Ferro-fluid seal for shaft in bore - consists of ring magnet fixed tightly in outer ring of polyamide or polypropylene where radial width of magnet exceeds its thickness

摘要

A ferro-fluid seal has a radially magnetised ring magnet attached to an annular carrier of rigid plastic material, and the axial thickness of the magnet is less than its radial width. The pref. material for the carrier ring is polyamide or polypropylene. A seal for a revolving shaft (3) in a bore (8) has a ring magnet (1) fixed to an outer carrier ring (2) of polypropylene. The gap round the shaft (3) is filled with ferrofluid liq. (10). The ratio of thickness (L) of the magnet (1) to its radial width (R) is 0.4, where the thickness is 0.5mm. The polymer ring (2) has dimensions such that it is pressed into the bore (8) and then provides a tight fit between the o.d. of the carrier ring (2) and the bore (8). The magnet (1) is made of sintered Sr or Ba ferrite or a sintered rare earth magnetic material. It can also be made of ferrite/polymer cpd.; its radial width is arranged so that at least 50% of the remanent field strength of the magnet is obtd. without magnetic back-circuit in the sealed gap. ADVANTAGE - The prod. is simple to make. It has a high pressure resistance. It can be used with very small axial length.