Flame-retardant polypropylene water-immersion dicing separation system and process thereof

Abstract

The invention discloses a flame-retardant polypropylene water immersion pelletizing separation system which comprises a pelletizing cavity, the pelletizing cavity is connected with a front-end extrusion unit, a water inlet of the pelletizing cavity is connected with a bypass pipeline, the discharging end of the pelletizing cavity is connected with a cooling unit, and the cooling unit comprises a spiral conveying coil pipe, a spiral cooling coil pipe and a cooling pipeline. The inlet end of the spiral conveying coil pipe is connected with the pelletizing cavity, the spiral cooling coil pipe is wound and attached to a gap between adjacent pipe rings of the spiral conveying coil pipe in a spiral mode corresponding to the spiral conveying coil pipe, the cooling pipeline and the spiral cooling coil pipe are connected end to end, the cooling pipeline comprises a plurality of main part pipes and throat part pipes, and the main part pipes and the throat part pipes are alternately arranged. And the throat pipe is communicated with the spiral conveying coil pipe through an intercepting pipe. The spiral cooling coil is attached to and wound around the gap between the adjacent pipe rings of the spiral conveying coil, materials in the spiral conveying coil are cooled through a milder non-contact type indirect cooling method, and therefore the adverse effect of sudden temperature drop on granules is improved.

Description

Technical Field

[0001] This invention relates to the field of processing equipment technology, specifically to a flame-retardant polypropylene water immersion pelletizing and separation system and its process. Background Technology

[0002] Flame-retardant polypropylene, as a key engineering plastic, has been widely used in many fields such as chemical, construction, home appliances, automotive, and medical. In its underwater pelletizing process, the water temperature control after the pellet is extruded from the die is crucial. If the pellet comes into direct contact with room temperature or low temperature process water after leaving the die, the surface of the pellet will cool and harden instantly, increasing the cutting resistance of the cutter in the pelletizing chamber. This not only increases energy consumption but also significantly accelerates cutter wear and shortens its service life.

[0003] To address this, existing technologies employ a zoned water temperature control scheme, which involves first introducing high-temperature process water into the pelletizing chamber to protect the cutter, and then transporting the mixture of the pre-cut high-temperature pellets and water to subsequent stages for cooling and solidification.

[0004] Currently, traditional cooling methods mainly rely on cooling water tanks or straight-pipe heat exchangers to cool the process water inside the main pipe by injecting a cooling medium into it. However, in this method, the internal cooling medium comes into direct contact with the high-temperature process water after being injected into the main pipe through branch pipes. This can easily cause a sudden drop in temperature in the granules near the injection point inside the main pipe, resulting in uneven shrinkage of the granules and deformation or surface wrinkling. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant polypropylene water immersion pelletizing and separation system and its process, so as to solve the technical problem of uneven cooling caused by the direct combination of cooling medium and process water in the main pipeline in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution: A flame-retardant polypropylene water immersion pelletizing and separation system, comprising: The pelletizing chamber has its feed inlet connected to the output end of the front-end extrusion unit to cut the extruded material strip into pellets. The water inlet of the pelletizing chamber is connected to a bypass pipeline supplying high-temperature process water. Driven by the high-temperature process water, the pellets enter the cooling unit through the discharge end of the pelletizing chamber. After being cooled by the cooling unit, they enter the dehydration unit for dehydration. The discharge end of the pelletizing chamber is connected to the cooling unit to cool the high-temperature process water mixed with the pellets. The cooling unit includes: A spiral conveying coil extending in a spiral direction, wherein the inlet end of the spiral conveying coil is connected to the outlet end of the pelletizing chamber, and the outlet end is connected to the dewatering unit; A spiral cooling coil, wherein the spiral cooling coil is wound in a spiral manner corresponding to that of the spiral conveying coil and attached to the gap between adjacent coils of the spiral conveying coil; The cooling pipeline is connected end to end to the spiral cooling coil. The cooling medium enters the spiral cooling coil to first cool the spiral conveying coil without interference before entering the cooling pipeline. The cooling pipeline includes multiple alternating main pipes and throat pipes. The throat pipes are connected to the spiral conveyor coil through a choke pipe to draw out impurities from the spiral conveyor coil.

