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Core Mold Plunger (piston)
Core Mold Plunger (piston) Quantity in Basket: None
Catalog No.: CM-4P
Price: $15.00
Shipping Weight: 0.10 pounds
Select diameter:
Optional Note:
This is one of the four plungers or pistons used in the CM-4a core mold. It is offered as a replacement part in case of damage to the original. The main reasons for damaged pistons are:
  • Use of tin/lead alloy (solder), causing the pistons to stick or solder to the cylinder walls as the mold temperature drops. This alone is not so much of a problem but the operator often will strike, hammer, pound, and otherwise apply force to the pistons in an attempt to make them break free (rather than simply raising the temperature so the solder becomes molten again). This destroys the pistons.
  • Attempting to drive the lead cores out of the mold by force because the metal being cast is not allowed to shrink (operation is too quick, not allowing sufficient cooling time between casts). If the cores are liquid, or if they have cooled sufficiently to shrink away from the cylinder, they should require little effort to eject. The cores should never be liquid when ejected as this is hazardous and may spray you with hot lead. But if a core does stick, the solution is to turn the mold upside down, and heat it with a broad flame from a hand-held propane torch (not a welding or actylene torch!). The temperature of the mold block should be raised to just beyond the melting point of the lead. It should never be heated to glow red, as this will destroy the mold.
  • Closing the top plate (sprue plate) while the pistons are still projecting above the top of the mold. This will dent, gouge and bend the pistons, destroying them. If this happens, the mold should be allowed to cool. Then the damaged piston needs to be gently bent straight, turned and pulled free.
Force is never appropriate in using the core mold. Heating to melt the lead first, and then removing the stuck piston normally works well. Eye protection and gloves should, of course, be worn to prevent injury and burns.

Note: Loc-Tite Anti-Seize is a silver colored lubricant that withstands high temperatures, and can be used to coat the pistons, underside of the sprue cutter, top of the mold block, and inside of the cylinders so that core materials are less inclined to stick. Usually one "treatment" will last for several hundreds of casts, and is easy to reapply with a swab once the mold cools. The Permatex company also makes a similar silver-colored lubricant. It is very "messy" to use but only a very small amount is needed to make a thin film coating on the steel.

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