A method for manufacturing an extended three-to-eight winding core tube

Abstract

This invention discloses a method for preparing an extended three-turn eight-coil core tube, comprising: performing surface activation pretreatment on the connecting concave surface of the first core tube to be welded and the connecting convex surface of the second core tube; performing non-contact heating on the surface-activated concave and convex surfaces to form a molten layer; driving the first and second core tubes axially aligned and pressed together using a multi-segment variable pressure mode, so that the connecting concave and convex surfaces are welded together to form a welded joint; and performing programmed annealing cooling on the welded joint to obtain the extended three-turn eight-coil core tube. This method not only completely solves the problem of crushing and alignment failure caused by loss of positioning structure stiffness due to heat conduction, achieving high-precision continuous alignment of non-circular inner holes, but also significantly improves the connection strength and long-term service reliability of the welded joint, meeting the requirements for long winding; simultaneously, the programmed annealing cooling eliminates the internal stress introduced by the welding thermal cycle, enhancing the dimensional stability of the finished product.

Description

Technical Field

[0001] This invention relates to the field of core tube technology, and in particular to a method for preparing an extended three-turn eight-winding core tube. Background Technology

[0002] ABS three-to-eight core tube is a tubular component used in winding equipment for films, paper, etc. Its inner hole has a non-circular irregular cross-section that transitions from three arc grooves to eight arc grooves to cooperate with the corresponding key on the winding shaft to transmit torque. Due to limitations in the core pulling stroke and cooling uniformity of the injection mold, the injection molding length of a single core tube is usually no more than 228mm. To meet the requirements of long winding, multiple short tubes need to be connected and lengthened.

[0003] Currently, the mainstream method for pipe connections is adhesive bonding. However, adhesive bonding not only has low strength and produces protrusions, but it also cannot guarantee the precise continuity of non-circular inner holes. Some related technologies use contact heating welding, but contact hot plate heating has the problem of melt adhering to the plate surface, affecting the cleanliness of the welding interface. Furthermore, the internal stress introduced by the thermal cycle is difficult to eliminate, resulting in insufficient reliability in long-term service. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an extended three-turn eight-winding core tube, so as to solve the technical problem that the current three-turn eight-winding core tube cannot meet the requirements for long winding.

[0005] In a first aspect, the present invention provides a method for preparing an extended three-to-eight core tube, used to connect at least two core tubes into a long tube that meets the length requirement. The core tube has concentric holes and eight connecting ribs connecting the outer wall of the concentric holes to the inner wall of the core tube, forming a three-to-eight structure. One end of the core tube is a connecting concave surface, and the other end is a connecting convex surface. The connecting concave surface has an annular connecting groove along the cross-section of the first concentric hole, and an annular positioning platform and several positioning blind holes along the cross-section of the first core tube. The opening of the annular connecting groove has an inlet surface. The connecting convex surface has an annular connecting platform adapted to the annular connecting groove, an annular positioning groove adapted to the annular positioning platform, and a positioning post adapted to the positioning blind holes. The method includes: Surface activation pretreatment is performed on the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded. The concave and convex surfaces of the connection after surface activation pretreatment are heated in a non-contact manner to form a molten layer; The first core tube and the second core tube are driven to be axially aligned and pressed together in a multi-stage voltage transformation mode, so that the connecting concave surface and the connecting convex surface are fused together to form a fusion joint. The fusion joint is subjected to programmed annealing and cooling to obtain an extended three-turn eight-coil core tube.

[0006] In some embodiments, the surface activation pretreatment of the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded includes: An atmospheric pressure plasma spray gun is used to uniformly sweep the connecting concave surface and the connecting convex surface for 5s~15s with a first working air pressure, and then to pressurize and sweep the positioning blind hole and the annular connecting groove for 10s~20s with a second working air pressure, so that the surface water contact angle of the connecting concave surface and the connecting convex surface is reduced to <20°. The angle between the nozzle axis of the atmospheric pressure plasma spray gun and the axis of the core tube is 30°~60°, and the second working air pressure is greater than the first working air pressure.

[0007] In some embodiments, the non-contact heating of the connecting concave surface and the connecting convex surface after surface activation pretreatment to form a molten layer includes: A short-wave infrared radiation heating device is used to pulse-heat the connecting concave surface and the connecting convex surface to a surface temperature of 225℃~240℃, and then hold the temperature for 10s~18s to form the molten layer with a depth of 0.6mm~1mm.

[0008] In some embodiments, after non-contact heating of the connecting concave surface and the connecting convex surface after surface activation pretreatment to form a molten layer, the method further includes: Before the first core tube and the second core tube are axially aligned and pressed together, the molten layer is subjected to low-power heat preservation radiation at 15% to 25% of the rated power of the short-wave infrared radiation heating device.

[0009] In some embodiments, driving the first core tube and the second core tube to axially align and press together in a multi-stage variable pressure mode, so that the connecting concave surface and the connecting convex surface are fused together to form a fused joint, includes: Drive the first core tube and the second core tube closer together at a speed of 150mm / s to 200mm / s until the distance between the connecting concave surface and the connecting convex surface is a preset distance; Subsequently, the pressing speed is immediately switched to 10mm / s~20mm / s, and an axial contact pressure of 0.02MPa~0.05MPa is applied, so that the annular connecting platform slides into the annular connecting groove under the guidance of the inlet surface, and the positioning post is introduced into the positioning blind hole. After the connecting concave surface and the connecting convex surface are fitted together, the axial contact pressure is increased to 0.5MPa~0.7MPa within 0.5s and held for 2s~5s, so that the connecting concave surface and the connecting convex surface are fused together under high pressure. The axial contact pressure gradient is reduced to 0.05MPa~0.08MPa, and the pressure is maintained for 3s~8s to form the fusion joint.

