A thick-walled nitrogen physical foaming core-pulling mold and a using process thereof

Abstract

The present application provides a kind of thick wall nitrogen physical foaming core-pulling mould and its using process, the mould includes the mould body with cavity, the feed end being communicated with cavity and the core-pulling mechanism being movably arranged on mould body, and the core-pulling core of core-pulling mechanism constitutes the side wall of cavity.The present application controls the core-pulling core to move from first position to second position by core-pulling mechanism after injection melt is filled to preset proportion, dynamically expands cavity volume and cooperates cavity pressure gradient release, guides supercritical nitrogen to uniformly nucleate and grow in mutual solution melt.Solve the quality defects of large bubble and uneven cell in nitrogen foaming process in thick wall plastic product in prior art, realize the accurate regulation of cavity volume by inclined plane transmission type core-pulling structure, and the weight reduction ratio of thick wall product is stably improved from 30%-40% to 50%-60% compared with traditional method, while the mechanical properties and structural integrity of product under high weight reduction are guaranteed, and it is suitable for batch production of thick wall products in various fields.

Description

Technical Field

[0001] This invention relates to the field of mold technology, and more specifically, to a thick-walled nitrogen physical foaming core-pulling mold and its application process. Background Technology

[0002] Currently, conventional thick-walled plastic products (wall thickness ≥ 15mm) are mostly formed by nitrogen physical foaming using a fixed mold cavity structure. In the traditional fixed cavity, due to the large melt thickness and long heat and mass transfer path of thick-walled products, the pressure inside the mold cavity is not released evenly during depressurization foaming. The surface melt cools and solidifies rapidly, and the nitrogen inside cannot diffuse evenly, which easily leads to local nitrogen accumulation, cell merging and rupture, and finally the formation of large bubbles. Moreover, the foaming weight loss rate can only reach 20%-30%.

[0003] In view of this, the applicant hereby submits this application after studying the existing technology. Summary of the Invention

[0004] This invention provides a thick-walled nitrogen physical foaming core-pulling mold and its application process, aiming to improve at least one of the above-mentioned technical problems.

[0005] To solve the above-mentioned technical problems, the present invention provides a thick-walled nitrogen physical foaming core-pulling mold for molding thick-walled plastic foam products, comprising:

[0006] A mold body having a cavity for molding the thick-walled plastic foam product; The feeding end is connected to the cavity and is used to inject a miscible melt of molten plastic and supercritical nitrogen into the cavity. A core-pulling mechanism is movably mounted on the mold body and is equipped with a core-pulling core, one end of which is used to form one side wall of the cavity. The core-pulling mechanism is configured such that, after the injection-molded miscible melt fills the cavity to a preset ratio, the core-pulling core is controlled to move from a first position to a second position, thereby dynamically expanding the volume of the cavity. In conjunction with the pressure release within the cavity, this guides supercritical nitrogen gas to uniformly nucleate and grow in the miscible melt.

[0007] As a further optimization, the core-pulling mechanism includes a core, a core-pulling drive component, a core mounting assembly, and a sliding seat. The core is mounted on the upper end of the core mounting assembly, and the core mounting assembly is slidably connected to the sliding seat. The core-pulling drive component is driven by the sliding seat and is used to drive the sliding seat to move laterally at the bottom of the core mounting assembly. The core mounting assembly is configured to be vertically movable within the mold body.

[0008] As a further optimization, the upper end of the sliding seat is constructed with a guide slope, which gradually decreases from one end near the core pulling drive component to the other end; the bottom end of the core mounting assembly is adapted to slide and connect with the guide slope.

[0009] As a further optimization, the mold body includes a guide plate, the guide plate is provided with a through groove running vertically through the top and bottom, and the core-pulling core is adapted to slide and connect with the through groove.

[0010] As a further optimization, when the core-pulling drive component drives the sliding seat to pull out the mold body laterally, it can drive the core-pulling element to descend, wherein the ratio of the lateral pulling distance of the sliding seat to the descent stroke of the core-pulling element is 20:1.

[0011] As a further optimization, a guide groove is provided inside the mold body, the guide groove extends along the output direction of the core pulling drive component, and the sliding seat is slidably connected to the guide groove.

[0012] As a further optimization, a moving positioning module is provided between the sliding seat and the mold body.

