1. Description of the Product

The eNM3A10 small ball rebound hardness tester is a rebound hardness tester that can accurately measure the hardness of a lightweight specimen, which has been difficult with conventional rebound hardness testers. Although rebound hardness is widely used to evaluate the strength of metallic and other materials, its hardness value tends to become apparently lower when lightweight specimens are tested. The eNM3A10 tester has provided a significant solution to this problem and enabled accurate measurement of the hardness of test specimens, whether they are small (5 mm at the thinnest) or even large machines of a complicated shape, in any testing direction. The tester also is portable and easy to use on site.

2. Description of the Technology

2.1 Conventional rebound hardness testers
A rebound hardness test uses an indenter dynamically hit against a specimen and does not require the measurement of the resulting indentation on the specimen. Instead, rebound hardness refers to the velocity ratio of an indenter before and after it hits the specimen, or the coefficient of restitution, which represents the before-impact kinetic energy of the indenter minus the energy used to form an indentation (plastic deformation). In other words, a specimen less likely to undergo plastic deformation has a larger coefficient of restitution, whereas a specimen more likely to undergo plastic deformation has a smaller coefficient of restitution.

The conventional rebound hardness test has difficulty having an indenter ejected by itself, therefore the indenter must be fixed on the tip of a metallic object that can be ejected. For this reason, even if the indenter alone is light, the whole indenter assembly hit against a specimen can weigh several dozen grams. Because such an indenter assembly suffers a loss of energy originating from vibration and other reasons when it hits a lightweight specimen, the coefficient of restitution, or hardness, of the specimen measures lower than actual. This is known as the “mass effect.”

To reduce the mass effect, reducing the weight of the indenter assembly is indispensable. Although it was realized only in the laboratory, an impact hardness test developed in 1987 adopted a mechanism to impact a small ball alone against a specimen. However, this tester was not commercialized because it was a stationary machine only usable for upward testing applications.

2.2 Small ball rebound hardness tester eNM3A10
The commercialized eNM3A10 tester hits an alumina ball alone of 3 mm in diameter and 0.06 g in mass against a specimen; measures the indenter ball velocity before and after it hits the specimen with a sensor; and calculates and indicates the coefficient of restitution. The test is completed instantaneously and does not require measurements of the indentation or any preliminary adjustments. Due to no variability between individuals, anyone can perform the test easily and with high accuracy. To ensure on-site safety and convenience, the tester is structured to prevent outer ejection of the ball indenter. In addition, once the tester completes a test, it can be reset easily to start another.

The ball indenter is held in a suitable manner to enable tests in all directions, including upward and downward. The test surface of a specimen needs to be #600 paper polished to ensure accurate measurement, but even #100 paper polish could achieve a near accurate coefficient of restitution with an error of some 2%. To accommodate the need to test complicated faces other than flat, the tester can be combined with an adapter for testing round bars and narrow portions. In addition to metallic materials, the eNM3A10 tester can test a wide range of materials, including wood, plastics and even food. Moreover, although still in the development stage, the tester could be used at temperatures from -196 to 1000℃, because it can complete a test instantaneously. Indeed, the eNM3A10 tester has great potential.

Fig. 1　Appearance of eNM3A10

The tester enables you to test the hardness block of 64 mm in diameter and 380 g in mass (as in the photo), either on a desk or held in the air with one’s hand.

3. Sales Results

The eNM3A10 small ball rebound hardness tester is the world’s first and currently only one rebound hardness tester using a small ball by itself (according to our own survey). The number of eNM3A10 units sold in Japan release is about 20, but the number of inquiries about the tester has been increasing, especially recently, for application in cases that go beyond the capacity of conventional rebound hardness testers.

4. Summary

The eNM3A10 small ball rebound hardness tester has been developed by a team of researchers who are interested in the project from various companies, universities and national research institutes. The team continues to work on the development of a tester with less mass effect.

Yamamoto Scientific Tool Laboratory Co., Ltd.

Corporate Member, 15-4, Sakae-machi 2-chome, Funabashi-shi, Chiba Prefecture 273-0018