Detailed explanation of the internal structure and main components of a reciprocating compressor
Detailed explanation of the internal structure of a reciprocating compressor
Reciprocating compressors are mainly composed of body, crankshaft, connecting rod, piston group, air valve, shaft seal, oil pump, energy adjustment device, oil circulation system and other components.
The following is a brief introduction to the main components of the compressor.
body
The body of the reciprocating compressor consists of two parts: the cylinder block and the crankcase, which are generally cast as a whole using high-strength gray cast iron (HT20-40). It is the body that supports the weight of the cylinder liner, crankshaft connecting rod mechanism and all other parts and ensures the correct relative position between the parts. The cylinder adopts a cylinder liner structure and is installed in the cylinder liner seat hole on the cylinder block to facilitate repair or replacement when the cylinder liner is worn.
crankshaft
The crankshaft is one of the main components of the reciprocating compressor and transmits all the power of the compressor. Its main function is to change the rotational motion of the motor into the reciprocating linear motion of the piston through the connecting rod. When the crankshaft is in motion, it bears alternating composite loads of tension, compression, shear, bending and torsion. The working conditions are harsh and require sufficient strength and stiffness as well as the wear resistance of the main journal and crankpin. Therefore, the crankshaft is generally forged from 40, 45 or 50-well high-quality carbon steel.
link
The connecting rod is the connecting piece between the crankshaft and the piston. It converts the rotational motion of the crankshaft into the reciprocating motion of the piston, and transmits the power to the piston to perform work on the gas. The connecting rod includes the connecting rod body, the connecting rod small end bushing, the connecting rod large end bearing bush and the connecting rod bolt. The connecting rod structure is shown in Figure 7. The connecting rod body bears alternating tensile and compressive loads during operation, so it is generally forged with high-quality medium carbon steel or cast with ductile iron (such as QT40-10). The rod body mostly adopts an I-shaped cross-section and a long hole is drilled in the middle as an oil passage. .
cross head
The crosshead is the component that connects the piston rod and connecting rod. It makes reciprocating motion in the middle body guide rail and transmits the power of the connecting rod to the piston component. The crosshead is mainly composed of a crosshead body, a crosshead pin, a crosshead shoe and a fastening device. The basic requirements for a crosshead are to be lightweight, wear-resistant and have sufficient strength. The crosshead body is a double-sided cylindrical structure, which is positioned with the sliding shoes through tongue and groove and connected together with screws. The crosshead sliding shoe is a replaceable structure, with bearing alloy cast on the pressure-bearing surface and oil grooves and oil passages. Crosshead pins are divided into cylindrical and tapered pins, drilled with shaft and radial oil holes.
filler
Packing is mainly a component that seals the gap between the cylinder and the piston rod. It can prevent gas from leaking from the cylinder into the fuselage. Some compressors are divided into pre-packing groups and post-packing groups according to the gas or user’s requirements for temperament. They are generally used in toxic, flammable, explosive, precious gas, oil-free and other compressors. The two groups of packing groups are There is a compartment in between.
Pre-packing is mainly used to seal the gas in the compressor cylinder from leaking out. The rear packing serves as an auxiliary seal. The sealing ring generally adopts a two-way seal. There is a protective gas inlet arranged inside the sealing ring. It can also be used in combination with the oil scraper ring. There is no lubrication point and no cooling device.
Piston group
The piston group is the general term for the piston rod, piston, piston ring and support ring. Driven by the connecting rod, the piston group makes reciprocating linear motion in the cylinder, thus forming a variable working volume together with the cylinder to achieve suction, compression, exhaust and other processes.
The piston rod connects the piston to the crosshead, transmits the force acting on the piston, and drives the piston to move. The connection between the piston and the piston rod usually adopts two methods: cylindrical shoulder and cone connection.
The piston ring is a part used to seal the gap between the cylinder mirror and the piston. It also plays the role of oil distribution and heat conduction. The basic requirements for piston rings are reliable sealing and wear resistance. The support ring mainly supports the weight of the piston and piston rod and guides the piston, but it does not have a sealing function.
When the cylinder is lubricated with oil, the piston ring uses a cast iron ring or a filled PTFE plastic ring; when the pressure is high, a copper alloy piston ring is used; the support ring uses a plastic ring or the bearing alloy is cast directly on the piston body. When the cylinder is lubricated without oil, the piston ring support rings are filled with polytetrafluoroethylene plastic rings.
air valve
The air valve is an important part of the compressor and is a wearing part. Its quality and working quality directly affect the gas transmission volume, power loss and operation reliability of the compressor. The air valve includes a suction valve and an exhaust valve. Each time the piston reciprocates up and down, the suction and exhaust valves open and close each time, thereby controlling the compressor and allowing it to complete the four working processes of suction, compression, and exhaust.
Commonly used compressor air valves are divided into mesh valves and annular valves according to the valve plate structure.
The annular valve is composed of a valve seat, a valve plate, a spring, a lift limiter, connecting bolts and nuts, etc. The exploded view is shown in Figure 17. The ring valve is simple to manufacture and reliable in operation. The number of rings can be changed to adapt to various gas volume requirements. The disadvantage of annular valves is that the rings of the valve plates are separated from each other, making it difficult to achieve consistent steps during opening and closing operations, thus reducing the gas flow capacity and increasing additional energy loss. The moving components such as the valve plate have a large mass, and there is friction between the valve plate and the guide block. Ring valves often use cylindrical (or conical) springs and other factors, which determines that it is not easy for the valve plate to open and close in time during the movement. ,fast. Due to the poor buffering effect of the valve plate, the wear is serious.
The valve plates of the mesh valve are connected together in rings to form a mesh shape, and one or several buffer plates that are basically the same shape as the valve plates are arranged between the valve plate and the lift limiter. Mesh valves are suitable for various operating conditions and are commonly used in low and medium pressure ranges. However, due to the complex structure of the mesh valve plate and the large number of valve parts, the processing is difficult and the cost is high. Damage to any part of the valve plate will cause the entire valve plate to be scrapped.
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