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    Home > Coatings News > Paints and Coatings Market > Development of in-line filtration devices for resin mould coatings

    Development of in-line filtration devices for resin mould coatings

    • Last Update: 2020-11-28
    • Source: Internet
    • Author: User
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    1 Foreword
    My company on furan resin sand moulding using the coating process coating, paint in the mixer configuration, manually added the middle groove, paint through the pump tube, diaphragm pump, pump port on the sink coating on the mould, from the mould flowing paint through the outflow pipe back to the middle groove, the process route of the paint cycle see Figure 1. Because the sand of the resin sand mould surface (mainly the back sand layer) in the mould flipping process, fell into the coating groove, mixed into the coating, with the recycling of the coating finally adhered to the coating surface, resulting in incomplete coating surface, thus affecting the surface quality of the casting and the internal quality, it is necessary to filter the sand particles mixed in the coating. For coating filtration, the filtration option to start selecting is to set up a static filter between the outflow tube and the middle slot to
    the
    . The granularity of the raw sand is 40-100 mesh, the first choice of filter for 60 mesh, paint can not pass through the filter, again select 40 purpose filters appear the same situation, clean the filter in the first 10s can also pass through the paint, 3 minutes later on the silt pile in the filter.
    2 Analysis of the principle of coating filtration
    Casting coatings are non-Newtonian fluids, generally fake plastic fluids with yield values and tentacles, whose fluidity characteristics are shown in Figure 2. If the cut stress on the coating is less than its yield τy, the coating does not flow. Paint from the flow outlet contact with the screen, is hindered, its cut rate is reduced, resulting in the screen surface of the paint cutting stress reduced, less fluidity, siltation part, the subsequent coating siltation on the top, resulting in the screen surface of the paint shear force reduced to zero, and ultimately no flow, the paint can no longer flow filter, completely silt in the filter. Casting coatings have the ability to shear and dilute, and their viscosity decreases with the increase of shear rate, as shown in Figure 3. If the screen is caused to move, the cutting force is provided for the contact surface of the screen and coating, thus creating a cut stress within the coating. When the cut stress exceeds the yield stress of the coating, the coating can flow through the screen. Since the paint bone is generally 320 mesh, as long as the size of the mesh selected screen is smaller than the sand grain, the sand grain can be guaranteed to filter out.
    3 Coating filtration device design
    the actual development of coating filtration device can be seen in Figure 4. Compared with Figure 2, in addition to the addition of coating filtration device, and arranged the paint self-flow tube, its role is to allow the configured paint from the paint mixer in gravity in the automatic flow into the middle groove, the flow of the coating through the ball valve control.
    (1) filtration device is composed
    the filtration device is composed of Figure 5. The diameter of the filter noil is about 60mm smaller than that of the sieve tube to avoid coating spillage. The inside is maintained at a slope of 20 degrees, so that the sand filtered out of the barrel can be discharged with the slope. The outside is maintained at a slope of 45 degrees and extends more than 30mm, allowing the discharged sand to be fully concentrated in the sand bucket. The diameter of the bottom of the filter cylinder is greater than 15mm, forming a diversion edge to prevent paint from flowing to the outside of the bottom of the barrel to reduce the cleaning of the equipment.
    (2) screening selection and testing
    according to GB/T 9442-1998 "silica sand for casting", the granularity of casting silicon sand with test sieve analysis, its sieve size and the basic size of the sieve hole should be in line with Table 1. The granularity of the test sand is detected using a test sieve for casting, according to JB/T 9156-99 casting test sieve, the basic size of the sieve and wire diameter can be found in Table 2.
    there are no clear national standards for screens in the global market. Take stainless steel mesh as an example, the manufacturing material is generally 1Cr18Ni9Ti stainless steel wire, the door width is generally 1000mm, each length is generally 30m. The specifications are in Table 3 (2).
    screen and casting test sieve hole structure and size definition is the same as Figure 6, in line with GB6004, both screen size does not contain wire diameter. However, when the nominal number of the two is the same, the actual mesh size is not the same, comparing Table 3 with Table 1, Table 2 can be known.
    in order to ensure that the selection of screen is right, the size of the screen screen needs to be measured. Because the wire diameter and perforation size are too small, the general measurement method can not be measured. Our method is to select the screen flat cut a 30mm×30mm size screen, placed on the optical microscope, the back press a polished gold sample to ensure reflective, magnify 100 times the observation, against the optical microscope on the size scale, can measure the size of the screen hole and wire. The tested stainless steel silk cloth for the design of the coating filter has a perforated size of 0.030-0.038mm (market nominal number: 60 mesh) and a wire size of 0.013mm. Compared to Table 3, the silk cloth should be 50-60 mesh specifications, but against Table 2 casting test sieve, the screen is 40-50 mesh. The screen is rolled into a cylindrical surface and pressed at the seam, i.e. made into a filter sieve.
    (3) the choice of the reducer
    the actual choice of horizontal pendulum needle reducer, the type of gearbox maintenance is convenient, while in the market generality of the gearbox, the type of single-stage variable speed ratio is the largest (the actual selection of variable speed ratio 87). The motor is powered by a three-phase asynchronous motor with a power of 0.75kW and a speed of 1450r/min. The output speed of the gearbox is 16.6r/min. Because the single-stage swing needle reducer has a large variable speed ratio, the first-stage gear change has reached the requirements, greatly reducing the size of the overall device. And because the bearings of the pendulum needle reducer can withstand a considerable bending moment, the conditions for the filter roller to adopt cantilever beam-type support provide conditions, further reducing the size of the device.
    (4) the installation of the filter device and the use of
    installation to ensure that the coating outlet of the groove into the filter outlet 100mm.
    use: start the motor, the filter cartridge automatically turns, the coating filter. After the sand particles in the filter cartridge have accumulated to a certain amount, they will be automatically discharged from the filter cartridge to the sand drum without human intervention. When the paint is observed flowing out of the filter cylinder, it indicates that there is too much sand in the filter cylinder, a temporary shutdown, from the barrel to manually clean out most of the sand inside the filter cylinder. Start the motor running unit again. After the daily showering operation is completed, pour the sand from the sand bucket into the showering tank and use the alcohol cleaning of the cleaning groove to clean and recycle the paint. Then stop and empty the sand accumulation of the filter cartridge, start the device, and continue to clean the filter cartridge with alcohol in a rotating state.
    4 Technical features of the filter
    (1) with a single-stage reducer, cantilever beam filter support, the maximum possible reduction of the size of the device, so that the device can be applied in a small space.
    (2) automatic sand flow technology. The device can automatically flow out of the sand particles wrapped in the coating, which fully guarantees the quality of the filtered coating.
    (3) coating closed cycle technology. After the coating is added to the mixing barrel, it flows through the pipe into the static bucket, into the diaphragm pump to the sink, and returns to the static bucket through the filter. Reduce the labor intensity of workers, reduce paint waste, keep the site clean.
    (4) paint recycling technology. After automatic sand collection, a small amount of paint with the sand particles flow out, daily manually poured into the paint tank, through cleaning and filtration, can be recycled again.
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