A production method for low-sag thick-wall polyethylene pipe

Abstract

The present invention discloses a production method of a low-sag thick-wall polyethylene pipe, which is characterized in that the production method is as follows: a material enters an extruder and is in a molten state after shearing and heating; the heating temperature of several different areas of an extrusion molding die is controlled; the present invention controls the heating temperature of several different areas on the die so that the temperature of the area where the raw material melt is lost the most is the highest, the temperature of the normal area is second, and the temperature of the area where the raw material melt is accumulated is the lowest, so that the discharge speed of the raw material melt in various areas of the die is different, and then the discharge speed of the area with high die temperature is the fastest, and the discharge speed of the area with low die temperature is the least, thereby achieving appropriate compensation for the area where the raw material melt is lost, reducing the excessive wall thickness of the area where the raw material melt is accumulated, and thus avoiding uneven thickness of the inner wall of the pipe caused by the sag phenomenon.

Description

Technical Field

[0001] The invention relates to the technical field of polyethylene pipe production, in particular to a production method of low-sag thick-wall polyethylene pipe. Background Art

[0002] In the production process of polyethylene pipes, especially the production of large-diameter thick-walled pipes with an outer diameter of ≥630mm and a wall thickness of ≥37.4mm, the inner wall of the pipe cannot be directly cooled by external cooling water, resulting in the material on the inner wall of the pipe being unable to cool down and solidify quickly. The melt (molten material) flows slowly to the bottom under the action of gravity, eventually resulting in uneven pipe wall thickness, the so-called sag phenomenon. The wall thickness needs to be increased overall and significantly to meet the minimum wall thickness requirements of the product standard. If the inner wall of the pipe is cooled by air, the cooling rate is too low and insufficiently practical. Spray cooling is used. , water vapor will be generated in the upper part of the pipe and condensed water will be generated in the lower part, resulting in uneven cooling, which will seriously affect the mechanical properties and appearance quality of the pipe. At present, the conventional solution is to lower the melt temperature or use raw materials with lower fluidity under low shear stress (low-sag raw materials, low-sag), but these methods often lead to a decrease in the appearance quality of the pipe, deterioration of mechanical properties or increase in production costs. Therefore, there is an urgent need for a production method that can effectively reduce the sag phenomenon, ensure the quality of the pipe and reduce production costs. To this end, a production method for low-sag thick-walled polyethylene pipes is proposed. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems and to provide a production method for low sag thick-wall polyethylene pipes.

[0004] In order to achieve the above object, the present invention provides the following technical solution: a method for producing a low-sag thick-walled polyethylene pipe, characterized in that the production method is as follows:

[0005] a. The material enters the extruder and becomes molten after shearing and heating;

[0006] b. Control the heating temperature of several different areas of the extrusion mold so that the raw material melt is discharged fastest in the local area with higher temperature of the mold and slowest in the local area with lower temperature of the mold, thereby achieving the effect of uniform wall thickness after the raw material melt flows, replenishing the area where the raw material melt is lost, and avoiding uneven plasticization of the inner wall of the pipe caused by high sag; the heating temperature of the area with the most raw material melt loss is the highest, and the heating temperature of the area where the raw material melt accumulates is the lowest. The area between the area with the most raw material melt loss and the area where the raw material melt accumulates is the normal area, and its temperature is between the highest and lowest temperatures;

[0007] It also includes setting at least one concave portion on the core mold corresponding to the area where the raw material melt loses the most, and setting at least one convex portion on the core mold corresponding to the area where the raw material melt accumulates; the area where the raw material melt loses the most and the concave portion are set in the 1 o'clock-3 o'clock area and the 9 o'clock-11 o'clock area of the core mold, and the raw material melt accumulation area and the convex portion are set in the 5 o'clock-7 o'clock area of the core mold.

[0008] More preferably, the method further includes the following steps after step b:

[0009] After leaving the die, the tube billet enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve. In conjunction with the segmented cooling system, the high-temperature tube billet is quickly solidified and shaped. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0010] Further preferably, the recessed size of the concave portion is larger than the protruding size of the convex portion.

[0011] Further preferably, a smooth transition is adopted between the concave portion, the convex portion and the normal area.

