D Recycled nylon fine sieve screens With the general promotion of nylon fine screens, more and more old sieves are replaced every year. According to statistics, there are about 60,000 to 80,000 old screens that are scrapped each year. In order to reuse the old nylon screen and reduce the production cost of the plant, since 1982, the Beijing Research Institute of Mining and Metallurgy and the Seventh Plastics Factory of Yantai City have cooperated to regenerate the old nylon mesh to produce a recycled nylon fine sieve. board.
a regeneration process
Pretreatment, the replaced processing plant waste sieve surface with a layer of iron rust and scale, must be pretreated prior to use. The pretreatment process is shown in Fig. 16. The main equipments include a flushing tank, an alkali water tank, a pickling tank, a drying box, and the like. After the treatment, the waste sieve pieces were pulverized into 4 to 6 mm granules (sieving powder) to be used as a raw material for reclaimed nylon fine sieving.
The molding process (Fig. 17) should mainly control the drying degree of the raw materials, heating, injection temperature, pressure, molding time, and the like. Since the water absorption of the polyamide material is generally above 3%, these residual moisture, which is affected by the high temperature during the injection process, accelerates the hydrolysis, degradation or formation of blisters of the amide group, resulting in defects in the product formation. Nylon waste materials have been aging, and should be prevented from further aging during injection heating. Therefore, before injection molding, the moisture content of the raw materials should be controlled within a certain range, and dried in a drying box. Polyamide plastics will oxidize (age) faster at temperatures above 130-150 Â° C, while injection molding temperatures are generally above 200 Â° C. Nylon raw materials should not be too long when they stay in the high temperature zone of the barrel. Injection molding also requires mold temperature. The molten plastic cannot be cooled too quickly in the mold. Otherwise, the stress of each part of the product will be uneven and the mechanical properties will be different. In general, the mold temperature should be 40 to 70 Â° C. [next]
The water absorption heat treatment of nylon fine sieve has two purposes: one is to make the fine sieve to form an equilibrium water absorption rate before use, to prevent water absorption deformation during production and use; the other is stability quality, and fully exert the excellent mechanical properties of nylon 1010.
Molding process parameters:
Degree of vacuum of 100kPa (760mm Hg)
Moisture index 0.1%
Injection barrel temperature 245ï½ž275Â°C
Nozzle temperature 240~260Â°C
Mold temperature 60~80Â°C
Injection pressure 60ï½ž100MPa
Molding cycle 300~400s
Equipment and mold. Nylon-like fine sieve each piece weighs less than 200g, but because of the large surface area of â€‹â€‹the sieve plate injection and the large size of the mold, the XS-ZY-500 injection machine is used.
Since the nylon sieve plate has a complicated shape, a large surface area, a small sieve hole, and a small deviation in requirements, it is necessary to have a high-precision mold. The mold is mainly composed of three templates, the first template is placed on the fixed template of the injection machine, and the injection hole and the flow channel are arranged; the second template is arranged with the needle-shaped wrapping sleeve; the third template is the molding cavity plate of the calculation sieve plate; The other templates are support and auxiliary mold parts, and complete demolding, ejection and other actions. Due to the small mesh opening, the width of the upper end of the tooth tip in the mold cavity is 0.24mm (the mesh hole is 0.2mm) and the 0.18mm (the mesh hole is 0.15mm). The mold clamping gap is not more than 0.03mm when injection, otherwise the mesh hole gap will occur. Uneven and even pores are not transparent. In order to ensure a high yield of injection molding, the parallelism of each template is also required. The processing of the mold cavity is the most critical. In the X62W universal milling machine, the cavity is machined, and the error is controlled within a certain range. The machining machine requires high precision.
Sieve material. Deck beneficiation plant material to replace waste down the main sieve, after pretreatment while incorporating 40% new material, as the material of recycled nylon fine screen, its main performance does not change, the nylon material 1010 Main performance:
Density 1.04~1.06t/m 3
Water absorption rate 0.8%
Molding shrinkage rate 1.0 to 2.5%
Tensile strength 52ï½ž55MPa
Tensile modulus of elasticity 1600MPa
Bending strength 89MPa
Flexural modulus 1300MPa
Impact strength gap 4ï½ž5kgcm/cm 2
No gap, continuous compression strength, 79MPa
Brinell hardness (HB) 0.71MPa [next]
Improvement of the product structure of the sieve plate. On the basis of investigating the use of nylon fine sieve in the existing production plant mine, the structure of the original product has been improved, and the sieve plate rib and the bottom surface of the sieve plate are changed to be 2 mm above the bottom surface of the sieve plate ( Figure 18), the deformation is eliminated or reduced, the strength is ensured, and the stability of the slurry flowing through the screen surface is improved.
b Industrial test results Recycled nylon fine screen was selected for industrial test in August 8, 1983 and February 1984 in Dashihe, and then put into production. The industrial test procedure and test results are shown in Figure 19.
The grade of the 8th and 9th systems using recycled nylon fine screen is 0.39% higher than other systems, which is 0.32 higher than the average of the whole plant. The classification efficiency of recycled nylon fine sieve is 1.71ï½ž10.93% higher than that of the original nylon fine sieve. Same as the original nylon fine sieve, all for more than 6 months. The recycled nylon fine sieve is 6.5 yuan per piece, which is 3.26 yuan cheaper than the original nylon fine sieve. The production cost can be saved by 33.4%. In addition, the waste sieve board has some recycling costs. The regenerated nylon fine mesh has good rigidity, small deformation and strong hydrophobicity, which is favorable for screening.
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