Basic knowledge of vacuum
Vacuum is a space filled with a gas with a pressure lower than the normal atmospheric pressure.The products around us use the technology that apply vacuum.It is used in a wide variety of fields, such as food, pharmaceutical products, home appliances such as refrigerators and television, electronic devices such as computers and smartphones, cars, ships, and infrastructure, even if they do not come to the word vacuum technology.In this series, we will explain the basic knowledge of vacuum technology, which is the foundation of many industrial technology.
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1st: What is vacuum?
Before you get an overview of vacuum technology, first define what vacuum is.The literal vacuum means truly sky, or nothing.Industrial vacuum is a state of space filled with a pressure gas with lower pressure than normal air pressure (JIS Z 8126-1 Vacuum Technology-Language-Part 1: General Term, ISO3529-1 vacuum Technology-Vocabulary-Part 1: General Terms).In other words, the lower pressure space that we live is vacuum.
To create an industrial vacuum, you need a container (vacuum container) to hold the vacuum and a vacuum pump that exhausts the air in the container.Vacuum containers are also called vacuum tanks and vacuum chambers.In this case, it is necessary to know the behavior of gas remaining in the vacuum container (gas molecular motion theory).The three elements of vacuum, including vacuum pumps, vacuum containers, and gas molecular motion theory.It may be four elements of vacuum, including the vacuum measurement necessary to know the pressure of gas and ingredients in the vacuum container (Fig. 1).
図1：真空技術の4要素The definition of vacuum by JIS and ISO contains important terms.First, what is pressure ...
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In the field of vacuum engineering, vacuums are classified into low vacuum, medium vacuum, high vacuum, ultra -high vacuum, and polar high vacuum depending on the pressure area (Fig. 2).
図2：圧力領域による真空の分類（JIS Z 8126 真空技術-用語-第1部：一般用語）低真空領域では、真空は、主に大気圧との圧力差を用いた力学的な用途で用いられます。例えば、工場で製品を搬送するときに製品を持ち上げる真空チャックがあります。船舶などから粉体の積み下ろしには、掃除機を大型化したバキュームアンローダーが用いられています。身近な例では、卵パックなどを成形する真空成型技術があります。これは、加熱したPETフィルムを真空の圧力差を使って力を生み出し、変形させるものです。このように、製品を吸引したり、変形させる場合、真空と大気の圧力差の限界値は、約105Paです。従って、搬送する製品の重量に応じて、真空チャックのパッドの大きさを設計する必要があります。
In the low vacuum region, vacuum is used for substance transport, especially water removal.Figure 3 is a state diagram of water.As shown in the arrow in Fig. 3, when the pressure of water (point p) at room temperature is reduced, the water evaporates and becomes a gas (water vapor).Therefore, if you put a water -containing object in vacuum, it will dry out.This is vacuum drying.It is used to manufacture instant miso soup and cup noodles.Also,……
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The vacuum is not a space with nothing, but the gas (gas) remains.The remaining gas is called a sparse gas, and to think about vacuum, it is necessary to know the nature of the rare gas.Vacuum engineering handles the viscosity, thermal conduction, and diffusion of sparse gases.This is a field of mobility phenomena or a transportation phenomenon.
In vacuum engineering, the phenomenon varies depending on whether the gas molecules are treated as viscous fluids (continuous body) or as independent transport of individual molecules.The indicator that determines the difference is the no -dimension of Knusen number kn.If D is a typical diameter such as a vacuum piping or a diameter inside the vacuum container (unit: m), and λ are the average free processes (the average distance that runs before the gas molecules collide with each other, unit: m)., Kn = λ/d can be expressed.The average free process is inversely proportional to pressure P.For example, in the case of air at 20 ° C, λ = (6).5×10-3)⁄pです。図5は、平均自由行程λの圧力依存性を示したグラフです。
図5：圧力による平均自由行程の変化（20℃の空気の場合）In vacuum engineering, ...
