Granit je vrsta magmatske stijene koja se vadi zbog svoje izuzetne čvrstoće, gustoće, izdržljivosti i otpornosti na koroziju. Ali granit je također vrlo svestran – nije samo za kvadrate i pravougaonike! U stvari, s povjerenjem redovno radimo s granitnim komponentama konstruiranim u oblicima, uglovima i krivuljama svih varijacija – s odličnim rezultatima.
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:
■ obradivo
■ precizno ravno kada se reže i završi
■ otporno na hrđu
■ izdržljiv
■ dugotrajan
Granitne komponente se također lako čiste. Prilikom kreiranja prilagođenih dizajna, obavezno odaberite granit zbog njegovih vrhunskih prednosti.

STANDARDI / PRIMJENE S VISOKIM TROŠENJEM
Granit koji ZHHIMG koristi za naše standardne površinske ploče ima visok sadržaj kvarca, što pruža veću otpornost na habanje i oštećenja. Naše superiorne crne boje imaju nisku stopu apsorpcije vode, što minimizira mogućnost da vaši precizni mjerači zahrđaju prilikom postavljanja na ploče. Boje granita koje nudi ZHHIMG rezultiraju manjim odsjajem, što znači manje naprezanja očiju za osobe koje koriste ploče. Odabrali smo naše vrste granita uzimajući u obzir termičko širenje kako bismo ovaj aspekt sveli na minimum.

CUSTOM APPLICATIONS
Kada vaša primjena zahtijeva ploču s prilagođenim oblicima, navojnim umetcima, utorima ili drugom strojnom obradom, poželjet ćete odabrati materijal poput crne ploče Jinan Black. Ovaj prirodni materijal nudi vrhunsku krutost, odlično prigušivanje vibracija i poboljšanu obradivost.

Važno je napomenuti da sama boja nije pokazatelj fizičkih svojstava kamena. Općenito, boja granita je direktno povezana s prisustvom ili odsustvom minerala, što možda nema utjecaja na kvalitete koje ga čine dobrim materijalom za površinske ploče. Postoje ružičasti, sivi i crni graniti koji su odlični za površinske ploče, kao i crni, sivi i ružičasti graniti koji su potpuno neprikladni za precizne primjene. Kritične karakteristike granita, koje se odnose na njegovu upotrebu kao materijala za površinske ploče, nemaju nikakve veze s bojom i sljedeće su:
■ Krutost (deformacija pod opterećenjem - označena modulom elastičnosti)
■ Tvrdoća
■ Gustoća
■ Otpornost na habanje
■ Stabilnost
■ Poroznost

Testirali smo mnoge granitne materijale i upoređivali ih. Konačno smo dobili rezultat, crni granit iz Jinana je najbolji materijal koji smo ikada poznavali. Indijski crni granit i južnoafrički granit su slični crnom granitu iz Jinana, ali su im fizička svojstva slabija od crnog granita iz Jinana. ZHHIMG će nastaviti tražiti više granitnih materijala u svijetu i upoređivati ​​njihova fizička svojstva.

Za više informacija o granitu koji je pravi za vaš projekat, molimo kontaktirajte nasinfo@zhhimg.com.

Različiti proizvođači koriste različite standarde. Postoji mnogo standarda u svijetu.
DIN standard, ASME B89.3.7-2013 ili Federalna specifikacija GGG-P-463c (Granitne površinske ploče) i tako dalje kao osnova za njihove specifikacije.

I možemo proizvesti preciznu inspekcijsku ploču od granita prema vašim zahtjevima. Slobodno nas kontaktirajte ako želite saznati više informacija o drugim standardima.

Ravnost se može smatrati kao da se sve tačke na površini nalaze unutar dvije paralelne ravni, osnovne ravni i ravni krova. Mjerenje udaljenosti između ravni predstavlja ukupnu ravnost površine. Ovo mjerenje ravnosti obično nosi toleranciju i može uključivati ​​oznaku stepena.

Na primjer, tolerancije ravnosti za tri standardne klase definirane su u federalnoj specifikaciji prema sljedećoj formuli:
■ Laboratorijski stepen AA = (40 + dijagonala na kvadrat / 25) x 0,000001" (jednostrano)
■ Stepen inspekcije A = Laboratorijski stepen AA x 2
■ Alatnica, klasa B = laboratorijska klasa AA x 4.

Za površinske ploče standardne veličine, garantujemo tolerancije ravnosti koje premašuju zahtjeve ove specifikacije. Pored ravnosti, ASME B89.3.7-2013 i Federalna specifikacija GGG-P-463c obrađuju teme koje uključuju: tačnost ponovljenog mjerenja, svojstva materijala granitnih površinskih ploča, završnu obradu površine, lokaciju tačke oslonca, krutost, prihvatljive metode inspekcije, ugradnju navojnih umetaka itd.

