Double-check materials specs before you order hot runners

By: 
October 11, 1998


Figure 1. Copper alloy torpedo tip shows the extensive wear caused by a 43 percent glass-filled nylon (right), as compared to a tungsten carbide alloy torpedo (left).

Figure 2. This tungsten carbide alloy tip, removed after about 350,000 shots, shows insignificant wear.

Two four-cavity molds were built for Eaton Controls (Kendallville, IN) to mold cams and top plugs used in a water level control switch. The molds were built to run about 1 million parts a year, and were equipped with copper alloy hot tip systems from Mold-Masters. However, then a seemingly routine application turned ugly. You see, the material being run was not originally specified as being a filled grade-an abrasive, nearly 45 percent glass-filled grade of nylon 6/12 to be more precise. You probably can guess what happened. Even with nickel plating, premature wear of the copper torpedo tips occurred after only 8 to 24 hours worth of production. The tips were, in the worst case, wearing out after fewer than 1500 shots. Eaton Controls was faced with poor process control, constant maintenance downtime, and the expense of replacing the tips.

Fortunately, Eaton Controls' supplier had a very special kind of technological expertise it could bring to bear to solve the problem. Mold-Masters powder injection molds metals and ceramics in-house for runnerless system components. It uses its hot runners to mold its hot runners, if you will. Its PIM compounding and production expertise enabled Mold-Masters to develop new high-performance tungsten carbide alloy torpedo tips. Tungsten alloy tips stand up much better to abrasion and corrosion from additives like flame retardants than, say, beryllium copper and even high-speed steel, and they also provide high thermal conductivity for precise gate temperature control. Tungsten carbide is extremely strong (68 to 70 Rockwell C).


So Mold-Masters replaced the copper alloy torpedo tips in Eaton Controls' tooling with its injection molded tungsten carbide alloy tips. The result? The replacement tips have been installed now for more than six months, and, so far, the molds have run more than 350,000 shots, 1.4 million parts, without a hitch. Part quality is flawless and no significant wear has been reported.

Figure 3. Eaton Controls' parts exhibit good gate vestige despite the very abrasive nature of the highly filled engineering resin in which they are run.

In addition, tungsten carbide alloy has since been standardized for use on Mold-Masters hot tip systems for tough engineering plastics, and also is molded for certain bimetallic valve liners. Mold-Masters recommends use of its tungsten carbide components in applications where demanding thermal and physical performance properties are required.

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