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2nd: How to make low and Nakamasa
前回は、真空の特徴と産業への応用、また、気体分子運動論を紹介しました。今回から2回にわたり、真空の作り方を解説します。今回取り上げるのは、圧力領域が105～10-1Paの、低・中真空領域です（105は、通常の大気圧）。真空を作るには、真空ポンプを使って容器中のガスを減らします（真空排気）。低・中真空を作るには、主に気体輸送式真空ポンプを使用します。
真空を作るために、真空ポンプを使って容器中のガスを減らすことを、真空排気といいます。言い換えれば真空排気とは、容器から一定量の体積を切り取り容器外に移すことで、その体積中に含まれるガスを容器から取り除くプロセスです（図1）。この排気プロセスによって一定の時間に切り取られた体積Sを、排気速度と呼びます。排気速度Sはm3・s-1、L・s-1、L・min-1などの単位で表されます。
図1：真空排気容積Vの真空容器を排気速度Sの真空ポンプで排気したとき、容器中の圧力は初期圧力p0として、p(t)=p0exp(-St⁄V)=p0exp(-t⁄τ)に従い、低下します。ここでτ=V⁄Sを排気の時定数といい、圧力がe-1≈1/2.7≈0.Indicates the time to increase 37 times.To reduce the pressure in the container quickly and shorten the time spent on vacuum exhaust, reduce the time constant τ for exhaust.That is, it is necessary to use a vacuum pump with a large exhaust speed S.
図2は容積1m3の真空容器を、排気速度が異なる2種類の真空ポンプで排気した際の容器内の圧力変化です。真空ポンプの排気速度は200L・min-1、または排気速度400L・min-1です。図2が示すような圧力の時間変化を排気曲線といい、排気速度の大きいポンプの方が圧力の低下が速いことが分かります。もちろん排気速度の大きいポンプは、大型でコストも増加するため、許容できる排気時間とコストのバランスを検討することが重要です。
図2：排気曲線の例（p0=105Pa）The type of vacuum pump is ...
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A commonly used vacuum pump has a rotating wing -shaped oil rotation pump (Fig. 3).The rotating pump pump in Fig. 3 is the pump body on the left and the right side.It is compact because it drives the pump axis directly on the motor axis without using a gear or belt.
図3：回転翼形油回転ポンプの製品例（引用：株式会社アルバック カタログより）A cylinder is attached to the pump shaft inside the pump.On both sides of the cylinder, a vane (rotation wing) called vane is inserted, and the vane is pressed into a pump case by a spring.In addition, the entire pump is immersed in the oil tank to maintain the airtight (Fig. 4).
図4：回転翼形油回転ポンプの作動原理（引用：株式会社アルバック カタログより）When the cylinder in the pump rotates, the space between the two vanes is connected to the intake port, increasing the volume with the rotation, and the gas flows.When the cylinder rotates further, the gas is isolated and compressed in the next vane, and is discharged by connecting to the atmosphere.There is an oil membrane around the pump room and the vane, preventing the inhaled air from wearing it and at the same time.Usually, to reduce the reach of the reach, such a pump is used in a two -stage row.
Figure 5 is an example of a change in exhaust speed due to the pressure of an oil rotation pump.The exhaust speed at 1,000 PA or more is determined by the rotation speed of the pump and keeps it constant.However,……
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There are fluid operation type vacuum pumps and mechanical vacuum pumps for the type of vacuum pump of the exercise transport type.The fluid operation type vacuum pump uses jets such as water, water vapor, oil, and air, and exhausts the gas by pushing out gas.On the other hand, the mechanical vacuum pump pushes out gas by mechanically giving the amount of exercise.The fluid operation type vacuum pump used in the low and medium vacuum region is sometimes called an ejector or jet pump.
Figure 8 is a schematic diagram of a steam jet pump.0 at the drive steam entrance at the top of the pump.25-1.When 6MPa's pressurized water vapor is introduced, the steam expands when passing through the nozzle and reaches the spread of the diffuser.At this time, the amount of exercise when the steam expands has a negative pressure gradient on the tip of the diffuser, and the gas entering from the inlet is exhausted from the discharge mouth with the driven water vapor.
