Graniit on tardkivimi tüüp, mida kaevandatakse selle äärmise tugevuse, tiheduse, vastupidavuse ja korrosioonikindluse tõttu. Kuid graniit on ka väga mitmekülgne – see ei sobi ainult ruutude ja ristkülikute jaoks! Tegelikult töötame enesekindlalt regulaarselt graniidist komponentidega, mis on konstrueeritud igasuguste kujude, nurkade ja kõveratega – suurepäraste tulemustega.
Through our state of the art processing, cut surfaces can be exceptionally flat. These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components. Granite is:
■ töödeldav
■ täpselt tasane pärast lõikamist ja viimistlemist
■ roostekindel
■ vastupidav
■ kauakestev
Graniidist komponente on ka lihtne puhastada. Eritellimusel disainide loomisel vali kindlasti graniit selle suurepäraste eeliste tõttu.

STANDARDID / SUUR KULUMISKOHT
ZHHIMG-i standardsete pinnaplaatide valmistamiseks kasutatav graniit on kõrge kvartsisisaldusega, mis tagab suurema vastupidavuse kulumisele ja kahjustustele. Meie Superior Black värvidel on madal veeimavus, mis minimeerib täppismõõturite roostetamise võimalust plaatidele kinnitamisel. ZHHIMG-i pakutavad graniidivärvid põhjustavad vähem pimestamist, mis tähendab plaatide kasutajatele vähem silmade väsimist. Oleme oma graniiditüübid valinud, võttes arvesse soojuspaisumist, et hoida see aspekt minimaalsena.

CUSTOM APPLICATIONS
Kui teie rakendus nõuab kohandatud kujuga, keermestatud sisestustega, piludega või muul viisil töödeldud plaati, peaksite valima sellise materjali nagu must Jinan Black. See looduslik materjal pakub suurepärast jäikust, suurepärast vibratsioonisummutust ja paremat töödeldavust.

Oluline on märkida, et ainuüksi värvus ei näita kivi füüsikalisi omadusi. Üldiselt on graniidi värvus otseselt seotud mineraalide olemasolu või puudumisega, millel ei pruugi olla mingit mõju omadustele, mis teevad sellest hea pinnaplaadimaterjali. On olemas roosasid, halli ja musti graniite, mis sobivad suurepäraselt pinnaplaatideks, samuti musti, halli ja roosasid graniite, mis on täppisrakendusteks täiesti sobimatud. Graniidi olulised omadused, mis puudutavad selle kasutamist pinnaplaadimaterjalina, ei ole värviga seotud ja on järgmised:
■ Jäikus (koormuse all olev läbipaine – mida näitab elastsusmoodul)
■ Kõvadus
■ Tihedus
■ Kulumiskindlus
■ Stabiilsus
■ Poorsus

Oleme testinud paljusid graniidist materjale ja neid materjale võrrelnud. Lõpuks jõudsime tulemuseni, et Jinani must graniit on parim materjal, mida me kunagi tundnud oleme. India must graniit ja Lõuna-Aafrika graniit on Jinani musta graniidiga sarnased, kuid nende füüsikalised omadused on Jinani musta graniidi omad nõrgemad. ZHHIMG otsib jätkuvalt maailmast rohkem graniidist materjale ja võrdleb nende füüsikalisi omadusi.

Et teie projekti jaoks sobivast graniidist rohkem rääkida, võtke meiega ühendust.info@zhhimg.com.

Erinevad tootjad kasutavad erinevaid standardeid. Maailmas on palju standardeid.
DIN standard, ASME B89.3.7-2013 või föderaalne spetsifikatsioon GGG-P-463c (graniidist pinnaplaadid) jne nende spetsifikatsioonide alusena.

Ja me saame toota graniidist täppiskontrollplaati vastavalt teie nõuetele. Võtke meiega ühendust, kui soovite lisateavet teiste standardite kohta.

Tasasust võib pidada kõigi pinna punktide paiknemiseks kahel paralleelsel tasapinnal, aluspinnal ja katuse tasapinnal. Tasapindade vahelise kauguse mõõt on pinna üldine tasasus. Sellel tasapinna mõõtmisel on tavaliselt tolerants ja see võib sisaldada klassi tähistust.

Näiteks on kolme standardklassi tasapinna tolerantsid määratletud föderaalses spetsifikatsioonis järgmise valemi abil:
■ Laboratoorse klassi AA = (40 + diagonaal ruudus/25) x 0,000001" (ühepoolne)
■ Kontrollklass A = laboriklass AA x 2
■ Tööriistaruumi klass B = laboriklass AA x 4.

Standardsuuruses pinnaplaatide puhul garanteerime tasapinna tolerantsid, mis ületavad selle spetsifikatsiooni nõudeid. Lisaks tasapinnale käsitlevad ASME B89.3.7-2013 ja föderaalne spetsifikatsioon GGG-P-463c teemasid, sealhulgas: korduvmõõtmise täpsus, pinnaplaatide graniitide materjali omadused, pinnaviimistlus, tugipunktide asukoht, jäikus, vastuvõetavad kontrollimeetodid, keermestatud sisestuste paigaldamine jne.

