Granit er en type magmatisk bjergart, der udvindes for sin ekstreme styrke, densitet, holdbarhed og korrosionsbestandighed. Men granit er også meget alsidig – det er ikke kun til firkanter og rektangler! Faktisk arbejder vi regelmæssigt med granitkomponenter, der er fremstillet i former, vinkler og kurver i alle variationer – med fremragende resultater.
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:
■ maskinbearbejdelig
■ præcis flad når den er skåret og færdiggjort
■ rustbestandig
■ holdbar
■ langvarig
Granitkomponenter er også nemme at rengøre. Når du laver brugerdefinerede designs, skal du sørge for at vælge granit på grund af dets overlegne fordele.

STANDARDER / ANVENDELSER MED HØJ SLIDTAGE
Den granit, som ZHHIMG bruger til vores standard overfladepladeprodukter, har et højt kvartsindhold, hvilket giver større modstandsdygtighed over for slid og skader. Vores Superior Black-farver har lav vandabsorption, hvilket minimerer risikoen for, at dine præcisionsmålere ruster, når de monteres på pladerne. De granitfarver, som ZHHIMG tilbyder, resulterer i mindre genskin, hvilket betyder mindre øjenbelastning for personer, der bruger pladerne. Vi har valgt vores granittyper under hensyntagen til termisk udvidelse for at holde dette aspekt minimalt.

CUSTOM APPLICATIONS
Når din applikation kræver en plade med brugerdefinerede former, gevindindsatser, slidser eller anden bearbejdning, bør du vælge et materiale som Black Jinan Black. Dette naturlige materiale tilbyder overlegen stivhed, fremragende vibrationsdæmpning og forbedret bearbejdelighed.

Det er vigtigt at bemærke, at farve alene ikke er en indikation af stenens fysiske egenskaber. Generelt er granits farve direkte relateret til tilstedeværelsen eller fraværet af mineraler, hvilket muligvis ikke har nogen indflydelse på de egenskaber, der gør et godt overfladeplademateriale. Der findes lyserøde, grå og sorte granitter, der er fremragende til overfladeplader, samt sorte, grå og lyserøde granitter, der er fuldstændig uegnede til præcisionsapplikationer. De kritiske egenskaber ved granit, hvad angår dens anvendelse som overfladeplademateriale, har intet at gøre med farve og er som følger:
■ Stivhed (nedbøjning under belastning - angivet ved elasticitetsmodul)
■ Hårdhed
■ Tæthed
■ Slidstyrke
■ Stabilitet
■ Porøsitet

Vi har testet mange granitmaterialer og sammenlignet dem. Endelig er vi nået til det resultat, at Jinan sort granit er det bedste materiale, vi nogensinde har kendt. Indisk sort granit og sydafrikansk granit ligner Jinan sort granit, men deres fysiske egenskaber er ringere end Jinan sort granit. ZHHIMG vil fortsætte med at lede efter flere granitmaterialer i verden og sammenligne deres fysiske egenskaber.

For at tale mere om den rigtige granit til dit projekt, bedes du kontakte osinfo@zhhimg.com.

Forskellige producenter bruger forskellige standarder. Der findes mange standarder i verden.
DIN-standarden, ASME B89.3.7-2013 eller den føderale specifikation GGG-P-463c (granitoverfladeplader) og så videre som grundlag for deres specifikationer.

Og vi kan fremstille præcisionsinspektionsplader i granit i henhold til dine krav. Du er velkommen til at kontakte os, hvis du vil vide mere om flere standarder.

Planhed kan betragtes som alle punkter på overfladen, der er indeholdt i to parallelle planer, basisplanet og tagplanet. Målingen af ​​afstanden mellem planerne er overfladens samlede planhed. Denne planhedsmåling har almindeligvis en tolerance og kan inkludere en karakterbetegnelse.

For eksempel er planhedstolerancerne for tre standardkvaliteter defineret i den føderale specifikation som bestemt af følgende formel:
■ Laboratoriekvalitet AA = (40 + diagonal i anden kvadrat/25) x 0,000001" (ensidig)
■ Inspektionsgrad A = Laboratoriegrad AA x 2
■ Værktøjsrumsklasse B = Laboratorieklasse AA x 4.

For overfladeplader i standardstørrelse garanterer vi planhedstolerancer, der overstiger kravene i denne specifikation. Ud over planhed behandler ASME B89.3.7-2013 og Federal Specification GGG-P-463c emner som: nøjagtighed af gentagne målinger, materialeegenskaber for overfladeplader i granit, overfladefinish, placering af støttepunkter, stivhed, acceptable inspektionsmetoder, installation af gevindindsatser osv.

