月: 2023年2月

What Is a Rubber Gasket

In engineering terms, sealing material used for rotating parts is called “packing” and sealing material used for stationary parts is called “gasket”, but rubber gaskets generally refer to rubber sealing material used for stationary parts.

Uses of Rubber Gaskets

Rubber gaskets are used not only in industrial and laboratory equipment, but also in many aspects of daily life, such as the lids of various containers, shower nozzles, and water pipes in the home.

For example, they are used at joints of pipes and valves to improve airtightness and liquid-tightness of these parts, preventing internal fluid leakage and contamination by foreign substances.

Principle of Rubber Gaskets

Rubber gaskets, as the name suggests, are made of rubber, and their function is achieved due to the rubber’s ability to expand and contract.

Rubber stretches because the macromolecules that make up the rubber are stretched by external forces, but the sulfur atoms maintain the connection (cross-linking) between the molecules and keep them together.

For this reason, even when rubber is stretched by external force, it will stretch without tearing up to a certain degree of external force.

On the other hand, when the external force is removed, the rubber returns to its original state and shrinks.

In addition, when the fluid stops flowing, only the external force in the vertical direction of the drawing is applied to the rubber packing due to the tightening of the piping, and the rubber packing returns to its original shape, and the external force from the fluid is applied again. It can be used repeatedly because it exhibits the same function once it is added.

The external force in the radial direction of the pipe caused by the pressure of the fluid flowing inside the pipe will cause the inner diameter side of the rubber gaskets to shrink in the radial direction, and it will also expand in the longitudinal direction of the pipe, which is the direction in which the liquid flows.

The rubber gasket expands and contracts to fill the gap in the piping, thus preventing leakage of fluid to the outside and contamination of foreign matter from the outside.

When the fluid stops flowing, rubber gaskets are subjected to external force only in the vertical direction, and the rubber gasket returns to its original shape and can be used repeatedly as it performs the same function when external force is applied again.

This property allows the rubber packing to be used in joints such as piping, as well as in areas that are opened and closed repeatedly, such as container lids.

However, since rubber gaskets cannot completely return to their original shape, their function will gradually deteriorate.

For this reason, they should be used within a certain period and replaced when they deteriorate.

Manufacturing Process of Rubber Gaskets

Rubber gaskets are manufactured in a variety of materials at a lower cost than sealing tape or other sealing materials.

Rubber gaskets can be manufactured in two ways: by punching rubber sheets into a predetermined shape or by injection molding using a die.

When a die is used, complex shapes such as a double ring can be manufactured.

Material of Rubber Gaskets

Various types of rubber can be used for rubber gaskets, and it is important to select the appropriate material depending on the type of fluid, temperature, and other factors.

Synthetic rubber is more commonly used for rubber gaskets than natural rubber.

Fluoro Rubber (FKM), Urethane Rubber (U), Silicone Rubber (VMQ), Ethylene-Propylene Rubber (EPDM), Butyl Rubber (IIR), Styrene-Butadiene Rubber (SBR), etc.

Types of Rubber

1. Nitrile rubber (Nbr)

Nitrile rubber is one of the most common synthetic rubbers and is a material with excellent oil resistance, abrasion resistance, and aging resistance, making it the first rubber to be considered as a packing material for situations where oil resistance is required.

Nitrile rubber also has excellent aging resistance, making it suitable for use in parts that will be used for long periods.

On the other hand, it is not suitable for use in places exposed to direct sunlight because of its weak weather resistance.

2. Fluoro Rubber (FKM)

Compared to other rubbers, fluoro rubber has superior heat resistance, oil resistance, weather resistance, and chemical resistance.

For this reason, it is often used for packing in situations where chemicals are used.

However, fluorinated rubber is susceptible to physical shock, so care must be taken when handling it.

3. Urethane Rubber (U)

Urethane rubber has high abrasion resistance and overall mechanical strength, which are its greatest characteristics and is suitable for packing used in environments with a lot of friction.

On the other hand, its weak water resistance makes it less suitable for use in wet or humid environments.

