Operation flow of vacuum furnace heat treatment process
What is the heat treatment process of vacuum furnace? After purchasing the vacuum furnace, some friends don't know how to operate it. Today, we will share the operation process of the heat treatment process of the vacuum furnace for your reference.
1. When the workpiece is quenched in vacuum, vacuum quenching oil should be used, which has low saturated vapor pressure.
2. The maintenance of vacuum furnace should be in the state of vacuum or pure nitrogen filling to avoid suction and moisture absorption when not in use.
3. The pressure rise rate of domestic vacuum furnace should be no more than 1.33pa/h, and the standard of some foreign enterprises is 0.67pa/h.
4. Vacuum tempering furnace should be equipped with quick cooling device. The pressure of cooling water should be greater than 0.2MPa, and the flow rate should be adjustable.
5. Nitrogen should not be used as cooling gas when treating titanium alloy, because titanium reacts with nitrogen at high temperature to form golden titanium nitride.
6. Cooling gas: nitrogen with 99.995% purity is generally used for steel, nitrogen or argon with 99.999% purity is used for superalloy, and argon with 99.995% purity is used for titanium alloy.
7. The vacuum heating is mainly radiation, and the workpiece should be kept at a distance in the furnace.
8. In the process of heating up, the workpiece and materials in the furnace will be deflated, which will reduce the vacuum.
9. Heating: after the workpiece is put in, the temperature can be raised when it is pre pumped to 6.67pa
10. The heating temperature of vacuum tempering, vacuum annealing, vacuum solution treatment and vacuum aging is generally the same as that of conventional treatment.
The vacuum furnace eliminates the oxidation and decarburization of the workpiece surface in the heating process, and can obtain a clean surface without deterioration layer. The heating chamber of the vacuum furnace is made of high-quality heat insulation materials with heat insulation walls and barriers, which can highly concentrate the electric heating energy in the heating chamber, with remarkable energy-saving effect. The following is a professional analysis of the functions of the vacuum furnace:
Vacuum quenching (tempering, annealing) is a treatment method to achieve the expected performance by heating and cooling the material or parts in vacuum according to the process specification.
Vacuum brazing is a welding process in which a group of weldments are heated to a temperature above the melting point of the filler metal but below the melting point of the base metal in vacuum, and a weld is formed by the wetting and flowing of the filler metal to the base metal (the brazing temperature varies with different materials).
Vacuum sintering is a method of heating metal powder products in vacuum to make adjacent metal powder grains form parts by adhesion and diffusion. Vacuum magnetization is mainly used for magnetization of metal materials.
The assembly method of the combined vacuum pump is slightly different from that of the integral type. Taking the small five piece rotary vane vacuum pump as an example, it is composed of the high and low end cover plates, the high and low vacuum pump cavity components and the middle diaphragm plates to form the whole vacuum pump body. The assembly sequence is as follows.
First of all, clamp the bottom of the middle partition plate assembly up on the long vice (100 caliber, 220 mm long), and pay attention not to use too much force to crush the sealing surface. When clamping, two pieces of iron (about 10 mm in thickness) less than the thickness of the vacuum pump assembly should be padded. Because the high and low rotor shafts of this kind of vacuum pump work synchronously through the cross joint at the shaft end, the high vacuum pump cavity group on the side of the vacuum pump wheel should be installed first. The specific method is to install the rotating plate and spring into the high rotor groove, pinch the rotating piece into the vacuum pump cavity, and then insert the shaft end with the convex head into the shaft hole of the middle diaphragm, and then insert the end cover The shaft seal hole on the disc is aligned with the rotor shaft, and the two sets of high-end plates are fixed on the middle partition plate with bolts. When the bolts are not too tight, tap the end cover gently with a small hammer to make the rotor and the vacuum pump cavity natural diagonal square (right angle), and then tighten the bolts with force. However, it should be noted that there should be no blockage when rotating the vacuum pump wheel, and then install another one Low vacuum end; The cross groove at the shaft end of the low rotor should be tightly connected with the convex head of the high rotor extending through the middle partition plate. After installing the low end end cover with the same method, tighten it. At the same time, tap the end cover with a hammer, and finally tighten the bolts. At this time, it takes a lot of effort to rotate the vacuum pump wheel at first. After a few weeks of rotation, one hand should rotate, but there should be no local wheel weight block. Then, the two end covers are disassembled again Hold on with your hands
Take out the rotor by rotating the blade and carefully observe whether there are uniform line scratches on the rotor. If so, it indicates that the assembly is appropriate. If there is a black line at one end of the rotor, it is necessary to further check whether there is taper at both ends of the rotor or vacuum pump cavity. If the two ends are the same size, it means that the rotor and the vacuum pump cavity are not square, and the rotor is installed askew. According to the position of the black line on the rotor, the correction effect can be corrected according to the position of the black line on the rotor If there is no light line mark on the rotor, it means that the rotor is not close to the vacuum pump cavity at all. At this time, the assembly pieces at both ends of the middle partition plate should be raised by one or two wires (only by reaming the four corner fastening bolt holes), so that the vacuum pump chamber and the rotor are close. If no other problems are found, apply insect glue paint solution to the sealing joint Auxiliary sealing, and finally loading and testing.
