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Physical Stress Analysis flat die pellet mill

The Physical Stress Analysis flat die pellet mill
Biomass utilization technology born Pyrolysis gasification technology, biomass pyrolysis liquefaction technology, biogas technology, and biomass Curing technology. Which cured molding technology to produce biomass fuel particles, can be used for industrial fuel, power plants and rural residents cooking and heating, and other fields, has been widely used in Sweden and other European countries. According to statistics, in 2005 the World biomass the solid molding fuel production has exceeded 4.2 million tons. China Curing technology of biomass research began in the 1980s in the biomass screw extrusion molding, the piston compression molding and granulators extrusion molding, etc. have a breakthrough. Flat die pellet mill processing of biomass particles is a curing molding technology, the advantages of recent years in the process of development of the biomass pelleting industry, flat die machine with its rugged, raw materials adaptable gradually made producers favor, this article will works flat die pellet mill processing of biomass particles, the formation mechanism of the biomass feedstock, process of the flat die machining biomass particles and features presentations and discussions.
Flat die pellet mill process and particle formation mechanism

Motor 2. Transmission case 3. Spindle 4. Feeding chamber 5. Pressure roller
6 are plate 7. Flat die cutter 9. Sweeping plate 10. Spout
Figure 1 flat die pellet mill
Figure 1 Flat die pellet mill, according to the state of motion of the execution units, flat die pellet mill movable roller, moving mode, mold roller double-acting three, the latter two is common in small flat die pellet mill, a large machine type generally used to move the roller. Points, the shape of the grinding rollers can be divided into the taper roller and two straight roller. Straight roller moving roller flat die pellet mill works shown in Figure 1: the drive spindle motor through the gear box, spindle driven grinding roller, roller around the spindle revolution around the roller shaft rotation. Processing particles, the biomass raw material is fed into the feeding chamber of the flat die machine, spread evenly on a flat die in the sub-feeder and the squeegee under the joint action of the spindle-driven pressure roller continuously rolled across the material layer, material extruded into the die hole, the material in the die hole experienced forming, security type process, after a certain time, to the cylindrical state is extruded, rotation of the cutter cut off the material, the formation of particles, the particles out of the sweep Flitches.

Figure 2 particle formation mechanism diagram
Figure 2 The process of pelletization biomass feedstock containing mainly cellulose, hemicellulose, and lignin and other substances, and its the flat molding machine between the mold roll forming mechanism is as follows (see Figure 2): the region of the feed material under gravity close on a flat die, the mutual position when the platen roller forward scrolling the material entering deformation nip, this time due to being squeezed, the raw material particles continuously into the voids between the particles, the air is discharged in the gap between the particles constantly updated, all big gaps between particles gradually are able to enter the particles occupy. Continue to scroll with the platen roller, a raw material to be compacted into the extrusion zone, part of the wedge-shaped area, the tapered bore portion of the die hole, and the front half portion are all extrusion zone, and the zone, the pressure continues to increase, and the particle itself deformed and plastic flow, in the direction perpendicular to the maximum principal stress is extended, and continue filling around smaller voids, and generate a lot of heat due to the increased friction between the pressure roller and the material, resulting in the raw materials containing lignin softening, the adhesive force increases, the combined effects inherent in the softening of lignin and biomass cellulose biomass gradually forming part of the residual stress, then stored in a molded block internal particles combined with a solid but not very stable. Molding block into the die orifice in the extrusion under the action of Paul-type segment, the segment is not conducive to the shape maintaining the residual stress is eliminated, and the particles are stereotyped.
Process and testing
The flat die machining biomass particles, the basic process shown in Figure 3, the biomass raw material after crushed and pulverized into the drying link. The water suitable materials are mixed into the flat die after quenching and tempering mechanisms tablets. After cooling and sieving out particles from the pellet mill, to be finished, and then packaged or bulk factory.

