Thermal spray application in the automotive sector

Plasma and Thermal Coatings have developed new coatings for automotive applications which have already found their way into production such as MMC aluminium oxide coated brake discs

Thermal spray coatings have been used within the aerospace industry in the manufacture of high value, high performance and critical gas turbine components for at least forty years.

Several hundred coatings have been developed and designed in to protect these highly engineered components from wear, corrosion and high temperature oxidation, where safety, quality and performance are pre-requisites which override cost considerations.

For this reason thermal spray coatings have historically been labelled high tech, high cost.

However with the availability of much lower materials costs, modern spray equipment and robotic application techniques these high performance aerospace standard coatings can be applied to automotive components cost effectively at high volume production rates.

These factors combined with the need to improve engine performances and efficiencies, to reduce weight and control emissions are having a dramatic effect on the automotive industry's acceptance of thermal spray coatings.

These benefits can be achieved with substantially less environmental pollutants when compared, for instance, with electro plating.

Plasma and Thermal Coatings over recent years have developed new coatings for automotive applications which have already found there way into production.

For example, grey cast iron brake discs are used in production vehicles as they provide good life, wear resistance and good performance characteristics.

Cast iron is relatively heavy, and in the quest for weight reduction, lower density materials have been investigated.

Aluminium metal matrix composite discs were developed to give similar strength characteristics to cast iron, however they do not provide the wear resistance at the surface and also require thermal protection from the heat generated by the braking action.

Plasma and Thermal Coatings Ltd has developed thermal spray application techniques for the deposition of an aluminium oxide coating designed to provide this wear and thermal protection.

The MMC aluminium oxide coated discs are approximately half the weight of cast iron and offer improved fuel economy, better acceleration, exceptional wear resistance, a high coefficient of friction, improved braking performance, and unlike carbon / carbon discs, they function just as well in the wet.

These coatings have been thoroughly tested in motor sport competition, and have already notched up several Grand Prix firsts.

Corrosive products (sulphuric acid), from the combustion of the diesel fuel, condense on the nozzle and attacks the base metal, imparing function and reducing component lifetime.

A plasma sprayed Molybdenum based coating is applied to the nozzle surface to provide protection against these aggressive condensates.

A turbocharger rotor spins at high speed within its housing.

As its rotational speed increases, and to some extent the operating temperature, the outside diameter of the rotor also increases.

If the clearances between the rotor blade tips and its housing were designed for optimal aerodynamic performance, this growth would cause the rotor blade tips to touch the bore of the housing.

The clearances are therefore larger than desirable due to mechanical considerations.

The thermal spray coating solution for this problem is to apply a soft abradable coating to the housing bore that can be rubbed away by the rotor blades without causing material loss from the rotor.

These coatings reduce the risk of blade damage and at the same time improve the efficiency and performance of the turbocharger by managing the rotor path tip clearance.

Other examples of applications are Lambda Sensor (Catalysor Emission Control), Crankshafts, Synchro Rings, Valves - Seats, Stems and Heads, and Piston Rings.

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