Recycling treatment method and treatment device for PVC pipe production chippings
By adding a wetting agent during the PVC pipe production process and utilizing roller pressing and rolling granulation technology, the problem of thermal degradation of PVC scraps has been solved, achieving efficient recycling and improving the quality of recycled granules and production continuity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUIZHOU ZHENGXIN PIPE MFG CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-05-26
AI Technical Summary
The debris generated during the production of PVC pipes consists of thin, fluffy flakes with low bulk density and large specific surface area, resulting in poor thermal stability. It is prone to thermal degradation during hot extrusion, affecting production continuity and product quality.
By adding a wetting agent to form moist agglomerates, pressing them into thin sheets using a roller press, breaking them into irregular particles, and then forming spherical particles through rolling granulation, the specific surface area is reduced and thermal degradation is inhibited.
It effectively improves the flowability and processing performance of the debris, inhibits thermal degradation, improves the uniformity and mechanical properties of the recycled particles, and reduces production costs.
Smart Images
Figure CN122077832A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of PVC pipe manufacturing technology, specifically to a method and apparatus for recycling PVC pipe manufacturing debris. Background Technology
[0002] Polyvinyl chloride (PVC) pipes are widely used in building water supply and drainage, power and communication, and municipal engineering due to their excellent corrosion resistance, mechanical strength, and low production cost. During production, the pipes need to be cut to specific lengths according to requirements. However, the debris generated from high-speed cutting of PVC pipes is mostly thin, fluffy flakes with extremely low bulk density, a very large surface area, and a loose structure that easily agglomerates and entangles. Furthermore, PVC is a heat-sensitive plastic with poor thermal stability, posing numerous risks for subsequent recycling and disposal.
[0003] To achieve recycling, some companies use a simple crushing and direct reuse method, that is, mixing the collected flocculent debris with fresh raw materials for pipe extrusion. However, because the debris is flocculent and has a very low density, it is difficult to disperse evenly in the mixture, resulting in feeding interruptions or fluctuations that seriously affect the continuity of production. More seriously, in the high-temperature melting section of the hot extruder, the flocculent debris is heated very unevenly due to its large specific surface area, and the surface is very prone to thermal degradation, producing hydrogen chloride gas, which causes the material to change color and significantly reduce mechanical properties, making it difficult to obtain qualified products.
[0004] Therefore, some companies have adopted the method of hot melt granulation and recycling, that is, heating, melting, extruding and granulating the scraps to make recycled granules. However, PVC is a heat-sensitive polymer, and the extremely large specific surface area of the flocculent scraps makes the heated area during the melting and plasticizing process much larger than that of ordinary granular waste, resulting in more severe thermal degradation. This can also lead to problems such as material discoloration and a significant decrease in mechanical properties. As a result, companies have to add a large amount of heat stabilizers, which significantly increases production costs.
[0005] Therefore, there is an urgent need for a recycling method that can effectively reduce the specific surface area of debris and improve its processing performance, which has important industrial application value and environmental significance. Summary of the Invention
[0006] The present invention aims to provide a method and device for recycling PVC pipe production debris, which improves the flowability and processing performance of the debris by reducing its specific surface area, thereby effectively inhibiting thermal degradation during subsequent hot processing.
[0007] To achieve the above objectives, the first aspect of this application provides the following technical solution: A method for recycling and processing PVC pipe manufacturing debris includes the following steps: S1, Wetting Aggregation: Adding a wetting agent to the debris to form wet aggregates; S2. Compaction: The moist agglomerates are fed into a roller press to be pressed into thin sheets, and then the thin sheets are crushed and screened to obtain irregular particles. S3. Rolling: Irregular particles are fed into the processing device for rolling granulation to form spherical particles; S4. Granulation and molding: After drying, the spherical particles are fed into a hot extrusion granulator, where they are melt-plasticized and granulated to obtain recycled particles.
[0008] As a preferred embodiment, the wetting agent is selected from water, alcohol solvents or mineral oil, and the amount of the wetting agent added is 5% to 20% of the mass of the debris.
[0009] As a preferred embodiment, the roller pressing device includes two counter-rotating pressure rollers, with a compaction gap of 1 to 3 mm between the two pressure rollers.
[0010] As a preferred option, in step S4, after drying and before feeding into the hot extrusion granulator, a screening process is also included to classify the spherical particles according to their particle size. Spherical particles with a particle size in the range of 2 to 5 mm are fed into the hot extrusion granulator, while particles with a particle size less than 2 mm or greater than 5 mm are returned to step S2 or S3 for reprocessing.
