Milling, Mixing or Dispersing Apparatus

This invention relates to apparatus for milling, grinding, mixing, dispersing, emulsifying, homogenising and similar functions hereinafter referred to as milling apparatus of the kind specified. Apparatus of the kind specified comprises a milling chamber for containing particulate material such as granules or beads hereinafter termed the milling or grinding charge and agitating means for submitting this charge and material to be milled or otherwise treated within the chamber to intense agitating and shearing forces. These means typically comprise rotating impellers such as vanes, discs and paddles. In use the material to be milled is caused to flow through the milling chamber and to be submitted to the intense agitation and shearing forces in admixture with the particulate material. Such apparatus are conventionally referred to as "sand mills" or "agitated bead mills" depending on the nature of the particulate material and or the manufactures preference.

In existing apparatus of the kind specified it has been found necessary to predisperse the particles to be milled in a carrier fluid thereby providing a reasonably homogenous slurry which is a satisfactory input to the milling chamber. Additionally the slurry has to be pumped into the chamber. Thus at the present time a predisperser or homogeniser has to be provided together with a feed pump and this greatly increases the overall cost of the apparatus.

According to the present invention, apparatus of the kind specified includes the feed pump which also serves to predisperse the particles in the slurry to be milled immediately prior to the entry of the of the fluid to the milling chamber.

According to the present invention there is provided milling apparatus of the kind specified comprising a milling chamber for containing a charge of particulate material and agitating means for submitting the particulate material and the material to be milled to agitating and shearing forces characterised by at least one predispersing chamber and a feed pump associated with the agitating means such feed pump subjecting the material to be milled to centrifugal forces driving the product radially against the walls of the chamber thereby predispersing the material before the main milling operation and feeding the predispersed material into the main milling chamber.

The main shaft carrying the agitating means preferably also carries the predispersing and pumping members. In a preferred embodiment the input to the apparatus is through the wall of a first predispersing chamber. A rotating screw threaded member in the first chamber pumps and predisperses the material through to a second chamber carrying a pumping ring with an aperture to allow passage of material into the main milling chamber.

A specific embodiment of the invention will now be described by way of example and with reference to the accompanying drawing which is a longitudinal section.

The milling apparatus in accordance with the particular embodiment comprises a generally cylindrical body 1 with end member 1A defining a milling chamber 2. An agitator 3 is mounted as a shaft to rotate in the milling chamber 2 between a bearing 4 in the front end wall of the body 1 and the drive shaft 5 of an air motor 6. The air motor 6 is threadably received in a socket 7 in the rear end part of the body 1. The agitator shaft 3 is a slidable fit onto the air motor shaft 5 and is fixed thereto by a drive pin 8.

An inlet port 9 for the grinding charge of beads (not shown) is provided in the upper wall of body 1 and a corresponding outlet port 10 is provided in the lower wall, the ports 9 and 10 being closed by plugs 11 and 12. Inlets and outlets 13 and 14 respectively for cooling liquid are formed in the upper and lower walls respectively of the body and are interconnected by a circumferential cooling passage 21. The shaft 3 being closely adjacent the wall of the chamber 2 at 15 no specific means for preventing the axial exit of beads are required. Lip seal 16 behind front bearing 4 serves to retain material being milled which exits through threaded hole 17.

Agitating vanes 18 extend a short distance radially outwardly from the main shaft portion of agitator 3. This short radial excursion is sufficient to provide the milling forces required but does not define channels so deep as to provide "dead" zones wherein satisfactory milling does not take place. A funnel shaped inlet member 19 for product to be milled is provided in the upper part of the body wall and the lower end part of this communicates with an input chamber 20 in which the product is predispersed. A screw thread 22 extends along this chamber and is handed to drive product in the direction of the arrow "a" towards the milling chamber 2. The front end of the predispersing chamber opens into an annular space 23 defined by a shoulder 24 in the housing wall and a recess 29 in the rear part of the agitator 3. A pumping ring 25 provided with a plurality, for example six, radial holes 26 is a shrink fit on a step 30 on agitator 3 within annular space 23. The radially outer ends of holes 26 terminate a short distance from shoulder 24 leaving a narrow gap 31. A lip seal 27 closes the rear of predispersing chamber 20.

A doubly cranked product discharge pipe 28 is pivotally engaged into hole 17. Milled product can alternatively be recycled back to the product inlet 19 or drawn off.

In use of the device the bead charge is inserted through port 9 and cooling liquid circulated. The product to be milled is poured into inlet member 19 and enters predispersing chamber 20. The screw 22 carries out work on the product with the development of some centrifugal force which throws the product against the chamber walls. This work predisperses the particles in the product. The product then enters space 23 and is thrown radially outwardly through holes 26 in ring 25 into narrow space 31 and against the shoulder 24. More predispersing work is thus carried out and the annular space 23 can thus be regarded as a second predispersing chamber. The product then enters the main milling chamber 2 is milled and leaves through pipes 17 and 28 for discharge or recirculation.

In an alternative apparatus the main shaft 3 forms an extension of an electric motor shaft. This is in accordance with the teachings of our copending Patent Application No. 41436/77.