[0013] The present invention also provides a process for using the mold described in any of the above claims, comprising the following steps: S1 Mold Closure: After the main body of the mold is closed, the core-pulling core is located in the first position and forms a cavity for the thick-walled plastic foam product with the mold core; S2 Injection: First, high-pressure nitrogen is injected into the injection molding machine barrel. Under high temperature and high pressure conditions, nitrogen forms a supercritical fluid state and fully dissolves with the molten plastic to form a homogeneous plastic-nitrogen single-phase system of miscible melt, which is then injected into the cavity. S3 Linkage Core Pulling: When the mutually soluble melt fills the cavity to a preset ratio value, the core is controlled to move from the first position to the second position, dynamically expanding the cavity volume so that the pressure in the cavity is released in a gradient, triggering the expansion and growth of nitrogen gas nuclei in the supercritical fluid state, and uniformly forming micro-bubble nuclei in the molten plastic. S4 Cooling and Shaping: Keep the core in the second position and cool the mold body to solidify and shape the foamed product; S5 Mold Opening: Open the mold body and eject the formed thick-walled plastic foam product.

[0014] As a further optimization, in step S2, the supercritical nitrogen pressure when nitrogen is injected into the injection molding machine barrel is 15.4 MPa, and the nitrogen accounts for 0.2%-0.5% of the total mass of the miscible melt.

[0015] As a further optimization, in step S3, the core is pulled out in conjunction with the filling when the mutually soluble melt fills 98% of the cavity volume.

[0016] By adopting the above technical solution, the present invention can achieve the following technical effects: 1. Significantly improved weight reduction ratio: Compared with the traditional fixed cavity foaming technology with a weight reduction limit of 30%-40%, this invention achieves a stable high weight reduction ratio of 50%-60% by dynamically expanding the cavity volume, with a maximum weight reduction of up to 60.21%, which significantly reduces the material cost and weight of thick-walled products.

[0017] 2. Significantly improved cell quality: Through precise linkage between the core-pulling action and the foaming process, the pressure inside the cavity is released in a gradient, guiding nitrogen molecules to nucleate and grow uniformly throughout the thick-walled melt. This solves the industry problem of large bubbles and cell merging in the central area of ​​thick-walled products, resulting in uniform and fine cells in the product and greatly improving the yield rate.

[0018] 3. Balancing mechanical properties and weight reduction: The uniform and dense microporous structure achieves significant weight reduction while preserving the mechanical properties of the plastic matrix. The product's bending strength and impact strength are improved compared to traditional foamed products, avoiding the problems of insufficient product strength and structural deformation under high weight reduction.

[0019] 4. Precise and controllable cavity volume: The 20:1 inclined plane transmission ratio is adopted to convert the large lateral stroke of the sliding seat into the small vertical stroke of the core pulling, realizing precise control of the cavity volume. By adjusting the core pulling stroke, the weight reduction ratio of the product can be precisely controlled within the range of 22%-60%, meeting the lightweight requirements of different products. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the thick-walled nitrogen physical foaming core-pulling mold of the present invention; Figure 2 This is a schematic cross-sectional view of the thick-walled nitrogen physical foaming core-pulling mold of the present invention; Figure 3 This is a schematic diagram of the cavity structure when the core is not removed according to the present invention; Figure 4 This is a schematic diagram of the cavity structure during core pulling in this invention; Figure 5 This is a schematic diagram of the core-pulling mechanism of the present invention; Figure 6 This is an exploded structural diagram of the core-pulling mechanism of the present invention; Figure 7 This is a comparison chart of the weight reduction ratio and bubble defects of products in various embodiments of the present invention; The markings in the diagram are: 1-panel, 2-hot runner plate, 3-A plate, 4-B plate, 5-mold foot, 6-core pulling mechanism, 7-base plate, 8-core pulling cylinder, 9-core pulling core, 10-moving positioning module, 11-front mold core, 12-rear mold core, 13-sliding seat, 14-guide slope, 15-cavity, 16-sliding block, 17-connecting seat, 18-mounting seat; 19-guide groove. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] Example 1 like Figure 1-7 As shown, a thick-walled nitrogen physical foaming core-pulling mold of the present invention includes a mold body, a feeding end and a core-pulling mechanism 6.

