Author: Editor

Coreless hose features

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The coreless hose is a hose type named from the processing point of view. As we all know, the traditional hose production is inseparable from the use of the core rod. This is because the inner diameter of the hose depends on the outer diameter of the mandrel, and the bonding between the layers is required to be supported by the mandrel. Especially when the hose is vulcanized, the mandrel plays the dual role of heat transfer and shaping. After the end of vulcanization, the relationship between the tube body and the mandrel is terminated by the core removal. In the whole process of the production of the coreless hose, the mandrel is removed from the beginning and replaced by compressed air. This is the origin of the name “coreless”.

The advantages of the coreless process are reflected in the following aspects:

1) Low labor intensity In the molding of cored hoses, the iron cores must be carried together when moving the semi-finished products, so the consumption of physical strength is very high; while the production by the coreless method, the physical labor is greatly reduced.

2) The simplification process can eliminate the multiple processes such as core, core removal, coating release agent, water-absorbing cloth, water-removing cloth, and finishing water cloth, thus shortening the process.

3) Saving the consumption of auxiliary materials. Due to the reduction of processes, some materials are no longer needed, such as cloth, release agent, iron core, etc. Among them, the cloth is the most abrupt. Since the water-coated cloth is vulcanized once, it is subjected to about 1 h at 145 to 155 °C. After 10-15 times of use, it is crisp and can no longer be used.

4) It helps to improve labor productivity. Because of the simplification of the process, the labor productivity is obviously improved, and the output of the class is improved.

(2) Insufficient coreless process

Although the coreless process has many advantages, it also has some shortcomings, mainly because the vulcanization cycle is obviously elongated, which is related to the two heat transfer (steam-water-product), although it does not affect the production, but it increases the energy consumption. Does not meet the requirements of energy saving and consumption reduction. It is necessary to solve it through improvements in materials or formulations.

(3) Core technology of coreless process

In order to ensure smooth and high-quality production of coreless hoses, the following key technologies must be mastered:

1) The appropriate molding aeration amount can generally be controlled in the range of 0.1 to 0.3 MPa.

2) Prevent semi-finished products from being deformed during parking. When moving semi-finished products between the upper and lower steps, care must be taken to prevent distortion.

3) Water bath vulcanization Because there is no core rod support, the conventional steam vulcanization is easy to twist and deform, and the appearance is difficult to guarantee. However, when the water bath is vulcanized, the buoyancy of the water offsets the downward pressure of the upper semi-finished product, which prevents the underlying semi-finished product from being Squashing.

Performance characteristics of vacuum resistant rubber

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The rubber that can be used for a long time under the negative pressure of 10-1〜133X10-8Pa is called vacuum-resistant rubber, and has the characteristics of high airtightness, low gas permeability, low weight loss and the like. Vacuum-resistant rubber is generally classified into four grades according to the negative pressure (less than atmospheric pressure) of the working environment.
Vacuum-resistant rubber products are mostly used in precision fields such as spacecraft, space stations and satellites. In addition to meeting the demanding vacuum resistance requirements, that is, to achieve 6×10-9 Torr, it is also necessary to withstand the strong cosmic radiation in space (the intensity reaches 1.0 × 104 rad). In addition, the cracking of the rubber under high-energy radiation greatly exceeds the cracking under normal pressure, which may increase the damage to the properties of the rubber. In short, under high vacuum and ultra-high vacuum conditions, the rubber is subjected to conditions far more severe than under normal conditions.

(1) Performance requirements for vacuum resistant rubber

The performance requirements of vacuum-resistant rubber, in addition to the conventional properties that elastomers should have, must meet the unique requirements of the following two aspects.

1) Air tightness is specifically to achieve high airtightness, low air leakage, low gas penetration and other requirements. The main cause of failure of rubber products in vacuum systems is leakage
Gas, so ensuring the lowest possible air leak rate is critical. However, the gas leakage rate varies with the type of rubber. In addition to the gas leakage rate, the gas permeability (the ability of the gas to diffuse in the rubber) is also an indicator that must be controlled.

2) Weight loss

Rubber products working in a vacuum system, due to high temperature and high energy radiation and the action of certain media, will chemically react during use to produce low molecular weight volatiles. These volatiles sublime under reduced pressure, resulting in weight loss. Sublimation is related to the structure and formulation of rubber. Under high vacuum conditions, the highest weight loss rate is butyl rubber (39%), and the lowest is fluororubber. This is why, although butyl rubber has good airtightness, it is not suitable for use under high vacuum conditions. Because the hair is bursting from the angle of use, the weight loss rate of the rubber in vacuum should not exceed 10%.

(2) Matching points of vacuum resistant rubber

1) The choice of gas tightness and weight loss rate must be balanced and should not be neglected. The determination of the specific rubber type is also determined according to the vacuum requirements. Generally, products requiring low vacuum, such as vacuum hoses for bulbs, can also be made of natural rubber. For products with high vacuum resistance, it is necessary to use a high acrylonitrile content of butadiene rubber or fluororubber because of the weight loss. For products that are resistant to ultra-high vacuum, Viton is preferred.

In addition, it is also necessary to consider that the high-vacuum-resistant rubber is subjected to high-temperature barbecue treatment before being put into use, so the ability of the main material to withstand the high temperature of the barbecue must also be taken into consideration, that is, the selected rubber type must withstand the vacuum performance, and must withstand the barbecue. The high temperature is suitable for use at 10-6~10-7Pa or higher. Therefore, almost non-fluororubber and high acrylonitrile nitrile rubber are the only ones.

