DE2137103A1 - Double walled thermoplast shell - formed from hollow rough inclosing mould - Google Patents

Abstract

A method of making double-walled shell-type thermoplastic articles introduces a rough from an extruder nozzle into the space between the parts of an open mould; the rough first enters between positive and negative mould parts defining the shell shape, then an initial closure piece (or sleeve) slides on one part to bridge the gap across to the other part. This seals the mould and the positive and negative parts are brought together, the gas pressure inside the rough being maintained, so that the final thin double-walled shell is produced. Typical uses include double-walled boat hulls or baths.

Description

Process for the production of double-walled5 bowl-shaped plastic objects In the manufacture of bottles and similar items made of plastic With a single wall, the blow molding process is usually used. With this one Method is a synthetic resin melt as a tubular item, for example This tubular plastic gob is extruded from a ring nozzle of an extruder is placed in an open, multi-part mold located immediately below the extruder entered. During the introduction of the plastic gob and during the closing the Form is blown compressed air into the plastic gob so that it expands and takes the shape of the interior of the hollow mold. According to the appropriate The mold is then opened and the solidified after cooling of the resulting molded body Taken molded body.

With this conventional blowing process, relatively short or flat and light hollow bodies, the walls of which are at least partially welded together are easily produced, albeit a considerable loss of material in Purchase must be made.

In the production of double-walled, bowl-shaped plastic objects however, large size and considerable depth result in this conventional one Blow molding process numerous difficulties. So the one emerging from the extruder expands Due to its great weight, plastic posts are very uneven, so that molded bodies with uneven wall thicknesses arise. In addition, the plastic post at Closing the two parts of a multi-part mold of great depth will be damaged, so from a production of such double-walled molded bodies with the help of the blow molding process so far has been refrained from.

It has therefore already been proposed to use double-walled molded bodies in the Manufacture way that its inner and outer walls are separated from each other in the low-pressure pressing process or manufactured by injection molding and then glued together to form the to obtain desired shaped body. In this procedure have to However, large areas of the walls are glued together, which in turn creates difficulties entails and is time consuming.

In the manufacture of plastic objects after injection; casting process the plastic, which is under an injection pressure of 1000 to 1500 kp / cm2, flows Mass direction dependent and the finished products have a weld seam while changes in the finished products occur. The first injected into the cavity of the mold In this process, synthetic resin is in contact with the inner walls of the mold for a longer period of time than the synthetic resin injected later, with the one at the beginning of the injection process The amount of resin introduced into the mold is pressed into the cavity # by the subsequent synthetic resin will. As a result, there is a different cooling of the gradually amount of resin injected into the cavity, so that no satisfactory molecular Bonding is achieved and very deep moldings make a difference between the top and the lower area, due to the high injection pressure required and the power requirement of such injection molding or injection molding machines is already one Such a plant is very expensive, which affects the manufacturing cost of the end product affects.

The invention aims to remedy this by means of a method which while maintaining the advantages of the previously known processing methods for thermoplastics Plastics the inexpensive production of large moldings in at least double-walled Education, like boats, bathtubs and the like. as well as of large-scale containers permitted, which have a high strength with absolutely constant wall thickness and due to their double-walled or multilayer structure, they have good thermal insulation properties own.

A method for production according to the invention is identified double-walled, shell-shaped plastic objects in which a thermoplastic Post from the nozzle of an extruder between the opposing parts a multi-part mold is introduced and the mold is closed while a predetermined gas pressure is maintained in the post, essentially by that the item of thermoplastic mass in the one from a mold core, a negative mold and an initial lock which is slidably arranged on one of these two partial molds existing open form introduced and by shifting the initial lock on the partial form supporting it up to the tight contact with the other partial form in the resulting initial cavity of the mold is injected that then by relative movement of the mold core and the negative mold, the shape is maintained the specified gas pressure in the plastic post is finally closed, so that the hollow plastic gob to a uniform shape the final cavity of the mold filling hollow body is deformed.

