Mold release agent and method of application for die casting

Abstract

A die cast mold release lubricant comprises a silicone compound. A method of application of the lubricant to a die cast mold as a release agent is disclosed where a die casting machine has a mold with mold halves forming a mold cavity when the mold halves abut against one another, a shot sleeve and a plunger which pushes molten material through the shot sleeve and into the mold cavity. The mold release agent is placed into the shot sleeve remote from the mold cavity, molten material is introduced into the shot sleeve, and the molten material and the mold release agent are forced into the mold cavity by movement of the plunger into the shot sleeve. The silicone compound preferably has a melting point of about 90-220° F., and a molecular weight of about 5500-50,000.

Description

RELATED APPLICATION [0001] This application is a continuation-in-part which claims priority benefit of U.S. utility patent application Ser. No. 10 / 447,812 filed on May 29, 2003.FIELD OF THE INVENTION [0002] This invention relates to improvements to pressure die casting mold release agents, and to an improved method of application of the mold release agent in the pressure die casting process. BACKGROUND OF THE INVENTION [0003] Pressure die casting is a well known process in which molten metal is forced under pressure and heat into a mold cavity of a mold of a die casting machine. The molten metal is introduced in a shot sleeve, and a plunger forces the metal into the mold cavity through a shot sleeve. While in the mold cavity the molten metal solidifies resulting in a molded part having a geometry conforming to that of the mold cavity. After the part is formed, it is then ejected from the mold cavity. Molded parts so produced have excellent dimensional tolerances, structural integrit...

AI Technical Summary

Benefits of technology

"The present invention provides a new and improved mold release agent for die casting. This agent is made of a single component silicone wax compound that has specific melting and molecular weight properties. The method of application involves placing the compound in the shot sleeve of the die casting machine and introducing molten material into the mold cavity through the plunger. The use of this new mold release agent can lead to higher quality casts and is also environmentally friendly."

Problems solved by technology

Friction may interfere with the efficient movement of the plunger through the shot sleeve.

This can result in stuck castings, soldering or other damage to the molded parts.

Further, low molecular weight lubricants have problems if used as mold release lubricants for die cast parts where secondary operations are performed, such as painting.

The powdery mold release agent is applied to the mold cavity halves electrostatically and in a vacuum, requiring incorporation of expensive capital equipment.

The composition of the lubricant is not defined, but it does state that “oily type lubricants cannot be used in the process.” Petroleum oil based mold release lubricants (i.e., “oily type lubricants”) have been used in the past, but have fell out of favor due to safety and environmental concerns.

Engine oils generally are not used for die cast lubrication due to the more extreme environment of die casting, which can include exposure to temperatures over 1300° F. At such temperatures low molecular weight materials such as those disclosed in Seiki may not provide adequate and uniform lubrication, especially in parts with relatively complex geometries.

However, the large amount of water creates enormous amounts of waste effluent which must be cleaned from the machine and which must be removed and treated at additional expense.

Also, large amounts of water cause thermal cycling of the mold halves, significantly shortening mold life.

In addition, uneven application of mold release agent can result in uneven temperatures across the mold, which may deleteriously affect part quality.

However, such two-component lubricants may not provide a continuous and uniform layer of lubricant on a die cast part, especially in molds with high temperatures and / or relatively complex geometries, as the waxes may pull to the hottest parts of the die.

Also, the use of the waxes disclosed in Kok et al may be more likely to burn at high temperatures, resulting in environmental release and possible marring of the surface of the die cast part.

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