1, the definition of the vacuum Vacuum system refers to the state of thin book gas below the atmospheric pressure in the area 2. Vacuum The degree of gas scarcity in vacuum is usually expressed by "high vacuum" and "low vacuum". High vacuum means vacuum "good", low vacuum means vacuum "poor". 3, the vacuum degree unit Usually use (Torr) as the unit, in recent years the international use (Pa) as the unit. 1 carrier =1 / 760 atmosphere =1 mmHg 4. Conversion of tuo and Pa 1 Tuo = 133.32 Pa or 1 Pa =7.510-3support from under 5, the average free course The mean distance of the gas particle, flown in two successive collisions, is expressed by the symbol "λ". 6.Flow The amount of gas flowing through any section per time, marked by "Q" in Pa · liter / second (Pa · L/s) or Tuo · liter / second (Torr · L/s). 7.Flow guide Represents the ability of the vacuum tube to pass through the gas. In liter / second (L/s), where the pipeline flow guide is equal to the pipeline flow rate divided by the pressure difference between the two ends of the pipe. The symbol is "U".U＝Q/(P2- P1) 8. Pressure or pressure The force of the gas molecule acting on the unit area of the vessel wall is indicated by the "P". 9, Standard atmospheric pressure The pressure is the pressure of 101325 per cm 2, symbol: (Atm). 10, * limit vacuum After the vacuum vessel is fully pumped, it is stabilized at a certain vacuum degree, which is called * limit vacuum. Usually, the vacuum vessel must be 12 hours of gas refining and then vacuum for 12 hours. * One hour is measured every 10 minutes, and the average value of 10 times is taken as * limit vacuum value. 11. Pump the gas rate At a certain pressure and temperature, the gas pumped away by the pump inlet per unit time is called the pumping rate, hereinafter referred to as the pumping speed.approach Sp＝Q/（P－P0） 12, Hot even vacuum meter The vacuum meter measures the vacuum degree by using that the potential of the thermocouple is related to the temperature of the heating element, and the temperature of the element is related to the thermal conduction of the gas. 13, ionizing vacuum meter (and heat Yin * ionization meter) Made of cylindrical collection *, grid and a filament located in the center of the grid, cylindrical collection * outside the grid. Hot Yin * emits electrons to ionize the gas molecules, the ions are collected * collected, and the vacuum gauge measures the gas pressure according to the size of the collected ion-flow. 14, the composite vacuum meter It consists of a hot couple vacuum meter and a hot Yin * ionizing vacuum meter, measuring from the atmosphere ~10-5Pa。 15, cold Yin * ionization meter There are a pair of Yin plates at both ends of the Yang cylinder. Under the action of external magnetic field, the panning discharge is formed to produce ions. According to the size of the ion flow collected by the Yang plate. 16. Resistance vacuum meter (Pirani vacuum meter) A vacuum meter in which the resistance of the heating element is related to the temperature, and the temperature of the element is related to the gas conduction is measured through a bridge circuit. 17. McCraw vacuum meter (compressed vacuum meter) The gas to be measured is compressed with mercury (or oil) into a small volume, and then the liquid column difference between the open tube and the closed tube is compared, and a vacuum gauge is directly calculated directly by using Boyle's law. 18, and the gauge B-A This is a Yin * with collecting * inverted hot Yin * ionization gauge. Collection * is a filament, placed in the center of the grid, with the filament placed outside of the grid, thus reducing the impact of soft X-rays, extending the lower measurement limit, and measuring ultra-high vacuum. 19. Water ring vacuum pump The impeller rotor of the pump rotates the water ring. A mechanical vacuum pump that periodically changes the volume between the water ring and the blade due to the eccentric rotation of the rotor. 20, reciprocating vacuum pump A mechanical vacuum pump pumping using the reciprocating movement of the piston. 21, oil seal mechanical vacuum pump The mechanical vacuum pump that uses oil to maintain the seal can be divided into fixed plate type, rotary plate type, sliding valve type, residual cycloid line type, etc. 22, the Roots vacuum pump Mechanical vacuum pump with a pair of synchronous high-speed rotating sole rotor, this pump can not be pumped separately, the front stage should be equipped with oil seal, water ring and other vacuum pump can be discharged straight into the atmosphere. 23, the turbomolecular vacuum pump There is a high-speed rotating impeller, when the gas molecules collide with the high-speed rotating turbine blade is driven to the outlet and then removed by the front pump. 24.Oil diffusion vacuum pump High-speed steam flow is ejected from the diffusion pump nozzle. Under the condition of molecular flow, the gas molecules continuously diffuse into the vapor flow, and are compressed by the steam belt to the pump outlet and then excluded by the front pump. 25, low-temperature vacuum pump A vacuum pump below 20K. 26. Cold trap (water-cold baffle) Set between a vacuum vessel and pump for gas or oil vapor. 