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What Is Acrylic Adhesive?

Acrylic adhesives are adhesives whose main ingredient is acrylic acid or its derivatives (methyl methacrylate, etc.).

They are classified into the first to third generations based on the presence or absence of chemical reactions during the curing process. Currently, the second generation (SGA: Second Generation Acrylic Adhesives), which involves a polymerization reaction during curing, is the most prevalent.

SGA includes two component types where the curing reaction occurs when the main and curing agents come into contact with each other. The first type is the one-component primer type, in which a primer is used instead of a curing agent, and curing occurs through heating. The second type is the two-component type, which is currently the most commonly used.

SGA exhibits excellent impact resistance, heat resistance, and water resistance, making it one of the most reliable structural adhesives with minimal degradation in adhesive properties even when subjected to heavy loads for extended periods.

Difference Between Acrylic Adhesives and Adhesives for Acrylic Resin

Although the names of these two types of adhesives are very similar, they have distinct properties. However, it is essential to note that both adhesives are referred to as “acrylic adhesives” in some cases.

Specifically, “acrylic adhesives,” the subject of this article, are adhesives that primarily contain acrylic acid and its derivatives, whereas “adhesives for acrylic resins” refer to bonding agents used to melt and join acrylic sheets, with entirely different adhesion principles and usage.

Uses of Acrylic Adhesives

Second-generation acrylic adhesives (SGA), currently the mainstream, are suitable for household and industrial applications, each serving various purposes. They are specifically useful for bonding the following substrates:

1. Metals
2. Thermoplastic resin
3. Thermosetting resins
4. Composite materials

Among these, two-component SGA excels at bonding different materials and large areas. It is employed, for example, in affixing motor magnets (permanent magnets) to stators in automobiles and bonding battery cells in electric vehicles.

SGA is also utilized as potting material for safeguarding electronic circuit boards. It finds applications in various other areas, including bonding plastics, metals, and tiles, as well as construction applications.

Principles of Acrylic Adhesives

Here is an overview of each generation of acrylic adhesives:

• First Generation: This type comprises acrylic monomers, acrylic oligomers, and curing agents, but no chemical reaction occurs during curing.
• Second Generation: It consists of almost the same composition as the first generation, but curing takes place through a polymerization reaction between the monomer and polymer. Compared to the first generation, it is characterized by superior adhesiveness, durability, and various other properties.
• Third Generation: Radical polymerization is initiated and cured by irradiating energy such as ultraviolet rays or electromagnetic waves. Second-generation acrylic adhesives (SGA), which are currently the mainstream, are classified into two components, one-component primer, and one-component types.

The two-component type comprises two components, A and B, with the primary ingredients being acrylic monomers and elastomers.

The difference in composition between the two liquids lies in Agent A, where cumene hydroperoxide is added as a polymerization initiator, and Agent B, where a reducing agent like a metal complex or thiourea derivative is included as a curing accelerator.

Mixing both solutions initiates a radical reaction and begins the curing of the acrylic monomer. Since the primary components of these two liquids are essentially the same, they are straightforward to mix, and even slight variations in the mixing ratio of the two liquids do not significantly affect the physical properties after curing. This ease of use is due to the fact that the mixing ratio of the two liquids does not need to be strictly 1:1.

The one-component primer type substitutes the hardener of the two-component type with a primer, and, like the two-component type, generates radicals and proceeds with curing. The one-component type contains a catalyst activated by heating and cures when heated.

SGA boasts features such as oil-surface adhesion, excellent resistance to shear and tension, and internal stress relaxation. However, acrylic adhesives containing methyl methacrylate have the drawback of emitting an acrylic odor.

Curing Time of Acrylic Adhesives

Acrylic adhesives cure through a chemical reaction, boasting extremely rapid curing times and robust adhesion. The typical curing time is approximately 5 minutes after application. However, when used to reinforce joints and prevent water leakage, it is necessary to allow for curing for about one day.

As a precaution when using the adhesive, it is advisable to wait briefly after application before clamping. This waiting period allows the adhesive components to disperse and permeate into the air and adhere to the material for proper curing and adhesion.

Waiting for a few minutes after application before clamping helps ensure proper adhesion and prevents volume shrinkage that occurs as the adhesive cures.

How to Remove Acrylic Adhesives

Due to their exceptional adhesive strength and durability, acrylic adhesives cannot be peeled off easily. Therefore, it is essential to choose a suitable method for removing acrylic adhesives based on their adhesive mechanism.

While the term “adhesion” is used to describe acrylic adhesives, they are technically a form of welding. A chemical reaction dissolves the adherend materials to form a single piece.

Organic solvents such as toluene and benzene are effective for removing solvent-based adhesives. These solvents contain components that dissolve plastics like acrylics. Organic solvents have the property of dissolving plastics and are effective in removing acrylic adhesives.

Once fully dissolved, removal can be challenging. In some cases, one adherend may need to be left in place while the other is physically destroyed. To avoid this, it is recommended to attempt solvent stripping as a first step.

