RU2455159C2 - Method of injection moulding and injection moulding machine - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to injection moulding. In compliance with proposed method, injection mould is closed in contact with moulding machine by pressure of fused metal exceeding that of mould opening force. Proposed device comprises injection mould with, at least, one forming cavity, injection moulding machine with cylinder for thermoplastic material equipped with injector, moving piston accommodated in said cylinder. Note here that injection moulding machine may displace for jointing injector with mould. Cylinder cross-section area exceeds maximum cross-section area of mould forming cavity.

EFFECT: automatic closure of mould, simplified design.

4 cl, 1 dwg

Description

The group of inventions relates to foundry, namely to piston injection molding, and can find application in electrochemical, electronic, automotive, instrument-making and other industries. The invention, in particular, can be used for the manufacture of permanent magnets or other products from thermoplastics, mainly of small sizes.

Currently known devices for producing molded plastic products that contain a cylinder, a heater for heating plastics, a piston and a power unit. In addition, methods are known for producing molded plastic products, which include the steps of heating thermoplastic masses, molding and curing them, and also in some cases adding solid filler to the plastic mass.

Known injection molding machine and method of injection molding of rubber materials for cold or hot runner technology, which includes the following steps: feeding the polymer material into the injection mold through the first cylinder-piston block containing the first piston and the first cylinder, through the second cylinder of the second cylinder-piston block, and the cylinder the first cylinder-piston block flows into the end of the second cylinder-piston block, remote from the injection mold, moreover, along the flow path between both cylinder-piston blocks edusmotren choke of variable cross section for adjusting the temperature of the rubber material and with a second piston cylinder unit of the second free flow path to the injection mold; moving the second piston into the second cylinder to introduce the rubber material located in the second cylinder into the injection mold, moreover, using the piston of the second cylinder-piston block, basically completely empty the cylinder of the second cylinder-piston block; retraction of the second piston (see RF patent for the invention No. 2362676, IPC VC 45/53).

However, the design of the described device is complex, which is associated with the presence of two cylinder-piston blocks in the injection unit, and the method is characterized by a rather high complexity.

Known DEVICE FOR CASTING UNDER PRESSURE OF POLYMERIC FORMED PRODUCTS, consisting of an injection machine and a mold, as well as a method of injection molding, implemented during operation of the device. In the mold there are at least two cavity corresponding to the dimensions of the manufactured molded products. It consists of at least three parts moving in relation to each other - front, middle and back, which fit snugly against each other along the connector planes parallel to each other under the action of the clamping force created by the pressure means. The injection machine is designed as a conventional standard injection machine. Each plane of the connector extends through at least one cavity. One channel is made in the mold for supplying molten polymer, which, on the one hand, ends in cavities, and, on the other hand, at the entrance to the surface of the mold, which is connected to the injection machine in the working position. The channel is made conical in the front and middle parts of the mold. On the parts of the mold there is a latch movable between two positions, by means of which, in the absence of the pressing force generated by the pressure means, in the first position only the front and the front parts of the mold are blocked between each other and in the second position due to the presence of residual force only the middle and back of the mold. The latch is moved from one position to another due to the action of the pressure means (see patent for the invention of the Russian Federation No. 2284913, B29C 45/12).

However, in the device for injection molding, energy and time are required to actuate the pressure means and retainer, and the method includes additional operations for locking the mold.

The objective of this solution is to increase the production speed of products while maintaining the quality of castings, unification and simplification of the foundry machine.

The technical result is to provide automatic locking of the mold while simplifying the design, as well as to increase productivity.

The specified technical result is achieved by the fact that in the inventive method of manufacturing products from thermoplastic materials by injection molding, according to the solution, create pressure in the molten material in the injection machine, move the injection machine to contact with the mold under the action of the created pressure, and injection of the molten material from the injection machine into the mold, while providing automatic locking of the mold in contact with the injection machine due to the excess compression force of the mold, creating me pressure of the molten material in the injection molding machine, power over the mold opening created by pressure of the molten material in the mold, the pressure is lowered in the molten material in the injection molding machine, injection molding machine is moved from the mold and extracting the finished product from the mold. A device for manufacturing products from thermoplastic materials by injection molding, according to the solution, includes a mold with at least one forming cavity, an injection machine containing a cylinder for thermoplastic material, equipped with a nozzle, a movable piston made with the possibility of placement in the cylinder, while the injection machine is movable with the possibility of movement to pair the nozzle with the mold, and the cross-sectional area of the cylinder is greater than the maximum cross-sectional area of the mold razuyuschey cavity. The nozzle is made cone-shaped, and in the mold a cone-shaped recess is made for mating with the nozzle. The injection machine is fixed with the ability to move on racks using springs.

