In the metallurgical industry, there are many kinds of rollers and conveying rollers that need to be strengthened or repaired. Among them, the continuous annealing furnace bottom roller of cold rolled strip steel is an important one. Cold-rolled strip steel depends on a set of rollers in furnace turn the implementation work, general of temperature in the annealing furnace of 450 ~ 1200 ºC, under the high temperature furnace roller continuous conveying steel strip, steel strip surface oxide film or deposition reduction of iron filings and activation, generate Fe, Fe3O4 and FeO and other compounds, with the roller surface under the action of friction, produce very big extrusion stress, When the protective film of the roll surface is destroyed, the exposed active metal surface will weld with the activated iron powder under compressive stress, causing the roll surface to form nodule, destroying the original roughness of the roll surface, and the strip steel will be scratched by nodule, affecting the surface quality.
Nodulation of the roller surface is actually adhesion wear. In order to reduce the loss caused by nodulation to the production of steel strip, the NiCr-Cr3C2 coating can be sprayed on the roller surface by supersonic flame spraying. It has the characteristics of high temperature oxidation resistance, thermal shock resistance and wear resistance. It can make the bottom rod work continuously for a long time at high temperature and withstand the periodic thermal shock. When the operating temperature of the low roller exceeds 900ºC, a strand of Co-based alloy is sprayed.
In the metallurgical production line, a large number of conveying rollers are used to transport all kinds of steel. After long-term use, wear and tear appear, which affects the quality of steel. Co-based WC coating can be sprayed on the surface of the conveyor roller, which generally works at 450ºC and has good wear resistance and comprehensive mechanical and mechanical properties.
Supersonic flame spraying has unique advantages in the field of spraying carbide ceramics, and the metallurgical industry has a great demand for carbide cermet coating, so it has been widely used.
In addition, the sunking roller on the hot galvanized line also needs to be protected by thermal spraying. The hot galvanized sheet has good corrosion resistance, processing formability, weldability and environmental protection, etc. It is widely used in various fields such as automobiles, construction, home appliances and national defense. At present, most of the hot zinc dipping units of the steel strip in the world's iron and steel enterprises adopt the sunk-roll device. The sunk-roll and other parts of the molten zinc production line are immersed in the molten zinc solution of 450~480ºC, which is easily corroded by the zinc solution with strong activity or precipitated Fe-Al-Zn intermetallic compound nodulation, which makes the surface of the roll pitting, pits and become rough. Affects the surface quality of galvanized steel plate. In order to prevent the direct contact between liquid zinc and submerged roll alloying corrosion reaction, resulting in the surface of the steel roll coarsening and affecting the quality of galvanized steel plate, the surface of the continuous submerged roll is generally sprayed to protect the treatment. The coating materials are WC-Co, Mob-Mo and Fe-Al thermal spraying powder. The corrosion resistance of WC-Co coating in zinc solution depends on its adhesive phase. Because the diffusion corrosion channel of zinc liquid in the coating is mainly along the cobalt-rich phase, when the bonding phase composition of the coating is mainly η phase (Co3W3C and Co6W6C, etc.), η phase can effectively prevent the diffusion of zinc liquid into the coating and delay the corrosion of zinc liquid on the coating. On the other hand, the WC particle size and CO content in the coating also directly affect the corrosion resistance and service life of the coating. Coatings with small WC grains and low Co content have higher wear resistance, while their corrosion resistance in Zn solution is poor. Therefore, appropriate WC particle size and appropriate Co content should be selected to achieve better comprehensive performance. When the WC grain size is 2~4μm and the CO content is 10% ~ 17%, the coating has the best performance.
Main Performance Indicators
1, the porosity is only 0.5%,
2, the microhardness of the coating is up to 1250HV0.2,
3. The bonding strength of coating and substrate is greater than 70MPa.
4, its service life can be up to 40 ~ 50 days,
5. Surface roughness: RA0.2