Granitoa arroka igneo mota bat da, bere erresistentzia, dentsitate, iraunkortasun eta korrosioarekiko erresistentzia handiagatik ateratzen dena. Baina granitoa oso polifazetikoa ere bada: ez da karratu eta laukizuzenetarako bakarrik! Izan ere, konfiantzaz lan egiten dugu forma, angelu eta kurba guztietako granitozko osagaiekin, aldizka, emaitza bikainak lortuz.
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:
■ mekanizagarria
■ Zehazki laua moztu eta amaitutakoan
■ herdoilaren aurkakoa
■ iraunkorra
■ iraupen luzeko
Granitozko osagaiak ere erraz garbitzen dira. Diseinu pertsonalizatuak sortzerakoan, ziurtatu granitoa aukeratzen duzula bere onura bikainak direla eta.

ESTANDARRAK / HIGADURA HANDIA DUTEN APLIKAZIOAK
ZHHIMG-k gure gainazaleko plaka estandarretarako erabiltzen duen granitoak kuartzo eduki handia du, eta horrek higadura eta kalteen aurkako erresistentzia handiagoa ematen du. Gure Superior Black koloreek ur xurgapen-tasa baxua dute, eta horrek zure zehaztasun-neurgailuak plaketan jartzean herdoiltzeko aukera gutxitzen du. ZHHIMG-k eskaintzen dituen granitoaren koloreek distira gutxiago eragiten dute, eta horrek esan nahi du plakak erabiltzen dituzten pertsonen begi-nekea txikiagoa dela. Gure granito motak aukeratu ditugu hedapen termikoa kontuan hartuta, alderdi hori ahalik eta txikiena izan dadin.

CUSTOM APPLICATIONS
Zure aplikazioak forma pertsonalizatuak, haridun txertaketak, zirrikituak edo bestelako mekanizazioa eskatzen duenean, Black Jinan Black bezalako material bat aukeratu beharko duzu. Material natural honek zurruntasun handiagoa, bibrazioen moteltze bikaina eta mekanizagarritasun hobea eskaintzen ditu.

Garrantzitsua da kontuan izatea kolorea bakarrik ez dela harriaren ezaugarri fisikoen adierazle. Oro har, granitoaren kolorea zuzenean lotuta dago mineralen presentziarekin edo gabeziarekin, eta horrek ez du eraginik izan gainazaleko plaka material ona egiten duten ezaugarrietan. Gainazaleko plaketarako bikainak diren granito arrosa, grisa eta beltza daude, baita doitasun aplikazioetarako guztiz desegokiak diren granito beltza, grisa eta arrosa ere. Granitoaren ezaugarri kritikoek, gainazaleko plaka material gisa erabiltzeari dagokionez, ez dute zerikusirik kolorearekin, eta hauek dira:
■ Zurruntasuna (kargaren peko deformazioa - Elastikotasun Moduluak adierazten du)
■ Gogortasuna
■ Dentsitatea
■ Higaduraren erresistentzia
■ Egonkortasuna
■ Porositatea

Granitozko material asko probatu eta alderatu ditugu. Azkenean emaitza hau lortu dugu: Jinango granito beltza ezagutu dugun material onena da. Indiako granito beltza eta Hegoafrikako granitoa Jinango granito beltzaren antzekoak dira, baina haien propietate fisikoak Jinango granito beltzarenak baino txikiagoak dira. ZHHIMGk munduan granitozko material gehiago bilatzen jarraituko du eta haien propietate fisikoak alderatuko ditu.

Zure proiekturako granito egokiari buruz gehiago hitz egiteko, jarri gurekin harremanetaninfo@zhhimg.com.

Fabrikatzaile ezberdinek estandar desberdinak erabiltzen dituzte. Munduan estandar asko daude.
DIN Araua, ASME B89.3.7-2013 edo GGG-P-463c Zehaztapen Federala (Granitozko Gainazaleko Plakak) eta abar beren zehaztapenen oinarri gisa.

Eta granitozko zehaztasun-ikuskapen plaka fabrikatu dezakegu zure eskakizunen arabera. Jar zaitez gurekin harremanetan estandar gehiagori buruzko informazio gehiago jakin nahi baduzu.

