Method and apparatus for forming hollow articles from a blank of organic polymeric material by cold-forming and articles thus formed

The invention relates to a device for molding a hollow body from a disc-shaped

A blank, which is a die, in which an annular recess for receiving the blank is provided, and a pressed against the outer edge of the blank annular clamping piston and a through the

Clamping piston has in the mold space of the die movable forming punch.

The invention can be applied to various plastics and metals, but an applicability is given in particular in such plastics, which undergo an increase in their strength in a cold working. The term "cold working" is understood to mean the processing or deformation of a material which is in its solid phase and at a temperature below its melting point. Therefore, instead of the term cold deformation "or Cold processing "is also the term processing or Apply deformation in the solid state; however, since the effects achieved by the invention are similar to those obtained by cold working various metals and the term "cold working" is usually applied in the context of solid state solidification, this term will be used hereafter, but it should be noted that For some plastics, the strength improves when the material in question is processed at a relatively high temperature, eg at a temperature significantly exceeding 100 ° C.

The previously known devices for cold working of plastics or metals are subject to various shortcomings. In a known device of the type described in the introduction, the annular recess in the die is completely filled by the inserted blank, wherein the restraining the edge of the blank clamping piston on the surface of the die comes to rest, so that during the molding process, the thickness of the clamped edge of the The blank remains unchanged. This initially results in the disadvantage that the edge of the hollow body produced and the parts of the side wall adjacent to the edge do not assume the properties of a cold-worked or cold-worked material. Moreover, to form the hollow body, a relatively high effort is required and there is a risk that the wall thickness of the side wall of the hollow body varies over the height of the hollow body.

The object of the invention is now to provide an improved apparatus for producing hollow bodies, with which the above-described defects are avoided. This object is achieved according to the invention in a device of the type described by the fact that the annular clamping piston which can be pressed against the outer edge of the blank can be pushed into the annular recess of the die.

By this measure, the edge of the inserted into the annular recess of the die blank can be compressed to the desired extent and thereby made thinner, wherein a portion of the material is displaced from the edge zone in the central region of the blank. The edge and the adjacent parts of the resulting hollow body obtained as a result of this measure the properties of a cold-worked or work-hardened material. Moreover, if a certain mechanical strength of the edge is desired, less material is needed as compared to a hollow body whose edge is not work-hardened.

A particularly favorable cold deformation is achieved if the axial mobility of the clamping piston in the annular recess of the die still a rotational movement is superimposed, because this also a work-hardened deformation in the circumferential direction is made possible. Namely, if the edge of the blank is not only compressed, but the material of the edge is also caused to flow in the circumferential direction or a tangential direction, the material is oriented and solidified in the direction of two axes.

The bottom of the hollow body can be additionally processed and shaped after the molding process, u.zw. between the forming die and a cooperating counter-punch, this process taking place at the end of the working stroke of the punch; hiebei the thickness of the bottom depends on the length of the working stroke of the forming die for forming the side wall in relation to the original thickness of the blank, the dimensions of the annular die opening and other factors, such as the friction between the material and the parts of the die.

After the hollow body has been formed by the drawing operation, the tubular wall thereof can be widened and further formed so as to obtain higher strength in the circumferential direction. For this purpose, a second operation may be performed while the material is still substantially at the same processing temperature.

The hollow body can be made of a blank which is composed of several layers, which may consist of the same material or of different materials, so that there is a multi-walled hollow body.

With the help of the device according to the invention, for example, containers can be produced whose edge on its outer surface predetermined irregularities, for example, projections, depressions or the like. having the attachment of screw or snap closures, ironing or the like. enable.

The plastics that can be processed according to the invention include halogenated ones

Hydrocarbon polymers, fluorocarbon polymers, polyamides, polyesters, polystyrenes, polyolefins and

Polypropylenes. In particular, polypropylenes undergo a remarkable improvement in their strength when

-3Nr.308392 they are deformed in the solid state, u.zw. either in the direction of an axis or in the direction of two

Axes.

The invention will be explained in more detail with reference to exemplary embodiments with reference to the drawings. Fig.l shows in an axial section an embodiment of a device according to the invention, wherein the device parts are shown in their retracted position of rest and the device is just fed to a disc-shaped blank. Fig. 2 is an axial section through the apparatus of Fig. 1, wherein the edge of the blank has been compressed by the gripping piston to push inward a portion of the material of the rim. Fig. 3 is an axial section through the apparatus of Fig.l and shows how the forming die has been moved down to produce a cup-shaped hollow body from the blank. 4 shows in an axial section the device in the open state and during ejection of the hollow body. 5 is an axial partial section through another embodiment of the inventive device for producing cold-formed and subsequently expanded hollow bodies, Figure 6 is a similar to Figure 5 representation of a device with which the material of the upper flange or edge of the hollow body in two Directions can be oriented.

