GB2120126A

GB2120126A - Stirrer ball mill

Info

Publication number: GB2120126A
Application number: GB08224289A
Authority: GB
Inventors: Armin Geiger
Original assignee: Buehler AG
Current assignee: Buehler AG
Priority date: 1982-05-19
Filing date: 1982-08-24
Publication date: 1983-11-30
Also published as: JPS58207956A; CH655449B; JPH0337982B2; GB2120126B

Abstract

A stirrer ball mill with a cylindrical stator (17) and a rotor 20 journalled in overhung manner has a milled product inlet (13) from which a tube (15) extends axially outwardly through a piston (12) for changing the volume of the milling bodies. The tube projects outwardly through an opening in the fixed end closure wall (16) of the stator 17. A swan neck tube (26), which extends to somewhat above the height of the milling chamber (11) and to which the material to be milled can be supplied is attached to the outer end of the tube (15) (Fig. 1). <IMAGE>

Description

SPECIFICATION A stirrer ball mill The invention relates to a stirrer ball mill and has particular reference to a stirrer ball mill comprising a cylindrical stator and a rotor journalled in overhung manner at one end of the stator, with the stator and rotor being able to carry stirrer tools and defining between them a milling chamber.

A typical stirrer ball mill of this kind normally features a milled product outlet at said one end of the stator, a milled product inlet at the other end of the stator and an axially adjustable piston, by means of which the volume of milling bodies in the milling chamber between stator and rotor can be varied.

This piston is conveniently provided at the product inlet end of the stator and can extend over the full stator cross-section. In some arrangements the milled product inlet is provided at the surface of the piston facing the milling chamber.

In a known stirrer ball mill in which the product supply takes place at the base of the vertically arranged stator (German laying open print DE-OS 22 40 751) a tube extends through an opening in a piston to a position immediately below the rotor where it can be secured to the stator by means of radial spokes. The piston can slide up and down along the product supply tube under the action of a pressure fluid, whereby the volume of milling bodies in the milling chamber between the cylindrical surface of the stator and the rotor can be changed. A disadvantage of this known stirrer ball mill is the fact that a dead space is present beneath the opening of the tube in which the product to be milled and the milling balls collect and thus do not take part in the milling process. Furthermore, the end of the tube projecting into the milling chamber is subjected to considerable stresses.

The removal of lumps following an operating pause is difficult because of the high position of the tube opening. Separation of the milled product from the milling ball is effected by means of a separating slot at the inlet and this is disadvantageous.

A stirrer ball mill is also known (German Patent DE-PS 20 51 003) in which the base of the stator is followed by a cylinder of reduced diameter in which a vertically movable piston is arranged. The supply of product takes place above the opening of the cylinder in the milling chamber. Thus, in this known stirrer ball mill, a rotor space in which the milling balls generally remain immobile is also present at the base region of the milling vessel. The geometry of this nown mill assumes the milled product-milling ball mixture to be flowable with the result that a dried-on cake of milled product-milling balls is difficult to break up. The supply of fresh milled product, i.e. material to be milled, is not suitable for this purpose because the cylinder, as mentioned, forms a dead space.

A stirrer ball mill is also already known (Germany laying open print DE-OS 28 32 903) in which the displacement piston is combined with the inlet separating device.

This is done either by providing a radial gap between the piston and the container wall, or by constructing the piston itself as an axial sieve. These separating devices prevent the milling bodies leaving the stirrer ball mill so long as the radial gap or the openings of the axial sieve, are smaller than the milling bodies. However, this once again gives rise to a considerable danger of blockage in the vicinity of the radial gap or the through flow openings of the displacement piston.

It is indeed also already known (German laying open print DE-OS 23 60 920) to effect the separation of milled material and milling bodies at the inlet by a swan neck tube which branches off from a base opening of the vessel. The use of this separating method in stirrer ball mills in accordance with German laying open print DE-OS 28 32 903 would however not be practicable because it would lead to the milling bodies entering into the space beneath the displacement piston.

