The ring die is the key part of the pellet machine and the most important wearing part of the pellet machine. According to statistics, the loss cost of the ring die accounts for more than 25% of the maintenance cost of the entire production workshop. It also has a direct impact on the quality of the extruded pellet feed. . Therefore, it is very important for feed producers to understand the characteristics of the ring mold and make the correct selection, reasonable use and effective maintenance of the ring mold. The following is a brief analysis of the characteristics, selection, use and maintenance of the ring die for your reference.
Ring die hole structure, compression ratio and roughness
Common ring die holes mainly include straight holes, stepped holes, outer tapered holes and inner tapered holes. Stepped holes are divided into release stepped holes (commonly known as decompression holes or release holes) and compression stepped holes. As shown in Figure 1, different die holes are suitable for different types of feed materials or different feed formulas.
The compression ratio of the ring die refers to the ratio of the effective length of the ring die hole to the minimum diameter of the ring die hole, and it is an index that reflects the extrusion strength of the pellet feed. The greater the compression ratio, the stronger the extruded pellet feed. For the compression ratio of the ring die of a straight hole, the effective length of the ring die hole is the total thickness of the ring die, and the minimum diameter is the diameter of the die hole itself; for the release stepped hole and outer tapered hole, the die The effective length of the hole is the total thickness of the ring die minus the length of the release hole or the length of the outer tapered hole. The diameter of the small diameter section is the diameter of the calculated compression ratio. For the compressed stepped hole and the inner tapered hole, This situation is special. Generally, the thickness of the ring die is taken as the effective length of the die hole. The minimum diameter is taken as the diameter of the small diameter segment. Of course, the meaning of the calculated ring die compression ratio is different from the previous two cases.
Roughness is also an important indicator to measure the quality of ring die. Under the same compression ratio, the larger the roughness value, the greater the feed extrusion resistance and the more difficult the discharge. Excessive roughness also affects the quality of the particle surface. The appropriate roughness value should be between 0.8 and 1.6.
Ring die working area, hole arrangement and opening rate???
The working area of ??the ring die refers to the product of the inner diameter circumference of the ring die and the effective width, and the effective width refers to the distance between the two overrun grooves of the ring die. Under the same working area, the inner diameter of the ring die is inversely proportional to the effective width. ???
The arrangement mode of the ring die drilling is generally arranged along the circumferential direction, and the small holes between the rows in the width direction are staggered with each other, so that the entire small holes drilled are arranged in an approximately equilateral triangle arrangement. If the diameter of the small hole is d, the wall thickness between the small hole and the small hole is a, and the ring die opening rate is ψ, it is not difficult to calculate according to the principle of equilateral triangle: ψ≈0.9d2/(d+a )2???
For example, for a ring die with a hole diameter of 4.5 mm, if the wall thickness between the holes is 2.6 mm, the ring die opening rate can be calculated as 36%. ???
It can be seen from the above formula that, in the case of a certain diameter of the die hole, to increase the opening rate of the ring die, the wall thickness between the die holes must be reduced, but the minimum wall thickness must meet the needs of the ring die strength. ???
The general rule is that the larger the die hole diameter, the higher the ring die opening rate.
Ring mold linear speed
The ring die linear velocity refers to the tangential velocity of the inner circle of the ring die. Its height affects the thickness of the material layer in the extrusion area and the time for the material to pass through the die hole, which in turn affects the granulator output and particle quality. When the linear velocity is too high, it may cause the material in the extrusion area to form a fault, the granulation is discontinuous, the produced particles are soft, and the powder is too much, and it is easy to slip for materials with a high moisture content, or even cannot granulate at all. ; Although the lower ring die linear velocity produces particles of good quality, it has a greater impact on output. The common linear speed of the ring die is generally between 6~9m/s.
Ring die installation
The ring die installation methods mainly include straight surface installation, cone surface installation and hoop installation. The straight-face type installation is simple, the ring die is not easy to tilt, but the ring die fixing bolt is easy to cut off, and it is not suitable for large-sized granulators. The conical surface mounting ring mold has good centering performance and large torque transmission. The ring mold fixing bolts are not easy to be cut, but it requires the assembler to be careful and master certain skills, otherwise the ring mold is easy to install obliquely. The hoop-type installation is more suitable for small-sized granulators. It is easy to install and takes a short time. The disadvantage is that the ring mold itself is asymmetric and cannot be dropped.
Selection of ring mold?
It can be seen from the characteristics of the ring die that there are many factors to consider when selecting a ring die. However, in actual work, some factors are usually already designed, such as the ring die installation method, ring die linear speed, and ring die working area. This has been determined when the pellet machine is purchased, and generally will not change. Other factors can be guaranteed by choosing a professional ring mold manufacturer, such as the ring mold material, heat treatment strength and wear resistance, die hole opening rate and roughness, etc. These factors are usually available for professional ring mold manufacturers To achieve the best performance requirements, users only need to do not want to buy cheap ring molds produced by manufacturers without technical and equipment guarantees. For example, the processing and heat treatment quality of die holes can only be guaranteed by special gun drills and vacuum heat treatment equipment. It is difficult to produce high-quality ring molds with ordinary drilling machines and heat treatment methods.
