IntroductionThe term resin metal casting refers to a relatively simple method of producing quality metallic castings using pure metal in a fine powder form mixed with polyester resin and catalyst. These are usually produced from a latex or silicone mould.
We will describe the procedure to enable you to produce fine quality castings either for your own pleasure or as a profit making venture and it is assumed that you already have a mould ready to use. No release agent is required when using latex or silicone, moulds.
As with all chemicals safety procedures must followed. We recommend that because of the smell of the resin it is advisable not to use this material in a domestic situation.A heated garage or outbuilding is ideal. The working temperature should be around 20ºC (68ºF).
THESE MATERIALS ARE UNSUITABLE FOR USE BY CHILDREN UNLESS UNDER SUPERVISION.
The casting is made following two procedures. 1. The outer shell/gelcoat layer and 2. the infill. The outer metal shell is a mix of about 3/4 parts of metal to 1 part of resin aiming for a just brushable paste. General purpose resin and Casting resin, work well but casting resin will accept more metal powder.
By adding up to 20% gelcoat you can reduce the amount of metal powder to 2/3 parts to 1 part resin with acceptable results.The infill resin is poured into the mould when the outer shell has cured. The infill resin can be loaded with low cost filler powder such as talc and microdol to reduce cost and shrinkage. Dried sand can also be added to the infill for added weight.
For larger castings Fillite should be used as part of the filler addition to extend the resin with the benefits of lower shrinkage and less heat generated.
Applying the outer shell First weigh out the resin, next add catalyst at a rate of 2% and mix thoroughly, (refer to catalyst chart on next page)The metal powder is then added at the required amount. All metals intermix, e.g. 4 parts of nickel silver to 1 part of Aluminium gives a pewter effect. catalyst can be added after the metal powder but will prove much more difficult to mix in. The catalysed mix is then applied to the mould surface.
Remember, that after adding Catalyst you have approximately 25 minutes working time before the mix sets.
If you are using a reversible latex mould you may find it easier to turn the mould inside out, paint on the resin/metal mix and then reverse.
If this is not possible the mix should be thinned enough to be able to revolve the mould until the surface is covered. If this method is used it is advisable to add a second coat to make sure the shell is thick enough.
InfillingAfter the outer skin has set (approx. 2 hours) simply add catalyst at 1% by weight to resin and add filler powder as required. This should set in about 30 mins.
A useful tip is to pigment the infill resin to the approximate shade of the finished casting, this will help disguise any thin areas in the metallic shell.Tiny casts should be done in a one shot resin/metal mix only. For larger casts the infilling can be in two or more layers; pebbles, metal or stones can be added which will not only save resin but also add weight.
While curing, the resin will get hot, so to preserve the mould it is advisable to remove the casting before the exotherm peaks. (resin is at its hottest).
See mixing catalyst chart for addition of hardener to resin.
Finishing and surface finishingAllow the casting to fully cure for at least 72 hours, cut back with wire wool and finish with metal polish. If polishing mops are available cut & polish back with cutting compounds. A coat of wax polish or clear lacquer will prevent tarnishing.
Antiquing can be achieved by painting on a spirit based stain, leave to dry then abrade and polish; shoe polishes can also be used. As an alternative graphite can be mixed to the resin. 5% - 15% by weight can be added depending on shade.
Castings can be treated chemically to obtain a patina, the method and chemicals used are often the result of experimentation. Patination can be fixed by wax polishing. Further Information on this subject is available on the internet.
For some sintered metals patination is not possible unless small quantities of other metals are added, e.g. Aluminium will need 10% Lead added and Brass will require the addition of a small quantity of Copper or Lead.
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