GB1578194A

GB1578194A - Apparatus for injection moulding of plastics or rubber compounds

Info

Publication number: GB1578194A
Application number: GB1036177A
Authority: GB
Original assignee: Statni Vyzkumny Ustav Materialu
Current assignee: Statni Vyzkumny Ustav Materialu
Priority date: 1977-03-11
Filing date: 1977-03-11
Publication date: 1980-11-05

Description

(54) APPARATUS FOR INJECTION MOULDING OF PLASTICS OR RUBBER COMPOUNDS (71) We, STATNI VYZKUMNY USTAV MATERIALU, of Praha, Czechoslovakia, a Czechoslovakian Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an injection moulding apparatus for manufacture of products made of plastics and of rubber compounds.

For injection of structural foam, i.e. of plastics having expanding characteristics, which provide in a mould an integral moulding with a porous core and a compact surface, a number of special, mostly custombuilt apparatuses are used at present. The expansion of the melt is achieved by a foaming agent introduced into the mould together with the melt. The foaming agent can be a material which decomposes at elevated temperatures, for instance azodicarbonamide or compressed gas, for instance nitrogen.

The thus prepared melt is injected into the mould at elevated speed either by means of a ram from a storage chamber after its filling by a plasticating screw or directly by an axial movement of the face of the plasticating screw from the plasticating chamber.

Apparatus for the injection of the material from a storage chamber have this chamber situated so that the motion of the piston is either parallel with, perpendicular to, or on the axis of the mould, which itself is perpendicular to clamping plates. When the injection is carried out perpendicularly to the axis of the mould, the chamber terminates in a nozzle parallel with the axis of the mould and which bears against a lateral wall of the mould. The mould is, provided with an inlet on one side of its partition plane, whereby the melt fills the mould cavity from one side to the other. This arrangement and process are used in case of a perpendicular arrangement of the injection unit relative to one or more clamping parts, for instance to a part with a vertical axis, where the surface of the moulding is horizontal and the injection is carried out from the lateral side of the press.

Universal arrangements for injection of structural foam and known plastics are designed so that a hydraulic accumulator with corresponding distributing means is connected to currently manufactured known machines. By this arrangement the original high injection pressure is maintained and the speed of the injection i.e. the movement of the screw is increased, but the maximum volume which could be originally injected is not increased.

The described known apparatuses using a chamber with an injection ram are designed solely for injection by low pressure technology as their chambers are designed for low injection pressures and larger volumes. The chambers are also, when compared with apparatus for injection of conventional homogenous mouldings, connected to clamping units having low clamping forces and weak tie-bars.

In current arrangements for high pressure injection of known materials also with foaming agents, operating at high speed and pressure, the weight of the mouldings is limited solely by the capacity of the injection unit. The weight of these mouldings is equal to current mouldings of known materials.

Due to the diverse assortment of mouldings, particularly of their weight and dimensions, the size of clamping plates and the maximum distance between the plates of the machine cannot be fully utilized while the installation of custom built machines is frequently not economical and the machines cannot be fully utilized.

When starting manufacture of moulded products with a large injection volume of structural foam, serious economic problems are encountered at present due to time lags and particularly due to inappropriate investment costs.

A substantial drawback of known apparatus is that for mouldings of nonfoamable materials, the manufacture of products having a weight greater than that corresponding to the maximum injection capacity, is impossible.

The manufacture of two component sandwich products with a compact surface layer and a foamed core is at present limited to special machines wih two injection units.

The actually used injection units, apart from the proper clamping units as an additional device, require, due to their length and weight, large -spaces in order that the injection nozzle can reach the circumference of the mould.

Low pressure injection units for structural foams which enable a manufacture of products of large size cannot be used for high pressure injection of foamed material as they do not allow mouldings with smooth surfaces to be produced.