The positive exhaust blower can be used in series with the vane pump to obtain a higher pumping speed and lower limit pressure under medium vacuum than when the vane pump is used alone. Roots vacuum pump, or roots blower, consists of a pair of cocoon shaped rotors mounted on two parallel shafts. The clearance between the rotor itself and between the rotor and the pump housing is typically about 0.2mm. The two rotors rotate synchronously in reverse at 3000rpm to 3500rpm. Since the clearance between the rotor and the pump housing is not sealed with oil, this speed is feasible.
The compression ratio of Roots vacuum pump, or the pressure ratio between inlet and outlet of pump, is related to pressure, and its maximum value is close to 100Pa. At higher pressure, the compression ratio of the pump is smaller, which is because the conductance in the sub clearance increases with the increase of pressure. In theory, the compression ratio should remain unchanged at a lower pressure, but it is actually decreased. The outgassing and the roughness of the rotor surface make the compression ratio lose at low pressure. When the rotor faces the high pressure side, the surface of the rotor will absorb gas, and when the rotor faces the high pressure side, a part of the adsorbed gas will be released. The maximum compression ratio is 44. The compression ratio of large J pump is higher than that of small pump, because the space occupied by clearance of large pump is smaller than that of pump volume. A light gas like nitrogen has a compression ratio of 15-20% less than that of air. The compression ratio is a static quantity, which is obtained under the condition of zero flow rate. During the measurement, the inlet of the pump is sealed and connected with a pressure gauge, and the exhaust port is connected with a closed coarse pump, and the whole system is pumped. Put the gas into the front pipe of Roots vacuum pump and vane pump, measure the pressure P (front stage pressure) at the exhaust port of Roots vacuum pump, and measure the pressure P1 at the air inlet. The compression ratio is obtained from P / P1.
Under high pressure, considerable heat will be produced when the roots vacuum pump is used to exhaust gas, which will cause expansion of the rotor and may damage the pump. In order to avoid overheating, the maximum pressure difference between the inlet and outlet of Roots vacuum pump is specified. The maximum pressure difference is generally 1000Pa, but exceeding this value in a short time will not cause damage to the pump. In order to avoid heating, roots vacuum pump is connected by compression pump or transfer pump.
In the common way of compressed exhaust, roots vacuum pump and rotary vane pump are used in series, and the rated pumping speed of rotary vane pump is 5 to 10 times lower than that of Roots vacuum pump. When pumping from atmospheric pressure, the bypass pipe around roots vacuum pump should be opened or the roots vacuum pump should be idle. At this time, the mechanical pump is responsible for all the pumping function, until the pressure of the front stage is lower than the pressure difference recommended by the manufacturer, then start the roots vacuum pump and close the bypass valve.
Shortly after the vacuum pump started to work, the minimum pressure P'g appeared. The vacuum pump continues to operate. Because of the increase of vacuum pump temperature, the saturated vapor pressure and viscosity of vacuum pump oil rise and viscosity drop, and the inlet pressure slightly rises to PG. PG is the stable minimum pressure obtained by the vacuum pump, and also the limit pressure of the vacuum pump.
The limit pressure of the rotary vane vacuum pump is related to the type of vacuum gauge used in measurement. When the compression vacuum meter is used, the limit pressure value is about one order of magnitude lower than that measured by the heat conduction vacuum meter (thermocouple or piezometer, etc.). This is because the former can only measure the partial pressure of permanent gas, the latter is the total pressure of the compressed gas. The current regulations of our country use compression vacuum gauge to measure the limit pressure of oil seal mechanical vacuum pump.
The circulating oil quantity of vacuum pump also affects the limit pressure of vacuum pump. With the increase of oil quantity, the better sealing effect is, the relationship between the limit pressure and oil quantity of vacuum pump changes, and the saturation vapor pressure Po of oil is achieved. In fact, there is a lot of air and water in the vacuum pump oil. After the vacuum pump oil enters the vacuum pump cavity, the air and water absorbed in the vacuum pump oil are released. The relationship between the limit pressure and the oil quantity of the vacuum pump develops upward.
Generally, the vacuum pump oil should be kept on the specified oil level, so that the circulating oil quantity of the vacuum pump should be kept to a certain extent. For double stage vacuum pump, vacuum pump oil can enter high vacuum stage only after degassing at low vacuum stage, so that the amount of air discharge of vacuum pump oil in high vacuum stage can be reduced, so as to reduce the limit pressure of vacuum pump.
The limit pressure of vacuum pump is related to the working temperature of vacuum pump oil. The higher the oil temperature, the higher the saturated vapor pressure of the oil, the higher the limit pressure of the vacuum pump.
When the concentration process USES air flotation, the sludge contains a large number of bubbles. In order to improve the sludge dewatering effect, flocculant is often needed to be added. In order to protect the floc from being damaged, high-speed rotation or large shear force should not be generated during the transport process. In addition, the choice of sludge pump, also should adapt to the type of dehydrator. For example, when the plate and frame filter press is used, the pressure changes from low to high and the flow changes from large to small in the mud process. At present, the centrifugal pump has a wide range of applications, but its shear force on the conveying medium is large. Diaphragm pump is used for corrosive media and dosing system. Plunger pumps are expensive and are used in very high pressure requirements. Screw pump and CAM rotor pump can be continuous, uniform transport medium, no turbulence, agitation, pulsation and shear phenomenon, especially suitable for pumping concentrated sludge, * to a large extent to maintain the characteristics of sludge, protect floc is not destroyed, so as to obtain * good dehydration effect. Related products:
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13.01.2021 09:08