In Fig.l to 4 can be seen serving for forming a hollow body press with a Matrizenaggregat -10-, which has a serving for molding chamber -11- and an annular recess -12- for receiving a disc-shaped blank -W-. An annular piston -13- for clamping the edge of the blank is mounted on guide rods -14- so that it can enter the enlarged upper part of the chamber -11- to the annular edge of the blank -W- with respect to the annular recess - 12- to brace.

A blank forming die 15 is disposed so as to pass through the cylindrical opening 16 of the clamping piston 13 to engage the portion of the blank W within the clamped edge. As shown in Fig. 2, there is an annular gap -17- between the inner edge of the recess -12- and the outer edge of the lower end of the punch -15-. The radial dimension of the annular gap -17- is considerably smaller than the original thickness of the blank and corresponds approximately to the thickness of the thickest part of the side wall -Cw- of the container shown in Figure 4 -C-. Thus, substantially the entire inner main body of the blank forms a supply of material which can be withdrawn from the space under the die to form the side wall of the container when the forming die -15- is inserted into the chamber. is moved into it.

An ejector piston -20- is slidably mounted in the die chamber -11- and can be moved upwardly to cooperate with the underside of the blank when the operation for molding the hollow body begins and then performed. The upward pressure of the ejector piston is relatively low, so that substantially no compression effect is exerted on the free outward flow of the blank material from the space under the plunger -15-, and that the material under the plunger -15- only so curved or bent is that a concave shape arises. When the hollow body has been completely formed, the underside of the ejector piston -20-, after having been pressed down by the forming punch, with only slight resistance, operates with an annular seat or stop -21- (FIG. together so that the bottom -Cb- of the hollow body is formed by the application of pressure by means of the punch -15-.

Optionally, the ejector piston -20- may remain in the lower part of the die chamber -11- while the die -15- makes its downward stroke. This arrangement is especially made when the hollow body to be formed is to receive a flat bottom. In addition, if a split die with laterally separable parts is used, the ejector piston may even be completely omitted.

The clamping piston or hold-down -13- detects the outer edge of the blank -W- with a sufficient axial pressure, so that the edge against being pulled out of the recess -12- is held while the hollow body is formed; however, the edge of the blank may optionally be pressed so as to obtain a different thickness, which may vary from about the full thickness of the original blank to a very small thickness. According to the drawings, the remaining thickness of the edge corresponds approximately to the thickness of the side wall of the finished container. You can interchangeable stops -22-, for example, a ring, provide to limit the downward stroke of the clamping piston.

The withdrawal of the material from the space under the die -15- is affected by the shape of this die and the frictional properties of the material's cooperating face of the die. The lower end -15- of the die -15- shown in Figs. 1-4 is made of a rubber-like material and has a rounded edge at -24- to facilitate flow of the material. The head -23- of the stamp may, for example, be coated with a fluorocarbon polymer. Furthermore, one can use Flude, which exert a lubricating effect. In the present case, the stamp

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- 15 - provided with an axial channel - 25 -, the 2.B. can be flowed through by air. On

Sealing ring - 26 - is arranged between the plunger -15 - and the clamping piston - 13--, to help prevent the Flud escape. The flud can enter the space under the blank in the

Chamber -11-- be supplied to the ejector -20- past, for example via a channel -27-, wherein a sealing ring -28- is provided on the circumference of the shaft of the ejector piston.

The withdrawal of material from the space below the punch -15- is affected by the frictional properties of the surface of the punch cooperating with the material to be molded. A stamp which is coated with polytetrafluoroethylene, has a very low friction, especially if the material of the blank has a low coefficient of friction.

It may also be desirable and convenient to supply a fluff around the periphery of the blank to prevent the material from getting caught and to help the material flow inwardly as it is compressed by the blank holder. For this purpose, radial channels -29- are provided, and at -30 and 31- arranged sealing rings prevent escape of the Fludes. This is of greater importance if the flange -Cf- of the hollow body is relatively wide, and if its thickness should be significantly reduced, so that material is present, which is to be drawn into the side wall of the container, u.zw. in addition to the material being pulled out of the space below the punch -15-. If the edge contains a substantial amount of material, this material is preferably compressed axially and gradually pushed inwardly as the punch moves down to form the side wall of the container. In particular, however, if the edge is narrow, as shown in Fig.l and 2, the material of the edge can be pressed inwards before the punch moves -15- down. In no case is the outer edge of the blank as a whole pulled inwards, as is the case with numerous presses for the manufacture of cup parts made of sheet metal.

Fig. 5 shows an industrial-purpose machine which operates at a high production speed. In this case, the die assembly -10'- is formed by laterally separable parts -10.1-, which can be moved by means of an actuator -34-. The matrix chamber -11'- is larger than the initial molded main body of the container -C '- and the side walls -C'w- and the bottom -C'b- are inflated by means of compressed air, which is conveyed through a channel -25'. - The stamp -15- is supplied after the container has been pulled first. An annular recess -12'- is formed on the die parts -10.1- to support the outer edge of the blank -W- and to form the container flange -C'f- in the closed position of the die assembly -10'-.

