DE2347776A1 - Blow moulding thermoplast using bag around blowing mandrel - to distribute pressure and reduce risk of blowthrough - Google Patents

Abstract

An injection blow moulding apparatus has the blowing mandrell surrounded by a permanent flexible bag, onto which the molten plastics is sprayed; the mandrel together with bag and thermoplastic blank on the bag is then transferred to a blow mould where the bag is inflated, bringing the blank into contact with the inner face of the mould. The bag is pref. of an elastomer resistant to the injection and blowing temps. The open end of the bag is clamped at the base of the mandrel. The uniformity of moulding achieved enables risk of blow through to be considerably reduced, which in turn enables thermoplastics to be used at a lower temp. approaching the crystalline point.

Description

DR. HANS ULRJCH MAY D 8 MDNCHEN 2, OTTOÜTRA3SE 1 a TELEGRAMS: MAYPATENT MUNICH

TELEPHONE CO8113 003082

F-15-P-1/1219 Munich, 2 Sep. 1973

F-15-G-1 / I219a ^Sch

Pile 15016

Firre 11 "Patent Company, P.O. Box 276, Dunellen, N.J.,. V.St.A.

Device and method for combined injection molding and

Continuous casting blow molding

Brief Summary (Abstract) of the Invention: According to the invention, the blow mandrel of a blow molding machine covered with a rubber hose or sack in such a way that the plastic is supported from the inside during a blow molding process will. The fluid that inflates the preform inflates the rubber bag and stands instead with the plastic of the Preform in contact with the inside of the sack. Cooling fluid circulates in the sack, whereby the preform is cooled from both sides and the working sequence is shortened. Fluid under higher pressure can be used without the risk of the preform becoming hot, and blow molding can therefore be done at lower temperatures at which the plastic begins to crystallize and can be oriented for greater strength.

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In injection molding machines, the mandrel goes into the mold cavity first an injection mold used, the surfaces of the mold cavity from the outer surfaces of the dome a distance have, which is equal to the desired thickness of the plastic coating to be applied to the mandrel. Then the plastic injected into the mold cavity and thereby the mandrel is coated with the material.

The mold is then opened and the mandrel inserted into a blow mold, whose cavity has the shape of the hollow body to be blown. Pressurized blowing fluid emerging from the mandrel is then directed against the plastic surrounding the mandrel and the plastic contacts outwardly away from the mandrel blown with the sides of the mold. After a short cooling time, the blow mold is opened and the mandrel is one Stripping station supplied, where the hollow body is stripped from the mandrel will.

In extrusion machines, a plastic hose is down extruded into an open blow mold, and a blow pin extends down from the extruder along the axis of the tube When the tube has reached a length that is greater than the length of the blow mold, the mold closes and squeezes the lower end of the hose while the upper end of the hose is pressed tightly around the blow pin. Blowing fluid emerging from the blow pin becomes the hose then blown to the shape of the mold cavity, and then

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the mold is opened to allow another section of tubing to be extruded. The finished hollow body is from the hose, cut off, and the mold closes on the new hose section and the blowing process is repeated

With both types of machine, the molding must remain in the blow mold until the plastic has cooled down enough that it retains its shape sufficiently. The blow mold is cooled by water or another cooling fluid that circulates through cooling channels in the mold wall.

The pressure of the air or other fluid used to blow the plastic must be limited. When the fluid is introduced into the blow mold with too high a pressure, the plastic wall is damaged at the weakest point by the fluid or pierce the point of greatest stress, and the temperature of the plastic must be controlled so that it is for Blowing is hot enough at the risk-free pressure to use.

