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Sealant is a sealing material that deforms with the shape of the sealing surface, does not flow easily, and has a certain degree of adhesion. It is an adhesive that is used to fill the gaps in the structure to play a sealing role. It is leak-proof, waterproof, vibration-proof, sound-proof, and heat-proof. It is usually made of asphalt, natural or synthetic resin, natural or synthetic rubber, and other dry or non-dry viscous materials, together with talc, white clay, carbon black, titanium dioxide and asbestos, and other inert fillers, and then add plasticizers, solvents, curing agents, accelerators and so on. It is widely used in construction, transportation, electronic instruments, and parts sealing.
Detailed classification of sealants
1. Classification by base material
- Rubber: This type of sealant is based on rubber. Common rubbers include polysulphide rubber, silicone rubber, polyurethane rubber, butyl rubber, etc.
- Resin type: This type of sealant is based on resin. Common resins are epoxy resin, unsaturated polyester resin, phenolic resin, polyacrylic resin, polychlorinated resin, etc.
- Oil-based: This type of sealant is based on oil. Common oils include various vegetable oils such as linseed oil, castor oil, and tung oil, as well as animal oils such as fish oil.
2. Classification by vulcanization method
This range of sealants uses moisture in the air for vulcanization. It also includes mainly one-component polyurethane, silicone rubber, and polysulphide rubber. The polymeric base material contains active genes. The sealant can be vulcanized into a reticulated structure by reacting chemically with the water in the air to form cross-linked bonds. The moisture in the atmosphere acts as a catalyst in the chemical reaction of vulcanization.
- Heat-altered sealants: Sealants made from polyvinyl chloride resins concentrated with plasticizers and rubber containing bitumen are two different types of heat-altered systems. The vinyl resin plasticizer is a liquid suspension at room temperature and hardens by conversion to a liquid through heating, whereas the rubber and bitumen sealant is thermally fused.
- Hydrolysis-hardened sealants: Sealants with dry surfaces for jointing or glazing are of this type and are mainly based on dry and semi-dry vegetable oils. The oils can be refined polymerized, blown, or chemically modified. The use of cobalt naphthenate as a drying agent speeds up the drying of the surface without hardening the interior.
- Solvent-soluble condensation sealant: This is a solvent-soluble, non-stick polymer-based sealant. The main sealants in this category are butyl interlocking, molecular weight polyisobutylene, acrylates of a certain degree of polymerization, colorful phonated polyethylene, and neoprene sealants.
- Non-drying sealants require permanent plasticity: these sealants generally include polybutylenes, medium molecular weight polyisobutylenes, high viscosity non-hydrolytic bonding materials such as benzene 2 alkene based oils, rod vegetable oils, blown semi-dry oils, or butyl rubber based sealants.
3. Classification by form
- Paste sealants: These are low-level sealants that generally use 3 main materials: oil and resin, polybutylene asphalt. It is commonly used to seal small windows with a maximum of + 5% or – 5% seam travel deformation and is generally valid for 2 years.
- Liquid elastomeric sealants: These sealants also include liquid polymers that are vulcanized to form an elastic state. They are capable of withstanding repeated joint deformations. Liquid elastomeric sealants have a service life of 15 to 20 years. These sealants have high adhesion and tensile strength and are soft at room temperature. The disadvantage is the high price – in general, the case must be primed with two-component sealant site mixing and inconvenient vulcanization sensitive to temperature and humidity, etc.
- Hot melt sealants: Hot melt sealants are also known as hot engineering sealants are sealants based on elastomeric and thermoplastic resin compounds. Hot melt sealants can be formulated to perform as close as possible to liquid elastomeric sealants but it is superior to liquid elastomeric sealants in that the vulcanizing agent does not have to be re-added.
- Liquid sealant: This type of sealant is mainly used as a mechanical fusion surface seal to replace the liquid sealing materials paper, asbestos, cork, and vulcanized rubber to avoid leakage of fluid from the fusion surface inside the machinery, so the liquid sealant is also known as a liquid gasket.
4. Classification by post-engineering performance
- Cured sealants: These sealants can be divided into two categories: rigid and flexible. Rigid sealants rarely have elasticity in the liquid formed after vulcanization or condensation Flexible sealants have elasticity and flexibility after vulcanization. The characteristic of rigid sealants is that they cannot be tilted and generally speaking the joints cannot travel. Flexible sealants remain flexible after vulcanization.
- Non-curing sealants: These sealants are soft, solidifying sealants that remain non-drying after engineering. This type of adhesive is generally available in the form of a scraper or brush and can be applied to joints with different viscosities and different properties of sealants.
