External gear pump

创建于05.13

(1)

① The low pressure gear pump is a three piece structure with a pump cover, a shell and a pump cover (Fig. K). A pair of gears installed in the housing 3 are driven by the drive shaft 5. Unloading grooves B are milled on the left and right sections of the shell 3, and the oil leaking through the end face of the shell flows back to the oil suction chamber through the unloading groove B, so as to reduce the axial thrust of the bearing caused by the oil pressure on the joint surface of the shell and the end cover, and reduce the screw load. The oil trap unloading groove E on the front and rear end covers of the pump can eliminate the oil trap problem when the pump is working. The holes a, C and D can send the oil leaking axially and lubricating the bearing back to the oil suction chamber, so that the sealing ring 6 of the transmission shaft is at low pressure, so it is not necessary to set a separate leakage pipe.

This kind of pump has no radial force balance device; the axial clearance is fixed, the axial clearance and its leakage will increase due to the increase of working load, so it is difficult to obtain high volumetric efficiency, so this kind of structure can only be used for low pressure gear pump (usually the rated pressure is below 12MPa). Domestic CB-B external gear pump belongs to this kind of pump, and its rated pressure is 2.5MPa.

② Figure m of high pressure gear pump shows the structure of gear pump with "8" shape floating shaft sleeve. The gear 5 is driven by the transmission shaft 4 with conical shaft extension. The "8" - shaped compensation area A1 of the floating shaft sleeve 6 is surrounded by the housing 1 and two concentric sealing rings 2 with the gear. The pressure oil is introduced from the high pressure oil guide hole B and acts on the "8" - shaped compensation area A1. The leakage oil hole a can lead the internal leakage oil into the oil suction chamber. When the pump is started or no-load and the oil pressure has not been established, the O-ring 2 can generate sufficient and necessary pre tightening contact force between the floating shaft sleeve 6 and the gear 5. The structure of the compensation device is simple. However, because the symmetrical center of the compensation area coincides with the symmetrical center of the end faces of the driving and driven gears, the action line of the hydraulic pressure (that is, the resultant force of the compensation hydraulic pressure) passes through the center of the floating shaft sleeve, while the resultant force line of the hydraulic reverse thrust on the other side of the shaft sleeve deviates from the center of the shaft sleeve to the oil pressure chamber, and these two forces form a couple on the shaft sleeve. The couple is easy to tilt the shaft sleeve, which will not only increase the end clearance and leakage, but also make the shaft sleeve floating inflexible and produce local wear. In order to overcome the above shortcomings, it is usually necessary to increase the matching length between the sleeve and the shell and improve the machining accuracy.

Figure n shows the structure of high pressure gear pump with floating side plate to realize automatic axial clearance compensation. In the pump, the backing plates 2 and 3, floating side plates 1 and 4 (the backing plate is 0.2mm thicker than the floating side plate) and sealing rings 5 and 6 (embedded in the oil drainage area inside the pump cover) are added between the housing 8, the front cover 9 and the rear cover 7. During operation, part of the pressure oil in the pressure oil area acts on the area surrounded by the sealing rings 5 and 6 through two small holes B on the floating side plate, reversely pushing the floating side plate to move inward slightly, so as to keep the axial clearance between 0.03 mm and 0.04 mm. In this way, more than 700% ~ 80% of the leakage can be controlled. Therefore, this kind of pump has high volumetric efficiency and is suitable for high pressure gear pump. The domestic cb-fx series medium and high pressure gear pump belongs to this kind of pump, and its rated pressure reaches 20MPa.

Figure o shows the structure of gear pump with automatic compensation of axial clearance and radial clearance. The left ends of the gear shafts 6 and 7 are in the housing 1 and the right end is in the cover plate 4. The shell is equipped with an axially floating side plate 3, which is similar to the floating sleeve in the end clearance compensation. The internal structure and shape of the shell can make the axial clearance and radial clearance be compensated at the same time. There is a large gap between the shaft hole of the side plate and the gear shaft, and between the depth of the shell and the width of the side plate, which is enough to make the side plate float axially and radially. On the outer end face of the side plate, there is a special shaped rubber sealing ring 2 embedded in the matching groove (see section A-A). The compensation area A1 is determined by the sealing ring, and the high-pressure oil in the pressure chamber of the pump is introduced through the high-pressure oil guiding hole B and acts on the area A1. The shape and size of area A1 balance the pressing force and thrust, and ensure that the axial clearance is the best value. Radial clearance compensation works within the angle Φ (see section B-B). The oil suction pressure acts on the rest of the circumference of the gear; the pressure of the oil pressure chamber acts on the inner surface of the side plate determined by the sector angle Φ of the gear and the width of the gear. This force presses the gear towards the oil suction chamber to the limit of the bearing clearance, and pushes the side plate towards the oil pressure chamber. The force acting on the side plate from the outside (working pressure × area A3) pushes the side plate towards the oil suction chamber, so it can automatically compensate within the range of Φ angle after radial wear. The compensation area A3 limited by the sealing ring 9 is designed to balance the force generated by it with the reverse thrust and keep the best clearance under a certain working pressure. At the bottom of the shell, the seal within the West angle range is guaranteed by two special elastic rings 5 (see section view C-C). The pre pressing force of the side plate on the gear is generated by the rubber sealing ring 9 in the radial direction and by the sealing rings 2 and 8 in the axial direction. The internal leakage oil passes through the shaft hole, and then leads into the oil suction chamber through the leakage hole a. Because the two kinds of clearance can be compensated to the best value, the gear pump with this structure can be used for higher working pressure.

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