Anti-carbonization screw assembly for injection molding machines and injection molding machines

Abstract

This invention relates to the field of injection molding technology and discloses an anti-carbonization screw assembly for injection molding machines and an injection molding machine. The anti-carbonization screw assembly for injection molding machines includes a screw body (1), a screw head (2), and a nozzle assembly (3). The screw body (1) is provided with a feeding section (11), a compression section (12), and a metering section (13) in sequence along the material conveying direction. The compression ratio of the screw body (1) is 2.2-2.4, which is the ratio of the screw groove depth of the feeding section (11) to the screw groove depth of the metering section (13). The screw head (2) is a fully conical structure. The nozzle assembly (3) is an integral molding structure and has a fully conical flow channel inside for molten plastic to pass through. The inner wall of the fully conical flow channel is a single continuous smooth conical surface. This reduces injection residue, eliminates residual dead corners, reduces the risk of carbonization, and improves the product yield.

Description

Technical Field

[0001] This invention relates to the field of injection molding technology, specifically to an anti-carbonization screw assembly for an injection molding machine and an injection molding machine. Background Technology

[0002] Injection molding is one of the main production methods for plastic products. Its core process involves drying plastic particles, which are then conveyed, compressed, and melted by the screw of an injection molding machine, and finally injected into the mold cavity to form the final product. During this process, the purity of the molten plastic directly affects the appearance quality of the product. Especially for electronic and automotive parts with high appearance requirements, "black spot" defects on the product surface are a major cause of scrap.

[0003] In existing technologies, when using high-viscosity plastics (such as PPE materials), the high compression ratio (e.g., 2.5) of the injection screw can lead to excessively high shear heat during melt transport, causing over-melting or even carbonization of the material. The carbides then adhere to the screw surface (see...). Figure 5 and Figure 6 ), the inner wall of the feed tube, and flow channel components such as the nozzle and center nozzle (see Figure 9 Especially the traditional split nozzle and middle nozzle structure (see...). Figure 7 and Figure 8 The joint surfaces of these components have gaps or dead corners, which can easily cause plastic residue to accumulate and form carbides after prolonged heating. These carbides are released with the melt during subsequent injection molding, forming black spots on the product surface (see...). Figure 12 and Figure 13 This results in a persistently high defect rate. Even with cleaning, the effects only last for a short time, severely impacting production efficiency and product quality. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that the injection molding process easily generates carbon deposits, resulting in a high rate of defective products with black spots. This invention provides an anti-carbonization screw assembly and injection molding machine for injection molding machines, which reduces injection residue, eliminates dead zones, reduces the risk of carbonization, and improves the product yield.

[0005] To achieve the above objectives, the present invention provides an anti-carbonization screw assembly for injection molding machines, comprising a screw body, a screw head, and a nozzle assembly, wherein... The screw body is provided with a feeding section, a compression section and a metering section in sequence along the material conveying direction. The compression ratio of the screw body is 2.2-2.4, which is the ratio of the screw groove depth of the feeding section to the screw groove depth of the metering section. The screw head has a fully conical structure; The nozzle assembly is a one-piece molded structure with an internally formed fully conical flow channel for the molten plastic to pass through. The inner wall of the fully conical flow channel is a single, continuous, smooth conical surface.

[0006] Preferably, the compression ratio of the screw body is 2.3.

[0007] Preferably, the screw groove depth of the feeding section is 5.4 mm, and the screw groove depth of the metering section is 2.35 mm.

[0008] Preferably, the length of the screw head is greater than 130mm.

[0009] Preferably, the length of the screw head is 142.88 mm.

[0010] Preferably, the outer conical surface of the screw head matches the inner conical surface of the full conical flow channel of the nozzle assembly, so that at the end of the injection stroke of the injection molding machine, the front end of the screw head can extend into the full conical flow channel of the nozzle assembly.

[0011] Preferably, the screw assembly further includes a check ring and a bushing, and the check ring, bushing, and screw head with a fully conical structure together form the three small parts of the screw.

