The extrusion blow molding machine is generally equipped with an ordinary single-screw extruder in small and medium-sized units, and an “IKV” extruder is configured in large and medium-sized blow molding machines or processing HMWHDPE materials.
These two types of extruders each have their own different characteristics. In the process of debugging and repairing, attention should be paid to their different characteristics, and debugging methods and measures suitable for their characteristics should be adopted.
1. Ordinary single screw extrusion hollow blow molding machine
The extrusion system of the hollow blow molding machine usually adopts a single screw extruder, and the structure of the screw and the barrel adopts different designs according to different raw materials. The design of the screw is usually based on the single-thread equidistant and unequal depth structure, and then functional designs such as pins and mixing heads are added to enhance the plasticizing effect and extrusion volume of the screw.
Ordinary single-screw extruder for hollow blow molding machine is mainly composed of a motor, transmission mechanism (belt drive or coupling), reduction box, barrel, screw, electric heater, etc.
1.1 Main precautions for debugging and use of ordinary single-screw extruder for hollow blow molding machine
1) When installing, it is necessary to ensure the straightness of the center line of the barrel and coincide with the center line of the transmission shaft of the reducer.
2) Cooling water is usually passed through the barrel feeding port and the reduction box to prevent the raw material at the feeding port from being heated and agglomerated and the temperature of the reducer being too high.
3) The temperature of the barrel section is usually set in a stepped shape, that is, the temperature of the feeding section is lower than the temperature of the melting section, and the temperature of the melting section is lower than the temperature of the metering section, with some exceptions for special raw materials.
4) When starting for the first time, it is necessary to check the rotation of the screw. From the root of the screw, it should rotate counterclockwise.
5) When starting the extruder, first run at a slower speed for a period of time, and then gradually increase to the normal production speed after the extrusion is normal.
6) For some special raw materials, such as PVC, PC, etc. when starting the extruder, it is necessary to adopt the gradual feeding method to prevent the screw from being overloaded and boring when starting.
7) If PVC, PC, ABS, and other plastic raw materials are used, when the production is over, the hopper door should be closed to squeeze out the raw materials in the barrel of the extruder. When PE and PP plastic raw materials are used for processing, there is no need to squeeze out the raw materials in the barrel of the extruder.
1.2 Maintenance of the transmission device of the extrusion hollow blow molding machine
The common single-screw extruder transmission device of the hollow blow molding machine usually includes a motor, a reduction box, a belt drive pair or a coupling, etc.
1) Electric motor
In the current industry, variable frequency speed regulation drive is generally used, and the motor is usually an ordinary motor or a special variable frequency motor. Common faults are mainly damaged to the bearing or damage to the winding insulation layer. Corresponding methods can be used for maintenance. The motor bearings are selected with E-grade precision bearings and filled with special grease for motor bearings.
First, the hard-tooth surface reduction box is used, and the box body adopts a two-half symmetrical split design. Before normal use, it is necessary to add gear oil to 2/3 of the level gauge. The common faults of the reducer mainly include bearing damage, gear shaft damage, tooth surface wear, oil leakage from sealing ring wear, etc., which need to be replaced. Special attention should be paid to the fact that the gearboxes of many blow molding machines are designed and manufactured by changing gears. During surveying and processing, attention must be paid to the displacement coefficient and characteristics of the gears to ensure that the repaired and replaced gears and other components are durable.
3) Belt drive
During debugging, attention should be paid to adjusting the parallelism of the two pulley axes to prevent premature wear and damage of the V-belt due to non-parallel axes, and pay attention to adjusting its tension to prevent insufficient transmission force caused by excessive tension and tension. Excessive wear and tear.
4) If the coupling is an elastic coupling when the rubber elastic block inside is worn a lot, it should be replaced in time. When the coupling is installed and debugged, special attention should be paid to ensure that the deviation of the coaxiality of its axis is within the allowable range.
2. IKV single screw extruder blow molding
IKV single-screw extruder is mainly used in large and medium-sized models in hollow blow molding machines, and most of the plastic raw materials it processes are HMWHDPE. Due to the processing characteristics of HMWHDPE materials, the following points should be paid attention to when debugging and using the IKV extruder.
1. The setting characteristics of process temperature during processing
The heating and heating of the barrel of the hollow blow molding extruder should be gradually increased, and then the temperature should be raised to the normal production temperature and then kept for 2 to 3 hours so that the extruder tends to be stable, and then the product can be run. If the holding time is short, the temperature measurement indication has reached the required temperature, but the actual internal temperature is low. At this time, if the plastic raw material is put into an extruder with a low temperature for extrusion, it will be overloaded due to excessive melt viscosity of the material. If the thrust bearing and reduction box of the extruder is damaged, it is also necessary to pay attention to whether the temperature at the connection between the extruder and the head is normal.
2. Start-up and debugging
After heating and maintaining a constant temperature for a period of time, you can start to work, press the “start” button, and then slowly enter the plasticization ratio, starting from 10% to gradually increasing to 40%, pay close attention to the changes in the host ammeter and resin pressure gauge when accelerating. Happening. Do not input too high plasticizing ratio as soon as the extruder is started, which will lead to screw breakage and overloading of the motor and frequency converter or DC motor drive.
When the plastic parison is extruded, no one is allowed to stand directly under or near the die of the storage machine head to prevent personal injury accidents caused by the screw breaking or the raw material being wet and foaming.