Use and Care Of Granite Surface Plates – Maintenance Tips
Cleaning and moisture:
One of the first principles of use and care of Granite Surface Plates is that you should clean the plate thoroughly. It is important that you dry it after cleaning for 5 hours before testing for tolerance. The choice of cleaning solution is important. If a volatile solvent is used (acetone, lacquer thinner, alcohol, etc.) the evaporation will chill the surface and distort it. So, it is necessary to allow the plate to return to normal temperature before using it to avoid measurement error. In case of water-based cleaner there will be some evaporative chilling. The plate will also retain the water, and this could cause rusting of metal parts which are in contact with the surface. Some cleaners will also leave a sticky residue after they dry. This will attract airborne dust, and actually increase wear, rather than decrease it.
A surface plate should be under constant temperature and with less than 50% relative humidity. Avoid direct sunlight or sudden draughts.
Clean the surface plate twice a day, before and after work. When a plate is soiled with oily or sticky fluids, it must be cleaned immediately. The plate should be supported firmly and leveled. Stands should be located on a stable foundation.
Scratches and Nicks:
The burrs due to scratches and nicks on granite plates should be removed with flat silicon carbide stone. Any hump, which shatters the surface, raises fractured material at the rim of the crater.
The surface plate is a datum and you should protect it against damage. Frequently wipe clean the top from dust and other particles. When you take measurements, spread a wiping cloth on the plate. This is for placing small tools and gauge blocks.
A common sign of damage is cuts on the surface. Always cover the top when the plate is not in use. Airborne abrasive dust is usually the greatest source of wear and tear on a plate. This is because it tends to embed in work pieces and the contact surfaces of gauges.
It is important to learn the use and care of Granite Surface Plates. Take care to avoid over-load on the plate. Wherever possible distribute the load on a surface plate. Also, avoid setting food or soft drinks on the plate since many soft drinks contain either carbonic or phosphoric acid. This is due to the fact that it can dissolve the softer minerals and leave small pits in the surface.
Rotation of plate:
When a specific work surface area receives hard usage, we suggest that you rotate the plate 180° on a periodic basis to increase wear life. The production of a contour map attained during calibration is particularly helpful in locating the parts of the plate.
We recommend periodic re-calibration of granite surface plates in the use and care of Granite Surface Plates. This is to determine resurfacing or replacement needs. The interval between calibration will vary with the grade of plate. You have to also consider wear resistance and with the conditions and frequency of use. Surface plates in the manufacturing department requires re-calibration every six months. Whereas plates in the laboratory requires re-calibration every year. Frequent monitoring of the work surface by scanning it with the repeat reading gauge is important. When the results differ from the grade value, as mentioned in the standard, then it should be re-calibrated.
Instrumentation for calibrating surface plate flatness is autocollimator, electronic level and laser interferometer. Also, you can use master straightedge with traveling indicator or with beam gauge, linear beam and detector and in-line flatness gauge.
Downgrading, resurfacing or replacement levels:
During recalibration, the surface plates that deviate from work surface flatness tolerance, has to be downgraded, resurfaced or replaced. This applies to plates which show repeat readings that exceed the in-house requirements. Plates which have objectionable scratches and nicks in the work area also have to be resurfaces or replaced.
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