EA027154B1 - Method of producing thick-walled mouldings from polymer material - Google Patents

Abstract

The invention relates to foundry for producing articles, mainly from thermoplastic polymer, using die casting, preferably thick-walled articles. The technical solution of the invention may be also used for producing articles from other materials. The invention is aimed at providing the technical result for preventing forming shrinkage cavities inside thick-walled mouldings by controlling the process of solidification of material thereof. The assigned task is solved by that the method for producing thick-walled polymer mouldings which is characterised in that polymer material melt is transformed to moulding 8 in a transfer mould (Fig. 5), the moulding is further drawn out therefrom and solidified, has specific features: in the process of solidification the moulding 8 is forcibly hardened at different rate. The embodiments of the invention: a transfer mould with an alterable cavity volume is used, in which a movable piston is arranged adapted to move back during moulding thus providing mixing polymer melt; the alterable cavity volume of the transfer mould is provided by that the transfer mould comprises a movable piston; the moulding is drawn out from the transfer mould by pushing it out by the movable piston; forced solidification of the moulding at different rate is performed based on heat insulation of some of its surfaces, for example, ends using heat-insulating material 17; forced solidification of the moulding at different rate is performed based on heating some of its surfaces and forced cooling some of its surfaces.

Description

The invention relates to foundry for the production of products, mainly from a thermoplastic polymer by injection molding, mainly thick-walled products. The technical solution of the invention can also extend to the receipt of products from other materials.

A known method of producing thick-walled castings [1], including from a polymeric material, which consists in the fact that the molten polymeric material is converted into a casting mold, which is removed 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 trimmer mechanism, a middle rotary part with a casting push mechanism and a fixed part.

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

A more efficient method for producing thick-walled castings from a polymeric material is known [2], which consists in the fact that the molten polymer material is converted into a casting mold that is removed from there and solidifies. In this case, an injection mold is used that contains the mechanism for trimming the casting, the mechanism for pushing the casting, and the mechanism for flashing the internal cavities of the casting.

This prototype method [2] allows you to get castings without burr in their internal cavities and with fewer shrinkage shells inside the material of the castings. However, the presence of these sinks is undesirable, as this reduces the quality of the castings.

Therefore, the objective of the invention is to obtain a technical result for preventing the formation of shrinkage cavities inside thick-walled castings by controlling the process of solidification of their material.

The problem is solved in that the method for producing thick-walled castings from a polymer material, which consists in the fact that the molten polymer material is converted into a casting that is removed from there and solidifies, has distinctive signs: during the solidification process, the castings are forced to solidify at different speeds.

The implementation of the forced curing of the casting in the process of solidification will contribute to the fact that the layers of the material of the casting will be oriented in a direction and their directed shrinkage will occur. As a result, the casting will turn out with a clearly arranged orientation of the layers of its material, without loosening caused by breaking bonds between the cold and warm layers. Castings made by this method will have a uniform structure, stable mass, have predictable properties, symmetry of the structure relative to any plane or axis passing through the center of the casting, which will eliminate the formation of shrinkage shells in the material of the castings.

The use of different rates of forced curing of the casting will allow varying the curing processes mentioned above for castings of various sizes, configurations and fabrication materials in order to prevent the formation of shrink shells in them.

Embodiments of the invention:

an injection mold with a variable volume of its cavity is used, in which a movable piston is located with the ability to move back during casting, providing mixing of the melt of the polymer material;

a variable volume of the mold cavity is provided due to the fact that the mold contains a movable piston;

removing the casting from the mold by pushing it with a movable piston; forced curing of the casting at different speeds is carried out on the basis of thermal insulation of some of its surfaces;

forced curing of the casting at different speeds is carried out on the basis of heating of some of its surfaces;

forced curing of the casting at different speeds is carried out on the basis of forced cooling of some of its surfaces.

