*Pellet mill ring die failure may be caused by various factors such as raw material characteristics, equipment parameters, mechanical failure or improper operation. The following is a specific analysis of the reasons:
I. Raw material related issues
1. Improper raw material humidity
◦ The moisture content of the raw material is too low (such as less than 10%), resulting in poor material fluidity, difficulty in extrusion molding, and easy clogging of the die hole.
◦ If the moisture content is too high (such as more than 18%), the material is easy to agglomerate, adhere to the surface of the ring die during extrusion, and hinder material discharge.
1. Inappropriate raw material particle size
◦ The raw material particles are too large or uneven in thickness, and the resistance increases during extrusion, and they cannot pass through the ring die hole smoothly.
1. Impurities in the raw material
◦ Mixed with hard objects such as metal, sand and gravel, clogging the die hole or jamming the gap between the pressure roller and the ring die, resulting in no material discharge.
1. Material formulation issues
◦ High-fiber (such as straw, forage) or high-fat (such as adding excessive vegetable oil) materials have poor fluidity and are easy to accumulate in the ring die.
2. Incorrect equipment parameter settings
1. Improper gap between roller and ring die
◦ The gap is too large (normally it should be 0.1~0.3mm), the extrusion pressure is insufficient, and the material cannot pass through the die hole;
◦ The gap is too small, the friction between roller and ring die is aggravated, which may cause the equipment to get stuck or excessively worn.
1. Unreasonable ring die speed
◦ The speed is too low, the material stays in the ring die for too long, and the accumulation is blocked;
◦ The speed is too high, the centrifugal force is too large, the material cannot effectively fit the ring die, and the extrusion efficiency decreases.
1. Insufficient steam addition
◦ Insufficient steam volume during granulation, insufficient material temperature (usually 75~85℃) and humidity, poor plasticity, and difficult to form and discharge.
3. Mechanical failure or component damage
1. Problems with the ring die itself
◦ The ring die hole is worn, deformed or blocked (such as long-term failure to clean residual materials), resulting in a smaller or blocked die hole diameter;
◦ The ring die is cracked or broken, affecting the extrusion molding effect.
1. Wear or failure of the pressure roller
◦ The surface of the pressure roller is severely worn (such as the groove becomes shallower), and the extrusion friction with the ring die is insufficient;
◦ The pressure roller bearing is damaged or poorly lubricated, resulting in obstructed rotation and failure to extrude materials normally.
1. Transmission system failure
◦ Belt slippage, gear wear or loose coupling, resulting in insufficient power transmission, abnormal operation of the ring die or pressure roller.
IV. Improper operation and maintenance
1. Uneven feeding or material interruption
◦ The feeding amount is suddenly reduced or interrupted, resulting in insufficient material in the ring die and failure to continue extrusion;
◦ Too much feeding, material accumulation at the entrance of the ring die, forming a blockage.
1. Insufficient preheating of the equipment
◦ The ring die is not preheated before starting (usually idling for 5~10 minutes), the ring die temperature is too low, the material adhesion is poor, and it is not easy to discharge.
1. Untimely cleaning of the ring die
◦ The residual material in the ring die hole is not cleaned in time after shutdown, and the material solidifies and blocks the die hole, and the next time the machine is started, the material cannot be discharged normally.
5. Other factors
• Ring die aperture does not match the material: if the aperture is too small, the material extrusion resistance is too large; if the aperture is too large, the particle hardness is insufficient, and it may break and clog in the die hole.
• Ambient temperature is too low: low temperature causes poor material fluidity, and higher temperature and pressure are required for extrusion. If the parameters are not adjusted, it is easy to have difficulty in discharging.
Troubleshooting suggestions
1. First check the raw material status (humidity, particle size, impurities) and adjust to the appropriate range;
2. Calibrate the gap between the roller and the ring die, and check whether the steam supply is normal;
3. Disassemble the ring die, clean the blocked die hole, and check the wear of the roller;
4. Gradually adjust the feed rate and equipment speed, and observe the discharging effect.
If the problem persists, it is recommended to contact the equipment manufacturer or professional technicians for in-depth maintenance.