The cracking causes of ring die are complex and should be analyzed in detail. But it can be mainly summarized as the following reasons.
1. The material used in the ring mold is one of the important reasons. At present, 4Cr13 and 20CrMnTid are mainly used in our country, which is relatively stable. But the material manufacturer is different,for the same material, trace elements will have a certain gap, will affect the quality of ring mold.
2. Forging process. This is an important link in the mold manufacturing process. For the high alloy steel mould, the requirements of material carbide distribution and other metallographic structure are usually put forward. It is also necessary to strictly control the forging temperature range, formulate the correct heating specifications, adopt the correct forging method, and slow cooling or timely annealing after forging. Non-standard process is easy to lead to the crack of the ring die body.
3. Prepare for heat treatment. According to the different materials and requirements of the die, annealing, tempering and other preparatory heat treatment processes are respectively used to improve the structure, eliminate the structure defects of forging and blank, then improve the workability. After proper preparation heat treatment of high carbon alloy steel die, the network carbide can be eliminated, which can make the carbide spheroidized and refined, and the distribution uniformity of carbide can be promoted. This is conducive to ensure quenching, tempering quality, improve the service life of the mold.
Pellet mill die heat treatment
1. Quenching and tempering. This is the key link in die heat treatment. If overheating occurs during quenching heating, it will not only cause greater brittleness of the workpiece, but also easy to cause deformation and cracking during cooling, which will seriously affect the service life of the mold. The process specification of heat treatment should be strictly controlled and vacuum heat treatment should be adopted. Tempering should be done in time after quenching, and according to the technical requirements to adopt different tempering process.
2. Stress-relieving annealing.The die should be subjected to stress-relieving annealing treatment after rough machining, in order to eliminate the internal stress caused by rough machining, so as to avoid excessive deformation or crack caused by quenching. For the die with high precision requirement, it also needs to undergo stress-relieving tempering treatment after grinding, which is beneficial to stabilize the die accuracy and improve the service life.
Opening hole rate of ring die
If the opening hole rate of ring die is too high, the possibility of ring die cracking will increase. Because of the different heat treatment level and process, there will be a big difference between each ring die manufacturer. Generally, our pellet mill die can improve the opening hole rate by 2-6% on the basis of the domestic first-class brand mold, and can ensure the service life of the ring mold.
Pellet mill die wear
certain thickness and the strength is reduced to the point that it cannot bear the pressure of granulation, cracking will occur. It is recommended that when the ring die is worn to the level which parallel roller shell groove, the ring die should be replaced in time.
When the pellet mill die in the process of granulation, the amount of material into the pellet mill die can’t be running at 100%.Although the ring die granulation yield is high,but such a long time of high strength operation, will also lead to the cracking of the ring die. We recommend control at 75-85% of the load to ensure the service life of the ring die.
If the ring die and the press roll are pressed too tightly, it is easy to crack. Generally, we require that the distance between the ring die and the press roll be controlled between 0.1-0.4mm.
sundries
It is easy to crack when the hard material such as iron appears in the pelleting material.
Installation of ring die and pelleting machine
The installation of ring die is not tight, there will be a gap between the ring die and the pelleting machine, and the ring die cracking will also occur in the process of pelleting.
After heat treatment, the ring die will be deformed greatly. If not repaired, the ring die will be cracked in use.
When the pelleting machine itself has defects, such as the main shaft of the pelleting machine shaking.
Post time: Nov-29-2022