Measurement of Surface Profile

There are three main ways to determine the surface profile of a grit blasted surface to confirm the roughness required has been achieved.

  1. Surface Comparators

    2. A visual and tactile comparison can be made to a precision-formed metal plate (normally nickel) that has three or four pre-formed profiles in its surface. These Comparators conform to International Standards such as ISO 8503. They are available for both grit and shot blasted surfaces and for Belzona® coatings it is important that the angular pattern is used not the dimpled as produced by shot blasting.

    Operation

    After removal of loose dust and debris from the surface, the profile is compared with those on the Comparator to ascertain which has the nearest profile. A magnifier not exceeding 7X magnification assists the process.

  2. Profile measuring gauges.

    3. These use a sharp stylus attached to an accurate dial or digital gauge to track the surface profile. They accurately measure the peak to valley height of the profile. They are accurate to 1-2 micron.

    Operation

    The gauge is initially set to zero using a glass plate underneath the foot of the instrument. It is then placed on the blasted surface where the foot rests on the tops of the peaks and the sharp stylus travels to the bottom of the valley. The gauge displays the peak to valley height. A number of readings are made and the average peak to valley height calculated. ASTM D4417 Method B calls for the mean of 10 readings to be taken from an agreed series of locations.

  3. Testex Tape

These take a permanent impression from the blasted surface, which can be simply measured using a snap gauge. This gives, with a single measure, the average maximum peak to valley height of the profile.

The Tapes are available in 2 different grades, the X Coarse (1.5-4.5 mils) being most suitable for Belzona coatings. Analogue and digital gauges are available for measuring the Tape thickness accurately. This test is covered by International standards such as ASTM D 4417 Method C.

Operation

The Testex tape is placed on the blasted surface. Using the burnishing tool with moderate pressure applied to the circular section of the tape, a replica of the profile is obtained in the Testex tape. The thickness of the Testex tape is measured using the snap gauge. By subtracting the tape thickness, (2mil or 50.8 microns), the average maximum peak to valley height of the blasted surface is obtained. The Testex tape can be kept as a permanent record of the test.

Test equipment suppliers

England
Elcometer Instruments Ltd
Edge Lane
Droylsden
Manchester
M43 6BU
Tel (0161) 3707611
Fax (0161) 3704999

Paint Test Equipment
3/4 The Courtyard
Greenfield Farm Estate
Congleton
Cheshire
CW 12 4TR
Tel (01260) 275614
Fax (01260) 299231

USA
Elcometer Inc
1893 Rochester Industrial Drive
Rochester Hills
Michigan 48309
Tel (810) 6500500
Fax (810) 6500501

Germany
Elcometer Instruments GmbH
Albblick 18
D-73730 Esslingen
Tel (0711) 366081
Fax (0711) 366455

Asia & Far East
Elcometer (Asia) Pte Ltd
896 Dunearn Road
Sime Darby Centre #03-09
Singapore 2158
Tel (65) 4622822
Fax (65) 4622860

 

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Posted 12/1/99

 
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