Brazing Laser Cut Steel
Brazing Laser Cut Steel
I had lunch with a customer who said he liked to pretin new saw plate. He was of the opinion that if you try and braze brand-new saw plate the tips may or may not stay on. It is a long-held belief in the saw and tool industry that, with the new saw plate, you braze the tips on and then knock them off. Once you’ve done that you can braze the tips on again and you won’t have to worry about tip loss.
Whereas this is one way to do it, this method requires a lot of labor. What follows is an explanation of why this is done and how to avoid having to do it.
Saw bodies were originally stamped out in the old days before lasers. When saw bodies are stamped the metal on the tips of the shoulders tends to be deformed. But the chemistry of the steel was left unchanged.
In laser cutting a laser burns a series of pinholes in the steel. As the laser is burning and turning the steel molten, there is a jet of gas that blows the molten steel out. You can use any gas. Compressed air is commonly used. You can use an inert gas such as CO2 to prevent oxidation of the hot steel. However the steel is still very hot when the laser moves on to the next hole so that, even if you use CO2, the hot steel is still exposed to the air and there is still an oxidation issue.
The hot steel is very susceptible to reaction with the oxygen in the atmosphere. So the edges of laser cut saw bodies have a pretty good-sized oxide layer. In addition there can be considerable carbon migration in the hot steel. The issue of carbon migration and hot steel is widely discussed and little understood.
In any case, current best practice in the tool industry calls for removing about .005 to .007 inches of steel before brazing. This process is commonly called gumming. Tool manufacturers either do it in their own shop or have it done by the plate manufacturer.
When ordering plate, it is very important to either specify or, at least, find out if the plates will come with the notches ground.
An additional problem with brazing new saw plate is the protective anti – rust coating. This protective coating is always something such as a grease, oil, plastic, synthetic or other carbon-based material. If this material is wiped into the notch it can cause brazing problems.
I was once called out on a consulting problem with a brazing issue. The person doing the gumming wanted to do a really good job. When he was through grinding out the notch he would take a cloth, spray it with WD-40 and wiped the notches clean with the cloth. What he was doing was applying a film of WD-40 into the notch. When he just used a clean rag to wipe the notches out the problem disappeared.
The same thing can happen with the gumming wheel. If the wheel grinds through the protective coating on the surface that it will become oil – laden and can contaminate the notch. This is not nearly as large a problem as poor handling.
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