What should be paid attention to in the design and manufacture of titanium heat exchangers?

Titanium and titanium alloy materials have high strength, good plasticity and toughness, and have sufficient corrosion resistance and high temperature strength. They are widely used in aerospace, shipbuilding, and chemical industries. Although the one-time investment of titanium equipment is huge, the reliability and service life of the equipment are greatly improved, and the economic benefits are obvious. At present, titanium alloy pipes are increasingly used in various industries, such as petroleum, chemical, energy and other industries, as applied materials in the field of ship equipment and seawater desalination technology. Research work on the weldability and welding process development of titanium and titanium alloys has received extensive attention.

my country's titanium industry has made great progress in the development process of the past few decades. Relevant departments attach great importance to the development and research of titanium and titanium alloy application technology, especially the application technology of marine titanium alloy, which has a significant increase in the consumption of titanium alloy. At present, the marine titanium alloys used in our country include TA2, TA16 and TA17, etc., which have been applied to a certain extent on ships. Most of the research on the performance of these titanium alloy products stays in the basic performance research, such as stretching, bending, etc., and there is no data that can be evaluated in depth. In addition, there are few reports on the research of titanium alloy pipelines, and it is necessary to continue to invest in titanium alloy scientific research. Funds, to carry out low-cost technical research, while ensuring that the product has good performance, can further reduce the processing and manufacturing costs of the product, and at the same time, it is necessary to conduct experimental research in a specific marine environment to accumulate more data to support the titanium alloy crafts improvement.

Application of titanium and titanium alloys in the field of ships

The superior performance of a ship indicates the strength of the navy's combat effectiveness. The ship is a platform for maritime transportation and combat, and is the most important equipment of the navy. Therefore, the material properties of the warship must be very good, while reducing the cost of service, ensuring the operation and maintenance of the ship system, and enhancing the combat capability of the ship. Titanium alloys have excellent mechanical properties, corrosion resistance, erosion and corrosion resistance, and high strength. They are used on ships to improve the reliability and effectiveness of ships and achieve weight reduction and load increase. At present, there have been a large number of experience in the use of pipeline materials in ships to prove that the service life of traditional materials is limited. Pipes made of steel pipes have a service life of only 1 to 2 years. Pipes made of copper-nickel alloy materials have a service life of only 1 to 2 years. 6 to 8 years, while the pipes made of titanium alloy materials have a service life of more than 40 years.

After decades of development, the level of titanium alloys for ships in China has been greatly improved, and a titanium alloy system for independent ships has been formed. Different ships have different strength requirements. Titanium alloys of different strengths are used in different parts, mainly for Heat-resistant and corrosion-resistant parts and special marine machinery in ship power engineering. Titanium alloys are widely used in ships, including hull structures, propulsion systems, power systems, auxiliary systems and special equipment. It can be said that titanium alloy materials can be used for all large equipment and components except for ship accessories and cabin facilities.
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Performance requirements for titanium containers and titanium alloy tubes for petrochemical industry

Titanium plate has the characteristics of low density, high specific strength, and corrosion resistance, and has great potential for application in the automotive industry. The use of titanium and titanium alloys on cars can save fuel, reduce engine noise and vibration, and improve life span. However, for a long time, automotive materials have always been the country for materials such as steel and Al. In order for Ti materials to enter the automotive market, in addition to its own functional advantages, costs must be further reduced to a level acceptable to the automotive industry. Ti titanium plate metallurgical parts for automobiles are a very promising category, but due to the current constraints of cost and other factors, the application and implementation of metallurgical parts are slow. Using leading titanium plate metallurgy technology to prepare Ti titanium plate metallurgical parts can not only greatly reduce the cost, but also help the promotion of Ti and its alloys in the automotive industry, making it another major application after the aerospace industry category. The development of low-cost titanium and its alloy titanium plates can provide low-cost materials for metallurgical parts of titanium and titanium plates for automobiles. Judging from the existing skills, the sponge Ti powder method, the hydrogenation dehydrogenation method and the metal hydride restoration method are mainly suitable for the automobile industry.

1. Sponge Ti powder method

This is currently a way to meet the needs of the automotive industry in terms of cost. The first step is to use the traditional production sponge Ti and the residual material in the process to crush it; the obtained titanium plates are often relatively coarse and rich in content. Cl element. U.S. Huachang Company chooses the gas phase method to introduce TiCl4 and Mg vapors into a tube furnace at 850°C successively to quickly produce fine Ti powder and MgCl2, but it is difficult to separate such fine powder from MgCl2, and the content of O is high; Japan creates one The spray response method sprays the gas onto the liquid Mg to generate particles. The test shows that about 100 grams of Ti powder with a particle size of tens of microns can be prepared for every 100 grams of Mg and 400 grams of TiCl4, and the production power has increased by 2 times. , The cost is reduced by 50%, and it is expected to be used as the material for titanium metallurgical Ti products.

