GB2207385A

GB2207385A - Casting method and pack

Info

Publication number: GB2207385A
Application number: GB08713465A
Authority: GB
Inventors: Herbert David Perriton
Original assignee: ROBNORGANIC SYSTEMS Ltd
Current assignee: ROBNORGANIC SYSTEMS Ltd
Priority date: 1987-06-09
Filing date: 1987-06-09
Publication date: 1989-02-01
Also published as: GB8713465D0

Abstract

A method of making casts of footprints, tyre marks or other impressions or marks which comprises: providing a watertight pack made of a flexible and substantially water-impermeable material and having two compartments enclosed therein separated by means which may be removed to allow the contents of the compartments to be mixed; one of said compartments containing Plaster of Paris or similar water-settable inorganic moulding material and the other containing water for setting the moulding material, or one of said compartments containing a room temperature - curable fluid silicone and the other containing a curing agent or accelerator for the silicone; removing the separating means and mixing the contents of the two compartments within the pack; dispensing the mixture from the pack into or onto the impression or mark and allowing the mixture to set to form a cast.

Description

CASTING METHOD AND PACK This invention concerns a method of making casts of impressions using a pack containing precise amounts of all the materials required for use in the method, particularly for on-site casting.

The method is particularly useful for making casts in plaster or similar materials at outdoor locations (for example in police work to make casts of footprints, tyre marks or other impressions or marks at scenes of crime) but the same general method may be used for other purposes and in other locations. Also, a silicone may be used instead of plaster where the latter is inappropriate on account of the heat generated in setting, for example for taking casts of impressions left in snow.

The invention thus provides a method of making casts of footprints, tyre marks or other impressions or marks which comprises: providing a watertight pack made of a flexible and substantially water-impermeable material and having two compartments enclosed therein separated by means which may be removed to allow the contents of the compartments to be mixed; one of said compartments containing Plaster of Paris (or another inorganic moulding material based for example on calcium sulphate and settable with water at room temperature) and the other containing water for setting the moulding material, or one of said compartments containing a room temperature - curable fluid silicone and the other containing a curing agent or accelerator for the silicone; removing the separating means and mixing the contents of the two compartments within the pack; dispensing the mixture from the pack into or onto the impression or mark and allowing the mixture to set to form a cast. The invention also includes a pack as just defined.

This method is very convenient and easy to use in comparison with the traditional method of mixing the casting material on the spot. It eliminates the need to weigh out appropriate quantities of the materials on site and it is fast and accurate and creates less mess and waste. The water-impermeability of the pack prevents water uptake and deterioration of plaster in storage and transport. These factors all contribute to making the method a very advantageous one, particularly in connection with police work.

The moulding material used may be Plaster of Paris or a similar material such as Crownstone (trade mark; manufactured by British Gypsum Limited for use primarily in dental moulding and believed to be based on Plaster of Paris). When a silicone moulding material is used, it may be any suitable room temperature - vulcanisable material such as Dow Corning 9161 or ICI Silcoset 105; in these circumstances the second compartment will contain an appropriate curing agent such as dibutyltinlaurate.

A reinforcing filler may be mixed with the moulding material, usually in amounts of up to 20% by weight. Suitable materials are short strand fibrous fillers such as glass fibre (e.g. 5-15%) or Wollastonite (e.g. 10-20%).

An anti-freeze agent such as methanol may be added to the water in the pack to prevent freezing.

It has been found that this does not interfere with the setting of the plaster.

The pack is preferably in the form of a sealed bag or envelope made of a laminate of aluminium and a plastic, for example a polyester such as polyethylene terephthalate (e.g. Mylar (trade mark) sheet) or a polyamide such as nylon (trade mark).

It is preferably tapered at one corner such that when the corner is cut off after mixing, a cone is provided for dispensing the mixture.

The means for separating the two compartments prior to use is preferably provided by a rod (which extends across the whole width of the pack between the compartments and is preferably bilobal in section) and a corresponding C-shaped clip of the same length.

The sheet material of the pack passes around the rod and is fastened to it by the clip. The clip is easily slid off to allow the contents of the pack to be mixed for use. The rod and the clip may be used to reinforce the cast prior to final setting.

For storage and transport, the pack may be placed in removable outer bag (e.g. a polyethylene bag) to provide further protection and to include printed directions for use or labelling. The bag is also useful for disposing the pack after use.

Claims

CLAIMS:

1. A method of making casts of footprints, tyre marks or other impressions or marks which comprises: providing a watertight pack made of a flexible and substantially water-impermeable material and having two compartments enclosed therein separated by means which may be removed to allow the contents of the compartments to be mixed; one of said compartments containing Plaster of Paris (or another inorganic moulding material based for example on calcium sulphate and settable with water at room temperature) and the other containing water for setting the moulding material, or one of said compartments containing a room temperature - curable fluid silicone and the other containing a curing agent or accelerator for the silicone; removing the separating means and mixing the contents of the two compartments within the pack; dispensing the mixture from the pack into or onto the impression or mark and allowing the mixture to set to form a cast.

2. A method according to claim 1 in which the pack is a sealed bag or envelope made of a laminate of aluminium and a polyester or other plastic.

3. A method according to claim 1 or claim 2 fn which the pack is tapered at one corner to provide a cone for dispensing the mixture after cutting off the corner.

4. A method according to any preceding claim in which the separating means is a rod around which the pack is secured by a C-shaped clip.

5. A method according to any preceding claim in which the moulding material is a Plaster of Paris or Crownstone.

6. A method according to any preceding claim in which a reinforcing fibrous filler is mixed with the moulding material.

7. A method according to any preceding claim in which methanol or another anti-freeze agent is added to the water for setting the moulding material.

8. A pack for use in the method of any preceding claim, the pack being watertight and made of a flexible and substantially water-impermeable material and having two compartments enclosed therein separated by means which may be removed to allow the contents of the compartments to be mixed; one of said compartments containing Plaster of Paris (or another inorganic moulding material based for example on calcium sulphate and settable with water at room temperature) and the other containing water for setting the moulding material, or one of said compartments containing a room temperature - curable fluid silicone and the other containing a curing agent or accelerator for the silicone.

9. A pack according to claim 8 in the form of sealed bag made of a laminate of aluminium and a polyester or other plastic and the separating means is a rod around which the pack is secured by a C-shaped clip.