As the upgrading of global electronic products continues to accelerate, the number of scrapped electronic devices is increasing rapidly, causing serious environmental pollution and a huge waste of resources. The issue of the recycling of electronic waste needs to be resolved. The biggest problem in the electronic waste recycling process is the recycling of printed circuit boards. At present, the processing of circuit boards in China (Guiyu, Taizhou, etc.) is mainly based on the wet method and the fire method. The wet method is a chemical method that can only recover metals such as precious metals and copper, and cannot recover other metals and non-metal components. Leachate and residues are corrosive and toxic, which is likely to cause more serious environmental pollution. The fire method uses high temperature, incineration, smelting, sintering, etc. to recover precious metals, which wastes a lot of resources and emits toxic gases, causing secondary environmental pollution. The method of scientifically processing circuit boards is a mechanical method (physical method). This method does not produce secondary pollution. The resource recovery rate is high, and it can reach nearly 100% recycling. The process is operable. The circuit board crushing is the key to the mechanical treatment method. The degree of circuit board crushing is directly related to whether the metal and nonmetal can be effectively dissociated, whether it can meet the particle size requirements of the separation process, and the separation efficiency of the metal and nonmetal The problem directly affects the recycling effect and is a key link in the entire mechanical processing process. China has made relevant reports on this issue, but it is not systematic and in-depth. Therefore, this article starts with the choice of crushing machine type to study the crushing performance and dissociation performance of different waste printed circuit board materials. On the basis of theoretical analysis, the crushing process of waste printed circuit boards is determined and optimized, and the crushing mechanism is discussed and analyzed.
1 Theoretical analysis According to different functions, crushing machinery includes two types of crushers and mills. According to the difference in structure and working principle, commonly used crushers include jaw, hammer, cone, impact and roller crushers, etc .; commonly used powder mills include ball mills, self-mills, fan mills, vibration mills and airflow mills Wait.
Under normal circumstances, the crushing machinery is selected through the properties of the material's hardness, strength, adhesion, etc., as well as the requirements for the particle size composition and maximum particle size of the processed material. Compared with minerals, plastics, etc., circuit boards have their unique crushing characteristics. First of all, the waste circuit boards are mainly composed of metal and electronic devices such as reinforced resin boards and copper wires attached to the resin boards after pretreatment, with high hardness and toughness. It is stronger and is easier to break under the action of shear force and impact force. In addition, most substrates have a fiber structure, which is more likely to be broken under shear. Conventional crushers such as jaw crushers mainly rely on squeezing force to crush the materials, and it is difficult to achieve the effect of fully dissociating the recovered materials. The hammer crusher uses impact and shear force as the main force, which is more suitable for the crushing of circuit boards. Through further analysis of the fragility of the circuit board, at the same time, due to the large two-dimensional size of the raw material, it cannot be directly crushed by the pulverizer; considering the uniformity of the particle size of the material after crushing, it is difficult to achieve the expected effect by single crushing; crushing The particle size requirements of the rear material should be (-3 0. 3) mm (3 mm> particle size> 0. 3 mm, the same below), a single shear crusher is difficult to meet the requirements. Therefore, this process intends to use 2-level crushing, that is, a combination of 1-level coarse powder crushing and 2-level fine powder grinding process. In the coarse powder process, a shear rotary rotary crusher with splitting and grinding as the main force is selected. ; In the process of fine powder, the impact rotary grinding machine is mainly used for impact and grinding.
The crushing process of the impact crusher determines the final particle size and particle size distribution of the particles. Therefore, the process parameters of the grinding process need to be determined before the experiment. At the same time, the particle crushing process needs to be clear to better control it and crush Machine improvements. The structure diagram of impact crusher and the crushing process of materials in impact crusher. The main working part is the rotor with hammer head. The rotor is composed of main shaft, disc, pin shaft and hammer head. The material enters the machine from the upper feed port and is crushed by the impact, shearing and grinding of the high-speed hammer. In the lower part of the rotor, there is a sieve plate. The particle size of the crushed material that is smaller than the mesh size is discharged through the sieve plate. The coarse particle size larger than the mesh size is retained on the sieve plate and continues to be hit and grinded by the hammer head. The board is discharged out of the machine. The crushing method of this crusher for materials mainly has the following forms: impact crushing and grinding effect of the high-speed rotating hammer head on the material; high-speed collision crushing effect between particles and lining board; collision crushing effect between particles.
