Production method of low-sag thick-wall polyethylene pipe

Abstract

The invention discloses a production method of a low-sag thick-wall polyethylene pipe, which is characterized in that the production method comprises the following steps: materials enter an extruder, and are in a molten state after being sheared and heated; controlling the heating temperatures of a plurality of different areas of the extrusion molding die; by controlling the heating temperatures of a plurality of different areas on the mold, the temperature of the area with the most loss of the raw material melt is the highest, the temperature of the normal area is the second, the temperature of the raw material melt accumulation area is the lowest, the discharging speeds of the raw material melt in all the areas of the mold are different, and then the discharging speed of the area with the high temperature of the mold is the highest; the area with the low temperature of the mold discharges fewest materials, proper compensation of a raw material melt loss area is achieved, the excessive wall thickness of a raw material melt accumulation area is reduced, and therefore the phenomenon that the thickness of the inner wall of the pipeline is not uniform due to the sagging phenomenon is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of polyethylene pipe production, in particular to a production method of a 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 not being able to cool down and solidify quickly. The melt (molten raw material) flows slowly to the bottom under the action of gravity, eventually causing 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 for pipes. If the inner wall of the pipe is air-cooled, the cooling rate is too low and insufficient for practicality. Spray cooling is used. , water vapor will be generated in the upper part of the pipe, condensed water will be generated in the lower part, the cooling will be uneven, and the mechanical properties and appearance quality of the pipe will be seriously affected; currently, 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 the 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 the production cost; for this purpose, 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 pipe.

[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: 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 molding die, so that the discharge speed of the raw material melt is the fastest in the local temperature of the die where the temperature is higher, and the discharge speed of the raw material melt is the slowest in the local temperature of the die where the temperature is lower, 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; among them, 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 is accumulated is the lowest. The area between the area with the most raw material melt loss and the area where the raw material melt is accumulated is a normal area, and its temperature is between the temperatures of the above two areas.

[0005] Further preferably, at least one concave portion is provided on the mandrel corresponding to the area where the raw material melt is lost the most, and at least one convex portion is provided on the mandrel corresponding to the area where the raw material melt is accumulated.

[0006] More preferably, the method further comprises the following steps after the above 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, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0007] Further preferably, the area with the most raw material melt loss and the concave portion are arranged 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 arranged in the 5 o'clock-7 o'clock area of ​​the core mold.

[0008] Further preferably, the recessed dimension of the concave portion is greater than the protruding dimension of the convex portion.

[0009] Further preferably, a smooth transition is adopted between the concave portion, the convex portion and the normal area.

[0010] Further preferably, a low-temperature module is provided in the direction of the discharge end of the core mold.

[0011] 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.

[0012] 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.

[0013] 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 lost the most is the highest, the temperature of the normal area is the second highest, 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 mold is different, and then the discharge speed of the area with high mold temperature is the fastest, and the discharge speed of the area with low mold temperature is the least, so as to achieve appropriate compensation for the area where the raw material melt is lost, reduce the excessive thickness of the wall in the area where the raw material melt is accumulated, and avoid uneven thickness of the inner wall of the pipeline caused by the sag phenomenon; By setting convex and concave parts on the core mold, the concave part can increase the extrusion amount of raw materials and make up for the raw materials lost due to high sag, and the convex part can reduce the extrusion amount of raw materials. During the sag process, the raw materials with excess standard wall thickness in the concave part flow to the normal area, and the raw materials in the normal area flow to the convex part. Through the reasonable setting of the concave part, the normal area, the curvature and the depth of the convex part, the minimum material consumption is finally achieved while ensuring the uniformity of the wall thickness of the pipeline; at the same time, a smooth transition is adopted between the convex part and the concave part 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 the stress concentration during the flow of raw materials and ensuring the mechanical properties and appearance quality of the pipeline; By setting up 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 molds; The segmented cooling setting can avoid the conventional water tank cooling method for the inner wall of the pipeline, which increases the cost and avoids the internal stress caused by the cooling rate of the cooling water being too fast, thereby improving the mechanical properties and appearance quality of the pipeline and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of the core mold of the patent of the present invention; Figure 2 It is a side view of the core mold of the patent of the present invention. DETAILED DESCRIPTION

[0015] The following further describes the production method of a low sag thick-wall polyethylene pipe according to the present invention with reference to the drawings.

[0016] See also Figure 1-Figure 2 As shown in, a production method of a low sag thick-wall polyethylene pipe is characterized in that the production method is as follows: 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 molding die, so that the discharge speed of the raw material melt in the local temperature of the die is the fastest, and the discharge speed of the raw material melt in the local temperature of the die is the slowest, 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, which is set in the 1-3 o'clock area and the 9-11 o'clock area of ​​the die; the heating temperature of the raw material melt accumulation area is the lowest, which is set in the 5-7 o'clock area of ​​the die; the area between the area with the most raw material melt loss and the raw material melt accumulation area is the normal area, and its temperature is between the temperatures of the above two areas.

[0017] If it is necessary to replace raw materials or adjust the wall thickness specifications of the production pipeline, due to the change in the sag of the raw material melt, the temperature of the low-temperature module can be adjusted to quickly cool the raw material melt on the inner wall of the pipeline to the specified value, so that it has 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.