In addition, the shelf life is about 10 years.

4. Silicone Rubber (VMQ)

The greatest feature of silicone rubber is its low impact on the human body.

It also has excellent heat resistance and flame resistance, and its shape does not change depending on temperature.

Since its price is relatively stable, it is often used in household products. Taking advantage of its safe characteristics, it is used in packing for rice cookers and products around water.

5. Ethylene Propylene Rubber (EPDM)

Ethylene-propylene rubber is a material with excellent resistance to weather, cold, and inorganic chemicals.

Originally, rubber was susceptible to direct sunlight and extreme cold, and became hard and crumbly, but EPDM has excellent weather and cold resistance, so it can be used outdoors without problems.

Ethylene-propylene rubber is used for rubber electric wires used outdoors. However, its oil resistance is weak, so it is a versatile material for use in environments where oil resistance is not required.

6. Butyl Rubber (IIR)

Butyl rubber is made by copolymerizing isobutylene with a small amount of isoprene. It has excellent anti-vibration, insulation, water, weather, chemical, and heat resistance.

It has a wide range of uses, from industrial products to household goods, and is an indispensable material for daily life.

7. Styrene Butadiene Rubber (SBR)

Styrene-butadiene rubber has excellent properties against animal and vegetable oils such as ethylene glycol and brake oil.

It also has superior resistance to abrasion and aging compared to natural rubber and is an inexpensive material.

It also has the advantage of being resistant to heat and easy to produce homogeneous products and is widely used in tires and hoses.

Conclusion

Rubber gaskets are used in various applications such as plumbing and household goods, and their characteristics vary greatly depending on their materials, shapes, and manufacturing methods.

It is necessary to use rubber gaskets made of materials, shapes, and manufacturing methods suitable for the materials and shapes to suit the use environment and applications.

In consideration of durability, it is also necessary to replace them when necessary.

Overview of Aluminum Oxide Coatings and Its Uses

Aluminum oxide coatings are type of surface treatment that artificially forms an oxide film on the aluminum surface.

Aluminum is easily oxidized by combining with oxygen in the air, and a very thin oxide film is formed on its surface when exposed to air.

Because it is protected by this naturally formed film, it is said to have relatively high corrosion resistance.

In addition, aluminum is lightweight and highly workable, and is used in all kinds of products around us, including daily necessities.

However, due to its high workability, the surface is easily scratched by bending and friction.

The oxide film that naturally forms on the aluminum surface is very thin, and depending on the operating environment, it may be corroded by chemical reactions or damaged by bending or friction, as mentioned above, and corrosion may significantly progress from the damaged area.

Therefore, aluminum oxide coatings are performed to artificially form an oxide film that protects the aluminum surface by passing an electric current through the aluminum in an electrolytic solution to promote oxidation.

The formation of this oxide film is expected to improve corrosion resistance, wear resistance, insulation, and strength.

There are many products that use anodized aluminum oxide coatings, including kettles, sashes, and smartphones for everyday use, and optical parts, automobiles, aircraft, semiconductors, and medical equipment for industrial use.

Principle of Aluminum Oxide Coatings

In aluminum oxide coatings, an oxide film is formed by electrolysis of aluminum in a sulfuric acid electrolytic solution with aluminum as the anode.

As shown in Figure 1, an anode and cathode are placed in the electrolytic solution, and when the aluminum product is placed on the anode side and energized from the electrode, an oxide film is formed on the surface of the aluminum product.

As shown in Figs. 2 and 3, this oxide film is an aggregate of hexagonal prismatic cells with pores inside.

Aluminum oxide coatings are performed based on this principle, but the characteristics vary depending on the method of treatment, so anodizing must be performed according to the application.

Types of Aluminum Oxide Coatings

1. General Aluminum Oxide Coatings

This is a commonly used aluminum oxide coatings that can be applied to small parts with complex structures as well as large products. This method is used to improve corrosion resistance and hardness.

