Sun Sealed
Sun Sealed
Rubber Material Types for Rubber Seals, Rubber Gaskets and O rings
IIR
Resistant to the same fluid types as EPDM , the distinctive properties of IIR rubber materials are very low gas and moisture permeability, excellent insulating properties, good ozone and weathering resistance, and resistance to a great many organic and inorganic media. IIR elastomer materials can be polymerised with various halogens (e.g. Chlorine / Bromine) to improve resistance to certain chemical media, but at the expense of electrical insulation and moisture resistance. They can be used from –40 to +120°C typically, and are mostly used in the production of tyre inner tubes, seals and gaskets, vacuum seals and membranes, and pharmaceutical goods.
CR
CR seal materials typically display good resistance to ozone, heat aging and chemicals. Good resistance to refrigerants, aliphatic hydrocarbons, mineral oils and greases. Typical trade name: Neoprene® (Dupont Dow Elastomers)
Chlorobutadiene rubbers contain chlorine in the polymer to reduce the reactivity to many oxidising agents, as well as to oil and flame. CR elastomers also have good resistance to ozone cracking, heat ageing and chemical attack. Some of the important applications of CR elastomers include Vee-belts, coated fabrics, cable jackets, tyre-sidewalls, seals and gaskets in contact with refrigerants, mild chemicals and atmospheric ozone.
CSM
CSM grades contain 24-43% chlorine content to provide excellent ozone and weather resistance, discoloration by sun and ultraviolet light, high resistance to many oxidising and corrosive chemicals, good resistance to dry heat to 150°C, low flammability and gas permeability, and also good resistance to hot water (when cured with lead oxide). The low temperature properties are generally limited, depending on the chlorine content of the CSM grade used, and the compression set is not very good.
CSM elastomers are generally useful in electrical applications, weather resistant membranes, hoses and acid resistant tank linings.
ECO
Generally resistance to high temperatures, oils, ozone, and flame with gas resistance comparable to NBR’s. The temperature range for continuous use is –40 to +120°C, but are generally unsuitable for rubber to metal bonding (they are corrosive to metals). ECO elastomers are suitable for use in seals, gaskets, diaphragms, cable jackets, belting etc, for a wide range of media. However, they are unsuitable for use with ketones and esters, alcohols, phosphate ester hydraulic fluids, sour gas, water and steam.
AEM
AEM rubber materials offer an unusual combination of physical properties; high heat resistance (up to 175°C), excellent ozone and weather resistance, moderate resistance to mineral oils, low temperature flexibility to –30°C, good resistance to hot water and high tensile strength. AEM applications are similar to ACM elastomers, but has the advantage where low temperature flexibility is concerned. They are typically moulded into O rings seals, boots and ignition wire jackets.
EPDM
EPDM elastomers have a fair tensile strength and excellent resistance to weathering and ozone, and chemical attack. They also exhibit excellent electrical insulation properties. Peroxide cured elastomers exhibit excellent heat ageing, and resistance to compression set from –40 to +150°C, more so if sulphur cured. They are resistant to a wide range of media, including hot water and steam to 200°C (in the absence of air), but are not considered compatible with mineral and synthetic lubricants, and hydrocarbon fuels. They are typically used in the production of window and door seals, wire and cable insulations, waterproofing sheets and hoses, and seals, O rings and gaskets.
FKM/FPM
Outstanding resistance to heat, weather, ozone, oxygen and oxidisers. Very low gas permeability. PPE FKM (FPM) seal materials include copolyme, terpolyme and tetrapolymer grades and bisphenol and peroxide cure systems.
FKM elastomers are highly fluorinated polymers containing few compounding ingredients. They are stable at very high temperatures (they can withstand 200°C / 400°F indefinitely, in service). By comparison, conventional elastomers would become brittle in 24 hours at this temperature, in air. FKM vulcanisates, in general, have outstanding resistance to oxygen, ozone, weather, flame and oxidative chemicals, and excellent resistance to swelling in a wide variety of media. However, they are not compatible with polar solvents (e.g. M.E.K.), some organic acids (e.g. Formic acid), certain methanol and ester based hydraulic fluids (e.g. Skydrol), ammonia and some amines. They are suitable in high-energy radiation environments up to about 106 Rads. Special grades of FKM may be required for use in hot water and steam applications.
