Interpretation of the main component repair and end face sealing issues of gear

Gear pumps can easily establish the pressure required for the mold head, which can reduce the back pressure of the extruder. According to the general rule, for every 1000 PSI decrease in back pressure of an extruder, its output at a given speed can increase by approximately 10%. Generally speaking, non-metallic soft honey gaskets are used for gear pumps at room temperature and low pressure; When subjected to medium pressure and high temperature, use a combination of metal and non-metal sealing gaskets or metal sealing gaskets; When there are significant fluctuations in temperature and pressure, choose elastic or self tightening gaskets; Under low temperature, corrosive media or vacuum conditions, high-performance gaskets should be considered. What needs to be explained here is the impact of flange conditions on gasket selection.

The selection principle of gear pump sealing gasket is that for situations with low requirements, it can be selected based on experience and replaced when it is not suitable. But for those occasions with strict requirements, such as explosive, highly toxic, and combustible gases, as well as highly corrosive liquid equipment, reaction tanks, and transportation pipeline systems, the selection should be based on the working pressure, working temperature, corrosiveness of the sealing medium, and the form of the sealing surface.

Gear pumps may experience some malfunctions during use, and it is hoped that users will pay strict attention to their use. Normal maintenance and upkeep are necessary in daily use, which can play an important role and value in the industry. As the usage time increases, gear pumps may experience malfunctions such as insufficient or even no oil pumping, mainly due to excessive wear and tear on the relevant parts. The wear parts of gear pumps mainly include the active shaft and bushing, the passive gear center hole and shaft pin, the pump housing cavity and gear, the gear end face and pump cover, etc. When the main technical indicators of the gear pump do not meet the requirements after wear and tear, it should be disassembled and separated, the worn parts and degree should be identified, and corresponding measures should be taken.

1. Repair of wear on the driving shaft bushing hole and the driven shaft hole

After the wear of the active shaft bushing hole, the wear marks can be removed by reaming method, and then a bushing that is enlarged to the corresponding size can be used. The wear of the driven shaft hole is also marked by the reaming method, and then the driven shaft is prepared according to the actual size of the reamed hole. Cracks in the shell can be repaired by welding with cast 508 nickel copper welding rods. The weld seam must be tight and porous, and the flatness error of the joint surface with the insulation gear pump cover should not exceed 0.05 millimeters. After the wear of the driving shaft and bushing of the gear pump, the clearance between them increases, which will inevitably affect the pump oil volume. In this case, the method of repairing the active shaft or bushing can be used to restore its normal fit clearance. If the active shaft has slight wear, simply press out the old bushing and replace it with a standard size bushing, and the clearance can be restored to the allowable range. If the active shaft and bushing are severely worn and the fit clearance exceeds the standard, not only should the bushing be replaced, but the diameter of the active shaft should also be increased by chrome plating or vibration welding, and then ground to the standard size to restore the fit requirements with the bushing.

2. Repair of the working surface of the gear pump cover

If the working surface wear of the pump cover is small, manual grinding can be used to remove the wear marks. That is, place a small amount of valve sand on the platform or thick glass plate, and then grind the pump cover on top until the wear marks are flat on the working surface. When the working surface wear of the pump cover exceeds 0.1 millimeters, the method of turning first and then grinding should be adopted.

3. Repair of the internal cavity of the gear pump casing

After the inner cavity of the insulated gear pump casing wears out, the inner cavity embedding method is generally adopted, which means that the inner cavity is enlarged and then embedded with cast iron or steel lining.

4. Repair of valve seat

There are two types of pressure limiting valves: ball valves and plunger valves. After the wear of the spherical valve seat, a steel ball can be placed on the valve seat, and then gently tapped with a metal rod until the ball valve fits tightly with the valve seat. If the valve seat is severely worn, you can first remove the wear marks by reaming, and then use the above method to make it tightly fit. After the plunger valve seat wears out, a small amount of valve sand can be added for grinding until it fits tightly.

5. Insufficient pump flow

The main causes of the malfunction are the closure of the suction or discharge valve, low inlet pressure, blocked outlet pipeline, leakage of the packing box, and low rotational speed. The solution is to first confirm whether the valve is closed, then check if the valve is open and confirm if the discharge volume is normal; Afterwards, perform fastening operations. When there are a large number of leaks that affect production, stop running, disassemble and inspect. Don't forget to check the actual speed of the pump shaft afterwards.

In addition, end face seals are not suitable for using retaining rings and require very small extrusion clearances. There is currently no fixed standard for this, so it is necessary to consider the actual situation for judgment. The function of adding a retaining ring is to protect the O-ring when there is no way to reduce the extrusion gap.

The influence of flange surface roughness. The roughness of the flange surface has a significant impact on the sealing effect, especially when non soft gaskets are used. The high roughness value of the sealing surface is one of the main reasons for leakage. For example, when turning a flange surface, the cutting pattern is a spiral line. When using a metal gasket, if the roughness value is large, the gasket cannot block the spiral groove formed by the cutting pattern. Under pressure, the medium will leak out along this groove. Soft gaskets have much lower requirements for the smoothness of the flange surface because they are prone to deformation and can block the machining tool lines, thereby preventing leakage. For soft gaskets, a flange surface that is too smooth is actually disadvantageous because the interface leakage resistance decreases at this time. So, the required surface roughness of the flange of the gear pump varies depending on the gasket.