[0012] Further preferably, a low-temperature module is provided in the discharge direction of the core mold.

[0013] Further preferably, a silicone sheet is provided between the low-temperature module and the core mold to slow down the conduction of high temperature in the direction of the feeding end of the core mold.

[0014] Further preferably, the segmented cooling includes water cooling for the outer wall of the pipeline and air cooling or indirect water cooling for the inner wall of the pipeline.

[0015] The beneficial effects of the present invention are as follows: by controlling the heating temperatures of several different areas on the mold, the temperature of the area where the raw material melt is most lost is made the highest, the temperature of the normal area is made the second highest, and the temperature of the area where the raw material melt is accumulated is made the lowest. This makes the discharge speed of the raw material melt in different areas of the mold different, thereby making the discharge speed of the area with high mold temperature the fastest and the discharge speed of the area with low mold temperature the least. This achieves appropriate compensation for the area where the raw material melt is lost, reduces the excessive thickness of the wall in the area where the raw material melt is accumulated, and thus avoids uneven thickness of the inner wall of the pipe caused by sag.

[0016] By setting convex and concave parts on the core mold, the concave parts can increase the extrusion volume of raw materials and make up for the raw materials lost due to high sag, while the convex parts can reduce the extrusion volume of raw materials. During the sag process, the raw materials with excess standard wall thickness in the concave parts flow to the normal area, while the raw materials in the normal area flow to the convex parts. Through the reasonable setting of the concave parts, normal area, convex curvature and depth, the minimum material consumption is ultimately achieved while ensuring the uniformity of the pipe wall thickness. At the same time, a smooth transition is adopted between the convex and concave parts to optimize the flow path of the raw materials, reduce the residence time of the raw materials in the mold, and reduce the probability of sag, thereby reducing stress concentration during the flow of raw materials and ensuring the mechanical properties and appearance quality of the pipe.

[0017] By setting up a low-temperature module, the inner wall material of the pipeline can be pre-cooled, thereby expanding the applicable raw material range of the concave and convex molds and reducing the production cost of the mold;

[0018] The segmented cooling setting avoids the conventional water tank cooling method for the inner wall of the pipeline, which increases the cost while avoiding the internal stress caused by the cooling water cooling rate being too fast, thereby improving the mechanical properties and appearance quality of the pipeline and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the overall structure of the core mold of the patent of this invention;

[0020] Figure 2 It is a side view of the core mold of the patent of this invention. DETAILED DESCRIPTION

[0021] The following further illustrates the production method of a low sag thick-wall polyethylene pipe according to the present invention with reference to the drawings.

[0022] See Figure 1-Figure 2 As shown in, a production method of low sag thick-wall polyethylene pipe is characterized in that the production method is as follows:

[0023] a. The material enters the extruder and becomes molten after shearing and heating;

[0024] b. Control the heating temperature of several different areas of the extrusion mold so that the raw material melt is discharged fastest in the local area with higher temperature of the mold and slowest in the local area with lower temperature of the mold, thereby achieving the effect of uniform wall thickness after the raw material melt flows, replenishing the area where the raw material melt is lost, and avoiding uneven plasticization of the inner wall of the pipe caused by high sag; the heating temperature of the area with the most raw material melt loss is the highest, and the heating temperature of the area where the raw material melt accumulates is the lowest. The area between the area with the most raw material melt loss and the area where the raw material melt accumulates is the normal area, and its temperature is between the highest and lowest temperatures;

[0025] It also includes setting at least one concave portion on the core mold corresponding to the area where the raw material melt loses the most, and setting at least one convex portion on the core mold corresponding to the area where the raw material melt accumulates; the area where the raw material melt loses the most and the concave portion are set in the 1 o'clock-3 o'clock area and the 9 o'clock-11 o'clock area of the core mold, and the raw material melt accumulation area and the convex portion are set in the 5 o'clock-7 o'clock area of the core mold.

