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GRRI
Granite Roll Radar Ins.
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Geo-Work has specialized in internal flaw inspection of granite rolls with radar equipment specifically developed for this purpose. Geo-Work developed this survey method with the support of the Technology Development Centre of Finland, a granite roll manufacturer, and insurance companies. The method utilizes stone penetrating radar equipment and a special antenna developed for the purpose in conjunction with computer application programs for the analysis work. Today we are the leading company in this field and have surveyed over 200 granite rolls in dozens of paper mills around the world.

With the GRRI survey it is possible to obtain numerous facts about the granite roll, please see the examples of roll images on the next page. Based on the information obtained from the roll it is possible to evaluate the potential effect on the operational qualities and safety of the roll. The information recorded from the initial survey is important. For example, in a case of an accidental impact to the roll it is possible to compare the new results to the previous one for any internal changes in the images. It can then be said with certainty whether the accident caused any changes inside the roll. Follow-up surveys also enable us to monitor the development of any initially small cracks over time. Thus the surveys make it possible to improve the safety of the working environment and control risks.

A granite roll is measured at forty to fifty stations depending on the size of the roll. The following are some examples of typical images:

Cracks: An internal crack generates a parabolic reflection on the radar profile. The suspected roll area is scanned at every two inches (50 mm) to measure the length and direction of the crack.

Structures: Granite is not homogeneous. The radar measurements are used to lay out the structural direction of the granite which possibly indicates the weakest direction.

Mineral Enclaves: The radar measurement detects large deviating targets in the shell, such as quartz, feldspar, and biotite enclaves (agglomerations). These reflections are different from those formed by cracks. The enclaves do not compromise safety, however, they may cause the roll surface to crumble locally affecting paper quality and roll life.

Rust: Strong radar reflections caused by rust penetrations are often found between the end flange and the granite body. They are wide near the surface and weaken toward the roll center, contrary to the reflections by cracks.

Filling: Variations in urethane or concrete filling in the center hole are detected by the radar. Dampers, centering supports, filler pipes may also be located.

Axial scan: There often is a step in the middle of the roll due to eccentric boring or sawing from each end. The shell thickness and varation in it are also measured.