A plastic workpiece spin melt connection structure and connection method

Abstract

The application discloses a spin fusion connecting structure and connecting method of plastic workpieces, which comprises a high-speed rotating workpiece A and a relatively fixed workpiece B. The butt joint end of the workpiece A is provided with a welding surface and a cylindrical centering ring extending axially from the inner wall, and the outer surface of the centering ring is provided with a melting ring. The butt joint end of the workpiece B is provided with a receiving cavity, and a radial gap δ is formed between the centering ring. The ring thickness of the melting ring is much smaller than the wall thickness of the welding surface, and the melting ring is completely melted before the welding surface in the spin fusion process. The molten plastic forms a liquid film in the radial gap, and the rotational shear generates a hydrodynamic pressure effect, which exerts a restoring force on the rotating workpiece in the opposite direction of the eccentricity, thereby realizing dynamic coaxial self-maintenance. The application migrates the principle of the hydrodynamic pressure bearing to the plastic spin fusion welding, overcomes the technical prejudice that "melting displacement needs to be prevented", reverses the positive feedback of the eccentricity amplification to negative feedback self-correction, reduces the coaxiality deviation after welding by 80-96%, does not need external tooling, and realizes the whole-process coaxiality control of pre-centering before welding, dynamic correction during welding and locking after welding.

Description

Technical Field

[0001] This invention relates to the field of plastic welding technology, specifically to a spin-melting connection structure and method for plastic workpieces, and particularly to a connection structure that achieves coaxiality self-holding throughout the spin-melting process. Background Technology

[0002] Split-type plastic reels (such as winding spools, I-beam reels, filter cartridges, etc.) are usually composed of multiple reel sections spliced ​​together or end caps spliced ​​with the reel body. Spin welding is widely used because it requires no glue and provides good sealing. However, maintaining coaxiality in spin welding is a core industry pain point.

[0003] Existing technologies mainly rely on external tooling or static geometric guidance to solve the coaxiality problem. For example, Chinese patent CN211619648U discloses a lightweight all-plastic winding spool and its welding fixture, which provides positioning by inserting external metal guide posts into guide holes; Chinese patent CN220262035U discloses a spin-welding fixture for plastic spools, which achieves positioning by multi-point clamping using external hydraulic clamps; and Chinese patent CN223035775U discloses a spin-welding check valve, which uses the conical end of the core frame to provide pre-assembly guidance.

[0004] The common drawback of the aforementioned prior art is that: Only static or pre-assembly guidance is provided: such as CN211619648U and CN220262035U, which rely on external tooling, and the tooling cannot constrain the displacement of the molten state after welding begins; while the conical surface of CN223035775U loses its guiding function rapidly after the frictional heat of the spin welding softens, and the fitting gap becomes an eccentric channel.

[0005] Existing technologies lack dynamic correction and post-weld locking functions. During spin welding (typically at 1000-2000 rpm), if initial eccentricity exists, the circumferential distribution of frictional contact pressure will be uneven. This results in higher heat generation and more melting on the eccentric side, causing the rotating workpiece to further shift towards the eccentric side, creating an eccentricity amplification positive feedback effect. Specifically, the linear velocity on the eccentric side... > Friction power The frictional power on the eccentric side increases by approximately 2e / R, and the melting rate increases accordingly. After the material softens, the axial load-bearing capacity on that side decreases, and the workpiece tilts further towards the eccentric side. None of the existing technologies can maintain coaxiality during high-speed rotation, and the cooling and shrinkage stage cannot lock it, resulting in the coaxiality deviation after welding being 3-5 times that of the initial deviation before welding, which seriously affects subsequent through-shaft assembly. Summary of the Invention

[0006] In order to overcome at least one deficiency of the existing technology, the present invention provides a spin-welding connection structure and connection method for plastic workpieces. Its core lies in overcoming technical bias and transforming "displacement caused by melting" from a problem that needs to be prevented into a usable centering resource, proposing a coaxial centering mechanism of "molten film liquid bearing centering".

