GB2128923A

GB2128923A - Centrifugal moulding machine

Info

Publication number: GB2128923A
Application number: GB08326416A
Authority: GB
Inventors: Carl Victor Leunig
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1982-10-08
Filing date: 1983-10-03
Publication date: 1984-05-10
Also published as: IT8349113A0; DE3336416A1; JPS59135140A; GB8326416D0; IT1171869B; NL8303407A

Abstract

A centrifugal moulding machine for making non-reinforced flexible endless belts of curable plastics material comprises a number of moulds 20 rotatably mounted on a turntable 10 and a number of moulding stations 100, 200, 300, 400, 500 located around the turntable, which rotates step by step. The machine also has a driving belt 30 for rotating some of the moulds on the turntable. Moulding material is introduced into a mould 20 at a station 100 and the mould is then moved into contact with the belt so that the mould is spun and the moulding material takes up the shape of the mould wall. While the mould and the material contained therein are rotated the mould is successively moved by the turntable to a curing station 300 where the material is cured, a cooling station 400 where the material is cooled and a removing station 500 where, after the mould has come to rest, the material formed into the desired belt is removed. <IMAGE>

Description

SPECIFICATION Centrifugal moulding machine This invention to machines for centrifugally moulding endless flexible belts of curable material, e.g. plastics material.

The usual way to manufacture endless flexible belts of plastics material is by injection moulding. However, several difficulties arise when thin elastomeric or semi-rigid cylindrical beltstructures are moulded by such methods.

For example, a constriction can be created between the mould and a mould core which restrains the flow of the moulding material during its injection. The constriction can also create pressure drops within the material and this causes weak spots in the finished product. In order to compensate for this effect, a moulding material with a low viscosity must be used. However, such materials tend to result in products with undesirable characteristics or they may require excessive mould temperatures. Air bubbles may also be entrained in the material in the mould causing additional problems. A further disadvantage is that the ejection of the moulded belt from the mould is extremely difficult because of its fragility and flexibility.

One way of overcoming these difficulties is to use a coreless-type moulding. U.S. Patent No. 3,609,814 discloses a method of making containers with a rotational casting machine.

However, the mechanism disclosed in this Patent is very complex.

The main object of this invention is to provide a machine, which is simple, for moulding thin belts centrifugally with a coreless mould.

Another object is to provide a machine for this purpose which is easy to operate.

According to this invention, a centrifugal moulding machine for making flexible endless belts of curable material comprises a turntable, means for rotating the turntable, a plurality of moulds rotatably mounted on, and circumferentially spaced apart around, the turntable, spinning means for selectively rotating the moulds relative to the turntable, and curing means disposed adjacent to said turntable for curing material in the moulds, the turntable being driven so that it moves each mould in turn towards the curing means after moulding material has been introduced into the mould and the mould has been rotated by the spinning means to distribute the material centrifugally around a wall of the mould, whereby the moulding material is cured to form a belt.

In operation moulding material is introduced into each mould in turn and the moulds are passed from one moulding station to another, the stations being disposed around the turntable.

An example of a machine in accordance with the invention is illustrated diagramatically in the accompanying drawings in which:~ Figure 1 is a plan view of the machine showing its major elements; and, Figure 2 is a sectional view of one of a number of moulds forming part of the machine.

The moulding machine shown in the drawings comprises a turntable 10, a plurality of moulds 20 spaced circumferentially around the turntable, and a driving belt 30. The moulds are rotatably mounted on the turntable. Disposed around the table are stations at which steps of moulding operations can be performed. The turntable may be mounted vertically or horizontally. Horizontal mounting, as shown in Fig. 1, is preferred to avoid adverse gravitational effects.

Each one of the moulds (as can be best seen in Fig. 2) has a main cylindrical body 22 and a tapered end 24. Towards the bottom of the body 22 there are a plurality of annular slots 26 provided to increase the rate of cooling of the mould. The mould ends with a tongue 28. The turntable is adapted to hold the mould rotatably at the tongue.

Each mould is provided with a cavity 40 within the body with an inner cylindrical wall 42 and a reservoir end 44. The cylindrical wall 42 has the size and external shape of the desired product, i.e., the thin belt which is to be moulded. The cylindrical wall is defined between an upper shoulder 46 and a lower shoulder 48. The purpose of these shoulders will be described in conjunction with the operation of the machine.

