Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Reexamination Certificate
2001-09-13
2004-06-08
Hong, William (Department: 3725)
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
C241S221000, C241S242000
Reexamination Certificate
active
06745961
ABSTRACT:
BACKGROUND OF THE INVENTION
Industrial-grade mixing devices are generally divided into classes based upon their ability to mix fluids. Mixing is the process of reducing the size of particles or inhomogeneous species within the fluid. One metric for the degree or thoroughness of mixing is the energy density per unit volume that the mixing device generates to disrupt the fluid particles. The classes are distinguished based on delivered energy densities. There are three classes of industrial mixers having sufficient energy density to consistently produce mixtures or emulsions with particle sizes in the range of 0 to 50 microns.
Homogenization valve systems are typically classified as high energy devices. Fluid to be processed is pumped under very high pressure through a narrow-gap valve into a lower pressure environment. The pressure gradients across the valve and the resulting turbulence and cavitation act to break-up any particles in the fluid. These valve systems are most commonly used in milk homogenization and can yield average particle sizes in the 0-1 micron range.
At the other end of the spectrum are high shear mixer systems, classified as low energy devices. These systems usually have paddles or fluid rotors that turn at high speed in a reservoir of fluid to be processed, which in many of the more common applications is a food product. These systems are usually used when average particle sizes of greater than 20 microns are acceptable in the processed fluid.
Between high shear mixer and homogenization valve systems, in terms of the mixing energy density delivered to the fluid, are colloid mills, which are classified as intermediate energy devices. The typical colloid mill configuration includes a conical or disk rotor that is separated from a complementary, liquid-cooled stator by a closely-controlled rotor-stator gap, which is commonly between 0.001-0.40 inches. As the rotor rotates at high rates, it pumps fluid between the outer surface of the rotor and the inner surface of the stator, and shear forces generated in the gap process the fluid. Many colloid mills with proper adjustment achieve average particle sizes of 1-25 microns in the processed fluid. These capabilities render colloid mills appropriate for a variety of applications including colloid and oil/water-based emulsion processing such as that required for cosmetics, mayonnaise, or silicone/silver amalgam formation, to roofing-tar mixing.
SUMMARY OF THE INVENTION
Existing colloid mills have suffered from a number of performance- and ease-of-use-related problems.
One such problem relates mechanical complexity and stability. In the past, colloid mills have had mill housings for the rotor/stator and separate electrical motors with direct drive, reduction gear-, or belt-drive systems connecting the motors to the mill rotors. Elaborate mechanical isolation is required because both the mill rotor and the electric motor have separate bearing systems. Furthermore, the mechanisms used to enable rotor-stator gap adjustment, worm gear arrangement in one commercial device, have been mechanically complex and potentially dynamic during operation primarily due to thermal expansion effects.
In the present invention, these problems are avoided by relying on a motor-driven shaft configuration. That is, the shaft that drives and connects to the rotor of the colloid mill extends to the electric motor stator of the electric motor. In this way, the mill rotor shaft is directly driven.
The benefits resulting from this configuration primarily concern simplicity. Complex gear or belt drive arrangements between a separate electric motor and the fluid processing components of the colloid mill are avoided. Moreover, the gap between the mill rotor and mill stator can be adjusted simply by axially translating the motor-driven shaft. The small movements, of typically less than a 0.1 inches, have no or negligible effect on the electromagnetic field generation in the electric motor. Moreover, in this configuration, only one set of thrust bearings are required, and these are located very close to the rotor, thus minimizing any thermal expansion effects on the mill rotor-stator gap.
In general, according to one aspect, the invention features a colloid mill comprising a mill stator, a mill rotor, an electric motor stator, and a motor-driven shaft. This motor-driven shaft functions as an electric motor rotor that operates in cooperation with the electric motor stator, but also extends from the electric motor stator to the mill rotor, providing a direct drive arrangement.
In specific embodiments, a gap adjustment system is provided that changes a gap between the mill stator and the mill rotor by axially translating the motor-driven shaft relative to the electric motor stator. Further, the electric motor driven shaft is axially supported to counteract forces generated between the mill stator and mill rotor by at least one thrust bearing, preferably an angular contact bearing set, that is located on the side of the electric motor stator proximal to the mill rotor. As a result, mere radial support bearings are needed on the distal side of the electric motor stator relative to the mill rotor.
Another problem that arises in existing colloid mill designs is related to the stability of the mill rotor-stator gap and specifically the system used to adjust the gap. One of the most common configurations utilizes a worm-gear arrangement. This system, however, is hard to calibrate and can jam or freeze in response to the forces generated between the mill rotor and stator.
This problem is solved in the present invention by providing a timing belt-based arrangement for adjusting the gap. Such a timing belt system provides for no backlash. As a result, a simple hand-operated knob or stepper motor arrangement can be used to control the gap.
Specifically, a thrust bearing is supported in a threaded sleeve that mates with the colloidal mill body. The timing belt engages the sleeve to rotate it relative to the body, thus adjusting the thrust bearings axially and thereby controlling the gap between the mill stator and mill rotor.
In general, according to another aspect, the invention features a gap adjustment system for a colloid mill. The system comprises at least one thrust bearing that supports a shaft carrying a mill rotor in proximity to a mill stator. A threaded sleeve in turn carries the thrust bearing, its threads mating with complimentary threads of a body of the colloid mill. A timing belt, which is supported by the colloid mill body, engages the threaded sleeve to enable rotation relative to the body to thereby translate the thrust bearings, yielding axial movement of the shaft. This changes the gap between the mill stator and mill rotor.
In specific embodiments, a knob is used to manually adjust the timing belt.
In other embodiments, an adjustment motor, such as a stepper motor is used to adjust the timing belt under microprocessor control.
Another problem that arises in existing mills concerns what happens when a customer requires a new colloid mill for a given manufacturing process to handle higher fluid processing rates. In the past, manufacturers have offered larger and smaller-sized colloid mills to meet customer demand. The problem, however, has been that typically when moving to colloid mills of a higher throughput the manufactures have simply offered larger versions of a geometrically similar mill rotor-stator configuration. Put another way, a colloid mill with a higher throughput had a rotor and stator that looked like the colloid mill with a lower throughput but were simply larger. This technique for modifying colloid mill rotor/mill stator configurations to handle higher fluid volumes yields different processing effects on those fluids. The larger colloid mills tended to process the fluid at different energy densities, typically higher than the smaller colloid mills. This was a problem to the customer since it required recalibration of the processing parameters of the fluid in order to maintain a consistent product.
The present invention uses t
APV North America Inc.
Hamilton Brook Smith & Reynolds P.C.
Hong William
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