According to a special feature of the invention, both the mold core and the negative form an initial lock that can be moved on them and these two Initial closures are after Bringing in the plastic gob in the open form to form the initial cavity up to the tight deposit pushed against each other. Preferably the gas pressure is within the plastic gob thereby kept constant at the predetermined value that during the final Closing the mold by moving the mold core and the negative mold together Part of the gas is released. To accelerate the solidification process of the In the finally closed form formed plastic molding can this quickly by supplying a cooling medium from outside within the mold be cooled down. One of two can also be used for the method according to the invention the edge edges fused together and / or glued together in parallel thermoplastic webs of existing plastic material items are used, these Web fed via take-off rollers through heating devices through feed rollers from which they one of their superimposed marginal edges with each other fusing welding device can be introduced into the open mold. Finally, the walls of the molded body can also be partially or completely interconnected fused and / or glued.

A more detailed explanation of the invention emerges from the following Description of some implementation examples based on the accompanying drawing; it show: Figure 1 - 4 in a schematic manner the individual process steps of the Method according to the invention as a section through a production mold; Figure 5 a Section through Fig. 1 along the line V-V; Figure 6 shows another embodiment of a device for the production of shell-like double-walled objects according to the invention Procedure seen from the side in partial section; Figure 7 shows a according to the invention Bathtub produced by the method in partial section; Figure 8 and 9 other configurations of bathtubs produced according to the method according to the invention, in turn, in partial section; FIG. 10 is a perspective view of a method according to the invention manufactured boat hull; FIG. 11 shows a section through FIG. 10 along the line XI-XI; and FIG. 12 is a perspective view of one in one according to the invention Process produced plastic hollow mold cast plastic molded body partially removed hollow shape.

In the case of the principle according to the invention shown in FIGS. 1-4 Process for the production of double-walled, bowl-shaped plastic objects a corresponding amount of plastic or a plastic gob a from an annular nozzle 9 of an extruder between the mold core 1 and the negative mold 2 of an open multipart form introduced, which also has a slidable on the outer surface of the mold core 1 arranged initial lock 5 has. The negative form 2 is then over the plastic plastic post a together with the initial closure 5 pushed up to a closing line X-X, so that the plastic post a in the upper and lower area respectively. in its edge areas of the negative form 2, the initial closure 5 and the mold core is enclosed. If necessary, a predetermined amount of air is used under pressure into the interior of the plastic gob a via a blow line 10 of the spray nozzle 9 blown to the plastic post a in the resulting initial cavity to expand. At the same time, the inside of the hollow initial closure 5 displaceably arranged mold core 1 slowly into the position shown in FIG pushed and finally into the closed position shown in Figure 4, in which the outer shape of the plastic gob a the cavity of the finally closed shape is equivalent to. Preferably, the volume of the initial cavity is substantially the same the final closing of the mold by moving the mold core 1 to Negative form 2 resulting cavity, since permanent wrinkles arise in the molded body, if the difference between the initial cavity and the final cavity of the Shape is too big.

In this way you can make a shaped body like a bathtub, which is double-walled with a space between the two walls according to FIG is formed, or in which the double wall in the sandwich style of two intimately interconnected layers, as shown in Figure 8, or in which the space between the double walls by means of a foam resin is filled in, as shown in FIG. Leave all these objects can be produced with a relatively low pressure of about 2 2 - 5 kp / cm2.

Plastic moldings produced by the process according to the invention have the same gloss and appearance as after the injection molding process manufactured plastic articles. The molecules of the plasticized masses, at which are high polymer compounds are chained together and uniformly oriented, so that produced by the process according to the invention Moldings free from the disadvantages of injection molded articles are. Articles produced by the method according to the invention also have a completely uniform wall thickness and the walls are also essential stronger than the comparable walls made by injection molding Objects. The method according to the invention provides particular advantages in Production of moldings of large dimensions, such as boats or bathtubs, which must have a very high strength, as such objects as a result of low residual stresses generated during the molding process and as a result of the none Directional constraint occurred resin flow are practically stress-free. The method according to the invention therefore allows the convenient production of multilayered or hollow-walled molded body with low pressure, such multi-layer Shaped body due to the high strength of their double-walled design and as a result the possibility of achieving excellent thermal insulation is particularly advantageous are.

While in Figures 1-4 the initial cavity by displacement of the initial closure 5 is formed on the mold core 1 to the negative mold 2, can in particular the initial closure 5 also on the negative mold 2 towards the mold core 1 be displaceable, or you can also on the mold core 1 and the negative mold 2, respectively arrange an initial lock 5 displaceably and this up to the closing line X-X slide against each other, as shown, for example, in the arrangement according to FIG is.

