Special Coatings & Teatments

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Chrome Plating / Tuff-Triding : The Valve Stem has a sliding motion relative to the fix Outer Valve Guide. Hence the Valve Stem should have two major properties. It should have good sliding & also lubricating properties & it should have a higher wear resistance to give a good life. Both these properties are achieved by Chrome Plating.

Typical Surface Hardness : Minimum 800 (HV -100 Gms Load) Equivalent to 62 HRC / 650 Brinell

Tuff-Triding (Liquid Nitriding) is an improvement over chrome plating. It has higher surface hardness & better sliding properties then chrome plating. It also has better corrosion resistance properties.
Typical Surface Hardness : Minimum 950 (HV -100 Gms Load) Equivalent to 66 HRC / 712 Brinell

Hard Facing : Valves of late have Stellite hard - facing on Valve Seat area. Stellite is either Cobalt base or Zinc base & hence very costly. It has a very high hot strength & good wear resistance properties. It looses very little hardness at elevated temperature.

Typical Hardness :

Grade Ni-60 : Min 30 HRC (Nickel Base Alloy)
Grade 6 : Min 40 HRC (Cobalt Base Alloy with High Cr & Tungsten)
Grade 12 : Min 48 HRC (Cobalt Base Alloy with Higher Cr & Tungsten)

Typical Hot Strength of Various Metals

Item	Hardness at room temp.	Hot hardness at 500^oC (HRC)	Hot Hardness at 700^oC (HRC)
En - 52	28	16
21 - 4 / N	38	28
Stellite Gr. Ni 60	30	Data N. A.
Stellite Gr. 6	40	35
Stellite Gr. 12	48	42
Super Alloy Nimonic 80 A	30	26	17

Cryogenically Treated Valves :
Cryogenic Treatment was invented for Space & Aeronautic components, but has now been commercialized & finds a variety of application including Engine Valves. It is a special Sub - Zero controlled treatment that improves the life of the component dramatically. It is used in Valves for extreme duty conditions like racing car engines etc., but is slowly gaining acceptance in a variety of applications.

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Engine Valves