What to Do When Acrylic Adhesives Turn White

When using acrylic adhesives whose main ingredient is cyanoacrylate, a white residue, known as “whitening,” may remain around the adherend.

To prevent this phenomenon, it is essential to eliminate dust and moisture from the adhesive surface and the surrounding area and select a low humidity work environment.

Using a curing accelerator that is less likely to cause whitening in advance is also a good practice. If whitening does occur, it can be removed through chemical removal using an organic solvent or physical removal using sandpaper.

What Is an Accumulator?

An accumulator is a “pressure accumulator” in Japanese, and is a device that converts the pressure energy of a fluid into other high-pressure fluid energy and stores it. It is mainly used in hydraulic and steam fluid equipment.

The English word “accumulate” means “to store” but there are different devices in different technical fields depending on what is to be stored or accumulated. For example, in the computer field, accumulators temporarily store calculation results and are used for the next calculation; in the electric power field they are used for storage batteries and accumulators; and in wind power generation, they are used for systems that circulate oil between windmills and generators to maintain balance.

In hydraulic and steam systems, the pressure energy of oil or steam is stored as nitrogen gas or steam pressure energy, and the gas is expanded to release energy when needed. In Japan, accumulators are pressure vessels regulated by the High Pressure Gas Safety Law and the Industrial Safety and Health Law.

Uses of Accumulators

Accumulators are often used in hydraulic systems and steam boilers. In hydraulic systems, accumulators are installed in the high-pressure circuit leaving the pump, and the high hydraulic pressure during operation compresses the nitrogen gas sealed in the accumulator. When the hydraulic pressure drops, the force of the nitrogen gas is used to raise the hydraulic pressure and maintain it.

In the boiler system, when there is a surplus of steam, it delivers steam with reduced pressure and stores the rest. On the other hand when there is a higher demand for steam it is able to output the necessary amount accordingly. In addition, the boiler can operate efficiently and stably because the accumulator absorbs the imbalance between the time variation of steam usage and the steam generation of the boiler.

The use of accumulators in water pumps also softens sudden pressure fluctuations during shutdown and prevents water hammer. The main purpose of accumulators is to use the energy of the stored pressure gas in the accumulator container as an auxiliary power source in an emergency. It is also effective in absorbing and buffering impact pressure in the pipe, and reducing wasteful power consumption of the system.

Principle of Accumulators 

Gas accumulators mainly use nitrogen, which is pressurized and contracted or expanded to transfer energy in and out. In the case of hydraulic systems, accumulators are installed in the high-pressure circuit exiting the pump. Inside the accumulator is a bag called a prada, which separates the oil side from the gas side. Nitrogen gas is sealed in the prada, and when the hydraulic pump is driven and the hydraulic pressure rises above the nitrogen gas pressure, the nitrogen gas is compressed.

When the pressure in the hydraulic system drops or the pump stops, the pressure energy of the nitrogen gas causes the prada to expand to maintain hydraulic pressure and also has the effect of reducing pulsations in the hydraulic pressure. The bladder, which seals the nitrogen gas inside the container, is made of a rubber-based material that expands and contracts. The container is made of carbon steel, stainless steel, aluminum, or synthetic materials that are free from corrosion.

The capacity of the container ranges from 0.5 to 450 liters, and the maximum allowable pressure is about 990 atmospheres. Prada-type accumulators are characterized by fast energy release and the ability to accumulate and release energy in fast cycles as needed. In addition, the equipment can be made compact, and maintenance is easy.

Other Information on Accumulators

Accumulators Gases

Nitrogen gas is often used as the gas that stores energy in accumulators. Nitrogen gas is a nonflammable and inert gas, which prevents deterioration of the metal used in accumulators. Another advantage is that it is inexpensive and has no risk of explosion.

Since the pressure of nitrogen gas gradually decreases with repeated operation, it is necessary to periodically inspect the accumulators to ensure that the pressure has not decreased. If accumulators are used in the suspension, a drop in gas pressure will make it impossible to absorb shocks from the road surface, resulting in a poor ride quality. If the pressure is low, replenish nitrogen gas. 

Car Systems Using Accumulators

Accumulators are used in automobile suspensions and brakes. Special-purpose vehicles with large body weight and multi-axle vehicles, for example, may not be able to absorb the shock fully with springs, so accumulators are used, which act as gas springs. Hydraulic suspensions using accumulators can also raise and lower the vehicle body freely.

Accumulators are used in brakes to recover energy during braking. In hybrid vehicles, when energy is recovered by the motor, there is a discrepancy between the braking force required by the driver and that of the accumulator. To eliminate this discrepancy, the accumulator appropriately assists the motor to provide the optimum braking force.

What Is a Thread Gauge?

A Thread Gauge is an inspection tool used to check if the male or female thread of a screw is manufactured in the correct shape.

