Thread construction for rotary worm compressor- expansion machines

Abstract From the Canadian patent

A rotary worm fluid working machine in which a casing enclosed rotor, cooperable with one or more rotary pinions is, provided with a plurality of spiral thread grooves each having convergent side surfaces so that teeth on the pinion wheel enter the thread grooves with a clearance diminishing to contact prior to tooth exit. The clearance reduces shock loading on the pinion wheel and reduces pinion wheel tooth seal wear in conical worm machines due to relatively lower rotor-pinion wheel tooth velocities in the region of tooth seal-rotor contact.