Reconditioning of pistons
Diesel engine pistons usually require replacement or reconditioning at fairly regular intervals even if the engine is operated under near-ideal conditions. Their service life is limited because they are mechanically and thermally highly loaded components and over time they will suffer from excessive wear of the piston ring grooves and/or hot corrosion at the piston top surface.
Depending on the condition of a given piston, QuantiServ recommends either full or partial reconditioning.
The entire top surface and ring groove area is first machined off and then rebuilt by either robotic MIG welding or SAW welding. Thereafter, the piston undergoes final machining before galvanic chromium plating or laser cladding of the ring grooves is carried out. The last step is grinding of the ring grooves, which completes the full reconditioning process.
If it is requested by the customer, then we can coat the top of the piston by a protective layer of Inconel. This can be a good solution for engines that suffer from excessive hot corrosion at the piston top.
If only the ring grooves are worn and if a piston is in otherwise good condition, then partial reconditioning is possible. A precondition is, however, that none of the ring grooves has worn so much that not only the chromium layer but the steel substrate itself has worn. In this case, partial reconditioning is not possible and full reconditioning is the only remedy.
During partial reconditioning, any remaining chromium is removed before the ring grooves are plated anew. The landing surfaces will be skimmed to remove any signs of fretting corrosion and if there are small internal cracks, then they will be repaired too.
With the introduction of the QS50K coating technology, QuantiServ has redefined the piston reconditioning process. This proprietary technology was developed by QuantiServ and offers the following important advantages:
- Fully automated process carried out by a robot. This results in a top-quality product due to the robot’s very high accuracy, repeatability and consistency.
- Faster than chromium plating, therefore shorter turnaround times
- Less heat input into the piston, eliminating any residual stresses
- Environmentally sound, non-toxic process
QS50K coated piston ring grooves are far harder than chromium plated ones. Accordingly, the life time and therefore time between overhaul (TBO) that we achieve today was far out of reach even one or two years ago. We are today able to guarantee a ring groove life time of up to 24,000 running hours on our reconditioned pistons!
The following pictures show the pistons of two different cylinders on a 76-bore two-stroke engine, installed in a power plant in the Canary Islands after approximately 6,000 running hours. No measurable wear was detected in the piston ring grooves.