Experimental Investigation of Transfer of PTFE on Bearing Steel

Polytetrafluoroethylene (PTFE) lubricant is commonly applied for dry contact due to its low friction properties. However, low strength properties can lead to short service-life due to high wear rate, especially under high contact load. The method to add PTFE into a solid contact during operation as a transfer layer has been one of the major attempts in this field. This study aims to investigate the influence of operating parameters, i.e., revolution cycle, sliding speed and applied load, on coverage area of transfer PTFE on the bearing steel (AISI 52100) disc. The experiments were performed on the modified pin-on-disc apparatus using a unidirectional ground disc. The areas with disc grinding direction parallel (parallel morphology) and perpendicular (perpendicular morphology) to the pin sliding direction were both examined. The ascending of transfer coverage area with an increasing revolution cycle within the first 1000 cycle was observed on the area with a sliding direction perpendicular to the disc grinding direction while the descending of transfer coverage area was found on the parallel case. The further increase in the revolution cycle led to only a small change in the transfer coverage area. With more revolution cycles, the pin wear rate increased as a decrease in transfer coverage area formed on the counter-face. Research suggested that the amount of transfer coverage area decreased with increasing sliding speed. However, it could be increased by increasing the applied load.

ABRASIVE DISC IMPREGNATION

In order to solve the problems of the effectiveness increase in parts machining with grinding there are developed impregnated abrasive discs. The impregnated grinding disc application allows increasing effectiveness, intensifying a process, increasing surface smoothness with minimum defects as compared with non-impregnated disc grinding. The investigations of grinding processes were based on the regulations of the theory of friction and wear, theory of cutting, physical-chemical mechanics of materials, physical and colloid chemistry, non-equilibrium thermodynamics. Physical-chemical processes accompanying grinding with impregnated grinding discs are investigated. It is defined that a cutting ability of a grinding disc and its durability increase, glazing decrease and quality improvement of a part worked take place. New methods for obtaining a composition for impregnation are tested. It is substantiated theoretically and confirmed experimentally grinding effectiveness increase at the introduction into an abrasive mass composition a film-forming matter – chromium diiodide.

Quality Index of Multi-Disc Grinding Process of Grainy Biomass

The main aim of the grinding process is size reduction. For such formulated purpose of grinding, the particles dimensions after grinding process are the major quality determinant indicated in many works concerning size reduction. In this paper original quality index integrating size reduction and energy consumption in the grinding process was proposed. The aim of the study is to create method for grinding process quality assessment. The problem was formulated as a question: (1) is it possible to create mathematical description of grinding process quality? (2) what grinding parameters influence on the grinding quality index? To resolve the problem, original quality index was developed and experiment on a multi-disc mill was conducted. On the basis of obtained results it was found that discs angular speed affects the grinding process quality.

Development of an In-House Test for Nut Integrity in F-Type Wheels

Nut embedded disc grinding wheels, also known as disc grinding or F-Type wheels, are required for many production jobs. Nut pull-out is a common problem encountered in disc grinding wheels. The present work proposes a simple fixture, using which the integrity of the nut in the grinding wheel can be assessed. This method can be adopted by any grinding wheel manufacturer for a realistic estimate of nut pull out strength in double disc grinding wheels.

Influence of Hand Disc Grinding on Surface Integrity of Nickel-Based Alloys: Numerical Approach

For complex part geometry, hand grinding is one of finishing and super finishing process the most used in mechanical industry. Surface integrity is today one major concern for industrials. The surface integrity is defined by a set of important characteristics of ground surface as surface geometric parameters (roughness, …), mechanical behaviour of the subsurface (hardness, residual stress, …) and structural changes of the material in the near surface. High heat and pressure, high strain and strain rate observed during hand grinding process, strongly influence surface integrity. Therefore, the surface behaviour, in terms of resistance to corrosion and crack initiation depends on how the process was conducted. The purpose of this study is to understand the effects of thermal and mechanical plastic deformation induced on the surface of components. The action of the disc-grinding wheel on the workpiece is modelled by a moving heat flux on the surface. The challenge is to be able to find the shape and intensity of thermomechanical load entering the workpiece in accordance with the hand disc grinding process and taking into account specific parameters of the process. In a first part, a mechanical description of the action of the disc-wheel on the surface is proposed in order to develop an analytic formulation of the grinding power and the heat flux density. They are function of the disc-grinding wheel velocity, the feed speed and the applied forces. This expression is then used in a finite element modelling to perform thermomechanical simulations of the hand disc-grinding process. In a first stage, heating and cooling are computed. They give maximum temperature reached, temperature gradients and cooling kinematic. In a second stage, thermomechanical computation is conducted in order to compute residual stresses induced by this abrasion process. A discussion based on experimental results obtained by XRD method is then proposed and some local explanation are given on the way the material structure has changed leading to a structural hardening in the 50 first microns beneath the ground surface.