The first and most obvious difference between the two technologies is the principal upon which they operate. The Immersion Mill utilizes a stationary basket with revolving pegs while the Turbomill employs a rotating basket with stationary pegs. Centrifugal force can create hydraulic packing in any basket type mill.

The spirally positioned rotating pegs within the Immersion Mill generate a pulsating involute discharge creating an exceptionally turbulent flow field within the basket. They direct the turbulence both axially and radially simulating the flow pattern of a high-speed disperser towards the bottom pegs at the bottom of the basket. Pressure from the top propeller, centrifugal force from the pegs acting on the bead field, and suction from the bottom propeller generate throughput. Open flow zone into the mill is unobstructed and equal to or larger than the open area of the discharge screens. This promotes throughput and is particularly effective in Counter-Peg mills.

The Turbomill has two basic designs. Both are inherently centrifugal. The older design uses a basket made entirely of screen material similar to the old open vertical sandmills, i.e. multiple perforations in an otherwise solid piece of metal. It draws the batch into the bottom and top of the basket and discharges thru the side. A stationary disc with rectangular blocks attached to its underside is centrally located within the basket and held in place by a support shaft connected to the upper portion of the machine. Rotating blocks are attached to the bottom screen and intermesh with the stationary blocks. The basket is attached to a rotating hollow shaft in which the stationary shaft is supported. A mechanical seal is provided in the area where the basket is attached to the rotating shaft.

The latest design of the Turbomill operates under the same principle but incorporates the following changes. The top of the basket is solid thereby permitting product entry only thru the bottom; the bottom input screen has been indented and shaped like a top hat with the discharge screen positioned circumferentially about the brim. The stationary disc has several perpendicular pegs screwed into it’s underside that locate within the “U” shaped trough created by the new screen design. Wedge wire screen replaces the perforated screen. The entry zone to the basket in both style machines is obstructed and substantially less in open area than the discharge zone.

Feature Immersion Mill Turbomill
High Viscosity Milling (100-400 poise) Yes No
Water Cooled Mill Head  Yes No
Hydraulic Packing  Light Heavy
Nano Grinding Capability Yes No
Mill Mounted Telescopic Stainless Steel Vapor Cover  Yes No
Explosion Proof Light Yes No
Counter-Peg Insert Yes No
Turbo-Charged Basket Yes No
Steel Shot Capability Yes Yes
Vertical Grid Side Screen (Prevents Bead Packing) Yes No
Variable Pitch Suction Control Yes No
Auto-Process Control Yes No
Maintenance Cart Yes No
Minimum Bead Size .25mm 1mm
Minimum Screen Slot Size .13mm .50mm
Mirror Polish On Mill For Easy Clean Yes No
Side & Bottom Discharge Flow Yes No
Submerged Mechanical Seal No Yes

Immersion Mill uses an easily accessible bushing not required to prevent contamination. Comparing model sizes on the Immersion Mill to the Turbomill can be deceptive because Netzsch claims somewhat higher product milling volumes/liters of beads. We know this can be troublesome and confusing to the customer because their expectations can fall short of reality when running difficult products. We have chosen, therefore to make our comparisons based upon bead volume in the basket.

A substantial portion of Turbomill power consumption is utilized in the mixing function generated by the fixed fins or paddles attached to the outside of the basket, hence the higher horsepower required on the two larger diameter models. There is also a substantial increase in power draw on the Immersion Mill when using the pumper blade. We have not, however, run out of horsepower. The Immersion Mill pumper is adjustable in pitch. The Turbomill is not.

Model Size Comparisons
Hockmeyer HP Bead Vol Netzsch HP Bead Vol
HM-1/4 2 .19 LTR MINI 2 .20 LTR
HM-2.5 10 2.5 LTR TM-10 10 2.6 LTR
HM-10 25 8.0 LTR TMC-50 50 9.6 LTR
HM-40 60 30 LTR TMC-150 150 26.5 LTR

Making a Premix with the Mill

Netzsch does not mention premixing with the Turbomill in their brochure. We know that while this is possible with most basket type mills, there is still merit to premixing on a disperser. This offers several benefits.

  1. Time to premix on a disperser is less than using a mill
  2. Smaller beads can be employed to yield a finer dispersion, faster.
  3. Possible contamination is minimized since the milling area is generally cleaner.

That being said, the Immersion Mill has proven itself capable of premixing and milling effectively. There is no reduction in overall time between the two techniques.

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