ZHHIMG granitoverfladeplader og granitinspektionsplader opfylder eller overgår alle kravene i denne specifikation. Der er i øjeblikket ingen definerende specifikation for granitvinkelplader, paralleller eller masterkvadrater.

Og du kan finde formlerne for andre standarder iDOWNLOAD.

For det første er det vigtigt at holde pladen ren. Luftbårent slibestøv er normalt den største kilde til slid på en plade, da det har tendens til at sætte sig fast i emner og kontaktfladerne på måleinstrumenter. For det andet skal du dække din plade for at beskytte den mod støv og skader. Levetiden kan forlænges ved at dække pladen, når den ikke er i brug, ved at rotere pladen med jævne mellemrum, så et enkelt område ikke udsættes for overdreven brug, og ved at udskifte stålkontaktpuder på måleinstrumenter med hårdmetalpuder. Undgå også at placere mad eller sodavand på pladen. Bemærk, at mange sodavand indeholder enten kulsyre eller fosforsyre, som kan opløse de blødere mineraler og efterlade små huller i overfladen.

Dette afhænger af, hvordan tallerkenen bruges. Hvis det er muligt, anbefaler vi at rengøre tallerkenen i begyndelsen af ​​dagen (eller arbejdsvagten) og igen i slutningen. Hvis tallerkenen bliver snavset, især med olieholdige eller klæbrige væsker, bør den sandsynligvis rengøres med det samme.

Rengør pladen regelmæssigt med flydende eller vandfri ZHHIMG overfladerens. Valget af rengøringsopløsninger er vigtigt. Hvis der anvendes et flygtigt opløsningsmiddel (acetone, lakfortynder, alkohol osv.), vil fordampningen afkøle overfladen og forvrænge den. I dette tilfælde er det nødvendigt at lade pladen normalisere sig, før den bruges, ellers vil der opstå målefejl.

Den tid, det tager for pladen at normalisere sig, varierer afhængigt af pladens størrelse og mængden af ​​køling. En time burde være tilstrækkeligt for mindre plader. To timer kan være nødvendige for større plader. Hvis der anvendes et vandbaseret rengøringsmiddel, vil der også være en vis fordampningskøling.

Pladen vil også tilbageholde vandet, og dette kan forårsage rust på metaldele i kontakt med overfladen. Nogle rengøringsmidler vil også efterlade en klæbrig rest, når de tørrer, hvilket vil tiltrække luftbårent støv og faktisk øge sliddet i stedet for at mindske det.

Dette afhænger af pladens brug og miljø. Vi anbefaler, at en ny plade eller præcisionsgranittilbehør gennemgår en fuldstændig rekalibrering inden for et år efter købet. Hvis granitoverfladepladen vil blive brugt flittig, kan det være tilrådeligt at forkorte dette interval til seks måneder. Månedlig inspektion for gentagne målefejl ved hjælp af et elektronisk vaterpas eller lignende enhed vil vise eventuelle slidpletter og tager kun et par minutter at udføre. Når resultaterne af den første rekalibrering er bestemt, kan kalibreringsintervallet forlænges eller forkortes efter tilladelse eller krav fra dit interne kvalitetssystem.

Vi kan tilbyde service til at hjælpe dig med at inspicere og kalibrere din granitoverflade.

Der er flere mulige årsager til variationer mellem kalibreringer:

• Overfladen blev vasket med en varm eller kold opløsning før kalibrering og fik ikke tilstrækkelig tid til at normalisere sig.
• Pladen er ikke korrekt understøttet
• Temperaturændring
• Kladder
• Direkte sollys eller anden strålevarme på pladens overflade. Sørg for, at loftsbelysning ikke opvarmer overfladen.
• Variationer i den vertikale temperaturgradient mellem vinter og sommer (Hvis det er muligt, skal den vertikale gradienttemperatur kendes på det tidspunkt, hvor kalibreringen udføres.)
• Pladen fik ikke tilstrækkelig tid til at normalisere sig efter forsendelse
• Forkert brug af inspektionsudstyr eller brug af ikke-kalibreret udstyr
• Overfladeændring som følge af slid

Hvor mange slags huller på præcisionsgranit?