ZHHIMG graniidist pinnaplaadid ja graniidist kontrollplaadid vastavad kõigile käesolevas spetsifikatsioonis esitatud nõuetele või ületavad neid. Praegu puudub graniidist nurkplaatide, paralleelplaatide või põhiruutude jaoks määratlev spetsifikatsioon.

Ja teiste standardite valemid leiate siitLAADI ALLA.

Esiteks on oluline hoida plaat puhtana. Õhus leviv abrasiivne tolm on tavaliselt plaadi suurim kulumisallikas, kuna see kipub kinnistuma toorikutesse ja mõõteriistade kontaktpindadesse. Teiseks katke plaat kinni, et kaitsta seda tolmu ja kahjustuste eest. Kulumisaega saab pikendada, kui plaati ei kasutata, plaati perioodiliselt pöörates, et üksik piirkond ei saaks liigset koormust, ja mõõteriistade terasest kontaktpatjade asendamisega karbiidist patjadega. Samuti vältige toidu või karastusjookide asetamist plaadile. Pange tähele, et paljud karastusjoogid sisaldavad kas süsihapet või fosforhapet, mis võib lahustada pehmemaid mineraale ja jätta pinnale väikeseid süvendeid.

See sõltub sellest, kuidas taldrikut kasutatakse. Soovitame võimalusel taldrikut puhastada päeva (või töövahetuse) alguses ja uuesti lõpus. Kui taldrik määrdub, eriti õliste või kleepuvate vedelikega, tuleks see tõenäoliselt kohe puhastada.

Puhastage plaati regulaarselt vedela või ZHHIMG veevaba pinnaplaadipuhastusvahendiga. Puhastuslahuse valik on oluline. Lenduva lahusti (atsetoon, lakilahusti, alkohol jne) kasutamisel jahutab aurumine pinda ja moonutab seda. Sellisel juhul on vaja lasta plaadil enne kasutamist normaliseeruda, vastasel juhul tekivad mõõtmisvead.

Taldriku normaliseerimiseks kuluv aeg sõltub taldriku suurusest ja jahutamise hulgast. Väiksemate taldrikute puhul peaks piisama ühest tunnist. Suuremate taldrikute puhul võib vaja minna kahte tundi. Veepõhise puhastusvahendi kasutamisel toimub ka mõningane aurustuv jahutamine.

Plaat hoiab ka vett kinni ja see võib põhjustada pinnaga kokkupuutuvate metalldetailide roostetamist. Mõned puhastusvahendid jätavad pärast kuivamist kleepuva jäägi, mis meelitab ligi õhus levivat tolmu ja suurendab kulumist, selle asemel et seda vähendada.

See sõltub plaadi kasutamisest ja keskkonnast. Soovitame uue plaadi või täppisgraniittarviku täieliku ümberkalibreerimise teha ühe aasta jooksul alates ostukuupäevast. Kui graniidist pinnaplaati kasutatakse palju, võib olla soovitatav seda intervalli lühendada kuue kuuni. Igakuine kontroll korduvate mõõtmisvigade suhtes elektroonilise loodi või sarnase seadme abil näitab kõiki tekkivaid kulumiskohti ja see võtab vaid paar minutit. Pärast esimese ümberkalibreerimise tulemuste kindlakstegemist võib kalibreerimisintervalli pikendada või lühendada vastavalt teie sisemisele kvaliteedisüsteemile.

Pakume teenust, mis aitab teil graniidist pinnaplaati kontrollida ja kalibreerida.

Kalibreerimiste erinevustel võib olla mitu võimalikku põhjust:

• Enne kalibreerimist pesti pinda kuuma või külma lahusega ja sellele ei antud piisavalt aega normaliseerumiseks.
• Plaat on valesti toetatud
• Temperatuuri muutus
• Mustandid
• Otsene päikesevalgus või muu kiirgussoojus plaadi pinnal. Veenduge, et laevalgustus pinda ei kuumutaks.
• Vertikaalse temperatuurigradiendi kõikumised talve ja suve vahel (võimalusel teadke vertikaalse gradiendi temperatuuri kalibreerimise ajal).
• Plaadil ei ole pärast saatmist piisavalt aega normaliseerumiseks
• Kontrolliseadmete ebaõige kasutamine või kalibreerimata seadmete kasutamine
• Kulumisest tulenev pinna muutus

Mitu tüüpi auke on täppisgraniidil?

Täppisgraniidist komponentide pilud

Paljudes tehastes, kontrollruumides ja laborites kasutatakse täpse mõõtmise alusena täppis-graniidist pinnaplaate. Kuna iga lineaarmõõtmine sõltub täpsest võrdluspinnast, millelt lõplikud mõõtmed võetakse, pakuvad pinnaplaadid parimat võrdlustasandit töö kontrollimiseks ja paigutamiseks enne töötlemist. Need on ideaalsed alused ka kõrguse mõõtmiseks ja pindade mõõtmiseks. Lisaks muudavad kõrge tasasus, stabiilsus, üldine kvaliteet ja töötlus need heaks valikuks keerukate mehaaniliste, elektrooniliste ja optiliste mõõtsüsteemide paigaldamiseks. Kõigi nende mõõtmisprotsesside puhul on hädavajalik hoida pinnaplaadid kalibreerituna.

