First, basic knowledge of rubber raw materials

The main characteristics of rubber:

It has good flexibility, variability, strength, and tear strength, and has good impermeability, impermeability, acid and alkali resistance and insulation.

Classification of rubber: divided into natural rubber and synthetic rubber two.

1. Natural glue (NR) :

The raw material of natural rubber comes from the rubber plant tree. Its advantages are: good elasticity, high strength, good insulation, small deformation, convenient processing. Its disadvantages are: oil resistance, poor temperature resistance, easy aging, are generally used and blended. General production of automobile tires and some shock-absorbing wear-resistant rubber parts.

2. Synthetic glue:

Synthetic adhesives are: styrene butadiene gum (SBR), butadiene gum (NBR), butadiene gum (BR), ethylene vinyl gum (EPDM), butyl rubber (IIR), neoprene gum (CR), acrylic glue (ACM), hydrogenated butadiene (HNBR), chlorosulfonated polyethylene (CSM), fluorine rubber (FKM), silicone rubber (MVQ) and so on.

2.1. Ethylene-polypropylene Adhesive (EPDM)

Advantages: Excellent aging resistance, weather resistance, good electrical insulation, good impact elasticity, oil resistance.

Disadvantages: slow vulcanization speed, self-adhesive energy, poor thermal tearing performance, poor processing performance.

Uses: Manufacture heat-resistant transport belts, steam hose, chemical resistant seals, shock pads and waterproof materials and automotive leather bowls, leather rings, etc.

2.2. Nitrile gum (NBR)

Advantages: Excellent oil resistance, but also has good heat resistance, aging resistance, wear resistance, corrosion resistance and other properties.

Disadvantages: poor cold resistance, acid resistance, electrical insulation and other properties, and poor resistance to tear strength.

Uses: Mainly used in the manufacture of oil seals, shaft seals and gaskets (O-rings) and other products, can also be used in the manufacture of oil-resistant hose, transport belt, rubber roller, vacuum hose, shock absorber products and textile accessories.

2.3 Styrene butadiene Glue (SBR)

Advantages: Good heat resistance, aging resistance and wear resistance.

Disadvantages: cold resistance, elasticity, resistance to flexion, cracking, tear resistance and other properties are poor, and the processing performance is poor, the plasticity change is small, the rolling deformation is large, and the self-viscosity is poor.

Uses: mainly used for pneumatic tires, followed by rubber shoes, rubber hose, tape, rubber roller, rubber cloth and model products, vacuum cleaner seal ring such as suction seal ring.

2.4 Neoprene rubber (CR)

Advantages: flexion resistance, heat resistance, aging resistance, acid and alkali resistance, and good elasticity, good air tightness. It is resistant to cold and water.

Disadvantages: poor storage stability, easy crystallization, poor electrical insulation

Uses: Mainly produces rubber parts in home appliances and air conditioners

2.5 Butadiene or butadiene rubber (BR)

Advantages: elasticity, low temperature resistance, good wear resistance.

Disadvantages: tensile strength, tear strength is low, wet slip resistance is not good, poor viscosity.

Uses: Mainly used in the manufacture of tires, but also can be used in the manufacture of wear-resistant products (such as rubber shoes, rubber rollers), cold-resistant products and shock-proof products.

2.6 Butyl Adhesive (IIR)

Advantages: The biggest feature is good air tightness, weather aging resistance, light aging resistance, chemical resistance are excellent, and high temperature resistance, cold resistance is good, long-term working temperature can be below 130℃; The effect of absorbing shock or shock is better, and the electrical insulation is better.

Disadvantages: elasticity is not as good as natural rubber, vulcanization speed is slow, processing performance, poor viscosity.

Application: Most suitable for inflatable inner tube, followed by underground cables, high voltage cables, radiation gloves, chemical equipment lining and shock-proof rubber products.

2.7 Acrylic Glue (ACM)

Advantages: It has good heat and oil resistance, stable performance in lubricating oil containing sulfur, phosphorus and chlorine additives. At the same time, aging resistance, oxygen and ozone resistance, ultraviolet resistance, good air tightness. Operating temperature range: about -25 ~ +150℃.

