1 Exhaust temperature is too high
High exhaust gas temperature is the most common failure of screw air compressors, and it is the most harmful. Usually, the working temperature of the screw air compressor is between 65 °C and 85 °C, and the maximum exhaust temperature is set to 100 °C. When this temperature is exceeded, the alarm will be automatically stopped. If the equipment is operated under high exhaust temperature conditions for a long time, too high temperature will change the physical coefficient values of the rotor and bearing materials, causing abnormal friction loss of the bearings and even bearing loose beads accidents.
Excessive oil temperature will also reduce the gas transmission coefficient and increase the power consumption, and the viscosity of the lubricating oil will also decrease. If the temperature is too high, the lubricating oil will be thermally decomposed under the catalysis of the metal to form free carbon and acid which are harmful to the work. Things and moisture (carbon formation), when severe, can cause the entire host screw to jam or stop jumping. Although the air compressor is equipped with a protection device for preventing high temperature, the presence of the fault causes the device to operate frequently, which affects the normal production of the enterprise.
Excessive temperature of the screw air compressor is generally caused by excessive temperature of the oil cooler and water cooler, or it may be due to sensor failure. Some alarms can be eliminated immediately by the controller page operation, but sometimes the alarm of excessive exhaust temperature occurs after the elimination. In addition to checking the circulating water, it is necessary to consider the problem of the lubricating oil. The common air compressor exhaust temperature is too high to detect and the possibility is as follows:
1. The actual exhaust temperature is not too high
The thermometer display is inaccurate; the temperature sensor is faulty; the controller is faulty; the temperature switch is faulty.
2. The actual exhaust temperature is too high
Lubricating oil is used for too long; oil filter plug is blocked; oil core is blocked; temperature control valve is faulty; lubricating oil level is too low; ambient temperature is too high; fan motor is reversed; fan motor does not turn; wind cooler is always dirty; The air cooler has serious fouling; the cooler exhaust passage is not smooth; the cooling water pressure is too low; the cooling water temperature is too high; the cooling water outlet pipeline is blocked; the oil cooler waterway is seriously fouled; the minimum pressure valve is stuck; The check valve is stuck; the oil shutoff valve cannot be fully opened; the temperature control spool seal is invalid.
Note that there are two types of high temperature: (1) the air compressor itself generates too much heat; (2) the normal heat generated does not go away.
For the first problem, you should look for the cause from the gas path, such as: damage to the exhaust valve at all levels, dirt, air backflow caused by valve failure, eddy current, resulting in a large amount of heat. The air compressor must pass the four strokes of inhalation, compression, work and exhaust to generate high-temperature and low-pressure gas. In order to ensure the normal suction of the lower-stage cylinder or the user's gas, the high-temperature gas must be forcedly cooled. In this case, part of the normal heat is emitted in the environment, and part of it is taken away by the cooling water (or cooling fan). Poor heat dissipation and poor circulation of the cooling system are the main causes of high exhaust temperatures. The radiator is clogged, the cooling water is insufficient, the pump is damaged, there may be too much scale, and the fan performance is poor.
2 thermal relay trips
The working principle of the thermal relay is to generate heat from the current flowing into the thermal element, so that the bimetal with different expansion coefficients is deformed. When the deformation reaches a certain distance, the link is pushed to break the control circuit, thereby making the contactor Loss of power, the main circuit is disconnected, and the overload protection of the motor is realized. As the overload protection component of the motor, the relay has been widely used in production due to its small size, simple structure and low cost.
Common causes of thermal relays
The current flowing through the superheat relay is seriously overloaded or the load is short-circuited; the rated current of the thermal relay does not match the actual load current; the motor operates too frequently; the thermal relay action mechanism is not working, so that the thermal element is overloaded for a long time and cannot protect the thermal relay; the thermal relay connection head has poor contact Causes fever and burns out.
