A method for preparing a high-permeability relaxation screen plate

Abstract

The present invention relates to a method for preparing a high-permeability screen relaxation screen plate, belonging to the technical field of polyurethane screen plates, and the present application uses an extrusion-lamination method to prepare a relaxation screen plate, and a thin sheet of TPU sheets with regular holes is stacked layer by layer, and is heat-bonded into one by pressurization, and the extruded sheet adopts the form of laser cutting and punching holes or mechanical die-cutting and punching holes or extrusion casting vacuum negative pressure suction holes, which is efficient and easy to make holes, and the entire molding cycle is within half an hour and the product defects are less. The thermoplastic polyurethane extrusion molding sheet has high efficiency, and the scraps in the processing process can be repeatedly recycled and melted for reprocessing, saving materials, less equipment investment, and has obvious advantages over the high cost of large-area casting machines and casting molds. The processing efficiency is high, the opening rate is large, and the screening efficiency is high. The method has the characteristics of high molding accuracy, thin screen hole ribs, few product defects, high degree of automation, no need for secondary processing, and good product appearance quality.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane sieve plates, and in particular to a method for preparing a high-permeability relaxation sieve plate. Background Art

[0002] In recent years, there are more and more examples of using relaxation screens for fine-grained depth grading screening and pre-powder removal in the design of coal preparation plants in my country, which are favored. For example, CN107511325A is a new structure relaxation screen plate structure, CN112191500A is a multi-amplitude composite relaxation screen, etc. Most examples in design and application are decent, but there are also examples that are not well considered. The relaxation screen is mainly used for the screening of sticky, fine, and wet materials that are difficult to screen, such as the grading of medium and fine particles of high-moisture raw coal and coke with high viscosity. It has the characteristics of high screening efficiency, long service life, wide particle size range, no blockage, and no adhesion. If the screen runs for 16 hours a day, its tension and stretching will exceed 500,000 times. Such a harsh use environment places high demands on polyurethane relaxation screen plates. High strength and good flexibility are the most basic requirements. The common practice of this sieve plate is that the cast polyurethane elastomer is formed into a plate by a casting machine and cast by a mold. The sieve hole has high precision and saves materials, but the casting mold fee is a large one-time investment, and the sieve hole permeability is greatly limited due to casting. As for the polyurethane elastomer material for the relaxation sieve plate, the NDI type polyurethane elastomer has the characteristics of good elasticity, high tear strength, outstanding flexibility, and excellent dynamic performance, but the cost is high, the processing technology is difficult to master, and the quality stability is difficult to control. Domestic companies mostly use PEA / TDI / MOCA type polyurethane elastomers, but the service life is relatively short. Regardless of the above-mentioned cast polyurethane sieve plate material, its scraps cannot be melted and reused repeatedly. Casting polyurethane is a thermosetting polymer and is difficult to reuse. The existing cast polyurethane sieve plate inevitably has a large amount of waste that is difficult to use, resulting in a high cost of casting sieve plate production. At present, there are few polyurethane relaxation sieve plates with TPU as raw material on the market. In summary, it is necessary to develop a preparation method for a high-permeability relaxation sieve plate. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention aims to provide a method for preparing a high-permeability relaxation screen plate.

[0004] A method for preparing a high-permeability relaxation screen plate, comprising the following steps: (1) preparing a TPU sheet with uniform arrangement of holes: extruding and calendering a TPU sheet through an extruder and then cutting and evenly punching holes; or melting TPU through an extruder to extrude a cast film, the cast film enters an air suction pattern roller, the air suction pattern roller is provided with a vacuum negative pressure air suction channel connected to an external negative pressure device along its axial direction, a plurality of broken hole grooves are uniformly distributed on the arc surface of the air suction pattern roller, the broken hole grooves are provided with an air suction channel connected to the negative pressure channel, a plurality of heating channels are uniformly provided around the axial direction of the air suction pattern roller near its arc surface to heat the pattern roller, at the broken hole grooves, the internal and external pressure difference suction force forms suction holes on the surface, the cast film enters the secondary calendering roller and then enters the cooling roller for cutting; thus, a TPU sheet with uniform arrangement of holes is obtained;

[0005] Extrusion molding TPU sheet, the raw material mixing effect is good, the plasticizing ability is stronger, reinforcing fillers can be added to further improve the strength of the screen plate, the extrusion is stable, the output is higher, the winding flatness is higher, the efficiency is improved, and the waste of fertilizer caused by pouring-wormhole operation is reduced. At the same time, the production line production has a significantly shortened production cycle, and there is no need for long-term vulcanization, post-vulcanization, aging and other process operations.