27.Gas town valve Oil seal mechanical vacuum pump in the compression chamber, and install the regulating valve, when open the valve and adjust the gas, the rotor to a certain position, the air through the hole into the compression chamber to reduce the compression ratio, so that most of the steam condensation and mixed with the gas is excluded from the pump of the valve is called gas valve. 28, vacuum freeze-drying Vacuum freeze-drying, also known as sublimation-drying. The principle is to freeze the material to turn the water into ice, and then sublimate the ice under a vacuum to dry it out. 29, vacuum evaporation In a vacuum environment, the material is heated and plated on the substrate is called vacuum evaporation, or vacuum coating. 30, vacuum drying The method of drying articles by using the characteristic of low boiling point in a vacuum environment. 31. Common name of the vacuum system (1) Main pump: in the vacuum system, the vacuum pump is used to obtain the required vacuum degree to meet the requirements of the specific process, such as the oil diffusion pump in the vacuum coating machine is the main pump. (2) Front pump: a vacuum pump used to maintain the front pressure of a vacuum pump that is lower than its critical front pressure. Such as the rots pump front configuration of the rotary plate or slide valve pump is the front pump. (3) Crude pumping pump: pump air from atmospheric pressure and pump the system pressure to another vacuum pump. Such as the vacuum coating machine in the sliding valve pump, is the crude oil pump. (4) Maintenance pump: in the vacuum system, the gas volume is very small, can not effectively use the front pump. For this purpose, a less capacity auxiliary pump is configured to maintain the main pump, which is called maintenance pump. Such as the diffusion pump outlet with a small rotary plate pump, is to maintain the pump.

1, Boyle's law  Volume V, pressure strength P, P · V= constant A certain mass of gas, when the temperature is constant, the pressure of the gas is inversely proportional to the volume of the gas. approach P1/P2＝V2/V1 2. Guy Lusac's Law When the pressure P is constant, the volume V of a gas of a certain mass is proportional to the * temperature of T:  V1/V2＝T1/T2= constant When the pressure is unchanged, the temperature of a certain mass of gas increases 1℃ (or P decreases), then its volume increases (or decreases 1 /) 273. 3. Charlie's Law When the volume V of the gas remains unchanged, the pressure P is proportional to the temperature T, namely:  P1/P2＝T1/T2 In a certain volume, a certain mass of gas, each temperature increases (or decreases) 1℃, its pressure increases (or decreases) 1 / 273. 4. Average free path: λ = (510-3)/P (cm) 5. Draw speed: S=dv/dt(L / sec) or S=Q / P Q= Flow (lift · l / s) P= Pressure (lift) V= volume (l) t= time (seconds) 6. Guide: C=Q / (P2-P1) (L / s) 7. Vacuum extraction time: for the extraction time from atmospheric pressure to 1 pressure: t=8V / S (empirical formula) V is the volume and S is the pumping rate, and t is usually chosen within 5 to 10 min. 8. Maintenance pump selection: Stie up＝Sfront/10 9. Estimation of the diffusion pump pumping rate: S=3D2(D= diameter cm) 10. Front pumping speed of Roots pump: S= (0.1~0.2) Sa net for catching birds(l/s) 11. Leak rate: Qleak＝V(P2-P1)/(t2-t1) Qleak-System leakage rate (mmHg · l / s) V-System Volume (l) P1-System medium pressure (mmHg) at vacuum pump stops P2-Pressure achieved in the vacuum chamber after time t (mmHg) The t-pressure from P1Up to P2Exapsed Time (s) 12. Selection of crude pump pumping speed: S=Q1/Pin advance(l/s)     S=2.3V·lg(Pa/Pin advance)/t S-Effective pumping rate of the mechanical pump Q1-Air leakage rate of vacuum system (liter / s) Pin advance-Pre-vacuum to be achieved (support) V-Vacuum system volume (L) t-achieve Pin advanceThe time required Pa-Atmospheric pressure value (support) 13. Front-stage pump pumping speed selection: The transmission pump with exhaust port pressure lower than one atmospheric pressure, such as diffusion pump, oil booster pump, Roots pump, turbine molecular pump, etc., requires the front pump to maintain its front pressure below the critical value. The selected front pump must be able to discharge the * * gas volume of the main pump. According to the pipeline, the constant flow principle of each section is as follows: PnSg≥PgS perhaps Sg≥Pgs/Pn Sg-Effective pumping rate of the front-stage pump (l / s) Pn-Main pump critical front pressure (* * exhaust pressure) (l / s) Pg-Vacuum chamber * high working pressure (support) The S-Main pump is working at the PgEffective pumping speed at.