Preferably, the air in the plastic post a is via a not shown Blow-off valve partially drained when the mold core 1 and the negative mold 2 when Closing the mold are pressed against each other to reduce the air pressure inside this To keep item a at a predetermined value. Such a relief valve can be arranged, for example, in a branch line of the blow line 10. on the other hand the air inlet formed in the molded body can also be connected to another line as soon as the extruder is withdrawn and the blow line is removed from the inlet removed to reduce the pressure in the item a, so that the pressing process in shorter Time can be performed than would otherwise be possible.

According to the invention, the dimensions of the bag or bubble-shaped Item a approximately the capacity of the mold core 1 and the negative mold 2 formed cavity approximated. The ring nozzle 9 has an elongated inside Core piece 11 to give the extruded material a shape that corresponds to the shape of the finished part comes very close. Preferably, the ring nozzle 9 has a Post-forming section with large transverse dimensions in order to be large in the case of molded articles To achieve walls of uniform thickness, this section forming the post is constructed in such a way that its outer walls support the nozzle for reinforce the extruded post to avoid sagging of the post as a result of its To prevent dead weight.

In the production of large moldings is an inevitable item A large dimension is required, with the extrusion of this item being the soft one Post near the outlet of the ring nozzle has the tendency due to its own weight to sag. In order to prevent this sagging of item a, a Ring nozzle provided with a large cross-section and at the same time the extrusion speed of the extruder adjusted to the sinking speed of the post, or you can lower the extruder itself faster than the item sinks.

In the implementation example described above, the initial closure 5, which is arranged displaceably on the mold core 1, first to the negative mold 2 closed. To a one-sided pressure of the initial closure 5 on the sinking To prevent item a, however, it is necessary to the negative form 2 at the same time with the initial lock 5 to the center line X-X of the Post a to move. To avoid damage to item a by something surrounding it To prevent an obstacle, the closing plane of the mold becomes during the closing of the mold Symmetry plane X-X of the item a adjusted by the locking device or the Extruder must be removed. The post's outer shoulder is fused and sealed, by placing the post between the initial closure 5 and a mating surface 2a of the negative mold 2 is pressed in. Here the upper part of the post a is fused and sealed, wherein one or more blowpipes 10 are used, while the other sides and the bottom of the post a is airtight according to the shape of the cavity are merged, although this process can sometimes be omitted.

As already mentioned, the initial lock 5, the negative form 2 and the mold core 1 formed an initial cavity when the initial closure 5 before is brought into engagement with the negative mold 2 when the mold is finally closed (Fig. 2).

During this process step, air is under a pressure of from about 1 - 5 kp / cm, which is sufficient to create the hose-like shape of the post a to maintain in the initial cavity, from a compressed air point, not shown forth into the interior of the hose-like item a via the blowpipes 10 of the annular nozzle 9 blown in. In this way, the thickness of the item a becomes practically uniform held and the walls of the tubular post a are prevented from to stick together by increasing the pressure of the air in the item a to a predetermined value is held when the item a through the individual parts of the multi-part mold is included.

A deformation of the item a corresponding to a change in shape of the The cavity can be facilitated by the fact that the mold core 1 against the negative mold 2 is pushed to close the mold as described below. aside from that the blown air can be heated or cooled as required.

When the mold is closed, the initial closure 5, the mold core 1 and the negative mold 2 are in the position shown in Figure 4, the post a is formed according to the shape of the cavity, but can be in the case of an end product with a hollow double wall or with a partially glued double wall the upper and lower ones fused or glued to the inner surface of the mold Parts of the post immediately after the mold is closed from the shoulder 2a of the Negative mold 2 and the shoulder la of the mold core 1 separated, at the same time again compressed air is blown through the blowpipe 10 in the item a and the Item is thereby pressed firmly against the inner walls of the cavity. Included the end product is preferably cooled and solidified until the next work cycle.

Appropriately, several such forms and their associated Closing devices arranged in groups one behind the other or in a circle. The multi-part molds can be provided with suitable cooling and heating devices are preferably provided to prevent the air flow around the molds and to adjust the air pressure to be introduced into the items.

In the implementation examples described above, the item a through the annular nozzle 9 of an extruder in the space between the individual Parts of the multi-part mold introduced and deformed there. The inventive However, the process is not limited to this type of introduction of the material, Rather, several webs of thermoplastic material can form a bag-like material Part are deformed while the material is heated and softened. Such Bag-shaped thermoplastics can instead of a post a of the multi-part form are fed.

