315 490 Experimental Methods in Physics An Introduction to Vacuum Technology

1. 315 490 Experimental Methods in Physics • An Introduction to Vacuum Technology • Dr. ThanusitBurinprakhon • Lecture 1-2: • 4. Vacuum Systems • 5. Vacuum pumps • Oil-sealed rotary pump • Diaphragm pump • Scroll pump • Oil diffusion pump • Turbo molecular pump

2. What makes up a vacuum system? • The object of vacuum technology is to generate a vacuum in a system, i.e. to reduce the number of gas particles in the system. • For a system of constant volume, at constant temperature this always corresponds to a reduction in gas pressure. • Essentially, a vacuum system consists of a chamber, generally called a vacuum chamber, connected to the pumping system via pipework. Connecting Tubing Vacuum Chamber Pumps Atmosphere Pvac Pressure Pout Patm Pvac Pin Regions Introduction to vacuum technology 4. Vacuum systems and pumps

3. Materials for vacuum systems Operating condition • Withstand a Pressure load of 1 bar (105 N/m2) in all direction. • Materials strength >= 1 bar + safety factor atmosphere Vacuum Pressure ~ 0 atmosphere atmosphere • Adequate yield strength and ultimate tensile strength • Adequate toughness and fatigue strength • Appropriate chemical and physical properties atmosphere Brass, Aluminum alloys, Mild steel, Stainless steel, Pirex glass Fundamental requirement Suitable material properties Introduction to vacuum technology 4. Vacuum systems and pumps

4. Vacuum chambers Pictures from Kurt J. Lesker Company “http://www.lesker.com/newweb/menu_chambers.cfm” Introduction to vacuum technology 4. Vacuum systems and pumps

5. Vacuum components • Vacuum flange types • KF/QF • ISO • CF http://en.wikipedia.org/wiki/Vacuum_flange Pictures from Kurt J. Lesker Company “http://www.lesker.com/newweb/menu_chambers.cfm” Introduction to vacuum technology 4. Vacuum systems and pumps

6. Vacuum pumps Pictures from Kurt J. Lesker Company “http://www.lesker.com/newweb/menu_chambers.cfm” Introduction to vacuum technology 4. Vacuum systems and pumps

7. Vacuum chamber Pressure gauge Pressure gauge Vacuum chamber V1 V1 Cold trap TMP Pressure gauge DP V3 Pressure gauge V3 V2 V2 Rotary pump Rotary pump Exhaust Exhaust (a) (b) Complete layout of vacuum system Introduction to vacuum technology 4. Vacuum systems and pumps

8. Examples of vacuum systems Introduction to vacuum technology 4. Vacuum systems and pumps

9. Types of Vacuum pumps (a) Gas transfer pumps • Positive displacement • Rotary vane pump • Diaphragm pump • Sroll pump Generate low to medium vacuum Remove Inlet compress Pump • Kinetic • Diffusion Pump • Turbo molecular pump • Molecular drag pump Outlet Generate high to ultra-high vacuum exhaust Introduction to vacuum technology 5. Vacuum pumps 9

10. Types of Vacuum pumps (b) Gas capture pumps • Titanium sublimation pump • Sputter-ion pumps (SIP) • Cryogenic Pumps Inlet Remove Pump trap For clean ultra-high vacuum Introduction to vacuum technology 5. Vacuum pumps 10

11. Pump Selection • The suitable pump, e.g. type and size, for a vacuum system is determined from the working/base pressure required and the quantity of gas to be pumped. • Each of the various types of vacuum pumps has a characteristic working pressure range in which it has a high efficiency. Introduction to vacuum technology 5. Vacuum pumps

12. Pump Selection Liquid Cryogenic pump Sputter Ion Pump (SIP) Turbo molecular pump backed by two stage rotary vane Oil diffusion pump & cold trap backed by rotary vane Roots Sorption Two stage rotary Single stage rotary 10-13 10-11 10-9 10-7 10-5 10-3 10-1 101 103 Pressure (mbar) Introduction to vacuum technology 5. Vacuum pumps

13. Oil-Sealed Rotary pump Pictures from Kurt J. Lesker Company http://www.lesker.com/newweb/Vacuum_Pumps Introduction to vacuum technology 5. Vacuum pumps

14. Oil-Sealed Rotary pump • Two basics designs of oil-sealed rotary pumps: • Rotary vane and • Rotary piston pumps Introduction to vacuum technology 5. Vacuum pumps

