DE2542045A1 - Removing hollow moulding with undercuts or depressions from mould - by temporary deformation and restoring the shaped of elastic recovery - Google Patents

Abstract

In mfr. of (pref. hollow) mouldings with >=1 depression or undercut where the moulding cpd. is cast, injected, extruded, etc. into a mould, the resulting moulding is removed from the tool in such a way that at least a predetermined section of the moulding adjacent the depression or undercut is temporarily deformed. After the moulding has been removed from the mould this section resumes its original position (as imparted to it during the moulding step) by virtue of the elastic recovery fo the moulding cpd. Used in the mfr. of tubes, pipes, pipe sections having grooves, beadings, corrugations, cut-outs, esp. from unplasticised thermoplastics or duroplastics. Since the undercuts, grooves, etc. are integrally moulded inot the intended article, there is no need for them to be machined after moulding.

Description

Method and device for producing molded articles The invention relates to a method for producing at least one depression or undercut having, preferably at least partially hollow, molded bodies, in particular hard, thermoplastic or thermosetting plastic, for example pipes or pipe fittings with beads, grooves, recesses or the like, in which Process of the material, e.g. by casting, injection molding, extrusion, extrusion or the like, is introduced into a mold and thereby fills the mold cavity, wherein the material is given the intended shape of the molded body.

The invention also relates to an implementation device of the procedure.

In the previously known method for producing pipes or Pipe fittings with beads, undercuts, grooves or other depressions split cores are used or the beads, undercuts, grooves etc. are subsequently produced by mechanical, metal-cutting shaping. That Removal of such a split core from the mold or the subsequent machining Shaping are time-consuming and cumbersome.

The invention is based on the object of avoiding these disadvantages and a method for producing at least one depression or undercut having shaped bodies to create compared to the previously known method is much easier and can be carried out in less time.

This object is achieved according to the invention in a method of the opening paragraph mentioned type solved in that after shaping when demolding the molded body at least one predetermined, to the recess or

Temporary undercut adjacent section of this molding is brought into a shape deviating from the intended shape of the molding, and that after removal from the mold, this section is due to the resilience of the material resumes its original position that was retained during the shaping process.

This procedure is based on the ability to recover or recall of plastics. Resilience is the property of the material understood, in a certain temperature range (so-called.

thermoelastic area) to be deformable and after deformation to return to the original shape. The resilience is especially at thermoplastic and thermosetting plastics.

The method according to the invention is therefore unnecessary even with hard thermoplastic and thermosetting materials the use of split cores or the subsequent machining design.

The depressions or undercuts, d.s. for example beads, Grooves, grooves, etc., can also be formed during the shaping of the molding, where they are briefly brought out of their intended shape when demoulding, However, this happens automatically after demolding, i.e. without any mechanical Exposure, take again. The provision is true to size, with the necessary Tolerances can be met without any problems. By the method according to the invention the wall thickness in the area of the recess or

Undercut not weakened.

When carrying out the method according to the invention, it is expedient that the temporary change in position of the predetermined section caused during demolding of the molded body is carried out by removing a core from the mold. Vice versa the temporary change in position of the predetermined section could also occur during application of the molded body take place from the mold surrounding this outside.

In an embodiment of the method according to the invention, it is provided that during the removal from the mold, and if necessary also afterwards, that of its position brought, predetermined section of the shaped body, preferably by supplying heat, is kept at the deformation temperature. This is especially true with thermoplastic and thermosetting plastics expedient to ensure that for resetting of the wall section brought from its original position during demolding necessary temperature is available.

The required temperature range can also be guaranteed in this way that to achieve a heat build-up in the area of the recess or undercut of the molded body this in the mentioned area at least during demolding is thermally insulated.

Another possibility, the temperature necessary for resetting to ensure, is that the molded body in the area of the recess or Undercut has a greater wall thickness than in its remaining parts. By increasing the wall thickness or reinforcing the cross-section in the area the deepening or

Undercut, this area remains at the deformation temperature for a long time than the remaining, thin-walled sections of the shaped body.

It is also possible that the cooling of the shaped body during the Demoulding is delayed. It can also be expedient for the demolding to be carried out intermittently takes place with a time delay.

