Technical Information

Surface Hardness

The mirror like surface finish generated by roller burnishing, combined with a hardened and denser surface, substantially increases part wear, life and corrosion resistance. The added strength improves the part’s fatigue resistance, resulting in decreased failures. The cold working condenses the grain structure of metal, producing an increase in surface hardness from 5% to 10%, within a penetration of 0.025mm to 0.75mm on the part’s surface.
Burnishing can be carried out on parts with a surface hardness up to 45 HRc.

The pattern diagram presents the effects of the roller burnishing process. As the roll contacts the pre-machined surface in area A it starts to apply a pressure to the material. Within area B the pressure increases until the yield point of the material is exceeded and a plastic deformation takes place within the depth D. Once the material has been subjected to the maximum compressive load the stresses reduce in area C leaving a smooth surface with compressive residual stress. These stresses can reach up to 0.75mm below the surface E resulting in increased surface hardness.

Before and After
Surface CHart

Surface Finish

By transferring the force applied by the hardened roller to the surface of a work piece, a plastic deformation of the material occurs. Although this force is relatively small, the use of highly polished rotating rolls in the tool generates sufficient force to deform the material beyond its yield point and produce a smooth surface having displaced the high peaks into the low valleys generated by the pre-machining process. The texture generated provides a surface with a high bearing capacity and low abrasion which is ideal for electric motor shafts and hydraulic and pneumatic valves.

The surface finish generated by boring, honing and grinding creates a peak and valley effect. The weaker peaks wear down and the result is a loose fit on mating parts. The sharp peaks will also cause premature wear in sealing materials used in hydraulic and pneumatic cylinders.

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