Special mold for low-sag thick-wall polyethylene pipe
By setting concave and convex parts on the mandrel and combining them with low-temperature module pre-cooling, the problem of uneven wall thickness of thick-walled polyethylene pipes was solved, production efficiency and cost were optimized, and the uniformity and quality of the pipes were ensured.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- HANGZHOU BAND MUNICIPAL PLASTIC PIPE CO LTD
- Filing Date
- 2025-04-26
- Publication Date
- 2026-04-17
AI Technical Summary
During the extrusion molding of thick-walled polyethylene pipes, the wall thickness becomes uneven due to the sag of the melt under its own weight. Traditional solutions affect production efficiency and cost, and traditional molds are difficult to compensate for the differences in the flow of raw material melt.
By setting concave and convex parts on the mandrel, the concave parts reduce the extrusion resistance in the loss area, while the convex parts increase the extrusion resistance in the accumulation area. Combined with pre-cooling by a low-temperature module, the raw material flow path is optimized and the melt distribution is balanced.
It achieves uniform pipe wall thickness, reduces scrap rate and production costs, expands the application range of molds, and ensures mechanical properties and appearance quality.
Smart Images
Figure CN224130416U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of mold technology, specifically a special mold for low melt sag thick-walled polyethylene pipes. Background Technology
[0002] When extruding thick-walled polyethylene pipes with a wall thickness ≥20mm, uneven wall thickness and sag occur due to the sag caused by the weight of the melt, especially in the lower half of the pipe where the wall thickness is significantly greater than that of the upper half, affecting product quality. Traditional solutions include lowering the extrusion temperature, increasing the cooling rate, or using low-sag raw materials, but these can easily lead to increased internal stress in the pipe, decreased production efficiency, and increased costs. Traditional molds use mandrels with a uniform structure, which cannot compensate for differences in the flow of the raw material melt, resulting in uneven wall thickness. Moreover, excessively high temperatures at the front end of the mandrel can exacerbate the sag deformation of the raw material melt. Therefore, a special mold for low-sag thick-walled polyethylene pipes is proposed. Utility Model Content
[0003] The main purpose of this utility model is to provide a solution that can effectively address the problems in the background art.
[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows: a special mold for low melt sag thick-walled polyethylene pipes, comprising a mold body, a spiral body disposed within the mold body for conveying and initially diverting raw material melt, an orifice mold connected to the mold body, and a core mold disposed within the orifice mold and connected to the spiral body. The core mold is characterized by having at least one concave portion and one convex portion. The concave portion corresponds to the area with the most raw material melt loss, and the convex portion corresponds to the area with the most raw material melt accumulation. The area between the area with the most raw material melt loss and the area with the most raw material melt accumulation is a normal area. A low-temperature module for pre-cooling is provided at the discharge end of the core mold.
[0005] Preferably, the concave and convex portions are smoothly transitioned to the normal area.
[0006] Preferably, the smooth transition is an arc transition or a sloped transition.
[0007] Preferably, the die is locked to the die body via a pressure ring.
[0008] Preferably, a silicone sheet is provided between the low-temperature module and the core mold to mitigate the conduction of high temperature in the direction of the core mold feed end.
[0009] Preferably, the low-temperature module can be cooled by oil, water, or high-temperature semiconductor cooling.
[0010] This invention has the following advantages: By setting concave and convex portions on the mandrel, the concave portions reduce the extrusion resistance in the raw material melt loss area, thereby increasing the extrusion amount of raw material melt and compensating for the loss due to high sag. The convex portions increase the extrusion resistance in the raw material melt accumulation area, thereby reducing the extrusion amount of raw material melt. During the sag process, the raw material exceeding the standard wall thickness in the concave portions flows to the normal area, while the raw material melt in the normal area flows to the convex portions, balancing the axial distribution of the raw material melt. Ultimately, this achieves the goal of minimizing material usage while ensuring uniform pipe wall thickness, reducing scrap rate and production costs. Furthermore, by setting a low-temperature module, the material on the inner wall of the pipe is pre-cooled, reducing sag and enabling the mandrel to be applicable to raw materials with different sag properties, thus expanding the applicability of the mandrel.
[0011] By using a smooth transition between the concave and convex parts with arcs or bevels, the flow path of the raw material is optimized, the residence time of the raw material in the mold is reduced, the probability of sag is reduced, thereby reducing stress concentration during the flow of the raw material and ensuring the mechanical properties and appearance quality of the pipe. Attached Figure Description
[0012] Figure 1 This is a schematic diagram of the overall structure of this utility model;
[0013] Figure 2 This is a cross-sectional view of the present invention;
[0014] Figure 3 This is a side view of the core mold of this utility model.
[0015] Legend: 1. Mold body; 2. Spiral body; 3. Mouth mold; 4. Core mold; 41. Recess; 42. Protrusion; 5. Low temperature module; 6. Pressure ring; 7. Silicone sheet. Detailed Implementation
[0016] To make the technical means, creative features, objectives and effects of this utility model easier to understand, the present utility model will be further described below in conjunction with specific embodiments.
