VACUUM SEALING TECHNIQUES BY A. ROTH II Senior Engineer, Israel Atomic Energy Commission PERGAMON PRESS OXFORD • LONDON • EDINBURGH • NEW YORK TORONTO • SYDNEY • PARIS • BRAUNSCHWEIG Pergamon Press Ltd., Headington Hill Hall, Oxford 4 & 5 Fitzroy Square, London W.l Pergamon Press (Scotland) Ltd., 2 & 3 Teviot Place, Edinburgh 1 Pergamon Press Inc., 44-01 21st Street, Long Island City, New York 11101 Pergamon of Canada, Ltd., 6 Adelaide Street East, Toronto, Ontario Pergamon Press (Aust.) Pty. Ltd., 20-22 Margaret Street, Sydney, N.S.W. Pergamon Press S.A.R.L., 24 rue des Ecoles, Paris Se Vieweg & Sohn GmbH, Burgplatz 1, Braunschweig Copyright @ 1966 Pergamon Press Ltd. First edition 1966 Library of Congress Catalog Card No. 66-17811 2558;66 CONTENTS PREFACE xiii CHAPTER 1. THE VACUUM AND SURROUNDING SPACE 1.1 The vacuum 1 11.1 Pressure and mean free path 1 11.2 Low, high and ultra-high vacuum 2 11.3 Vacuum systems 3 1.2 Interaction between the surrounding space and the vacuum 5 12.1 Gas flow, throughput and impedance 5 12.2 Gas permeation 6 1.3 Real and virtual leaks 7 13.1 Real leaks and tightness 8 13.2 Virtual leaks and degassing 9 13.3 Leak detection 9 13.31 Pressure rise method 9 13.32 Test gas methods 11 1.4 The seals and their classifications 11 14.1 Vacuum tightness, the essential requirement 12 14.2 Functional requirements 13 14.21 Electric current transmission 13 14.22 Motion transmission 13 14.23 Material transfer 13 14.24 Radiant energy transmission 18 14.3 Special requirements 18 14.31 Bakeability for ultra-high vacuum 18 14.32 Low temperature (cryogenic) seals 19 14.33 Corrosion resistance 21 14.34 Cost requirements 22 CHAPTER 2. PERMANENT SEALS 2.1 Prefabricated vessels and pipes 23 21.1 Selection criteria for vessels and pipes 23 21.11 Mechanical strength 23 21.12 Permeability to gases 27 21.13 Degassing 34 21.2 Metal vessels and pipes 43 21.3 Glass (quartz) vessels and pipes 46 21.4 Elastomer and plastic pipes 52 2.2 Metal to metal welding and brazing 57 22.1 Welding 57 22.11 Welding methods 58 22.12 Weldability of metals and alloys 67 v Vl CONTENTS 22.2 Brazing 70 22.21 Brazing methods 71 22.22 Brazing materials 73 22.3 Vacuum sealing by welding and brazing 83 22.31 Cleaning of the metal surfaces 83 22.32 Welded seals 88 22.33 Brazed seals 93 2.3 Glass to glass (and quartz) seals 101 23.1 Sealing principles 101 23.11 Viscosity and softening points 101 23.12 Expansion matching 107 23.13 Annealing 112 23.2 Working procedures for glass and quartz 116 23.21 Cleaning of glass 116 23.22 Cutting methods for glass 119 23.23 Heating methods for glass-glass sealing 121 23.3 Glass to glass (and quartz) sealing techniques 126 23.31 Butt seals 128 23.32 Side seals 130 23.33 End seals 131 23.34 Ring seals 131 23.35 Graded seals 131 2.4 Glass to metal seals 134 24.1 Sealing principles 134 24.11 Glass-metal bond 135 24.12 Expansion matching 138 24.13 Control of the cooling; annealing 142 24.14 The shape of the seal 143 24.2 Heating and working techniques 151 24.21 Steps taken in completing glass-metal seals 151 24.22 Heating methods used in glass-metal sealing processes 152 24.3 Matched seals 154 24.31 Matched glass-metal seals with soft glasses 154 a) Platinum seals 154 b) Iron-nickel alloy seals 156 c) Iron-chromium alloy seals 156 d) Iron-nickel-chromium alloy seals 157 e) Nickel seals 157 f) Iron seals 162 g) Copper seals 162 h) Titanium seals 162 24.32 Matched glass-metal seals with hard glasses 162 a) Tungsten seals 162 b) Molybdenum seals 166 c) Iron-nickel-cobalt alloy seals 167 d) Zirconium seals 169 24.4 Unmatched seals 169 24.41 Housekeeper seals 170 24.42 Quartz to metal seals 181 24.43 Glass-metal compression seals 185 CONTENTS Vii 24.5 Faults in glass-glass, and glass-metal seals and their detection 189 2.5 Cerumic to glass and ceramic to metal seals 197 25.1 Sealing principles and materials 197 25.11 Sealing principles 197 25.12 Materials used in ceramic-metal seals 200 25.2 Sealing techniques 201 25.21 Ceramic-glass and ceramic-glass-metal seals 201 a) Glass-ceramic seals 201 b) Ceramic-glaze-metal seals 203 c) Ceramic-glass-metal seals 205 25.22 Ceramic-metal