Basic structure of piston refrigeration compressor

Basic structure of piston refrigeration compressor Piston refrigeration compressor is mainly composed of body, crankshaft, connecting rod, piston group, valve, shaft seal, oil pump, energy adjustment device, oil circulation system and other components. 1. Body Body: Including the cylinder block and the crankcase, it is generally made of high strength gray cast iron (HT20-40) to form a whole. It is the body that supports the weight of the cylinder liner, crankshaft connecting rod mechanism and all other components and ensures the correct relative position between the components. The cylinder adopts the cylinder liner structure and is installed in the cylinder sleeve seat hole on the cylinder block, which is convenient for maintenance or replacement when the cylinder liner is worn. Therefore, the structure is simple and maintenance is convenient. 2. Crankshaft Crankshaft: The crankshaft is one of the main components of the piston refrigeration compressor, which transfers the full power of the compressor. Its main function is to change the rotary motion of the motor to the reciprocating linear motion of the piston through the connecting rod. When the crankshaft is in motion, it bears an alternating composite load of tension, compression, shearing, bending and torsion. The working conditions are harsh, requiring sufficient strength and rigidity, and the wear resistance of the main journal and the crankpin. Therefore, the crankshaft is generally forged with high-quality carbon steel No. 40, 45 or 50, but now it has been widely cast using nodular cast iron (such as QT50-1.5 and QT60-2). 3. Connecting rod: The connecting rod is the connecting piece between the crankshaft and the piston. It converts the rotary motion of the crankshaft into the reciprocating motion of the piston, and transmits power to the piston to do work on the steam. The connecting rod includes a connecting rod body, a connecting rod small-end bushing, a connecting rod big head bush and a connecting rod bolt. The connecting rod body is subjected to tensile and compressive alternating loads during work, so it is generally forged with high-quality medium carbon steel or cast with nodular cast iron (such as QT40-10). . The small end of the connecting rod is connected with the piston through a piston pin, and a bush is added in the pin hole to improve the wear resistance and impact resistance. The connecting rod small-end bushing is usually made of tin phosphor bronze ZQSn10-1 into an overall cylindrical shape, the outer round car has a ring groove and drilled oil holes, and the inner surface has an axial oil groove. The big end of the connecting rod is connected to the crankshaft. The big end of the connecting rod is generally made into split type, which is convenient for assembly, disassembly and maintenance. In order to improve the wear condition between the big end of the connecting rod and the crank pin, bearing alloy bearing bushes, that is, big connecting head bushes, are generally installed in the big head holes. There are two types of connecting rod big-end bearing bushes, thin-walled and thick-walled. The upper shell of the bearing bush also has oil holes at the places corresponding to the oil holes of the connecting rod. The connecting rod bolt is used to connect the big end of the split connecting rod and the big head cover. The connecting rod bolt is a severely stressed part in the crank connecting rod mechanism. It is not only subject to repeated stretching and vibration and impact, but it is easy to loosen and break, resulting in serious accidents. Therefore, there are strict requirements on the design, processing and assembly of connecting rod bolts. Connecting rod bolts are usually made of 40Cr, 45Cr steel, etc., and adopt fine thread, which requires a certain pretension during installation, so as to avoid loose knocking between the upper and lower connecting rods of the connecting rod and the crank pin when the load changes, accelerating machine parts Damage. 4. Piston group Piston group: Piston group is the general name of piston, piston pin and piston ring. Driven by the connecting rod, the piston group makes a reciprocating linear movement in the cylinder, thereby forming a variable working volume together with the cylinder, etc. to achieve the processes of suction, compression, and exhaust. Pistons-Pistons can be divided into two types: cylindrical and disc. The pistons of China's series refrigeration compressors all adopt a cylindrical structure, which is composed of three parts: a top part, a ring part and a skirt part. The top of the piston forms the working surface of the closed cylinder. The outer ring of the piston ring part is provided with a ring groove for installing the piston ring. The depth of the ring groove is slightly larger than the radial thickness of the piston ring, so that the piston ring has a certain room for movement. The piston skirt plays a guiding role in the cylinder and bears side pressure. The material of the piston is generally aluminum alloy or cast iron. Gray cast iron pistons have been widely used in refrigeration compressors in the past, but due to the high quality and poor thermal conductivity of cast iron pistons, in recent years, the pistons of series refrigeration compressors have all used aluminum alloy pistons. The advantages of aluminum alloy pistons are light weight and good thermal conductivity, and the surface has good wear resistance after anodizing. But aluminum alloy pistons have lower mechanical strength and poor wear resistance than cast iron pistons. Piston pin-The piston pin is a part used to connect the piston and the small end of the connecting rod, and bears a complex alternating load during work. The damage of the piston pin will cause serious accidents, so it is required to have sufficient strength, wear resistance, fatigue resistance and impact resistance. Therefore, the piston pin is usually made of 20 # steel, 20Cr steel or 45 # steel. Piston ring-Piston ring includes steam ring and oil ring. The main function of the steam ring is to form a seal between the piston and the cylinder wall to prevent the compressed vapor from leaking from the gap between the piston and the cylinder wall. In order to reduce the leakage of compressed steam from the lock port of the ring, the lock ports should be staggered when installing multiple steam rings. The role of the oil ring is to distribute oil and scrape off excess lubricant on the cylinder wall. The steam ring can be installed one to three times. The oil ring is usually installed only one and is installed under the steam ring. The common oil ring has two types of cross-section and groove. The slope of the oil ring should be upward when installed. 