An annular hold-down 13'- is actuated by a plurality of actuators -35-. The stamp -15- serving to form the material is actuated by means of a power actuator -36-. After a hollow body has been pulled and expanded in the lateral direction, the originally closed Matrizenaggregat is opened, and the hollow body is thereby blown down, that further compressed air via the channel -25'- is fed, so that the hollow body to a conveyor belt -37 - is delivered.

In the arrangement of Figures 5 and 6, it is possible to save the space for an ejector piston and the time required for its operation. In the closed die assembly, the space between the punch -15- and the inner edge -17'- of the recess -12'- as previously limited to a thickness which is considerably smaller than the original thickness of the blank, u.zw. approximately to the maximum thickness of the side wall of the container to be manufactured, so that the main part of the blank is taken down within the annular blank below the punch -15- so that the material is drawn out at the curved outer edge of the punch to the side wall of the container to build.

The relative friction between the lower end of the plunger and the material is one of the factors determining the rate of material delivery from the space below the plunger. A polytetrafluoroethylene-impregnated material with a very low coefficient of friction was used in a device according to the invention, with good results being obtained.

Fig. 6 shows a device similar to that of Fig. 5, but in which a means is provided for deforming the material of the flange -C "f- of the container -C" - in the direction of two axes. Referring to Fig. 6, the hold-down 13 "is provided with means by which the hold-down is rotated to deform the material of the container rim in the circumferential direction during or after the molding process or both during the molding process and thereafter.

6, the ring-shaped hold-down 13 "is provided with a ring gear 40, which meshes with a splined gear 41 which is non-rotatably connected to a shaft 42 which is connected by a belt. 43- is driven, which runs over a pulley -44- and a drive pulley -45-.

The annular retainer -13 "- is actuated by an annular piston -35" - while the plunger -15 "- is actuated by a piston -36". One channel -25 "- to

Feeding a Fludes extends through the punch and the associated piston, so that a fed

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Flud can help to shape or eject the hollow body or both to shape and eject. The other parts shown in Figure 6 such as lines, seals, etc. require no closer

Explanation since its operation is understandable with reference to the drawings.

The blank -W- may be formed by a single homogeneous layer of material, or it may be constructed as a layered composite whose layers are made of the same material or different materials.

The device according to Figures 5 and 6 is particularly suitable for the production of containers whose edges have outer irregularities, for example projections or depressions for receiving screw or snap caps, ironing or the like.; the separable parts of the die release such containers readily after being formed in the closed die.

In one particular case, the invention was used to make a container having a full diameter opening of the container body, a straight side wall, and a flange at the top. This container had a diameter of 100 mm and a height of 140 mm. First, a sheet of polypropylene of known type was produced by extrusion and then cooled. For a finished container with a weight of 30 g, a flat piece of material with a thickness of 3.8 mm is needed. The sheet was cut into blanks using a steel die, with the diameter of the blanks being equal to the diameter of the flange on the finished container. Such a blank or disc was heated to about 160 ° C (melting point of the material 168 ° C) and then drawn in the manner described. The disc was at its outer edge under a high pressure of over 70 kg / cm² clamped. A die equal in diameter to the inner diameter of the container was then used to stretch the disk and give it the desired shape of the container. No counter punch was used in this operation, and the material was only pulled out of the space below the bottom of the punch. With the exception of a non-lubricated nylon head section, the stamp was steel. The stretching was fast, u.zw. at a speed of about 75 mm / sec, but it should be noted that significantly higher operating speeds are possible. After forming the container, air was supplied via a channel in the center of the stamp head to strip the hollow body from the stamp.

In contrast to known thermoforming processes in which a pressure of many hundreds of kg / cm is used for molding² required for the whole surface of the blank, it is only necessary in the invention, a total pressure of about 80 kg / cm² to apply the flange. To give an example, it should be noted that to form an open bucket with a diameter of 305 mm and a capacity of 19 1 requires only a total force of about 15 t.

Experience has shown that this results in a uniform distribution of the material in the container wall, especially when the drawing depth corresponds to about 1.5 times the diameter. At a drawing depth corresponding to the diameter, the floor can be made the same thickness as the wall; For this purpose, it is only necessary to adjust the amount of material in a simple manner. The wall thickness depends largely on the friction of the punch. A smooth stamp makes it easier for the wall thickness of the floor to become low, while a high-friction stamp leads to a stretching of the side wall. In a typical case, it was found in a container with a capacity of 3.78 1, that the wall thickness of the side wall at a drawing depth corresponding to the l, 15 times the diameter near the flange 6.35 mm, in the middle 5.44 mm and 5.1 mm near the bottom of the container.