GB2197819A

GB2197819A - Aggregate moulding process

Info

Publication number: GB2197819A
Application number: GB08628297A
Authority: GB
Inventors: Henk Felix Schwimmer
Original assignee: HELIX LIGHTING Ltd
Current assignee: HELIX LIGHTING Ltd
Priority date: 1986-11-26
Filing date: 1986-11-26
Publication date: 1988-06-02
Also published as: GB8628297D0

Abstract

A process for producing seamless hollow articles comprises placing a predetermined quantity of solid or liquid curable plastics material or curable monomer, together with a predetermined quantity of at least one particulate mineral type material, into a mould. The mould is heated to cure the plastics material or monomer while the mould is rotated substantially continuously and simultaneously about one or more, preferably two, axes. The mould is then cooled, optionally while still being rotated. Once cool the article can be removed from the mould. The particulate material does not melt during the process, and may be a natural mineral, either coloured or clear, or may comprise different coloured materials, and the plastics may be transparent or translucent. The effects produced may be veined marble, granite, and tertazo, and the article may be a lamp holder. The plastics may be polymethylmethacrylate, polycarbonate, polyvinyl resin, or polyester. <IMAGE>

Description

AGGREGATE MOULDING PROCESS The present invention relates to a rotational moulding process, and more particularly to such a process where the material being moulded comprises a plastics material and an aggregate.

It is known to mould hollow articles by blow moulding, or by moulding around a removable mandrel e.g.

a balloon. However these methods cannot be used to produce decorative articles in which the pattern is given by particles of aggregate. Rotational and centrifugal moulding processes are also known but have not been used for mouldings incorporating aggregates.

It is an object of the present invention to provide a process which will enable hollow articles including aggregate to be moulded.

According to the present invention there is provided a process for producing seamless hollow articles comprising the steps of providing a mould, inserting into said mould a predetermined quantity of solid or liquid curable plastics material or curable monomer together with a predetermined quantity of at least one particulate mineral type material, and heating said mould to cure said plastics material or monomer while rotating the mould substantially continuously and simultaneously about one or more axes, cooling said mould, optionally while still rotating it, and removing the article from the mould. Preferably the rotation is about two axes.

Preferably the predetermined quantity of plastics material is selected to be sufficient to form a plastics skin exteriorly of the article and also to bind together the particulate material.

Advantageously, the predetermined quantity of particulate material is sufficient for there to be a layer at least one particle thick over substantially the entire article.

The thickness of the wall of the article may be of the order of 41 inch (6.5 mm).

The plastics material, at least when cured, is preferably transparent or at least translucent, whereby the particulate material may be visible therethrough.

The particulate material may be coloured, and in the case where two or more materials are present, each may be differently coloured.

The mould may be heated to a temperature between 200 and 4500C, the exact temperature depending on the plastics material in use.

The plastics material may be thermoplastic or thermosetting together with suitable stabilisers and internal or external plasticisers, lubricants etc.

Preferably the plastics material is a powdered thermosetting resin, ideally of the type having an intermediate thermoplastic stage at the curing temperature.

The particulate material may be: a natural mineral, e.g. granite or quartz; glass, either coloured or clear; or any otherparticulatematerial having a melting point higher than the temperatures used for curing the plastics material.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which the single Figure is a diagrammatic representation of a machine which can be used to carry out the process of the invention.

Referring now to the figure, the machine has three mould carriers 1, each attached to an arm 2. The three arms 2 are journalled for stepwise rotation in the direction of arrow A from one phase of the process to the next. The three steps are loading one batch and unloading the previous batch, heating to cure the plastics material, and cooling.

Each mould carrier 1 may carry one or more moulds, depending on the size of the articles to be moulded. The mould carrier is a disc which is rotatable about a central point in a direction indicated by arrow B.

The axle 3 about which rotation occurs is rotatable about a pivot point 4 on a respective arm 2 in a direction indicated by arrow C.

