VOLLRATH-bead-mills type VMSM are used for wet grinding of suspensions and pigment pastes. They are well proven and widely used in the paint and coatings industries. The bead mill belongs to the family of agitator-mills and agitator-ball-mills. In the wet grinding of paints and varnishes, the classic ball mill has been completely replaced by the agitator-ball-mill, because it grinds and disperses continuously and more efficiently.
The working principle is that a shaft fitted with grinding discs, rotates within a fixed grinding chamber that has been charged with the chosen grinding beads. The mill-base is pumped through the grinding chamber and the disc rotation move the beads and mill-base mixture at high speed. The product is separated from the grinding beads at the outlet by a slotted screen.
VOLLRATH supplies vertical bead mills respectively agitator ball mills with a vertically arranged grinding chamber. Thus, the bead package is evenly distributed and the geodetic pressure between the beads is maximized. Bead pressure and shear rate are very high, which also applies to the achieved grinding performance and the color strength. Horizontal bead mills or agitator ball mills with a horizontal grinding chamber do not have these advantages and are thereby disadvantageously designed and built.
Because of VOLLRATH’s unique square shaped (with rounded corners) grinding chamber and special grinding discs, a very high turbulence and torque is transmitted between the discs, the mill base/beads mixture and the grinding chamber. This ensures a very high output and an excellent efficiency. The Vollrath bead mill is very easy to clean and product losses are low because the grinding chamber volume is small in relation to the grinding capacity.
Frequency converter operation / Control / Optimizing
The drives of both the grinding shaft and feed pump are fully controlled by frequency converters. Having full speed control of the grinding shaft and product pump allows:
- Optimal grinding conditions for any product can be achieved.
- Mill base dwell time within the grinding chamber and the amount of work respectively particle size reduction on the product is controlled by the selected shaft- and pump-speeds.
- Easy start-up of the mill using the high torque of the drive at the frequency converter (1.5-fold).
- A slow shaft speed selected when cleaning ensures minimal wear.
If one pass through a single grinding chamber is not sufficient to develop the product to the required specification, there are three options:
- a second or third pass through the grinding chamber.
- re-circulating grinding.
- using a double-chamber-bead mill.
Automation / Production data acquisition
Optionally all production parameters can be made available on an interface, including the input grinding work in kWh. By executing the control with PLC and the operating with touch screen, the recipes can be stored with all set point parameters. In the event of repetition, a recipe is called up and the corresponding parameters are set automatically. In many cases remote maintenance is also installed.
The mill base is pumped from its holding vessel, passed through the grinding chamber and then returned to the same vessel, whilst being stirred continually to keep it homogeneous at all times. This process is continued until the desired specification is achieved. The VOLLRATH single-chamber bead-mill type VMSM 1/..B is ideal for “Re-Circular grinding”. The optimally dimensioned slotted screen in a flow-favorable position ensures high volume flows. Due to the design of this screen, highly viscous and thixotropic products can also be grind without problems to “press the bead mill” (example: high solids, offset printing inks).
For large production runs where the required grind specification cannot be achieved in one pass or the output is low, the VOLLRATH double-chamber-bead-mill type VMSM 2/..B is the best option. This mill is with 2 grinding chambers piped in series. The first chamber can be filled with big beads for coarse grinding and the second chamber can be filled with smaller beads for very efficient fine grinding. For very difficult products 3 or 4 grinding chambers can be linked in series. With a grinding process over a double-chamber bead mill, almost all products can be grind ready – e.g. in the lacquer industry. So, ready-to-use grinding is simple and efficient with the VOLLRATH-double-chamber-bead-mill: From the large-scale disperser one pass through the double chamber bead mill into the tank for letdown.
Laboratory and doing test
Trials can be carried out in the VOLLRATH laboratory to establish optimum through-put rates and machine sizing etc.
Explosion protection (ATEX)
Explosion-proof bead-mills according to EC-Directive (ATEX) are standard at VOLLRATH.
Robust machine construction and excellent service
VOLLRATH bead-mills are of a robust construction ensuring many years service and the specific operating costs are low. Vollrath bead mills are continuously optimized. The grinding shaft is sealed with a high quality double mechanical seal. Wear parts and exchangeable mechanical seals are available from our extensive stores. An excellent service is guaranteed.