[0026] If it is necessary to replace the raw materials or adjust the wall thickness specifications of the production pipeline, the temperature of the low-temperature module can be adjusted due to the change in the sag of the raw material melt, so that the raw material melt on the inner wall of the pipeline can be quickly cooled to the specified value, thereby having a specific viscosity. The specific viscosity of different raw materials can be obtained by interpolating the viscosity values measured by the rotor rheometer at different temperatures, so that the raw material melt with the same initial conditions can be obtained without changing the core mold, thereby reducing production costs.

[0027] The recessed size of the concave portion is larger than the protruding size of the convex portion; the sizes of the concave and convex portions are calculated based on the viscosity and cooling time of the raw material at low shear stress and selected based on the results of finite element simulation; a smooth transition of an arc or an inclined surface is adopted between the concave, convex and normal areas; by arranging convex and concave portions on the core mold, the concave portion can increase the extrusion amount of the raw material and make up for the raw material lost due to high sag, and the convex portion can reduce the extrusion amount of the raw material. During the sag process, the raw material with excess standard wall thickness in the concave portion flows to the normal area, and the raw material in the normal area flows to the convex portion. Through the reasonable setting of the concave portion, normal area, convex curvature and depth, the minimum material consumption is ultimately achieved while ensuring the uniformity of the wall thickness of the pipeline; at the same time, a smooth transition is adopted between the convex portion and the concave portion to optimize the flow path of the raw material, reduce the residence time of the raw material in the mold, reduce the probability of sag, thereby reducing stress concentration during the flow of the raw material and ensuring the mechanical properties and appearance quality of the pipeline.

[0028] In one embodiment, a low-temperature module is provided in the discharge direction of the core mold; and a silicone sheet is provided between the low-temperature module and the core mold to slow down the high-temperature conduction in the feed direction of the core mold; the low-temperature module can be cooled by oil, water or high-temperature resistant semiconductors; through the setting of the low-temperature module, the inner wall material of the pipeline can be pre-cooled, thereby expanding the applicable raw material range of the concave and convex molds and reducing the production cost of the mold.

[0029] In one embodiment, the following steps are further included after step b:

[0030] After leaving the die, the tube billet enters the sizing box, where its outer wall conforms to the inner wall of the sizing sleeve. The high-temperature tube billet is rapidly solidified and shaped in conjunction with the segmented cooling system. A haul-off machine pulls the cooled pipe at a uniform speed to the cutting station, where it is cut to a predetermined length. During segmented cooling, the outer wall of the pipe is water-cooled. A spray device is installed around the outer wall of the pipe to rapidly reduce the outer wall temperature by spraying cooling water. The outer wall cooling temperature is generally controlled at 20-25°C. The inner wall of the pipe is air-cooled by blowing cold air inside the pipe to reduce the inner wall temperature. The air cooling speed is controlled at 5-10m / s and the air cooling temperature is controlled at 50-55°C. Alternatively, indirect water cooling can be used. A cooling water jacket is installed on the inner wall of the pipe to indirectly cool the inner wall through the cooling water jacket, keeping the inner wall temperature controlled at 40-45°C. This avoids the cost of conventional water tank cooling while also preventing internal stress on the inner wall caused by excessively fast cooling of the cooling water. This improves the mechanical properties and appearance quality of the pipe, while reducing production costs. Example

[0031] First, the material enters the extruder, and after shearing and heating, the raw material is in a molten state;

[0032] Then, the heating temperature of several different areas of the extrusion die is controlled so that the temperature of the area with the most raw material melt loss is set to the highest, the heating temperature of the normal area is set to the second highest, and the temperature of the raw material melt accumulation area is set to the lowest, thereby increasing the discharge speed of the raw material melt loss area, thereby compensating for the raw material melt loss area;

[0033] After leaving the die, the tube billet enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve. In conjunction with the segmented cooling system, the high-temperature tube billet is quickly solidified and shaped. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length. Example

[0034] First, the material enters the extruder, and after shearing and heating, the raw material is in a molten state;

[0035] Then, the extruder extrude the raw material through the forming die, and at least one concave portion is provided on the core die corresponding to the area where the raw material melt loses the most, and at least one convex portion is provided on the core die corresponding to the area where the raw material melt accumulates, so that the extrusion amount of the concave portion is greater than the extrusion amount of the convex portion, and during the drooping process, the raw material melt with excess standard wall thickness in the concave portion flows to the normal area, and the raw material melt in the normal area flows to the convex portion, so that the wall thickness of the pipe after shaping is uniform;

