Friday, January 28, 2011

Duals always are better....

Things have been moving slowly around the shop.  I am deep into refinishing some funiture and since this is not Vintage Woodworks, I will spare you all the details.  Anyway, I still wanted to post something, so I dug this up from the past project folder.

I had a customer that wanted me to split an exhaust manifold for a 218 dodge flathead in a '47 plymouth coupe.  I repeatedly told him that I have never done this but he was adimate that I give it a whirl.  Besides, I always wanted to try and why not make some cash on the side doing it? 

I started with a couple of original manifolds.  One had a couple of broken tabs so it was sacarficed as the donor manifold for the outlet.

The unwanted parts were cut out and the nesaccary pieces were fitted with as close of fit as possible. 

Cast iron can be a major pain in the ass to weld, but it doesn't have to be.  By taking your time and using the correct materials and procedures, many of the common complaints can be avoided.  First and foremost, it is imperative that you be able to control the heat during preaheating, during welding and during the cool down period.  Cast iron is brittle and has virtually no ductility.  When heated, cast expands at a tremedous rate and when it cools down, the forces of the contraction can be much high than the tensile strength of many filler materials.

For this project, I tried a cast iron rod and flux that my locl welding supply sold me.  I do not know if it was me or if it was the material, but I could not get it to join two pieces together.  It was fantastic if I was trying to build material up for machining.  So, I ended up using a 308 stainless rod.  Stainless has a high nickel content and the nickel is what makes this process so user freindly.  As you weld, the molten nickel rod mixes with the high carbon cast iron.  The nickel allows the carbon to dissolve to form a high nickel/carbon mixture.  As the part cools, the carbon seperates out into graphite ant the molten nickel/carbon mixture turns into a material mostly made up of nickel with graphite dispersed in it.  The mixture now has enough ductility to be able to contend with the forces associated with contraction of the cooling material and thus, not crack.

I used my BBQ grill to preheat and cool the cast at a controlled rate.  I preheated it to as high as the grll would go and then used a torch to get the areas where I want to weld to a very dull red.  Once I was done welding, I placed the manifold back into the grill and slowly lowered the heat over several hours until it was cool enough to handle.

mmm, tasty

Once everthing was cool, I ground the welds down and visually checked for cracks.