O granito é un tipo de rocha ígnea que se extrae pola súa extrema resistencia, densidade, durabilidade e resistencia á corrosión. Pero o granito tamén é moi versátil: non só serve para cadrados e rectángulos! De feito, traballamos con confianza con compoñentes de granito deseñados en formas, ángulos e curvas de todas as variacións de forma regular, con excelentes resultados.
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:
■ mecanizable
■ precisamente plano unha vez cortado e rematado
■ resistente á ferruxe
■ duradeiro
■ de longa duración
Os compoñentes de granito tamén son fáciles de limpar. Ao crear deseños personalizados, asegúrate de escoller o granito polas súas vantaxes superiores.

ESTÁNDARES / APLICACIÓNS DE ALTO DESGASTE
O granito utilizado por ZHHIMG para os nosos produtos de placas de superficie estándar ten un alto contido de cuarzo, o que proporciona unha maior resistencia ao desgaste e aos danos. As nosas cores Superior Black teñen baixas taxas de absorción de auga, o que minimiza a posibilidade de que os seus calibres de precisión se oxiden ao colocalos nas placas. As cores de granito que ofrece ZHHIMG resultan en menos brillo, o que significa menos fatiga visual para as persoas que usan as placas. Escollemos os nosos tipos de granito tendo en conta a expansión térmica nun esforzo por manter este aspecto mínimo.

CUSTOM APPLICATIONS
Cando a súa aplicación require unha placa con formas personalizadas, insercións roscadas, ranuras ou outros mecanizados, convén elixir un material como o negro Jinan. Este material natural ofrece unha rixidez superior, unha excelente amortiguación de vibracións e unha maquinabilidade mellorada.

É importante ter en conta que a cor por si soa non é un indicador das calidades físicas da pedra. En xeral, a cor do granito está directamente relacionada coa presenza ou ausencia de minerais, que poden non ter ningunha influencia nas calidades que fan que un bo material para placas superficiais sexa unha superficie. Hai granitos rosa, gris e negro que son excelentes para placas superficiais, así como granitos negros, grises e rosa que son totalmente inadecuados para aplicacións de precisión. As características críticas do granito, no que respecta ao seu uso como material para placas superficiais, non teñen nada que ver coa cor e son as seguintes:
■ Rixidez (deflexión baixo carga, indicada polo módulo de elasticidade)
■ Dureza
■ Densidade
■ Resistencia ao desgaste
■ Estabilidade
■ Porosidade

Probamos moitos materiais de granito e comparámolos. Finalmente, obtemos o resultado: o granito negro de Jinan é o mellor material que coñecemos. O granito negro indio e o granito surafricano son similares ao granito negro de Jinan, pero as súas propiedades físicas son inferiores ás do granito negro de Jinan. ZHHIMG seguirá buscando máis materiais de granito no mundo e comparando as súas propiedades físicas.

Para falar máis sobre o granito axeitado para o seu proxecto, póñase en contacto connosco.info@zhhimg.com.

Os diferentes fabricantes empregan diferentes estándares. Hai moitos estándares no mundo.
Norma DIN, ASME B89.3.7-2013 ou Especificación Federal GGG-P-463c (Placas Superficiais de Granito) e así sucesivamente como base para as súas especificacións.

E podemos fabricar placas de inspección de precisión de granito segundo as súas necesidades. Póñase en contacto connosco se desexa obter máis información sobre máis estándares.

A planitude pódese considerar como todos os puntos da superficie contidos dentro de dous planos paralelos, o plano base e o plano do tellado. A medida da distancia entre os planos é a planitude xeral da superficie. Esta medida de planitude adoita ter unha tolerancia e pode incluír unha designación de grao.

Por exemplo, as tolerancias de planitude para tres graos estándar defínense na especificación federal segundo a seguinte fórmula:
■ AA de grao de laboratorio = (40 + diagonal ao cadrado/25) x 0,000001" (unilateral)
■ Grao de inspección A = Grao de laboratorio AA x 2
■ Sala de ferramentas Grao B = Laboratorio Grao AA x 4.

Para placas de superficie de tamaño estándar, garantimos tolerancias de planitude que superan os requisitos desta especificación. Ademais da planitude, a norma ASME B89.3.7-2013 e a especificación federal GGG-P-463c abordan temas como: precisión de medición repetida, propiedades dos materiais dos granitos das placas de superficie, acabado superficial, localización dos puntos de apoio, rixidez, métodos de inspección aceptables, instalación de insercións roscadas, etc.

