted. It is also possible to adopt a mechanism for carrying a heat conducting part, adjusted to a prescribed temperature, in contact with a desired portion of the preforms. In order to carry out the molding and stretching, it is enough to establish a uniform state of temperatures in the preforms by blowing air, adjusted to a prescribed temperature, in the heating station 6 downstream, immediately before molding and stretching.

Industrial Application As explained above, in the molding and stretching apparatus of this invention, the transport members of the preform transporting mechanism only move to a degree corresponding to the feeding step. In addition, the clamping / releasing mechanism needs only to conduct its preform holding / releasing operation in a fixed position. The transport mechanism is therefore simpler and less expensive than an arrangement of the prior art in which the transport members are circulated along the transport line. In addition, the blow molding apparatus of the invention heats intermittently or discontinuously the preforms by radiant heat, using a configuration in which, for example, thermal sources are placed in positions corresponding to the stop positions of the preforms individual Unlike the heating systems of the prior art, the invention thus allows the temperature of the internal surface of the preforms to increase adequately without excessively increasing the temperature of the outer surface thereof. In addition, as the difference between the temperatures of the surfaces, internal and external, can be reduced, it is possible to establish a state of temperature where the temperature of the inner surface is higher, namely, a state of temperature suitable for molding, in a short time after heating. Furthermore, the invention provides a cooling system for cooling the preforms by blowing air thereon, after they have passed the peak temperature, due to heating. This system allows the temperature of the outer surface of the preforms to decrease rapidly, enabling the establishment of a temperature state suitable for molding, in a much shorter period of time than that of the prior art.

Claims (21)

CLAIMS;

1. A blow molding apparatus comprising: a preform heating means, for radiant heating of cylindrical preforms having an opening at one tip end and a closed bottom at the other end; a molding and stretching means, for molding and axial stretching of the heated preforms so as to form hollow moldings in a prescribed manner; and a preform transport means, for intermittently conveying the preforms through the heating means, towards the molding and stretching means, at a prescribed speed step; characterized in that the transport means includes: a linear member extending in a preform transport direction; several preform transport members that are supported by the linear member, and are positioned at regular intervals in the conveying direction of the preform, and are capable of being inserted into the openings of the preforms; a transport mechanism adapted to move the linear member to a retracted position, in a retracting feeding passage, lowering it from its initial position to a lowered position, where the transport members are released from the preforms by moving the linear member from the backward position in a direction opposite to the direction of transport, and then raising it, and then moving it forward from the retracted position towards the initial position; and a clamping / releasing mechanism, adapted to hold the preforms while the transport members supported by the linear member are moving from the initial position to the retracted position, and to release and deliver the preforms to the transport members, his arrival to the retracted position.

2. A blow molding apparatus according to claim 1, characterized in that the clamping / releasing mechanism comprises: a pair of clamping plates, left and right, placed in the transport direction, and preform holding sections that are formed at intervals in the transport direction, said intervals being equal to the intervals of the transport members, when the clamping plates are closed; the clamping sections hold the preforms during the closing of the clamping plates and release them during the opening of said plates.

A blow molding apparatus according to claim 2, characterized in that the heating means comprises radiant heat sources placed along a preform transport line of the transport medium, a radiant heat source is placed in a position which corresponds to all preform stop positions.

4. A blow molding apparatus according to claim 3, characterized in that the radiant heat source is constituted by a heating tube that encloses a filament as a heating element, and the filament has spiral sections, in the stopping positions. of the preform, and extends in straight portions, in the remaining positions.

5. A blow molding apparatus according to claim 4, characterized in that it also comprises a preform rotating means for rotating the preforms carried by the preform transport means, around its axis; the preform rotating means rotates the preforms to vary the orientation of the outer peripheral surface portion of the preform towards the heat source, at least between adjacent stop positions.

6. A blow molding apparatus according to claim 5, characterized in that it further comprises an air cooling means for cooling the preforms, after radiant heating, by blowing air thereon, the air cooling medium cools each preform in a point of time after its temperature has passed through a peak value.

7. A blow molding apparatus according to claim 6, characterized in that the air cooling means blows air in the axial direction of the preforms.

