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Abstract: Aiming at the damage that appears in the rolling bearing of the hot drawing roller during the manufacturing process of the polyester industrial yarn，the reasons related with the polyester spinning process，structure of the hot drawing roller and common fault analysis are analyzed． The results show that the main reasons causing the early failure are the special conditions of high temperature，high velocity and changing tension，and the good results are achieved through utilizing the corresponding improvement measures.
Key words: rolling bearing; hot drawing roller; fault analysis; improvement
1. Introduction to Polyester Spinning Process
At present, melt spinning technology is mainly used in the production of polyester industrial raw silk. The main production process is as follows: the qualified polyester chips are selected by vibration screening to obtain uniformly sized chips and sent into the silo. After vacuum pumping, the chips are sent into the storage tank by a Roots blower with nitrogen gas. The chips in the storage tank fall into the drying tower by gravity, and after drying, they fall into the storage tank. After passing the laboratory test and meeting the standards, they are sent into the storage tank by a Roots blower with nitrogen gas and then into the screw extruder. The pressure of the extruder is determined based on the characteristic viscosity of the raw material, the selected temperature, and the specifications of the product. The melt extruded by the screw extruder enters the spinning box, and is accurately measured by the metering pump before being distributed to the spinning components to produce raw silk. It is cooled by the side blowing device, oiled, and stretched on three pairs of stretching rollers before being wound into shape by the winding machine. The production process flow is shown in Figure 1.
1- Spinning components; 2- Side blowing device; 3- Oiler; 4- Hot stretching roller; 5- Winding machine
Figure 1 Production process flow of polyester industrial raw silk
2. Working principle of hot drawing roller
Hot drawing roller is an important equipment for the production of polyester industrial raw silk. There are 3 pairs of 5 sets of hot drawing rollers per ingot, which complete the tensioning, drawing, and shaping of polyester industrial raw silk, making the raw silk have excellent properties such as high fracture strength, small fracture elongation, good dimensional stability, moisture resistance, and wear resistance.
During the operation of the hot stretching roller, due to special conditions such as stretching tension (dynamic load), speed, and ambient temperature, the bearings matched with it should meet strict requirements such as high temperature, high speed, and corrosion resistance. The hot drawing roller in the article uses imported TS2-6010L1CC3P5 single row deep groove ball bearings, which are specialized bearings for chemical fiber equipment with spherical grooves and can withstand radial loads. The bearing has an inner diameter of 50 mm, an outer diameter of 80 mm, a width of 16 mm, a mass of 0.25 kg, and is equipped with a brass solid cage; The bearing material is fully quenched GCr15 high carbon chromium bearing steel; The radial clearance of the bearing is greater than the standard clearance; The tolerance level meets the ISO standard of level 5.
In actual production, each ingot has 3 pairs of hot drawing rollers, abbreviated as 1G, 2G, and 3G. According to the process requirements, 1G adopts single-stage heating, using one heater and one Pt100 platinum resistance thermal sensor, with water as the heating medium; 2G and 3G adopt dual stage heating, with 2 heaters and 2 Pt100 platinum resistance thermal sensors, and the heating medium is water vapor. Production process setting: 1G temperature is 65 ℃; The temperature of the first and second stages of 2G and 3G is 196 ℃; The rotational speed is 600 r/min for 1G, 2350 r/min for 2G, and 3000 r/min for 3G.
The hot drawing roller is mainly composed of a hot roller motor, a wire guide disc, a heater, and a temperature control system. The hot roller motor provides the power required for stretching; The wire guide disc serves as a heat carrier to stretch the filament bundle; The heater provides the temperature required for stretching; The temperature control system controls the temperature of each zone, consisting of temperature rotary transmitters, temperature sensors, etc.
The double-layer induction heating system of the hot drawing roller places temperature sensors at corresponding positions in each zone, and the temperature rotary transmitter sends the temperature signal of each zone to the temperature control system in a time-sharing manner to control the on/off time ratio of the induction heating coil current in each zone, achieving the purpose of constant temperature control.
Place the Pt100 platinum resistance thermal sensor near the inner layer of the rotating roller to ensure that the roller heating system is turned off when the temperature exceeds the set limit.
3. Common faults of hot drawing rollers
Due to the effects of environmental temperature, speed, and stretching tension, common faults that occur during the operation of hot stretching rollers include: (1) temperature control system failure; (2) Motor vibration, abnormal noise, and high temperature; (3) Heater malfunction; (4) Uneven roughness of the guide wire disc, etc. Temperature control system failures usually include communication failures, transformer failures, platinum resistance short circuits, etc. The causes of motor vibration and abnormal noise include mechanical friction (including stator and rotor friction), bearing oil shortage or damage, poor rotor dynamic balance, impurities in lubricating oil, etc; The reasons for the high temperature of the electric motor include abnormal temperature control, lack of oil in the bearings, and poor ventilation. Heater faults include short circuits or open circuits in the heater coil, which can cause section tripping in severe cases. Uneven roughness of the guide wire disc will seriously affect the stretching, shaping, and quality of the finished yarn.