By covering the blow pin with a balloon or sack and Covering the outside of the sack with the plastic to be blown has achieved a number of new results. There is one thing in that higher pressure can be used to blow the parison. The bag prevents the blowing fluid comes into contact with the plastic and it exists

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there is no risk of the plastic being blown through. Since higher pressure can be used to blow, can plastic at a lower temperature and after cooling to the temperature at which it begins to crystallize, be blown. This enables orientation of the molecules, and by using a biaxially deformed sack becomes the plastic of the preform both circumferentially and axially (or in other directions under a right Angle to each other) so stretched that the hollow body has a biaxial orientation with the resulting greater strength and in the case of some plastics with clear transparency.

Another advantage is achieved if the sack is attached to different Sections of its extension has different wall thicknesses. There is then a sequential expansion of the different sections of the sack such that corresponding sections of the preform are blown at different times will. For example, the upper or lower part of the molding can be blown in front of any other section.

A blowing fluid, such as a liquid, can be used at temperatures which are substantially lower than the temperature of the plastic, and the fluid can circulate through the sack during and immediately thereafter, depending on the situation the molding removed from the inside as well as from the outside

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ORIGINAL INSPECTED

is cooled; this results in a significantly faster cooling, a shorter working sequence of the machine and increased Production.

The invention is suitable for use with both injection molding as well as continuous casting blow molding machines.

The invention is explained in more detail below with reference to the drawing explained. Show it:

Pig. 1 is a diagrammatic representation of an injection blow molding machine chine, whereby the molds, the plastic and the blow pin covered by the sack are im Section are shown;

Pig. 2 shows a greatly enlarged section of a blow mold with one versus Pig. I differently shaped cavity, with the plastic on the Blow pin not yet blown;

Pig. 3 is a section along line 3-3 of Pig. 2;

Pig. 4 is a greatly enlarged partial illustration of a section des in Pig. 2 shown blow pin;

Pig. Figure 5 is a perspective view of one having the Pig blow pin. 2 connected closed Circuit for supplying cooling and blowing fluid to the mandrel;

Pig. 6 is a perspective view of an injection blow molding machine with a blow pin covered by a sack according to the invention;

Pig. 7 one of the pig. 6 similar illustration, with the blow mold in the closed position and the state the plastic and the sack are shown at the end of the blowing process; and

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Pig. 8 shows an enlarged detailed view of ventilation openings for the blow pin according to Pig. 6 and 7.

Pig. 1 shows an injection blow molding machine 10 having a turret head 12 with four blow pins 14, 15, 16 and 17, which are angularly spaced from different sides of the turret 12 protrude by 90 ° each. The turret 12 is rotated about an axis 20 when the blow pins 14-17 from a station to be brought to the next.

The first station of the machine 10 is an injection station 22 with a ■ 'Porm 24 from an extruder 26 through a Blow head 28 plastic is supplied. The blow pin 14 extends into a cavity 30 of the porm 24.

The blow pin 14 is covered by a balloon or sack 32 attached to the blow pin in a manner referring to Pig. 2 and 4 attached to a descriptive manner. The blow pin 14 with the bag 32 covering it extends into the cavity 30. When the Porm 24 is closed, plastic 34 is injected into the cavity 30 such that the entire sack 32, the Is spaced from the inner surface of the Pormhohlraums 30 so that it is coated.

The. Injection mold 24 is of conventional design with channels 26 for the circulation of cooling fluid; the porm 24 is opened to remove the plastic 34. The porm opens like this

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far that the turret 12 rotate and the blow pin 14, the bag 32 and plastic 34 counterclockwise about the center 20 into that of the blow pin 15 in Pig. I ingested Position can move.

During this movement of the turret 12 through an angle of 90 °, the blow pin 15 is in the position of the blow pin 16 in Pig. 1 assumed position and the blow pin 16 in the moved by the blow mandrel 17 position. The blow pin 17 moves into the open mold 24 and is there ready for Pick-up of plastic 34 from the blow head .28 at the beginning of the next work sequence of the machine. The way the form works 24 when opening and closing and how the turret works 12 when transferring the blow pins from one station to the next are known in injection-blow molding technology, and no further explanation is required in this regard for an understanding of the invention.

