Slush Molding Plastisols


This process is used when part of the mold is open.
Slush molding is an excellent method for producing hollow open-end objects. It is an inverse of the dipping process in which the inside of the mold is coated rather than the outside. Awide variety of products are manufactured in this way including toys, dolls, shoes, seat covers, and automotive parts. Open end molds are used and the excess plastisol poured off after a gelling period. Fine details can be obtained and undercuts present few problems. The mold cavity is usually 1-2" taller than the actual part so that some plastisol can be trimmed after molding.

 

Procedure

1. The mold cavity should be coated with a layer of mold release. We recommend MRV 1000 IPA. Please see MRV 1000 IPA instructions.

2. The mold cavity is filled with plastisol.

3. The mold is then heated using an oven, or liquid bath of hot oil or molten salt. Thin walled molds are desireable for quick heat transfer. The thickness of the coating will depend on the temperature of the bath /oven, the time heated in the bath /oven, and the gellation temperature of the plastisol. In an oven, the top of the mold must be covered or a layer of gelled material will form at the open surface.

4. After gelling a coat in the mold the excess plastisol is emptied and the mold is allowed to drain until the dripping stops (about 3 to 5 minutes). Plastisol that is drained from the mold is poured through a strainer and reused. The vinyl buildup produces a very even surface.

5. After the draining process the mold is heated again to cure the plastisol. The cure time is usually 3 to 8 minutes.

6. The mold and plastisol can be air or water cooled to 150°F. The heat transfer liquid must be water souluble if water cooling. Extract the part by pulling and twisting the part. The collapsed part has good memory and will "snap" back into place after extraction.

Heat Transfer liquids for the Slush Molding process

A number of heat transfer liquids are available for using in a gel bath: plasticizers, molten salt, or any other liquid that can reach 350° to 400°F. When using liquids heat generally will transfer much quicker. Do NOT use water, water can contaminate plastisol and make it unuseable.

Mold making

Electroplated molds are used most often in this process due to quick heat transfer. Electroforming is used most often because of the strong, thin, highly detailed durable molds formed in the process. Electroplating can be done over a number of substrates including silicone. Call a professional mold maker for more information.