[0011] Secondly, this application provides a processing apparatus for performing the basic scheme of the first aspect of rolling granulation. The processing apparatus includes a frame, on which a rotatable disc is mounted via bearings, and a motor is mounted on the frame to drive the disc to rotate. The frame also drives a pressure plate located directly above the disc via a cylinder. Irregular particles are squeezed and kneaded by the relative rotational motion between the disc and the pressure plate, causing them to roll and form spherical particles.
[0012] Preferably, the rotational speed of the disc is 20-60 rpm, the gap between the pressure plate and the disc is 0.5-2 mm, the pressure applied by the cylinder is 0.1-0.5 MPa, and the rolling time is 5-15 minutes.
[0013] In some embodiments, a baffle is fixed to the outer periphery of the disk, the sidewall of the baffle is inclined downward toward the center of the disk, and a plurality of atomizing nozzles are evenly spaced at the top of the baffle along the circumferential direction, the spraying direction of the atomizing nozzles being toward the central region of the disk.
[0014] Furthermore, the baffle is evenly provided with multiple discharge ports along the circumference, and a gate is installed at each discharge port.
[0015] As a preferred embodiment, the surface of the disc is provided with multiple protrusions. These protrusions on the disc surface create localized point-contact compression and shearing of the irregular particles during the rolling process, enhancing the rolling force of the particles, effectively preventing them from slipping on the disc, significantly shortening the spherical formation time, and simultaneously improving the surface density of the spherical particles.
[0016] Working principle and beneficial effects of the present invention: This application first adds a wetting agent (such as water) to the collected flocculent debris and stirs it. The surface tension of water causes the loose flocculent debris to adhere to each other, forming a moist agglomerate with a slightly reduced volume, thus achieving preliminary compaction. In addition, water is used to increase the friction between the material and the pressure roller. If water is not added first for wetting and the compaction in step S2 is performed directly, a series of problems will occur, such as material slippage, inability to feed, rebound and loosening, and dust flying.
[0017] The moist agglomerates are fed into a roller press, where two counter-rotating rollers compress the material into continuous sheets. These sheets are then crushed and screened to obtain irregular particles. A conventional crusher can be used for crushing and screening. This step significantly increases the bulk density of the debris through mechanical pressure, greatly reduces the specific surface area, and does not produce thermal degradation throughout the process.
[0018] Irregular particles are fed into the processing device for rolling granulation. At this point, the pressure plate is directly above the disc. The irregular particles are poured onto the disc, and the baffle acts to hold the material in place, with multiple gates on the baffle closed. Multiple atomizing nozzles, evenly spaced along the circumference of the baffle, spray water towards the center of the disc, thus wetting the irregular particles. Subsequently, a cylinder drives the particles to press down on the pressure plate, maintaining a gap of 0.5–2 mm between the pressure plate and the disc. Then, a motor starts, driving the particles to rotate at 20–60 rpm. During this relative rotation between the disc and the pressure plate, the irregular particles are subjected to compression, kneading, and rolling, eliminating sharp edges and gradually forming spherical particles. The specific surface area of the spherical particles is further reduced, and thermal degradation is significantly inhibited, solving the problems of discoloration and significant decline in mechanical properties associated with existing technologies. Furthermore, the spherical particles have better flowability, and the recycled particles produced by uniform melting and plasticization through hot extrusion are uniform and can be reused in a high proportion for pipe production.
[0019] In addition, the spraying of water softens the surface of the granules, making them easier to compact during the rolling process. Furthermore, the water distributed on the surface of the granules absorbs some heat during the squeezing and friction process and carries away the heat through evaporation or convection, thereby inhibiting temperature rise and preventing the PVC surface from softening, sticking, or thermally degrading.
[0020] If irregular particles are fed directly into the S4 granulation process without undergoing rolling granulation, the numerous sharp edges and corners of the particles can easily bridge each other, causing blockages at the feed inlet of the hot extrusion granulator. Furthermore, during hot extrusion, the irregular particle shape leads to inconsistent heating areas and heat transfer paths; sharp edges melt first, followed by flatter areas, resulting in uneven melting and plasticization, and consequently, uneven recycled granules produced by hot extrusion. Additionally, the rapid temperature rise at the sharp edges preferentially degrades, causing yellowing and discoloration of the material. Therefore, rolling granulation of irregular particles to form spherical particles is essential.
[0021] After the rolling process is complete, the cylinder lifts the pressure plate to a high position, increasing the disc's rotation speed. The spherical particles move outward under centrifugal force and are ejected from the discharge port, completing the unloading. The discharged spherical particles are dried and then screened. Qualified particles with a diameter of 2-5 mm are sent to a hot extrusion granulator; particles smaller than 2 mm or larger than 5 mm are returned to step S2 or S3 for reprocessing. The qualified particles are then melt-plasticized and pelletized in the hot extrusion granulator to finally obtain recycled particles. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the results from the processing device of the present invention; Figure 2 Figure 1 Vertical cross-sectional view at the flange; Figure 3 for Figure 1 Top view of the middle disk; Figure 4 for Figure 3 A cross-sectional view. Detailed Implementation
[0023] The following detailed description illustrates the specific implementation method: The reference numerals in the instruction manual include: motor 1, rim 2, frame 3, pressure plate 4, cylinder 5, atomizing nozzle 6, irregular particles 7, baffle 8, disc 9, gate 10.
