WO2011079917A1

WO2011079917A1 - A blow-molding system with a stretch rod including one or more valves, a rod for a blow moulding system and a method for operating a blow-moulding

Info

Publication number: WO2011079917A1
Application number: PCT/EP2010/007729
Authority: WO
Inventors: Roger Studer
Original assignee: Norgren Gmbh
Priority date: 2009-12-17
Filing date: 2010-12-17
Publication date: 2011-07-07

Abstract

A blow-molding system (100) is provided by the present invention. The blow- molding system (100) comprises a blow molding housing (101) defining a mold cavity (102). The blow-molding system (100) also comprises a stretch rod (103) movable within the mold cavity (102). The stretch rod (103) includes a first stretch rod component (103A) defining a first fluid flow path (104). The stretch rod (103) also includes a first valve (106) coupled to the first stretch rod component (103A) and adapted to selectively provide a fluid communication path between the first fluid flow path (104) and the mold cavity (102).

Description

A BLOW -MOLDING SYSTEM WITH A STRETCH ROD INCLUDING ONE OR

MORE VALVES, A ROD FOR A BLOW MOULDING SYSTEM AND A METHOD

FOR OPERATING A BLOW -MOULDING

TECHNICAL FIELD

The present invention relates to blow molding systems, and more particularly, to a blow-molding system with a stretch rod including one or more valves.

BACKGROUND OF THE INVENTION

Blow molding is a generally known process for molding a preform part into a desired product. The preform is in the general shape of a tube with an opening at one end for the introduction of pressurized gas, typically air; however, other gases may be used. One specific type of blow molding is stretch blow molding (SBM). In a typical SBM application, a valve block provides both low and high-pressure gas to expand the preform into a mold cavity. The mold cavity comprises the outer shape of the desired product. SBM can be used in a wide variety of applications; however, one of the most widely used applications is in the production of Polyethylene terephthalate (PET) products, such as drinking bottles. Typically, the SBM process uses a low-pressure fluid supply in combination with a stretch rod that is inserted into the preform to stretch the preform in a longitudinal direction and radially outward and then uses a high- pressure fluid supply to expand the preform into the mold cavity. The low-pressure and high-pressure supply can be controlled using one or more blow-molding valves. The resulting product is generally hollow with an exterior shape conforming to the shape of the mold cavity. The gas in the preform is then exhausted through one or more exhaust valves. This process is repeated during each blow-molding cycle.

As can be appreciated, with the high speed of the molding cycle that is currently achievable, even small losses in energy during each molding cycle can result in substantial increases in operating costs. One of the major costs associated with stretch blow molding systems is the compressed gas used to expand the preform. The amount of gas required and the amount of energy required to pressurize the gas can be significant. Therefore, decreasing the amount of gas required during each molding cycle can substantially reduce the operating costs of the blow-molding system. In most applications, the pressurized gas that fills the mold cavity is the only portion of the gas that is considered useful. Therefore, the remaining areas of the system filled with gas, for example, the gas in fluid conduits between each control valve and the mold cavity is considered dead volume. Gas in the dead volume is essentially wasted. This is because the gas in the dead volume does not fill the mold cavity, and therefore, is not required for the molding process, yet the gas is exhausted at the end of a molding cycle when the mold cavity is exhausted.

Due to the large amount of energy wasted by pressurizing the dead volume of a system, prior art systems have attempted to limit the loss of pressurized gas by forming valve blocks around the stretch rod or the mold cavity in order to limit or otherwise reduce the dead volume associated with a system. These prior art systems attempt to position the valves closer to the stretch rod and thus, the preform, in order to minimize the distance the pressurized gas is required to travel before reaching the mold cavity that must also be exhausted at the end of a blow-molding cycle, i.e., minimize the dead volume. While these prior art systems position the valve closer to the mold cavity, the pressurized gas is still required to travel through conduits that are external to the mold cavity.

