GB2059812A - Painting can interiors - Google Patents

Abstract

In the spray-painting of can interiors, the cans (16) are set rotating and raised into the spraying position by an axially-movable rotating spindle (6) which carries a plate (14) that abuts the base (17) of the can. The can is held on the plate magnetically or by suction. <IMAGE>

Description

SPECIFICATION Method and apparatus for spray-painting containers The present invention relates to a method and an apparatus for spray-painting containers, especially tins, closed at the bottom in which the open end of the tin is aligned with a spray nozzle mounted on a frame and rotated, whereupon the rotating tin is moved axially to the spraying nozzle, painted internally, and then discharged.

Apparatuses suitable for carrying out such a method are known and are generally provided with a device for individually feeding the tins.

to a position of readiness. This feeding device may be a feed spider or a feed screw. Moreover, a device is provided for accelerating and driving the tin about its axis at a predetermined rated or desired speed engaging the tin with adhesion. The acceleration and driving of weight-eccentric, two-part drawn tins poses considerable problems, esepcially when these are already decorated with silver paint-free or UV paints. For an economical method of operation speeds of rotation of 3500 revs. per minute are desirable. This applies especially to painting methods in which a relative movement along the direction of the axis of the tin is provided between spraying system and tin.

In the so-called stationary spraying system, in which the parts are rotated only relative to each other during the spraying operation, speeds of 1 200 rpm are still required however.

In both methods of operation the radial tin speed or movement is produced by pressure contact between the wall of the tin and a friction roller. To enable the friction roller to exert sufficient pressure on the circumference of the tin to obtain sufficient acceleration, four to six counter pressure or guide rollers are provided which have to be rotatably engaged thereby. This means that with each individual internal spraying operation it is necessary not only to accelerate the tin weight of, for example, 33g to the nominal or required speed, but in addition also the weight of all the counter pressure rollers and associated components, which with regard to their mass amounts to double or treble that of the tin mass. The situation is aggravated in that between the driving elements and the tin circumference only a relatively slight slip should occur.This is required on the one hand to protect the outer decoration, whereby, it is still necessary, however, to use paints or varnishes of high mechanical resistance for the outer decoration. The slight slip would, however, also be desirable in view of the paint or varnish consumption. This consumption with the occurrence of the slip should be so in excess that a completely closed pain image is obtained despite the occurrence of a slip.

A further substantial difficulty in the acceleration and driving device for the tin of the known painting systems resides in that for these driving devices the tin requires a flange at the free end. This flange firstly has the purpose of making the jacket of the tin more rigid and resistant to the friction and acceleration forces. The flanged edge also has the function of stabilising the position of the tin within the driving device, since at high speeds the weight-eccentric bottom gives the tin the inclination to break out laterally. Since, however, the flanged edge has also to be painted therewith, the internal spray nozzle also has to spray paint in positions outside the tin so that painting of the flanged edge is reliably en- sured.This results in a number of additional measures to collect the paint, to clean the surrounding machine components and to protect operators against paint fumes. The paint consumption may also be thus increased by 10%. This extra consumption of paint is of no benefit to the painting of the tin, but has subsequently to be laboriously removed from the machine components. Misty components have to be destroyed by means of after-burner devices. Furthermore, the known devices have the spraying nozzle already mentioned for internally painting the tin, which is preferably fixedly arranged. Moreover, a driving device may be provided to move the rotating tin axially relative to the spraying nozzle. Moreover, conventional control and valve devices for controlling the devices and devices ensuring a predetermined working cycle are provided.

It is an object of the invention to develop further a method and an apparatus of the kind mentioned above such that the difficulties shown can be substantially minimized. It is also an intention to especially protect the tin itself and its outer decoration. Furthermore, the paint consumption for the internal painting should be limited to the required extent. A further object is to enable the internal painting to be carried out without the tin requiring an edge flanging. Finally, the arrangement is to be designed to be labour saving and utilize less installation.