[0010] In some embodiments, performing programmed annealing and cooling on the welded joint to obtain an extended three-turn eight-coil core tube includes: Maintain the axial position lock of the first core tube and the second core tube, and apply a slight axial pressure of 0.05MPa~0.08MPa; The welded joint is heated to 80°C to 85°C at a rate of 5°C / min to 8°C / min and held at that temperature for 5 min to 15 min. After the heat preservation is completed, the tube is cooled to 70℃±2℃ using controlled air cooling at a cooling rate of 0.8℃ / min~1.5℃ / min, and then cooled to 40℃~50℃ at a cooling rate of 2℃ / min~3℃ / min. After that, it is naturally cooled to <40℃, and the axial position lock and axial micro-pressure are released to obtain the extended three-turn eight-coil core tube.

[0011] In some embodiments, the top of the annular positioning platform and the bottom of the annular positioning groove are in clearance fit, and the difference between the height of the annular positioning platform and the depth of the annular positioning groove is a preset difference, which is adapted to the compression amount of the molten layer.

[0012] In some embodiments, before performing surface activation pretreatment on the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded, the method further includes: The first core tube and the second core tube are respectively fixed in the welding fixture, and the coaxiality of the first core tube and the second core tube is controlled to be ≤0.1mm, and the circumferential relative rotational freedom of the first core tube and the second core tube is locked.

[0013] In some embodiments, the core tube is made of ABS.

[0014] Secondly, the present invention also provides an extended three-turn eight-coil core tube, comprising at least one first core tube and at least one second core tube, wherein the first core tube and the second core tube are connected together based on the above-described preparation method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: By using surface chemical activation and non-contact clean heating, material contamination and adhesion problems caused by hot plate contact are avoided. The multi-stage pressure variation mode provides sufficient stress relaxation time for the positioning protrusion in the thermal softened state, enabling it to complete adaptive deformation introduction under low resistance. This not only completely solves the problem of crushing and alignment failure caused by loss of positioning structure stiffness due to heat conduction, achieving high-precision continuous alignment of non-circular inner holes, but also significantly improves the connection strength and long-term service reliability of welded joints, meeting the requirements of long winding. At the same time, programmed annealing cooling eliminates the internal stress introduced by the welding thermal cycle, enhancing the stability of the finished product. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation method of the extended three-turn eight-winding core tube according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of an extended three-turn eight-coil core tube as shown in an embodiment of the present invention; Figure 3 A schematic diagram of the connecting concave surface shown in an embodiment of the present invention. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0018] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, it should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Unless otherwise specified, the raw materials used in the following examples and comparative examples are commercially available industrial products, and all conditions not otherwise specified are conventional.

[0020] The technical solution of this invention can be applied to industrial scenarios requiring long core tubes, such as film winding, paper processing, and cable winding. As described in the background art, existing three-to-eight core tubes are limited by the core-pulling stroke and cooling uniformity of the injection mold, and the length of a single injection molding tube is usually no more than 228mm, which cannot meet the needs of winding equipment for long core tubes. If adhesives are used to connect short tubes through connectors, the connectors form protrusions on the inner and outer surfaces of the tube wall, causing the core tube to be unable to smoothly pass through the winding shaft or to damage the film surface during winding; at the same time, the difference in the coefficient of thermal expansion between the adhesive layer and the ABS substrate will cause interface cracking under the alternating stress of repeated winding and unwinding, resulting in insufficient connection reliability. On the other hand, contact hot plate heating has the problem of melt adhering to the plate surface, affecting the cleanliness of the weld interface, and the internal stress introduced by the thermal cycle is difficult to eliminate, resulting in insufficient long-term service reliability.

[0021] To this end, the present invention achieves perfect continuity of non-circular irregular inner holes in the axial and circumferential directions after welding by sequentially performing surface chemical activation on the mating surfaces, forming a molten layer through non-contact radiation heating, driving the two tubes to be precisely pressed together in a three-stage pressure change mode, and performing programmed annealing treatment on the welded joint area after welding. At the same time, it enables the strength and long-term service reliability of the welded joint to reach the level of the base material, meeting the requirements for long winding.

[0022] See Figure 1 , Figure 1 This is a flowchart illustrating a method for preparing an extended three-to-eight-winding core tube according to an embodiment of the present invention. This method is used to connect at least two core tubes with a three-to-eight-winding structure to form a long tube that meets the required length. Figure 2 and 3 As shown, the core tube has concentric holes and eight connecting ribs connecting the outer wall of the concentric holes to the inner wall of the core tube, forming a three-to-eight structure; one end of the core tube is a connecting concave surface and the other end is a connecting convex surface; the connecting concave surface has an annular connecting groove along the cross-section of the first concentric hole, and an annular positioning platform and several positioning blind holes along the cross-section of the first core tube, and the opening of the annular connecting groove has an inlet surface; the connecting convex surface has an annular connecting platform adapted to the annular connecting groove, an annular positioning groove adapted to the annular positioning platform, and a positioning post adapted to the positioning blind holes.

[0023] To achieve a high-precision extended connection between the two short tubes, the two ends of the core tube are designed with concave and convex connecting surfaces, forming a coupling structure that can be interlocked. The insertion of the concentric holes achieves initial radial centering, the conical engagement of the annular connecting platform and the annular connecting groove provides axial guidance and secondary centering, and the final engagement of the positioning pin and the positioning blind hole achieves precise circumferential locking. During assembly, the annular connecting platform with the convex connecting surface is inserted into the annular connecting groove with the concave connecting surface under the guidance of the guide surface. Simultaneously, the positioning pin is guided into the positioning blind hole, and the annular positioning platform is embedded in the annular positioning groove. The conical design of the guide surface generates automatic radial and circumferential correction forces when the two tubes approach each other axially, ensuring precise alignment of the irregularly shaped inner holes.