ZHHIMG granitne površinske ploče i granitne inspekcijske ploče ispunjavaju ili premašuju sve zahtjeve navedene u ovoj specifikaciji. Trenutno ne postoji definirajuća specifikacija za granitne kutne ploče, paralele ili glavne kvadrate.

A formule za ostale standarde možete pronaći uPREUZMI.

Prvo, važno je održavati ploču čistom. Abrazivna prašina u zraku obično je najveći izvor habanja ploče, jer se obično ugrađuje u radne komade i kontaktne površine mjernih instrumenata. Drugo, pokrijte ploču kako biste je zaštitili od prašine i oštećenja. Vijek trajanja može se produžiti pokrivanjem ploče kada se ne koristi, periodičnim okretanjem ploče kako se jedno područje ne bi prekomjerno koristilo i zamjenom čeličnih kontaktnih pločica na mjernim instrumentima karbidnim pločicama. Također, izbjegavajte stavljanje hrane ili bezalkoholnih pića na ploču. Imajte na umu da mnoga bezalkoholna pića sadrže ugljičnu ili fosfornu kiselinu, koje mogu otopiti mekše minerale i ostaviti male udubljenja na površini.

Ovo zavisi od toga kako se tanjir koristi. Ako je moguće, preporučujemo čišćenje tanjira na početku dana (ili radne smjene) i ponovo na kraju. Ako se tanjir zaprlja, posebno masnim ili ljepljivim tekućinama, vjerovatno ga treba odmah očistiti.

Redovno čistite ploču tekućinom ili ZHHIMG sredstvom za čišćenje površina bez vode. Izbor otopina za čišćenje je važan. Ako se koristi hlapljivo otapalo (aceton, razrjeđivač laka, alkohol itd.), isparavanje će ohladiti površinu i iskriviti je. U tom slučaju, potrebno je omogućiti ploču da se normalizira prije upotrebe ili će doći do grešaka u mjerenju.

Količina vremena potrebna za normalizaciju ploče variraće u zavisnosti od veličine ploče i količine hlađenja. Sat vremena bi trebalo da bude dovoljno za manje ploče. Za veće ploče mogu biti potrebna dva sata. Ako se koristi sredstvo za čišćenje na bazi vode, doći će i do hlađenja isparavanjem.

Ploča će također zadržavati vodu, što bi moglo uzrokovati hrđanje metalnih dijelova koji su u kontaktu s površinom. Neka sredstva za čišćenje će također ostaviti ljepljivi ostatak nakon što se osuše, koji će privući prašinu iz zraka i zapravo povećati habanje, umjesto da ga smanji.

Ovo zavisi od upotrebe ploče i okruženja. Preporučujemo da se nova ploča ili precizni granitni pribor potpuno rekalibriraju u roku od godinu dana od kupovine. Ako će se granitna ploča intenzivno koristiti, preporučuje se skraćivanje ovog intervala na šest mjeseci. Mjesečna inspekcija za ponovljene greške mjerenja pomoću elektronske libele ili sličnog uređaja pokazat će sve tragove habanja u razvoju i traje samo nekoliko minuta. Nakon što se utvrde rezultati prve rekalibracije, interval kalibracije može se produžiti ili skratiti kako to dozvoljava ili zahtijeva vaš interni sistem kvaliteta.

Nudimo usluge pregleda i kalibracije vaše granitne ploče.

Postoji nekoliko mogućih uzroka za varijacije između kalibracija:

• Površina je oprana vrućim ili hladnim rastvorom prije kalibracije i nije joj bilo ostavljeno dovoljno vremena za normalizaciju
• Ploča je nepravilno poduprta
• Promjena temperature
• Nacrti
• Direktna sunčeva svjetlost ili drugo toplotno zračenje na površini ploče. Pazite da stropna rasvjeta ne zagrijava površinu.
• Varijacije vertikalnog temperaturnog gradijenta između zime i ljeta (Ako je ikako moguće, znajte vertikalni gradijent temperature u trenutku kalibracije.)
• Ploči nije dato dovoljno vremena za normalizaciju nakon isporuke
• Nepravilna upotreba opreme za inspekciju ili upotreba nekalibrirane opreme
• Promjena površine usljed habanja

Koliko vrsta rupa ima na preciznom granitu?