According to the present invention there is provided a method of spray-painting containers such as tins which are closed at the bottom, wherein the container with open end is aligned with a frame-mounted spraying nozzle and rotated, whereupon the rotating container is moved axially to the spraying nozzle, painted and removed, characterised by the feature that a flat retaining surface is driven by means of a spindle constantly at required speed and, whilst simultaneously producing a magnetic or pneumatic retaining force, is moved against a surface of the bottom of a resting container and the container with axial engagement is suddenly accelerated to desired speed with a slip of less than 10 mm.

In connection with chucks also for tins it is known to use magnetic or pneumatic retaining forces. Thus, DE-Gbm 6 752 437 shows an apparatus for painting or spraying a hollow body by electrostatic means. Herewith the hollow body by means of a suction cup is supported inverted whereby the suction cup engages the closed bottom. The suction cup is itself supported on a conveyor chain. This arrangement concerns a static internal coating since neither the tin nor the suction cup is rotated. Hence, the problems are not posed as are caused in accordance with the above explanations particularly with the necessity of accelerating and driving the tin up to a speed of 1000 to 3500 rpm and more.

It is known, moreover, for trimming the open ends of metal tins, to provide a chuck which not only engages the bottom surface but also the regions of the body of the tin close to the bottom and in which a mechanically guided cutting head engages in the open end of the tin and urges it against the chuck whereby chuck and cutting device are driven.

Herein also, the chuck may be provided with a pneumatic device to increase the retaining force of the chuck and to facilitate the ejection of the trimmed tin (see DE-OS 2 456 097).

In this known apparatus, the tin is supported at both ends and clamped mechanically and driven from both ends.

This arrangement is not possible for internal painting since the end of the tin and the entire interior of the wall of the tin have to remain free for the coating operation. It is for this reason with internal painting devices, frictional engagement over the outer jacket is almost exclusively used even though the frictional drive creates the risk of damage to the external decoration. Added to this is the consideration that the trimming of the tins occurs directly after drawing, thus before the tin is provided with an external decoration. Moreover, relative movements between tin and chuck are of no consequence. Also the tin with the chucks may be accelerated from standstill.

The invention is based on the unexpected realization that for the purpose of internal painting a tin closed at one end may be accelerated and driven from a static position almost suddenly or immediately to the desired speed of 1000 to more than 3500 rpm without any significant slip from the stable bottom surface of the tin alone, so that the drive of the tin does not cause any deformation of the tin nor any darnage whatsoever of the outer decoration. The single drive from the bottom surface also permits painting of the interior to be carried out without the body of the tin being provided with an edge flange or flanged edge. It has been surprisingly found that the tin may be accelerated from a complete standstill in the course of a uniformly continuous movement not only in circumferential direction but also in axial direction.The slip occurring thereby even at speeds of 3500 rpm lies far below 10 mm measured between the clamping surface and the bottom surface ring surface which is in contact with the clamping surface. Clamping may be effected by permanent magnets or by air suction. It has been found that these clamping forces despite the one-sided support of the tin are fully adequate to reliably accelerate the tin in the centered position and also to safely retain and center the displacement forces emanting from the spraying nozzle.Of particular advantage herewith is that not only the acceleration and the drive alone &commat;&commat;n can be effected from the base end with maximum preservation of the wall and the external decoration, but that even when slowing down the tin it is possible to exert braking forces merely on the base end, and thus in such a manner that tin under the action of the residual rotary forces alone during lift-off from the clamping surface from the flush position with the rotary axis, drifts automatically sideways and so over a discharge table surface and may be conducted to a known discharge device without necessitating any special kind of additional conveyor, driving or deflecting device. This also substantially simplies the apparatus.The quantity of paint may also be restricted to the required quantity, since there is no flanged edge and therefore no measures are necessary to paint the flanged edge. This also simplifies the apparatus for collecting excessive paint quantities and extracting by suction excessive solvent vapours.