Repeat Measurements and Flatness

Nii tasapinnalisus kui ka korduvad mõõtmised on täpse pinna tagamiseks kriitilise tähtsusega. Tasapinnalisust võib pidada kõigi pinna punktide paiknemiseks kahel paralleelsel tasapinnal – aluspinnal ja katusepinnal. Tasapindade vahelise kauguse mõõt on pinna üldine tasasus. Sellel tasapinnalisuse mõõtmisel on tavaliselt tolerants ja see võib sisaldada ka klassi tähistust.

The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:

DIN standard, GB standard, ASME standard, JJS standard... erinev riik erineva standardiga...

Lisateavet standardi kohta.

In addition to flatness, repeatability must be ensured. A repeat measurement is a measurement of local flatness areas. It is a measurement taken anywhere on the surface of a plate that will repeat within the stated tolerance. Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.

Selleks, et tagada pinnaplaadi vastavus nii tasapinnalisuse kui ka korduvmõõtmise spetsifikatsioonidele, peaksid graniidist pinnaplaatide tootjad oma spetsifikatsioonide alusena kasutama föderaalset spetsifikatsiooni GGG-P-463c. See standard käsitleb korduvmõõtmise täpsust, graniidist pinnaplaadi materjaliomadusi, pinnaviimistlust, tugipunktide asukohta, jäikust, vastuvõetavaid kontrollimeetodeid ja keermestatud sisestusdetailide paigaldamist.

Checking Plate Accuracy

Mõne lihtsa juhise järgimisega peaks graniidist pinnaplaati investeering kestma aastaid. Pinnaplaadi täpsuse kontrollimise sagedus varieerub sõltuvalt plaadi kasutamisest, töökoja keskkonnast ja vajalikust täpsusest. Üldine rusikareegel on, et uus plaat tuleks täielikult ümber kalibreerida ühe aasta jooksul alates ostmisest. Kui plaati kasutatakse sageli, on soovitatav seda intervalli lühendada kuue kuuni.

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

An effective inspection program should include regular checks with an autocollimator, providing actual calibration of overall flatness traceable to National Institute of Standards and Technology (NIST). Comprehensive calibration by the manufacturer or an independent company is necessary from time to time.

Variations Between Calibrations

Mõnel juhul esineb pinnaplaatide kalibreerimiste vahel erinevusi. Mõnikord võivad need erinevused olla tingitud sellistest teguritest nagu kulumisest tingitud pinnamuutus, kontrollseadmete ebaõige kasutamine või kalibreerimata seadmete kasutamine. Kaks kõige levinumat tegurit on aga temperatuur ja tugi.

One of the most important variables is temperature. For instance, the surface might have been washed with a hot or cold solution prior to calibration and not allowed sufficient time to normalize. Other causes of temperature change include drafts of cold or hot air, direct sunlight, overhead lighting or other sources of radiant heat on the surface of the plate.

There also can be variations in the vertical temperature gradient between winter and summer. In some cases, the plate is not allowed sufficient time to normalize after shipment. It is a good idea to record the vertical gradient temperature at the time the calibration is performed.

Another common cause for calibration variation is a plate that is improperly supported. A surface plate should be supported at three points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered.

Only three points can rest solidly on anything but a precision surface. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same three points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. Consider using steel stands with support beams designed to line up with the proper support points. Stands for this purpose are generally available from the surface plate manufacturer.

If the plate is properly supported, precise leveling is only necessary if an application specifies it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

Extend Plate Life

Mõne juhise järgimine vähendab graniidist pinnaplaadi kulumist ja pikendab lõpuks selle eluiga.

Esiteks on oluline hoida plaat puhtana. Õhus leviv abrasiivtolm on tavaliselt plaadi suurim kulumisallikas, kuna see kipub kinnistuma töödeldavatesse detailidesse ja mõõteriistade kokkupuutepindadesse.

It also is important to cover plates to protect it from dust and damage. Wear life can be extended by covering the plate when not in use.

Pöörake plaati perioodiliselt, et üksik ala liigselt ei koormataks. Samuti on soovitatav kalibreerimisel terasest kontaktpadjad asendada karbiidist kontaktpatjadega.

Avoid setting food or soft drinks on the plate. Many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.

Where to Relap

Kui graniidist pinnaplaat vajab uuesti pindamist, kaaluge, kas lasta see teenus teostada kohapeal või kalibreerimiskeskuses. Alati on eelistatav lasta plaat uuesti pinda panna tehases või spetsiaalses asutuses. Kui aga plaat pole liiga palju kulunud, tavaliselt nõutavast tolerantsist 0,001 tolli piires, saab selle kohapeal uuesti pinda panna. Kui plaat on kulunud punktini, kus see on tolerantsist väljas rohkem kui 0,001 tolli või kui see on tugevalt auklik või sälkuline, tuleks see enne uuesti pindamist saata tehasesse lihvimiseks.

