Saw-Blade Cleaning Are Solutions Safe for Pitch Removal?

Wood resin (pitch) is an acidic material and is readily soluble in basic solutions, as well as many solvents such as paint thinner. People have advocated a variety of household cleaners for cleaning saw blades. Many household cleaners contain ammonia or other basic ingredients. Oven cleaner (lye), household ammonia, washing soda, and baking soda all make basic solutions in water (they are listed here in order of decreasing basic strength). It is not surprising that all these suggested products have been reported to work for removing wood resin from cutting tools.

However, it has been reported by C. McCracken of Freud that “alkaline cleaners and those with nitrates are damaging to the cobalt binder in carbide and should be avoided”. Mr. McCracken further reported that carbide is composed of tungsten carbide particles in a matrix of cobalt. Carbide is fastened to the steel substrate with silver solder and copper.

Will typical cleaning solutions dissolve/corrode carbide teeth? Of the materials present—cobalt, tungsten carbide, copper. and silver—will any dissolve or even corrode in the presence of household cleaning chemicals?

Chemistry Theory - Typical solvents will have no effect on these materials. None of these materials is soluble in basic solutions. However, solutions containing ammonia will slowly corrode/dissolve copper and silver in the presence of air. There also is some possibility of ammonia attacking cobalt. It would appear possible that given enough time, ammonia-containing solutions might attack the bond that holds the teeth on, and possibly the cobalt binder. Note: many kinds of acid solutions will dissolve cobalt, more or less rapidly, as well as steel. So one should not use acidic solution to clean blades, nor does it make any sense to do so given that pitch best dissolves in basic solutions.

Experiment - A famous scientist once stated, “theory guides, experiment decides.” I placed a polished carbide tool bit blank in a strong solution of room temperature sodium hydroxide (lye). After one hour there was a slight discoloration of the carbide bit at the liquid/air interface. Examination of the bit under magnification revealed no change in the surface. I concluded that there was no significant corrosion of the carbide under these conditions.

The experiment was repeated with a room temperature solution of ammonia many times stronger than household ammonia. After 1½ hours the solution was slightly colored indicating some small amount of cobalt had dissolved. However, examination of the carbide surface did not reveal any detectable change in the surface. I conclude there was no significant corrosion of the carbide.

Overall conclusion - Long exposure to ammonia containing solutions could affect the bond holding the carbide to the steel. But, long exposure to any water containing solution will rust the steel substrate, so lengthy soaking is neither recommended, nor necessary. Neither basic solutions nor ammonia containing solutions attack carbide at any significant rate at room temperature.

It would appear that an hour of cleaning in basic household cleaners will not harm carbide, and indeed the experience of many people confirms this presumption. Nevertheless, the technical staff at Freud recommends against cleaning carbide with basic or ammonia-containing household cleaners. If one cleans with these products anyway, because they are so effective, it would seem prudent to carefully inspect the cutters after cleaning for any possible damage and soak for as little time as is necessary. Of the chemicals mentioned, baking soda would be the most mild, and it has been reported effective.