Need info on coining 1

[Timelord]

(also posted in Machines and machining engineering)

I'm looking for information on coining. The application is a vending machine that makles coins as you watch. What I need is some information on the tonnage required for coining and if the speed is critical. I have seen coining presses in the mint on TV and they operate at high speed. Can you press a coin slowly? I want to use hydraulics with a small motor (cycle time around 30 to 45 sec.). Does anybody know of any good sources of information on the coining process either on the web or books?

TIA

Timelord

 

[ornerynorsk]

Hydraulics and slow speed work fine. There is a nice little medallion press in the Statue of Liberty base gift shop that produces a souvenir coin with a minimum of relief and impression, approximately half-dollar sized, planchet is annealed copper about .090 to .100, and the press develops 200 tons. You would need much more tonnage for a sculpted bas-relief such as the $20 St Gaudens or similar. A dime is minted approx under 89 tons of force. Hope this helps!

 

[ubrales]

Coins can be produced at slow speeds or at high speeds. In both cases the process is different. At slow speeds, the force is utilized to cause the metal to yeild, work hardening occurs throughout the coining process and therefore higher tonnages is required. At high speeds, the process is an impact process and deformation occurs before the metal has an opportunity to work harden, and coining can be done at lower tonnages.

In all types of coining, the press must be capable of absorbing the impact load or the coining tonnage without a breakdown of the lubricant film in the bearings - in other words, make sure it is a coining press.