GB2219236A

GB2219236A - Injection nozzle

Info

Publication number: GB2219236A
Application number: GB8811811A
Authority: GB
Inventors: Kwai-Sum Tse
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-05-19
Filing date: 1988-05-19
Publication date: 1989-12-06
Anticipated expiration: 2008-05-19
Also published as: GB2219236B; CN1037678A; GB8811811D0; CN1013178B

Abstract

A nozzle for the injector of an injection of moulding apparatus has a through bore (12) for the passage of plastics material, a valve member (17) housed in the bore and spring means (11) biassing the valve member in a first direction against a valve seat (26) in the bore to close the bore against the flow of plastics material, the valve member (17) being arranged so that the pressure of plastics material being forced through the nozzle in a direction opposite to the first direction will lift the valve member (17) off the valve seat (26) against the force of the biassing means (11) to allow the plastics material to flow through the nozzle. A modified nozzle is shown in Fig. 3 (not shown). <IMAGE>

Description

INJECTION NOZZLE FOR AN INJECTION MOULDING MACHINE The present invention relates to a nozzle for an injection moulding machine.

In an injection moulding process molter plastics material is injected into a heated mould through a nozzle which co-operates with the mould. The molten plastics material is forced through the nozzle by a rotatable screw or auger which is pushed forwards under hydraulic pressure. The injector is heated to keep the plastics material molten. After sufficient plastics material has been injected into the mould, forwards movement of the auger is arrested and this allows a sliding collar disposed about the auger to be urged backward under the pressure of the injected pl astics Rate rial in the mould to form a .seal against the auger. This results in a comparatively large volume of excess molten plastics material being left between the mould and the sliding collar.

It has been found that in order to minimise structural distortion in the moulded product, it is desirable to shut off the supply of the molten plastics material at a point as close as possible to the entry to the mould in order to leave a minimal residual volume of the excess molten material in the injector and thereby limit the reduction of pressure of the plastics material in the mould. Various ways have been proposed to achieve this In one devisee the tip of the nozzle is allowed to cool so that the plastics material solidifies to form a seal at the entry to the mould, heaters being provided in the nozzle to reheat the tip to remove the seal for the next moulding operation. In another device, a plug is mounted in the nozzle and moved by a hydraulically operated arm to block off the nozzle tip.This has the drawback that the plastics material is required to follow a circuitous route past the plug when being injected, and an additional control is required to operate the plug.

According to a first aspect of the present invention there is provided a nozzle for an injector of an injection moulding apparatus, which nozzle includes a resiliently biassed valve member so located at or adjacent an outlet end of the nozzle as to shut off the supply of injection moulding material and to leave a minimal residual volume of material between the valve member and a mould with which the nozzle is to co-operate.

In another aspect the present invention provides a nozzle for an injector of an injection moulding apparatus, the nozzle having a through bore for the passage of plastics material, a valve member housed in the bore and biassing means biassing the valve member in a first direction against a valve seat in the bore to close the bore, the valve member being arranged so that the pressure of plastics material being forced through the nozzle in a direction opposite to the first direction will lift the valve member off the valve seat against the force of the biassing means to allow the plastics material to flow through the tip.

An embodiment of an injection nozzle according to the present invention will now be described, by way of example only, by reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section of an injector according to the present invention; Figure 2 is an enlarged cross-section of that part of Figure 1 which is encircled and Figure 3 is a cross-section of an alternative construction of the injector of Figures 1 and 2.

Referring to Figures 1 and 2 of the drawings, an injector 1 for an injection moulding machine comprises a barrel 2 formed from elements 3, 4, 5 and 6. A rotatable screw or auger 7 is provided in the barrel 2.

An injection nozzle 8 is coaxially mounted, by means of a screw threaded connecting piece 9, upon the outlet end 5 of the barrel 2. The injection nozzle 8 defines coaxially thereof a cylindrical housing 10 for a compression spring 11 and includes a plurality of through bores 12. A bearing 13 is coaxially screw threaded in a forward end 14 of the housing 10 to provide an annular bearing surface 15, and a stop wall 16 at an inner end of the bearing 13.

A valve member 17 includes a conical head 18, a frusto-conical valve surface 19, and a stem 20 which slidably extends through the bearing 13, into the housing 10, and through an annular collar 21. The valve member 17 is locked by a circlip 22 against forward movement relative to the collar 21. The circlip 22 is fixed on a free end 23 of the stem 20 extending beyond the collar 21. The collar 21 has a radial flange 24 for co-acting with the compression spring 11. Further, the flange 24 extends across the housing 10 to avoid lateral displacement of the stem 20.

An outlet end of injection nozzle 8 defines an annular seat 25 for an annular valve seat 26.

Mounted removably (e.g. by means of a screw thread) at the outlet end is a nozzle tip 27 which serves to retain the annular valve seat 26 in position.