FKM elastomers provide high compression set resistance if compounded with bisphenol cure systems. Generally they are serviceable down to –30°C, but specialist grades (such as Endura® V91A) can provide effective sealing down to –45°C. Electrical insulation properties are not particularly outstanding, but would be adequate for sheathing where elevated temperatures, ozone, chemical and flame resistance are required (e.g. shaft seals, O rings and gaskets, diaphragms and cable sheathing).
FVMQ
FVMQ elastomers are modified silicone rubbers, with superior fluid resistance, but limited to about 175°C (347°F).
HNBR
The hydrogenation process of NBR elastomers provide excellent heat and ozone resistance. Peroxide cured HNBR’s have the best compression set and heat resistance, and high-nitrile (ACN) HNBR elastomers have better resistance to mineral oils. HNBR’s combine best resistance and low temperature flexibility, although they are more expensive than NBR’s. HNBR’s are useful where resistance is required to ozone and weather, ageing in hot air and industrial lubricants, hot water and steam to 150°C, amine based corrosion inhibitors and sour gas (H2S), and high-energy radiation. HNBR’s fill the gap between NBR’s and FKM’s in many areas of application where resistance to heat and aggressive media are required simultaneously, and may therefore provide a lower cost alternative to FKM elastomers.
NR
Natural rubber (tapped from the cultivated rubber tree) exhibits high tensile strength, abrasion resistance, resilience, tear strength and low hysteresis. The chemcially similar polyisoprene has lower strength properties than the natural form but better low-temperature properties. Both rubbers are susceptible to degradation by weathering characteristics, and both show poor resistance to mineral and petroleum-based oils and fuels.
Typical long-term operating range is from -50°C to 70°C.
Main applications for natural rubber materials, apart from tyres, are for vibration mounts, springs and bearings.
NBR (BUNA N)
NBR elastomers are available in five basic grades; based on acrylonitrile content, giving proportional physical and chemical properties. NBR’s typically have (depending on increased ACN content), decreasing low temperature flexibility, increasing compression set, gas permeability, improved heat ageing and ozone resistance, improved tensile and abrasion strength, hardness and density. NBR’s are used where good resistance is required, to aromatic hydrocarbons at –40 to +120°C (e.g. gaskets and seals, hoses and cable jacketing), typically in the oil and gas industry.
High Nitrile: >45% ACN content
Medium Nitrile: 30-45% ACN content
Low Nitrile: <30% ACN content
The higher the ACN content, the higher the resistance to aromatic hydrocarbons. The lower the ACN content, the better the low temperature flexibility. The best overall balance for most applications is medium ACN content.
FFKM
This is the most chemically resistant elastomer available and is effectively a rubber form of PTFE. It displays other properties which prove most valuable in applications where purity, high temperatures and retention of sealing force are paramount.
ACM
ACM elastomers offer excellent heat resistance; they can typically be used at temperatures of 150°C (up to 175°C for limited periods). They provide high resistance to oxygen, ozone and industrial oils. Resistance to water is generally poor, and compression set and low temperature flexibility depend on base polymer and compounding choice. ACM elastomers are used primarily used where combined resistance to heat and oils is required.
AU / EU
These elastomers generally show outstanding tensile strength, tear and abrasion resistance, and give excellent protection against oxygen and ozone (except in hot climates, due to greater risk of microbiological attack in AU types, and ultraviolet light in the case of EU types. EU elastomers have a better low temperature flexibility (-35°C typically) and both have excellent resistance to high-energy radiation (106 Rads).
Polyurethane rubbers are used where high abrasion resistance and oil / solvent resistance are required together, e.g. hydraulic seals and gaskets, diaphragms, hoses and roller-skate and skateboard wheels. In all applications, consideration should be given to hydrolysis and limited heat resistance.
VMQ
The distinctive properties of silicone rubbers are outstanding resistance to ozone and corona, outdoor weather and sunlight. Special compounds will withstand up to 300°C; however, in the absence of air, silicones can revert to a paste, even at lower temperatures. The usual high temperature limit, quoted for continuous service, is 200°C. Silicones have an excellent reputation for their low temperature flexibility (some compounds to –90°C) and electrical insulation, which are maintained fairly constant at the full range of service temperatures. Electrically conductive compounds are also available.
