Using Castaldo® Mold Cream and
Castaldo
Mold Lock Formers

 

How to make molds without using a knife. The powder / cream separation technique.

 
 

The best molds are made with the traditional technique of using a very sharp knife to cut the rubber into two or more parts. This method gives the mold maker total control over the process and allows multi-part molds, spiral cores, undercuts and an endless variety of other features that are useful in successfully releasing wax patterns from the mold without breakage.

Simple molds, however , can also be made without cutting by using the powder or cream separation technique. The method is largely limited to two-dimensional models but is very easy to use once it is learned.

The technique works with any vulcanizing rubber including Castaldo White Label®, Gold Label®, No Shrink Pink®, Econosil®and Super High Strength™ silicone jewelry molding rubber. It will NOT work with liquid molding rubber compounds because the powder or cream will be washed away.

"jewelers talc". Baby powder is often talc, sometimes not -- read the label.

 
 

Castaldo Mold Cream contains mica powder and other, more effective ingredients. It works better and is easier to control -- just spread it on with your finger or a tool.

 Go to Castaldo Mold Cream Page 

 
 
 

To make a separation mold, prepare the bottom half of the mold by placing layer after layer of rubber in the bottom of a mold frame as you normally would. Spread powder or cream on that half.

Note that the powdered surface will control your parting line and you will not be able to change it later. Make sure it is where you want it to be. You may need to create a depression or cut-out in the rubber for the model to sit in properly. With silicone molding rubbers, merely push the model into the rubber to the proper line. With natural rubber, use a scissors or knife to make a cut-out.

 
 

You must similarly prepare seats for the sprue rod and the injection cone button.

Then prepare the top half of the mold, spread powder or cream on that as well, and vulcanize normally.

In a traditional mold that is cut with a knife, registration locks that position the top and bottom halves of the mold properly are easily formed in the rubber itself after vulcanization. This is not possible with the separation technique, so other methods have to be used.

Small squares of rubber can be added to the corners of one half of the mold before it is powdered and corresponding pieces cut out of the other half of the mold.

 
 

A much easier technique is to use Castaldo®Mold Lock Formers. These are small metal pieces that are imbedded in the rubber and automatically form matching locks during vulcanization

Go to Castaldo Mold Lock Formers Page 

 
 
 

 

It is often hard for beginners to find the parting line while trying to open the mold, so it is often useful to put a tiny scrap of paper, aluminum foil, or anything else that won’t melt during vulcanization at the parting line as an easy locator.

Take the mold out of the frame when it is finished and using a screwdriver or similar tool, open the mold at the parting line. The mold must be opened HOT, right out of the press. Place the tip of a screwdriver or similar tool at the separation point you have marked and pry or pull it open.

 






 


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