Figure 3 biomass fuel pelleting process
Figure 3 the manufacturing processes of biomass, fuel can pellets biomass pelleting process steps is roughly similar, however, due to the different physical properties of raw materials, molding machine works, the specific process or different grain flat die mechanisms critical The process steps are detailed below:
Crushed part of the flat die mechanism grain, raw material particle size is smaller the particles to each other filling, chimeric, the smaller the average energy consumption per unit of production of the pellet mill, wearing parts flat die and pressure roller wear rate is slower, the higher the resistance to water and granulated hardness indicators, however, causes the crushing part of the energy consumption of a sudden jump in the blind pursuit of the particle size decreases, so should meet the flat die pellet mill processing requirements of the premise, the particle size is as large as possible. In fact, the raw materials can suppress large particle size is one of the advantages of the flat die machine, the general crop stalks and other raw materials, the maximum particle Dimension requires less than 2 × 2 × 30mm for wood raw material, the more stringent requirements .
Dried link dried main purpose is to adjust the rate of the water content of the raw material, to make it stable and uniform suitable granulation machining, in granulation molding process, a suitable moisture on the one hand be able to pass the pressure of the pressure roller, on the other hand can play lubricant, auxiliary particle mutual filling, thereby promoting material molding. However, the moisture content is too large, the water easily between the particles forming the isolation layer so that the interlayer can not be closely integrated and easy expansion of the extruded particles disperse, can not be formed, thus the control suitable raw materials moisture is particularly important in the process. Generally collected from the nature of the biomass feedstock moisture distribution between 20-40%, can reach 55%, the flat die pellet mill processing biomass raw material, it is required the raw material in the 10-14% moisture content between when processing corn stover sugar more raw, slightly higher water content allows. The conventional drying process generally belt dryer, drum dryer, van dryer, and other equipment, however, have to admit that this part of the energy consumed considerable. I believe that solar drying technology is more mature, fully equipped with solar greenhouse dehumidifier biomass feedstock to turn throwing equipment, general biomass feedstock drying temperature lower level, between about 40-70 ℃ This goes cryogenic use in the field of solar energy use to adapt, compared with conventional drying process, you can save a lot of conventional energy sources, reduce fixed investment, significant economic benefits.
The granulating link, dry good material into the granulation link, without quenching, direct processing. Conditional manufacturers optional automatic control system and mold roller automatic gap device. The automatic control system based on the changes in the host current regulation of feeding motor inverter to adjust the volume of feed in real time, which can effectively avoid the occurrence of the phenomenon of blocking machine. The mold roll automatically adjusted gap device can collect the mold roll gap data to control the hydraulic system, through feedback, contrast, so that the gap and the setting value coincide, and can change at any time in the production process. In general, the start-up phase, roller gap should be as small, which can reduce the starting torque to reduce motor load. Into the steady-state operation, the mill roll gap should be slightly larger than the compression stroke, which can be increased to obtain a hard, smooth particles. Can set the input control system of the gap varies with time after starting, the machine can automatically adjust the mold roll gap. The the pressure roller peace mold are easy to wear pieces need to be changed regularly, the service period of the pressure roller can be a little longer, but the best can peacefully die with replacement. Generally, the flat die can work 800-2000 hours, depending on the components of the material and processing technology.
The use of the above process, we developed Machinery Research Institute of China Agricultural Mechanization Sciences Research Institute livestock PM60 flat die pellet mill performance assessment test in June 2007-August. Wherein the part of the test data are as follows:
Table 1 PM60 flat die pellet mill processing biomass pellet test data
Table 1 Experimental data of PM60 flat die pellet mill raw material particle diameter (mm) Productivity (kg / h) tons of material power consumption (kw · h / t) particle density (kg/m3) forming rate (%) of Korean pine 1091649.11.2193 white pine sawdust and straw mixture 1082354.71.2994.5 1085052.91.2695.3
Known by the test results the PM60-type flat die pellet mill for processing sawdust, sawdust and straw mix of biomass raw materials, molding rate, tons of power consumption more than 93% in less than 55 kwh hour production capacity of around 800kg-900kg.