The device according to the invention for carrying out the method, with an, optionally divided, shape and at least one core for training the recess or undercut of the molding, is characterized by that the core in the area of the recess or

Undercut of the molded body is formed undivided, and that the dimension of the core measured essentially transversely to the direction of discharge of the core is greater than the clear width of the core between its dispenser and the Recess or undercut surrounding molded body.

In an embodiment of this device it is provided that in the area the recess or undercut of the molded body a shape or the core is arranged outside at least partially surrounding heating device.

It is useful here that the heating device, in particular, which can be regulated a ring that surrounds the shape electrical resistance heating or a thermostat heating with liquid media.

It is also advantageous that the shape in the area of the recess or Undercut the molded body with thermal insulation, e.g. ceramic elements or synthetic resins.

The invention is described below with reference to the drawing, in which an embodiment of a device according to the invention and various embodiments of moldings produced by the process according to the invention are shown, described in more detail.

1 shows a section through a device according to the invention when introducing the material, FIG. 2 shows a section through the device according to 1 during demolding, FIG. 3 shows a section through the device according to FIG Fig. 1 after demolding, Fig. 4 is a diagram to illustrate the method, 5 to 12 different exemplary embodiments of the method according to the invention produced beads on tubes, Fig. 13 to 17 different embodiments of pipes or fittings manufactured by the method according to the invention, 18 shows a side view of FIG. 179; FIG. 19 shows a view of one according to the invention Process produced pipe cleaning cover and FIG. 20 shows a section along a line XX-XX in Fig. 19.

The device lmfaZ shown in FIGS. 1 to 3 is one of two Molded parts 1,2 formed mold and a core 3.

The parting line between the molded parts 1, 2 is denoted by 4. the Device is used to produce a tubular shaped body 5, which is on his one end has a recess running around it in the form of a bead 6. For shaping of this bead 6 is the core 3 at its end with a circumferential thickening 7 provided and the molded parts 1, 2 are at their end faces facing the parting line 4 provided with corresponding rounded depressions 8, 9.

The core 3 is formed undivided in the area of the bead 6 and its Dimension D1 measured transversely to the discharge direction 10 is greater than the clear width D2 of the molded body surrounding the core 3 between its discharge end 11 and the thickness 6 5. In the area of the bead 6, the molded part 2 is of an annular heating device 12 surrounded in the form of an electrical resistance heater.

The device works as follows: The molded body 5 is known in the art Injected way (Fig. 1). The molded body 5 is then not in the area of the bead 6 cooled, but kept at the deformation temperature by the heating element 12; the The remaining part of the molded body 5 is cooled as before. The core sleeve 2 is then pulled out together with the core 3, wherein the part kept warm expands and slides over the core bead (Fig. 2). In order to restore the original shape reach, the core pull is stopped until the molded body is sufficient in the bead area has cooled down. As a rule, however, you can do without stopping the core pull will. Finally, the mold halves 1, 2 are separated after the core 3 is completely has been pulled out of the molded body 5 (Fig. 3).

Generally applies to thermoplastics and thermosetting plastics produced by injection molding can be processed that the cycle starting with the injection process in the Shape up for removing the molding from the mold, in three main sections can be divided into: a) in the area of the viscous melt, in which as a rule the material is pressed into the mold and fills it, b) in the area of the Forming or reshaping in which the material is shaped or later again reshaped and converted into another shape, and c) into the area the rigidity in which the material no longer allows any change in shape.

These three areas are not sharply delimited and are made of material to material of different widths, so that one can choose the temperature range according to the specific behavior of the respective material. Basically can be used for all thermoplastics that are hard at service temperature, similar to those listed above Behavior correspond, undercuts are demolded.

During the demolding process with soft thermoplastics without special Temperature control at room temperature succeeds, it this process with hard thermoplastics, such as polyvinyl chloride hard, acrylic # butadiene styrene, polypropylene or Polymethyl methacrylate etc., or hard thermosetting plastics such as epoxies, no longer without special thermal process control possible if the demolding is an elongation of the Requires material that is greater than the elastic limit. The thermal Process management consists essentially in the area of forming and reshaping is divided both in terms of time and temperature by suitable measures, Furthermore, that the parts to be demoulded falling in this area are still in this area Remain in the state while the rest of the fitting is already in the rigid phase stepped. So it will be in besti, th Fitting areas o namely Cut the undercut cross-section - the cooling is delayed accordingly.

