Difference between revisions of "Gasket Types"

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[[File:NPS_Case_Styles_Gaskets.png|400px]]
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[[File:Gaskets-Wikipedia.jpg|thumb|Gasket types: 1. o ring, 2. fiber washer, 3. paper gaskets, 4. cylinder head gasket<br>Credit: Sonett72, Wikipedia]]
 
==Description==
 
==Description==
 
For further information, please see AIC wiki [http://www.conservation-wiki.com/wiki/Using_Gaskets_to_Seal_Exhibit_Cases Gaskets for Exhibit Cases]
 
For further information, please see AIC wiki [http://www.conservation-wiki.com/wiki/Using_Gaskets_to_Seal_Exhibit_Cases Gaskets for Exhibit Cases]
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[[File:Gaskets NPS.jpg|thumb|Gasket types<br>Credit: National Park Service]]
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A compressible material used in an interface to reduce gaps and create tighter fitting joints. Gaskets are held under pressure to reduce leakage, transmission, and or vibration.  As such, in museums, gaskets can be used to minimize air exchange between sealed cases and museums, to compensate for alignment irregularities between two edges, and to reduce potential for the transfer of dust, dirt, pollutants and pests. In the past, [[natural rubber]], [[paper]], [[metal]], [[felt]], [[asbestos]], and [[cork]] were used for gaskets.  More recently, synthetic options, called elastomers have become available.
  
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Gaskets are rubbery substances used at the interface of adjoining materials to reduce gaps and create tighter fitting joints. In exhibit cases, gasketry materials are frequently used at the junction of the exhibit cabinet and moveable access panels and doors. Gaskets are not only necessary at the entry- ways to the display chamber but also for the maintenance and lighting chambers. Using a gasket to seal gaps in exhibit case construction provides several conservation benefits:
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Examples of some elastomers include:
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{| class="wikitable"
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|-
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! Material
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! Durometer Shore A (hardness)
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! General properties
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! Resistant to:
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! Attacked by:
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! Commercial names
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|-
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| Polyethylene foam
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| 50-60
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| Strong, lightweight, closed cell. Available as sheets, strips or rods
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| Excellent UV, ozone and chemical resistance. Water repellent
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|
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| Plastazote, Evasote, Climaloc, Magic Foamcord
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|-
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| [[Ethylene propylene diene]] monomer (EPDM)
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| 30-90
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| Excellent resistant to  ultraviolet light, ozone, oxidants, heat, and compression set
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| Resists the swelling effects of   polar chemicals, animal and vegetable oils.
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| Mineral oils and solvents,  aromatic hydrocarbons
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|
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|-
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| [[Ethylene vinyl acetate]] closed-cell elastomeric seal (EVA)
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|
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| Closed cell foam that is  lightweight, odorless with good flexibility and softness
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| Excellent ozone, chemical  resistance.  Good acoustic properties
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| low resistance to heat and  solvents
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|
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|-
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| [[Fluorocarbon]]  (FKM)
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| 50-95
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| Excellent fluid resistance.  Work well at low temperatures.
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| Very good chemical resistance to  acids and oils as well as hydrocarbon and halogenated solvents
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| Ketones, low molecular weight  esters and nitro-containing hydrocarbons.
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| Viton
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|-
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| [[Isoprene]]  (butyl rubber)
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| 40-80
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| Excellent resistance to heat,  oxygen and water.
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| Low gas permeation.  High vibration absoprtion (dampening)
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| Hydrocarbons solvents and oils
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|
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|-
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| [[Nitrile rubber]] (NBR, Buna-N)
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| 20-100
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| Good physical properties. Broad  temperature range.
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| Resistant to water, petroleums  and oils
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|
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|
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|-
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| [[Polychloroprene]]
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| 15-95
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| Good weathering, flame  retardant.  High tensile and tear  strength
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| Moderate chemicals and acids,  ozone, oils fats, greases and  many  solvents.
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| Strong oxidizing acids, esters,  ketones, chlorinated, aromatic and nitro hydrocarbons
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| [[Neoprene]]
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|-
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| [[Polytetrafluoroethylene]] (PTFE)
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| 73
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| Good electrical insulator.  Inflammable and stable to light. Inert, often used in drug and food contact
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| Hydrophobic and very resistant  to all solvents, acids, and bases
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| Low strength and susceptible to  creep at room temerpature.
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| [[Teflon]]
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|-
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| [[Silicone resin|Silicone rubber]] (dimethyl silicone)
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| 50-70
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| Most stable of all  elastomers.  Resistant to sunlight,  oxygen and moisture. No odor or taste.
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| Resistant to high and low  temperature ranges, fatigue, most chemicals, oils, oxygen, and ozone
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| Poor resistance to aromatic  solvents.  May have residual silicone  oil that creeps to other surfaces.
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|
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|-
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| Styrene  butadiene (SBR, Buna-S)
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| 40-100
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| Low cost, general purpose  elastomer.  Excellent flex and strength
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| Resistant to alcohols and  ketones
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| Petroleum based fluids
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|
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|-
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| Aramid
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|
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|
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|
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|
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|
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|-
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| Cellular  silicone sponge (poly-dimethyl siloxane also referred to as PDMS)
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|
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| silicone rubber that has been  foamed into a uniform unicellular structure. It has the same characteristics  as silicone rubber and is shaped by either extrusion or cutting.
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|
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|
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|
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|-
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| Magnetic gaskets
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| 79-80
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| A silicone rubber gasket filled with magnetite.  Can be molded and extruded as needed
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|
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|
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| Elastosil R781 (Wacker)
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|}
  
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*Controls air exchange between the case and the room
 
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*Provides a sealed case that supports environmental control
 
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*Inhibits the entry of unwanted pests, airborne soils, and atmospheric pollutants
 
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* Safeguards against the accidental entry of water
 
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Over the years, gasketry products have been made from a wide range of natural and synthetic materials. Today the manufacturing industry produces gaskets primarily from synthetic, rubber like polymers called elastomers.
 