Silicones have a low level of combustible components; even when exposed to flame, the elastomer is reduced to a non-conducting silica ash. Silicones also exhibit excellent compression set and high physiological inertness (tasteless, odourless and completely non-toxic).Silicones are also resistant to bacteria, fungi, a wide range of media including high energy radiation to 106 Rads, and excellent release properties (except to glass). The main limitations are low tensile properties and poor resistance to acids, alkalis, and steam above 120°C. Silicone elastomeric parts are used for electrical insulation, gaskets and O-rings (static or low dynamic applications only), food and pharmaceutical goods.
SBR
Produced as a substitute for NR (Natural Rubber); in general, SBR’s can be used in similar applications as NR / IR elastomers, except in severe dynamic applications (e.g. requiring low heat build-up on flexing). SBR’s can be used in tread compounds on car tyres, but not truck tyres. SBR’s have inferior weathering and chemical resistance to most other elastomers.
TFE/P (also known as FEPM)
The base polymer is solely produced by the Asahi Glass company, and sold under the name ‘Aflas’. TFE/P vulcanisates exhibit similar thermal stability to FKM elastomers, but better electrical resistance and a different chemical resistance profile (e.g. sour gas, acids and alkalis, ozone and weather, steam and water, all
hydraulic and brake fluids, alcohols and high energy radiation). However, they are not compatible to aromatic hydrocarbons, chlorinated hydrocarbons (e.g. M.E.K. and acetone), organic acetates and organic refrigerants.
FKM elastomers exhibit better compression set, and the low temperature flexibility is relatively poor (except in certain fluids that would plasticise the rubber to some extent. It is always recommended to carry out functional tests under working conditions. TFE/P elastomers are finding wide application; mainly in oil field operations and chemical processing as o rings, rubber seals and rubber gaskets, cable insulating and jacketing, and hose liners.
About the Author
PPE manufacture and supply high performance moulded rubber seals and rubber gaskets to various industries around the world.
|
|
YO LA TENGO Summer Sun 2003 NEW SEALED CD $10.99 |
|
|
Sun MicroSystems Slide Rail Kit 594-5010-01 New Sealed $124.99 |
|
|
AD&D TSR DSR3 VEILED ALLIANCE 2411 NEW SEALED D&D Dungeons & Dragons Dark Sun $19.95 |
|
|
Blood on the Sun (DVD, 2004)- Sealed $5.00 |
|
|
SUN RA HELIOCENTRIC WORLDS JAZZ SEALED LP RECORD $29.99 |
|
|
Wet Seal Sun dress size small great for Spring dark peach with white flowers $4.99 |
|
|
Sealed Pack – 1440 Swarovski 2028/2058 16ss, 20ss COLOR Flatbacks no-hotfix $63.99 |
|
|
Sealed Pack – 1440 Swarovski 2028/2058 16ss, 20ss COLOR Flatbacks no-hotfix $84.53 |
|
|
GEORGE ROBERT TOM HARRELL – SUN DANCE “SEALED” VINYL LP $12.05 |
|
|
TAFOLLA, JOEY – Out Of The Sun SEALED VINYL LP $15.06 |
|
|
NEW Sealed Sun nVidia Quadro FX 370 371-3990 X4100A-Z $99.00 |
|
|
V/A SUN The Roots Of Rock Vol 8 SONNY BURGESS Sealed UK $12.99 |
|
|
79-93 Mustang Sunroof Weatherstrip Sun Roof Seal Loop $32.95 |
|
|