The individual described arrangements of machines have the following characteristic features limiting their universal technolo tidal application: with constructions of mould clamping parts designed for low closing forces, only low injection pressures are possible; - apparatuses for two component injection have, complicated injection units both from the point of view of hydraulic circuiting and control circuits and space require agents, - in apparatuses which have an additional injection chamber with a ram in the chamber, the material is injected from the chamber instead of from the plasticating screw injection cylinder, which is removed to another place and is a simple plasticating screw cylinder without an axial motion of the screw; According to the invention, there is provided injection moulding apparatus for moulding plastics or rubber materials, the apparatus comprising a mould holder, a transfer unit having a chamber and a transfer ram adapted to sweep the area of the transfer chamber to transfer material from the chamber into a mould held by the mould holder via a transfer passage, and an injection unit having a cylinder and a reciprocable plasticising screw in the injection cylinder, the transfer passage being arranged to provide communication between the mould, the transfer- chamber and the injection cylinder, so that material can be fed into the mould from the transfer - chamber, and from the injèction cylinder irrespective of the position of the transfer ram, in the trans fer -chamber, the apparatus also including a hydraulic circuit for actuating the transfer ram and the plasticising screw.

The arrangement according to the invention facilitates high grade and economically advantageous injection moulding of large volume plastics products. It will be appreciated that because the transfer chamber can have a large volume, a large volume of melt can be injected into the mould in one moulding operation.

A conventional injection moulding machine can be adapted by adding to it a transfer unit, and a hydraulic circuit connecting the injection unit and the added transfer unit. The size of moulding which can be produced by a particular machine is governed by the size of the mould which can be received in the mould holder, and the clamping force which can be applied across mould halves. Within these limitations, it is possible to obtain, with a machine to which a transfer unit has been added, mouldings which are several times larger than can be obtained from the unmodified machine.

The apparatus of the invention can be used for various moulding materials. For foamed mouldings, foaming agents can be added to the chips in the feed hopper of the apparatus, or alternatively the agents can be added to the plastics material before this reaches the hopper. As a third alternative, a continuous addition of a gas, for example nitrogen, can be introduced into the melt in the transfer chamber.

The constructional arrangement according to this invention enables a number of modifications of both the fundamental technology of injection of foamed plastics and the technology of injection without foaming agents where the main parameters of the apparatus are utilized to a maximum. Using the technology of injection with a foaming agent several times increased volume, dimensions and weight of the products is achieved in addition to the mentioned advantages. The communication between the injection and transfer chambers, and the possibility of mutually independent or dependent movement of the pistons, allows the injection technology to be varied in quality and quantity, and also the manufacture of moulded multi-layered products. The possibility of programming the speed of movement of the piston of the transfer chamber and of the screw of the injection cylinder is particularly relevant to this end. Furthermore, the injection of the melt of two polymer types with melt volume control into the mould cavity gives flexibility. For instance a material without a foaming agent can be fed first, followed by a feed with a foaming melt. Programming of the temperature of the melt, particularly for filling the mould with the melt by means of a discharge valve in the transfer chamber is also possible. A combination of a low pressure and high pressure injection is furthermore made possible. The construction of passages of the transfer chamber and the use of twin hoppers enables also production of a two colour moulding.

The relatively small mass of the transfer unit and hydraulic circuit of the apparatus according to this invention allows it to be added to current injection presses at low costs, as an alternative to installation of expensive custom-built machines.

The prolongation of the operating cycle of actual presses due to a longer cooling time enables their better utilization and simultaneously a prolongation of their operational life.

In order to reduce, when changing from one melt type to another, the amount of transient products containing both melt types, the entire melt path is made so that the total volume of channels and ducts, and the cross-sectional changes therealong, are as small as possible. In this way, optimum scavenging conditions are obtained.

In the accompanying drawings:- Figure 1 is an elevation with parts in section of a first embodiment of an injection apparatus according to the present invention, shown by way of example; Figure 2 is a view similar to Figure 1 of a further embodiment of injection apparatus according to the present invention, Figure 3 is a longitudinal sectional view of the transfer chamber shown in Figure 2.

The injection apparatus shown in Figure 1 comprises a screw injection part, a mould clamping part, an inserted mould 6, a bridge 4 and a transfer chamber 7 with a hydraulic transfer cylinder 12.

The screw injection part connected to the clamping part of the injection apparatus comprises an injection cylinder 1 housing a screw 23 for plasticizing the material and filling the injection cylinder cavity 35 as well as for injecting the material into the mould cavity and controlling the melt pressure in the filled mould cavity. The discharge end 2 of the injection cylinder 1 bears against an inlet nozzle 8 of the transfer chamber 7.