2. Hydrodehydrogenation method

This method is due to the wide planning of the titanium plate size, low cost, less stringent requirements for materials, and easier technology to complete. Through years of improvement and implementation, it has become the primary method for preparing Ti powder at home and abroad. However, the titanium plates prepared by this method tend to have a high content of O, N, etc. The Northwest Research Institute of Nonferrous Metals in China selected hydrogenation and dehydrogenation technology to hydrogenate and dehydrogenate the ingots and produced high-quality titanium plates with low O, N, and Cl. It has outstanding functions and has been able to produce O content of less than 0.20%. Titanium plate has been mass-produced, and it is expected to supply stable titanium plate for metallurgical parts of automobile titanium plate.

3. Metal hydride restoration method

TiCl4 can be restored with hydrogen at 3500°C, and TiO2 can be restored with carbon heat above 1800°C. In order to reduce the reaction temperature, the former Soviet Union scientists proposed to use CaH2 to restore TiO2 and TiCl4, which can be carried out at a temperature of 1100 to 1200 ℃, the reaction generates TiH2, and then de-H to obtain Ti powder. Because this method does not have a Cl element to participate in the reaction, it is possible to obtain a titanium plate with extremely low Cl content. Although the Ti powder produced by this method has a higher H content, it is reported that the presence of a small amount of H is beneficial to the sintering of the titanium plate and the improvement of the microscopic arrangement, and can be completely removed in the subsequent vacuum sintering and annealing process.
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The reaction of titanium alloy materials such as titanium rods and titanium tubes in air is closely related to temperature.

Titanium alloys are widely used because of its series of excellent properties. However, titanium alloys have high friction coefficients, are very sensitive to adhesive wear and fretting wear, have poor wear resistance, are easy to ignite at high temperature and high speed friction, and have relatively poor resistance to high temperature oxidation. The shortcomings seriously affect the safety and reliability of its structure and greatly limit its application. Therefore, improving the surface properties of titanium alloys such as wear resistance, high temperature oxidation resistance and corrosion resistance is an urgent problem to be solved. In addition to improving the composition and preparation process of the alloy, surface modification of titanium alloy is currently the most effective method.

In recent years, electron beam surface treatment technology has developed rapidly. When the electron beam with high energy density acts on the surface of the material, the surface of the material has physical, chemical or mechanical properties that are difficult to achieve by conventional methods, and the wear resistance and corrosion resistance of the material surface are significantly improved. And high temperature oxidation resistance. A domestic engineering technology company used pulsed high-current low-energy electron beams for surface treatment of titanium alloys and achieved good results.

The material used in the experiment is TA15 titanium alloy (Ti-6.5Al-2Zr-1Mo-1V). After the surface of the sample is polished, the surface is modified with a high-current pulsed electron beam. The electron beam acceleration voltage is 27kV, the target distance is 80mm, and the pulse The number of times is 10, and the pulse interval is 45s.

The hardness test of the obtained sample shows that as the depth increases, the hardness value first decreases and then increases, and finally tends to a fixed value. This special oscillating curve distribution can be explained as: under the pulsed high-energy rapid irradiation, a heating shock wave will sprout in the energy absorbing layer of the material, and it will be reflected back when it encounters the interface. Multiple irradiations cause interference and superposition of stress waves with each other, presenting a complex stress distribution state, resulting in a special distribution of cross-section microhardness.

The wear volume of the sample after electron beam treatment is 3 times higher than that of the original sample, indicating that the wear resistance of TA15 titanium alloy after electron beam treatment is improved. The reasons may be the following three aspects:

(1) The high energy of the electron beam is instantly deposited in a small area of ​​the subsurface layer of the material, so that the material quickly rises to the phase transition temperature or the melting temperature, and then the substrate heat conduction to achieve ultra-high-speed cooling (about 109K/s) to make the surface of the material The quenching effect occurs, which plays a role of solid solution strengthening, so the wear resistance of the surface is improved;

(2) The electron beam rapid solidification process will refine the grains of the surface layer of the material, thereby improving the wear resistance of the material;

(3) When the electron beam pulse acts on the surface of the material, the temperature begins to rise rapidly, and the inwardly propagating compressive thermal stress wave is generated due to the restraint of the rapid outward thermal expansion of the material surface. The residual stress forms a compressive stress distribution, which is beneficial to improve wear resistance.

