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What Is Urethane Rubber?

Urethane rubber is a polymer with urethane bonds and is a type of synthetic rubber with excellent elasticity and rigidity (Figure 1).

It has the advantage of long-term use, especially in mechanical strength and wear resistance. The properties of urethane rubbers vary greatly depending on the composition of the material and the bonding method.

There are two main types of urethane rubbers: polyester urethane rubbers (AU), which have ester bonds in the main chain, and polyether urethane rubbers (EU), which have ether bonds in the main chain.

AU has ester bonds and is easily hydrolyzed, but it has excellent oil resistance and mechanical strength.

EU, on the other hand, is inferior to AU in terms of oil resistance and mechanical strength, but is resistant to hydrolysis and has excellent water resistance.

 

Applications of Urethane Rubber

Urethane rubber is used for rolls, tires, conveyor belts, and soles of sports shoes. A typical example that takes advantage of its abrasion resistance is belt compares used in factories.

However, care must be taken when using it in acidic or high humidity environments, as it will deteriorate. The high elasticity of the material is also used for the soles of sports shoes.

The reason for this wide variety of applications is that the elasticity and other properties can be freely changed depending on the composition of the material and the manufacturing method.

Causes and Countermeasures for Urethane Rubber Degradation

Causes of urethane rubber degradation in the natural environment include light, heat, oxygen, water, and microorganisms. Among these, degradation due to light and heat is decomposition by oxidation reaction, which causes cleavage of urethane bonds and degradation of physical properties.

To counteract this degradation, the addition of UV absorbers or antioxidants is effective. The next example of water-caused degradation is hydrolysis of urethane bonds, and polyester urethane rubbers are more susceptible to degradation than polyether urethane rubbers.

In the case of polyester systems, ester bonds are also subject to degradation due to hydrolysis. This type of degradation can be prevented by adding carbodiimide compounds.

Microbial degradation caused by fungi is a typical example. It is known that urethane rubber is more susceptible to microbiological degradation than other high-molecular compounds such as plastics.

Also, in this type of degradation, this is true for polyester urethane rubber, which is more susceptible to degradation than polyether urethane rubber.

The reported mechanisms include hydrolysis of ester bonds by esterases produced by microorganisms.

Principle of Urethane Rubber

Types and Characteristics of Urethane Rubber

Urethane rubbers are used in a wide variety of applications, and their properties can also be controlled by manufacturing methods.

The synthesis method uses a polyaddition reaction between polyol, represented by glycol, and diisocyanate. The following three manufacturing methods are mainly employed.

Mirable type: This is one of the most common manufacturing methods used to process synthetic rubber. After generating a dough from raw materials, it is poured into a mold and pressed to form.

This is a very simple method that allows for high production efficiency. On the other hand, it has disadvantages such as susceptibility to hydrolysis and poor material properties.

Thermoplastic type: This is a manufacturing method that applies a resin processing method and is also called the injection type. After heating and melting urethane rubber pellets, they are injected into a mold and molded. This method has the advantage of low-cost production, but the manufacturing equipment is expensive, so mass production is a prerequisite for this method.

Castable urethane type: Liquid urethane rubber is mixed with a curing agent and vulcanized in the mold. Vulcanization cross-links urethane rubber molecules to obtain high elasticity.

After one day of this process, the product is molded and manufactured. Many companies have introduced this method because the manufacturing facilities are inexpensive and complex shapes can be processed at the same time. However, manufacturing efficiency is low because of the time required for production.

What Is Urethane Foam?

Urethane Foam (formal name: polyurethane) is a polymer containing urethane bonds, which is obtained by mixing and reacting two main raw materials.

It is widely used in various applications depending on the blending of the main raw materials and the molding method, and can be classified into foamed foam products (hereinafter referred to as Urethane Foam) and non-foamed products.

Foamed foam products  and non-foamed products are broadly classified. Urethane Foam is classified into soft and hard, depending on the application. Non-urethane foam products range from soft and flexible like rubber to tough and resilient like those used in tires.

Uses of Urethane Foam

Among urethane foam products, soft urethane foam is the most commonly seen product used in everyday items such as cushions, sofas, and other furniture, bedding, clothing, and daily necessities.

Rigid Urethane Foam is also used in a wide range of industrial products such as building materials as a heat insulator and sound absorber due to its excellent heat insulation properties, lightness, and ease of molding. Both flexible and rigid foams can be molded at will, making it possible to create parts with a high level of design.

Non-form products, on the other hand, are used as raw materials for tires, tubes, and rollers. In addition, urethane is used in a wide variety of fields, such as paints and waterproofing materials that take advantage of its high weather resistance and waterproofing properties, as well as textiles and synthetic leathers.

Principle of Urethane Foam

The raw materials, polyisocyanate and polyol, form polymers by urethane bonding, and the type and additives are selected to produce urethane foam according to the purpose.

Polyisocyanate is a compound that has two or more isocyanate groups in one molecule. Typical examples are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI).