In addition, the pressurized gas is typically introduced in a small space between the stretch rod and an opening in the mold cavity. In order to increase the speed in which a molding cycle can be completed, the stretch rod is made with a cross-sectional area as small as possible to allow a maximum opening for the introduction and exhaust of the pressurized fluid. However, as the cross-sectional area of the stretch rod decreases, the net volume in the cavity that needs to be pressurized increases. This is because the net volume pressurized is essentially equal to the interior volume of the blow-molded container minus the volume of the stretch rod inserted into the container. For example, it is typical in the prior art to provide a stretch rod with a diameter of approximately 14 mm (0.6 inches). This results in a relatively small area of the blow mold cavity being filled by the stretch rod when the stretch rod is inserted into the cavity.

The present invention overcomes these and other problems and an advance in the art is achieved. The present invention provides a stretch rod for a SBM system where pressurized fluid is supplied to the mold cavity through the stretch rod. Because the pressurized fluid is supplied to the mold cavity through one or more fluid flow paths formed in the stretch rod rather than adjacent the stretch rod, the cross-sectional area of the stretch rod can be increased. In one embodiment, the diameter of the stretch rod can be increased from approximately 14 mm (0.6 inches) to approximately 21 mm (0.8 inches) resulting in a further reduction in the volume of the mold cavity that needs to be pressurized. Further, the stretch rod includes one or more integrated valves for supplying pressurized fluid to a blow-molding cavity. With the valves located in the stretch rod, pressurized fluid located in the stretch rod no longer needs to be exhausted at the end of a molding cycle. Rather, only the pressurized fluid provided to the mold cavity needs to be exhausted. Therefore, the present invention further reduces the dead volume associated with the blow-molding system.

SUMMARY OF THE INVENTION

A blow-molding system is provided according to an embodiment of the invention. The blow-molding system comprises a blow-molding housing defining a mold cavity. According to an embodiment of the invention, the blow-molding system also comprises a stretch rod movable within the mold cavity. The stretch rod can include a first stretch rod component defining a first fluid flow path. According to an embodiment of the invention, the stretch rod can also include a first valve coupled to the first stretch rod component and adapted to selectively provide a fluid communication path between the first fluid flow path and the mold cavity.

A stretch rod for a blow-molding system is provided according to another embodiment of the invention. According to an embodiment of the invention, the stretch rod comprises a first stretch rod component defining a first fluid flow path. The stretch rod can also include a first valve coupled to the first stretch rod component and in fluid communication with the first fluid flow path.

A method for operating a blow-molding system is provided according to an embodiment of the invention. The blow-molding system includes a mold cavity, a stretch rod, a first fluid flow path formed in the stretch rod, and a first valve coupled to the stretch rod. According to an embodiment of the invention, the method comprises a step of inserting the stretch rod into the mold cavity. The method can also comprise a step of supplying a first pressurized fluid to the first fluid flow path. According to an embodiment of the invention, the method also comprises a step of opening the first valve to provide a fluid communication path between the first fluid flow path and the mold cavity, thereby pressurizing the mold cavity to a first pressure.

ASPECTS

According to an aspect of the invention, a blow-molding system comprises:

a blow-molding housing defining a mold cavity;

a stretch rod movable within the mold cavity and including:

a first stretch rod component defining a first fluid flow path; and a first valve coupled to the first stretch rod component and adapted to selectively provide a fluid communication path between the first fluid flow path and the mold cavity.

Preferably, the stretch rod further comprises:

a second stretch rod component defining a second fluid flow path; and

a second valve adapted to engage a portion of the second stretch rod component to selectively provide a fluid communication path between the second fluid flow path and the mold cavity.

Preferably, a portion of the second valve is coupled to the first stretch rod component.

Preferably, the second valve comprises a valve member formed on the first stretch rod component and a valve seat formed on the second stretch rod component.

Preferably, the first and second stretch rod components are coaxially aligned and movable with respect to one another.

Preferably, the blow-molding system further comprises a stretch rod end cap coupled to the first stretch rod component and adapted to form a substantially fluid-tight seal with the second stretch rod component.

Preferably, the first valve comprises a movable valve member and a valve seat formed at an end of the first stretch rod component.