[0007] As a preferred embodiment of the present invention, the diameter of the throat tube is smaller than the diameter of the main tube so as to create a negative pressure relative to the inside of the spiral conveyor coil when the cooling medium passes through this position.

[0008] In a preferred embodiment of the present invention, a stripping filter is provided inside the spiral conveying coil. The stripping filter has stripping holes and is located at the lowest point inside the spiral conveying coil. The edge of the stripping filter is connected to the inner wall of the spiral conveying coil to form a material gathering area. The material gathering area is used to collect impurities stripped from the surface of the granules. A flow-cutting opening penetrating the spiral conveying coil is provided in the material gathering area, and the flow-cutting opening is connected to the flow-cutting pipe.

[0009] As a preferred embodiment of the present invention, the interception opening is provided with a control valve that can be selectively opened.

[0010] In a preferred embodiment of the present invention, the inlet end of the spiral conveying coil is connected to the outlet end of the pelletizing chamber through a first reducing pipe. The flow cross section of the first reducing pipe is gradually narrowed along the material flow direction to increase the flow velocity of the mixture from the pelletizing chamber.

[0011] In a preferred embodiment of the present invention, the outlet end of the spiral conveying coil is connected to the dewatering unit through a second reducing pipe. The flow cross section of the second reducing pipe is gradually expanded along the material flow direction to reduce the flow velocity of the mixture flowing to the dewatering unit.

[0012] A process for pelletizing using the aforementioned flame-retardant polypropylene underwater pelletizing system includes the following steps: S1. The flame-retardant polypropylene molding strip formed by the front-end extrusion unit is introduced into the pelletizing chamber and pelletized under the protection of high-temperature process water in the pelletizing chamber. S2. The granules are driven by high-temperature process water into the spiral conveying coil and are cooled without interference by the spiral cooling coil that is spirally wound and attached to the outside of the spiral conveying coil. The high-temperature process water is cooled to a suitable temperature before impurity removal and dehydration. S3, impurity removal and dehydration respectively include: Impurity removal: After the cooling medium flows through the spiral cooling coil, it enters a cooling pipeline with alternating main pipes and throat pipes, and impurities in the spiral conveying coil are sucked out through the intercepting pipe connected to the throat pipe; Dehydration: The cooled and impurity-removed mixture is fed into a dehydration unit for solid-liquid separation to obtain flame-retardant polypropylene granules.

[0013] Compared with the prior art, the present invention has the following advantages: This invention utilizes high-temperature process water to protect the cutter within the pelletizing chamber. During the feeding process after pelletizing, a spiral conveying coil with an extremely long heat exchange tube diameter cools the process water containing the pellets. Furthermore, spiral cooling coils are attached and wound around the gaps between adjacent coils of the spiral conveying coil. This gentler, non-contact, indirect cooling method cools the material within the spiral conveying coil, mitigating the adverse effects of sudden temperature drops on the pellets. Combined with the throat tube and the intercepting tube, impurities in the spiral cooling coil are extracted and removed during feeding, further improving the quality of the output pellets. Attached Figure Description

[0014] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 For the present invention Figure 1 Enlarged view of point A in the middle; Figure 3 This is a cross-sectional schematic diagram of the spiral cooling coil of the present invention.

[0016] The labels in the diagram represent the following: 1. Front-end extrusion unit; 2. Pelletizing chamber; 3. Cooling pipeline; 4. Main pipe; 5. Throat pipe; 6. Dewatering unit; 7. Spiral conveying coil; 8. Spiral cooling coil; 9. Cut-off pipe; 10. First reducing pipe; 11. Second reducing pipe; 12. Cut-off opening; 13. Aggregating zone; 14. Control valve; 15. Dewatering machine; 16. Peeling filter. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figure 1 As shown, this invention provides a flame-retardant polypropylene water immersion pelletizing and separating system, including a pelletizing chamber 2. The feed inlet of the pelletizing chamber 2 is connected to the output end of the front-end extrusion unit 1 for cutting the shaped strips extruded by the front-end extrusion unit 1 into pellets. The pellets are driven by high-temperature process water and enter a cooling unit through the discharge end of the pelletizing chamber 2. After being cooled by the cooling unit, they enter a dehydration unit 6 for dehydration. The discharge end of the pelletizing chamber 2 is connected to the cooling unit to cool the high-temperature process water mixed with the pellets. The front-end extrusion unit 1 includes a raw material bin, an extruder, a pump body, and a hot runner system connected in sequence. The end of the hot runner system is equipped with a die head for melting the flame-retardant polypropylene raw material and extruding it into strips through the die head.