Disadvantages: poor cold resistance, water resistance, steam resistance and organic and inorganic acids, alkalis. In methanol, ethylene glycol, ketone ester and other water-soluble solution expansion is serious. At the same time, the elasticity and wear resistance are poor, the electrical insulation is poor, and the processing performance is poor.

Uses: Can be used to manufacture oil, heat, aging resistant products, such as seals, hose, chemical lining and so on.

2.8 Hydrogenated nitrile butadiene rubber (HNBR)

Advantages: high mechanical strength and wear resistance, better heat resistance than NBR when cross-linked with peroxide

It has the same properties as nitrile butadiene rubber. Operating temperature range: about -30 ~ +150℃.

Disadvantages: Higher price.

Application: Mainly used in oil and high temperature sealing products.

2.9 Chlorosulfonated Polyethylene (CSM)

Advantages: ozone resistance and excellent aging resistance, weather resistance is better than other rubber. Flame retardant, heat resistance, solvent resistance and resistance to most chemicals and acid and alkali resistance is good. The electrical insulation is acceptable, and the wear resistance is similar to that of styrene butadiene rubber. Operating temperature range: about -20 ~ +120℃.

Disadvantages: poor tear resistance, poor processing performance.

Uses: wire and cable sheath, hose, tape, rubber roller chemical lining.

2.10 Fluorine Rubber (FKM)

Features: Good wear resistance, good weather aging resistance, light aging resistance, ozone aging resistance, radiation resistance, gasoline, benzene, toluene, alcohol, weak acid excellent, the use of temperature range: about -20 ~ +200℃, special grade -35 ~ +250℃(can work at 250℃ for a long time).

Disadvantages: This glue is expensive.

Uses: Mainly produces vacuum resistance, high temperature resistance (such as aircraft, rockets) chemical corrosion resistant oil, high temperature resistant rubber products.

2.11 Silicone Rubber (MVQ)

Advantages: both high temperature (up to 300 ° C) and low temperature (minimum -100 ° C), is currently the best cold and high temperature resistant rubber; At the same time, it has excellent electrical insulation, high stability to thermal oxidation and ozone, and large chemical inertness.

Disadvantages: low mechanical strength, poor oil resistance, solvent resistance and acid and alkaline resistance, more difficult to vulcanize, more expensive.

Uses: Used to make high and low temperature products (rubber hose, seals, etc.), high temperature resistant wire and cable insulation layer. Because it is non-toxic and odorless, it is also used in the food and medical industries.

3. Mixing rubber:

Vulcanizing agent, accelerator, active agent, reinforcing agent, filler, softener, antioxidant, anti-cross agent and other additives are added to the raw rubber in the rubber mixing machine, and the obtained rubber is called mixing rubber.

2. Basic knowledge of rubber process

Noun explanation:

1. Rubber: It is an organic polymer elastic compound with:

(1) Long chain polymer (molecular weight in tens of thousands to hundreds of thousands of more)

(2) The movement of each chain of the molecular chain is lively.

(3) It is easy to rotate and curl between the chain nodes of the molecular chain.

(4) Low intermolecular force.

(5) The room temperature is not shaped.

(6) The molecules can be cross-linked, and have the necessary properties before and after cross-linking.

2. Vulcanization: under certain conditions, the crosslinking process of rubber molecules from linear structure into a network structure is called vulcanization.

3. Aging:

Rubber products in the process of molding processing, long-term storage and use, due to the role of oxygen, ozone, variable metal ions and other chemical substances, by mechanical stress, light, high-energy radiation and other physical effects of mold, insects and other organisms and erosion, will gradually become soft and sticky, hard, brittle or cracked, physical properties reduced, this phenomenon is called aging.

4. Scorch:

In the various processing operations and storage processes before vulcanization, due to the heat or high temperature conditions generated by the mechanical action, the rubber material produces early vulcanization, resulting in a decrease in plasticity, so that the subsequent operation is difficult to carry out, this phenomenon is coke or early vulcanization.

5. Three elements of vulcanization:

That is, vulcanization time, vulcanization temperature and vulcanization pressure are called the three elements of vulcanization.

