Not wishing to teach Grandma how to suck eggs you understand . . . .
Briefly some cast snippets for you guys.
The basic problem with cast ferrous objects is that when welded the weld material deposited shrinks, as all metals do as they cool, the shrinking speed is faster than the cast and hence the weld cracks.
That is the simplified basic problem.
Basic remedies are to pre-heat the subject, keeping heat on if you can during welding. If it is just a crack then stop holes must be drilled at the end of the cracks. If it is two or more lumps / pieces then making a bevel from both sides helps in preparing the joint.
Also in preparation drilling either side of the break and installing knurled pins into holes making an interference fit helps alignment and strength also.
Preparing a cooling bath of fine material such as sand and post heat should be considered.
When using MIG welding I have had great experiences with a very slow jive of pre heat, weld a 1/4 inch, heat and peen simultaneously, heat and weld and peen weld and repeat and nauseum. The peening stretches the deposited material and stops the cracking. Once the joint is closed, backgrind the weld and weld over again. Failure to peen at any time is direct path to a cracked weld.
If you have no patience dont start.
I have used mild steel MIG wire, high nickel stick rods, done it with TIG and bared stick nickel rods, done it with stainless wire or rods.
Brazing is much easier.
Understanding why the part broke in the first place is the critical step most fail to understand. Often it is just abuse or the same spelled differently ie too much power.
If it is a classic flaw in the design of the casting you will have to remedy that first.
Brazing is brilliant for making a new surface for machining and bearing installation when the old one has worn out the cast as it thrashed around.
Because brazing is softer, home made mills in the drill press and dremel tool fondling has been known to make things work. Brazing is so kind on the restoration as it can easily be worked and blended in and after paint is hard to spot.
Silver solder is remarkably strong and is great for small item repair.
Cleanliness is a vital ingredient in any of the above, welding detests hydro carbons be they paint, grease, oil or fuel.
If you want a cheap and easy workshop dye penetrant for cracks my preferred route is finely shaved soap stone and dyed diesel fuel.
Clean and dry the suspected area. Using Q tip or larger dab dyed diesel alog or around the crack. Dry by wiping surface clean thoroughly, do not apply heat.
Gently lightly dust crack area with soap stone dust. Watch dust turn pink as fuel gets drawn out of crack into the dust. You will be amazed at the results.
Have fun
Glad to pass on what others have taught me.
R
|