The susceptibility of wood-cutting tools to corrosive wear☆
Abstract
The machining of green (wet) wood results in unique cutting tool problems. The non-homogeneous multicomponent nature of cutting tools and the water and water solubles in the wood result in electrochemical action. Both mechanical and corrosive tool wear mechanisms are thus active in such wood cutting.
The relative magnitudes of mechanical and electrochemical effects were determined by analyzing tool life data in terms of simple models of the individual wear mechanisms. It was demonstrated that under conditions conducive to electrochemical action the major part of the total wear was due to corrosion.
Some of the factors determining the corrosion susceptibility of cemented carbide tools were studied by measuring the electrical potentials developed between tool components in solutions typical of those found in various woods. The results of these tests indicate that electrochemical action can be influenced by changing the tool binder material, the relative percentage of the tool binder material in the tool and the carbide grain size.
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Cited by (19)
Prediction of hardmetal corrosion based on the binder response
2024, International Journal of Refractory Metals and Hard MaterialsFor 100 years WC-Co has been the quintessential hardmetal, finding extensive application whenever high hardness and wear resistance are required. However, recent concerns regarding health and economic factors have motivated both industry and academia to explore alternative composites. Consequently, numerous hard phases and metallic binders are currently under evaluation. To expedite and streamline the development process, a crucial question arises: “Can the corrosion resistance of hardmetals be predicted based on the electrochemical behavior of their binders?”. To help answer this question, this work compares the corrosion resistances of various hardmetal composites (WC-Co, WC-Ni, WC-CoNi, WC-CoCr, WC-NiCr, WC-CoNiCr, WC-NiCrMo, and WC-FeCoNi) to the corrosion resistances of binder analogues (Co, Ni, CoNi, CoCr, NiCr, CoNiCr, NiCrMo, and FeCoNi) in a 0.5 M NaCl solution using electrochemical techniques: open circuit potential monitoring, polarisation curves and galvanic current between WC and binder measured with zero resistance ammeter (ZRA).
According to the wood species and the type of metallic materials, the wear of woodcutting tools is very different. The metallic nature of cutting tools, the water and water-soluble components in the wood result in an electrochemical mechanism of corrosion. Of course, both a mechanical wear and an electrochemical action are responsible of the total wear of metallic tools. The objective of this study is to characterise the electrochemical action of the wood medium on the corrosion of the woodcutting tool materials.
To carry out the corrosion tests, a corrosive medium is obtained by infusing wood shavings into water to obtain a juice of wood. In a second step, we have selected several metallic materials used in woodcutting and a wood specie, namely oak. Electrochemical measurements (Rp, Ecorr and i = f(E) curve) were carried out during 24 h in a medium containing a water-soluble extract of oak (=an oak juice). The electrochemical behaviour of each metallic material was characterised and the morphology of the corroded surface was observed by SEM. It is shown that the electrochemical corrosion is not negligible and can be very important on cutting materials. Further experiments are in progress to characterise the effect of the mechanical wear by tribocorrosion measurements.
WC-based hardmetals are materials that are widely used in applications where abrasion resistance is required. This paper describes the results of tests that were performed using a modified ASTM G65 rubber wheel test system incorporating an abrasive (silica sand) and media (sulphuric acid, deionised water, and calcium hydroxide solution). The first of these media was used in order to simulate conditions found in ash disposal equipment found in coal-fired power stations. The calcium hydroxide solution was intended to simulate conditions found in forming tools used in the manufacture of ceramic roofing tiles.
Under very acidic conditions (pH 1.1), undermining of WC grains by binder dissolution appeared to be the rate-governing step in determining volume loss. Under mildly acidic conditions (pH 2.6 and 6.3) there was more evidence of WC grain fracture and correspondingly less of binder dissolution. Exposure to the alkali (pH 13 Ca(OH)2 solution) caused the least wear.
Results were correlated with physical and microstructural and parameters commonly used for quality assurance in the hardmetal industry. Corrosion–abrasion synergies were also evaluated using the same test rig in conjunction with the respective acidic solutions, but omitting the silica sand.
These results are complemented by SEM examination of wear surfaces and of metallographically polished cross-sections of wear surfaces, and by bend strength evaluation of samples after simultaneous exposure to the various media and silica sand and the media in isolation.
This work is focused on developing an understanding of the wear mechanisms of cemented tungsten carbide tools in machining particleboard. Cutting experiments were conducted on several grades of cemented tungsten carbide tools using a high speed lathe, and their wear characteristics were determined. It was found that wear occurred predominantly on the clearance face of the tools for most grades tested. It was also found that the amount of wear after the same cutting distance correlates well with the bulk hardness of the tool material. The amount of wear generally decreased with an increase in hardness, a decrease in grain size and a decrease in binder content of the cutting tool material. Examination of the worn surfaces inside a scanning electron microscope showed that the cutting edge was worn by preferential removal of the metal binder phase from between the tungsten carbide grains. It is suggested that removal of the binder weakens the bond between the tungsten carbide grains leading to their mechanical removal from the clearance face. It is concluded that the main wear mechanism for cemented tungsten carbide tools in machining particleboard is the removal of the binder phase by plastic flow and micro-abrasion, which is followed by fragmentation and dislodging of the WC grains.
Improving the performance of aqueous cutting fluids by galvanic-cathodic protection of cutting tools
1988, WearThe tool wear enhancing characteristic, commonly observed with aqueous cutting fluids, appears to arise primarily from electrochemical corrosive wear due to galvanic action which, combined with other wear mechanisms, results in an overall increase in the rate of tool wear. As a counter measure against such a detrimental effect, galvanic-cathodic protection is proposed, comprising an auxiliary anode attached to a cutting tool. Results from the tool wear tests conducted using a zinc-coated high speed steel tool indicate that such protection may prove remarkably effective in reducing the detrimental characteristics of aqueous cutting fluids, thereby improving their general performance.
Wear behavior of wood-cutting edges
1987, WearThe performance of cutting edges has been extensively researched for many types of wood-cutting tools, usually with respect to tool geometry. The wear behavior of saw chain cutters, however, has received little attention and forms the subject of this investigation.
In a series of field experiments, the relative “life to resharpening” of new steel and chromium-plated steel cutters was determined. A subsequent laboratory investigation was undertaken to ascertain the wear rates of the cutters. Chromium-plated cutters proved to be superior but the difference in wear rates was much greater than the difference in life to resharpening.
From optical and scanning electron microscopy observations of the worn cutters, it is concluded that abrasive wear is the dominant deterioration process.
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Paper presented at the International Conference on Wear of Materials 1981, San Francisco, CA, U.S.A., March 30–April 1, 1981.