The role of the three elements of vulcanization in the vulcanization process and the relationship between them:

1. Vulcanization stages:

From the whole vulcanization time, it can be divided into four stages, namely: vulcanization induction stage, hot sulfur stage, positive sulfur stage and supersulfur stage.

1.1 vulcanization induction stage (scorch stage)

At this stage, the crosslinking has not yet begun, the rubber has good fluidity in the mold cavity, and the length of time at this stage determines the scorch property and operation safety of the rubber.

From the end of this stage, the rubber material begins to harden and lose fluidity, such as in pressing vulcanization, the rubber material stops flowing in the mold, depending on the additives used, this stage can be long or short.

1.2 Hot vulcanization stage

After the induction stage, the cross-linking process begins at a certain speed, and the initial cross-linking process is low, and the properties are also low, but by the late stage of this stage, the tensile strength and elasticity of the vulcanized rubber cannot reach the ideal level, but at this time, the tear resistance and dynamic cracking properties exceed the corresponding values in the positive vulcanization stage.

1.3 Positive vulcanization stage

At this stage, the physical and mechanical properties of the vulcanized rubber respectively reach or approach the optimal point or achieve the best comprehensive balance between them. The temperature and time taken at this stage are respectively positive vulcanization temperature and positive vulcanization time, collectively referred to as positive vulcanization conditions.

1.4 Persulfur stage

After the positive vulcanization stage, continued vulcanization will enter the over-sulfur stage. For general rubber, at the beginning of this stage, the physical properties are basically stable stage, that is, the vulcanization flat period, after the flat period, that is, the sulfur stage, in this stage there will be two situations: a: natural rubber appears "recovery" phenomenon. b: Most synthetic adhesives (except butyl adhesives) harden.

2. Three elements of vulcanization

2.1 vulcanization temperature: temperature is one of the most important control conditions in the rubber vulcanization process. When rubber vulcanization temperature began to develop, it was generally controlled in the range of 140℃-150℃. However, in order to improve production efficiency and shorten the vulcanization time, the temperature is now controlled between 180±5℃.

2.2 The relationship between curing temperature and curing time is generally as follows:

Vulcanization temperature (℃) 130 140 150 160 170

Curing time (min) 30 15 7.5 3.75 1.8

From the above situation, every time the temperature rises by 10 ° C, the vulcanization time will be reduced by half, but it is also affected by the following factors:

Rubber is a poor heat conductor, so for thick products, it is difficult to use high temperature to make the inner and outer layers of rubber at the same time reach a flat range.

2.3 The high temperature resistance of various rubber varies (such as natural rubber needs to be vulcanized at low temperature for a long time) after the vulcanization temperature is increased to a certain extent, the rubber performance is more or less affected.

2.4 High temperature also destroys the fibers in rubber products, which will reduce the strength of textiles. For example, the cloth product is continuously heated at 240 ° C for 4 hours, then the cloth will be completely destroyed, so when increasing and selecting the vulcanization temperature, the rubber type, vulcanization system, vulcanization process method and product structure should be considered.

3. Curing pressure

It is an important condition for rubber vulcanization and plays an important role in the quality of the finished product. The ultimate pressure of various presses in this part: Taiwan 200T (including vacuum) is 21Mpa; Huzhou 150T is 18.6Mpa; Huzhou 100T is 20 Mpa.

3.1 vulcanization pressure can play the following roles in the vulcanization of products:

3.1.1 Improve the density of the compound and remove bubbles;

3.1.2 Promote the flow of rubber material in the mold cavity so that it quickly fills the mold cavity;

3.1.3 Make the adhesive material fit closely with the mold surface to obtain a smooth surface and clear pattern;

3.1.4 Improve the adhesion of rubber and cloth layer, metal skeleton and the bending resistance of the product.

In short, the vulcanization pressure plays an important role in the quality of the product, but the effect on the vulcanization speed is very small and basically not considered.

4. Curing time

A cross-linking process of vulcanization must be completed within a certain time.

The length of curing time must be subject to the curing effect of achieving positive curing time, and too short a time will make the product less sulfur. Too long will lead to over-sulfur products.

Therefore, the vulcanization time must be strictly observed in the vulcanization production process, and the process discipline is absolutely not allowed to extend or shorten the vulcanization time at will.