GB2317138A

GB2317138A - Rotational moulding of an acoustic hood

Info

Publication number: GB2317138A
Application number: GB9713990A
Authority: GB
Inventors: Peter Godfrey Knowles
Original assignee: ROTATIONAL MOULDINGS Ltd
Current assignee: ROTATIONAL MOULDINGS Ltd
Priority date: 1996-09-13
Filing date: 1997-07-03
Publication date: 1998-03-18
Also published as: GB9619126D0; GB9713990D0

Abstract

There is disclosed an acoustic hood formed by a rotational moulding technique and comprising an outer skin of thermoplastics material and an inner skin formed from a thermoplastic material incorporating a blowing agent. The preferred material for both skins is polyethylene and in one embodiment of the process of manufacture a single shell-like moulding is formed and cut in half to form a pair of hoods.

Description

Acoustic Hood This invention concerns an acoustic hood, of the kind, (hereinafter termed "of the kind referred to") particularly, though by no means exclusively, suitable for housing a telephone instrument in a public place.

The choice of materials from which acoustic hoods are made has a critical and not entirely understood influence on their effectiveness in providing a relatively quiet zone in an otherwise noisy environment.

The present invention is based on an appreciation of the possibility of utilising materials which have been found satisfactory for loudspeaker enclosures for the manufacture of acoustic hoods of the kind referred to.

According to the present invention there is provided an acoustic hood ofthe kind referred to formed by a rotational moulding technique and comprising an outer skin of thermoplastics material and an inner skin formed from a thermoplastic material incorporating a blowing agent.

The inner skin may be totally encapsulated by the outer skin or the inner skin may be exposed on the inside surface of the hood.

The thermoplastics materials may be of polyethylene.

The blowing agent may be Diphenyloxide - 4,4' - disulphohydrazide.

The invention will be further apparent from the following description which concerns, by way of example only, the manufacture of two forms of acoustic hood embodying same, and with reference to the figures of the accompanying drawing.

Of the drawing : Figure 1 shows a perspective view of a first form of hood; Figure 2 shows a cross-section through the hood on the line II-II of Figure 1; Figure 3 shows a perspective view of a second form of hood; and Figure 4 shows a cross-section through the hood on the line IV-IV of Figure 3.

Both forms of hood are manufactured in a mould, generally formed in two halves which can be secured together at mating flanges. A vent tube extends through a wall of one of the mould halves at a position where an accessory such as an ashtray can be fitted to the hood in the resulting aperture.

A charge of polyethylene powder is introduced into the mould and the mould is mounted on a rotational moulding machine to form a fused skin over the mould surface. Whilst the skin is still hot a further charge of polyethylene powder incorporating a blowing agent is introduced into the mould. Moulding is continued to form porous polyethylene material over the skin.

A suitable blowing agent is diphenyloxide -4,4' - disulphohydrazide available as Genitron (Registered Trade Mark) from Schering Industrial Chemicals, which may be added to the polyethylene at 1-5% and typically 2% by volume.

As best seen from Figures 1 and 2 in the first form of hood the fused skin 10 completely encapsulates the porous material 11 which completely fills the interior of the moulding. the hood comprises a back 12, sides 13 and 14, curved top 15 and bottom shelf 16 which is fitted with an ashtray or coin tray 17 at the position where the vent tube entered the mould.

In the arrangement of Figures 2 and 3 wherein like parts are indicated by like reference numerals, two hoods are formed by cutting a single box-like shell moulding in half. The resulting hoods have the same parts as the hood of Figures 1 and 2, the only difference being that the top is squared off. In this hood, the porous material 11 is exposed on the inner surfaces of the hood. The cut edges 30 may be covered with trim if desired. The shell moulding is produced by introducing a first charge of thermoplastic material into a box-like mould through a vent tube to form a fused skin over the surface of the mould and then introducing a second charge of thermoplastic material incorporating a blowing agent to form a coating over the fused skin.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof as defined by the appended claims.

Claims

1. An acoustic hood of the kind referred to formed by a rotational moulding technique and comprising an outer skin of thermoplastics material and an inner skin formed from a thermoplastic material incorporating a blowing agent.

2. An acoustic hood according to claim 1 wherein the inner skin is totally encapsulated by the outer skin.

3. An acoustic hood according to claim 1 herein the inner skin is exposed on the inside surface of the hood.

4. An acoustic hood according to any preceding claim wherein the thermoplastics material is of polyethylene.

5. An acoustic hood according to any proceeding claim wherein the blowing agent is diphenyloxide -4,4' - disulphohydrazide.

6. A method of manufacturing an acoustic hood according to claim 1, wherein a first charge of thermoplastic material is introduced into the mould through a vent tube to form a fused skin over the entire mould surface and wherein a second charge of thermoplastics material incorporating a blowing agent is introduced into the mould to fill the fused skin.

7. A method according to claim 6 wherein the hood has a bottom shelf and an ashtray or coin tray is fitted into the shelf at the position where the vent tube entered the mould.

8. A method of manufacturing a pair of acoustic hoods according to claim 3 wherein a first charge of thermoplastics material is introduced into a box-like mould through a vent tube to form a fused skin over the surface of the mould and wherein a second charge ofthermoplastic material incorporating a blowing agent is introduced into the mould to form a coating over the fused skin, all to form a shell-like moulding which is cut in half to form the pair of hoods.

9. A method according to claim 8 wherein trim is applied to the cut edges of the hoods.