Mounting in metallography is the process of encapsulating a sampled material with a plastic shell to prepare the sample for other metallographic grinding and polishing steps. Put differently, mounting is carried out to protect coated or fragile materials during preparation for perfect edge retention.
Mounting is crucial if you need to protect layers and also helps you handle sharp, small, and irregularly-shaped samples safely and conveniently.
Cold mounting and hot mounting are two mounting techniques used for various tasks. Although both techniques offer various advantages, the quality required and the number of specimens determine the type of techniques to use.
Hot mounting is best used for large numbers of samples coming to the lab successively. It allows the resulting mounts to be of uniform shape and size, high quality, and require a short process time. Hot mounting takes place under pressure with a high temperature. A pressure of up to 50kN and a temperature of up to 200oC is applied during the sample embedding.
The two types of hot mounting processes are thermoplastic and thermosetting resin. The thermoplastic resin hardens during the chemical reaction without or with pressure, while thermo-setting resins cure at elevated temperatures under pressure.
For cold mounting, the resin is mixed with an accelerator or hardener to provide the melting compound. Then, the polarization process occurs to form the block. While it is possible for the process to give off heat, you can control the heat generation with a cool air blow setting or ice.
The three types of cold mounting processes available are Epoxy, Polyester, and Acrylic cold mounting.
- Epoxy cold mounting has a relatively long curing time but has the lowest shrinkage of all three. As a result, it is suitable for mounting all types of materials.
- Acrylic resins have negligible shrinkage and short curing time. The hardened acrylic is resistant to most chemicals and thermoplastic.
- Polyester has a relatively short curing time and is ideal for labs with low sample volume.