月: 2022年12月

What Is a Corrosion Prevention Film?

Corrosion prevention film is a film mixed or coated with a rust inhibitor, or a film that suppresses rust by preventing oxygen and water vapor. Vaporizable rust inhibitors are used as rust inhibitors.

Rust prevention is an important issue for quality control of metal products. Conventionally, coatings with grease or oil have been used to prevent rust. These coatings had to be removed before processing or assembly, which involved labor and equipment costs and environmental impact. Corrosion prevention film eliminates these problems because it prevents rust without the use of rust prevention oil. For films that prevent oxygen and water vapor, the burden on the environment is even smaller because no corrosion prevention agents are used in the film.

Uses of Corrosion Prevention Films

Corrosion prevention films are used to prevent rust on metal products. Those for steel are often used, but there are also those for non-steel.

Uses of automotive parts storage are a specific example. Automobile parts are often stored for long periods of time and are metal products that require special rust prevention. Conventionally, they were stored in double packaging: rust-proof paper for rust prevention and plastic bags for sealing. Corrosion prevention film can be sealed by heat sealing, so a single sheet can perform these functions and reduce costs.

Larger sheet types are commercially available and can be used for packaging large machinery.

Principle of Corrosion Prevention Films

Corrosion prevention film is made of polyethylene or other plastic containing an evaporative rust inhibitor. This vaporizable rust inhibitor is effective in preventing rust.

When the vaporizable rust inhibitor evaporates from the corrosion prevention film, it fills the space sealed by the film. During this process, the vaporizable rust inhibitor dissolves into the surface of the wrapped metal and the moisture in the space. The dissolved rust inhibitor suppresses the electrochemical reaction that causes rust, making rust less likely to occur.

Since the rust inhibitor is vaporizable, it can penetrate into minute crevices that cannot be reached by coating methods, such as application, and rust can be prevented in every nook and cranny.

Depending on the type of rust inhibitor, the reaction mechanism of rust prevention varies. For example, nitrites used in corrosion prevention films for steel, for example, inhibit the reaction of oxygen and water with metal by dissolving into condensing water. Carboxylates of amines, also used for steel, dissociate into amine and carboxylic acid and then reattach on the surface of the metal, thereby exhibiting rust inhibiting effects.

For barrier types that do not contain vaporizable rust inhibitors, the rust inhibiting effect is achieved by preventing oxygen and water vapor from entering the bag. Generally, rusting occurs rapidly when humidity exceeds 60-70%, so it is important to prevent moisture from entering the bag to avoid such high humidity.

What Is an Explosion Proof Vacuum Cleaner?

Explosion-proof vacuum cleaners are industrial devices designed to safely operate in environments where flammable gases, vapors, or dust may be present. Certified by U.S. National Recognized Testing Laboratories (NRTLs) and other certifying bodies, these cleaners operate within temperature ranges that prevent ignition, thus mitigating the risk of explosions. Available in dry, wet, electric, and pneumatic variants, they cater to various industrial needs based on location and required suction volume.

Applications

Explosion-proof vacuum cleaners serve critical roles across diverse sectors, including automotive, aerospace, chemical, pharmaceutical, military, and food industries. They are essential for collecting combustible materials like grains, starches, and metal dust, particularly in the automotive and aviation sectors where metal processing generates flammable dust. Their use is crucial in preventing dust-related explosions by safely handling potentially ignitable materials.

Operating Principles

By cooling and reducing the generation of heat during suction, explosion-proof vacuum cleaners prevent temperature rises that could lead to explosions. They feature conductive stainless steel filters to avoid electrostatic charges and check valves to prevent backflow of aspirated materials. Equipped with HEPA filters, they capture fine particulate matter, ensuring safety in environments such as clean rooms and pharmaceutical plants. Casters designed for these vacuum cleaners are typically anti-static to further reduce risks.

