Restoring Heavy Machinery By Welding
Listed inMaintenance & Repair
The benefits of using hardfacing solid wires
By Peter Wilkins, ESAB
Heavy machinery in quarries wears out. Welding and weld overlay techniques are the most frequently used for renovating steel parts in almost every industrial sector.
Weld overlay is a highly cost-effective way of creating wear-resistant layers on various machinery parts - digging tools, shovel teeth, tracks, rails, wheels, rolls etc. In the most extreme environments buckets, crushers and screens may need to be refurbished monthly, so replacement is rarely the sensible option. In most cases so long as you can get arc welding equipment to them and someone with welding skills, refurbishment is the way to go. Sometimes pre-heating of the parts may be necessary and so gas has to be brought to site. Larger companies will often have their own repair and maintenance teams, others may need to employ a contractor.
The traditional method of welding is manual metal arc electrodes, a relatively slow process, but very convenient in terms of working on site. The main requirement is a power source and so long as you have that you can weld.
There are also higher productivity versions called flux-cored wires. These do the same thing in terms of the composition of the weld, are a lot faster but sometimes need a gas shield.
One good example of the advantage of refurbishment over replacement is twin-wire submerged arc welding with flux-cored wires of pistons for large diesel engines. Larger pistons with diameters of 700mm or more can be refurbished with a productivity gain of 25% without any increase in production costs. Piston ring grooves wear continuously since they are constantly on the move. The piston head surface also wears, largely because of the extreme thermal conditions inside the cylinder.
In a demonstration project carried out by ESAB and a partner, two layers of hard surfacing, with OK Flux 10.80, achieved a surface hardness of 350HB (~37 HRC). Flux-cored wires in the twin-wire mode allowed the replacement of solid wire to basic flux-cored wire (two 2.4mm wires instead of single 4mm solid). The wire selected for this demonstration project was OK Tubrod 15.21S (containing 0.5% molybdenum), offering a high degree of cracking resistance.
Thanks to this technique the deposition rate was increased by 50%, there were fewer weld defects and a more consistent bead deposit. Grooves were machined out of the solid material and the resulting pistons refurbished with fewer layers at a higher welding speed.
Another example is railway wheels. Worn wheels can be given original profiles using a lathe turning process. But this can result in the loss of a significant amount of still useful material and smaller wheels.
A better way of dealing with wear is to rebuild the worn part by welding the surface, using a suitable filler material. Welded material is as good or perhaps even better than the original base material. Fine grinding can restore the wheel to a profile identical to the original. Welding can be carried out without removing the wheel or the bearing housings and both can be welded at the same time using two submerged arc-welding heads.
The axle, complete with wheels, is rolled in on rails into the bottom of the machine, build-up welding is performed and the axle is then rolled out again. The manipulator, which is down in a ditch, clamps the axle with the wheels and rotates the wheels. For welding in the best position, the manipulator and the wheel set can be tilted ±50 degrees.
Two automatic A6 welding heads are mounted on ESAB MKR columns and booms, allowing the heads to be positioned in the desired position in relation to the wheels. The welding process is either single wire or twin wire (two wires connected to the same power source). The power sources are two ESAB LAF 1250 for a maximum of 1,250A.
The welding process controller is an ESAB computerized PEH process controller. Flux is automatically fed from floor level to the welding heads, by means of pressure and hoses with compressed air.
ESAB’s hardfacing solid wires (OK13.90, OK13.89 and OK13.91) are often used for repair and maintenance in industries like railways, mining, quarrying, agriculture and scrap yards as they can build up highly wear-resistant layers on machinery parts.
For more information call ESAB Publicity on tel: (0800) 3893152; email: [email protected]