2) The compounding agent plasticizer has low volatilization point and large dosage, and it is best to use less or not. Although the amount of anti-aging agent is not large, it is volatile and should be used sparingly. It is not advisable to use white carbon black for the filler. The proper amount of carbon black can reduce the gas permeability and help to withstand the vacuum.

Essentials of preparation process of antistatic rubber compound

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1) When mixing black antistatic rubber compound, the structure of carbon black is easily damaged after mechanical shearing, and the plasticity is increased. As a result, the antistatic property (ie, electrical conductivity) is impaired, so that the kneading can reach a uniform dispersion degree. Be careful to prevent refining. The plasticity of the rubber compound should be controlled at 0.4~0.45.

2) The hot-smelting time of the film-out type should not be too long, and the pitch should not be too small. The reason is the same as above.

3) The deeper the vulcanization cross-linking, the smoother the electrostatic path and the better the electrostatic discharge effect.

Antistatic agent and related additives

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The antistatic properties of rubber have a lot to do with rubber, but it is equally important to use suitable antistatic additives. It can even be said that its significance is even worse. At present, antistatic agents for commonly used rubbers fall into two categories: conductive carbon blacks and ionic surfactants. They are suitable for black and light colored products, respectively.

1) Among the carbon black carbon blacks, the conductive varieties are acetylene black, conductive furnace black, conductive black, etc.; and the most used and most widely used acetylene black, because its price is relatively low. Moreover, since it contains a large amount of volatile matter, the electrical conductivity is somewhat poor, and this can satisfy the need for antistatic. In addition, conductive carbon black can also provide some reinforcing effects, including increased tensile stress and hardness. When used as an antistatic agent, the amount of acetylene black is generally from 20 to 30 parts. However, it is not suitable for light-colored antistatic products, nor for products with high hygienic requirements (such as medical antistatic products).

2) Ionic surfactants Their antistatic properties are derived from surface polarity and are also related to their ability to diffuse and to be compatible. If such surfactants have good compatibility with rubber, their diffusion and migration will be constrained, and the conductivity will be pinned. Conversely, if the compatibility is too poor, it will spread out and migrate too quickly. Sex is also difficult to last. Therefore, the principle chosen should be to match the compatibility of the rubber. Theoretically, the hydrophilic group in the surfactant-type antistatic agent molecule has a good antistatic effect because it can form a uniform molecular layer on the surface. The antistatic agent SAS variable has been formulated into natural rubber, and the amount of such antistatic agent is preferably 7 to 10 parts.

3) Vulcanization system should note that in the antistatic formula of black products (with carbon black as antistatic agent), it is not advisable to use effective or semi-effective vulcanization systems such as low sulfur high or no sulfur, because the crosslinked structure of these systems is single. The main disulfide bond is not conducive to the formation of long-chain structure of carbon black, thus affecting the establishment of conductive channels. Conventional high sulfur and low vulcanization systems should be used as much as possible to improve electrical conductivity. Typical vulcanization system ratios are: sulfur 2.5, zinc oxide 5, stearic acid 2, accelerator 1.5. In the case of using a light-colored antistatic agent, since the surfactant has a plasticizing effect, the distance between the rubber molecules is increased, and the performance is affected, and the level of sulfur (3-3.5 parts) can be appropriately increased.

4） The filling system uses a large amount of silicate filler to adsorb the surfactant, which will offset its antistatic effect. In addition, it also affects the foaming of the sponge, so it is best to use calcium carbonate as a filler.

5） Plasticizers, such as the production of antistatic sponge products, can use more plasticizers to facilitate foaming.

Antistatic rubber application

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More and more applications have raised the antistatic requirements, especially with the expansion of rubber in electronic computer applications, the probability of static electricity is also increasing, and people’s awareness of static electricity is also increasing. In many countries, antistatic measures are increasingly standardized. The most important of these is the development of various antistatic devices, one of which is antistatic rubber. Antistatic rubber products must not only act to remove static electricity, but also prevent electric shock accidents caused by leakage of low voltage lines. Depending on the application, antistatic rubber can be classified into the following categories.


1） Antistatic rubber is required in some places where it is prone to danger, such as roads and tires that tend to accumulate static electricity. Compared with metal or concrete paving materials, they are more secure and hygienic in the workplace, and they also have good antistatic effects.


2 ）The possibility of fire and explosion during the transportation of flammable and explosive liquids exists. In this case, rubber hoses with good electrical insulation properties are prone to fire. If the oil hose is antistatic, it can ensure the safety of oil transportation.


3） Anti-static conveyor belts used in explosive and flammable places can eliminate accidents caused by sparks, especially in places where tape is used to transport chemical fiber, which can effectively prevent fire accidents caused by fibers being adsorbed on the surface of the belt.


4) Anti-static rubber shoes are also anti-static bulk products. The volume resistance of these special shoes on the ground is 10 103〜8Ω∙CM. When the shoes are grounded, the current through the human body should be <5mA. anti-static rubber shoes used in hospital operating rooms. To remove static electricity generated by the floor, moving stretchers, and tool cart wheels.


5) Some factories have high-purity production sites and need to establish a long-term antistatic environment. Antistatic equipment must be used.