A calibration facility has the equipment and factory setting providing the optimum conditions for proper plate calibration and rework if necessary.

Kohapealse kalibreerimis- ja pinnatöötlustehniku ​​valimisel tuleks olla väga hoolikas. Küsige akrediteeringut ja veenduge, et tehniku ​​kasutatavatel seadmetel oleks jälgitav kalibreerimine. Kogemus on samuti oluline tegur, kuna graniidi täppislihvimise õigeks õppimiseks kulub aastaid.

Critical measurements start with a precision granite surface plate as a baseline. By ensuring a reliable reference by using a properly calibrated surface plate, manufacturers have one of the essential tools for reliable measurements and better quality parts.Q

Checklist for Calibration Variations

1. Pinda pesti enne kalibreerimist kuuma või külma lahusega ja sellele ei antud piisavalt aega normaliseerumiseks.

2. Plaat on valesti toetatud.

3. Temperatuuri muutus.

4. Mustandid.

5. Otsene päikesevalgus või muu kiirgussoojus plaadi pinnal. Veenduge, et laevalgustus pinda ei kuumutaks.

6. Vertikaalse temperatuurigradiendi kõikumised talve ja suve vahel. Võimaluse korral teadke vertikaalse gradiendi temperatuuri kalibreerimise ajal.

7. Plaadil ei antud pärast saatmist piisavalt aega normaliseerumiseks.

8. Kontrollseadmete ebaõige kasutamine või kalibreerimata seadmete kasutamine.

9. Kulumisest tulenev pinna muutus.

Tech Tips

• Kuna iga lineaarmõõtmine sõltub täpsest võrdluspinnast, millelt lõplikud mõõtmed võetakse, pakuvad pinnaplaadid parimat võrdlustasandit töö kontrollimiseks ja paigutamiseks enne töötlemist.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Tõhus kontrolliprogramm peaks hõlmama regulaarseid kontrolle autokollimaatoriga, mis tagab üldise tasapinnalisuse tegeliku kalibreerimise, mida saab jälgida riikliku kontrolliasutuse poolt.

Graniiti moodustavate mineraalosakeste hulgas on üle 90% päevakivi ja kvarts, millest päevakivi on kõige rohkem. Päevakivi on sageli valge, hall ja lihapunane ning kvarts on enamasti värvitu või hallikasvalge, mis moodustavad graniidi põhivärvi. Päevakivi ja kvarts on kõvad mineraalid ja neid on terasnoaga raske liigutada. Mis puutub graniidi tumedatesse laikudesse, peamiselt musta vilgukivi, siis on ka teisi mineraale. Kuigi biotiit on suhteliselt pehme, pole selle pingetaluvus nõrk ja samal ajal on neid graniidis väike kogus, sageli alla 10%. See on materjali seisund, milles graniit on eriti tugev.

Teine põhjus, miks graniit on tugev, on see, et selle mineraalosakesed on tihedalt üksteisega seotud ja üksteise sisse põimitud. Poorid moodustavad sageli vähem kui 1% kivimi kogumahust. See annab graniidile võime taluda tugevat survet ja niiskus ei tungi sinna kergesti.

Graniitkomponendid on valmistatud kivist, millel puudub rooste-, happe- ja leeliskindlus, hea kulumiskindlus ja pikk kasutusiga, ilma erilise hoolduseta. Graniidist täppiskomponente kasutatakse enamasti masinatööstuse tööriistades. Seetõttu nimetatakse neid graniidist täppiskomponentideks või graniidist komponentideks. Graniidist täppiskomponentide omadused on põhimõtteliselt samad, mis graniidist platvormidel. Sissejuhatus graniidist täppiskomponentide tööriistadesse ja mõõtmisse: täppistöötlus ja mikrotöötlustehnoloogia on masinatööstuse olulised arengusuunad ning neist on saanud oluline näitaja kõrgtehnoloogilise taseme mõõtmiseks. Tipptehnoloogia ja kaitsetööstuse areng on lahutamatult seotud täppistöötluse ja mikrotöötlustehnoloogiaga. Graniitkomponente saab mõõtmisel sujuvalt libistada ilma paigalseisuta. Tööpinna mõõtmine ja üldised kriimustused ei mõjuta mõõtmise täpsust. Graniitkomponendid tuleb projekteerida ja toota vastavalt nõudluse poole nõuetele.

Rakendusvaldkond:

Nagu me kõik teame, valib üha rohkem masinaid ja seadmeid täppisgraniidist komponente.

Graniidist komponente kasutatakse dünaamilise liikumise, lineaarmootorite, CMM-i, CNC-i, lasermasinate...

Lisateabe saamiseks võtke meiega ühendust.

Graniidist mõõteseadmed ja graniidist mehaanilised komponendid on valmistatud kvaliteetsest Jinan Black graniidist. Tänu oma suurele täpsusele, pikaealisusele, heale stabiilsusele ja korrosioonikindlusele on neid üha enam kasutatud tänapäevase tööstuse tootekontrollis ja sellistes teadusvaldkondades nagu mehaanika, lennundus ja teadusuuringud.