Utori na preciznim granitnim komponentama

Za mnoge fabrike, inspekcijske sobe i laboratorije, precizne granitne površinske ploče se oslanjaju kao osnova za tačno mjerenje. Budući da svako linearno mjerenje zavisi od tačne referentne površine sa koje se uzimaju konačne dimenzije, površinske ploče pružaju najbolju referentnu ravan za inspekciju rada i raspored prije mašinske obrade. One su također idealne osnove za mjerenje visine i mjerenje površina. Nadalje, visok stepen ravnosti, stabilnosti, ukupnog kvaliteta i izrade čini ih dobrim izborom za montažu sofisticiranih mehaničkih, elektronskih i optičkih mjernih sistema. Za bilo koji od ovih procesa mjerenja, neophodno je da površinske ploče budu kalibrirane.

Repeat Measurements and Flatness

I mjerenje ravnosti i ponovljena mjerenja su ključni za osiguranje precizne površine. Ravnost se može smatrati kao da se sve tačke na površini nalaze unutar dvije paralelne ravni, osnovne ravni i ravni krova. Mjerenje udaljenosti između ravni predstavlja ukupnu ravnost površine. Ovo mjerenje ravnosti obično nosi toleranciju i može uključivati ​​oznaku stepena.

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... različite zemlje s različitim standardima...

Više detalja o standardu.

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.

Kako bi se osiguralo da površinska ploča ispunjava i specifikacije ravnosti i specifikacije ponovljenog mjerenja, proizvođači granitnih površinskih ploča trebaju koristiti Federalnu specifikaciju GGG-P-463c kao osnovu za svoje specifikacije. Ovaj standard se odnosi na tačnost ponovljenog mjerenja, svojstva materijala granitne površinske ploče, završnu obradu površine, lokaciju tačke oslonca, krutost, prihvatljive metode inspekcije i ugradnju navojnih umetaka.

Checking Plate Accuracy

Slijedeći nekoliko jednostavnih smjernica, investicija u granitnu površinsku ploču trebala bi trajati dugi niz godina. U zavisnosti od upotrebe ploče, okruženja u radionici i potrebne tačnosti, učestalost provjere tačnosti površinske ploče varira. Opšte pravilo je da se nova ploča potpuno rekalibrira u roku od godinu dana od kupovine. Ako se ploča često koristi, preporučljivo je skratiti ovaj interval na šest mjeseci.

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

U nekim slučajevima postoje varijacije između kalibracija površinskih ploča. Ponekad faktori poput promjene površine usljed habanja, nepravilne upotrebe opreme za inspekciju ili upotrebe nekalibrirane opreme mogu objasniti ove varijacije. Međutim, dva najčešća faktora su temperatura i podloga.

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

Slijeđenje nekoliko smjernica smanjit će habanje granitne ploče i u konačnici produžiti njen vijek trajanja.

Prvo, važno je održavati ploču čistom. Abrazivna prašina u zraku obično je najveći izvor habanja ploče, jer se obično ugrađuje u radne komade i kontaktne površine mjernih instrumenata.

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.

Povremeno rotirajte ploču kako se jedno područje ne bi prekomjerno koristilo. Također se preporučuje zamjena čeličnih kontaktnih pločica na mjernim instrumentima karbidnim pločicama.

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

Kada je potrebno obnoviti površinu granitne ploče, razmislite o tome da li da se ta usluga obavi na licu mjesta ili u kalibracijskom centru. Uvijek je poželjno da se ploča obnovi u fabrici ili u posebnom centru. Međutim, ako ploča nije previše istrošena, uglavnom unutar 0,001 inča od potrebne tolerancije, može se obnoviti na licu mjesta. Ako je ploča istrošena do te mjere da je više od 0,001 inča izvan tolerancije ili ako je jako oštećena ili izgrebana, tada je treba poslati u fabriku na brušenje prije ponovnog oblaganja.

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

Prilikom odabira tehničara za kalibraciju i obnovu površine na licu mjesta treba biti vrlo pažljiv. Zatražite akreditaciju i provjerite da li oprema koju će tehničar koristiti ima sljedivu kalibraciju. Iskustvo je također važan faktor, jer je potrebno mnogo godina da se nauči kako pravilno obrađivati ​​precizni granit.

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. Površina je oprana vrućim ili hladnim rastvorom prije kalibracije i nije joj bilo ostavljeno dovoljno vremena za normalizaciju.

2. Ploča je nepravilno poduprta.

3. Promjena temperature.

4. Nacrti.

5. Direktna sunčeva svjetlost ili drugo toplotno zračenje na površini ploče. Pazite da gornja rasvjeta ne zagrijava površinu.

6. Varijacije vertikalnog temperaturnog gradijenta između zime i ljeta. Ako je ikako moguće, znajte vertikalni gradijent temperature u trenutku kalibracije.