Varieties

Explosion-proof vacuum cleaners are categorized into dry, wet, and wet-dry types, with pneumatic and electric drive systems:

• Dry: Suitable for materials without moisture, capable of collecting dust and flammable powders in explosive atmospheres.
• Wet: Designed for suctioning moist or liquid-containing materials, using cyclone separators to efficiently separate moisture and oil.
• Wet/Dry Type: Versatile for both dry and wet materials, with models allowing simultaneous or pre-selected vacuuming based on material condition.
• Drive Systems: Available in pneumatic for spark-free operation and electric for convenience, with specific models offering continuous motor operation and easy cleaning.

Adhering to standards like IEC, NFPA, ATEX, and certifications from NRTLs, explosion-proof vacuum cleaners are tailored for safe operation in defined hazardous areas, safeguarding against potential ignition sources.

What Is an Explosion Proof Motor?

Among machines that use electricity, electric machines and equipment used in factories and plants are extremely dangerous because they handle high voltages such as 100 VAC and 200 VAC. Especially in explosive or hazardous atmospheres or in dusty areas that can cause dust explosions, sparks generated by electrical machinery and equipment can ignite gas or dust.

As a result, accidents such as explosions and fires may occur.

Therefore, explosion-proof electrical equipment must be used in such hazardous locations or atmospheres. Motors often used in factories and plants are no exception. Explosion proof motors are motors that can be used safely in such hazardous atmospheres.

Based on a standard called the “Guideline for Explosion-Proof Guidance for Factory Electrical Equipment,” these motors are designed and manufactured so that they can be used safely and securely in hazardous and explosive atmospheres.

These motors are used in many places where hazardous or explosive atmospheres are likely to occur, such as chemical plants and petrochemical factories.

They may also be used in other outdoor applications.

Uses of Explosion Proof Motors

Motors are widely used in pumps, blowers, and other industrial machinery, and are so directly connected to industry that it is no exaggeration to say that there is no factory or plant that does not use a single motor or that does not have a single motor.

However, because they operate at high voltage and high current, if flammable gases, large amounts of steam, or large amounts of dust are present, or if steam or other substances are present, they can enter the interior and cause an explosion, creating a dangerous situation.

Similarly, when used outdoors, rain and other elements can enter the product, creating a dangerous situation.

Explosion proof motors can be used safely under such conditions. They are widely used in factories that handle flammable hazardous substances, such as in the petrochemical industry, and in factories that handle other flammable substances.

Explosion-proof motors are also sometimes used when motors are used outdoors because of the danger of rain getting inside.

Principle of Explosion Proof Motors

Explosion proof motors are not merely sealed or isolated inside. Broadly classified, there are three types of Explosion proof motors based on the type of construction of their explosion-proof motor.

The first is the safety-increase explosion-proof motor. These motors are designed to prevent ignition sources and can be used in hazardous atmospheres.

Other types are called “internal pressure explosion-proof” and are protected from flammable gases by constantly injecting (purging) inert gases, such as nitrogen or air, into the inside. This ensures that the internal pressure is always higher than that of the ambient environment, eliminating the risk of flammable gases getting inside, so that even in hazardous atmospheres, the device can be used without any problems.

However, this structure requires gas purging, so equipment for that purpose is necessary.

Finally, there is the explosion-proof type. This type has a special construction so that if flammable gas gets inside and causes an explosion, the case or cover will not be damaged and the explosion will not become an ignition source.

The choice of which of these motors to use is not an easy one, and must be determined by the atmosphere in which it will be used.

If the atmosphere is hazardous, the frequency and duration of flammable gases that cause the hazard must determine the type of motor to be purchased and used.

What Is an Anti-Vibration Mount?

Anti-vibration mounts are designed to suppress the transmission of vibrations from equipment that generates vibrations to the outside, such as at manufacturing sites where fine processing is required or in situations where precision optical experiments are conducted.

Conversely, a vibration isolator suppresses vibration transmitted externally.