The corrosion performance test showed that the corrosion potential of the original sample increased from -258.3mV to -107.5mV after the electron beam surface treatment, and the polarization resistance increased from 0.796k/cm2 of the original sample to 2.424k/cm2. At the same time, the self-corrosion current was higher than that of the original sample. Significant decline. This shows that the corrosion resistance of the sample is significantly improved. The main reasons for the improvement of corrosion performance are:

(1) The high temperature caused by the strong current pulsed electron beam irradiation on the surface of the sample can vaporize or desolute the adsorbed or adhered impurities on the surface of the material, and play a cleaning role;

(2) The surface of the material melts quickly, and then solidifies at the same high speed. This process inhibits equilibrium crystallization, and can obtain a dense non-equilibrium structure with uniform composition, which also inhibits the occurrence of self-corrosion to a certain extent;

(3) The rapid cooling of the surface layer of the material refines the surface grains, which leads to a reduction in the area ratio of the cathode and anode and reduces the corrosion rate.
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Titanium alloy parts processing plays an important role in machinery manufacturing

In recent years, with the development of the automobile industry, the world's automobile production and ownership have increased day by day. In 2009, my country's automobile industry advanced by leaps and bounds, with automobile production and sales exceeding 13 million, surpassing the United States and Japan to become the world's largest automobile production and sales country. While automobiles bring convenience to people's travel, they also have three major problems in fuel consumption, environmental protection, and safety. Focusing on sustainable development considerations, it is particularly urgent to reduce fuel consumption and reduce emissions. According to statistics from international authorities, about 60% of the fuel used in automobiles is consumed by the weight of the automobile. For every 10% weight reduction of a car, exhaust emissions can be reduced by 10% and fuel consumption can be reduced by 7%. It can be seen that reducing the weight and weight of automobiles is an effective measure to achieve the above goals.

There are two main ways to realize automobile lightweight: one is to optimize automobile frame structure; the other is to use lightweight materials in automobile manufacturing. At present, the light alloys used in automobiles mainly include metals such as aluminum, magnesium, and titanium alloys.

1. Application and characteristics of titanium alloy in automobiles

Titanium alloy is a new type of structural and functional material. It has excellent comprehensive properties, low density and high specific strength. The density of titanium is 4.51g/cm3, which is between aluminum (2.7g/cm3) and iron (7.6g/cm3). The specific strength of titanium alloy is higher than that of aluminum alloy and steel, and the toughness is equivalent to that of steel. Titanium and titanium alloys have good corrosion resistance, better than stainless steel, especially in the marine atmosphere, they resist the corrosion of chloride ions and have good corrosion resistance in a micro-oxidizing atmosphere. The working temperature of titanium alloys is wider, and low temperature titanium alloys are at -253℃. It can also maintain good plasticity, and the working temperature of heat-resistant titanium alloy can reach about 550°C, and its heat resistance is significantly higher than that of aluminum alloy and magnesium alloy. At the same time, it has good processability and welding performance.

The excellent properties of titanium and titanium alloys have attracted the attention of various cutting-edge industries since the industrial production of titanium. With the start of the titanium industry, in the mid-1950s, titanium entered the automobile industry. Entering the 1990s, with the global energy shortage and the strengthening of people’s awareness of environmental protection, especially in the automotive industry, the United States, Japan, and Europe have successively promulgated a series of ecological regulations to regulate fuel efficiency, CO2 emissions, vehicle weight reduction, The safety and reliability of automobiles put forward higher requirements. Many developed countries and well-known automobile manufacturers are actively developing and increasing research investment in titanium for automobiles. Provides powerful power for automotive titanium. In the new century, my country's titanium industry has gradually entered the automotive field.

2. Titanium parts used in automobiles

The uses of titanium in automobiles are mainly divided into two categories. The first category is used to reduce the mass of internal combustion engine reciprocating parts (for internal combustion engine parts that perform reciprocating motion, even reducing the mass of a few grams is important); the second category Is used to reduce the total mass of the car. According to the design and material characteristics, titanium is mainly distributed in engine components and chassis parts in the new generation of automobiles. In the engine system, titanium can be used to make parts such as valves, valve springs, valve spring holders and connecting rods; in the chassis parts are mainly springs, exhaust systems, half shafts and fasteners.

According to the information, in addition to the above mentioned key points, there are also: rocker arms, suspension springs, piston pins, turbocharger rotors, fasteners, lug nuts, car stop brackets, door projection beams, brakes Caliper piston, pin shaft bolt, clutch disc, pressure plate, shift button, etc.

