Granit är en typ av magmatisk bergart som utvinns för sin extrema styrka, densitet, hållbarhet och korrosionsbeständighet. Men granit är också mycket mångsidig – den är inte bara för kvadrater och rektanglar! Vi arbetar faktiskt regelbundet med granitkomponenter konstruerade i former, vinklar och kurvor av alla varianter – med utmärkta resultat.
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:
■ maskinbearbetbar
■ exakt platt vid snitt och färdigställning
■ rostbeständig
■ hållbar
■ långvarig
Granitkomponenter är också lätta att rengöra. När du skapar specialdesignade konstruktioner, se till att välja granit för dess överlägsna fördelar.

STANDARDER / APPLIKATIONER MED HÖGT SLITAGE
Graniten som ZHHIMG använder för våra standardprodukter av ytplattor har ett högt kvartsinnehåll, vilket ger större motståndskraft mot slitage och skador. Våra Superior Black-färger har låg vattenabsorption, vilket minimerar risken för att dina precisionsmätare rostar när de fästs på plattorna. Granitfärgerna som ZHHIMG erbjuder resulterar i mindre bländning, vilket innebär mindre ögonansträngning för personer som använder plattorna. Vi har valt våra granittyper med hänsyn till termisk expansion i ett försök att hålla denna aspekt minimal.

CUSTOM APPLICATIONS
När din applikation kräver en platta med specialformade former, gängade insatser, spår eller annan bearbetning, bör du välja ett material som Black Jinan Black. Detta naturliga material erbjuder överlägsen styvhet, utmärkt vibrationsdämpning och förbättrad bearbetbarhet.

Det är viktigt att notera att färg ensam inte är en indikation på stenens fysiska egenskaper. I allmänhet är granits färg direkt relaterad till närvaron eller frånvaron av mineraler, vilket kanske inte har någon betydelse för de egenskaper som gör ett bra ytplattmaterial. Det finns rosa, grå och svarta graniter som är utmärkta för ytplattor, såväl som svarta, grå och rosa graniter som är helt olämpliga för precisionstillämpningar. De kritiska egenskaperna hos granit, vad gäller dess användning som ytplattmaterial, har ingenting att göra med färg och är följande:
■ Styvhet (nedböjning under belastning - indikeras av elasticitetsmodulen)
■ Hårdhet
■ Densitet
■ Slitstyrka
■ Stabilitet
■ Porositet

Vi har testat många granitmaterial och jämfört dem. Slutligen har vi fått resultatet att Jinan svart granit är det bästa materialet vi någonsin känt till. Indisk svart granit och sydafrikansk granit liknar Jinan svart granit, men deras fysikaliska egenskaper är sämre än Jinan svart granit. ZHHIMG kommer att fortsätta leta efter fler granitmaterial i världen och jämföra deras fysikaliska egenskaper.

För att prata mer om vilken granit som passar ditt projekt, vänligen kontakta ossinfo@zhhimg.com.

Olika tillverkare använder olika standarder. Det finns många standarder i världen.
DIN-standarden, ASME B89.3.7-2013 eller Federal Specification GGG-P-463c (granitplattor) och så vidare som grund för deras specifikationer.

Och vi kan tillverka precisionsinspektionsplåtar i granit enligt era krav. Välkommen att kontakta oss om ni vill veta mer om fler standarder.

Planhet kan betraktas som att alla punkter på ytan befinner sig inom två parallella plan, basplanet och takplanet. Måttet på avståndet mellan planen är ytans totala planhet. Detta planhetsmått har vanligtvis en tolerans och kan inkludera en graderingsbeteckning.

Till exempel definieras planhetstoleranserna för tre standardkvaliteter i den federala specifikationen enligt följande formel:
■ Laboratorieklass AA = (40 + diagonal i kvadrat/25) x 0,000001" (ensidig)
■ Inspektionsgrad A = Laboratoriegrad AA x 2
■ Verktygsrum klass B = Laboratorieklass AA x 4.

För ytplattor i standardstorlek garanterar vi planhetstoleranser som överstiger kraven i denna specifikation. Förutom planhet behandlar ASME B89.3.7-2013 och Federal Specification GGG-P-463c ämnen som: noggrannhet i upprepade mätningar, materialegenskaper hos ytplattor i granit, ytfinish, placering av stödpunkter, styvhet, acceptabla inspektionsmetoder, installation av gängade insatser etc.