[0019] The pelletizing chamber 2 is connected to the output end of the front-end extrusion unit 1. The pelletizing chamber 2 has a cutting cavity 2, and a cutter is installed inside the cutting cavity. The cutter is driven by a drive motor mounted on a frame. The water inlet of the pelletizing chamber 2 is connected to a bypass pipe supplying high-temperature process water. The extruded strip is cut into pellets within the pelletizing chamber 2 by the high-temperature process water, forming a mixture of pellets and process water. Because the extruded strip hardens instantly upon contact with cooler water, cutting and pelletizing it at this time would easily cause cutter wear. Therefore, contact between the extruded strip and the high-temperature process water reduces the rate of hardening upon discharge, thus protecting the cutter. The discharge end of the pelletizing chamber 2 is connected to a cooling unit to cool the high-temperature process water mixed with the pellets. The cooling unit includes: The spiral conveying coil 7 extends in a spiral direction. The inlet end of the spiral conveying coil 7 is connected to the outlet end of the pelletizing chamber 2, and the outlet end is connected to the dewatering unit 6.

[0020] The spiral cooling coil 8 is wound in a spiral manner corresponding to that of the spiral conveying coil 7 and attached to the gap between adjacent coils of the spiral conveying coil 7.

[0021] Cooling pipe 3 is connected to spiral cooling coil 8 at both ends. The cooling medium enters spiral cooling coil 8 to first cool spiral conveying coil 7 without interference before entering cooling pipe.

[0022] The cooling pipe 3 includes multiple alternating main pipes 4 and throat pipes 5. The throat pipes 5 are connected to the spiral conveyor coil 7 through the choke pipe 9 to suck up impurities in the spiral conveyor coil 7.

[0023] The dewatering unit 6 includes a dewatering machine 15, whose inlet is connected to the outlet of the spiral cooling coil 8, and is used to dewater the cooled granules.

[0024] Among them, the front extrusion unit 1, pelletizing chamber 2 and dehydration unit 6 are the commonly used structures of the current flame-retardant polypropylene underwater pelletizing system, which will not be described in detail here.

[0025] Furthermore, the spiral cooling coil 8 can cool down the high-temperature mixture passing through the cutting chamber 2. Through its spiral structure, it can be extended or set into multiple sections according to the factory space, thereby extending the flow time of the mixture, increasing the contact area between the mixture and the pipe wall, achieving the purpose of efficient cooling, and simultaneously saving a lot of factory space and optimizing the equipment layout.

[0026] Furthermore, the bent pipes in the spiral cooling coil 8 have a good peeling effect on impurity particles precipitated on the surface of the granules. The structural design of the spiral conveying coil 7 extends the conveying time of the granules while increasing their impact on the pipe wall or mutual friction, thereby improving the ability of surface impurities to fall off. This causes most impurities to concentrate and fall off in the spiral conveying coil 7, and the adsorption structure set at this position can suck out all the impurities, making the manufacturing process more efficient.

[0027] In actual manufacturing, the spiral conveying coil 7 and the spiral cooling coil 8 can be connected by surface contact to expand the contact area and improve heat exchange efficiency. Furthermore, thermally conductive silicone grease or thermally conductive epoxy resin can be applied to the contact position between the spiral conveying coil 7 and the spiral cooling coil 8 to fill the micro gaps and reduce the contact thermal resistance.

