EA030546B1 - Method of producing thick-walled mouldings from polymers - Google Patents

Abstract

The invention relates to casting for producing articles, mainly from a thermoplastic polymer, using injection moulding, primarily thick-walled articles. The technical solution of the invention may be also used for producing articles from other materials. The objective of the invention is providing the technical result for improvement of efficiency of producing thick-walled polymer mouldings by preventing or reducing formation of shrinkage cavities therein. Said objective is attained by provision of a method for producing thick-walled polymer mouldings (Fig. 7) comprising transformation of polymer material melt in a mould into a moulding that is withdrawn therefrom and cooled, wherein the method has the following distinguishing feature: after withdrawal of a moulding 8 from the mould, in the course of cooling, it is subjected to squeeze reduction, e.g., by means of a yoke 20. Embodiments: the moulding is subjected to squeeze reduction from the side of its end surfaces; from the side of its non-end surfaces; from the side of all its surfaces.

Description

The invention relates to foundry for the production of products mainly from thermoplastic polymer by injection molding, mainly thick-walled products. The technical solution of the invention may also extend to the receipt of products from other materials. The objective of the invention is to obtain a technical result for increasing the efficiency of the method for producing thick-walled polymer castings by preventing or reducing the formation of shrink holes in them. The task is solved by the fact that the method of obtaining thick-walled polymer castings (Fig. 7), which consists in converting the melt of polymer material into a mold, into a casting that is extracted from there and cooled, there is a distinguishing feature: after extraction from the mold, the casting 8 is in process its cooling, it is subjected to compression, for example, using the clamp 20. Embodiments of the invention: the casting is subjected to compression from its end surfaces; from its non-faceted surfaces; from all its surfaces.

030546 B1

030546 B1

030546

The invention relates to foundry for the production of products mainly from thermoplastic polymer by injection molding, mainly thick-walled products. The technical solution of the invention may also extend to the receipt of products from other materials. A method of obtaining thick-walled castings from polymers [1], which consists in the fact that in the mold form the molten polymer material is converted into a casting, which is extracted from there and solidifies. The method is based on the operation of an injection molding machine with an injection mold containing a movable part with a casting trimming mechanism, a middle turning part with a pushing mechanism of the casting and a fixed part.

However, this method is not effective due to the fact that relatively many shrink holes form in the finished casting, and the internal cavities of the casting are obtained with a shroud, which must then be cut by using additional equipment after removing the casting from the mold.

A more efficient method is known for producing thick-walled castings from a polymeric material [2], which consists in converting a melt of a polymeric material into a casting form into a casting, which is extracted from there and solidified. At the same time, a casting mold was used, containing a casting trimming mechanism, a casting pushing mechanism and a flashing mechanism for the internal cavities of the casting.

Such a prototype method [2] makes it possible to obtain castings without shading in their internal cavities and with a smaller number of shrink holes inside the material of the castings. However, it is still not sufficiently effective, since the presence of these shells is undesirable, their presence reduces the quality of castings.

Therefore, the object of the invention is to obtain a technical result for increasing the efficiency of the method for producing thick-walled castings from polymeric material by preventing or reducing the formation of shrink holes in them.

The task is solved by the fact that the method of obtaining thick-walled polymer castings, which consists in converting the melt of polymer material into a mold, which is extracted from there and cooled down, has a distinguishing feature: after being removed from the mold, it undergoes compression during the cooling process.

Compressing the casting during its cooling will increase the flexibility of the solidifying layer of material and direct it to the center of the casting in the direction of shrinkage forces in order to prevent a gap between the cold and warm zones or minimize the size of the expansion of the cavity. Castings produced by this method will have a homogeneous structure, a stable mass, have predictable properties, symmetry of the structure with respect to any plane or axis passing through the center of the casting, which will eliminate or significantly reduce the formation of shrink holes in the polymer casting material, increasing the efficiency of the way they are produced .

Embodiments of the invention:

the casting is subjected to compression from its end surfaces; the casting is crimped from its non-faceted surfaces; casting is subjected to compression from all its surfaces.

The invention is illustrated by illustrations, where in FIG. 1 shows the general scheme of the mold before starting the method for producing thick-walled castings from polymeric material; in fig. 2 is the same as in FIG. 1, but when melt is injected into the mold (intermediate position of the piston); in fig. 3 is the same as in FIG. 2, but when ejecting the casting; in fig. 4 is the same as in FIG. 3, but with the release of the casting from the mark of the mold; in fig. 5 shows an example of the process of cooling a casting extracted from a mold with four stages of its transformation; in fig. 6 - the proposed form of casting with compensating end protrusions; in fig. 7 shows an example of a scheme for applying additional forces to the non-face surface of a cast with a clamp; in fig. 8 shows an example of a scheme for applying additional forces to all surfaces of a casting using a pressurized working medium in an airtight vessel.

