About Seals- Chapter Four some seals

Mackintosh

About Metal Bellows
: G4 q/ }, ?2 YMetal bellows perform the function of sealing environments, carrying gases, liquids and slurry, mechanical coupling, and performing electrical contact amongst other things. They are durable and flexible when used within design specifications.  Metal bellows are cylindrical vessels readily compressible and extensible as a result of numerous annular convolutions.
The most important specifications to consider when searching for metal bellows include inside diameter, outside diameter, free length, and spring rate.  The inside diameter specifies the minimum inner diameter of the bellows.  The outside diameter specifies the minimum outer diameter of the bellows.  The free length is the unloaded length of the bellows along the convolutions.  The spring rate is the spring force that the bellows applies.  Common materials of construction for metal bellows include aluminum, beryllium copper, brass, copper, Hastelloy, Inconel, Monel, nickel, phosphor bronze, stainless steel, steel, tantalum, and titanium.  Methods of construction for metal bellows can be electroforming, chemical deposition, mechanical forming, and welding.  Electroformed bellows are made by depositing layers of metal, usually nickel based, on a mandrel of aluminum. When the desired thickness is reached the mandrel is melted away leaving behind the bellows.  Chemical deposition is a method of forming bellows by electro-depositing metal on a mandrel.  Mechanically formed bellows include both roll-formed and hydroformed types.  Welded bellows are a series of convoluted rings or washers, which are stacked on top of each other and welded on the inside and outside circumference.
Other important parameters to consider include profile or shape of the bellows, applications, and features.  Common profiles or shapes for metal bellows include round and square or rectangular.  Applications include aerospace, automotive, chemical, motion coupling, fluid coupling, electrical contacts, HVAC, high purity, marine, petrochemical, and semiconductor.  Common features of metal bellows include cryogenic rated, flange, hermetic sealing, medically rated, necks, and vacuum rated.  Cryogenic rated bellows are used in cryogenic systems to handle very low temperature gases.  A flange is a fitting used to attach the bellows to equipment or piping.  Hermetic sealing on bellows is used in high and low pressure applications in either liquid or gaseous media.  Medically rated bellows are used in applications to insure a high degree of sanitation.  Necks are rigid tube-like lengths running from the end of the bellows.  Vacuum rated includes any vacuum application to very high vacuum.  Suppliers of metal bellows can often provide assembly services.
About O-rings
O-rings are solid-rubber, doughnut shaped seals. When pressed between two mating surfaces, O-rings block the passage of liquids or gases. O-rings can form a static or dynamic seals. A static seal is where the O-ring does not move and is used simply for containing pressure or maintaining a vacuum. Dynamic seals can be reciprocating (like a piston and cylinder), or rotating (shaft rotating in a housing).  Axial squeeze and radial squeeze are two methods for applying an O-ring. An axial squeeze is when the ring is compressed parallel to a line drawn through the center or axis of the ring. In a radial squeeze the ring is compressed between the internal diameter (ID) and overall diameter (OD).  Also, a boss seal is an O-ring, however it just doesn't fit the standard sizes for an O-ring. A boss is a cylindrical projection on a casting or forging. The end of that projection is machined to provide a flat, smooth surface for sealing. Straight threads used with O-rings provide a better seal than tapered threads used alone.
O-rings are typically available in standard sizes per industry standards.  These include "AS568" standard sizes (001-475), "AS568-" boss gasket sizes (901- and up), British Standard metric sizes, JIS standard sizes, JASO standard sizes, AS871, and custom.  When custom o-rings are required, the width or thickness, insider diameter, and outside diameter are important to consider.  Common materials of construction for o-rings include butyl (-75° to 250° F), cast polyurethane (-40° to 125° F), ethylene propylene (EPDM) (-70° to 275° F), fluorosilicone (-100° to 350° F), fluorocarbon/fluorosilicone blend (-25° to 400° F), highly-saturated nitrile (-40° to 300° F), Hydrin (-60° to 300° F), neoprene (chloroprene) (-45° to 230° F), nitrile (Buna-N) (-30° to 275° F), polyacrylate (-25° to 350° F), polyurethane (Millable) (-40° to 180° F), SBR (BUNA-S) (-30° to 275° F), silicone (-65° to 450° F), and Thiokol (-30° to 300° F). Exact specifications should be clarified by the vendor, as chemical and physical properties of an O-ring can differ based on manufacturing technique.
The hardness rating on a Shore A scale for O-rings, can be <30 durometer, 30 durometer, 35 durometer, 40 durometer, 45 durometer, 50, durometer, 55 durometer, 60 durometer, 65 durometer, 70 durometer, 75 durometer, 80 durometer, 85 durometer, 90 durometer, and >90 durometer.  Common features for o-rings include FDA approved or 3A sanitary classification, AMS/MIL spec, peroxide cured, and chlorinated.
Piston Rings - Piston rings are used for sealing cylinders. They can work at higher temperatures than elastomeric, fabric, or polymer seals.
' l% a1 ?8 V  oAbout Plugs, Stoppers and Inserts