[0028] Among them, such as Figure 2 As shown, the inlet end of the spiral conveyor coil 7 is connected to the outlet end of the pelletizing chamber 2 via a first reducing pipe 10. The flow cross-section of the first reducing pipe 10 is gradually narrowed along the material flow direction to increase the flow velocity of the mixture from the pelletizing chamber 2, thereby ensuring that the slurry can be smoothly and quickly "pulled out" of the pelletizing chamber 2 and preventing blockage. At the same time, the faster flow velocity generates moderate turbulence to prevent particles from sticking together in the initial stage.

[0029] like Figure 2 As shown, the outlet end of the spiral conveyor coil 7 is connected to the dewatering unit 6 via a second reducing pipe 11. The flow cross-section of the second reducing pipe 11 is gradually widened along the material flow direction to reduce the flow velocity of the mixture flowing towards the dewatering unit 6. The water flow velocity is naturally slowed down, creating a state closer to laminar flow. This allows sufficient time for gentle heat exchange between water and particles.

[0030] Furthermore, in the actual process, when the material strip enters the cutting chamber after being extruded from the extruder, its surface undergoes degradation, producing low-molecular-weight substances, carbonized particles, and gases that adhere to the surface of the melt strip, forming impurities and making the cut particles rough. When the material strip is cut into granules and transported in water, the cooled impurities harden on the granule surface, forming particles that detach during transport. This detachment process makes the granule surface smoother, improving product quality. However, the detached impurities can contaminate the process water and even clog pipelines. Therefore, in existing technologies, filter plates are installed in the dewatering machine 15 or at the outlet to filter these impurities.

[0031] In this device, the design of the cooling pipe 3 allows the cooling pipe 3 to not only transport the cooling medium to cool the spiral conveying coil 7, but also to adsorb the impurities that have detached from the spiral conveying coil 7 through the pressure difference design, thereby simultaneously improving the product output quality and purifying the process water.

[0032] Specifically, such as Figure 1 and Figure 2 As shown, the cooling pipe 3 and the spiral cooling coil 8 are connected end to end. The cooling medium enters the spiral cooling coil 8 and first cools the spiral conveying coil 7 without interference before entering the cooling pipe. The cooling pipe 3 includes multiple alternating main pipes 4 and throat pipes 5. The throat pipe 5 is connected to a choke pipe 9. The inlet diameter of the choke pipe 9 is smaller than the particle diameter. The other end of the choke pipe 9 is connected to the spiral conveying coil 7.

[0033] The diameter of the throat tube 5 is smaller than that of the main tube 4 so that a negative pressure is formed relative to the inside of the spiral conveyor coil 7 when the cooling medium passes through this position.

[0034] In practical use, the cooling medium with constant pressure inside the spiral cooling coil 8 increases its pressure at the throat section due to the narrowing of the pipe diameter, forming a pressure difference with the inside of the spiral conveying coil 7. This causes the medium to adsorb the contents of the spiral conveying coil 7 from that position, thereby removing fine impurities.

[0035] The action of removing impurities can reduce the possibility of clogging in the dewatering unit 6 of the subsequent dewatering unit 6. Furthermore, when the process water removed in the filter dewatering unit 15 is reheated and injected into the bypass pipeline for recycling, the purity of the circulating water can be improved, as well as the product quality of the output granules.

[0036] Furthermore, to avoid excessive adsorption of process water during the adsorption process and to more accurately and significantly adsorb impurities detached from the granules, this device further includes a stripping filter 16 inside the spiral conveyor coil 7. Figure 3As shown, the stripping filter plate 16 has stripping filter holes, which can further strip impurities from the surface of the granules when they rub against each other. The stripping filter plate 16 is located at the lowest point in the spiral conveying coil 7, that is, the lowest position in the spiral conveying coil 7. The edge of the stripping filter plate 16 is connected to the inner wall of the spiral conveying coil 7 to form a material gathering area 13. The material gathering area 13 is used to collect impurities stripped from the surface of the granules. A flow-cutting opening 12 is provided in the material gathering area 13, which penetrates the spiral conveying coil 7 and is connected to the flow-cutting pipe 9.