According to an aspect of the invention, a stretch rod for a blow-molding system comprises:

a first stretch rod component defining a first fluid flow path; and

a first valve coupled to the first stretch rod component and in fluid communication with the first fluid flow path. Preferably, the stretch rod further comprises:

a second stretch rod component defining a second fluid flow path; and

a second valve adapted to engage a portion of the second stretch rod component and in fluid communication with the second fluid flow path. Preferably, a portion of the second valve is coupled to the first stretch rod component.

Preferably, the first and second stretch rod components are coaxially aligned. Preferably, the stretch rod further comprises a stretch rod end cap coupled to the first stretch rod component and adapted to form a substantially fluid-tight seal with the second stretch rod component.

According to another aspect of the invention, a method for operating a blow- molding system including a mold cavity, a stretch rod, a first fluid flow path formed in the stretch rod, and a first valve coupled to the stretch rod, the method comprises steps of:

inserting the stretch rod into the mold cavity;

supplying a first pressurized fluid to the first fluid flow path; and

opening the first valve to provide a fluid communication path between the first fluid flow path and the mold cavity, thereby pressurizing the mold cavity to a first pressure.

Preferably, the blow-molding system further includes a second fluid flow path formed in the stretch rod and a second valve coupled to the stretch rod, the method further comprises steps of:

closing the first valve to close the fluid communication path between the first fluid flow path and the mold cavity;

supplying a second pressurized fluid to the second fluid flow path; and

opening the second valve to provide a fluid communication path between the second fluid flow path and the mold cavity, thereby pressurizing the mold cavity to a second pressure. Preferably, the method further comprises steps of:

closing the second valve to close the fluid communication path between the second fluid flow path and the mold cavity; and

exhausting pressurized fluid in the mold cavity while retaining at least a portion of the pressurized fluid supplied to the first and second fluid flow paths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a blow-molding system according to an embodiment of the invention.

FIG. 2 shows a cross-sectional view of the blow-molding system during a pre- blowing stage according to an embodiment of the invention.

FIG. 3 shows a cross-sectional view of the blow-molding system between a pre- blowing stage and a blowing stage according to an embodiment of the invention.

FIG. 4 shows a cross-sectional view of the blow-molding system during a blowing stage according to an embodiment of the invention.

FIG. 5 shows a cross-sectional view of the blow-molding system according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 - 5 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 shows a cross-sectional view of a portion of a blow- molding system 100 according to an embodiment of the invention. The blow-molding system 100 shown in FIG. 1 comprises a blow-molding housing 101, a mold cavity 102 defined by the blow- molding housing 101, a stretch rod opening 5, an exhaust flow path 10, and a stretch rod 103. It should be appreciated that the various components shown in FIG. 1 are not drawn to scale. For example, in actuality, the mold cavity 102 may be much larger compared to the stretch rod 103 than shown. Only a portion of the stretch rod 103 is shown in the figures.

According to an embodiment of the invention, the stretch rod 103 is adapted to be at least partially received in the mold cavity 102. As a result, the blow-molding housing 101 can include a stretch rod receiver 12. In some embodiments, the stretch rod receiver 12 can form a substantially fluid-tight seal between the stretch rod 103 and the stretch rod opening 5. The stretch rod receiver 12 may include one or more seals 6, such as O-ring seals, for example. In the embodiment shown, the stretch rod receiver 12 also forms the exhaust flow path 10. The exhaust flow path 10 may be in fluid communication with an exhaust valve (not shown) as is typical in the prior art.