For the implementation of the method, an injection mold is used, made, for example, in the form of an injection molding mold (Fig. 1). It contains a stationary detachable part 1 and a movable detachable part 2, made with the possibility of its forward and reverse, and with a shaping cavity 3 of variable volume located in it, in which the sign is located in the form of a piston 4 mating with its surface, provided with at least one rod 5, which may be integral with the piston 4. More than one rod 5, the sign may contain (not shown) in the case of, for example, strengthening its design or in the case of injection molding of products with a central bore.

For better extraction of the casting from the mold, the surface of the piston 4 and the surface of the forming cavity 3 mating with it are different from the cylindrical form.

The surface of the piston 4 and the mating surface of the shaping cavity 3 may be different from a cylindrical shape. For example, they can be made (not shown) with rectilinear or curved mating surfaces of complex shape.

The piston is made with the possibility of its direct stroke x (in Fig. 2 - along the left arrow) under the action - 1 030546

via melt 7, injected under pressure p (in Fig. 2 - along the figured arrow to the right) through the stationary part 1 to the forming cavity 3 of the movable part 2, and with the possibility of pushing out the casting 8 (Fig. 3, 4) in the direct course Y ( in Fig. 3 - on the left arrow).

For melt injection 7 (FIG. 2), the fixed part 1 is provided with a nozzle 9, to which the output part of the injection molding machine (not shown) is fed to supply the melt 7.

The rod 5 is movably in the guide 10, sandwiched between the insert 11 and the lid 12 of the detachable part 1. The insert 11 in it is enclosed by the housing 13 and is equipped with a cooling jacket 14 to which coolant is supplied (not shown).

The detachable part 1 is made with the possibility of its movement with the help of the closing unit of the opening of the injection molding machine (only its fixed and movable plates 15 and 16 are shown). Between the end of the mark and the nozzle 9, a feature of the device (not shown) of the movable plate 16 is formed with a guaranteed gap Δ (Fig. 1) as an element of the hydraulic resistance "nozzle-flap".

In the process of cooling the casting 8 (Fig. 5) extracted from the mold, four stages of its transformation (A - D) can be observed: stage A - without impact from outside on the hot casting 8 with the same temperature throughout its material structure; stage B - with the impact of additional forces f on the end surfaces 17 of the cooling casting 8, which has a pronounced central zone 18, with a warmer temperature than the peripheral part; stage C - as in stage B, but the said central zone is reduced, and a significant portion of the end surfaces 19 has acquired a funnel shape; stage D - fully cooled casting 8.

The ends of the piston 4 (Fig. 1) and the guide 10 of the mold for casting under pressure, facing the inside of the molding cavity 3, can have a special shape, which is used to produce casting 8 (Fig. 6) with protrusions 20.

A possible variant of the scheme of application of additional forces f to the periphery of the casting 8, for example, with the help of a collar 21 grasped by it or a cartridge with special jaws (not shown), with the help of a collet and other means of girth.

A possible variant of the scheme of simultaneous effects of force on all surfaces of the casting. This may be a symbiosis (not shown) of any of the above methods, or placing the casting 8 in a sealed vessel 22, where working fluid 23 under pressure P, for example gas or liquid, is fed through a valve (not shown).

Carry out the casting under pressure using the above-described mold as follows.

In the initial position (Fig. 1) of the plates 15 and 16 of the injection molding machine, the detachable parts 1 and 2 of the mold are closed and under pressure, and the rod 5 together with the piston 4 are in the extreme right position.

Then (Fig. 2) the injection unit of the injection molding machine (not shown) is fed to the inlet of the mold, through which the melt 7 is fed through the nozzle 9 under the pressure p. Overcoming the hydraulic resistance created by the mutual arrangement with a guaranteed clearance Δ of the nozzle 9 and the piston 4, the laminar jet of the melt 7, entering the gap Δ, hits the end of the piston 4, sharply changing its direction along this end. Therefore, together with the displacement X of the piston 4 with its rod 5 under the action of the pressure of the melt 7, the particles of this melt are mixed (its turbulent motion), which contributes to the elimination of the negative effects of "free jet" and "cold junction" in the boundary melt flows 7, close to the surface of the forming cavity 3.

Thermal casting mode when this is regulated by the flow of coolant (not shown) in the cooling jacket 14 and, if necessary, around the stationary part 2 (not shown).

Under the action of the pressure of the melt 7, the rod 5 will move to the extreme left position. The piston 4 also occupies the extreme left position, forming the necessary volume of the shaping cavity 3, in which the hot melt will be located.

