GB/T 36133-2018Refractory materials—Determination of thermal conductivity (Platinum resistance thermometer method) (English PDF)

4.1.2 Heating furnace

The heating chamber of the heating furnace shall be able to accommodate two straight bricks of 230mm×114mm×75mm. Set two support frames at the bottom to make the test piece evenly heated. The temperature of the heating furnace at each test temperature point is controlled to ±5°C. The temperature difference between any two points of the test piece is not more than 10°C. The temperature shall be stable within 15min before the start of the heating step of the hot wire. During the constant temperature period, the temperature fluctuation measured by the thermocouple on the outside of the test piece shall not exceed ±0.5°C. In addition, four holes shall be set on the furnace wall to place four hollow alumina protective tubes. Two hot wire heating leads and two resistance measuring leads are respectively buried in the protection tube. A certain distance shall be maintained between the holes to reduce the conductivity during the heating process.

4.1.3 Thermocouple

It is used to measure the temperature outside the test piece. It shall be composed of platinum or platinum rhodium wire and match the final test temperature.

4.1.4 Hot wire heating system

The hot wire heating system includes AC power, current divider and breaker.

Generate a stable current of 0A~10A (0V~50V). Hot wire heating shall use stable alternating current. The test power shall be between 1W/m and 125W/m, which is equivalent to 0.15W~18.75W of hot wire power between 150mm resistance measurement leads. The system shall also have a device for measuring current and voltage drop. Its full-scale accuracy should reach ±0.5%.

4.1.5 Data logging system

Data recording system includes DC power supply, digital voltmeter, program recorder, relay, current divider. In order to measure the change of the resistance of the hot wire, a low (such as 100mA) constant DC current needs to be superimposed on the AC heating current of the hot wire. Record the DC voltage drop of the hot wire section between the resistance measurement leads to calculate the temperature change of the hot wire. Because the rate of change of the hot wire resistance during measurement is only one millionth of its absolute resistance value, it needs to use a data logging system with sufficient resolution. The programmed digital voltmeter shall be able to automatically change the range and automatically calibrate. The digital resolution is (that is, the accuracy reaches six and a half digits). The sensitivity of the temperature-time recording equipment shall be at least 0.2µV/mm, or the […]

5.1 Refractory brick

Choose 2 straight bricks with uniform structure and density or specimens of the same size to form a test piece. The minimum size of a single specimen is 200mm×100mm×50mm. The recommended size is 230mm×114mm×65mm or 230mm×114mm×75mm. The hot wire measuring rack is placed in the center of two closely contacted specimens. Process a step on the contact surface of the upper and lower specimens, so as to embed hot wire, as shown in Figure 2. In order to ensure that the sample is in close contact with the hot wire, the maximum height of the specimen step shall not be greater than 0.8mm. Ensure that its minimum height is not less than the diameter of the hot wire used. In order to ensure that the test piece does not shake, the average height error of the two steps shall be within 0.1mm. In addition, the flatness of the upper and lower specimen contact surfaces shall not be greater than 0.1mm/100mm. After the steps are processed, put the two specimens together. Make the two steps coincide with each other. Shake the test piece to detect whether it is shaking. If it is not shaking, it shall pass the test. After the step height and the flatness of the close contact surface have reached the requirements, the resistance measurement lead groove is carved on the step of a specimen. In order to match the solder joints of the hot wire and the resistance measurement lead, tools can be used to dig pits at the solder joints for modification.

5.2 Refractory castable

Prepare refractory castable according to GB/T 4513.5. The cast blocks of refractory castable can be cut into specimens meeting the size requirements according to 5.1. Or use a special mold to directly form a specimen that meets the requirements of 5.1. When using a disposable hot wire rack, it can be poured directly into the test piece.

5.3 Refractory plastic and ramming material

Prepare refractory plastic or refractory ramming material according to GB/T 4513.5. After forming, immediately press the hot wire measuring rack into two 230mm×114mm×65mm or 230mm×114mm×75mm specimens. A certain pressure shall be applied when drying to make close contact between the specimens.

5.4 Low-strength materials

Use a notching machine or a knife with a saw blade thickness of not more than 0.5mm to carve a groove for pressing into the hot wire measuring rack on the 230mm×114mm brick surface of one of the specimens.

8.3 Slope calculation

Use a suitable linear regression method to calculate the slope (B) from the linear interval in the RT versus ln(t) curve measured in each test. The linear interval of RT versus ln(t) curve can be determined by computer analysis software or visual inspection. In order to avoid the deviation of RT to the high temperature section when linear regression of the ln(t) curve, it is recommended to use the ln(t) time axis of uniform interval for analysis. This may require collecting resistance data over a longer period of time before performing the linear regression analysis step or collecting more data points at a uniform sampling rate. If the linear interval is not found on the curve, the reason may be that the material is not suitable for this test method, or the test operation has made an error. The test shall be repeated at this time.

8.4 Thermal conductivity calculation

According to the slope (B) of RT to ln(t) based on the data collected during each heating process of the hot wire and the polynomial regression coefficient calculated in 8.2, use formula (7) or formula (8) to calculate the thermal conductivity.

The Fourier heat flow equation for a linear heat source is shown below: […]