In-depth analysis of the requirements of UL94 standard for thermal fuses

In-depth analysis of the requirements of UL94 standard for thermal fuses: ensuring the quality and safety of international wholesale purchases

Introduction
In today’s global market, thermal fuses, as an important plastic material product, are widely used in electronics, electrical, automotive, home appliances and other fields. For international wholesale buyers, it is crucial to ensure that the purchased thermal fuses meet relevant safety standards. As one of the authoritative standards for evaluating the flammability of plastic materials, the UL 94 standard has clear requirements for the performance and safety of thermal fuses. This article will explore the specific requirements of the UL 94 standard for thermal fuses in depth to help you better understand and select thermal fuse products that meet the standards.

I. Overview of UL 94 Standard
The full name of the UL 94 standard is “Devices and Appliances – Flammability of Plastic Materials for Parts in Devices and Appliances”, which is “Devices and Home Appliances – Flammability of Plastic Parts”, which is formulated by Underwriters Laboratories (UL). This standard is mainly used to evaluate the combustion characteristics and flame retardant properties of plastic materials when exposed to flames or heat sources, and provide a basis for the safety of materials in various applications.
UL 94 standard applies to various plastic parts used in devices and household appliances, including plastic products such as thermal fuses. Its test methods and classification system are designed to simulate the flame conditions that materials may encounter in actual use, so as to determine the flame retardant level of the materials and provide guidance for manufacturers, engineers and purchasers to select appropriate materials.

2. Classification and requirements of thermal fuses in UL 94 standard
According to UL 94 standard, the flame retardant properties of thermal fuses are mainly evaluated through different test methods and classification levels. The following are the specific classifications and requirements:
(I) Horizontal burning test (HB grade)
Test method: Place the thermal fuse sample horizontally, ignite one end of the sample, and observe the speed of flame propagation along the sample.
Requirement: The thermal fuse burns at a rate of less than 76mm/min (for samples with a thickness of less than 3mm) during the test or stops burning before burning to a length of 100mm. HB grade is considered to be a grade with lower flame retardancy, but it still indicates that the material has a certain degree of self-extinguishing property and can prevent the rapid spread of flames to a certain extent.
(II) Vertical combustion test (Grade V)
Grade V-2:
*Test method: Place the hot melt sample vertically, ignite the bottom of the sample, remove the flame, and observe the afterflame and afterglow time of the sample, as well as whether there are burning drips.
Requirement: The total afterflame and afterglow time of the hot melt shall not exceed 30 seconds. Burning drips are allowed, but the drips cannot ignite the absorbent cotton below. Grade V-2 is a relatively low grade of flame retardancy in the vertical combustion test, but it still meets the basic flame retardancy requirements.
Grade V-1:
Test method: Same as Grade V-2, place the hot melt sample vertically, ignite the bottom of the sample, and observe after removing the flame.
Requirement: The sum of the afterflame and afterglow time of the thermal fuse shall also not exceed 30 seconds, but unlike the V-2 grade, no burning dripping is allowed. This shows that the V-1 grade thermal fuse has better performance in preventing the spread of flames and preventing dripping from igniting other objects.
V-0 grade:
Test method: In line with the V-1 grade, place the thermal fuse sample vertically, ignite the bottom and observe its burning.
Requirement: The sum of the afterflame and afterglow time of the thermal fuse shall not exceed 10 seconds, and no burning dripping is allowed. V-0 grade is the highest flame retardant grade in the vertical burning test, indicating that the material can be extinguished quickly when exposed to flames, effectively preventing secondary combustion caused by flames and propagating dripping.
(III) 5VB and 5VA tests (only applicable to materials with a thickness greater than 3mm)
5VB level:
Test method: Apply flame to the thermal fuse sample five times for 5 seconds each, and observe the burning condition of the sample after each application of flame.
Requirement: The time for the flame to burn through from the sample surface to the substrate exceeds 60 seconds, or the burning length of the sample does not exceed 50mm. The 5VB level test is more stringent, simulating the burning characteristics of the material under longer time and more intense flame action, and is suitable for occasions with higher requirements for flame retardancy.
5VA level:
Test method: Also apply flame to the thermal fuse sample five times for 5 seconds each, and observe its burning condition.
Requirement: During and after the flame application, the thermal fuse sample cannot have burning drips and cannot be completely burned. 5VA level is one of the highest flame retardant performance levels in the UL 94 standard, and is suitable for applications with extremely high requirements for material flame retardancy, such as aerospace, electronic equipment, etc.
(IV) Other categories
HF-1, HF-2 and HBF:
Mainly used for foam materials.
HF-1: During the test, the flame of the material extinguishes itself within 2 seconds, the afterglow time does not exceed 30 seconds, and there is no burning dripping.
HF-2: The flame of the material extinguishes itself within 3 seconds, the afterglow time does not exceed 30 seconds, and burning dripping is allowed.
HBF: The flame of the material extinguishes itself within 15 seconds, and there is no burning dripping.
VTM-0, VTM-1, VTM-2:
Applicable to film materials with a thickness of less than 0.25mm.
VTM-0: Similar test requirements to V-0, that is, the sum of the afterflame and afterglow time does not exceed 10 seconds, and there is no burning dripping.
VTM-1: Similar to V-1, the total afterflame and afterglow time does not exceed 30 seconds, and there is no burning dripping.
VTM-2: Similar to V-2, the total afterflame and afterglow time does not exceed 30 seconds, and burning dripping is allowed, but the dripping cannot ignite the absorbent cotton below.