In particular, FIG. 6 shows webs 16 made of a thermoplastic material Material, which from both sides of a multi-part mold via take-off rollers 17 are supplied, from which they pass through heating chambers 19 with heaters 20 and are continued via feed rollers 18 in such a way that they are essentially perpendicular to the bottom and parallel to the closing line X-X of the mold opposite one another be fed into the mold. The edges of the two webs are made by heating rollers 22 melted and glued together, while hot air through a blow line 23 blown into the space between the two parallel sheets so that their central areas cannot stick to one another and the two to one another glued webs to form the desired bag-shaped item a.

This bag-shaped item a is then supported by movable heaters 21 further heated so that it is close to the melting point on both sides except for one of the thermoplastic material lying temperature is heated. After removing the heater 21, two initial closures 5, which are on the Mold core 1 and the negative mold 2 are arranged displaceably, by means of hydraulic cylinders towards the closing line X-X of the mold until they touch each other so that the Shoulder parts of this bag-shaped post a melted and connected to one another will. At the same time, hot air is blown under pressure into the interior of the post a, so that it is in the initial cavity, which is formed by the mold core 1J 2 and the two initial locks is limited. Then over Hydraulic cylinder gradually the mold core 1 and the negative mold 2 slowly towards each other pushed until the mold is finally closed while the air is trapped in it bag-shaped item a is held at the predetermined pressure. In this way the bag-shaped item a is formed into a bowl-shaped plastic body.

The procedure described above can also be modified somewhat, than these beans instead of two continuous sheets of thermoplastic material cut to a predetermined length and then two lengths of sheet at a time be put together in parallel, while a release agent such as a silicone oil or for example Calcium carbonate in powder or flake form placed between the two pieces of sheet to prevent them from sticking together. However, you can also use an adhesive like a vinyl acetate emulsion on the surfaces of the two to be joined together Apply pieces of membrane or glue on foam beads or plates, if a foam in the cavity of the double walls of the prefabricated part embedded should be. In the latter case, the edges of the two pieces of sheet can be connected to each other are fused, so that a given bag-shaped structure results. Then this bag-like structure by heater or the like.

heated and in the cavity between the parts of a multi-part Shape are given as described above, so that a plastic body with three-layer wall -can be produced.

In another implementation using a bag-like Structure instead of a post extruded through the ring nozzle of an extruder a hollow body with practically the same volume as the desired finished part produced in the usual blow molding process and then in a separate molding mechanism molded or cooled. The blown hollow body is placed in a heating chamber introduced and heated to a predetermined temperature close to the boiling point, this temperature naturally depends on the material used. Thereupon the heated and softened material is placed in the cavity of a corresponding mold introduced while it is connected to a blow line and when closing the shape in the manner described above, the shape and formation of the inner Walls of the closed shape adapts, with heated compressed air or the like. In the interior of the bag-like structure is introduced through the blow line.

In this way, as in the example described above, a produce corresponding double or multi-walled bodies.

With the help of the method according to the invention can also be easily Manufacture reinforced articles, such as the one in the the hull shown in Figures 10 and 11 is the case. Here's a tension Ribbed 25 made of steel or the like. Embedded in the material to be deformed and is deformed simultaneously with this. FIG. 11 shows a molded body 27 made of resin, which is arranged between the inner wall 26 and the outer wall 28 of the boat hull is, with these two walls merge seamlessly into one another.

Another application example of the #> # method according to the invention shows Figure 12, in which in the hollow wall of a double-walled, according to the Hollow body produced according to the invention is the same or different Resins are filled and, after curing, the inner and outer walls of this Hollow body are removed, so that ultimately only the cavity between them both walls filling filler remains.

Here are expediently in the cavity of the to be trained cupped body air ducts introduced, one of them being, namely the inlet line, to an injection molding machine or other suitable plastic injection device is connected to fill the cavity with a resin of suitable hardness while the air or another gas is sucked off via the other line, which is thus serves as an outlet line. The multi-part mold is closed at the same time, so that the material follows the shape and formation of the inner walls of the mold adapts. As a material use any of the synthetic resins, which are generally used for the various molding operations, where it is generally about phenolic resins, polyurethanes and polyester resins, which should not be mixed with fiberglass. The filling of the synthetic resin in the cavity between the inner wall and the outer wall of this as a hollow shape serving molded body for the production of the bucket-shaped object according to FIG 12 can take place while this shaped body is still in the form in which it was made, or while it is in a molding box after it was removed from the multi-part mold after appropriate cooling.