This delay can be achieved by the following measures: a) suitable radiators that keep the corresponding parts of the mold at a higher temperature hold as the rest of the shape; b) Thermal insulation materials that absorb the heat in the Damming the area of the undercuts and not draining them off as quickly as steel; she can be structurally arranged between two steel surfaces; c) appropriate choice the cross-sections. By reinforcing the cross-sections at the undercuts they remain at the forming or deformation temperature longer than thinner molded parts.

to a) There are both electrical resistance heaters with suitable Controllers possible as well as thermostatic heaters, the liquids as heat exchangers use. The choice depends on the construction of the form; to b) As heat insulators Both ceramic elements and synthetic resins are suitable for the applied Temperatures and pressures are resistant enough, the type and choice depends depending on the material to be processed, e.g. Teflon, phenolic resin molding compounds, polyphenylene sulfide etc.

In general, method a) takes precedence for delay admitted as it is the easiest to master.

The behavior of the material polyvinyl chloride hard is shown below 4 will be explained in more detail with reference to the diagram in FIG.

In the diagram of FIG. 4, the time t and up are on the abscissa axis the ordinate axis shows the temperature T in C. In detail here mean: A - processing temperature upper limit B - processing temperature favorable for the material C - processing temperature lower limit D - demolding undercut E - recovery in original form F - calibration G - final demolding T1 - range of viscous flow behavior, viscous, unstable phase T2 - mold filling under pressure molding formation relaxation T3 - area of forming in the rubber-elastic, plastic state, material flexible, suitable for forming T4 - area of the rigid phase no more shape change possible (excluding shrinkage) without structural destruction or structural change (gold flow) t1 - time range for shaping (injection) t2 - reprinting, stabilizing t3 - Time range for demolding the undercut t4 - Time range for reset in original form t5 - time range for reshaping (calibration) t6 - time range for final demolding The diagram in FIG. 4 shows the idealized cooling curve.

The material decomposes above temperature A. The possible one The processing range is between A and C, the most favorable setting is roughly in the range B and for PVC between 170 and 20,000 Temperature range falls in the area of injection and mold filling. The injection times are generally relatively short; since no heat is supplied after the mold has been filled, the temperature of the material falls as a function of time and reaches the point D, in which the material is still soft, but its final one Has reached the basic shape; With the right choice of processing conditions, it is possible to demold the molding without losing its basic shape. The point D is to be chosen so that the residual stresses are minimal; for rigid PVC it is between 120 and 1400C, here the undercut can be demolded. The demolding of the Undercutting is expediently carried out very quickly, since on the one hand the cooling progresses, on the other hand, resetting to the original shape within the temperature range D to E should be done if to achieve tight tolerances until the point is reached F certain fitting zones still need to be calibrated, which is entirely possible.

The # reset process must be set up in such a way that it stops when the Freezing temperature of the material (for PVC-Hart between 70 up uFd 90 C) safe is finished. The final demolding of the molding is in the beginning under G. rigid phase made. The associated time ranges depend on the temperature conditions and must be coordinated accordingly.

The method described above for injection molded parts can be analogous also for the production of undercuts on other moldings, for example Containers, wide-mouth bottles, lids, pipe connectors, pipe branch pieces etc. - especially for beads of pipe sleeves. These are suitable especially materials (thermoplastics that are hard at room temperature) that support the general known methods of socket forming (deformation on Expanding cores, Blowing process) because of their specific properties, for example not sufficient broad transformation phase (diagram points C to F in Fig. 4), made difficult to access like the group of polyolefins. However, you can also use the classic Materials of hard thermoplastics or thermosetting plastics such as polyvinyl chloride hard, acrylic butadiene styrene, Epoxies that meet the idealized cooling diagram, according to the procedure be demolded.

The method is based on the property that the diagram in Fig. 4 phase of viscous flow behavior (zone A to C) shown not just once, but can be achieved repeatedly. It is therefore necessary to use the thermoplastic to heat beyond the actual area of deformation or reshaping, which can be done in shapes that are very similar to injection molding tools. After this the point B (Fig. 4) has been reached, the thermal process proceeds as in procedure described above.