A ring gauge is used to measure male threads. The shape of a screw is standardized, but there are various specifications. For example, thread outer diameter, effective diameter, thread pitch, and thread valley diameter.

Measuring these parameters one by one is time-consuming. However, using screw thread gauges, it is possible to quickly determine whether the manufactured screw shape is acceptable or not. Thread gauges are widely used in screw manufacturing.

Uses of Thread Gauges

Thread gauges are mainly used in the manufacturing of screws. Thread shapes are standardized, but there are various specifications.

For example, thread outer diameter, effective diameter, thread pitch, and thread trough diameter. Measuring these parameters one by one is time-consuming.

Screw thread gauges allow us to quickly determine whether the manufactured screw shape is good or bad. They are widely used in screw manufacturing because of their ability to improve operational efficiency.

Principle of Thread Gauge

The principle of thread gauge depends on the type used. Thread gauges commonly used in manufacturing are as follows:

1. Limit Screw Thread Gauge

The limit thread gauge is an inspection jig used to easily determine if a manufactured screw shape is acceptable or not. Using gauges made to the upper and lower limit specifications of the screw to be inspected, the shape is judged as good or bad by passing through one gauge and not the other.

For a male thread such as a bolt, the ring gauge on the upper end of the gauge will pass the ring gauge on the lower end of the gauge, but not the ring gauge on the lower end of the gauge.

If the product is a nut or other female thread, it will pass the plug gauge at the lower end of the gauge, but will not pass the plug gauge at the upper end. Also, the standard here refers specifically to the effective diameter of the screw. 

2. Thread Gauge for Wear Inspection

The wear inspection thread gauge is a gauge used to guarantee the accuracy of the limit thread gauge. The limit screw thread gauge wears out as it is passed through the object to be inspected. As the amount of wear increases, it becomes impossible to make correct judgments.

Therefore, a thread gauge for wear inspection is used to check whether the limit screw thread gauge has not exceeded the wear limit for correct inspection. A ring gauge for wear inspection is used to inspect the wear of the limit screw plug gauge, and a plug gauge for wear inspection is used to inspect the wear of the limit screw ring gauge. 

3. Standard Thread Gauge

Thread gauges are made according to the standard thread profile and standard dimensions of the screw standard, and are a set of a plug gauge and a ring gauge. Thread gauges are the standard for measurement.

Compared to the limit screw thread gauge, the quality assurance accuracy is inferior. However, it is not necessary to prepare a set of both the thread side and the stop side like the limit screw thread gauge. This allows the cost to be kept low. 

4. Pipe Screw Thread Gauges

There are two main types of pipe screw thread gauges. There are two main types of pipe thread gauges: parallel thread gauges and tapered thread gauges.

The parallel thread gauges are used to measure the threads at the threaded end and the tapered end. Thread gauges for tapered threads are notched on the end face and are accepted as long as the tip of the thread is within the notch.

Types of Thread Gauges

Thread gauges are broadly classified into ring gauges and plug gauges. From there, they can be classified in detail as described above.

Ring gauges are used to inspect screws. They are called ring gauges because they are ring-shaped with a female thread in the center of the disk so that the screw to be inspected can be screwed in.

On the other hand, a brag gauge inspects a female thread. They are called plug gauges because they are used by screwing them into the female threads to be inspected.

What Are Bevel Gears?

Bevel Gears are gears with teeth carved on a conical surface, and each axis is angled rather than parallel. They are used to transmit power by changing the direction of the axis of rotation.

Bevel Gears are named as such because they look like umbrellas. They are classified into straight bevel gears, spiral bevel gears, helical bevel gears, zerol bevel gears and hypoid gears according to the tooth shape.

Materials used for bevel gears include carbon steel for machine structural purposes, alloy steel for machine structural purposes, rolled steel for general structural purposes, cast iron, stainless steel, nonferrous metals, MC nylon and duracon.

Uses of Bevel Gears

Bevel gears are used to transmit power by changing the direction of a rotating shaft. In bevel gears using straight, spiral, and helical gears, the axes of rotation of the two gears intersect. The angle of intersection is generally 90°, but may be acute or obtuse. Gears whose axes do not intersect are called hypoid gears.

Familiar examples are hand-turned coffee mills, hand-turned mixers, and hand drills. They are also used in differential gears in the automotive field, as well as in machine tools and printing machinery. They are especially useful in differential equipment.

Hypoid gears differ from spiral bevel gears in that multiple teeth engage simultaneously and there is tooth slippage. This allows them to withstand large torques and to produce little noise. Hypoid gears are often used to drive automobiles and trains.

Principle of Bevel Gears

Bevel gears are gears with pitch conical surfaces that contact each other without sliding. Gears are determined by module, number of teeth, reduction ratio, material, surface treatment, shaft hole shape, shaft hole diameter, and precision.

Straight bevel gears have a straight tooth trace and are relatively easy to manufacture. Reduction ratios of up to about 1:5 are possible. If no specific gear is specified, they are generally used as bevel gears for transmitting power.

