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HVOF Applications

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The applications of the thermal spray industry are nearly endless. Examples of applications in this industry include aerospace, farm implements, down hole tooling, and pulp and paper. The thermal spray industry brings both economic and ecological upside to each of these industries. Unlike chrome and similar plating technologies, thermal spray waste is easily collected, the scrap can be sold for profit and there is no environmental clean up to contend with. Additionally the thermal spray process allows designers to use less expensive, lighter and more easily processed base materials. Some common applications of thermal spray are given below. 


Landing Gear

HVOF Application
Landing Gear System

Electroplated hard chrome coatings have been used for decades to protect the sliding parts of landing gear systems. A landing gear is a large hydraulic unit which is attached to the underside of an aircraft. It is subject to a great deal of stress and side-loading, both on landing and during taxiing across airports with a loaded aircraft. Any coating used must be able to withstand the stresses created during taxi and landing. For more then 70 years chrome has proven to be a relatively cheap and effective solution, however environmental legislation has forced the aerospace industry to design the next generation of aircraft to be “hard chrome plating free”. As a result of this legislation HVOF coatings have become the accepted and proven alternative to electroplated hard chrome coatings. 
 
The use of HVOF coatings in the landing gear industry:
  • Eliminates all environmental issues and health concerns associated with electroplated hard chrome coatings.
  • Enhances fretting and sliding wear resistance. HVOF coatings typically exhibit 4 to 20 times the wear life of hard chrome.
  • Reduces manufacturing and maintenance, repair & overhaul (MRO) turn around times by up to a factor of 10.
  • Dramatically increases mean time between overhaul and repair and reduces MRO costs and aircraft downtime accordingly.
 
Kennametal Stellite’s Jet Kote® HVOF equipment is widely acknowledged in the aerospace industry, and our Jet Kote® coatings and HVOF equipment have been used in the aircraft industry for more then two decades. Our JK120H powder has successfully replaced hard chrome in many industries including aircraft landing gear.

Gas Turbines

HVOF Application
Gas Turbine

Thermal spray coatings find wide application in the area of gas turbines. A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between.  The gas turbine functions to create energy by drawing air into the compressor section. This air is then combined with jet fuel at very high temperatures to form high velocity gases, which exit through the turbine section of the engine to provide energy. The friction and combustion created by the many moving parts of the gas turbine generates massive amounts of heat, making the many parts of the gas turbine susceptible to sliding and abrasive wear as well as temperature damage.  
 
Almost every component of the gas turbine engine has some type of coating on it to prevent the damage caused by wear and temperature. HVOF coatings are used in the hot section of the engine to coat the shroud with high temperature metals that will not damage the edge of the engine’s turbine blades, yet provide the tight clearance necessary for the engine to function properly. HVOF coatings are also applied to the rotating sleeves or bearing found in the hot section of the engine. Common coatings used in this application include T-800 and Chromium carbide Nickel Chrome coatings. 

Pulp and Paper

HVOF Application
Pulp and Paper operation

HVOF coatings are used in the pulp & paper industry to combat abrasive wear that results from the fibrous nature of paper products as well as the chemical additives routinely used in the manufacture of paper products. Wear problems in the pulp and paper industry are thinly-spread across the whole range of pulp and paper operations, and are often made more complex by the presence of a corrosive environment. Two common applications of thermal spray in the pulp and paper industry are the maintenance of Yankee Dryers and sorter rolls. 
 
Sorter rolls are used to screen the size of the wood chips entering into the paper manufacturing process. Wood chips typically enter via the chip in-feed deck to begin the sorting process. They enter primary sorter rolls and are fed along the top surface of these rolls. The chips that are of the correct size or smaller, fall between the spaces of the rolls. The chips which are too large are carried along the rolls to be deposited for re-chipping. The sizing process continues through a set of secondary and tertiary rolls before it is completed. During this sizing and sorting process it is common for high & low spots of wear to occur on the rolls, causing the operators to re-gauge the spaces between the rolls. By coating the rolls with HVOF coatings it is possible to limit the amount of abrasive wear the rolls experience, thus eliminating the high & low spots which typically occur in the rolls.
 
Yankee dryers are used for the drying and/or creping of tissue and related paper stock.  The dryers are large and are made from cast iron. During the paper manufacture process Yankee dryers are heated internally to high temperatures using steam. The stress caused by this high temperature is coupled with other stresses that arise during operation due to pressure-roll line loads, centrifugal forces and thermal stresses.   Consequently loss of wall thickness due to wear is a significant problem. Thermal spray hardfacing is a widely accepted practice for re-building worn Yankee dryer surfaces.

Oil & Petrochemical

HVOF Application
Sub-sea ball valve

In the oil and petrochemical industry productivity improvements are a constant target. Consequently long life, reliability, and reduced down time are key issues. HVOF coatings are employed because of their ability to operate in the most extreme, i.e. high pressure, erosion, corrosion, abrasion environments. 
 
Sub-sea ball valves are crucial parts which are used during sub-sea oil exploration. Sub-sea oil exploration has been going on in the North Sea for 40 years, however there has been a limit to how far beneath the surface companies can go to extract much deeper oil and gas reserves. New approaches are being applied to develop deeper offshore discoveries , up to 3,000 metres below the surface. One of the challenges of deeper drilling is that divers are unable to carry out maintenance at depths of over 250 meters because of higher pressures from both the water and the sub-sea environment. Equipment needing maintenance needs to brought to the surface for repair , which results in increased downtime and expense.
 
At depths of over 250 meters pressures of up to 150 bar on sub-sea ball valves is common. The soft, polymeric seals traditionally used are unreliable at these pressures. Dense tungsten-carbide coatings, applied using HVOF technology, are needed for the balls and seals to be leak-tight. During high-pressure testing the mirco-hardness of HVOF coatings offers excellent resistance to abrasion when sand or other piping/process debris is present. These coatings are also dense and provide a better surface to achieve a satisfactory gas seal compared to other coatings, and the HVOF coatings do not require sealing of the coating surface to achieve the leak-tight sealing requirements between the ball and seat rings.

 

Additional Information:
To view product relevant to this process, please view our HVOF and Thermal Spray Powders product page
For more information on HVOF Spray Deposition, click here
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