図8：蒸気ジェットポンプの構造(引用：株式会社大阪真空機器製作所カタログより)With such a jet pump, ...
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3rd: How to make high and ultra -high vacuum
前回は、低・中真空の作り方を説明しました。今回は、高真空・超高真空領域の特徴と真空ポンプを解説します。第1回で述べたように、10-1Pa以下の高真空・超高真空領域では、ガス分子の平均自由行程が長くなり、分子同士がほとんど衝突しない分子流領域になります。そのため、ガスの熱伝導や粘性が圧力の減少とともに低下します。この圧力領域は真空断熱などに用いられます。また、物質を高温で気化させて基板上に堆積させ薄膜を作ることや、表面の分析にも用いられます。
10-1～10-5Paを高真空、10-5Pa以下を超高真空といいます。10-9Pa以下を極高真空と呼ぶこともありますが、ほとんどの場合、第1回で説明したクヌーセン数Kn>10を満たすため、この圧力範囲では分子流領域になります。分子流領域では、真空容器の中のガス分子は、他の分子と衝突することなく容器の壁から反対の壁に到達します。ガスの熱伝導や粘性は、１秒間に壁に衝突するガス分子の数に比例し、ガスの圧力にも比例します。
Let's consider the number of gas molecules that actually collide with the wall.The number of gas molecules that collide with the unit area wall per second is called the frequency of incidence.In the case of air at 20 ° C, the frequency of incidence is γ = 1 as P (PA)..0×1018p(個･cm-2･s-1)です。ほとんどの物質では、表面の原子は1cm2当たり1014個程度なので、壁に衝突したガス分子が全て表面にとどまるとすると、圧力がp≈10-4Paでは1秒程度で表面を覆い尽くすことになります。つまり、……
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Here are some vacuum pumps often used in high and ultra -high vacuum.Figure 2 is an outline of the turbo molecular pump.The turbo molecular pump has a structure in which the motion wings rotating around the ally and the fixed wings are alternately lined up.It is called a turbo molecular pump because it resembles the turbine wing of the turbo jet engine.The motion wings rotate at high speed at 18,000 to 90,000 times per minute, and the line speed of the wing reaches several hundred m/s, which is close to the gas molecule.
図2：ターボ分子ポンプ（引用：日本真空協会関西支部編、わかりやすい真空技術（第2版）、1998年、P.101）The figure is a schematic diagram of the exhaust principle of the turbo molecular pump of the motion wing and the static wing. The gas molecule (red circle) entering from the top of the figure collides to the lower surface of the motion wing with a left -handed line speed. The pump wings have unevenness when viewed in the micro, and the molecules that collide with the surface of the motion wing stay on the surface for a while, so the collision gas molecules jump out in a random direction regardless of the flying direction. 。 At this time, the blue part is wider than the red part of the figure, so the gas molecules that collide with the motion wing flow down as a whole. The gas molecule that pops out of the motion wing has the speed of the heat movement (red arrow in the figure) and the left -hand speed of the motion wing (the blue dotted arrow in the figure), so only on the lower surface of the wing. It collides. At this time, the molecules are also flowing further because the lower side is wide. The general turbo molecular pump combines about 10 steps of such dynamic wings. Due to such an exhaust principle, the turbo molecular pump operates as a vacuum pump, the wing line speed must be the same as the gas molecule speed. if,……
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In high and ultra -high vacuum, gas -entangled vacuum pumps are often used.Here, we will introduce the Cryio Pump, which is a representative gas pump.The crio pump is a vacuum pump that uses a helium frozen machine to cool the adsorbent such as activated carbon with a large surface area, captures gas on the surface of the adsorption material and exhausts it.The freezer creates a high -pressure helium gas with a compressor of about 20 atm, and the piston called a cold storage agent is cooled to make a low temperature by inflating the heat insulation.