[0036] After leaving the die, the tube billet enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve. In conjunction with the segmented cooling system, the high-temperature tube billet is quickly solidified and shaped. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length. Example

[0037] First, the material enters the extruder, and after shearing and heating, the raw material is in a molten state;

[0038] Then, the heating temperature of several different areas of the extrusion die is controlled so that the temperature of the area where the raw material melt is lost the most is set to the highest, the heating temperature of the normal area is set to the second highest, and the temperature of the area where the raw material melt is accumulated is set to the lowest, thereby increasing the extrusion speed and extrusion volume in the area where the raw material melt is lost;

[0039] Then, at least one concave portion is provided on the core mold corresponding to the area where the raw material melt loses the most, and at least one convex portion is provided on the core mold corresponding to the area where the raw material melt accumulates. The extrusion amount of the concave portion is greater than the extrusion amount of the convex portion. During the drooping process, the raw material melt with a standard wall thickness in the concave portion flows into the normal area, and the raw material melt in the normal area flows to the convex portion, so that the wall thickness of the pipe after shaping is uniform;

[0040] After leaving the die, the tube billet enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve. In conjunction with the segmented cooling system, the high-temperature tube billet is quickly solidified and shaped. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0041] The protection scope of the present invention is not limited to the above embodiment and its variations. Conventional modifications and replacements made by those skilled in the art based on the contents of this embodiment fall within the protection scope of the present invention.

Claims

1. A method for producing a low sag thick-wall polyethylene pipe, characterized by: a. The material enters the extruder and becomes molten after shearing and heating; b. Control the heating temperature of several different areas of the extrusion mold so that the raw material melt is discharged fastest in the local area with higher temperature of the mold and slowest in the local area with lower temperature of the mold, thereby achieving the effect of uniform wall thickness after the raw material melt flows, replenishing the area where the raw material melt is lost, and avoiding uneven plasticization of the inner wall of the pipe caused by high sag; the heating temperature of the area with the most raw material melt loss is the highest, and the heating temperature of the area where the raw material melt accumulates is the lowest. The area between the area with the most raw material melt loss and the area where the raw material melt accumulates is the normal area, and its temperature is between the highest and lowest temperatures; It also includes setting at least one concave portion on the core mold corresponding to the area where the raw material melt loses the most, and setting at least one convex portion on the core mold corresponding to the area where the raw material melt accumulates; the area where the raw material melt loses the most and the concave portion are set in the 1 o'clock-3 o'clock area and the 9 o'clock-11 o'clock area of the core mold, and the raw material melt accumulation area and the convex portion are set in the 5 o'clock-7 o'clock area of the core mold.

2. The method for producing a low sag thick-walled polyethylene pipe according to claim 1, characterized in that: The following steps are also included after step b: After leaving the die, the tube billet enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve. In conjunction with the segmented cooling system, the high-temperature tube billet is quickly solidified and shaped. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

3. The method for producing a low sag thick-walled polyethylene pipe according to claim 1, characterized in that: The recessed size of the concave portion is larger than the protruding size of the convex portion.

4. The method for producing a low sag thick-wall polyethylene pipe according to claim 3, characterized in that: A smooth transition is adopted between the concave portion, the convex portion and the normal area.

5. The method for producing a low sag thick-walled polyethylene pipe according to claim 4, characterized in that: The smooth transition is an arc transition or an inclined plane transition.

6. The method for producing a low sag thick-walled polyethylene pipe according to claim 1, characterized in that: A low-temperature module is provided at the discharge end of the core mold.

7. The method for producing a low sag thick-wall polyethylene pipe according to claim 6, characterized in that: A silicone sheet is provided between the low-temperature module and the core mold to slow down the conduction of high temperature in the direction of the feeding end of the core mold.

8. The method for producing a low sag thick-wall polyethylene pipe according to claim 2, characterized in that: The segmented cooling includes water cooling for the outer wall of the pipeline and air cooling or indirect water cooling for the inner wall of the pipeline.

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