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Brazing with Trimetal Shim

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Brazing with Trimetal Shim

 Braze alloy / Copper / Braze alloy sandwiches

  

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Steel and carbide both grow during heating.  Steel grows about 2.5 to 3 times as much as carbide.   A soon as the braze alloy sets it locks the parts in place and the steel shrinks about 2.5 times as much as the carbide.  This puts a great deal of stress on the carbide.   This heat stress alone can crack the carbide or it can put the carbide under enough stress that an outside impact, such as normal cutting, can break a tool tip. 

Specifying shims

“V” Back   .335” W x .230” l x .230” H 
Each leg
Length   0.225”
Thickness 0.010” 
Braze alloy is Bag-24
Length 0.335
Quantity 

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Trimetal Shims And Hi Impact Braze Alloy

 

Executive Summary

Trimetal shims are superior for brazing large parts such as carbide on snow plow blades.    Hi Impact braze alloy (AWS Bag-22) is better than trimetal shims on smaller parts such as saw mill tips.  Get a Free Quote on Trimetal Shim and Brazing Alloy. 

Tests done by:

Don Anderson, Head of /cutting tool R&D, Weyerhaeuser Technical Center

Kieth Dietrich,  Head Engineer Systi Matic Saw Co.

Carrol Sizemore, President, Cascade Southern saw co.

Tom Walz, President Carbide Processors, Inc.   

Conclusions:

The 50% Cadmium free alloy was about 30% weaker than the standard 50% alloy

Trimetal shims were effective on larger parts but did not seem to add anything on the smaller saw mill tips.  

The effectiveness of a trimetal shim depends to a great deal on the braze alloy used on it.   

At that time Weyerhaeuser, Systi Matic, Cascade Southern and Carbide Processors were all using trimetal shims.  All tried trimetal shims and, in independent tests,  all came to the same conclusion that the effectivenss of the shim in smaller parts, such as tips on saw mill saws, depended on the braze alloy used.   

No one saw any advantage in shims on small tips and there were great disadvantages.  

Production Saws

However trimetal shims are widely used on smaller saws.   Production saw companies use automatic brazing equipment which uses ribbon alloy.  The use of a copper inner layer makes the alloy much easier to handle at the flow point of the braze alloy on the outer layers.  This does not improve the saw blade but it certainly does not hurt it either.   

Trimetal shims are sometimes used to successfully to solve problems.

A proper braze joint is between 0.003” to 0.005”, has had the tip moved at temperature to allow release of flux gases and has been heated to about 50 F over the liquidus point.   

If the brazing is done properly the Hi Impact as wire makes a much stronger joint than the shim because the wire allows for the flow of braze alloy back onto the plate.  Research we did with Black and Decker shows that this adds about 25% more to the strength.  It is especially important because the shoulder or fillets provide added strength for impact that comes from directions other than straight on which is almost always the case.  

Trimetal shims are still recommended in some literature on the grounds that stronger is always better.  They are also recommended because they are much more expensive.  

 Problems

  1. If the brazer does not know how to handle the release of flux gasses at the flow point they can ‘saw’ the tip back and forth and force all the braze alloy out of the joint.  With a trimetal shim there is at least a layer of copper left to provide cushioning.
  2. If too much force is used to heat the tip then there is a tendency for the braze alloy to be forced out the sides.  See our Article on Pushing Braze Alloy out of the Braze Joint.
  3. If bad carbide used then it will crack more easily.  Trimetal shims can help a little here but it is like putting high performance shocks on a car with bald tires.  

b2b lead generation