Hardfacing of Valve Seat & Trim

Hi Nithya,

Stellite is deposited on the surface , by welding and by spraying methods . You need the welding machine (preferable Generator dc+) consumable such as the stellite MMAW electrode or barewire for TIG.Stellite is available in various grades and it is advisable to select the one that is specified in the valve data sheet.Both are availabe in the market.Consumable manufacturers/seller will assist in finalising the welding method and setting of parameters such as current , pre-heat, interpass etc dependng upon the material and dimension of the valve seat you are wanting to overlay with Stellite.

The same could also be done with Spraying, (has limitation though , regards to the thickness build-up required as compared to when done by welding) .The spray can be done using HVOF , Metal Arc or Plasma Spray.

In case you find difficulty in getting stelliting, you may consider substituting it by a hestalloy grade after discussing with the valve manufacturer.

The required specialised services are widely available .Please let me know your location so that I can suggest a suitable one.

thanks a lot. that was very informative. One more thing i would like to know is: I observed that generally, for hardfacing trims, the hardness specified for the seat ring in the valve body is more than the wedge/gate seating surface hardness... Why is it so?

thanks

application

Dear Mr. Tyer,

This is a design feture designers are following,as it is less cost to replace the weared out wedge/gate seating parts compared with replacing the body seat ring.The body seat rings are welded to the body or assembled using shrink fit.Removing this ring for repairing activities is a difficult task and usually needs expert.

Sayed Sarhan

visit Delora Stellite at www.stellite.com Deloro Stellite is a global provider of innovative solutions to challenging wear problems. Our specialist products and services help extend the life of components in demanding environments where heat, corrosion and abrasion limit their life.

A weld overlay of stellite (also referred to as Colmonoy) is applied either manually or, more commonly, with automatic welding equipment and then machined to the required tolerences.

sometimes the word "stelliting" is used in place of Hardfacing, possibly because Stellite was the first material used for this application. Normally because of the Cobalt contet in this alloy, it is used where temperautres above 3000 F a"re involved, otherwise you can safely use Ni Cr B Si alloys for the hardfacing and these can give different hardnesses as per your requirement. Normally the hardness of a stellite overlay is around RC 40, but the Ni Cr B Si alloys have hardnesses ranging from RC 20 to RC 60 and can be used by spraying or melting a rod of different diameters from 1/16 ti 1/4 inch by a small welding torch to give you a pore-free dense coating. These alloys are stable upto about 1800 F

vshwn7@aol.com

Engine valves for the automobile, aircraft and stationary engines used stellite on the exhaust valves.

This was applied by a typical brazing technic of preheating the valve as it rotated and then applying the stellite rod material with a torch. Later in the mid 80's, the company developed an automated process of depositing stellite from a powder but still used oxygen and acelyne with argon.