Eelised

----Kaks korda kõvem kui malm；

---- Minimaalsed mõõtmete muutused tulenevad temperatuurimuutustest；

----Väänamisvaba, seega töö ei katke;

----Peeneteralise struktuuri ja ebaolulise kleepuvuse tõttu ilma servade või eenditeta, mis tagab pika kasutusea jooksul kõrge tasapinnalisuse ega kahjusta teisi osi ega instrumente;

----Magnetiliste materjalidega töötamise tõrgeteta töö;

----Pikk eluiga ja roostevaba, mille tulemuseks on madalad hoolduskulud.

Täppis-graniidist pinnaplaadid on täpselt lihvitud kõrge tasapinnaga, et saavutada täpsus ja neid kasutatakse keerukate mehaaniliste, elektrooniliste ja optiliste mõõtmissüsteemide paigaldamise alusena.

Mõned graniidist pinnaplaadi ainulaadsed omadused:

Kõvaduse ühtlus;

Täpne koormustingimustes;

Vibratsiooni neelav;

Lihtne puhastada;

Mähiskindel;

Madal poorsus;

Mitteabrasiivne;

Mittemagnetiline

Graniidist pinnaplaadi eelised

First, the rock after a long period of natural aging, uniform structure, coefficient minimum, the internal stress completely disappear, not deformed, so the precision is high.

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Precision Granite Base Can Improve Machine Tool Performances

Requirements are constantly increasing in mechanical engineering in general and in machine tool construction in particular. Achieving maximum precision and performance values without increasing costs are constant challenges to being competitive. The machine tool bed is a decisive factor here. Therefore, more and more machine tool manufacturers are relying on granite. Due to its physical parameters, it offers clear advantages that cannot be achieved with steel or polymer concrete.

Granite is a so-called volcanic deep rock and has a very dense and homogeneous structure with an extremely low coefficient of expansion, low thermal conductivity and high vibration damping.

Below you will discover why the common opinion that granite is mainly only suitable as machine base for high-end coordinate measuring machines is long outdated and why this natural material as a machine tool base is a very advantageous alternative to steel or cast iron even for high-precision machine tools.

We can manufacture granite components for dynamic motion, granite components for linear motors, granite components for ndt, granite components for xray, granite components for cmm, granite components for cnc, granite precision for laser, granite components for aerospace, granite components for precision stages...

High Added Value Without Additional Costs
The increasing use of granite in mechanical engineering is not so much due to the massive increase in the price of steel. Rather, it is because the added value for the machine tool achieved with a machine bed made of granite is possible at very little or no extra cost. This is proven by cost comparisons of well-known machine tool manufacturers in Germany and Europe.

The considerable gain in thermodynamic stability, vibration damping and long-term precision made possible by granite cannot be achieved with a cast iron or steel bed, or only at relatively high cost. For example, thermal errors can account for up to 75% of the total error of a machine, with compensation often attempted for by software – with moderate success. Due to its low thermal conductivity, granite is the better foundation for long-term precision.

With a tolerance of 1 μm, granite easily meets the flatness requirements according to DIN 876 for the degree of accuracy 00. With a value of 6 on the hardness scale 1 to 10, it is extremely hard, and with its specific weight of 2.8g/cm³ it almost reaches the value of aluminium. This also results in additional advantages such as higher feed rates, higher axis accelerations and an extension of the tool life for cutting machine tools. Thus, the change from a cast bed to a granite machine bed moves the machine tool in question into the high-end class in terms of precision and performance – at no extra cost.

Granite’s Improved Ecological Footprint
In contrast to materials such as steel or cast iron, natural stone does not have to be produced with a great deal of energy and using additives. Only relatively small amounts of energy are required for quarrying and surface treatment. This results in a superior ecological footprint, which even at the end of a machine’s life surpasses that of steel as a material. The granite bed can be the basis for a new machine or be used for completely different purposes such as shredding for road construction.

Nor are there any shortages of resources for granite. It is a deep rock formed from magma within the earth’s crust. It has ‘matured’ for millions of years and is available in very large quantities as a natural resource on almost all continents, including all of Europe.

Conclusion: The numerous demonstrable advantages of granite compared to steel or cast iron justify the increasing willingness of mechanical engineers to use this natural material as a foundation for high-precision, high-performance machine tools. Detailed information about granite properties, which are advantageous for machine tools and mechanical engineering, can be found in this further article.

A repeat measurement is a measurement of local flatness areas. The Repeat Measurement specification states that a measurement taken anywhere on the surface of a plate will repeat within the stated tolerance. Controlling local area flatness tighter than overall flatness guarantees a gradual change in surface flatness profile thereby minimizing local errors.

Most manufacturers, including imported brands, adhere to the Federal Specification of overall flatness tolerances but many overlook the repeat measurements. Many of the low value or budget plates available in the market today will not guarantee repeat measurements. A manufacturer who does not guarantee repeat measurements is NOT producing plates that meet the requirements of ASME B89.3.7-2013 or Federal Specification GGG-P-463c, or DIN 876, GB, JJS...

