Motorsport Coatings
Wallwork Cambridge have a suite of high technology coatings available for autosport components that will allow race engines to run hotter, faster with increased stresses and lower frictional losses. Without such coatings many modern bespoke racing engines simply will not function optimally.
This is one area where racing engine manufacturers are leading series-production vehicle manufacturers to a lower friction future. Within a few years we will see relatively low cost cars fitted with coated valvetrain components. Where autosport's goal is enhanced performance via lower friction, theirs is lower fuel consumption and emissions also via increased lubricity.
Key reasons for utilising coatings on racing engine components
- Prevention of corrosion
- Reduction of wear
- Improving the coefficient of Friction
- Improvement in materials compatibility problems
- Modification of other material problems
By modification of the wear behaviour of substrate material - coatings such as Diamolith DLC, Nitron MC and NitronCA can prevent one of a small number of wear properties taking place. These problems are not isolated and many occur simultaneously.
The effects of abrasive, adhesive and fretting wear as well surface fatigue can be mitigated by the use of coatings whether on one or both counter facing surfaces
Coatings are utilised in a range of environments inside and outside of the engine. High temperatures, thermal cycling, high sliding velocities, high contact stresses and amplitudes, immersion in water, fuels and oils are all situations where we place coatings therefore it is vital that the coating we select can not only perform the primary duty but also withstand the rigours the environment it operates within.
Wallwork Cambridge's impressive R and D capability with an in-house team of engineers and scientists and an extensive and well equipped laboratory - allow us to develop new variants of coatings for the autosport sector. One such coating Nitron O which has been designed for the enhancement of Titanium alloys by a novel duplex process is a genuine step towards the development of lighter more powerful engines
Examples of Coating applications within the engine.
| Pistons | Coatings such as Nitron CA and DLC can be adapted to improve frictional effects and provide the thermal barrier effect. They will also prevent damage from knocking and hot-sports. |
| Piston rings TiN, CrN and DLC | has been used extensively on rings for several years. These coating are effective when the piston is at TDC and BDC when the piston velocity is zero and therefore the lubrication regime is no longer hydrodynamic. The low dry friction coefficient of the coating system helps to prevent the ring sticking in its groove |
| Piston Pins | One of the first components to benefit from the use of coatings Nitron MC. it is now widely used |
| Connecting rods | Coatings applied to the thrust faces. The benefits of the coatings can be further enhanced by super-finishing prior to deposition |
| Valves | TiN is popular for reducing frictional effects in both austenitic stainless steel and titanium alloy valve stems. Diamolith DLC can offer enhanced friction whilst CrN and Nitron CA can offer thermal barrier benefits. On the combustion face the reduced conduction through the stem should aid in fuel conversion efficiency and improved cylinder filling by having a cooler valve head and seat. |
| Spring retainers | Valve spring retainers, particularly made from Titanium are commonly coated in TiN and CrN to prevent wear damage from the interface with the flat edges of the spring |
| Valve Shims | Coatings reduce the friction effects caused at the contact between the rocker and the shim minimising the potential of bending load experienced by the valve. DLC is a popular coating in this application |
| Cam followers | Cam and bucket followers (on both OHV and OHC engines) operate under high contact pressures which are ever increasing to allow greater acceleration of the valve in the opening and closing of the lift profile. These high contact pressures and sliding velocities have a deleterious effect on friction and contact temperatures. Nitron MC and Diamolith DLC provide the necessary improvements in friction improvements whilst super polished CrN can perform better at elevated contact temperatures (> 400°C) |
| Rockers | Almost always coated with DLC to mitigate frictional forces. |
| Camshafts | As with the followers, cams have been coated for a number of years to reduce the fiction effect in contact with the associated counter face. DLC and Nitron MC are the most popular coatings within this application |
| Gears CrN and DLC | Have been used to reduce frictional effects in the gear train whilst some teams have resorted to coating titanium gears in the timing drive. R and D programmes have looked at applying coatings at lower temperatures to facilitate coating of temperature sensitive materials best suited for cyclically stressed gears. |
| Bearings | Bearings have been routinely coated for several years. Optimising the heat treatment, surface finish (by pre-coat polishing) followed by the application of a PVC/PECVD thin film coating have shown to optimise the load bearing capabilities, as well as reducing the friction. CrN is a very popular coating for this application |
| Fasteners | Replacement of plated coatings such as Cadmium and Chromium to improve corrosion resistance. CrN and DLC will provide a more than competitive alternative. The elimination of galling (cold welding) will be provided by duplex treatments such as CrN-Ag applied by PVD means and Nitron- Lubrica a sprayed dry film lubricant |
Future developments and economic consideration
Designers within the racing industry see the key driving forces of automotive engine coating development as being one or more of the following.
- Lower friction
- Greater reliability
- Greater load capacity
- Lower part cost
The dynamic of engineering progress in racing teams is easy to understand - designers want greater power, greater longevity and more highly loaded components. All of these drivers are the same within series-production engines.
It cannot be overstated that the use of carbon based coatings DLC and WC-C in engine applications have been a revelation and has attracted a lot of R and D funding. In that regard Wallwork Cambridge have recently signed into a collaboration programme to look at the developing carbon based coatings to further improve efficiencies in a wide variety of automotive applications.