LEGO STAR WARS – AT-ST 30054 UK NEW / SEALED – SUN POLYBAG PROMO $6.99 |
|
|
Sun Ra – Space Is the Place [Impulse! CD] NEW / SEALED $12.99 |
|
|
Leonda – Woman In The Sun (CD 2007) NEW SEALED PSYCH CD $7.88 |
|
|
Alan Price – Rising Sun ~ Album LP Record Vinyl SEALED $6.00 |
|
|
RIMINI PROJECT – A Day In The Sun CD SINGLE New/Sealed! $2.98 |
|
|
KYUL JUNG – 1st Album (Sun & Shine) KOREA CD *SEALED* $13.99 |
|
|
GORDON GANO & RYANS under the sun LP + MP3 new SEALED 180g VIOLENT FEMMES bogmen $17.99 |
|
|
NIK FREITAS sun down LP + MP3 new SEALED team love 180g $14.99 |
|
|
1 CENT CD: Suv ‘Follow The Sun’ 2005 electro 2CD SEALED $0.01 |
|
|
Leonda – Woman In The Sun (CD 2007) NEW SEALED CD $7.88 |
|
|
S.U.N. – HYPNOTIKI (1992) (SUN) (NEW/SEALED) CD $4.98 |
|
|
Silencer ^ Found on the Sun CD NEW SEALED ex-Angel Dust Thrash Metal $7.99 |
|
|
SEALED 1977 The STYLISTICS Sun & Soul LP R & B VOCAL $9.99 |
|
|
1 CENT CD: Dom ‘Sun Bronzed Greek Gods’ REMASTER SEALED $0.01 |
|
|
1997 Del Webb’s Sun City Hilton Head SEALED Sales VHS $7.99 |
|
|
7 Worlds Collide The Sun Came Out 2LP sealed seven mp3 $23.98 |
|
|
More Sun Splashin’-16 Hot Summer Hits! V/A NEW SEALED $1.00 |
|
|
LOUISE FREEMAN SIGNED,SEALED DELIVERED 12″ SUN TOWN $5.40 |
|
|
CHARLIE RICH “LOT”FULLY REALIZED+3 SEALED,SUN LB.,G-385 $12.99 |
|
|
Charlie Rich Sun Years LP SEALED $9.99 |
|
|
Advanced Dungeons and Dragons Dark Sun Boxed Set SEALED $49.99 |
|
|
Advanced Dungeons and Dragons Dark Sun FOREST MAKER SEALED $44.99 |
|
|
THE VEILS Sun Gangs VINYL LP RECORD + mp3 SEALED! NEW! $14.94 |
|
|
Bare Escentuals SUN-KISSED Blush.85g XL New SEALED $12.99 |
|
|
BRIAN WILSON THAT LUCKY OLD SUN 2008 CAPITOL 5099923414211 SEALED 180 GRAM LMTD $32.00 |
|
|
A Place in the Sun 1951 DVD New Elizabeth Taylor SEALED $2.94 |
|
|
Eddie Gale Ghetto Music new sealed free jazz CD Sun Ra $59.99 |
|
|
Golden Sun The Lost Age (GBA Gameboy) NEW SEALED RARE! $59.99 |
|
|
Duel in the Sun DVD Gregory Peck 1946 Brand New Sealed $2.94 |
|
|
Blood On The Sun DVD James Cagney 1945 Brand New Sealed $2.94 |
|
|
SEALED PSYCH PROG HENDRIX Eire Apparent Sun Rise LP 1969 US Buddah Original !! $31.00 |
|
|
NEW Pfaltzgraff EVENING SUN Coffee Center Canister seal $44.99 |
|
|
Shaming of the Sun by Indigo Girls BRAND NEW-SEALED IN SHRINK WRAP- . $7.99 |
|
|
Charlie Rich The Sun Story Vol 2 FACTORY SEALED LP vinyl record $9.59 |
|
|
Linkin Park A Thousand Suns +, CD + DVD + MP3. TWN NTSC ALL REGION New & sealed. $22.20 |
|
|
1 CENT CD: Orbo & The Longshots ‘Prairie Sun’ Norway Americana SEALED $0.01 |
|
|
SEALED SUN RA LIVE IN JAPAN AT PIT-INN 1988 7INCH 3VINY $229.99 |
|
|
Golden Sun: Dark Dawn Nintendo DS 2010 Factory Sealed Brand New $9.99 |
|
|
ON KA’A DAVIS Djoukoujou CD SUN RA Fela Kuti NEW Seal $13.99 |
|
|
STEVE APPLETON – When The Sun Comes Up CD *SEALED* $14.94 |
|
|
4x SUN HYDRAULICS 990-011-007 T11-A CAVITY SER 1 CARTRIDGE SEAL KIT BUNA N 25735 $18.15 |
|
|
MUDHONEY – UNDER A BILLION SUNS – SEALED US LP/CD $34.99 |
|
|
Jane Monheit – In The Sun (+1 Bonus) Korea CD *Sealed* $14.99 |
|
|
Hasbro My Little Pony SunShimmer Sun Shimmer SEALED MAIL ORDER 2004 Limited Ed $4.99 |
|
|
MEDAL of HONOR : RISING SUN SONY PLAYSTATION 2,PS2 NEW, SEALED $17.99 |
