Created on:2021-11-09 13:05

Brief introduction of quick repair method of CB-B gear pump

Brief introduction of quick repair method of CB-B gear pump

After CB-B gear pump is used for a period of time, its performance will decline. The investigation shows that the main damage forms of gear pump are uniform wear and scratches of shaft sleeve, pump shell and gear. The uniform wear amount is generally 0.02 ~ 0.50mm and the scratch depth is generally 0.05 ~ 0 ~ 50mm. Due to time constraints, it is urgent to repair in a short time after damage, and the secondary service life after maintenance, maintenance cost and on-site operability of maintenance work must also be considered. Arc spraying and adhesive coating technology in rapid repair method are introduced below.

(1) Arc spraying repair technology of gear pump.

1) Principle and characteristics of arc spraying. Arc spraying technology has developed rapidly in materials, equipment and applications in recent 20 years. Its working principle is that two sprayed metal wires are used as melting electrodes and driven by a motor at variable speed. A short circuit is generated at the intersection of the spray gun mouth to cause arc melting. With the help of compressed air, particles are atomized into particles and sprayed at high speed to the pretreated workpiece surface to form a coating. It has the advantages of high spraying efficiency, low equipment investment and use cost, simple equipment, convenient and flexible operation, convenient on-site construction and safety.

2) Arc spraying repair technology of gear pump. When the uniform wear and scratches of the inner hole of the shaft sleeve, the outer circle of the shaft sleeve, the gear shaft and the pump housing are 0.02 ~ 0.20mm, the arc spraying repair process with high hardness, strong bonding force with the parts and good wear resistance should be adopted. Arc spraying process: workpiece surface pretreatment - preheating - spraying bonding bottom layer - spraying working layer - cooling bucket coating processing.

In the spraying process, the workpiece shall be free of oil and rust, the surface shall be rough and uniform, the preheating temperature shall be appropriate, the bottom layer shall be combined evenly and firmly, the working layer shall be smooth and flat, the material particles shall be fused and bonded reliably, and the wear resistance and corrosion resistance shall be good. The quality of spraying layer is closely related to the workpiece surface treatment method and spraying process. Therefore, it is very important to select the appropriate surface treatment method and spraying process. In addition, during sand blasting and spraying, the non sprayed part adjacent to the sprayed surface shall be bound with thin iron sheet or copper sheet.

① Workpiece surface pretreatment. The bonding strength between the coating and the substrate is related to the cleanliness and roughness of the substrate. Before spraying, the pretreatment of substrate surface, such as cleaning, degreasing and surface roughening, is an important process in the spraying process. Firstly, the spraying part shall be degreased with gasoline and acetone, and the fatigue layer and oxide layer shall be removed with file, fine sandpaper and oilstone to expose the natural color of the metal. Then the coarsening treatment is carried out. The coarsening treatment can provide surface compressive stress, increase the bonding area between the coating and the substrate, purify the surface, reduce the stress during coating cooling and ease the internal stress of the coating, so it is conducive to the increase of bonding force. Sand blasting is the most commonly used coarsening process. The sand particles are sharp and hard. Quartz sand and emery can be selected. The rough fresh surface is easily oxidized or polluted by the environment, so it shall be sprayed in time. If it is placed for more than 4h, it shall be re roughened.

② Surface preheating treatment. The temperature difference between the coating and the substrate surface will cause shrinkage stress of the coating, resulting in cracking and spalling of the coating. Preheating of the substrate surface can reduce and prevent the above adverse effects. However, the preheating temperature should not be too high, so as not to cause oxidation on the substrate surface and affect the bonding strength between the coating and the substrate surface. The preheating temperature is generally 80 ~ 90 ℃, which is usually completed by neutral flame.

③ Spray bonding bottom layer. A thin layer of metal is sprayed in advance before spraying the working coating to provide a clean and rough surface for the subsequent coating, so as to improve the bonding strength and shear strength between the coating and the substrate. The bonding base material is generally chromium iron nickel alloy. The main principle of selecting spraying process parameters is to improve the bonding strength between coating and substrate. In the spraying process, the relative moving speed between the spray gun and the workpiece is greater than the flame moving speed. The speed is determined by the parameters such as coating thickness, spraying wire feeding speed, arc power and so on. The distance between the spray gun and the workpiece surface is generally about l50mm. Other specification parameters of arc spraying are determined by the characteristics of spraying equipment and spraying materials.

④ Spray the working layer. The deposits adhering to the underlying surface shall be removed with a wire brush, and then the working coating shall be sprayed immediately. The material is carbon steel and low alloy wire, so that the coating has high wear resistance and low price. The thickness of spraying layer shall be determined according to the wear amount of workpiece, machining allowance and other relevant factors (diameter shrinkage, clamping deviation, uneven diameter of spraying layer, etc.).

⑤ Cool. After spraying, the temperature rise of the workpiece is not high, and generally it can be directly air cooled.

⑥ Spraying layer processing. Machining to the size required by the drawing and the specified surface roughness.

(2) Surface sticking repair technology of gear pump.

1) Principle and characteristics of surface bonding. In recent years, surface adhesion technology has been widely used in equipment maintenance in China. It is suitable for the repair of parts and equipment of various materials. Its working principle is that the adhesive added with special fillers such as molybdenum disulfide, metal powder, ceramic powder and fiber is directly coated on the surface of materials or parts to make it have the functions of wear resistance and corrosion resistance. It is mainly used for surface strengthening and repair. Its process is simple, convenient, flexible, safe and reliable. It does not need special equipment. It only needs to apply the prepared glue to the cleaned part surface and repair it after curing. It is often operated at room temperature without thermal impact and deformation of the part.

2) Coating process of adhesive coating. When the uniformity of the small area of the outer circle of the shaft sleeve, the fitting surface of the shaft sleeve end face, the gear end face or the inner hole of the pump housing is 0.15 ~ 0.50mm and the scratch depth is more than 0.20mm, the adhesive repair process should be adopted. Coating process of adhesive coating; Initial cleaning - pre-processing - final cleaning and activation treatment - Preparation of repair agent bucket coating - curing bucket trimming, cleaning or post-processing.

Although the bonding process is relatively simple, the construction requirements are quite strict. Satisfactory bonding effect can be obtained only by selecting a good adhesive and strictly adhering to the correct process method.

① Initial cleaning. The surface of parts must be free of grease, water, rust, dust, etc. It shall be cleaned with gasoline, diesel or kerosene first, and finally with acetone.

② Pre processing. Grind it into a certain groove network with fine sandpaper to expose the natural color of the matrix.

③ Finally, cleaning and activation treatment. Use acetone or special cleaning agent, and then treat with sand blasting, flame or chemical method to improve surface activity.

④ Prepare repair agent. When using the repair agent, the agent (a) and curing agent (b) shall be fully mixed in strict accordance with the specified proportion, the color shall be consistent, and shall be used up within the specified time.

⑤ Coating. First, apply a thin layer of repair agent on the bonded surface, scrape it repeatedly to fully soak it with the parts, then apply it evenly to the specified size, and leave fine I allowance. Move in one direction as much as possible during coating. Reciprocating coating will wrap air in the glue to form bubbles or pores.

⑥ Curing. Press the steel plate coated with release agent on the workpiece. Generally, it takes 24h for curing at room temperature and 2 ~ 3H for heating curing (about 80 ℃).

⑦ Trimming, cleaning or post-processing. Finish boring or finish the bonded surface to the required size with assorted file, fine sandpaper and oilstone.

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