The invention is illustrated by illustrations, where in FIG. 1 shows a general diagram of an injection mold before starting to implement a method for producing thick-walled castings from a polymeric material; in FIG. 2 is the same as in FIG. 1, but when injected into the injection mold of the melt (intermediate position of the piston); in FIG. 3 is the same as in FIG. 2, but when pushing the casting; in FIG. 4 is the same as in FIG. 3, but upon release of the casting from the sign of the mold; in FIG. 5 shows a diagram of the curing processes of a casting extracted from an injection mold by providing thermal insulation of its ends; in FIG. 6 shows a diagram of the curing processes of a casting extracted from an injection mold by ensuring its heating; in FIG. 7 shows, for comparison, the pour point of a casting extracted from an injection mold using known methods [1, 2] for producing thick-walled castings from a polymeric material; in FIG. 8 shows diagrams of the structures of the bonds between the layers of the material of the casting after its shrinkage transformations, respectively, in diagram M — for arbitrary cooling according to the method diagram of FIG. 7; in scheme N, with controlled limited cooling or additional heating along the ends of the casting; in scheme O - the same as in scheme Ν, but along the periphery of the casting; on the diagram P is a view of the structures of the bonds between the layers of the material of the casting from its end according to the scheme O.

- 1 027154

To implement the method, an injection mold is used, made, for example, in the form of a mold for injection molding (Fig. 1). It contains a fixed detachable part 1 and a movable detachable part 2, made with the possibility of its forward and reverse motion, and, with a variable-volume forming cavity 3 located in it, in which there is a sign in the form of a piston 4, mating with its surface and equipped as 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, for example, of strengthening its structure or in the case of injection molding of products with a central hole.

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 shape.

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

At the end of the sign from the piston 4 side and in the detachable fixed part 1, at least one hole 6 is made (in Fig. 1-4 one such hole is shown on the sign and two on the detachable fixed part 1). Moreover, the hole 6 in the end of the sign from the side of the piston 4 is made at the end of the rod 5, passed through the piston 4.

Moreover, the sign is made with the possibility of its direct stroke X (in Fig. 2 - in the direction of the arrow to the left) under the action of the melt 7 injected under pressure P (in Fig. 2 - in the direction of the arrow in the right) through the fixed part 1 into the forming cavity 3 of the moving part 2 and with the possibility of pushing out the casting 8 (Fig. 3, 4) from the reverse stroke Υ (in Fig. 3 - in the arrow to the left).

For injection of the melt 7 (Fig. 2), the fixed part 1 is provided with a nozzle 9, to which the output part of the injection machine (not shown) is supplied for feeding the melt 7.

The rod 5 is movably located in the guide 10, sandwiched between the insert 11 and the cover 12 of the detachable part 1. The insert 11 therein is enclosed by a housing 13 and provided with a cooling jacket 14 where coolant (not shown) is supplied.

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 sign and the nozzle 9, a feature of the device (not shown) of the movable plate 16 is a guaranteed gap Δ (Fig. 1) as an element of the hydraulic resistance of the nozzle-damper.

Injection molding is carried out 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 releasable 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), an injection unit of the injection machine (not shown) is brought to the mold inlet, with the help of which molten 7 is fed through the nozzle 9 under pressure P. Overcoming the hydraulic resistance created by the mutual arrangement with the guaranteed clearance Δ of the nozzle 9 and piston 4 , the laminar jet of melt 7, entering the gap Δ, hits the end face of the piston 4, sharply changing its direction along this end. Therefore, together with the displacement of X of the piston 4 with its rod 5 under the action of the pressure of the melt 7, particles of this melt mix (its turbulent motion), which helps to eliminate the negative effects of a free jet, cold junctions in the boundary flows of the melt 7 when the melt 7 forms a cavity 3, close to the surface of the forming cavity 3.

The thermal casting mode is controlled by the supply of coolant (not shown) to the cooling jacket 14 and, if necessary, around the stationary part 2 (not shown).

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

After that, the flow of melt 7 through the nozzle 9 is stopped. The melt 7 cools down, hardening and forming in the forming cavity a specific shape defined by the contour of the forming cavity 3. Due to the previously obtained turbulence effect of the flow of melt 7, which eliminates the above-mentioned negative effects, inside the obtained casting cold junctions are not formed, gas and shrinkage porosities, shells are significantly reduced, and on its surface, as well as on the surface of the forming cavity 3, it is not formed soot.

