What Is an Adhesion Tester?
An adhesion tester is a testing device widely and generally used to evaluate the hardness of surfaces of metals, resins, rubber products, and other materials.
Devices to evaluate the hardness of metals are often called “hardness testers,” while those to evaluate the hardness of relatively soft materials such as resin and rubber are often called “adhesion testers,” but there is no clear definition in practice. There are also adhesion testers used to measure the mineral content of water.
The correct definition of hardness is a numerical value based on the results of a test to evaluate hardness, such as the change in a product when something called an indenter is pressed into the part to be measured. There are various methods of testing to indicate hardness. There are many types of materials to be measured, including metals and resins, and it is important to select the method of measuring hardness according to the application.
Uses of Adhesion Testers
Typical applications of adhesion testers are as follows:
1. Rockwell Hardness
A type of indentation hardness test, in which an indenter, such as a diamond or hard ball, is applied to the material to be measured under a defined load to create an indentation. The depth of the indentation is used to measure the hardness.
First, the indenter is subjected to a standard push load to determine the origin of the depth. Then, an additional load is applied to the indenter and held for a certain period until it reaches the specified test load, after which the load is returned to the reference load. The hardness is evaluated based on the difference between the depth at which the reference load is first applied and the depth at which the load is returned to the reference load.
This test is mainly used to evaluate the hardness of heat-treated steel materials. It is widely used together with the Vickers hardness test, which is a hardness test for metals. However, since the test load is higher than that of the Vickers hardness test, a specimen that can withstand the test load is required.
2. Vickers Hardness
This is a type of indentation hardness test in which a diamond is pressed against the material to be measured as an indenter to make an indentation, and the hardness is measured from the load applied and the surface area of the indentation. The size of the indentation is measured with a metallographic microscope.
This test is mainly used to evaluate the hardness of metals, but it can be used to evaluate a very narrow range of hardness. It is also used to evaluate the depth of hardening in heat-treated metals. It is called effective hardened layer depth.
3. Shore Hardness
Shore hardness is a type of rebound hardness, which is measured by dropping an indenter with a diamond attached to the tip of a copper rod onto the object to be measured and measuring the height of the indenter’s rebound after striking the object. In the rebound height test, the indenter is dropped from a specific height and measured from the magnitude of rebound (height of rebound) after hitting the object.
Therefore, no power supply is required. On-site testing of large buildings, etc., is possible.
Principle of Adhesion Testers
There are two main methods for evaluating hardness: indentation hardness and rebound hardness.
1. Indentation Hardness
A hard material called an indenter, such as diamond, is pressed against the material to be measured, and the hardness is determined by the depth of the indentation. Brinell hardness, Rockwell hardness, Vickers hardness, etc. are used to evaluate the hardness of metals.
2. Rebound Hardness
The hardness is measured by the amount of rebound of the indenter after it strikes the material to be measured. Shore hardness is one of the main tests.
Other Information on Adhesion Testers
1. Food Adhesion Tester
Measuring instruments for measuring the hardness of food products are called rheometers or rheotesters. Foods to be measured by rheometers are much softer than the so-called hardness tester categories in this volume and cannot be measured by the above mentioned adhesion testers.
The measurement unit of the rheometer, like other hardness units, is not specified, so the unit of measurement is either the same as that of the load cell or force tester used in the measurement, or, if a compression plate is used, it is indicated as per surface accuracy of the compression plate (N/㎟), etc. However, as with other hardness values, data correlation is weak, so evaluation is based on relative comparisons between data measured with the same measuring instrument.
2. Water Adhesion Tester
Water hardness is what is referred to as hard water or soft water. Water hardness is the sum of 2.5 times the amount of calcium (Cax2.5) and 4 times the amount of magnesium (mgx4) contained in water, and is measured using a chemical reaction measuring instrument and reagents. The unit is expressed in mg/L (U.S. hardness), with higher values indicating hard water and lower values soft water.