Protective plugs, stoppers and inserts for the end of a shaft, tube, pipe, fitting, connector, screw, bar, or other shape. Plugs, stoppers and inserts fit into a hole or cavity.  Plugs are available in many different shapes and materials.  Plugs come in a variety of different cross sections.  These include round, button plug, square, rectangular, and screw cap or plug.  Common features include threaded, tapered, and expanded tube plug.  Threaded plugs, stoppers, and inserts have a female thread.  The thread can be straight or tapered (NPT).  Tapered sides provide a snug fit.  Some can be used as either a cap or a plug.  Tapered caps and plugs are versatile and can be used for straight tubes and bars, male and female NPT threads, and male straight threads.  Expanding tube plugs are used in moderate pressure applications, such as condenser and heat exchanger tubes.
  q+ ^" N( i9 Y0 D( eImportant round plug specifications when searching for plugs, stoppers, and inserts include the NPT size, BSP size, diameter, and round plug features.  NPT threads for round plugs, stoppers, and inserts range from 1/8” to 6”.  BSP sizes include &frac14; BSP, 3/8 BSP, and &frac12; BSP.  The diameter applies to round caps and plugs only.  For straight threads the major thread diameter is the important diameter.   (For example: .25 for a &frac14; straight thread).  This does not apply where cap/plug or object being capped/plugged has a tapered (NPT or BSP) thread.  Features of round plugs include flange, knurled or faceted head, slotted head, and recessed socket.  Important dimensions to consider when searching for square or rectangular plugs include width and length.  The width is the smaller cross sectional dimension for rectangular caps or plugs.  If the section is a square, the width and length are the same dimension.  The length is the larger cross sectional dimension for rectangular caps or plugs.  If the section is a square, the width and length are the same dimension.
Common materials of construction for plugs, stoppers, and inserts include aluminum, EVA, fiber, cork, or wood, nylon or polyamide, polyetheretherkeytone (PEEK), polyethylene (PE), polypropylene (PP), silicone rubber, styrene butadiene rubber (SBR), stainless steel, and vinyl.  Additional features to consider for plugs, stoppers, and inserts include lift or pull tab or ring, ribbed, and vented.  Lift or pull tabs allow for easy removal.  Pull plugs are designed for "through-hole" applications.  They use a smaller diameter "pull section" to pull the plug until it is snug in the hole.  Ribs are found on plugs only.  The ribs are on the mating part of the plug and help to provide a secure fit inside a tube.  Ribs are available on round, square, and rectangular plugs.  Vented plugs are commonly used in the medial industry.  The vent allows air flow during gas sterilization and prevents the cap from blowing off during extreme heat conditions.
+ X/ q1 l* M- ]5 |3 ^Solid Elastomeric Rings - Solid elastomeric rings are compression seals of differing cross sections. Some examples are X or multiple rings, rectangular rings, tetraseals, trapezoid rings, T-section rings, delta rings, D-rings, H-rings, heart rings, and diamond rings.
About Switch Boots
1 T8 j3 ^  _" k5 zSwitch boots protect switches from contaminants such as dirt, dust, gas, and liquids.  They are generally tough, pliable silicone rubber devices available for toggle, pushbutton, rocker and rotary switches. They protect the switch and seal its mounting hole against harm from washdown, salt water, lubricants, cleaning solvents, dust, dirt, grease and other environmental elements. Switch boots are designed for commercial, industrial and military applications.
9 x9 P1 X, Z; x" F" Q* x: PSwitch boots are available in two configurations, half boot and full boot. Half boots are designed to allow the switch actuator to protrude from the seal.  Full boots completely protect and cover the switch actuator.
In addition to protecting toggle, pushbutton, rocker and rotary switches, some types of switch boots are specially designed to protect circuit breakers, and other types can protect handset switches and other telecommunications devices.  Circuit breaker boots (for lever, rocker or pushbutton types) are designed to seal out dust, dirt and moisture without compromising breaker tripping, manual operation or position status viewing.
Some switch boots are designed to adhere to specific standards or exceed ratings specifications, to allow their use in specialized applications. Along this line, some switch boots are manufactured to military specifications (MIL-SPEC), and others are EMI /RFI shielded, armored, or contain a secondary inner seal. EMI / RFI shielded switch boots guard against spurious electronic signals entering or leaving equipment through the switch mounting hole. Armored devices are designed for applications where either mechanical abuse is expected or for medical / food processing applications as the armored actuator is typically washdown capable.  Secondary inner seal devices protect against the entry of contaminants in the event the upper portion of the boot is cut, torn or punctured.
9 U! i, n! }6 [Way Covers and Shields - Accordion bellows and way covers are fabric or rubber covers used to protect machine slides and ways.
0 T$ [% ]$ ^; }, E! y$ H- aWheel End / Oil Bath Seals - Seals used in the sealing of truck wheels.
Machine Way Wipers - Way wipers provide a seal between a machine slide or way and a stationary surface.

MDS

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