GB2323321A - Moulding an article and releasing from the mould - Google Patents

Abstract

A moulding apparatus comprises a female mould tool 10 a male mould tool 12 arranged to mould a hollow article. Two hollow flexible tubes 28, 28a are mounted in circumferential grooves 26, 26a in the surfaces of the two tools 10, 12. The tubes 28, 28a are flexible between an expanded condition in which they protrude beyond the tool surfaces into the mould cavity 14, and a contracted condition in which they are contracted into the grooves 26, 26a. A fluid in the form of air is pumped into and out of the tubes 28, 28a to control their expansion and contraction. The tubes are contracted after the moulded article has hardened to enable the article to be removed from the tools 10, 12.

Description

An Apparatus and Method for making an Article The present invention relates to an apparatus and method of making an article and in particular to the moulding or casting of plastic materials.

Some articles because of their shape are inherently difficult and complicated to mould. This is normally the case for example if the article has a rebate, undercut, recess or indentation in its surface.

For example, if a cylindrical article is to be moulded it can generally be moulded using a female tool which defines the outer surface of the mould cavity and a male tool which defines the inner surface of the mould cavity.

When the article has been formed it can be slid out of the female tool and off the male tool. However, if such an article is to be made with grooves or other depressions in its inner and/ or outer surfaces, the process becomes more complicated. The projections on the male mould have to be retractable into the mould so that the article can be slid off it, and the female mould has to be made in two halves so that it can be split to remove the moulded article or retractable projections have to be provided.

It is an object of this invention to provide an improved apparatus and method for making articles by casting or moulding having recesses.

According to a first aspect of the invention there is provided a moulding apparatus comprising a mould tool having a mould surface defining part of a mould cavity, an inlet to the mould cavity to permit the introduction of a material into the cavity, at least one recess in the mould surface, a hollow flexible member mounted in the or each recess and a pump means to selectively inflate or deflate the or each flexible member between an expended condition in which the or each flexible member protrudes above the mould surface into the mould cavity and a contracted condition in which the or each flexible member is contracted into the recess.

The mould surface may extend in a direction substantially parallel to the direction in which an article formed in the mould will be removed from the mould cavity.

The or each flexible member may be made from a resilient material and in its natural state adopt a shape closely corresponding to its expanded condition.

The pump means may be arranged to lower the pressure of fluid in the or each flexible member to cause it to contract.

The pump means may be arranged to selectively increase the pressure of the fluid within the or each flexible member to hold it in an expanded condition.

The moulding apparatus may further comprise a pressure monitoring means for monitoring the pressure within the mould cavity.

Preferably, an electronic control means may be arranged to control the pump means in response to a signal derived from the pressure monitoring means to maintain the pressure of the fluid within the or each flexible member at or above the pressure within the mould cavity, at least during introduction of material into the mould cavity, thereby to hold the or each flexible member in an expanded state.

The or each flexible member may be held within the recess by a retaining means formed as a part of the flexible member.

According to a second aspect of the invention there is provided a method of moulding an article using a moulding apparatus as described with reference to said first aspect of the invention in which the method comprises the steps of increasing the pressure within each flexible member to cause it to adopt its expanded state, introducing through the inlet a material to be moulded in the mould cavity, allowing the material introduced into the cavity to solidify to form an article, reducing the fluid pressure in each flexible member to deflate it to its contracted state and removing the article from the mould tool.

The invention will now be described by way of example with reference to the accompanying drawing in which: Fig. 1 is a section through a moulding apparatus according to a first aspect of the invention; Fig.2 is a section through part of the apparatus of Fig.1; and Fig.3 is a perspective view of an article moulded using the apparatus of Figs.1 and 2.

Referring to Fig.1, the moulding apparatus comprises a female lower tool 10 and a male upper tool 12 which in combination define a mould cavity 14.

The lower female tool 10 has a cylindrical side surface 6 and a base 18 which define a substantially cylindrical cavity 20. The cylindrical side surface 6 is tapered outwardly towards the top of the female tool 10 so as to supply a small draft to the tool which enables an article moulded therein to be more readily removed.

The upper or male tool 12 has a substantially cylindrical portion 22 of narrower diameter than the cavity 20 in the lower tool 10. The male portion 22 has a curved side surface 24 which tapers towards its lower end, and an end surface 16. When the tools 10, 12 are closed, as shown in Fig. 1, the end surface 16 of the male portion 22 defines an inner end surface of the mould cavity, and is spaced from the base 18 of the cavity 20 in the female tool 10, which defines an outer end surface of the mould cavity 14. The curved side surfaces 6, 24 are spaced apart to define outer and inner side surfaces of the mould cavity 14.

The side surface 6 of the cavity 20 in the female mould tool 10 has a recess in it in the form of a circumferential groove 26 of part circular crosssection. A ring resilient hollow tube 28 of circular cross-section is located in the groove 26. The cross-sectional diameters of the groove 26 and the tube 28 are substantially the same so that the tube 28 fits snugly in the groove 26.

The tube 28 is attached to the female mould tool 10 at the base of the groove 26 by means of a flange 30 formed as an integral part of the tube 28 on the outer periphery of the tube 28. The flange 30 is a push fit within a narrow slot 32 formed in the base of the groove 26. In its normal or natural state the tube 28 protrudes above the top of the groove 26 so that it is proud relative to the surface 6 of the cavity 20 and projects into the mould cavity 14.

The tube 28 has a hole 34 in it which is aligned with a drilling 38 through the female mould tool 10. A tube 36 extends through the drilling 38 and the hole 34 into the flexible tube 28 and is connected to a pump means 40 which can pump a fluid in the form of air into and out of the tube 36.