These polyisocyanates react with polyols having two or more hydroxyl groups in a single molecule to form urethane foam bonds. If a cross-linking agent is added as needed, burette and allophanate bonds can be formed. The elasticity varies depending on the density of the crosslink, with higher density resulting in harder properties.

Types of Urethane Foam

Urethane Foam and non-foam product forms are available.

1. Urethane Foam

Urethane Foam includes soft urethane foam, hard urethane foam, and semi-hard urethane foam, which has characteristics in between the two. Both types are manufactured by adding catalysts, blowing agents, foaming agents, and flame retardants to the raw materials polyisocyanate and polyol.

Flexible Urethane Foam
The foam of flexible urethane foam is produced by carbon dioxide gas generated during mixing and reaction of isocyanate and polyol, and is a continuous series of bubbles. The foam is soft, cushiony, and resilient, and is used in cushions and sofas, as mentioned above.

Rigid Urethane Foam
In rigid urethane foam, the foaming agent is vaporized by the reaction heat of isocyanate and polyol, in addition to stirring and mixing, and each foam in rigid urethane foam is a small independent foam. Each independent foam of rigid urethane foam is filled with gas derived from the blowing agent, thus achieving a high thermal insulation effect.

For this reason, as mentioned earlier, it is used as a building material for heat insulation and sound absorption. Since the curing reaction proceeds quickly, the raw materials are often mixed and sprayed at the work site to produce a foam form.

Semi-Rigid Urethane Foam
Semi-hard Urethane Foam is a material with hardness somewhere between that of soft urethane foam and hard urethane foam. It is characterized by high resilience and high elasticity and is used in mattresses.

2. Non-Foam

There are two types of non-foam materials: thermosetting and thermoplastic.

Thermosetting ones are used in car and motorcycle tires, while thermoplastic ones are used as materials for molded items such as car bumpers and synthetic leather. Other uses include paints, elastic fibers, adhesives, and waterproofing materials.

How to Select Urethane Foam

When selecting urethane foam, it is important to confirm the following points:

1. Airtightness

Rigid urethane foam used as a construction material is easy to cut, but if you make a mistake when filling a wall, there is a possibility that there will be a gap. Depending on the level of the installer, airtightness may be low, so it is important to confirm that airtightness can be secured.

2. Flammability

Urethane foam itself is highly flammable. As mentioned above, fire-retardant gypsum board is generally applied on top of the urethane foam, so it is not likely to catch fire directly. However, if fire is a concern, it is safer to use rock wool or similar materials.

3. Safety

There is a disease called “sick building syndrome,” which has become common nowadays. This is a symptom of allergic reactions caused by toxic gases emitted from building materials used.

What Is an Insert Nut?

An Insert Nut is a material used to increase the strength of the fastening portion of a plastic material. Since resin is less strong than bolts, insert suts, which are mainly made of metal, are embedded in resin to strengthen the joint.

The outer surface of the insert nut is knurled so that it can be adhered to the resin, and the inner surface is a nut-threaded member.

Insert nuts are generally made of free-cutting brass or lead-free brass, which has excellent machinability and ductility. Aluminum or stainless steel may also be used. Resin inserts are also available and are used for automotive and other applications.

There are two methods of inserting insert nuts into plastic parts: inserting the insert nut when the plastic is molded, or inserting the insert nut after the plastic is molded.

Usage of Insert Nut

Insert nuts have a wide range of applications for reinforcing fasteners of plastic parts. The main uses are for fastening parts of resin parts in automobiles, motorcycles, trains, aircraft, and other transportation equipment, smartphones, home appliances, and industrial machinery.

Particularly in the automotive industry, plastic parts are being used to reduce weight in order to improve fuel efficiency. In addition, environmentally friendly bioplastics are increasingly being adopted.

Insert nuts are widely used to fasten these plastic parts. Insert nuts themselves are also being developed made of high-strength resin, contributing to weight reduction.

In machine tools, insert nuts are often used in machining centers, NC machine tools, servo motors, and control panel housings for inverters, etc.

Types of Insert Nuts

There are many types of insert nuts, depending on the combination of shape, material, and insertion method.

There are two types of insert nut shapes: standard type and flange type. The standard type is the most common type and the least expensive. The standard type is further divided into two types: single-sided and double-sided.

The single-sided type has a fixed mounting direction for press-fitting, while the double-sided type is chamfered on both sides so that it can be inserted from either side during press-fitting.

The flange type has a flange on one side and can be inserted in only one direction.

There are also different methods of inserting insert nuts into plastic members.

Other Information on Insert Nuts

Insert Nut Insertion Method

There are two methods of embedding insert nuts into resin: insert during molding and insert after molding.

Post-molding inserts are mainly used for thermoplastic resins that soften when heat is applied.

For thermosetting resins, which harden when heat is applied, post-molding inserts can also be used, although most of them are done at the time of molding.

1. Insert during molding
When molding a resin material, an insert nut is attached to the mold and the resin is poured into the mold. Although the insert nut needs to be assembled to the mold, the resin is melted and inserted around the insert nut, so it has excellent strength after cooling. 

