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Rubber
Industry Precision Tolerances
The dimensional tolerances given below provide a
guideline of what can be considered "precision" in a rubber product.
Although tighter tolerances are frequently available, there are many
factors that must be considered. Please contact
Molding Solutions
with any specific questions.
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Dimension
Size
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Fixed
Dimensions
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Closure
Dimensions
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Above
0.00" to 0.40"
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±0.006"
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±0.008"
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Above
0.40" to 0.63"
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±0.008"
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±0.010"
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Above
0.63" to 1.00"
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±0.010"
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±0.013"
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Above
1.00" to 1.60"
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±0.013"
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±0.016"
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Above
1.60" to 2.50"
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±0.016"
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±0.020"
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Above
2.50" to 4.00"
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±0.020"
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±0.025"
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Above
4.00" to 6.30"
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±0.025"
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±0.032"
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Above
6.30" Multiply By:
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±0.004/In.
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±0.005/In.
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Reprinted with permission from RMA Rubber Handbook for Molded Products
For
more information about industry standards for rubber products, contact:
The Rubber Manufacturers Association
1400 K Street, N.W.
Washington, D.C. 20005
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Rubber
Compounds
Choosing
a rubber compound:
The information below allows the identification of the compound types
that have the required characteristics for a specific application. Keep
in mind that these results are achieved under laboratory test
conditions and that results may vary in a specific application. Always
test a specific compound in each application to assure that it will
perform as required. Molding Solutions cannot be held responsible for
improper use of this information.
RUBBER
SELECTION TABLE
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CHARACTERISTIC
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BEST
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GOOD
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MARGINAL
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POOR
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VARIES
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Abrasion
Resistance
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AU/EU, BR
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NBR, SBR, CR, CSM , CM, NR, IR, FKM,
EPDM
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IIR, ACM, ECO
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VMQ,
FVMQ
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~
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Acid
Resistance
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EPDM, CR, FVMQ, CSM , CM
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FKM, IIR, NR, IR , NBR, ECO
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SBR, VMQ, AU/EU, BR
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ACM
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~
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Alkaline
Resistance
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EPDM, FVMQ, CM
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IIR, CSM, NR, IR , NBR, CR
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FKM, SBR, ECO, BR
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ACM, VMQ
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AU/EU
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Compression
Set
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NR, IR
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NBR, FKM, SBR, VMQ , CM, ECO, BR
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FVMQ
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CR, IIR, ACM, AU/EU ,
CSM
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EPDM
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Fuel
Resistance, Aliphatic Hydrocarbon
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FKM, FVMQ, ACM
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NBR, ECO, AU/EU
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CSM, CM
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CR, VMQ, EPDM, SBR , IIR, NR, IR, BR
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~
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Resistance
to Gas
Permeability
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ECO
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FKM, CSM, CM, AU/EU , IIRBR
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EPDM, CR, NR, IR
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FVMQ, SBR, VMQ,
ACM
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~
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Heat
Resistance, Aging @ 212°F
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FKM, VMQ, FVMQ, ACM
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EPDM, CR, IIR, CSM , ECO, NBR, SBR, CM
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NR, IR, AU/EU, BR
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~
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~
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LP
Gas & Fuel Oil Resistance
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NBR, FKM, FVMQ, ECO
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CM, CR, ACM, CSM
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AU/EU
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VMQ, EPDM, SBR, IR , NR,
BR
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~
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Ozone
Resistance
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FKM, IIR, VMQ,
FVMQ, CSM, CM, AU/EU
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EPDM, CR, ACM, ECO
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NBR
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SBR, NR, IR, BR
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~
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Resilience, Rebound
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FVMQ, NR, IR
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VMQ, FKM, SBR, BR , NBR, ECO
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EPDM, CR, ACM, CSM
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IIR, CM, AU/EU
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~
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Steam
Resistance
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EPDM
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IIR
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NBR, SBR, CR, VMQ , ECO, NR, IR, BR
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FKM, CSM, FVMQ, ACM , CM, AU/EU
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~
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Tear
Resistance
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AU/EU
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NBR, CR, NR, IR , BR, SBR, ECO, IIR
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FKM, EPDM, CSM, CM
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VMQ, ACM
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FVMQ
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Vibration
Dampening
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IIR
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CR, ACM, NR, IR , FVMQ, CM, ECO
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NBR, FKM, EPDM, SBR , VMQ, CSM, AU/EU, BR
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~
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~
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Water
Resistance
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FKM, EPDM, VMQ,
FVMQ, NR,
IR ,
BR
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NBR, SBR, IIR, CM , CSM,
ECO
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CR
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AU/EU,
ACM
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~
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Weather
Resistance
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FKM, EPDM, IIR, VMQ , FVMQ, ACM, CSM, CM, AU/EU
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ECO
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NBR, SBR, CR
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BR, NR, IR
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~
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Characteristics
of Rubber Compounds
BUTADIENE
RUBBER
(BR) An elastomer with properties somewhat similar to natural rubber.