The invention is illustrated in the drawing, which shows a block diagram of the proposed device, where

1 - injection machine;

2 - cylinder;

3 - heating element;

4 - loading hopper;

5 - nozzle;

6 - outlet;

7 - a piston;

8 - power unit;

9 - a movable rod;

10 - thermoplastic material;

11 - rack;

12 - spring;

13 - base.

14 - mold;

15 - punch;

16 - forming element;

17 - matrix;

18 - forming cavity;

19 - a cover;

20 - sprue.

The claimed group of inventions includes a method for producing molded products from thermoplastic material and a device for implementing the method.

The proposed device contains an injection machine mounted above the mold with the possibility of vertical movement until it comes into contact with it to ensure the closure of the mold and the exact dosage of plasticized by thermal action of plastic.

Injection molding machine 1 comprises a hollow cylinder 3 with a heating element 2 (for example, an electric heater located on the outside of the cylinder), a piston 7 arranged to be placed in the cylinder cavity and connected to a power unit 8 designed to move the piston 7 in the vertical direction. The cylinder 3 is equipped with a loading hopper 4 in the upper part, designed to accommodate granular thermoplastic material 9 to obtain molded products. The piston 7 is mounted on the movable rod 10 of the power unit 8 (for example, the rod of a hydraulic or pneumatic cylinder, or a gear rack of a linear mechanical transmission), designed to move the piston 7 in the vertical direction with the force necessary to ensure the casting pressure, while in the initial position the piston 7 is located above the feed hopper 4 to provide a clearance sufficient for passage of granular thermoplastic material 9 from the feed hopper 4 into the cavity of the cylinder 3. The lower part of the cylinder (nozzle) 5 is made and in the form of a protruding cone with an outlet 6 in the center. The injection machine 1 is mounted on two vertical posts 11 with the possibility of movement along them and is held in its initial position in the upper part by means of springs 12, while the posts 11 and the power unit 8 are fixedly mounted on the base 13. In the working position, the injection machine 1 is located in bottom of racks 11.

Under the injection machine 1 on the base 13, a seat is made for the location of the mold 14. The mold 14 contains located on each other with the possibility of fixation from displacement in the horizontal plane: a punch 17 made with the possibility of fixation in a horizontal plane on the seat of the base, as well as with the possibility of placing, if necessary, 17 forming elements on the punch; matrix 16, in which at least one forming cavity 18 is made; a cover with a gate 15. The gate is a hole corresponding to the outlet 6 in the lower part of the cylinder 3, while the upper part of the hole is conical for tight coupling with the nozzle 5 of the injection molding machine 1 when it is in working position. The mold 14 may also contain other constituent elements, depending on the complexity and number of molded products.

An important condition in the design of the device to achieve a technical result is the ratio of the cross-sectional area of the cylinder of the injection molding machine and the maximum total cross-sectional area of all forming cavities in the matrix, namely, the cross-sectional area of the cylinder exceeds the cross-sectional area of all cavities to ensure automatic closing of the mold.

An embodiment of the device using a movable mold is possible, for example, by arranging the mold on a part of the base that is adjustable in height to provide the possibility of the initial location of the gate at a minimum distance from the nozzle. It is also possible the initial location of the piston inside the cylinder, while for the supply of granular material or pre-molten mass in the cylinder there is a side hole in which the material is fed by means of a screw. In addition to the vertical arrangement of the elements of the injection molding machine, it is possible to sequentially place the power unit with the rod and piston, cylinder, mold in a horizontal plane.

The inventive device for producing molded products from thermoplastic materials by injection molding works as follows. First, they turn on the power of the heating element, as a result of which the cylinder is heated to a temperature above the melting temperature of the granules of thermoplastic material; material in the cylinder cavity melts from heating to a homogeneous viscous mass. At this time, the mold is sequentially assembled - the forming elements (for example, rods) and the matrix are installed on the punch, the cover is installed on top, and then the mold is placed under the injection molding machine on the seat of the base; at the same time, the mold remains easily collapsible - its components are freely separated from each other when displaced in the vertical direction.

After that, the power unit is actuated, which extends the movable rod and lowers the piston into the cylinder. A lowering piston covers the gap between the loading hopper and the cylinder cavity, and then compresses the molten mass in the cylinder, as a result of which the pressure inside the cylinder rises until it becomes sufficient to compress the springs, after which the pressure remains at the same level, and the cylinder moves with the piston down along the struts, compressing the springs, until it stops with the nozzle in the conical part of the gate. Such a movement of the cylinder is possible due to the fact that a small pressure increase is not sufficient to extrude a molten mass with a high viscosity through the outlet of small diameter in a very short period of time the cylinder moves to the mold. As a result of contact with the injection machine, the mold is locked between the cylinder and the base, the movement of the cylinder stops, and the piston continues to move under the action of the movable rod of the power unit.

