Sulzer Pump Service Reliability Tips
Material Galling & Hardness Differential
What causes galling of materials?
A gall results from wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together.
Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of the crystal structure beneath the surface.
Why a Differential?
In general, for good galling resistance, a minimum hardness differential up to 100 Brinell Hardness Number (BHN) is needed. While API 610 requires a minimum 50 BHN differential, Sulzer improves on that by requiring 100 BHN differential.
However, if both rotating and stationary materials are very hard (>400 BHN per API 610), then the differential is not as crucial to maintain.
Many other factors go into establishing close clearance material combinations, and although non-galling performance is typically a priority, it might not be the only factor.
Sulzer has vast testing, research and experience in material couple choices for providing the best performance for your situation.
E10441 en 11.2016, Copyright © Sulzer Ltd 2016
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