Titanium alloy valve structure features
(1) In order to reduce the media on the sealing surface of the direct erosion and because of the rapid contraction and expansion of the channel vortex zone.
(2) Titanium is more expensive. For economic and reasonable use of titanium, titanium parts should not be made of titanium as far as possible in the parts that do not contact with corrosive media.
(3) The mechanical properties of titanium material change with temperature, and its value is larger than that of ordinary carbon steel or alloy steel. Its strength index decreases with the rise of temperature. For example, the tensile strength and yield strength at 250 ~ 300℃ are about 50% of that at room temperature. Therefore, even if the design temperature is not high, it should be selected according to the strength value at the design temperature. Titanium has a high yield ratio and good durable strength. Therefore, when the design temperature is below 316℃, the tensile strength value at this temperature often determines the design strength index. The strength index of industrial pure titanium cannot be improved by heat treatment. Titanium thermal expansion coefficient is small, when titanium and other materials used together, attention should be paid to the stress caused by the expansion value difference.
(4) The plastic deformation range of industrial pure titanium and α -titanium alloy during pressure processing is small and easy to produce rupture. However, increasing the deformation speed or decreasing the deformation temperature may lead to the rupture in machining. Therefore, it is best not to design large deformation of cold working parts. Where flanging is required, the bending radius should be as large as possible. The gap tolerance between the pipe and tubesheet hole connected by strength expansion should be small, so as not to crack the titanium tube.
(5) when choosing titanium bolts, it is necessary to consider the stress relaxation problem caused by creep of titanium at room temperature. It is best not to use titanium bolts as forced sealing connectors. When titanium bolts are required for corrosion resistance, the structural design should consider the ease of regular tightening of bolts to ensure sealing. Titanium and stainless steel, also has friction bonding and occlusion phenomenon. Titanium thread is easy to bite, can use different materials or large gap thread matching or with appropriate lubricant to solve. Should use less tapping internal thread, as far as possible to use the tool back groove car thread structure. Similarly, the adjustment and action of titanium valve controlled by handwheel rotating valve stem should be guaranteed by material properties and the process of each part.
(6) structure design to maximize the elimination of cracks and can store water concave, in order to avoid titanium in some media gap corrosion phenomenon. In particular, titanium and tetrafluoride crevices are more susceptible to corrosion than titanium-titanium crevices, because titanium is not resistant to corrosion in solutions containing small amounts of soluble fluoride, which causes dull damage. Therefore, special care should be taken when using ptfe plastic pads, fluorinated rubber gaskets and binders.
(7) Due to the high chemical activity and special physical and mechanical properties of titanium, the general cutting method can be used for cutting, but compared with other commonly used metals, there are special requirements, master certain processing technology, pay attention to in the process of processing. In order to prevent the temperature rise is too large, the lower cutting speed should be used. Generally speaking, the cutting speed should be 25% ~ 50% lower or lower than that of steel with the same hardness. Adopt large feed quantity, feed quantity has little influence on temperature rise. Do not stop cutting in the process of cutting, otherwise it will cause hardening or sintering, extrusion crack and damage the tool. The cutting edge of the tool should be sharp, otherwise the tool is easy to wear, because the cutting tool wear and cutting amount is not proportional to the beginning of the wear is very small, once the tool becomes dull, wear immediately intensified. Use enough cutting fluid (5% sodium chloride aqueous solution, emulsified oil and other lubricating coolants with oil/water volume ratio of 1∶20) to lubricate the cooling, reduce the heat on the blade, and wash away chips.