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Characteristics of the flat die pellet mill processing biomass fuel particles
In the processing process of the biomass fuel particles, we found that the various working parts of the flat die pellet mill exhibits the following characteristics:
1 feeding characteristics
Material into the flat die machine station feeding room, feed room play a cache of materials and feeding grab the finished material to the grinding roller wedge angle feed. There are two characteristics of the feeding chamber, one feeding space is vast, specialized extrusion the biomass feedstock large diameter pressure rollers provide a space, fluffy biomass feedstock feeding space; by gravity directly feeding the principle of efficient and practical.
Biomass raw materials like crushed material such as sawdust, twigs, tree branches and straw powder, crude fiber content, light and fluffy, not easy feeding. A spacious feeding room, first for the material to provide a broad space for feeding. Second, we allow the pressure with a large diameter roller, thereby increasing the grab angle, grab enhance crude fiber materials. According to estimates, the sawdust raw bulk density of about 200kg/m3, a porosity of about 75%, the material itself is light and fluffy, compression ratio above 6 made of particles, which on feedstock space of higher demand. Spacious feeding room flat die machine, PM60 flat die machine, for example, its effective feeding volume about 120dm3, single feeding up to 24kg, machine can meet demand.
Secondly, the material fed into the process is a process naturally falling under gravity. Do not need to force feed, raw materials can be straight into the station suitable for extrusion. This feed is clearly superior to the ring die pellet mill, ring die machine work, corresponding to the different materials need to explore the the corresponding stock guide plates parameter of, the nature of the material slightly change you have to change the guide plate, which limits The ring mold machine adaptability of raw materials.
2-level models sex
Movable roller flat die pellet mill, the flat die is fixed to the machine base, the material is extruded from the die orifice of the stationary forming particles cut by the cutter. Ring die pellet mill, ring die is a rotation of the rotating ring die often the particles left on the chassis, and part of the particles are smashed, molding rate. Flat die pellet mill Zhongping mold still way conducive to the increase in the rate of the particles forming.
Core working parts of the pellet mill, flat die structure parameters is appropriate to directly determine the quality of the pros and cons of the particles. Processing of different materials, shall be equipped with a different template. The opening area of the template, the die hole size, die holes arranged manner other elements are as important factors of the performance of the granulation. The smaller the aspect ratio of the die hole, the greater the yield, but the smaller the particle density, the worse the quality. The aspect ratio is too large, easily blocked machine. From the practical experience to see products with the same specifications as the production of the same raw material, the thickness of the flat die than small ring mold many.
Compared with the ring mold, flat die advantage is that the structure is simple, compact, can be both positive and negative, and low cost. The templates are easy to wear pieces need to be changed regularly, the symmetry of the structure of the flat die template reversible side after excessive wear and tear, the template can be anti-loaded, which greatly improved the life of the flat die. Increased consumable life helps to reduce production costs.
3 pressure roller features
Platen roller, flat die machine the characteristics of the pressure roller is the lower speed, large diameter, compared to some models of ring mold machine, its speed or even less than ring molded roll half, while the larger diameter can be increased pressure roll angle of grab. This makes the work of the pressure roller on the material has a strong grab force, and reduce the possibility of slippage.
However, the work of the pressure roller is not overall doing pure rolling, its axial point of view, the inside and the outer side of the pressure roller will slip occurs, this sliding action of the working principle of the machine is a flat die, and is not due to material changed. The author believes that the presence of a sliding action, of course, to some extent, to accelerate the wear of the pressure roller, but the objective is to enhance performance of the extrusion granulator, the flat die pellet mill more crude fiber-containing raw material in the processing raw materials to become a leader. Following from motion analysis and stress analysis of the sliding action of the discussion.

The force of the pressure roller of the Figure 4
In Figure 4 Forces and Moments exerted on the ROLLER to the clockwise rotation of the platen roller shown in Figure 4, for example, the work of the flat die pellet mill, the platen roller must exist a pure rolling circumference line H in a pure rolling line H medial pressure roller occur ahead of sliding, called slip scrolling; lag sliding occurs outside of the pure rolling line, pressure roller, called slip scrolling.
Arbitrary point A of contact with the material in the pressure roller, its force is shown in Figure 4, extruded materials and receive the material is applied to the pressure roller reaction force of N, N size changes, but always pointing along the radius a radial direction; between the roll and the material may also be the presence of the frictional force F, F must be in a tangential direction, but point to be discussed.
When the machine enters the steady state, the pressure roller is in a state of equilibrium, the establishment of a cylindrical coordinate system as shown in Figure, the Z axis is the axis of the grinding roller, grinding rolls outermost sectional center of the Z-axis 0 to the vertical direction of radius angle coordinates of 0:00. By flat molded roll rotation is driven, the driving torque does not exist, therefore, its own moment of zero, the torque balance equation can be obtained:
Where: ②
Z coordinates, assuming pure rolling line H ① formula can be written as: ③
Obviously, ③ the right-hand side slip the total torque scroll zone, the left side of the resultant moment slip scroll zone, two moment reverse. In slip scroll District, mill roll speed faster, relative to materials sliding force F along the tangent point on the direction of the resultant moment is counterclockwise, the relationship can be inferred by the torque balance slip ③ left-hand side describes scroll zone suffered total torque must be clockwise, so most of the region by force point suffered friction force F should be below the tangential point (Figure 4).

