GB2024094A

GB2024094A - Method for rapid release of cold-moulded objects

Info

Publication number: GB2024094A
Application number: GB7922558A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-06-28
Filing date: 1979-06-28
Publication date: 1980-01-09

Abstract

A method of cold moulding a settable substance such as glass fibre reinforced concrete, plaster or clay is provided wherein an inert liner, made from polyvinyl chloride (or other plastics material), paper or cardboard conforming to the shape of the mould is located in the mould. The settable substance is poured into the liner, squeezed to remove excess fluid, and allowed to partially harden for less than six hours after which the thus formed moulded object is turned out from the mould complete with the liner and allowed to complete the hardening process, the mould then being available for reuse. The liner may be removed from the object before hardening is complete.

Description

SPECIFICATION Method for rapid release of cold-moulded objects The present invention relates to a method for securing the rapid release of a cold-moulded object from a bed mould.

In the manufacture of objects by coldmoulding techniques e.g. from concrete and more particularly glass fibre reinforced concrete (GRC), the raw material is generally poured into the mould, usually made of wood or metal, optionally subjected to a pressing operation, for example with GRC to remove excess water, and then allowed to stand for 24 hours or more in order to allow the material to harden. After hardening the object is then removed from the bed-mould. If an attempt is made to remove the object before it has fully hardened the material may "flow" resulting in a loss of form or shape. This is especially noticeable if the mould is designed to produce an object with a particular topographical surface design.

We have now developed a method for coldmoulding which allows for a rapid release, that is in less than 6 hours, of the object from the bed mould without any loss of form.

In our method the bed-mould is lined with an inert liner conforming precisely to the outline of the mould and preferably capable of retaining the bed-mould shape when removed therefrom.

Accordingly, therefore, the present invention provides a method of cold-moulding a settable substance in a bed mould wherein the said bed mould includes an inert liner of material conforming to the shape of the said mould outline, the settable substance poured into the lined mould, allowed to at least partially harden off for a period of up to six hours, the thus formed moulded object removed from the bed mould together with the liner and allowed to complete the hardening off process.

A particularly suitable material for use as a liner is polyvinyl chloride (PVC) sheet which can be vacuum formed into the precise shape of the bed mould. Other plastic materials, such as polyethylene or polypropylene, may also be employed as the liner material provided that such material can be formed into the bed mould shape and is inert towards the moulding material. Paper and cardboard treated to be inert to the moulding material may also be employed.

In the context of the present application "inert" not only means chemically non-reactive but also that the material must not form any type of bond with the moulding material.

Thus when moulding concrete the liner material must not absorb water.

The present invention also includes a method of manufacturing a liner and bed mould wherein the liner having the precise internal dimensions of the object to be formed by moulding is first formed by vacuum forming in a suitable mould, removed from the mould and subsequently used as a male mould in the production of the bed mould from a settable material.

An example involving the use of the method of the present invention in the manufacture of a GRC slab having a raised diagonal cross on one surface will now be described.

A wooden mould having a diagonal cross formed as an insert in the base thereof is first produced, the dimensions being about 2.0mm in excess of the required slab size. A 2mm thick sheet of PVC is formed into the mould shape by a conventional vacuum forming technique to yield a liner. This liner is then inverted in a tray and bed mould formed around it from plaster of paris or other suitable material.

A bed-mould prepared as described above and including a PVC liner is filled with raw GRC. Pressure is applied to the GRC to dewater is, after which the bed mould is removed, e.g. by inverting the mould onto a tray, from the raw GRC and liner. The GRC is then allowed to harden for about 1 hour at the end of which time the PVC liner is removed and the slab allowed to harden off completely without loss of shape or change in dimensions.

In this process the bed mould is re-usable immediately after removal of the moulded object and liner may also be re-used after it too has been removed. Thus the need for a large number of moulds and liners for mass producing a cold moulded slab is obviated.

The process may also be employed with materials other than GRC which can be cold moulded, such as conventional concrete, reconstituted stone, plaster of paris, clay and similar materials.

If the object to be moulded is required to have topographical shapes on both surfaces, the moulding material may be poured between a pair of bed moulds each containing a liner. Both bed moulds may be removed for re-use as soon as the moulding material has hardened sufficiently to be supported in the desired form by the liners themselves.

1. A method OT cold-moulding a settable substance in a bed mould wherein the said bed mould includes an inert liner of material conforming to the shape of the said mould outline, the settable substance poured into the lined mould, allowed to at least partially harden off for a period of up to six hours, the thus formed moulded object removed from the bed mould together with the liner and allowed to complete the hardening off process.