Spiral bevel gears are characterized by the curved tooth trace. They have the advantages of high strength, quiet rotation, and high efficiency due to the large area per tooth. Zerol bevel gears are spiral bevel gears with a cross-torsion of approximately zero on the shaft, and have the characteristics of both immediate and spiral bevel gears.

Gears can accurately transmit power and motion, but in principle, they generate noise. To reduce noise, it is necessary to take measures such as proper backlash, increasing the gear meshing ratio, downsizing the tooth profile, using plastic gears, and proper lubrication.

To improve tooth contact, an appropriate bulge may be added in the direction of the tooth flanks. This is called crowning.

How to Select Bevel Gears

When selecting bevel gears, special consideration should be given to tooth strength and allowable tooth surface load. The bending strength of a tooth is the allowable circumferential force of the tooth calculated from the strength of the tooth base during mesh transmission. It increases with increasing tooth module size.

The allowable tooth surface load is the circumferential force specified to prevent progressive pitting. The smaller of the two circumferential forces is multiplied by the pitch circle radius of the gear to obtain the allowable torque of the gear. This value should be selected so that it is greater than the design torque actually used. The characteristics of each gear are described in the manufacturer’s technical data.

Some manufacturers also provide a list of gears that meet their requirements by entering the conditions of use on their website. This is useful when narrowing down specifications from broad conditions.

Other Information on Bevel Gears

Bevel Gear Design

When designing bevel gears, it is important to tentatively determine the reduction ratio and shaft angle and check the gear specifications because, unlike spur gears, there are limitations on the combination of the number of teeth on the meshing gears and the dimensions such as the bevel angle are different.

After tentatively determining the shape and mounting posture, strength calculations are performed. If the conditions are not satisfied, the module is enlarged and the dimensional calculations are redone again. Gear strength and other meshing calculations can be approximated with spur gears.

When the load is large, when repeated loads are applied, or when the gear is operated continuously for a long period of time, a large safety factor can be used to provide a margin against impact loads and fatigue.

For material selection, carbon steel is generally used and its surface hardness is increased by quenching, but for some applications, alloy steel or other materials are used and their hardness is increased by quenching. Generally, only the tooth flanks are quenched by high-frequency induction hardening, while other parts are tempered.

In addition to calculating dimensions and strength, lubrication must also be considered in gear design. Lubrication and lubrication systems are determined and designed for easy maintenance.

What Is a YAG Laser?

A YAG laser is a solid-state laser that uses crystals of yttrium (Yttrium), aluminum (Aluminum), and garnet (Garnet).

Principle of YAG Lasers

LASER stands for “Light Amplification by Stimulated Emission of Radiation” in English.

First, energy is applied externally to a YAG crystal using a flash lamp or laser semiconductor. This causes the electrons in the crystal to move from the lower to the upper level and enter an excited state.

After a short time, the excited electrons attempt to return to the ground state (transition), emitting light in the process. The emitted light hits other electrons in the excited state, causing them to transition in the same way, which results in further light emission. This is called induced emission.

The wavelength and characteristics of the light emitted depend on the rare earth elements doped into the YAG crystal. The most commonly used YAG lasers are Nd: YAG lasers doped with neodymium (Nd) and Er: YAG lasers doped with erbium (Er), and the doping element is selected according to the wavelength to be emitted.

The fundamental wavelength of the widely used Nd: YAG laser is 1064 nm, and when passed through a nonlinear optical crystal, light at 532 nm, the second harmonic, and 355 nm, the third harmonic, can also be extracted.

Applications of YAG Lasers

YAG lasers are widely used in the research, industrial, and medical fields.

In the industrial field, they are used for microfabrication, marking, trimming, metal welding, and cutting. Nd: YAG and Yb: YAG lasers are particularly popular for welding and other applications.

In the medical field, they are widely used for cataract treatment in ophthalmology, removal of spots and birthmarks in cosmetic dermatology, and abscess incision and cavity treatment in dentistry.

Cautions When Using the YAG Laser

The Er: YAG laser is a mid-infrared laser with a wavelength of 2.94 μm. It is a highly safe laser that has low tissue penetration and is absorbed by surfaces. However, Er: YAG lasers are invisible to the eye, although they reflect off mirrors and metals. Therefore, protective goggles specially designed for the Er: YAG laser must be worn by everyone present during use. Always make sure that the power is turned on and off and that there are no unrelated people in the vicinity before using the laser.

Always be aware of your surroundings so that you do not focus your attention only on the area to be irradiated by the laser, and never irradiate unrelated areas to avoid accidents.

What Is an X-Ray Generator?

An X-ray generator is a device that generates X-rays, a type of radiation. X-rays were discovered by Dr. Wilhelm Convert Roentgen in 1895. It was the great discovery of the century because of its property of penetrating matter, and X-rays astonished people of that time.

Today, X-ray generators are used in a wide variety of locations, taking advantage of their penetrating properties for industrial applications such as medical and industrial machinery, as well as for physical and chemical research purposes. It can be said that this technology is widely known, especially since it is used in medical applications as X-rays.