15. Oil-Sealed Rotary pump: • Gas removal mechanism Introduction to vacuum technology 5. Vacuum pumps

16. Oil-Sealed Rotary pump: • Function of oil in oil-sealed rotary pumps: • Lubrication of bearings and sliding surfaces. • form a vacuum seal between the vane and the pump chamber. • Heat transfer from the pump chamber to the outer walls of the pump. • Gas removal mechanism. • Operating pressure range: • Single stage: 103-5x10-3 mbar • Two-stage: 103-5x10-4 mbar • Applications: • Furnaces • coating systems • laser applications • backing for UHV pumps • Advantages • good reliability • low cost operation • Disadvantages • Oil contamination • Oil degradation Introduction to vacuum technology 5. Vacuum pumps

17. Diaphragm pump • Working principle: • A flexible metal or polymeric diaphragm seals a small volume at one end. • At the other end are two spring-loaded valves, one opening when the volume's pressure falls below the "outside" pressure, the other opening when the volume's pressure exceeds the "outside" pressure. • A cam on a motor shaft rapidly flexes the diaphragm, causing gas transfer in one valve and out the other. Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

18. Diaphragm pump • Characteristics: • low pumping speeds (<10 cfm) • a poor ultimate vacuum (1 Torr to 10 Torr). • use two stages in series—to produce a lower vacuum • use two stages in parallel —to increase pumping speed • Low cost • Exhaust to atmosphere • Applications: • roughing pumps • vacuum filtration • thin film evaporation • Distillation • gel drying applications Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

19. Scroll pump • Working principle • Two open spiral metal strips are nested together. One spiral is fixed while the other "orbits"—its center point describes a small circle but the spiral does not rotate. • As the moving spiral orbits, it touches the stationary spiral at everchanging positions. The shape of the spirals means at one orbital point there is an open (crescent-shaped) volume connected to the inlet. • A little later in the orbit, the connection with the inlet closes, trapping a volume of gas. • Continuing the orbit causes this volume to decrease, compressing the gas until it reaches a minimum volume and maximum pressure at the spirals' center, where the outlet is located. In this orbital position, the inlet is again connected to the large open volume. Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

20. Scroll pump • Characteristics: • two nested spiral stages are mounted in series • producing an ultimate vacuum in the 10-2Torr range • pumping speed of roughly 12–25 cfm • exhausting at atmospheric pressure • suitable temperature range of 5–40º C • Applications: • clean, dry processes • dry backing pumps for high vacuum pumps Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

21. Diffusion pump Inlet • Working principle: • boiling a low vapor pressure, high molecular weight, nonreactive fluid • forcing a dense vapor stream up a central column and out as a conical vapor curtain, through jets that are angled downward • Gas molecules from the chamber randomly enter the curtain and are pushed toward the boiler by momentum transfer from the fluid molecules • When the vapor curtain reaches the cold wall, the temperature change of perhaps 200–250º C immediately returns it to liquid form at a low vapor pressure. Outlet Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

22. Diffusion pump • Advantages • ultimate vacuums in the 10-4 -10-7Torr, depending on size • pumping speeds range from perhaps 30 L/s to 50,000 L/s • low cost • vibration- and noise-free • Disadvantages • Back_stream oil vapor • Special oil is required for UHV Expensive) • Need a backing pump Leybold: DIP1200 • Applications • molecular beam systems • large scale vacuum furnace processing • space simulation chambers Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps

23. Turbo molecular pump • Working principle: • Resembles jet engines. • Consists of a stack of rotors, each having multiple, angled blades, rotate at very high speeds between a stack of stators. • Gas molecules randomly entering the mechanism and colliding with the underside of the spinning rotor blade are given momentum toward the pump's exhaust. • The compression ratio for N2 across the pump may exceed 108. That is, if the partial pressure in the foreline is 10-4Torr, the chamber partial pressure may be 10-12Torr, 108 times lower. Picture from: http://www.google.co.th/imglanding Introduction to vacuum technology 5. Vacuum pumps

24. Turbo molecular pump • Applications • all vacuum applications between 10-4 and 10-10Torr • replacing diffusion pumps • Characteristics: • ultimate vacuum of most turbos lies between 10-7Torr and 10-10Torr • pumping speeds range from 50 L/s to 3,500 L/s • a turbo with magnetically levitated bearings gives true dry option Source: Kurt J. Lesker Company http://www.lesker.com/ Picture from: http://en.wikipedia.org/wiki /File:Axial_compressor.gif Introduction to vacuum technology 5. Vacuum pumps

25. Turbo molecular pump • Advantages: • highly regarded as clean pumps • enables rapid cycle times • Pumping speed is independence of gas • Disadvantages: • A backing pump with a separate roughing line is usually unnecessary. • not suitable for dusty processes or those for which small high frequency vibration might be a problem • Low compression ratio for light gas • High cost per unit capacity • Bearing maintenance • Precaution: • Over-heating of the blades may occur if pressure at pump inlet is higher than 10-2 mbar Source: Kurt J. Lesker Company http://www.lesker.com/ Introduction to vacuum technology 5. Vacuum pumps