When manufacturing a bowl-shaped object by filling it a synthetic resin in a hollow mold in the aforementioned manner can be polyethylene or another synthetic resin, which can be easily removed, to form the walls the hollow mold can be used - or a silicone resin or the like can also be used in then pour in the shaped body, which is then used as a hollow mold, while this shaped body is still in the closed form and has not yet cooled down. The poured Silicone resin then coats the surfaces of the cavity of the molded body, whereby any excess is removed. Then the aforementioned synthetic resin is in these Filled cavity and takes its shape. With this method, the Easily remove the walls of the hollow molded body that served as a hollow mold, as shown in Figure 12, so that in a simple manner a molded body results, which consists of the synthetic resin filled into the hollow mold.

In general, the blow molding process is used for the production of hollow bodies considered advantageous as the required shape is less expensive than that of other molding process. The disadvantage of this method, however, is that it It is very difficult to find objects with a high level of accuracy in terms of wall thickness and the other dimensions. On the other hand, by pouring and injection molds to produce objects whose dimensions are met very precisely can be and which have a predetermined and completely uniform wall thickness, however, such procedures require an expensive form; because the shaped surfaces are very must be machined accurately and in the manufacture of large items a large shape must be used.

The present invention retains the advantages of conventional molding processes, because objects produced by the method according to the invention in their dimensions and wall thicknesses can be determined very precisely. In the first place, these arise Objects in the form of bowls with a hollow double wall, any of the various designs described above can be used. Such Shell-shaped moldings can then be used as a hollow mold and with a suitable one Synthetic resin are filled, and finally the hollow shape can be separated. As a result, the inventive method allows in contrast to the casting or Injection molding processes involve the use of inexpensive molding equipment and reuse the material used to manufacture the hollow mold. For making a hollow mold Particularly suitable if the object is made of polyester or polyethylene one other viscous material is produced, which is difficult after shaping is to be removed from the mold, with the inner surfaces of the hollow mold covered with a silicone resin layer can be coated in order to facilitate the removal of the molding from the hollow mold, or you can fill the hollow form with a perfectly binding material, to produce a molded body with a three-layer wall.

Expectations:

Claims (6)

Claims Process for the production of double-walled, shell-shaped Plastic articles in which a thermoplastic post emerges from the nozzle of a Extruder between the opposing parts of a multi-part mold is introduced and the mold is closed, while in the post a predetermined Gas pressure is maintained, characterized in that the item (a) is made of thermoplastic Mass in a mold core (1), a negative mold (2) and one on one of these both Tcilformen displaceably arranged initial lock (5) existing open Form introduced and by shifting the initial lock on the one carrying it Partial form up to tight contact with the other valve form in the resulting form Initial cavity of the mold is included that then by relative movement of the The mold core and the negative mold form the mold while maintaining the specified gas pressure is finally closed in the plastic post, so that the hollow plastic post deformed into a hollow body that evenly fills the final cavity of the mold will. 2. The method according to claim 1, characterized in that both the mold core (1) and the negative mold (2) have an initial lock that can be displaced on them (5, 5) and wear these two initial closures after inserting the plastic post (&) into the open form to form the initial cavity until it is sealed Shelf can be pushed against each other. 3. The method according to claim 1 and 2, characterized in that the Gas pressure inside the plastic gob (a) thereby constant on the predetermined value is held that during the final closing of the Mold by moving the mold core (1) and the negative mold (2) together a part of the Gas is released. 4. The method according to any one of claims 1 - 3, characterized in, that to accelerate the solidification process of the finally closed Form trained plastic molded body this by special supply of a cooling medium is rapidly cooled from the outside inside the mold. 5. The method according to any one of claims 1 - 4, characterized in that that of two fused and / or glued together at the edge edges parallel folded thermoplastic webs (16, 16) of existing plastic posts (a) is used, these webs over take-off rollers (17, 17) through heating devices (19, 20) through feed rollers (18, 18) are fed, from which they one their superimposed marginal edges merging with one another welding device (22) can be introduced into the open mold (1, 2, 5, 5). 6. The method according to any one of claims 1 - 5, characterized in, that the walls of the molding partially or completely fused together and / or glued. Patent attorney,