A backflushing plastic melt filter

Abstract

The present application relates to the technical field of plastic processing, and discloses a backflushing plastic melt filter, which comprises a machine body, a piston slidably arranged in the machine body, a separation chamber penetrating through the outer peripheral wall of the piston in the radial direction, two conical filter screens respectively installed at the two open ends of the separation chamber, and the two conical filter screens oppositely arranged with the cone tips pointing to the inside of the separation chamber. The conical filter screen comprises an annular fixing ring, a filter screen body and a support strip. The present application increases the effective filtering area through the conical filter screen, the impurities are more easily stripped off during backflushing due to the conical surface structure, the backflushing efficiency is improved, and the service life of the filter screen is prolonged. The multiple pistons are parallel filtered, the processing capacity is improved, the switching of a single piston does not affect the normal filtering of other pistons, and continuous production is realized without shutdown. The limiting structure realizes the quick disassembly and assembly of the filter screen, and reduces the maintenance difficulty and replacement time.

Description

Technical Field

[0001] This invention relates to the field of plastic processing technology, specifically to a backwash type plastic melt filter. Background Technology

[0002] In the processing of plastics, including extrusion, granulation, and recycling, melt filtration is a crucial step in ensuring product quality and stable production. Plastic melts contain various solid impurities such as carbonized particles, metal fragments, and unmelted materials; failure to remove these impurities in a timely manner will directly affect the surface quality and mechanical properties of the finished products.

[0003] Currently, backflushing plastic melt filters are widely used in the plastics processing industry. They filter the melt by installing a separation chamber inside a piston, with filter screens at both ends of the chamber. During operation, the melt enters the filter screen from both ends of the separation chamber, impurities are trapped on the filter screen surface, and the clean melt flows out, completing the filtration process. When impurities accumulate to a certain level on the filter screen surface, the piston is driven to move, using the filtered clean melt to backflush the filter screen, peeling off and discharging the impurities adhering to the screen surface, thus achieving online regeneration of the filter screen.

[0004] However, existing backwash melt filters generally use planar circular filter screens, whose effective filtration area is limited by the cross-sectional dimensions of the separation chamber. With a fixed equipment volume, it's difficult to further increase the filtration area, leading to easy clogging, high backwashing frequency, and low production efficiency. Furthermore, the surface of the planar filter screen is perpendicular to the melt flow direction, resulting in greater adhesion of impurities during backwashing. These impurities are not easily completely removed by the reverse melt flow, and residual impurities gradually accumulate, causing permanent clogging and shortening the filter's lifespan. In addition, existing filter screens are mostly fixed using bolts or retaining rings, making disassembly and assembly cumbersome. Replacing the filter screen requires specialized tools and is time-consuming, further impacting equipment production efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a backwash plastic melt filter to solve the problems of small filtration area and poor backwashing effect of the planar filter screen in the prior art, as well as the cumbersome disassembly and replacement of the filter screen, as mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: To achieve the above objectives, the present invention provides the following technical solution: a backflushing plastic melt filter, comprising a body, a piston slidably passing through the body, a radially penetrating separation chamber formed on the outer peripheral wall of the piston, and two conical filter screens respectively installed at the two open ends of the separation chamber, the two conical filter screens being arranged facing each other with their cone apexes pointing towards the interior of the separation chamber; the conical filter screen includes an annular fixing ring, a filter screen body, and a support strip, the filter screen body being fixedly installed at the end of the annular fixing ring facing the interior of the separation chamber and being conical in shape, the support strip being disposed on the outer wall of the filter screen body and providing support thereto, and a limiting structure being provided at the end of the annular fixing ring away from the interior of the separation chamber.

[0007] Preferably, the filter body is a multi-layer metal woven mesh or sintered metal fiber felt; the support strips are multiple, and each support strip is arranged at intervals along the generatrix of the conical surface of the filter body.

[0008] Preferably, the machine body is provided with a liquid inlet and a liquid outlet on both sides; there are at least two pistons; the liquid inlet is connected to both ends of each of the separation chambers; each of the separation chambers has a discharge hole on its wall; and each discharge hole is connected to the liquid outlet.

[0009] Preferably, a first drain hole is provided on one side of the machine body; when the piston moves to the first position, the port of the separation chamber facing the liquid inlet is connected to the first drain hole; the machine body is provided with a first connecting channel for connecting the liquid inlet and the port of the separation chamber facing the liquid outlet.

