How to quickly repair and care the gear pump of the hydraulic system

CB gear pumps are commonly used in agricultural machinery hydraulic systems. After using the gear pump for a period of time, its performance will decrease. The investigation shows that the main form of gear pump damage is uniform wear and scratch of the bushing, pump casing and gear. The uniform wear is generally between 0.02-0.50mm. The depth of the mark is generally between 0.05 and 0.50 mm. Due to the limitation of agricultural time, it is urgent to repair in a short time after the damage, and the secondary service life of the gear pump after maintenance and the maintenance cost and the on-site operability of the maintenance work must also be considered. This article describes the arc spray and stick coating techniques in the quick fix method.

Arc Spray Repair Technology for Gear Pumps 1. Principle and Characteristics of Arc Spray Technology Arc coating technology has developed rapidly in materials, equipment and applications for nearly 20 years. Its working principle is to use two sprayed wires as melting electrodes. The variable speed drive, which is short-circuited at the nozzle mouth, causes an arc to melt, is atomized by compressed air into particles, and is sprayed at a high speed onto the pretreated working surface to form a coating. It is a spraying method with high spraying efficiency, high bonding strength and good coating quality. It has the advantages of high energy utilization rate, low equipment investment and low cost, simple equipment, convenient and flexible operation, convenient on-site construction and safety.

2. The arc spray repairing process of the gear pump has a uniform hardness and a strong joint strength with the part body when the inner hole of the bushing, the outer circle of the bushing, the gear shaft and the pump casing are evenly worn and scratched between 0.02-0.20mm. , good wear resistance, good arc spray repair process. Arc spraying process: working surface pretreatment → preheating → spraying bonding bottom layer → spraying working layer → cooling → coating processing.

In the spraying process, the workpiece is required to be free of oil, rust, uniform surface roughness, proper preheating temperature, uniform and firm bottom layer, smooth and smooth working layer, reliable fusion of material particles, good wear resistance and corrosion resistance. The quality of the sprayed layer is closely related to the surface treatment method and the spraying process of the workpiece. Therefore, it is very important to choose the appropriate surface treatment method and spraying process. In addition, the non-spray portion adjacent to the surface to be coated is bundled with a thin sheet of iron or copper during the spraying and spraying process. (1) The pre-treatment coating on the surface of the workpiece is related to the basic bonding strength and the cleanliness and roughness of the substrate. Pre-treatment of the basic surface, such as cleaning, degreasing and surface roughening, is an important process in the spraying process before spraying. First, the spraying part should be degreased with gasoline and acetone, and the fatigue layer and the oxide layer should be removed with a trowel, fine sandpaper and oil stone to expose the metallic color. Then, the roughening treatment is performed, and the roughening treatment can provide surface compressive stress, increase the bonding area between the coating and the substrate, purify the surface, reduce the stress during cooling of the coating, and moderate the internal stress of the coating, so that the adhesion is increased. . Sand blasting is a common roughening process of Zui. The sand is sharp and hard, and quartz sand and silicon carbide can be used. The rough fresh surface is easily oxidized or polluted by the environment, so it should be sprayed in time. If it is placed for more than 4 hours, it should be re-roughened.

(2) The temperature difference between the surface pre-heat treatment coating and the surface of the substrate causes the coating to produce shrinkage stress, causing cracking and peeling of the coating. Preheating of the surface of the substrate can reduce and prevent the aforementioned adverse effects. However, the preheating temperature should not be too high, so as to avoid oxidation of the surface of the substrate and affect the bonding strength of the coating to the surface of the substrate. The preheating temperature is generally 80-90 ° C, which is usually done with a neutral flame.

(3) Spray bonding The primer layer is pre-sprayed with a thin layer of metal before spraying the working coating to provide a clean, rough surface for the subsequent coating, thereby improving the bonding strength and shear strength between the coating and the substrate.

The chrome-nickel alloy is generally used as the bonding underlayer material. The main principle of selecting the spray process parameters is to increase the bond strength of the coating to the substrate. During the spraying process, the relative moving speed of the spray gun and the workpiece is greater than the moving speed of the flame. The speed is determined by the thickness of the coating, the feeding speed of the coated wire, and the arc power. The distance between the spray gun and the surface of the workpiece is generally about 150 mm. Other specification parameters for arc spraying are determined by the characteristics of the spray equipment and the spray material.

(4) Spraying the working layer should first remove the deposit on the surface of the bonded bottom layer with a wire brush, and then immediately spray the working coating. The material is carbon steel and low alloy wire, which makes the coating have high wear resistance and low price. The thickness of the sprayed layer shall be determined according to the wear amount of the workpiece, the machining allowance and other relevant factors (diameter shrinkage, clamping deviation, uneven thickness of the sprayed layer, etc.).

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

(6) Spray coating processing to the dimensions required by the drawings and the specified surface roughness.

Surface coating and repair technology of gear pump 1. Principle and characteristics of surface adhesive coating In recent years, surface adhesive coating technology has been widely used in equipment maintenance in China, and is suitable for repairing parts and equipment of various materials. The working principle is to directly apply the adhesive of special filler such as molybdenum disulfide, metal powder, ceramic powder and fiber to the surface of the material or part to make it wear-resistant and corrosion-resistant, mainly used for surface strengthening and repair. . Its process is simple, convenient, flexible, safe and reliable. It does not require special equipment. It only needs to apply the glue to the surface of the cleaned parts. After curing, it can be trimmed. It is often operated at room temperature and will not make parts. Produces thermal power equivalent effects and deformations.

2, the coating process of the adhesive coating, the outer circumference of the sleeve, the end face of the sleeve, the end face of the gear or the small area of ​​the inner hole of the pump casing, the uniform wear amount is between 0.15-0.50mm, and the scratch depth is above 0.2mm. At the time, it is advisable to use a tack coating process. Coating process of adhesive coating: initial cleaning → pre-processing → post-zui cleaning and activation treatment → preparation of repair agent → coating → curing → trimming, cleaning or post-processing.

Although the adhesive coating process is relatively simple, the actual construction requirements are quite strict. It is not always possible to obtain a high adhesive strength by simply selecting a good adhesive. It is necessary to select a suitable adhesive, and to apply a suitable adhesive in strict accordance with the correct process, and to strictly follow the correct process to obtain a satisfactory adhesive coating effect.

(1) There must be no grease, water, rust, dust, etc. on the surface of the initial cleaning parts. It should be washed first with gasoline, diesel or kerosene, and then with acetone.

(2) The pre-machining is ground into a certain groove mesh with fine sandpaper to expose the original color of the substrate.

(3) After the Zui cleaning and activation treatment is carried out with acetone or a special cleaning agent. It is then treated with sand blasting, flame or chemical treatment to increase surface activity.

(4) Preparation of repairing agent When using the agent, the agent (A) and the curing agent (B) should be thoroughly mixed according to the prescribed ratio, and the color should be consistent, and it should be used up within the prescribed time.

(5) The coating repairing agent is first thinly coated on the surface of the adhesive repairing surface, repeatedly scraped to fully wet the parts, and then uniformly applied to the specified size, leaving a finishing allowance. The coating is moved as far as possible in one direction, and the reciprocating coating will enclose air in the glue to form bubbles or pores.

(6) The curing is coated with a release agent on the steel plate for work. Generally, it takes 24 hours to cure at room temperature, and 2-3 hours after heating and curing (about 80 ° C).

(7) Trimming, cleaning or post-processing for fine boring or finishing of the sticky surface to the required size with assorted enamel, fine sandpaper and whetstone.