MOULD AND DIE INDUSTRY 142 / NORTON WINTER PRECISION TECHNOLOGY TOOL GRINDING APPLICATION NOTES FOR THE PREPARATION OF SPECIMENS FOR MICROSCOPIC EXAMINATIONS PRACTICAL EXECUTION Specimen preparation starts with mounting of the workpiece if applicable. Depending on the state of the specimen, it is rough-ground with silicon carbide abrasive paper or with Norton Winter diamond grinding wheels. The specimen is then polished with Norton Winter Diaplast® compound or Norton Winter Diaplast® suspension. SAMPLE MOUNTING In most cases. the standard mounting media are plastics, which are processed either hot or cold. It is important that the mounting medium should bond to the specimen without any gaps, otherwise abrasive or polishing agents may be deposited between the specimen and the mount. The hardness of the mounting medium should be matched to the hardness of the specimen in order to avoid edge rounding. GRINDING The surface state of the specimens before polishing is critical for the economic efficiency of polishing with Norton Winter Diaplast® and for the quality of the final polish. Proper rough grinding can greatly reduce polishing time, enabling economical application of Norton Winter Diaplast® and giving good surface quality. It is important to ensure that any unevenness caused by sawing is completely removed by the grinding operation. POLISHING Polishing with Norton Winter Diaplast® diamond compound or Norton Winter Diaplast® suspension can be effected on both manual and automatic polishing machines. A separate polishing disc with polishing cloth must be used for every diamond grit size. Norton Winter polishing cloths can be used on commercial standard machines. Before starting polishing, slightly moisten the polishing cloth and distribute the polishing agent evenly on the polishing cloth. There are some cases where Norton Winter diamond suspensions are easier to handle than diamond compounds, as diamond distribution on the polishing cloth is more even. Diamond suspensions are preferable for automated polishing operations as feeding during the process is possible. Norton Winter Diaplast® diamond compound is soon saturated with the swarf of the material being machined, so that a little Norton Winter Diaplastol thinner must be applied in order to maintain the cutting action of the diamond grit. A thin cooling and lubricating film must be maintained. The polishing pressure to be applied is dependent on the specimen material and the diamond grit size. As a rule, high polishing pressure can be used with hard materials, and lower pressure should be used for finer diamond grits. The selection of the grit sizes to be used depends mainly on the hardness of the specimens and their individual structural constituents. The greater the hardness of the material to be polished the coarser the grit to be used at the beginning. The finest grit sizes (D0.25 to D1) are generally not used with very hard materials. Remember that the polishing process not only removes the scratch marks of the last grinding operation, but it may be required to remove sufficient material from the specimen surface to expose an undamaged microstructure. This means it is often necessary to start with a larger diamond grit size than would be necessary for removal of the scratch marks from the last grinding operation. NOTE When polishing with Norton Winter Diaplast® it is important to avoid any transfer of coarser grit to the next finer polishing operation. It is essential not only to keep the polishing device clean, but also to clean the specimens between the individual polishing stages. This may be done under running water with the aid of a brush (for coarser grit sizes) or with a cotton pad (for finer grit sizes). It is also recommended to use an ultrasonic cleaning bath between each polishing step. MOULD AND DIE INDUSTRY POLISHING
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