[0024] The mold body, from top to bottom, includes a panel 1, a hot runner plate 2, an A plate 3, a B plate 4, mold feet 5, and a base plate 7. A front mold core 11 and a rear mold core 12 are located between A plate 3 and B plate 4. The upper end face of the core-pulling piece 9, together with the front mold core 11 and the rear mold core 12, forms a cavity 15 for molding 16mm thick-walled PP square strip products. In this embodiment, B plate 4 also serves as a guide plate, with a through groove running vertically through it. The core-pulling piece 9 is slidably connected to the through groove, thus allowing it to move only vertically. A plate 3 is the front mold plate, also known as the fixed mold plate, connected to the feed end (gate) on panel 1. B plate 4 is the rear mold plate, also known as the moving mold plate, capable of opening and closing. The structural functions of these mold bodies are existing technology and will not be elaborated upon here.

[0025] The core-pulling mechanism 6 is located inside the mold body and above the base plate 7, and includes a core 9, a core-pulling drive component, a core mounting assembly, and a sliding seat 13. In this embodiment, the core-pulling drive component is a core-pulling cylinder 8, which is located outside the mold body. The core mounting assembly includes a sliding block 16, a connecting seat 17, and a mounting seat 18 from bottom to top, and the three are fixedly connected by bolts. The mounting seat 18 is provided with multiple mounting slots, and the core 9 is fixed in the mounting slots by fitting and limiting. The upper end of the sliding seat 13 is constructed with a guide slope 14, which gradually decreases from one end near the core-pulling cylinder 8 to the other end. The guide slope 14 is concave to form a groove, and the sliding block 16 is adapted to slide and connect with the groove portion of the guide slope 14. The retraction of the core-pulling cylinder 8 pulls the sliding seat 13 outward. Since the core mounting assembly is limited laterally, it can only move vertically. Therefore, the support surface of the guide ramp 14 for the core mounting assembly gradually decreases, causing the core mounting assembly to gradually lower the core 9. In one embodiment, the inclination angle of the guide ramp 14 is 2.86°, corresponding to a ratio of 20:1 between the lateral extension distance of the sliding seat and the descent stroke of the core. This angle design balances transmission efficiency and self-locking performance, ensuring the core position remains stable during the core-pulling process.

[0026] Preferably, a guide groove 19 is provided inside the mold body, extending along the output direction of the core-pulling cylinder 8. The sliding seat 13 is slidably connected to the guide groove 19. A moving positioning module 10 (or a core-pulling limiting mechanism) is provided between the sliding seat 13 and the mold body. The moving positioning module adopts an adjustable limiting block structure, which can precisely adjust the descent stroke of the core within a range of 5-11mm, thereby realizing the production of products with different weight reduction ratios. There are various positioning methods, which will not be elaborated here. The core-pulling cylinder 8 is connected to the sliding seat 13 through a connecting piece, providing a stable driving force for the core-pulling action.

[0027] The process of using the thick-walled nitrogen physical foaming core-pulling mold in this embodiment includes the following steps: S1 Mold Closure: After the main body of the mold is closed, the core-pulling cylinder 8 is in the extended state, the sliding seat 13 is in the innermost position, and the core-pulling core 9 is in the first position (highest position). Its upper end face, together with the front mold core 11 and the rear mold core 12, forms a 16mm thick product cavity 15. The cavity 15 is sealed and the pressure is uniform.

[0028] S2 Injection: High-pressure nitrogen gas at 15.4 MPa is injected into the injection molding machine barrel (not shown in the figure). Under high temperature conditions of 210℃, the nitrogen gas forms a supercritical fluid state and is fully miscible with the molten PP raw material to form a homogeneous "plastic-nitrogen" single-phase system of miscible melt. Nitrogen accounts for 0.3% of the total mass of the miscible melt. The miscible melt is then injected into the cavity 15 from the feed end through the hot runner system.

[0029] S3 Linkage Core Pulling: When the mutually fused melt fills 98% of the cavity 15 volume, the injection molding machine sends a signal to the core pulling cylinder 8. The core pulling cylinder 8 begins to slowly retract, driving the sliding seat 13 to move laterally outward along the guide groove 19. The guide slope 14 of the sliding seat 13 cooperates with the sliding block 16 to convert the lateral movement of the sliding seat 13 into the vertical descent movement of the core mounting assembly and the core pulling core 9. The core pulling core 9 moves from the first position to the second position, with a core pulling stroke of 7mm, corresponding to a lateral withdrawal distance of 140mm for the sliding seat.

