When and Why Do I Need Cooling for
Three Roll Mill Rollers?
A client who intends to use three roll mill for algae exfoliation visited our lab the other day, trying to process several kilos of algae harvested from the Norwegian sea. We seldom do such large samples. However, they explained that only a small amount of oil can be extracted and they need a significant amount to test the results. For such a novel application, we gladly agreed.
As the milling went along, the rollers, which are made from stainless steel, got warm and raised the concerns of our client. They want the rollers to stay below 40°C to prevent the algae material being oxidized. And we had to turn on the cooling system, which can maintain the roller temperature ±2-3°C around ambient temperature.
It is very common for rollers to get warm after a prolonged period of continuous running. The roller surface temperature increases as a result of heavy friction between the rollers brought by the high shearing force necessary for successful grinding. When the surface temperature exceeds 70°C, damage to the gear system might occur. Under such circumstances, active water cooling is recommended. If, in this customer’s case, a certain temperature is required to prevent deterioration of the material, water cooling is of utmost importance as well.
The mechanism behind water cooling is not a complicated one. As you can see in the illustration above, water is first pumped into the built-in water tank on the machine, usually with a submersible type pump (so that it can be placed in a larger water container for recycling). This cooling water goes in through the pink tunnel and flows into the blind hole inside the roller. The blind hole is designed with a slight slope so that water eventually flows back into the water tank. There is a water outlet through which warm water gets out of the tank. The water recycles in and out of the larger water container, such as a bucket, and does it job keeping the desired temperature. Be sure to adjust the water flow by controlling the pump to keep the liquid level constant in the water tank. The same system can be used to heat up the rollers if hot liquid is pumped into the rollers. Our cooling/heating system requires 1/4 inch pipes according to NPT (National Pipe Thread Tapered Thread) standard. The pipe's outer diameter should be 0.540 in.
Last but not least, although we call it water tank, water is not the most desired liquid for the job. We recommend the use of at least 50/50 coolant and water. Coolant with anti-corrosion additives, such as this one, includes a corrosion inhibitor that balances the negative acidic effects that can develop over time in antifreeze and water solutions. It also stabilizes the pH level which helps reduce rust and prevents electrolysis, mineral deposits and pre-existing scale build-up from forming resulting in potential core damage for long term protection.
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