GB2100656A

GB2100656A - Mould gate for permitting the introduction of stiff moulding compound into a mould chamber

Info

Publication number: GB2100656A
Application number: GB08119029A
Authority: GB
Inventors: Holdt John Warren Von
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-06-19
Filing date: 1981-06-19
Publication date: 1983-01-06

Abstract

A mould gate (24) for admitting plastics material into a mould comprises a hollow member defining a bore (28) having a longitudinal axis (30) and an inner wall (32) separating the bore from a mould chamber (20). Apertures (34) extend through the inner wall (32), being peripherally spaced from the longitudinal axis (30) and inclined at an angle of 30 DEG to 90 DEG to the longitudinal axis, diverging outwardly in the direction of the mould chamber (20). The apertures (34) may be arcuate slots. The inner wall (32) may have a centrally-positioned peak (36) pointing towards the bore and having sloping sides to assist in directing molten plastics material towards the apertures (34). Ribs (40) may be provided extending radially from the central portion of the inner wail (32) towards the periphery thereof to reinforce the inner wall. <IMAGE>

Description

SPECIFICATION Mould gate permitting the indtroduction of stiff moulding compound into a mould chamber specification This invention relates to a mould gate which works effectively for all moulding compounds, but exhibits the added advantage of working effectively with ultra-stiff moulding compounds, for example, glass-filled materials and the like, such as may be used for moulding high-strength buckets or any other desired article.

Conventionally, it has been found to be difficult to inject very stiff moulding compounds into an injection moulding system through a mould gate. Even if ultra-high pressure injection is used, stagnant areas can develop in the mould gate, and degradation of the moulding compound can then take place here.

Particularly in the case of thin-walled plastics moulded members, such as the bottom of a bucket, the stiff moulding compound typically in the prior art enters at right-angles to the narrow channel of the mould which defines the bucket bottom. The turning of the stiff moulding compound and its spreading through the narrow channel is a major source of flow resistance, so that even large capacity injection mould systems pass such compounds only with difficulty through the orifice of the mould gate when a small, centrallylocated orifice in the mould gate is used.

By another technique, a mould gate with a larger orifice may be used to reduce flow resistance but this leaves a large sprue projecting from the bottom of the bucket, which then must be cut away.

It is an object of this invention to provide a mould gate which permits easier injection of a stiff moulding compound into the mould cavity, especially when the cavity is of very narrow dimensions, such as in the moulding of the bottom of a bucket, while avoiding stagnant areas in the mould gate and consequent scorching or burning of the moulding compound. Furthermore, with the gate of this invention, a shortened sprue may be obtained, being achieved by the gate having a reinforced, thin wall.

Accordingly, it becomes possible by the use of the mould gate of this invention to injection mould ultra-stiff materials, which had previously been impractical for use in injection moulding machinery of similar capacity while using a conventional mould gate.

In accordance with a first aspect of this invention there is provided a mould gate for admitting plastics material into a mould, the gate comprising a hollow member which defines a bore having a longitudinal axis and which has an inner wall separating the bore from a mould chamber positioned between mould parts, with aperture means extending through said inner wall, said aperture means being peripherally spaced from the longitudinal axis and inclined at an angle of from 30 to 90 with respect to the longitudinal axis, diverging outwardly in the direction towards the mould chamber.

In accordance with a second aspect of the invention there is provided a mould gate for admitting plastics material into a mould, the gate comprising a hollow member which defines a bore having a longitudinal axis and which has an inner wall separating the bore from a mould chamber positioned between mould parts, with aperture means extending through said inner wall, said aperture means being peripherally spaced from the longitudinal axis and inclined at an angle with respect to the longitudinal axis, diverging outwardly in the direction towards the mould chamber, and said inner wall including rib means extending radially from a central portion of the inner wall towards the periphery thereof to reinforce said inner wall against pressure imparted by the injection of a moulding compound through the gate.

The mould gate of this invention may also have an inner wall which defines a centrallypositioned peak pointing towards the bore and having sloping sides. The purpose of this is to assist in directing molten plastics material towards the peripherally-spaced aperture means, to eliminate a potential stagnant area in the immediate vicinity of the central portion of the inner wall. The elimination of a stagnant area in the mould gate of this invention reduces the possibility of over-heating any moulding compound which remains too long in the stagnant area, and thus degrades due to excessive exposure to heat.

It is also preferable for the inner wall to include rib means pointing towards the bore and extending radially from a central portion of the inner wall towards the periphery thereof. The purpose of this is to reinforce the inner wall against the high pressure imparted by the injection of moulding compound through the mould gate. If the inner wall is thus reinforced, it may be made thinner than would otherwise be possible without running the danger of blowing out the end of the mould gate.

A thinner inner wall permits the use of shorter flow length aperture means, which, in turn, can result in a shorter mould sprue. This sprue may be positioned in a recess of a moulded bucket, if desired, so that there is no need for a step of cutting away the mould sprue after removal of the moulded article from the mould, as has sometimes been necessary in prior art processes.