ZHHIMG-ytplattor och inspektionsplattor i granit uppfyller eller överträffar alla krav som anges i denna specifikation. För närvarande finns det ingen definierande specifikation för vinkelplattor, parallella eller vinkelhakar i granit.

Och du kan hitta formlerna för andra standarder iLADDA NER.

För det första är det viktigt att hålla plattan ren. Luftburet slipmedel är oftast den största källan till slitage på en platta, eftersom det tenderar att fastna i arbetsstycken och kontaktytor på mätinstrument. För det andra, täck över plattan för att skydda den från damm och skador. Livslängden kan förlängas genom att täcka över plattan när den inte används, genom att rotera plattan regelbundet så att ett enda område inte används för mycket, och genom att byta ut stålkontaktplattorna på mätinstrumentet mot hårdmetallplattor. Undvik också att placera mat eller läsk på plattan. Observera att många läskedrycker innehåller antingen kolsyra eller fosforsyra, vilket kan lösa upp de mjukare mineralerna och lämna små gropar i ytan.

Detta beror på hur plattan används. Om möjligt rekommenderar vi att rengöra plattan i början av dagen (eller arbetspasset) och igen i slutet. Om plattan blir smutsig, särskilt med oljiga eller klibbiga vätskor, bör den förmodligen rengöras omedelbart.

Rengör plattan regelbundet med flytande eller vattenlös ZHHIMG-rengöring för ytor. Valet av rengöringslösningar är viktigt. Om ett flyktigt lösningsmedel används (aceton, lackförtunning, alkohol etc.) kommer avdunstningen att kyla ner ytan och deformera den. I detta fall är det nödvändigt att låta plattan normaliseras innan den används, annars kommer mätfel att uppstå.

Den tid som krävs för att plattan ska normaliseras varierar beroende på plattans storlek och hur mycket kylning den får ske. En timme bör räcka för mindre plattor. Två timmar kan behövas för större plattor. Om ett vattenbaserat rengöringsmedel används kommer det också att ske en viss avdunstningskylning.

Plattan kommer också att hålla kvar vattnet, vilket kan orsaka rost på metalldelar som kommer i kontakt med ytan. Vissa rengöringsmedel lämnar också en klibbig rest efter att de torkat, vilket lockar till sig luftburet damm och faktiskt ökar slitaget snarare än minskar det.

Detta beror på plattans användning och miljö. Vi rekommenderar att en ny platta eller ett precisionsgranittillbehör genomgår en fullständig omkalibrering inom ett år efter inköp. Om granitytplattan kommer att användas flitigt kan det vara lämpligt att förkorta detta intervall till sex månader. Månatlig inspektion för upprepade mätfel med hjälp av ett elektroniskt vattenpass eller liknande apparat visar eventuella slitagepunkter och tar bara några minuter att utföra. Efter att resultaten av den första omkalibreringen har fastställts kan kalibreringsintervallet förlängas eller förkortas enligt vad som tillåts eller krävs av ert interna kvalitetssystem.

Vi kan erbjuda tjänster för att hjälpa dig inspektera och kalibrera din granitytplatta.

Det finns flera möjliga orsaker till variationer mellan kalibreringar:

• Ytan tvättades med en varm eller kall lösning före kalibrering och fick inte tillräckligt med tid att normaliseras
• Plattan är felaktigt stödd
• Temperaturförändring
• Utkast
• Direkt solljus eller annan strålningsvärme på plattans yta. Se till att takbelysning inte värmer upp ytan.
• Variationer i den vertikala temperaturgradienten mellan vinter och sommar (Om möjligt, känn till den vertikala gradienttemperaturen vid tidpunkten då kalibreringen utförs.)
• Plattan fick inte tillräckligt med tid att normaliseras efter leverans
• Felaktig användning av inspektionsutrustning eller användning av icke-kalibrerad utrustning
• Ytförändring till följd av slitage

Hur många typer av hål finns det på precisionsgranit?