[0024] Example: Thin, flake-like and flocculent debris generated from high-speed sawing of PVC pipe production lines is collected. This debris is loose and flocculent, has poor flowability, and is difficult to feed directly. The processing method includes the following steps: S1. Add 100 kg of the above-mentioned debris into the mixer, using deionized water as a wetting agent, and spray it evenly through the atomizing nozzle 6 at 10% of the debris mass (i.e., 10 kg), while stirring for several minutes. After stirring, the debris changes from a loose flocculent state to a moist agglomerate, the volume shrinks, the bulk density increases, the surface is evenly wetted and no free water flows out.
[0025] Step S1 utilizes the surface tension of water to bind the loose, flocculent debris together, forming a slightly reduced, moist agglomerate to achieve initial compaction. Water is also used to increase the friction between the material and the pressure roller. If water is not added first for wetting and compaction is performed directly in step S2, a series of problems will occur, such as material slippage, inability to feed, rebound and loosening, and dust flying.
[0026] S2. The moistened agglomerates are fed into a roller press device. The two counter-rotating rollers of the roller press device press the material into continuous thin sheets. The sheets are then crushed and screened to obtain irregular particles 7. Conventional crushing and screening machines can be used for crushing and screening. This step significantly increases the bulk density of the debris through mechanical pressure, significantly reduces the specific surface area, and does not produce thermal degradation throughout the process.
[0027] S3. The irregular particles 7 are fed into the processing device for rolling granulation. S4. Granulation: After drying, the spherical granules are fed into a conventional hot extrusion granulator, where they are melt-plasticized and granulated to obtain recycled granules.
[0028] like Figures 1-4 As shown, the processing device includes a frame 3, on which a rotatable disc 9 is mounted via bearings, and a motor 1 is mounted on the frame 3 to drive the disc 9 to rotate; the frame 3 also drives a pressure plate 4 located directly above the disc 9 via a cylinder 5; the irregular particles 7 are squeezed and kneaded by the relative rotational motion between the disc 9 and the pressure plate 4 to roll and form spherical particles.
[0029] The outer perimeter of the disc 9 is fixed with a rim 2 and a retaining 8 from the outside to the inside. The sidewall of the retaining 8 slopes downward toward the center of the disc 9. Six atomizing nozzles 6 are evenly spaced along the circumference at the top of the retaining 8, and the spraying direction of the atomizing nozzles 6 is toward the central area of the disc 9. Four discharge ports are evenly opened along the circumference of the retaining 8, and a gate 10 is installed at each discharge port.
[0030] At this point, the pressure plate 4 is directly above the disc 9. Irregular particles 7 are poured onto the disc 9, and the baffle 8 acts as a barrier to stop the material. The four gates 10 on the baffle 8 are closed. Six atomizing nozzles 6, evenly spaced along the circumference at the top of the baffle 8, spray water towards the center of the disc 9, i.e., towards the irregular particles 7 to wet them. Subsequently, the cylinder 5 drives the pressure plate 4 to press down on the disc 9, maintaining a gap of 2mm between the pressure plate 4 and the disc 9. Then, the motor 1 starts and drives the disc 4 to rotate at 60 rpm. During the relative rotation between the disc 9 and the pressure plate 4, the irregular particles 7 are squeezed, kneaded, and rolled, eliminating sharp edges and gradually forming spherical particles. The specific surface area of the spherical particles is further reduced, and thermal degradation is significantly inhibited, solving the problems of material discoloration and significant decline in mechanical properties in existing technologies. Furthermore, the spherical particles have better flowability, and the recycled particles produced by uniform melting and plasticization and hot extrusion are uniform and can be reused in pipe production at a high rate.
[0031] In addition, the spraying of water softens the surface of the granules, making them easier to compact during the rolling process. Furthermore, the water distributed on the surface of the granules absorbs some heat during the squeezing and friction process and carries away the heat through evaporation or convection, thereby inhibiting temperature rise and preventing the PVC surface from softening, sticking, or thermally degrading.
