Consumables for Gridding and Polishing – Hitech Europe
Purpose of this step is to guarantee the best planarity of the sample, removing almost all the structural alterations of the surface caused by the previous operations (cutting).
This is achieved by passing the sample on abrasive papers with decreasing grain size, placed on the working wheel of the polishing machine. During this operation, the papers have to be continuously wet, in order to avoid the heating of the sample and to maintain clean the papers of any residue of the sample and the grains of abrasive. Also the sample has to be cleaned when you switch from one paper to another, to remove grains of abrasive of the previous passage, because they could alterate the next paper. The passage of the sample from one paper to another, with a finer grain, must allow the complete removal of
machining marks of the previous abrasive paper.
The grinding is possible using an automatic or manual polishing machine.
In the manual grinding, when the operator uses a machine with only working wheels rotation, is suggested to check the sample surface, between one paper passage to the other, to be sure that there are no scratches due to the previous step.
In case of automatic grinding, it is possible to set the working wheel speed, where the abrasive paper is placed , the pressure applied on the sample (not too much in order to avoid the creation of new signs on the surface) and the time of the cycle. With the most technologically advanced polishers other parameters can to be set, which customize the grinding process according to the operator’s needs, as the direction of rotation of the wheels (clockwise/counterclockwise), the head rotation speed.
Purpose of the operation is to remove the alterations produced on the sample in the previous phases, to obtain a mirror surface, necessary for the observation with an optical microscope. The mechanical polishing consists in lightly pressing the sample surface on a rotating wheel where there is the cloth soaked in abrasive particles in suspension in a liquid or paste, mixed with extender. Generally are used, in descending order, three different grain sizes of diamond (6, 3, 1 μ), in liquid suspension or in paste, combined with cloths with different surfaces and tissues. The diamond allows a fast material removal and guarantees the maintenance of its planarity. Thanks to its hardness, the diamond offers excellent results, unreachable from any other type of abrasive
Also in this step it is essential the intermediate cleaning of the sample, in order to avoid contaminations, and it is suggested, always for the same reason, to appropriately store the cloth. In the polishing step are used, also, suitable thinners for each type of diamond abrasive, useful to facilitate the transition of the sample on the cloth, avoiding possible frictions.
Once polishing is ultimated, the sample should be washed carefully with running water, and degreased with ethyl alcohol, then quickly dried with a jet of hot air.
As for the grinding step, for the polishing of samples it is possible to use either automatic or manual polishing machines.