WEAR, EROSION AND CORROSION OF EXHAUST VALVES

Low quality fuels for diesel engines cause damage to  exhaust valves and seats. Erosion, wear and in particular corrosion are the main cause. Impurities in the fuel like vanadium, sulphur and sodium form low melting salts which deposit on the sealing surface of the valve and cause serious degradation of the stellite coating.   Particles of silicon and aluminium stemming from the catalytic cracking of fuels are causing erosion of the valve and seat faces.

RECONDITIONING BY PLASMA ARC WELDING

Reconditioning of the exhaust valve spindle and seat by replacement of the stellite hardface by Plasma Arc Welding has been scientifically proven to be the best method. This requires specialized equipment, well controlled welding and heat treatment procedures as well as experienced people. The principle of this method is that the stellite is supplied in powder form and applied to the valve base material with Plasma Arc Transfer (PAT). 

• Approved workshop for Sulzer RTA Exhaust Valves.
• The advantages of PAT compared with conventional welding are: 
• Less dilution between stellite and base material
• Improved and reproducible welding quality
• Microstructure and surface that prevents microcracking and reduce the tendency of formation of deposits
• A wide range of powders for various base materials and applications. 

The preheating and stress relieving of the valve and spindle is equally important to avoid cracking between the base material and the stellite. We have built a purpose made oven with electronic temperature profile control to remove the residual stresses. Finally, we have specialized grinding equipment for reboring the final profile of the valve.