Introduction To The Processing Technology Of Steel Lined PTFE Pipe

1. Tetrafluoroethylene (PTFE)-sodium naphthalene solution treatment bonding method Polytetrafluoroethylene (PTFE)-sodium naphthalene solution treatment bonding method: Sodium naphthalene solution treats fluorine-containing materials, mainly through the chemical reaction between the corrosive liquid and the PTFE plastic, tearing off some fluorine atoms on the surface of the material, thus leaving a carbonized layer and some polar groups on the surface. Sodium naphthalene solution treats fluorine-containing materials, mainly through the chemical reaction between the corrosive liquid and the PTFE plastic, tearing off some fluorine atoms on the surface of the material, thus leaving a carbonized layer and some polar groups on the surface. Infrared spectra show that polar groups such as hydroxyl, carbonyl and unsaturated bonds are introduced into the surface, which can increase the surface energy, reduce the contact angle, improve the wettability, and change from difficult to stick to sticky. This is the best method among all the methods currently studied and is also the more commonly used method. Sodium naphthalene tetrahydrofuran is generally used as the corrosive liquid. The treatment and bonding steps are as follows: (1) Preparation of treatment solution: Add a certain amount of metallic sodium to a solution of tetrahydrofuran and naphthalene, where the mass fraction of metallic sodium is controlled at 3% to 5%, and stir at room temperature for about 2 hours until the solution turns dark brown or black; (2) Immerse the PTFE workpiece to be treated in the solution for about 5 to 10 minutes, take it out and soak it in acetone solution for 3 to 5 minutes; (3) Take out the workpiece from the acetone solution, rinse it with clean water and place it in a dark place to dry naturally; (4) Choose epoxy resin, silicone or polyurethane as adhesive, evenly apply it to the treated surface to be bonded and bond it immediately. After standing at 24 to 30°C for 24 hours, it can be firmly bonded. 2. Steel-lined PTFE straight tube is commonly known as loose liner tube. This process uses a film cut from PTFE rods and is wound and sintered to form. It is suitable for normal pressure and positive pressure pipelines (such as three waste treatment pipelines, etc.), but not suitable for pipelines with negative pressure (such as pump inlet and outlet and pipelines that can generate negative pressure due to drop or sudden cooling). The specific process of the winding pipe loose lining method of polytetrafluoroethylene lined pipeline technology is: the polytetrafluoroethylene rod produced by mold pressing is cut into thin strips by lathe, and the polytetrafluoroethylene thin strips are wound on the mold of pre-designed size by manual or mechanical methods. After reaching the required thickness, three to four layers of alkali-free glass ribbons are wound on the outside in the same way. The outermost layer is tied with iron wire, and then sent to the sintering furnace for molding. After sintering, it is taken out and cooled with water, and then demolded by manual or mechanical methods, and then put into the steel pipe, and it is completed after flanging. The wound tube is the first type of tube that is produced more and used more widely. When producing this type of polytetrafluoroethylene tube, there is a large degree of freedom, which can be from small diameter to large diameter (up to Φ 2000mm or more). The tube is wound with a turning film and then sintered. Its integrity and uniformity are related to the tension during winding, the thickness of the film, the cleanliness of the film surface, the temperature and time during sintering, etc., which are difficult to master. Due to the large number of winding layers, it is difficult to control the process, and it is difficult to ensure the integrity and uniformity after sintering. Therefore, the maximum wall thickness of the wound tube does not exceed 3mm. There are many production processes, and the control is not strict. The processing method is mainly manual, the quality is unstable, and there is a lack of effective detection means. In addition, the wall of the loosely lined wound tube is thin. When the negative pressure and temperature difference fluctuate greatly, the pipeline is easy to collapse and the flange flange is easy to break. Selection requirements for steel pipes and flanges for PTFE-lined pipes and pipe fittings 1. The pipes are made of national standard seamless steel pipes. Due to process requirements, the effective diameter of the pipe inside the lining is smaller than the nominal diameter of the steel pipe. The designer and the user determine the diameter of the steel pipe after conducting the necessary effective flow standards. 2. The flanges can be forged or determined by the contract according to the needs of the user in accordance with national standards such as HG, GB, JB, ANSI, JIS, BS, and DIN. Due to the sealing surface processing technology, it is recommended to use plate-type flat-weld flanges and necked flat-weld flanges. The sealing surfaces are all flat sealing types. In order to facilitate pipeline installation, flat-weld ring movable flanges can be provided to users. Lined PTFE lining layer test, inspection and scope of use 1. Pipes and pipe fittings are subjected to water pressure test at 1.5 times the design pressure. 2. All PTFE lining layers are 100% inspected for integrity after water pressure test, and the leakage point inspection method adopts spark test. 3. Scope of use a. Operating temperature -20~200℃ b. Operating pressure ≤2.5Mpac. Allowable negative pressure DN≤250mm is -0.09Mpa, DN＞250mm is -0.08Mpad. It can transport strong acid, strong alkali, organic solvent, strong oxidant, toxic, volatile and flammable chemical media of any concentration. 3. Commonly known as internally wrapped steel wire tight liner. Manufacturing process: First, several layers of PTFE film are wound on the mold, and then steel wire (0.5-1mm) is spirally wound on the PTFE film, and then several layers of PTFE are wound on the outside of the steel wire, and finally placed in the furnace for winding and forming. The PTFE lined pipe made by this process has a smooth inner wall, and the outer wall forms a spiral line corrugation due to the volume of the steel wire and its external elastic force. It is lined into the steel pipe, and the gap between the outer wall of the PTFE lined pipe and the inner wall of the steel pipe is filled with filling resin (squeezing out the residual air). This filling resin can be tightly bonded to the steel pipe. At the same time, it can be tightly wrapped on the outer wall of the spiral PTFE liner. After the filling resin is cured, a spiral corrugation that bites with the corrugation of the outer wall of the liner is formed. This structure is similar to the combination of nuts and bolts. On the one hand, it can effectively limit and compensate the thermal expansion and contraction of the PTFE liner; on the other hand, the stiffness of the steel wire is used to significantly improve the ability of the PTFE liner to withstand negative pressure. Fourth, commonly known as push (squeeze) lined straight pipe, it is a pipe commonly used in developed countries in the 1990s. Manufacturing process: First, imported PTFE powder is used, pushed (squeezed) into a pipe, and then it is forcibly pulled into a seamless steel pipe (the outer diameter of the liner is slightly larger than the inner diameter of the steel pipe by 1.5-2mm) to form a tight lining without gaps. In order to eliminate the pressure, it is placed in a furnace and heated to 180oC for constant temperature treatment, so that it can be used at a temperature below 180℃. At the same time, the axial tensile strength of the push (extrusion) pressure pipe is significantly better than that of the winding pipe. This pipe has ideal resistance to positive and negative pressure. 5. Powder molding lining process F4 powder molding lining is an isotropic, isobaric and isothermal manufacturing process. It has undergone the process evolution of extrusion pipe (loose lining, tight lining), PTFE tape winding, and PTFE winding with steel wire and steel mesh. So far, F4 powder molding lining technology is the latest fifth generation product of F4 lining. It can be used under higher positive and negative pressure, high temperature and strong corrosion conditions. At a temperature of 200℃ and a vacuum of less than 0.096MPa, sudden cooling and heating or alternating hot and cold operations will not cause the polytetrafluoroethylene layer to fall off, bulge, shrink, expand and deform, thereby achieving steel-fluorine isotropic.