2. Hard Aluminum Oxide Coatings

This treatment method is used to achieve even higher hardness than general aluminum oxide coatings, and are performed in an electrolyte at a low temperature over a long period of time. The oxide film is several times thicker than that of general anodizing, and is used for automobile engines and aircraft, where high durability is required.

3. Glossy Aluminum Oxide Coatings

Before applying aluminum oxide coatings, chemical polishing process is performed to make the surface shiny. This process is used for decorative and reflective materials because of its beautiful appearance.

4. Color Aluminum Oxide Coatings

Immediately after forming an oxide film, the surface is immersed in a dye solution to color it. Coloration can be controlled by the dye concentration, immersion time, and thickness of the oxide film. It is used for water bottles, etc., where light weight and design are required.

Anodized Aluminum Film Thickness and Factors Causing Variation in Film Thickness

1. Aluminum Oxide Coatings Thickness

The thickness of the anodized aluminum oxide film formed by general anodizing, the most common type of anodizing, is usually in the range of 5 to 25 microns, and is set in consideration of usage conditions.

The thickness of the anodized aluminum oxide coatings formed by hard anodizing is in the range of 20 to 70 microns.

Hard anodized aluminum oxide coatings are often applied to parts that require sliding properties, such as automobile engine parts, and a greater film thickness is set than for general anodized aluminum oxide coatings in order to provide wear resistance.

2. Factors Causing Variation in Film Thickness

Despite the anodizing process, variations in the thickness of the anodized aluminum oxide coatings are caused by two factors: one is the distribution of electric currents, and the other is the distribution of temperatures.

Variation due to current distribution
Since anodizing is performed using an electrochemical reaction, uneven electrical distribution causes variations in the thickness of the anodized aluminum oxide coatings.

Depending on the distance between the anode and cathode where the aluminum product is held, variations in film thickness can occur between multiple aluminum products. In addition, when multiple aluminum oxide coatings are performed at once, the current distribution differs depending on the position of the anodes and cathodes, which leads to variations in film thickness.

When multiple aluminum oxide coatings are performed at once, dummy aluminum is hung near aluminum products in locations and conditions where film thickness is likely to increase to release the current.

Variations due to temperature distribution
Aluminum oxide coatings are performed in an electrolytic solution, and the temperature distribution of the electrolytic solution can cause variations in the thickness of the anodic oxide film.

During aluminum oxide coatings, the bath is agitated to maintain a uniform temperature in the electrolyte bath. When the temperature is kept uniform, the electrolyte can flow freely and the temperature distribution of the electrolyte becomes uniform.

However, in the area of the diffusion layer near the aluminum product, the electrolyte has a relatively difficult time moving and the temperature distribution becomes non-uniform. This causes variations in the thickness of the anodized aluminum oxide film. To counter this problem, methods to promote the flow of the electrolyte, such as the use of injection nozzles, are used.

Disadvantages of Aluminum Oxide Coatings

The anodized aluminum oxide coatings formed on the aluminum surface by anodizing has the disadvantage of being inflexible and brittle, which can lead to cracking and peeling of the anodized oxide coating when the anodized area is bent or processed.

In addition, there is a weakness in heat resistance, and there is a concern that the normal anodized aluminum oxide film may crack or peel due to thermal expansion under high-temperature environments exceeding 100 ºC.

Although aluminum oxide coatings improves corrosion resistance and hardness, it is weak in solutions of strong acids and bases, and there is also the problem of dissolution in such solvents.

In addition, wet contact with metals increases the risk of corrosion. Therefore, it is necessary to devise a treatment method according to the intended use.

What Is a Fiber Optic Connector?

FC connector is a type of fiber optic connector, which is a terminal for optical fiber, and is used to connect optical fiber cables.

Since this optical connector is a component that connects optical fiber cables, it plays a very important role in connecting optical devices, which are precision equipment.

Fiber optic connector is metal components used for fixing optical cables that need to be tightened with screws.

Fiber optic connector, including FC connector, is one of the most important components in the construction of optical measuring instruments and optical communication systems, and various types of fiber optic connector is available on the market for use in different environments and for different applications.