[0024] Optionally, the top of the annular positioning platform and the bottom of the annular positioning groove are in clearance fit, and the height of the annular positioning platform is greater than the depth of the annular positioning groove. The difference between the height of the annular positioning platform and the depth of the annular positioning groove is a preset difference value, which is adapted to the compression amount of the molten layer. For example, the preset difference value is 0.2mm to 1mm. This preset difference value can be measured based on the compression amount of the molten layer to ensure that under the action of welding pressure, the main welding end faces of the connecting convex surface and the connecting concave surface can be fully fitted and compacted, avoiding the obstruction of the tight bonding of the welding surface due to the positioning platform touching the bottom prematurely.

[0025] Optionally, the core tube is made of ABS (acrylonitrile-butadiene-styrene copolymer).

[0026] like Figure 1 As shown, the preparation method of the extended three-turn eight-winding core tube in this embodiment specifically includes steps S1 to S4, which are detailed below: S1, perform surface activation pretreatment on the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded.

[0027] In this step, thermoplastic engineering plastics such as ABS have low surface free energy and exhibit chemical inertness. If directly heated for welding, the diffusion and entanglement of molecular chains at the interface are restricted, making it difficult to achieve the same weld strength as the base material. Furthermore, during storage after injection molding, the pipe end surface adsorbs organic pollutants and moisture from the environment, forming an extremely thin, weak boundary layer. This step, through surface activation pretreatment, breaks the CH and CC bonds on the polymer surface and generates free radicals. These free radicals react with oxygen in the air, introducing polar functional groups such as -OH and -COOH to eliminate the chemical inertness of the ABS material surface. This allows the chemically activated surface to form stronger intermolecular hydrogen bonds and even localized chemical bonds at the interface during subsequent welding, elevating the weld interface from physical adsorption-level adhesion to molecular-level fusion, thus improving the intrinsic strength of the weld joint.

[0028] S2, Non-contact heating is applied to the concave and convex surfaces of the connection after surface activation pretreatment to form a molten layer.

[0029] In this step, the molten ABS melted by the contact hot plate tends to adhere to the hot plate surface, causing stringing and surface defects. Furthermore, direct contact with the hot plate leads to overheating of the surface layer and underheating of the subsurface layer. This step uses a non-contact heating method to radiate heat the connecting concave and convex surfaces. The radiant energy is absorbed by the polymer molecules and converted into molecular thermal kinetic energy, causing the end-face material to heat up layer by layer from the outside in. By controlling the temperature, the surface material enters a viscous flow state, forming a uniform molten layer with a depth of 0.6mm to 1mm, while the subsurface layer only reaches a highly elastic softened state. This completely eliminates the problem of sticking to the mold, and the molten layer is clean and free of contamination.

[0030] S3, drive the first core tube and the second core tube to be axially aligned and pressed together in a multi-stage variable pressure mode, so that the connecting concave surface and the connecting convex surface are fused together to form a fused joint.

[0031] In this step, under constant speed and pressure docking, the positioning post, preheated to a leathery state by heat conduction, may experience creep crushing or rigid collision jamming under high speed and pressure. This step improves efficiency through an initial rapid approach phase, a medium-speed introduction phase with low-speed precise alignment to prevent structural damage, a high-pressure welding phase using high pressure to promote molecular chain diffusion, and a gradient decompression phase slowly releasing stress to prevent joint cracking. This allows the molten materials on both sides to fully contact, flow, and mix under pressure, forming a network of mutual diffusion and entanglement of molecular chains at the interface, thus forming a solid connection joint with sufficient mechanical strength after cooling.

[0032] S4, perform programmed annealing and cooling on the fusion joint to obtain an extended three-turn eight-coil core tube.

[0033] In this step, the thermoplastic undergoes rapid heating and cooling during the welding process. The weld zone experiences residual internal stress due to non-uniform shrinkage and freezing of molecular chain orientation, which can easily lead to environmental stress cracking and dimensional instability during subsequent use. This step addresses this by using programmed annealing cooling after welding. This allows the polymer chains to acquire sufficient thermal mobility, systematically releasing the frozen internal stress through chain relaxation. Sufficient time is also given for the molecular chains at the interface to diffuse deeply across the interface and fully entangle, thereby significantly reducing the residual internal stress of the weld joint and significantly improving dimensional stability. During slow cooling, the deep diffusion of molecular chains causes the weld interface to nearly disappear at the molecular scale, further enhancing the tensile strength and resistance to environmental stress cracking to the level of the base material. This ensures that delayed cracking failure will not occur under subsequent long-term alternating loads and temperature and humidity changes.

[0034] In some embodiments, prior to S1, the method further includes: The first core tube and the second core tube are respectively fixed in the welding fixture, and the coaxiality of the first core tube and the second core tube is controlled to be ≤0.1mm, and the circumferential relative rotational freedom of the first core tube and the second core tube is locked.

