Frequently Asked Questions About Three Roll Mills

1. What is the run rate of your three roll mill?

Our redesigned and cutting edge 2.5x5 lab model can process 0.75-3.75 gallons or 6.0-30.0 lbs material per hour. The 6 x 12 model can process 1.8-8.8 gallons or 9.0-44.0 lbs per hour, and the 9x26 model can process 0.5-17.2 gallons or 14.0-68.8 lbs per hour.

2. Can we cool or heat up the rollers of a three roll mill?

Yes. The rollers are cored with holes to take cooling water or hot oil. Normally the cooling water (or antifreeze for cars) is pumped into the holes to cool the rollers during operation. The same mechanism can be used to heat up the rollers if hot liquid is pumped into the rollers. We had a customer who pumped hot oil into the rollers to heat the rollers up to 60C.

3. Is it okay to hook the machine directly to a regular tap for cooling the rollers?

Yes, you can hook the machine directly to a regular tap. Water goes in, water comes out, and the rollers are cooled effectively. However, in order to recycle and be conservative with water use, we recommend the use of a 5-gallon water tank and a household pump.

If the cooling water flows into the machine, it means that the cooling water flow is too strong. So the incoming water controlling valve should be closed a little bit, and meanwhile loose the water drainage screw, let the water inside gear box flow out and increase the size of water drainage hose.

4. What is the material of your ceramic rollers?

The rollers are made from cold iso-static pressed and fired 99.5% alumina, and ground to 5m concentricity and 0.5m surface finish.

5. To make ceramic pastes (alumina and titania), what kind of roller should I use? Also, the powders I will be working with are of nanometer scale (50-300nm), will this be a problem?

You will need the ceramic rollers since otherwise metallic contamination will occur. We have customers in dye solar cell research using our ceramic roller model to make TiO2 pastes for exactly the same reason.

Working with powders of nanometer scale will not create a problem. Yes, when the particle size gets to the nano range, the particles tend to agglomerate. Three roll mill is a machine designed especially to solve this problem, i.e., to deglomerate and disperse the particles into viscous materials.

6. We tested the three roll mill and found some leaking from the side, what caused the leaking and how to prevent the leaking?

Our three roll mill is very similar to that of others. One common issue we observed in some of our new customers when they use our machine the first time is leaking from the side.

There are normally two causes for leaking at the side. 

a. One is that the rollers are not parallel. The narrower side will have paste coming out. Please adjust accordingly.

b. The end plates do not fit on the rollers tightly. The rollers are machined to ~0.002-0.005mm tolerance concentricity. The end plate arcs are ground to about the same. However they will not exactly match. At the same time, when the roller gap changes, the gap between the roller and end plates will change too. When you set up, please use one hand to press the end plate against the roller and then gently tighten the screw to fix end plate position. Do not over tighten the end plate screw. After a few months’ use, the end plates will match roller very well.

7. Why is the transmission making noise?

If the gears make noise during operation, the gears could be misaligned. Since the distance between rollers are adjustable and thus the gears can also move. If the rollers are not rotating parallel to each other, it will cause the gear to misaligned and make noise. It should be corrected immediately to prevent any damages to the gears.

8. What might cause poor grinding?

I. The vehicle and pigment are not properly and thoroughly mixed.
II. If the paste is too thin.
III. If paste is leaking off both ends of rolls.
IV. If the rolls are set too far open

9. What to do if the motor is overload?

I. Check if the voltage on power line is low by testing it at full load.
II. Make sure the paste is mixed properly.
III. Make sure having enough lubrication which heats up bearings.
IV. Check if parts (Apron or guide blocks) are pressed too tightly against the rolls.

10. Why is there resistance when adjusting bearing blocks or freeze bearing block?

When the machine is used for an extended period of time, some material could leak into the sides of the rollers and spread into the bearing blocks. It will cause resistance when adjusting the rollers and in some case the rollers would freeze if the problem is not taken care of. Proper cleaning and lubrication will be needed and should be performed according to manufacturers’ suggestions.

11. I am planning to grind 200nm ceramic dust down to 5 microns or even smaller particles, can your three roll mill achieve this? What gap size should I set?

Yes, three roll mills are very efficient in breaking up agglomerates. With 200nm ceramic dust, you should easily see results under 5 microns. Some of our customers even reach sub-micron levels.

Gap size is usually set at 25 microns. Three roll mill relies on the tremendous shear force between the rollers to achieve the desired fineness and this gap size does not equal the final fineness that could be reached.

A feeler gauge is provided as an accessory to measure the gap size. Run the 25 micron feeler through the gap and you should feel some resistance. There are a total of 4 knobs, 2 for the feeding rollers and 2 for the discharge rollers. Turn the knobs slowly to micro-adjust the roller gap. One sixteenth of a turn usually changes the gap size by 2-3 microns. 

12. Is your three roll mill CE certified?

Yes, our three roll mills are CE certified.

13. What is the flow rate of your Lab Model cooling system?

The recommended flow rate for our lab model cooling system is 100 gallons per hour. The immersion pump we used that works really well with it was 130 gph.

14. Can the pressure of end plates and apron be adjusted?

The pressure of the end plates and apron can both be adjusted by turning the knob. The endplates should only be touching the roller with slight pressure during the milling process. The apron should only be touching the roller when taking the material out; And the pressure should be as low as possible while still able to scrape the material out.

15. How to clean three roll mill rollers?

We have a customer who uses our Three Roll Mill to make lipstick destined for Wal-Mart. They shared their preferred method to clean rollers using Mineral Spirits, or also known as White Spirits. They said this mild solvent is great for cleaning up oils and greases, so great for lipsticks. Also, this low volatility petroleum distillate is inexpensive, and safe.

16. What is the minimum gap setting between 2 rollers?

The minimum can be close to 0, however, given that rollers heat up over time if not cooled, we recommend 75/50 micron gap size. There should definitely be some gap so that material can flow through and shear force can work. In addition, besides material not being able to flow through, rollers should not touch, as they will damage each other.

17. How to measure gap distance between rollers?

There is no gauge that can give specific readouts of the gap distance, however, distance is easily set using a feeler gauge. Included with every order is a set of feeler gauges at no cost to the customer. Four hand wheels to adjust the rollers make it easy to use.

18. How to lubricate three roll mill?

The machine has sealing lubrication structure for the gears. It is required to add industry gear oil; the oil lever should reach half of the oil gauge. It can not add more than that to prevent the oil from spraying out. The bearing base has been added oil before shipping, it is unnecessary to put more oil in for the new machine first time operation. After running 120 hours, the oil can be injected by oil injection tool.

  • The lubrication oil must be added into transmission axle through lubricating nipple.
  • Lubrication oil should be added very often at those places, such as: every adjusting screw, high/low speed roller bearing base and base orbit, to prevent the gear teeth from choking.
  • One major maintenance shall be carried out after six month continuous operation. Dismantle all those moving part and clean it. Apply new oil and inspect the oil cycling situation. Correct the problem if it is found.

19. How do I check the fuse of a three roll mill?

The machine has a fuse box in the back of the machine. First, turn off and unplug your machine. Then take out the cartridge using a screwdriver. (Please see Figure 1.)

You will see two fuses - the one exposed is in use, and the other one in the cover is a spare. (Please see Figure 2.) Replace the fuse if it is blown. The 5mm x 20mm, 8A 250V, fast blow fuse should be available in a local electronic supply store or online. If not found, please contact THT for assistance.