[0037] In actual use, the impurities that are peeled off in the spiral conveying coil 7 will enter the aggregation zone 13 through the peeling filter holes and form an aggregate as the process water flows. Additionally, the impurities that fall off after the granules above the peeling filter plate 16 rub against the peeling filter holes will fall into the aggregation zone 13, forming an artificially induced aggregation of impurities. This prevents the impurities from being too loosely distributed throughout the spiral conveying coil 7. Then, the impurities can be discharged more concentratedly from the intercepting pipe 9 through the intercepting opening 12.

[0038] Furthermore, a control valve 14 that can be selectively opened is provided inside the interception opening 12. By selectively opening and closing the control valve 14, the adsorption action can be opened in a controllable manner, thereby making the material suction more flexible.

[0039] Alternatively, a variable diameter structure can be used, with the diameter of the intercepting pipe 9 at this position controlled intermittently by external machinery, thereby forming a controllable suction node. Combined with movable valves, this makes suction more flexible.

[0040] For example, a variable diameter structure includes a flexible hose made of a flexible material, with a mechanical pushing structure, such as a telescopic rod, on the outside of the hose. The end of the telescopic rod radially squeezes the hose from the outside, thereby changing the cross-sectional diameter of the hose, thereby increasing the water pressure through which the cooling water flows, and creating a negative pressure environment.

[0041] At this time, the control valve 14 can be set as a simple valve without electrical control connection. Under normal conditions, the simple valve is fixed at the opening by magnetic attraction. When the diameter of the hose changes and negative pressure is generated, the simple valve is synchronously attracted and opened to form a connection.

[0042] By controlling the opening and closing of valve 14, the spiral cooling coil 8 can be selectively connected to or closed with the throat pipe 5. Thus, through the synergistic effect of valve 14 and throttle pipe 9, impurities in the spiral conveying coil 7 can be intermittently drawn out from the throttle opening 12 and discharged into the cooling pipe.

[0043] Specifically, the control valve can be a mature miniature solenoid valve or piezoelectric valve from the existing technology. It is opened intermittently through an external control module, thereby drawing the process water mixed with impurities in the spiral conveyor coil 7 into the cooling pipe and then discharging it.

[0044] Another method for pelletizing using the above-mentioned flame-retardant polypropylene underwater pelletizing system includes the following steps: S1. The flame-retardant polypropylene molding strip formed by the front-end extrusion unit 1 is introduced into the pelletizing chamber 2 and pelletized under the protection of high-temperature process water in the pelletizing chamber 2. S2. The granules are driven by high-temperature process water into the spiral conveying coil 7 and are cooled without interference by the spiral cooling coil 8 which is spirally wound and attached to the outside of the spiral conveying coil 7, so that the high-temperature process water is cooled to a suitable temperature before impurity removal and dehydration. S3, impurity removal and dehydration respectively include: Impurity removal: After the cooling medium flows through the spiral cooling coil 8, it enters the cooling pipeline 3, which has alternating main pipes 4 and throat pipes 5. Impurities in the spiral conveying coil 7 are sucked out through the intercepting pipe 9 connected to the throat pipe 5. Dehydration: The cooled and impurity-removed mixture is fed into the dehydration unit 6 for solid-liquid separation to obtain flame-retardant polypropylene granules.

[0045] In step S3, the opening degree or frequency of the choke opening 12 can be adjusted by controlling the valve 14 to control the rate of impurity extraction.

