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Making A Hollow Casting Using 3-D Brush-On Mold | |||||||||
 Mr. Maslyn will now
demonstrate how to make a hollow casting using plaster. First, a
soap solution is applied to the inside of the mold surface with a
sponge, brush or spritz bottle. This will aid in releasing the
plaster from the rubber. Next, the rubber mold is “seated”
inside the support shell. Make sure that the parting seam of the
rubber mold is aligned and even. The plaster pieces of the support shell are then assembled. They should align and fit together easily. Elastic bands or “mold straps” are then used to secure the pieces, and will hold everything together during casting. Plaster is then mixed (as directed) and poured into the mold cavity. A Word About Rotational Casting - The goal of rotational casting is to build layer upon layer of casting material against the interior mold surface until a suitable thickness is attained (usually plaster or a fast cast resin such as Smooth-Cast 300 - cast to a thickness of 3/8” or 1 cm). Castings that have been rotationally cast are hollow (which saves on material cost), lightweight and yield a virtually flawless surface finish. The key to success in rotationally casting a piece is to rotate the mold (held in place by the support shell) at 360 degrees and at a constant rate. Rotational casting can be done by hand or by machine. Mr. Maslyn rotates the mold by hand and strives to build a uniform coating on the mold surface. The working time of this plaster is about 10 minutes, and the mold is rotated until the plaster no longer flows. A second batch of plaster is mixed and poured into the mold cavity, and the mold is again rotated for about 10 minutes. This layer of plaster bonds to the first. This process is repeated twice more, and an ultimate thickness of about 3/8” (1 cm) is attained. Demold After 45 minutes, the support shell is removed and the rubber mold is easily removed from around the plaster casting. Again, we see that the finished casting reflects every last bit of detail taken from the original. And, as stated before, you can make one or many castings from this single mold. Sections of How to Make Molds and Castings Moldmaking Materials Moldmaking Process Moldmaking Problems and Solutions Other Pourable Mold Configurations And Techniques Making A Brush-on Rubber Mold Using Liquid Plastics Making A Hollow Casting Using 3-D Brush-On Mold Spraying Mold Rubber Mold Making Review |
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