The performance of an anti-vibration mount is determined by the natural frequency of the mount itself. The lower the natural frequency, the less the anti-vibration mount can follow the vibration from the surroundings, and thus the higher the anti-vibration mount’s performance.

Air springs are often used to realize such a mount, which can provide anti-vibration mounts not only in the horizontal direction but also in three dimensions.

The viscous resistance of air damps vibrations quickly.

Uses of Anti-Vibration Mounts

Anti-vibration mounts are often used in the manufacture of precision equipment, such as semiconductors and liquid crystal displays, which are vibration sensitive, by means of vibration reduction using air springs.

Anti-vibration mounts are particularly useful when pumps, machine tools, and other equipment that generate vibration are used on a stand to suppress the transmission of vibration to the outside.

In the case of measurement using a precision instrument, the vibration of the tabletop during work or from external sources can be quickly suppressed, thereby improving the efficiency of the measurement time.

Most anti-vibration mounts can be used for both anti-vibration and anti-shock (elimination of external vibrations).

Principle of Anti-Vibration Mounts

Vibration isolation is the process of suppressing as much as possible the vibration transmitted from a vibrating machine or other vibrating object.

Vibrations transmitted through gases are greatly attenuated by obstacles along the way, so they are not transmitted very far.

In the case of solids, however, the solid acts as a medium and propagates the vibration, making control of the vibration very important.

To suppress the propagation of vibrations in a solid, the frequency at which the solid is inherent (natural frequency) must be controlled. If a solid has a natural frequency that is the same as the frequency of the propagating vibration, it will vibrate violently.

Therefore, the propagation of vibration can be reduced by making the frequency of propagation and the natural frequency as far apart as possible.

In particular, the smaller the natural frequency, the lower the rate of vibration transmission, which is why anti-vibration mounts are equipped with air springs or coil springs. The natural frequency is as low as 10 Hz or less.

In the air spring method, compressed air is filled into an air spring consisting of metal fittings and a rubber membrane. The air supply is used to maintain the level of the platform.

On the other hand, the coil spring method has the advantage of not requiring air, but has the disadvantage that the spring deflects and tilts when the center of gravity of the mounted object moves.

What Is a Gantry Type Machining Center?

A gantry type machining center is a type of machining center that is automatically controlled by CNC (computer numerical control) commands.

It is classified as the largest machining center and consists of a spindle, table, column, NC unit, and automatic tool changer (ATC). It is so called because the structure supporting the spindle, which rotates the cutting tool, is gantry-shaped when viewed from the front of the machine.

Because of its structure which allows for a large width and length of the table for loading the cutting workpiece, it is used for heavy-duty cutting of large products. Because it is a very large facility, it is used only in a limited number of processing plants.

Because of the large size of double-column machining centers, there are only a limited number of domestic manufacturers of these machines. On the other hand, demand for double-column machining centers is increasing for use in larger semiconductor facilities and in the production of molds for electric vehicles.

Uses of Gantry Type Machining Centers

The gantry type machining centers currently in operation in Japan are capable of machining workpieces up to 12 m or more in length, 4 m or more in width, and 1 m or more in height, so their main applications are for large products.

Because of their extremely precise positioning and cutting accuracy, they are used in the machining of rotating parts for wind and hydropower generation equipment, nuclear power generation equipment, structural parts for aircraft, large vacuum chambers for semiconductor manufacturing equipment. They are also used for chambers for FPD manufacturing equipment such as liquid crystal and organic EL, parts for large ship motors, and parts for the automotive and aerospace industries. The principle of the double-column machining center is as follows.

Principle of Gantry Type Machining Centers

The structure of a gantry type machining center consists of a table on the floor for loading the workpiece to be machined, columns on either side of the table (the vertical pillars of the “gantry”), crossrails connecting the columns above the floor, and a spindle that moves on the crossrails.

Although large, it is suitable for precision cutting because of its high-precision positioning of around 2μm, and can be used for a variety of machining operations by changing the spindle attachment. However, the equipment itself is very expensive and the machining cost is also high.