4. Causes and Improvement of Bearing Malfunctions
The hot drawing roller bearings work in high temperature, high speed, and variable tension environments, effectively ensuring lubrication, heat dissipation, ventilation, and temperature rise of the bearings, in order to avoid bearing failures.
4.1 Impact of Lubricating Oil Quality
For the special working conditions of hot drawing roller bearings, imported 68 # anti-wear hydraulic oil lubricated bearings should generally be selected. The oil supply should be determined based on the bearing structure, clearance, and speed. Usually, the oil supply for each hot drawing roller is 1 mL/h, and the oil supply for the slitting roller is 0 6 mL/h.
In addition, bearing failures are closely related to the cleanliness of lubricating oil, with a theoretical allowable filtration accuracy of 5 μ m. At the same time, the cleanliness of lubrication pipelines and connecting components should be ensured.
4.2 Effects of Lubrication
The bearings of the hot drawing roller are lubricated with oil mist. Lubricating oil mist is an extremely small oil droplet that does not settle in long-distance conveying pipes. It can be continuously blown to the lubrication area, forming a new oil film on the lubrication surface. The adhered oil droplets combine with each other and are adsorbed on the surface of the moving pair. Its advantages are that the new oil film forms quickly, heat dissipation is fast, and it avoids the harmful impurities of corrosive motion pairs caused by the cracking of lubricating oil due to multiple compressions and shearing. Moreover, the oil is completely used for lubrication, avoiding waste and environmental pollution.
The oil mist lubrication conveying pipe is a rubber hose, which is long and prone to bending, especially in narrow, dim environments where multiple pipes intersect and wrap around each other. This may lead to the accumulation of lubricating oil mist, causing the hot drawing roller bearings to not receive timely and sufficient lubrication. The oil mist lubrication device is suitable for an ambient temperature of 5-40 ℃ and an air pressure of 0.2 MPa. If the ambient temperature exceeds 40 ℃ in summer, the oil mist lubrication device cannot work properly, and the fluctuation of air pressure will also cause poor bearing lubrication.
Figures 2 and 3 show the damage to the TS2-6010L1CC3P5 bearing of GRMOTOR company. Due to poor lubrication, the bearing and rotor were sintered together. Figure 4 shows the stretching caused by high temperature. The damage to the roller bearing components is shown in Figures 5 and 6, which illustrate the spraying treatment of the damaged protrusions.
Figure 2 Damage to the stretching roller bearing caused by poor lubrication
Figure 3 Wear of the bearing positioning projection (about 1 mm)
Figure 4 Damaged hot drawing roller bearing parts
The improvement measures are as follows: (1) Increase air conditioning facilities and control the ambient temperature of the oil mist lubrication device to not exceed the specified value; (2) Control the inlet pressure of compressed air in the oil mist lubrication device to avoid pressure fluctuations; (3) Regularly inspect and replace problematic oil circuits in a timely manner to avoid oil accumulation, maintain smooth pipelines, and achieve effective lubrication.
Figure 5 Spray treatment of damaged axis positioning protrusion
Figure 6 Electroplating and spraying treatment of worn convex platform
4.3 Poor heat dissipation of electric motor
The electric motor provides the power required for the hot stretching roller to stretch, and has certain requirements for the temperature and humidity of the environment. If the heat dissipation and ventilation conditions are poor, a high temperature field will be formed around the motor, causing a rapid increase in heat generation, a sharp deterioration in working conditions, a decrease in working performance, and ultimately burnout. The motor malfunction caused by poor heat dissipation and ventilation is shown in Figure 7.
The improvement measures are: (1) controlling the temperature and humidity on site; (2) Timely remove oil and dust accumulation from the cooling fan of the electric motor.
Figure 7 Motor malfunction caused by poor heat dissipation
4.4 Poor temperature control
The hot stretching roller heater provides the temperature required for stretching. Due to poor temperature control, short circuits or open circuits in the heater coil can cause abnormal temperature in the hot drawing roller bearings.
Regularly inspect the Pt100 platinum resistance thermal sensor to ensure its normal working condition; Ensure good heat dissipation and avoid short circuits or open circuits in the heater coil.
5. Conclusion
After taking corresponding measures, the failure rate of the hot drawing roller and its bearings has been greatly reduced, achieving the expected results. In the production process of polyester industrial raw silk, due to the high temperature, high speed, and variable tension environment in which the hot drawing roller bearings work, the bearings can only avoid faults by receiving good lubrication, timely heat dissipation and ventilation, and necessary temperature rise control. Bearing damage is caused by both technical and management reasons. Only by improving technical level and strengthening equipment management can bearing failures be effectively avoided from happening again.
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2024-08-21