Roll Hardness Tester - 6 Steps to Test the Roll Profile

Each factory has its own recommendations for measuring the roll hardness. However the method is very similar in all cases and some general principals can be applied.

1. To prepare the roll hardness tester for use, press the plunger against hard surface and press firmly until the push-button springs out. The hammer is now ready to make an impact.

2. Begin at one end of the roll and not too close to the edge. To carry out an impact, place the roll hardness tester perpendicular to the paper roll. Push the hammer against the surface of the roll at a moderate speed until the impact is triggered. For best results, impact at the same angle and try to apply the same pressure for each reading. Repeat this procedure to obtain a profile across the entire roll in the cross machine direction.

3. The impact angle alters the reading on the scale as the rebound of the hammer mass is affected by gravity. Therefore it is imperative to always use the same impact angle. (TAPPI T 834 om-07 recommends measuring horizontally). Higher values will be obtained on the same roll when impacting horizontally as opposed to impacting vertically.

4. How the results are reviewed depend very much on the working practice of the paper factory. A typical method is this: First, calculate an average from all readings taken; Second, check the variations, i.e. the range between the maximum and the minimum values and third, determine whether or not this exceeds the specified tolerance.

5. It is recommended to check the calibration of the roll hardness tester on a regular basis. The TAPPI Standard T 834 om-07 recommends performing a calibration check each week, or prior to use if you use it less regularly.

6. The impact plunger recoils when it deploys. Always hold the roll hardness tester in both hands.


For More Information About Roll Hardness Testers and other Next Generation Tools, visit the Proceq Website

Rebound Hammer - Two Measuring Principles

Rebound hammers are used to determine the compressive strength of concrete. Compressive strength test results are, among other things, used to determine that the concrete mixture as delivered meets the requirements of the specification. Structural failures due to weaker than defined concrete mixes can be catastrophic and may lead to loss of life. Therefore, quality checks are of paramount importance to serious construction companies. In addition, non-destructive testing is faster and far more economical than destructive testing on samples.

Mechanical rebound hammer measure the mechanical travel of the hammer mass on the rebound. It is affected by its friction on the guide rod, the friction of the drag pointer on the scale, the influence of gravity during its travel and the relative velocity between unit and mechanical parts.
Electronic rebound hammers, on the other hand, use the true rebound coefficient that represents the physical rebound coefficient: Q = 100*((Energy Restored)/(Energy Input))
These rebound hammers measure the velocity of impact and of rebound, immediately before and after the impact, computing the fraction of energy loss to the specimen under test. The true rebound coefficient is virtually free of error sources inherent in traditional concrete test hammers. It is measured optically making the use of a drag and drop pointer redundant. Thus the true rebound coefficient is less dependent on friction on the guide rod, the influence of gravity during the travel of the drag pointer and the relative velocity between unit and specimen. Rebound hammers that measure with the true rebound coefficient do not need correction for the impact direction. Consequently, impact direction conversion curves as required with mechanical hammers, are also redundant.


To find out more about roll hardness testing visit us at Proceq

Proceq manufactures quality nondestructive portable testing instruments for metal hardness, concrete properties and roll hardness tester. Proceq invented the Equotip portable metal hardness tester and the world’s first portable concrete test hammer, the Schmidt concrete test hammer.

Roll Hardness Testing - Why is it Important?

The roll hardness of the paper roll has to be hard enough to guarantee a smooth unwinding at the one hand and has to be just hard enough to ensure a damage-free shipping and handling at the other hand.

A reliable measurement of the roll hardness profile is of critical importance in determining whether a roll is good or bad:

Rolls that are wound too soft typically may go out of round during transport and storage. If this happens it causes irregularities whilst unwinding and the only way to compensate for the effects is to slow down the speed of the unwinding machine leading to a loss in production.

Rolls that are wound too tightly can lead for example, to bursts within the roll, corrugations on the surface as the web is stretched too tightly.

Rolls that are wound too soft or too hard can cause serious problems when handling and this leads to loss in production. The reason for this variations in roll hardness are many, such as difference in moisture content, variations in the caliper (thickness) of the sheets or simply that the winding machine has not been set up correctly.

These variations are very difficult to detect without the aid of a roll hardness tester and if they go serious problems can result. Non-uniform hardness profiles can result in production down times for both producers and converters alike, making it one of the most important factor in determining whether or not a paper roll is good or bad.

To find out more about roll hardness testing visit us at Proceq


Proceq manufactures quality nondestructive portable testing instruments for metal hardness, concrete properties and paper roll hardness. Proceq invented the Equotip portable metal hardness tester and the world’s first portable concrete test hammer, the Schmidt concrete test hammer.