The moving piston compresses the molten mass more strongly, increasing the pressure inside it to a value sufficient to squeeze the mass out of the outlet, which leads to the injection of the thermoplastic mass through the gate into the die cavity until it is completely filled. In this case, the filled mold does not open under the action of the pressure of the liquid mass inside due to the fact that the cross-sectional area of the cylinder exceeds the sum of the maximum areas of all cavities in the matrix. This is because the pressure of the molten mass inside the cylinder and in the cavity of the matrix is the same, however, by definition P = F / S, therefore, the forces F = P S acting on the mold cover above and below have a different value proportional to the contact area liquid with a cap (the force exerted on the cap from above is equal to the force exerted by the fluid on the lower bottom of the cylinder due to the hard contact between the cap and the cylinder). Thus, the necessity of using locking devices of the mold is excluded, since the pressure force of the lid is always, at any pressure in the molten thermoplastic mass, greater than the force tending to open the mold.

After the matrix cavity is completely filled with plastic mass, the movement of the liquid from the cylinder through the gate is stopped, due to the heat dissipation through the cover, the molten mass cools and crystallizes (freezes), closing the fluid outlet through the gate. However, the pressure of the injection machine on the mold is maintained until all of the plastic mass in the mold solidifies. Then turn off the power unit and raise the piston up, the pressure inside the cylinder drops, and under the action of the springs, it rises to its original position, freeing the mold. After that, the lid is removed and the hardened thermoplastic material is removed from the gate, the matrix is also separated from the punch and the finished product is removed from the forming cavity. The device is ready to work again, the whole process is repeated.

A method of manufacturing products from thermoplastic materials by injection molding, a distinctive feature of which is the stage of self-closing of the mold, is as follows. First, the thermoplastic material is melted, for example, directly in an injection machine by heating it in a cylinder using a heating element. Then create pressure in the molten material in the injection machine, for example, lowering a piston of the corresponding diameter into the cylinder. Using the fact that the pressure in the liquid acts uniformly in all directions, the force is transferred from the piston to the cylinder, thereby moving the injection machine to contact with the stationary mold. The pressure in the molten material in the injection machine is increased, while the piston continues to act on the molten material, while the cylinder loses its ability to move further after contact with the mold occurs, as a result of which injection of molten material from the injection machine into the mold occurs. This ensures that the mold is automatically locked in contact with the injection machine due to the excess compression force of the mold created by the pressure of the molten material in the injection machine over the opening force of the mold created by the pressure of the molten material in the mold. This is possible if the area of the cylinder, which is affected by the liquid material in it in the direction of movement of the piston, exceeds the area of the mold, which is affected by the liquid material in it in the direction opposite to the movement of the piston. The pressure is kept constant for a certain time sufficient for the material to solidify in the mold, and then the pressure in the molten material is lowered in the injection machine, moving the piston out of the cylinder. Then the injection machine is moved from the mold, releasing it, and the finished product is removed from the mold.

A current sample of the inventive device was made, which carries out the inventive method during operation, which confirmed the industrial applicability of the solution. The advantage of the proposed solutions is the expansion of the product range, quick reconfiguration to a new product, reducing the development time of products, the possibility of manufacturing small and large series.

Claims (4)

1. A method of manufacturing products from thermoplastic materials by injection molding, characterized in that they create pressure in the molten material in the injection machine, move the injection machine to contact with the mold under the action of the generated pressure, and inject the molten material from the injection machine into the mold at the same time provide automatic locking of the mold in contact with the injection machine due to the excess compression force of the mold created by the pressure of the molten material in the injection machine e, over the force of opening the mold created by the pressure of the molten material in the mold, lower the pressure in the molten material in the injection machine, move the injection machine from the mold, and remove the finished product from the mold. 2. Device for manufacturing products from thermoplastic materials by injection molding, characterized in that it includes a mold with at least one forming cavity, an injection machine containing a cylinder for thermoplastic material, equipped with a nozzle, a movable piston made with the possibility placement in the cylinder, while the injection molding machine is movable with the ability to move to pair the nozzle with the mold, and the cross-sectional area of the cylinder is greater than the maximum cross-sectional area echeniya cavity. 3. The device according to claim 2, characterized in that the nozzle is cone-shaped and a cone-shaped recess is made in the mold for interfacing with the nozzle. 4. The device according to claim 2, characterized in that the injection molding machine is fixed with the ability to move on racks using springs.

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