Can the pellet machine ring die still be used if there are microcracks on the surface?

In the field of pellet production, the pellet machine is a key equipment, and its operating stability and production efficiency directly affect the economic benefits of the enterprise. The ring die, as the core component of the pellet machine, plays a pivotal role in the entire pellet production process.

Analysis of ring die cracking

Ring die plays a core and key role in pellet machine, and has a decisive influence on pellet forming, quality and production efficiency.

Due to its high cost, thin wall and dense die holes, it will inevitably be affected by various complex factors in the long-term production and operation process, such as material friction, roller extrusion force, alternating stress and harsh working environment, etc. These factors will cause different degrees of wear and damage on the surface of ring die, among which the appearance of microcracks is a common problem that cannot be ignored.

Material factors

This is an internal factor that affects the performance of ring die and the generation of microcracks. Ring die is usually made of high-strength alloy steel or stainless steel. These materials need to have good strength, toughness, wear resistance and fatigue resistance. However, in actual production, due to fluctuations in raw material quality and improper production process control, the material performance may be unstable.

• Uneven material will cause uneven stress distribution in various parts of the ring die when it is subjected to force, and it is easy to produce stress concentration in weak parts. When local stress exceeds the yield strength of the material, plastic deformation will occur in the parts.
• Residual internal stress in the material is also one of the important reasons for the generation of microcracks. In the manufacturing process of the ring die, such as forging, heat treatment and other process links, if the operation is improper, residual internal stress will be formed inside the material.
  These internal stresses are superimposed with the stress generated by the external load during the use of the ring die, which increases the local stress level of the ring die. When the sum of internal and external stresses exceeds the strength limit of the material, it will promote the initiation and expansion of microcracks.

Unreasonable porosity and thickness

The porosity and thickness of the ring die are key parameters affecting its strength and performance.

• The porosity refers to the ratio of the total area of ​​the ring die hole to the total effective area of ​​the ring die. If the porosity is too high, the effective bearing area of ​​the ring die will be reduced, thereby reducing the strength and toughness of the ring die.
  During the operation of the pellet machine, the ring die needs to withstand multiple loads such as extrusion, friction of the material and extrusion force of the roller. When the porosity is too high, the ring die is more likely to deform and fatigue under the action of these loads, thereby generating microcracks.
• The thickness of the ring die also has an important influence on its strength. If the thickness of the ring die is too thin, its ability to resist deformation and fracture will be weakened. In actual production, some companies may choose a thinner ring die in order to pursue higher production efficiency or reduce costs.
  However, this practice often sacrifices the strength and reliability of the ring die. Studies have shown that when the opening rate of the ring die exceeds a certain threshold and the thickness is lower than the reasonable range, the probability of microcracks in the ring die will increase significantly.

Operation factors

Operation factors are factors that cause microcracks on the surface of the ring die during the operation of the pellet machine due to improper operation of the operator or unreasonable setting of equipment operating parameters. These factors can be effectively controlled by strengthening operator training and standardizing equipment operation procedures.

Improper installation

The installation quality of the ring die has an important impact on its normal operation and service life. During the installation process, if eccentric installation or uneven force occurs, the ring die will be subjected to uneven loads during operation, resulting in local stress concentration of the ring die.

For example, when the concentricity deviation between the ring die and the pressure roller is too large, the extrusion force of the pressure roller on the ring die will be concentrated on one side of the ring die, causing the ring die on that side to be subjected to excessive stress.

In this case, the ring die is prone to deformation and wear, which in turn causes microcracks. In addition, if the tightening torque of the fastening bolts of the ring die is uneven, it will also cause uneven force on the ring die during operation, increasing the risk of microcracks.

Unreasonable operating parameters

The operating parameters of the pellet machine, such as the gap between the ring die and the pressure roller, the feed rate, the main engine speed, etc., have an important impact on the working state and life of the ring die. If these parameters are set unreasonably, the ring die will be subjected to excessive load, thereby accelerating the generation of microcracks.