While the shape design according to this process by the injection pressure can be made, the required pressure must be used in the pipe flow forming by, for example, mechanically, hydraulically and / or electrically driven supply devices, are applied and become effective in point B of the T / t diagram.

In Figs. 5 to 12 are extruded tubes made of thermoplastic material shown, in which at one end a bead 20 or 21,22,23,24,25,26,27 is molded according to the method according to the invention. With a and b here are the different wall thicknesses are indicated in each case, whereas with 28,29,39 the parting lines are designated.

13 shows one produced by the method according to the invention conical pipe fitting 31 with associated Sawtooth clamp 32. A sealing ring 33 serves to complete the pipe connection.

14 to 16 show a closure cap 34 and pipe fittings 35,36, the undercuts, grooves, grooves formed by the process according to the invention or the like.

37,38,39,40.

Finally, FIGS. 17 and 18 show the production of a in cross section versatile container 41 with a bottom 42 and a retracted container neck 43.

Dig. 19 and 20 show a pipe cleaning cover in view and section, two possible variants of the pipe connection resp. the cover design are shown. The cover 51 is circular-ring-shaped Groove 52 provided in the left in Fig. 20 with a radially inward protruding lip and in the right side in FIG. 20 with a recess 54 is provided.

The method according to the invention is very diverse for production Suitable for undercuts. The depth of the undercut depends on the elasticity and the resilience of the thermoplastic or thermoset used, while the problem-free demolding is significantly influenced by the shape angle over which the material is to be peeled off.

Claims (11)

P a t e n t a n s p r c h fi e: o's method for producing at least one recess or undercut having, preferably at least partially hollow, molded bodies, in particular hard thermoplastic or thermosetting plastic, for example pipes or Pipe fittings with beads, grooves, recesses or the like, with which method the material, e.g. by casting, injection molding, extrusion, extrusion or the like, is introduced into a mold and thereby fills the mold cavity, wherein the material is given the intended shape of the shaped body, characterized in that that after shaping when demolding the molded body at least one predetermined, section of this shaped body adjoining the recess or undercut temporarily in a shape deviating from the intended shape of the shaped body is brought, and that after demolding this section due to the resilience the material returns to its original position, which was preserved during the shaping process occupies. 2. The method according to claim 1, characterized in that the when Demolding caused a temporary change in position of the predetermined section of the Shaped body takes place by removing a core from the mold. 3. The method according to claim 1 or 2, characterized in that during removal from the mold and, if necessary, afterwards, the removed from its position, predetermined section of the shaped body, preferably by supplying heat, to the deformation temperature is held. 4. The method according to any one of claims 1 to 3, characterized in that that to achieve a heat build-up in the area of deepening or Undercut the shaped body this in the mentioned area at least during the demolding is thermally insulated. 5. The method according to any one of claims 1 to 4, characterized in that that the shaped body has a larger one in the region of the recess or undercut Has wall thickness than in its remaining parts. 6. The method according to claim 1 or 2, characterized in that the cooling of the molding is delayed during demolding. 7. The method according to any one of claims 1 to 6, characterized in that that the demolding takes place intermittently with a time delay. 8. Device for performing the method according to one of the claims 1 to 7, with an, optionally divided, shape and at least one core for Formation of the deepening or undercut of the molded body, characterized in that that the core (3) in the region of the recess or undercut (6) of the molded body (5) is formed undivided, and that the essentially transverse to the direction of application of the core measured dimension (D1) of the same is larger than the clear width (D2) of the core (3) between its discharge end (11) and the recess or Undercut (6) surrounding molded body (5). 9. Apparatus according to claim 8, characterized in that in the area the recess or undercut (6) of the molded body (5) a shape (1,2) respectively. the core (3) outside at least partially surrounding heats in the direction (12) is arranged. 10. The device according to claim 9, characterized in that the, in particular a controllable heating device (12) which surrounds the mold (1, 2) in a ring shape electrical resistance heating or thermostat heating with liquid Media is. 11. Device according to one of claims 8 to 10, characterized in that that the shape (1,2) in the region of the recess or undercut (6) of the molded body (5) Provided with thermal insulation, e.g. ceramic elements or synthetic resins is.