Hardness is a parameter that characterizes the ability of a material to resist the pressure of foreign objects into its surface. It refers to the softness of the feedback when a person touches the silicone with his hand. It reflects the hardness of the material and corresponds to the resistance of the material to local deformation, especially plasticity. The ability to deform, indent or scratch.
As a kind of rubber, the hardness of silica gel is generally characterized by Shore Hardness.
For silica gel, the Shao's hardness is the static extrusion measurement method. According to the different hardness ranges, three hardness testers, Shao A, Sha C, and Sha D are used.
Corresponding to the three units of HA, HC and HD, the most commonly used for liquid silica gel and solid silica gel is the Shao A hardness tester.
1. Liquid and solid silica gel
Common hardness ranges from Shao A0 to A70 degrees, solid silica gel is Shao A 30-70 degrees, and liquid silica gels lower than Shao A0 degrees are also available, but they need to be customized because they are less used, and they need to be measured with a Shao C hardness meter.
There are two types of liquid silica gel: one is manual operation and the other is machine operation: the hardness of manual operation can be 0-70 Shore A, and the hardness of machine operation can be 20-90 degrees.
The hardness of manually operated silica gel ranges from 0 to 70 degrees, and the best performance is from 25 to 35 degrees. The higher or the lower the hardness, the performance will gradually decrease. Liquid silica gel can also produce materials from A80 to A90 degrees, but it will be more brittle and not often used.
When it is higher than Shao A90, the silica gel is measured with a Shao D hardness tester. This kind of silica gel has a high hardness but no elasticity.
2. The difference between liquid and solid silicone
If you make a more complicated mold, it is better to use solid silica gel. If you use a simpler mold, it is better to use liquid silica gel. Solid silica gel has requirements for the operation process and must be molded by machine, while liquid silica gel can be manually operated. There is an advantage in tension, and liquid silica gel has an advantage in feel.
a. The difference between the shape of liquid silica gel and solid
It can be seen from the appearance: one solid and one liquid.
1) Liquid silica gel is in a liquid state and has fluidity. It is a highly transparent and safe food-grade material. No auxiliary materials such as vulcanizing agents are added during molding, and it is sealed and fed.
2) Solid silica gel is in a solid state and has no fluidity. It is also a transparent and environmentally friendly material. A vulcanizing agent needs to be added to accelerate the vulcanization molding time during molding.
b. The difference between liquid silica gel and solid in the field of use
1) Liquid silicone is generally used in baby products, kitchen products and medical products. It can directly contact food and human body.
2) Solid silicone is generally used in daily necessities, industrial miscellaneous parts, and auto parts.
3) Safety of liquid silica gel and solid silica gel: Liquid silica gel is a highly transparent and safe food-grade material. When molding, no auxiliary materials such as vulcanizing agent are added, and it is sealed and fed.
Solid silica gel is a transparent material. It needs to add a vulcanizing agent during molding to speed up the vulcanization molding time.
3. Hardness of commonly used silicone products
The silicone strap is generally A70 degrees;
Silicone phone case A60 degrees;
Silicone keys are generally A50 degrees;
Silicone pacifiers are generally A30 to 40 degrees;
The silicone chest pad shows A0 degrees.
The choice of the hardness of liquid silica gel or solid silica gel mainly depends on its working conditions. If the force is large, the higher the deformation rate is required to use the higher hardness silica gel, and the elasticity is required, and the low hardness silica gel is not easy to tear.
In addition to hardness, other physical parameters, such as tensile strength, tear strength, elongation at break and other parameters are also very important. Sometimes electrical performance indicators such as volume resistivity, dielectric constant and other indicators need to be considered.