The second station of the machine 10 is a pretreatment station 38. The blow mandrel 15 at this station 38 has a sack 32 'which is covered with plastic 34', which is placed on the blow mandrel 15 in the mold 24 in the manner described for the blow mandrel 14 was applied. Each blow pin 15 with the applied plastic 34 ¹ remains at the pretreatment station 38 until the next movement of the turret 12, and during this time the plastic 34 ^f fm essentially cools down to the temperature desired for blowing. This cooling time is determined by the dwell period of the turret

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ORIGINAL INSPECTED

head 12; however, the desired cooling changes with the amount of plastic applied at different times 34 ', depending on the shapes available on the machine to form a particular hollow body are. The degree of cooling also depends on the temperature at which blowing is to take place. This in turn depends depends on the pressure to be used and the degree of orientation of the molecules required for a specific hollow shape or is desired. The rest period in the pretreatment station 38 is not intended to adapt to the desired one Cooling can be changed, but the extent of cooling can be changed can be controlled at the pretreatment station by controlling the temperature of the atmosphere surrounding the plastic 34 ' is or that the plastic during dwell in the pretreatment station 38 of a different thickness Is exposed to radiant heat.

The machine has a blow station 40 with a blow mold 42 into which during the previous movement of the turret head 12 has moved the blow pin 16 while the mold 42 was open. When the mold 42 is closed and openings 44 dispense blowing fluid in the blow pin 16, a sack 32a expands on the blow pin 16 and moves plastic 34a into contact with the surfaces of the mold cavity 46 of the mold 42. Fig. 1 shows the expanded bag 32a and the plastic 34a, the have assumed the outline of the mold cavity 46.

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The mold 42 has channels 36a for cooling fluid, and the plastic 34a must be cooled in the mold 42 to a temperature that is deep enough to make the plastic self-supporting before being molded from the plastic Hollow body can be removed from the mold 42. This time required for cooling the hollow body has hitherto been a Limiting factor on the output of injection blow molding machines been. In the invention, the sack 32a can be filled with water or other liquid a temperature which causes the plastic 34a to cool from the inside, and at the same time the plastic is penetrated. Contact with the walls of the mold 42 cooled from the outside · By cooling the plastic from both sides, the Cooling time can be reduced significantly. This shortens the working sequence of the molding machine and the production output considerably increased.

When the hollow body blown in form from the plastic 34a, which is a bottle 50 in FIG

Temperature has cooled, the mold 42 is opened and the turret 12 rotates a further 90 ° and moves the blow pin to a stripping station 52, where the blow pin 17. jnit a bottle 50 is shown held by the bottle neck 54 on the blow pin. The blow pin 17 has a Sack 32b, shown in Fig. 1 in a deflated state, with draining of the fluid upon completion of cooling has taken place at the blow station 40 while the

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Blow dome moved from the blow station to the stripping station 52 Has · At the stripping station 52, a stripping plate 56 moves into engagement with the bottle neck '54 and pushes the ! • tab axially along the blow pin 17, whereby the bottle is separated from the blow pin. Thus, the manufacture of the bottle 50 on the molding machine is completed.

Fig. 2 shows the mandrel 16 in a shape 4-2 · that of the shape 42 of Fig. 1 is similar, but the mold cavity 46 'is a different shape and the channels 36 · for cooling the mold also have a different shape. The bag 32a is on the blow pin 16 fastened with clamping rings 56 which clamp the material of the sack 32a in circumferential grooves 57 which extend around the outer surface of the blow pin 16 extend. Two bings 56 are shown, one on the outside of the mold 42 * and the other on their inside. The mold 42 'closes tightly against the outer surface of the bag 32a, thereby not excluding any plastic 34a the mold cavity between the sack and the clamping surface of the mold 42 'pressing against the surface of the sack 32a, can be extruded.

