Tue, 11 Sep 2018 03:00:52 +0000

Vacuum furnace supply

How to control temperature in vacuum furnace

Vacuum furnace is a kind of vacuum system (made of vacuum pump, vacuum measuring device, vacuum valve, etc.) which is used in the special space of the furnace cavity to discharge some material from the furnace cavity, so that the pressure in the furnace cavity is less than a standard atmospheric pressure, and the space in the furnace cavity can realize the vacuum state. This is vacuum furnace.
Vacuum furnace as a special precision equipment, they are very high for the whole temperature control requirements. Generally speaking, how to effectively control the whole temperature is often the core technology supply in the whole vacuum furnace. In fact, his temperature control is basically carried out by the system. Through 0.1% intelligent temperature system control instrument, according to the way of process curve, the overall control is carried out. Can effectively control some of the temperature inside, the whole process of cooling and heating can also be self-running, stop the PC terminal self-control, fully realize the technical control of industrial curve temperature.
In addition, the whole process of vacuum furnace temperature control, the same system can be set, relatively speaking, there are many different curve settings, and each curve settings can be divided into several different control stages, each temperature control curve is set by some PID parameters. In contrast, they have more systematic settings, and they also have more automatic and coordinated settings. The whole system can be adapted to a variety of thermocouples and preset temperature curves.
Relatively speaking, the whole temperature controller output current signal triggered units, can be converted into some voltage signals, output control of DC voltage and current, so as to control the effective current signal, to ensure that the temperature in the vacuum furnace is in accordance with the set temperature to keep warm, after the completion of the temperature control In the whole vacuum temperature sensor and control technology for the whole heat treatment process requirements are relatively high, which is also the most critical technology.

The following four points need to be noted when heating vacuum furnace.

1. When testing furnace temperature uniformity, attention should be paid to the location and binding mode of temperature measuring contact and the distance from heating element. Often (at least monthly) brushes, brooms or compressed air, vacuum cleaners and other cleaning furnace furnace and bricks, to prevent furnace oxide scale and other impurities dropped on the heating elements, short circuit, or even burned bricks. The bottom plate, crucible, pot and other heat-resistant steel components are used for a period of time, it is better to hang up and knock, remove the oxide scale. If impurities such as oxide scale are not removed in time, they will react with refractory bricks and melt the furnace wire.
2. To avoid heat treatment products, especially copper, aluminum, zinc, tin, lead and other electrical heating elements contact, whether fine powder, melt or steam, to prevent erosion on the surface of the electric heating body to form a “pit”, section smaller, and finally overheating and burning.
3. After the vacuum furnace is heated, the furnace door can not be opened for a long time. When the temperature is above 400 C, no sharp cooling is allowed. For electric heating elements, it is easy to cause oxidation and skin loss when the temperature is high, and the heat and cold changes are great. For molybdenum reheating furnace, EI is often used in maintenance and should be cooled below 200 c to stop the protection gas.
4, the draw rod and the wire clip should be in good contact, and the draw rod should be in contact with the clamp and should be smooth. The rod can not be reddened. The maximum temperature of the clamp can not exceed 60 degrees when supplying power. Attention should be paid to the fact that the bolts of the lead-out rod wiring clamp are easy to oxidize and loosen due to the thermal expansion, cold contraction and creep elongation during the heating and stopping of the furnace.

Installation, commissioning and acceptance steps of vacuum furnace

1. Refer to the furnace layout, installation location and civil conditions provided by the reference paper, select the permanent installation site and carry out civil construction. Installation site should be smoke-free, clean environment, dry air, should not be put together with other equipment, maintain room temperature of 10-35 degrees Celsius, smooth and clean ground.
2. When installing graphite heating element and water cooled electrode, we should pay attention to:
A. be extremely careful when taking graphite elements to prevent damage.
B. Be sure to tighten bolts reliably to achieve good electrical contact, not to exert too much force, to avoid thread breakage.
3. According to the vacuum system diagram, the vacuum system is positioned, assembled and connected with the furnace body. When assembling, O type sealing ring is coated with a thin layer of vacuum grease, and the flange is tightened evenly.
4. According to the water-cooling system diagram, the inlet pipe and drain pipe are connected to the inlet and drain of the furnace respectively, and the pressure is 0.1-0.15MPa, the temperature is not lower than 15 C, not higher than 30 C. It is better to provide circulating water and anti-rust water.
5. Provide a pneumatic gas source with a minimum pressure of 0.5 MPa, which can be used for industrial nitrogen. If compressed air is used, the pneumatic “three big pieces” (such as oil mist, pressure reducer, water filter) are provided.
6. Connect the pipeline to the recharge pipeline according to the recharge system diagram, and recommend that high purity nitrogen with purity of 99.99%-99.999% be provided as recharge.
7. Connect the power supply to the corresponding electrical junction according to the electrical wiring diagram, check the voltage of the nuclear power supply, connect the control box, the power box and the electric cables between the furnace body.
8. Install other spare parts, including pipes, measuring instruments and meters.
9. Furnace body and control box are grounded, grounding resistance is less than 4 Euros, gauge cables for instruments and vacuum meters should also be grounded.
Commissioning and acceptance of vacuum furnace
After the complete set of equipment has been installed according to the technical requirements, it can be commissioned and checked according to the following items when there are no defects and good grounding.
1. Check items
1) appearance quality check: the outer surface should be smooth and smooth without serious dent and mechanical bruise.
2) The main purchased kit specifications, certificate of inspection: such as vacuum unit, magnetic voltage regulator, electronic potentiometer, temperature control microprocessor, vacuum relay, etc.
2. Commissioning of cold stove
1) Mechanical, pneumatic, electrical linkage debugging, adjusting the transfer time of workpiece transfer time < 25S, the whole linkage in the case of loading 200 kg, three consecutive movements should be coordinated and stable, accurate and reliable.
A. vacuum interval hot start or close travel time to less than 8 S.
B. the moving time of the workpiece vehicle to the heating chamber is adjusted to 12 to 15 S.
C. the lift or fall travel time of the workpiece vehicle is adjusted to less than 3 S.
D. the workpiece vehicle is retreated to the cooling chamber and the travel time is adjusted to 12 to 15 S.
E. Loading 200Kg for linkage test, the total travel time is less than 25S continuous action should be coordinated and stable, accurate and reliable.
2) the commissioning of the air-cooled fan has a rotation speed of about 2900r/min, and the rotation is flexible without any abnormal phenomena.
3) alarm system debugging should be accurate, safe and reliable.
4) measuring insulation resistance greater than or equal to 20 thousand ohm.
5) measure the cold degree of vacuum of the furnace, and the pressure rise rate is close to 0.5Pa/h.
3. Thermal commissioning
1) When the vacuum degree of the furnace is not less than 13.3 pa, the vacuum degree of the furnace should not be less than 13.3 PA during the whole process of the furnace temperature rising slowly to 1300 PA.
2) limit vacuum measurement: not less than 6 x 1.0-4Pa.
3) working vacuum measurement: not less than 2.7Pa (in 1000 empty furnace).
4) Pressure rise rate measurement: when the vacuum furnace is heated to 1200 C, the pressure rise rate should reach 0.5Pa/h when the furnace temperature is cooled below 100 C after full baking degassing.
5) Recharge body debugging: when the vacuum degree of the cooling chamber is 1.33 Pa, the vacuum valve of the vacuum insulation and cooling chamber is closed, and nitrogen is immediately filled into the cooling chamber furnace 0.06 MPa, the time should be 2.5 (seconds), and the vacuum degree of the heating chamber should not be less than 670 Pa.