(l/s) 14. Calculation formula of diffusion pump pumping speed: S=Q / P= (K · n) / (P · t) (l / s) Where: S-The extraction rate of the tested pump (l / s) N-Upgrade on the oil column (grid) Time (seconds) P-Pressure measured near pump port (support) K-Dropper coefficient (· l / s) K＝V0·(L/n)·(Υ0/Υm)+Pa△Vt among V0-Original volume of dropper and vacuum hose (l) L-Length of the dropper scale section (mm) Number of cells of the n-dropper scale part (cells) Υ0-Specific gravity of the oil (g / cm3) Υm-The specific gravity of mercury (g / cm3) Pa-Local atmospheric pressure (support) △Vt-Corresponding volume on the scale of the dropper (l / case) 15. The geometric extraction speed calculation formula of rotary wafer vacuum pump: S= π ZnLKv(D2-d2)/(24×104) (l/s) Where Z is the number of wafers, n is the speed (rpm), L is the pump chamber length, D is the pump chamber diameter, d is the rotor diameter (cm), KvIs the volume utilization coefficient (generally take 95%). 16, O-type rubber groove depth of B=0.7D D is the rubber diameter, groove width C=1.6B 17, square rubber groove depth of B=0.8A A is the square rubber side length, and the groove width is C=1.67B

   

Definition of vacuum A pressure state lower than atmospheric pressure is called a "vacuum" or a "negative pressure".  The force generated by the vacuum The force generated by vacuum is the adsorption force, which is the area (pressure area of the vacuum pressure between the differential pressure and the vacuum pressure. The product of the adsorption area). Therefore, the maximum vacuum adsorption force will not exceed the force of atmospheric pressure. Changes in the atmospheric pressure can also cause changes in the adsorption force. Vacuum system composition  Vacuum system is a combination of components composed of a vacuum generator or vacuum pump, vacuum suction cup, vacuum pressure switch, vacuum filter, vacuum safety valve, etc. Vacuum system has the following characteristics: ·  The structure of the vacuum adsorption mechanism is simple. ·  The suction position does not require precise positioning. ·  Suitable for workpieces with surface smoothing or curved surfaces. ·  When absorbing the workpiece, the surrounding foreign bodies will be inhaled, so it is necessary to set the filter. ·  To obtain a large suction force, a larger adsorption area is needed. ·  Vacuum suction cup is more rubber material, easy to aging wear.   Vacuum supply valve: supply compressed air to the vacuum generator to control the disconnection of the vacuum. Vacuum failure valve: in order to quickly let the workpiece after the vacuum suction, control the breaking of the vacuum failure air.throttle valve: control the damage flow rate when the workpiece is detached to control the detachment time and prevent the workpiece from being blown away. Vacuum filter: prevent the dust around the suction cup and causing the failure of the stop valve, vacuum generator and sensor. Public number "mechanical engineering wencui", the engineer's gas station! Vacuum pressure switch: in the vacuum suction, when reaching the fixed vacuum pressure to get the signal, as the starting point of the cylinder and whether the suction is confirmed. Two typical gas paths of vacuum system composed by vacuum generator. Vacuum pressure regulating valve: to prevent the pulsation of the vacuum source and control the set vacuum pressure. Vacuum switching valve: controls the switch to supply the vacuum from the vacuum pump. Vacuum generator or vacuum pump with multiple suction cups problem  Ideally, a vacuum generator with a suction cup, or a vacuum tube with a suction cup. For a vacuum generator or vacuum pump has multiple suction cups, when one workpiece falls off, the vacuum pressure drops and other workpieces will fall off. The following countermeasures can be taken: ·  Use a throttle valve to reduce the suction and unsuction vacuum pressure changes. · Each suction cup is equipped with a vacuum switch valve, which can be switched to prevent the impact of other suction cups. ·  The vacuum pump system can also use the vacuum tank and the vacuum pressure reducing valve to stabilize the vacuum pressure · The vacuum safety valve is used to limit the vacuum drop, so that the vacuum of other suction cups is not affected.  Other points of attention for the vacuum system ·  As a power failure countermeasure, the supply valve should be open-open or with self-maintenance function. ·  The suction and handling of workpieces can be confirmed by vacuum pressure switch. When absorbing heavy objects and dangerous goods, the visual confirmation should be carried out by vacuum table. ·  In a harsh environment, a vacuum filter should be installed before the pressure switch, but the hole of the filter is blocked, which will affect the pressure difference between the suction part and the vacuum generator, resulting in the real suction judgment error, this must be paid attention to. · Compared with the positive pressure with a higher pressure, the vacuum pressure is more likely to be affected by the piping resistance. In particular, the vacuum arrival time is greatly affected by the inner diameter and length of the pipe, so the small volume is selected as far as possible.