|
|
KEITH JARRETT – SUN BEAR CONCERTS – 6 CD’s BOX SET BRAND NEW & SEALED $97.96 |
|
|
Mars Lasar – Karma (Gemini Sun) CD *Sealed* $19.99 |
|
|
DR JOHN Night Tripper Sun Moon LTD 180G Vinyl LP SEALED $22.10 |
|
|
R.E.M. AROUND THE SUN CASSETTE INDONESIA TAPE SEALED $16.49 |
|
|
Motorized SUN FLOWER Ferry Boat Model Kit by ARII – SEALED! $24.99 |
|
|
COUNTRY SUN – NEW & SEALED CD ALBUM $6.24 |
|
|
Arctic Monkeys – When The Sun Goes Down – UK CD sealed $7.88 |
|
|
Don’t Let The Sun SEALED NEW OUT OF PRINT HK DVD Drama Natalie Ng Emily Kwan $5.39 |
|
|
JOHNNY CASH “Greatest” LP 1960′s Sun Records SEALED NM $75.00 |
|
|
SUN RA When Sun Comes Out SATURN Sealed Vinyl LP $14.00 |
|
|
SUN RA We Travel The Spaceways SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SUN RA Visits Planet Earth SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SONNY CHARLES THE SUN STILL SHINES SEALED DISCO LP $15.00 |
|
|
SUN RA Night Of The Purple Moon SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SUN RA The Magic City SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SUN RA Other Planes Of There SATURN Sealed Vinyl LP $14.00 |
|
|
The Doors – Waiting for the Sun – Gatefold LP *SEALED* – EKS 74024 $29.99 |
|
|
BRIAN WILSON THAT LUCKY OLD SUN JAPAN MINI LP CD SEALED $5.99 |
|
|
SUN RA My Brother The Wind Vol. 2 SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
Tokio Hotel Darkside Of The Sun JAPAN CD OBI SEALED $9.99 |
|
|
SUN RA My Brother The Wind SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SUN RA Monorails And Satelites SATURN Sealed Vinyl LP $14.00 |
|
|
SUN RA Live At Montreux INNER CITY Sealed 180 Gram Vinyl 2 LP $16.00 |
|
|
Linkin Park A Thousand Suns JAPAN CD OBI SEALED+1 $9.99 |
|
|
THE BEST OF SUN RECORDS Various Artists NEW SEALED 2CD $7.88 |
|
|
Golden Sun: The Lost Age Brand New/Sealed (Game Boy Advance/GBA) RARE $129.99 |
|
|
THE MODERN ART (SUN DIAL) All Aboard The Mind Train CD HEAVY PSYCH NEW SEALED $9.99 |
|
|
MINT SEALED LP – PHIL ALVIN & SUN RA Unsung Stories OG! $14.90 |
|
|
COMMAND & CONQUER TIBERIAN SUN (PC RTS Games) NEW & SEALED * 98 / XP / VISTA / 7 $14.95 |
|
|
Sun Microsystems Solaris 2.6 Media Intel Platform Edition 5/98 New Still Sealed $9.99 |
|
|
SUN RA AND THE ARKESTRA – SOUND OF JOY (LP-DELMARK RECORDS DS-414) *SEALED* $15.90 |
|
|
SALLYANGIE – Children Of The Sun – LP NEW SEALED 180g $23.68 |
|
|
WEBKINZ SUN BEAR VIRTUAL WORLD PET NEW SEALED TAG $14.95 |
|
|
Big Big Sun – Stop The World – Rock LP SEALED $7.99 |
|
|
Glass Tiger – Diamond Sun – Rock LP SEALED $9.99 |
|
|
20″ Sun King Pin Wheels 14mm Sealed F/F NEW Pair Black $109.99 |
|
|
BLACK SUN ENSEMBLE Tragic Magic LP Record SEALED 1991 $32.50 |
|
|
SUN RA Cosmic Tones for Mental Therapy SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SUN RA Nubians Of Plutonia SATURN Sealed 180 Gram Vinyl LP $16.00 |
|
|
SEALED Gary Baker JADED IN BETWEEN Red Sun CANADA PRESS $8.00 |
|
|
BRAND NEW GENUINE MERCEDES 123 SUN ROOF FOAM SEAL SELF ADHESIVE $8.00 |
|
|
Scorpions – Under The Same Sun CD Single + Patch SEALED $1.00 |
|
|