The mould clamping part of the injection apparatus having a movable clamping plate 5 and a stationary clamping plate 3 is positioned on a frame 30 of the apparatus. The mould 6 with its clamping surface 16 6 against the bridge 4 is positioned between the movable clamping plate 5 and the stationary clamping plate 3. The movable clamping plate.5 is guided by tie-bars 32 (see Figure 2) - for clamping the mould 6. Preferably three tie-bars 32 are provided in three corners of the clamping plates 3 and 5 which are of tetragonaf form.

The transfer means comprises the hydrau lic transfer cylinder l2, to which the transfer chamber 7 is fixed by a connecting element 11, the axis of the transfer chamber 7 being parallel with the plane of the stationary clamping plate 3. A transfer ram 10 is positioned in the transfer chamber 7 which together with the walls of the chamber 7 provides a cavity 13 for the melt. A first connecting passage 17 is formed in the end wall 15 of the chamber 7, and a second connected ing passage 18 interconnects the passage 17 with the cavity 13 for the melt. The passages 17, 18 form a transfer passage providing communication between the mould 6, the transfer chamber 7 and the injection cylinder 1. The connecting passage 17 interconnects the discharge end 2 of the injection cylinder 1 with the discharge nozzle 9 of the transfer chamber 7 and the mould 6.

A closing and throttling valve 14 is provided in the discharge nozzle 9; it can be however also be positioned in the end wall 15 of the transfer chamber 7 in the connecting passage 17 between the passage 18 and the discharge nozzle 9. The axis of the injection cylinder 1 passes through the end wall 15 of the transfer chamber 7, where the connecting passages 17 and 18 meet. A connecting element 26 (Figure 2) is connected to the discharge opening of the connecting passage 17 toward the mould 6. The granules of the plastics material are fed to the screw 23 by hopper 33. Both hydraulic cylinders 12 and 31 are controlled by control means 34 via hydraulic circuit 36.

In the alternative arrangement of the injection apparatus as shown in Figures 2 and 3 the transfer chamber 7 is positioned upstream of the stationary clamping plate 3.

Contrary to Figure 1 this alternative construction does not require a bridge 4 between the mould 6 and the clamping plate 3, and enables deeper mouldings to be manufactured. The interconnection of the transfer chamber 7 with the mould 6 requires a longer discharge nozzle 9 corresponding to the thickness of the plate 3.

The discharge end 2 of the injection cylinder 1 is connected with the mould 6 so that the melt flows from the inlet nozzle 8 of the transfer chamber 7 through the inlet valve 19 of the discharge nozzle 9 into the cavity 13 - for the melt in the transfer chamber 7. The melt is forced from the chamber 7 by the transfer ram 10 which is provided around its circumference with a recess (Figure 3) providing a passage fdr the melt in case the ram 10 bears, on the end wall 15 of the transfer chamber 7. The melt flows thereafter through the discharge valve 20 to the discharge nozzle 9. An inlet channel 27, an outlet channel 28, the passages controlled by the valves 19 and 20 and the transfer chamber 7 together form a transfer passage providing, communicatidn between the mould 6, the transfer chamber 13 and the injection cylinder 1. The inlet valve 19 and the discharge valve 20 are independently controlled by control elements 21. In the described embodiment of the transfer chamber 7 both valves 19 and 20, are shown as rotary slide valves provided with recesses 25 enabling the melt to flow around a 90" bend. The transfer chamber 7 is provided with an external heating element 22 with proper regulation, independent of the regulation of the injection cylinder 1. A supply 24 for providing further modifiers (e.g. gas) allowing the quality, structure, processing characteristics, or the like of the material to be modified enters the end wall 15 of the transfer chamber 7 upstream of the discharge nozzle 9. A resilient seating 29 is provided for the transfer chamber 7 to enable a proper engagement of the discharge nozzle 9 by the injection cylinder 1 to the mould 6.

The arrangement according to this inven tion makes it possible to process, by using various technological methods, both polymers and copolymers as well as combinations or modifications therof. A process showing the operation of the apparatus is described, by way of example, in the following para graphs.

