Thermal spray coatings in steel production

2024-05-25

Different coating solutions are required in different application environments. The following examples are focused on the technical services developed to meet the surface roughness requirements of bridle rolls and to accommodate the high temperature wear and corrosion challenges of furnace rolls.

Bridle rollsts
Bridle rolls are used to control the strip tension and are mainly used in continuous pickling lines, continuous annealing lines and continuous galvanizing lines. In order to control the strip tension, the roll surface must be rough enough to prevent sliding between the roll and the steel plate, and also not so rough, so that the strip surface has a distinct surface texture. Inaddition, the roller surface must be wear-resistant in order to maintain this suitable surface roughness over a long service life.
In the past, a chrome plating process was often used, and hard chrome plated coatings have been replaced by tungsten carbide coatings due to the excellent wear resistance of HVOF tungsten carbide coatings. The average roughness of the coating during the chromium plating process is Ra = 6 μm, which ensures sufficient friction between the strip and the rolls without affecting the surface quality of the strip. The surface roughness after HVOF is often greater than the surface roughness of the chrome plating process, and further grinding and machining processes need to be used to ensure the roughness of the sprayed coating to avoid various damages that might happen during using process.

The service life of Bridle rolls sprayed with tungsten cobalt carbide coating greatly exceeds service life of chrome plated rolls. Industrial tests out on a continuous annealing line showed that the Ra of chrome plated rolls was reduced from 6 μm to 2 μm after 8 months, whereas the roughness of thedetonation sprayed tungsten carbide-cobalt coating was only reduced from 6 μm to 3 μm after 36 months of use. Similar results were found for the guide rolls sprayed with tungsten carbide-cobalt coating compared with the chrome plated rolls.

Hearth rolls

Rolling most cold rolled steel requires heat treatment in a continuous annealing line to improve the ductility of the plate. The steel plate passes through the various parts of the heat treatment furnace in a horizontal or vertical direction. In a horizontal continuous annealing line, the rolls that are supporting the steel plate are usually 100-150 mm in diameter; In a vertical continuous annealing line, the diameter of the rolls are 900-1600 mm in order to avoid high surface stresses on the steel plate. The furnace made up with a rapid heating zone, an insulation zone, a cooling zone and an over aging zone. The heating gas is reduced N2-5% H2, and the temperature is determined by the composition of the steel and the plate thickness. The annealing temperature of most cold rolled steel is 730~830℃. With special heat treatment it can went up to 1200 ℃.
high-temperature reducing conditions and withstand multiple thermal cycles without failure. The surface is wear-resistant and can maintain the required minimum surface roughness to avoid sliding or extrusion of the steel plate on the surface of the rolled parts. Control of strip movement is becoming increasingly important due to increased productivity and higher strip running speeds. Finally, the roll must be able to resist agglomeration on the surface due to the adhesive accumulative of foreign particles/oxides. When the surface of the roll is smooth, the average load on the roll surface is relatively low, but when the load on the surface of the roll increases due to the formation of adhesions, it makes the surface of the heat softened steel strip show pits and abrasions, defects that are difficult to eliminate in the subsequent leveling process. The presence of defects such as pits and abrasions on the roll surface will increase the generation of adhesions and affects the surface quality of the steel plate.

(END)

This article is excerpted from a note on the wechat public account "Hinte coating".

Company product profile:
Luoyang Golden Egret Geotools Co.,Ltd. founded in2012,is wholly-owned by iisted company XiamenTungsten Co.,Ltd (XTC).As a backbone cemented carbideenterprise of XTC with registered capital of 1.05billionRMB and first investment of ibillion RMB,GEOTOOLSspecializes in producing and selling high quality tungstenpowder,Tungsten Carbide Powder, carbide anvils,carbideroll rings,carbidesubstrates for PDC bit,mining drill bitsand hard facing materials.
Based on decades of production experience of WC based hard-facing materials, world-class technologies and modernautomatic production lines, GEOTOOLS dedicates into development and production of high quality hard facing materialwith high hardness, best wear resistance, best corrosion resistance and application solutions.
XTC brand Thermal Spray Powder mainly includes Wc- based & Cr3C2-based. The WC coating has high hardnessdurable wear resistance, abrasion resistance, corrosion resistance and high bonding strength, mainly used in oil &gas valves, mining tools, injection screws and printing machinery parts, The Cr3c2 coating has higher thermalstability and anti-oxidation, which can be used in a high temperature and corrosive environment, e.g. inner- wall ogas pipeline and pump.
With high degree of sphericity & excellent alloy organization, cemented carbide pellet is mainly used in weldingas an additive material of PTA Powder and tubular weldina rod to improve the wear resistance of the work pieces.
GEOTOOLS provides mono-crvstalline WC-based, coarse-arain wC-based, casting WC-based and other kinds ofPTA powder. With the high quality material, most advanced production lines and word-class technologies, the PTAcoating has high hardness, durable wear resistance, high welding velocity, and low porosity characteristics. Mainlyused in Mining, Oil driling, agriculture machinery, and machining for welding and repairing.
The hard phase of GEOTOOLS tube rods is tunasten or its products with high wear resistance. Tubular welding rods aresuitable for flame brazing and widely used for surface strengthen for oil and mining drill bits.

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