2. A method according to claim 1 wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method for rapid release of cold-moulded objects The present invention relates to a method for securing the rapid release of a cold-moulded object from a bed mould. In the manufacture of objects by coldmoulding techniques e.g. from concrete and more particularly glass fibre reinforced concrete (GRC), the raw material is generally poured into the mould, usually made of wood or metal, optionally subjected to a pressing operation, for example with GRC to remove excess water, and then allowed to stand for 24 hours or more in order to allow the material to harden. After hardening the object is then removed from the bed-mould. If an attempt is made to remove the object before it has fully hardened the material may "flow" resulting in a loss of form or shape. This is especially noticeable if the mould is designed to produce an object with a particular topographical surface design. We have now developed a method for coldmoulding which allows for a rapid release, that is in less than 6 hours, of the object from the bed mould without any loss of form. In our method the bed-mould is lined with an inert liner conforming precisely to the outline of the mould and preferably capable of retaining the bed-mould shape when removed therefrom. Accordingly, therefore, the present invention provides a method of cold-moulding a settable substance in a bed mould wherein the said bed mould includes an inert liner of material conforming to the shape of the said mould outline, the settable substance poured into the lined mould, allowed to at least partially harden off for a period of up to six hours, the thus formed moulded object removed from the bed mould together with the liner and allowed to complete the hardening off process. A particularly suitable material for use as a liner is polyvinyl chloride (PVC) sheet which can be vacuum formed into the precise shape of the bed mould. Other plastic materials, such as polyethylene or polypropylene, may also be employed as the liner material provided that such material can be formed into the bed mould shape and is inert towards the moulding material. Paper and cardboard treated to be inert to the moulding material may also be employed. In the context of the present application "inert" not only means chemically non-reactive but also that the material must not form any type of bond with the moulding material. Thus when moulding concrete the liner material must not absorb water. The present invention also includes a method of manufacturing a liner and bed mould wherein the liner having the precise internal dimensions of the object to be formed by moulding is first formed by vacuum forming in a suitable mould, removed from the mould and subsequently used as a male mould in the production of the bed mould from a settable material. An example involving the use of the method of the present invention in the manufacture of a GRC slab having a raised diagonal cross on one surface will now be described. A wooden mould having a diagonal cross formed as an insert in the base thereof is first produced, the dimensions being about 2.0mm in excess of the required slab size. A 2mm thick sheet of PVC is formed into the mould shape by a conventional vacuum forming technique to yield a liner. This liner is then inverted in a tray and bed mould formed around it from plaster of paris or other suitable material. A bed-mould prepared as described above and including a PVC liner is filled with raw GRC. Pressure is applied to the GRC to dewater is, after which the bed mould is removed, e.g. by inverting the mould onto a tray, from the raw GRC and liner. The GRC is then allowed to harden for about 1 hour at the end of which time the PVC liner is removed and the slab allowed to harden off completely without loss of shape or change in dimensions. In this process the bed mould is re-usable immediately after removal of the moulded object and liner may also be re-used after it too has been removed. Thus the need for a large number of moulds and liners for mass producing a cold moulded slab is obviated. The process may also be employed with materials other than GRC which can be cold moulded, such as conventional concrete, reconstituted stone, plaster of paris, clay and similar materials. If the object to be moulded is required to have topographical shapes on both surfaces, the moulding material may be poured between a pair of bed moulds each containing a liner. Both bed moulds may be removed for re-use as soon as the moulding material has hardened sufficiently to be supported in the desired form by the liners themselves. CLAIMS

2. A method according to claim 1 wherein the liner retains the shape of the bed mould after removal therefrom.

3. A method according to claims 1 or 2 wherein the liner is a plastics material.

4. A method according to claim 3 wherein the liner is formed from polyvinyl chloride.

5. A method according to claim 1 or claim 2 wherein the liner is formed from treated paper or cardboard.

6. A method according to any one of the preceding claims wherein the settable substance is glass fibre reinforced concrete and is subjected to a pressing operation after being poured into the lined bed mould.

7. A method according to any one of the preceding claims wherein the liner is removed from the moulded object before hardening is complete.

8. A method according to any one of claims 2 to 7 wherein two bed moulds including inert liners are employed and are positioned face to face, the settable substance is poured therebetween and the bed moulds removed as soon as the said substance has hardened off sufficiently to be supported by the liners.

9. A method of cold moulding a settable substance substantially as herein described with reference to the example.

10. A method of manufacturing a liner and bed mould for use in the method as claimed in any one of claims 2 to 9 wherein the liner, having the precise internal dimensions of the object to be formed by moulding is first formed by vacuum forming in a suitable mould, removed from the mould and subsequently used as a male mould in the production of the bed mould from a settable material.