Laboratory Two-roll Mill

The trough. A laboratory two-roll mill is used to hand-process plastics and the like. It looks like an old fashioned "wringer" from a washing machine mounted horizontally, but it isn't. The rolls counter-rotate, to be sure, but they do so at different rates to create a shearing action in the trough formed between them. In this case, one roll is turning 1.375 times faster than the other, because one drive sprocket has 16 teeth and the other has 22. Plastics are generally very poor at thermal conductivity, so this shearing action is very important to achieve a melt.

Temperature controller. The rolls are heated internally with electrical heat rods, and the mill is designed to have a safe operating range up to 500 degrees F. No external heater, or pump, or special thermal fluid is required, and there is nothing to leak.

The rolls themselves are made from half-inch walled 316 stainless steel. The thick walls give the rolls a great deal of thermal inertia, and facilitate maintaining the temperature accurately with the attached controller. Temperature is measured directly from the rolls with a radiant-energy sensor adjacent to blackened areas at the ends of the rolls.

Shearing plastics to melt them requires a lot of force. The rolls of our mill are driven at roughly one revolution every two seconds by a 7.5 Horsepower, single phase motor (240 volts) through a heavy-duty speed-reducing gearbox. No plastic has ever stalled this machine, or even slowed it perceptively. The weak link in this system is actually the drive chains, and you can see how massive they are.

The rolls are generously sized at six inches in diameter, and have a nineteen inch working length. There is an additional two inches on the end of each roll that is blackened for temperature monitoring.

Turnbuckle roll spacing adjustment The spacing between rolls is adjustable with two "turnbuckle" wheels at either end of the rolls.

Our two-roll mill is reversible, which facilitates cleaning, and may be stopped almost instantly with either of two "knee" bars mounted on either side of the mill.

It should be obvious from the pictures that this machine could be very dangerous in the wrong hands. The drive chains are exposed to enable them to be greased easily, and the mill rolls could easily pass a human hand through or worse — with terrible effect. For this reason, no sale will be made without a signed liability waiver. In other words, if you buy it and do something which gets you hurt with it, we are in no way responsible.

We have just reduced the asking price 25% for the two-roll mill shown here, and are now asking $14,250 plus $1/mile from Pensacola, Florida, for delivery (Continental US only, please).

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