[0030] The dynamic descent of the core-pulling element 9 expands the overall volume of the cavity 15, allowing the pressure within the cavity 15 to be gradually released from 8.025 MPa to 10.33 MPa without any pressure holding action. This slow, gradual pressure release triggers uniform nucleation of nitrogen molecules in the supercritical melt. The core-pulling action simultaneously optimizes the stress distribution within the melt, breaking down the mass transfer barriers of the thick-walled melt. This enables nitrogen molecules to uniformly form microbubble nuclei throughout the entire 16 mm thick melt, effectively preventing the formation of large bubbles due to localized nitrogen accumulation.

[0031] S4 Cooling and Shaping: After the core puller 9 reaches the preset stroke, it remains in the second position. The mold temperature control system continues to cool the mold, maintaining the mold temperature at 15℃ for 45 seconds. During the cooling process, micro-cells continue to grow within the stable cavity 15 space, and the cell walls gradually solidify as the plastic melt cools, ultimately forming a microporous foam structure with uniform pore size and dense structure.

[0032] S5 Mold Opening: After the product has completely cooled and solidified, the mold is opened, the core-pulling cylinder 8 extends and drives the sliding seat 13 to reset, the core-pulling core 9 returns to the first position, and at the same time the ejection mechanism ejects the molded thick-walled foam block product, completing the entire molding cycle.

[0033] The 16mm thick-walled PP square strip product produced using the mold and process described in this embodiment achieves a 55% weight reduction, no large air bubbles in the product cross-section, an average cell diameter of 50-100μm, and a cell density of 10. 8 -10 9 The product has a density of [number] pieces per cm³, a smooth appearance without shrinkage marks, a flexural strength of 25 MPa, and an impact strength of 5 kJ / m², with all performance indicators meeting quality standards. Compared to traditional fixed-cavity foamed products, the weight reduction ratio of this embodiment is increased by 37.5%, the flexural strength by 22%, and the impact strength by 25%.

[0034] Example 2 The difference between this embodiment and Embodiment 1 is that the core-pulling stroke is set to 5mm, corresponding to a lateral pulling distance of 100mm for the sliding seat. All other process parameters are exactly the same as in Embodiment 1.

[0035] The product produced using the mold and process of this comparative example achieved a final weight reduction of 35.4%. The bubbles in the gate area and the middle weld position were basically uniform, but there were still a few bubbles with a diameter of 2-3mm at the end position. This result indicates that when the core pulling stroke is insufficient, the volume expansion of cavity 15 is limited, and the nitrogen pressure cannot be fully released. Not only is it difficult to exceed 40% in weight reduction, but some bubble defects will still remain.

[0036] Example 3 The difference between this embodiment and Embodiment 1 is that the core-pulling stroke is 9mm, corresponding to a lateral pulling distance of 180mm for the sliding seat. Other process parameters are the same as in Embodiment 1.

[0037] The product manufactured using the mold and process described in this embodiment achieves a final weight reduction of 51.4%. The product exhibits excellent foaming properties, with uniform and fine bubbles in the gate area, intermediate weld points, and end positions, free from large air bubble defects. By adjusting the core-pulling stroke, the weight reduction ratio can be flexibly controlled to meet the weight and strength requirements of different application scenarios.

[0038] Example 4 The difference between this embodiment and Embodiment 1 is that the core-pulling stroke is 11mm, corresponding to a lateral pulling distance of 220mm for the sliding seat. Other process parameters are the same as in Embodiment 1.

[0039] The product manufactured using the mold and process described in this embodiment achieved a final weight reduction of 60.21%. The product exhibited good foaming properties, with only a small number of tiny air bubbles less than 1 mm in diameter appearing at the ends. Overall quality met the requirements. This invention achieves an ultra-high weight reduction of over 60% for thick-walled products, breaking through industry technical bottlenecks.

[0040] Comparative Example 1 This comparative example uses a traditional fixed-cavity mold without core pulling to produce products of the same specifications, and other process parameters are the same as in Example 1.

[0041] The product manufactured using the mold and process described in this comparative example had a final weight reduction of only 22%. The product's gate area, intermediate weld points, and end points all showed obvious large air bubbles with a diameter greater than 5 mm and uneven cell structure. The product's bending strength was only 18 MPa, and its impact strength was only 3.5 kJ / m². The product quality was substandard.