2. Insert after molding
There are three methods of inserting after resin molding: expansion method, press-fit method, and thermal press-fit method.

Expansion Method
Insert nut is press-fitted into the bottom hole of the resin member and fixed to the resin member by expanding the tip of the nut. After the insert nut is driven into the plastic member with a hammer, the tip of the insert nut is expanded by pushing the expansion plate downward using a special punch or other tool.

This method is characterized by the fact that it is not affected by the shape of the boss into which the nut is inserted on the material side, and it does not require a heat source.

Press-fit method
This is the most common method. A press or hammer is used to press-fit the nut into the plastic material without using a heat source. Although a larger boss diameter can prevent the boss from cracking, it is necessary to change to the thermal press-fit method depending on the resin material.

Thermal press-fit method
This method uses a heat source to press-fit the insert nut into the plastic part. The insert nut is set in the bottom hole of the part, and the nut is press-fitted while being heated by a soldering iron, ultrasonic welding machine, or thermal press-fit machine.

By applying heat to the insert nut, the heat is transferred to the resin material and softens it, allowing the insert nut to be easily press-fitted into place. Also, since the resin is melted as it is press-fitted, the melted resin is absorbed into the nut, increasing its strength. This method is not affected by the boss shape on the resin member side.

What Is an Angular Contact Bearing?

An Angular Contact Bearing is a bearing that can support loads parallel to the axis (axial load) and loads perpendicular to the axis in one direction (radial load) simultaneously.

It is similar to deep groove bearings, but there is a difference. The grooves on the outer ring of a deep groove bearing are symmetrical in the axial direction, while the grooves on the outer ring of an angular contact bearing are slanted at a certain angle. This allows them to support both axial and radial loads.

Angular contact bearings are used to support shafts of pumps, various compressors, press machines, elevator hoisting machines, etc.

Uses of Angular Contact Bearing

Angular contact bearings are used in sets of several pieces. In this case, they are designed to support axial loads in a single direction or in both directions by changing the way they are combined.

1. Single Row Type

Two bearings are used in a single row, facing each other, with adjustable internal clearance. Capable of supporting radial loads and axial loads in one direction. Suitable for applications such as machine tool spindles, where rigidity and rotational accuracy of bearings are required.

They are also used in pumps, various compressors, screw chillers, elevator hoisting equipment, etc.

2. Double-Row Type

This is a structure in which a pair of angular contact bearings are installed in a single bearing as a back-to-back combination. It can support axial loads in both directions. Since it can also support moment loads, it is used as a fixed side bearing. Used in compressors, presses, automatic guided vehicles, belt conveyors, etc.

3.Combination Type

Multiple single-row type bearings are combined. There are three types of combination types: front combination, back combination, and parallel combination. If the axial load is in a single direction, large loads can be supported. Applications include pumps, compressors, screw chillers, and elevator hoisting equipment.

Principle of Angular Contact Bearing

Angular contact bearings can support both radial and axial loads by having a contact angle. The contact angle is the angle between the direction perpendicular to the axis and the direction of the load applied between the raceways and rolling elements when both radial and axial loads are applied to the bearing.

The larger the contact angle, the greater the capacity to take axial loads, and the smaller the contact angle, the wider the operating range up to higher speeds.

Since a radial load causes a bifurcation force on the axial load, the axial load, several bearings are used together to accommodate the bifurcation force.

Other Information on Angular Contact Bearing

1. Angular Contact Bearing Orientation and Assembly

Angular contact bearings are used in multiples because of their contact angle. There are several types of assembly methods, such as DB type with back contact angle, DF type with front contact angle, DT type with parallel contact angle, and other combinations of three or more bearings, each of which has its own characteristics.

The DB type is the most commonly used method of assembly, in which the back faces of the bearings are aligned with each other. It can handle radial loads and axial loads in both directions. It can support the largest moment loads of all combinations.

If the bearing is a pressurized type, the clearance can be adjusted simply by setting the inner ring with a nut. The DB type is superior in its ability to take moment loads.

The DT type can accommodate radial loads and axial loads in one direction by stacking the bearings in the same direction. Since axial loads are supported by two bearings, it is used when axial loads in one direction are large. 

2. Pressurized

When two bearings are used opposite each other, as in the case of angular contact bearings, the axial clearance may be negative. This condition is called pressurizing and can accommodate larger moments.

This is especially true for the DB type (back-to-back assembly), because when two angular contact bearings are back-to-back assembled, the distance between the points of action becomes larger due to the contact angle between them, and thus the bearing can withstand more moments.

Preloading not only increases the moment capacity, but also enables adaptation to high speed rotation, improves the positioning accuracy and rotational precision of the bearing, and suppresses vibration and abnormal noise. Three preload levels are usually available: light, medium, and heavy preload.

Preload is set by grinding the ring end faces to create a step between the inner and outer rings. The preload can also be increased or decreased by stepping the width of the inner and outer ring spacers.

What Is Alumina?