[0006] (2) Laminated sheet: stack the evenly arranged TPU sheets with holes in sequence, press them into the male mold iron plate with a sieve core on the surface, place the sieve core in the suction hole, and get the laminated unit. Then enter the mold, release the lower plate of the multi-layer press to the lowest position, and then push the assembled laminated unit into the hot plate of the multi-layer press in layers. After lamination according to the established lamination process, a high-permeability relaxation sieve plate is obtained.

[0007] Furthermore, the step (1) of punching holes comprises one of laser cutting punching and mechanical die cutting punching.

[0008] The lamination process is a process of stacking sheets impregnated or coated with resin, feeding them into a laminator, and curing them under heating and pressure to form thermosetting products such as fiberglass. Thermoplastic polyurethane elastomers are thermoplastic.

[0009] Furthermore, the lamination process in step (2) is to pre-press at 150°C~16°C and a pressure of 7.5~8MPa for 1~2min, then maintain the pressure at 160°C~170°C and a pressure of 9.5~10MPa for 50~60s, then increase the temperature to 170~180°C, maintain the temperature at 3.5~5MPa for 1~2min, and finally release the pressure to take out the lamination unit and cool it naturally at 25~30°C.

[0010] Furthermore, the vacuum degree of the vacuum negative pressure suction channel in step (1) is 0.2MPa~0.3MPa, and the diameter of the hole groove is 6~10mm.

[0011] Furthermore, in the step (1), the temperature of the cast film entering the suction roller is 150-160° C., and the speed of the suction roller is 1-1.5 m / s.

[0012] Furthermore, the volume of the sieve hole core in step (2) is the same as the volume of the sieve holes of the high-permeability relaxation sieve plate.

[0013] Beneficial effects of the present invention:

[0014] This application uses the extrusion-lamination method to prepare the relaxed sieve plate. The mechanization and automation of the production are high, the product quality is stable, and the dry process is suitable for mass production. The lamination process of this application is to stack the thin TPU sheets with regular holes layer by layer, and heat-bond them together by pressurization. The extruded sheets are punched by laser cutting or mechanical die-cutting or extrusion casting vacuum negative pressure suction holes. The efficiency is high and the holes are easy to make. The TPU sheets with regular holes are stacked to form sieve holes, and the sieve hole core is used for further shaping during lamination. In daily production practice, it is found that when the vacuum negative pressure of the bubble film forming machine is too large, the bubbles of the single-layer bubble film are all broken, forming a film material without blisters. By adjusting the pressure of the air negative pressure suction and the temperature of the TPU cast film entering the roller, the TPU cast film enters the single layer, the negative pressure forms a hole-opening effect, and enters the cooling roller after the secondary calendering roller, and the hole shape is fixed; the existing forming machinery-bubble film forming machine can be used to achieve online one-time punching, and the suction flower roller is provided with a vacuum negative pressure suction channel connected to the external negative pressure device along its axial direction, and the suction flower roller is evenly distributed with a plurality of hole grooves, and the hole groove is provided with a suction channel connected to the negative pressure channel, and the suction flower roller is evenly provided with a plurality of heating channels around its axial direction near its arc surface to heat the flower roller, and at the hole groove, the internal and external pressure difference suction force forms suction holes on the surface, which saves processes compared to punching after extrusion, and can also save energy consumption, reduce costs, and improve production efficiency. Although the extruded sheet can still be punched online by laser cutting or mechanical die cutting, the cut scraps need to be recycled and melted and extruded again.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The preparation method of the high-transmittance relaxation screen plate disclosed in the present invention has a molding cycle much lower than the existing casting method and centrifugal method. A new extrusion-lamination method has been developed, and a thermoplastic polyurethane elastomer is used. The entire molding cycle is within half an hour and the product has fewer defects. The thermoplastic polyurethane extrusion molding sheet is efficient and the output can reach 1000kg / h. The relaxation screen plate is laminated by TPU sheets, and the scraps in the processing process can be repeatedly recycled and melted for reprocessing, and the cost caused by waste is greatly reduced. The screen hole precision is high, materials are saved, and equipment investment is small. Compared with the high cost of large-area casting machines and casting molds, it has obvious advantages. The processing efficiency is high, the opening rate is large, and the screening efficiency is high. Compared with casting and centrifugal sheeting and then punching, this method has the characteristics of high molding precision, thin screen hole ribs, fewer product defects, high degree of automation, no need for secondary processing, and good product appearance quality. DETAILED DESCRIPTION