Types of Gantry Type Machining Centers

Gantry type machining centers are classified into the following types according to the way each part moves. Each of the following types has a different rigidity, or direction to improve accuracy, and is selected mainly according to the axial direction in which accuracy is desired.

1. Fixed Crossrail Type

The column is fixed, and the spindle moves left and right on the crossrail. The spindle itself moves up and down, and the table moves in a direction perpendicular to the crossrail.

2. Crossrail Moving Type

The column is fixed; the spindle moves left and right on the crossrail, and the crossrail moves up and down. The table moves in the same way as in the fixed crossrail type.

3. Gantry Type

The table is fixed, and the column moves along the table. There are two types of crossrail movement: fixed type and movable type.

Structure of Gantry Type Machining Centers

A gantry type machining center consists of the following components:

1. Spindle

The spindle is used to mount and control the rotation of the cutting tools. In gantry type machining centers, the spindle number is No. 50 to accommodate heavy-duty cutting. The shank is larger than that of No. 40, which is often used in machining centers.

2. Bed

The bed is equipped with a guide surface to guide the table and supports the bottom of the machining center.

3. Table

The table is a surface on which the workpiece is placed and has grooves for holding and securing the workpiece with T-shaped nuts. The table is wide enough to accommodate workpieces over 2 m in length, and a crane is often used to remove and install workpieces.

4. Column

This is a column-like entity connected to the bed and extending vertically, and is the component that supports the main spindle. The main feature of the gate type is that the column is supported by two columns, which form a gate-like shape.

5. Operation Panel

This is an operation panel for operating the machine tool, such as creating NC programs and manually operating the machine by means of handles.

6. Cross Rail

Crossrail is a rail that supports the spindle. It can be divided into two types: a movable type in which the crossrail moves up and down and a fixed type in which the spindle moves up and down.

What Is a Cast Heater?

Cast heaters are used to heat metal surfaces evenly and efficiently.

Sheathed heaters, air-cooled tubes, etc., are cast into brass, aluminum, iron, etc. The heat is generated by the conduction heat when it comes in contact with the object to be heated. They have excellent resistance to overuse, shock, and vibration.

Various shapes are available, and by casting air- and water-cooled tubes, temperature control for rapid and slow cooling is possible. Rapid heating is also possible by attaching heat-dissipating fins to the outer surface.

This type of heater is suitable for use in synthetic fibers and engineering plastics, etc., where a highly precise temperature distribution is required.

Uses of Cast Heaters

Because of their high corrosion resistance and uniform temperature distribution, cast heaters are used in a wide range of applications.

They are used in home appliances such as ovens, ranges, irons, electric pots, hot plates, and electric kettles.

As commercial equipment, they are used in ovens, electric furnaces, casting parts, presses, air conditioning/heating units, kitchen equipment, electric kilns, etc.

As industrial equipment, they are used for tank heating, chemical heating, heat insulation, low-melting-point metal melting, extrusion molding machines, valve/pipe heat insulation, heating, etc.

Principle of Cast Heaters

Since a sheath heater is built into the casting, heating with uniform temperature distribution can be achieved.

Although less efficient than heating an object directly, it can be easily managed since there is no need to drain the liquid for maintenance, etc.

It is used as an indirect heating method when the space inside the tank or tanks is to be effectively utilized, or when a direct heat source cannot be installed as a countermeasure against ignition or odor.

The surface where the heater is mounted is machined to enhance heat conduction.

Sheathed heaters cast into aluminum can be processed into a variety of shapes.

Heater elements can be replaced when sheath heaters are inserted into grooves machined into aluminum plates. SUS and Bs can be used for the plate material.

Cartridge heaters inserted into the holes in the aluminum plate can be replaced with the plate attached. Arbitrary temperature distribution can be set by changing the heater power and arrangement. 

What Is Silver Paste?

Silver paste is a conductive adhesive consisting of silver particles dispersed in resin.