Both are critical to ensure a precision surface for accurate measurements. Flatness specification alone is not sufficient to guarantee measurement accuracy. Take as an example, a 36 X 48 Inspection Grade A surface plate, which meets ONLY the flatness specification of .000300". If the piece being checked bridges several peaks, and the gage being used is in a low spot, the measurement error could be the full tolerance in one area, 000300"! Actually, it can be much higher if the gage is resting on the slope of an incline.

Errors of .000600"-.000800" are possible, depending upon the severity of the slope, and the arm length of the gage being used. If this plate had a Repeat Measurement specification of .000050"F.I.R. then the measurement error would be less than .000050" regardless of where the measurement is taken on the plate. Another problem, which usually arises when an untrained technician attempts to resurface a plate on-site, is the use of Repeat Measurements alone to certify a plate.

The instruments that are used to verify repeatability are NOT designed to check overall flatness. When set to zero on a perfectly curved surface, they will continue to read zero, whether that surface is perfectly flat or perfectly concave or convex 1/2"! They simply verify the uniformity of the surface, not the flatness. Only a plate that meets both the flatness specification AND the repeat measurement specification truly meets the requirements of ASME B89.3.7-2013  or Federal Specification GGG-P-463c.

Ask us about or flatness specification and repeat measurement promise by calling +86 19969991659 or emailing INFO@ZHHIMG.COM

Yes, but they can only be guaranteed for a specific vertical temperature gradient. The effects of thermal expansion on the plate could easily cause a change in accuracy greater than the tolerance if there is a change in the gradient. In some cases, if the tolerance is tight enough, the heat absorbed from overhead lighting can cause enough of a gradient change over several hours.

Granite has a coefficient of thermal expansion of approximately .0000035 inches per inch per 1°F. As an example: A 36" x 48" x 8" surface plate has an accuracy of .000075" (1/2 of Grade AA) at a gradient of 0°F, the top and bottom are the same temperature. If the top of the plate warms up to the point where it is 1°F warmer than the bottom, the accuracy would change to .000275" convex ! Therefore, ordering a plate with a tolerance tighter than Laboratory Grade AA should only be considered if there is adequate climate control.

A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.

The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. All zhhimg steel stands have support beams designed to line up with the proper support points.

If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

Why Choose Granite for Machine Bases and Metrology Components?

The answer is 'yes' for almost every application. The advantages of granite include: No rust or corrosion, almost immune to warping, no compensating hump when nicked, longer wear life, smoother action, greater precision, virtually non-magnetic, low co-efficient of thermal expansion, and low maintenance cost.

Granite is a type of igneous rock quarried for its extreme strength, density, durability, and resistance to corrosion. But granite is also very versatile– it’s not just for squares and rectangles! In fact, Starrett Tru-Stone confidently works with granite components engineered in shapes, angles, and curves of all variations on a regular basis—with excellent outcomes.

Through our state of the art processing, cut surfaces can be exceptionally flat. These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components. Granite is:

machineable
precisely flat when cut and finished
rust resistant
durable
long lasting
Granite components are also easy to clean. When creating custom designs, be sure to choose granite for its superior benefits.

STANDARDS / HIGH WEAR APPLICATIONS
The granite utilized by ZhongHui for our standard surface plate products has high quartz content, which provides greater resistance to wear and damage. Our Superior Black and Crystal Pink colors have low water absorption rates, minimizing the possibility of your precision gages rusting while setting on the plates. The colors of granite offered by ZhongHui result in less glare, which means less eyestrain for individuals using the plates. We have chosen our granite types while considering thermal expansion in an effort to keep this aspect minimal.

CUSTOM APPLICATIONS
When your application calls for a plate with custom shapes, threaded inserts, slots or other machining, you’ll want to select a material like Black Diabase. This natural material offers superior stiffness, excellent vibration dampening, and improved machinability.

Yes, if they are not too badly worn. Our factory setting and equipment allow the optimum conditions for proper plate calibration and rework if necessary. Generally, if a plate is within .001" of the required tolerance, it can be resurfaced on-site. If a plate is worn to the point where it is more than .001" out of tolerance, or if it is badly pitted or nicked, then it will need to be sent to the factory for grinding prior to relapping.

Great care should be exercised in selecting an on-site calibration and resurfacing technician. We urge you to use caution in selecting your calibration service. Ask for accreditation and verify the equipment that the technician will use has a National Inspection Institution traceable calibration. It takes many years to learn how to properly lap precision granite.

ZhongHui provides quick turn-around on calibrations performed in our factory. Send your plates in for calibration if possible. Your quality and reputation depend on the accuracy of your measurement instruments including surface plates!

Our black surface plates have a significantly higher density and are up to three times as stiff. Therefore, a plate made of the black does not need to be as thick as a granite plate of the same size to have equal or greater resistance to deflection. Reduced thickness means less weight and lower shipping costs.

Beware of others who use lower quality black granite in the same thickness. As stated above, properties of granite, like wood or metal, vary by material and color, and is not an accurate predictor of stiffness, hardness, or wear resistance. In fact, many types of black granite and diabase are very soft and not suitable for surface plate applications.