Lautasuna gainazaleko puntu guztiak bi plano paraleloren barruan daudela kontsidera daiteke, oinarrizko planoaren eta teilatuaren planoaren barruan. Planoen arteko distantziaren neurketa gainazalaren lautasun orokorra da. Lautasun neurketa honek normalean tolerantzia bat izaten du eta kalifikazioaren izendapena izan dezake.

Adibidez, hiru maila estandarren lautasun-tolerantziak zehaztapen federaletan definitzen dira, formula honen bidez zehaztuta:
■ Laborategiko mailako AA = (40 + diagonal karratua/25) x 0,000001" (aldebakarrekoa)
■ A ikuskapen maila = AA laborategiko maila x 2
■ Tresna-gela B maila = Laborategiko AA maila x 4.

Tamaina estandarreko gainazaleko plaketarako, zehaztapen honen eskakizunak gainditzen dituzten lautasun-tolerantziak bermatzen ditugu. Lautasunaz gain, ASME B89.3.7-2013 eta GGG-P-463c zehaztapen federalak honako gai hauek jorratzen dituzte: neurketa errepikakorraren zehaztasuna, gainazaleko plaken granitoen materialen propietateak, gainazalaren akabera, euskarri-puntuaren kokapena, zurruntasuna, ikuskapen-metodo onargarriak, haridun txertatzeen instalazioa, etab.

ZHHIMG granitozko gainazaleko plakek eta granitozko ikuskapen-plakek zehaztapen honetan ezarritako baldintza guztiak betetzen edo gainditzen dituzte. Gaur egun, ez dago granitozko angelu-plaken, paraleloen edo eskuadra nagusien zehaztapenik.

Eta beste estandar batzuen formulak aurki ditzakezu hemen:DESKARGATU.

Lehenik eta behin, garrantzitsua da plaka garbi mantentzea. Airean dagoen hauts urratzailea izan ohi da plaka baten higadura-iturri handiena, lan-piezetan eta neurgailuen kontaktu-gainazaletan itsatsita geratzen baita. Bigarrenik, estali plaka hautsetik eta kalteetatik babesteko. Higadura-bizitza luzatu daiteke plaka erabiltzen ez denean estaliz, plaka aldian-aldian biratuz eremu bakar batek gehiegi erabili ez dezan, eta neurgailuetako altzairuzko kontaktu-padak karburozko padekin ordezkatuz. Gainera, saihestu janaria edo freskagarriak plakan jartzea. Kontuan izan freskagarri askok azido karbonikoa edo fosforikoa dutela, eta horrek mineral bigunagoak disolbatu eta zulo txikiak utz ditzakeela gainazalean.

Hori platera nola erabiltzen den araberakoa da. Ahal bada, platera egunaren hasieran (edo lan-txandan) eta berriro amaieran garbitzea gomendatzen dugu. Platera zikintzen bada, batez ere fluido koipetsu edo itsaskorrekin, berehala garbitu beharko litzateke ziurrenik.

Garbitu plaka aldizka likidoarekin edo ZHHIMG ur gabeko gainazaleko plaken garbitzailearekin. Garbiketa-soluzioen aukera garrantzitsua da. Disolbatzaile lurrunkor bat erabiltzen bada (azetona, laka-mehetzailea, alkohola, etab.), lurruntzeak gainazala hoztu eta desitxuratu egingo du. Kasu honetan, plaka normalizatzen utzi behar da erabili aurretik, bestela neurketa-erroreak gertatuko dira.

Plaka normalizatzeko behar den denbora plakaren tamainaren eta hozte-kopuruaren araberakoa izango da. Ordubete nahikoa izan beharko litzateke plaka txikiagoetarako. Bi ordu behar izan daitezke plaka handiagoetarako. Uretan oinarritutako garbitzaile bat erabiltzen bada, lurruntze-hozte pixka bat ere egongo da.

Plakak ura ere atxikiko du, eta horrek gainazalarekin kontaktuan dauden metalezko piezen herdoila eragin dezake. Garbitzaile batzuek hondakin itsaskor bat uzten dute lehortu ondoren, eta horrek aireko hautsa erakarriko du, eta higadura handituko du, gutxitu beharrean.

