Muffle Furnace

Content
1. What is a muffle furnace？
    1.1. Definition
    1.2. Working principle
2. Muffle furnace application
3. Muffle furnace temperature
    3.1. Muffle furnace temperature controller
    3.2. The maximum temperature of muffle furnace
4. Types of muffle furnace
    4.1. Box-type muffle furnace
    4.2. Tube muffle furnace
    4.3. Crucible muffle furnace
    4.4. Atmosphere muffle furnace
5. Muffle furnace specifications
    5.1. Ceramic fiber muffle furnace
    5.2. High temperature muffle furnace
    5.3. Mini muffle furnace
    5.4. Vacuum tube furnace
    5.5. Vacuum atmosphere furnace
6. Calibration of muffle furnace
7. Muffle furnace safety precautions
8. How to buy muffle furnace?

Muffle furnace is a universal heating device. It is an oven that separates the fuel from the material to be heated and burned. With the advent and development of high-temperature electric heating, today's muffle ovens are designed electrically.

Muffle furnace working principle can be divided into two steps:
(1) Furnace temperature automatic control principle: According to the deviation of the furnace temperature to the given temperature, automatically turn on or disconnect the heat source energy supplied to the furnace, or continuously change the size of the heat source energy, so that the furnace temperature is stable with a given temperature range to meet the needs of the heat treatment process. According to the proportion of deviations, integration and differentiation to produce control effects (PID control), is a widely used form of control in process control.

(2) When the muffle furnace starts to heat up, the brick-laying body in the furnace absorbs a lot of heat to increase its own temperature, and when the furnace is stopped and cools down, this part of the heat is dissipated to the space; this part forms the heat storage loss of the furnace body.

As muffle furnace is a heating equipment, Its application range is also relatively wide.

1. Thermal processing: industrial work piece handling, cement, building materials industry, thermal processing or treatment of small work pieces.

2. Pharmaceutical industry: used for drug testing, pretreatment of medical samples, etc.

3. Analytical chemistry industry: As a sample treatment in the fields of water quality analysis and environmental analysis. It can also be used for oil analysis.

4. Coal quality analysis: used to measure moisture, ash content, volatile content, ash melting point analysis, ash composition analysis, and elemental analysis.

5. In laboratory: When heating samples in the laboratory, in order to prevent the sample from being contaminated during the heating process, a muffle furnace will be used to heat the sample, and the muffle furnace will isolate the sample from the fuel, so that the pollution situation will be avoided. Today, muffle ovens are widely used in laboratory sample processing.

Temperature controller is often referred to as the temperature control instrument, and its role is to display the temperature signal sent by the temperature sensor or transmitter on the one hand; On the other hand, the measured temperature value is compared with the setpoint and the temperature-controlled M signal is output. In the box-type muffle furnace temperature control, if the control accuracy requirements are not high, an analog bit control temperature controller can be used, otherwise, the digital intelligent temperature control instrument is used, and the latter is currently more used.

The maximum temperature of the muffle furnace is divided according to the rated temperature: muffle furnace below 1000°C, 1200°C, 1300°C, 1400 °C, 1600 °C, 1700°C, 1800°C muffle furnace.

Box-type muffle furnace is a furnace with a chamber-shaped furnace. This oven is equipped with a controllable chimney. The product is heated, insulated and cooled during the entire heating process, the product is fixed, and the feed and discharge are carried out through a single door or groove. Also known as batch production furnaces.
Component: furnace door, electric heating element, furnace shell, control box, furnace lining, etc
Application: It is suitable for elemental analysis and determination in laboratories, industrial and mining enterprises, scientific research institutes, and colleges

Tube muffle furnace is the quartz or corundum furnace tube into the furnace heating, heating area, constant temperature area to place the workpiece heating furnace, the two ends of the sealed flange can achieve pre-vacuum, can pass into a variety of protective gas, oxidation gas and reducing gas.
Application: It is suitable for heating and sintering small workpieces and small samples

Crucible muffle furnace is one of the simplest smelting equipment, In this kind of furnace, the alloy is melted in the crucible, the heat is transferred to the crucible charge, and charge and combustion products do not directly contact, so the alloy chemical composition is almost not affected by the furnace gas, the temperature of alloy liquid is more uniform, which is its main advantage. Its disadvantages are low thermal efficiency, high fuel consumption, and small crucible capacity.
Application: It is mainly used to melt non-ferrous metals whose melting point is not too high, such as copper, aluminum, and its alloys.