The present invention will be described further, by way of example, with reference to the accompanying schematic drawings, in which: Figure 1 is a vertical section in simplified form through apparatus for carrying out the method of the invention; Figure 2 is a vertical section on an enlarged scale of a detail of the apparatus of Fig. 1, wherein the clamping surface is provided with a device producing magnetic retaining forces; and Figure 3 is a vertical section through a fragmentary detail of a modified embodiment of the device of Fig. 2 in the region of the clamping surface.

The apparatus shown in Fig. 1 includes a stand-mounted frame 1. The frame 1 has two slide guide sections 2 on tJO vertical portions on which sections there arts mounted sliding bearings 4 of a horizontally extending table or frame portion 3. The table or frame portion 3 has spaced apart vertical apertures through each of which a spindle 6 projects. Each spindle 6 is rotatably mounted on the frame section 3 by means of bearings 5 and axially secured relative to the frame section 3 by spring rings 8 or the like. Each spindle 6 may be rotated in its bearings 5 in the direction of arrow 7.

Securely splined to the lower end of the spindle 6 and located under the frame section 3 is a gearwheel 9 around which a driving element, more especially a toothed belt 10, is looped. As indicated by chain-dotted lines in Fig. 1, denoted by-reference numeral 6 a plurality of such spindles 6 are mounted in frame section 3. Each spindle has a gearwheel 9. The toothed belt 10 is looped around all the gearwheels 9 and around the driving pinion of a driving motor 40 which is secured on the underside of the frame section 3.

Hence all spindles 6 may be rotated simultaneously via the drive 9, 10 and 40.

At the upper end of each spindle 6 an engaging or clamping plate 1 3 is supported which in the example of Fig. 2 is secured by screwing to the head end of the spindle 6.

The clamping plate 1 3 has an upwardly facing, flat, horizontal engaging or clamping surface 14 in which permanent magnets 1 5 are arranged in recesses and for producing the required retaining force.

As evident from Fig. 1, the frame 1 above the guide sections 2 supports a table surface or plate 11 which has recesses 1 2 in alignment with the spindles 6. The inner width of the recesses 1 2 is such that the clamping plates 1 3 may pass freely through the recesses 1 2 of the table plate 11. The surface of the table plate 11 for each recess 1 2 has braking elements 1 8 associated therewith and located in definite manner, the significance of which will be dealt with further below.

A container to be painted on its inside surface is denoted by 1 6. In the embodiment shown, the container is a tin of typical crosssection for drawn tins. It is evident that the tin has a cylindrical body without a flanged edge and which via a frusto-conical section 1 7a merges into a flat ring surface, which defines a dome-shaped central base section 1 7. As evident from Fig. 2, the diameter of the clamping plates 1 3 is sufficiently large, so that the permanent magnets 1 5 are located level with the ring surface of the base.On the other side, the base of the clamping plate 1 3 is sufficiently small such that the diameter of the tin 1 6 exceeds the diameter of the clamping plate 1 3. This causes, as evident from Fig. 2, during the lowering of the spindle 6, when the clamping plate 1 3 passes downwardly through the recess 1 2 and below the table top 11, the frusto-conical base section 1 7a to come into contact with the frame mounted braking elements 1 8 so that the tin 1 6 is lifted-off the clamping plate 1 3 and at the same time is slowed down from the high operating speed.The arrangement is such that the interaction of the torques acting on the tin lifted-off the clamping plate 1 3 causes such to be rotated along the table plane, out of the aligned position with the axis of rotation 80 of the spindle 6 and laterally away from the table surface, whereby with suitable guidance it reaches a reception region for conveying away. This operation occurs fully independently and merely by using the residual momentum or torques originating from the high speed in combination with the braking torques exerted by the frame trestle and which only engage in the base region of the tin.

In alignment with the axis of rotation 80 of the tin above the table surface 11 mounted in the frame an internal spraying nozzle 25 is arranged which communicates via a supply conduit 26, 27 with a control valve 28 and a paint source. Thus, each spindle 6 has an internal spraying nozzle associated therewith.