A shoulder 58 is provided on the blow pin 16, and there is a piece between the blow pin and the inner surface of the bag Clearance 58c extending far to the left of shoulder 58 in FIG. 2 is present. This leeway is used during the Injection of plastic into the mold at injection station 22 (Fig. 1) is maintained by supplying fluid

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into the sack 32a, with essentially the same pressure, with which the plastic is injected into the mold.

A circumferential air manifold 59 extends around one end of the mold 42 ', and that side of the manifold is closed by a cover 60. Pass channels 61 provided angularly at intervals around the mold from the air distributor 59 to the outer surface of the bag 32a at areas where the bag 32a collapses towards the blow pin can, d. H. to the area of the sack surface lying outside the clearance 58c.

At the injection station, the plastic is prevented from entering the channel 61 by having a sufficient amount in the sack Pressure is maintained to prevent the plastic from collapsing the sack into clearance 58c. Less equalizing pressure in the sack is needed if each channel 61 is located near the end of the clearance 58c is (see. Pig. 2).

When the blowing process has ended and the hollow body has deselected itself so far that it retains its shape, a partial vacuum is formed around the blow pin 16 to compress the sack. The sack can only collapse when air can enter between the outer surface of the sack and the inner surface of the finished hollow body. When a vacuum is first drawn around the mandrel, the bag 32a is inserted into the

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Clearance 58 depressed. This opens up a scope between the sack and the inner surface of the neck of the blown bottle · air from the channels 61 flows into this game « space between the sack and the bottle, namely over the longitudinal section of the sack, which is during the blowing process has not expanded. In addition, the expanded sack is squeezed away from the blown bottle while Air flows further to the left in Fig. 2 along the outer surface of the bag.

Fig. 2 illustrates how various parts of the preform be blown one after the other. In order to achieve an expansion of some parts of the bag 32a before other parts are the walls of the sack 32a around the area 66 are thicker than any other parts of the sack length. So if the sack 32a is inflated, as indicated by the dash-dotted lines in Fig. 2, the left of the area widens 66 lying part of the sack in front of the wall on the area 66, by regulating the rigidity or elasticity of the walls of the sack 32a in different areas, the plastic 34a can be sequential with respect to different longitudinal sections be blown.

As the sack expands from the position shown in phantom in Fig. 2, the plastic will soon be in contact with the side of the mold cavity at a midway point between the right and left ends of the cavity.

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brought to the area. Further widening the sack stretches the plastic in both directions from this central area as the left end of the bag extends to the left end of the porm cavity moves and the stiffer right end of the bag widens to the right end of the Pormhohlraumes. So will the plastic is stretched both circumferentially with the increase in the diameter of the bag and axially, thereby increasing a biaxial orientation of the plastic material results when the plastic is blown at a temperature that is low enough to allow the molecules to orientate. Sa the sack prevents the blowing fluid from coming into contact To get with the plastic 34a, the blowing fluid can have a have extremely high pressure without the risk of it piercing a weak section of the plastic, and 'that Blowing under higher pressure allows the plastic to blow. 34a at a lower temperature at which the plastic has already started to crystallize.

The part of the blow pin that extends into the cavity of the porm 16 has a central partition 70 which extends longitudinally of the blow pin, as in Pig. 2 dashed is shown. Water or other blowing and cooling fluid flows into the space on one side of the partition wall 70 through a Inlet channel 72 and flows out of the space on the other side of the partition wall 70 through an outlet channel 74 · These channels are in communication with lines 76 and 78, respectively, which are part of a closed circuit, as with reference to Pig. 5

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is explained. Thus, the fluid supplied in the channel 72 flows out and through the openings 44 on one side of the blow pin circulates substantially circumferentially around the blow pin in the inflatable bag 32a; this liquid or another Fluid returns to the interior of the blow pin on the other side of the partition 70 through the openings 44 that open on this side of the! partition. The blowing and cooling fluid then flows out through the outlet channel 74, as before was explained. Fig. 5 shows the mandrel 16 in a mold cavity 80 which tapers to a distal end of the mold larger diameter and not, as in Fig. 2, reduced. This difference depends on the one you want Shape of the hollow body to be blown. As with the other shapes, the blow pin 16 is shorter than the shape, so that the blown Plastic is stretched both axially and circumferentially. Fig. 5 shows the outline in dot-dash lines 32b and 32c of the sack as it expands in the mold cavity 80, with differences in local expansion result from greater resistance to expansion.