Sealed Milk Can $19.99 Summer Breeze brings together all the elements of a beautiful summer day. Leaves and delicate forget-me-nots on a garden trellis accent the soft yellow of the morning sun. From the days when milk cans were transported to market in horse-drawn wagons comes this mini-replica in stoneware, showcasing the The Pfaltzgraff Co.’s historic embossed logo. Comes with handles and a sealed lid to keep contents fresh. This piece is sure to bring of hint of yesteryear into your kitchen. 7 1/4″ high, holds 28 oz. |
|
|
Archangel Michael- Sealed Sleeves $27.4 “Michael: The Right Hand of God- Regent of the sun, leader of the celestial armies is ready to head into battle! Back & sleeves display the archaic Seal of MIchael, and the back reads: “”Michael; The Right Hand of God.”"” |
|
|
Sun $10 Sun |
|
|
The Sun $5.99 The Sun |
|
|
Into The Sun $8.49 Into The Sun |
|
|
Sealed Canisters, Set of 3 $69.99 Summer Breeze brings together all the elements of a beautiful summer day. Leaves and delicate forget-me-nots on a garden trellis accent the soft yellow of the morning sun. Tight-fitting plastic seals on the lids of these canisters will help keep your baking supplies or snacks fresh. 3 qt., 2 1/2 qt. & 2 qt. canisters. |
|
|
Sealed $12.93 No Synopsis Available |
|
|
Sun On Sun $7.99 Sun On Sun |
|
|
Sealed with a Kiss $100 Sealed with a Kiss |
|
|
Sealed Cargo $10.99 Sealed Cargo |
|
|
Sun Mountain H2NO Stand Bag $269.99 The H2NO is waterproof when the rainhood is used as designed in conjuction with the bag. Like Sun Mountain does with high-end rainwear, waterproof fabrics and high-quality waterproof YKK zippers were added and the seams have been sealed. |
|
|
Sun Tube Reflector: HY $137.23 Sun Systems Sun Tube • Comes completely assembled with pre-wired lamp cord & strain relief. • All wiring contained inside a sealed junction box. • Integrated mounting bracket accommodates standard chrome "V" hangers. • 6-inch tube allows unrestricted air to pass over the lamp. • Made with high-temperature borosilicate glass. • 95% German aluminum reflector offers excellent reflectivity & diffusion • Advanced reflector design offers a re-strike bend for maximum output & performance • Unique brackets allow for either horizontal or vertical hanging. • Optional wings sold separately.(RE808) • Glass is 19 1/2" long-overall length is 27" long by 6" diameter. |
|
|
In the Sun $110.99 Andrea Kahn In the Sun – Mounted Print |
|
|
In The Sun $19.99 James Tissot In The Sun – Premium Poster |
|
|
Frigoverre Glass Pitcher #N/A… |
|
|
Sunpentown SC-12 26-Pound Rice Dispenser $35.65 Holds up to 26-lbs of rice, compact design fit in most cabinets. Accurately dispenses 1 cup of rice with each press. A much better solution than keeping your rice in those unattractive and un-resealable rice bags from the market. removable bin easily transfers the rice to your cooker. Features and Functions: Unique design: keeps grams dry and fresh User friendly: 1 press design (1 press = 1 cup of… |
Tags: batteries, battery, bearings, formula, hub, juju, maw, mobile, sun sealed and delivered, sun sealed bearing
This entry was posted on Friday, March 20th, 2009 at 6:11 pm and is filed under Music. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.