Core pins can be one of the hardest parts of a mold to cool, given their generally small size, which doesn’t always allow for effective water cooling. David LeMaistre, v.p. of Crafts Technology, Elk Grove Village, Ill., told the audience at the recent Molding 2016 Conference in New Orleans (see this month's Close Up) that there is at least a partial solution. “Some customers call it a game-changer,” he said. For the past eight years, the company has offered custom core pins made from tungsten carbide in a cobalt binder via powder metallurgy. It has sold around 2000 of these pins to about 50 customers.
One outstanding characteristic of this cemented tungsten carbide is thermal conductivity equivalent to beryllium copper alloys, which had reduced cycle time by 24% to 40% in some applications. What’s more, these pins provide extremely low deflection, owing to stiffness two to three times that of tool steel, and substantially greater wear life, owing to the hardness of tungsten carbide. Low coefficient of friction helps with release. The latter property has helped customers with sticking problems and “squealing” on ejection of parts like syringe barrels.
Longer wear helped a molder of 30% glass-filled PP, whose Be Cu core pins lasted only four to five weeks. The carbide pins have run 24.7 for over a year now on the same cycle with no sign of wear and considerable savings in downtime.
Low deflection was a benefit for a molder of narrow blood tubes in 64 cavities, which experienced 0.020 in. deflection with standard pins. The carbide pins deflected less than 0.001 in., which allowed a 33% reduction in cycle time from 11.8 to 7.8 sec.