Slots på præcisionsgranitkomponenter

For mange fabrikker, inspektionsrum og laboratorier anvendes præcisionsplader af granit som grundlag for nøjagtig måling. Fordi enhver lineær måling afhænger af en nøjagtig referenceoverflade, hvorfra de endelige dimensioner tages, giver overfladeplader det bedste referenceplan til arbejdsinspektion og layout før bearbejdning. De er også ideelle grundlag for at foretage højdemålinger og måle overflader. Ydermere gør en høj grad af fladhed, stabilitet, generel kvalitet og udførelse dem til et godt valg til montering af sofistikerede mekaniske, elektroniske og optiske målesystemer. For alle disse måleprocesser er det bydende nødvendigt at holde overfladepladerne kalibrerede.

Repeat Measurements and Flatness

Både planhed og gentagne målinger er afgørende for at sikre en præcis overflade. Planhed kan betragtes som alle punkter på overfladen, der er indeholdt i to parallelle planer, basisplanet og tagplanet. Målingen af ​​afstanden mellem planerne er overfladens samlede planhed. Denne planhedmåling har normalt en tolerance og kan omfatte en karakterbetegnelse.

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 ... forskellige lande med forskellige standarter ...

Flere detaljer om standarden.

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.

For at sikre, at en overfladeplade opfylder både specifikationerne for planhed og gentagne målinger, bør producenter af granitoverfladeplader bruge den føderale specifikation GGG-P-463c som grundlag for deres specifikationer. Denne standard omhandler nøjagtighed af gentagne målinger, materialeegenskaber for granitoverfladeplader, overfladefinish, placering af støttepunkter, stivhed, acceptable inspektionsmetoder og installation af gevindindsatser.

Checking Plate Accuracy

Ved at følge et par enkle retningslinjer bør en investering i en granitoverfladeplade holde i mange år. Afhængigt af pladens brug, værkstedsmiljøet og den nødvendige nøjagtighed varierer hyppigheden af ​​kontrol af overfladepladens nøjagtighed. En generel tommelfingerregel er, at en ny plade skal gennemgå en fuld rekalibrering inden for et år efter købet. Hvis pladen bruges ofte, anbefales det at forkorte dette interval til seks måneder.

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

I nogle tilfælde er der variationer mellem kalibreringer af overfladeplader. Nogle gange kan faktorer som overfladeændringer som følge af slid, forkert brug af inspektionsudstyr eller brug af ikke-kalibreret udstyr forklare disse variationer. De to mest almindelige faktorer er dog temperatur og understøtning.

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

Ved at følge et par retningslinjer vil du reducere slid på en granitoverflade og i sidste ende forlænge dens levetid.

For det første er det vigtigt at holde pladen ren. Luftbårent slibestøv er normalt den største kilde til slid på en plade, da det har tendens til at sætte sig fast i emner og kontaktfladerne på målere.

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.

Drej pladen med jævne mellemrum, så et enkelt område ikke udsættes for overdreven brug. Det anbefales også at udskifte stålkontaktpuder på måleinstrumenter med hårdmetalkontaktpuder.

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

Når en granitplade skal slibes, bør man overveje, om denne service skal udføres på stedet eller på et kalibreringsanlæg. Det er altid at foretrække at få pladen slibet på fabrikken eller et dedikeret anlæg. Hvis pladen dog ikke er for slidt, generelt inden for 0,001 tommer af den krævede tolerance, kan den slibes på stedet. Hvis en plade er slidt til et punkt, hvor den er mere end 0,001 tommer uden for tolerancen, eller hvis den er stærkt grubet eller hakket, skal den sendes til fabrikken til slibning inden slibes igen.

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

Der skal udvises stor omhu ved valg af en tekniker til kalibrering og overfladebehandling på stedet. Bed om akkreditering, og verificer, at det udstyr, som teknikeren vil bruge, har en sporbar kalibrering. Erfaring er også en vigtig faktor, da det tager mange år at lære, hvordan man korrekt sliber præcisionsgranit.

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. Overfladen blev vasket med en varm eller kold opløsning før kalibrering og fik ikke tilstrækkelig tid til at normalisere sig.

2. Pladen er ikke korrekt understøttet.

3. Temperaturændring.

4. Udkast.

5. Direkte sollys eller anden strålevarme på pladens overflade. Sørg for, at loftsbelysning ikke opvarmer overfladen.

6. Variationer i den vertikale temperaturgradient mellem vinter og sommer. Hvis det overhovedet er muligt, skal den vertikale gradienttemperatur kendes på det tidspunkt, hvor kalibreringen udføres.