Granules of a polymer are fed into the injection cylinder 1 with 0.5% of a foaming agent and 10% of glass fibres. The mixture is homogenized by the screw 23 positioned at the extremity of the injection cylinder 1 facing the discharge nozzle 9. An overpres sure of 60 atmospheres is in the hydraulic circuit. The melt flows through the inlet channel 27 and through the inlet valve 19 of the discharge nozzle 9 into the cavity 13 in the transfer chamber 7 which is maintained at a constant temperature depending on the type of the polymer to be plastified.

The ram 10 in the transfer chamber 7 moves to its rearmost position during this stage of operation. After the required amount of the melt is obtained, the screw stops rotating.

The proper injection into the mould is accomplished by first increasing the pressure in the hydraulic circuit, for instance to 150 atmospheres and subsequently opening the discharge valve 20, enabling the melt to enter the cavity in the mould 6, where it is injected by the ram 10 at high speed via the discharge channel 28. After the transfer chamber 7 has been emptied, the discharge valve 20 is immediately closed and the following cycle of plasticizing by the screw proceeds.

When two different materials are being fed, a material from the hopper 33 containing a foaming agent is first plasticized. After the required amount of this material has been received in the transfer chamber, the feed is changed over to the second material, of which a rather small amount is pressed into the transfer chamber. A larger amount of the second material fills the cavity 35 downstream of the screw. The process of injection is the same with the difference, that first the melt in front of the screw is pressed out, followed by the melt from the transfer chamber.

WHAT WE CLAIM IS: 1. Injection moulding apparatus for moulding plastics or rubber materials, the apparatus comprising a mould holder, a transfer unit having a chamber and a transfer ram adapted to sweep the area of the transfer chamber to transfer material from the chamber into a mould held by the mould holder via a transfer passage, and an injection unit having a cylinder and a reciprocable plasticising screw in the injection cylinder, the transfer passage being arranged to provide communication between the mould, the transfer chamber and the injection cylinder, so that material can be fed into the mould from the transfer chamber, and from the injection cylinder irrespective of the position of the transfer ram in the transfer chamber, the apparatus also including a hydraulic circuit for actuating the transfer ram and the plasticising screw.

2. Apparatus as claimed in claim 1, wherein the transfer unit is positioned within a bridge fixed on a stationary clamping plate of the mould holder.

3. Apparatus as claimed in claim 1, wherein the transfer unit is fixed on a frame and can be connected with a mould by a connecting member through an opening in a stationary clamping plate of the mould holder.

4. Apparatus as claimed in any preceding claim, wherein an extension of the axis of the injection cylinder passes through an end wall of the transfer unit, and the end wall is formed with a first, connecting passage for material passing from the injection cylinder to a mould, and with a second passage between the connecting passage and the transfer chamber.

5. Apparatus as claimed in any preceding claim, wherein the mould holder comprises a stationary clamping plate and a movable clamping plate, and both clamping plates are on one and the same side of the transfer unit.

6. Apparatus as claimed in claim 4, wherein a connecting element with a discharge nozzle, controlled by a closing and throttling valve is connected to a discharge opening of the connecting passage.

7. Apparatus as claimed in claim 6, wherein a supply duct is provided in the end wall of the transfer chamber upstream of the discharge opening of the nozzle, for supplying modifiers into the melt.

8. Apparatus as claimed in any one of claims 1 to 7, wherein the transfer chamber

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

13 and the injection cylinder 1. The inlet valve 19 and the discharge valve 20 are independently controlled by control elements 21. In the described embodiment of the transfer chamber 7 both valves 19 and 20, are shown as rotary slide valves provided with recesses 25 enabling the melt to flow around a 90" bend. The transfer chamber 7 is provided with an external heating element 22 with proper regulation, independent of the regulation of the injection cylinder 1. A supply 24 for providing further modifiers (e.g. gas) allowing the quality, structure, processing characteristics, or the like of the material to be modified enters the end wall

15 of the transfer chamber 7 upstream of the discharge nozzle 9. A resilient seating 29 is provided for the transfer chamber 7 to enable a proper engagement of the discharge nozzle 9 by the injection cylinder 1 to the mould 6.

The arrangement according to this inven tion makes it possible to process, by using various technological methods, both polymers and copolymers as well as combinations or modifications therof. A process showing the operation of the apparatus is described, by way of example, in the following para graphs.