[0032] If irregular particles 7 are fed directly into the granulation process of S4 without undergoing rolling granulation, the numerous sharp edges of the particles 7 can easily cause bridging and blockage of the feed inlet of the hot extrusion granulator. Furthermore, during hot extrusion, the irregular shape of the particles results in inconsistent heating areas and heat transfer paths; sharp edges melt first, followed by flatter areas, leading to uneven melting and plasticization, and consequently, uneven recycled granules produced by hot extrusion. Moreover, the rapid temperature rise at the sharp edges preferentially degrades, causing yellowing and discoloration of the material. Therefore, it is necessary to roll and granulate the irregular particles 7 to form spherical particles.
[0033] After the rolling process is completed, cylinder 5 lifts the pressure plate 4 to a high position, opens the gate 10, and increases the rotation speed of the disc 9. The spherical particles move outward under centrifugal force and are ejected from the discharge port, completing the unloading. The discharged spherical particles are located between the retaining edge 8 and the surrounding edge 2. After collection and drying, they undergo a screening process. Qualified particles with a diameter of 2-5 mm are sent to the hot extrusion granulator; particles smaller than 2 mm or larger than 5 mm are returned to step S2 or S3 for reprocessing. The qualified particles are melt-plasticized and pelletized in the hot extrusion granulator, ultimately yielding recycled particles.
[0034] Comparative example: The irregular particles 7 obtained in step S2 were directly granulated in step S4. During the feeding process, the hopper was frequently blocked, and manual tapping was required to assist in feeding. The recycled particles obtained from granulation were dark yellow, indicating that the irregular particles 7 were directly hot-extruded without rolling, resulting in severe thermal degradation.
[0035] The recycled granules obtained from the examples and comparative examples were reused in pipe production at a ratio of 50%, and 110mm diameter drainage pipes were produced using the same type of pipe extrusion production line. The test results are shown in Table 1 below: Table 1
[0036] The results show that the recycled pellets produced in this application have excellent performance, with the mechanical properties of the pipes retaining ≥94% at a 50% recycling rate, and a good appearance. However, omitting the rolling step leads to feeding difficulties and product defects.
[0037] It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of this invention. These modifications and improvements should also be considered within the scope of protection of this invention, and will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.
Claims
1. A method for recycling and processing PVC pipe manufacturing debris, characterized in that, Includes the following steps: S1, Wetting Aggregation: Adding a wetting agent to the debris to form wet aggregates; S2. Compaction: The moist agglomerates are fed into a roller press to be pressed into thin sheets, and then the thin sheets are crushed and screened to obtain irregular particles. S3. Rolling: Irregular particles are fed into the processing device for rolling granulation to form spherical particles; S4. Granulation and molding: After drying, the spherical particles are fed into a hot extrusion granulator, where they are melt-plasticized and granulated to obtain recycled particles.
2. The method for recycling and processing PVC pipe manufacturing debris according to claim 1, characterized in that: The wetting agent is selected from water, alcohol solvents or mineral oil, and the amount of the wetting agent added is 5% to 20% of the mass of the debris.
3. The method for recycling and processing PVC pipe manufacturing debris according to claim 2, characterized in that: The roller pressing device includes two counter-rotating rollers, with a compaction gap of 1 to 3 mm between the two rollers.
4. The method for recycling and processing PVC pipe manufacturing debris according to claim 3, characterized in that: In step S4, after drying and before feeding into the hot extrusion granulator, a screening process is also included to classify the spherical particles according to their particle size. Spherical particles with a particle size in the range of 2 to 5 mm are fed into the hot extrusion granulator, while particles with a particle size less than 2 mm or greater than 5 mm are returned to step S2 or S3 for reprocessing.
5. A processing apparatus for performing rolling granulation as described in any one of claims 1 to 4, characterized in that: The processing device includes a frame on which a rotatable disc is mounted via bearings, and a motor that drives the disc to rotate is mounted on the frame. The frame also has a pressure plate located directly above the disc, which is driven by a cylinder. The irregular particles are squeezed and kneaded by the relative rotational motion between the disc and the pressure plate, causing them to roll and form spherical particles.
6. The processing apparatus according to claim 5, characterized in that: The rotating speed of the disc is 20-60 rpm, the gap between the pressure plate and the disc is 0.5-2 mm, the pressure applied by the cylinder is 0.1-0.5 MPa, and the rolling time is 5-15 minutes.
7. The processing apparatus according to claim 6, characterized in that: A baffle is fixed to the outer periphery of the disc, the sidewall of the baffle is inclined downward toward the center of the disc, and a plurality of atomizing nozzles are evenly spaced on the top of the baffle along the circumferential direction, the spraying direction of the atomizing nozzles is toward the central area of the disc.
8. The processing apparatus according to claim 7, characterized in that: The baffle is evenly provided with multiple discharge ports along the circumference, and a gate is installed at each discharge port.
9. The processing apparatus according to claim 8, characterized in that: The surface of the disk is provided with multiple protrusions.