[0012] Preferably, the inner diameter of the fully conical flow channel of the nozzle assembly gradually decreases from the inlet end to the outlet end without steps or seams.

[0013] A second aspect of the present invention provides an injection molding machine comprising an anti-carbonization screw assembly for injection molding machines as described above.

[0014] Preferably, the anti-carbonization screw assembly of the injection molding machine is used for injection molding high-viscosity PPE plastic materials.

[0015] According to the above technical solution, the screw compression ratio is reduced from the existing technology (e.g., 2.5) to 2.2-2.4, directly reducing the shear strength of the screw on high-viscosity PPE materials. After reducing the compression ratio, the plasticizing process is gentler, the melt temperature rise is reduced, and the breakage or oxidation reaction of plastic molecular chains is suppressed from the source, thus significantly reducing the probability of carbide formation. Furthermore, the screw head is changed to a smooth, full-cone shape, and the nozzle assembly is changed from a split type (nozzle + center nozzle) to a one-piece design, with the internal flow channel being a single, continuous, smooth conical surface. This one-piece structure completely eliminates seams, and the smooth, full-cone inner wall has no steps or abrupt changes, ensuring no stagnation points in the melt flow path. The full-cone screw head and the full-cone flow channel form a linear fit, allowing the screw head to penetrate deeper into the nozzle flow channel at the end of injection, almost completely pushing out any remaining material. This avoids the material remaining in the nozzle for a long time and being heated, completely eliminating the physical breeding ground for carbide formation. Through a triple mechanism of "reducing shear heat, eliminating dead zones in the flow channel, and reducing end residues", the amount of carbides during injection molding is significantly reduced, the defect rate of black spots on the product surface is reduced from about 10% to an extremely low level, and the equipment cleaning cycle is significantly extended, resulting in substantial improvements in both production efficiency and product quality. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the screw compression ratio in the anti-carbonization screw assembly for injection molding machines provided by the present invention; Figure 2 This is a schematic diagram of the screw body in the anti-carbonization screw assembly for injection molding machines provided by the present invention; Figure 3 This is a schematic diagram of the screw head structure in the anti-carbonization screw assembly for injection molding machines provided by the present invention; Figure 4 This is a schematic diagram of the nozzle assembly in the anti-carbonization screw assembly for injection molding machines provided by the present invention; Figure 5 This is an enlarged view of the carbide coating on the screw surface present in existing technology; Figure 6 This is a schematic diagram of the carbide coating on the screw surface present in the prior art; Figure 7 This is a schematic diagram of the structure of a split nozzle and a middle nozzle in the existing technology; Figure 8 This is a schematic diagram of the combination of a split nozzle and a middle nozzle in the existing technology; Figure 9 This is a schematic diagram of the carbide coating on the surface of the nozzle in existing technology; Figure 10 This is a schematic diagram of the assembly of the three small screw components; Figure 11 This is a schematic diagram of the three small parts of the screw assembly; Figure 12 This is an illustration of black spots appearing on injection-molded finished products in existing technology. Figure 1 ; Figure 13 This is an illustration of black spots appearing on injection-molded finished products in existing technology. Figure 2 .

[0017] Explanation of reference numerals in the attached figures 1-Screw body, 2-Screw head, 3-Nozzle assembly, 11-Feeding section, 12-Compression section, 13-Metering section. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] In this invention, unless otherwise stated, directional terms such as "internal," "entry end," and "exit end" in the terminology only represent the orientation of the term in its normal use or are common terms understood by those skilled in the art, and should not be regarded as limitations on the term.

[0020] See Figures 1 to 4 This invention provides an anti-carbonization screw assembly for injection molding machines, comprising a screw body 1, a screw head 2, and a nozzle assembly 3, wherein... The screw body 1 is provided with a feeding section 11, a compression section 12 and a metering section 13 in sequence along the material conveying direction. The compression ratio of the screw body 1 is 2.2-2.4, which is the ratio of the screw groove depth of the feeding section 11 to the screw groove depth of the metering section 13. Screw head 2 has a fully conical structure; The nozzle assembly 3 is a one-piece molded structure with a fully conical flow channel inside for the molten plastic to pass through. The inner wall of the fully conical flow channel is a single continuous smooth conical surface.

