How to Braze Cast Iron (with Videos) [2019]


How to Braze cast ironLooking for a detailed guide on how to braze cast iron?

You are in the right place.

Let’s learn it all step by step.

What is Brazing:

The way of attaching two different portions of metal for forming a sturdy load tolerate joint is known as brazing. In this joining process, filler metal follows into the joint. Its melting point is lower than adjacent metal.

It is just like soldering. But the required temperature is high.
You must apply the proper brazing rod. For joining metal piece, the brazing rod must be melted. You will need a high power flame torch.

The mixture of carbon, iron, and silicon is known as cast iron. It is used in a water pipe, house transmission, piston, etc. Brazing is the better idea for remaking cast iron. Brazing is stronger and harder in compare of CI base metal.

Properties of Cast iron:

For alloy, hardness is 150-220
For nonalloy, the hardness is near about 300-600
2500 -50000 psi is tensile strength
Better wear resistance
Powerful rigidity
Good corrosion  resistance

Basic concept:

If you are using a flux build rod, iron melting will not be a problem.
When you reach over 1400 degree, the rod captures extreme label of heat. It helps to penetrate the hole of metal.
For changing hairline crack shape –unlock the porous for drilling and grind out and form a shape like u.
At 600 degree it turns red. However, continue to apply the heat.
Melting flux core rod is hard.  Be patient.

After a while,(up to 1400 degree) The rod will melt. You need to graze it now. At this moment the flux core will fuse down.

Then cut the rod for repairing. You will have the possibility of strong welding.

Merits and drawback of brazing:

Merits: It has some benefits than other metal joining system

o Base metal does not melt
o Proper trigger control with tolerance.
o Clear and clean joining
o Second time joining is not required
o Together braising is possible between similar and nonsimilar metal. For example –ceramics
o Uniform heating creates less thermal buckle
oFor forming a fresh joint, it reduces the cost
o For safety issues, it can coat and clad
o Easy mass production
o No sensitive process

What are the drawbacks of brazing?

Weak joint. However, it is more significant than filler.
Under high temperature, the brazed joint can smash down.
It demands a high range of cleanliness.
Often extra fluxing is requiring for maintaining cleanness.
Different joint color makes a visual disorder

Brazing cast iron with MAPP gas:

Actual MAPP gas can be applied To the mixture of oxygen to eat brazing, soldering and also welding.  Its high temperature infuses the hydrogen.  It becomes molten steel and turns into the brittle particle.

(Note: MAPP Gas: It is a commercial name.  It is a composition of
Methyl, Acetyle, Propyne, Propadiene)

Brazing cast iron with bronze:

The bronze is a filler type metal. It is tremendously ductile. It can absorb stress. Keep these points in mind while brazing.

Brazing cast iron stove:

Metal should be clean.
With the oxy-propane heat that area about 10 to 15 minutes.
After  15 minutes stop the heat.
Slowly cool it.
Now you will experience a crack.

Brazing cast iron cylinder heads :

It absorbs too much oil. So cleaning is important. Steam clean can be the better option.
Let it dry after cleaning.
Grid the visible crack.
Dye penetrating test is necessary for overheating crack.
Ensuring cleaning start the work.
The maximum crack pass is single.
By hammer, slang off after root pass.

Best brazing rod for cast iron:

Copper brazing
Silver copper
Silver copper and zinc
Copper aluminum
Brass brazing

Can you weld cast iron with a wire feed welder?

It is difficult to weld cast iron with wire feed welder for its chemical shape. To do it:

Preheat is required for avoiding damage
For heating use torch
Before welding decrease the temperature
Weld the cast iron slowly.
Take a break after 1 or 2 inch
Use wire brush for flux core
Slowly cooldown cast iron

Brazing cast iron engine block:

The engine block is a serious problem. However, it can be solved. It is possible by arc welder and proper rod.

Weld or braze cast iron:

It is a big debate. However, the simple answer is: It depends on nature. Like, grey cast iron brazing is better. Braze melts the metal entirely. Sometime brazing looks ugly.

How to braze cast iron exhaust manifold:

Apply preheat until  the piece stinking
Load it with flux
Cut off the flange.
Remove for adjusting

What are the types of cast irons?

Grey iron:

It is the best form of cast iron.
It has 2% to 5% silicon. It makes separate graphite particles
Graphite makes it grey
It’s a form of 95 % metallic iron
2.50 to 4.50 %  carbon contains commercial grey iron
Less carbon cast iron

How do you test Grey iron?

Torch test: Molten puddle have no spark
Spark test: Small range of red spark will show
Appearance test:  Usually it is sand free. Dull grey color may be light.
Fracture test: Good quality iron is tough.

What is White iron?

It is formed from grey iron by heating grey iron in molted position.  After becomes cool, those stays combine, and white iron is formed.

It is combined carbon.
Very hard
Brittle
Silvery white look

What is Malleable Iron?

Malleable Iron is made from white iron. At 1700 degree F at 150 hours the carbon combination becomes separate. However, it is different from the grey type.

Quite similar to real iron
High strength
Toughness
Ductility
Shock resistance
Brazing can be done.

We tried to give the basic knowledge about brazing cast iron.  What is better brazing or welding is depends on the project, your choice, and situation.