As placas de superficie de granito ZHHIMG e as placas de inspección de granito cumpren ou superan todos os requisitos establecidos nesta especificación. Na actualidade, non existe unha especificación definitoria para placas angulares, paralelas ou escuadras mestras de granito.

E podes atopar as fórmulas para outros estándares enDESCARGAR.

En primeiro lugar, é importante manter a placa limpa. O po abrasivo transportado polo aire adoita ser a maior fonte de desgaste dunha placa, xa que tende a incrustarse nas pezas de traballo e nas superficies de contacto dos calibres. En segundo lugar, cubra a placa para protexela do po e dos danos. A vida útil pódese prolongar cubrindo a placa cando non se use, xirándoa periodicamente para que unha soa área non reciba un uso excesivo e substituíndo as almofadas de contacto de aceiro nos calibres por almofadas de carburo. Ademais, evite colocar alimentos ou refrescos na placa. Teña en conta que moitos refrescos conteñen ácido carbónico ou fosfórico, que pode disolver os minerais máis brandos e deixar pequenos buratos na superficie.

Isto depende de como se utilice a placa. Se é posible, recomendamos limpala ao comezo do día (ou da quenda de traballo) e de novo ao final. Se a placa se ensucia, especialmente con fluídos oleosos ou pegañentos, probablemente debería limparse inmediatamente.

Limpar a placa regularmente con líquido ou cun limpador de placas de superficie sen auga ZHHIMG. A elección das solucións de limpeza é importante. Se se usa un disolvente volátil (acetona, diluínte de laca, alcol, etc.), a evaporación arrefriará a superficie e distorsionaraa. Neste caso, é necesario deixar que a placa se normalice antes de usala ou produciranse erros de medición.

O tempo que tarda a placa en normalizarse variará segundo o seu tamaño e a cantidade de arrefriamento. Unha hora debería ser suficiente para placas máis pequenas. Poden ser necesarias dúas horas para placas máis grandes. Se se usa un limpador a base de auga, tamén haberá certo arrefriamento por evaporación.

A placa tamén reterá a auga, e isto podería causar oxidación nas pezas metálicas en contacto coa superficie. Algúns produtos de limpeza tamén deixarán un residuo pegañento despois de secar, o que atraerá o po no aire e, de feito, aumentará o desgaste, en lugar de reducilo.

Isto depende do uso da placa e do ambiente. Recomendamos que unha placa nova ou un accesorio de granito de precisión reciba unha recalibración completa nun prazo dun ano desde a súa compra. Se a placa de granito vai sufrir un uso intensivo, pode ser aconsellable acurtar este intervalo a seis meses. A inspección mensual para detectar erros de medición repetidos cun nivel electrónico ou un dispositivo similar mostrará calquera punto de desgaste en desenvolvemento e só leva uns minutos realizarse. Unha vez determinados os resultados da primeira recalibración, o intervalo de calibración pode ampliarse ou acurtarse segundo o permita ou o requira o seu sistema de calidade interno.

Podemos ofrecerche un servizo para axudarche a inspeccionar e calibrar a túa placa de superficie de granito.

Hai varias posibles causas para as variacións entre calibracións:

• A superficie lavouse cunha solución quente ou fría antes da calibración e non se lle deu tempo suficiente para normalizarse.
• A placa está mal apoiada
• Cambio de temperatura
• Borradores
• Luz solar directa ou outra calor radiante na superficie do prato. Asegúrate de que a iluminación superior non quente a superficie.
• Variacións no gradiente de temperatura vertical entre o inverno e o verán (se é posible, coñeza a temperatura do gradiente vertical no momento en que se realiza a calibración).
• A placa non ten tempo suficiente para normalizarse despois do envío
• Uso inadecuado de equipos de inspección ou uso de equipos non calibrados
• Cambios superficiais derivados do desgaste

Cantos tipos de buratos hai no granito de precisión?