Although its properties are not quite that of Natural Rubber, in some
cases its low temperature characteristics are better.
Specific gravity.................................0.91
Compression set..................................B
Elongation, max............ ..................6x
Hardness, Shore A............................ 40-80
Brittle point (F).................................-100
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BUTYL RUBBER (IIR) A petroleum product
made of co-polymerizingisobutylene and isoprene (for desired degree
necessary to vulcanization). Has excellent resistance to gas
permeation, making it useful for vacuum applications.
Specific gravity....................................0.92
Tensile strength...................................3,000
Elongation, max...................................3x
Hardness, Shore A................................40-80
Brittle point (F).....................................-80
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CHLORINATED POLYETHYLENE (CM) An
elastomer made from a high density polyethylene, with limited
resistance to petroleum oils, and good resistance to oxidation.
Chlorination is canbe varied. Resistance to petroleum oils improves
with increased chlorine content. Seldom used alone, can be blended to
improve flame and impact resistance.
Specific gravity.............................1.16 to 1.32
Tensile Strength.....................................4,000
Elongation, max.....................................5x
Hardness, Shore A..................................40-90
Brittle point (F).......................................-40
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CHLOROPRENE / NEOPRENE (CR) Among the
earliest of the synthetic rubbers, can be compounded for service at
temperatures of --65° to +300°F, and most are either
resistant to deterioration from exposure to petroleum lubricants, or to
oxygen. (Neoprene is a Trademark of DuPont)
Specific gravity.......................................1.24
Tensile strength.......................................4,000
Elongation, max.......................................6x
Hardness.................................................30-90
Brittle Point..............................................-80
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CHLORINATED SULFONATE POLYETHYLENE (CSM)
The ethylene monomer with some hydrogen replaced by chlorine and
sulphur groups is the main constituent of this elastomer.
Specific gravity........................................1.18
Tensile strength (psi)..............................3,000
Elongation, max......................................6x
Hardness, Shore A..................................50-90
Brittle point (F).......................................-70
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EPICHLOROHYDRIN (CO, ECO) A recent
addition to the oil resistant polymers; aliphatic polyether with
cholorofunctional side chains. Both CO and ECO have excellent
resistance to hydrocarbon oils, fuels and ozone. The corrosive nature
of epychlorohydrinis a sometimes limiting factor in some applications.
Specific gravity.................................36 to 1.27
Tensile strength.......................................2,500
Elongation, max.......................................4x
Hardness, Shore A....................................40-90
Brittle point (F)....................................10 to-50
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ETHYLENE PROPYLENE COPOLYMER (EPM/EPDM)
Elastomers prepared from ethylene and propylene monomers , at times
with a small amount of a third monomer (Etlylene Propylene Terpolymer).
Excellent resistance to phosphate ester type hydraulic fluids.
