Application status and Prospect of surface strengthening technology in single screw pump rotor

                                                                                                                                                                                                   Huang Jiping, Yang Ling, Feng Shengqiang

(1) Ningbo Zhenhai reducer Co., Ltd., Ningbo 315200, Zhejiang; 2. Hangzhou Xinglong Pump Co., Ltd., Hangzhou 310018; 3. Ningbo Branch of China Academy of weapons and materials science, Ningbo 315103, Zhejiang Province

Abstract: the failure of screw in screw pump is mainly wear failure. The development level of surface strengthening technology of screw pump rotor is introduced. On this basis, laser alloying technology, thermal spraying conventional coating technology and rare earth reinforced ceramic coating technology are introduced respectively. The wear resistance and corrosion resistance of rare earth reinforced ceramic coating are introduced. The future development trend and application prospect are prospected.

introduction

The rotor and stator of screw pump are a key part of the whole machine. The most common failure form of screw is wear and corrosion. Its life directly affects the quality of the unit. The existing wear-resistant materials and surface strengthening technology can not effectively improve the service life of the rotor, which is still far from the imported rotor. Therefore, researchers have been exploring to extend the wear life of screw by adopting high alloy wear-resistant and corrosion-resistant materials and improving the hardness of the parts. However, this method will make the content of precious metals in the material increase continuously. In addition, the wear and corrosion of screw pump occur on the surface of the parts, and the high alloy materials in the center are also a waste. In view of this situation, the coating with wear-resistant and corrosion resistance and sealing technology for ceramic coating defects can give full play to the role of coating materials, greatly reduce the manufacturing cost of parts and save precious metal resources. This technology has good social and direct economic benefits.

1. Technical gap at home and abroad

In the aspect of strengthening the surface of screw, developed countries in Europe and America, especially Germany, have always been in the forefront. For example, the best screw wear resistance protection technology in Germany is the new technology of bezalioj spiral edge coating developed by Battenfeld extrusiontechnik, which makes the extrusion production safety, reliability and wear resistance reach the best state. The results of trial production show that the wear resistance of the screw with bexalit coating protection technology is 100% higher than that of the conventional nitriding screw. The company adopts the repeatable plasma powder - inlaid coating technology. The metal bonding between the base material and the inlay layer is complete and thorough, so the stress cracks in preheating and cooling can be avoided during cladding. The next plasma nitriding process makes the performance between screw screw and barrel wall further improved.

At present, there is still a big gap between the domestic technology and the achievements in the reinforcement treatment of screw surface compared with the developed countries in Europe and America. For example, the life of domestic high chromium white cast iron rotor is 78% of that of imported Ni hard white cast iron; that of 45 × steel base rotor surface spray welding Ni60 + WC pre protection rotor is 33%; 45 # the carbon nitrogen penetration treatment life of 45 # 45 # the life of 45 # the life of 45 # the life of 45 # the life of 45 # the life of 45 # the life of 45 # the life of the plated hard chromium rotor on the steel base rotor is less than 22%. It can be seen that although many treatments have been carried out on the rotor substrate surface in China, the results are not satisfactory.

Laser alloying technology

Laser alloying technology has been put forward in China, which has high cost performance, high temperature adhesion and wear resistance and excellent corrosion resistance to strengthen the surface of screw, so as to meet the demand of plastic raw materials. The laser alloying composite coating is made up of high-tech nano ultrafine alloy powder on the surface of the easily worn screw. The screw matrix material is 40Cr steel, and the super fine alloy powder (1-5 μ m) with excellent red hardness and good corrosion resistance is adopted. The A1 ultrafine alloy powder (1-5 μ m) with good adhesion and wear resistance and nano carbon pipe mixed alloy are used. The mass ratio is 1:1:1, and the chemical elements are C, W, Co, Cr, Ni, Mo, etc. The surface cladding technology of solid-state laser is used to realize the metallurgical combination of coating and substrate. The service life of the screw after laser alloying is increased by at least 2 times. At the end of last century, Ma'anshan Mine Research Institute has developed a new hard surface pre protection rotor technology based on 45 steel for the service life of high chromium cast iron rotor used in the pump rotor of wet jet jet jet machine, which is based on 45 steel. The technology adopts spray welding technology. By adding CR, Mo and w on nickel base, the formation of the rotor is promoted under the condition of high temperature of oxyacetylene The second phase hexagonal and cubic carbide with high hardness and high wear resistance promotes the formation of dispersion distribution between Laves and the second phase to strengthen the spray welding layer matrix.