Spår på precisionskomponenter i granit

För många fabriker, inspektionsrum och laboratorier används precisionsplattor i granit som grund för noggrann mätning. Eftersom varje linjär mätning är beroende av en noggrann referensyta från vilken de slutliga måtten tas, ger plattorna det bästa referensplanet för arbetsinspektion och layout före bearbetning. De är också idealiska baser för att göra höjdmätningar och mäta ytor. Dessutom gör en hög grad av planhet, stabilitet, övergripande kvalitet och utförande dem till ett bra val för montering av sofistikerade mekaniska, elektroniska och optiska mätsystem. För alla dessa mätprocesser är det absolut nödvändigt att hålla plattorna kalibrerade.

Repeat Measurements and Flatness

Både planhet och upprepade mätningar är avgörande för att säkerställa en precisionsyta. Planhet kan betraktas som att alla punkter på ytan är inneslutna inom två parallella plan, basplanet och takplanet. Måttet på avståndet mellan planen är ytans totala planhet. Denna planhetsmätning har vanligtvis en tolerans och kan inkludera en sortbeteckning.

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 ... olika länder med olika standar ...

Mer information 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.

För att säkerställa att en ytplatta uppfyller både specifikationerna för planhet och upprepade mätningar bör tillverkare av granitplattor använda den federala specifikationen GGG-P-463c som grund för sina specifikationer. Denna standard behandlar noggrannhet i upprepade mätningar, materialegenskaper hos granitplattor, ytfinish, placering av stödpunkter, styvhet, acceptabla inspektionsmetoder och installation av gängade insatser.

Checking Plate Accuracy

Genom att följa några enkla riktlinjer bör en investering i en granitplatta hålla i många år. Beroende på plattans användning, verkstadsmiljö och erforderlig noggrannhet varierar frekvensen för att kontrollera ytplattans noggrannhet. En allmän tumregel är att en ny platta ska genomgå en fullständig omkalibrering inom ett år efter inköpet. Om plattan används ofta är det lämpligt att förkorta detta intervall till sex månader.

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 vissa fall finns det variationer mellan kalibreringar av ytplattor. Ibland kan faktorer som ytförändringar till följd av slitage, felaktig användning av inspektionsutrustning eller användning av okalibrerad utrustning förklara dessa variationer. De två vanligaste faktorerna är dock temperatur och stöd.

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

Att följa några riktlinjer minskar slitaget på en granitplatta och förlänger i slutändan dess livslängd.

Först är det viktigt att hålla plattan ren. Luftburet slipmedel är oftast den största källan till slitage på en platta, eftersom det tenderar att fastna i arbetsstycken och kontaktytor på mätare.

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.

Rotera plattan regelbundet så att ett enskilt område inte utsätts för överdriven användning. Det rekommenderas också att byta ut kontaktplattorna i stål på mätinstrument mot kontaktplattor i hårdmetall.

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

När en granitplatta behöver slipas om, överväg om du vill utföra denna tjänst på plats eller på kalibreringsanläggningen. Det är alltid att föredra att plattan slipas om på fabriken eller en dedikerad anläggning. Om plattan däremot inte är alltför sliten, vanligtvis inom 0,001 tum från den erforderliga toleransen, kan den slipas om på plats. Om en platta är sliten så mycket att den är mer än 0,001 tum utanför toleransen, eller om den är kraftigt gropig eller hackig, bör den skickas till fabriken för slipning innan den slipas om.

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

Stor noggrannhet bör iakttas vid val av en tekniker för kalibrering och ytbehandling på plats. Be om ackreditering och verifiera att den utrustning som teknikern kommer att använda har en spårbar kalibrering. Erfarenhet är också en viktig faktor, eftersom det tar många år att lära sig hur man korrekt slipar precisionsgranit.

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. Ytan tvättades med en varm eller kall lösning före kalibrering och fick inte tillräckligt med tid att normaliseras.

2. Plattan är felaktigt stödd.

3. Temperaturförändring.

4. Utkast.

5. Direkt solljus eller annan strålningsvärme på plattans yta. Se till att takbelysning inte värmer upp ytan.

6. Variationer i den vertikala temperaturgradienten mellan vinter och sommar. Om möjligt, känn till den vertikala gradienttemperaturen vid tidpunkten för kalibreringen.

