Building up a Bearing Surface

I don't think you will be happy with the braze.

Putting the material on, will require a tremendous amount of heat to be put in as well.

I know people who bore the housings out. The easiest way that I have seen, is by a machinist who setup a tripod and welded to the arm itself, and then a cutter that acted as a boring head, and he opened up the bore size a little larger. This was on a big excavator, so he was limited on dismantelling and setting up the boom on a boring mill.

You should also look at the following: http://www.belzona.com/prod1k.aspx

Belzona Metallic Polymers

for the Repair and Protection of Machinery and Equipment

Take Care,

Keith From Canada

I would like to recommend not brazing the pin.....beacuse the brazing and brass bushings will wear faster (in the dirty enviroment) if that is what you are using......you could chrome plate, metallize or replace it.....the size should be not costly to do.

regards, Joe

this part is doubtless case hardened and brazing would be too soft to last very long.

A good machine shop could make and case harden a new part, but for 1-2 pieces it might not pay to do it.

Was any lubrication neglected to cause this condition?

Chemistry of pin will determine, Preheat temp, filler metal, post weld stress relief temp. and necessity. Best bet for lasting repair is weld metal buildup and machine down o.d. not brazing.

DO NOT BRAZE ! Suggest chrome plating the pin to reduce wear on pin. Bore out the bearing holeto oversize, press in new bearing. When it wears, press out old bearing and press in a new bearing. Done all the time in engines and other rotating equipment.

Turn the pin down to clean up, drop shrink fit sleeve on, turn to size

Allow me to add my opinion.

DO NOT BRAZE. As has been already said, the resulting material is too soft.

To determine which corrective action to take, remove the pin and have someone perform a hardness test on it. If it has a hardness of 20 to 30 Rc, it is not a hardened material. If it is significantly above that, say 40 to 50 Rc, it is hardened.

Due to the amount of material to be added, chrome plating by itself may not be enough since a .5 mm thick layer may cause problems.

If the pin is not hardened, spray welding to restore material then grinding back to size would be a better choice. If you want the hard surface of chrome plating, turn the spray welded part slightly undersize, then chrome plate, then grind to size.

If it is hardened, spray welding will still work but the part will need to be rehardened. As before, apply enough material to make the part oversize, then machine to size.

Get quotes from your local machine shops, heat treaters or plating companies for each of these options. You may find that it is more cost effective to buy a new pin.

Locate a shop in your area that does thermal spraying (also known as flame spraying, or metallizing). This process was originally developed for just such an application as yours.

While the process has evolved into a variety of processes and related equipment, including HVOF, plasma etc, a basic wire process is the cheapest. This would involve the shop removing some material, roughing up the newly exposed surface and applying a suitable sprayed on metal coating, and finally turning it down to size. Typically, the coating would be applied with a wire fed combustion "gun" which looks like a paint spray gun except that it uses an oxy-acetylene or similar gas mixture to create a hot flame into which an appropriate alloy wire is fed which then melts and is atomized with the addition of a compressed air stream. Alternately, it could be a powder fed combustion gun, an electric arc gun (which uses compressed air to spray molten metal from two wires that are fed together and melted by an electric arc) or another variation of the process, but depending on the shop, combustion fed wire is usually the cheapest. The result is a part that is actually better and longer wearing than the original! There is plenty of information on the web if you are interested in learning more about the process. It is used for many applications, including in all jet engines, the manufacture of piston rings for internal combustion engines, and on and on, yet is largely unknown to the general public.

I spent over a decade working for the largest manufacturer and distributor of thermal spray equipment and supplies so I know your application well.

This is likely what one poster meant by "spray welding".

Thanks everyone for the time you have taken to answer my question. I can now see that brazing is out of the question and my choices are chrome plating (I have noticed that some of the smaller pins on the dipper arm are plated), building up with spray welding or some composite material or purchase of a new pin. Where I am located in France is quite rural and limited with regard to machine/fabrication shops but I think I will get quotations, if possible for building the pin back up as most of the other smaller pins on the boom and dipper arm are due for replacement and it may be more cost effective to have several done in one go.

Thanks again, John