7. Pladen har ikke haft tilstrækkelig tid til at normalisere sig efter forsendelse.

8. Forkert brug af inspektionsudstyr eller brug af ikke-kalibreret udstyr.

9. Overfladeændring som følge af slid.

Tech Tips

• Fordi hver lineær måling afhænger af en nøjagtig referenceoverflade, hvorfra de endelige dimensioner tages, giver overfladeplader det bedste referenceplan til arbejdsinspektion og layout før bearbejdning.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Et effektivt inspektionsprogram bør omfatte regelmæssige kontroller med en autokollimator, der giver en faktisk kalibrering af den samlede planhed, der kan spores tilbage til den nationale inspektionsmyndighed.

Blandt de mineralpartikler, der udgør granit, er mere end 90% feldspat og kvarts, hvoraf feldspat er den største mængde. Feldspat er ofte hvid, grå og kødrød, og kvarts er for det meste farveløs eller gråhvid, hvilket udgør granittens grundfarve. Feldspat og kvarts er hårde mineraler, og det er vanskeligt at bevæge dem med en stålkniv. Hvad angår de mørke pletter i granitten, primært sort glimmer, er der også nogle andre mineraler. Selvom biotit er relativt blød, er dens evne til at modstå stress ikke svag, og samtidig findes der en lille mængde i granit, ofte mindre end 10%. Det er i denne materialetilstand, at granit er særligt stærk.

En anden grund til, at granit er stærk, er, at dens mineralpartikler er tæt bundet til hinanden og indlejret i hinanden. Porerne udgør ofte mindre end 1% af klippens samlede volumen. Dette giver granitten evnen til at modstå stærke tryk og trænger ikke let ind af fugt.

Granitkomponenter er lavet af sten uden rust, syre og alkali, god slidstyrke og lang levetid, ingen særlig vedligeholdelse. Granitpræcisionskomponenter bruges mest i værktøjsfremstilling i maskinindustrien. Derfor kaldes de granitpræcisionskomponenter eller granitkomponenter. Egenskaberne ved granitpræcisionskomponenter er grundlæggende de samme som for granitplatforme. Introduktion til værktøjsfremstilling og måling af granitpræcisionskomponenter: Præcisionsbearbejdning og mikrobearbejdningsteknologi er vigtige udviklingsretninger inden for maskinindustrien, og de er blevet en vigtig indikator for at måle et højteknologisk niveau. Udviklingen af ​​banebrydende teknologi og forsvarsindustrien er uadskillelig fra præcisionsbearbejdning og mikrobearbejdningsteknologi. Granitkomponenter kan glide glat under målingen uden stagnation. Måling af arbejdsfladen, generelle ridser påvirker ikke målenøjagtigheden. Granitkomponenter skal designes og produceres i henhold til efterspørgselssidens krav.

Anvendelsesfelt:

Som vi alle ved, vælger flere og flere maskiner og udstyr præcisionskomponenter i granit.

Granitkomponenter bruges til dynamisk bevægelse, lineære motorer, CMM, CNC, lasermaskiner...

velkommen til at kontakte os for mere information.

Granitmåleinstrumenter og mekaniske komponenter i granit er lavet af Jinan Black-granit af høj kvalitet. På grund af deres høje præcision, lange holdbarhed, gode stabilitet og korrosionsbestandighed er de blevet mere og mere anvendt i produktinspektion i den moderne industri og inden for videnskabelige områder som mekanisk, luftfart og videnskabelig forskning.

Fordele

----Dobbelt så hårdt som støbejern;

----Minimale dimensionsændringer skyldes temperaturændringer;

----Fri for vridning, så der ikke er afbrydelse af arbejdet;

----Fri for grater eller fremspring på grund af den fine kornstruktur og ubetydelig klæbning, hvilket sikrer en høj grad af fladhed over en lang levetid og ikke forårsager skader på andre dele eller instrumenter;

----Problemfri drift til brug med magnetiske materialer;

----Lang levetid og rustfri, hvilket resulterer i lave vedligeholdelsesomkostninger.

Præcisionsgranitoverfladepladerne er præcisionsslebet til en høj standard for planhed for at opnå nøjagtighed og bruges som base for montering af sofistikerede mekaniske, elektroniske og optiske målesystemer.

Nogle af de unikke egenskaber ved granitoverfladen:

Ensartethed i hårdhed;

Nøjagtige forhold under belastning;

Vibrationsabsorberende;

Let at rengøre;

Indpakningsbestandig;

Lav porøsitet;

Ikke-slibende;

Ikke-magnetisk

Fordele ved granitoverfladeplade

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.