[0010] Preferably, a second drain hole is provided on the other side of the machine body, and the second drain hole and the first drain hole are arranged axially spaced along the piston; when the piston moves to the second position, the port of the separation chamber facing the liquid outlet is connected to the second drain hole; the machine body is provided with a second connecting channel for connecting the liquid inlet and the port of the separation chamber facing the liquid inlet.

[0011] Preferably, a plurality of hydraulic cylinders are fixedly installed at the rear end of the machine body, and the piston rod end of each hydraulic cylinder is fixedly connected to the rear end of the corresponding piston.

[0012] Preferably, the inner edges of the openings at both ends of the separation chamber are provided with raised rings, and a pair of rectangular slots are provided on the inner wall of the opening of the separation chamber outside the raised rings; the annular fixing ring is installed on the outer end face of the raised rings; the limiting structure includes a rectangular shell and a locking tongue, the locking tongue is slidably installed in the rectangular shell and embedded in the rectangular slots.

[0013] Preferably, a pull rod is connected to the end of the latch away from the rectangular slot, a spring is sleeved on the pull rod, the pull rod passes through the side wall of the rectangular housing and a retaining ring is fixed at the protruding end; the spring abuts against the latch and the inner wall of the rectangular housing.

[0014] Preferably, the end face of the locking tongue facing the rectangular slot has a chamfer.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention replaces the traditional flat filter screen with a conical filter screen. The conical structure has a larger effective filtration area within the same installation space, which can increase the filtration throughput and reduce the melt flow rate without increasing the size of the equipment, thus slowing down the accumulation rate of impurities on the filter screen surface. At the same time, the inclined surface of the conical structure causes the melt to flow from the top of the cone to the bottom of the cone during backwashing, generating an expansion scouring effect. Impurities adhering to the cone surface are more easily peeled off from the filter screen surface as a whole, improving backwashing efficiency and extending the service life of the filter screen. 2. This invention utilizes the cooperation between the convex ring and the limiting structure. After the locking tongue of the limiting structure is embedded in the rectangular slot, the annular fixing ring is clamped and fixed between the convex ring and the limiting structure, thereby achieving axial and reliable fixation of the conical filter screen at the opening end of the separation chamber. Pulling the pull rod outward causes the locking tongue to disengage from the rectangular slot, thus releasing the lock and enabling quick disassembly and assembly of the filter screen, reducing maintenance difficulty and replacement time. 3. The present invention has an inlet and an outlet on both sides of the machine body, and at least two pistons. The inlet is connected to both ends of each separation chamber. Each separation chamber has a discharge hole on its wall and each discharge hole is connected to the outlet. The melt is diverted through the inlet to both ends of each separation chamber for parallel filtration, which greatly improves the filtration capacity. The movement and switching of a single piston does not affect the normal filtration of other pistons, providing a structural basis for achieving backwashing without stopping the machine. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0017] Figure 1 This is a schematic diagram of one side structure of a backwash plastic melt filter according to the present invention; Figure 2 This is a schematic diagram of the other side of a backwash plastic melt filter according to the present invention; Figure 3 This is a cross-sectional view of the body of a backwash plastic melt filter according to the present invention; Figure 4 This is a schematic diagram of the piston structure in a backwash plastic melt filter according to the present invention; Figure 5This is a schematic diagram of the conical filter screen and limiting structure in a backwash plastic melt filter according to the present invention; Figure 6 In a backwash type plastic melt filter of the present invention Figure 5 Enlarged view of point A; In the diagram: 1. Body; 2. Piston; 3. Separation chamber; 4. Conical filter screen; 5. Limiting structure; 6. Discharge hole; 7. Hydraulic cylinder; 11. Liquid inlet; 12. Liquid outlet; 13. First drain hole; 14. Second drain hole; 41. Annular fixing ring; 42. Filter screen body; 43. Support bar; 44. Convex ring; 45. Rectangular slot; 51. Rectangular shell; 52. Locking tongue; 53. Pull rod; 54. Spring; 55. Retaining ring. Detailed Implementation

[0018] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Please see Figures 1-6An embodiment of the present invention provides a backwash type plastic melt filter, including a body 1, a piston 2 slidably inserted inside the body 1, a separation chamber 3 extending radially through the outer peripheral wall of the piston 2, and two conical filter screens 4 respectively installed at the two open ends of the separation chamber 3, the two conical filter screens 4 being arranged facing each other and the cone apexes pointing towards the interior of the separation chamber 3; the conical filter screen 4 includes an annular fixing ring 41, a filter screen body 42 and a support bar 43, the filter screen body 42 being fixedly installed at the end of the annular fixing ring 41 facing the interior of the separation chamber 3 and being conical in shape, the support bar 43 being disposed on the outer wall of the filter screen body 42 and providing support thereto, and a limit structure 5 being provided at the end of the annular fixing ring 41 facing away from the interior of the separation chamber 3.