To remove the molded casting 8 (Fig. 3), a direct stroke Υ of the movable detachable part 2 is performed. In this case (Fig. 3), the piston 4, remaining in place due to the engagement of the casting 8 with the end face of the rod 5, pushes the casting 8 out while the movable part 2, which is located at a distance from the fixed part 1. In this case, the casting 8 is located between them, holding its protrusions in the holes 6 of the end face of the rod 5 and the end of the fixed part 1.

In the final stage of the forward stroke of the movable demountable part 2 (Fig. 4), the casting 8 (Fig. 4) is detached from the piston 4 of the sign. At the end of the stroke of the movable plate 16 of the injection machine

- 2 027154 said opening of the movable part 2 with the fixed part 1, the protrusions of the casting 8 come out of the holes 6 on the end of the rod 5, forming a shank in the casting 8, and the protrusion on the fixed part 1 is still held in its hole 6. This can be implemented in several ways :

holes 6 at the end of the rod 5 and the fixed part 1 are the same in size and shape, but on the fixed part 1 they are larger in number (as shown), respectively, the holding force of the casting 8 is greater there;

holes 6 are the same in number (not shown) in the mentioned places, but at the end of the rod 5 the size of the holes 6 is smaller, therefore, the casting 8 remains on the fixed part 1 of the mold;

holes at the end of the rod 5 and fewer in number, and they are smaller in size than on the plate (not shown), so the casting 8 also remains on the stationary part 1 of the mold.

As a result, the piston 4 with the rod 5 takes its initial position with respect to its location in the mold (Fig. 1).

The final removal of the casting 8 from the end of the stationary part 1 (Fig. 4) occurs either by tearing the material out of the holes 6 under the action of the applied force, manually or by means of an automatic device (not shown), or due to the shrinkage of the casting material 8, when the protrusion size is 18 holes 6 is reduced, and he freely leaves from there with the formation of protrusions at the end of the casting 8.

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

Another way to remove the casting 8 from the mold is to ensure its free fall under the action of gravity. In this case, the movable part 2 is structurally able to disconnect its two halves (not shown) at the end of the mold opening stroke, and the freed casting 8 freely falls down, for example, into a special technological container. The opening and closing of such halves of the movable part 2 of the mold can be carried out using any known mechanical, hydraulic or pneumatic actuators (not shown).

It is also possible to extract the cast using the piston 4, for example, by the force of a compression spring located behind the piston 4 (not shown). The cycle of the mold with such a spring-loaded piston is similar to that for the mold without it (Fig. 1-4).

A method is also possible for extracting the casting by feeding compressed air into the forming cavity 3 behind the piston 4 through an air channel (not shown). As a result, the piston 4 returns to its original position.

As an embodiment of this method, it is possible for compressed air to flow through an air channel (not shown) made directly in the stem 5 through a check valve (not shown) located in the piston 4.

In this case, compressed air through the opening check valve will act directly on the casting 8, pushing it out of the forming cavity 3.

There is also a way to extract the casting 8 using special pushers (not shown), passed through the piston 4 or through the piston rod 5 and piston 4. When the movable part 2 of the mold is opened to the left when opening (Fig. 3), such pushers under the action of their mechanism drive (not shown) push the casting 8.

After extraction of the casting in the process of solidification of the casting, it is forced to cure at different speeds.

Such forced curing of the casting 8 is carried out either on the basis of heating (Fig. 5) or cooling (Fig. 6) of some of its surfaces.

For example, convection heat removal from less critical surfaces of the casting 8 can be limited or prevented, for example, by providing thermal insulation of its ends, for example, by means of a heat-insulating material 17.

In this case of forced curing, the cooling of the surface along the periphery of the casting 8 (position A in Fig. 5) occurs quickly, at a speed determined by the ambient temperature, and the cooling of the ends is prevented by the use of thermal insulation material 17. As a result (position B in Fig. 5), cold and warm areas in the casting. Particles of material under the action of shrink forces P tend to the center of the casting 8, entraining particles located directly at the isolated surfaces (ends). Due to the equality of temperatures and, accordingly, the fluidity of the non-solidified melt inside and at the ends, the material without ruptures of internal bonds gradually rushes to the center of the casting 8. Its ends acquire a concave shape (position C in Fig. 5), and shells do not form inside the product ( position Ό in Fig. 5). Those. the formation of possible internal cavities (shrinkage shells) inside the casting 8 is replaced by the concavity of its end surfaces, which, if necessary, are modified mechanically to achieve the required dimensions of the casting 8.