Around the turntable there are a number of stations at which different steps of the moulding operations are performed. The moulds are sequentially moved from one station to another by rotating the turntable 10 step by step about its central upright axis. At a first station 100 in Fig. 1 a metered volume of liquid moulding material is placed into the reservoir 44 of a mould. At the next station 200 the mould is rotated by contact with a belt 30, which is itself continuously driven. If the turntable is mounted horizontally, i.e. with its axis of rotation being vertical, as shown, centrifugal force acting upon the liquid moulding material as the mould is rotated about its axis causes the mould material to creep up into the inner cylindrical wall 42 of the mould.

The upper shoulder 46 acts as a retaining wall during this step so that the moulding material is not thrown out of the cavity 40.

Furthermore, both the shoulders 44 and 46 co-operate with the inner cylindrical wall 42 to give the moulding material the desired thin tubular shape. A similar action may be obtained with the turntable in a vertical position (i.e., with its axis of rotation being horizontai) except that the mould material flows laterally.

At a station 300 the mould is heated by suitable heating means such as a bank of infra-red heaters 310. The temperature of the mould is monitored by an infra-red control sensor 320 or other suitable means. During this step the moulding material which is thermal-setting is cured.

Station 400 is a cooling station at which the mould is cooled by air circulated across the mould from a cooling means 410. In order to keep the cooling air away from the heating station a baffle 420 is provided between the stations 300 and 400.

At the stations 300 and 400 the mould is still spun about its vertical central axis by the belt 30 thus ensuring that the final product is uniform. At a station 500 the mould has moved out of contact with the belt 10 and is allowed to coast to a stop. The finished product, i.e., the thin belt is then ejected from the mould manually, by mechanical means or by a vacuum or air pressure device.

The belt 30 is disposed around the turntable 10 and is driven by drive pulley 32. At the stations where it is required to rotate the moulds (e.g. 200), the belt engages the lower part 24 of each mould. At other stations (e.g.

500), where rotation is not desired, the belt is passed around idle pulleys 34.

This simple arrangement enables the machine to use a single driving means for rotating the moulds instead of using a motor for each mould.

The operation of the machine has been described with reference to a heat-cured molding material. Other types of moulding materials, such as R.F.-cured, micro-wave cured or U.V.-cured moulding materials can be used with the machine by providing the right curing means, and a corresponding mould. For example, if a U.V.-cured moulding material is used then the mould must be made of a material which is transparent to U.V.

Claims

1. A centrifugal moulding machine for making flexible endless belts of curable material, the machine comprising a turntable, means for rotating the turntable, a plurality of moulds rotatably mounted on, and circumferentially spaced apart around, the turntable, spinning means for selectively rotating the moulds relative to the turntable, and curing means disposed adjacent to said turntable for curing material in the moulds, the turntable being driven so that it moves each mould in turn towards the curing means after moulding material has been introduced into the moulds, and the mould has been rotated by the spinning means to distribute the material centrifugally around a wall of the mould, whereby the moulding material is cured to form a belt.

2. A machine according to Claim 1, for use with heat-curable moulding material, wherein the curing means comprises a heat source.

3. A machine according to Claim 2, wherein the heat source is a source of infrared waves.

4. A machine according to Claim 1, in which the curing means comprises a source of ultra-violet waves.

5. A machine according to Claim 1, in which the curing means comprises a source of microwaves.

6. A machine according to Claim 1, in which the curing means comprises a source of radio frequency waves.

7. A machine according to any one of Claims 1 to 6, further comprising cooling means disposed adjacent to said turntable and wherein, in operation, the turntable moves each mould in turn from the curing means toward the cooling means.

8. A machine according to Claim 7, further comprising belt removing means for removing belts from the moulds disposed adjacent the turntable and wherein the turntable, in operation, moves each mould from the cooling means to the removing means where the cured moulding material is removed from the mould.

9. A machine according to Claim 8, wherein the spinning means spins each mould while it is adjacent the curing means and the cooling means.

10. A machine according to any one of the preceding Claims, in which the spinning means comprises a driving belt and means for driving the belt, each mould coming into contact with the belt and being rotated thereby in selected positions as the turntable moves the moulds.

11. A machine according to any one of the preceding Claims, in which the turntable has a vertical axis of rotation.

12. A machine according to any one of Claims 1 to 10, in which the turntable has a horizontal axis of rotation.

13. A machine according to Claim 11, in which the moulds have vertical axes of rotation on the turntable and each mould has a cylindrical moulding wall bounded by shoulders at its top and bottom and a reservoir space for receiving liquid moulding material below the bottom shoulder, the moulding material being caused by centrifugal force to flow from the reservoir space on the cylindrical wall when the mould is spun by the spinning means.

14. A machine according to Claim 1, substantially as described with reference to the accompanying drawings.