8. A blow molding apparatus according to claim 7, characterized in that the clamping / releasing mechanism comprises: a plurality of groups of rollers, placed at intervals of the transport direction, equal to the intervals of the transport members; and a roller movement mechanism for moving the rollers of the individual groups, to approach and move away from each other in order to hold and release the preforms.

9. A blow molding apparatus, characterized in that it comprises: a preform heating means for radiant heating of the cylindrical preforms, having an opening at one tip end and a closed bottom at the other end; a molding and stretching means for molding and axially stretching the heated preforms so as to form hollow moldings in a prescribed manner; and a preform conveying means for intermittently conveying the preforms through the heating means to the molding and stretching means, at a prescribed rate step; characterized in that the heating means comprises radiant heat sources placed along the conveying line of the preform of the conveying means, a radiant heating source is placed in a position corresponding to all the stopping positions of the preform.

A blow molding apparatus according to claim 9, characterized in that the radiant heat sources are constituted by a heating tube which encloses a filament as a heating element, and the filament has spiral sections in the stop positions of preforms and extends straight into the remaining positions.

11. A blow molding apparatus according to claim 10, characterized in that it also comprises a preform rotation means for rotating the preforms carried by the preform transport means, around its axis; the preform rotation means rotates the preforms to vary the orientation of the outer peripheral surface portion of the preform, towards the heating source, at least between adjacent stop positions.

12. A blow molding apparatus according to claim 9, characterized in that it further comprises a preform rotation means for rotating the preforms carried by the preform transport means, around its axis; the preform rotation means rotates the preforms to vary the orientation of the outer peripheral surface portion of the preform, towards the heat source, between adjacent stop positions.

13. A blow molding apparatus comprising: a preform heating means for radiant heating of cylindrical preforms having an opening at one tip end and a closed bottom at the other end; a preform temperature adjusting means for adjusting the radially heated preforms to a temperature suitable for blow molding; a molding and stretching means for axial molding and stretching of the preforms whose temperature has been adjusted so as to form hollow moldings in a prescribed manner; and a transport means for transporting the preforms through the heating means and the temperature adjusting means towards the molding and stretching means; characterized in that the heating means comprises an intermittent heating system for intermittently conducting the radiant heat of the preforms.

A blow molding apparatus according to claim 13, characterized in that the intermittent heating system comprises a radiant heat source for radiant heating of the preforms; and a drive control means for capacitating / incapacitating the radiant heat source, at prescribed intervals.

A blow molding apparatus according to claim 13, characterized in that the intermittent heating system comprises a radiant heat source for radiant heating of the preforms, and a shutter member for blocking radiant heat from the radiant heat source; the shutter member intermittently locks the preforms, isolating them from the heat source.

16. A blow molding apparatus according to claim 13, characterized in that the temperature adjustment means of the preform comprises an air cooling medium for cooling the preforms, after radiant heating, by blowing air thereon, the air cooling medium cools each preform in a point of time after its temperature has exceeded a peak value.

17. A blow molding apparatus according to claim 16, characterized in that the air cooling medium blows air in the axial direction of the preforms.

18. A blow molding apparatus comprising a preform heating means for heating with radiant heat the cylindrical preforms having an opening at its end tip and a closed bottom at its other end; a preform temperature adjusting means for adjusting the radially heated preforms to a temperature suitable for blow molding; a molding and stretching means for molding and biaxial stretching of the preforms whose temperature was adjusted, so as to form hollow moldings in a prescribed manner; and a transport means for transporting preforms through the heating means and the temperature adjusting means towards the molding and stretching means; characterized in that the preform temperature adjusting means comprises an air cooling means for cooling the preforms, after radiant heating, by blowing air thereon; the cooling medium with air cools each preform at a point of time after which its temperature has passed a peak value.

19. A blow molding apparatus according to claim 18, characterized in that the air cooling means blows air in the axial direction of the preforms.

20. A blow molding apparatus according to claim 18, characterized in that the air cooling means blows air containing moisture onto the preforms.

21. A blow molding apparatus according to claim 18, characterized in that it further comprises means for imparting a local temperature change to the preforms, after they have been cooled by the cooling system.