[0022] During operation, contaminated molten plastic enters the conical filter 4 from the two openings of the separation chamber 3. The melt flows along the conical surface, and impurities are intercepted on the inner wall surface of the filter body 42, while clean melt flows out through the mesh and collects in the internal channel of the separation chamber 3 for final output. The piston 2 can slide axially within the body 1, thereby switching between the filtration and backwashing positions. When one side of the filter needs cleaning, the piston moves to disengage that side of the filter from the main flow channel, and backwashing of the filter is achieved by injecting clean melt or flushing fluid in the reverse direction.

[0023] Compared to traditional flat filters, the conical filter screen 4 has a larger effective filtration area, which can significantly increase the filtration throughput without increasing the overall size of the equipment. It also reduces the flow velocity of the melt as it passes through the filter screen, thus reducing the load and pressure loss on the screen. Furthermore, during backwashing, the melt flows from the apex to the bottom of the cone. As the cone cross-section expands, the flow velocity gradually decreases, creating an expansion scouring effect. This hydrodynamic action makes it easier for impurities adhering to the cone surface to be peeled off and discharged from the filter screen surface, thereby significantly improving backwashing efficiency, effectively extending the filter screen's service life, and reducing maintenance frequency and operating costs.

[0024] The filter body 42 is a multi-layered woven metal mesh or sintered metal fiber felt. Multiple support bars 43 are arranged at intervals along the generatrix of the conical surface of the filter body 42. The multi-layered woven metal mesh is made of metal wires of different diameters and mesh counts, forming a gradient pore size through the combination of thick and thin wires, achieving step-by-step interception. The sintered metal fiber felt is a three-dimensional mesh structure formed by high-temperature sintering of metal fibers, possessing high porosity, high strength, and uniform pore size distribution. Both can achieve fine, graded filtration and deep interception, effectively improving filtration efficiency and impurity capacity. The support bars 43 are tightly attached to the outer wall of the filter body 42 and extend along the warp direction of the conical surface. They are typically made of high-strength materials such as stainless steel or alloy steel and are uniformly fixed by welding or fasteners. This ensures that the filter body 42 maintains the stability of its conical profile when subjected to high molten pressure and back pressure, avoiding localized depressions or damage caused by stress concentration, and ensuring the structural integrity of the filter during long-term operation.

[0025] The machine body 1 has an inlet 11 and an outlet 12 on both sides, and at least two pistons 2 arranged symmetrically or in parallel. The inlet 11 is directly connected to both ends of each separation chamber 3 to ensure a balanced flow distribution when the melt is input. Each separation chamber 3 has multiple outlet holes 6 on its wall, and each outlet hole 6 is connected to the outlet 12 through an internal flow channel to form a highly efficient collection system. After entering through the inlet 11, the melt is distributed to both ends of each separation chamber 3. Driven by the pistons 2, it passes through the conical filter screen 4 for filtration. Particulate impurities are trapped by the filter screen, and the purified melt flows from the outlet holes 6 to the outlet 12 for centralized discharge. The parallel filtration of multiple pistons can significantly improve the processing capacity and adapt to high flow conditions. When a single piston 2 moves and switches, such as for backwashing or filter screen replacement, it does not affect the normal filtration operation of other pistons 2, providing a stable structural basis for backwashing without stopping the machine, thereby ensuring continuous operation of the equipment and reducing maintenance costs.