Ranuras en compoñentes de granito de precisión

Moitas fábricas, salas de inspección e laboratorios empregan placas de superficie de granito de precisión como base para medicións precisas. Dado que cada medición lineal depende dunha superficie de referencia precisa da que se toman as dimensións finais, as placas de superficie proporcionan o mellor plano de referencia para a inspección e o deseño do traballo antes do mecanizado. Tamén son bases ideais para realizar medicións de altura e superficies de calibración. Ademais, o seu alto grao de planitude, estabilidade, calidade xeral e man de obra convértenas nunha boa opción para montar sistemas de calibración mecánicos, electrónicos e ópticos sofisticados. Para calquera destes procesos de medición, é imprescindible manter as placas de superficie calibradas.

Repeat Measurements and Flatness

Tanto a planaridade como as medicións repetidas son fundamentais para garantir unha superficie precisa. A planaridade pódese considerar como todos os puntos da superficie contidos dentro de dous planos paralelos, o plano base e o plano do tellado. A medición da distancia entre os planos é a planaridade xeral da superficie. Esta medición de planaridade adoita ter unha tolerancia e pode incluír unha designación de grao.

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

Estándar DIN, estándar GB, estándar ASME, estándar JJS... diferentes países con diferentes soportes...

Máis detalles sobre o estándar.

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.

Para garantir que unha placa de superficie cumpra as especificacións de planitude e repetición de medicións, os fabricantes de placas de superficie de granito deben usar a especificación federal GGG-P-463c como base para as súas especificacións. Esta norma aborda a precisión da repetición de medicións, as propiedades do material do granito das placas de superficie, o acabado superficial, a localización do punto de apoio, a rixidez, os métodos aceptables de inspección e a instalación de insercións roscadas.

Checking Plate Accuracy

Seguindo unhas cantas pautas sinxelas, un investimento nunha placa de superficie de granito debería durar moitos anos. Dependendo do uso da placa, do ambiente do taller e da precisión requirida, a frecuencia de comprobación da precisión da placa de superficie varía. Unha regra xeral é que unha placa nova reciba unha recalibración completa nun prazo dun ano desde a súa compra. Se a placa se usa con frecuencia, é aconsellable acurtar este intervalo a seis meses.

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

Nalgúns casos, existen variacións entre as calibracións das placas de superficie. Ás veces, factores como o cambio na superficie resultante do desgaste, o uso incorrecto do equipo de inspección ou o uso de equipo non calibrado poden explicar estas variacións. Non obstante, os dous factores máis comúns son a temperatura e o soporte.

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

Seguir unhas cantas pautas reducirá o desgaste dunha placa de granito e, en definitiva, prolongará a súa vida útil.

En primeiro lugar, é importante manter a placa limpa. O po abrasivo transportado polo aire adoita ser a maior fonte de desgaste dunha placa, xa que tende a incrustarse nas pezas de traballo e nas superficies de contacto dos calibres.

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.

Xire a placa periodicamente para que unha soa área non reciba un uso excesivo. Ademais, recoméndase substituír as almofadas de contacto de aceiro nas medicións por almofadas de carburo.

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

Cando sexa necesario rectificar a superficie dunha placa de granito, considere se se debe realizar este servizo in situ ou nas instalacións de calibración. Sempre é preferible rectificar a superficie da placa na fábrica ou nunha instalación específica. Non obstante, se a placa non está demasiado desgastada, xeralmente dentro de 0,001 polgadas da tolerancia requirida, pódese rectificar a superficie in situ. Se unha placa está desgastada ata o punto de estar máis de 0,001 polgadas fóra da tolerancia, ou se está moi danada ou rabuñada, debe enviarse á fábrica para a súa rectificación antes de rectificala.

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

Débese ter moito coidado á hora de escoller un técnico de calibración e repavimentación in situ. Solicite a acreditación e verifique que o equipo que empregará o técnico teña unha calibración rastrexable. A experiencia tamén é un factor importante, xa que leva moitos anos aprender a lapear correctamente granito de precisión.

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. A superficie lavouse cunha solución quente ou fría antes da calibración e non se lle deu tempo suficiente para normalizarse.

2. A placa non está ben apoiada.

3. Cambio de temperatura.

4. Borradores.

5. Luz solar directa ou outra calor radiante na superficie da placa. Asegúrate de que a iluminación superior non quente a superficie.

6. Variacións no gradiente vertical de temperatura entre o inverno e o verán. Se é posible, coñeza a temperatura do gradiente vertical no momento en que se realiza a calibración.

