The effect of an organic pentasulfide EP additive in turning and milling operations

Coopération avec Ecole Centrale LyonBecause a cutting fluid could be equally used for different cutting operations, this study proposed to investigate the behavior of a well-known extreme-pressure additive (pentasulfide) in both turning and milling operations of a steel workpiece. The experimental approach is based on the coupling of mechanical tests (turning, milling, and tribological tests) with physico-chemical characterizations (Auger Electron Spectroscopy and X-Ray Photoelectron Spectroscopy) of the friction surfaces (chip and tool). In the case of milling, it was shown that the presence of a pentasulfide additive has a beneficial effect on the specific cutting energy (kc) and flank wear (Vb). These results are correlated with the presence of iron sulfides (FeS and FeS2) on the flank face of the cutter mill and on the chip face in contact with the mill. No such additive effects are found in case of turning. A lubrication model is proposed for the case of milling based on an indirect lubrication of the tool/workpiece and tool/chip contacts due to the transfer of iron and its reaction with sulfur compounds to produce iron sulfides. Because milling is a discontinuous cutting process, this lubrication mechanism is much more efficient than that observed in turning. Indeed, the tool faces are re-fed iron sulfides each time they leave the workpiece

Tribological aspect of lubrication in form tapping of high strength steel

Collaboration avec le LTDSThis study aims at analyzing the tribochemical mechanisms of lubrication during the process of form tapping and consequently optimizing the formulation of the lubricant. In order to correlate the tribochemical reactions with the performance of a lubricant, we measure the alteration of tapping torque according to ASTM D5619 standard. The objective of the study also relates to the identification of the additives and the association of their properties to the performance of lubrication. The goal is to characterize the nature of the tribofilm created at the bottom of the threads which is the zone the most severely affected by the working tool. X-ray Photoelectron Spectroscopy (XPS) is used to characterize the surface of formed threads. This study demonstrates a link between the sulphur reactions on the metallic surface and the friction reducing performance of lubricant during form tapping.Thèse CIFRE TOTA

Tribological aspect of lubrication in form tapping of high strength steel

Collaboration avec le LTDSThis study aims at analyzing the tribochemical mechanisms of lubrication during the process of form tapping and consequently optimizing the formulation of the lubricant. In order to correlate the tribochemical reactions with the performance of a lubricant, we measure the alteration of tapping torque according to ASTM D5619 standard. The objective of the study also relates to the identification of the additives and the association of their properties to the performance of lubrication. The goal is to characterize the nature of the tribofilm created at the bottom of the threads which is the zone the most severely affected by the working tool. X-ray Photoelectron Spectroscopy (XPS) is used to characterize the surface of formed threads. This study demonstrates a link between the sulphur reactions on the metallic surface and the friction reducing performance of lubricant during form tapping.Thèse CIFRE TOTA

Evaluation of Lubricant Viscosity and Base Oil Effects by Form Tapping Test

In order to correlate the effect of lubricant viscosity and base oil on the efficiency of a lubricant, we measure the variation of tapping torque according to ASTM D5619 standard. Three fully formulated lubricants containing the same additive package but having different viscosities are tested in the first part of the experiment. The effect of chemically active and chemically non-active paraffinic base oils combined with a sulphur additive is studied in the second part. The nature of the tribofilm created at the bottom of the threads formed during the second part of the study is characterized by X-ray Photoelectron Spectroscopy (XPS). The aim is to associate the surface analysis results with the efficiency obtained during the form tapping tests. The results show that the lubricant viscosity does not have any influence on the tapping torque values whereas physico-chemical interactions between different base oils and a sulphur additive can modify importantly the overall efficiency of lubricant

Mechanical and physico-chemical study of sulphur additives effect in milling of high strength steel

The authors would like to express their appreciation to the TOTAL France Company for the technical and financial contribution to this study and to Béatrice Vacher for TEM images.Most machining operations require the presence of a cutting fluid in order to ensure their success due to the intensity of thermal and mechanical conditions generated on the cutting tools. In some cases of severe machining, the fluid contributes to lubrication in a physicochemical way thanks to the additives it contains. This study aims to analyze the tribochemical mechanisms of lubrication during milling operations and subsequently at optimizing the lubricant formulation. The objective of this study is also to identify and to compare, the performance of various Extreme Pressure (EP) sulfur-containing additives, and to understand their action mechanisms in metal cutting. Physico-chemical analyses are carried out by means of Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) with the purpose of detecting the nature of additive reaction products on the surfaces involved in cutting and correlating them with the milling results. The polysulfide additive is found to exhibit the best efficiency (decrease of specific cutting energy and tool wear) in the tested milling conditions. A correlation is found between the additive chemical reactivity and the milling test results.Thèse CIFRE TOTA

Evaluation of Lubricant Viscosity and Base Oil Effects by Form Tapping Test

In order to correlate the effect of lubricant viscosity and base oil on the efficiency of a lubricant, we measure the variation of tapping torque according to ASTM D5619 standard. Three fully formulated lubricants containing the same additive package but having different viscosities are tested in the first part of the experiment. The effect of chemically active and chemically non-active paraffinic base oils combined with a sulphur additive is studied in the second part. The nature of the tribofilm created at the bottom of the threads formed during the second part of the study is characterized by X-ray Photoelectron Spectroscopy (XPS). The aim is to associate the surface analysis results with the efficiency obtained during the form tapping tests. The results show that the lubricant viscosity does not have any influence on the tapping torque values whereas physico-chemical interactions between different base oils and a sulphur additive can modify importantly the overall efficiency of lubricant

Experimental simulation of chemical reactions between ZDDP tribofilms and steel surfaces during friction processes

International audienceFriction tests are performed in a controlled environment (Ultra High Vacuum), between steel surfaces and a ZDDP tribofilm at different contact severities. According to AES analyses, evidence of chemical reactions activated by friction is given. The reaction of the ZDDP tribofilm with the native iron oxide could partially explain its antiwear behavior