5. Steam valve and shaft seal Steam valve and shaft seal: The steam valve is an important component of the compressor and is a wearing part. Its quality and working quality directly affect the compressor's steam transmission, power loss and reliability of operation. The steam valve includes an intake valve and an exhaust valve. The piston reciprocates up and down once, and the intake and exhaust valves are opened and closed once, respectively, to control the compressor and complete the four working processes of intake, compression, and exhaust. Due to the frequent opening and closing of the valve and the great impact on the performance of the compressor, the steam valve needs to meet the following requirements: the flow resistance of the gas flowing through the valve should be small, there must be sufficient passage cross section, the passage surface should be smooth, and the opening and closing should be timely , Closed tightly, tough and wear-resistant. Shaft seal-The role of the shaft seal is to prevent refrigerant vapor from leaking out along the extended end of the crankshaft, or to prevent outside air from leaking when the pressure in the crankcase is below atmospheric pressure. Therefore, the shaft seal should have good sealing, safety and reliability, simple structure, easy assembly and disassembly, and have a certain service life. Shaft sealing devices are mainly of mechanical type and packing type. Currently commonly used mechanical shaft seals are mainly friction ring type and bellows type. Among them, the domestic series of piston refrigeration compressors mostly use friction ring shaft seals. This shaft seal is composed of a movable ring (friction ring), a fixed ring, a spring and a spring seat, a pressure ring, and two "0" shaped oil-resistant rubber rings. composition. A rubber seal ring is embedded in the movable ring groove and sleeved on the shaft together with the movable ring. Under the action of the spring force and the pressure ring, the movable ring and the rubber ring are pressed together on the shaft and the movable ring is closely attached to the fixed ring on. When working, the spring seat and the spring, the rubber seal ring on the shaft and the movable ring rotate together with the crankshaft, and the fixed ring and the rubber ring on it are fixed. Therefore, the movable ring and the fixed ring move relative to each other during work, and the tight friction surface acts as a seal to prevent refrigerant leakage. The rubber ring on the shaft is used to seal the gap between the shaft and the movable ring, and the oil-resistant rubber seal on the fixed ring The ring plays the role of preventing the leakage of lubricating oil in the shaft seal chamber. 6. Energy adjustment device: Energy adjustment device: In the refrigeration system, as the heat load of the cold room changes, its cooling consumption also changes, so the cooling capacity of the compressor should also be adjusted as necessary. The adjustment of the compressor's cooling capacity is realized by an energy adjustment device. The so-called compressor energy adjustment device is actually an exhaust gas amount adjustment device. It has two functions, one is to realize the no-load start of the compressor or start under a small load state, and the other is to adjust the cooling capacity of the compressor. The adjustment methods of the compressor displacement are: 1 ° opening the suction valve of some cylinders; 2 ° changing the speed of the compressor; 3 ° using a bypass valve to bypass the exhaust of some cylinders back to the suction chamber, which This method is used for co-current compressors; 4 ° changes the size of the additional clearance volume. The adjustment method of the suction valve piece of the top opening cylinder is a widely used adjustment method. The domestic series of piston refrigeration compressors all adopt the air volume adjustment device of the suction valve piece of the top opening portion of the cylinder. The principle of the air volume adjustment device of the valve plate is very simple, that is, the suction valve plate of some cylinders is lifted up by the ejector rod, so that it is normally open, so that the pressure of the piston cannot be increased during the compression process, and the steam is sucked in The air valve is discharged back to the suction side, so the cylinder has no exhaust volume, so as to achieve the purpose of adjusting the amount of air transmission, that is, energy adjustment. The energy adjustment device of the jack-in suction valve can be divided into three parts: actuator, transmission mechanism and oil distribution mechanism. It is mainly composed of oil distribution valve, oil cylinder, oil piston, tie rod, rotating ring, ejector rod and spring. There are two convex circles on the tie rod, which are respectively embedded in the rotating rings outside the two cylinder sleeves. If oil is not supplied to the cylinder, due to the action of the spring on the left side of the oil piston, the oil piston is at the right end of the cylinder, the ejector rod outside the cylinder liner is at the highest position of the chute of the rotating ring, and the steam suction valve piece is pushed open , So the cylinder is unloaded. When the pressure oil is supplied to the cylinder through the oil distribution valve, due to the action of the oil pressure, the oil piston and the rod are moved to the left against the spring force, and the rotating ring is rotated by a convex circle on the rod to a certain angle, and the ejector rod is correspondingly When the ejector rod spring is lowered and slides to the lowest position of the chute, the suction valve plate falls on the valve seat under the action of gravity and spring force and can freely open and close, then the cylinder is in a working state. When the compressor is started, because the machine has not yet rotated and the oil pressure is zero, the suction valve pieces of all cylinders are pushed open by the ejector rod, and the cylinder has no compression effect, thus achieving no-load start.

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