[0018] In one embodiment, at least one concave portion is provided on the mandrel at the region corresponding to the area where the raw material melt is lost the most, the concave portion is provided in the 1 o'clock-3 o'clock region and the 9 o'clock-11 o'clock region of the mandrel, and at least one convex portion is provided on the mandrel at the region corresponding to the accumulation region of the raw material melt; the convex portion is provided in the 5 o'clock-7 o'clock region of the mandrel; the concave size of the concave portion is greater than the convex size of the convex portion; the sizes of the concave portion and the convex portion 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 portion, the convex portion and the normal area; by providing the convex portion and the concave portion on the mandrel, the concave portion can be Increase the extrusion amount of raw materials and make up for the raw materials lost due to high sag. The convex part can reduce the extrusion amount of raw materials. During the sag process, the raw materials with extra standard wall thickness in the concave part will flow to the normal area, and the raw materials in the normal area will flow to the convex part. Through the reasonable setting of the concave part, normal area, convex part curvature and depth, the minimum material consumption can be achieved while ensuring the uniformity of the wall thickness of the pipe. At the same time, a smooth transition is adopted between the convex part and the concave part 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 the stress concentration in the flow of raw materials and ensuring the mechanical properties and appearance quality of the pipe.

[0019] In one embodiment, a low-temperature module is provided in the direction of the discharge end 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 direction of the feed end 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.

[0020] In one embodiment, the following steps are also included after the above step b: After the tube billet leaves the die, it enters the sizing box, so that the outer wall of the tube billet fits the inner wall of the sizing sleeve, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe according to the fixed length; the outer wall of the pipe is water-cooled during segmented cooling, and a spray device is set around the outer wall of the pipe to quickly reduce the temperature of the outer wall of the pipe by spraying cooling water. The cooling temperature of the outer wall is generally controlled at 20-25℃; the inner wall of the pipe is air-cooled, and cold air is blown inside the pipe to reduce the temperature of the inner wall of the pipe. The air cooling wind speed is controlled at 5-10m / s, and the air cooling temperature is controlled at 50-55℃; indirect water cooling can also be used, and a cooling water jacket is set on the inner wall of the pipe. The inner wall of the pipe is indirectly cooled by the cooling water jacket, so that the temperature of the inner wall of the pipe is controlled at 40-45℃; avoiding the use of conventional water tank cooling, increasing costs while avoiding the internal stress of the inner wall of the pipe due to the excessive cooling rate of cooling water, improving the mechanical properties and appearance quality of the pipe, and reducing production costs.

[0021] Embodiment 1: First, the material is fed into an extruder, and the raw material is in a molten state after shearing and heating; Then, the heating temperatures of several different areas of the extrusion molding die are 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 second, and the temperature of the raw material melt accumulation area is set to the lowest, so as to increase the discharge speed of the raw material melt loss area, thereby realizing compensation for the raw material melt loss area; 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, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0022] Embodiment 2: First, the material is fed into an extruder, and the raw material is in a molten state after shearing and heating; Then, the extruder extrudes the raw material through the forming die, and at least one concave portion is provided on the core mold corresponding to the area where the raw material melt flows most, and at least one convex portion is provided on the core mold 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; 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, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0023] Embodiment 3: First, the material is fed into an extruder, and the raw material is in a molten state after shearing and heating; Then, the heating temperatures of several different areas of the extrusion molding die are 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 second, and the temperature of the area where the raw material melt is accumulated is set to the lowest, so as to increase the extrusion speed and extrusion amount of the area where the raw material melt is lost; Then, at least one concave portion is provided on the mandrel corresponding to the area where the raw material melt flows most, and at least one convex portion is provided on the mandrel 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 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; 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, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

[0024] The protection scope of the present invention is not limited to the above embodiments and their variations. Conventional modifications and replacements made by those skilled in the art based on the contents of this embodiment all fall within the protection scope of the present invention.

Claims

1. A method for producing a low sag thick-wall polyethylene pipe, the characteristics of which include: 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 molding die, so that the discharge speed of the raw material melt is the fastest in the local temperature of the die where the temperature is higher, and the discharge speed of the raw material melt is the slowest in the local temperature of the die where the temperature is lower, 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; among them, 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 is accumulated is the lowest. The area between the area with the most raw material melt loss and the area where the raw material melt is accumulated is a normal area, and its temperature is between the temperatures of the above two areas.

2. The method for producing a low sag thick-wall polyethylene pipe according to claim 1, characterized in that: It also includes providing at least one concave portion on the core mold corresponding to the area where the raw material melt is lost the most, and providing at least one convex portion on the core mold corresponding to the area where the raw material melt is accumulated.

3. The method for producing a low sag thick-wall 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, and cooperates with the segmented cooling system to quickly solidify and shape the high-temperature tube billet. The traction machine pulls the cooled pipe to the cutting position at a uniform speed and cuts the pipe to a fixed length.

4. The method for producing a low sag thick-wall polyethylene pipe according to claim 2, characterized in that: The raw material melt loss area and the concave part are arranged 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 part are arranged in the 5 o'clock-7 o'clock area of ​​the core mold.

5. The method for producing a low sag thick-wall polyethylene pipe according to claim 4, characterized in that: The recessed dimension of the concave portion is greater than the protruding dimension of the convex portion.

6. The method for producing a low sag thick-wall polyethylene pipe according to claim 5, characterized in that: A smooth transition is adopted between the concave part, the convex part and the normal area.

7. The method for producing a low sag thick-wall polyethylene pipe according to claim 6, characterized in that: The smooth transition is an arc transition or a slope transition.

8. The method for producing a low sag thick-wall polyethylene pipe according to claim 2, characterized in that: A low temperature module is arranged at the discharge end of the core mold.

9. The method for producing a low sag thick-wall polyethylene pipe according to claim 8, 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.

10. The method for producing a low sag thick-wall polyethylene pipe according to claim 3, 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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