Chemical Attack as a Factor in the Wear of Woodworking Cutters

Studies have shown that an electro-potential affects the dulling rate of woodworking cutters. This implies that chemical reactions are important although most work has been based on mechanical factors. Acetic acid and polyphenolic extractives were studied for their effect on tool steels. CH3COOH (0.6 percent) etched carbon steel to a depth of 0.06 micron in 30 minutes while 0.004HCl etching was slight. Both had a pH of 3.0. Polyphenols with two or more adjacent hydroxyl groups are able to form chelates of iron. Ellagitannins and gallotannins are of this type. Tropolones possess an alcohol group adjacent to a carbonyl group and have been shown to cause corrosion. Radiata pine sapwood lacking in polyphenolic extractives having adjacent hydroxyls was found able to react with iron and it is suggested that compounds with these properties may be found bound to the cell wall. Ten percent gallotannin (pH 3.0) etched iron as effectively as CH3COOH. Solutions at pH 4.5 to 6.0 of gallic acid, pyrogallol, gallocatechin, catechin, afzelechin, engelitin and 0.06 percent CH3COOH (p114.0) were compared. Etching rate was greater for compounds with three vicinal phenolic groups than for those with two. Compounds with isolated phenol groups showed little effect and CH3COOH was intermediate. Tungsten carbide was less affected than iron. Slow speed edge durability studies with P. radiata, E. sideroxylon, and E. regnans and various cutter steels showed etching to occur after 3-9 inches (1-3 minutes) of cutter travel. A negative potential on the cutter eliminated discernible corrosion when immersed in pH 3.0 CH3C00H and a positive potential resulted in rapid attack. Similar results occurred with gallotannin and gallotannin-NaCl solutions. Cathodic protection was verified by cutting experiments.

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