7. Ploči nije dato dovoljno vremena za normalizaciju nakon isporuke.

8. Nepravilna upotreba opreme za inspekciju ili upotreba nekalibrirane opreme.

9. Promjena površine usljed habanja.

Tech Tips

• Budući da svako linearno mjerenje zavisi od tačne referentne površine sa koje se uzimaju konačne dimenzije, površinske ploče pružaju najbolju referentnu ravan za inspekciju rada i raspored prije obrade.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Učinkovit program inspekcije trebao bi uključivati ​​redovne provjere autokolimatorom, omogućavajući stvarnu kalibraciju ukupne ravnosti koja se može pratiti do Nacionalnog inspekcijskog organa.

Među mineralnim česticama koje čine granit, više od 90% čine feldspat i kvarc, od kojih je feldspat najzastupljeniji. Feldspat je često bijele, sive i boje kože, a kvarc je uglavnom bezbojan ili sivkasto bijel, što čini osnovnu boju granita. Feldspat i kvarc su tvrdi minerali i teško ih je pomicati čeličnim nožem. Što se tiče tamnih mrlja u granitu, uglavnom crnog tinjca, postoje i neki drugi minerali. Iako je biotit relativno mekan, njegova sposobnost da se odupre naprezanju nije slaba, a istovremeno ih ima u maloj količini u granitu, često manje od 10%. Ovo je materijalno stanje u kojem je granit posebno jak.

Još jedan razlog zašto je granit čvrst je taj što su njegove mineralne čestice čvrsto povezane jedna s drugom i ugrađene jedna u drugu. Pore često čine manje od 1% ukupne zapremine stijene. To granitu daje sposobnost da izdrži jake pritiske i ne prodire lako u njega vlaga.

Granitne komponente su izrađene od kamena koji ne hrđa, otporan je na kiseline i alkalije, ima dobru otpornost na habanje i dug vijek trajanja, te ne zahtijeva posebno održavanje. Precizne granitne komponente se uglavnom koriste u alatima mašinske industrije. Stoga se nazivaju preciznim granitnim komponentama ili granitnim komponentama. Karakteristike preciznih granitnih komponenti su u osnovi iste kao i karakteristike granitnih platformi. Uvod u alate i mjerenje preciznih granitnih komponenti: Precizna obrada i tehnologija mikroobrade su važni pravci razvoja mašinske industrije i postale su važan pokazatelj za mjerenje visokog tehnološkog nivoa. Razvoj najsavremenije tehnologije i odbrambene industrije je neodvojiv od precizne obrade i tehnologije mikroobrade. Granitne komponente se mogu glatko kliziti tokom mjerenja, bez stagnacije. Mjerenje radne površine, opšte ogrebotine ne utiču na tačnost mjerenja. Granitne komponente moraju biti dizajnirane i proizvedene prema zahtjevima potražnje.

Područje primjene:

Kao što svi znamo, sve više mašina i opreme bira precizne granitne komponente.

Granitne komponente se koriste za dinamičko kretanje, linearne motore, CMM, CNC, laserske mašine...

slobodno nas kontaktirajte za više informacija.

Granitni mjerni uređaji i granitne mehaničke komponente izrađeni su od visokokvalitetnog Jinan crnog granita. Zbog svoje visoke preciznosti, dugog vijeka trajanja, dobre stabilnosti i otpornosti na koroziju, sve se više koriste u inspekciji proizvoda moderne industrije i naučnim oblastima kao što su mehanička, vazduhoplovna i naučna istraživanja.

Prednosti

----Dvostruko tvrđe od lijevanog željeza；

----Minimalne promjene dimenzija su zbog promjena temperature;

----Bez cijeđenja, tako da nema prekida rada;

----Bez neravnina ili izbočina zbog fino zrnate strukture i neznatne ljepljivosti, što osigurava visok stepen ravnosti tokom dugog vijeka trajanja i ne uzrokuje oštećenja drugih dijelova ili instrumenata;

----Besprijekoran rad za upotrebu s magnetskim materijalima;

----Dug vijek trajanja i otpornost na hrđu, što rezultira niskim troškovima održavanja.

Precizne granitne površinske ploče su precizno obrađene do visokog standarda ravnosti kako bi se postigla tačnost i koriste se kao osnova za montažu sofisticiranih mehaničkih, elektronskih i optičkih mjernih sistema.

Neke od jedinstvenih karakteristika granitne površinske ploče:

Ujednačenost tvrdoće;

Tačni uslovi pod opterećenjem;

Apsorber vibracija;

Lako se čisti;

Otporno na omotavanje;

Niska poroznost;

Neabrazivno;

Nemagnetski

Prednosti granitne površinske ploče

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.