[0007] To achieve the above objectives, the present invention provides a spin-welding structure for plastic workpieces, comprising a workpiece A that rotates at high speed during welding and a workpiece B that is relatively fixed during welding, wherein workpieces A and B each have a structurally complementary butt joint end; wherein: the butt joint end of workpiece A has a welding surface formed by an outer annular end face; a cylindrical centering ring extending axially outward from the inner wall of workpiece A, wherein at least one fusion ring is disposed on the outer surface of the cylindrical centering ring near the welding surface of workpiece A; The workpiece B has a corresponding welding surface formed by the outer annular end face and a receiving cavity for accommodating a cylindrical centering ring. The inner wall of the receiving cavity is locally enlarged near the end to form a radial cavity to accommodate the cylindrical centering ring. The inner surface of the cylindrical surface of the enlarged section of the receiving cavity and the outer surface of the cylindrical centering ring form a radial gap δ. The thickness of the molten ring is much smaller than the wall thickness of the welding surface, so that the molten ring melts completely before the welding surface during the spin welding process. The molten plastic forms a liquid film in the radial gap. The liquid film generates a hydrodynamic pressure effect under the action of rotational shearing, and applies a restoring force opposite to the eccentric direction to the rotating workpiece segment to achieve dynamic coaxial self-holding effect.

[0008] Preferably, the cylindrical centering ring is integrally injection molded with workpiece A, with a wall thickness of 0.8-1.2mm. The end of the cylinder is provided with a 30° guide chamfer and a length of 2mm to facilitate initial insertion into the cavity. The inlet of the cavity is provided with a 30° guide chamfer and a length of 2mm to cooperate with the chamfer at the end of the cylinder to guide insertion.

[0009] Preferably, the height of the molten ring is 0.13-0.25 mm, the radial gap δ is 0.15 to 0.30 mm, and the radial height of the molten ring is less than the radial gap δ.

[0010] Preferably, the wall thickness of the welded surface is asymmetrically distributed along the circumference, and the wall thickness of the welded surface on the eccentric side is defined as t. h The sidewall thickness is t l , where t h / t l Between 1.3 and 1.8, the heat capacity of the eccentric side is greater than that of the opposite side, and the heating rate of the eccentric side is lower than that of the opposite side during melting, thus suppressing over-melting on the eccentric side.

[0011] Preferably, the outer surface of the cylindrical centering ring is provided with axially distributed guide grooves evenly distributed circumferentially. The depth of the guide grooves is 0.1 to 0.3 mm and the width is 0.5 to 1.0 mm, which are used to guide the molten plastic to form a continuous liquid film evenly distributed circumferentially when the molten ring melts. To prevent the molten plastic from forming flash on the inner wall and causing residual glue, a diameter-enlarging groove is preferably provided at the end of the cavity wall away from the welding surface. The groove is 0.3-0.5 mm deep and 2-3 mm axially wide. Even if there is a small amount of excess melt, it will flow into this groove instead of overflowing onto the inner wall. After cooling, the melt in this groove solidifies without affecting the smoothness of the inner wall.

[0012] Preferably, the outer surface of the cylindrical centering ring is further provided with micro-serrations, the depth of which is 0.1 to 0.2 mm and the tooth pitch is 0.5 to 1.0 mm. After welding and cooling, the micro-serrations are embedded in the weld material to form a mechanical interlock, constituting a post-weld coaxiality locking structure.

[0013] Preferably, the matching of the cylindrical centering ring and the receiving cavity provides rigid pre-alignment before welding when the two workpiece sections are joined, so that the initial eccentricity is ≤0.1mm.

[0014] Preferably, the material of the fusion ring is the same as that of the workpiece section or is a compatible thermoplastic. After welding and cooling, the cylindrical centering ring is fused with the workpiece B to form an inner diameter shaping element.

[0015] The present invention also provides a spin-welding method for joining plastic workpieces, employing the joining structure described in any one of claims 1 to 8, comprising the following steps: S1: Pre-assemble or integrally form the molten ring onto the outer surface of the cylindrical centering ring; S2: Workpiece A and workpiece B are connected to the cavity through a cylindrical centering ring to provide rigid pre-alignment, so that the initial eccentricity is ≤0.1mm; S3: Clamp and fix workpiece B, drive workpiece A to rotate at speed ω, and apply axial pressure to generate heat through friction on the welding surface. S4: Due to its thin wall, the molten ring melts completely before the welding surface. The molten plastic forms a liquid film in the radial gap δ between the cylindrical centering ring and the inner wall of the cavity containing workpiece B. The rotational shearing generates a hydrodynamic pressure effect, applying a restoring force F opposite to the eccentric direction to the rotating workpiece A. r This creates a negative feedback self-correction effect, achieving dynamic coaxiality self-maintenance. S5: The welding surface then melts and the welding is completed. Rotation stops, and axial pressure is maintained to enter the cooling stage. S6: During the cooling process, the molten material solidifies and forms a post-weld coaxiality locking structure with the cylindrical centering ring; S7: After cooling is complete, the cylindrical centering ring fuses workpieces A and B together and forms an inner diameter shaping element.