[0042] As can be seen from the above embodiments and comparative examples, this invention, through the deep synergy between the inclined plane transmission core-pulling mechanism and the nitrogen foaming process, successfully achieves a stable and high weight reduction of 50%-60% for block products with thick walls of 15mm and above. Simultaneously, it completely solves the quality defects of large air bubbles and uneven cell structure, significantly improving the product's mechanical properties and structural stability. The technical solution of this invention not only solves a long-standing technical problem in the industry but also provides new ideas and methods for lightweight design of thick-walled products.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A thick-walled nitrogen physical foaming core-pulling mold for molding thick-walled plastic foam products, characterized in that, include: A mold body having a cavity for molding the thick-walled plastic foam product; The feeding end is connected to the cavity and is used to inject a miscible melt of molten plastic and supercritical nitrogen into the cavity. A core-pulling mechanism is movably mounted on the mold body and is equipped with a core-pulling core, one end of which is used to form one side wall of the cavity. The core-pulling mechanism is configured such that, after the injection-molded miscible melt fills the cavity to a preset ratio, the core-pulling core is controlled to move from a first position to a second position, thereby dynamically expanding the volume of the cavity. In conjunction with the pressure release within the cavity, this guides supercritical nitrogen gas to uniformly nucleate and grow in the miscible melt.

2. The thick-walled nitrogen physical foaming core-pulling mold according to claim 1, characterized in that... The core-pulling mechanism includes a core, a core-pulling drive component, a core mounting assembly, and a sliding seat. The core is mounted on the upper end of the core mounting assembly, and the core mounting assembly is slidably connected to the sliding seat. The core-pulling drive component is driven by the sliding seat and is used to drive the sliding seat to move laterally at the bottom of the core mounting assembly. The core mounting assembly is configured to be vertically movable within the mold body.

3. The thick-walled nitrogen physical foaming core-pulling mold according to claim 2, characterized in that... The upper end of the sliding seat is provided with a guide slope, which gradually decreases from one end near the core pulling drive component to the other end; the bottom end of the core mounting assembly is adapted to slide and connect with the guide slope.

4. The thick-walled nitrogen physical foaming core-pulling mold according to claim 3, characterized in that... The mold body includes a guide plate, which has a through groove running vertically through the mold. The core-pulling core is adapted to slide and connect with the through groove.

5. The thick-walled nitrogen physical foaming core-pulling mold according to claim 4, characterized in that... When the core-pulling drive component drives the sliding seat to pull out the mold body laterally, it can drive the core-pulling part to descend. The ratio of the lateral pulling distance of the sliding seat to the descent stroke of the core-pulling part is 20:

1.

6. The thick-walled nitrogen physical foaming core-pulling mold according to claim 2, characterized in that... The mold body is provided with a guide groove, which extends along the output direction of the core pulling drive component, and the sliding seat is slidably connected to the guide groove.

7. The thick-walled nitrogen physical foaming core-pulling mold according to claim 3, characterized in that... A moving positioning module is provided between the sliding seat and the mold body.

8. A process for using the mold according to any one of claims 1-6, characterized in that... This includes the following steps: S1 Mold Closure: After the main body of the mold is closed, the core-pulling core is located in the first position and forms a cavity for the thick-walled plastic foam product with the mold core; S2 Injection: First, high-pressure nitrogen is injected into the injection molding machine barrel. Under high temperature and high pressure conditions, nitrogen forms a supercritical fluid state and fully dissolves with the molten plastic to form a homogeneous plastic-nitrogen single-phase system of miscible melt, which is then injected into the cavity. S3 Linkage Core Pulling: When the mutually soluble melt fills the cavity to a preset ratio value, the core is controlled to move from the first position to the second position, dynamically expanding the cavity volume so that the pressure in the cavity is released in a gradient, triggering the expansion and growth of nitrogen gas nuclei in the supercritical fluid state, and uniformly forming micro-bubble nuclei in the molten plastic. S4 Cooling and Shaping: Keep the core in the second position and cool the mold body to solidify and shape the foamed product; S5 Mold Opening: Open the mold body and eject the formed thick-walled plastic foam product.

9. The application process according to claim 8, characterized in that... In step S2, the supercritical nitrogen pressure when nitrogen is injected into the injection molding machine barrel is 15.4 MPa, and the nitrogen accounts for 0.2%-0.5% of the total mass of the miscible melt.

10. The application process according to claim 8, characterized in that... In step S3, the core is pulled out when the mutually soluble melt fills 98% of the cavity volume.

Images