Piston type
In the piston type refrigerator, the friction parts that need lubrication are [3]: the wall surface of the piston and cylinder; Connecting rod big end bearing bush and crank pin; Connecting rod small end bearing bush and piston pin; Piston pin and piston pin seat; Bearing shells and main journals of front and rear sliding bearings, static and dynamic friction sealing surfaces of main shaft seals, etc. In small low-speed refrigerators, the simplest lubrication method is splash lubrication. That is, in the crankcase of the refrigerator, with the help of the rotary stirring oil surface of the connecting rod big end of the crankshaft, the lubricating oil is thrown to the friction surface for lubrication. However, for some friction surfaces, the lubricating oil is difficult to reach, the lubrication is insufficient, and large friction and wear are likely to occur. Therefore, this lubrication method is of poor reliability and has rarely been used alone.
In the new and old series of refrigerators, the forced circulation lubrication is mostly used, that is, the oil is forced to be delivered to each lubricating point by the oil pump. The lubrication of piston refrigerator is mostly an internal drive system, that is, the lubrication system does not set up a separate oil tank and oil pump station, but uses the crankcase of the refrigerator as the lubrication oil tank. The special lubrication pump is connected to one end of the crankshaft, and the lubrication device and the refrigerator form a whole.
The oil pump absorbs oil from the crankcase through a screen type coarse filter with holes of 0.28-0.154mm, and then the filtering accuracy is 10-20 μ M paper or powder metallurgy type fine oil filter presses out the lubricating oil of the refrigerator. One way of lubricating oil is sent to the front end of the crankshaft to lubricate the shaft seal, front main bearing, crank pin and small end of the connecting rod. The other way of pressure oil is sent to the rear end of the crankshaft to lubricate the rear main bearing, crank pin and small end of the connecting rod. In addition, the pressure oil is also sent to the oil distribution valve to control the energy regulating structure. The lubricating system shall also be equipped with pressure gauge, pressure regulating valve and other necessary components. The pressure regulating valve is used to regulate the pressure of lubricating oil and allow excess lubricating oil to flow back to the crankcase. In this system, the oil extruded from the small end of the connecting rod and the oil thrown from the large end of the connecting rod are used to lubricate the friction surface of the cylinder.
The lubricating pumps used in the refrigerator usually include three types: external gear type oil pump, internal gear type oil pump (commonly known as crescent pump) and cycloidal rotor type oil pump (commonly known as plum pump). After the location of the oil suction port of the external gear pump is determined, the rotation direction of the pump is fixed and irreversible. For fully enclosed and semi enclosed refrigerators, it is difficult to identify the direction of the pump from the outside because the refrigerator housing is connected with the motor housing, which is likely to cause the wrong direction of the gear pump and cause lubrication failure. Therefore, the external gear pump is rarely used in refrigerators. For the internal gear pump, the crescent body (separating the oil suction and pressure chambers to ensure the sealing of the top of the internal and external gears) can be made into a structure with automatic positioning. No matter how the rotation direction of the gear is, the position of the oil suction and pressure ports will not be changed, so there is no restriction on the rotation direction of the oil pump. Therefore, it is widely used in the new series of closed and semi closed refrigerators. The cycloidal rotor pump is similar to the internal gear pump, which can also achieve unlimited rotation direction of the pump. In addition, the cycloidal rotor pump has simple tooth shape, easy processing, compact structure, and has broad application prospects in the refrigerator.
Screw type
The lubricating parts of the screw type refrigerator include: the rotating meshing part of the convex and concave screw (also called the male and female rotors); The relative sliding surface between the rotating screw and the shell; Sliding bearings at the front and rear of the screw; The balance piston of the driving screw and the mechanical seal friction surface of the shaft end. The above lubricating parts are provided with oil ports which are connected with pressure oil. The oil holes with different sizes and a certain distance apart on the energy regulating valve or housing can make the lubricating pressure oil spray directly onto the rotor, which can cool and lubricate the rotor and housing, and seal the gap between moving parts to reduce the leakage of compressed gas and reduce the running noise.
Since the pressure of the lubricating oil regulated by the pressure regulating valve is usually 0.2-0.3MPA higher than the condensing pressure, the amount of lubricating oil can be equivalent to 1% - 2% of the air transmission volume of the refrigerator. The lubricating pump can be directly driven by the rotor itself or made into an external drive type. The oil separator is usually used as the oil tank of the lubrication system. The centrifugal gravity type and packing gravity type oil separators are widely used.
In addition, two-stage oil separators are also commonly used in screw type refrigerators. The lubricating oil separated from the two-stage oil separators can be directly pressed to the suction chamber without oil pump by using the differential pressure between suction and discharge to lubricate the bearings, balance pistons, etc. Tubular oil cooler is widely used in this kind of lubrication system to keep the oil temperature at 20-50 ℃. The cooling medium can evaporate and cool the lubricating oil with water or the refrigerant of the refrigerator itself. The differential pressure between the inlet and outlet of the fine filter in the lubrication system shall not exceed 0.1MPa, otherwise the filter element shall be cleaned or replaced.
Centrifugal
The main lubrication parts of the centrifugal refrigerator are the speed increasing gear, main bearing and mechanical seal at the shaft end. Generally, the gear box can also be used as the lubricating oil tank, in which an electric heater is installed to preheat the lubricating oil. The oil pump is used to pump the oil to the specially designed high-level oil tank, and then the high-level oil tank will lead the oil to the required lubricating part. This method can prevent the oil pump from suddenly failing in the oil supply system or the chiller from suddenly powering off and shutting down, when the oil pump has no oil supply and the chiller still keeps running or continues to rotate at a high speed by inertia, "Burn" or "bite" accident of equipment friction parts caused by non lubrication.