Alumina is a compound known as aluminum oxide, consisting of aluminum and oxygen. Its chemical formula is Al2O3, and it appears as a white solid with a high melting point. Alumina is renowned as the primary component in materials like corundum, ruby, and sapphire.

There are different forms of alumina, and two noteworthy ones are:

• α-Alumina: Recognized for its heat resistance, insulation, and chemical resistance. It finds applications in refractory materials, cutting tools, and abrasives.
• γ-Alumina: Possessing a large specific surface area, it is used as a catalyst support.

Applications of Alumina

Alumina is primarily derived from the calcination of aluminum hydroxide (Al(OH)3). It exhibits various crystal forms, with α-alumina being the most stable and versatile.

α-Alumina boasts an exceptionally high melting point, outstanding heat resistance, hardness, insulation properties, and chemical resistance. These attributes make it suitable for a diverse range of applications, including refractory materials, spark plugs, semiconductor substrates, grinding and polishing tools, and crucibles.

Properties of Alumina

Aluminum, the element with atomic number 13, forms aluminum oxide (chemical formula: Al2O3), commonly known as alumina. Abundant in the Earth’s crust, aluminum ranks as the third most plentiful element, following oxygen and silicon.

Naturally occurring in the form of corundum, it transforms into ruby and sapphire when infused with trace elements like iron, chromium, and titanium. Bauxite, a reddish-brown ore, serves as a rich source of aluminum. Dissolving bauxite in caustic soda generates sodium aluminate, which, upon hydrolysis, yields aluminum hydroxide. Sintering aluminum hydroxide culminates in the production of alumina.

Alumina exhibits diverse crystal structures, with α-alumina being notably stable. Subjecting γ-alumina to high temperatures triggers a transformation through intermediate alumina phases, ultimately leading to α-alumina. α-Alumina boasts a melting point exceeding 2000°C and exhibits remarkable heat resistance and hardness.

Toxicity of Alumina

Alumina itself is non-toxic and generally safe. However, when handling alumina in a dusty form, protective gear such as goggles and dust masks should be employed, as they may pose risks to the eyes, skin, and respiratory system. Studies have reported lung retention and inflammation in rats when alumina is inhaled.

With a Mohs hardness rating of 9, alumina offers exceptional wear resistance and durability, making it a valuable biomedical ceramic. It finds use in applications like artificial joints and bones, where long-term implantation in the human body necessitates harmlessness. Previous research has yielded negative results in biological safety tests, including acute toxicity and hemolysis tests. Alumina itself is also non-carcinogenic.

Distinguishing Ceramics and Alumina

Alumina falls within the category of ceramics, which encompasses inorganic materials. The term “ceramics” originally referred to products like pottery, glass, and cement. However, it has evolved to encompass all products formed by heating inorganic materials at high temperatures, resulting in their hardening. Materials used for ceramics include alumina, zirconia, silicon nitride, and silicon carbide.

Ceramics are categorized into two main types:

• Old Ceramics: Made from natural materials like clay and silica stone.
• Fine Ceramics: Crafted from materials that have been modified for increased purity or that have undergone artificial preparation, resulting in enhanced properties. Fine ceramics are highly functional and hold added value, finding essential use in various fields like electronics and biomaterials. Alumina, when highly purified, falls under the category of fine ceramics.

What Is Aluminum Casting?

Aluminum Casting is a product made by processing aluminum alloy with a method called casting.

Casting refers to the process of heating an aluminum alloy at a temperature higher than its melting point, melting it, pouring it into a mold made in the desired shape, and cooling it to make a product. There are two main types of molds: sand casting and metal mold casting.

The advantages of the sand mold casting method are low cost, support for large shapes, and small-lot production. The advantages of the metal mold casting method are mass production and high dimensional accuracy. The mold casting method also includes the gravity method and die casting method.

Uses of Aluminum Casting

Aluminum Casting is often used in automobiles because of its light weight, excellent workability, electrical and thermal conductivity, recyclability, and corrosion resistance.

Parts in actual use include the following:

• Engine parts (cylinder blocks, cylinder heads, etc.)
• Body parts
• Suspension parts, etc.

Reducing the weight of automobiles leads to improved fuel efficiency and operability. In addition, the thermal conductivity is utilized to reduce cooling of parts that generate heat.

Principle of Aluminum Casting

Sand casting and Mold casting (gravity casting) are two different aluminum casting methods.

1. Sand Casting Method

1. A wooden mold is used to create the shape of the product and the aluminum inlet into which the aluminum is poured.
2. Sand mixed with an additive for hardening is filled into the mold.
3. The sand mold is completed by removing the wooden mold (product shape and hot water outlet) from the sand mold.
4. The upper and lower sand molds are made according to the above procedure.
5. Align the completed sand molds top and bottom.
6. Molten aluminum is poured from the hot water outlet into the top and bottom sand molds.
7. After pouring, the mold is cooled and hardened.
8. After hardening, the sand mold is broken and the aluminum casting is removed.
9. After removing unnecessary parts and machining the surface, the casting is complete.