No. The specialized equipment and training necessary to rework these items requires that they be returned to the factory for calibration and rework.

Yes. Ceramic and granite have similar characteristics, and the methods used to calibrate and lap granite can be used with ceramic items as well. Ceramics are more difficult to lap than granite resulting in a higher cost.

Yes, provided that the inserts are recessed below the surface. If steel inserts are flush with, or above the surface plane, they must be spot-faced down before the plate can be lapped. If required, we can provide that service.

Yes. Steel inserts with the desired thread (English or metric) can be epoxy bonded into the plate at the desired locations. ZhongHui uses CNC machines to provide the tightest insert locations within +/- 0.005”. For less critical inserts, our locational tolerance for threaded inserts is ±.060". Other options include steel T-Bars and dovetail slots machined directly into the granite.

Inserts that are properly bonded using high strength epoxy and good workmanship will withstand a great deal of torsional and shear force. In a recent test, using 3/8"-16 threaded inserts, an independent testing laboratory measured the force required to pull an epoxy-bonded insert from a surface plate. Ten plates were tested. Out of these ten, in nine cases, the granite fractured first. The average load at the point of failure was 10,020 lbs. for gray granite and 12,310 lbs. for black. In the single case where an insert pulled free of the plate, the load at the point of failure was 12,990 lbs.! If a work piece forms a bridge across the insert and extreme torque is applied, it is possible to generate enough force to fracture the granite. Partially for this reason, ZhongHui gives guidelines for the maximum safe torque that can be applied the epoxy bonded inserts: https://www.zhhimg.com/standard-thread-inserts-product/

Yes, but only at our factory. At our plant, we can restore almost any plate to 'like-new' condition, usually for less than half the cost of replacing it. Damaged edges can be cosmetically patched, deep grooves, nicks, and pits can be ground out, and the attached supports can be replaced. In addition, we can modify your plate to increase its versatility by adding solid or threaded steel inserts and cutting slots or clamping lips, per your specifications.

Why Choose Granite?
Granite is a type of igneous rock formed in the Earth millions of years ago. The composition of igneous rock contained many minerals such as quartz that is extremely hard and wear-resistant. In addition to hardness and wear resistance granite has approximately half the coefficient of expansion as cast iron. As its volumetric weight is approximately one third that of cast iron, granite is easier to manoeuvre.

For machine bases and metrology components, black granite is the colour most used. Black granite has a higher percentage of quartz than other colours and is, therefore, the hardest wearing.

Granite is cost-effective, and cut surfaces can be exceptionally flat. Not only can it be hand lapped to achieve extremes of accuracy, but re-conditioning can be performed without moving the plate or table off-site. It is entirely a hand lapping operation and generally costs much less than re-conditioning a cast iron alternative.

These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components such as the granite surface plate.

ZhongHui produces bespoke granite products that are created to support specific measurement requirements. These bespoke items vary from straight edges to tri squares. Due to the versatile nature of granite, the components can be produced to any size required; they are hard wearing and long-lasting.

Advantages of Granite Surface Plates
The importance of measuring on an even surface was established by British inventor Henry Maudsley in the 1800s. As a machine tool innovator, he determined that consistent production of parts required a solid surface for reliable measurements.

The industrial revolution created a demand for measuring surfaces, so engineering company Crown Windley created manufacturing standards. The standards for surface plates were first set by Crown in 1904 using metal. As the demand and cost for metal increased, alternative materials for the measuring surface were investigated.

In America, monument creator Wallace Herman established that black granite was an excellent surface plate material alternative to metal. As granite is non-magnetic and doesn’t rust, it soon became the preferred measuring surface.

A granite surface plate is an essential investment for laboratories and test facilities. A granite surface plate of 600 x 600 mm can be mounted on a support stand. The stands provide a working height of 34” (0.86m) with five adjustable points for levelling.

For reliable and consistent measurement results, a granite surface plate is crucial. As the surface is a smooth and stable plane, it enables instruments to be carefully manipulated.

The main advantages of granite surface plates are:

• Non-reflective
• Resistant to chemicals and corrosion
• Low coefficient of expansion compared with cart iron so less affected by temperature change
• Naturally rigid and hard-wearing
• The plane of the surface is unaffected if scratched
• Will not rust
• Non-magnetic
• Easy to clean and maintain
• Calibration and resurfacing can be done onsite
• Suitable for drilling for threaded support inserts
• High vibration damping

For many shops, inspection rooms and laboratories, precision granite surface plates are relied on as the basis for accurate measurement. Because every linear measurement depends on an accurate reference surface from which final dimensions are taken, surface plates provide the best reference plane for work inspection and layout prior to machining. They also are ideal bases for making height measurements and gaging surfaces. Further, a high degree of flatness, stability, overall quality and workmanship make them a good choice for mounting sophisticated mechanical, electronic and optical gaging systems. For any of these measurement processes, it is imperative to keep surface plates calibrated.