The object of the present invention is to provide a stirrer ball mill of the initially named kind in which the advantages of the milled product inlet at the surface of the displacement piston facing the milling chamber are maintained without blockage problems occurring on passage of the milled product through the piston, and without milling bodies being able to enter the space on the side of the piston remote from the milling chamber.

In order to satisfy this object there is provided in accordance with the present invention a stirrer ball mill comprising a cylindrical stator; a rotor journalled in overhung manner at one end of the stator, the stator and rotor being able to carry stirrer tools and defining between them a milling chamber; a milled product outlet at said end of the stator; a milled product inlet at the other end of the stator; and an axially adjustable piston, by means of which the volume of milling bodies in the milling chamber between stator and rotor can be varied, provided at this other end of the stator, with the piston extending over the full stator cross-section and with the milled product inlet being provided at the surface of the piston facing the milling chamber, characterised in that a first tube extends axially outwardly from the milled product inlet through the piston and projects outwardly through an opening in the solid closure wall of the stator; and in that a swan neck tube to which the milled product can be supplied is connected to the outer end of the first tube and extends to somewhat above the height of the milling chamber.

As a result of this construction the milled product always emerges at the surface of the piston facing the milling chamber, despite the avoidance of separating slots at the product inlet and without the danger of milling bodies entering into the space on the side of the piston remote from the milling chamber. Thus dead spaces in the inlet region of the milling vessel are avoided in the same way as problems due to the formation of material lumps after longer operating pauses, and without the danger of blockage during operation having to be accepted.

Advantageous further developments of the invention are set forth in the subclaims.

The invention will now be described in the following by way of example only and with reference to the drawings which show: Figure 1 a partially sectioned side view of a stirrer ball mill in accordance with the invention, the stirrer ball mill having a vertical axis of rotation, and Figure 2 a corresponding part view of a further embodiment with a horizontal axis of rotation.

A cylindrical rotor 20 which is journalled in overhung fashion at its upper end face in a rotary bearing 29 is concentrically arranged in a vertically upright, cylindrical stator 1 7. A drive pulley 31 which can be rotatably driven, for example by V-belts, is secured to the drive shaft 30.

The main milling chamber 11 is located between the stator 1 7 and the rotor 20 and is closed at its upper end by a sieve separating ring 32 with slots 33 through which the processed milled material can pass but not however the milling balls 34 located in the milling chamber 11.

An annular chamber 35 from which the product outlet 36 branches off is located above the sieve separating ring 32.

Stirrer tools 22 which project into the milling chamber 11 are secured to the cylindrical outer surface of the rotor 20.

Further stirrer tools 21 which are preferably axially displaced relative to the stirrer tools 22 of the rotor 20 extend from the cylindrical inner wall of the stator 17.

At its lower region the stator 1 7 is constructed as a cylinder 17' in which a vertically adjustable piston 1 2 with a vertical axis is sealingly arranged. The lower side of the piston 1 2 is flat whereas the upper surface 14 rises somewhat towards the sides. The cylinder 1 7 is preferably a separate component which is rigidly connected via flanges at 37 to the actual stator.

The lower end face 1 9 of the rotor is constructed as a shallow cone and carries stirrer tools 22'. Stirrer tools 21' are also preferably attached to the surface 14 of the piston 1 2 in the radially outer regions.

At the center the piston 1 2 has a product relet omening 1 3 which is preferably flush with the surface 14 which faces the rotor 20.

The opening 1 3 is located in a tube 1 5 which is fixedly attached in a corresponding bore 38 of the piston 1 2 and extends away from the rotor 20 along the axis 39 of the mill.

