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Daily cold storage system maintenance method Disassembly and failure analysis of scroll compressor How to solve the phenomenon that the low temperature of the high and low temperature test chamber cannot be maintained Piston refrigeration compressor classification Refrigeration unit in artificial environment simulation laboratory

The common oil shortage failures of scroll refrigeration compressors are here

The common oil shortage failures of scroll refrigeration compressors are here The compressor has been short of oil for a long time-the mechanism and the friction pairs are overheated, resulting in bearing sintering and shaft holding. The compressor is short of oil for a short time-the mechanism and the friction pairs are abnormally worn, resulting in large vibration and noise. 1.How to ensure proper oil quantity When the compressor discharges the refrigerant, it also discharges a small amount of refrigerating machine oil. Even if there is only 0.5% oil rate, if the oil cannot be circulated back to the compressor through the system. Taking 5HP as an example, the circulation volume is about 330kg / h under ARI operating conditions, then all the oil in the compressor can be taken out in 50 minutes, and the compressor will burn out in about 2 to 5 hours. Therefore, in order to ensure that the compressor does not run short of oil, we should proceed from the following two aspects: 1. Make sure that the refrigerant oil discharged from the compressor returns to the compressor. 2. Reduce the oil rate of the compressor. (Frequent compressor startup is not conducive to oil return.) Second, how to ensure that the discharged refrigeration oil returns to the compressor 1. The flow rate of the refrigerant in the suction pipe (about 6m / s) should be ensured to return the oil to the compressor. The flow direction has a downward slope, about 0.8cm / m. 2. Prevent the freezing oil from staying in the evaporator. 3. Make sure that the oil return hole of the gas-liquid separator is too large, which will cause wet compression. If it is too small, the oil return will be insufficient. 4. There should be no part of the system where oil stays. 5. Make sure that there is enough refrigerating machine oil in the compressor under the condition of long piping high drop, usually confirm with the compressor with oil mirror. Third, how to reduce the oil rate of the compressor 1. Make sure that the refrigerant does not dissolve into the refrigerator oil when the machine is shut down (use crankshaft heater). 2. Avoid over-wet operation, because too much oil will be caused by foaming. 3. An oil separator device is provided inside. 4. Oil bubbling inside the compressor makes the oil easily taken out of the compressor. 4. High drop of long piping When the piping length is larger than the allowable value, the pressure loss in the piping becomes larger, which reduces the amount of refrigerant in the evaporator, resulting in a decrease in capacity. At the same time, when there is oil stagnation in the piping, the compressor is starved of oil, resulting in compressor failure. When the refrigeration oil in the compressor is insufficient, the refrigeration oil of the same brand as the compressor should be added from the high pressure side. 5. The necessity of setting up oil return bend When the drop exceeds 10m ~ 15m, an oil return elbow should be installed on the side of the trachea. Necessity: When the machine is stopped, avoid the freezing oil attached to the piping to return to the compressor, causing liquid compression. On the other hand, in order to prevent the poor oil return of the gas pipe, the compressor will run out of oil. Oil return bend setting interval: set a oil return bend every 10m drop. 6. How to ensure proper viscosity of refrigeration oil 1. The refrigerating machine oil and refrigerant are miscible. When the machine is shut down, the refrigerant is almost completely dissolved in the refrigerating machine oil, so a crankshaft heater needs to be installed to prevent dissolution. 2. The refrigerant containing liquid should not be returned to the compressor during operation, that is, to ensure that the compressor suction has superheat. 3. During starting and defrosting, liquid return phenomenon should not occur. 4. Avoid running in an overheated state and avoid oil degradation. 5. The size of the oil return hole of the gas-liquid separator should be appropriate: ① Excessive aperture will cause liquid refrigerant to be sucked and cause excessive humidity operation ②The pore size is too small will make the oil return not smooth, leaving the oil in the gas-liquid separator 7. The main cause of compressor motor damage 1. Abnormal load and stall. 2. Short circuit of winding caused by metal shavings. 3. The contactor problem. 4. The power supply is out of phase and the voltage is abnormal. 5. Insufficient cooling. 6. Use the compressor to evacuate. 8. The main cause of abnormal load or stall If the pressure ratio is too large or the pressure difference is too large, the compression process will be more difficult. The increased frictional resistance caused by lubrication failure and the motor stall in extreme cases will greatly increase the motor load. If the load increases to the thermal protection action, and the protection is automatically reset, it will enter the "lock-rotation-thermal protection-lock-rotation" dead cycle, frequent start and abnormal load, the winding will withstand high temperature test, will reduce the enameled wire Insulation performance. After the insulation performance of the winding has deteriorated, if there are other factors (such as metal chips forming a conductive circuit, acid lubricant, etc.), it is easy to cause short circuit and damage. 1. Short circuit of winding caused by metal shavings Sources of metal shavings include copper pipe shavings left during construction, welding slag, internal wear of compressors, and metal shavings that fall when parts are damaged. During operation, the metal chips or debris will fall on the winding under the drive of the air flow. The normal vibration of the compressor during operation and the winding twisted by the electromagnetic force at each start-up will promote the relative movement and friction between the metal shavings interposed between the windings and the winding enameled wire. Sharp metal chips can scratch the insulation layer of the enameled wire, cause a short circuit, and cause the motor to burn out. 2. Contactor problem In order to be safe and reliable, the compressor contactor should simultaneously disconnect the three-phase circuit. The contactor must be able to meet demanding conditions such as fast cycling, continuous overload and low voltage. They must have a large enough area to dissipate the heat generated by the load current, and the selection of contact materials must prevent welding under high current conditions such as starting or blocking. Otherwise, after the contactor contacts are welded, all controls that rely on the contactor to disconnect the compressor power circuit (such as high and low pressure control, temperature control, defrost control, etc.) will be completely invalid, and the compressor is in an unprotected state. Therefore, when the motor burns out, checking the contactor is an essential process. 