Solder is used as a conductive bonding method, but with solder the temperature must be raised to nearly 250°C, and the resin parts to be bonded are likely to be damaged by the heat.

On the other hand, silver paste can be sintered at temperatures as low as 100°C, thus minimizing damage to the material. It is often used for the purpose of conducting and fixing electronic components, such as capacitors, to the underlying substrate.

Uses of Silver Paste

Silver paste can be sintered at low temperatures and is widely used for circuit boards of electronic devices, electrodes of displays, and piezoelectric components. In recent years, demand for flexible printed circuit boards (flexible printed wiring boards) has been increasing, and silver paste is used to create wiring on resin film. This type of wiring board can be made at a lower cost than copper foil laminated together.

In dye-sensitized solar cells, which are attracting attention as next-generation solar cells, silver paste is used to create wiring on transparent conductive glass in order to further enhance the conductivity of the conductive glass.

Principle of Silver Paste

Silver paste is a method of obtaining conductivity by bringing the contained silver particles into contact with each other using a hardening reaction caused by heating a resin.

1. Resin

Epoxy resins are mainly used for silver paste, and the relationship between the structure and properties of epoxy resins has been analyzed, and curing agents have also been developed. The curing reaction of epoxy resin proceeds by polymerization reaction between epoxy and curing agent, enabling the creation of a strong three-dimensional bonded structure.

When amines are used as curing agents, polymerization proceeds through the reaction of amines with epoxy groups or amino groups with hydroxyl groups. The initial liquid state changes to a gel-like state with heating, and after a certain time, it transitions to a rubber-like state and finally to a glass-like state.

When the transition to glass is completed, the series of curing reactions is over. The temperature at which the transition to glass occurs is called the glass transition temperature.

2. Silver Particles

As a conductive mechanism, micrometer-sized silver particles contact each other to conduct electricity. To ensure good electrical connection between particles, flat flake-shaped silver particles are generally used instead of spherical particles.

Upon heating, the silver particles are incorporated into the three-dimensional molecular structural changes of the epoxy resin. When heated, the entire material shrinks as it cures, allowing the silver particles to make contact with each other and thus acquire conductivity. In addition to silver particles, gold paste and nickel paste are also available.

Types of Silver Paste

There are many types of resins used as adhesives and conductive particles to be blended, and a great variety of conductive adhesives have been developed and sold in the market. It is necessary to make a selection in consideration of performance, application, cost, usage, and other factors.

Resins used include epoxy, phenol, acrylic, urethane, and silicone resins. For electronic component connection applications, heat reaction curing epoxy systems are the most common.

Epoxy adhesives are characterized by excellent adhesive strength to metals, high heat resistance, and low-volume shrinkage during curing. On the other hand, silver conductive particles are widely used as conductive particles. Silver is common in electronic materials because of its stable conductivity, resistance to oxidation, good storage stability, and high thermal conductivity.

Spherical or flake-shaped particles are used for silver conductive particles, and there are different types depending on the size of the particles and the amount of silver in the mixture, depending on performance.

Other Information on Silver Paste

Thermal Conductivity of Silver Paste

The thermal conductivity of silver alone is very high at 429 W/mK, but the resin used is as low as 1 W/mK, so the overall thermal conductivity of epoxy silver paste is about 30 to 50 W/mK. To increase this thermal conductivity, it is necessary to increase the content of silver particles. However, the amount of resin content decreases accordingly, resulting in a significant decrease in adhesive strength, and manufacturing cost is also a concern.

Furthermore, if the average particle size of silver particles is too small, the issue of heat conduction paths cannot be secured, and if the average particle size of silver particles is too large, sintering becomes difficult. Therefore, in recent years, high thermal conductivity of silver paste with silver nanoparticles has been developed.

This is due to the fact that silver nanoparticles bond the silver particles together and create many paths for heat conduction. Products with thermal conductivity of about 240 W/mK are now available.

