Solving Brazing Problems-part 2

There are many things that can cause brazing problems to occur.  In the first part of this series, Solving Brazing Problems, we discussed how cleaning the steel before brazing and cleaning the saw tips can have a great effect on the braze joint.  In this next section we will be discussing how Braze alloy and Flux affects brazing. Using the wrong type of brazing flux, not using enough brazing flux, or using the wrong type or amount of braze alloy can cause a lot of brazing problems and can be the cause of many of your problems with tip loss and tip breakage.  By changing the type or amount of brazing flux and braze alloy you use in the brazing process, you can eliminate many of your brazing problems, and reduce tip loss and tip breakage by a lot.  There are so many different types of braze alloy, it may be hard to figure out which type to use for your specific application.   We have a guide that explains how to choose the right braze alloy that can help you choose the best braze alloy to use for your specific application.  You can also find a more in depth guide on How to braze on our website or in our book Braze Failure Analysis.

Some of the most common causes of braze failure are:

  • improper cleaning of the parts
  • surface condition of the parts
  • using the wrong braze alloy
  • improper fluxing, improper braze joint thickness
  • brazing at the wrong temperature
  • gas entrapment
  • overheating the parts
  • or a combination things

 

Using the wrong braze alloy is the major reason for saw tip breakage and loss and was considered the number one reason in 1987.  The most common and best braze alloy for creating strong bonds between Steel saw plate and carbide tips is a AWS Bag-3 with 50% silver and 16% Cadmium.   This braze is rarely used because the federal law started restricting the use of Cadmium and leveling large fines.  For several years many people switched to Bag-24 and Bag-7 Braze alloys instead.  In 1996 we started using a Braze alloy AWS Bag-22 and found that worked much better and created a much stronger joint than the Bag-24 and Bag-7 braze alloys, and did not contain any Cadmium.  If you are having braze problems and are not using this alloy then the simplest thing to do is try this braze alloy.  We call this alloy “High Impact” alloy.

AWS

Silver

Copper

Zinc

Nickel

Cadmium

Manganese

Tin 

Melt pt.

Flow pt.

BAg-3

50

15.5

15.5

3

16

 

 

1170 F

1270 F

Bag-24

50

20

28

2

 

 

 

1220 F

1305 F

Bag-7

56

22

17

 

 

 

5

1145 F

1205 F

BAg-22

49

16

23

4.5

 

7.5

 

1260 F

1300 F

 

Black Flux vs. White Flux

We have seen dramatic changes in braze performance just because of a simple change from Black flux to white flux.  Black flux is identical to white flux except that black flux has extra Boron added.  Flux absorbs oxygen from the air and keeps oxygen out of the joint during brazing.  Because of the extra Boron, black flux will give greater protection during heating.  There is more information on the different types of Flux in our Brazing Flux article. 

There was a test conducted to demonstrate the performance of black flux verses white flux.  A brazer brazed tips on half a saw with black flux and the same tips on the other half of the saw with white flux.  Then the tips were hit with a hammer.  The black flux tips held with absolutely no problems.  The white flux tips broke or came out or both.  

Too thin a braze joint.

We have seen instances where the braze joint was so thin that the tips were essentially resting just against the steel.  It was the fillets that were holding the tip on rather than the proper bond between steel and tungsten carbide. 

Having too thin of a braze joint can be caused by either not using enough braze alloy  or by pushing the saw tip into the pocket too hard instead of allowing the pocket to suck the saw tip in.  When the saw tip gets pushed into the pocket, it pushes the braze alloy out of the joint creating too thin of a layer between the saw tip and the steel plate and forms a very weak joint.

It is also important to make sure there is an even layer of braze alloy.  The braze alloy should have a thickness of .003” to .005”.  We pretin our saw tips with a standard .010” of braze alloy material wich allows for 60% to 70% of the material to be used to create fillets and still provide enough material to create a proper braze joint thickness.

 

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