Mold Casting Method (Gravity Casting)

1. A mold is made according to the shape of the product.
2. Molten aluminum is poured into the mold by gravity*.
3. After the molten aluminum is poured into the mold, it is cooled and hardened.
4. After hardening, the mold is removed and the aluminum casting is taken out.
5. After removing unnecessary parts and machining the surface, the product is complete.

*The method of injecting by pressure as well as gravity is called the die casting method.

Other Information on Aluminum Casting

1. Anodizing of Aluminum Casting

The surface of aluminum casting can be anodized to improve corrosion and wear resistance. Anodizing is also called anodic oxidation treatment. It is a treatment method in which aluminum is oxidized by passing an electric current through it in an electrolytic solution to produce a film that is thicker than the film produced by natural oxidation.

Aluminum casting contains a large amount of elements other than aluminum to increase its strength. Examples include silicon, copper, and magnesium. When anodizing aluminum casting, these elements may inhibit the formation of the coating. This is due to the segregation of elements other than aluminum in the casting, which changes the current-carrying conditions. To improve the situation, it is necessary to carefully remove dirt and undissolved fine particles from the casting surface, and to perform the treatment in a short time.

2. Defects in Aluminum Casting

Pinholes are one of the defects that occur in aluminum casting and are numerous fine needle-like bubbles. The size of the bubbles varies depending on the manufacturing conditions, but is about 0.1 mm. Pinholes occur when moisture in the air becomes hydrogen gas in the molten metal and is released outside the casting during the solidification process. They tend to occur in thick-walled parts of the product or parts that were difficult to cool.

Pinhole countermeasures include reducing contact between the molten aluminum alloy and air, and sufficiently drying raw materials and tools to prevent moisture contamination. It is also necessary to remove hydrogen gas from within the alloy as much as possible before solidification.

Defects other than pinholes include sinkholes, hot water borders, hot water wrinkles, seizures, and galling. These defects can be prevented mainly through maintenance such as temperature control of the mold and polishing of the mold.

What Is Aluminum Die Casting?

Aluminum Die Casting is a special casting method in which aluminum alloy or zinc alloy is melted and pressed into a mold. Aluminum die casting is characterized by its ability to mass-produce products of complex shapes with high dimensional accuracy and beautiful surfaces.

For this reason, aluminum die casting is highly regarded among metalworking methods. It is often confused with aluminum casting, however it is a different casting method from aluminum die casting because it refers to a method in which a metal such as aluminum alloy or copper is made into a liquid at a temperature higher than its melting point, poured into a mold, and cooled to harden. In addition, aluminum die casting uses metal molds, whereas sand molds are generally used for aluminum casting.

Aluminum die casting is characterized by high production costs because it requires the design and fabrication of molds from a block of metal.

Uses of Aluminum Die Casting

Aluminum die casting is mainly used in automotive parts. Among them, steering related parts are in high demand in recent years. This is because aluminum die casting can manufacture products with complex shapes and high precision in large quantities and in a short time.

Aluminum die casting is not only used for automotive parts. It is also used in various products in our daily lives, such as personal computers, cell phones, digital cameras, refrigerators, and washing machines.

Aluminum die casting can also be used to produce small parts, thus contributing to product weight reduction.

Principle of Aluminum Die Casting

Aluminum die casting is a casting method that uses molds. The die casting machine consists of a die clamping device that opens and closes the die, an injection device that ejects the molten metal into the die, and an extrusion device that pushes the metal out of the die.

In aluminum die casting, aluminum alloy is first melted. At this time, metals other than aluminum are also melted to produce an alloy with the desired composition, so careful adjustment and control of the composition is necessary. After the aluminum alloy is melted, the die is cleaned and the die is closed with a die clamping device. The closed mold is then filled with the molten aluminum alloy by an injection device.

Aluminum die casting is characterized by a fine surface structure because the molten metal is injected into the mold and cooled rapidly. This fine surface structure makes the surface of aluminum die casting hard and enables the production of strong products.

On the other hand, the disadvantage of aluminum die casting is that the rapid cooling process tends to create casting voids. These casting voids occur not only on the surface, but also in the center of the product where it finally solidifies. If casting cavities occur in aluminum die casting, the expected product performance will not be achieved, such as reduced strength. Therefore, aluminum die casting requires temperature control during die casting and careful consideration of the mold shape.

Other Information on Aluminum Die Casting

1. The Difference Between Aluminum Die Casting and Aluminum Casting

Aluminum die casting is formed by melting aluminum alloy or zinc alloy and press-fitting it into a die. Generally, the material is heated to approximately 500°C to 700°C to melt, poured into the mold at low speed, and then cooled under high pressure to form the mold.

Aluminum casting, on the other hand, involves melting a liquid aluminum alloy in a high-temperature furnace and pouring it into a metal or ceramic mold. Aluminum casting basically does not apply any external force, but uses the input of liquid metal by falling and subsequent flow. Aluminum die casting is sometimes referred to as gravity casting.