Specific gravity..........................................86
Tensile Strength.........................................3,000
Elongation, max.........................................6x
Hardness, Shore A.....................................30-90
Brittle Point (F)..........................................-90
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FLUOROCARBON (FKM) Due to its wide
spectrum chemical compatibility and temperature range and low
compression set, this is the most significant elastomer development in
recent times. Of major importance in the seal industry.
Specific gravity...........................................1.85
Tensile strength...........................................2,500
Elongation, max...........................................3x
Hardness, Shore A........................................60-95
Brittle point (F).............................................-40
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to Compound Table
FLUOROSILICONE (FVMQ) Provide chemical
properties similar to those of fluorinated organic elastomers:
excellent resistance to hydrocarbon fuels, petroleum oils and silicone
fluids.
Specific gravity..............................................0.98
Tensile strength..............................................1,200
Elongation, max................................................4x
Hardness, Shore A.............................................60-80
Brittle point (F)..................................................-85
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NATURAL RUBBER (NR) Found in the juices
of many plants (shrubs, vines and trees), the principal of which is the
HeveaBrasiliensis, native to Brazil. Especially vulnerable to petroleum
oils, natural rubber has been all but completely replaced by synthetics
for seal use.
Specific gravity..............................................0.92
Tensile strength..............................................4,000
Elongation, max..............................................7x
Hardness, Shore A...........................................30-90
Brittle point (F).................................................-80
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NITRILE BUTADIENE (NBR) A copolymer of
butediene and acrylonitrile, due to its excellent resistance to
petroleum products and wide temperature range, the most widely used
elastomer in the seal industry. Somewhat vulnerable to ozone, sunlight
or weather.
Specific gravity.............................................1.0
Tensile strength..........................................4,000
Elongation, max..............................................4x
Hardness, Shore A......................................40-90
Brittle point (F)...............................................-40
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POLYACRYLATE (ACM) This material has
outstanding resistance to petroleum fuel and oil, and possesses
complete resistance to oxidation, ozone and sunlight, and an ability to
resist flex cracking. It has good resistance to hot air.
Specific gravity...........................................1.09
Tensile strength.........................................2,500
Elongation, max...........................................4x
Hardness, Shore A.....................................40-85
Brittle point (F).............................................-40
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POLYISOPRENE (IR) A synthetic elastomer
with characteristics equal to, or similar to, those of Natural Rubber.
Specific gravity.....................................0.91
Tensile strength...................................4000
Elongation, max.......................................7x
Hardness, Shore A...............................30-90
Brittle point (F)........................................-80
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SILICONE (SI / VMQ / PVMQ) The silicones
are a group of materials made from silicone, oxygen, hydrogen and
carbon which have poor tensile strength, and resistance to tear and
abrasion, but exceptional heat and compression set resistance. High
strength silicones have also been developed, but do not normally
compare to natural rubber.
Specific gravity.....................................0.98
Tensile strength...................................1,200
Elongation, max.......................................7x
Hardness, Shore A...............................30-85
Brittle point (F).............................-90 to -180
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to Compound Table
STYRENE BUTADIENE (SBR) Best known as
Buna S , this, along with natural rubber, account for 90% of the total
world rubber consumption. Its chemical composition is of styrene and
butadiene rubber, and it is not recommended for exposure to ozone,
petroleum oils or sunlight.
Specific gravity......................................0.94
Tensile strength....................................3,500
Elongation, max....................................6x
Hardness, Shore a..................................40-90
Brittle point (F).....................................-80
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URETHANE (AU /EU) Exhibit outstanding
mechanical and physical properties in comparison with other elastomers,
especially in its resistance to oils, hydrocarbon fuels, oxygen, ozone
and weathering. Its toughness and abrasion resistance is particularly
suitable for seals in systems of high pressures, shock loads and
abrasive contamination.
Specific gravity...............................1.05 to 1.30
Tensile strength....................................10,000
Elongation, max....................................7x
Hardness, Shore A.................................40-100
Brittle point (F).................................-60 to -90
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to Compound Table
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