Figure 5 material force
Figure 5 Forces exerted on the material to clear the platen roller by the force, and can analyze the material by the force, the material by the force shown in Figure 5, an arbitrary point B of the extrusion material in the grinding rollers, the material compression roller and the force applied, respectively, and a reaction force. A plane in contact with a flat die, the material by the frictional force S in the horizontal direction and vertical direction of the supporting force T. Material force balance equation:
Slip scroll zone any cross-section:
Pure rolling line where the cross-section:
Slip scroll area of any cross-section:
Movement from the pressure roller and material force, we can make the following analysis:
(1) It can be seen from the above three groups balanced contrast, produce slip when rolling and slip rolling, compared with the pure rolling in the vertical direction and the horizontal direction is equivalent to the urging force of the re-allocation. As can be seen from the formula ④ slip scroll zone, the material in the horizontal direction on the force increases, so the horizontal direction of extrusion enhanced. As can be seen from the formula ⑨ slip scroll zone, the material in the vertical direction on the force increases, the vertical direction of extrusion enhanced. The two sliding action of the effect is not negative.
(2) by the motion analysis known in the slip scroll zone, press roller ahead of the slide, so the material per unit length in the radial direction of the flat die, the pressure roller on the increase in the extrusion stroke, which corresponds in the vertical The direction of growth of the material pre-compression stroke. Scroll zone, the pressure in the slipping roller lag sliding, for the material of the unit length in the radial direction of the flat die, flat die extrusion stroke increases, which is equivalent to increase in the horizontal direction on the pre-compression stroke. This could explain why the ring die pellet mill the peace die pellet machine processing the same raw material, the product of the same specifications, flat die machine template thickness is much thinner than the ring mold thickness: Although both template extrusion granulation, but the two sliding action of the flat mold machine equivalent to an increase of the material of the compression stroke.
(3) from the formula ④, ⑤ and formula to ⑧, ⑨ can be seen, the two sliding action causes the generation of the frictional force, the frictional force F between the pressure roller and the material produced two shearing action. Slip ahead of the scroll area sliding grinding roller generate strong shearing of the material in the vertical direction, this shearing closer to the more obvious template center. Lag sliding slip scroll area of the grinding rollers generate strong shearing of the material in the horizontal direction, the more shearing away from the more obvious template center.
Test from spout inside observation, we found that the the intermediate laps die hole of the flat die a quick feed, more inside the ring and the outer ring of the die hole, the material more slowly. Relieved cutter observed, the middle laps of the material to be extruded shorter length will fracture and fall. And extrusion materials inside the ring and the outer ring mold hole is not easy to automatically broken and fall, many even long to more than 200mm out of the template. This is because, by a large shearing force due to the presence of the two shearing, template inner and the outer material, the material particles are sufficiently rubbing and cutting, tearing, thereby filling, fitting, and so the more on both sides, forming particles more dense texture, a material more slowly. The reason why the flat die machine has superior performance when processing more crude fiber content materials, it is precisely because of these two strong shearing the material fully pretreatment.
(4) slip rolling and slip scroll exist will lead to increased wear of the parts of the pressure roller flat die design flat die design into a symmetrical structure, can use with both positive and negative, which will effectively reduce the vulnerability of piece cost.
4 Conclusion
As people's awareness of environmental protection, as well as the increase of the national environmental protection efforts, more and more pressing social demand for clean alternative energy; Central Document No. 1 this year, explicitly stipulates that "to promote non-grain and oil crops as the main raw material for biomass energy research and development "; development of biomass pellet fuel in line with national policy, the wishes of the people. Performance and stable molding machine plays an important role in the molding process of the biomass fuel particles. Combination of solar drying process, PM60-type flat die pellet mill processing sawdust, sawdust and straw mixed materials such as biomass fuel particles, forming rate, tons of power consumption more than 93% in less than 55 kwh hour production capacity of around 800kg-900kg . From the experimental results and the theoretical analysis, the flat die pellet mill is the ideal model for processing biomass pellet fuel.
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