Figure 6 is the appearance of the clio pump.Figure 7 schematically shows the inside of the pump.In most of the clio pumps, the helium frozen machine is two steps, and the first stage is about 80k.This stage covers the inside of the pump and absorbs heat inflow from outside the pump.Also, in the intake port, ...
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4th: How to measure vacuum
Last time, I explained the characteristics of the high and super high vacuum regions and vacuum pumps.This time, I will explain the pressure measurement in the vacuum container.Even if the container is exhausted with a vacuum pump, I do not know how much gas remains.Therefore, pressure measurement in the vacuum container is required.An instrument that measures the pressure of vacuum is called a vacuum meter.Vacalms include a vacuum meter that measures the pressure based on the machine phenomenon, a vacuum meter that uses transportation phenomena such as thermal conductors, and a vacuum meter that uses the ionization phenomenon.
A vacuum meter is a device that measures the pressure of the thin gas, and is sometimes called a vacuum gauge.The general pressure gauge shows the pressure difference from the atmospheric pressure based on the atmospheric pressure.This is called a gauge pressure, which is called a positive pressure, and the following is a negative pressure (Fig. 1).On the other hand, the pressure gauge handled in vacuum engineering displays pressure with no gas at all.This is called absolute pressure.The vacuum meter displays absolute pressure below the atmospheric pressure.
図1：絶対圧とゲージ圧As described in the first time, pressure is the force per area, and if you measure the force, you can see the pressure inside the vacuum container.However, low pressure reduces the change in power, and there is a limit to seeking pressure from measurement of force.Therefore, in addition to the measurement of the force, a vacuum meter that measures gas thermal conduction and viscosity and converts it to pressure, and a vacuum meter that is ionized gas, that is, ionties, and measuring ions as current, and converted to pressure.increase.Table 1 is the main vacuum meter and the pressure range used.The vacuum meter is classified into three types: vacuum meters based on gas machine phenomena, vacuum fuzzing using gas transportation phenomena, and vacuum metals using gas ionization.
表1：主な真空計と使用圧力範囲A vacuum meter based on the gas machine phenomenon, that is, a vacuum meter that directly measures pressure as a force ...
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Vacals that use the gas transport phenomenon include Pirani's vacuum, a thermal electric fabric, and a crystal friction.Here are three things.
Pirani's vacuum meter is a vacuum that uses the fact that gas thermal conductors depend on pressure.Figure 4 is the measurement principle of Pirani's vacuum.Inside the sensor, thin metal wires such as platinum, tungsten, nickel, etc. are stretched, and current flows from the outside via the current terminal.The wire generates heat due to the joule heat that occurs at this time.Since the electrical resistance of metal is proportional to the absolute temperature, adjusting the current so that the wire electrical resistance is constant will always be constant the temperature of the wire.The fever of the wire is ...
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When it comes to high and ultra -high vacuum, it becomes difficult to measure pressure using gas transportation phenomena, reducing thermal conduction and viscosity.Therefore, a vacuum meter is used to ionize the gas molecules, that is, to measure ions as an ions.Cool cathode ionization vacuum meter is a vacuum meter that ionizes gas using vacuum discharge.In addition, a vacuum meter is a vacuum meter that ionizes gas using electrons released from heated filament.Vacals using gas ionization include a pabled -true meter, a triple tube -type ionization vacuum, and a beyardo -alpart vacuum.I will explain these three.