The nozzle tip 27 includes a generally conical cavity 28 adapted to receive and surround the conical head 18 of valve member 17, defining therebetween a narrow frusto-conical gap 29 for passage of molten plastics material, A coaxial cylindrical outlet opening 30 is provided in the forward end of the nozzle tip 27 adjacent the apex 18' of the conical head 18 for injection of the molten plastics material into a mould (not shown) co-operating with the injection nozzle 8.

In a rest position, the spring 11, acting on the stop wall 16 and flange 24, biasses the valve member 17 into a closed position in which the valve surface 19 sealingly engages an inner circumferential edge 26' of the valve seat 26.

In use, the injector I is heated to keep the plastics material in the barrel 2 molten. The auger 7 is simultaneously rotated and moved rearwardly to feed the molten plastics material forwards into the barrel 2 to fill up the space in the barrel 2 previously occupied by the auger 1, and into the through bores 12. The auger 7 is driven forwards under hydraulic pressure. When the auger 7 is driven forwards, the pressure of fluid plastics material acting upon the valve surface 19 is such as to overcome the bias of the spring 11, thus to lift the valve surface 19 off the valve seat 26. This permits flow of the molten plastics material through the gap 29 and out of the outlet 30 in the nozzle tip 27, into the mould (not shown).

The annular collar 21 extends axially from flange 24 towards the stop wall 16. In use, movement of the valve member 17 causes the collar 19 to abut the stop wall 16 thereby to limit the extent of the forward movement of valve member 17, and prevent the conical head 18 from sealing the outlet opening 30 of the nozzle tip 27.

To seal the housing 10 from the molten plastics material, a cap-nut 31 is screw threaded in a rear end 32 of the housing 10.

It will be appreciated that the bearing 13, the valve member 17 and the valve seat 26 are subject to wear and tear, and therefore they are, provided as readily replaceable with spare, parts. Moreover, the injection nozzle 8 can be used as an accessory and connected to injectors 1 of different injection moulding machines by using different connecting pieces 9 having appropriate screw threads.

Referring now to Figure 3 of the drawings, it will be seen that an arrangement similar to that of Figure 2 is shown, with like parts given the same numerals.

In the arrangement of Figure 3 the separate bearing 13 for the valve stem 20 in Figures 1 and 2 embodiment is not used. Instead, the forward end of the housing 10 has a reduced diameter outlet 13' providing an annular bearing surface 15' for the valve stem 20.

It is to be noted that in these two arrangements, the valve sealing the plastics in the mould is provided in the injection nozzle 8 and not in the barrel 2 as in conventional arrangements. This reduces considerably the volume of excess molten plastics material, thus reducing . or obviating structural distortion in the moulded product. Moreover, the sealing is operated by the spring 11, and this avoids the need for additional controls as in the prior art arrangements described.

In the embodiments described the valve seat 26 is provided by a separate member. It will be appreciated, however, that valve seat 26 may instead be provided by an annular step in the inner wall of the injection nozzle 8.

It is to be understood that the invention may be performed otherwise than as has been particularly described. The invention The includes within its scope all those modifications and changes which would be apparent to one skilled in the art.

Claims

1. A nozzle for an injector of an injection moulding apparatus, which nozzle includes a resiliently biassed valve member so located at or adjacent an outlet end of the nozzle as to shut off the supply of injection moulding material and to leave a minimal residual volume of material between the valve member and a mould with which the nozzle is to co-operate.

2. A nozzle as claimed in Claim 1, and in the form of an accessory for an existing injection moulding apparatus.

3. A nozzle as claimed in Claim 1 or 2 which nozzle has a through bore for the passage of plastics material, a valve member housed in the bore and spring biassing means biassing t~ < e valve member in a first direction against a valve sea) in the bore to close the bore, the valve member r being arranged so that the pressure of plastics material being forced through the nozzle in a direction opposite to the first direction will lift the valve member off the valve seat against the force of the biassing means to allow the plastics material to flow through the nozzle.

4. A nozzle as claimed in claim 3, wherein the valve member comprises a conical head on a stemt, a base of the conical head contacting the valve seat to close the bore.

5. A nozzle as claimed in claim 4, wherein the conical head is housed in a complementary tapering portion of the bore defined by a conical inner wall to form a narrow passageway between the head and wall for the plastics material.

6. A nozzle as claimed in claim 5, including means for limiting the movement of the valve member off the valve seat to prevent the conical head forming a seal against the conical inner wall.

7. A nozzle as claimed in any one of claims 4 to 6, wherein the apex of the conical head is adjacent an outlet opening of the tip which connects with a mould.

8. A nozzle as claimed in any one of claims 4 to 7, wherein the base of the conical head has a frustoconical portion, and the valve seat is formed by a step in the bore wall, the frusto-conical portion engaging the inner circumferential edge of the step to form a seal.