[0021] Through the above technical solutions, the screw compression ratio is reduced from the existing technology (e.g., 2.5) to 2.2-2.4, directly reducing the shear strength of the screw on high-viscosity PPE materials. Lowering the compression ratio results in a gentler plasticizing process and a smaller increase in melt temperature, inhibiting the breakage or oxidation of plastic molecular chains at the source, thus significantly reducing the probability of carbide formation. Furthermore, the screw head 2 is changed to a smooth, full-conical shape, and the nozzle assembly 3 is changed from a split type (nozzle + center nozzle) to a one-piece design, with the internal flow channel being a single, continuous, smooth conical surface. This one-piece structure completely eliminates seams, and the smooth, full-conical inner wall has no steps or abrupt changes, ensuring a smooth melt flow path without stagnation points. The full-conical screw head 2 and the full-conical flow channel form a linear fit, allowing the screw head 2 to penetrate deeper into the nozzle flow channel at the end of injection, almost completely pushing out any remaining material. This avoids the material remaining in the nozzle for a long time and being heated, completely eliminating the physical breeding ground for carbide formation. Through a triple mechanism of "reducing shear heat, eliminating dead zones in the flow channel, and reducing end residues", the amount of carbides during injection molding is significantly reduced, the defect rate of black spots on the product surface is reduced from about 10% to an extremely low level, and the equipment cleaning cycle is significantly extended, resulting in substantial improvements in both production efficiency and product quality.

[0022] A compression ratio of 2.5 generates excessive shear heat for high-viscosity materials such as PPE, leading to over-melting, decomposition, and carbonization, resulting in a black spot defect rate of approximately 10%. If the compression ratio is too low (e.g., 2.0), although the shear heat is lower, it may lead to insufficient compaction of plastic particles, inadequate gas expulsion, and uneven melt density, thus affecting the mechanical properties and dimensional stability of the product. Therefore, to achieve the optimal balance between suppressing carbonization of high-viscosity materials and ensuring plasticization quality, a compression ratio of 2.3 for the screw body 1 is preferred. With a compression ratio reduced to 2.3, the shear force and temperature rise are significantly reduced, the melt temperature is controlled below the material's thermal decomposition temperature, and the amount of carbonaceous material generated is greatly reduced, solving the black spot problem at its source. Simultaneously, a compression ratio of 2.3 still provides sufficient compaction and shearing action, allowing the PPE material to fully melt and mix uniformly, establishing a stable injection back pressure, ensuring a dense product structure, no pores, and meeting strength requirements.

[0023] In this embodiment, the preferred screw groove depth of the feeding section 11 is 5.4 mm, and the screw groove depth of the metering section 13 is 2.35 mm. The 5.4 mm depth is smaller than the 6.25 mm depth in the prior art, resulting in stronger constraint and thrust on solid particles, preventing slippage or uneven conveying, and ensuring stable material entry into the compression section. Simultaneously, the slightly shallower screw groove allows particles to begin initial compression at the end of the feeding section, reducing sudden load changes in the compression section, making the melting process smoother, and avoiding localized severe frictional heating. The shallower 2.35 mm screw groove allows the melt to experience stronger shearing action as it passes through the metering section, which is beneficial for the uniform dispersion of various additives and improves melt homogeneity. Furthermore, the shallow screw groove can establish a more stable and higher melt pressure, ensuring timely and accurate pressure transmission during screw advancement in the injection stage, reducing injection fluctuations, and improving product dimensional accuracy. In this way, through precise screw groove depth design, a low-shear, smooth-transition plasticizing process is achieved, while ensuring good conveying efficiency, mixing effect, and pressure stability. This represents the optimal geometric match for high-viscosity PPE materials at a compression ratio of 2.3. Together, these factors ensure a significant reduction in carbides and a substantial decrease in the product's black spot defect rate.