One preferred embodiment of moulding gate in accordance with the invention will now be described by way of example and with reference to the accompanying drawing, in which: Figure 1 is a fragmentary, longitudinal sectional view through an injection moulding system for producing a moulded bucket, utilizing the mould gate of this invention; Figure 2 is an enlarged, fragmentary, longitudinal sectional view of the inner end of the mould gate of Fig. 1; and, Figure 3 is an enlarged sectional view taken along the line 3-3 of Fig. 1.

The injection moulding system indicated generally at 10 is specifically shown to be a bucket mould, but it should be understood that the mould gate of this invention may be utilized in conjunction with any type of moulding system for the manufacture of any moulded article.

An outer mould 12 is shown, being generally of conventional design, as is a mould core 1 4 which includes a push rod 16 for the removal of the bucket. and cooling passageways 18, all of which may be of conventional design. The outer mould 12 and the mould core 14 together define a mould cavity 20 having the desired shape of the bucket, including an end wall chamber 22 which may be relatively thin, as shown.

A mould gate 24 is shown bolted to an upper portion 26 of the outer mould 12. The mould gate 24 is a hollow, generally cylinderical member having a central bore 28 which, in turn, defines a longitudinal axis 30.

The mould gate 24 is bounded by an inner wall 32 separating the bore 28 from the mould chamber 20, and specifically from the end wall chamber 22, as shown.

This inner wall 32 is apertured by a plurality of separate apertures 34 extending through the inner wall 32. The apertures 34 are art formed as arcuate slots.

In accordance with this invention, the apertures 34 are spaced from the longitudinal axis 30, and in vertical cross-section are aligned at a divergent angle as shown in Fig. 2, preferably of from 30 to 60 with respect to the longitudinal axis 30, with the apertures 34 diverging outwardly in the direction towards the mould chamber 20. Specifically, the angle may be about 45 The inner wall 32 also defines a centrally positioned generally conical peak or cusp 36, pointing towards the bore 28 and having sloping sides 38 to assist in directing molten plastics materials towards the peripherallyspaced apertures 34.

The moulding compound passes from a chamber 29, where it is heated into molten form, into the bore 28 of the mould gate 24, for insertion into the mould cavity 20 through the apertures 34.

The sloping sides 38 of the central peak 36 tend to cause a flow of plastics material outwardly away from the longitudinal axis 30 in the vicinity of the inner wall 32 as plastics material passes through the gate 24, which eliminates the stagnant central area previously referred to.

The mould gate of this invention may also include radially extending ribs 40 on the inside of the inner wall 32, which extend from a central portion of the inner wall 32 towards the periphery thereof, for the purpose of reinforcing the inner wall against the pressure imparted by the injection of the moulding compound through the gate 24. With this reinforcement, the thickness of the inner wall 32, and the coresponding thickness dimension of the apertures 34, can be reduced substantially without the danger of the inner wall 32 bursting due to pressure created within the valve gate 24. As stated above, this reduced thickness, i.e. flow length, of apertures 34 reduces the height of the resulting sprue that is produced on the moulded article. If desired, this sprue may be positioned so that it is in a recessed portion of the bucket for example, so that the bucket can stand evenly without interference from any mould sprue, so that the sprue does not have to be cut away in a separate operation after the moulding step.

Claims

1. A mould gate for admitting plastics material into a mould, the gate comprising a hollow member which defines a bore having a longitudinal axis and which has an inner wall separating the bore from a mould chamber positioned between mould parts, with aperture means extending through said inner wall, said aperture means being peripherally spaced from the longitudinal axis and inclined at an angle of from 30 to 90 with respect to the longitudinal axis, diverging outwardly in the direction towards the mould chamber.

2. A mould gate as claimed in claim 1, in which said inner wall defines a centrallypositioned peak pointing towards said bore and having sloping sides to assist in directing molten plastics material towards said peripherally-spaced aperture means.

3. A mould gate as claimed in claim 1 or 2, in which said aperture means comprise a plurality of spaced, outwardly diverging apertures positioned peripherally through the inner wall about said axis.

4. A mould gate as claimed in claim 3, in which each aperture is an arcuate slot.

5. A mould gate as claimed in any preceding claim, in which said inner wall includes rib means pointing towards said bore and extending radially from a central portion of the inner wall towards the periphery thereof to reinforce said inner wall against pressure imparted by the injection of a moulding compound through the gate.

6. A mould gate for admitting plastics material into a mould, the gate comprising a hollow member which defines a bore having a longitudinal axis and which has an inner wall separating the bore from a mould chamber positioned between mould parts, with aperture means extending through said inner wall, said aperture means being peripherally spaced from the longitudinal axis and inclined at an angle with respect to the longitudinal axis, diverging outwardly in the direction towards the mould chamber, and said inner wall including rib means extending radially from a central portion of the inner wall towards the periphery thereof to reinforce said inner wall against pressure imparted by the injection of a moulding compound through the gate.

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7. A mould gate as claimed in claim 6, in which said inner wall defines a centrallypositioned peak pointing towards said bore and having sloping sides to assist in directing molten plastics material towards said perpherally-spaced aperture means.

8. A mould gate as claimed in claim 6 or 7, in which said aperture means are inclined at an angle of from 30 to 60 with respect to the longitudinal axis.

9. A mould gate substantially as hereinbefore described with reference to the accompanying drawing.