The main machine of the plastic pelletizing equipment is the extruder, which is composed of extrusion system, transmission system and heating and cooling system. Extrusion system includes screw, barrel, hopper, head, and die, plastic through the extrusion system and plasticized into a uniform melt, and in the process of establishing pressure, by the screw continuous extrusion head.
(1) screw: is the most important part of the extruder, it is directly related to the scope of application and productivity of the extruder, made of high-strength corrosion-resistant alloy steel.
(2) barrel: is a metal cylinder, generally with heat, high compressive strength, strong wear-resistant, corrosion-resistant alloy steel or alloy steel lined with composite steel pipe made. Cylinder and screw with the realization of the plastic crushing, softening, melting, plasticizing, exhaust and compaction, and to the molding system continuous and uniform delivery of rubber. Generally the length of the barrel is 15-30 times of its diameter, so that the plastic can be fully heated and fully plasticized as a principle.
(3) hopper: the bottom of the hopper is equipped with a cut-off device, in order to adjust and cut off the flow of material, the side of the hopper is equipped with sight holes and calibration measurement device. (4) the head and mold: the head is composed of alloy steel inner sleeve and carbon steel jacket, the head is equipped with molding die. The role of the head is to rotate the movement of the plastic melt into a parallel linear movement, uniform and smooth introduction into the mold set, and give the plastic to the necessary molding pressure. Plastic in the barrel plasticization compaction, through the porous filter plate along a certain flow channel through the neck of the head into the head molding mold, mold core mold sleeve appropriate coordination, the formation of the cross-section of the ever-decreasing annular gap, so that the plastic melt in the core line around the formation of a continuous and dense tubular cladding layer. In order to ensure that the head of the plastic flow reasonable, to eliminate the accumulation of plastic dead ends, often placed in the diversion sleeve, in order to eliminate pressure fluctuations in plastic extrusion, there are also set up pressure equalization ring. The head is also equipped with mold correction and adjustment devices, easy to adjust and correct the concentricity of the die core and die sleeve. Heating and cooling are necessary conditions for the plastic extrusion process to be able to carry out.
(1) now extrusion machine is usually used for electric heating, divided into resistance heating and induction heating, heating pads installed in the body, the neck, the head of each part. The heating device heats the plastic in the barrel from the outside to warm it up to reach the temperature required for the process operation.
(2) The cooling device is set up to ensure that the plastic is in the temperature range required by the process. Specifically, it is to exclude the excess heat generated by the shear friction of the screw rotation, in order to avoid the high temperature of the plastic decomposition, scorching or shaping difficulties. Barrel cooling is divided into water-cooled and air-cooled two kinds, generally small and medium-sized extruder using air-cooled is more appropriate, large-scale water-cooled or a combination of the two forms of cooling; screw cooling is mainly used in the center of the water-cooled, the purpose is to increase the rate of material solids transport, stabilize the amount of rubber, while improving product quality; but the cooling at the hopper, one is to strengthen the role of solid material transport, to prevent the plastic particles due to the temperature of the viscous plastic plugging The second is to ensure that the transmission part of the normal work. In the plastic pelletizing machine group, leading to plastic pelletizing machine group in the operation of the friction clutch disengagement, unit interlocking stop the reason can be divided into four categories:
(1) the main motor system failure
1, the main motor torque is too high or too low; 2, the main motor speed is too low; 3, the main motor bearing temperature is too high; 4, the main motor winding temperature is too high; 5, the main motor water-cooling of the cooler Inlet and outlet temperature is too high; 6, the main motor bearing lubricating oil pump outlet flow is too low; 7, the main motor bearing lubricating oil pump outlet pressure is too low; 8, the main motor water-cooled cooler water leakage is too high.
(2) transmission system failure
1, gear box gearshift position deviation; 2, friction clutch instrument air pressure is too high; 3, friction clutch speed difference is too large; 4, gear box lubricating oil pump outlet pressure is too low; 5, gear box lubricating oil pump outlet oil temperature is too high; 6, the friction clutch internal faults, etc..
(3) plastic granulator screw process section failure
1, throttle valve before and after the melt pressure is too high; 2, the head of the melt pressure is too high; 3, before and after the screen changer melt pressure difference is too large; 4, drive the valve rotating faults.
(4) underwater pelletizing system failure
1, pelletizing motor winding temperature is too high; 2, the pelletizer rotational speed is too low; 3, the pelletizer torque is too high; 4, the pellet water bypass automatic switching fault; 5, the pellet water pressure is too high or too low; 6, the pellet water flow rate is too low; 7, the pelletizer clamping bolts are not tightened; 8, pelletizer bypass water valve is not closed; 9, the pelletizer hydraulic clamping Pressure is too low; 10, cut grain motor failure; 11, hydraulic cutter axial feed pressure is too low.