sintered seals 208 25.23 Active metal processes 211 a) Hydride process 212 b) Active metal powders 213 c) Carbide seals 214 d) Active metal core seals 214 e) Massive active metal seals 215 f) Active metal alloy seals 215 25.24 Compression (diffusion) seals 216 25.25 Various ceramic-metal seals 218 25.3 Possibility of brazing ceramic-metal seals 220 25.4 Ceramic-metal seal shapes 222 25.41 Butt seals 222 25.42 Cylindrical seals 222 25.5 Testing of glass-ceramic and ceramic-metal seals 224 2.6 Sealing and sealing-off 225 26.1 Sealing vacuum devices 225 26.11 Drop sealing 225 26.12 Butt sealing 226 26.13 Diffusion seal 227 26.2 Sealing-off glass exhaust tubes 228 26.21 Sealing-off small diameter tubes 228 26.22 Sealing-off large diameter tubes 230 26.23 Sealing-off quartz exhaust tubes 230 26.3 Sealing-off metal exhaust tubes 231 26.31 Cold sealing-off 231 26.32 Sealing-off with valves 233 26.33 Brazed seal-off 234 CHAPTER 3. SEMI-PERMANENT AND DEMOUNTABLE SEALS 3.1 Waxed seals 236 31.1 Sealing waxes 236 31.2 Vacuum sealing technique with waxes 236 3.2 Sealing with paints and plastics 244 32.1 Irreversible adhesives 244 32.2 Sealing of plastics and the use of plastics for sealing 247 3.3 Sealing with epoxy resins 248 33.1 Epoxy adhesives 248 33.2 Preparing the adhesives and completing the joints 253 33.21 Mixing 253 viii CONTENTS 33.22 Applying 253 33.23 Curing 255 33.24 Dismantling 255 33.25 Strength 255 33.3 Vacuum sealing with epoxy resins 256 33.31 Butt joints 256 33.32 Lap joints 257 3.4 Silver chloride seals 258 3.5 Soft soldering 260 35.1 Vacuum sealing with soft soldering techniques 260 35.11 Soft soldering alloys 260 35.12 Soft soldering of metal parts 261 35.13 Soft soldering of glass and ceramic parts 266 35.2 Vacuum sealing with solder glasses 269 3.6 Ground and lapped seals 274 36.1 Flat seals 275 36.2 Conical and cylindrical ground seals 277 36.3 Spherical ground seals 285 36.4 Assembling and maintenance of ground seals 287 3.7 Liquid seals 293 37.1 Hydrostatic seals 294 37.2 Mercury sealed ground and gasket joints 295 37.21 Cup seals 297 37.22 Immersion seals 298 37.23 Guard seals 299 37.3 Mercury and gallium sealed glass frit 299 37.4 Oil seals 300 37.5 Surface tension seals 303 37.6 Molten metal seals 305 3.8 Gasket seals 306 38.1 Sealing mechanism of gaskets 306 38.2 Leaking mechanism in gasket seals 311 38.21 Leak through the seal 312 38.22 Leak through the gasket 313 38.23 Guard vacuum in the seals 314 38.3 Gaskets; materials and shapes 319 38.31 Rubbers for gaskets 319 38.32 Fluorocarbons for gaskets 323 38.33 Metals for gaskets 328 38.34 Gasket shapes 345 38.4 0-ring seals 345 38.41 0-ring groove seals 347 a) Grooves with rectangular cross section 348 b) Grooves with triangular cross section 355 c) Grooves with trapezium cross section 356 d) Grooves with semi-circular and elliptical cross section 359 e) Grooves for rectangular flanges 360 38.42 Spacer seals 361 38.43 Conical seals 369 CONTENTS ix 38.44 Corner seals 380 38.45 Step seals 382 38.46 Cemented seals 384 38.47 Standard flanges and unions for 0-ring seals 388 38.48 Assembling and maintenance of 0-ring seals 396 38.5 Thick gasket seals 403 38.51 Plane seals 403 a) Plane flange seals 403 b) Groove seals 407 c) Seals with gaskets of special shapes 410 38.52 Conical seals 413 38.53 Cylindrical seals 416 a) Rubber tubing joints 416 b) Compression gasket seals 418 c) Lip seals 420 38.54 Dumbbell seals 421 38.55 Shear seals 423 38.56 Ridge seals 425 a) Tongue seals 426 b) Knife edge seals 427 38.57 Inflatable gasket seals 437 38.58 Assembly and maintenance of gasket seals 438 38.6 Thin gasket seals 440 38.61 Plane seals with thin gaskets 440 38.62 Groove and knife-edge seals 440 38.63 Surface friction seals 443 CHAPTER 4. TRANSMISSION OF THE ELECTRIC CURRENT THROUGH SEALS 4.1 Selection criteria for electrical lead-throughs 445 41.1 Insulation 445 41.11 Bulk resistivity 445 41.12 Surface resistivity 447 41.13 Dielectric properties 449 41.14 Electrolytic effects 451 41.2 Loading current 451 41.3 Frequency 452 41.4 Temperature 452 4.2 Permanent lead-throughs 452 42.1 Rod seals 453 42.2 Stem seals 458 42.3 