Pump Packing Sleeves Material
Packing sleeves are surrounded in the stuffing box by packing. The sleeve must be smooth so that it can turn without generating too much friction and heat. Thus, the sleeve materials must be capable of taking a very fine finish, preferably a polish. Cast-iron is therefore not suitable. A hard bronze is generally used for pumps handling clear water, but chrome or other stainless steels are sometimes preferred. For pumps subject to abrasives, hardened chrome or other stainless steels give good results. In most applications, a hardened chromium steel sleeve will be technically adequate, and the most economical choice. For severe or unusual conditions, coated sleeves are used. Ceramic coatings, applied using a plasma spray process, have also been used. Chromium oxide and aluminum oxide are the most common ceramic coatings. Both are extremely hard and resist abrasive wear well.
Ceramic coatings have been replaced in some applications by tungsten carbide coatings applied using a high-velocity oxyfuel (HVOF) process. The superior impact resistance and bond strength of these coatings is well documented. Another coating that is widely used on pump sleeves is a nickel-chromium-silicon-boron self-fluxing coating. This coating has a good resistance to galling and moderate resistance to abrasive wear.
Sleeves intended for coating should be machined with an undercut, so that the coating does not extend to the edge of the sleeve. This will prevent chipping at the edge, especially with the more brittle ceramic coatings.