Ways to reduce the cost of titanium alloys. Although titanium and titanium alloys entered the field of automobile manufacturing as early as the 1950s, their development was relatively slow, mainly due to price factors. In order to satisfy the use of titanium in the automobile industry, titanium manufacturers carried out smelting, processing, and manufacturing. A lot of work. To meet the needs of the automotive industry.

3. Reduce processing costs

The processing cost, which accounts for more than 60% of the total cost, is the focus of research on cost reduction in various countries. In the production process of titanium parts, not only the process is complicated, but also a large amount of residual titanium is generated during the production process, and the production cycle is long, which leads to an increase in the production cost of the parts. It hinders its wider promotion and application.
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Advantages, Disadvantages and Applications of Titanium Alloy Fasteners

Titanium is a very active metal. In the liquid state, it reacts very quickly with oxygen, nitrogen, hydrogen and carbon. Therefore, the smelting of titanium alloys must be carried out under the protection of higher vacuum or inert gas (ar or ne). Crucibles for smelting are all water-cooled copper crucibles. The specific smelting process mainly includes three methods: (1) Non-consumable electrode arc furnace smelting. Alloy smelting is carried out under the protection of vacuum or inert gas. The process is mainly consumable electrode smelting to prepare electrodes. (2) Vacuum consumable electrode electric arc furnace smelting The consumable electrode made of titanium or titanium alloy is used as the cathode, and the water-cooled copper crucible is used as the anode. The molten electrode enters the crucible in the form of droplets, forming a molten pool. The surface of the molten pool is heated by the electric arc and is always liquid, and the surrounding area where the bottom and the crucible are in contact is forced to cool, resulting in bottom-up crystallization. The molten metal in the molten pool becomes a titanium ingot after solidification. (3) Vacuum consumable electrode condensed shell-protected smelting The smelting device is shown. This furnace is developed on the basis of vacuum consumable electrode electric arc furnace. It is a furnace type for casting special-shaped parts that combines smelting and centrifugal casting. Its biggest feature is that there is a thin solid shell of titanium alloy between the water-cooled copper crucible and the molten metal, the so-called solid shell. This solid shell of the same material is used as the lining of the crucible to form a molten pool to store titanium liquid , To avoid the crucible pollution to the titanium alloy liquid. After pouring, the layer of condensed shell left in the increased loss can be used as the lining of the crucible.

In recent years, with the development of science and technology and the needs of production, new methods and equipment for smelting titanium alloys and other active metals have been researched and developed, mainly electron beam furnaces, plasma furnaces, vacuum induction furnaces, etc., and have achieved a certain degree of application. However, from the comparison of technical and economic indicators such as power consumption, melting speed, and cost, consumable electrode electric arc furnace (including condensing shell furnace) smelting is still the most economical and applicable smelting method at present. Due to the physical-chemical properties of titanium, the casting process of titanium alloys has its own unique requirements and characteristics, whether it is the molding material rate or the process method. One is a molding material that requires a very high refractoriness; the other is that the pouring must be carried out under the protection of a higher vacuum or inert gas, sometimes with centrifugal force. The material of the connecting shell is different, and the fusion shell is divided into three different systems.

(1) Pure graphite shell system. Graphite powders of different particle sizes are used as refractory fillers and sanding materials, and resins are used as adhesives. The shell has high strength, light weight, low cost, and a wide range of raw materials. Suitable for centrifugal or gravity pouring.

(2) Refractory metal surface layer shell system. It is a composite system, except that the surface layer requires special processes due to different modeling materials (tungsten powder and other refractory metals), and the back layer from the modeling material to the shell making process is the same as the investment casting of cast steel.

(3) Oxide ceramic shell system. The surface and back layer of the shell are made of oxide as the modeling material, so the shell strength is high, and the thermal conductivity is the smallest among the three kinds of shells. It is suitable for pouring thin-walled castings with complex shapes.

Titanium castings poured by the above three shell systems have little difference in chemical composition and mechanical properties; but there are obvious differences in surface quality. The shrinkage rate of the latter two shells is significantly smaller than that of graphite shells, so the dimensional accuracy of the castings.
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Precautions for processing titanium alloy parts during processing