A second flexible tube 28a is located in a similar circumferential groove 26a in the side surface 24 of the male portion 22, and is held in position by a similar integral flange 30a. The second flexible tube 28a is connected to a second pump 40a by a tube 36a located in a drilling 38a.

The female mould 10 has an inlet or gate 42 through which plastic moulding material in a liquid or molten state can be injected into the mould by a third pump 44.

Operation of the three pumps 40, 40a, and 44 is controlled by an electronic control unit 46.

The pressure within the mould cavity 14 is monitored by means of a pressure monitor (not shown) connected to the electronic control unit 46.

The electronic control unit 46 controls and monitors the pressure by means of the pressure monitor and the speed at which the plastic moulding material is being pumped into the mould cavity 14 and also controls the flow of air into and out of the hollow tubes 28, 28a. By using a signal derived from the pressure monitor the electronic control unit 46 is operable to control the pump means 40, 40a and electronically controlled valves (not shown) connected to them so as to selectively pump air into or out of the hollow tubes 28, 28a.

To mould an article using the apparatus two mould tools 10, 12 are closed so that the mould cavity 14 forms a closed volume. The pump 44 is then energised and plastic moulding material is injected into the cavity 14 through the gate 42 in the female tool 10. The pressure within the mould cavity 14 will then rise and the air pressure inside the tubes 28, 28a is increased by the pumps 40, 40a under the control of the control unit 46 so as to be equal to or slightly in excess of the pressure of the air and moulding material in the mould cavity 14. This ensures that the tubes 28, 28a are prevented from collapsing under the pressure of the moulding material and air within the mould cavity 14.

The moulding material is then allowed to solidify or harden so as to form a moulded article 48 as shown in Fig.3.

When the moulding material has hardened or solidified, the air within the tubes 28, 28a is pumped out by the pump means 40, 40a which causes them to collapse. Because each of the tubes 28, 28a is secured by the flanges 30, 30a within its respective groove 26, 26a the tubes 28, 28a retract within the grooves 26, 26a leaving the grooves 50, 50a in the outer and inner surfaces of the moulded article 48.

In their fully collapsed state as shown in Fig.2 the tubes 28, 28a are completely retracted into the grooves 26, 26a so that they are below the level of the side surfaces 6, 24 of the mould tools 10, 12. In this condition the male mould tool 12 can be lifted vertically out of the interior cavity it has formed in the moulded article 48 and the article 48 can be lifted vertically out of the cavity 20 in the female mould tool 10. The extraction of the male mould tool 12 from the interior cavity within the moulded article 48 is substantially parallel to the surface 24 and similarly the direction in which the article 48 is lifted from the female mould tool is substantially parallel to the surface 6.

As the flexible core defined by the tube 28 has been retracted into its groove 26 there is no need to split the female tool 10 and the article 48 can be easily removed from the cavity.

It will be appreciated that the cross-section of the tubes 28, 28a need not be cylindrical and could take a variety of shapes so as to produce different shaped grooves in the article to be manufactured.

Furthermore, the inflatable members 28, 28a could take other forms such as for example they could be spherical inflatable members used to produce part spherical indentations on the inside or outside of an article.

It will be appreciated by those skilled in the art that the term moulding as meant herein encompasses those processes in which a material is heated to a liquid state and injected into a mould cavity such as for example injection moulding and also to other processes in which the material is in a liquid state and is poured or injected into the mould cavity and allowed to set or harden such as casting.

Claims (11)

1. A moulding apparatus comprising a mould tool having a mould surface defining part of a mould cavity, an inlet to the mould cavity to permit the introduction of a material into the cavity, at least one recess in the mould surface, a hollow flexible member mounted in each recess and a pump means to selectively inflate or deflate the or each flexible member between an expanded condition in which the or each flexible member protrudes above the mould surface into the mould cavity and a contracted condition in which the or each flexible member is contracted into the recess.

2. Apparatus according to Claim 1 in which the mould surface extends in a direction substantially parallel to the direction in which an article formed in the mould will be removed from the mould cavity.

3. Apparatus according to Claim 1 or Claim 2 wherein the or each flexible member is made from a resilient material and in its natural state adopts a shape closely corresponding to its expanded condition.

4. Apparatus according to any of Claims 1 to 3 wherein the pump means is arranged to lower the pressure of fluid in the or each flexible member to cause it to contract.

5. Apparatus according to any foregoing claim wherein the pump means is arranged to selectively increase the pressure of the fluid within the or each flexible member to hold it in an expanded condition.

6. Apparatus according to any preceding Claim in which the apparatus further comprises a pressure monitoring means for monitoring the pressure within the mould cavity.

7. Apparatus as claimed in Claim 6 in which an electronic control means is arranged to control the pump means in response to signal derived from the pressure monitoring means to maintain the pressure of the fluid within the or each flexible member at or above the pressure within the mould cavity at least during introduction of material into the mould cavity thereby to hold the or each flexible member in an expanded state.

8. Apparatus as claimed in any preceding claim in which the or each flexible member is held within the recess by a retaining means formed as part of the flexible member.

9. A method of moulding an article using a moulding apparatus as claimed in any of Claims 1 to 8 in which the method comprises the steps of increasing the pressure within each flexible member to cause it to adopt its expanded state, introducing through the inlet a material to be moulded into the mould cavity, allowing the material introduced into the cavity to solidify to form an article, reducing the fluid pressure in each flexible member to deflate it to its contracted state and removing the article from the mould tool.

10. A moulding apparatus substantially as hereinbefore described with reference to the accompanying drawings.

11. A method of moulding an article substantially as hereinbefore described with reference to the accompanying drawings.