[0026] A first drain hole 13 is provided on one side of the machine body 1 to discharge impurities during the backwashing process. In normal filtration, the piston 2 is in the second position, at which point the inlet 11 is directly connected to the port of the separation chamber 3 facing the inlet 11. Under pressure, the melt flows axially through the conical filter screen 4 along the separation chamber 3. Impurities are trapped inside the filter screen, while the clean melt flows out through the port of the separation chamber 3 facing the outlet 12 and is discharged normally through the discharge hole 6. When impurities accumulate to a certain level inside the filter screen, the piston 2 moves to the first position. At this point, the port of the separation chamber 3 facing the inlet 11 is connected to the first drain hole 13. Simultaneously, the machine body 1 has a first connecting channel connecting the inlet 11 and the port of the separation chamber 3 facing the outlet 12. At this time, the melt from the inlet 11 enters the separation chamber 3 through the first connecting channel towards the outlet 12, and flows in the opposite direction along the axial direction of the separation chamber 3 through the conical filter screen 4 facing the inlet 11. This direction is opposite to the normal filtration direction, thereby using the fluid impact force to peel off the impurities attached to the inside of the filter screen. The backwash melt carrying impurities is quickly discharged from the system through the first drain hole 13, effectively restoring the filtration efficiency of the filter screen. In addition, during the backwashing process, due to the design of the first connecting channel, some clean melt can still be discharged normally through the discharge hole 6, ensuring the continuity of the production process and avoiding efficiency loss caused by downtime cleaning. The entire backwashing mechanism achieves channel switching through the movement of the piston 2, with a compact structure and simple operation, suitable for filtration systems of high-viscosity melts.

[0027] A second drain hole 14 is provided on the other side of the machine body 1. The second drain hole 14 and the first drain hole 13 are arranged axially along the piston 2. When the piston 2 moves to the second position, the port of the separation chamber 3 facing the liquid outlet 12 is connected to the second drain hole 14. The machine body 1 is provided with a second connecting channel for connecting the liquid inlet 11 and the port of the separation chamber 3 facing the liquid inlet 11. At this time, the melt from the liquid inlet 11 enters the port of the separation chamber 3 facing the liquid inlet 11 through the second connecting channel, flows in the opposite direction through the conical filter screen 4 facing the liquid outlet 12, peels off impurities, and is discharged through the second drain hole 14. When the piston 2 switches between the first position and the second position, it can clean the two conical filter screens 4 respectively, ensuring that the filter screens at both ends of the separation chamber 3 can be cleaned and regenerated without stopping the machine.

[0028] Several hydraulic cylinders 7 are fixedly installed at the rear end of the main body 1, and the piston rod end of each hydraulic cylinder 7 is fixedly connected to the rear end of the corresponding piston 2. A pressure sensor can be used to monitor the pressure difference between the inlet 11 and the outlet 12 to determine the degree of filter clogging. When the pressure difference reaches a preset threshold, backwashing is triggered. The hydraulic cylinders 7 drive the piston 2 to slide axially back and forth in the piston chamber (a cavity matching the piston 2 is opened in the main body 1), so that the piston 2 switches between the filtration station, the first sewage discharge station, and the second sewage discharge station. Through the independent control of multiple hydraulic cylinders 7, the backwashing sequence of each separation chamber 3 can be staggered as needed to avoid large fluctuations in system pressure caused by simultaneous backwashing of all filters.