5 also shows a diagrammatic closed circuit through which blowing fluid flows from outlet line 78 through a valve 82 and a cooling device 84 to a blowing fluid storage tank 86, from which the blowing fluid is returned to the supply line 76 by a pump 88.

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The Pxunpe 88 is driven by a motor 90 with a power supply line 92 is connected and a speed control 94 has to regulate the rate of supply of the blowing fluid to the blowing mandrel. The automatic regulation for starting and switching off the blown fluid flow according to the work sequence of the blow molding machine is of conventional design and is therefore not described. Using the Blowing fluids as a coolant on the inside of the blown hollow body is one of the features according to the invention. The valve 82 is under the pressure of a spring 96 which is adjustable to change the back pressure in the blow pin, and this valve 82 is adjusted so that the back pressure can be adjusted as desired, so that the required Blowing pressure is obtained. In the closed system, a relief valve 98 is built in, whereby the pump 88 delivers Fluid can flow back through a branch around the valve 82 to the blow fluid Vprratstank 86.

The cooling device 84- is a conduit with heat radiation rods; However, it provides only an example of an apparatus for cooling flowing through the conduit is fluid, and it can not find any other cooling device using a function of the scattering to amount of heat.

Figures 6 and 7 show the application of the invention to an extrusion blow molding machine. A plastic hose 102 is made extruded down from an extruder 104 through a

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Extrusion mold 106, which is arranged above jaws 108 is. A mandrel 110 extends downwardly from the extruder 104, and this mandrel 110 resides in the extruded one Hose 102 and is substantially concentric therewith.

A blow mold 112 consists of two Pormhälften 114 and 116, those in Pig · 6 separated from each other and in Pig. 7 are shown closed. The blow pin 110 is the same as that referring to Pig. 1-5 described blow pins covered by a sack 120 and enclosed.

When the tube 102 has been extruded enough to reach the bottom of the Pormhohlraumes Porm 112, the The jaws 108 are brought together by clamping forces and press the tube 102 tightly around the outer surface of the sack 120 (cf. Pig. 7); then the pom halves 114 and 116 are brought together so that their lower edges 124 are the lower end of the tube Press 102 tightly together so that a lower end 102a protrudes in Pig under the edges 124

Blowing fluid is then supplied to the blow pin 110 and the sack 120 is expanded, forcing the tube 102 outwardly into contact with the surfaces of the porous cavity formed by the closed halves 114 and 116.

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When the plastic in the mold 112 is fully blown out, the mold cools the plastic to a hold that holds the shape Temperature, and then the blow mold is opened, the sack is squeezed and the shaped bottle is removed from the blow pin removed·

According to FIG. 8, the blow mandrel 110 has ventilation lines 126 which extend through. Holes 128 in the sides of the blow pin 110 and open through the sides of the sack 120, allowing air between the outside of the sack and the inside of the blown Hollow body can cause the sack to be compressed

Ventilation holes that allow air to escape from the molds during the blowing of the plastic as well as an entry of air allow the release of vacuums when finished hollow bodies To be removed from the molds are openings or channels of small cross section that prevent plastic from entering the openings are not allowed · Such ventilation openings are known and are used in conventional blow molding machines used; a description of these ventilation openings is therefore not necessary to understand the invention

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Claims (1)