According to an embodiment of the invention, one or more fluid flow paths 104, 105 are defined by the stretch rod 103. As is shown, according to an embodiment of the invention, the stretch rod 103 comprises a first stretch rod component 103 A and a second stretch rod component 103B. The first and second stretch rod components 103 A, 103B can define the first and second fluid flow paths 104, 105. In the embodiment shown, the first and second fluid flow paths 104, 105 are coaxially arranged along a longitudinal axis Y-Y. However, it should be appreciated that in other embodiments, the first and second fluid flow paths 104, 105 are arranged adjacent one another and do not share a common axis. In such embodiments, the stretch rod 103 may include an outer housing to surround the first and second stretch rod components 103 A, 103B. According to an embodiment of the invention, the first fluid flow path 104 can be defined by an interior surface of the first stretch rod component 103 A. In the embodiment shown, the second fluid flow path 105 is defined in part, by an interior surface of a second stretch rod component 103B and an outer surface of the first stretch rod component 103 A. According to an embodiment of the invention, the first and second stretch rod components 103 A, 103B comprise hollow cylinders; however, other shapes and configurations may be provided. It should be appreciated that while two stretch rod components 103 A, 103B are shown along with two fluid flow paths 104, 105, in other embodiments a single stretch rod component and a single fluid flow path may be defined by the stretch rod 103 (See FIG. 5). According to an embodiment of the invention, the first stretch rod component 103 A is movable with respect to the second stretch rod component 103B. The position of the first stretch rod component 103 A with respect to the second stretch rod component 103B can be controlled using an external control mechanism that does not form part of the present invention. For example, in prior art SBM systems, a mechanical device is provided that controls the position of the stretch rod. In the present invention, a similar device may be employed that can control the position of each of the stretch rod components 103 A, 103B. Alternatively, a separate control device may be provided for each stretch rod component 103 A, 103B. The control device may also control the position of the first and second stretch rod components 103 A, 103B with respect to the blow-molding body 101. For example, the control device can actuate the first and second stretch rod components 103 A, 103B to one or more positions, which is described in more detail below. Almost all SBM systems employ a device to control the position of the stretch rod. Therefore, the particular control device used in the present invention should in no way limit the scope of the present invention. As an alternative, the position of each of the first and second stretch rod components 103 A, 103B may be controlled manually.

According to an embodiment of the invention, the stretch rod 103 can include two or more valves 106, 107. According to an embodiment of the invention, the valves 106, 107 can comprise integral components of the stretch rod 103. In other words, the valves 106, 107 may not be remotely located from the stretch rod 103. The valves 106, 107 can be provided to control fluid communication between the first and second fluid flow paths 104, 105 and the mold cavity. Therefore, the valves 106, 107 can control a supply of first and second pressurized fluids to the mold cavity. In some embodiments, the first and second pressurized fluid may comprise the same type of fluid, i.e., they may both be air. However, other fluids may be used, such as nitrogen or other inert gases, for example. Therefore, the invention should not be limited to requiring air. According to an embodiment of the invention, the first and second fluids may be pressurized to different pressures. For example, the pressurized fluid supplied to the first fluid flow path 104 and controlled by the first valve 106 may comprise a pre-blowing pressure while the pressurized fluid supplied to the second fluid flow path 105 and controlled by the second valve 107 may comprise a blowing pressure. While the particular pressures may vary according to the intended application, in one embodiment, the pre-blowing pressure may be provided to pressurize the mold cavity 102 to a pressure of approximately 6 bar (87 psi) while the blowing pressure may be provided to pressurize the mold cavity 102 to a pressure of approximately 40 bar (580 psi). It should be appreciated that these pressures are merely examples and the particular invention is certainly not limited to these values.

In the embodiment shown in FIG. 1, the stretch rod 103 is substantially withdrawn from the mold cavity 102. It should be appreciated that in use, a preform would typically be provided in the mold cavity 102 for molding into a final product. The preform is omitted from the drawings in order to simplify the figures. With the stretch rod 103 withdrawn from the mold cavity 102, the exhaust fluid pathway 10 is open to the mold cavity 102. It should be appreciated, that the exhaust fluid pathway 10 may be in fluid communication with an exhaust valve (not shown), as is generally known in the art, in order to control exhaust out of the mold cavity 102. In some embodiments, the exhaust fluid pathway 10 may be in fluid communication with a pressure-recycling tank (not shown) in order to reuse a portion of the pressure exhausted from the mold cavity 102 at the end of a blow-molding cycle. In still other embodiments, the exhaust fluid pathway 10 may be formed as a third stretch rod component (not shown) similar to the first and second stretch rod components 103 A, 103B.