Thus, once a mould carrier 1 and the mould or moulds carried thereby is in a work station, either heating or cooling, the moulds are rotated simultaneously about two of their axes. Needless to say, the mould carrier is not rotated in the loading/unloading work station.

In operation, the moulds, having been filled with predetermined quantities of plastics and aggregate, are loaded onto the mould carrier which is then rotated into the heating work station. Doors 5 are provided to enclose this work station when the mould carrier is in place. The temperature during the heating phase may vary depending on the plastics material being used, but is generally in the range 200-4500C. The mould carrier is biaxially rotated as described for a time sufficient to cure the plastics, after which the doors 5 are opened and the mould carrier passes to the cooling work station, being replaced in the heating work station by a newly loaded mould carrier.

In the cooling work station, the mould or moulds are sprayed with water or other cooling fluid from jet 6 while still being biaxially rotated. Once sufficiently cool, the mould carrier is again rotated to the loading/ unloading work station and the cycle is repeated thereafter.

The moulds are filled with a predetermined quantity of curable plastics material together with a predetermined quantitiy of aggregate, which may comprise any particulate material which will not melt during the heating phase.

The plastics material may be an acrylic material e.g. polymethylmethacrylate, a polycarbonate, a polyvinyl resin or a polyester. Particularly advantageous plastics materials are powdered thermosetting resins, especially those which undergo a thermoplastic stage at the temperature in the heating phase.

The plastics material cures first at the heated surface of the mould to form a skin of cured resin onto which the particles of aggregate settle during the biaxial rotation. The remaining resin then cures between the particles to hold them in place and to form a strong article.

The aggregate used may be a single material or a combination of materials, in which case they may be differently coloured. Examples of aggregate which may be used are granite, quartz, marble, glass, and other minerals and stones. The moulding process is such and the quantity of aggregate used is such that the particles form themselves, during biaxial rotation, into a layer at least one particle thick covering the entire surface of the article.

The end product has a smooth seamless finish due to the exterior plastics material and depending on the aggregate used, there are a number of pleasing visual effects which may be achieved. Among the effects may be listed - veined marble, granite, and terrazo effect.

The produced articles may fulfil any number of decorative effects, such as lamp holders, and the like.

Claims

CLAIMS:

1. A process for producing seamless hollow articles comprising the steps of providing a mould, inserting into said mould a predetermined quantity of solid or liquid curable plastics material or curable monomer together with a predetermined quantity of at least one particulate mineral type material, and heating said mould to cure said plastics material or monomer while rotating the mould substantially continuously and simultaneously about one or more axes, cooling said mould, optionally while still rotating it, and removing the article from the mould.

2. A process as claimed in claim 1, wherein said rotation is performed simultaneously about two axes.

3. A process as claimed in either claim 1 or claim 2, wherein the predetermined quantity of plastics material is selected to be sufficient to form a plastics skin exteriorly of the article and also to bind together the particulate material.

4. A process as claimed in any one of the preceding claims, wherein the predetermined quantity of particulate material is sufficient for there to be a layer at least one particle thick over substantially the entire article.

5. A process as claimed in any one of the preceding claims, wherein the thickness of the wall of the article is of the order of Smm or more.

6. A process as claimed in any one of the preceding claims, wherein the plastics material, at least when cured, is transparent or at least translucent, whereby the particulate material may be visible therethrough.

7. A process as claimed in any one of the preceding claims, wherein the particulate material is coloured, and in the case where two or more particulate materials are present, each is differently coloured.

8. A process as claimed in any one of the preceding claims, wherein the mould is heated to a temperature between 200 and 4500C.

9. A process as claimed in any one of the preceding claims, wherein the plastics material is a powdered thermosetting resin of the type having an intermediate thermoplastic stage at the curing temperature.

10. A process as claimed in any one of the preceding claims, wherein the particulate material is a natural mineral.

11. A process for producing seamless hollow articles substantially as described herein with reference to the accompanying drawings.