It is important to set the correct pressure parameters for a successful mounting of metallographic samples. Proper pressure will ensure that the sample is held firmly, the mounting material is evenly distributed, and the final mount does not have bubbles or cracked surfaces. All of these factors affect the accuracy of a later metallographic examination. You can get consistent results by understanding how to adjust the parameters according to key factors.
Firstly, the sample material and its thickness as a guide to pressure setting. For soft materials such as aluminum or copper, lower pressure is required. This pressure ranges between 15 MPa to 30 MPa. A pressure that is too high can cause samples to be deformed, changing their microstructure and ruining the analysis. Higher pressure (30 MPa-60 MPa) for harder materials like steel or titanium is required. Harder samples are less likely deform and higher pressure will help the mounting material adhere tightly to the surface of the sample. The mounting material must be applied with slightly more pressure to thicker samples than to thin ones.
mounting materials play a major role. Thermosetting (like epoxy resins), often requires lower pressures, between 10 MPa and 25 MPa. These materials are cured by chemical reactions, and do not require high pressure to form. Thermoplastics (such as phenolics) require higher pressures (20 MPa-50 MPa), because they are softened when heated, and then hardened when cooled. This ensures that they conform closely to the samples and prevent shrinkage gaps. Check the manufacturer's instructions, as each brand may have different pressure recommendations.
The mounting machine model and the cavity size are also important. The mounting cavity size (e.g. 25mm) is best with lower pressure. Larger cavities (e.g. 50mm) require higher pressure in order to fill the space. Modern machines come with digital displays that make it simple to monitor and adjust pressure values. Start with a low pressure, and then gradually increase the pressure. Checking the mount after every trial will help you avoid over-pressurization.
Post-mount inspection can help you fine tune your settings. Check the sample after mounting for bubbles or loose edges. If bubbles are visible, slightly increase the pressure in the next run. If the sample has been deformed, reduce the pressure. Making notes about the settings for various sample-material combinations can be useful for future reference.
Setting pressure parameters on metallographic mounting machine requires that you balance the sample properties, mounting materials, and machine specifications. You can achieve high-quality mounts by following these guidelines, and then adjusting them based on the results of real-world testing.