The advantages of aluminum die casting are its high dimensional accuracy and the ability to produce even complex shapes. This is because the molten aluminum alloy is fed into the mold under pressure, so the aluminum alloy is instantly distributed to every corner of the mold. On the other hand, aluminum casting may not achieve the desired dimensions or may cause wrinkles on the surface. This is because the high-temperature aluminum alloy has relatively low fluidity, and it takes time for it to spread to all corners of the mold by simply dropping it into the mold.

As a result, aluminum casting shrinks as it solidifies, which can result in defects such as dimensional changes and wrinkles created during flow. Aluminum die casting is also characterized by high dimensional accuracy and excellent surface roughness. Since the aluminum alloy is spread instantaneously, manufacturing time can be shortened, which has the advantage of enabling mass production of products.

Another feature that distinguishes aluminum die casting from aluminum casting is that the surface roughness remains high quality, which reduces finishing and inspection processes. One disadvantage of aluminum die casting, however, is the high cost of mold design and manufacturing. For this reason, aluminum die casting using sand molds may be more cost-effective for small-lot production.

Another disadvantage of aluminum die casting is that it is not suitable for parts that require high strength. Due to the manufacturing process, aluminum die casting involves air and evaporated mold release agent during the molding process. This creates cavities called nests, which reduce the strength of the product.

2. Materials for Aluminum Die Casting

Aluminum die casting materials include casting and elongation materials, and a large number of die casting materials are available in a series headed by ADC.

The main component systems of aluminum die casting materials are Al-Si and Al-Mg, to which elements such as Cu and Mn are added. Each material is selected according to the corrosion resistance, castability, and impact resistance required for aluminum die casting.

The metallographic structure of aluminum die casting materials is a matrix phase of Al solid solution. The matrix can be a lamellar Al-Si eutectic or precipitation strengthened by fine precipitates such as Mg2Si, Al2Cu, etc., and the properties exhibited differ accordingly.

Normally, aluminum alloys are subjected to heat treatment after casting and machining to prepare crystal grains and form micro-precipitates. However, in aluminum die casting, heat treatment is often not performed to avoid air and gas entrained in the die castings from expanding and forming defects due to heat treatment.

However, vacuum die casting and non-porous die casting methods, which have recently been increasingly applied, are characterized by the fact that these defects are less likely to occur. Therefore, in recent aluminum die casting, it is possible to bring out the characteristics of materials by adding heat treatment process.

What Is an Aluminum Container?

Aluminum containers are containers made of aluminum. They are available in a wide range of sizes, from small containers for home storage to truck bed-sized containers and containers large enough for human habitation.

Uses and Shapes of Aluminum Containers

Since most parts of aluminum containers are made of aluminum, they are lighter than steel, with a specific gravity of about 30%, and are strong, rust-resistant, and relatively long-lasting.

Because of their rust resistance, they are often used for outdoor storage and warehousing and are less expensive than ordinary commercial sheds.

Some can be as large as 6 square meters, which is considerable for a shed. In recent years, in addition to warehouses, the use of aluminum containers as prefabricated buildings or storage units has been increasing.

The basic form of an aluminum container is a box-shaped type called a fixed type, as shown in Figure 1. In this example, the box-shaped aluminum container has double doors on the front.

Since aluminum is easy to process, it can be customized with sliding doors or windows, depending on the size, in addition to the double doors shown in Figure 1.

Aluminum containers are also lightweight, making them suitable for transporting objects, and they are often used on the back of trucks for transportation purposes.

The legal service life of aluminum containers of 6 meters or less is 2 years, while that of containers over 6 meters is 7 years.
Larger sizes include 2-ton, 6-ton, and 10-ton containers.

Aluminum containers are also available in foldable types.

The Schematic Diagram of a Folded Aluminum Container

In this example, as shown in Figure 2a, the front is a vertical opening door, which can be folded by folding this door, the rear door, and the side walls, as shown in Figure 2b.

Many small aluminum containers are designed to be stable and easy to carry when stacked. Recently, they have become popular for storing camping equipment.

Since aluminum containers are heat-resistant, they can be used to hold hot items and can be locked with a key even when exposed to rain.

Cautions for Using Aluminum Containers

Aluminum containers are easy to process, so they are increasingly being used not only for storage and sheds but also for offices and residences. In this case, they can be customized to improve livability by installing air conditioners, soundproofing, and windows. However, depending on the intended use and size, an application for a building permit may be required.

If the total floor area of an aluminum container is 10 m2 or less, a building permit is not required even if it is used as a building, but there are exceptions in other various conditions as well. Therefore, when purchasing or using aluminum containers, be sure to confirm whether or not an application is required.

Aluminum containers are available in a wide range of sizes and shapes. Please select the size and shape according to the intended use, check the application requirements when purchasing and using them, and use them in compliance with the law.

What Is Anodized Aluminum?