[0016] Preferably, the rotational speed ω and radial clearance δ in step S3 satisfy the relationship: ω≥k s ·δ 3 / (C·η·D·L 3 The restoring force F mentioned in step S4 r Satisfy: F r =C·η·ω·D·L 3 ·e / δ³, where: k s The equivalent stiffness (N / m) for eccentric lateral force (caused by uneven distribution of frictional contact pressure, k) s ≈λp·A / R, where λ is a correction coefficient, ranging from 0 to 1, p is the axial pressure, A is the weld surface area, R is the radius of rotation of the gap, C is the bearing constant (related to eccentricity), η is the dynamic viscosity of the molten plastic (Pa·s), ω is the rotational speed (rad / s), D is the diameter of the cylindrical centering ring (m), L is the axial length of the cylindrical centering ring (m), e is the eccentricity (m), and δ is the radial clearance (m). Furthermore, the laminar flow condition Re = ρ·v·δ / η < 1000 must be satisfied, where v = ω·D / 2 is the linear velocity, and ρ is the density of the molten plastic. This condition ensures that the molten plastic is in a laminar state within the gap to generate an effective dynamic pressure gradient. Eccentric lateral force equivalent stiffness k s It can be derived from the relation k s The value is estimated by ≈λp·A / R, and its precise value can be obtained through static mechanical calibration tests. The test reproduces the axial clamping condition of the spin-melting process, applies lateral loads in stages, and collects the eccentric offset. The slope is calculated using each set of lateral loads and the corresponding eccentric offset; the slope is the equivalent stiffness ks of the eccentric lateral force, and the correction coefficient λ can be calculated simultaneously. At the same time, the maximum eccentricity is obtained through actual measurement of the deformation during assembly and clamping of workpieces A and B. The maximum lateral eccentricity disturbance force that occurs during the welding process can be calculated as k. s The design must ensure the dynamic pressure restoring force F generated during the welding process. r It is greater than or equal to the maximum lateral eccentricity disturbance force.

[0017] The beneficial effects of this invention are: This invention is the first to apply the principle of hydrodynamic bearings to the field of plastic spin melting. The greater the eccentricity, the higher the liquid film pressure on the narrow gap side, and the resulting restoring force F. r The larger ∝e is, the more the existing "eccentric amplification positive feedback" effect is reversed into a "negative feedback self-correction" effect, reducing the coaxiality deviation after welding by more than 90%.

[0018] This invention requires no external auxiliary tooling. The four stages—rigid pre-alignment before welding, liquid film floating center and thermal difference suppression of overmelting during welding, and sawtooth interlocking after welding to prevent shrinkage and drift—are seamlessly connected in one go.

[0019] This invention innovatively uses a cylindrical centering ring and a molten ring to form the inner diameter shaping element after melting, which completely eliminates the problem of flash and residual glue on the inner wall. The innovative sawtooth interlocking design increases the welding strength by more than 20%. Attached Figure Description

[0020] Figure 1 This is a three-dimensional structural diagram of workpiece A and workpiece B of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of workpiece A and workpiece B of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure of workpiece A and workpiece B during welding according to the present invention; Figure 4 for Figure 3 Enlarged structural diagram at point A in the middle.

[0021] Explanation of reference numerals in the attached drawings: 1-Workpiece A, 2-Workpiece B, 3-Welding surface, 4-Melting ring, 5-Radial gap δ, 6-Liquid film, 7-Micro-serrated texture, 8-Axial guide groove, 9-Cylindrical centering ring. Detailed Implementation

[0022] To enable those skilled in the art to better understand the specific technical solutions, implementation processes, and effects of the present invention, detailed descriptions are provided below in conjunction with specific embodiments. However, it should be noted that these are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the technical concepts and practical guidance described in the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1: ABS plastic roll Material: ABS (melt viscosity η≈200Pa·s, Tg=105°C, density ρ≈1050kg / m³) Structural parameters: outer diameter 200mm, inner diameter 180mm, wall thickness 20mm.

[0024] Workpiece A and workpiece B have corresponding welding surfaces and a wall thickness of 4mm.

[0025] The inner wall of workpiece A has an axially extending cylindrical centering ring with a wall thickness of 0.8 mm and a length of 6 mm, both made of ABS. The outer surface is machined with micro-serrations with a depth of 0.15 mm and a tooth pitch of 0.8 mm, as well as 8 axial guide grooves with a depth of 0.2 mm and a width of 0.8 mm. The ring height of the melting ring is 0.18 mm.

[0026] Workpiece B is partially enlarged near its end to form a receiving cavity that accommodates the cylindrical centering ring. The inner surface of the enlarged cylindrical section of the receiving cavity and the outer surface of the cylindrical centering ring form a radial gap δ=0.20mm.