Common troubleshooting methods for thermal relays:
1. The specification of the thermal relay should be properly selected. If it is too small, the thermal relay will malfunction, and the main current will easily burn the main circuit of the thermal relay; if it is too large, the thermal relay will not operate. Therefore, when selecting a thermal relay, the intermediate value in the rated range of the thermal relay should be exactly the same as the rated current value of the motor load being controlled, so that the thermal relay has a certain current adjustment range as the best.
2. Check the circuit for faults and replace the appropriate thermal relay after removing the short circuit fault.
3. Change the operation of the motor to reduce the number of starts the motor.
4. Replace the qualified thermal relay with sensitive action.
5. Try to remove the oxide layer from the terminal and the thermal relay terminal and re-tighten the main wiring of the thermal relay.
3 head resistance is too large
Air compressor overload can also cause the air switch to trip. The overload of the air compressor is usually caused by the excessive resistance of the air compressor head, which causes the starting current of the air compressor to be too large, causing the air switch to trip.
The role of lubricating oil in screw air compressors is very important. Its role is mainly in four aspects: cooling, lubrication, sealing, noise reduction, and the quality of oil, the amount of oil directly affects the air compressor The normal operation and the service life of the air compressor, especially the head part of the air compressor, are most obvious. There are three main conditions that cause the head resistance to increase:
1. The viscosity of the lubricating oil is large.
2. The head is cokeed; when the head is cokeed, the air compressor rotor is running, the friction is prevented from increasing, and the air compressor current is increased;
3. Excessive amount of lubricant in the head will also increase the resistance. After the air compressor is stopped, the oil shut-off valve is not closed in time, and a large amount of lubricating oil enters the machine head, causing the starting resistance to be too large when the air compressor is restarted.
The treatment methods are:
1. Check whether the machine head and the motor can rotate freely by manually cranking the air compressor to judge whether the resistance increases. When the ambient temperature is lowered, the viscosity of the oil is increased, the resistance is also increased, the starting current of the motor is increased, and the starting time of the air compressor is prolonged. The ambient temperature at that time can be determined based on the exhaust gas temperature.
The time for starting the motor on the air switch is slightly extended under the condition of ensuring safety to meet the extension of the starting time of the air compressor when the viscosity of the oil increases, to ensure the normal start of the air compressor. Do not extend too large and extend the use of other electrical equipment.
2. The oil coking in the machine head is a phenomenon often occurs in the case of a screw air compressor in which the oil is poor or the temperature is high. Due to the coking of the machine head, the frictional resistance increases, the load of the unit increases, and the current increases. In severe cases, the screw and the rotor are glued together, and the unit cannot rotate freely.
3. The function of the oil shut-off valve is to cut off the oil filler pipe in time when the air compressor is stopped, to prevent the residual pressure in the oil and gas barrel from pressing a large amount of lubricating oil into the machine head, resulting in excessive lubricating oil in the machine head. The most direct way to solve the problem of excessive oil in the machine head is to open the machine head, release part of the lubricating oil inside the machine head, and repair or replace the oil shut-off valve.
4 unloading valve failure
Air compressor unloading valve function: When the gas consumption changes, the intake valve adjusts the opening degree of the valve body through the control system to match the gas consumption. It is the valve that controls the intake and non-intake of the air compressor (solenoid valve) ).
The most intuitive way to judge whether the unloading valve is closed or not is to remove the air filter and you can clearly see whether the air intake baffle of the unloading valve is closed or open. If the air intake baffle is stuck due to mechanical impurities, the unit can be smoothly opened after cleaning; if the air inlet baffle is stuck on the guide rod, the guide rod is ground with sandpaper, and a small amount of grease is applied on the guide rod; If the unloading valve is seriously damaged, the unloading valve needs to be replaced.
5 power failure
1. First check whether the power supply wiring of the air compressor is correct, whether the power switch has been closed, to prevent someone from accidentally shutting down; whether the power fuse is blown, and whether the power supply voltage reaches 90% or more of the rated voltage.
2. Check whether all components of the pressure relay of the air compressor power supply are damaged, and whether the pressure relay is given a proper value.