[0029] The inner edges of the openings at both ends of the separation chamber 3 are provided with raised rings 44, which serve as a mounting reference surface for the annular fixing ring 41 to ensure accurate positioning. A pair of symmetrically distributed rectangular slots 45 are formed on the inner wall of the opening of the separation chamber 3, located outside the raised rings 44. The dimensions of the rectangular slots 45 match the locking tongue 52, allowing for reliable locking in conjunction with the limiting structure 5. The limiting structure 5 is fixedly installed on the end face of the annular fixing ring 41 facing away from the interior of the separation chamber 3. The limiting structure 5 includes a rectangular housing 51 and a locking tongue 52. The locking tongue 52 is slidably installed within the rectangular housing 51 and can slide in a direction perpendicular to the axial direction of the separation chamber 3, enabling smooth extension and retraction of the locking tongue 52. During installation, the annular retaining ring 41, together with the limiting structure 5, is pushed into the opening of the separation chamber 3. After the end of the locking tongue 52 contacts the edge of the opening of the separation chamber 3, it automatically retracts into the rectangular housing 51 under the guidance of the inclined surface, overcoming the resistance of the spring 54. When the annular retaining ring 41 abuts against the end face of the convex ring 44, the locking tongue 52 moves to the position of the rectangular slot 45 and automatically pops out and embeds into the rectangular slot 45 under the action of the spring 54, so that the annular retaining ring 41 is clamped and fixed between the convex ring 44 and the limiting structure 5, thereby completing the stable locking of the conical filter screen 4. The end of the locking tongue 52 away from the rectangular slot 45 is connected to a pull rod 53. A spring 54 is sleeved on the pull rod 53. The pull rod 53 passes through the side wall of the rectangular housing 51 and a retaining ring 55 is fixed at the protruding end. The retaining ring 55 is used to prevent the pull rod 53 from falling out of the rectangular housing 51 and to ensure the integrity of the structure. Spring 54 abuts against the locking tongue 52 and the inner wall of the rectangular housing 51. Spring 54 always applies an elastic bias force to the locking tongue 52 in the direction of the rectangular slot 45, keeping the locking tongue 52 locked in the absence of external force and preventing accidental loosening. When disassembly is required, pull the lever 53 to make the locking tongue 52 overcome the resistance of spring 54 and disengage from the rectangular slot 45. Then, the annular fixing ring 41 and the limiting structure 5 can be pulled out from the opening end of the separation chamber 3, achieving quick disassembly and maintenance. The end face of the locking tongue 52 facing the opening end of the separation chamber 3 has a chamfer. During installation, the chamfer of the locking tongue 52 first contacts the edge of the opening of the separation chamber 3. The chamfer guides the locking tongue 52 to automatically retract, allowing the annular fixing ring 41 and the limiting structure 5 to be pushed in smoothly. After being pushed in, the locking tongue 52 automatically pops out under the action of spring 54 and embeds into the rectangular slot 45 to complete the locking, achieving one-step automatic locking in the installation process and improving the convenience of operation.

[0030] Working principle: During operation, the plastic melt filter first enters the internal space of the machine body 1 through the inlet 11. Then, the melt is evenly distributed through the internally designed flow channel system, and delivered to the inlets at both ends of the separation chamber 3 corresponding to each piston 2. Inside the separation chamber 3, the melt flows from both ends towards the center. When it passes through the conical filter screen 4, the solid impurities it contains are effectively intercepted by the inner wall surface of the filter screen body 42, while the clean melt enters the central region of the separation chamber 3 through the precision mesh on the filter screen body 42. Subsequently, the clean melt is collected through the outlet 6 and finally continuously discharged from the outlet 12, thus completing the entire filtration process.

[0031] As the filtration process continues, the amount of impurities accumulated on the surface of the conical filter screen 4 gradually increases, causing the system pressure difference between the inlet 11 and the outlet 12 to rise continuously. When the pressure difference reaches the preset backwash pressure threshold, the control system automatically triggers the backwashing procedure. At this time, the hydraulic cylinder 7 starts to move, driving the corresponding piston 2 to move axially to the first drain position. At this position, the port of the separation chamber 3 facing the inlet 11 is connected to the first drain hole 13, and the inlet 11 is connected to the port of the separation chamber 3 facing the outlet 12 through the first connecting channel. The clean melt from the inlet 11 is introduced into the port of the separation chamber 3 facing the outlet 12 through the first connecting channel, and flows in reverse through the conical filter screen 4 facing the inlet 11. This reverse-flowing melt generates a flushing effect, peeling off and carrying away the impurities attached to the filter screen surface, and finally discharging them from the system through the first drain hole 13.

[0032] After cleaning the filter screen at this end, hydraulic cylinder 7 continues to drive piston 2 to move to the second drain station, performing the same reverse cleaning operation on the conical filter screen 4 facing the outlet 12. The cleaned impurities are discharged through the second drain hole 14. After the backwashing process is completed, hydraulic cylinder 7 drives piston 2 to accurately return to the filtration station, and the equipment immediately returns to normal filtration status. The backwashing sequence of each piston 2 is independently controlled by hydraulic cylinder 7 and is staggered, thereby ensuring that when any piston is performing backwashing, the other pistons continue to maintain normal filtration operation, achieving continuous production.