[0027] Thermal difference compensation: The wall thickness of the weld surface is distributed in a wedge shape with an asymmetrical distribution, and the eccentricity tends to the side. h =4.0mm, opposite side t l =2.5mm, t h / tl =1.6.

[0028] Process parameters: rotation speed ω = 1200 rpm (125.7 rad / s), axial pressure 0.8 MPa. Spin-melting time 10 seconds, including 2 seconds for the molten film centering ring to melt, 8 seconds for the welding surface to melt, and 20 seconds for pressure holding and cooling.

[0029] Example 2: PP plastic roll Material: PP (η≈150Pa·s). Outer diameter 400mm, inner diameter 340mm.

[0030] The molten ring has a height of 0.20 mm, and other specifications are the same as in Example 1. The radial clearance between the molten ring and the inner wall of the second workpiece section is δ = 0.25 mm. Thermal difference compensation t h / tl =1.5. Rotation speed 800 rpm, spin melting for 14 seconds.

[0031] Example 3: PC plastic roll Material: PC (η≈350Pa·s). Outer diameter 100mm, inner diameter 80mm.

[0032] The molten ring has a height of 0.13 mm, and other specifications are the same as in Example 1. The radial clearance between the molten ring and the inner wall of the second workpiece section is δ = 0.15 mm. Thermal difference compensation t h / tl =1.8. Rotation speed 1800rpm, spin melting for 6 seconds.

[0033] Comparative Example 1: Traditional planar butt welding The workpiece is made of the same ABS material as in Example 1, with a plain flat end, no cylindrical centering ring, and no thermal compensation. Initial coaxiality (initial eccentricity 0.05mm) is ensured using conventional external fixtures, and spin welding is performed under the same rotational speed and pressure.

[0034] Comparative Example 2: Cylindrical positioning and guiding spin welding only Using ABS workpieces of the same material as in Example 1, pre-assembly guidance is performed with cylindrical positioning at the ends (initial eccentricity 0.05mm), without molten rings, without thermal differential compensation, and without serrated interlocking.

[0035] The coaxiality of the inner hole, the uniformity of the flash, the tensile strength of the weld, and the residual adhesive on the inner wall of the welded workpiece were inspected using a coordinate measuring machine. The results are shown in the table below:

[0036] Experimental verification showed that in Comparative Examples 1 and 2, the initial eccentricity was significantly amplified by 3.6 to 7.0 times during the spinning process. This was because the increased frictional work on the eccentric side led to overmelting and collapse. However, in Examples 1-3, the post-weld deviation not only did not amplify but actually decreased to 0.02-0.04 mm. This demonstrates that after the molten ring of the present invention melts and forms a liquid film within 2 seconds, according to the Reynolds equation, the hydrodynamic pressure restoring force generated on the narrow gap side (as calculated in Example 1, F)... r The force (≈2420N) is much greater than the eccentric lateral force, successfully turning the "positive feedback" into "negative feedback" and realizing dynamic buoyancy.

[0037] In Example 1, t h / t l The design with a value of 1.6 results in a larger heat capacity on the eccentric side, with a heating rate that is only 62.5% of that on the opposite side. This thermodynamically suppresses excessive melting on the eccentric side, forming a dual mechanical and thermal protection with the liquid film floating core. This improves the uniformity of flash (maximum / minimum ratio) from 2.1-3.5 in the comparative example to 1.12-1.18.

[0038] Test data showed that Comparative Examples 1 and 2 had 0.2-0.8 mm of residual adhesive (burrs rolled in) on the inner wall. However, in Examples 1-3, due to the guidance of the flow groove of the centering ring, the molten material was confined within the gap. After cooling, the micro-serrations (0.15 mm deep) on the outer surface of the centering ring formed a mechanical interlock with the inner wall of the cavity, which not only eliminated the residual adhesive but also increased the welding strength by more than 28% compared to Comparative Example 1, completely solving the coaxiality drift problem caused by cooling shrinkage.

[0039] The present invention has been described in detail above with reference to the embodiments. It should also be noted that the specific technical features described in the above embodiments can be combined and modified in any suitable manner without contradiction. The present invention will not further describe all possible combinations. Furthermore, other variations and combinations based on the various technical features of the present invention should also be considered as part of the content disclosed in this invention and fall within the protection scope of this invention.