3. Conventional coating technology of thermal spraying

In recent years, the coating of spray ceramic has shown excellent performance in the aspect of wear resistance, but the damage of the coating of screw rotor is often caused by the peeling off of the coating. At present, the direct reason for coating peeling is that the combination of coating and substrate is unfavorable, which leads to the premature peeling of coating, which has been widely agreed. Through observation and analysis, it is found that the corrosion at the interface between the coating and the substrate seriously weakens the combination of the coating, which makes the rotor fall off after a period of time. This phenomenon is more prominent in corrosive wet media.

Under the existing technical conditions, porosity and porosity are the defects of coating, whether the coating is formed by sintering or various spraying techniques. If the corrosion medium can be blocked through the internal porosity of the coating, the porosity of the coating and the corrosion of the substrate interface, and the anti-corrosion ability of the interface and the structural strength of the coating itself can be further improved, the bonding strength of the coating can be effectively improved. Under the comprehensive action of the composite technology, the hot spraying ceramic coating can be used in the screw pump under the existing technical conditions Application on rotor.

4 rare earth reinforced ceramic coating technology

In recent years, Ningbo Zhenhai reducer Co., Ltd. has developed rare earth reinforced ceramic coating technology through cooperation with Hangzhou Xinglong Pump Co., Ltd. and Ningbo Branch of China Academy of military science, and achieved the effect of excellent anti-wear and corrosion resistance. The main ways of this technology are: the surface anti-corrosion coating of screw rotor - the treatment of rare earth toughened ceramic powder, the high energy thermal spraying ceramic coating, and the vacuum organic sealing treatment of the coating. The results of the test are shown in Table 1. The wear test is conducted by dry wear of bolt disc. For the wear body, the ￠ 5mmgcr15 steel ball is selected, and the load is 30n and 90N respectively. The speed is 500r/min and the wear time is 30min. The hardness of Cr12MoV steel is HRC58-62 after quenching and tempering heat treatment.

Table 1 friction and wear properties of coating and matrix materials

Table 2 shows the comparison of the corrosion resistance test results between coating and matrix materials. It can be seen from the figure that the corrosion performance of rare earth ceramic coating is the best. The corrosion medium is HCl aqueous solution corrosion, hcl+ deionized water (10% HCl), pH value 1, strong acid. After 800H, 1500h and 2000h salt spray test, no corrosion occurred on the surface. In contrast, the corrosion of wc30% + Fe coating, CRC coating and Cr12MoV steel matrix is much more serious than that of rare earth ceramic coating, especially after 800H, the surface corrosion of Cr12MoV steel has been very serious. The surface corrosion of the four materials is shown in Figures 1 to 4.

                     Table 2 corrosion resistance of coating and base material

The test results of coating deformation resistance are shown in Fig. 5 and Fig. 6. Brinell hardness indentation method was used in the experiment. The diameter of steel ball was 10 mm and the load was 1800 n. The test samples were subjected to 1500 h corrosion test before indentation test.

5 outlook

In the field of thermal spraying wear-resistant coating, especially in the field of screw pump technology, there are few reports on using vacuum infiltration technology to plug coating defects, and there is no application result. The research in this field has advanced technology in China and has the advantage of leading technology in the screw pump industry.

Ningbo Zhenhai reducer Co., Ltd. takes advantage of the advanced equipment and technology of national defense industry, adopts advanced supersonic flame spraying technology and plasma spraying technology in spraying technology, and obtains excellent coating quality. The vacuum sealing technology is adopted in the coating anticorrosion technology, which effectively overcomes the preparation defects of spray coating and improves the structural strength of the coating.

At present, the application of vacuum infiltration technology on coating to plug the defects in coating has been studied, but the progress is slow. Due to the limitation of blocking agent, it lags behind foreign countries in the field of nanoparticle infiltration agent. At present, the vacuum sealing agent imported from Hungary by a Research Institute of ordnance industry adopts silicate nano particle technology, which makes the sealing of micro arc oxidation layer and anodized layer of aluminum and magnesium alloy obtain good effect, and the corrosion resistance of the coating is doubled. At the same time, in the treatment of the interface between the coating and the substrate, the crack free coating technology and crystallization free coating treatment were adopted, which effectively improved the corrosion resistance of the substrate, made the 45 steel substrate reach the acid and alkali corrosion resistance of stainless steel, and effectively increased the corrosion resistance of the coating.