Granules of a polymer are fed into the injection cylinder 1 with 0.5% of a foaming agent and 10% of glass fibres. The mixture is homogenized by the screw 23 positioned at the extremity of the injection cylinder 1 facing the discharge nozzle 9. An overpres sure of 60 atmospheres is in the hydraulic circuit. The melt flows through the inlet channel 27 and through the inlet valve 19 of the discharge nozzle 9 into the cavity 13 in the transfer chamber 7 which is maintained at a constant temperature depending on the type of the polymer to be plastified.

The ram 10 in the transfer chamber 7 moves to its rearmost position during this stage of operation. After the required amount of the melt is obtained, the screw stops rotating.

The proper injection into the mould is accomplished by first increasing the pressure in the hydraulic circuit, for instance to 150 atmospheres and subsequently opening the discharge valve 20, enabling the melt to enter the cavity in the mould 6, where it is injected by the ram 10 at high speed via the discharge channel 28. After the transfer chamber 7 has been emptied, the discharge valve 20 is immediately closed and the following cycle of plasticizing by the screw proceeds.

When two different materials are being fed, a material from the hopper 33 containing a foaming agent is first plasticized. After the required amount of this material has been received in the transfer chamber, the feed is changed over to the second material, of which a rather small amount is pressed into the transfer chamber. A larger amount of the second material fills the cavity 35 downstream of the screw. The process of injection is the same with the difference, that first the melt in front of the screw is pressed out, followed by the melt from the transfer chamber.

WHAT WE CLAIM IS: 1. Injection moulding apparatus for moulding plastics or rubber materials, the apparatus comprising a mould holder, a transfer unit having a chamber and a transfer ram adapted to sweep the area of the transfer chamber to transfer material from the chamber into a mould held by the mould holder via a transfer passage, and an injection unit having a cylinder and a reciprocable plasticising screw in the injection cylinder, the transfer passage being arranged to provide communication between the mould, the transfer chamber and the injection cylinder, so that material can be fed into the mould from the transfer chamber, and from the injection cylinder irrespective of the position of the transfer ram in the transfer chamber, the apparatus also including a hydraulic circuit for actuating the transfer ram and the plasticising screw.
2. Apparatus as claimed in claim 1, wherein the transfer unit is positioned within a bridge fixed on a stationary clamping plate of the mould holder.
3. Apparatus as claimed in claim 1, wherein the transfer unit is fixed on a frame and can be connected with a mould by a connecting member through an opening in a stationary clamping plate of the mould holder.
4. Apparatus as claimed in any preceding claim, wherein an extension of the axis of the injection cylinder passes through an end wall of the transfer unit, and the end wall is formed with a first, connecting passage for material passing from the injection cylinder to a mould, and with a second passage between the connecting passage and the transfer chamber.
5. Apparatus as claimed in any preceding claim, wherein the mould holder comprises a stationary clamping plate and a movable clamping plate, and both clamping plates are on one and the same side of the transfer unit.
6. Apparatus as claimed in claim 4, wherein a connecting element with a discharge nozzle, controlled by a closing and throttling valve is connected to a discharge opening of the connecting passage.
7. Apparatus as claimed in claim 6, wherein a supply duct is provided in the end wall of the transfer chamber upstream of the discharge opening of the nozzle, for supplying modifiers into the melt.
8. Apparatus as claimed in any one of claims 1 to 7, wherein the transfer chamber

has an end wall provided with an inlet valve for controlling the flow of melt to the trans fer chamber, and a discharge valve.
9. Apparatus as claimed in claim 8, wherein the transfer chamber is provided with a resilient support, for pressing the in jection cylinder toward the mould to position the discharge nozzle and for compensation of any axial misalignment due, for instance, to pressure or heat distortion.
10. Apparatus as claimed in any preceding claim, wherein the mould holder comprises a stationary and a movable clamping plate and three tie bars connecting the plates and at corners thereof.
11. Apparatus as claimed in any preceding claim, wherein the injection unit is provided with twin hoppers adapted for the sequential feeding of each of two kinds of plastics to the cylinder.
12. Injection moulding apparatus substantially as described, with reference to, an as illustrated in Figure 1, or Figures 2 and 3 of the accompanying drawings.