Ultra high molar mass polyethylene (UHMWPE) is a thermoplastic engineering plastic with excellent comprehensive properties. At present, UHMWPE pipes have been widely used in fields such as mining, electricity, coal, petroleum, and chemical industry. In the application process of UHMWPE pipes, the connection of pipes is a key link. The author has conducted a special discussion on the secondary processing of UI-IMWPE, such as thermal deformation and welding [I3], and proposed the basic theory and method of pipe connection; However, there is no special discussion on the preparation of pipe fittings, and there are no other literature reports. The lack of matching and standardization of pipe fittings seriously restricts the application of pipes. Based on years of research and application, this article proposes a preparation method for UHMWPE pipe fittings, hoping to be helpful to UHMWPE pipe manufacturers and users. 1. Overview of UHMWPE pipe fittings: UHMWPE pipe fittings, like other high temperature resistant materials of pipe fittings, mainly include elbows, tees, and reducers. However, due to the fact that UHMWPE pipes are special types of pipes, there are currently no national or industry standards, and the specifications of UHMW-PE pipes are often determined according to user requirements. Therefore, UHMWPE pipes cannot be produced by professional manufacturers like other bulk pipes such as PE and PVC pipes. Therefore, the preparation method of UHMWPE pipe fittings must be simple and flexible; The manufacturing equipment is special, but the investment is small, so there is no need to pursue high production efficiency. The connection between pipe fittings and pipes should use flanged connections for easy installation and disassembly. The so-called flanging refers to the use of thermal deformation technology, which turns the pipe end outward by an edge to increase the outer diameter, maintain the inner diameter, and increase the cross-sectional area of the pipe end. The so-called flange connection refers to the installation of a steel flange at the end of a pipe, and the fastening of pipes or fittings with bolts through the steel flange; The sealing between pipes or between pipes and fittings can be achieved very well by flanging, without the need for additional sealing gaskets.
The preparation method of 2 UHMWPE pipe fittings proposed in this article is to use the forming and processing equipment of UI-1MWPE pipes or use pipes as raw materials for processing.
2.1 After determining the pipe diameter of the elbow, there are two parameters for the elbow, one is the angle, and the other is the radius of curvature. Regarding angles, ISO standards and national standards have the same regulations for elbows of various materials, ranging from 90 to 45. And 22.5.; Regarding the curvature radius, there are significant differences in the provisions of international and national standards due to different materials and preparation methods. For UHMWPE elbows, casting and injection methods are not suitable for preparation; Therefore, a larger radius of curvature should be chosen. In practical applications, UHMWPE pipes are often used to replace or renovate old pipelines, so the requirements for elbow angles are relatively complex. In addition to the three angles specified in ISO and national standards, there are also many other angles; For the radius of curvature, there are no strict requirements. This article proposes a method for preparing UHMWPE elbows that can arbitrarily change the angle, grade difference, and curvature radius based on the provisions of ISO and national standards and practical requirements.
2.1.1 The preparation of equipment elbows is achieved by adding a set of auxiliary devices on the UHMWPE pipe extrusion production line. Specifically, at the outlet of the pipe, an auxiliary device is used to apply a force perpendicular to the extrusion direction to the pipe, gradually single arm bending torsion springs the pipe during the extrusion process to achieve the required angle and curvature radius, and preparing various elbows. This method is simple and easy to implement, and the biggest advantage is that the wall thickness of the elbow pipe is uniform, and it can even achieve a wall thickness greater than the wall thickness of the inner bending surface, which is crucial for the service life of the elbow. The schematic diagram of the auxiliary device structure is shown in Figure l. The external force applied is achieved through the power arm. The simplest external force is either manual or mechanical; The pushing speed must match the extrusion line speed of the pipe. The external force is transmitted to the extruded pipe through the roller, and the curvature of the roller is the same as the outer diameter of the pipe. The pipe is bent under the force, and the power arm can stop at any position; Therefore, an elbow with any angle (0-90o) can be obtained. The center distance between the hinge axis and the pipe is the curvature radius of the elbow, and the difference in curvature radius can be achieved by changing the position of the roller.
2.1.2 The unfurled and finished 90o elbows in the process are shown in Figure 2. The length of the straight section at both ends of the unfurled elbow is determined based on three factors, and the required length for flanging is determined; The flanges cannot interfere with each other; Convenient construction. After determining the curvature radius and angle of the elbow, start the extruder to extrude the pipe. First, extrude the straight section. When the length of the straight section meets the requirements, push the power arm, and the roller moves along a certain radius of the circular trajectory. The linear speed of the roller movement matches the linear speed of the pipe extrusion until the desired angle is reached. Remove the power arm and roller, continue to extrude the straight section at the other end of the elbow. Once the requirements are met, stop extruding, cut off, and obtain an unfurled elbow. Cover the unfurled elbow with a captive flange and flange both ends to obtain the finished UHMWPE elbow.
