In the fast paced world of quality control in foundries, ensuring quality and getting quick results is vital. However, the process of verifying samples can often be a challenging and time consuming task. In this article, we explore easy solutions to produce a verification analysis in thirty seconds and maintain consistency across every sample.
The heart of Struers commitment to quality in the UK lies in a fully equipped laboratory situated in Rotherham at the Advanced Manufacturing Park. This state-of-the-art facility is open to individuals wishing to improve sample preparation results. Michael Bell, Struers applications specialist, can provide new techniques and insights to verification and hardness testing checks. The company provides a full solution to sample preparation in foundries that will improve both the quality and speed of quality control checks. The comprehensive range of equipment covers every aspect of the sample preparation process, from cutting to grinding, polishing, and, most importantly, verification and hardness testing. Remaining at the forefront in providing innovative solutions, the company consistently pushes the boundaries of what's possible. Whether customers are dealing with cast iron, aluminium, or any other material, Struers has the expertise, technology, and commitment to help achieve unparalleled consistency.
For the full methods of grinding and polishing cast iron or aluminium see the article published in the February/March 2024 issue of Foundry Trade Journal.
VERIFICATION
The materials used in practical applications today are a mixture of various chemical elements, often also referred to as ‘alloys’. Steel and cast iron, for example, are essentially alloys based on iron (Fe) with carbon (C) alloying additions, which are responsible for the hardness of the ferrous material. Microstructural analysis enables us to draw conclusions regarding the properties of the alloy, including its strength, hardness and ductility. The sample is ready for the final verification stage; this process should take no longer than thirty seconds. StructureExpert provides a full solution and is designed to be used in both the production and laboratory areas. It removes all the additional work to position and adjust samples on verification equipment. The automatic analysis removes subjectivity and errors that can be caused by manual analysis. To start the sample is simply placed face down on the equipment to verify the sample according to the required tolerances for:
- The size and number of grains per area.
- Form, distribution and size of graphite particles.
- Nodule size ferrite/pearlite content and proportion carbide.
- Phase for volume fraction and phase percent measurement.
The system operates on a modular basis, allowing companies to acquire only the specific options that align with their requirements. Often, samples can have uneven back/shapes, which can extend verification time using traditional methods; as the sample is placed facedown, the operator can see instant results. In just thirty seconds, users can efficiently verify a prepared sample with StructureExpert, utilising a magnified, crystal clear and high resolution digital image. This cutting-edge technology provides automatic illumination, focus and calibration to ensure maximum consistency of results. Reports can be effortlessly saved to the PC with a few clicks, and operators need minimal training, which is readily provided by the Struers team. The revolutionary feature of the automatic report generation eliminates the need for manual alterations, while results can be seamlessly transferred to Excel for easy storage. Unlike conventional manual verification technology, StructureExpert maintains a constant distance from the camera. This completely eradicates the need for time consuming, continuous height adjustments and calibrations, reducing operator time, while enhancing the image quality. The straightforward user interface and automated processes guarantee quick and consistent results, making a significant advancement in verification processes.
HARDNESS TESTING
Foundries tend to focus on two hardness test methods, Rockwell and Brinell. Rockwell is a fast method, usually less than ten seconds whilst Brinell is used for hardness testing larger samples in materials with a coarse or inhomogeneous grain structure. Rockwell is a fast, relatively low cost method for cast iron and can provide an instant image ready for analysis and no need for optical measurement. The Rockwell hardness is calculated by measuring the depth of an indent, after an indenter has been forced into the specimen material at a given load.
The indenter material is a conical diamond or sintered carbide ball, depending on the scale being used. Rockwell tests are not sensitive to surface preparation as other hardness testing methods are, as the depth of penetration is measured and no optical measure of the geometry of the indent is performed. It is important that a sample is clean and smooth for the hardness test to get good results. (For advice on grinding and polishing stages refer to the article published in the February/March 2024 issue of Foundry Trade Journal.) However, if the surface is too rough with scratches or dirt, it may cause a misreading of the indent size; a solution is to ensure samples are cleaned properly. When performing a Rockwell test a minor preload is applied before the main load is put on and unloaded. The readout of the hardness value is performed while the minor pre-load is still applied. The Rockwell hardness test utilises one of six different main loads of 15kgf, 30kgf, 45kgf, 60kgf, 100kgf, or 150kgf. This gives thirty different Rockwell scales. Each one is characterised by a different combination of indenter type and main load and is suitable for certain materials or applications. Depending on which standard adhered to, there can be ISO 15 or even ASTM 30 methods. Rockwell can be used for most materials. For more in-depth application guidance see www.struers.com/en/Knowledge/Hardness-testing.
There are two types of Rockwell tests: regular Rockwell and Superficial. Regular methods are where the minor load is 10kgf, the major load is 60, 100 or 150kgf and is classified by a letter system which uses the letters A to H and K. Superficial Rockwell is used for thinner specimens where the minor load is 3kgf and major loads are 15, 30 or 45kgf, the classification uses the letters N,T, W, X and Y – this gives combinations as for example: 15T, 30N and 45Y. Generally, the tested material should not be mounted in resin because the Rockwell test uses the motion of the indenter to measure the hardness and not the indentation area. There are many conversion tables for Rockwell which can often cause confusion, Struers can provide a free poster to Foundry Trade Journal readers simply complete the form found at: https://forms.office.com/e/RVk7MFWb1h.
Struers Duramin-160 provides immediate Rockwell results. High precision load cell technology means that Duramin-160 delivers even higher precision than required by standards. It is operated via an integrated touchscreen and can have a motorised Z-axis. The equipment is suitable for various sample sizes and shapes. Duramin-160 can be used for more advanced tests, for example the Jominy test. All Struers hardness testers can be supported by an experienced service team, ensuring the equipment is optimised. Brinell hardness testing is required for aluminium samples. The indentation gives a relatively large impression with a tungsten carbide ball. The size of the indent is read optically to determine the hardness. Typical applications are forgings and castings where the structural elements are large and inhomogeneous or structures too coarse for other methods to give a representative result. The Duramin-40 is popular with foundries as it delivers immediate Brinell results and reliability and can provide Vickers, Knoop test results. The whole test cycle can be fully automated, ensuring the same method is used every time. In the past year, MechTest made significant strides in operational efficiency by partnering with the Struers team, resulting in a remarkable 20-hour weekly reduction in labour hours. Specialising in materials engineering and failure analysis, MechTest sought to enhance throughput in hardness testing while elevating standards in quality, consistency, and documentation. Chris Branton, operations manager and co-owner of MechTest, said: “Our new Duramin-40 AC3 gives us fully automated hardness mapping.”
In an era where precision is paramount, Struers is an industry leader in providing cutting-edge technology and methodologies. With a global network of experts. For an on site demonstration of Struers preparation, verification or hardness testing methods, Tel: +44 845 604 6664, email: [email protected] or visit: www.struers.com