Application of HB3000+ Vibration Stress Relief in Eliminating Stress in Grinding Machine Gear Ring

Vibration stress relief, also known as vibration stress elimination, is a method of subjecting workpieces, including castings, forgings, welded components, etc., to vibration treatment at their natural frequencies for several to tens of minutes, in order to eliminate and homogenize their residual stresses and achieve stable dimensional accuracy. In the production of cement equipment manufacturing enterprises, the elimination of residual stress in mill gears and their attachments is crucial for the service life of the equipment. Due to production scale, cycle, and efficiency considerations, vibration stress relief has gained significant attention as a method for eliminating and homogenizing residual stress in workpieces. Since the application of this method in the production of grinding machine gear rings in recent years, our company has made remarkable achievement in improving the deformation resistance of workpieces, workpiece accuracy stabilization, mechanical properties enhancement, funds saving and quality improvement.

1. Analysis of the Mechanism of Stress Generation in Castings

The generation of residual stresses in casting is the result of the combined effects of thermal stress, structural stress, which is influenced by the shape and size of the workpiece and casting technology, and tissue stress caused by material heterogeneity in structure and composition. Among these, the structural stress formed during solidification and cooling of the workpiece is not only related to the uneven wall thickness and asymmetric shape of its various parts, but also to casting technology such as pouring and molding. The residual stresses determined by structural conditions are illustrated from three aspects below:

(1) Residual stress maintaining balance within the cross-section of the workpiece

Taking a casting cylindrical workpiece, such as a gear ring, as an example, residual stresses are generated by the temperature gradient formed due to faster cooling of the surface and slower cooling of the core. During initial solidification, the surface cools rapidly and contracts, experiencing tensile stress, while the core remains in a compressive stress state (as shown in Figure 1a). At this time, the core, at a higher temperature, exhibits plasticity and undergoes compressive plastic deformation under the influence of compressive stress, reducing the actual size of the core. As cooling continues to a certain temperature, the core contracts, experiencing tensile stress due to the constraint of the already hardened surface, while the surface experiences compressive stress (as shown in Figure 1b).

(2) Residual stress maintaining mutual balance between structures.

(3) Residual stress caused by the resistance of the molding sand.

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