This method of controlled cooling of castings is also useful because the layers of material of the castings are gradually oriented, and directed shrinkage of their material occurs. Casting 8 is obtained with a clearly arranged orientation of the layers, without loosening caused by breaks in bonds between cold and warm layers. As a result, parts manufactured by this method have a homogeneous structure, stable mass, predictable properties, and symmetry of the structure relative to any plane or axis passing through the center of the casting 8.

As an embodiment of the method, some surfaces of the casting 8 can be not insulated, but heated (Fig. 6), thereby maintaining the flexibility of the surface layer, for example, at the ends of the casting 8, sufficient to entrain the shrink forces to its center. The positions EH of the curing processes of the casting 8 of this embodiment are similar to the positions L-Ό of the curing processes of the casting 8 of FIG. 5.

With this embodiment of the curing of the casting 8, its surface sections can be heated by exposure to thermal radiation, blowing with a heated gas, washing with a heated liquid, contact with a heated body, and also bulk in the inner zone of the casting, for example, by exposure to ultra-high frequency radiation.

In other cases, for example, during the manufacture and / or exposure of products in a room with a high temperature, it is possible to cool some surfaces of the casting with heating of others or without heating.

For cases when special requirements are imposed on the ends, and not on the peripheral surface, or when a change in the properties of the material is required by orienting the layers of material transverse to the axis, heating or thermal insulation can be carried out not at the ends, but along the periphery of the casting. In this case, a saddle shape of the ends of the casting 8 will form.

For a better understanding of the shrinkage elimination effect described above, for comparison in FIG. 7 shows a pouring diagram of a casting 8 extracted from an injection mold using known methods [1, 2] for producing thick-walled castings from a polymeric material.

After removing the casting 8 (position I of FIG. 7), the solidification process begins in it along with the inevitable process of shrinkage of the material. It is indisputable that the temperature change, and, accordingly, the shrinkage rate throughout the casting 8 is uneven: the surface layers cool faster than in the center of the casting (position 1 in Fig. 7). The shrinkage process determines the contraction of the material particles to the geometric center of the casting 8 under the action of internal shrinkage forces R.

When the casting is arbitrarily cooled, the entire outer surface hardens faster, forming a crust that is not able to deform under the action of shrinkage forces and the still warm material inside breaks off in several places from the cold crust, forming large cavities (voids) and small pores inside (K, L positions Fig. 7), despite the fact that the filling of the mold cavity with the melt is carried out in full without the ingress of gases and the formation of voids.

In contrast to the casting 8 (Fig. 7) obtained by known methods [1, 2], in the castings obtained by the invented method (Fig. 5, 6) such voids (shrinkage shells) are not formed and the quality of the casting is improved.

Ideally, the structure of the bonds between the layers of material after shrinkage transformations can schematically look as follows (Fig. 8). Scheme M — optional cooling according to FIG. 7 according to known methods [1, 2], scheme N — limited cooling or additional heating at the ends according to the invented method, scheme O — the same along the periphery, P — same as position O, end view of the casting 8.

Information sources.

1. Auth. St. USSR No. 161555, class Β22Ό 17/10, 1988.

2. Patent KI 2010667 C1, IPC Β22Ό 17/22, priority from 1990.12.13, published 1994.04.15 (prototype).

Claims (2)

CLAIM 1. A method of producing thick-walled castings from a polymer material, which consists in the fact that the molten polymer material is converted into a casting that is removed from there and solidifies, and during the solidification process, the casting is forced to cure at different speeds, for this part of the surface of the casting is insulated, another part of the casting is heated or forced to cool, characterized in that during thermal insulation of the surfaces the casting is limited or prevented by convection heat removal from those parts overhnosti casting, which will not be exploited, and the other part of the surface heated by thermal radiation, or heated gas is blown or washed by a heated fluid, or provide contact with a heated body, or ultrahigh frequency radiation exposure on the inner casting zone. 2. The method according to claim 1, characterized in that the thermal insulation or heating of these surfaces of the casting is carried out on the periphery of the casting.