Among the methods for splicing optical fibers, unlike fusion splicing, splicing using optical connectors is more versatile because the splicing part can be easily connected and disconnected manually while maintaining sufficient strength of the splicing part.

Uses of Fiber Optic Connectors

Connecting fiber optic cables using fiber optic connectors, including FC connectors, can be easily connected and disconnected by hand, while maintaining a sufficiently high level of strength in the connection area.

Therefore, the connection of optical fiber cables using optical connectors is very versatile.

Among them, fiber optic connectors are used to connect the screw-tightening method, which is used for connections where strength is required to secure optical fiber cables.

In addition to their use in optical equipment and measuring instruments, they are also used in CATV, LAN and public communication lines.

Principle of Fiber Optic Connectors

Fiber optic connectors can be classified into multi-fiber and single-fiber types, of which fiber optic connectors can be included in the single-fiber type.

Among single fiber optic connectors, FC connectors can be included in the sleeve joint method.

In the sleeve joint method, the optical fiber to be connected is first positioned and fixed in the center of a cylindrical ferrule, and then the cylindrical ferrules are aligned with each other inside the sleeve at the time of connection.

The cross-section of the sleeve is C-shaped among split sleeves, and it is spring-loaded, so the cylinders of the ferrules are held together in an optimum manner by the spring, making it easy to align the axes and angles.

In order to position the optical fiber around the cylindrical ferrule, the optical fiber is bonded through a hole that is slightly larger than the diameter of a typical optical fiber (0.125 mm) by about 0.5 μm.

Most of these cylindrical ferrules are made of zirconia among ceramics, which has a linear expansion coefficient almost equal to that of optical fibers, so that temperature changes in the storage and use environment of optical connectors are almost the same. This allows the optical fiber to be used stably without being subjected to thermal stress.

Another advantage is that the end face of the cylindrical ferrule can be polished clean together with the optical fiber.

Precautions for Using Fiber Optic Connectors

There are three points to note when using fiber optic connectors as follows.

• Operating temperature range
  The upper limit of the operating temperature range requires that the ambient operating temperature plus the temperature rise of the fiber optic connectors itself must fall within the upper limit.
• Storage temperature range
  The storage temperature range is the storage temperature when the fiber optic connector is packaged before it is mounted. After mounting, the operating temperature range applies.
• Inserting and extracting connectors
  Connectors must be inserted and extracted properly all the way to the back. When inserting, it is necessary to confirm that the connector is securely locked, and when removing, it is necessary to confirm that the lock is unlocked before proceeding.

There are various other detailed precautions, so be sure to properly check the specifications of each product before use.

Factors Causing Failure of Fiber Optic Connectors

There are three major causes of fiber optic connectors failure.

• Initial failure
  A pattern in which the device itself has malfunctioned before use.
  ・Poor contact caused by flux or cleaning fluid.
  ・Poor contact caused by base coating liquid
• Accidental failure
  Pattern of failure mainly due to mechanical or physical stress.
  ・Failure due to physical damage to the product
  ・Damage due to insertion or removal of entire cable
  ・Damage due to improperly oriented insertion
• Abrasion failure
  Failures that occur while the equipment is in use.
  ・Failure due to corrosion of contacts or poor contact 　caused by insertion/extraction exceeding the specified 　number of times.
  ・Contact failure due to use under the conditions 　specified in the regulations
  ・Damage due to wear and tear of the locking part 　caused by operating the locking part for more than the 　specified number of insertions and removals.

Lifetime of Fiber Optic Connectors

The life of fiber optic connectors can be due to poor contact or damage to the device itself, but there is no degradation over time.

The life of FC connectors can be caused by mechanical, environmental, or electrical degradation, and the life of FC connectors is greatly affected by external factors such as the environment in which the fiber optic connectors are used and the level of demand for FC connectors from the equipment to which it is connected. Among these factors, the life of a single fiber optic connectors are determined by its contact resistance and the number of times it is inserted and removed.