[0024] In existing technologies, the screw head is relatively short, and at the end of the injection stroke, the tip of the screw head cannot penetrate deeply into the nozzle, resulting in a large amount of molten plastic remaining in the cavity between the nozzle and the screw head. This residual material is repeatedly heated during each molding cycle, making it highly susceptible to carbonization and the formation of black spots. To address this issue, in this embodiment, the length of the screw head 2 is preferably greater than 130 mm. This allows the extended, fully tapered screw head to penetrate deeper into the flow channel of the integrated fully tapered nozzle at the injection completion position, pushing out almost all the melt in the flow channel and reducing the amount of residual material to an extremely low level, physically cutting off the source of material for carbide formation.

[0025] In this embodiment, a screw head 2 length of 142.88 mm is further preferred. This longer, fully tapered screw head provides a smoother taper transition, resulting in a smoother change in the flow channel cross-sectional area as the melt enters the nozzle from the feed tube, avoiding sudden contraction or turbulence that might occur with a short screw head. This, in turn, reduces injection resistance, resulting in smoother melt flow and less additional shear heat generated by flow resistance, further reducing the risk of material overheating and carbonization.

[0026] In traditional injection molding, even with optimized nozzles and screw heads, a cavity still exists between them. After injection, a large amount of melt remains in this cavity, repeatedly heated during each molding cycle, eventually carbonizing. To solve this technical problem, the outer conical surface of the screw head 2 is preferably matched with the inner conical surface of the full-conical flow channel of the nozzle assembly 3. This allows the tip of the screw head 2 to extend into the full-conical flow channel of the nozzle assembly 3 at the end of the injection stroke. Through precise matching of the outer and inner conical surfaces, during injection, the outer surface of the screw head and the inner surface of the nozzle form a complete, smooth, stepless conical flow channel. The melt flows through this area without encountering any obstruction or dead zone, achieving true streamlined flow and completely eliminating the possibility of material carbonization due to retention.

[0027] like Figure 10 and Figure 11 As shown, in this embodiment, the screw assembly also includes a check ring and a separator. The check ring, separator, and the fully conical screw head 2 together form the three small components of the screw. The check ring is a key component behind the screw head. During the injection stage, it moves forward to seal the flow channel, preventing the high-pressure melt from flowing back from the gap between the screw head and the feed tube; during the plasticizing stage, it retracts and opens, allowing the melt to be conveyed forward. After the check ring, the fully conical screw head, and the separator are assembled together, the relative movement surfaces and contact surfaces between the three components must be designed to be smooth and without sharp angles. This ensures that even during the reciprocating motion of the check ring, no additional material retention gaps or excessive shearing hotspots are generated. The separator is usually installed between the check ring and the screw head, serving as a limiter, support, and separator, preventing the check ring from directly impacting the screw head step. The introduction of the separator makes the movement stroke of the check ring controllable and stable, avoiding uneven gaps or new dead angles caused by impact deformation. Meanwhile, the surface of the separator itself is also designed to be smooth and without sharp edges, ensuring that its mating surfaces with the screw head and check ring will not become material accumulation points. The axial dimension chain of the fully tapered screw head, separator, and check ring has been optimized to ensure a smooth transition of the entire front end profile after assembly.

[0028] In existing technologies, seams inevitably exist at the junction of the split nozzle and the central nozzle. Furthermore, multiple tapered chamfers designed to accommodate different functions create steps within the flow channel. These seams and steps result in high flow resistance and slow flow velocity, causing some material to stagnate and gradually carbonize under sustained high temperatures. In this embodiment, the nozzle assembly 3 preferably features a fully conical flow channel with a gradually decreasing inner diameter from the inlet to the outlet, free of steps or seams. This eliminates any gaps that could trap material and any steps that could obstruct its flow. As the melt passes through, each part is in motion, completely eliminating localized carbonization caused by physical structural defects. Simultaneously, the smooth, abrupt melt flow path avoids turbulence, eddies, and additional friction caused by sudden channel contraction or expansion. This significantly reduces shear stress and flow resistance as the melt flows through the nozzle, thereby reducing temperature rise due to flow friction and further suppressing the risk of material overheating and decomposition. Moreover, even after long-term production, the smooth, continuous fully conical inner wall is easily cleaned. Operators can simply wipe or use cleaning materials to restore the inner wall to cleanliness, without the need for disassembly or the use of special tools to treat stubborn carbon deposits at the joints, significantly shortening equipment maintenance time.

