Patterns and its preparation
A wide range of materials are appropriate for the cast (wood, plaster, plastics, leather, metal, acrylic, etc.). Polystyrene is less appropriate since it requires special precautions. Any material must be dry. In order to cast the material a casting box must be built around the pattern. The sides of the casting box are fixed with screws. Porous master patterns of plaster or wood must be sealed. We recommend to use our ALWA ACRYLIC SEALER (art. no. 9535000). Any pattern must be pre-treated with ALWA SURFACE TENSION REMOVER (art. no. 9500000), which removes the surface tension and ensures a smooth coverage of ALWA RELEASE LACQUER (art. no. 9510000). First, a thin layer of ALWA SURFACE TENSION REMOVER is applied on the prepared patterns with a cloth. After approx. 5 – 10 min. the ALWA SURFACE TENSION REMOVER is vented. Then, ALWA RELEASE LACQUER is applied with a brush or a spray gun. For fine structures several layers (min. 3 – 4) should be applied with a spray gun. ALWA RELEASE LACQUER is soluble in water, therefore, moisture penetration should be avoided. Hot air can accelerate the drying of the release film (the drying of the release film takes approx. 30 min. at RT).
Before casting, make sure that the pattern and the mixture of casting resin and aluminium powder have a temperature between 19 – 22 °C. At temperatures above 22 °C shrinkage may arise and at temperatures below 19 °C the cast material expands.
Mix the resin components well. Afterwards add the filler into the resin and stir until you reach a homogeneous mixture and no aluminium lumps are left. Leave the finished mixture for venting until no more air bubbles appear. After airing, carefully stir the mixture. Then thoroughly mix in the hardener powder (3 % on the resin content) for approx. 3 – 5 min. Lumps of the hardener powder must be crashed before adding it into the mixture. Please note that as little air as possible should be stirred into the mixture. For larger batch quantities mix the resin compound in two or more mixing containers. In this case, the hardener powder must be added simultaneously. For homogenisation, the resin compound of two or more mixing containers has to be mixed among each other to achieve a simultaneous curing of the mixture. Only then you get a homogeneous hardener and temperature distribution (same reaction behaviour of the total mixture).
As the resin contains flammable solvents, ex-proof mixers should be used. We highly recommend using our ALWA SPECIAL MIXERS since they ensure that as little air as possible is stirred into the mixture. After the hardener has been stirred into the mixture and vented for 3 – 5 min., the mixture must be cast in a thin stream within 8 – 10 min. on the prepared pattern. First, the mixture is poured slowly into the deepest part of the pattern. In order to prevent that aluminium lumps are cast into the mixture, a sieve can be used. When the pattern is completely covered with the mixture, the rest of the material can be added faster. The curing process should be protected from the effects of cold and heat. After adding the hardener powder, the resin gel time starts after approx. 18 min. and a fast temperature increase can be noticed. The resin compound cures just as quickly. Reaction temperatures up to 130 °C can be reached. Since the resin compound cures quickly, patterns of wax can also be moulded. After the resin compound is cured, approx. 50 min. after the hardener powder has been added, the backside of the mould is sprinkled with aluminium spray grit, which then is spread with a hand brush (prevents a sticking at the back of the surfaces). Tools and containers should be cleaned with a solvent (e.g., acetone) directly after using. Before the temperature peak has been reached, the mould expands in length. Therefore, the screws of the casting box sides are removed to enable a free expansion. Cast drive-in nuts are very useful for demoulding. Depending on the master pattern it might be reasonable to wait until the cast has been cooled down to 60 °C or to RT.