The tooth top cylinder and both sides of the gears meshing with each other are close to the inner wall of the pump casing. A series of sealed working cavities K are formed between each tooth groove and the inner wall of the casing. The D and G chambers separated by the meshing gear teeth are the suction chamber and discharge chamber respectively connected with the pump suction inlet and discharge port. As shown in the figure (external meshing).
When the gear rotates in the direction shown in the figure, the volume of the suction chamber D gradually increases and the pressure decreases because the meshing gear teeth gradually exit the meshing state. Under the action of the pressure difference between the liquid surface pressure in the suction pool and the low pressure in chamber D, the liquid enters the suction chamber D from the suction pool through the suction pipe and the pump suction port. Then it enters the closed working space K and is brought to the discharge chamber G by the rotation of the gear. Because the teeth of the two gears gradually enter the meshing state from the upper side, the teeth of one gear gradually occupy the tooth space of the other gear, so that the volume of the discharge chamber located on the upper side gradually decreases, and the pressure of the liquid in the chamber increases, so the discharge from the pump The discharge port discharges out of the pump. The gears rotate continuously, and the above-mentioned liquid suction and discharge processes are carried out continuously.
The most basic form of a gear pump is that two gears of the same size mesh and rotate with each other in a closely fitting casing. The interior of this casing is similar to an "8" shape. The two gears are installed inside. The outer diameter and both sides of the gear are in line with the The housing is a tight fit. The material from the extruder enters between the two gears at the suction port and fills this space. It moves along the housing as the teeth rotate, and is finally discharged when the two teeth mesh.
Working principle of gear pump
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The working principle of the gear pump is shown in the figure. It is a separated three-piece structure. The three pieces refer to the pump cover 4, 8 and the pump body 7. The pump body 7 is equipped with a pair of teeth with the same number, the width is close to the pump body and meshes with each other. Gear 6, this pair of gears, both end covers and the pump body form a sealing chamber, and the sealing chamber is divided into two parts by the tooth tops and meshing lines of the gears, namely the oil suction chamber and the pressure oil chamber. The two gears are respectively fixed on the driving shaft 12 and the driven shaft 15 supported by needle bearings with keys, and the driving shaft is driven to rotate by the electric motor.
The structure of the gear pump is as shown in the figure. When the driving gear of the pump rotates in the direction of the arrow in the figure, the gear on the right side of the gear pump (suction chamber) is disengaged, and the gear teeth withdraw from the space between the teeth, causing the sealing volume to increase, forming Due to partial vacuum, the oil in the tank enters between the teeth through the oil suction pipeline and the oil suction chamber under the action of external atmospheric pressure. As the gear rotates, the oil sucked between the teeth is brought to the other side and enters the oil pressure chamber. At this time, the gear teeth enter into mesh, so that the sealing volume gradually decreases, and the oil in the part between the gears is squeezed out, forming the oil pressure process of the gear pump. When the gear meshes, the tooth contact line separates the oil suction chamber and the oil pressure chamber, which plays the role of oil distribution.
When the driving gear of the gear pump is continuously rotated by the motor, the gear teeth are disengaged from the meshing side, and oil is continuously sucked from the tank due to the enlarged sealing volume. Drain oil, this is how a gear pump works.
The front and rear covers of the pump and the pump body are positioned by two positioning pins 17 and fastened with 6 screws as shown in Figure 3-3. In order to ensure that the gear can rotate flexibly while ensuring minimal leakage, there should be an appropriate clearance (axial clearance) between the gear end face and the pump cover. The axial clearance for small flow pumps is 0.025~0.04mm, and for large flow pumps 0.04~0.06mm.
The gap (radial gap) between the tooth top and the surface of the pump body has a small impact on leakage due to the long sealing belt and the shear flow formed by the tooth top linear velocity and the direction of oil leakage. The problem is: when the gear is subjected to an unbalanced radial force, the tooth top should avoid collision with the inner wall of the pump body, so the radial gap can be slightly larger, generally 0.13~0.16mm.
Classification and structural characteristics of gear pumps
1. According to the form of gear meshing, it can be divided into: external meshing type and internal meshing type.
2. According to the tooth curve, it can be divided into: involute tooth form and cycloid form
3. According to the tooth surface form, it can be divided into: spur gear type, helical gear type, herringbone gear type, and arc tooth surface gear type.
4. According to the number of meshing gears: two-gear type and multi-gear type
5. According to the number of gear stages, it can be divided into: single-stage gear pump and multi-stage gear pump
Gear pumps have simple structure, easy processing, small size, light weight, strong self-priming ability and insensitivity to oil contamination, so they are widely used. my country's gear pump industry has two major competitive advantages: on the one hand, it has the competitive advantage of low cost; on the other hand, the rapid growth of the domestic construction, petroleum, petrochemical, and environmental protection markets and major water diversion projects have also contributed to the development of my country's gear pump industry. provided important support. my country's continuously growing market space is a prerequisite for the domestic gear pump industry to maintain its advantages.
However, disadvantages such as unbalanced radial force, large flow pulsation, loud noise, short bearing life, poor interchangeability of parts, difficulty in repairing after wear, and inability to adjust the displacement limit the scope of use of gear pumps. It cannot be used as a variable pump.
Has the following characteristics
1. Good self-priming performance.
2. The suction and discharge direction completely depends on the rotation direction of the pump shaft.
3. The flow of the pump is not large and continuous, but there is pulsation and loud noise; the pulsation rate is 11% to 27%, and its unevenness is related to the number and shape of gear teeth. Helical gears have smaller unevenness than spur gears, and people The unevenness of helical gears is smaller than that of helical gears. The fewer the number of teeth, the greater the pulsation rate.
4. The theoretical flow rate is determined by the size and rotation speed of the working parts and has nothing to do with the discharge pressure; the discharge pressure is related to the load pressure.
5. It has a simple structure, low price, few wearing parts (no need for suction and discharge valves), impact resistance, reliable operation, and can be directly connected to the motor (no need for a reduction device).
6. There are many friction surfaces, so it is not suitable to discharge liquid containing solid particles, but oil.
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