Quick Repair of Hydraulic Gear Pumps Using Arc Spray Technology

       CB series gear pumps are often used in agricultural machinery hydraulic systems. After a gear pump has been used for a period of time, its performance will decline. The investigation shows that the main forms of gear pump damage are uniform wear and scratches on the shaft sleeve and pump casing. Due to the limitation of agricultural time, it needs to be repaired in a short time after damage, and the secondary service life of the gear pump after repair, the repair cost and the on-site operability of the repair work must also be considered. 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 casing are between 0.02mm and 0.20mm, arc spraying with high hardness, strong bonding with the part matrix and good wear resistance should be used. Repair process. The process of arc spraying: working surface pretreatment → preheating → spray bonding bottom layer → spray working layer → cooling → coating processing.



    1) Workpiece surface pretreatment

   The bonding strength of the coating to the substrate is related to the cleanliness and roughness of the substrate. Before spraying, cleaning, degreasing and surface roughening of the substrate surface is an important process in the spraying process. First, the sprayed part should be degreasing with gasoline and acetone, and the fatigue layer and oxide layer should be removed with a file, fine sandpaper, and oil stone to expose the metal color. Then roughening treatment is carried out. The roughening treatment can provide surface compressive stress, increase the bonding area between the coating and the substrate and purify the surface, reduce the stress when the coating is cooled, and ease the internal stress of the coating, so it is conducive to the increase of adhesion. . Sandblasting is the most commonly used roughening process. The sand should be sharp and hard. Quartz sand, emery, etc. can be used. The roughened fresh surface is easily oxidized or polluted by the environment, so it should be sprayed in time, and if it is left for more than 4 hours, it should be re-roughened.

    2) Surface preheating treatment

    The temperature difference between the coating and the substrate surface will cause shrinkage stress in the coating, causing cracking and spalling of the coating. Preheating of the substrate surface can reduce and prevent the aforementioned adverse effects. However, the preheating temperature should not be too high, so as not to cause the surface of the substrate to oxidize and affect the bonding strength of the coating and the surface of the substrate. The preheating temperature is generally 80 ℃ ~ 90 ℃, and it is usually done with a neutral flame.

    3) Spray bonding the bottom layer

    A thin layer of metal should be pre-sprayed before spraying the working coating. The base material for bonding is generally a chromium-iron-nickel alloy to provide a clean and rough surface for the subsequent coating, thereby improving the bonding strength and shear resistance between the coating and the substrate. strength. The main principle of selecting spraying process parameters is to improve the bonding strength of coating and substrate. During the spraying process, the relative moving speed of the spray gun and the workpiece is determined by the coating thickness, the feeding speed of the spraying filament, the arc power and other parameters. The distance between the spray gun and the surface of the workpiece is generally about 150mm. Other specification parameters for arc spraying are determined by the characteristics of the spraying equipment and the sprayed material.

    4) Spray the working layer

    The deposit should be removed with a wire brush from the surface of the bonded substrate, then the working coat should be applied immediately. The material is carbon steel and low alloy wire, which makes the coating have higher wear resistance and lower price. The thickness of the sprayed layer should be determined according to the wear amount of the workpiece, the machining allowance and other related factors (diameter shrinkage, clamping deviation, uneven diameter of the sprayed layer, etc.).

    5) Cool down

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

    6) Spray coating processing

    Machined to the dimensions required by the drawing and to the specified surface roughness.