Forming an anodized aluminum film is also called anodizing. Anodizing is a surface treatment in which an oxide film (anodized film) is artificially formed on aluminum’s surface. By the substance forming on the aluminum it becomes anodized aluminum. By forming an anodized aluminum film, it is possible to improve corrosion and wear resistance. Unlike the plating process, an anodized aluminum film does not just cover the surface, but is formed in a manner that dissolves and penetrates the product itself to cover the surface, thus providing a more durable surface treatment.

Applications of Anodized Aluminum

Anodized aluminum is used in a wide range of fields, from household products to industrial products. This is because forming an anodized aluminum film provides high corrosion resistance, high wear resistance, surface properties (water repellency, etc.), and high decorative properties such as coloring.

It’s used in household products like lunch boxes, kettles, pots, cell phones, sashes, etc. and in industrial products such as construction materials, automotive parts, optical parts, semiconductor parts, medical equipment, etc.

Principle of Anodized Aluminum

Aluminum, the base material from which anodized aluminum is formed, easily bonds with oxygen and forms a thin oxide film when in contact with air. For this reason, aluminum has the property of being resistant to rust, in other words, it has good corrosion resistance. However, the thickness of this naturally formed oxide film is very thin.

Depending on the environment, chemical reactions can cause corrosion, which can extend to raw aluminum. Therefore, an artificial oxide (anodized aluminum) film is formed to protect the aluminum.

The main component of anodized aluminum is amorphous alumina (Al2O3). An anodic oxide film made of anodized aluminum has the shape of a porous layer with many pores extending in the direction of film thickness.

Other Information on Anodized Aluminum

1. Anodized Aluminum’s (film) Formation Method

The basic formation method of anodized aluminum (anodized aluminum film) is as follows. The anodizing process is similar to this method.

The aluminum product is attached to a jig and placed in an electrolytic solution. Connect an electrode to the jig and apply positive electricity, and at the same time apply electricity to the cathode in the same manner. The electrolysis produces an oxide film (anodized aluminum film) on the surface.
The thickness of the oxide film (anodized aluminum film) produced at this time is proportional to the electrolysis time. Since the anodized aluminum film is formed while dissolving the aluminum surface, its surface shape reflects the shape of the aluminum surface.

In other words, even if the aluminum surface has minuscule irregularities, an anodized aluminum film is formed reflecting the shape of the surface, so the surface cannot be flattened like a coating. 

2. Cautions While Forming Anodized Aluminum Film 

There are five points to be noted when forming anodized aluminum film.

The degree of film growth varies depending on whether the aluminum processing was done by cutting or electrical discharge machining, resulting in differences in the expected dimensions after the anodized aluminum film is formed.

If an anodized aluminum film is formed when materials other than aluminum, such as iron, copper, or stainless steel are joined, there is a possibility that, aside from aluminum, the materials will melt.

If an anodized aluminum film is formed on parts composed of different types of aluminum alloys at the same time, uneven color and thickness will occur.

If anodized aluminum film is formed on a part that has a hole shape designed to fit together, the fit may not function depending on the dimensional accuracy of the anodized aluminum film thickness.
Consider that the depth of the hole in the fit and the shape of the through hole or stop hole, etc., may cause a difference in the dimensional accuracy of the anodized aluminum film thickness.

As mentioned above, the thickness of the anodized aluminum film produced will vary depending on the shape of the part on which the anodized aluminum film is formed, the processing method used, and other factors. Therefore, prior consideration and confirmation are important when forming an anodic oxide film on parts that require precise dimensions.

3. Disadvantages of Anodized Aluminum

Anodized aluminum is not flexible and brittle, and parts with anodized aluminum coating may peel or crack when processed or bent. Also, each material has a different rate of thermal expansion (coefficient of thermal expansion). Aluminum alloys before oxidation treatment and anodized aluminum after oxidation treatment have different coefficients of thermal expansion.

Especially in high temperature environments (>100°C), the difference in thermal expansion rates between the two materials will increase, causing the anodized aluminum film to delaminate or crack.

4. Anodized Aluminum Coloring Methods

Anodized aluminum can be colored in a variety of colors. There are two main coloring methods: electrolytic coloring and dye coloring.

Electrolytic Coloring
Electrolytic coloring is a method in which parts of anodized aluminum film are secondarily electrolyzed in an electrolytic solution containing metal salts such as tin and nickel to deposit metal in the pores of the anodized aluminum film, which is a porous layer, for coloring. Anodizing with this method can give anodized aluminum a metallic hue such as black, bronze, or yellow. Electrolytic coloring not only colors the anodized aluminum film but also reinforces it.

Dye Coloring
Dye coloring is a method of coloring anodized aluminum by placing dye inside the pores of the porous layer of the anodized aluminum film. This is called color anodizing.

After the anodized aluminum film is colored by the dye, a sealing process is applied. To put it simply, this is a process to cover the hole where the dye has been inserted so that the anodized aluminum coloring will not peel off. However, care must be taken because if the anodized aluminum film itself peels off, the coloring will also peel off.