What Is a Mold Cleaning Agent?

Mold Cleaning Agents Remove Grease and Organic Contaminants

Mold cleaning agents are metal mold cleaning agents, often in spray form. Mold cleaning agents are used to clean organic substances such as grease and rust inhibitors from molds. The appropriate mold cleaning agent depends on the strength of the cleaning power and the type of mold. When cleaning numerous molds or large molds, the cleaning agent should be diluted in a tank rather than a spray type, and the molds should be washed by pouring the cleaning agent over the molds.

Check the Safety of Mold Cleaning Agents Before Handling Them

Mold cleaning agents contain various compounds depending on the product. Some products may contain compounds that fall under poison control laws, so it is necessary to check the safety data sheet (SDS) for proper handling before use.

Uses of Mold Cleaning Agents

Mold Cleaning Agents Remove Dirt From Molds

Mold cleaning agents are used to clean metal molds. Mold cleaning agents are used to remove organic matter adhering to molds. Typical examples include the removal of product debris, burns, and additives from molds used in the processing of rubber, resin, and other organic materials.

Can Also Be Used for Metal Parts Other Than Molds

Since mold cleaning agents are suitable for cleaning adhered organic matter, they can also be used to remove oil stains on metal machine parts in addition to molds. Spray-type mold cleaning agents can also be used to remove rust inhibitors and metal scraps from wires.

Characteristics of Mold Cleaning Agents

Mold Cleaning Agents Contain Ingredients That Break Down and Remove Organic Matter

Mold cleaning agents are used to remove organic matter from molds. Molds used in the manufacturing process are subject to contamination from the product itself, such as tar, dirt, and lubricating oil used to drive the machine. In particular, molds that are processed and formed at high temperatures accumulate various kinds of adhesions. Mold cleaning agents are designed to break down and remove such strongly adhered organic contaminants. To prevent chemical injury caused by the cleaning agent, appropriate protective equipment should be worn after checking the safety data sheet when using the product.

Mold Cleaning Agent Ingredients Vary by Product and Must Be Controlled in Accordance With the Respective Regulations

Some mold cleaning agents are composed of aliphatic hydrocarbons and alcohol-based compounds. Mold cleaning agents containing these components can be used to clean metal machinery as well as molds. Mold cleaning agents composed of aliphatic hydrocarbons strip dirt from molds. Therefore, the dirt can be removed by wiping it off after applying the cleaning agent. Mold cleaning agents may fall under various laws and regulations, therefore, appropriate management is required in accordance with the laws and regulations.

What Is an Oxygen Monitor?

An oxygen monitor is a measuring instrument used to determine the concentration of oxygen in the air.

It is sometimes called an oxygen sensor or an oxygen meter. Oxygen monitors are needed because oxygen is an essential substance for human life.

Monitoring oxygen levels is extremely important, especially in confined work benches that are prone to oxygen deprivation. In addition, many scientific and industrial fields require accurate oxygen concentration control in terms of process control and equipment maintenance. Depending on the requirements of the scientific and industrial sectors, measurement systems are available for a variety of measurement conditions.

Typical examples include zirconia sensors, which are used for product control in semiconductor manufacturing, energy conservation in automobiles, and exhaust gas purification. For more information on oxygen monitors, please refer to the figure below.

Uses of Oxygen Monitors

Uses of oxygen monitors can be broadly classified into two categories: “for prevention of oxygen deprivation” and “for oxygen concentration control.”

1. Monitoring of Oxygen Concentration for the Purpose of Preventing Oxygen Deprivation (Detection and Monitoring)

Oxygen monitoring plays an extremely important role in maintaining vital activities in enclosed spaces. This is because it is said that if the oxygen concentration falls below 15%, a person will have difficulty breathing. If it falls below 7%, brain function will be impaired, and if it falls below 4%, death will occur. The equipment can be portable or wall-mounted.

