For the ring die of 4Cr13 materials, the quality source must start from ingots: 4Cr13 steel ring die chemical composition (mass fraction %) is :C content of 0.36 ~ 0.45,Cr content of 12 ~ 14,Si content of 0.60,Mn content of 0.80,S content of 0.03,P content of 0.035.In actual use, the service life of ring die with about 12% Cr content is more than 1/3 less than that of ring die with 14% Cr content.Therefore, the source of ring die quality starts from the steel bar, which not only ensures that Cr content is over 13%, but also requires that the size and shape meet the requirements of forging.
2. Quality of ring die forging of sawdust pellet machine. For the process of ring die forging of 4Cr13 materials, the heating temperature and time are appropriate.
1) heating temperature and time is too long, forging stock yellow-white, estimates are that more than 1200 ℃, the temperature is seen as forging stock surface burnt, integral overheating, organization bulky grain uneven phenomenon;
2) poor uniformity of furnace temperature.In the heating process, the temperature is not uniform, which makes the forging overheat or partially overheat.The larger the forging size, the more serious this phenomenon is.It is difficult to eliminate this defect in the subsequent heat treatment process, which is also a common cause of ring die cracking.
3) due to defects such as segregation, non-metallic inclusions, and loose, etc. in the ingot, it is necessary to improve and eliminate them through forging deformation, which is the foundation for forging to achieve good comprehensive mechanical properties.For the forgings with high longitudinal and lateral performance, good combined forging technology should be adopted, and single forging technology is difficult to guarantee the quality.
4) the cooling temperature and speed are not controlled well after forging. If the cooling speed is very slow, the austenite recrystallization is easy to happen, and the grains that have been refined in the forging will grow abnormally, resulting in mixed crystals.
5) annealing treatment: it is advisable to control the hardness of the blank of ring die, which is between hb170-220. If the hardness is too high, the drill bit will break easily when drilling, resulting in dead hole. If the hardness is too low, the finish of the die hole will be affected.
The ring die is usually made of carbon (alloy) steel or stainless steel through forging, cutting, drilling, heat treatment and other processes.When drilling the annular die, the perforated gun should be used to drill to ensure the quality of each hole.During heat treatment, vacuum quenching equipment should be adopted to avoid surface oxidation and decarburization which often occurs in common equipment, so as to obtain higher hardness.
The perforation rate on the surface of the ring mould directly affects the output of the granulator and the strength of the ring die.High opening rate, high output of granulator, low intensity of circular mould;On the contrary, the strength of ring mold increases and the yield of granulator decreases.Due to the difference of material selection and size of ring die, it is still difficult to get the correct value of hole opening rate of ring die to better coordinate its output and service life.For ring dies with a diameter of 2~12mm, the opening rate of die holes should generally be selected between 20% and 30%.The smaller the die hole, the smaller the opening rate, and conversely, the larger the opening rate.The manufacturer can adopt the close test method to determine the opening rate of the ring die according to the selected ring die materials, the shape structure and size of the ring die, so as to ensure the ring die has enough strength to prevent it from breaking when bearing and shorten its service life.
When designing the shape structure of circular mould, the number of grooves distributed along the radial direction should be reduced as far as possible, and its depth should be reduced.Because the furrow groove along the radial distribution is the most likely place to generate stress concentration.Under the action of long-term alternating stress, it is easy to produce microcracks at this position first, then gradually expand, and finally cause ring die fracture.
The above analysis shows that there are two main failure reasons in the production process, one is abrasive wear and the other is fatigue failure.It is not practical to avoid the failure of ring die fundamentally, only to improve the manufacturing, production and use conditions of ring die, so as to extend the service life of ring die and save cost.
Service life of ring die:
The service life of ring die is carried out by means of statistics of ring die production at feed manufacturer.