[0035] In this embodiment, the welding fixture can employ a high-precision three-jaw self-centering chuck or a V-block clamping mechanism to ensure that the outer wall of the core tube is reliably clamped without deformation. After clamping, the outer diameter runout can be measured at multiple points along the axial direction of the core tube using a laser alignment instrument or dial indicator, and the fixture position can be adjusted to control the coaxiality between the first and second core tubes within an accuracy range of ≤0.1mm. The coaxiality threshold can be determined comprehensively based on the guide gap between the annular connecting platform and the annular connecting groove, as well as the fit tolerance between the positioning post and the positioning blind hole. If the coaxiality exceeds the tolerance, the guide structure may jam or scrape during subsequent pressing, resulting in skewing of the welded joint or misalignment of the internal connecting ribs. Simultaneously, the circumferential relative rotational freedom of the first and second core tubes is locked by anti-rotation positioning keys or circumferential clamping blocks on the fixture, preventing relative rotation of the two core tubes around the axis due to torque or vibration during the pressing process. By using circumferential locking, it is ensured that the eight connecting ribs inside the first and second core tubes after welding maintain a one-to-one correspondence in the circumferential direction, thereby ensuring the continuity of the cross-sectional area and the fluidity of the fluid channel inside the long tube, and avoiding local pressure loss or stress concentration caused by misalignment of the connecting ribs.

[0036] In some embodiments, S1 includes: An atmospheric pressure plasma spray gun is used to uniformly sweep the connecting concave surface and the connecting convex surface for 5s~15s with a first working air pressure, and then to pressurize and sweep the positioning blind hole and the annular connecting groove for 10s~20s with a second working air pressure, so that the surface water contact angle of the connecting concave surface and the connecting convex surface is reduced to <20°. The angle between the nozzle axis of the atmospheric pressure plasma spray gun and the axis of the core tube is 30°~60°, and the second working air pressure is greater than the first working air pressure.

[0037] In this embodiment, the angle between the nozzle axis of the atmospheric pressure plasma spray gun and the axis of the core tube is set to 30°~60°. The plasma jet can act simultaneously on the sidewall of the annular connecting groove and the root of the annular positioning platform on the connecting end face in an oblique incidence manner, avoiding the shielding effect caused by the complex concave structure when incident vertically. For example, the connecting concave and convex surfaces are uniformly swept for 5s~15s with a first working gas pressure of 0.2MPa~0.4MPa, and the sweeping path moves at a uniform speed along the circumference, covering the entire connecting surface. Subsequently, the positioning blind hole and the annular connecting groove are pressurized and swept for 10s~20s with a second working gas pressure greater than the first working gas pressure (e.g., 0.5MPa~0.7MPa), respectively, to ensure that the plasma can penetrate into the micropores and the bottom of the groove, achieving all-round activation. During the sweeping process, the distance between the plasma spray gun and the workpiece surface is maintained at 8mm~15mm. After the above treatment, the surface water contact angle of the connecting concave and convex surfaces is reduced to <20°, so that the surface changes from hydrophobic to hydrophilic.

[0038] In a specific scenario, the two core tubes to be welded are made of ABS (acrylonitrile-butadiene-styrene copolymer). Before entering the plasma treatment station, the surface may have residual release agent and oil contamination from transportation. After the plasma spray gun sweeps at a 45° axial angle and 0.3 MPa pressure for 10 seconds, the surface water contact angle drops from the initial 75° to about 15°, significantly improving melt wettability. Subsequently, the annular connecting groove and positioning blind hole are pressurized and swept at 0.6 MPa pressure for 15 seconds to ensure that the groove and the dead corner area at the bottom of the hole are also fully activated.

[0039] In some embodiments, S2 includes: A short-wave infrared radiation heating device is used to pulse-heat the connecting concave surface and the connecting convex surface to a surface temperature of 225℃~240℃, and then hold the temperature for 10s~18s to form the molten layer with a depth of 0.6mm~1mm.

[0040] In this embodiment, the wavelength range of short-wave infrared radiation is typically 0.76 μm to 2 μm, which can be efficiently absorbed by polymer materials such as ABS, enabling rapid volumetric heating from the surface inwards. During the heating process, closed-loop temperature control (such as real-time feedback of surface temperature from an infrared thermometer) is used to heat the surfaces of the connecting concave and convex surfaces to 225°C to 240°C and reach thermal equilibrium. This temperature is then maintained for 10 to 18 seconds. This temperature range is higher than the glass transition temperature (approximately 110°C) and melting point (approximately 220°C) of ABS, but lower than the thermal decomposition initiation temperature (approximately 270°C), ensuring sufficient melting while preventing thermal degradation of the material. Under the above temperature and time conditions, the molten layer depth can reach 0.6 mm to 1 mm, providing sufficient molten material to fill the microscopic gaps at the connection interface during subsequent pressing, while avoiding structural collapse and deformation during pressing due to an excessively deep molten layer.

[0041] The pulsed control mode of short-wave infrared radiation heating can effectively suppress the heat accumulation effect. When the control system detects that the surface temperature is close to the upper threshold (e.g., 240°C), it automatically cuts off the radiation power; when the temperature drops back to the lower threshold (e.g., 225°C), the power is reconnected, forming a pulsed heating curve. Compared with continuous full-power heating, the control method in this embodiment can control the surface temperature fluctuation within ±3°C, effectively preventing local overheating.

[0042] In some embodiments, after S2, the method further includes: Before the first core tube and the second core tube are axially aligned and pressed together, the molten layer is subjected to low-power heat preservation radiation at 15% to 25% of the rated power of the short-wave infrared radiation heating device.

[0043] In this embodiment, the power density of the low-power radiation is low and insufficient to further increase the surface temperature of the molten layer, but it can effectively compensate for the heat lost due to convection and conduction, so that the surface temperature of the molten layer connecting the concave and convex surfaces is always maintained in the range of 215°C to 225°C during the short transition period while waiting for the pressing process, thus avoiding premature solidification of the surface layer or a sharp increase in viscosity due to the temperature dropping below the glass transition temperature.