Uses of X-Ray Generators

X-ray generators are widely used for medical purposes. X-ray examination, which everyone has heard of, is another technology that uses X-rays.

When the human body is irradiated with X-rays, low-density areas such as the skin and lungs are penetrated by the X-rays, while high-density areas such as bones and teeth are not penetrated and are absorbed.

The X-ray beam is also used in industrial applications to check products, as it can be used to check the inside of products without destroying them. This technology is also used in familiar places such as baggage screening at airports.

Principle of X-Ray Generators

An X-ray generator, also called an X-ray tube, consists of a target, which serves as the anode, and a filament, which serves as the cathode, inside a vacuum.

When a high voltage (tens to hundreds of thousands of volts) is applied between the electrodes, hot electrons are ejected from the cathode filament and travel at high speed to the anode target. X-rays are generated when they hit the target.
When electrons strike the target and enter the atom, most of their energy is converted to heat. Some of the electrons collide with electrons in the atom, forming an unstable state (an excited state). When an atom enters an excited state, it releases energy to return to a stable state. X-rays are produced as energy during the transition from the excited state to the stable state. There are two main types of X-rays produced.

1. Characteristic X-Rays

Characteristic X-rays are X-rays that are emitted when excited electrons transition to the stable state. Since X-rays equal to the energy difference between electron orbitals are generated, they have strong energy at a single wavelength. Since the energy between electron orbitals is unique for each element, the element-specific X-rays are also generated. This property is used in X-ray fluorescence (XRF) to analyze the composition of materials.

2. Continuous X-Rays

X-rays are produced when thermal electrons collide with a target and rapidly decelerate. The X-rays are also called bremsstrahlung X-rays because they are produced during the braking process. The wavelength of the X-rays produced depends on where on the target they strike, so they are compound wavelengths. They are used in fluoroscopy and other applications. The majority of the X-rays emitted are continuous X-rays.

Other Information on X-ray Generators

1. Tubes of X-Ray Generators

The tube of an X-ray generator is a vacuum tube, mainly made of glass, with a positive electrode (anode) and a negative electrode (cathode) inside the tube. The tube bulb has a filament (converging electrode) at the cathode and a target at the anode.

When a high voltage is applied to both electrodes using a high-voltage transformer or other high-voltage power supply, thermal electrons are emitted from the filament to the target. Tungsten is used for the filament, and tungsten or molybdenum is used for the target.

There are two types of tubes: fixed-anode X-ray tubes, which do not have a rotating anode structure, and rotating-anode X-ray tubes, which have a rotating anode structure. In the rotating type, an umbrella-shaped target is rotated at high speed to prevent local overheating of the target surface. This increases the tube current and thus the X-ray intensity.

Rotating anode X-ray tubes sometimes emit abnormal noise due to misalignment of the axis of rotation or distortion of the bearings after years of use. If the X-ray tube walls are made of glass, continued use of the tube in such a condition may cause the anode to melt or the anode axis to bend, destroying the tube itself.

2. Notification of Use Regarding X-Ray Generators

The following actions are required when installing an X-ray generator for industrial use.

• Central government agencies: Notification to the National Personnel Authority within 30 days of installation
• Public institutions: Notification to the Personnel Affairs Commission of each prefecture at least 30 days before the planned installation
• Private companies: Notify the Labor Standards Inspection Office within 30 days before installation

It is also important to carefully check the local government’s notification rules for X-ray equipment, as notification to the local government may also be required when changing the location of the equipment or when disposing of the equipment. Equipment with a 1 cm dose equivalent rate of external radiation exceeding 20 μSv/h must be installed in a radiation equipment room. On the other hand, equipment that is shielded below 20 μSv/h does not need to be installed in a radiation equipment room.

In addition, when using an X-ray generator, an X-ray work supervisor must be appointed for each controlled area from among those who have obtained an X-ray work supervisor license in principle. However, if the irradiation area is not irradiated unless it is separated from the

What Is an X-Ray Diffractometer?

An X-Ray Diffractometer is a device that measures the diffraction phenomenon that occurs when a material is irradiated with X-rays.

The X-ray diffractometer consists of an X-ray generator to generate X-rays, a goniometer to measure the diffraction angle, and a detector to measure the X-ray intensity.

They are often used to measure materials with crystalline properties, such as single crystals, powders, and thin films. They are utilized in the research and development and analysis of various materials, including organic materials, inorganic materials, alloys, and proteins.

Uses of X-Ray Diffractometers

X-Ray Diffractometers are used to measure the diffraction phenomena that occur when a sample is irradiated with X-rays. By analyzing the diffraction patterns obtained, it is possible to evaluate the crystallinity, orientation, and lattice defects of the sample.

X-ray diffractometers are not suitable for measuring non-crystalline materials such as amorphous materials, however they can be used to measure a variety of materials such as crystalline powders, thin films, and alloys.

