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Abstract
A new method for lubricating the tools of a pelletizing press is described, based on the use of dry lubricants mixed with polystyrene balls as a carrier. The solid lubricant is introduced into the die, applied to the walls of the compacting chamber by the movement of the punches, and then ejected following the normal pelletizing cycle. Hence, a very thin film of lubricant remains on the walls and makes it possible afterwards to pelletize a uranium dioxide powder. The process has been applied to a double rotary press in which one half is used to “pelletize” the lubricant and the other half to obtain the required production of UO2 pellets. Pellets have been fabricated from a loose virgin powder which had not been granulated.
The process does not lead to contamination of the UO2 pellets because the deposit of lubricant is very thin and uniform. It is applicable whatever the shape and the dimensions of the pellets may be, owing to the good flow rate of the polystyrene balls. Moreover, the polystyrene compact splits as soon as the applied pressure is released since the balls are elastic; a closed cycle can therefore be operated. Other advantages of the process are also described. The reproducibility of the UO2 pellets fabricated by this technique indicates its efficiency.
Notes
* Manuscript received 2 June 1969. Contribution to a Symposium on “Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy” to be held in Eastbourne on 24-26 November 1969.