Consistent with the linear velocity of the hammerhead. The impact is completed in an instant. Knowing from the rotation speed n, the time for each revolution of the rotor is 60 / n. It can be assumed that the impact time is approximately the time when the hammer head crosses a single unit in the smallest dimension order in the circumference, that is t = 60 d / (2n r), d is the smallest dimension of the particle, that is, the smallest diameter (thickness of the circuit board). From the impulse formula: F c = mp (dv / dt) (1) to get 60dF c 2 rn = 2m p rn 60 ( 2) In the formula, mp is the mass of monomer particles. Furthermore, F c = m (2n r) 2 60 60d = m (nr) 2 91. 281 59 d (3) From equation (3), the functional relationship between the material particles and F c, n and r is obtained. When the feed of the grinder requires a single particle size of 10 mm 10 mm 2 mm (plate thickness is about 2 mm), the calculated bulk density of the material = 615 kg / m 3, the bulk coefficient is 1. 21, available Calculate the relationship between m. F c and n and r.
(A) The relationship between F c and n (b) The relationship between F c and r When n = 1 440 r / min, r = 0.2 m, the impact of the monomer particles in the impact crusher can be calculated The force is 68. 15 N, which is equivalent to 68. 15 N. The force acts on the surface of the particles with an area of ​​only 3.5 mm 2 (hammer blade width 7 mm). The calculated pressure is 19.471 4 MPa. The impact resistance is about 1 176 J / m 2. When the impact strength of the circuit board substrate is exceeded, the material can be completely broken.
2 Experimental methods 2.1 Equipment and materials According to the above theoretical analysis, this test uses a combination of shear rotary crusher (research on the preset data of new type materials for airflow crusher) and impact rotary grinding machine for level 1 and Level 2 crushing. Shear crusher n = 1 440 r / min, r = 0.25 m. According to the particle force relationship deduced above, determine the impact rotary mill n = 2 000 r / min, r = 0.2 m . Using the 8411 electric vibrating screen to classify the crushed materials, the 7-level particle size distribution is obtained. The 1st level particle size is 1.2 mm, the 2nd level is (-1. 2 0. 8) mm, and the 3rd level is (-0 . 8 0. 6) mm, level 4 is (-0. 6 0. 45) mm, level 5 is (-0. 45 0. 3) mm, level 6 is (-0. 3 0. 15) mm, Level 7 is-0.15 mm. The materials are used circuit boards with electronic components (PCBs) and circuit board plants without electronic components. PWBs are used. PCBs are taken from the Shanghai Waste Acquisition Station, PWBs were purchased from Shanghai Huafeng Circuit Board Factory. 2. 2 Experimental process 2. 2. 1 Pretreatment of waste circuit boards Due to the electronic devices attached to PCBs, including capacitors and other harmful substances containing lead and arsenic, and there are reusable electronic components, they are selectively disassembled before breaking It is necessary to dismantle the toxic components and valuable components first, which is a necessary treatment process for electronic waste. Therefore, the disassembly pretreatment is required before it is broken. 2. 2. 2 Crushing, shearing and crushing: The state of the materials before and after the first-level crushing of PCBs 2. 2. 3 Classification and analysis processing The classified materials are classified using a grading vibrating screen (divided into 17 levels). After the classification, each particle level is analyzed The particle size, shape, dissociation degree, etc. of the material can further optimize the crushing process. The average particle size of the crushed material is calculated according to the following formula: D = idimiimii = 1, 2, 3, & (4) where: D is the average particle size of primary crushing (mm); di is the average particle size of all levels of particles ( mm); mi is the mass of particles at all levels (kg).
F Type Glass Lid,Glass Pan Lid,Tempered Glass Pan Lid,Toughed Glass Lid
Hebei Bozheng Glasswork Co.,Ltd , https://www.bozhengglass.com