Repeat Measurements and Flatness
Both flatness and repeat measurements are critical to ensure a precision surface. Flatness can be considered as all points on the surface being contained within two parallel planes, the base plane and the roof plane. The measurement of distance between the planes is the overall flatness of the surface. This flatness measurement commonly carries a tolerance and may include a grade designation.

The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:
Laboratory Grade AA = (40 + diagonal² / 25) x 0.000001 inch (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4

In addition to flatness, repeatability must be ensured. A repeat measurement is a measurement of local flatness areas. It is a measurement taken anywhere on the surface of a plate that will repeat within the stated tolerance. Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.

To ensure a surface plate meets both the flatness and repeat measurement specifications, manufacturers of granite surface plates should use Federal Specification GGG-P-463c as a basis for their specifications. This standard addresses repeat measurement accuracy, material properties of surface plate granites, surface finish, support point location, stiffness, acceptable methods of inspection and installation of threaded inserts.

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

Checking Plate Accuracy
By following a few simple guidelines, an investment in a granite surface plate should last for many years. Depending on plate usage, shop environment and required accuracy, frequency of checking the surface plate accuracy varies. A general rule of thumb is for a new plate to receive a full recalibration within one year of purchase. If the plate is used frequently, it is advisable to shorten this interval to six months.

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

An effective inspection program should include regular checks with an autocollimator, providing actual calibration of overall flatness traceable to National Institute of Standards and Technology (NIST). Comprehensive calibration by the manufacturer or an independent company is necessary from time to time.

Variations Between Calibrations
In some cases, there are variations between surface plate calibrations. Sometimes factors such as surface change resulting from wear, incorrect use of inspection equipment or use of noncalibrated equipment can account for these variations. The two most common factors, however, are temperature and support.

One of the most important variables is temperature. For instance, the surface might have been washed with a hot or cold solution prior to calibration and not allowed sufficient time to normalize. Other causes of temperature change include drafts of cold or hot air, direct sunlight, overhead lighting or other sources of radiant heat on the surface of the plate.

There also can be variations in the vertical temperature gradient between winter and summer. In some cases, the plate is not allowed sufficient time to normalize after shipment. It is a good idea to record the vertical gradient temperature at the time the calibration is performed.

Another common cause for calibration variation is a plate that is improperly supported. A surface plate should be supported at three points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered.

Only three points can rest solidly on anything but a precision surface. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same three points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. Consider using steel stands with support beams designed to line up with the proper support points. Stands for this purpose are generally available from the surface plate manufacturer.

If the plate is properly supported, precise leveling is only necessary if an application specifies it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

It is important to keep the plate clean. Airborne abrasive dust is usually the greatest source of wear and tear on a plate, as it tends to embed in workpieces and the contact surfaces of gages. Cover plates to protect them from dust and damage. Wear life can be extended by covering the plate when not in use.

Extend Plate Life
Following a few guidelines will reduce wear on a granite surface plate and ultimately, extend its life.

First, it is important to keep the plate clean. Airborne abrasive dust is usually the greatest source of wear and tear on a plate, as it tends to embed in workpieces and the contact surfaces of gages.

It also is important to cover plates to protect it from dust and damage. Wear life can be extended by covering the plate when not in use.

Rotate the plate periodically so that a single area does not receive excessive use. Also, it is recommended to replace steel contact pads on gaging with carbide pads.

Avoid setting food or soft drinks on the plate. Many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.

Where to Relap
When a granite surface plate needs re-surfacing, consider whether to have this service performed on-site or at the calibration facility. It is always preferable to have the plate relapped at the factory or a dedicated facility. If, however, the plate is not too badly worn, generally within 0.001 inch of the required tolerance, it can be resurfaced on-site. If a plate is worn to the point where it is more than 0.001 inch out of tolerance, or if it is badly pitted or nicked, then it should be sent to the factory for grinding prior to relapping.

A calibration facility has the equipment and factory setting providing the optimum conditions for proper plate calibration and rework if necessary.

Great care should be exercised in selecting an on-site calibration and resurfacing technician. Ask for accreditation and verify the equipment that the technician will use has a NIST-traceable calibration. Experience also is an important factor, as it takes many years to learn how to correctly lap precision granite.

Critical measurements start with a precision granite surface plate as a baseline. By ensuring a reliable reference by using a properly calibrated surface plate, manufacturers have one of the essential tools for reliable measurements and better quality parts.

Checklist for Calibration Variations

1. The surface was washed with a hot or cold solution prior to calibration and was not allowed sufficient time to normalize.
2. The plate is improperly supported.
3. Temperature change.
4. Drafts.
5. Direct sunlight or other radiant heat on the surface of the plate. Be sure that overhead lighting is not heating the surface.
6. Variations in the vertical temperature gradient between winter and summer. If at all possible, know the vertical gradient temperature at the time the calibration is performed.
7. Plate not allowed sufficient time to normalize after shipment.
8. Improper use of inspection equipment or use of noncalibrated equipment.
9. Surface change resulting from wear.

Tech Tips
Because every linear measurement depends on an accurate reference surface from which final dimensions are taken, surface plates provide the best reference plane for work inspection and layout prior to machining.

Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.