Mold Base (Kirksite) Alloys


Eastern Alloys manufactures mold-base alloys, also known as Kirksite alloys. Kirksite is a moderate strength zinc-base alloy that was developed primarily as a forming tool alloy. Dies cast from Kirksite provide low-cost tooling because the alloy can be accurately cast, requiring a minimum of finishing. In addition, Kirksite has been used as a general purpose casting alloy for non-stressed components.

Typical uses for Kirksite alloys are:

  • Press dies and punches for sheet metal forming.
  • Molds for ceramics and rubber.
  • Injection molding and compression molding dies.
  • Tube bending dies.
  • Mandrels for metal spinning.
  • Low stressed non-sparking tools and repair parts.

Because of the alloy's excellent fluidity and low melting temperature, casting temperatures are low, 800-850°F. Higher casting temperatures should be avoided due to possible iron contamination from the cast iron kettles normally used to melt the alloy. Iron pickup can cause poor casting surface quality and brittleness. Melting in a silicon carbide crucible is preferred as a safeguard against iron pickup. The alloy is normally cast in permanent, plaster or sand molds.

Kirksite is readily machined and polished. Castings can be successfully plated following procedures used for zinc die-castings. Kirksite can also be cast in rubber tooling as a replacement for slush casting alloy (ZA-5) when higher strengths are required, with a sacrifice in fluidity.


Ultimate Tensile Strength 35,000 psi
Elongation in 2" 2.0%
Impact Strength 6 ft-lbs
Melting Range 717-745°F
Density 0.25 lb/cu in
Brinell Hardness 100
Solidification Shrinkage 0.14"/ft

Tooling Process

Kirksite Pattern

Step 1:  Kirksite drawings.

Step 2:  Making of the Kirksite pattern.

Step 3:  Using the pattern, a sand mold is produced.

Step 4:  Kirksite is poured into the sand mold.

Step 5:  The Kirsite casting is machined to final dimensions.

Step 6:  Finished Kirksite tool ready for production.

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