Titanium plate heat exchanger is a new type of high-efficiency heat exchanger with corrugated heat transfer surface, which is widely used in the heating, cooling, condensation and evaporation process of chemical, petroleum, metallurgy, electric power, shipbuilding, ocean, medicine and other industrial sectors . With people's further understanding of the superiority of the plate heat exchanger and the expansion of its application fields, the plate heat exchanger has developed rapidly and has now become the main heat exchange equipment. Due to its high efficiency, compactness and excellent corrosion resistance, titanium plate heat exchangers have become the first choice for many strong corrosive conditions. Titanium plates for plate heat exchangers are mainly pure titanium plates with a thickness of less than 1.0mm, which have special requirements for the strength, elongation, cupping, and grain structure of the plate. In order to increase the development of plate heat exchangers, make them more widely used in various fields, fully realize the localization of titanium plates for plate heat exchangers, and improve the quality of plate refueling, it is necessary to study the organization of various rolling processes for plate refueling And the impact of performance, to further improve the rate of plate replacement pressing.
How does the rolling process affect the structure and performance of the titanium plate used in plate heat exchangers?
The first rolling process uses one-way rolling. Due to the unidirectional rolling process, the plate elongates along the rolling direction, the crystal grains are elongated, and become columnar crystals into a band-like structure. The number of grains in each direction of the columnar crystal is different, and the number of grain boundaries is also different, so the processing structure produces anisotropy, high strength, poor plasticity and deep drawing performance. The second rolling process uses reversing rolling. After the commutation rolling, the grains in the longitudinal and transverse directions are elongated and become columnar crystals. In the last pass of cold rolling, the processing rate is greater than 50%, causing the grains to be broken. The columnar crystals that have been broken after recrystallization annealing re-nucleate and crystallize into equiaxed grains. Compared with the first rolling process, the mechanical properties are greatly improved, especially the plastic deep drawing properties. However, the metallographic examination found that there are still slip lines in the fine structure, indicating that the recrystallization is still insufficient, and the temperature or the time needs to be increased. The difference between the third rolling process and the second rolling process is that the heat treatment process is different. The electric furnace is used for heating, and the plates are stacked for annealing, which reduces the pollution on the surface of the titanium plate, and the holding time is slightly extended. The metallography presents an equiaxed grain structure, the grains are smaller than those of the second rolling process, and they are complete and fully recrystallized, so the mechanical properties are also better than those of the second rolling process.
Through the above test, the mechanical properties obtained by the three rolling processes are different from the microstructure, and the mechanical properties of the plate using the third rolling process, especially the cupping value and elongation are better than the first two The mechanical properties of one rolling process state, and the grain size is 1 to 1.5 levels smaller than the second rolling process state, which meets the conditions of plate replacement and pressing, and the forming rate reaches about 95%, which can be used for plate heat exchangers. Titanium plate has higher utilization rate and considerable profit margin, which is worthy of promotion.
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