Hori plakaren erabileraren eta ingurunearen araberakoa da. Gomendatzen dugu plaka berri bat edo granitozko osagarri zehatz bat erosi eta urtebeteko epean berriro kalibratzea. Granitozko gainazaleko plakak erabilera handia izango badu, komenigarria izan daiteke tarte hori sei hilabetera laburtzea. Maila elektroniko bat edo antzeko gailu bat erabiliz errepikatutako neurketa-erroreen hileroko ikuskapenak higadura-orbanak erakutsiko ditu eta minutu gutxi batzuk besterik ez ditu behar egiteko. Lehenengo berriro kalibrazioaren emaitzak zehaztu ondoren, kalibrazio-tartea luzatu edo laburtu daiteke, zure barne-kalitate-sistemak baimentzen edo eskatzen duen moduan.

Zure granitozko gainazaleko plaka ikuskatzen eta kalibratzen laguntzeko zerbitzua eskain dezakegu.

Hainbat arrazoi posible daude kalibrazioen arteko aldaketen kasuan:

• Gainazala disoluzio bero edo hotz batekin garbitu zen kalibrazioa egin aurretik, eta ez zitzaion denbora nahikorik eman normalizatzeko.
• Plaka gaizki euskarria dago
• Tenperatura aldaketa
• Zirriborroak
• Eguzki-argia zuzenean edo beste bero erradiatzaile bat plakaren gainazalean. Ziurtatu goiko argiak ez duela gainazala berotzen.
• Neguaren eta udaren arteko tenperatura-gradiente bertikalaren aldaketak (Ahal bada, jakin ezazu gradiente bertikalaren tenperatura kalibrazioa egiten den unean.)
• Bidalketaren ondoren, plakak ez du behar adina denborarik izan normalizatzeko
• Ikuskapen-ekipoen erabilera desegokia edo kalibratu gabeko ekipoen erabilera
• Higaduraren ondoriozko gainazaleko aldaketa

Zenbat zulo mota daude granito zehatzean?

Granitozko zehaztasun-osagaien zirrikituak

Fabrika, ikuskapen-gela eta laborategi askotan, granitozko gainazal-plaka zehatzak erabiltzen dira neurketa zehatzak egiteko oinarri gisa. Neurketa lineal bakoitza erreferentzia-gainazal zehatz baten mende dagoenez, eta bertatik azken dimentsioak hartzen dira, gainazal-plakek erreferentzia-plano onena eskaintzen dute lanaren ikuskapenerako eta mekanizatu aurretik diseinurako. Altuera-neurketak egiteko eta gainazalak neurtzeko oinarri aproposak ere badira. Gainera, lautasun, egonkortasun, kalitate orokorra eta fabrikazio-maila handiak aukera ona bihurtzen dituzte neurketa-sistema mekaniko, elektroniko eta optiko sofistikatuak muntatzeko. Neurketa-prozesu horietako edozeinetarako, ezinbestekoa da gainazal-plakak kalibratuta mantentzea.

Repeat Measurements and Flatness

Lautasuna eta errepikapen-neurketak funtsezkoak dira gainazal zehatz bat bermatzeko. Lautasuna gainazaleko puntu guztiak bi plano paraleloren barruan daudela kontsidera daiteke, oinarrizko planoaren eta teilatuaren planoaren barruan. Planoen arteko distantziaren neurketa gainazalaren lautasun orokorra da. Lautasun-neurketa honek normalean tolerantzia bat izaten du eta kalifikazio-izendapena izan dezake.

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

DIN estandarra, GB estandarra, ASME estandarra, JJS estandarra... herrialde desberdinak euskarri desberdinekin...

Xehetasun gehiago estandarrari buruz.

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.

Gainazaleko plaka batek lautasunaren eta neurketa errepikatuaren zehaztapenak betetzen dituela ziurtatzeko, granitozko gainazaleko plaken fabrikatzaileek GGG-P-463c zehaztapen federala erabili beharko lukete beren zehaztapenetarako oinarri gisa. Arau honek neurketa errepikatuaren zehaztasuna, gainazaleko plakaren granitoaren materialaren propietateak, gainazalaren akabera, euskarri puntuaren kokapena, zurruntasuna, ikuskapen metodo onargarriak eta haridun txertatzeen instalazioa jorratzen ditu.

Checking Plate Accuracy

Jarraibide sinple batzuk jarraituz gero, granitozko gainazaleko plaka batean egindako inbertsio batek urte asko iraun beharko luke. Plakaren erabileraren, tailerreko ingurunearen eta behar den zehaztasunaren arabera, gainazaleko plakaren zehaztasuna egiaztatzeko maiztasuna aldatu egiten da. Oro har, plaka berri batek erosketa egin eta urtebeteko epean berriro kalibratzea da. Plaka maiz erabiltzen bada, komeni da tarte hori sei hilabetera laburtzea.