Principle of X-Ray Diffractometers

Figure 1. Diffraction conditions of Bragg

X-rays irradiated on a material are scattered by electrons in the material. In the case of crystals and other materials in which atoms are arranged with some degree of regularity, the scattered X-rays interfere with each other, amplifying or attenuating each other, and the scattering intensity increases only in a certain direction. This is called X-ray diffraction.

In X-ray diffraction, it is known that the X-ray scattering intensity increases when the Bragg equation 2d sinθ = nλ (d: lattice spacing θ: Bragg angle n: integer λ: wavelength of the irradiated X-ray) holds. In other words, if the wavelength λ is fixed, the lattice plane spacing d can be determined for various diffraction angles 2θ (angle between incident and diffracted X-rays). In this way, the atomic arrangement of the measured material is clarified from the measured diffraction pattern.

Types of X-Ray Diffractometer

The main types of X-ray diffractometers are powder X-ray diffractometers, single-crystal X-ray diffractometers, and thin-film X-ray diffractometers. These are classified according to the way X-rays are irradiated and detected.

1. Single Crystal X-Ray Diffractometer (SC-XRD)

Figure 2. Single crystal X-ray diffractometer

In this method, X-rays are irradiated while the crystal is rotated about a certain axis, and the diffraction pattern is measured as a two-dimensional image. A three-dimensional model of the crystal structure can be obtained by calculating the obtained two-dimensional diffraction pattern using dedicated software.

2. Powder X-Ray Diffractometer (PXRD)

Figure 3. Powder X-ray diffractometer

PXRD is a method of measurement in which the angle of incidence of the irradiated X-rays and the position of the detector are moved to obtain diffraction intensity data for a diffraction angle of 2θ. It is mainly used for identification and qualitative analysis of substances with known diffraction patterns. It is the most commonly used measurement method because it requires a small amount of sample and is easy to adjust the sample. 

3.Thin Film X-Ray Diffractometer (GI-XRD)

This is a method of measurement in which the incident angle of the irradiated X-rays is fixed so that it is almost parallel to the substrate surface, and the detector is moved. In-Plane measurement can also be performed by moving the detector in a direction parallel to the substrate surface. Since the influence of the substrate is relatively small and information on the area close to the surface can be obtained, this method is mainly used to identify the crystal structure of thin films and interfaces and for qualitative analysis.

Each of these methods has different characteristics, so it is necessary to select the one best suited to the purpose of use and the sample to be measured. Depending on the purpose of use, it may be better to use an X-ray scattering system, which is a similar measurement system. Other accessory devices can be used to change the type of light source and to change the measurement environment, such as temperature and pressure, while performing measurements.

What Is a Self-Tapping Screw?

Self-Tapping Screws are screws that can form threads when they are screwed in, even if the female threads (wood, metal, etc.) do not have threads.

Since no processing of the mating side (female thread side) is required, this type of screw is very efficient in terms of work efficiency and cost.

Uses of Self-Tapping Screws

Self-Tapping Screws are mainly used to fasten wood, steel plate, aluminum alloy plate, and resin.

Self-Tapping Screws can be used for a wide variety of applications as long as the material is thin. Self-Tapping Screws are available in six different thread shapes, and it is important to select one depending on the material to be fastened.

Features of Self-Tapping Screws

Self-Tapping Screws are characterized by the fact that they can be used to fasten different parts together by simply screwing them into a pre-drilled hole to form a female thread. With ordinary screws, a pre-drilled hole and tapping (threading) are required to create a female thread in advance.

Self-Tapping Screws are widely used by professionals and DIYers alike because they require less work to fasten two parts and have stronger fastening force. On the other hand, once a screw is tightened, it is difficult to loosen.

The disadvantage is that if the screw is not tightened properly, the shape of the screw is memorized on the female thread.

1. Difference From Drill Screws

The difference between a drill screw and a threaded screw is whether or not a pre-drilled hole is required. Drill screws have a drilled tip and can be pre-drilled, tapped, and tightened in a single process, and are mainly used to fasten steel and other metals.

2. Difference From Wood Screws

Self-Tapping Screws can be used for a wide range of materials such as wood, steel plates, aluminum alloy plates, and resin, while wood screws are, as the name suggests, for wood only. This is because wood contains moisture, and as it dries out over time, the wood becomes thinner, causing it to loosen and come off with regular self-tapping screws.

Wood screws are not threaded at the bottom of the neck and are slightly thicker, so that they do not loosen and can be securely fastened even if the wood becomes thin.

Other Information on Self-Tapping Screws

1.Types of Self-Tapping Screw Heads

There are three types of self-tapping screw heads: pan head, countersunk head, and truss head.

• Self-Tapping Screws
  This is the most widely used self-tapping screw.
• Flat Head Self-Tapping Screw
  This type of screw has a flat, dish-shaped head and is used when the entire head is to be embedded. Therefore, a conical hole for embedding the head must be drilled in the material beforehand.
• Truss Head Self-Tapping Screws
  Truss-head Self-Tapping Screws are used when the diameter of the head is larger than that of a flat-head self-tapping screw and the tightening strength is required.