2.2 Tees According to ISO and national standards, there are two types of angles for various materials of tees, namely 90o tees (T) and 45o tees (Y). The requirements for the length of the tee vary depending on the material and manufacturing method; For UHMWPE tees, the straight section length is similar to that of elbows, and the principles followed for each section length are the same
2.1.2. In practical applications, users sometimes need special angle tees, and the method shown in Figure 3 can be used to meet the requirements by changing the angle of the branch pipe flange. In Figure 3, 45 can be added. The standard tee has been changed to a special tee of 28o. The preparation method of UHMWPE tee proposed in this article is based on the principle of hot melt welding using pipes as raw materials. The preparation methods for reducing and equal diameter tees are the same.
2.2.1 After determining the pipe diameter and angle of the tee, select the corresponding UHMWPE pipe material as the raw material. The following is an example of a 90 * equal diameter tee to illustrate the cutting method. Use an angle saw to cut a right angle groove on the straight pipe, with the depth of the groove being the radius of the pipe; Make a tenon on the branch pipe to match the groove on the straight pipe, as shown in Figure 4. The length of straight and branch pipes should be reserved with flanged parts. For large diameter pipes, especially 45. It may be difficult to cut the three-way joint with an angle saw. A marking hand saw can be used to cut the joint, and then the groove and tenon can be repaired to ensure a tight fit. 2.2.2 The preparation of the equipment tee is actually the fusion welding and bending cold rolled sheet air conditioning bracketof the straight pipe and branch pipe along the intersecting line. To achieve fusion welding, the equipment must provide pressure and heat to the welding area, so that the area around the junction line melts under pressure conditions, and ensure that the adjacent parts of the welding area do not deform. The processing equipment for the tee is designed around these three requirements, and its principle is that the simple split external mold consists of two parts, which are fastened with bolts and can be disassembled; Used to restrict the movement of branch pipes and straight pipes to ensure their positioning; The external heating element embedded at the junction line provides heat for the welding area and prevents other parts from deforming outwards; The movable core rod is composed of three parts, which can be inserted and withdrawn from three directions, and together with the external mold, forms a cavity in which the branch and straight pipes are positioned and limited; Similarly, the built-in heating element on the core rod also provides heat for the welding area and prevents other parts from deforming inward; The pressure plate provides pressure for the welding area.
After the completion of the cutting process, the branch and straight pipes are placed in the fastened outer mold, and the core rod is inserted by external force (hydraulic or spiral). The linked pressure plate compresses the branch and straight pipes tightly; Electrify the heating element to generate heat, with a temperature controlled between 180 to 200 cI=. The area near the junction line of the branch and straight pipes expands and melts due to heat. Under the limitations of the external mold and core rod, the branch and straight pipes are fused together, and the heating time varies according to the thickness of the pipe wall; Power off, cool to below 8o cI=, extract the core rod, open the outer mold, and obtain an unfurled tee. Cover the flange and flange the three pipe ends to obtain the finished IJH tee. The most critical issue in the processing of the tee is the quality of the fusion welding of the branch and straight pipes. There are many factors that affect the quality of fusion 3d flexible welding platform by large machining, among which three points should be paid special attention to:
Firstly, the size of the cutting material should be standardized, especially the fit between the tenon and groove should be tight;
Secondly, the heating temperature should not be too high, otherwise it will cause oxidation and degradation of the joint surface. The mechanical strength of the degraded small molecule products is very low, which will seriously affect the strength of the fusion joint; The third is that the heating time should be long enough to ensure complete melting at the welding site. The finished tee needs to undergo pressure and impact tests to ensure the quality of the tee.
3. The UHMWPE pipe fittings prepared using the method described in this article have identical properties to UHMWPE pipes. The application of pipe fittings is basically the same as other plastic pipe fittings, but two points should be noted in practical applications: UHMWPE pipes are often used to transport highly abrasive media, and the service life of elbows is always lower than that of straight pipes; Therefore, when designing pipelines, elbows should be designed in positions that are easy to replace. In special circumstances, wear-resistant ceramic elbows of the same specification can be selected. For IJHMWPE tees, the strength of the fusion joint should reach over 95% of the pipe strength, but the fusion joint is a place of stress concentration after all; Therefore, during installation and use, efforts should be made to avoid significant forces at the fusion joint. When subjected to significant forces, the tee should be reinforced and armored. Conclusion: UHMWPE pipe fittings belong to a variety of small batch products, and their preparation methods should be simple and flexible. The pipe fitting preparation method proposed and completed in this article meets this requirement. The preparation of elbows is achieved by using a pipe extrusion equipment to add a set of auxiliary devices at the outlet of the pipe, achieving the processing of various specifications of elbows with any angle and a certain gradient curvature radius. Using pipes as raw materials, after cutting, various specifications of tees can be processed on a relatively simple device
Link to this article：Preparation and application of ultra-high molar mass polyethylene pipe fittings
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