5. Classification by application
- Construction sealants: used for very simple wall inlays.
- Silicone sealant (neutral): used for waterproof sealing.
- Silicone structural sealant: used for structural bonding and fixing.
- Arson sealant: used as a fireproof seal.
- Butyl glue: used as the first seal of insulating glass.
- Foam rubber: used as a seam, and waterproof role.
The role and characteristics of common sealants
Common sealants can be divided into elastic sealant, liquid sealant, and sealing putty three categories.
1. Elastic sealant
- It is used to absorb the impact of mechanical vibrations, which does not reduce the wear rate of machinery and does not lead to oil, water, and gas leaks.
- It prevents damage to components or chips caused by stresses in the sealed space due to the harsh environment (cyclic high and low temperatures).
- It protects products in the electronics industry from moisture, corrosion, scratches, and other adverse environmental influences and ensures maximum durability of the protected parts.
- Soft elastic sealants can also be used as liquid tank sealants in high-efficiency air filters. After curing, the liquid tank sealant is an elastic gel, which is used specifically for sealing in high-efficiency air filters. It creates an airtight, airtight seal in the aluminum tank.
- Excellent weather resistance.
- Unique repairability.
- Very stable sealing properties.
- Higher low stress (absorption of stresses arising from thermal expansion and contraction without cracking).
- Excellent aging resistance.
- Chemical stability.
- Corrosion resistance.
- quick and easy handling.
- In addition to the above advantages, a good soft elastic sealant has better elastic recovery.
2. Liquid sealants
It is a new type of polymeric static sealing material in a liquid state. The difference between the liquid sealant and liquid sealing putty is that the liquid sealant must be given a certain tightening force to play its sealing role, which is why some people call it a “liquid gasket”. Unlike solid gaskets such as rubber, asbestos, metal, and paper, it is fluid and therefore does not suffer from the inevitable compression deformation that occurs when a solid gasket is sealed. Due to its fluidity, it can fill the depressions and gaps between the bonding surfaces, eliminating interface leakage, and is, therefore, a more ideal static sealing material.
- The liquid sealant itself is in a liquid state, so it has good fluidity and can fill the gaps in the narrow joints of metal surfaces, forming a uniform, stable and continuous film with viscosity, viscoelasticity, or peel ability, thus making the sealing effect between the joint surfaces of various parts of the equipment.
- The liquid sealant has good sealing performance under certain tightening forces, good pressure, heat, and oil resistance. It has good stability to the medium (oil, water) and does not corrode the metal. At the same time, it is liquid, unlike solid gaskets, which must be compressed and deformed when sealing, so there is no internal stress, relaxation, creep, and elastic fatigue, which lead to leakage. Leakage. The sealant is a material with good adhesive elasticity and does not crack or peel off when subjected to vibration, shock, and excessive compression, as is the case with solid gaskets. In addition, the sealant is simple to manufacture, cheap, and easy to store, making it an ideal material for static sealing of mechanical products.
3. Sealing putty
- Putty series putty is a surface filling material for pre-treatment of the construction surface before the construction of lacquers. The main purpose is to fill the pores of the construction surface and correct the deviation of the curve of the construction surface, to lay the foundation for obtaining a uniform and smooth paint surface.
- Putty is a type of building decoration material, a layer of white – putty – on the surface of a freshly purchased rough room. Putty is usually putty with a whiteness above 90 and a fineness above 330. Putty is used as a base material for wall repair and leveling, laying a good foundation for the next decorative step (painting and wallpapering). Putty is divided into two types: internal and external. External putty has to resist the wind and the sun, so it has high adhesive strength and a slightly lower environmental index. Interior wall putty has a better overall index and is healthy and environmentally friendly, so it is not used externally for interior walls and not internally for exterior walls. Usually, the putty is gypsum or cement-based, so that the surface is rough and easy to bond firmly. However, it is necessary to apply an interface agent to the base to seal the base and improve the adhesion of the wall surface, so that the putty can be bonded to the base better.
- For large roof panels, expansion joints, joints between daughter walls and roofs. Waterproofing of external wall panels, mobile homes, and bathrooms. Waterproof sealing of various temporary and permanent joints in basements, human defense projects, tunnels, subways, culverts, and various water supply and drainage projects. Bonding and sealing of concrete with rubber, plastic, ceramic, and various metal materials.
It has good plasticity and can be formed into any shape by hand without sticking to the hands; the molecular chain of polysulphide rubber is saturated, so the putty is made with good oil resistance, solvent resistance, water resistance, aging resistance, air permeability, and low-temperature flexibility. The disadvantage is that it has a smell.