There are various other types of self-tapping screws, such as Bind Head Tapping Screws and Round Self-Tapping Screws. 

2. Poor Fastening

Self-Tapping Screws are used to tighten screws, but they can also be used to tighten and remove screws. Insufficient torque may be applied when fastening the screw, and the self-tapping screw may not seat.

Conversely, applying too much tightening torque in an attempt to solve this problem can easily lead to various problems, such as breaking the fastening object or self-tapping screw itself.

To prevent problems before they occur, the appropriate size of the pre-hole, based on conditions such as the outside diameter of the self-tapping screw, is listed on the screw package or other information.

Repeated installation and removal of self-tapping screws will gradually reduce the fastening strength and eventually destroy the screw holes. In addition, the axial force may also gradually decrease as the material being tightened undergoes changes over time due to vibration or heat, so it is necessary to conduct tests under a variety of conditions and consider countermeasures.

What Is a Thrust Ball Bearing?

Thrust Ball Bearings are bearings that can rotate smoothly while sustaining axial loads, which are loads in the same direction as the length of the rotating shaft.

Because they are specialized to carry axial loads, they cannot carry radial loads acting in a direction perpendicular to the axial load. Although axial load is sometimes referred to as thrust load, both terms are used with the same meaning.

Uses of Thrust Ball Bearings

Thrust Ball Bearings can support high axial loads and are used in a wide range of applications, from household machinery to industrial machinery.

In familiar applications, thrust ball bearings are used in home appliances such as refrigerators, vacuum cleaners, printers and peripheral equipment, and fishing reels.

In industrial machinery, they are often used in the main spindles of machine tools such as CNC lathes, milling machines, and machining centers.

When a CNC lathe or similar machine drills the center of a workpiece, the spindle is subjected to a high load in the thrust direction.

The impact and load from machining can affect machining accuracy, but thrust ball bearings can be assembled to minimize the axial displacement of the spindle.

Principle of Thrust Ball Bearing

Thrust Ball Bearings consist of three major parts. These are metal balls called rolling elements, a cage that prevents the rolling elements from rubbing against each other, and a raceway. The raceway is a washer-shaped part with grooves in which the rolling elements roll.

To ensure smooth rotation under high loads, the rolling elements and raceways are made of heat-treated ferrous alloy steel. Some of them use ceramic rolling elements.

They are also finished to have a smaller surface roughness. Uniformity of size between rolling elements, etc. is also very important.

Depending on the conditions of use, appropriate lubricant may be required in some cases. Lubricating oil reduces frictional resistance and also plays a role in cooling the bearing when it is used under high loads and rotating at high speeds, which generates heat.

Types of Thrust Ball Bearings

Thrust Ball Bearings are broadly divided into two types: Single Thrust Ball Bearings and Double Thrust Ball Bearings.

1. Single Thrust Ball Bearing

This type consists of a single row of rolling elements and two raceways that sandwich the rolling elements above and below. Single Thrust Ball Bearings support loads in only one direction. 

2.Double Thrust Ball Bearing

This type has two rows of rolling elements and consists of three raceways. Double-Type Thrust Ball Bearing can support loads in both directions. However, the increased thickness requires more space for assembly. 

3. Other Thrust Ball Bearings

There are two types of thrust ball bearings, called “Aligning type” and “With aligning washers”, for both single and double types.

Aligning Seat Type
Aligning type bearings have a spherical raceway mounting seat. By attaching it to a spherically machined mating part, the position of the raceway is automatically held at the position of the center axis of rotation. This has the effect of suppressing misalignment of the rotating orbit.

With alignment washers
Aligning washers are added to spherically machined raceways. Thrust Ball Bearing with Aligning Washers can be used without spherical machining on the mounting surface of the mating parts to which the thrust ball bearing is mounted. However, more space is required.

Other Information on Thrust Ball Bearings

Precautions for Using Thrust Ball Bearings

When installing a bearing, it is important to carefully consider how the load is applied to the shaft and how it is best supported, and then select a bearing that is suitable for the application and purpose. It is also important to ensure that the mounting surfaces of the raceway and thrust ball bearing are sufficiently rigid to support the loads to be supported, to prevent problems with the bearings.

Lubrication should also be taken into consideration when the bearing is used under high load and high RPM conditions. Lubricant not only reduces frictional resistance, but also cools the heated thrust ball bearing.

What Is Zinc?

Zinc (element symbol: Zn) is a transition metal element with atomic number 30. Zinc alone has an atomic weight of 65.38, a density of 7.12 g/cm3, a melting point of 419.5°C, and a boiling point of 907°C. It is a silvery-white metal with a bluish tint. It is an amphoteric metallic element, soluble in both acids and alkalis.