• If the gap between the ring die and the pressure roller is too small, the friction between the ring die and the pressure roller will increase, resulting in increased wear on the surface of the ring die. In this case, the material on the surface of the ring die will gradually become thinner and the strength will decrease due to excessive wear, making microcracks prone to occur.
  At the same time, too small a gap will also increase the resistance of the material during the extrusion process, resulting in an increase in the pressure on the ring die, further accelerating the expansion of microcracks.
• Excessive feed rate is also one of the common causes of microcracks in the ring die. When the feed rate exceeds the rated processing capacity of the pellet machine, the ring die needs to withstand a greater extrusion force to extrude the material.
  This will cause the load of the ring die to increase sharply, resulting in uneven stress distribution inside the ring die, and microcracks are easily generated in the stress concentrated area. In addition, excessive feed rate may also cause material accumulation in the ring die, causing local overheating of the ring die, further reducing the strength of the ring die and accelerating the generation of microcracks.
• Excessive main engine speed will also have an adverse effect on the ring die. When the main engine speed is too high, the linear speed of the ring die increases, and the residence time of the material in the ring die is shortened, resulting in insufficient extrusion and molding of the material in the die hole.
  At the same time, the high-speed rotating ring die will also be subject to greater centrifugal force, which increases the radial stress of the ring die. Under the combined effect of these factors, the ring die is prone to fatigue damage, which in turn generates microcracks.

Lack of regular maintenance

Regular maintenance is an important measure to ensure the normal operation of the pellet machine and extend the service life of the ring die. However, in actual production, some companies often ignore the maintenance of equipment, resulting in the equipment being in a poor operating state for a long time.

• If the ring die is not cleaned for a long time, the material will accumulate on the surface of the ring die and in the die hole. These accumulated materials will not only affect the molding quality of the pellets, but also increase the load of the ring die, causing local overheating of the ring die.
  Under the action of high temperature and high load, the material properties of the ring die surface will change, and microcracks are prone to occur.
• Lack of regular inspection is also one of the causes of microcracks. Regular inspection can timely detect wear, deformation and other potential problems on the surface of the ring die, and take corresponding measures to repair or replace them.
  If these problems are not discovered in time, the problems will gradually worsen during the continued operation of the ring die, eventually leading to the generation of microcracks. For example, a pellet production company did not inspect and maintain the ring die for a long time during the use of the pellet machine.
  When the quality of the pellets was found to have declined, the ring die was inspected. As a result, a large number of microcracks appeared on the surface of the ring die, and some of the microcracks had expanded into larger cracks, seriously affecting the normal use of the ring die.

Parts and components are worn and not replaced in time

During the operation of the pellet machine, some parts, such as the clamp, transmission wheel, die bushing, transmission key, etc., will gradually wear out due to long-term friction, extrusion, etc. If these worn parts are not replaced in time, the stress state of the ring die will change, and then microcracks will occur.

Studies have shown that the service life of a ring die with microcracks on the surface is usually 30%-50% shorter than that of a normal ring die, which not only increases the equipment maintenance cost of the enterprise, but also affects the continuity and stability of production.

Can it still be used if there are microcracks?

At present, the industry has not yet formed a unified and clear standard and conclusion on whether the ring die of the pellet machine can continue to be used after microcracks appear on the surface. Different companies and operators often make judgments based on their own experience, such as the severity of cracks and the use of ring molds.

Through visual observation and magnifying glass inspection, you can get a preliminary understanding of the distribution and surface characteristics of microcracks. Observe whether the cracks are concentrated in a certain area, whether they are distributed linearly or in a disorderly state.

At the same time, pay attention to the opening width of the cracks. If the opening width is wide, it means that the cracks may have developed to a certain extent, which has a greater impact on the strength of the ring mold.

Or use non-destructive testing technology to detect that the depth of microcracks on the surface of the ring mold reaches 3mm-5mm, and the distribution is relatively dense in the circumferential direction of the ring mold, which indicates that the strength of the ring mold has been greatly affected and there is a greater risk of continuing to use it.

Generally speaking, if the crack depth exceeds a certain proportion of the ring mold wall thickness (such as 10%-15%), or the crack length is long and the number is large, resulting in serious damage to the structural integrity of the ring die, then the risk of continuing to use the ring mold is greater and may need to be replaced in time.