BGAS Painting Study Material Chapter 2 continuation

Profile measurement

If a profile requirement is specified, it is the inspector’s duty to ensure that the specification requirements are met. This can be done in two ways.

1. By measuring – using gauges with and without replica tape.
2. By assessing – using surface comparators.

The dial gauges are still very often used.  The dial gauges fall into two categories

1. Surface Profile Needle Gauge
2. Dial Micrometers with Replica Tape.

Surface Profile Needle Gauge.

The gauge is applied to the blasted substrate and the needle can be felt to locate a trough.  Then by applying a slight pressure to allow the flat ‘foot’ of the gauge to sit firmly on the peaks of the blasted substrate, the needle will pass into the trough as far as it can.

Surface profile needle gauge.

1. We need to zero the gauge when the point of the needle is on the same plane as the flat foot, i.e. on a smooth piece of glass.
2. Applying slight pressure to the foot to ensure that it is perfectly flat on the glass.
3. By loosening the locking screw, the bezel can now be moved.  The bezel should be moved till the zero on the gauge is immediately behind the needle.
4. Then tighten the locking screw and the gauge is ready for use.
5. Several readings are taken, usually more than ten, in random Positions over the substrate, and the average Calculated. This type of gauge is not ideally suited for curved areas such as pipes.
6. It is normal to work to an average figure.

Continue..............

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