[0044] In some embodiments, S3 includes: Drive the first core tube and the second core tube closer together at a speed of 150mm / s to 200mm / s until the distance between the connecting concave surface and the connecting convex surface is a preset distance; Subsequently, the pressing speed is immediately switched to 10mm / s~20mm / s, and an axial contact pressure of 0.02MPa~0.05MPa is applied, so that the annular connecting platform slides into the annular connecting groove under the guidance of the inlet surface, and the positioning post is introduced into the positioning blind hole. After the connecting concave surface and the connecting convex surface are fitted together, the axial contact pressure is increased to 0.5MPa~0.7MPa within 0.5s and held for 2s~5s, so that the connecting concave surface and the connecting convex surface are fused together under high pressure. The axial contact pressure gradient is reduced to 0.05MPa~0.08MPa, and the pressure is maintained for 3s~8s to form the fusion joint.

[0045] In this embodiment, the multi-segment pressure variation mode is executed by the axial drive unit (such as a servo motor with a ball screw or a hydraulic servo system). After the short-wave infrared heating completes the heat preservation stage, the control system sends a pressing start signal, and the axial drive unit performs multi-segment actions according to the preset position-speed-pressure curve.

[0046] For example, the first and second core tubes are initially driven closer together at a relatively high speed of 150mm / s to 200mm / s. This stage is the rapid feed stage, aimed at shortening the non-contact travel time and improving production efficiency. When the control system detects through the displacement sensor that the distance between the connecting concave and convex surfaces reaches a preset distance (e.g., 5mm to 10mm), it immediately triggers a speed switch. It should be noted that this preset distance can be adjusted according to the outer diameter and structural complexity of the core tubes, and is usually set as a safe distance to ensure that the front end of the annular connecting table just enters the range of influence of the guide surface of the annular connecting groove.

[0047] Subsequently, the control system immediately switches to a low pressing speed of 10mm / s to 20mm / s, while simultaneously applying an axial contact pressure of 0.02MPa to 0.05MPa. Under these low-speed and low-pressure conditions, the annular connecting platform adaptively slides into the annular connecting groove under the guidance of the guide surface, and the positioning pin simultaneously enters the positioning blind hole. The inclined or arc-shaped structure of the guide surface plays a guiding and corrective role: when there is a slight circumferential or radial deviation between the annular connecting platform and the annular connecting groove, the guide surface can force the annular connecting platform to slide into the correct position along the inclined surface, achieving self-centering. The cooperation between the positioning pin and the positioning blind hole further ensures circumferential positioning accuracy and prevents misalignment of the connecting ribs of the two core tubes after welding; the duration of this low-speed stage is 2s to 4s to ensure that the guide structure is fully in place.

[0048] When the displacement sensor and / or pressure sensor detects that the end faces of the connecting concave and convex surfaces have come into contact (i.e., the travel has reached the contact position), the control system increases the axial contact pressure to 0.5MPa~0.7MPa within 0.5s, entering the high-pressure holding and welding stage. The impact effect generated by this rapid pressure increase helps to expel air bubbles and low-molecular-weight volatiles in the molten layer, while simultaneously allowing the molten materials on both sides to flow fully and mix under high pressure. The holding time lasts for 2s~5s. During this period, the molten layer material creeps into the micro-gap under pressure, and the molecular chains at the interface gain sufficient kinetic energy and free volume to diffuse and entangle with each other, forming a connection strength.

[0049] After the high-pressure holding period, the control system gradually reduces the axial contact pressure gradient to 0.05MPa~0.08MPa. Gradual pressure reduction refers to reducing the pressure in stages at a set pressure reduction rate (e.g., 0.1MPa / s~0.2MPa / s), rather than releasing it instantaneously. The purpose of this gradual pressure reduction is to release the residual stress inside the welded joint gradually, preventing cavitation or microcracks from forming inside the joint due to a sudden pressure drop. After reducing the pressure to a low level, the pressure is held for 3s~8s. This stage is the joint shaping stage, ensuring that the welded joint remains stable in position under lower pressure.

[0050] In a specific scenario, the two ABS core tubes to be welded have an outer diameter of 120mm and a wall thickness of 8mm. During the rapid feed phase, they move relative to each other at a speed of 180mm / s. When the gap narrows to 8mm, a switching is triggered. Subsequently, they are guided in at a low speed of 15mm / s and a pressure of 0.03MPa. After about 3 seconds, the annular connecting platform slides completely into the annular connecting groove. After bonding, the pressure is increased to 0.6MPa within 0.5s and held for 3s. At the moment of pressure increase, a small amount of molten material can be observed being uniformly squeezed out from the joint gap, indicating that the molten layer material has flowed sufficiently and filled the interface. Then, the pressure is reduced to 0.06MPa at a rate of 0.15MPa / s and held for another 5s before entering the cooling and waiting state.

[0051] In some embodiments, S4 includes: Maintain the axial position lock of the first core tube and the second core tube, and apply a slight axial pressure of 0.05MPa~0.08MPa; The welded joint is heated to 80°C to 85°C at a rate of 5°C / min to 8°C / min and held at that temperature for 5 min to 15 min. After the heat preservation is completed, the tube is cooled to 70℃±2℃ using controlled air cooling at a cooling rate of 0.8℃ / min~1.5℃ / min, and then cooled to 40℃~50℃ at a cooling rate of 2℃ / min~3℃ / min. After that, it is naturally cooled to <40℃, and the axial position lock and axial micro-pressure are released to obtain the extended three-turn eight-coil core tube.

[0052] In this embodiment, this step can be performed collaboratively by a cooling unit (including a heating element, a temperature sensor, and a controllable air-cooling system) and an axial locking mechanism. After the gradient depressurization and pressure holding stage of step 103 is completed, the control system automatically switches to the programmed annealing and cooling process.