[0029] On the other hand, the present invention also provides an injection molding machine, which includes the anti-carbonization screw assembly for injection molding machines as described above. Furthermore, this anti-carbonization screw assembly for injection molding machines is used for injection molding high-viscosity PPE plastic materials. PPE is an engineering plastic with high viscosity and high heat resistance, but relatively poor thermal stability. Its molecular chains are rigid, resulting in poor flowability after melting. It is extremely sensitive to shear heat and readily undergoes oxidative cross-linking or degradation at high temperatures, generating yellow or black carbonization points. The screw assembly of this injection molding machine is not only specifically designed with a low compression ratio to address the high viscosity characteristics of PPE, reducing shear heat and preventing the melt temperature from exceeding its thermal decomposition threshold, but its fully conical, dead-angle-free flow channel also prevents the PPE melt from undergoing thermal oxidative cross-linking due to prolonged heating in stagnant areas. Simultaneously, the use of an integrated nozzle and an extended screw head ensures minimal PPE residue after each injection, reducing the time it is repeatedly heated within the high-temperature nozzle. Ultimately, this injection molding machine can achieve clean and stable injection molding of high-viscosity materials such as PPE, solving the long-standing industry pain point of high scrap rate of PPE products with black spots, and greatly expanding the material adaptability range of the injection molding machine.

[0030] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A carbonization-resistant screw assembly for an injection molding machine, characterized in that, The anti-carbonization screw assembly for injection molding machines includes a screw body (1), a screw head (2), and a nozzle assembly (3), wherein, The screw body (1) is provided with a feeding section (11), a compression section (12) and a metering section (13) in sequence along the material conveying direction. The compression ratio of the screw body (1) is 2.2-2.

4. The compression ratio is the ratio of the screw groove depth of the feeding section (11) to the screw groove depth of the metering section (13). The screw head (2) has a fully conical structure; The nozzle assembly (3) is a one-piece molded structure and has a fully conical flow channel inside for molten plastic to pass through. The inner wall of the fully conical flow channel is a single continuous smooth conical surface.

2. The anti-carbonization screw assembly for injection molding machines according to claim 1, characterized in that, The compression ratio of the screw body (1) is 2.

3.

3. The anti-carbonization screw assembly for injection molding machines according to claim 2, characterized in that, The screw groove depth of the feeding section (11) is 5.4 mm, and the screw groove depth of the metering section (13) is 2.35 mm.

4. The anti-carbonization screw assembly for injection molding machines according to claim 1, characterized in that, The length of the screw head (2) is greater than 130mm.

5. The anti-carbonization screw assembly for injection molding machines according to claim 4, characterized in that, The length of the screw head (2) is 142.88 mm.

6. The anti-carbonization screw assembly for injection molding machines according to claim 1, characterized in that, The outer conical surface of the screw head (2) matches the inner conical surface of the full conical flow channel of the nozzle assembly (3) so that at the end of the injection stroke of the injection molding machine, the front end of the screw head (2) can extend into the full conical flow channel of the nozzle assembly (3).

7. The anti-carbonization screw assembly for injection molding machines according to claim 1, characterized in that, The screw assembly also includes a check ring and a mesmer. The check ring, the mesmer, and the screw head (2) with the full conical structure together form the three small parts of the screw.

8. The anti-carbonization screw assembly for injection molding machines according to claim 1, characterized in that, The nozzle assembly (3) has a fully conical flow channel with an inner diameter that gradually decreases from the inlet end to the outlet end and has no steps or seams.

9. An injection molding machine, characterized in that, The injection molding machine includes an anti-carbonization screw assembly for injection molding machines as described in any one of claims 1-8.

10. The injection molding machine according to claim 9, characterized in that, The anti-carbonization screw assembly for injection molding machines is used for injection molding high-viscosity PPE plastic materials.

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