UL94 flame retardant grade is the most widely used material flammability standard. It is used to evaluate the ability of materials to extinguish after being ignited. It is a public standard for daily testing whether materials are flame retardant or not. UL94 can be judged by various methods according to the burning speed, burning time, drip resistance and whether the droplet burns after ignition. Many values can be obtained for each tested material according to color or thickness. When the material of a product is selected, its UL grade shall meet the thickness requirements. UL grade shall be reported together with thickness value. It is not enough to report only UL grade without thickness.

As UL94 flame retardant grade is an American Standard, people have a variety of understanding of UL94 flame retardant grade standard after translation. Therefore, many factories have their own set of "V-0" grade, which brings great inconvenience to upstream and downstream enterprises. Here are some common misunderstandings about UL94 flame retardant grade:

Flame retardant grade (from Hb, V-2, V-1 to V-0)

HB: the lowest flame retardant grade in UL94 standard. For samples 3 to 13 mm thick, the combustion rate is required to be less than 40 mm per minute; For samples less than 3 mm thick, the combustion rate is less than 70 mm per minute; Or go out in front of the 100mm mark.

V-2: after two 10 second combustion tests on the sample, the flame goes out within 30 seconds. 30 cm below the cotton wool can be ignited.

V-1: after two 10 second combustion tests on the sample, the flame goes out within 30 seconds. Do not ignite cotton wool below 30cm.

V-0: after two 10 second combustion tests on the sample, the flame goes out within 10 seconds. No combustibles can fall.

Myth 1: the V-0 level can only be reached when the fire goes out

This is the understanding of some factories. There is only one standard for them to judge whether materials are flame retardant: self extinguishing when leaving the fire, that is, "materials cannot be ignited". Once there is combustion, they will be rated as "flame retardant enough". The reason why you can't understand the standard is that you can't understand it completely.

Myth 2: HB grade is not a flame retardant grade, Any material without flame retardant treatment can be marked with HB grade

In fact, Hb grade is the lowest flame retardant grade in UL94 standard, which is usually called "slow burning grade": for samples with a thickness of 3 to 13 mm, the burning speed is required to be less than 70 mm / min, or extinguished before the standard of 100 mm.

Myth 3: the higher the flame retardant grade, the better，V-0 must be better than V-2

Plastics used for different purposes have different requirements for flame retardancy. In reality, people generally hope that the flame retardant level of materials is higher. But in fact, all kinds of flame retardant test methods have limitations, and their conclusions are relative. Therefore, it is not that the higher the flame retardant level, the better.

For example, it is generally considered that UL94V-0 materials are better than V-2 materials. However, some electrical products require materials with arc ignition resistance. At this time, grade V-2 is better than grade V-0. Because the UL94V-2 material will not form electric conduction and coking under the action of electricity, the possibility of ignition is greatly reduced, while the UL94V-0 material is the opposite.

Myth 4: UL yellow card certification only has the natural color of V-0 level, so no matter what color products are made, they can claim to be V-0 level

This is caused by the careless interpretation of UL flame retardant grade standard - although it is possible that natural color materials can reach V-0 grade and other color products can also reach it, this is only possible, not all. Different materials, different flame retardant systems, the influence degree of color is even different.

Generally qualified high-quality silicone silicone has excellent heat resistance, cold resistance, dielectric property, ozone resistance and atmospheric aging resistance. The outstanding performance of silicone rubber is that it can be used for a long time at -60℃ to +250℃.

Heat resistance：Organic silicone sealing ring has better heat resistance than ordinary rubber. After testing, it can be used almost forever under the high temperature environment of 150℃ without performance change. It can be used continuously for 10000 hours under the environment of 200℃. Therefore, it is widely used in electrical equipment with high temperature environment requirements. For example: super capacitors for new energy vehicles, shockproof gaskets for high-voltage equipment, etc.

Cold resistance：Ordinary rubber has lost its own characteristics at minus 20℃～30℃, while organic silica gel still has good elasticity at minus 60℃～70℃. Some organic silica gel sealing rings made with special formula can also withstand the test of extremely low temperature environment, such as low temperature sealing ring.

It is recommended to use most of the products that are not diluted by hydrogen and silica gel.

Thermal conductive silicone grease is a thermal conductive organic silicone grease composite made of organic silicone as raw material and excellent thermal conductive materials. The thermal conductive silicone grease is almost never solidified and can be kept in good condition for a long time at the temperature of -50℃ to 230℃. It not only has excellent electrical insulation, but also has excellent thermal conductivity. At the same time, it also has the properties of low freeness, high and low temperature resistance, water resistance, climate aging resistance and so on.

At present, thermal conductive silicone grease is widely coated in various electronic products, and there are various brands and materials of thermal conductive silicone grease on the market. How can we judge the performance of thermal conductive silicone grease?

1. Thermal conductivity:

This parameter is one of the important indexes to judge the performance of thermal conductive silicone grease. It refers to the heat transferred by the material (1m thick) with a surface temperature difference of 1°C (k,°C) on both sides through an area of 1 square meter under the condition of stable heat transfer“ λ” Indicates that the unit is watt/meter · degree (w/m·K, where "K" can be replaced by ℃). The higher the thermal conductivity, the better the performance of silicone grease. Of course, the price is more expensive.

2. Thermal resistance:

Thermal resistance is a comprehensive parameter reflecting the ability to prevent heat transfer. In the engineering application of heat transfer, in order to meet the requirements of production process, the heat transfer can be strengthened by reducing the thermal resistance, or the heat transfer can be restrained by increasing the thermal resistance. In thermal conductive silicone grease, the product with smaller thermal resistance has better heat transfer effect.

3. Solid content:

In thermal conductive silicone grease, this coefficient refers to the mass percentage of the remaining part in the total amount after drying silicone grease under specified conditions. In fact, it is more accurate to call it "nonvolatile solid content". The higher the solid content, the higher the viscosity of silicone grease and the harder it feels.

4. Oil content:

Generally speaking, the lower the oil content of the thermal conductive silicone grease, the better, because the silicone grease with high oil content will separate some grease after storing for a long time, which will hinder the heat conduction to a certain extent. Therefore, when replacing the thermal conductive silicone grease, we need to remove the grease separated from the silicone grease first to prevent the performance of the thermal conductive silicone grease from declining.