3. Absence of power phase and abnormal voltage The power supply voltage variation range cannot exceed ± 10% of the rated voltage. The voltage imbalance between the three phases cannot exceed 3%. If the compressor is running when a phase loss occurs, it will continue to run but will have a large load current. The motor winding will quickly overheat, and the compressor will be thermally protected under normal conditions. When the motor winding is cooled to the set temperature, the contactor will be closed, but the compressor will not start up, there will be locked rotation, and enter the "locked-thermal protection-locked rotation" dead cycle. If the compressor starts when a phase loss occurs, the compressor will not start, and there is a stall, and enters the "lock-rotation-thermal protection-lock-rotation" dead cycle. The method of calculating the percentage of voltage unbalance is the ratio of the maximum deviation of the phase voltage to the average value of the three-phase voltage and the average value of the three-phase voltage. As a result of the voltage unbalance, the unbalance of the load current during normal operation is the percentage point of the voltage unbalance 4-10 times. 4. Insufficient cooling of the compressor motor A large amount of refrigerant leakage or low evaporation pressure will cause the system mass flow to decrease, which prevents the motor from being well cooled. The motor will frequently protect after overheating. Nine, the main reason for compressor liquid damage-liquid return Back to the liquid, it is easy to cause liquid hammer accidents. Even if no liquid shock is caused, the return fluid of the high-pressure cavity structure will dilute or wash away the lubricating oil on the sliding surface, and aggravate the wear. The return fluid from the low-pressure chamber structure will dilute the lubricating oil in the oil sump. The lubricating oil containing a large amount of liquid refrigerant has a low viscosity and cannot form an adequate oil film on the friction surface, resulting in rapid wear of moving parts. In addition, the refrigerant in the lubricating oil will boil when it encounters heat during transportation, which will affect the normal transportation of the lubricating oil. The further away from the oil pump, the more obvious and serious the problem. If the bearing on the motor end is severely worn, the crankshaft may settle to one side, which may easily cause the stator bore and the motor to burn. For refrigeration systems where liquid return is difficult to avoid, the installation of a gas-liquid separator and the use of evacuation shutdown control can effectively prevent or reduce the harm of liquid return. Ten, the main reason for compressor liquid damage-start with liquid On the oil sight glass, bubbles can be clearly observed when starting with liquid. The basic reason for starting with liquid is that a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil suddenly boils when the pressure drops suddenly, and causes the foaming of the lubricating oil. The refrigerant with liquid start enters the crankcase by means of "refrigerant migration". Since the partial pressure of refrigerant vapor in the lubricating oil is low, the refrigerant vapor on the oil surface will be absorbed, resulting in the phenomenon that the air pressure in the oil sump is lower than that of the evaporator. The lower the oil temperature and the lower the steam pressure, the greater the absorption of refrigerant vapor. The steam in the system will slowly "migrate" to the compressor. The longer the downtime, the more refrigerant will migrate into the lubricant. Refrigerant migration will dilute the lubricant. It is also easy to cause liquid blow to the low pressure chamber. Neither liquid refrigerant nor a mixture of oil and refrigerant is a good lubricant, which can cause wear and even seizure. At this time, because the motor is immersed in the liquid, the overload protector on the motor will not operate. The installation of crankcase heaters, gas-liquid separators and the use of evacuation shutdown control can effectively prevent or reduce refrigerant migration. Eleven, the main reason for compressor liquid damage-too much lubricating oil For low-pressure chamber compressors, high-speed rotating components such as rotors will frequently hit the oil surface. If the oil surface is too high, it will cause a large amount of lubricant splash. Once the splashed lubricating oil enters the intake port and is brought into the cylinder, it may cause liquid hammer. Twelve, the main cause of compressor high temperature damage The overheating of the motor due to problems such as over-range use, abnormal power supply, overloaded motor, refrigerant leakage, and excessively high condensing pressure caused by overheating of the motor, high exhaust gas temperature, and burnt lubricant. The compressor surface temperature is one of the important indicators to judge whether the compressor is overheated. If the surface temperature exceeds 135 ° C, the compressor is generally considered to be in a severely overheated state; if the surface temperature is below 120 ° C, the compressor temperature is normal. If the motor generates a large amount of heat and the power supply is abnormal, it will cause the motor to generate more heat. For example, the voltage is unstable, the voltage is too low or too high, the voltage is unbalanced, and the lack of equal power is abnormal. Frequent compressor start-up, connecting rod holding shaft, piston biting cylinder, insufficient lubrication or lack of oil will greatly increase the heat. Excessive use of a compressor can easily cause overheating and damage to the motor, and insufficient cooling of the motor. Low evaporation temperature and small refrigerant mass flow rate lead to insufficient motor cooling. When the amount of refrigerant leakage is relatively large, the refrigerant mass flow rate will also be small, resulting in insufficient cooling of the motor. 13. The main reason for the high exhaust temperature The main reasons for the exhaust temperature overheating are as follows: high return air temperature, large motor heating capacity, high compression ratio, high condensation pressure, and improper refrigerant selection.

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