The welding performance of titanium, titanium alloy, and titanium wire has many remarkable characteristics. These welding characteristics are determined by the physical and chemical properties of titanium and titanium alloy. When welding titanium and titanium alloys, the possibility of hot cracks in the welded joints is very small. This is because the content of impurities such as S, P, and C in titanium and titanium alloys is small, and the low melting point eutectic formed by S and P is not easy to appear On the grain boundary, coupled with the narrow effective crystallization temperature range, the shrinkage of titanium and titanium alloys is small during solidification, and the weld metal will not produce thermal cracks. When welding titanium and titanium alloys on time, cold cracks can appear in the heat-affected zone, which is characterized by cracks that occur several hours or even longer after welding, which is called delayed cracks. Studies have shown that this kind of crack is related to the diffusion of hydrogen bombs during welding. During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower-temperature heat-affected zone. The increase in hydrogen content increases the amount of TiH2 precipitated in this zone, which increases the brittleness of the heat-affected zone. In addition, the volume expansion during the precipitation of hydrides causes greater structural stress. , Coupled with the diffusion and accumulation of hydrogen atoms to the high-stress parts of the region, resulting in the formation of cracks. The method to prevent this kind of delayed cracking is mainly to reduce the source of hydrogen in the welded joints. When invoices are issued, the fire suppression treatment is also carried out.

When welding titanium and titanium alloys, porosity is a common problem. The root cause of the formation of pores is the result of the influence of hydrogen. The formation of pores in the weld metal mainly affects the fatigue strength of the joint. The main technological measures to prevent pores are:

(1) The protective neon gas should be pure, and the purity should not be less than 99.99%

(2) Thoroughly remove organic matter such as oxide scale and oil stains on the surface of the weldment and the surface of the welding wire.

(3) Apply good gas protection to the molten pool, and control the flow and flow rate of argon to prevent turbulence and affect the protection effect.

(4) Correct selection of welding process parameters and increase the right to use the deep pool residence time to allow bubbles to escape, which can effectively reduce pores.

The gas shielding problem of titanium and titanium alloy welding is the primary factor affecting the quality of welded joints. When welding titanium and titanium alloys, the heat input should be as small as possible. The source of hydrogen should be strictly controlled to prevent cold cracks. At the same time, attention should be paid to prevent the generation of pores. As long as welding is carried out in strict accordance with the welding process requirements and effective gas protection measures are taken, high-quality welded joints can be obtained.
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Reasons and characteristics of the inner edge of the titanium tube

Titanium rod barrel burnishing is to grind the parts and abrasives in dilute acid or dilute alkali with emulsifier (or corrosion inhibitor) and follow the rotation of the drum to obtain a bright appearance. It is suitable for the disposal of small parts and parts that are difficult to polish and polish. Correct selection of roller burnishing standards can improve productivity and quality

(1) The shape of the roller

The shape of the roller is round, hexagonal and octagonal, among which the polygonal shape is good for practicality. This is because the radii of the barrel wall from the axis are not equal, and there is a certain point of view, so the rolling parts are easy to change the position, the chance of collision with each other increases, the grinding is uniform, and the efficiency is high, which can shorten the rolling time.

(2) The size of the drum

The direct alignment is 50mm-100mm, and the length varies with the number of grids. The length of the first pattern roller is 600-800mm; the second pattern is 800-1500mm. Usually the larger one is better. This is because the parts are subjected to high pressure and friction in the drum, so the amount of cutting is also increased. But for those parts that are afraid of being stressed and easily deformed, a small roller can be used and the length of the roller can be increased.

1) Data for roller

There is a direct relationship between the rotation speed of the drum and the scraping amount of the parts within a certain range, that is, the faster the rotation speed, the greater the scraping of the metal surface. However, when the speed exceeds a certain upper limit, it drops instead. Because when the rotating speed is too fast, the centrifugal force of the parts in the drum increases, which reduces the friction. Usually it is appropriate to control at 45r/min.

2) Abrasives and solutions for roller burnishing

Abrasives for rolling include pumice, quartz, granite skin angles, shells, iron filings and ceramic fragments. The size of the abrasive particles should be larger or smaller than each hole of the Cen part. The amount of content in the drum is also an important factor affecting the quality of the agricultural surface of the parts. The amount of people inside the drum is usually 70% of the drum volume. Regarding heavier parts or threaded parts, the load should be controlled at 80%-90%. The solution in the drum should be added to about 95% of the drum volume (note: when adding acidic solution to the drum, you should add enough water first, and then add acid to avoid corrosion of parts during the tumbling process, because of the increase in time. , The concentration of the built-in solution gradually decreases, or even loses its effect. Therefore, the concentration of the solution should be checked and replaced at intervals. The burn-in time should not be too long, otherwise the parts will be damaged. That is, use a brush to remove the surface of the parts. Burr, terbium, residual oil and corrosion sludge, etc., and make the parts have a certain luster. Be sure to point out that elastic, rigid or thin-walled parts should be taken out in time after the finishing of rolling, otherwise it will easily cause hydrogen seepage or local over-corrosion .
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