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Portable Hardness Testers: Rebound vs. Ultrasonic Based Testers

便携式硬度计选型指南

Selecting the right testing apparatus can be confusing. In this article we'll examine what you need to consider

when choosing an instrument for your application.

Many customers call with questions regarding the selection of a portable hardness tester. When deciding

between Ultrasonic or a Rebound type testers there are a few parameters to consider.

Techniques

Each instrument gathers information on hardness from a certain zone within the sample. Ultrasonic Testers,

such as the SU‐300, use a Vickers diamond to penetrate the surface to a predetermined load. Information on

material hardness is determined from an area closer to the surface; however, penetration depth will depend

on the specific model, with loads of 10N, 20N or 50N.

Rebound Testers, such as the SH‐300 and SH500, throw a steel ball to the surface and measure the height of

the rebound, so hardness depends on the material composition deeper inside the sample.

Roughness

Rebound testers are not recommended for use on samples with surface roughness over 3.2 µm. Standard

deviation between measurements begins to increase when samples have a surface rougher than 0.8 µm and

becomes too high at 3.2 µm (assuming a load of 20N, at 50N the maximum is 5 µm).

Thickness

Sample thickness also influences the hardness tester decision. Rebound Testers require sample thickness of

<13mm, while the SU‐100 is suitable for <4mm.

Material Composition

Another important point when selecting an instrument is determining if the sample surface is different than

the bulk. If there is no difference, the limits explained above will work fine. If they are different, it is important

to decide where you want the information to come from. Understanding this will explain why hardness

variation exists between various tools and techniques.

Should I use a handheld tester?

Many companies use bench top systems as their quality control tools and want the ease of a portable tester

for faster, on‐site or in‐field use. No matter what type of hardness tester you prefer it is important to

understand that the standard bench top Vickers & Rockwell Testers also get their hardness information from a

specific area on the sample. When surface and bulk are the same, comparative values are easy to be used but

when they are different comparing portable testers to bench top systems can be a challenge, or even

impossible.