Peninging vacuum meters are a vacuum meter that uses the discharge phenomenon in vacuum and measuring pressure in the medium to high vacuum regions, and is a kind of cold cathedic ionization.Cool cathode ionization vacuum meters are sometimes called cold cathode gauge.This vacuum meter uses the fact that the current of the high -voltage discharge is proportional to the pressure in the container.For discharge, the pening discharge using a permanent magnet is used (Fig. 7).Unlike the enthusiastic ionucometer described later, there are no high -temperature parts such as filaments, and there is little risk of failing even if the atmosphere is introduced during operation, so it is often used for vacuum devices that are frequently introduced.on the other hand,……
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5th: Vacuum materials and parts
Last time, I explained how to measure the vacuum.This time, I will explain the materials that can be used in vacuum.In order to reduce the achievement pressure, it is important to reduce gas generated from vacuum containers and parts in the container.In addition, vacuum containers and pipes have connections such as flange, so it is necessary to seal so that gas does not leak from the atmosphere.It is necessary to reduce gas release and transparency from such a seal.I will explain how to find leaks such as vacuum containers and how to deal with them.
真空容器や真空内で用いる部品は、機械強度などの特性を吟味することはもちろん、真空環境に置いた時にガスを放出しないことが求められます。真空容器の中で発生するガスは二通りあります。一つは、容器や容器内に使用されている部品などの材料中や、材料表面から発生するガスです。もう一つは、容器や配管などの接続部分のガスケットから透過したものです（図1）。ガスの発生量は、ガスの圧力(p)×体積(V)で表すことができ、pV値と呼びます。毎秒当たりのpV値を流量といい、Pa･m3･s-1またはPa･L･s-1で表します。真空容器内に流入するガスの流量Qが小さいほど到達圧力が下がることになります。到達圧力とは、容器内のガスの発生量と真空ポンプの排気量が釣り合って到達できる最低圧力です。式で表すと、真空容器を排気速度Sの真空ポンプで排気した場合、到達圧力はp=Q/Sになります。
図1：真空容器からの脱ガス以上のことから、到達圧力によって、どの程度ガスの発生量を考慮しなければいけないのかを考えてみましょう。例えば、食品の保存に使う真空パックなどの低真空ならば、ガスの発生量が多い安価なプラスチックを用いても問題になりません。むしろ、大気圧との差による1kgw･cm-2の力に耐える強度があるかが重要になってきます。一方、……
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Elastoma is a generic term for highly elasticity, such as rubber, and other polymer materials. The elastomer used in vacuum technology has a rubber gasket used for vacuum sealing, such as a vacuum window or a piping flange connection. A vacuum gasket is often called an O -ring because the cross -section is often circular and ring -shaped. The shape of the O-ring is specified in JIS B2401-1 O-ring-Part 1: O-ring. Those that are relatively commonly used related to vacuum are exercise O -rings (P), fixing O -rings (g), and vacuum flange O -rings (V). The material is generally called the old JIS, and there are from the first to the fourth type. Among them, the first and fourth types are used for vacuum. Table 1 is the main elastoma and its characteristics used in vacuum technology. Typical materials of the O -ring include nitrile rubber (NBR), chloroprene (CR), silicone rubber (VMQ), and fluorine rubber (FKM).
表1：主なOリングの材質と識別記号材質と識別記号(引用：真空技術基礎講習会運営委員会編、わかりやすい真空術(第3版)、日刊工業新聞社、2010年、P.228)| 材質 | 代表的な商品名 | 識別記号(旧JIS) | 特徴 |
|---|---|---|---|
| ニトリルゴム(NBR) | ブナN | 第1種A、第1種B | 使用温度範囲:-25-110°Cガス透過係数が比較的小さい酸・ケトン類に弱い |
| クロロプレン(CR) | ネオプレン | – | 使用温度範囲:-30~110°Cガス透過係数が比較的小さい酸・ケトン類に弱い |
| シリコーンゴム(VMQ) | シラスティック | 第4種C | 使用温度範囲:-100~230°Cガス透過係数が大きい酸・ケトン類に弱い |
| フッ素ゴム(FKM) | バイトン | 第4種D | 使用温度範囲:-20~200°Cヘリウム透過係数がやや大きいアルカリ・ケトン類に弱い |
What is nitrile rubber (NBR)?