One of its characteristics is that it has a relatively high ionization tendency, and this property can be used for battery electrodes and zinc plating. It is also an essential trace element in living organisms, and plays an important role in maintaining normal sense of taste and in constituting enzymes that regulate metabolism.

Chemical Properties of Zinc

Figure 2. Chemical properties of zinc and image of zinc ore

Chemical Reactions

When left in the air, zinc on its own gradually forms an oxide film and loses its metallic surface luster. It is insoluble in water, but dissolves in non-oxidizing acids by emitting hydrogen gas, and dissolves in alkaline solutions to form zinc acid-alkali complex salts.

For example, when reacting with hydrochloric acid, zinc chloride and hydrogen are the products. When reacting with sodium hydroxide, tetrahydroxozinc(II) ion and hydrogen are formed. In addition, when carbon dioxide is present, basic carbonates are formed.

Compounds of Zinc

Natural zinc ores include sphalerite (blende or sphalerite, chemical formula: ZnS), anorthite (hemimorphite or calamine, chemical formula: Zn4Si2O7(OH)2・H2O), smithsonite (chemical formula: ZnCO3), and zincite (chemical formula: ZnO). Zinc ore is basically produced in a state in which it is combined with other elements such as sulfur, silicon, and oxygen.

Sphalerite is considered to be a particularly important ore as a source of zinc. Sphalerite may also contain rare metals such as indium and gallium.

Uses of Zinc

Figure 3. Examples of industrial applications of zinc

• Alloys
  Uses for alloys include brass (copper and zinc), nickel silver (copper, zinc and nickel) and die castings.
• Zinc plating
  Zinc’s property of having a greater ionization tendency than iron is utilized in zinc plating. When zinc plating is applied to the surface of steel materials, a thin film of zinc on the surface prevents water and oxygen from entering the material, thus inhibiting the formation of iron rust.
  In addition, since the ionization tendency of zinc is greater than that of the internal steel, even if the steel is exposed due to scratches, etc., the surface zinc will preferentially dissolve to protect the internal steel. Zinc plating is used in various fields such as automotive parts, electrical products, computers, and building materials.
• Zinc Rich Paint
  Paints containing 70% to 95% zinc powder are called zinc-rich paints and are used for rust-preventive coatings. In addition to direct coating, it can also be used as a repair agent for hot-dip galvanizing.
  Epoxy resins are generally used for organic zinc rich paints and alkyl silicates for inorganic zinc rich paints as spreading agents to form the coating film.
• Battery Electrodes and Electrolyte
  In manganese dry cell batteries, zinc is used for the negative electrode and zinc chloride for the electrolyte. Other uses for zinc chloride include activated carbon, dyes, and agrochemical production.
• Zinc Oxide
  The white powder of zinc oxide is also used in pigments, sunscreens, and pharmaceuticals. It is also widely used in cosmetics, especially as a substitute for lead, which was once used in face powder and is highly toxic. Zinc is considered to be extremely low in toxicity compared to lead.
• Zinc Sulfate
  Zinc sulfate is used as a solution to coagulate liquid rayon in the rayon manufacturing process. It is also used as an additive in eye drops and is sometimes added to powdered formulas for child care, pets, and livestock to strengthen their mineral content. In addition, it is used to prevent damage to crops from pesticides such as Bordeaux solution, which is a fungicide.

2. Zinc in the Human Body and Foods

Zinc is present in the adult body in amounts of approximately 2,000 mg, and is mostly distributed in various muscles, bones, skin, liver, and brain. It is involved in various reactions in the body as a structural component of zinc-containing enzymes (DNA polymerase, RNA polymerase, alcohol dehydrogenase, carbonic anhydrase, etc.), which have metabolic regulating effects. Typical roles include DNA synthesis, protein synthesis, removal of reactive oxygen species, and maintenance of normal taste.

According to the 2020 Dietary Reference Intakes, the recommended intake of zinc is set at about 11 mg/day for adult males and 8 mg/day for adult females. A deficiency of zinc can cause symptoms such as dermatitis, taste disorders, and immune dysfunction. In children, it has also been noted that growth retardation may occur.

Zinc is abundant in fish, shellfish, and meat, and specific foods include oysters, pork liver, and lean beef. It is also found in soybean flour and nuts.

When zinc is taken together with citric acid and vitamin C, its intake efficiency is said to increase. On the other hand, phytic acid, which is abundant in rice bran and brown rice, inhibits the absorption of zinc, so it is necessary to consider food combinations.

3. Zinc Supplements

Zinc is available commercially as a stand-alone supplement, as well as in combination with other ingredients such as multivitamins and minerals. Zinc in supplements takes a variety of salt forms, including zinc gluconate and zinc sulfate.

Supplements are generally taken with water during or after meals. Coffee, tea, and other beverages containing caffeine or tannins may bind them to the nutrients and inhibit their absorption.

Excessive consumption of zinc may also cause copper deficiency, nausea, vomiting, stomach problems, and immune disorders.