III. Test procedures for thermal fuses in UL 94 standard
Sample preparation: According to the requirements of UL 94 standard, the size, shape and thickness parameters of thermal fuse samples should meet the specified standard dimensions. At the same time, the samples need to be adjusted under specific environmental conditions before testing to ensure the accuracy and comparability of the test results.
Test condition selection: According to the characteristics of the thermal fuse and the actual application, select appropriate test methods and conditions, such as horizontal burning test, vertical burning test, 5VB and 5VA test, etc.
Test process: During the test, the operating steps specified in the UL 94 standard are strictly followed, and various parameters such as flame application time, afterflame and afterglow time, burning dripping materials, etc. are accurately recorded.
Result evaluation and classification: According to the test results, the flame retardant performance of the thermal fuse is evaluated and classified according to the classification level of the UL 94 standard to determine whether it meets the specific flame retardant requirements.

IV. Why should we pay attention to the requirements of the UL 94 standard for thermal fuses
Safety guarantee: The requirements of the UL 94 standard for thermal fuses are intended to ensure their safety in various application scenarios. Thermal fuses that meet this standard can effectively prevent the spread and spread of flames when exposed to flames or heat sources, reduce fire risks, and protect the safety of personnel and equipment.
Market access requirements: In many countries and regions, especially in developed countries such as Europe and the United States, the UL 94 standard has become one of the important access requirements for plastic material products to enter the market. For international wholesale buyers, purchasing thermal fuses that meet UL 94 standards is a basic condition for meeting local market regulations and standards, which helps avoid economic losses such as returns and fines caused by non-compliance with standards.
Improve product competitiveness: Thermal fuse products that have passed UL 94 certification are more competitive in the market. It conveys information about product quality and safety and reliability to customers and consumers, which helps to enhance customers’ trust and recognition of products, thereby increasing the market share and brand image of products.

V. How to choose a thermal fuse supplier that meets UL 94 standards
Check the certification certificate: Request suppliers to provide UL 94 certification certificates issued by UL or other authorized agencies to ensure that their products have been rigorously tested and meet the corresponding standard requirements.
Understand the test report: Carefully review the UL 94 test report provided by the supplier to understand the specific performance of the thermal fuse under different test conditions, such as flame retardant grade, burning time, dripping, etc., so as to evaluate whether it meets your specific application needs.
Investigate the production process and quality control system: Visit the supplier’s production plant to understand its production process and quality control process, ensure that it can strictly control the quality of raw materials and production links during the production process, ensure the stability and consistency of thermal fuse products, and thus improve the reliability of products in compliance with the UL 94 standard.
Request sample testing: Before cooperating with a supplier, you can ask it to provide samples and send the samples to an independent third-party testing agency for UL 94 testing to verify whether its products truly meet the standard requirements and avoid the risks caused by untrue certificates or reports provided by the supplier.
Investigate customer evaluation and market reputation: Understand other customers’ evaluation and feedback on the supplier, as well as the market reputation of its thermal fuse products. Good customer evaluation and market reputation usually indicate that the supplier has high product quality and credibility, and can more reliably provide products that meet the UL 94 standard.

VI. Conclusion
The specific requirements of the UL 94 standard for thermal fuses cover many aspects, including different test methods such as horizontal burning, vertical burning, 5VB and 5VA tests, and corresponding flame retardant grade requirements. These requirements provide clear guidelines for evaluating the flame retardant performance of thermal fuses, helping to ensure their safety and reliability in various applications. For international wholesale buyers, fully understanding and strictly requiring suppliers to comply with the UL 94 standard is the key to ensuring product quality, meeting market access requirements, and improving market competitiveness. When selecting a thermal fuse supplier, be sure to conduct a strict review and evaluation to ensure that the purchased products meet the UL 94 standard, providing strong protection for your business development and customer interests.