Atmosphere muffle furnace is an integrated box furnace and tube furnace with double characteristics of a high-temperature furnace, atmosphere furnace appearance and high-temperature furnace about the same, on this basis added air inlet and outlet. Furnace body sealing welding, furnace door has a high-temperature resistant silica-gel sealing ring, can play a good sealing effect. So the user can be pre-vacuumed, but also through a variety of atmospheres. The vacuum effect is slightly worse than tube furnace but does not affect the use, generally can reach 0.05MP.
Application: Suitable for large samples and atmosphere requirements of the experiment and production

Muffle furnace has widely used in laboratory, the actual temperature of the muffle furnace in the laboratory is closely related to the experimental results. After a long time of use, or the wrong way of use, the actual temperature of the experimental electric furnace and the temperature displayed by the temperature control system will be inconsistent, so it is necessary to carry out regular calibration, to ensure the experimental efficiency of muffle oven. Here are some methods for calibrating muffle furnace.

1. The calibration work should be carried out without loading the furnace and using a verified and qualified standard device.

2. Install standard thermocouple. Insert the standard thermocouple through the measuring port under the condition of power outage, and place the measuring end of the thermocouple in the central sample analysis position to ensure that the true temperature of the working area in the furnace can be reflected. Connect the reference end of the thermocouple to the input end of the standard display instrument, and a digital thermometer is placed next to the reference end to obtain the compensating temperature of the reference end. The measuring ports should be tightly blocked with asbestos to prevent heat leakage.

3. Set test points. The position of the test points should be distributed on the three horizontal planes of the experimental electric furnace working area, forming the upper, middle and lower three layers. The middle layer is the working face parallel to the ground through the geometric center of the working area. The distance between the test points and the inner wall of the working area is not less than ten percent of the length of each side. If the test furnace box is small, the position of the test point can be adjusted appropriately, usually placed in the central position, or the measuring end of the standard thermocouple and calibrated thermocouple.

4. Calibration temperature selection. Generally, the lower limit and upper limit of the calibration temperature of the newly purchased muffle oven should be selected. Any temperature between the upper and lower limits can be selected in use, and the actual common temperature can also be selected according to the needs of users, to facilitate the calibration of temperature uniformity.

5. Start calibration temperature. Set the temperature controller of the calibrated resistance furnace to the required nominal temperature, usually from low temperature to high temperature, so that the furnace can work normally, start reading after stability, record the temperature of all test points every two minutes, a total of 15 times in 30 minutes. The measured value is the actual temperature after correction. For small resistance furnace, only the temperature deviation of resistance furnace can be calibrated.

6. Calculation of temperature deviation. The millivolt value corresponding to the temperature measured by the standard thermocouple is the sum of the millivolt value displayed by the standard instrument and the corresponding millivolt value displayed by the digital thermometer. The temperature measured by the standard thermocouple each time can be obtained by checking the thermocouple indexing table.

1. When using muffle furnace, the furnace temperature shall not exceed the rated temperature, so as not to burn the electric heating element.

2. Muffle furnaces and controllers must be operated in an area where relative humidity does not exceed 85% and where there is no conductive dust, explosive gases or corrosive gases.

3. The muffle furnace controller should be limited to use in the ambient temperature range of 0-40 °C.

4. Do not pull out the thermocouple suddenly at high temperature to prevent the jacket from bursting.

5. Keep the furnace clean and remove oxides in time.

6. The furnace temperature shall not exceed the maximum temperature during use, so as not to burn the electric heating element, and it is forbidden to pour various liquids and molten metals into the furnace chamber.

7. After the muffle furnace is used, the power supply should be cut off to cool it naturally. Should not immediately open the door, to avoid the furnace suddenly cold broken, such as urgent use, can first open a small seam, let the cooling speed up, until the temperature drop to 200℃ below, can open the door.

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