The tube 1 5 extends slidingly and sealingly through the base 1 6 of the cylinder 17 and opens at its outer end in a piston 24 which is located in a further cylinder 23 secured to the base 16. The piston 12, the tube 15 and the further auxiliary piston 24 form a constructional module. A swan neck tube 26 is attached at the lower end to the opening of the tube 1 5. The swan neck tube 26 has a Ushaped, upwardly curved region 26' outside of the cylinder 23, then extends vertically upwardly parallel to the axis 39 to the side of the stator 17, and is finally led away downwards via a further U-shaped downwardly curved region 26". A flexible hose 28 is secured to the end 26" ' of the swan neck tube 26.

An electrical piston stroke measuring device 27 is arranged between the vertical part 26" " of the swan neck tube 26 and the cylinder 17' secured to the stator. The space 1 8 beneath the piston 12, which is hermetically sealed against the environment, is filled with a hydraulic oil which is supplied by a supply container 40 in which hydraulic oil is present up to a specific level. The surface of the hydraulic oil can be subjected to air pressure via an air supply line 41, which can be selectively connected to the container 40 by means of a valve 42.

A guide 43 which is secured to the stator 1 7 and facilitates the vertical movement of the swan neck tube 26 is located in the upper region of the vertical part 26" " of the swan neck tube 26.

A further part of the milling chamber 11' is formed beneath the cone surface 1 9 of the rotor 20, as a result of the supply of product in accordance with the invention through the base opening 1 3 and as a result of the arrangement of the further stirrer tools 21' and 22'.

A pressure chamber 25, which can likewise be connected to a source of pressurised air via a line 44 and a valve 45, is located between the base 1 6 and the piston 24.

The manner of operation of the stirrer ball mill of the invention is as follows: When milling operation has finished the valve 45 is opened and the space 25 is pressurised. As a result the piston 1 2 which forms the actual base of the milling chamber 11, 11' is lowered. If necessary the vessel 40 can be ventilated via a further valve 46.

As soon as the piston 1 2 has reached its lowest position the volume of milling bodies in the part 11 of the milling chamber is minimal. This is advantageous for the renewed starting up of the mill.

The starting up of the mill takes place with the piston 1 2 in its lowest position which significantly facilitates the starting up procedure. After the mill has been started up the piston 12 is moved upwardly, by opening the valve 22 and, if required, by ventilating the pressure space 25. In so doing any cake of dried milling product-milling balls is broken up by the stirrer tools 22' and 21' in the base region of the stator 1 7. The piston 1 2 can be raised to a desired level by suitable control of the valve 42.

In permanent operation the mill can be compensated for loss of milling bodies by a continuous upward readjustment of the piston 12.

The instantaneous position of the piston 1 2 can easily be read from a scale 47 arranged on the swan neck tube 26, preferably in a region of the guide 43.

As the curve 26" of the swan neck tube 26 lies above the sieve separating ring 33 the milling balls 34 cannot return to the product hose 28. On the other hand granulate 48 which is supplied via the product hose 28 can also not straightforwardly enter the milling chamber 11, 11'. Thus an entry slot or a nonreturn valve is avoided by the arrangement of the swan neck 26.

Fig. 2 shows an embodiment with a horizontal axis of rotation and manual adjustment of the volume of milling bodies. The nonillustrated regions, in particular at the milled material outlet are constructed in the same way as in the embodiment of Fig. 1.

As seen in Fig. 2 a cylindrical rotor 120, which, in analogy to the first embodiment, is journalled in an overhung manner at its nonillustrated end, is concentrically arranged in the horizontally disposed cylindrical stator 117.

Stirrer tools 1 22 which project into the milling chamber 111 are secured to the cylindrical outer surface of the rotor 1 20. Further stirrer tools 121 which are preferably axially displaced relative to the stirrer tools 1 22 of the rotor extend from the cylindrical inner wall of the stator 117.

A cylinder 117' in which an axially displaceable piston 11 2 is sealingly arranged is secured to the stator 11 7 at the right hand end.

