Introduction
In the evaluation of material weathering, photoaging testing machines are commonly used equipment, and their temperature control parameters are crucial to the accuracy of test results. Blackboard temperature and black label temperature are two key temperature indicators that are often confused or misused. This article will systematically explain the definitions, measurement principles, application differences and standard basis of the two to help users choose and interpret correctly.
Definition and principle
Chalkboard temperature refers to the temperature measured by a specific ferrous sheet metal sensor, typically made of stainless steel or similar with a black light-absorbing coating. Its design simulates the heat build-up effect of the material surface under light, reflecting the maximum surface temperature possible for the specimen.
The black label temperature is measured by a black insulated panel sensor with a black surface but a thermal insulation layer on the back to reduce the effect of heat conduction. It focuses more on assessing the thermal stress of radiant heat on materials, especially for materials with dark colors or strong light absorption.
The difference between the two stems from the sensor structure: the blackboard sensor has a lower heat capacity and fast response; Due to the thermal insulation design, the temperature of the black label sensor is usually higher than the temperature of the blackboard, which can better reflect the pure radiant heating effect.
Comparison of measurement methods
When measuring, the sensor is placed on the same plane as the specimen and receives the same lighting conditions. The blackboard temperature sensor is directly exposed, while the black label temperature sensor is insulated on the back, resulting in a different thermal equilibrium state. The following is a comparison of key features:
| Blackboard temperature | It reflects the immediate heating temperature of the material surface, which is greatly affected by air convection |
| Black label temperature | Reflecting the temperature dominated by radiant heat, the insulation design reduces heat loss |
| Applicable standards | It is commonly found in industry standards such as automobiles and coatings |
| Applicable standards | It is widely used in plastics, textiles and other international standards |
| Typical difference | It is usually 5°C to 20°C below the Black Label temperature |
Influencing factors
Light intensity, spectral distribution, airflow velocity in the chamber, ambient humidity, and sensor maintenance status all affect the measured values. For example, accelerated airflow results in lower blackboard temperature readings with less impact on blackboard temperature. Regular cleaning of the sensor surface to avoid coating aging or contamination is the basis for ensuring reliable data.
Standard application
Different industry standards have clear requirements for temperature parameters. For example, some materials testing standards specify the use of black label temperatures because they are closer to the actual heating conditions of the material; The rapid screening test may use blackboard temperature. Users should choose according to the purpose of the test and the standard specifications, and clearly indicate the type of temperature used in the report.
Selection suggestions
When selecting temperature parameters, consider the color of the material, heat absorption and the end-use environment. It is recommended to give priority to the black label temperature for dark materials; For heat-sensitive materials, both temperatures can be monitored simultaneously for a comprehensive evaluation. Before testing, it is recommended to determine the temperature conditions through pre-experiments to ensure that the test conditions match the actual aging scenario.
Epilogue
Blackboard temperature and black label temperature have their own emphasis in photoaging testing, and understanding their physical significance and measurement differences can help improve the consistency and comparability of the test. In actual operation, reasonable selection based on standard requirements and material properties is the key to obtaining reliable aging data.
References
1. International Standards Organization, Standard for Test Methods for Artificial Climate Aging, 2020.
2. Technical Guide to Weathering Testing Materials, Industrial Press, 2018.
3. Research on temperature parameters of photoaging equipment, Journal of Environmental Testing, 2021.