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

Kasu batzuetan, gainazaleko plaken kalibrazioen artean aldaketak daude. Batzuetan, higaduraren ondoriozko gainazalaren aldaketa, ikuskapen-ekipoen erabilera okerra edo kalibratu gabeko ekipamenduen erabilera bezalako faktoreek azal dezakete aldaketa horiek. Hala ere, bi faktore ohikoenak tenperatura eta euskarria dira.

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

Jarraibide batzuk jarraitzeak granitozko gainazaleko plakaren higadura murriztuko du eta, azken finean, bere bizitza luzatuko du.

Lehenik eta behin, garrantzitsua da plaka garbi mantentzea. Airean dagoen hauts urratzailea izan ohi da plaka baten higadura-iturri handiena, piezetan eta neurgailuen kontaktu-gainazaletan txertatzeko joera baitu.

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.

Biratu plaka aldian-aldian, eremu bakar batek gehiegi ez erabiltzeko. Gainera, gomendagarria da neurgailuetan altzairuzko kontaktu-plakak karburozko plakekin ordezkatzea.

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

Granitozko gainazaleko plaka bat berriro gainazalizatu behar denean, kontuan hartu zerbitzu hau bertan edo kalibrazio instalazioan egin behar den. Beti da hobe plaka fabrikan edo instalazio dedikatu batean berriro gainazalizatzea. Hala ere, plaka ez badago oso higatuta, normalean beharrezko tolerantziatik 0,001 hazbeteko barruan, bertan berriro gainazalizatu daiteke. Plaka bat tolerantziatik 0,001 hazbete baino gehiago kanpo geratzen den punturaino higatuta badago, edo oso zulatua edo koska badago, fabrikara bidali behar da berriro gainazalizatu aurretik leundu dezaten.

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

Kontu handiz ibili behar da tokian bertan kalibratzeko eta gainazalak konpontzeko teknikari bat aukeratzerakoan. Eskatu akreditazioa eta egiaztatu teknikariak erabiliko duen ekipamenduak kalibrazio trazagarria duela. Esperientzia ere faktore garrantzitsua da, urte asko behar baitira granito zehatza behar bezala lapatzen ikasteko.

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. Gainazala disoluzio bero edo hotz batekin garbitu zen kalibrazioa egin aurretik eta ez zitzaion denbora nahikorik eman normalizatzeko.

2. Plaka ez dago behar bezala euskarrituta.

3. Tenperatura aldaketa.

4. Zirriborroak.

5. Eguzki-argia zuzenean edo bestelako bero erradiatzailea plakaren gainazalean. Ziurtatu goiko argiak ez duela gainazala berotzen.

6. Neguaren eta udaren arteko tenperatura-gradiente bertikalaren aldaketak. Ahal bada, jakin ezazu kalibrazioa egiten den unean gradiente bertikalaren tenperatura.

7. Bidalketaren ondoren, plakak ez du behar adina denborarik izan normalizatzeko.

8. Ikuskapen-ekipoen erabilera desegokia edo kalibratu gabeko ekipoen erabilera.

9. Higaduraren ondoriozko gainazalaren aldaketa.

Tech Tips

• Neurketa lineal bakoitza azken dimentsioak hartzen diren erreferentzia-gainazal zehatz baten mende dagoenez, gainazal-plakek erreferentzia-plano onena eskaintzen dute lanaren ikuskapenerako eta mekanizatu aurretik diseinurako.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Ikuskapen programa eraginkor batek autokolimadore batekin aldizkako egiaztapenak izan beharko lituzke, Ikuskapen Agintaritza Nazionalera trazagarria den lautasun orokorraren kalibrazio erreala eskainiz.

