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Understanding UL94 Ratings and Flame Retardant Materials

by: May 31,2024 299 Views 0 Comments Posted in Injection Molding


UL 94 is a standard established by Underwriters Laboratories (UL) to evaluate the flammability of plastic materials used in devices and appliances. It provides a classification system based on the material's ability to resist ignition and sustain burning when exposed to a small flame or ignition source. Flame retardant thermoplastics, crucial in various industries including electronics, automotive, and construction, undergo rigorous testing to meet UL 94 standards.


Test methods

The UL 94 standard classifies materials into different categories based on their flammability characteristics. Here are the test methods for the different grades.

Horizontal burn test (HB)

The test method is to clamp one end of the test piece horizontally and horizontally into 45±2 degrees, take an iron net, fixed horizontally under the test piece 10±1mm, the burner (flame height of 20mm or so) into a 45 degree, move to the other end of the test piece to contact with the sample 6mm, and timer for 30±1 seconds and then move away, to be burned to the test piece to the mark of 25mm when the test piece to start another timer. If the specimen reaches the 25 mm mark within 30±1 seconds, start another timer and remove the burner.

50w Vertical Flame Test

The burner (flame height of about 20mm) touches the center point below the sample and burns for 10±0.5 seconds, then remove the Bunsen burner at a speed of 300mm/s, at least 150mm away from the specimen, and record the time of spontaneous combustion for the first time. After the spontaneous combustion stops, the second combustion is carried out immediately, and after burning for 10±0.5 seconds, the Bunsen burner is moved away, and the time of the second spontaneous combustion and the time of blazing red after the flame is extinguished are recorded.

500w Vertical combustion test

Step one

The specimen will be fixed horizontally with a jig or fixture, the burner will be moved to the bottom of the specimen at 20±5 degrees from the horizontal, the tip of the flame will contact the center of the bottom of the specimen and burn for 5±0.5 seconds, then the burner will be removed for 5±0.5 seconds, and this action will be repeated for five times, and then the specimen will be removed after the fifth time of combustion, and then the specimen will be observed and recorded as to whether or not there are any holes in the specimen.

Step two

Keep the burner (flame height of 125mm or so) and the level of 20±5 degrees to move to the side of the specimen, so that the tip of the flame inner flame (high 40mm ± 2mm) contact the bottom side of the sample, burning 5±0.5 seconds, move away from the burner for 5±0.5 seconds, repeat this action for five times, in the fifth combustion after the move and record the time of spontaneous combustion and the time of blazing red after the flame is extinguished.

Advantages of UL 94 Compliance: 

Compliance with UL 94 standards offers several advantages for manufacturers and end-users. Firstly, it ensures the safety and reliability of products by reducing the risk of fire hazards. Secondly, it enhances the marketability of products by demonstrating adherence to stringent safety standards. Additionally, UL 94 compliance may be a regulatory requirement in certain industries, especially those involving electronics, building materials, and transportation.


Materials with UL 94

Currently, UL 94 qualified injection molding materials include ABS, PC, ABS/PC, PP, PA, PEEK, and others. If you have UL 94 requirements, you can note when placing an order, or you can contact mila@pcbway.com to select the right material for your order.

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