According to the embodiment shown in FIG. 1, the stretch rod 103 is withdrawn from the mold cavity 102, the first valve 106 is shown open, and the second valve 107 is shown closed. According to an embodiment of the invention, the first valve 106 is coupled to the first stretch rod component 103 A. According to an embodiment of the invention, the first valve 106 comprises a check valve with a valve member 109 that is adapted to seal against a first valve seat 110. According to an embodiment of the invention, the first valve 106 comprises a biasing member 111. The biasing member 111 shown in FIG. 1 comprises a spring; however, other types of biasing members may be provided. The biasing member 11 1 may be provided to supply a biasing force on the valve member 109. According to an embodiment of the invention, the biasing member 111 biases the valve member 109 towards the valve seat 110 formed on the first stretch rod component 103 A. According to an embodiment of the invention, the biasing member 1 11 may be configured such that when pressurized fluid is supplied to the first fluid flow path 104 above a threshold pressure, a force created by the fluid acting on a first face 112 of the first valve member 109 is greater than a force created by the biasing member 111. Therefore, the pressurized fluid in the first fluid flow path 104 can bias the valve member 109 away from the valve seat 110 to open the first valve 106. It should be appreciated that the supply of pressurized fluid to the first fluid flow path 104 may be controlled using a valve (not shown), such as used in the prior art, positioned upstream from the stretch rod 103. According to an embodiment of the invention, once pressurized fluid is no longer being supplied to the first fluid flow path 104, the pressure in the first fluid flow path 104 drops to below the threshold pressure. According to an embodiment of the invention, the drop in pressure is due, in part, because the pressure supplied to the first fluid flow path 104 may be provided at a higher pressure than a desired mold cavity 102 pressure. As the pressure in the first fluid flow path 104 drops to below the threshold pressure, the first valve 106 can close due to the biasing member 111. With the first valve 106 closed, pressurized fluid between the upstream valve and the first valve 106, i.e., fluid in the first fluid flow path 104 can remain in the first fluid flow path 104. Therefore, the first fluid flow path 104 is no longer a dead volume area. It should be appreciated that in other embodiments, the first valve 106 may comprise other configurations, such as a solenoid-actuated valve. In embodiments employing a solenoid-actuated valve, control of the first valve 106 can be accomplished substantially independent of the pressurized fluid supplied to the first fluid flow path 104.

As mentioned above, in FIG. 1, the second valve 107 is shown closed. According to an embodiment of the invention, the second valve 107 comprises a valve member 113 and a valve seat 114. According to an embodiment of the invention, the valve member 113 is formed on the first stretch rod component 103 A. The valve member 113 may comprise an at least partially compressible material suitable for forming a fluid-tight seal. According to an embodiment of the invention, the valve seat 114 is formed on the second stretch rod component 103B. As shown, the second valve 107 is therefore coupled to the stretch rod 103. The second valve 107 may therefore be considered integral to the stretch rod 103. In other embodiments, the second valve 107 may comprise a configuration similar to the first valve 106. In other words, the second valve 107 may comprise a check valve. Such a configuration may be desired in embodiments where the first and second stretch rod components 103 A, 103B are not coaxially aligned.

In addition to the first and second valves 106, 107, a substantially fluid- tight seal may be formed between the second stretch rod component 103B and a stretch rod end cap 108. According to an embodiment of the invention, the stretch rod end cap 108 may be coupled to the first stretch rod component 103 A. For example, the stretch rod end cap 108 may threadedly engage the first stretch rod component 103 A. In some embodiments, the seal is formed between the second stretch rod component 103B and the stretch rod end cap 108 when first stretch rod component 103 A is retracted as shown in FIG. 1.

