Loading in Grinding: Chemical Reactions in Steels and Stainless Steels

Abstract

Loading in grinding – both chemical, in which the grit and the oxidized surface of the workpiece react, and mechanical, in which chips become embedded within the pores of the wheel – causes significant problems such as increased wheel wear, higher grinding temperatures, and poor surface finish. This paper investigates the chemical reactions that occur between the aluminum-oxide abrasive and both steel and stainless steel and their effect on wheel wear and grinding forces. Tests were done on mild steel and stainless steel under dry conditions, with poor and moderate cooling and in the presence of steam. X-ray diffraction was used to measure aluminum deposits on the contact and rear faces of the chip and on the workpiece in regions where cutting was dominant and/or plowing and rubbing were dominant. Normal and tangential forces and wheel wear were measured and loading was quantified visually. Loading in stainless steels was found to occur almost immediately due to the mutual solubility of Cr2O3 and Al2O3 during the rubbing and plowing regimes, but during cutting there was not sufficient time to form an oxide layer. Coolant drastically reduces loading in stainless steel. Steam acts as a catalyst in oxide-layer formation, decreasing loading in regular steels and increasing loading in stainless steels. Wheel wear due to loading was found to be sporadic, with large groups of grits being ripped out of the wheel. Assessing loading via the visual appearance, or “blackness”, of the wheel can lead to incorrect conclusions.