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Grinding Cracks of Ball Screw
Cause analysis of grinding cracks after IF quenching of ball screw

Ball screw IF quenching grinding cracks reasons:

1, Bad raw materials

The main performance of the GCr15 material network carbide level of tolerance or the spheroidizing annealing organization is not qualified (with lamellar pearlite). Through the analysis of non-uniformities crack screw carbide, microstructure analysis, appear network carbide level of tolerance or the spheroidizing annealing organization not qualified screws are about 40% of the total. Carbide non-uniformities cause the screw srrface after induction hardening exist the surface hardness and surface stress uneven, more concentrated carbide parts the internal stress is more concentrated. When screw grinding, since the part of the internal stress that exceeds the yield strength of the material, it will produce grinding cracks. Lamellar pearlite exist, causing screw surface after induction hardening coarse grains, reducing the yield strength of steel, when screw grinding at the position of internal stress exceeds the yield strength of the material will produces grinding cracks.

2, Screw IF quenching bad heat treatment

Mainly of quenching temperature too high or tempering insufficient. Through analysis, statistics, resulting screw grinding cracks about 20% to 30% of the total screws. When the large ball screw IF quenching, intermediate frequency power output is too high, quench speed is too slow, can possible make screw quenching temperature too high, the screw after quenching martensite level partial upper limit (martensitic level 5), and possibly even exceeded (martensite ≥5 level). Coarse martensite steel will be reduced by 40%. When screw grinding the process parameters are not standardized, the grinding heat generated during grinding cause "secondary tempering" of the screw surface. Moreover, the grinding heat even raised the screw surface temperature to reach the screw materials "hardening temperature", in the cooling effect of grinding fluid, screw surface to form a "secondary hardening", causing the surface coarse grains, reducing the yield strength of steel, causing the screw surface cracks. After the large ball screw quenching, hardened layer deeper, internal stress (including heat stress and transformation stress) is larger, insufficient tempering (tempering temperature is low or tempering time is short), screw quenching the formation of internal stress eliminating incomplete. Screw quenching, tempering, internal residual stress and grinding stress generated during grinding superimposed, when the superimposed stress exceeds the yield strength of steel, will form a crack in the surface of the screw.

3, Screw grinding the process parameters not standardized

The reason cause the grinding cracks of screws are about 30% to 40% of the total. Screw grinding process parameters irregularities, the grinding heat generated during grinding cause "secondary tempering" on the screw surface. Moreover, the grinding heat even raised the screw surface temperature to reach the screw materials "hardening temperature", in the cooling effect of grinding fluid, screw surface to form a "secondary hardening", causing the surface coarse grains, reducing the yield strength of steel, causing the screw surface cracks.

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