What precautions should be taken when using the heating system of a vacuum furnace?
The heating system of the vacuum furnace has the following precautions during use:
**I. Resistance heating system**
1. Heating element selection:
- According to the required heating temperature and process requirements, select suitable heating elements such as resistance wire, silicon carbon rod or silicon molybdenum rod. Different heating elements have different maximum operating temperatures and characteristics. For example, silicon molybdenum rods are suitable for high temperature environments, but are easy to break at low temperatures, while nickel-chromium alloy wires are suitable for medium and low temperatures.
- Consider the parameters such as resistivity, oxidation resistance, thermal expansion coefficient of the heating element to ensure that it can operate stably under the working conditions of the vacuum furnace. For example, at high temperatures, the oxidation resistance of the heating element is crucial, otherwise it is easy to be damaged by oxidation.
2. Installation and fixing:
- Correctly install the heating element to ensure good insulation and fixing between it and the furnace wall or supporting structure. Use high-temperature resistant insulating materials such as ceramic tubes, asbestos boards, etc. to prevent the heating element from directly contacting the metal parts and causing short circuits.
- For large vacuum furnaces, multiple heating elements may need to be used in parallel or in series. At this time, pay attention to the connection method and electrical parameter matching between the elements to ensure uniform heating.
3. Heating and cooling control:
- Heating should be done slowly to avoid damage to the heating element due to excessive thermal stress caused by rapid temperature changes. According to the characteristics of the heating element and the requirements of the workpiece in the furnace, a reasonable heating curve should be formulated to control the heating rate to be generally between a few degrees Celsius and tens of degrees Celsius per minute.
- Cooling should also be done slowly, especially at high temperatures. Sudden cooling may cause the heating element to break due to uneven thermal expansion and contraction. Natural cooling or inert gas auxiliary cooling can be used, but be careful not to cool too fast.
4. Regular inspection and maintenance:
- Regularly check the appearance of the heating element to see if there is any breakage, deformation, oxidation, etc. If any problems are found, the heating element should be replaced in time to ensure the normal operation of the vacuum furnace.
- Clean the dust and impurities on the surface of the heating element to prevent it from affecting the heating efficiency and service life. After each use, when the furnace temperature drops to a certain level, it can be cleaned with compressed air or a vacuum cleaner.
**II. Induction Heating System**
1. Induction Coil Design:
- The shape, size and number of turns of the induction coil should be reasonably designed according to the size of the vacuum furnace, the shape and size of the heated workpiece and the required heating power. Ensure that the induction coil can generate a uniform magnetic field around the workpiece to achieve uniform heating.
- Select the appropriate coil material, generally copper material, because copper has good electrical and thermal conductivity. At the same time, the stability and durability of the coil under high temperature and vacuum environment should be considered.
2. Induction Power Supply Parameter Setting:
- According to the material, size and heating requirements of the workpiece, correctly set the output frequency and power of the induction power supply. Different materials and processes require different frequency and power ranges. Too high or too low parameters may affect the heating effect and equipment life.
- Pay attention to the stability and reliability of the induction power supply to avoid uneven heating or equipment damage due to power supply fluctuations. Voltage stabilizers and overcurrent protection devices can be equipped to ensure the normal operation of the power supply.
3. Cooling and Insulation:
- The induction coil will generate a lot of heat during operation and needs to be effectively cooled. Water cooling is usually used to ensure that the cooling water flow rate and pressure are stable to prevent the coil from overheating and damage.
- Ensure good insulation between the induction coil and the furnace body to prevent leakage and short circuit. Use high-temperature resistant and high-insulation insulating materials, such as ceramic tubes, mica sheets, etc., to ensure reliable insulation.
4. Safety protection:
- The induction heating system will generate a strong electromagnetic field, which may affect the human body and surrounding electronic equipment. During operation, protective equipment that meets the requirements should be worn, such as radiation protection clothing, insulating gloves, etc. At the same time, the vacuum furnace should be placed away from sensitive electronic equipment to reduce electromagnetic interference.
- Regularly check the grounding of the induction coil and power supply to ensure good grounding and prevent leakage accidents.
**Three, microwave heating system**
1. Microwave generator maintenance:
- Regularly check the working status of the microwave generator, including the output power and frequency stability of the magnetron. If abnormalities are found, the magnetron should be repaired or replaced in time.
- Keep the microwave generator clean to prevent dust and impurities from entering the equipment and affecting its performance. Compressed air or a vacuum cleaner can be used for cleaning, but be careful to operate under power outage.
2. Waveguide system inspection:
- Check whether the waveguide system is tightly connected and whether there is any looseness or leakage. Microwave leakage will not only reduce the heating efficiency, but also may cause harm to the human body, so ensure that the waveguide system is well sealed.
- Observe whether there is dust or foreign matter in the waveguide system. If there is, it should be cleaned in time to ensure the transmission efficiency of microwaves.
3. Material handling:
- The heated material should be of suitable size and shape to ensure that microwaves can penetrate the material evenly. For large or irregularly shaped materials, rotation or stirring can be used to improve the uniformity of heating.
- The material cannot contain metal impurities, because metal will reflect microwaves, causing local overheating and even damage to the equipment. Before putting the material in, it should be strictly inspected and screened.
4. Safe operation:
- The operator should undergo professional training and understand the principles and safe operating procedures of microwave heating. During the operation, the operating procedures must be strictly followed to avoid safety accidents caused by misoperation.
- Install microwave leakage detection device and regularly perform microwave leakage detection on vacuum furnace to ensure the safety of equipment. If leakage is found, stop using it immediately and carry out repairs.