Labyrinth effect: the shaft is very uneven on the microscopic surface, and the packing can only partially fit, but the part is not in contact, so there is a slight gap between the packing and the shaft, like a labyrinth, with a pressure medium in the gap. It is throttled several times to achieve the seal.
Bearing effect: There is a thin liquid film between the packing and the shaft, so that the packing and the shaft are similar to the sliding bearing, which has a certain lubrication effect, thus avoiding excessive wear of the packing and the shaft.
Performance index of packing material
1. Compression ratio: the ratio of the thickness of the material to the initial thickness when loading
2. Rebound rate: the ratio of the rebound amount of solid material when unloading to the amount of compression at the time of loading
3, wear resistance: the degree of loss caused by the relative motion between the two materials
4, self-lubricating: the material itself has lubricity performance
5. Stress relaxation rate: the percentage of stress attenuation under stress relaxation state
6. Heat loss: the percentage of mass lost after the substance is burned within the specified time of the specified temperature.
7. Acid loss: the percentage of mass lost after the material has been treated in the acid solution of the specified operating procedure.
8. Alkali loss: Percentage of mass lost after treatment of the material in an alkaline solution of the specified operating procedure
(1) Seals are one of the basic components of mechanical equipment. Most mechanical equipment cannot be separated from seals and corresponding sealing technology. For most mechanical equipment, although the sealing technology is not the main technology, it is often the key technology to determine the quality and technical level of the equipment. It is impossible to imagine that a high-tech equipment has obvious leakage and leakage. As an important functional basic component, the seal plays an important role in ensuring efficient, long-term, stable and safe operation of mechanical equipment, and has important functions of blind leakage, energy conservation and pollution control. Since the reform and opening up, after more than 20 years of development and technology introduction, China has formed a certain production capacity and scale on sealing technology, materials and seals. In terms of the quantity and quality of the products, it basically meets the demand for seals in the domestic electromechanical industry. However, due to the late start of China's sealing industry and the poor foundation, China's sealing technology is still about 10 years behind the international advanced level. China's car steering, shock absorption, braking and engine oil seals and other seals are basically trusted to import, large metallurgy, energy equipment seals are also mainly imported. Of course, in the period of re-opening, China has also created some new sealing technologies and products. For example, flexible graphite textile packing is the international technology and products developed by our car. Due to the gap between sealing technology and product quality, the versatility indicators of some electromechanical equipment products in China are low and energy consumption is high.
Expanded PTFE ribbon gasket is a new type of sealing product. It is a breakthrough in the field of sealing of new technologies at home and abroad. It has changed the traditional way of using static sealing. It is a new concept of high quality and practical sealing tape. A full range of functional sealing products with a wide range of meanings. Expanded PTFE strip gaskets, which replace PTFE gaskets and other sealing materials with their excellent properties, are increasingly popular and widely used in various types of sealing industries. Expanded PTFE strip gasket, because of its softness and large compression ratio, it is easy to form in three-dimensional space, and can be inserted into micro cracks and damage to fill and seal, especially in acid, alkali, corrosion and non-metal equipment, large The joint effect of the caliber container is outstanding, and the device connection for brittle material can be effectively protected. For non-metallic devices such as glass, ceramics, graphite, plastics, etc., it has an extraordinary effect. It can compensate and balance the errors caused by defects, machining, rigid deformation, installation misalignment, etc., balance the unevenness of the preload, and effectively solve the leakage problems of various facilities under complex conditions.
In order to solve the problem that the polytetrafluoroethylene sheet is difficult to bond, the following methods are commonly used:
1. Sodium-naphthalene complex chemical treatment
The chemical treatment of fluorine-containing materials mainly involves chemical reaction between the etching solution and the PTFE plastic to tear off some of the fluorine atoms on the surface, thus leaving a carbonized layer and some polar groups on the surface. Infrared spectroscopy revealed that polar groups such as a hydroxyl group, a carbonyl group, and an unsaturated bond were introduced into the surface. These groups can increase the surface energy, the contact angle becomes small, the wettability increases, and it becomes sticky from sticky to sticky. This is a better and more classical method in the current research methods.
2. High temperature melting method
The principle is: at a high temperature, the crystal form of the PTFE surface is changed, and some substances with high surface energy and easy adhesion are embedded, such as SiO1 and Al powder. After cooling, a layer of a layer embedded with a tacky substance is formed on the surface. Since the molecules of the easily viscous substance have entered the PTFE surface layer and destroyed it is equivalent to the intermolecular damage, the bonding strength is high. The downside is that PTFE emits a toxic substance when sintered at high temperatures.
3. Radiation grafting method
The method requires the energy of Co60, and the PTFE is placed in a polymerizable monomer such as styrene, reverse butadiene or methacrylate, and the monomer is chemically graft polymerized on the surface of the PTFE by Co60 radiation, thereby making PTFE The surface forms a layer of graft polymer that is easy to bond. The downside is that PTFE loses its original smoothness and luster.
4. Low temperature plasma technology
Low-temperature plasma refers to ionized gas generated by low-pressure discharge (glow, corona, high-frequency, microwave). Under the action of electric field, free electrons in gas obtain energy from electric field and become high-energy electrons. Molecules and atoms in a gas collide. If the energy of an electron is greater than the excitation energy of a molecule or atom, it generates excitation molecules and excitation atoms, radicals, ions, and rays with different energies. The active particles in a low-humidity plasma generally have energy that is close to or exceeds the bond energy of carbon-carbon or other carbon-containing bonds, and thus can chemically or physically interact with the gas or solid surface of the introduction system.
PTFE plates are used for gasket seals and lubricants working in a variety of media, as well as electrical insulation for use at various frequencies. Capacitor medium, wire insulation, electrical instrument insulation. Corrosion-resistant lining material and sealing lining, supporting sliders, guide rails, and electrical insulation parts.
PTFE turning board features: PTFE turning board, film, belt made of PTFE molded blanks turning, it has excellent dielectric properties, no aging, good chemical corrosion resistance and broad The range of intensity of use. The film is a non-oriented film, and the non-oriented film is pressed into a oriented and semi-oriented film.
The PTFE plate is divided into two types: a molded plate and a turning plate. The molded plate is formed by molding a polytetrafluoroethylene resin at a normal temperature, and then sintered and cooled. The turning plate is made of PTFE resin by compacting, sintering and rotary cutting. The role of the PTFE plate design sliding support structure stair (ATb type) is that in the event of an earthquake, the sliding stairs can be used as a separate unit to vibrate in small amplitudes separately, instead of violently vibrating with the main building or the earth, thus reducing the earthquake. The destructiveness is to ensure that the passages are not protected from damage during the earthquake, so that personnel can be evacuated in time. Polytetrafluoroethylene is a material with a low coefficient of friction in solids (smaller than ice). At the same time, the pressure of the PTFE sheet is greater than 30 MPa, and the tensile strength of the product itself is greater than 15 MPa (equivalent to the construction). The strength of C15砼) is more than 150. The choice of this part is two points: excellent slidability and reliable strength and elongation.