Lead screw and nut assemblies for high-vacuum applications

Abssac has long been associated with supplying products into the nuclear physics industry and has recently supplied lead screw and nut assemblies for use within a high-vacuum diagnostic tool for particle accelerators.

The lead screw assembly is used to displace two disk-like structures that captivated a precision aperture, which, in turn, shapes a supersonic gas jet passing through them. Changing the distance between the disks - within fine tolerances - enables the tailoring of the gas jet shape for diagnosis purposes. Some of the criteria of the application are finite repeatable linear accuracy, reliability, and the need to work continuously in a vacuum environment of 10-6 mbar.

The high-vacuum environment also means that out-gassing of the plastic materials employed for the nut could pose a problem to final diagnostics. After some consultation with various material suppliers, the material chosen for the nut was Toray Torelina PPS resin with GFRP (Torelina Polyphenylene Sulfide). This high-performance resin provides excellent heat resistance, flame retardancy, chemical resistance and physical strength.

Abssac has also supplied the 2mm pitch flanged nut already degassed and certified using a GCMS (gas chromatograph mass spectrometer), which recorded the emitted compounds by mass number on a certified calibrated graph. After a two-hour treatment and subsequent GCMS analysis, the nuts were ready to be fitted to the 6mm diameter stainless steel screw and shipped in a sealed atmosphere packaging.