Claims (■ '! · / Device for injection-blow molding with an injection mold, a blow pin extending into this, a holder for the blow pin at one end thereof, a device for injecting molten material into the injection mold and a blow mold surrounding a cavity, characterized in that the blow pin (16; 110) is surrounded by a sack (32; 120), that in order to form a preform molten material is sprayed onto the sack (32; · 120), that means are provided are for moving the holder (12) for the transput of the blow pin (16; 110), the sack (32; 120) and the preform from the injection mold to a blow mold and to pestle the Blow pin (16; 110) in a position »in which the blow pin extends into the blow mold and the preform therein carries, wherein the preform is smaller than the blow mold cavity and the blow mandrel (16; 110) has a channel (44), is supplied by the pluid to expand the bag (32; 120) and whereby the pressure of the from the blow pin (16; 110) exiting fluid, which is transferred to the preform via the sack (32; 120), the preform in contact with the Inner surface of the SOrmhohlraumes is widened, while the bag (32; 120) through the out of the blow pin (16; 110) emerges Pluid is inflated. 509815/1051 2. Device according to claim 1, characterized in that that the sack (32; 120) is made of elastomeric material that is free of damage at the temperature of the material injected into the injection mold can be used. 3. Device according to claim 1, characterized in that that the bag (32) has an open end, which at a point behind the Pormhohlraum and the holder (12) fits adjacent over the blow mandrel (16), and that fastening means (56, 57) are provided which the Fasten the bag (32) to the blow pin (16) near the open end thereof. 4. Apparatus according to claim 3, characterized in that the means for fastening the sack (32) to the blow pin (16) comprise: a clamping ring (56), the blow pin (16) completely filling the open end of the sack (32) and has a circumferential groove (57) into which the bag (32) is clamped by the clamping ring (56), a shoulder (58) provided behind the groove (57) on the blow pin (16) and a clearance (58c) between the Blow pin (16) and the sack (32) near the shoulder (58). 5. Device according to claim 1, characterized by means for circulating fluid simultaneously into and out of the sack (32) while in the sack (32) 5098 15/1 OB 1 . 23Λ7776 ΊΟ. Itruck is set up to expand the sack and the preform. 6, device according to claim 3 _f, characterized in that the fluid circulation means have: a pump (88), a fluid supply source (86) with a significantly lower temperature than the preform for cooling the sack (32) and the preform by conduction through the wall of the Sack (32) from the inner surface of the preform in contact with the sack (32), the blow mold being provided around the mold cavity (80) and cooling chambers for cooling the mold and the molded article by contact of the outer surface of the molded article with the inner surface of the cavity ( 80). 7. Device according to claim 6, characterized by a closed circuit in which the blowing fluid for the blowing mandrel (16) flows, a partition (70) in the blowing mandrel (16) for regulating the fluid flow, a device (82) which for controlling the outflow rate of the fluid from the mandrel (16) is adjustable independently of the fluid supply rate for building up pressure in the sack (32), and by means (84) for cooling the fluid as it flows from the mandrel outlet back to the fluid supply source . 8. Apparatus according to claim 1, characterized by means (88, 76) for supplying fluid 509815/1051 to the blow mandrel (16) for expanding the sack and the preform in contact with the wall of the mold cavity (80), wherein the fluid feed device I ¹ IuId can be fed with a pressure by which the sack and the preform are expanded when the plastic of the The preform3 has a temperature at which the plastic starts to crystallize 9. The device according to claim 1, characterized - gekennzeich.net, that the sack (32a) side wall is different Has elasticity in different areas of the sack (32a), so that areas of greater elasticity expand in front of areas of lesser elasticity, creating a selective expansion sequence of the preform is attainable. 10. The device according to claim 1, characterized in that the bag is shorter and one has a smaller cross-section than the blow mold cavity, whereby the plastic applied to the sack in the injection mold is stretched both circumferentially and axially during the expansion of the bag in the Pormhohlraum to effect a biaxial orientation of the molecules of the plastic. 