[0046] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A fire-retardant polypropylene water immersion pelletizing separation system characterized by, It comprises: A cutting cavity (2) whose inlet is connected with the output end of the front-end extrusion unit (1) for cutting the formed strip extruded by the front-end extrusion unit (1) into granules, and whose water inlet is connected with a bypass pipeline for supplying high-temperature process water, so that the granules are driven by the high-temperature process water to pass through the discharge end of the cutting cavity (2) into a cooling unit, and then into a dehydration unit (6) for dehydration after being cooled by the cooling unit, and the discharge end of the cutting cavity (2) is connected with the cooling unit for cooling the high-temperature process water mixed with the granules; The cooling unit comprises: A spiral conveying coil pipe (7) extending in a spiral direction, whose inlet end is connected with the discharge end of the cutting cavity (2), and whose outlet end is connected with the dehydration unit (6); A spiral cooling coil pipe (8) which is wound in a spiral corresponding to the spiral conveying coil pipe (7) and attached to the gap between adjacent pipe coils of the spiral conveying coil pipe (7); A cooling pipeline (3) which is connected with the spiral cooling coil pipe (8) at the head and tail, and through which a cooling medium enters the spiral cooling coil pipe (8) to non-interferingly cool the spiral conveying coil pipe (7) and then enters the cooling pipeline; The cooling pipeline (3) comprises a plurality of main pipes (4) and throat pipes (5) arranged alternately, and the throat pipes (5) are communicated with the spiral conveying coil pipe (7) through a cutoff pipe (9) to suck impurities in the spiral conveying coil pipe (7).

2. The water-immersed cutting and separating system for the flame-retardant polypropylene according to claim 1, characterized in that: The diameter of the throat pipe (5) is smaller than that of the main pipe (4) to form a negative pressure inside the spiral conveying coil pipe (7) when the cooling medium passes through the position.

3. The water-immersed cutting and separating system for the flame-retardant polypropylene according to claim 2, characterized in that: A stripping filter (16) is arranged in the spiral conveying coil pipe (7), the stripping filter (16) is provided with stripping filter holes, the stripping filter (16) is arranged at a low point in the spiral conveying coil pipe (7), the edge of the stripping filter (16) is connected with the inner wall of the spiral conveying coil pipe (7) to jointly form a polymeric material area (13), the polymeric material area (13) is used for collecting impurities stripped from the surface of the granules, and a cutoff opening (12) penetrating through the spiral conveying coil pipe (7) is arranged in the polymeric material area (13), and the cutoff opening (12) is connected with the cutoff pipe (9).

4. The water-immersed cutting and separating system for the flame-retardant polypropylene according to claim 3, characterized in that: A control valve (14) capable of being selectively opened is arranged in the cutoff opening (12).

5. The water-immersed cutting and separating system for the flame-retardant polypropylene according to claim 1, characterized in that: The inlet end of the spiral conveying coil pipe (7) is connected with the discharge end of the cutting chamber (2) through a first reducing pipe (10), and the flow cross section of the first reducing pipe (10) is arranged in a tapering manner along the material flow direction, so as to increase the flow speed of the mixture from the cutting chamber (2).

6. The fire-retardant polypropylene water immersion cutting and separating system according to claim 1, characterized in that: The outlet end of the spiral conveying coil pipe (7) is connected with the dehydration unit (6) through a second reducing pipe (11), and the flow cross section of the second reducing pipe (11) is arranged in a diverging manner along the material flow direction, so as to reduce the flow speed of the mixture flowing to the dehydration unit (6).

7. A process for pelletizing using the flame retardant polypropylene dedicated underwater pelletizing system as claimed in claim 1, wherein, The method comprises the following steps: S1, introducing the fire-retardant polypropylene formed strip from the front-end extrusion unit (1) into the cutting chamber (2) to form granules under the protection of high-temperature process water in the cutting chamber (2); S2, the granules enter the spiral conveying coil pipe (7) under the driving of high-temperature process water, and are cooled without interference by the spiral cooling coil pipe (8) which is wound in a spiral manner and attached to the outside of the spiral conveying coil pipe (7), so as to cool the high-temperature process water to a suitable temperature and then remove impurities and dehydrate; S3, the impurity removal and dehydration respectively comprise: Impurity removal: the cooling medium flows through the spiral cooling coil pipe (8) and then enters the cooling pipeline (3) with alternately arranged main pipes (4) and throat pipes (5), and the impurities in the spiral conveying coil pipe (7) are sucked through the intercepting pipe (9) connected with the throat pipe (5); Dehydration: the mixture after cooling and impurity removal is sent to the dehydration unit (6) for solid-liquid separation to obtain fire-retardant polypropylene granules.

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