  
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Elastomer type:
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[[Category:Materials database]][[Category:MWG]][[Category:Comparisons]][[Category:Gaskets]]
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To ensure that the gasket will not contaminate the case interior, select an elastomer proven to be stable through testing. The following are some examples of stable elastomers.
 
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Silicone rubber (dimethyl silicone): most stable of all elastomers, silicone is resistant to high and low temperature ranges, fatigue, most chemicals, oils, oxygen, and ozone.
 
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Cellular silicone sponge (poly-dimethyl siloxane also referred to as PDMS): silicone rubber that has been foamed into a uniform unicellular structure. It has the same characteristics as silicone rubber and is shaped by either extrusion or cutting.
 
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Ethylene propylene diene monomer (EPDM): resistant to ultraviolet light, ozone, oxidants, heat, compression set and resists the swelling effects of polar chemicals.
 
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Ethylene vinyl acetate closed-cell elastomeric seal (EVA): similar to other elastomers in flexibility and softness, EVA has relatively low resistance to heat and solvents but excellent ozone resistance.
 

Latest revision as of 10:22, 3 March 2023

Gasket types: 1. o ring, 2. fiber washer, 3. paper gaskets, 4. cylinder head gasket
Credit: Sonett72, Wikipedia

Description

For further information, please see AIC wiki Gaskets for Exhibit Cases

Gasket types
Credit: National Park Service

A compressible material used in an interface to reduce gaps and create tighter fitting joints. Gaskets are held under pressure to reduce leakage, transmission, and or vibration. As such, in museums, gaskets can be used to minimize air exchange between sealed cases and museums, to compensate for alignment irregularities between two edges, and to reduce potential for the transfer of dust, dirt, pollutants and pests. In the past, Natural rubber, Paper, Metal, Felt, Asbestos, and Cork were used for gaskets. More recently, synthetic options, called elastomers have become available.

Examples of some elastomers include:

Material Durometer Shore A (hardness) General properties Resistant to: Attacked by: Commercial names
Polyethylene foam 50-60 Strong, lightweight, closed cell. Available as sheets, strips or rods Excellent UV, ozone and chemical resistance. Water repellent Plastazote, Evasote, Climaloc, Magic Foamcord
Ethylene propylene diene monomer (EPDM) 30-90 Excellent resistant to ultraviolet light, ozone, oxidants, heat, and compression set Resists the swelling effects of polar chemicals, animal and vegetable oils. Mineral oils and solvents, aromatic hydrocarbons
Ethylene vinyl acetate closed-cell elastomeric seal (EVA) Closed cell foam that is lightweight, odorless with good flexibility and softness Excellent ozone, chemical resistance. Good acoustic properties low resistance to heat and solvents
Fluorocarbon (FKM) 50-95 Excellent fluid resistance. Work well at low temperatures. Very good chemical resistance to acids and oils as well as hydrocarbon and halogenated solvents Ketones, low molecular weight esters and nitro-containing hydrocarbons. Viton
Isoprene (butyl rubber) 40-80 Excellent resistance to heat, oxygen and water. Low gas permeation. High vibration absoprtion (dampening) Hydrocarbons solvents and oils
Nitrile rubber (NBR, Buna-N) 20-100 Good physical properties. Broad temperature range. Resistant to water, petroleums and oils
Polychloroprene 15-95 Good weathering, flame retardant. High tensile and tear strength Moderate chemicals and acids, ozone, oils fats, greases and many solvents. Strong oxidizing acids, esters, ketones, chlorinated, aromatic and nitro hydrocarbons Neoprene
Polytetrafluoroethylene (PTFE) 73 Good electrical insulator. Inflammable and stable to light. Inert, often used in drug and food contact Hydrophobic and very resistant to all solvents, acids, and bases Low strength and susceptible to creep at room temerpature. Teflon
Silicone rubber (dimethyl silicone) 50-70 Most stable of all elastomers. Resistant to sunlight, oxygen and moisture. No odor or taste. Resistant to high and low temperature ranges, fatigue, most chemicals, oils, oxygen, and ozone Poor resistance to aromatic solvents. May have residual silicone oil that creeps to other surfaces.
Styrene butadiene (SBR, Buna-S) 40-100 Low cost, general purpose elastomer. Excellent flex and strength Resistant to alcohols and ketones Petroleum based fluids
Aramid
Cellular silicone sponge (poly-dimethyl siloxane also referred to as PDMS) silicone rubber that has been foamed into a uniform unicellular structure. It has the same characteristics as silicone rubber and is shaped by either extrusion or cutting.
Magnetic gaskets 79-80 A silicone rubber gasket filled with magnetite. Can be molded and extruded as needed Elastosil R781 (Wacker)

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