[0053] At the start of annealing cooling, the axial positions of the first and second core tubes are initially locked. This locking is achieved through a clamping mechanism (such as a pneumatic or hydraulic clamp) to ensure that the two core tubes do not undergo relative axial displacement during cooling and shrinkage. Simultaneously, an axial micro-pressure of 0.05 MPa to 0.08 MPa is applied. This micro-pressure value is lower than the yield stress of the material at high temperature, which can compensate for thermal shrinkage without causing excessive deformation.

[0054] The heating stage then begins: the welded joint is heated to 80°C to 85°C at a rate of 5°C / min to 8°C / min using a heating element (either the low-power mode of the short-wave infrared heating device in step 102 or an independently set circumferential heating band). This raises the joint temperature to the annealing temperature range of ABS material (typically 10°C to 20°C below the glass transition temperature), allowing the polymer chains to gain sufficient mobility for stress relaxation. After reaching the target temperature, the joint is held for 5 to 15 minutes. During this time, the temperature distribution inside the joint tends to be uniform, and the residual stress is fully released.

[0055] After the heat preservation period, the controlled cooling stage begins. Controlled air cooling is used at a rate of 0.8℃ / min~1.5℃ / min to cool the joint temperature from 80℃~85℃ to 70℃±2℃. A lower cooling rate is used in this stage because the polymer experiences maximum volume shrinkage when cooling from the annealing temperature to near the glass transition temperature; slow cooling promotes the orderly stacking of molecular chains. Subsequently, cooling continues at a rate of 2℃ / min~3℃ / min to 40℃~50℃. As the volume shrinkage decreases, the cooling rate can be appropriately increased to shorten the process cycle. Finally, air cooling is stopped, allowing the workpiece to cool naturally in the air to <40℃. At this point, the joint is fully cured and can withstand certain mechanical stress. The control system releases the axial position lock and axial micro-pressure, and the finished extended three-turn eight-coil core tube is removed from the workstation via the unloading mechanism.

[0056] Throughout the programmed annealing and cooling process, the internal microstructure of the weld joint undergoes an evolution from disorder to order. As the joint begins to cool from its melting temperature of 225°C to 240°C, the mobility of the polymer molecular chains gradually decreases. During annealing at 80°C to 85°C, the chain segments gain activation energy, enabling them to overcome intermolecular barriers and rearrange, thus relaxing the orientation and internal stress frozen during the high-pressure welding stage. Subsequently, during slow cooling, the molecular chains gradually fold and arrange themselves to form a more complete crystalline structure, ultimately resulting in a weld joint that meets the requirements for both dimensional stability and mechanical properties.

[0057] This invention employs atmospheric pressure plasma surface activation treatment to reduce the water contact angle between the concave and convex surfaces of the connection to below 20°, significantly improving the wetting and spreading ability of the molten material at the interface. Subsequently, short-wave infrared pulse radiation heating at 225°C~240°C forms a uniform molten layer of 0.6mm~1mm, avoiding the surface contamination risk of contact heating. Simultaneously, closed-loop temperature control suppresses fluctuations within ±3°C, ensuring batch consistency in the molten state. During the multi-stage variable pressure pressing stage, a four-stage speed and pressure coordination control—rapid feeding, low-speed guiding, high-pressure welding, and gradient depressurization—ensures the self-alignment accuracy of the annular connecting platform and the annular connecting groove, while rapidly increasing to 0.5MPa~0.7MPa within 0.5s to promote full entanglement of molecular chains. Gradual depressurization then gradually releases the internal stress of the joint, thereby achieving not only a seamless connection... The precise alignment of the concave and convex surfaces at the macroscopic geometric scale and the molecular-level fusion at the microscopic interface, along with the circumferential locking of the positioning posts and blind holes, ensure the circumferential alignment accuracy of the eight internal connecting ribs after the connection of multiple core tubes, guaranteeing the overall structural consistency of the long tube. Simultaneously, the programmed annealing process during the cooling stage (heating to 80℃~85℃ followed by staged slow cooling) effectively eliminates residual welding stress, resulting in a more perfect joint crystallization structure. The final extended three-turn eight-core tube with an outer diameter bulge ≤0.5mm and a coaxiality deviation ≤0.15mm achieves or even exceeds 90% of the performance of the base material in terms of axial tensile strength and bending strength. Furthermore, the entire preparation process requires no solvents or adhesives, avoiding chemical pollution. It is applicable to various thermoplastic materials such as ABS, modified ABS, and glass fiber reinforced ABS, demonstrating good process versatility and industrial application value.

[0058] As an example and not a limitation, to more intuitively illustrate the technical advantages of the preparation method provided in the embodiments of this application compared with the traditional process, the following provides a comparison of the specific implementation scenarios and the performance of the obtained long tubes of the present invention and the traditional solution under the same test conditions (the material of the core tube to be fused is ABS, the outer diameter is 120mm, the wall thickness is 8mm, the target total length after fusion is 456mm, and the ambient temperature is 25℃).

[0059] The present invention provides the following solution: The first and second core tubes to be welded are respectively fixed in the welding fixture, the coaxiality is calibrated to 0.08mm, and the circumferential relative rotational freedom is locked.

[0060] Activation stage: The atmospheric pressure plasma spray gun is used to uniformly sweep the connecting concave and convex surfaces for 12 seconds at a first working air pressure of 0.3 MPa with the nozzle axis at a 45° angle to the core tube axis. The sweeping path is spiral from the outer edge to the inner edge. Then, the annular connecting groove and the four positioning blind holes are pressurized and swept for 18 seconds with a second working air pressure of 0.6 MPa. After the treatment is completed, the surface water contact angle measured by the contact angle measuring instrument is reduced from the initial 78° to 16°.