[0017] The present invention is described below with specific examples, but is not intended to be limiting of the present invention. Example 1

[0018] Step 1: Preparation of evenly arranged TPU sheets with holes: Thermoplastic polyurethane DesmopanDP1485A, TPU particles are dried to a moisture content of less than 0.05%, zone 1 is 150°C, zone 2 is 168°C, zone 3 is 185°C, zone 4 is 202°C, zone 5 is 205°C, and the die lip temperature is 177°C; extruded from the feeding station through a twin-screw extruder, cut by a three-roll calender, a tractor, and a cutter, the upper roll of the three-roll calender is 80°C, the middle roll is 75°C, and the lower roll is 80°C, and then evenly punched with holes by a Sangong SCM-55 laser, the TPU sheet specification is 1.6m wide, 1.5mm thick, and the output is 1000kg / h, Keya SK96SK96 twin-screw extruder, the extruder extrudes and calenders the TPU sheet and evenly punches holes after cutting, to obtain an evenly arranged TPU sheet with holes; Step 2: Step 1, laminated sheet: stack the evenly arranged TPU sheets with holes in sequence, press them into the male mold iron plate with a sieve core on the surface, the volume of the sieve core is the same as the volume of the sieve holes of the high-penetration sieve relaxation sieve plate, the sieve core is placed in the suction hole to obtain a laminated unit, and then enter the mold, release the lower pressing plate of Guangdong Yintong YT-300RS hot pressing multi-layer press to the lowest position, and then push the assembled laminated unit into the hot plate of the multi-layer press in layers, according to the established lamination process, pre-press at 150℃ and pressure 7.5MPa for 1min, then hold the pressure at 160℃ and pressure 9.5MPa for 50s, then heat to 170℃, keep warm at 3.5MPa for 1min, finally release the pressure and take out the laminated unit. After natural cooling and lamination at 30℃, the polyurethane sieve plate -C-φ20-2 500×300×15-90A-polyether type is obtained. Example 2

