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Seals Index


Gaskets


Introduction

Gaskets seals are the most widely used method of sealing contained volumes. Gaskets are generally only used as face seal between flat surfaces including flanges of all shapes and complicated face joints.   There are gasket/ jointing materials available for virtually any fluid at any operating temperature. Flange Design

The flange design is important when engineering a joint sealed by gaskets.   The following criteria need to be considered.

  • Flange surface finish -
  • Area of seal surface - to ensure high clamping pressure
  • Bolt placement - to ensure sufficient even clamping pressure
  • Flange material strength - the surfaces must remain flat under the high clamping forces.
  • Flange material to be - compatible with gasket material
  • Bolt size and design - to ensure that the bolts will provide sufficient force under operating conditions

The most common flange shape is a circular pipe flange. However gaskets can be used to seal very complicated faces which have a large number of seperate pressurised cavities.



Gasket Variants

  • Elastomer Sealing Strip - Basic elastomer solid or expanded strip or moulding - window seal etc
  • Soft Cut sheet- Gaskets that are flexible including gasket papers,cork, rubbers, fibre based materials,felts, foams, plastics etc
  • Flange Gaskets- Supplied to suit flanges to standards specification i.s BST, ANSI, JIS, ASA
  • Spiral Wound gaskets - for flange sealing- suitable for high pressures (700 bar), high temperatures (1600 oC)
  • Corrugated Metal gaskets -suitable for irregular shapes- can be faced with sealing materials
  • Solid/ expanded metal seals -for complicated shapes such as cylinder head gaskets. - Sometimes with flexible sealing materials bonded to surfaces
  • Metal reinforced gaskets i.e graphite or mica reinforce with metal perimeter rings or wire reinforcement


Gasket Materials

Natural Rubber 110 0C Max Temp.--
Good Mechanical Properties. Resistant to Water.  Fair to good resistance to acids and alkalis.  Poor resistance to oils petrol.  Poor Resistance to Weathering.
 
Butyl 150 0C Max Temp.-
Very good resistance to water, alkalis, many acids. Poor resistance to oils, petrol, and most solvents.
 
Nitrile 150 0C Max Temp.-
Very good resistance to water.  Fair resistance to alkalis, acids. Excellent resistance to oils and petrol.
 
Polysulphide660C Max Temp.-
Very good resistance to water.  Good resistance to alkalis, fair resistance to acids. Excellent resistance to oils, petrol, aliphatic and aromatic hydrocarbon solvents .  Poor mechanical Properties
 
Neoprene1200C Max Temp.-
Good resistance to water and alkalis, fair resistance to acids. good resistance to non-aromatic pertroleum, fatty oils, solvents (except aromatic, chlorinated or ketone types).  Excellent mechanical Properties
 
Acrylic2300C Max Temp.-
Good heat resistance.  Poor low temperature properties. Poor resistance to water, alkalis and some acids.  Poor resistance to steam steam at high temperatures.  Fair to good resistance to alkalis and acids. Good resistance to oils, petrol, aliphatic and aromatic hydrocarbon solvents
 
Hypalon-Chlorosulphonated Polyethylene2300C Max Temp.-
Good Mechanical properties  Excellent resistance to oxidising chemicals, ozone weathering. .Relatively good resistance to oils and greas.  Poor resistance to oils, petrol, aliphatic and aromatic hydrocarbon solvents
 
Viton/Kel-F/Fluoroelastomer 2300C Max Temp.-
Good Mechanical properties  Excellent resistance to ozone weathering. .Can be used at high temperatures with with many fuels, lubricants, hydraulic fluids, solvents.  
 
Asbestos Derivatives 6000C Max Temp.-
Large number of composites and combinations- Asbestos is not really acceptable for use in UK for health reasons
 
Cork Composites1200C Max Temp.-
Low Cost.  Compressible allowing substantial deflection with negligible side flow. Will conform to irregular surfaces.   High resistance to oils.  Good resistance to water and many chemicals.  Should not be used with inorganic acids and alkalis, oxidising solutions, live steam
 
Cork Rubber 1500C Max Temp.-
Low Cost.  Defined compressiblity. good fatigue resistance. Chemical resistance dependent on rubber used
 
PTFE/Teflon/ PolyTetrfluoroethylene 2500C Max Temp.-
Excellent resistance to allmost all chemicals and solvents.   Good heat resistance. Exceptional low temperature properties.  Low compressibility. Low resilience tends to creep under stress.
 
Filled PTFE/Teflon up to 2500C Max Temp.-
Improved mechanical properties - however filling material can impair chemical properties
 
PTFE/Teflon composites(lined) up to 2500C Max Temp.-
Chemical properties comparable with virgin PTFE. Inner gasket material providing improved resiliance and deformability
 
Polythene700C Max Temp.-
Resists most solvents- Poor heat properties
 
Neoprene Impregenated wood fibre800C Max Temp.-
No porous - good for glycol, oil, and petrol
 
SBR bonded Cotton1050C Max Temp.-
Good Water resistance
 
Nitrile Rubber - Cellulose fibre1050C Max Temp.-
Oil Resistant up to reasonably high temperatures
 
Inorganic Fibre10000C Max Temp.-
Excellent heat properties - poor mechanical properties
 
Graphite /Carbon Fibre10000C Max Temp.-
Excellent heat properties - Excellent chemical and mechanical properties based on product selected.
 
Felt-Pure--
Resilient, compressible, and strong but not impermeable.  Resists medium strength mineral acids and dilute mineral solutions if not intermitently dried.  Resists oils greases, waxes, most solvents. Damaged by alkalis.
 
Felt-PTFE Impregated1300C Max Temp.-
Good chemical and heat resistance
 
Lead2600C Max Temp.-
Good general chemical resistance. Best conformity of all metals
 
Tin2600C Max Temp.-
Good resistance to neutral chemicals . Attacked by acids and alkalis
 
Aluminium4300C Max Temp.-
High corrosion resistance. Slightly attacked by strong acids and alkalis
 
Copper & Brass4300C Max Temp.-
Good corrosion resistance at moderate temperatures
 
Nickel7600C Max Temp.-
High corrosion resistance
 
Monel6500C Max Temp.-
High corrosion resistance.   Good for use with wide range of acids and alkalis.  Attacked by strong hydrochloric and oxidising acids.
 
Inconel10000C Max Temp.-
Excellent heat and oxidising resistance.
 
Stainless Steel6000C Max Temp.-
High corrosion resistance depending on grade used.
 
Leather1000C Max Temp.-
Low cost.  Limited chemical and heat resistance.   Not recommended against pressurised steam, acid or alkli solutions.
 


Links Providing information on Gaskets
  1. James Walker ...Well known UK Supplier
  2. Garlock... A supplier of a wide range of seal products
  3. Allstate Gaskets... Gasket Information
    ...Allstate Gaskets... Gasket Information Chemical Resistance Chart
  4. Klinger... A Packing supplier
  5. Johnson Packings ... A supplier of various pump and valve packing materials

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Last Updated 25/01/2013