Claims

1. A spin-welding structure for plastic workpieces, comprising a workpiece A that rotates at high speed during welding and a workpiece B that is relatively fixed during welding, wherein workpieces A and B each have a structurally complementary mating end; characterized in that, The workpiece A has a welding surface formed by an outer annular end face at the butt joint end; a cylindrical centering ring extending axially outward from the inner wall of the workpiece A, with at least one fusion ring disposed on the outer surface of the cylindrical centering ring near the welding surface of the workpiece A. The workpiece B has a corresponding welding surface formed by the outer annular end face and a receiving cavity for accommodating a cylindrical centering ring. The inner wall of the receiving cavity is locally enlarged near the end to form a radial cavity to accommodate the cylindrical centering ring. The inner surface of the cylindrical surface of the enlarged section of the receiving cavity and the outer surface of the cylindrical centering ring form a radial gap δ. The thickness of the molten ring is much smaller than the wall thickness of the welding surface, so that the molten ring melts completely before the welding surface during the spin welding process. The molten plastic forms a liquid film in the radial gap. The liquid film generates a hydrodynamic pressure effect under the action of rotational shearing, and applies a restoring force opposite to the eccentric direction to the rotating workpiece segment to achieve dynamic coaxial self-holding effect.

2. The spin-welded connection structure according to claim 1, characterized in that, The cylindrical centering ring has a wall thickness of 0.8-1.2 mm, and the end of the cylinder is provided with a 30° guide chamfer and a length of 2 mm to facilitate initial insertion into the cavity. The inlet of the cavity is provided with a 30° guide chamfer and a length of 2 mm to cooperate with the chamfer at the end of the cylinder to guide the insertion.

3. The spin-welded connection structure according to claim 1, characterized in that, The height of the molten ring is 0.13-0.25 mm, the radial gap δ is 0.15 to 0.30 mm, and the radial height of the molten ring is less than the radial gap δ.

4. The spin-welded connection structure according to claim 1, characterized in that, The wall thickness of the welded surface is asymmetrically distributed along the circumference, and the wall thickness of the welded surface on the eccentric side is defined as t. h The sidewall thickness is t l , where t h / t l Between 1.3 and 1.

8.

5. The spin-welded connection structure according to claim 1, characterized in that, The outer surface of the cylindrical centering ring is provided with axial guide grooves evenly distributed along the circumference, the depth of which is 0.1 to 0.3 mm and the width of which is 0.5 to 1.0 mm.

6. The spin-welded connection structure according to claim 1, characterized in that, The outer surface of the cylindrical centering ring is also provided with micro-serrations, the depth of which is 0.1 to 0.2 mm and the tooth pitch is 0.5 to 1.0 mm.

7. The spin-welded connection structure according to claim 1, characterized in that, The matching of the cylindrical centering ring and the receiving cavity provides rigid pre-alignment before welding when the two workpiece sections are joined, so that the initial eccentricity is ≤0.1mm.

8. The spin-welded connection structure according to claim 1, characterized in that, The material of the molten ring is the same as that of the workpiece section or is a compatible thermoplastic. After welding and cooling, the cylindrical centering ring is fused with the workpiece B to form an inner diameter shaping element.

9. A spin-welding method for joining plastic workpieces, employing the joining structure described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Pre-assemble or integrally form the molten ring onto the outer surface of the cylindrical centering ring; S2: Workpiece A and workpiece B are connected to the cavity through a cylindrical centering ring to provide rigid pre-alignment, so that the initial eccentricity is ≤0.1mm; S3: Clamp and fix workpiece B, drive workpiece A to rotate at speed ω, and apply axial pressure to generate heat through friction on the welding surface. S4: Due to its thin wall, the molten ring melts completely before the welding surface. The molten plastic forms a liquid film in the radial gap δ between the cylindrical centering ring and the inner wall of the cavity containing workpiece B. The rotational shearing generates a hydrodynamic pressure effect, applying a restoring force F opposite to the eccentric direction to the rotating workpiece A. r This creates a negative feedback self-correction effect, achieving dynamic coaxiality self-maintenance. S5: The welding surface then melts and the welding is completed. Rotation stops, and axial pressure is maintained to enter the cooling stage. S6: During the cooling process, the molten material solidifies and forms a post-weld coaxiality locking structure with the cylindrical centering ring; S7: After cooling is complete, the cylindrical centering ring fuses workpieces A and B together and forms an inner diameter shaping element.

10. The method according to claim 9, characterized in that, The rotational speed ω and radial clearance δ in step S3 satisfy the following relationship: The restoring force described in step S4 , where k s Where is the equivalent stiffness of the eccentric lateral force (N / m), C is the bearing constant, D is the diameter of the cylindrical centering ring, L is the axial length of the cylindrical centering ring, and e is the eccentricity.

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