Kekerasan bahan memberikannya kemampuan untuk menolak ubah bentuk kekal ketika beban dikenakan. Dari sudut pandangan kejuruteraan, menentukan kekerasan bahan adalah penting kerana daya tahan terhadap hakisan atau geseran oleh unsur yang berbeza cenderung meningkat dengan kekerasan secara amnya. Semakin besar kemampuan bahan untuk menolak ubah bentuk semakin besar kekerasannya.
Fundamentals of the hardness of the material
The hardness of material depends on its viscosity, toughness, strain, strength, ductility, viscoelasticity, plasticity, and elastic stiffness. The hardness of materials is tested by various hardness testing procedures that are non-destructive, quick, and efficient.
What is hardness testing?
The assessment of material’s resistance to permanent deformation such as wear, scratch, indentation, and abrasion is known as hardness testing. It is one of the common types of quality control checking phenomenon performed to test the hardness of materials. It is used to test the current condition of material and is one of the easiest tests to be available and performed at laboratories etc.
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Zinc metal has myriad biological and industrial uses and is found in abundance in Earth’s crust. Zinc generally has bluish-white color and is brittle at room temperature that can be polished for a brighter finish. Zinc is used primarily to protect the metal against unwanted corrosion that is meant to galvanize steel. However, other alloys of zinc are essential for a wide range of applications, including brass.
Importance of zinc
There are a number of different zinc minerals from where zinc is recovered in addition to being recycled from scrap. Zinc alloys are quite stronger and tougher than the zinc metal itself. In addition, to be beneficial for a healthy life of humans and animals, zinc has enormous benefits. Due to its non-reactive nature in water or air, zinc is applied in thin layers to steel and iron products to protect them from rusting. Zinc is extensively used for wide purposes such as in chemicals, rubber industry, fluorescent lights, TV screens, dry cell batteries, and agricultural applications. Therefore, testing the hardness of zinc is critical before it can be used for a wide range of purposes to prevent any colossal damage in any field of life.
The hardness of zinc metal
Let’s discuss the general physical properties of zinc metal that will determine the hardness of zinc metal:
- Toughness: Pure zinc is generally brittle and has low toughness. However, as compared to other die casting alloys, zinc alloys have high impact strength in general.
- Conductivity: The conductivity of zinc is generally moderate for a metal. However, the powerful electrochemical properties serve well in alkaline batteries and galvanizing process.
- Ductility: Zinc becomes malleable and ductile between 212-302oF, whereas, increased temperatures revert it to a fragile state. Zinc alloys are far better at this property that allows using more complex fabrication methods as compared to pure metal.
- Strength: Zinc has a tensile strength that is approximately half of the mild carbon steel and is generally considered a weak metal.
Testing hardness for zinc metal
There are various hardness tests that have been practiced to measure the hardness of various metals. The hardness test for the specific material is chosen based on the size, condition, part, and the type of material that generally refers to the homogeneity of the material.
Hardness tests often require a flat, polished and ground surface so that the hardness indents are located in the correct region and various weld regions can be identified. There are various hardness testing methods used to test the hardness of zinc. The most common types of tests used for measuring zinc hardness are Brinell hardness test, Rockwell hardness test, Mohs hardness test, and The Knoop hardness test.
Brinell hardness test
Invented by Dr. J.A. Brinell in 1900, Brinell hardness tests have been widely used for testing engineering materials today. A desktop machine is used by Brinell test, and a load of an object is applied to it of a specific diameter to a hardened sphere.
The Brinell hardness number is obtained by dividing the used load (in kgs) by the measured indentation surface area (in sq. millimeters), present on the test surface. The Brinell tests are least affected by the coarse grain structures of materials by providing the measurement over a large area as compared to other tests.
Ujian kekerasan Rockwell
Rockwell hardness test is one of the famous hardness tests that is widely used and acknowledged for its accuracy. The hardness refers to resistance to penetration as measured by the Rockwell scale. This test was first used in 1919 and was developed originally by Stanley P. Rockwell. The hardness of zinc can be measured in the simplest way possible by Rockwell hardness test as it works by pressing an indenter of a specific load to the material surface and then measuring the distance that indenter was able to penetrate. To give accurate results, there are 30 different scales used for Rockwell hardness tests. Each scale is chosen based on the test material, metal sample, limitations of each scale, and the homogeneity of the material. The intender (or brale) is either spherical diamond-shaped or can be a steel ball of some specific diameter. Relatively high loads are applied in this method via tungsten carbide to the parts.
Ujian kekerasan Knoop
The Knoop hardness test is ideal for the testing of thin layers and to overcome the cracking in brittle materials. This method serves to be an alternate to Vickers test (used majorly for hard materials) to facilitate microhardness testing range. The indent is measured by measuring the long diagonal optically and is generally an asymmetrical pyramidal diamond.
Mohs hardness test
Zinc hardness can be measured by one of the oldest method known as Mohs hardness test that was devised in 1812 by German mineralogist Friedrich Mohs. This method involves identification of substances of defined or known hardness that might have scratched the material surface. The hardness results are measured in nano, micro, and macro scales. Minerals are ranked along the Mohs scale to give the numerical values to the physical property that is composed of ten minerals given random hardness values. Mohs hardness test has been expected to provide precise measurement of hardness, especially for minerals and brittle substances like zinc instead of industrial materials such as ceramics and steel.
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