Nowadays there are several competing processes for making grinding tools. In general, either batch furnaces without a special atmosphere or hot presses are used, a further distinction being made in hot presses between sintering presses with a direct flow of current and indirectly heated sintering presses. Currently the most widespread are batch furnaces: they are relatively cheap to purchase, building the mould for the tools is somewhat less complex and the principle has been in use a relatively long time - so manufacturers have very broad experience of this method. The mould is placed in a preheated furnace, the temperature being set approximately 50 to 100 deg C above the sintering temperature being aimed for. The mould is provided with a thermocouple and often also with a form of hood and a supply of protective gas. As soon as the desired sintering temperature is reached in the mould, it is removed from the furnace and immediately compressed to final thickness under a hydraulic press. As heating and compression follow one another, it is important to find precisely the right time for pressing - this is a fairly critical point with this method.
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