At present, what is generally faced in feed mills is how to select the appropriate die hole form and ring die compression ratio according to the feed variety and formula produced by the feed factory. In general, straight holes and release stepped holes are suitable for processing compound feed; outer tapered holes are suitable for processing high-fiber feed such as defatted bran; inner tapered holes and compressed stepped holes are suitable for processing grass powder. Feed. The reason for the design of the release stepped hole mentioned above is that for certain types of feed, especially small-diameter feed, the wall thickness of the ring die cannot reach the minimum requirements under the condition of ensuring a reasonable compression ratio, so that the ring If the die strength is not enough, the ring die burst phenomenon often occurs in production, and the thickening measures have to be taken. The method is to increase the thickness of the ring die and increase the relief hole (release hole) while ensuring the effective length of the die hole.
For the selection of the compression ratio of the ring die, due to the different formulas, the different raw materials used, and the granulation process is also different, the specific suitable compression ratio depends on the various feed manufacturers to explore in the production, which can only be based on Past experience gives a rough range. Generally speaking, a compression ratio between 9 and 13 should be used for livestock and poultry feeds; a compression ratio between 13 and 16 should be used for fish feeds; a compression ratio between 20 and 25 should be used for shrimp feeds; heat-sensitive Feed should use a compression ratio between 7-9; forage and straw feed should use a compression ratio between 6-9. In addition, feed producers can also slightly increase or decrease the actual compression ratio according to their own quality requirements. For example, choosing a slightly lower compression ratio is beneficial for increasing production, reducing energy consumption, and reducing ring mold wear, but it also reduces feed quality. If the particles are not strong enough, the pulverization rate is high; otherwise, it is beneficial to the quality of the particles, such as smooth appearance of the particles, increased density, small pulverization rate, etc., but it will increase production costs.
Use of ring mold
Correctly adjusting the working gap between the ring die and the pressing roller is the key to the use of the ring die. In general, the gap between the ring die and the pressure roller is preferably between 0.1 and 0.3 mm. Normally, the new pressure roller and the new ring die should use a slightly larger gap, the old pressure roller and the old ring die should use a smaller gap, the larger hole ring die should use a slightly larger gap, the smaller hole ring It is better to choose a slightly smaller gap for the mold, a large gap for materials that are easy to granulate, and a small gap for materials that are difficult to granulate. For the operator, it is necessary to have practical operating experience, and be able to skillfully select and adjust the ring die gap.
The following points should also be noted during the use of the ring mold: ① Generally, newly purchased ring molds need to be "washed" with oil before starting to remove burrs in the mold holes. If it is a ring die with a large die hole of φ2.5 or more purchased from a regular manufacturer, it is not necessary. For a ring die with a die hole of φ2.5 or less, it is generally necessary to "wash the mold" with oil for a few minutes to two before normal production. More than ten minutes is better. For the ring die with poor die hole roughness, sometimes it is necessary to mix 20% to 50% of fine sand in the oil and grind it before normal production. ②During the use of the ring mold, it is necessary to avoid the mixing of large pieces of hard particles such as gravel, sand, iron, bolts and iron filings in the material, so as not to accelerate the wear of the ring mold or cause excessive impact on the ring mold , Causing the ring die to burst. If iron enters the die hole, it must be punched out or drilled in time. ③ For the ring mold installed symmetrically on both sides, it can be installed and used in reverse after a certain period of production to make the ring mold wear evenly. ④Do not tilt the ring mold after installation, otherwise it will cause uneven wear; the bolts for fastening the ring mold must reach the required tightening torque to avoid shearing of the bolts and damage to the ring mold.
Ring mold maintenance
Reasonable maintenance of the ring mold is one of the necessary measures to ensure that the ring mold can work normally and extend its service life. In normal work, you should pay attention to the following points: ① When the ring mold needs to be replaced, it should be non-corrosive The oil feed squeezes out the original feed so that it can be discharged smoothly when used again, and can prevent the die holes from corroding. ②After using the ring mold for a certain period of time, it should be regularly checked whether there are local protrusions on the inner surface of the ring mold, and whether the material guide port of the die hole is flattened, sealed, or turned over. If so, apply a polisher or use other tools to smooth out the protruding part of the inner surface of the ring mold, and then chamfer the material guide port to make necessary repairs to the ring mold to extend the service life of the ring mold. When repairing, it should be noted that the lowest part of the inner surface of the ring mold should be 2mm higher than the bottom of the overrun groove, and there is still an adjustment margin for the eccentric shaft of the pressure roller after repair, otherwise the ring mold should be scrapped. ③If most of the die holes are blocked by materials, the material can be softened by oil soaking or cooking, and then granulated again; if granulation is still not possible, you can drill the materials that block the die holes with an electric drill After it comes out, it is grinded with oily materials and fine sand before use. ④The ring mold must be stored in a dry, clean place, and the specifications are marked. If it is stored in a humid place, it may cause corrosion of the ring mold, thereby reducing the service life of the ring mold or affecting the discharge effect.