FIG. 2 shows a cross-sectional view of the blow-molding system 100 according to another embodiment of the invention. According to an embodiment of the invention, FIG. 2 shows the blow-molding system 100 after the stretch rod 103 has been inserted into the mold cavity 102 and during a pre-blowing stage. According to the embodiment of the invention shown in FIG. 2, the stretch rod 103 has extended at least partially into the mold cavity 102. The sealing members 6 can provide a substantially fluid-tight seal between the stretch rod receiver 12 and the stretch rod 103. In the embodiment shown in FIG. 2, the first stretch rod component 103 A is in a first actuated position. According to an embodiment of the invention, in the first actuated position, the first stretch rod component 103 A is partially extended from the second stretch rod component 103B. As a result, the seal between the stretch rod end cap 108 and the second stretch rod component 103B has broken. Further, in the embodiment shown in FIG. 2, pressurized fluid is supplied to the first fluid flow path 104, which overcomes the biasing member 111 to open the first valve 106. As a result, the first valve 106 opens and provides a fluid communication path between the first fluid flow path 104 and the mold cavity 102. Therefore, pressurized fluid at a first pressure can flow from the first fluid flow path 104 through the first valve 106 and into the mold cavity 102.

According to an embodiment of the invention, the stretch rod 103 can remain in the position shown in FIG. 2 for a pre-determined amount of time. According to another embodiment of the invention, the stretch rod 103 can remain in this state until the mold cavity 102 is pressurized to a pre-determined pressure, which may be measured by a pressure sensor 220, for example. The pressure sensor 220 may be coupled to suitable electronics (not shown) via lead 221 extending from the blow-molding housing 101, for example. While the pressure sensor 220 is shown towards the bottom of the mold cavity 102, it should be appreciated that the pressure sensor 220 may be located any place within the mold cavity 102 and the particular location shown is merely illustrative and should in no way limit the scope of the present invention.

FIG. 3 shows a cross-sectional view of the blow-molding system 100 according to an embodiment of the invention. According to an embodiment of the invention, FIG. 3 shows the blow-molding system 100 between the pre-blowing stage and a blowing stage. In the embodiment shown in FIG. 3, the first stretch rod component 103 A is still in the first actuated position; however, the first valve 106 is closed. As a result, the first face 112 of the valve member 109 is sealed against the valve seat 110, thereby closing the fluid communication path between the first fluid flow path 104 and the mold cavity 102. According to an embodiment of the invention, the first valve 106 may have moved to the closed position due to the force of the biasing member 111 if the pressurized fluid is no longer supplied to the first fluid flow path 104, for example. According to an embodiment of the invention, if pressurized fluid is no longer supplied to the first fluid flow path 104, the pressure in the first fluid flow path 104 may fall to below the threshold pressure and the biasing member 111 will bias the valve member 109 to the position shown in FIG. 3. It should be appreciated however, that while the pressure of the fluid in the first fluid flow path 104 may decrease slightly to below the threshold pressure, at least some pressurized fluid remains in the first fluid flow path 104. This may be especially true if the upstream valve is simply closed and not exhausted. According to another embodiment of the invention, the first valve 106 may be closed under the force of a solenoid, for example. In this embodiment, the pressure in the first fluid flow path 104 may remain substantially constant. Therefore, it should be appreciated that an upstream valve is not necessary for the present invention.

FIG. 4 shows a cross-sectional view of the blow-molding system 100 according to another embodiment of the invention. According to an embodiment of the invention, FIG. 4 shows the blow- molding system 100 during a blowing stage. In the embodiment shown in FIG. 4, the second valve 107 is shown in an open position. According to an embodiment of the invention, the second valve 107 can be opened by actuating the first stretch rod component 103 A to a second actuated position. In the second actuated position, the first stretch rod component 103 A has extended further than previously shown. As a result, the valve member 113 of the second valve 107 is no longer sealed against the valve seat 114 formed on the second stretch rod component 103B. With the second valve 107 opened, pressurized fluid in the second fluid flow path 105 can enter the mold cavity 102. The second valve 107 therefore, selectively provides a fluid communication path between the second fluid flow path 105 and the mold cavity 102. Because the first valve 106 has already closed, the pressurized fluid in the second fluid flow path 105 is substantially prevented from entering the first fluid flow path 104. According to one embodiment of the invention, the pressurized fluid in the second fluid flow path 105 comprises a fluid at a higher pressure than the fluid in the first fluid flow path 104. For example, the fluid in the second fluid flow path 105 may comprise a blowing pressure of approximately 40 bar.

