Brinell Hardness Tester

1. What are the advantages of Brinell hardness testers?

Brinell hardness testers can be used to inspect the hardness of non-homogeneous materials (the materials where the properties are not persistent throughout the specimen). This non-destructive testing works by using varied forces as well as different indenters.

2.     What are the testing standards for Brinell hardness testers?

Brinell hardness testers follow US, European, and International standards:

• US standard (ASTM International)

  “ASTM E10-14: Standard method for Brinell hardness of metallic materials”.

• International (ISO) and European (CEN) Standard

  “EN ISO 6506-1:2005: Metallic materials – Brinell hardness test – Part 1: test method”.

  “EN ISO 6506-2:2005: Metallic materials – Brinell hardness test – Part 2: verification and calibration of the testing machine”.

  “EN ISO 6506-3:2005: Metallic materials – Brinell hardness test – Part 3: calibration of reference blocks”.

  “EN ISO 6506-4:2005: Metallic materials – Brinell hardness test – Part 4: Table of hardness values”.

3.     What is the working methodology of the Brinell hardness test?

The Brinell hardness testing machine presses a tungsten carbide ball into the sample, and optically measures the diameter of the impression. This instrument is performed using a Brinell hardness test unit. The other parameters of the Brinell machine include the following features:

  Loads: From 1 kgf to 3000 kgf

  Indenter sizes: 1, 2.5, 5 and 10 mm

  Maximum hardness: 650 HBW

There are two types of technological remedies to counter Brinell measurement error issues, which have been developed over the years. Automatic optical Brinell scopes, like the B.O.S.S. system, employ computers as well as image analysis to view the indentations in a constant manner. This standardization helps in eliminating the operator subjectivity so that these operators remain less prone to view in-tolerance results automatically if the sample’s result goes out-of-tolerance.

Brinell units work as per the ASTM E103 standards while measuring the samples using Brinell hardness parameters along with a Rockwell hardness method. This method delivers the most repetitive results with greater speed since the notions of optical interpretations are eliminated by using an automatic mechanical depth measurement.

However, in this method, the results may not be strictly consistent with Brinell results due to the application of varied test methods – a counterbalance to the outcomes may be required for some materials. It will be easier to establish the right values in those cases where this arises as an issue.

4.     What is the procedure to calculate Brinell hardness?

The Brinell hardness test can be easily explained as an indentation hardness test, which consists of two basic steps:

Step one: Implement the known force through the known indenter perpendicular to the test material. Hold the known force for a specific duration (dwell time).

Step two: Measure the diameter of the resultant indentation in a minimum of two directions perpendicular to each other. Take the mean of these diameter measurements. The Brinell hardness value is then computed from this mean value using the mathematical formula designed exclusively for this purpose. Else, the value can be detected more frequently from a chart based on the given formula.

The Brinell hardness test is an optical method where the indentation size left by the indenter is measured. Contrary to the similar optical Vickers method, which involves a pyramid-shaped indenter being pressed into the specimen, the Brinell testing method uses a spherical indenter. The larger the indent left in the workpiece (specimen) surface by the Brinell indenter with a well-defined ball diameter and test force, the softer will be the test material. In order to calculate the Brinell hardness (HBW) according to the ISO 6506 standards, the hard spherical metal (tungsten carbide) indenter is pressed into a workpiece (specimen) with a well-defined test load (between 1 kgf to 3000 kgf).

The Brinell hardness (HBW) is determined from the quotient of the applied test force (F in newtons (N)) as well as the surface area of the residual indent upon the specimen (the indent projection) after removing the test force, as seen in the formula below. To determine the surface area of the residual spherical indentation, the arithmetic average (d) of the two perpendicular diagonals (d1 and d2 in mm) is used, since the base area of Brinell indents is not accurately round.

Usually, this formula is not calculated for every single test to determine the hardness value. On the other hand, the hardness value can be calculated from tables or specially programmed test software. It shows the hardness value for all standardized ball diameters along with the test loads as a function of the average indent diameter (d), as mentioned in the above table.

The test force must be selected such that the average indent diameter (d) is between 0.24 D and 0.6 D.

In order to adhere to these limits, the test force must be synchronized with the ball diameter, which results in varied force-diameter indexes otherwise called load factors or loading levels. Here, the quotient of the test force and square of the ball diameter is maintained as constant (B = 0.102*F/D2). There are five common force-diameter indexes including 1, 2.5, 5, 10, and 30. The testing of material with varied ball diameters as well as test forces must be performed within the same force-diameter index to achieve the comparable test results as mentioned in the above table.

The ball diameter should be chosen in such a way that the indent covers the widest possible workpiece area, which is considered as the representative for the specimen.

According to the ISO 6506 standards, the test load should be increased to its ultimate value within a minimum of two seconds to a maximum of eight seconds. Usually, the dwell time for the test load comes around 10 to 15 seconds. If the dwell time gets extended, the time duration in seconds should also be mentioned in the hardness value, e.g.: 210 HBW 5/250/30 (dwell time of 30 s).

5.     What are the typical Brinell Hardness numbers for metals?

6.     What are the steps to be completed before going ahead with the Brinell hardness testing process?

Before conducting the Brinell hardness test, it is mandatory to prepare the surface of the test material.

Surface preparation

Before placing the sample material in the Brinell hardness test unit, it should be either:

  Ground

  Machined

  Polished

  Lapped

Loads

• Sample thickness ASTM: At least 10 times the indentation depth
• Sample thickness ISO: At least 8 times the indentation depth
• Indentation time: 10-15 seconds

The outcome of the Brinell Hardness tester is widely used in the industries from accepting commercial shipments to varied quality control purposes. These outcomes correlate with other metallic characteristics including tensile strength, ductility, wear resistance, etc. Our Brinell hardness testers can withstand even the harshest environment, if required, with the help of an air filtration system to guard the interiors against dust.

7.     What are the most common Brinell hardness test methods available in the market?

There are many common Brinell hardness test methods, with an equivalent material as well as hardness ranges. Most of the test methods can be achieved on any Brinell hardness testing machine.

The Brinell methods are largely classified into four subgroups such as HB2.5, HB5, HB10, HB30 each suitable for a varied group of materials. Each subgroup has an identical force/diameter ratio (F/D2). The measured Brinell hardness can be compared only within individual subgroups.

* Materials mentioned in the tabulation are examples of typical materials only.

Explanation

• HBW 2.5/187.5: Brinell 2.5 mm tungsten carbide ball with 187.5 kgf load.
• HBW 5/750: Brinell 5.0 mm tungsten carbide ball with 750 kgf load.