2. Oxygen Concentration Control in Industrial Processes

In some industrial heat treatment processes in the chemical industry, ceramics, metals, etc., oxygen concentration must be kept low. The combustion process in industrial furnaces also requires monitoring and control of oxygen concentration to optimize combustion efficiency and the oxidation-reduction process.

Oxygen monitors for such industrial applications can be exposed to intense chemical reactions in high-temperature environments. Products that are resistant to harsh environments are required.

Principle of Oxygen Monitors

The two main operating principles of oxygen monitors are the “galvanic cell type” and the “zirconia solid electrolyte type.” Other types include “magnetic type” and “wavelength tunable semiconductor laser spectroscopy type.

1. Galvanic Cell Type

The galvanic cell consists of a resin membrane that allows oxygen from the outside world to pass through, gold (Au) and lead (Pb) electrodes, and an electrolyte (potassium hydroxide solution). The following reactions take place at each electrode:

• Anode: Pb + 2OH- → Pb2+ +H2O + 2e-
• Cathode: O2 + 2H2O + 4e- → 4H2O

Electrons emitted at the anode reach the cathode, where oxygen taken in from the air takes up the electrons emitted at the anode. Since the flow of electrons (current) is proportional to the oxygen concentration, the oxygen concentration can be measured by measuring the current. Since this reaction occurs spontaneously, no power supply is required to drive the sensor.

2. Zirconia Solid Electrolyte Method

This method uses a zirconia cell, taking advantage of the fact that zirconia exhibits the properties of a solid electrolyte at temperatures of 500°C or higher. Zirconia can conduct oxygen negative ions (O2-) in a solid state, and the ions are conducted from a gas with high oxygen concentration (in the air) to an atmosphere with low oxygen concentration (in an industrial furnace, for example).

This ionic conduction generates a potential difference, and electrodes are placed on the high O2 concentration side and the low O2 concentration side, respectively, generating an electromotive force. The relationship is just like the positive and negative electrodes of a battery.

• High O2 concentration side: O2 + 4e- → 2O2-
• Low O2 concentration side: 2O2- → O2 + 4e-

The electromotive force generated between the electrodes obeys the Nernst equation (see below), so the partial pressure of oxygen at each electrode can be determined.

• E= (RT/4F) -ln (PA/PB)
• (R: gas constant, T: temperature, F: Faraday constant, PA: oxygen partial pressure at high concentration (in air), PB: oxygen partial pressure at low concentration)

Temperature is measured by thermocouples attached to the zirconia. In an atmosphere of approximately 400°C or lower, the target gas is introduced into the device via a sampling tube, and the zirconia cell is heated to a predetermined temperature by a platinum heater or other means (sampling method). This is because zirconia requires a temperature of 500°C or higher to function as a solid electrolyte.

Types of Oxygen Monitors

Different products should be used for oxygen meters intended to prevent oxygen deprivation and those intended to maintain low oxygen concentrations in industrial processes.

1. Oxygen Monitor for the Purpose of Preventing Oxygen Deprivation

Portable and stationary oxygen analyzers designed to prevent oxygen deficiency use galvanic battery-powered oxygen analyzers. This type does not require a power supply to drive the sensor.

The life of the sensor is approximately 2 to 3 years. However, the usable environment is limited to an atmosphere similar to the general environment, and the accuracy is about ±0.5%O2. The instruments are available in portable and wall-mounted types, and some are explosion-proof.

2. Oxygen Monitor for Industrial Use

Zirconia type oxygen monitors are suitable for measuring oxygen concentration in high-temperature industrial processes such as industrial furnaces, etc. In atmospheres above 700°C, the direct insertion type is used, where the sensor part is inserted directly into the atmosphere.

For temperatures below 400°C, the sampling method is appropriate, whereby the ambient gas in the furnace is drawn in through a sampling tube, etc., and the zirconia cell is heated separately. The correct choice should be made according to the application.

What Is an Oxygen Sensor?

An oxygen sensor is a sensor that measures the concentration of oxygen in the atmosphere of a measurement space.

