Heat Set Core Oil

What It Does:

A core is used to make hollow spaces in metal castings. After the main pattern has been rammed up in the sand mold and pulled, a core can be placed in the cavity to create a void in the casting.

An example of a common feature created with a core is the bore of a cannon. The pattern for the cannon is first molded in sand. After the pattern is removed, a hard sand core is then placed in the cavity to create the bore of the cannon. The core prevents the molten metal from completely filling the space. After the metal hardens the casting is pulled from the foundry sand. The core sand is then removed from the inside of the casting to reveal the bore of the cannon.

How To Use It:

BCS The core oil is mixed with sand to form the core sand. The recommended mixture is 1 Ounce by Weight of oil to 20 Ounces by Weight of the foundry sand. It may be necessary to spray the sand with clean water if it becomes too dry to hold its shape when making the core. The water should only be added after the oil is mixed with the sand.

It is important to carefully weigh the items. A good kitchen type digital scale or digital postal scale is required for best results.

Mixing can be done by hand for small quantities (1 Oz oil with 20 Oz Sand). The sand and oil must be very throughly mixed to be sure that all the sand is covered with the oil. I have used a hand held electric kitchen mixer with good results and it is a lot easier than manual mixing.

A typical cylinderical core is made as follows:

  • Check the sand moisture level by squeezing a handful tightly in one hand. If the sand holds it shape it is ready to use. If it is too crumbly, lightly spray the sand with water and mix throughly.
  • Coat the inside of the core "core box" with an appropriate release agent. Spray funiture polish works well for core boxes made from PVC pipe. Dry release powder works well for wooden core boxes.
  • Pack sand into the core box and ram tightly.
  • Gently "rap" one half of the core box to loosen it from the core.
  • Carefully place the core on a tray and gently rap the other half of the box. The core should now be resting on the tray ready for baking.
  • Bake the core in an oven set to 425 Deg F. The time required depends on the thickness of the core. The 3/4 inch core shown requires about 1/2 an hour. Baking the core releases some fumes and should only be done with adequate ventillation. It is recommended that an electric toaster oven be used out of doors. Care should be taken not to allow the temperature in the oven to exceed 450 F. because the core will start to break down at 500 F.

This core sand can only be used once as a core sand. After shake out the sand can be mixed in with Budget Blend water bonded molding sand, or discarded.

The mixed oil and sand has a limited shelf life. It is recommended that only the amount needed be mixed and used in the same day.


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