Beryllium copper and H-13 tool steel are the best choices for plunger tips. BeCu is the overwhelming choice and has almost 10X the heat transfer properties of H-13. Even though H-13 does have slower heat transfer it develops a higher hardness in heat treatment, 48-50 Rc. It may also be nitrided. With very good alignment and a graphite lube, steel tips can give exceptionally long life. The clearance for BeCu plunger tips should be .0009 per inch of diameter.
Plunger tips must have an adequate internal cooling chamber and should have .100 inch radius in all corners of the ID to lessen chances of fatigue and cracking. A rough, as cast, ID is best for good water flow. Plunger tips may be reworked but should not be turned down to less than 1/2 inch wall. It should be noted that the shoulder must always be square to the back of the tip.
Water cooling must be monitored. Water temperature should be about 65 degrees and 50 psi pressure.
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