How to Braze- Part 4
Welcome to our series on how to braze! We have put together a tutorial on how to braze and broken it up into 4 parts. We have added a new post every few days so be sure to look back at some of our previous posts so you can take advantage of this valuable information. In part 1-3 of this series we discussed saw plate, Flux, and carbide tips. In our final section we will be discussing braze alloy or silver solder, and how different types and amounts of braze alloy can create a stronger joint.
When brazing carbide tips you will need:
- Braze Alloy or silver solder
- Brazing Flux
- Carbide tips
- Steel saw plate
- Also, you will need a tool to heat the braze alloy
- And you will also need a tool to help guide the carbide tip onto the saw plate.
*For successful brazing the quality of the materials used is very important and can have a significant effect on reducing the amount of tip loss and breakage you experience. We proudly sell what we believe to be some of the best brazing flux, Braze alloy, and Carbide Tips in the industry.
Part 4: Braze alloy- What kind and how much Braze Alloy to use, and how to apply the Braze Alloy to create a strong joint
Braze Alloy (Silver Solder, High Temp Silver Solder, High Silver Solder)
Braze alloy acts as both a bonding agent and a cushion between the carbide saw tip and the steel.
The steel saw plate must be clean and oxide free. The carbide saw tip must be clean and readily wettability. If this is the case then the braze alloy forms two kinds of bonds. One is a pure physical bond. The other is a chemical bond. This gives you a bond strength that is greater than the strength of either the steel or the carbide.
The steel grows about 3 to 5 times as much as the carbide does during brazing. When you take the torch away the parts lock together and then they start shrinking. Because the steel will shrink 3 to 5 times as much as the carbide it wants to bend the carbide. Carbide does not bend except in extremely special circumstances. What you end up with is a highly stressed joint.
The braze alloy between the steel and the carbide must be in the range of at least 0.003” to 0.005” to keep the carbide from breaking.
If you push the tip in and shove all the molten braze alloy out of the joint then the saw tips will break.
Four Kinds Of Braze Alloy
There are four kinds of braze alloy most commonly used to braze carbide to steel.
1. 50% Silver with Cadmium
This is the traditional braze alloy and still widely used. It is easy to use and works very well. Unfortunately the government has drastically tightened the restrictions on cadmium exposure. You can use this braze alloy safely with proper ventilation. However the cadmium fumes out and deposits on its surroundings. Cadmium is also very easy to detect. Stories of companies that have been in a lot of trouble for cadmium exposure have made this alloy much less popular than it used to be.
2. 50% Silver without Cadmium (cad – free)
This is probably the most popular alternative to the cadmium alloy. It is about as easy to use as the cadmium alloy. Unfortunately it is about 30% weaker than the cadmium alloy in terms of tip loss and tip breakage.
3. 49% Silver with Manganese
This is a cadmium free braze alloy that is as strong as the cadmium alloy but it flows differently. Many people won’t use it because it requires a change in procedure.
4. 56% Silver with Tin
This alloy is very easy to use but also very weak. It is an excellent alloy for hobbyists and has a great color match with stainless steel. It can be used for brazed tools but is generally not successful in medium to severe applications.
You can find Braze alloy wire that is easily cut to size for you specific application.
How Much Braze Alloy To Use
We normally pretin tips so that there is a layer of braze alloy on them that is 0.010” thick. This is enough to leave a layer of about 0.005” thick between the carbide and the steel while still creating nice fillets on the side. The side fillets (fill – etts) can greatly add to the strength, as much as 30 to 40%.
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