[0017] like Figure 1-3As shown, a special mold for low-melting-sag thick-walled polyethylene pipes includes a mold body 1, a spiral 2 disposed within the mold body 1 for conveying and initially diverting the raw material melt, an orifice mold 3 connected to the mold body 1, and a core mold 4 disposed within the orifice mold 3 and connected to the spiral 2. The core mold 4 is characterized by having at least one recess 41 and a protrusion 42. The recess 41 corresponds to the area with the most raw material melt loss, and the protrusion 42 corresponds to the area with the most raw material melt accumulation. The area between the area with the most raw material melt loss and the area with the most raw material melt accumulation is a normal area. A low-temperature module 5 for pre-cooling is provided at the discharge end of the core mold 4. By providing the recess 41 and the protrusion 42 on the core mold 4, the recess... Section 41 reduces the extrusion resistance in the raw material melt loss area, thereby increasing the extrusion amount of raw material melt and compensating for the loss due to high sag. Section 42 increases the extrusion resistance in the raw material melt accumulation area, thereby reducing the extrusion amount of raw material melt. During the sag process, the raw material exceeding the standard wall thickness in the concave section 41 flows to the normal area, while the raw material melt in the normal area flows to the convex section 42, balancing the axial distribution of the raw material melt. Ultimately, this achieves the goal of minimizing material usage while ensuring uniform pipe wall thickness, reducing scrap rate and production costs. By setting the low-temperature module 5, the material on the inner wall of the pipe is pre-cooled, reducing sag and enabling the mandrel 4 to be applicable to raw materials with different sag properties, thus expanding the applicability of the mandrel 4.
[0018] In one embodiment, the concave portion 41, the convex portion 42, and the normal area are smoothly transitioned; the smooth transition is an arc transition or a slope transition; by using an arc or slope smooth transition between the concave portion 41 and the convex portion 42, the flow path of the raw material is optimized, the residence time of the raw material in the mold is reduced, the probability of sag is reduced, thereby reducing stress concentration during the flow of the raw material and ensuring the mechanical properties and appearance quality of the pipe.
[0019] In one embodiment, the die 3 is locked to the die body 1 by a pressure ring 6.
[0020] In one embodiment, a silicone sheet 7 is provided between the low-temperature module 5 and the core mold 4 to reduce the high temperature conduction in the direction of the core mold 4's feed end, thereby isolating the high temperature in the direction of the core mold 4's feed end and ensuring the stability of the low-temperature module 5; the low-temperature module 5 can be cooled by oil, water, or high-temperature resistant semiconductor cooling.
[0021] When this utility model is used, the raw material melt entering the mold body 1 is conveyed and diverted by the spiral body 2 and then enters the core mold 4 area. The concave part 41 on the core mold 4 increases the flow rate of the raw material melt in the upper half, and the convex part 42 on the core mold 4 restricts the flow rate in the lower half to compensate for the wall thickness difference caused by sagging. The low temperature module 5 cools the discharge end of the core mold 4, thereby reducing the internal temperature of the pipe, increasing the melt viscosity, and reducing the sagging.
[0022] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this utility model is defined by the appended claims and their equivalents.
Claims
1. A special mold for low melt sag thick-walled polyethylene pipes, comprising a mold body (1), a spiral (2) disposed within the mold body (1) for conveying and initially diverting the raw material melt, a die (3) connected to the mold body (1), and a core mold (4) disposed within the die (3) and connected to the spiral (2), characterized in that: The core mold (4) is provided with at least one recess (41) and one protrusion (42). The recess (41) corresponds to the area where the raw material melt is lost the most, and the protrusion (42) corresponds to the area where the raw material melt is accumulated. The area between the area where the raw material melt is lost the most and the area where the raw material melt is accumulated is a normal area. The core mold (4) is provided with a low temperature module (5) for pre-cooling in the discharge end direction.
2. A die for low sag thick wall polyethylene pipe specialty according to claim 1, characterized in that: The concave portion (41), convex portion (42) and normal area are smoothly transitioned.
3. A die for low sag thick wall polyethylene pipe specialty according to claim 2, characterized in that: The smooth transition is either an arc transition or a sloped transition.
4. The low sag thick wall polyethylene pipe specialty mold of claim 1 wherein: The die (3) is locked to the die body (1) by a pressure ring (6).
5. The low sag thick wall polyethylene pipe specialty mold of claim 1 wherein: A silicone sheet (7) is provided between the low-temperature module (5) and the core mold (4) to slow down the high temperature conduction in the direction of the feeding end of the core mold (4).
6. A die for low sag thick wall polyethylene pipe specialty according to claim 5, characterized in that: The low-temperature module (5) can be cooled by oil, water, or high-temperature semiconductor.