Industrial Lubrication and Tribology

W.F. Sales; G. Guimarães; Á.R. Machado; E.O. Ezugwu

2002 Industrial Lubrication and Tribology

doi: 10.1108/00368790210424121

Many machining researches are focused on cutting tools mainly due to the wear developed as a result of high temperatures generated that accelerate thermally related wear mechanisms, consequently reducing tool life. Cutting fluids are used in machining operations to minimize cutting temperature although there is no available indicator of their cooling ability. In this study, a method to determine the cooling ability of cutting fluids is proposed. A thermocouple technique was used to verify the chip‐tool interface temperature of various cutting fluids during turning operation. The method consists of measuring the temperature drop from 300°C up to room temperature after heating a standardised AISI 8640 workpiece and fixing it to the chuck of a lathe and with a constant spindle speed of 150 rpm the cutting fluid was applied to a specific point. The temperature was measured and registered by an infrared thermosensor with the aid of an AC/DC data acquisition board and a PC. The convective heat exchange coefficient, h , was determined and used to classify the cooling ability of the cutting fluids. The machining tests showed that the application of the fluid with better cooling ability will not always guarantee lower chip‐tool interface temperature.

Ruijun Zhang; Shenghua Li; Yuansheng Jin; Yucong Wang; Simon C. Tung

2002 Industrial Lubrication and Tribology

doi: 10.1108/00368790210424158

The frictional behavior of a Mo alloy‐coated piston ring sliding against cast iron cylinder bore was recorded as a function of temperature using a reciprocating tribotester and a fully formulated synthetic engine oil, with and without a friction modifier. It was observed that, as temperature increased in a stepwise mode, friction coefficients in the presence of MoDTC exhibited two local minimal values. Only one minimal friction coefficient value at 340–355 °C (μ = 0.065) was observed in the absence of MoDTC. Chemical characterization of worn tracks of the cylinder bore using reflected FTIR spectroscopy, Raman spectroscopy and ESCA, indicated that both the base stock and the tribological additives, ZDTP and MoDTC, experienced tribochemical reactions yielding MoO 3 , MoS 2 and carbonaceous species as temperature ramped up stepwise. MoO 3 and MoS 2 reaction film formation are partially responsible for the local minimal friction coefficient found at the lower temperature and the ratio of the ordered carbon species accounts partially for the other local minimal friction coefficient found at the higher temperature.

Walter Holweger

2002 Industrial Lubrication and Tribology

doi: 10.1108/00368790210424176

Demand on for‐life lubrication needs to control all mechanisms being present in the tribocontact. Herein we present elementary chemical mechanisms supported by lubricants leading to effective destruction of machinery elements over long time. The chemical process may overtake all other essential mechanisms in for‐life lubrication. As far as known these mechanisms offer a fascination world of unknown reactions.