Category: Rubber

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.

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.

Underwater detection by sound wave transmission, reflection, transmission and attenuation, or removal
The rubber products for the purpose of noise are collectively referred to as underwater acoustic rubber. Rubber as a polymer is widely used in this field due to its damping property.

In the military, water and underwater ships use underwater acoustic rubber to monitor and identify the location of enemy ships, or to conceal themselves. In economic construction, it is used to probe submarine deposits, especially oil and gas. In addition, it is used to determine the location of shipwrecks and salvage shipwrecks, and to track fish stocks during fishing operations.

Under the function of water acoustic rubber, it can be divided into noise reduction, anti-sound and sound transmission. Among them, anti-sound and sound-transparent rubber are used to locate enemy ships, which is called “active sonar.” That is, the party engaged in the war determines the orientation and movement of the enemy submarine by means of underwater acoustic rubber. In addition, underwater ships, such as submarines, can also use noise-reducing rubber to reduce their own underwater noise, to avoid the search and tracking of enemy anti-submarine ships and anti-submarine aircraft, thus preventing target exposure and shielding and protection. This is called “passive sonar.”

The manufacturing points of several underwater acoustic rubbers are briefly described below.

(1) Silencing rubber

The main material should be selected from the characteristic acoustic impedance (the product of the rubber density and the propagation speed of the acoustic wave in the rubber) matching (close to) the acoustic impedance of the propagation medium (water). The preferred host materials are butyl rubber and nitrile rubber. Some bubble-like fillers such as cork powder and mica powder can be added to the rubber compound to enhance the sound absorption effect.

(2) Soundproof rubber

It is mainly used for the sound-permeable window of the shroud and the transducer of the sonar. The suitable rubber types are natural rubber, neoprene, butyl rubber and urethane rubber. Their sound transmission coefficient can reach more than 90%. In addition to being used to detect submarines, sound-permeable rubber can also detect mines. It can be used to detect submarine oil and gas fields in civilian use. Performance requirements are high sensitivity to water, sound and signal transmission, ie no distortion. It is also required that the characteristic acoustic impedance of the rubber used matches the characteristic acoustic impedance of the water. Natural rubber, neoprene, butyl rubber and urethane rubber are preferred for the rubber used.

(3) Anti-sound rubber

Used to eliminate and reduce noise interference. The focus of the formulation design is that the characteristic acoustic impedance of the rubber and the characteristic acoustic impedance of the water are large, and the rubber is required to have a microporous structure. There is air in the micropores. When the air content is greater than 50%, the shear modulus decreases and the wave velocity decreases, which results in high reflectivity at the interface between the foam and water. When the reflection coefficient is greater than 80%, it is effective. Eliminate the flow of water and the noise emitted by the device itself.