According to an embodiment of the invention, the blow-molding system 100 can remain in the position shown in FIG. 4 for a pre-determined amount of time. According to another embodiment of the invention, the blow-molding system 100 can remain in the position shown in FIG. 4 until the pressure in the mold cavity 102 reaches a threshold pressure. Once the blowing stage ends, the second valve 107 can be closed. According to one embodiment of the invention, the second valve 107 can be closed by de-actuating the first stretch rod component 103 A from the second actuated position. Once the first stretch rod component 103 A is de-actuated from the second actuated position, the second valve 107 closes and the fluid in the second fluid flow path 105 is no longer in fluid communication with the mold cavity 102. However, at least some pressurized fluid remains in the second fluid flow path 105, which can be used in a subsequent blowing stage. According to one embodiment, the pressure in the second fluid flow path 105 remains substantially constant after the second valve 107 is closed. Advantageously, the pressurized fluid in the second fluid flow path 105 does not have to be exhausted at the end of the blowing stage and the second fluid flow path 105 no longer comprises a dead volume. According to an embodiment of the invention, the second valve 107 can operate substantially independent of pressurized fluid in the second fluid flow path 105. Therefore, in some embodiments, an upstream valve may not be necessary for controlling the pressurized fluid supplied to the second fluid flow path 105 as described above for the pressurized fluid supplied to the first fluid flow path 104.

According to an embodiment of the invention, the blow-molding cycle ends by exhausting the mold cavity 102. In the embodiment shown, the stretch rod 103 is withdrawn from the mold cavity 102 to expose the exhaust fluid flow path 10 to the mold cavity 102 in order to exhaust the mold cavity 102. As can be appreciated, while the pressurized fluid in the mold cavity 102 is exhausted, the pressurized fluid in the first and second fluid flow paths 104, 105 remains in the first and second fluid flow paths 104, 105, respectively. Further, pressurized fluid that is located between any upstream valves and the first and second valves 106, 107 can remain pressurized at the end of a blow-molding cycle. Advantageously, during the exhausting stage, the present invention can exhaust fluid in the mold cavity 102 that was used to mold the preform without having to exhaust fluid in fluid lines leading to the mold cavity 102. The present invention therefore, substantially reduces dead volume typically associated with prior art blow-molding systems. The present invention therefore, requires less pressurized fluid to operate than in the prior art. The present invention therefore, requires less energy to operate than in the prior art.

FIG. 5 shows the blow-molding system 100 according to another embodiment of the invention. In the embodiment shown in FIG. 5, the stretch rod 103 only comprises a first stretch rod component 103 A and the second stretch rod component 103B that is described above is omitted. As a result, the stretch rod 103 only defines a first fluid flow path 104 and a first valve 106. The first fluid flow path 104 may provide pressurized fluid to the mold cavity 102 during both the pre-blowing stage and the blowing stage. In other embodiments, the first fluid flow path 104 may provide pressurized fluid to the mold cavity 102 during one of the pre-blowing or the blowing stage. In the embodiment shown in FIG. 5, a second fluid flow path may be provided in the stretch rod receiver 12, for example. It should be appreciated that control of the pressurized fluid from the first fluid flow path 104 to the mold cavity 102 can be accomplished in a manner similar to that described above. In the embodiment shown in FIG. 5, because the valve seat 110 and end cap 108 are larger than the first stretch rod component 103 A, the stretch rod receiver 12 may be adjustable to expand to accommodate the enlarged area of the valve seat 110 and end cap 108, for example. The present invention as described above improves blow-molding systems by eliminating or substantially reducing the dead volume of the system. By incorporating one or more valves 106, 107 in the stretch rod 103, fluid can be supplied to the mold cavity 102 through the stretch rod 103. Because the valves 106, 107 comprise a portion of the stretch rod 103 and are not located remotely or attached outside of the blow- molding system 100, pressurized fluid supplied to either the first or second fluid flow paths 104, 105 formed in the stretch rod 103 does not have to be exhausted at the end of a molding cycle. Rather, the valves 106, 107 can close to retain at least a portion of the pressurized fluid in the fluid flow path 104, 105, respectively. In a subsequent blowing cycle, the pressurized fluid retained in the stretch rod 103 can be utilized to pressurize the mold cavity 102. Advantageously, substantially only the fluid that actually fills the mold cavity 102 is exhausted, thereby eliminating or substantially reducing the dead volume of the blow-molding system 100.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other blow-molding systems, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.

