Date | 2026-06-24 07:45:00
When engineers specify BMC or SMC, they look at present mechanical properties and electrical figures. They also face a more practical question: how long will this part last?
Low-voltage apparatus housings are expected to serve for more than ten years, energy storage insulating parts must match the life of the battery system, and automotive components must survive the full vehicle life cycle. Life data has to be available at the material selection stage, which brings in a fundamental discipline — chemical kinetics — and its central tool for life prediction, the Arrhenius equation.
Ageing of a polymer is, at bottom, a chemical change.
In long service, BMC/SMC is exposed to heat, oxygen, light and moisture, and undergoes irreversible reactions such as crosslinking and degradation. At the micro scale these reactions alter molecular structure; at the macro scale they appear as falling performance — lower strength, degraded insulation.
Temperature is the single most important accelerator of ageing. The failure of most polymers is a thermally activated chemical reaction: the higher the temperature, the faster the reaction and the shorter the life. If the relationship between temperature and ageing rate can be described quantitatively, ageing can be accelerated at high temperature and the service life at ambient temperature calculated back from it.
That is the core value of the Arrhenius equation.
The Arrhenius equation describes the relationship between reaction rate and temperature:
k = A · exp(-Ea / RT)
Here k is the reaction rate constant, Ea the activation energy, R the gas constant and T the absolute temperature.
For life prediction the equation is rearranged into a relationship between time to failure and temperature. Accelerated ageing tests are run at several temperatures, the time for the property to fall to a critical value is measured at each, and the result is extrapolated to the actual service temperature to give the expected life.
For a thermosetting composite such as BMC/SMC, within a sensible temperature range well below the heat deflection temperature, the ageing mechanism stays stable and the Arrhenius approach applies well.
In electrical insulation, the Arrhenius method has been standardised as the determination of the temperature index (TI).
The temperature index is the long-term service temperature class at which a specified property — flexural strength, for example — falls to 50% of its original value under thermal ageing. The test logic is as follows:
Choose three or four ageing temperatures above the expected service temperature.
Expose specimens to long-term heat at each temperature and test the property at intervals.
Record the time taken for the property to fall to 50% at each temperature.
Plot the Arrhenius graph and extrapolate to the target service temperature.
This is the technical meaning behind the figures in the company standard Q/JTJ0001-2025: temperature index ≥155 °C for the BMC 16 series and ≥170 °C for the 18 series. The first holds more than 50% of its initial strength over long service at 155 °C; the second achieves the same life at 170 °C.
Long-term heat resistance: heat deflection temperature of BMC is 200–280 °C, and the material can be used continuously at 130 °C with a very low rate of property loss.
Indoor service life: BMC lasts 15–20 years indoors, which covers the design life of the great majority of low-voltage apparatus and distribution equipment.
Outdoor weathering: after ten years of outdoor exposure, BMC retains more than 60% of its strength. This comes from the three-dimensional crosslinked network of the thermosetting resin — chain movement is restricted, and resistance to thermo-oxidative ageing is far stronger than that of thermoplastics.
Comparison across materials: in a thermal ageing comparison of BMC, SMC, GPO-3 and epoxy, BMC showed the highest degree of crystallinity and the best property retention after ageing.
They give a basis for design life. Low-voltage apparatus and energy storage equipment carry explicit design life requirements, and the temperature index gives engineers a quantifiable basis for material selection.
They give a method for accelerated verification. Where a customer requires a ten-year warranty, no one needs to wait ten years; accelerated ageing delivers an equivalent verification within weeks.
They support export certification. The temperature index is a standardised parameter within the IEC 60216 system and carries international recognition.
They give confidence in real applications. Data is one thing; long-term verification in demanding service is more telling. As a supplier to companies including Siemens, Chint and ABB, Wenzhou Jintong has seen its BMC/SMC materials used in volume for years in high-voltage apparatus and energy storage equipment at these customers, and reliability across the product life cycle has been tested in practice. Laboratory data and engineering experience corroborate each other, and together they form a complete basis for judging long-term life.