The piston 11 2 has a product inlet opening 11 3 at its center which is preferably flush with the surface 114 of the piston 11 2 facing the rotor 1 20. A tube 11 5 which extends away from the rotor 120, and the bore 151 of which communicates with the opening 113, is attached to the piston 11 2. The tube 11 5 is provided with an external thread 1 52 and emerges through the rear closure wall 11 6 of the cylinder 117', in which it is guided. The external thread 1 52 is a trapezoidal thread the outer surface of which is guided by the end closure wall 11 6.

A retaining sleeve 1 55 which serves to axially secure a threaded sleeve 156, the internal threads of which engage with the external threads 1 52 of the tube 11 5, is centrally secured to the end closure wall 116..

Hand grips 1 57 are secured to the threaded sleeve 1 56 and make it possible to rotate the threaded sleeve 1 56 in the retaining sleeve 1 55 and thus to axially displace the tube 11 5 together with the piston 11 2. Co-rotation of the piston 11 2 and the tube 11 5 is prevented by a pin 1 61, which is secured to the piston 11 2 parallel to the machine axis 11 9 and is axially displaceable in a guide bore 1 58 of the end closure wall.

The adjusted axial position of the piston 11 2 is secured by tightening a counter nut 162, having hand grips 163, on the external thread 1 52 against the threaded sleeve 156.

The swan neck tube 1 26 is again secured to the end of the tube 11 5 remote from the rotor 120 by a nut 165. The curved portion 126" lies above the milling chamber 111.

Claims

1. A stirrer ball mill comprising a cylindrical stator; a rotor journalled in overhung manner at one end of the stator, the stator and rotor being able to carry stirrer tools and defining between them a milling chamber; a milled product outlet at said end of the stator; a milled product inlet at the other end of the stator; and an axially adjustable piston, by means of which the volume of milling bodies in the milling chamber between stator and rotor can be varied, provided at this other end of the stator, with the piston extending over the full stator cross-section and with the milled product inlet being provided at the surface of the piston facing the milling chamber, characterised in that a first tube (15, 11 5) extends axially outwardly from the milled product inlet (13, 11 3) through the piston (12, 11 2) and projects outwardly through an opening in the solid closure wall (16, 116) of the stator (17);; and in that a swan neck tube (26, 1 26) to which the milled product can be supplied is connected to the outer end of the first tube (15, 115) and extends to somewhat above the height of the milling chamber (11, 111).

2. A stirrer ball mill in accordance with claim 1 and characterised in that the milled product inlet (13, 113) is provided at the centre of the surface (14, 114) of the piston (12, 11 2) which faces towards the milling chamber (11, 11'; 111).

3. A stirrer ball mill in accordance with claim 1 or claim 2 and characterised in that the first tube (15) is sealingly passed through an end closure wall (16) of the stator.

4. A stirrer ball mill in accordance with claim 3 and characterised in that a pressure fluid can be introduced into a chamber (18) formed between the piston (12) and the end closure wall (16).

5. A stirrer ball mill in accordance with one of the preceding claims and characterised in that stirrer tools (21', 22') are also arranged at the surface (14) of the piston (12) and/or at the lower end face (19) of the rotor (20).

6. A stirrer ball mill in accordance with one of the preceding claims wherein the stator is provided with an end closure wall and characterised in that a further cylinder (23) is arranged outside of the end closure wall (16) in fixed connection therewith, in that an auxiliary piston (24) connected with the tube (15) is slidably arranged in this further cylinder thus defining a pressure chamber (25) between said auxiliary piston (24) and said end closure wall (16), and in that a pressure fluid can be supplied to said pressure chamber (25).

7. A stirrer ball mill in accordance with one of the preceding claims and characterised in that a piston stroke measuring device (27) is attached to the swan neck tube.

8. A stirrer ball mill in accordance with one of the claims 1 to 5 and characterised in that the first tube (15) is axially adjustable by a manually actuatable mechanical adjustment mechanism (152, 155, 156, 162, 163).

9. A stirrer ball mill substantially as herein described and as illustrated in the accompanying drawings.