Titanium valve structure characteristics
(1) titanium alloy valve runner, to reduce the medium on the sealing surface of the direct erosion and due to the rapid contraction and expansion of the channel to produce vortex zone.
(2) Titanium is more expensive, economical and reasonable use of titanium, parts not in contact with the corrosive medium, should just try to use titanium parts.
(3) The mechanical properties of titanium changes in temperature, its value are larger than the average carbon steel or alloy steel. Its strength index decreases with temperature rise, such as 250 ~ 300 when the tensile strength and yield strength of about 50% at room temperature. Therefore, even in the case of design temperature is not high. It should be selected according to the intensity of the design temperature. Titanium is under a high yield strength and long lasting strength. Therefore, when the design temperature is below 316 C, the design strength index is often the tensile strength at this temperature. Industrial titanium cannot be heat treatment to improve the strength index value. The thermal expansion coefficient of titanium is small, when titanium and other materials used in combination, pay attention to the stress caused by deficient expansion value.
(4) Industrial titanium and α-titanium alloy plastic deformation when the pressure is slight, prone to rupture. Increasing the speed of deformation or reducing the temperature of the deformation may lead to rupturing in the process. Therefore, it is best not to design a large deformation of cold workpieces. Where flanging is required, the bend radius should be fixed as large as possible. With the strength of the expansion of pipe and tube plate tube hole clearance between the smaller tolerance to avoid titanium tube rupture.
(5) When using titanium bolts. It is necessary to consider the problem of stress relaxation caused by the creep phenomenon of titanium also at room temperature. It is best not to use titanium bolts as the compulsory sealing connector. When titanium bolts are required owing to corrosion resistance, the design of the structure should be considered to be easy to tighten the bolts regularly to ensure the sealing. Titanium, like stainless steel, also has frictional bonding and bite. Titanium thread site easily, you can use different materials or larger gaps with the thread or with a suitable lubricant solution. Should be less need to tap the internal thread. Try to use with the groove retractable car threaded structure. Similarly, the rotation of the valve stem by handwheel control titanium valve adjustment and action should be through the material properties and the various parts of the technology to guarantee.
(6) Structure design to maximize the elimination of cracks and can be kept in the recess, in order to avoid titanium in some media crevice corrosion phenomenon. In particular, the gap formed between titanium and tetrafluoride is more susceptible to corrosion than the gap between titanium and titanium because titanium is not resistant to solutions containing small amounts of soluble fluoride, which destroys the passive state. Therefore, special care should be made when using PTFE plastic mats, fluorine-containing rubber gaskets and adhesives.
(7) Due to its high chemical activity and special physical and mechanical properties, titanium can be machined by general machining methods. However, compared with other commonly used metals, there are unique requirements for mastery of certain machining techniques and processing Pay attention to the process. To prevent excessive temperature rise, lower cutting speed should be utilized, generally, it should be 25% ~ 50% lower than the cutting speed of the steel with the same hardness. With a large amount of feed, feed rate on the temperature rise is low. Do not end the cutting process, otherwise it will cause work hardening or sintering, cracking and damage to the tool. Cutting edges should be sharp, or extremely comfortable to wear, because the cutting tool wear and cutting disproportionate, the beginning of the wear and tear is small, once the tool blunt, wear immediately intensified. Use sufficient cutting fluid (5% sodium chloride solution, oil to water volume ratio of 1:20 emulsified oil, such as lubricating oil cooling lubrication, decreasing the blade edge heat, and washed away the chip.
4 titanium valve structure design
4.1 sealing pair
Globe valve with a flat seal structure, the valve body and the valve sealing Vice stop is also pointed out directly.
Titanium valve as a fluid control mechanism, valve and valve seat sealing effect is of great importance. According to the different working conditions of the valve, the general requirements of the valve sealing surface have good scratch resistance, corrosion resistance, suitable hardness, good thermal stability of the organization, crack resistance and reasonable technology and so on. Therefore, the disc, valve seat material selection titanium alloy Ti60, 260 ~ 300HB, the sealing surface allowable pressure 45MPa.
4.2 on the seal set
In order to enhance the sealing quality, the upper sealing structure is set, that is, the chamfer fit between the valve disc nut and the bonnet when the titanium shut-off valve is fully opened and the precision requirement of the chamfering process is higher.
4.3 Body and bonnet seal
Titanium body sealing between the flange and the bonnet rubber gasket, and its sealing effect is mainly by pre-installation pressure and working pressure of the working medium so that the deformation of the ring to achieve.
4.4 packing seals
The size of the stuffing box is designed according to the GB standard, and the stuffing gland and stuffing box are serialized. Install packing to avoid scratching the valve stem. Packing the gland when the net force to be uniform. Stems by the filler effect is easy to cause punctate corrosion and abrasion, is one of the reasons for the filler leaks, the solution is to reduce the content of chloride ions, sulfur ions in the filler, or the use of corrosion inhibitors and improve valve stem finish. Stem movement must also overcome the friction of the packing. Depending on the analysis, the choice of PTFE split wire braided seal packing. The material has high temperature, self-lubricating and chemical resistance, good flexibility, impermeability, low friction coefficient, improve the valve's anti-leakage ability.
4.5 Body
Titanium body structure size, form, material, medium-flange structure, connecting bolt size and medium flow path according to the standard design. Owing to the more expensive titanium, the thickness was calculated using the thin-walled formula at the time of design and the valve body strength and the number of connecting flange bolts in the flange were checked.
4.6 valve covers
Titanium bonnet and valve body together to form a pressure housing,. Valve cover to of medium pressure and temperature and other technical parameters and the valve is basically the same. Therefore, both in the design and calculation methods have similarities. Valve cover structure size and form according to GB standards, the valve cover flange size design and calculation of the equivalent flange.
4.7 valve stems
When the medium flows in from below the valve flap, the valve rod force and torque along the maximum axial load in the closed position, then the titanium valve stem compression. When the intermediate flows in from above the valve flap, the maximum load is in the open position and the valve stem is pulled.
The development of the petroleum, chemical, aerospace, shipbuilding and marine industries has promoted the rapid development of the valve industry. The titanium alloy valve structure, material and production processes conducted a more in-depth research and development, thereby enhancing the reliability of the valve and pipeline control equipment life, to meet the field of valve technology development requirements. At present, the flange of titanium valve has a national standard, passed the identification of the relevant authoritative organizations, successfully applied to a new generation of strategic projects in marine and offshore engineering.