After that, the melt 7 is stopped through the nozzle 9. The melt 7 cools, solidifying and forming a mold in a mold cavity defined by the contour of the mold cavity 3. Thanks to the previously obtained effect of the melt flow turbulence 7, which eliminates the above mentioned negative effects, inside the resulting casting cold junctions are not formed, the gas and shrinkage porosities of the shell are significantly reduced, and on its surface, as well as on the surface of the forming cavity 3, is not formed agar.

To extract the molded casting 8 (Fig. 3) carry out a straight course Y of the movable detachable part 2.

After the casting 8 is removed from the mold, the split parts 7 and 2 are closed by the action of the injection molding machine and are under pressure according to FIG. 1. Next, the cycle of the mold is repeated.

It is also possible to extract the casting 8 using special pushers (not shown) passed through the piston 4 or through the rod 5 of the piston 4 and the piston 4. When the movable part 2 of the press 2 030546

the mold when opening is retracted to the left (Fig. 3), such pushers push the casting 8 under the action of its drive mechanism (not shown).

After removing the hot casting 8 from the mold at once, the entire structure of its material has the same temperature (stage B in FIG. 5).

Then, at the beginning of cooling (stage B in FIG. 5), when a clearly pronounced central zone 18 with a warmer temperature than the peripheral part appears in the casting, additional forces f are applied to the end surfaces 17 of the cooling casting 8. This forces the colder outer layers quickly cooling material to strive to the center of the casting 8, not allowing them to stop. As a result, the warmer central zone is reduced in size (stage C in FIG. 5). At the same time, a significant portion of the end surfaces 19 acquires a funnel-shaped form 19. After the temperature is equalized throughout the entire structure of the casting material 8 and the distinct central zone 18 disappears, the impact on the casting 8 by additional forces f is stopped.

The result is a fully cooled casting 8 (stage D in FIG. 5) without shrink cavities or cavities in its material, as is observed with traditional casting methods, or with small dimensions of these cavities or cavities.

In this case, the funnel-shaped form 19 of the end surfaces 17, if necessary, can be removed by machining or it can be compensated for by the initially molded protrusions 20 (FIG. 6), which are eliminated during cooling under the action of shrinking forces and additional forces f.

A possible variant of the scheme of simultaneous action of force on all surfaces of the casting 8. This may be a symbiosis (not shown) of any of the above methods, or placing the casting 8 in a sealed vessel 22, where the working medium 23 is fed through a valve (not shown) under pressure P, for example gas or liquid.

The ends of the piston 4 (Fig. 1) and the guide 10 of the mold for casting under pressure, facing the inside of the molding cavity 3, can have a special shape, which is used to produce casting 8 (Fig. 6) with protrusions 20.

This scheme (Fig. 5) can be implemented (not shown), for example, on presses, clamps, clamping devices, spring mechanisms, using weights, as well as any of their options, allowing you to compress the casting 8 from both ends simultaneously or from one of the them focusing on the other.

A possible option (Fig. 7) is the application of additional forces f to the periphery of the casting 8, for example, with the help of a collar 21 which is grasped by its efforts F or (not shown) a cartridge with special jaws, with a collet and other means of girth.

It is also possible (Fig. 7) to simultaneously act on all surfaces of the casting 8. This may be a symbiosis (not shown) of any of the above methods or placing the casting 8 in an airtight vessel 22, to which working valve 23 under the valve (not shown) is fed pressure P, for example gas or liquid.

Due to the methods described above (Figs. 5, 7, 8), the application of additional forces f to the casting 8, unlike the castings traditionally obtained [1, 2], in the casting 8, voids (shrink holes) are not formed or are insignificant. Therefore, the quality of the casting is greatly improved.

Information sources.

1. USSR author's certificate No. 161555, cl. B22D 17/10, 1988.

2. Patent RU 2010667 C1, IPC B22D 17/22, priority from 1990.12.13, published 1994.04.15 (prototype).

Claims (3)

CLAIM 1. A method of producing thick-walled polymer castings, which consists in converting a melt of a polymer material into a casting mold into a casting (8), which is extracted from there and cooled down, and during its cooling it is subjected to compression, characterized in that said reduction is carried out by putting additional forces (f) on the end surfaces (17) of the cooling casting (8) until a clearly pronounced central zone (18) with a warmer temperature appears than the peripheral part, forcing the cooler The hot layers of the rapidly cooling material tend to the center of the casting (8), preventing them from stopping, and after equalizing the temperature throughout the structure of the casting material (8) and the disappearance of the pronounced central zone (18), they stop the impact on the casting (8) with additional forces (f ). 2. The method according to claim 1, characterized in that the casting is also subjected to compression from its non-faceted surfaces. 3. The method according to claim 1, characterized in that the casting is subjected to compression from all its surfaces. - 3 030546