11. The device according to claim 10, characterized by a turret head (12) on which the blow pin (14-17) and through which the blue thorn (14-17) 509815/1051 23A7776 is movable from one station to the next, through a pretreatment station (38), which the coated sack (32) is supplied after leaving the injection station (22), through a blow station (40) at which the blow mold cavity is provided and which the blow mandrel (14-17) and the sack (32) are fed after leaving the pretreatment station (38) and by one following the blow molding station (40) Stripping station (52), the blow pin (14-17) and the finished Hollow bodies are fed through the turret head (12) after blowing at the blow molding station (40). 12 «device according to claim 1, characterized that in the blow pin (16) openings (44) for the discharge of blowing fluid from the blow pin (16) Various locations along its length are provided for expanding the sack (32), the material of the sack (32), if it is pulled together into a position in contact with the blow pin (16), has sufficient rigidity, see above that the material of the sack (32) does not pass through the openings (44) and into the mandrel (16) is extruded through the bridge of the injection mold when on the outside of the sack (32) in the form of a preform is applied. 13 · Injection blow molding process, marked β t by enclosing a blow dome (16) with an uninflated sack (32), coating of the sack (32) with molten! unit st off in an injection mold, Eatf e 509815/1051 • Λν of the coated blow pin (16) from the injection mold and inflating the bag (32) to expand the plastic in Contact with a surrounding surface 14. The method according to claim 13, characterized that molten plastic is applied to a sack made of an elastomeric material at the blowing temperature of the molten Plastic retains its elastomeric properties including its "memory", 15 · Method according to claim 13 »marked by aliblowing the sack (32) in a blow mold cavity, Cooling of the blow mold by circulating a cooling fluid through channels (36a) into the cavity forming the mold cavity Walls and cooling of the mold material from its inside by the circulation of cooling fluid in the sack 032) and out of this while the sack (32) is being filled with cooling fluid. 16. The method according to claim 13 »characterized by circulating cooling fluid in the blow mandrel (16), from local areas of the blow pin (16) into the sack (32), from this into the blow pin (16) at other local areas the same and then through an outlet channel (74) of the blow pin (16) naoh outside. 509815/1051 IJ, method according to claim 13, characterized in that the plastic-covered sack (32) located on the blow pin (16) passes through a pretreatment station (38) between the injection mold and a blow mold to regulate the temperature of the plastic located on the sack Blow mandrel (16), the sack (32) and its cover are brought into a blow mold cavity which is longer than the blow mandrel (16) and the sack (32) in the axial direction of the blow dome (16) and the sack (32), that the sack (32) is inflated, the molded plastic having a reduced temperature at which the plastic has started to crystallize, and the plastic is biaxially oriented. is benefited by stretching in the circumferential direction and in the axial direction due to the inflation of the bag (32), 18, method according to claim 13, characterized that the molded plastic is applied to the sack in a liquid state, that the inflation of the sack is delayed until the molded plastic begins to set, and that then by inflation of the sack the molded plastic is stretched 19. The method according to claim 18, characterized in, that the bag is expanded both in terms of its diameter and its length to Stretching the molded plastic in the circumferential direction and in the axial direction, so that a biaxial orientation of the molecules of the plastic is achievable. 509815/1051 20. Yerfahren for blow molding, characterized in that around one in an open blow mold arranged sack (120) around a plastic tube (102) is extruded over a length which is greater than that Length of the mold that the mold is closed and thereby compresses the lower end (102a) of the hose (102) and that Tube (102) and the bag (120) in a cavity of the mold encloses that the bag (120) is inflated so that it is the Hose (102) completely fills that then the hose (102) in contact with the inner surfaces of the mold cavity is expanded while the bag (120) is further inflated, that the tube (102) is cooled and that air is admitted between the hose (102) and the sack (120) so that the sack (120) can collapse. 509815/1051