In an isolated and enclosed space, it is extremely important to measure oxygen concentration in order to maintain vital activities. Oxygen sensors play a major role in this oxygen concentration measurement.

It is said that when oxygen levels fall below 15%, people have difficulty breathing; when oxygen levels fall below 7%, brain function is impaired; and when oxygen levels fall below 4%, death occurs. Oxygen sensors are needed in various scientific and industrial fields, and a wide range of oxygen concentration measurement conditions and systems have been developed to meet the requirements of these fields.

A typical sensor is the zirconia sensor. Zirconia sensors are also used for product control in semiconductor manufacturing, energy conservation in automobiles, and exhaust gas purification.

Uses of Oxygen Sensors

Measurement of oxygen concentration is performed in two major roles: first, to detect and monitor oxygen concentration in order to prevent oxygen deficiency, which can save human lives. Secondly, they are used in controlling oxygen concentration in the production process of industrial products, etc.

1. Prevention of Oxygen Deprivation

Examples of applications for acid deprivation prevention include safety management at civil engineering sites, such as tunnels and underground construction, and oxygen inhalation management and hyperbaric resuscitation in the medical field. Products for these applications can be portable or wall-mounted.

2. Oxygen Concentration Control

Oxygen concentration control is used in the chemical, ceramics, and metals industries for process control in the manufacture of industrial products. One of the characteristics of industrial product manufacturing is that they are often used in high-temperature environments during heat treatment processes.

An example familiar to us in our daily lives is its use in automobile and motorcycle engines. By detecting the oxygen concentration in the exhaust gas, they play a role in adjusting the fuel concentration.

Principle of Oxygen Sensors

The measurement principles of oxygen sensors include galvanic cell type, zirconia individual electrolyte type, magnetic type, and wavelength tunable semiconductor laser spectroscopy type.

1. Galvanic Cell Type

The galvanic cell type has a simple structure and is used in portable oxygen meters. It consists of gold and lead electrodes, a resin membrane, and an electrolyte solution, and uses a mechanism in which an electric current corresponding to the oxygen concentration flows when oxygen passes through the membrane and dissolves in the electrolyte solution.

2. Zirconia Individual Electrolyte Method

The zirconia individual electrolyte method uses zirconia as a solid electrolyte. Zirconia can conduct oxygen negative ions (O2-) in a solid state, and the ions are conducted from a gas with high oxygen concentration (high O2 pressure side) to an atmosphere with low oxygen concentration (low O2 pressure side).

In a zirconia electrolyte oxygen sensor, electrodes are placed on the O2 high-pressure side and the O2 low-pressure side, respectively, and they are electrically connected to each other. The O2- electrode on the low O2 pressure side receives electrons from the transmitted O2-.

The electrons released at the low O2 pressure side (negative electrode) flow back to the high O2 pressure side (positive electrode). The electromotive force generated between the electrodes can be used to determine the partial pressure of oxygen at each electrode using a relationship called the Nernst equation, as shown below.

　E= (RT/4F) – 1n (PA/PB)

Where R is the gas constant, T is the temperature, F is Faraday’s constant, and PA and PB are the oxygen partial pressures on the high and low O2 pressure sides, respectively. The temperature is measured by a thermocouple installed in the zirconia, and PA is based on the oxygen partial pressure in a normal atmosphere.

Other Information on Oxygen Sensors

Deterioration of Oxygen Sensors

Zirconia oxygen sensors used in the manufacturing process of industrial products need to be carefully monitored for deterioration. They are used in high-temperature environments, and a variety of gases can also degrade or affect the zirconia cell. Reducing gases, such as halogens, are also degradation factors.

In automotive applications, oxygen sensors can degrade or fail, causing an increase in toxic substances in the exhaust gases. Also, fuel consumption can deteriorate when fuel is more concentrated than necessary; when O2 sensors deteriorate, parts should be replaced at a dealer or service facility.