The internal spraying nozzles face radially downwards, so that adjacent internal spraying nozzles 25 may have a common paint collecting device 25a associated therewith.

The association of the internal spraying nozzle with the initial position of preparation of a tin 1 6 to be spray painted is such that after engagement of the tin by the upwardly travelling clamping surface 14 the spindle is first raised to an upper dead centre position which corresponds to the maximum approach of the internal spraying nozzle 25 and the base 17, 17a. Only then is the valve 28 of the internal spraying system triggered, so that at first the bottom of the tin is spray-painted, whereupon, during the subsequent lowering movement of the spindle 6, the inside surface of the tin is painted continuously from base to edge in a spiral.

The tin is moved by known devices such as a feed spider 20 or feed screw individually over a supply surface, e.g. the top surface of a table 11 into a position of readiness in alignment with the axis 80, whereby the clamping plate 1 3 with the spindle 6 is located below the upper surface of the table 11.

The supply spider 20, via shafts 21, 22, which are mounted in suitable manner, e.g. at 30 in the frame 1, may be constantly driven via a belt drive 31, 32, 33 at uniform speed by the power take-off shaft 34 of a driving motor 35. It is thus to be assumed that for each spindle 6 a supply device 20, 21 is provided. The drive of the supply device may be either intermittent or cyclic.

The driving motor 35 in the example shown is provided to simultaneously produce a cyclic vertical up-and-down movement of the frame section 3. For this purpose a connecting rod 36 is connected to the underside of the frame section 3 via a universal joint 37. The crank pin of the connecting rod in the example shown engages in the groove of an eccentric disc 38 which is driven by the motor 35. By means of the speed control of the motor 35 and the adjustment or development of the eccentric disc 38, the length of stroke and the speed of stroke of the frame section may be readily and accurately adjusted and varied as required.

The motor 40 for driving the spindles 6 during operation of the apparatus is driven constantly and at uniform speed, so that the spindles 6 are constantly driven at the required nominal speed.

As soon as a tin 1 6 is located at each painting station of the apparatus according to Fig. 1 in a position of readiness in alignment with the associated axis of rotation, a cycle is triggered and the frame section 3 is raised via the eccentric drive 38 in accordance with the double arrow 41. Herewith the clamping plate 1 3 plunges through the recess 1 2 of the table top 11 and finally comes into contact with the ring surface at the bottom of the tin located in the position of readiness.It has surprisingly been found that, via this ring surface, the tin with the clamping surface 14 with suitable dimensioning of the magnetic forces of the magnets 15, may be so reliably braced that the resting tin 1 6 almost suddenly and without occurrence of any significant slip in the region of the ring surface or contact surface be acelerated to the nominal speed without the centered position of the tin being changed. The tin 1 6 suddenly accelerated in this manner is carried along upwards with the upwardly displaced clamping plate 13, and thus to the uppermost dead centre position of the spindle 6. In this region, as already mentioned, the painting operating is initiated.This causes the base to be reliabiy spray-painted first, whereby this operation is benefitted by the fact that in the region of the upper dead centre, despite uniform rotation of the eccentric disc 38, the lowering movement of the clamping plate 1 3 becomes only slowly noticeable and continues with acceleråtion only with further rotation of the eccentric disc 38.

In this manner, after the interior base of the tin has been carefully spray-painted, the operation is spirally continued therefrom to the open end and terminates on reaching the unflanged edge, so that only small quantities of paint can leave the tin and have to be trapped by the drip collecting device 25a and to be discharged.

Tests have shown that instead of magnetic retaining forces also pneumatic retaining forces can be effectively used, whereby the suction force in the region of the clamping surface 14 can be brought into effect via a central bore in the spindle 6. Such a pneumatic clamping effect is indicated in the modified example of Fig. 3. Herein, the spindle 52 has a longitudinal bore 54 which at the upper surface at 55 leads to a mushroom-shaped ejecting device 53 subjected to a spring bias.