Granitoa osatzen duten mineral partikulen artean, % 90 baino gehiago feldespatoa eta kuartzoa dira, eta horien artean feldespatoa da gehienbat. Feldespatoa askotan zuria, grisa eta haragi-gorria izaten da, eta kuartzoa gehienbat koloregabea edo zuri grisaxka da, eta horiek osatzen dute granitoaren oinarrizko kolorea. Feldespatoa eta kuartzoa mineral gogorrak dira, eta zaila da altzairuzko labana batekin mugitzea. Granitoan dauden orban ilunei dagokienez, batez ere mika beltza, beste mineral batzuk ere badaude. Biotita nahiko biguna den arren, tentsioari aurre egiteko duen gaitasuna ez da ahula, eta, aldi berean, kantitate txikia dute granitoan, askotan % 10 baino gutxiago. Hau da granitoa bereziki sendoa den material-baldintza horretan.

Granitoa sendoa izatearen beste arrazoi bat da bere mineral partikulak elkarri estu lotuta daudela eta elkarren artean txertatuta daudela. Poroek askotan arrokaren bolumen osoaren % 1 baino gutxiago hartzen dute. Horrek granitoari presio handiak jasateko gaitasuna ematen dio eta hezetasunak ez du erraz zeharkatzen.

Granitozko osagaiak harriz eginda daude, herdoilik, azido eta alkali erresistenteak, higadura erresistentzia ona eta bizitza erabilgarri luzea, mantentze berezirik behar ez dutenak. Granitozko zehaztasun osagaiak gehienbat makineria industriako tresnetan erabiltzen dira. Horregatik, granitozko zehaztasun osagaiak edo granitozko osagaiak deitzen zaie. Granitozko zehaztasun osagaien ezaugarriak funtsean granitozko plataformen berdinak dira. Sarrera tresneriara eta granitozko zehaztasun osagaien neurketara: Zehaztasun mekanizazioa eta mikromekanizazio teknologia makineria fabrikazio industriaren garapen norabide garrantzitsuak dira, eta goi-mailako teknologia neurtzeko adierazle garrantzitsu bihurtu dira. Punta-puntako teknologiaren eta defentsa industriaren garapena zehaztasun mekanizaziotik eta mikromekanizazio teknologiatik bereizezina da. Granitozko osagaiak leunki irristatu daitezke neurketan, geldirik egon gabe. Lan gainazalaren neurketa, marradura orokorrek ez dute neurketaren zehaztasunean eragiten. Granitozko osagaiak eskariaren eskakizunen arabera diseinatu eta ekoitzi behar dira.

Aplikazio eremua:

Dakigunez, gero eta makina eta ekipamendu gehiagok aukeratzen dituzte granitozko osagai zehatzak.

Granitozko osagaiak mugimendu dinamikorako, motor linealetarako, cmmrako, cncrako, laser makinetarako... erabiltzen dira.

Ongi etorri gurekin harremanetan jartzera informazio gehiago lortzeko.

Granitozko neurketa-gailuak eta granitozko osagai mekanikoak kalitate handiko Jinan granito beltzez eginda daude. Beren zehaztasun handia, iraupen luzea, egonkortasun ona eta korrosioarekiko erresistentzia direla eta, gero eta gehiago erabiltzen dira produktuen ikuskapenean industria modernoan eta mekanika aeroespaziala eta ikerketa zientifikoak bezalako arlo zientifikoetan.

Abantailak

----Burdinurtua baino bi aldiz gogorragoa;

---- Dimentsio-aldaketa txikiak tenperatura-aldaketen ondorioz gertatzen dira;

----Turtu gabe, beraz, ez dago lana etenik;

---- Ale finen egitura eta itsaskortasun hutsala direla eta, ez du bizarrik edo irtengunerik, eta horrek bizitza luzean zehar lautasun maila handia bermatzen du eta ez du beste pieza edo tresnei kalterik eragiten;

---- Material magnetikoekin erabiltzeko arazorik gabeko funtzionamendua;

---- Bizitza luzea eta herdoilgaitza, mantentze-kostu txikiak lortuz.

Granitozko gainazaleko plaka zehatzak lautasun maila altuan lautzen dira zehaztasuna lortzeko, eta neurketa-sistema mekaniko, elektroniko eta optiko sofistikatuak muntatzeko oinarri gisa erabiltzen dira.

Granitozko gainazaleko plakaren ezaugarri berezi batzuk:

Gogortasunean uniformetasuna;

Zehatza karga-baldintzetan;

Bibrazioen xurgatzailea;

Erraz garbitzen da;

Bilgarriarekiko erresistentea;

Porositate baxua;

Ez-urratzailea;

Ez-magnetikoa

Granitozko gainazaleko plakaren abantailak

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.