(1) Appearance inspection
Visual inspection is adopted for the appearance inspection of resistance furnace. The shape and structure of resistance furnace shall be kept intact. Name, specification, model, temperature range, manufacturer and factory code shall be used. The shape and structure of temperature control instrument of resistance furnace shall be good, indicating that physical quantity, symbol, graph and physical quantity shall conform to one standard, and shall be clear and correct. There must be good contact between compensating wire and thermostat. Turn on the power supply and observe the operation of the resistance furnace.
(2) Insulation resistance
After instrument short circuit, insulation resistance meter shall be used to measure power supply terminal. The insulation resistance of equipment shell shall not be less than 20mo.
(3) Temperature parameters
At the same time, the temperature uniformity, temperature fluctuation and furnace temperature accuracy can be calibrated.
calibration method
(1) Selection of calibration temperature point
Generally, the calibration point should be the upper limit point or lower temperature point of the high temperature furnace, or the common temperature point can be selected according to the needs of users.
(2) Location of calibration points
For box type resistance furnace with capacity greater than 0.15m3, three calibration points shall be configured. The corresponding positions of the central point (thermocouple positioning point) and each central point (5-10) cm are respectively located in Fig. 1. Use the letters a, B, and C to indicate the front, middle, and back points.
For well type or tubular furnace with capacity less than 0.15m3, one calibration point shall be provided. It is located at the center of the temperature measurement area (the point where the thermocouple is located).
According to the size and shape of the furnace working area, the sensors are placed in the working area according to the number and position specified.
(3) Calibration procedure
① Preparation before calibration
The calibration device of resistance furnace is formed by measuring thermocouple, compensating conductor switch and measuring instrument. By appropriate means, the test thermocouple is fixed at each measurement position shown in the above figure and marked, and the reference end of the thermocouple is extracted from the furnace. Using compensation lead, thermocouple is connected to measuring instrument through switch, and pay attention to the consistency of polarity. Thermocouple compensation wire, switch and measuring instrument are checked to be normal.
② Temperature calibration
The resistance furnace is in no-load state (air furnace) and can be calibrated at special requirements (half load or full load). When the load is calibrated, the thermocouple terminals should be as close to the workpiece as possible. According to the actual needs of users, the shape, size and layout of materials, the position and requirements of measuring points are calibrated. During the calibration, the detection should be carried out according to the commonly used heating method, without cooling detection, and the fan resistance furnace should be used. During the calibration, the fan should operate normally.
After power transmission, pay attention to the display value of thermocouple on the measuring instrument. When the temperature reaches the set temperature and is stable for 30 minutes, the resistance furnace reaches the thermal stability state and starts the temperature parameter calibration. For 30 minutes, the temperature of each point was measured every 1 minute, and the temperature of each point was recorded and measured 10 times. According to the method of 5.2.4, the temperature uniformity, temperature fluctuation and temperature precision are calculated.
If the calibration temperature parameter exceeds the specified range of 3.2, the constant temperature time of calibration temperature is allowed to be extended appropriately, but the constant temperature and total measurement time of calibration temperature point shall not exceed 2 h.
After calibration, the temperature in the furnace should be lower than 300 ℃, and the thermocouple can be removed.
On 2018-08-08 11:45:46