[0061] Heating stage: The short-wave infrared radiation heating device (wavelength 1.2μm) heats both ends of the face with pulsed radiation. The closed-loop temperature control system controls the surface temperature at 232℃±2℃ and holds it at that temperature for 14 hours. After the holding period, the depth of the molten layer is indirectly assessed to be approximately 0.85mm by a laser thickness gauge.

[0062] During the pressing stage: The servo drive system first feeds rapidly at a speed of 180 mm / s, triggering a switch when the distance between the two end faces decreases to 8 mm. Then, it guides the material in at a low speed of 15 mm / s and a contact pressure of 0.035 MPa. The annular connecting table adaptively slides into the annular connecting groove under the guidance of the inclined guide surface, and the positioning pins are simultaneously guided into the positioning blind holes. After bonding, the system increases the axial pressure to 0.62 MPa within 0.5 seconds and holds the pressure for 3.5 seconds, during which a small amount of annular molten material is visibly overflowing uniformly from the joint edge. Subsequently, the pressure is gradually reduced to 0.065 MPa at a rate of 0.18 MPa / s and held for 6 seconds.

[0063] Annealing and cooling stage: The axial clamp maintains the locked position and applies a micro pressure of 0.065 MPa. The circumferential heating belt heats the joint to 83°C at a rate of 6.5°C / min and holds it at that temperature for 12 minutes. After holding, the joint is cooled to 70°C by controlled air cooling at 1.2°C / min, then to 45°C at 2.5°C / min, and finally cooled naturally to 38°C. The locking and micro pressure are then released to obtain the finished long tube.

[0064] The measured results of the obtained long tube are as follows: the outer diameter bulge of the welded joint is 0.25 mm (uniform annular); the coaxiality deviation of the entire tube measured by the coordinate measuring machine is 0.09 mm; the positioning post and the positioning blind hole are perfectly aligned, and the circumferential misalignment angle of the 8 internal connecting ribs is <0.5°; a standard dumbbell-shaped sample was cut along the joint for tensile testing, and the average tensile breaking strength was measured to be 46.3 MPa (the tensile strength of the base material is 50.2 MPa, and the joint strength coefficient reaches 92.2%); the joint cross-section was observed under an optical microscope, and the fusion line completely disappeared, the interface showed a continuous sponge-like interpenetrating network structure, the internal bubble pore size was <0.05 mm, and the number of bubbles per unit area was only 2~3 / cm².

[0065] Traditional solution: Use traditional hot plate welding process to connect two ABS core tubes of the same batch and specifications, with the hot plate temperature set at 230℃.

[0066] Surface treatment stage: The operator used 80-grit sandpaper to manually polish the concave and convex surfaces of the connection to remove surface stains and increase roughness. The polishing time was about 30 seconds. Then, the surface debris was wiped off with anhydrous ethanol. No contact angle test was performed after polishing. Polishing scratches and a small amount of wiping cotton remained on the surface.

[0067] Heating stage: Press both ends of the plate simultaneously against a hot plate heated to 230℃, with a contact pressure of 0.05MPa and a heating time of 25s (the heating time needs to be extended because the heat transfer efficiency between the hot plate and the end face is lower than that of infrared radiation). After heating, remove the hot plate. It can be seen that the surface of the molten layer on the end face has local stringing and uneven ripples due to the adhesion and pulling effect when the hot plate is separated. The effective molten layer depth is only 0.4mm~0.5mm and the thickness is uneven.

[0068] Pressing Stage: Within 3 seconds after removing the hot plate, the operating equipment pushes the two core tubes towards each other at a constant speed (80mm / s) and applies a constant axial pressure of 0.55MPa in one go, holding the pressure for 4 seconds. During the pressing process, due to the lack of a sufficiently low guide speed between the annular connecting platform and the annular connecting groove to fully correct deviation, and the absence of segmented pressure buffering, the annular connecting platform impacts the guide surface edge of the annular connecting groove under high-speed advancement, resulting in slight scraping. After the pressure holding period, the pressure is released directly and all at once (without gradient pressure relief).

[0069] Cooling stage: Active annealing was not used. Instead, an industrial fan was used to force-cool the welded joint. The joint temperature dropped from about 220°C to room temperature (25°C) in just about 3.5 minutes. The cooling rate was much higher than the reasonable range (average about 56°C / min).

[0070] The measured results of the long tube were as follows: the outer diameter bulge of the welded joint was extremely uneven, with one side bulging by 0.55 mm and the other side by only 0.12 mm (significant deviation); the coaxiality deviation of the entire tube measured by the coordinate measuring machine was 0.35 mm (exceeding the process requirement of ≤0.15 mm); due to the positioning pin not being fully aligned with the positioning blind hole during pressing (circumferential misalignment of about 2.5°), the eight internal connecting ribs showed a stepped misalignment at the joint; the tensile test showed an average tensile breaking strength of only 28.6 MPa (joint strength coefficient of about 57.0%); the joint cross-section under a microscope showed obvious interface fusion lines, many unfused areas, and internal bubble pores with diameters generally >0.2 mm, with a bubble density of 25~30 per unit area / cm², and a large number of radial microcracks (length about 0.1 mm~0.3 mm) were generated due to forced air cooling.