In the above causes of failure, the frequency of more: the main motor system of the main motor torque is too high or too low; transmission system of the friction clutch failure; plastic granulator screw process section of the system of the melt pressure is high; underwater cutting granulator system failure and so on. Main motor torque is too high
Reason analysis: oil lubrication system failure, the main motor output shaft and gear box in and out of the shaft alignment is bad, the motor and clutch vibration and other reasons will damage the main motor bearings, resulting in high torque. In addition, feeding load is too large or material melting bad will also lead to the main motor torque is too high.
Solution: Regularly check and clean the lubricating oil system, measure the main motor bearings with vibration measuring instrument and infrared thermometer and form a trend graph. If the trend value is exceeded, determine whether the main motor idling current value or power value exceeds the specified value, and judge whether the bearings should be replaced. Regularly check the alignment between the output shaft of the main motor and the input shaft of the gearbox, and the alignment must be checked after the first start-up or three months of operation with replacement bearings. Conduct electrical test inspection to determine the cause of rotor imbalance; conduct vibration speed test on the clutch, and readjust the dynamic balance if it exceeds the specified value. Regularly check the barrel heating and cooling system to ensure that the material is heated evenly and melted sufficiently. If the main motor power curve and melt pressure curve increase instantly when the extruder is started, it indicates that the feeding volume of the feeding system is too large instantly, and the feeding volume should be reduced.
Main motor torque is too low
Reason analysis: Twin-screw idling due to feeding system failure will lead to low torque of main motor.
Solution: Check to determine whether there is a failure of the additive system or the main material discharging system, clear the blockage.
Friction clutch failure
Reason analysis: instantaneous starting voltage of the main motor is too low, the friction disk, friction plate overheating, friction disk and friction plate aging, friction disk air pressure is too low and other reasons can lead to clutch disengagement.
Solution: When the main motor is started, avoid the peak of electricity consumption, reduce the feeding load, restart the interval of at least 30 minutes; in the summer, repeated more than two times to start the main motor, it should be longer interval or use a fan to force the cooling. Blow and wipe the surface of friction disk and friction plate with a cloth, if the wear is heavy or the surface appears "glassy" phenomenon, the friction disk and friction plate should be replaced. Confirm that the air pressure is sufficient to allow the friction disk and friction disk to fit together.
High melt pressure
Reason analysis: high filter mesh, polypropylene powder melt index is low and feed a large amount of material, low temperature of each section of the barrel so that the material is not completely melted, low template openings so that the head of the material extrusion is blocked, and other reasons can lead to high melt pressure.
Solution: When producing low melt index products, use low mesh filters, increase the throttle opening to reduce back pressure; timely replacement of filters, monitor the quality of various additives and the ash content of polypropylene powder. Reduce the feed load. Under the condition of not affecting the quality of the extruded products, increase the barrel temperature of each section, so that the polypropylene melt temperature increases, and increase the fluidity of the material. After the extruder stops, increase the head temperature and constant temperature for a period of time, thoroughly rinse and clean the template.
Underwater pelletizing system failure
Reason analysis: cutter wear or cutter edge damage, pellet water flow is too low, the pelletizer vibration is too large, the cutter and the template fit is not tight, the material melt index fluctuations in the flow rate of the discharge of material is not consistent, the pellet temperature of the water is too high and so on can lead to the underwater pelletizing system to stop the whole set of interlocking stop.
Solution: After stopping, visually inspect the cutter blade for excessive wear or damage, if so, all cutters should be replaced. Check and confirm whether the pellet water internal leakage, pellet water tank filter and cooler is clogged, if clogged should be manually cleaned; check whether the inlet and outlet pressure of the pellet water pump is normal, if it is not normal, then overhaul the pellet water pump and the valves on the pump pipeline. Check whether the alignment between the knife shaft and the pelletizing motor is out of alignment, whether there is any damage to the bearing assembly of the knife shaft, and whether the dynamic balance of the cutter rotor is out of balance. Check the contact between the four moving wheels of the pelletizing trolley and the guide rails for clearance during operation. Control the volatile content in the polypropylene powder to eliminate vibration to the cutter and cutter shaft when flowing through the moldboard hole. Reduce the temperature of the hot oil at the template, check the temperature distribution of the cylinder and template, and whether the flow, pressure and temperature of the cylinder cooling water are normal; confirm the time setting of "water, knife and material" arriving at the template to prevent the pellet water from arriving at the template too early to make the template holes frozen and blocked. Pelletizer closed the head, should quickly feed the amount of up to the set load of the extruder.