Claims

CLAIMS We claim:

1. A blow-molding system ( 100), comprising:

a blow-molding housing (101) defining a mold cavity (102);

a stretch rod (103) movable within the mold cavity (102) and including:

a first stretch rod component (103 A) defining a first fluid flow path (104); and

a first valve (106) coupled to the first stretch rod component (103 A) and adapted to selectively provide a fluid communication path between the first fluid flow path ( 104) and the mold cavity ( 102) .

2. The blow-molding system (100) of claim 1, wherein the stretch rod (103) further comprises:

a second stretch rod component (103B) defining a second fluid flow path (105); and

a second valve (107) adapted to engage a portion of the second stretch rod

component (103B) to selectively provide a fluid communication path between the second fluid flow path (105) and the mold cavity (102).

3. The blow-molding system ( 100) of claim 2, wherein a portion of the second valve (107) is coupled to the first stretch rod component (103 A).

4. The blow-molding system (100) of claim 3, wherein the second valve (107) comprises a valve member (113) formed on the first stretch rod component (103 A) and a valve seat (114) formed on the second stretch rod component (103B).

5. The blow-molding system (100) of claim 2, wherein the first and second stretch rod components (103 A, 103B) are coaxially aligned and movable with respect to one another.

6. The blow-molding system (100) of claim 5, further comprising a stretch rod end cap (108) coupled to the first stretch rod component (103 A) and adapted to form a substantially fluid-tight seal with the second stretch rod component (103B).

7. The blow-molding system (100) of claim 1, wherein the first valve (106) comprises a movable valve member (109) and a valve seat (110) formed at an end of the first stretch rod component (103 A).

8. A stretch rod (103) for a blow-molding system (100), comprising:

a first stretch rod component (103 A) defining a first fluid flow path (104); and a first valve (106) coupled to the first stretch rod component (103 A) and in fluid communication with the first fluid flow path (104).

The stretch rod (103) of claim 8, further comprising:

a second stretch rod component (103B) defining a second fluid flow path (105);

and

a second valve (107) adapted to engage a portion of the second stretch rod

component (103B) and in fluid communication with the second fluid flow path (105).

10. The stretch rod (103) of claim 9, wherein a portion of the second valve (107) is coupled to the first stretch rod component (103 A).

11. The stretch rod (103) of claim 10, wherein the second valve (107) comprises a valve member (113) formed on the first stretch rod component (103 A) and a valve seat

(114) formed on the second stretch rod component (103B).

12. The stretch rod (103) of claim 9, wherein the first and second stretch rod components (103 A, 103B) are coaxially aligned.

13. The stretch rod (103) of claim 12, further comprising a stretch rod end cap (108) coupled to the first stretch rod component (103 A) and adapted to form a substantially fluid-tight seal with the second stretch rod component (103B).

14. The stretch rod (103) of claim 8, wherein the first valve (106) comprises a movable valve member (109) and a valve seat (110) formed at an end of the first stretch rod component (103 A).

15. A method for operating a blow-molding system including a mold cavity, a stretch rod, a first fluid flow path formed in the stretch rod, and a first valve coupled to the stretch rod, the method comprising steps of:

inserting the stretch rod into the mold cavity;

supplying a first pressurized fluid to the first fluid flow path; and

16. The method of claim 15, wherein the blow-molding system further includes a second fluid flow path formed in the stretch rod and a second valve coupled to the stretch rod, the method further comprising steps of:

supplying a second pressurized fluid to the second fluid flow path; and opening the second valve to provide a fluid communication path between the second fluid flow path and the mold cavity, thereby pressurizing the mold cavity to a second pressure.

The method of claim 16, further comprising steps of:

closing the second valve to close the fluid communication path between the

second fluid flow path and the mold cavity; and