In both the electrolytic and dye-coloring anodizing) processes, the density of the coloring depends on the thickness of the coating, the time and temperature applied to the process, and other conditions. This is because the amount of metal and dye that can enter the hole varies depending on the conditions. The greater the amount, the darker the color.

What Is Argon Gas?

Argon gas’ element number is 18 and its symbol is Ar. The etymology of the word means “lazy” in Greek and refers to its non-reactive characteristics.

Argon is used to create an inert atmosphere and is used in this way to produce titanium and other reactive elements. It is also used by welders to protect welds and in incandescent light bulbs to stop oxygen from corroding filaments.

Because argon is the most abundant of the noble gases (0.93%v/v in air), its coexistence with oxygen is problematic.

Properties of Argon Gas

Argon is a colorless, odorless gas and a noble gas belonging to group 18 of the periodic table of elements. Group 18 elements include helium, neon, krypton, xenon, and radon in addition to argon. All of these elements exist in the atmosphere in gaseous form.

The most important characteristic of noble gases is that they are inert gases with very low reactivity due to their very stable electron configuration (however, even noble gases can be made to react under certain conditions.) Inert gases are used to avoid chemical reactions that accelerate degradation, which occurs in oxidation and hydrolysis reactions between the sample and oxygen or moisture in the air.

In particular, purified argon and nitrogen gases are the most commonly used inert gases due to their natural abundance (78.3% N2 and 1% Ar in air) and low cost. In particular, while argon is more expensive than nitrogen, its inertness is lower than nitrogen, making argon suitable for materials and environments where it would react with nitrogen. Argon has about the same solubility as oxygen and is 2.5 times more soluble in water than nitrogen.

Argon has a lower conductivity of heat than air, so better thermal insulation can be achieved by adding argon to the gaps between glass.

Uses of Argon Gas

As an inert gas with very low reactivity, argon provides an inert atmosphere that prevents it from reacting with oxygen in semiconductors and steel. Argon gas is used in arc welding to prevent reactions with molten metal.

Argon is also used in fluorescent tubes and low-energy light bulbs. Fluorescent bulbs contain trace amounts of mercury and argon, and argon assists in the discharge of the filament. The low reactivity of argon is used to extend the life of the filament.

In food products, argon is also used as an encapsulating gas for wine. This is not only to prevent oxidation but also because argon, which is heavier than air, effectively flushes oxygen out of wine bottles.

Argon also has a lower thermal conductivity than air or nitrogen. For this reason, double-glazed windows use argon to fill the gaps between the panes.

Thus, argon is used in various industrial fields, especially because of its low reactivity and because it is the most abundant noble gas.

Hazards of Argon Gas

Argon gas is a non-hazardous substance when used normally. Argon is present in the air at about 1%, and we inhale it with oxygen and nitrogen when we breathe. Argon itself is not toxic, and inhalation of low concentrations has no effect. Argon is also an inert gas (nonflammable), so it will not react with other substances or cause fires in normal environments.

On the other hand, inhalation of high concentrations may cause asphyxiation, so environments with high concentrations should be avoided.

Since it is often handled filled in cylinders, there is a risk that the gas concentration in a room may become high due to leakage from the cylinders. This can be remedied by immediately stopping the source of the leak and providing adequate ventilation in the room. When handling liquefied argon, the cylinder itself becomes very cold due to the heat of vaporization when argon evaporates, so there is a danger of frostbite if you touch it with bare hands. In such cases, protective equipment can be used to ensure safe handling.

Argon Gas’ Purification Method

High-purity argon for cylinder gas is produced by separating argon from the air. In this case, the “deep-cooled air separation method” is used. In this method, water and carbon dioxide are first removed from the air by pretreatment, and then the purified air is cooled to a very low temperature of -170 to -190℃ to separate the gases in the air using the difference in vapor pressure (i.e., the difference in boiling points).

Incidentally, the boiling point of nitrogen is -195.8°C, oxygen is -183.0°C, and argon is -185.7°C. Using this method, oxygen, nitrogen, and argon are separated and purified from air, respectively.

Cylinders of Argon Gas

Argon gas is usually sold in cylinders. Types of cylinders include general containers and cryogenic containers. While a high-pressure gas-related qualification is required for the production and sale of argon gas, no specific qualification is required for the use of gas cylinders.

In general containers, argon is filled at a high pressure of 14.7 MPa in its gaseous state. Cylinders are available in sizes of 7000L, 1500L, and 500L, depending on the amount of argon filled. A 7000L cylinder weighs approximately 60 kg, so care must be taken when carrying and transporting it.

In addition, very high purity argon gas may be required depending on the intended use, but argon gas is sold in cylinders of gas with a purity of up to 99.9999% (six nines).

In cryogenic containers, argon is filled in a liquid state. Since the amount of argon filled is greater than that of ordinary containers, they are suitable for large volume consumption. It also reduces the frequency of replacing cylinders, which helps to keep costs down. Cylinders are available in sizes of 127,000 L or 36,000 L. Because they are quite heavy, they require a distributor or specialized contractor to carry and transport them.