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The difference between transparency and leak is that the gas passes through the material, and is a leak when passing through the gap between the materials.The size of the gas transparency and leak (leak) are both represented by the flow rate.Ideally, there is no leak in a vacuum device.However, there is almost always a leak, such as joints such as welding and flange stickers.
リークの大きさは、必要とする到達圧力と密接に関係があります。一般的に、必要な到達圧力と真空ポンプの排気速度から許容リーク量を設定します。図3は、許容リーク量の分類を表します。リークが10-10~10-7の場合はガスの透過、10-7~10-4の場合はガス漏れ、10-4~10-1の場合は水漏れです。ガスの透過とガス漏れの大半はファインリーク、ガス漏れの一部と水漏れはグロスリークの範囲になります。
図3：許容リーク量(引用：真空技術基礎講習会運営委員会編、わかりやすい真空技術(第3版)、日刊工業新聞社、2010年、P.155)Finding a leak is called a leak test.Then how do you ...
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6th: Handling and maintenance of vacuum equipment
Last time, I explained the vacuum materials and parts.This time, the final round.I will explain how to handle vacuum equipment.In addition, from the design and manufacturing of the device and the perspective of the user, we will talk about the precautions for handling vacuum equipment safely.We will also describe the concept of maintenance of equipment that is indispensable for using vacuum devices and the inspection of inspections.Finally, we will also introduce the technical trends for environmental conservation, which are currently undergoing urgent issues.
What should I pay attention to when handling vacuum equipment?It is also important to minimize the release gas in the vacuum, maintain the flange and seal so that there is no dirt or scratches, and to notice the daily changes in vacuum equipment.
How can vacuum exhaust be faster to the necessary pressure areas?It is not economical to use a vacuum pump with a large exhaust speed.As described in the 5th, it is important to reduce the release gas as much as possible to reduce the pressure quickly.Therefore, in handling vacuum devices, it is a rule of thumb that the container does not bring something that is the source of gas release.
When used with pressure below the middle vacuum, the parts to be inserted into the vacuum container are well dried in advance with an organic solvent or detergent.The tools used for assembly work are distinguished from other tools for vacuum, and are washed in advance to remove oil.Be careful of iron tools, as rust occurs when oil is gone.Also, when you touch the vacuum containers and parts used in vacuum with bare hands, ...
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First, we will talk about the basic concept of maintenance of vacuum equipment.Vacuum devices also have a failure as well as general machinery.The probability of failing within a certain period is called a failure rate.In many cases, the graph that indicates the time change of the failure rate after the introduction of the device is known to be a bathtub type (Fig. 2).This is because the initial failure that occurs immediately after the introduction decreases over time, and after a certain failure rate, the failure rate due to the deterioration of the device increases.
図2：故障率曲線The failure of the device is fatal for companies because it is directly linked to the suspension of production lines.So, in order to lower the failure rate as much as possible ...
Wash and remove the oil.Be careful of iron tools, as rust occurs when oil is gone.Also, when you touch the vacuum containers and parts used in vacuum with bare hands, ...
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Various efforts are being made to build a sustainable society in the future.One is the construction of a recycling -oriented society that minimizes the impact on the environment by circulating resources throughout society.In addition, there is a construction of a low -carbon society that suppresses carbon dioxide release into the atmosphere by consumption of fossil fuels.In addition, various initiatives are being implemented under administrative initiative.Companies also require environmentally friendly corporate activities as one of CSR (Corporate Social Responsitude).These are also called greening of society.
Among the vacuum technology explained so far, technology development that can contribute to these is underway.For example, a semiconductor manufacturing plant is said to have thousands of vacuum pumps operating and account for 12 to 14%of the power consumption of the entire factory.Dry pumps are mainly used, but energy -saving effects are created by controlling the motor of power by controlling the power motor, and the use of auxiliary pumps to reduce the number of units.Also, in the crio pump used in high vacuum, ...
Wash and remove the oil.Be careful of iron tools, as rust occurs when oil is gone.Also, when you touch the vacuum containers and parts used in vacuum with bare hands, ...
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