7. Plattan fick inte tillräckligt med tid att normaliseras efter leverans.

8. Felaktig användning av inspektionsutrustning eller användning av okalibrerad utrustning.

9. Ytförändring till följd av slitage.

Tech Tips

• Eftersom varje linjär mätning är beroende av en noggrann referensyta från vilken de slutliga måtten tas, ger ytplattor det bästa referensplanet för arbetsinspektion och layout före bearbetning.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Ett effektivt inspektionsprogram bör inkludera regelbundna kontroller med en autokollimator, vilket ger faktisk kalibrering av den övergripande planheten som kan spåras till den nationella inspektionsmyndigheten.

Bland mineralpartiklarna som granit består av är mer än 90 % fältspat och kvarts, varav fältspat är den största förekomsten. Fältspat är ofta vit, grå och rödaktig, och kvarts är mestadels färglös eller gråvit, vilket utgör granitens grundfärg. Fältspat och kvarts är hårda mineraler och är svåra att röra vid med en stålkniv. När det gäller de mörka fläckarna i graniten, främst svart glimmer, finns det även några andra mineraler. Även om biotit är relativt mjuk är dess förmåga att motstå stress inte svag, och samtidigt finns det en liten mängd av dem i graniten, ofta mindre än 10 %. Det är i detta materialtillstånd som graniten är särskilt stark.

En annan anledning till att granit är stark är att dess mineralpartiklar är tätt bundna till varandra och inbäddade i varandra. Porerna utgör ofta mindre än 1 % av bergets totala volym. Detta ger graniten förmågan att motstå starka tryck och fukt penetrerar den inte lätt.

Granitkomponenter är tillverkade av sten utan rost, syra och alkalibeständighet, god slitstyrka och lång livslängd, inget särskilt underhåll. Granitprecisionskomponenter används mestadels inom verktygstillverkning inom maskinindustrin. Därför kallas de granitprecisionskomponenter eller granitkomponenter. Egenskaperna hos granitprecisionskomponenter är i princip desamma som hos granitplattformar. Introduktion till verktygstillverkning och mätning av granitprecisionskomponenter: Precisionsbearbetning och mikrobearbetningsteknik är viktiga utvecklingsriktningar inom maskintillverkningsindustrin och de har blivit en viktig indikator för att mäta högteknologisk nivå. Utvecklingen av spetsteknik och försvarsindustrin är oskiljaktig från precisionsbearbetning och mikrobearbetningsteknik. Granitkomponenter kan skjutas smidigt i mätningen utan att stagnera. Allmänna repor vid mätning av arbetsytan påverkar inte mätnoggrannheten. Granitkomponenter måste designas och produceras enligt efterfrågesidans krav.

Användningsområde:

Som vi alla vet väljer fler och fler maskiner och utrustningar precisionskomponenter i granit.

Granitkomponenter används för dynamisk rörelse, linjärmotorer, CMM, CNC, lasermaskiner...

välkommen att kontakta oss för mer information.

Granitmätinstrument och mekaniska komponenter i granit är tillverkade av högkvalitativ Jinan Black-granit. Tack vare deras höga precision, långa livslängd, goda stabilitet och korrosionsbeständighet har de använts alltmer inom produktinspektion inom modern industri och inom vetenskapliga områden som mekanik, flyg- och rymdteknik och vetenskaplig forskning.

Fördelar

----Dubbelt så hårt som gjutjärn;

----Minimala dimensionsförändringar beror på temperaturförändringar;

----Fri från vridning, så det finns inget avbrott i arbetet;

----Fri från grader eller utskjutande delar på grund av den fina kornstrukturen och obetydliga klibbigheten, vilket säkerställer en hög grad av planhet under en lång livslängd och orsakar ingen skada på andra delar eller instrument;

----Problemfri drift för användning med magnetiska material;

----Lång livslängd och rostfri, vilket resulterar i låga underhållskostnader.

Precisionsgranitytplattorna är precisionsöverlappade till hög planhet för att uppnå noggrannhet och används som bas för montering av sofistikerade mekaniska, elektroniska och optiska mätsystem.

Några av de unika egenskaperna hos granitytplattan:

Likformighet i hårdhet;

Noggranna förhållanden under belastning;

Vibrationsabsorberande;

Lätt att rengöra;

Omslagsbeständig;

Låg porositet;

Icke-slipande;

Omagnetisk

Fördelar med granit ytplatta

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.