[0071] As can be seen, under the same material and size conditions, the preparation method provided in this application embodiment removes interface contamination and introduces polar groups through plasma deep activation, forms a uniform and sufficiently thick molten layer through infrared pulse heating, achieves precise self-guided introduction and full diffusion of molecular chains through multi-segment variable pressure pressing, and completely releases thermal history internal stress through programmed annealing. This makes the welded joint significantly superior to the traditional hot plate welding scheme in terms of macroscopic mechanical strength, microstructure integrity, geometric dimensional accuracy, and internal flow channel consistency (reduced misalignment of connecting ribs). It completely solves the common technical problems in the industry of low joint strength, easy deformation, many defects, and misalignment of connecting ribs in traditional processes.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for preparing an extended three-turn eight-coil core tube, characterized in that, For connecting at least two core tubes into a long tube that meets the length requirement, the core tube has concentric holes and eight connecting ribs connecting the outer wall of the concentric holes to the inner wall of the core tube, forming a three-to-eight structure; one end of the core tube is a connecting concave surface, and the other end is a connecting convex surface; the connecting concave surface has an annular connecting groove along the cross-section of the first concentric hole, and an annular positioning platform and several positioning blind holes along the cross-section of the first core tube, the opening of the annular connecting groove has an inlet surface; the connecting convex surface has an annular connecting platform adapted to the annular connecting groove, an annular positioning groove adapted to the annular positioning platform, and a positioning post adapted to the positioning blind holes; the method includes: Surface activation pretreatment is performed on the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded. The concave and convex surfaces of the connection after surface activation pretreatment are heated in a non-contact manner to form a molten layer; The first core tube and the second core tube are driven to be axially aligned and pressed together in a multi-stage voltage transformation mode, so that the connecting concave surface and the connecting convex surface are fused together to form a fusion joint. The fusion joint is subjected to programmed annealing and cooling to obtain an extended three-turn eight-coil core tube.

2. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The surface activation pretreatment of the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded includes: An atmospheric pressure plasma spray gun is used to uniformly sweep the connecting concave surface and the connecting convex surface for 5s~15s with a first working air pressure, and then to pressurize and sweep the positioning blind hole and the annular connecting groove for 10s~20s with a second working air pressure, so that the surface water contact angle of the connecting concave surface and the connecting convex surface is reduced to <20°. The angle between the nozzle axis of the atmospheric pressure plasma spray gun and the axis of the core tube is 30°~60°, and the second working air pressure is greater than the first working air pressure.

3. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The non-contact heating of the concave and convex connecting surfaces after surface activation pretreatment to form a molten layer includes: A short-wave infrared radiation heating device is used to pulse-heat the connecting concave surface and the connecting convex surface to a surface temperature of 225℃~240℃, and then hold the temperature for 10s~18s to form the molten layer with a depth of 0.6mm~1mm.

4. The method for preparing the extended three-turn eight-coil core tube as described in claim 3, characterized in that, After the surface activation pretreatment of the connecting concave surface and the connecting convex surface is subjected to non-contact heating to form a molten layer, the process further includes: Before the first core tube and the second core tube are axially aligned and pressed together, the molten layer is subjected to low-power heat preservation radiation at 15% to 25% of the rated power of the short-wave infrared radiation heating device.

5. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The method of driving the first core tube and the second core tube to axially align and press together in a multi-segment variable pressure mode, so that the connecting concave surface and the connecting convex surface are fused together to form a fused joint, includes: Drive the first core tube and the second core tube closer together at a speed of 150mm / s to 200mm / s until the distance between the connecting concave surface and the connecting convex surface is a preset distance; Subsequently, the pressing speed is immediately switched to 10mm / s~20mm / s, and an axial contact pressure of 0.02MPa~0.05MPa is applied, so that the annular connecting platform slides into the annular connecting groove under the guidance of the inlet surface, and the positioning post is introduced into the positioning blind hole. After the connecting concave surface and the connecting convex surface are fitted together, the axial contact pressure is increased to 0.5MPa~0.7MPa within 0.5s and held for 2s~5s, so that the connecting concave surface and the connecting convex surface are fused together under high pressure. The axial contact pressure gradient is reduced to 0.05MPa~0.08MPa, and the pressure is maintained for 3s~8s to form the fusion joint.

6. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The programmed annealing and cooling of the welded joint yields an extended three-turn eight-coil core tube, comprising: Maintain the axial position lock of the first core tube and the second core tube, and apply a slight axial pressure of 0.05MPa to 0.08MPa; The welded joint is heated to 80°C to 85°C at a rate of 5°C / min to 8°C / min and held at that temperature for 5 min to 15 min. After the heat preservation is completed, the tube is cooled to 70℃±2℃ using controlled air cooling at a cooling rate of 0.8℃ / min~1.5℃ / min, and then cooled to 40℃~50℃ at a cooling rate of 2℃ / min~3℃ / min. After that, it is naturally cooled to <40℃, and the axial position lock and axial micro-pressure are released to obtain the extended three-turn eight-coil core tube.

7. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The top of the annular positioning platform and the bottom of the annular positioning groove are fitted with a clearance, and the difference between the height of the annular positioning platform and the depth of the annular positioning groove is a preset difference, which is adapted to the compression amount of the molten layer.

8. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, Before performing surface activation pretreatment on the connecting concave surface of the first core tube and the connecting convex surface of the second core tube to be welded, the process further includes: The first core tube and the second core tube are respectively fixed in the welding fixture, and the coaxiality of the first core tube and the second core tube is controlled to be ≤0.1mm, and the circumferential relative rotational freedom of the first core tube and the second core tube is locked.

9. The method for preparing the extended three-turn eight-coil core tube as described in claim 1, characterized in that, The core tube is made of ABS.

10. An extended three-turn eight-coil core tube, characterized in that, It includes at least one first core tube and at least one second core tube, and is manufactured by connecting the first core tube and the second core tube according to the preparation method described in any one of claims 1 to 9.

Images