Selection principle: choose the class that matches the actual service temperature, and take the most economical option that still meets the life requirement. For export products, prefer grades that come with a temperature index test report and international certification.
How long can BMC/SMC last? It is not a question to answer by impression.
From the Arrhenius equation of chemical kinetics to the IEC 60216 temperature index standard, and on to measured data showing 15–20 years indoors and more than 60% strength retention after ten years outdoors, this body of theory, method and data forms a scientific system for predicting the life of thermosetting composites. As a long-term supplier to companies including Siemens, Chint and ABB, Wenzhou Jintong has supplied BMC/SMC materials in volume for years into high-voltage apparatus and energy storage equipment at these customers, and reliability across the product life cycle has been confirmed in engineering practice. Laboratory data and field application corroborate each other, giving engineers a double basis for selection decisions.
Ageing of a polymer is a chemical change. In long service, BMC/SMC is exposed to heat, oxygen, light and moisture and undergoes irreversible reactions such as crosslinking and degradation, altering molecular structure at the micro scale and showing as falling performance at the macro scale — lower strength, degraded insulation. Temperature is the strongest accelerator: the failure of most polymers is a thermally activated chemical reaction, and the higher the temperature, the faster the reaction and the shorter the life.
The equation describes the relationship between reaction rate and temperature: k = A · exp(-Ea / RT), where k is the rate constant, Ea the activation energy, R the gas constant and T the absolute temperature. For life prediction it is rearranged into a relationship between time to failure and temperature: accelerated ageing at several temperatures gives the time for the property to fall to a critical value, and that is extrapolated to the actual service temperature. For a thermosetting composite such as BMC/SMC, within a sensible range well below the heat deflection temperature, the ageing mechanism is stable and the method applies well.
It is the long-term service temperature class at which a specified property, such as flexural strength, falls to 50% of its original value under thermal ageing. The determination runs as follows: choose three or four ageing temperatures above the expected service temperature; expose specimens to long-term heat at each and test at intervals; record the time for the property to fall to 50% at each temperature; plot the Arrhenius graph and extrapolate to the target temperature. The higher the index, the longer the life at a given temperature.
Under the company standard Q/JTJ0001-2025, the BMC 16 series has a temperature index of ≥155 °C and the 18 series ≥170 °C. The first holds more than 50% of its initial strength in long service at 155 °C; the second reaches the same life at 170 °C.
On heat resistance, the heat deflection temperature of BMC is 200–280 °C and continuous service at 130 °C is possible with a very low rate of property loss. Indoors, BMC lasts 15–20 years, covering the design life of most low-voltage apparatus and distribution equipment. Outdoors, strength retention remains above 60% after ten years of exposure, thanks to the three-dimensional crosslinked network of the thermosetting resin, which restricts chain movement and resists thermo-oxidative ageing far better than thermoplastics. In a thermal ageing comparison of BMC, SMC, GPO-3 and epoxy, BMC showed the highest degree of crystallinity and the best property retention after ageing.
As a guide: for indoor low-voltage apparatus housings, the BMC 16 series with a temperature index ≥155 °C, giving an expected life of 15–20 years; for high-temperature industrial environments at 80–100 °C continuously, also the BMC 16 series, giving 10–15 years; for automotive engine bays at 120–150 °C continuously, the BMC 18 series at ≥170 °C, covering the vehicle life cycle; for outdoor power equipment exposed to sun and temperature cycling, BMC/SMC with a weathering package at ≥155 °C, retaining more than 60% strength after ten years. The principle is to match the class to the actual service temperature and take the most economical option that meets the life requirement; for export products, prefer grades with a temperature index test report and international certification.
For technical data sheets, grade recommendations, or a discussion about your specific requirements:
📧 wendy.qiu@smcbmc.com 📞 +86-13868305300