[0033] When the conical filter 4 reaches the end of its service life and needs replacement, the operator can pull the lever 53 outwards to allow the locking tongue 52 to overcome the resistance of the spring 54 and disengage from the rectangular slot 45, thereby releasing the lock on the annular retaining ring 41. Then, the annular retaining ring 41, along with the limiting structure 5, can be pulled out from the opening end of the separation chamber 3 to remove the old conical filter 4. When installing a new conical filter 4, the annular retaining ring 41 and the limiting structure 5 are pushed in as a whole from the opening end of the separation chamber 3. At this time, the chamfer at the end of the locking tongue 52 will first contact the edge of the opening of the separation chamber 3, and the inclined surface will guide the locking tongue 52 to automatically retract. When the annular retaining ring 41 is fully against the end face of the convex ring 44, the locking tongue 52 will automatically pop out under the elastic force of the spring 54 and accurately embed into the rectangular slot 45, thereby firmly clamping and fixing the annular retaining ring 41 between the convex ring 44 and the limiting structure 5, achieving quick and reliable replacement of the conical filter 4.

[0034] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A backwash type plastic melt filter, comprising a body (1), wherein a piston (2) is slidably disposed within the body (1), and a radially penetrating separation chamber (3) is formed on the outer peripheral wall of the piston (2), characterized in that, The two opening ends of the separation chamber (3) are respectively equipped with conical filters (4), the two conical filters (4) are arranged facing each other and the cone apex points to the inside of the separation chamber (3); the conical filter (4) includes an annular fixing ring (41), a filter body (42) and a support strip (43). The filter body (42) is fixedly installed on the end of the annular fixing ring (41) facing the inside of the separation chamber (3) and is conical in shape. The support strip (43) is arranged on the outer wall of the filter body (42) and provides support for it. The end of the annular fixing ring (41) away from the inside of the separation chamber (3) is provided with a limiting structure (5).

2. The backwash type plastic melt filter according to claim 1, characterized in that, The filter body (42) is a multi-layer metal woven mesh or sintered metal fiber felt; there are multiple support bars (43), and each support bar (43) is arranged at intervals along the generatrix direction of the cone surface of the filter body (42).

3. A backwash type plastic melt filter according to claim 1, characterized in that, The machine body (1) is provided with an inlet (11) and an outlet (12) on both sides respectively; there are at least two pistons (2); the inlet (11) is connected to both ends of each separation chamber (3); each separation chamber (3) has a discharge hole (6) on its wall; and each discharge hole (6) is connected to the outlet (12).

4. A backwash type plastic melt filter according to claim 3, characterized in that, The machine body (1) has a first drain hole (13) on one side; when the piston (2) moves to the first position, the port of the separation chamber (3) facing the liquid inlet (11) is connected to the first drain hole (13); the machine body (1) has a first connecting channel for connecting the liquid inlet (11) and the port of the separation chamber (3) facing the liquid outlet (12).

5. A backwash type plastic melt filter according to claim 4, characterized in that, The other side of the body (1) is provided with a second drain hole (14), and the second drain hole (14) and the first drain hole (13) are arranged at an axial distance along the piston (2); when the piston (2) moves to the second position, the port of the separation chamber (3) facing the liquid outlet (12) is connected to the second drain hole (14); the body (1) is provided with a second connecting channel for connecting the liquid inlet (11) and the port of the separation chamber (3) facing the liquid inlet (11).

6. A backwash type plastic melt filter according to claim 3, characterized in that, A number of hydraulic cylinders (7) are fixedly installed at the rear end of the machine body (1), and the piston rod end of each hydraulic cylinder (7) is fixedly connected to the rear end of the corresponding piston (2).

7. A backwash type plastic melt filter according to claim 1, characterized in that, The inner edges of the openings at both ends of the separation chamber (3) are provided with protruding rings (44), and a pair of rectangular slots (45) are provided on the inner wall of the opening of the separation chamber (3) outside the protruding rings (44); the end of the annular fixing ring (41) facing away from the interior of the separation chamber (3) is fixedly installed with a limiting structure (5), the limiting structure (5) includes a rectangular shell (51) and a locking tongue (52), the locking tongue (52) is slidably installed in the rectangular shell (51), and the locking tongue (52) is embedded in the rectangular slots (45).

8. A backwash type plastic melt filter according to claim 7, characterized in that, The end of the latch (52) away from the rectangular slot (45) is connected to a pull rod (53), and a spring (54) is sleeved on the pull rod (53). The pull rod (53) passes through the side wall of the rectangular housing (51) and a retaining ring (55) is fixed at the protruding end. The spring (54) abuts against the latch (52) and the inner wall of the rectangular housing (51).

9. A backwash type plastic melt filter according to claim 7, characterized in that, The locking tongue (52) has a chamfer on one end face facing the rectangular slot (45).

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