9. A nozzle as claimed in claim 8 wherein the step is formed by an insert in the bore.

10. A nozzle as claimed in any one of claims 3 to 9, wherein the valve member comprises a stem which is slidably received in a wall of a housing for the biassing means.

11. A nozzle as claimed in claim 10, wherein the biassing means comprises a compression spring around the stem, the spring bearing at one end on the housing wall and at its other end on a flange provided on the stem.

12. A nozzle as claimed in claim 11, wherein the flange is formed on a collar on the stem.

13. A nozzle as claimed in claim 12, wherein the collar is located by a circlip on the stem.

14. A nozzle as claimed in any one of claims 10 to 13, wherein the said wall of the housing which receives the valve member stem is removable from the housing.

15. A nozzle as claimed in any one of the preceding claims, wherein the nozzle is removably mountable on a said injector.

16. A nozzle as claimed in any one of claims 10 to 15, comprising a first part housing an inlet for c necclon to a Doay or tne injector, a second part connected at one end to the first part and having a through bore, and a third part connected to the second part at the other end thereof, said third part having an outlet arranged to cooperate with a mould, said housing for said biassing means being formed by said second part, a passageway being provided through a wall of said second part for the passage of plastics material from the inlet of the first part to the outlet of the third part.

17. A nozzle as claimed in claim 16, wherein said valve seat is held in said second part by said third part.

18. An injection moulding apparatus which includes a nozzle as claimed in any one of the preceding Claims.

18. A nozzle for an injection moulding machine, substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.

19. A replaceable nozzle for an injection moulding machine adapted to inject plastics material into a mould through the nozzle, wherein the nozzle includes a resilently biassed non-return valve.

Amendments to the claims have been filed as follows 1. A nozzle for an injector of a plastics injection moulding apparatus, which nozzle includes a through passage for delivery of a plastics material in a delivery direction to an injection mould, the nozzle further including a valve member located at or adjacent an outlet end of the nozzle and housed in the passage, the valve member being biassed by spring biassing means in a direction opposite to said delivery direction against a valve seat in the passage to close the passage, the arrangement being such that, in use, the pressure of the material being forced through the nozzle lifts the valve member off the valve seat against the force of the biassing means to allow the material to flow through the nozzle and that on a predetermined pressure drop in the nozzle, the valve is re-seated on its valve seat under the influence of the biassing means.

2. A nozzle according to Claim 1, and in the form of an accessory for an existing injection moulding apparatus.

3. A nozzle as claimed in Claim 1 or 2, wherein the valve member comprises a conical head on a stem, a base of the conical head contacting the valve seat to close the passage.

4. A nozzle as claimed in Claim 3, wherein the conical head is housed in a complementary tapering portion of the passage defined by a conical inner wall to form a narrow passageway between the head and wall for the plastics material.

5. A nozzle as claimed in Claim 4, including means for limiting the movement of the valve member off the valve seat to prevent the conical head forming a seal against the conical inner wall.

6. A nozzle as claimed in any one of Claims 3 to 5, wherein the apex of the conical head is adjacent the outlet end of the nozzle.

7. A nozzle as claimed in any one of Claims 3 to 6, wherein the base of the conical head has a frustoconical portion, and the valve seat is formed by a step in the passage wall, the frusto-conical portion engaging the inner circumferential edge of the step to form a seal.

8. A nozzle as claimed in Claim 7, wherein the step is formed by an insert in the passage.

9. A nozzle as claimed in any one of the preceding Claims, wherein the valve member comprises a stem which is slidably received in a wall of a housing for the biassing means.

10. A nozzle as claimed in Claim 9, wherein the biassing means comprises a compression spring around the stem, the spring bearing at one end on the housing wall and at its other end on a flange provided on the stem.

11. A nozzle as claimed in Claim 10, wherein the flange is formed on a collar on the stem.

12. A nozzle as claimed in Claim 11, wherein the collar is located by a circlip on the stem.

13. A nozzle as claimed in any one of Claims 9 to 12, wherein the said wall of the housing which receives the valve member stem is removable from the housing.

14. A nozzle as claimed in any one of the preceding Claims, wherein the nozzle is removably mountable on a said injector.

15. A nozzle as claimed in any one of Claims 9 to 14, comprising a first part housing an inlet for connection to a body of the injector, a second part connected at one end to the first part and having a through passage, and a third part connected to the second part at the other end thereof, said third part having an outlet arranged to cooperate with a mould, said housing for said biassing means being formed by said second part, a passageway being provided through a wall of said second part for the delivery of plastics material from the inlet of the first part to the outlet of the third part.

16. A nozzle as claimed in Claim 15, wherein said valve seat is held in said second part by said third part.

17. A nozzle for an injection moulding machine, substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.