[0019] Step 1: Preparation of evenly arranged TPU sheets with holes: Thermoplastic polyurethane DesmopanDP9392A / AU is extruded from the feeding station through a twin-screw extruder. The TPU sheet specifications are 1.6m wide and 0.3mm thick. The Keya SK96SK96 twin-screw extruder has a temperature of 148°C in zone 1, 165°C in zone 2, 180°C in zone 3, 195°C in zone 4, and 200°C in zone 5. The die lip temperature is 183°C. The TPU is melted and extruded into a cast film through the extruder. The bubbles are made of Cathay GTPE-1500. Film forming machine, cast film enters the suction flower roller, the temperature entering the suction flower roller is 160°C, the suction flower roller speed is 1.5m / s, the suction flower roller is provided with a vacuum negative pressure suction channel connected to the external negative pressure device along its axial direction, the vacuum degree of the vacuum negative pressure suction channel is 0.3MPa, the diameter of the hole groove is 10mm, the depth is 3.8mm, a plurality of hole grooves are evenly distributed on the arc surface of the suction flower roller, the hole groove is provided with a suction channel connected to the negative pressure channel, and the suction flower roller is close to its arc surface There are multiple heating channels evenly opened around its axial direction to heat the flower roller. At the hole groove, the internal and external pressure difference suction forms suction holes on the surface. The cast film enters the 155℃ secondary calendering roller and then enters the cooling roller for cutting. The cooling roller temperature is 38℃, and the TPU sheet with holes is evenly arranged. The second step is laminated board: the evenly arranged TPU sheets with holes are stacked in sequence and pressed into the male mold iron plate with a sieve core on the surface. The size of the sieve core is the same as the size of the sieve hole of the high-permeability sieve relaxation sieve plate. The sieve core is placed in the suction hole to obtain Laminating unit, then enter the mold, release the lower pressure plate of Guangdong Yintong YT-300RS hot pressing multi-layer press to the lowest position, and then push the assembled laminating unit into the hot plate of the multi-layer press in layers. According to the established laminating process, pre-press at 160℃ and pressure 8MPa for 2min, then maintain the pressure at 170℃ and pressure 10MPa for 60s, then heat to 180℃, maintain the temperature at 5MPa for 2min, finally release the pressure and take out the laminating unit. After natural cooling and lamination at 30℃, the polyurethane sieve plate -C-φ10-2 500×300×15-90A-polyether type is obtained. Example 3

[0020] Compared with Example 1, the holes in this embodiment are punched by mechanical die-cutting with a needle roller of a Heinock film punching machine, and the other steps are the same.

[0021] The high permeability relaxation sieve plates of Examples 1 and 2 were subjected to performance testing. The performance test results are shown in Table 1.

[0022] Table 1 Performance test results of Example 1 and Example 2

[0023]

[0024] Note: Refer to GB / T33091-2016 polyurethane sieve plate for testing.

Claims

1. A method for preparing a high-permeability relaxation screen plate, characterized in that: The method comprises the following steps: (1) melting TPU particles through an extruder to extrude a cast film, and the cast film enters an air suction pattern roller, and a vacuum negative pressure air suction channel connected to an external negative pressure device is opened along the axial direction of the air suction pattern roller, and a plurality of hole grooves are evenly distributed on the arc surface of the air suction pattern roller, and an air suction channel connected to the negative pressure channel is opened in the hole groove, and a plurality of heating channels are evenly opened around the axial direction of the air suction pattern roller near the arc surface to heat the pattern roller, and at the hole groove, the internal and external pressure difference suction force forms suction holes on the surface, and the cast film enters the secondary calendering roller and then enters the cooling roller for cutting; and a uniformly arranged TPU sheet with holes is obtained; (2) a laminated sheet: the uniformly arranged TPU sheets with holes are sequentially laminated. The laminated sheets are stacked, pressed into a male iron plate with a sieve core on the surface, and the sieve core is placed in the suction hole to obtain a laminated unit. The laminated sheet is then molded, and the lower pressing plate of the multi-layer press is released to the lowest position. The laminated unit is then pushed into the hot plate of the multi-layer press in layers. After lamination according to a predetermined lamination process, a high-permeability relaxation sieve plate is obtained. The lamination process is to pre-press at 150°C~16°C and a pressure of 7.5~8MPa for 1~2min, then maintain the pressure at 160°C~170°C and a pressure of 9.5~10MPa for 50~60s, then heat to 170~180°C, and maintain the temperature at 3.5~5MPa for 1~2min, and finally release the pressure to take out the laminated unit and cool it naturally at 25~30°C.

2. The method for preparing a high permeability relaxation screen plate according to claim 1, characterized in that: The vacuum degree of the vacuum negative pressure suction channel in step (1) is 0.2MPa-0.3MPa, and the diameter of the hole groove is 6-10mm.

3. The method for preparing a high permeability relaxation screen plate according to claim 1, characterized in that: In the step (1), the temperature of the cast film entering the suction roller is 150-160° C., and the speed of the suction roller is 1-1.5 m / s.

4. The method for preparing a high permeability relaxation screen plate according to claim 1, characterized in that: The volume of the sieve hole core in step (2) is the same as the volume of the sieve holes of the high-permeability relaxation sieve plate.

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