Pin seals 462 42.4 Ribbon seals 465 42.5 Disc and cup seals 467 4.3 Demountable lead-throughs 471 43.1 Waxed and resin sealed lead-throughs 471 43.2 Gasket-sealed lead-throughs 473 43.3 Commercially available lead-throughs 481 CHAPTER 5. THE TRANSMISSION OF MOTION THROUGH SEALS 5.1 Mechanical transmission 491 51.1 Classification 491 X CONTENTS 51.2 Transmission of motion by tilting the vacuum device 494 51.3 Transmission of motion through elastic pipes 494 51.4 Transmission of motion using bellows 498 51.5 Transmission of motion using diaphragms 505 51.6 Transmission of motion using ground seals 508 51.7 Transmission of motion using gasket seals 510 51.71 0-ring seals for transmitting motion 511 51.72 Rim seals for transmitting motion 514 51.73 Cylindrical and conical seals for transmitting motion 515 51.74 Lip seals for transmitting motion 517 51.75 Spring-loaded lip seals for transmitting motion 520 51.76 Friction seals for transmitting motion 522 51.77 Commercially available shaft seals 525 51.78 Seals for angular displacement 529 51.8 Motion seals using a guard vacuum 537 5.2 Magnetic transmission 539 52.1 Translation using magnetic fields 539 52.2 Rotary motion transmitted by magnetic fields 541 5.3 Actuation by heat transfer or electric current 543 53.1 Motion based on thermal expansion 543 53.2 Irreversible motion by burning-out 544 53.3 Actuation with electric current 545 CHAPTER 6. SEALS USED IN THE TRANSFER OF MATERIALS 6.1 Seals for the transfer of gases 546 61.1 Cut-offs 546 61.11 Principles 546 61.12 Actuating devices in cut-offs 547 a) Raising devices 547 b) Locking devices 549 61.13 Closing systems in cut-offs 552 a) Cut-offs with simple liquid seals 552 b) Cut-offs with floats 552 c) Cut-offs with sintered glass 556 d) Cut-offs with molten metals 557 61.2 Stopcocks 558 61.21 Shapes and dimensions 558 61.22 Greased stopcocks 562 61.23 Greaseless stopcocks 565 61.3 Valves 566 61.3( Principles and classification 566 61.32 Closing systems of valves 571 a) Closing systems using liquid seals 571 b) Closing systems using molten metals 572 c) Closing systems using silver chloride 575 d) Closing systems based on fusing glass joints 576 e) Closing systems based on ground joints 576 f) Closing systems using clamped elastomer tubes 580 g) Closing systems using diaphragms 581 CONTENTS XI h) Closing systems using gasket seals (plate, flap, plug, nose, gate, plunger, butterfly and ball valves) 583 61.33 Sealing systems of valves 616 a) Packed valves 616 b) Packless valves 617 61.34 Operating systems of valves 619 a) Mechanical movement (manually operated valves) 619 b) Pneumatically operated valves 619 c) Electromagnetically operated valves 624 d) Valves operated by thermal expansion 631 61.35 Valves for specific purposes 632 a) Seal-off valves 633 b) Throttling valves 633 c) Air-admittance valves 633 d) Baffle valves 635 e) Non-return valves 637 f) Bakeable (and ultra-high vacuum) valves (ground joint, fused glass, molten metal and all-metal valves) 638 g) Multi-way valve blocks 653 61.36 Maintenance of valves 659 61.4 Gas-leaks and metering devices 659 61.41 Principles and classification 659 61.42 Pinholes, orifices and cracks used as leaks 664 61.43 Capillaries and flattened tubes used as leaks 668 61.44 Porous plugs used as leaks 671 61.45 Annular impedances used as leaks 673 61.46 Needle valves 676 61.47 Temperature-actuated leaks 679 61.48 Diffusion leaks 682 61.49 Pulsed leaks 685 61.5 Techniques for opening sealed gas container 687 61.51 Opening by striking 688 61.52 Opening by bending 690 61.53 Opening by punching 691 61.54 Opening by squeezing 692 6.2 Transfer of liquids through seals 693 62.1 Continuous transfer 693 62.2 Metered transfer 693 6.3 Transfer of solids through seals 697 63.1 Vacuum locks 697 63.11 Vacuum locks using sliding rods 698 63.12 Vacuum locks using rotating plugs 698 63.13 Vacuum locks using chambers with double ports 700 63.2 Electrolytic transfer through glass walls 702 CHAPTER 7. SEALS USED IN TRANSMITTING RADIATION 7.1 Windows 704 71.1 Selection according to the radiation 704 71.11 Windows for light 704 71.12 Windows for ultraviolet 705