7. Non se lle concedeu á placa tempo suficiente para normalizarse despois do envío.

8. Uso inadecuado do equipo de inspección ou uso de equipo non calibrado.

9. Cambio superficial resultante do desgaste.

Tech Tips

• Dado que cada medición lineal depende dunha superficie de referencia precisa da que se toman as dimensións finais, as placas de superficie proporcionan o mellor plano de referencia para a inspección do traballo e o deseño antes do mecanizado.
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• Un programa de inspección eficaz debería incluír comprobacións regulares cun autocolimador, que proporcionen unha calibración real da planitude xeral rastrexable ata a Autoridade Nacional de Inspección.

Entre as partículas minerais que compoñen o granito, máis do 90 % son feldespato e cuarzo, dos cales o feldespato é o máis abundante. O feldespato adoita ser branco, gris e vermello carne, e o cuarzo é maioritariamente incoloro ou branco agrisado, que constitúen a cor básica do granito. O feldespato e o cuarzo son minerais duros e é difícil movelos cun coitelo de aceiro. En canto ás manchas escuras no granito, principalmente mica negra, hai algúns outros minerais. Aínda que a biotita é relativamente branda, a súa capacidade para resistir a tensión non é débil e, ao mesmo tempo, teñen unha pequena cantidade no granito, a miúdo inferior ao 10 %. Esta é a condición material na que o granito é particularmente forte.

Outra razón pola que o granito é forte é que as súas partículas minerais están fortemente unidas entre si e incrustadas unhas nas outras. Os poros adoitan representar menos do 1 % do volume total da rocha. Isto dálle ao granito a capacidade de soportar fortes presións e non é facilmente penetrado pola humidade.

Os compoñentes de granito están feitos de pedra sen resistencia á ferruxe, aos ácidos e aos álcalis, boa resistencia ao desgaste e longa vida útil, sen mantemento especial. Os compoñentes de precisión de granito úsanse principalmente na ferramenta da industria da maquinaria. Polo tanto, denomínanse compoñentes de precisión de granito ou compoñentes de granito. As características dos compoñentes de precisión de granito son basicamente as mesmas que as das plataformas de granito. Introdución á ferramenta e medición de compoñentes de precisión de granito: a mecanización de precisión e a tecnoloxía de micromecanización son importantes direccións de desenvolvemento da industria de fabricación de maquinaria e convertéronse nun indicador importante para medir un nivel de alta tecnoloxía. O desenvolvemento de tecnoloxía de vangarda e a industria da defensa son inseparables da mecanización de precisión e a tecnoloxía de micromecanización. Os compoñentes de granito pódense deslizar suavemente na medición, sen estancamento. A medición da superficie de traballo, os arañazos xerais non afectan a precisión da medición. Os compoñentes de granito deben deseñar e producirse segundo os requisitos da demanda.

Campo de aplicación:

Como todos sabemos, cada vez máis máquinas e equipos escollen compoñentes de granito de precisión.

Os compoñentes de granito utilízanse para movemento dinámico, motores lineais, CMM, CNC, máquina láser...

Póñase en contacto connosco para obter máis información.

Os dispositivos de medición de granito e os compoñentes mecánicos de granito están feitos de granito negro de Jinan de alta calidade. Debido á súa alta precisión, longa duración, boa estabilidade e resistencia á corrosión, utilízanse cada vez máis na inspección de produtos da industria moderna e en áreas científicas como a mecánica aeroespacial e as investigacións científicas.

Vantaxes

----Dúas veces máis duro que o ferro fundido;

----Os cambios mínimos de dimensión débense aos cambios de temperatura;

---- Libre de espremer, polo que non hai interrupción do traballo;

---- Libre de rebabas ou protuberancias debido á estrutura de gran fino e á adherencia insignificante, o que garante un alto grao de planitude durante unha longa vida útil e non causa danos a outras pezas ou instrumentos;

---- Funcionamento sen problemas para o seu uso con materiais magnéticos;

----Longa vida útil e sen ferruxe, o que resulta en baixos custos de mantemento.

As placas de precisión de granito están lapeadas con precisión cun alto estándar de planitude para lograr a precisión e utilízanse como base para montar sofisticados sistemas de medición mecánicos, electrónicos e ópticos.

Algunhas das características únicas da placa de superficie de granito:

Uniformidade na dureza;

Preciso baixo condicións de carga;

Absorbente de vibracións;

Fácil de limpar;

Resistente á envoltura;

Baixa porosidade;

Non abrasivo;

Non magnético

Vantaxes da placa de superficie de granito

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.