Braking herein occurs not by direct engagement of braking elements on the base of the tin, but indirectly via a freely rotatable intermediate member 51 which in turn forms the clamping surface of the spindle 52 and on the other hand has an external collar which together with suitable formed surfaces forming the recess in the table top 11 a forms the braking device 50. Herein too the spindle 52 is constantly driven at required speed. The spindle, the intermediate member 51, the ejecting device 53 and the tin are suddenly clamped together into a unit by the pneumatic retaining force, which suddenly assumes the required speed. During the lowering of the spindle the intermediate member 51 reaches the braking position, so that the tin together with the intermediate member 51 are braked and lifted-off the clamping surface by the ejecting device.

The same apparatus may also be used with advantage for preferably simultaneous exter nai painting, since the tin is supported only in the region of the base surface by means of which it is driven. An external spraying nozzle 75 may have associated therewith conventional devices for catching excess paint and nozzle 75 may be connected to the conduit system 27 via a valve 76.

Claims (9)

1. A method of spray-painting containers such as tins which are closed at the bottom, wherein the container with open end is aligned with a frame-mounted spraying nozzle and rotated, whereupon the rotating container is moved axially to the spraying nozzle, painted and removed, characterised by the feature that a flat retaining surface is driven by means of a spindle constantly at required speed and, whilst simultaneously producing a magnetic or pneumatic retaining force, is moved against a surface of the bottom of a resting container and the container with axial engagement is suddenly accelerated to desired speed with a slip of less than 10 mm.

2. A method as claimed in claim 1, in which with cyclic vertical reciprocation of the spindle, the spraying operation is triggered when the spindle reaches the upper, deadcentre position and on reaching maximum approximation from the bottom of the container and spraying is continued during the downward movement of the spindle.

3. A method as claimed in claim 1 or 2, in which on completion of the spraying operation the container rotating at required speed is lifted-off the flat surface of the spindle and slowed-down in the region of the bottom by applying braking forces in such a manner that the container, subject to the action of the residual rotary forces, is' turned laterally out of the aligned position with the rotary axis.

4. A method as claimed in any of claims 1 to 3, in which the slip is less than 5 mm.

5. Apparatus for carrying out the method as claimed in any of claims 1 to 4 having a device for individually feeding the containers to a prepared position, a device engaging the tin by contact of adhesion for accelerating and driving the tin about the axis at a predeter mined required speed, a spraying nozzle for internally painting the container, a driving device for moving the rotating container and the spraying nozzle relative to each other in an axial direction, and control and valve devies for controlling the apparatus and devices according to a predetermined working cycle, characterised by at least one vertical spindle adapted to be driven constantly at a required speed, having a flat engaging surface with an engaging device associated therewith acting with magnetic force or with suction force, in which the engaging surface is displaceable in the direction of the axis of rotation from a prepared position of readiness into the plane of supply of containers and to an upper deadcentre position and therein the spraying operation triggered, and that the downward stroke path of the spindle has a braking device which co-operates with the bottom of the rotating container associated therewith, in such a manner that the container is removable from the engaging surface and so slowed down that, subject to the action of the residual rotary forces it automatically travels laterally with rotation over a container discharge plane.

6. Apparatus as claimed in claim 5, in which a plurality of spindles freely rotatable, but axially non-displaceable are mounted in a common vertically reciprocatable sliding frame which frame supports a rotary drive common to all spindles and which frame is vertically reciprocatable via interchangeable or adjustable crank arms or eccentrics cyclically relative to the internal spraying nozzles, supply and discharge planes and braking devices.

7. A method for painting containers substantially as herein described with reference to and as illustrated in the accompanying drawings.

8. A container whenever spray-painted in accordance with the methods as claimed in any of claims 1 to 4 or claim 7.

9. Apparatus for painting containers substantially as herein described with reference to and as illustrated in the accompanying drawings.