Description Pulverizer Mill Slewinq Ring Classifier Vane Adíustment Svstem Technical Field This invention relates to pulverizer mills, i. e. a pulverizer plant used for crushing coal or other minerals from a coarse aggregate state to a fine ground product (powder).

Background Art The pulverized product (powder) is transported from the mill by an air stream introduced beneath the grinding zone of the mill. The classifier forms an integral part of the pulverizer mill and performs the function of separating large particles from the product/air stream as it exits the mill.

The most common type of pulverizer mill is known as a "Vertical Spindle Mill"since its principle of operation relies upon the rotation of a horizontal table (i. e. bowl) mounted on a central vertical spindle within an enclosed casing. Raw material (i. e. coarse aggregate coal/mineral) is fed onto the table and crushed by rotating rollers or balls which are forced into contact with the table by an appropriate means of tensioning.

The mill is normally pressurized by air introduced beneath its rotating table. This air stream enters the grinding zone around the table periphery and so carries crushed particles upwards to the classifier situated within the top of the mill casing.

The classifier incorporates a ring of vanes suspended or supported vertically on individual spindles in the annular space between the mill casing and the classifier cone. The vane spindles protrude through glands or plain bushings at the top of the mill casing to provide a means of adjusting the vane position.

The vanes impart a swirling motion to the product- laden air stream as it enters the classifier. The centrifugal force thus exerted on the crushed particles results in the larger of these particles being thrown outwardly to the sloping wall of the classifier cone.

Accumulations of these larger particles then fall or slide down the inside of the classifier cone back into the mill's grinding zone for reprocessing, while the fine particles remain suspended in the air stream and are blown out from the mill through the exit opening.

The angular position of each vane (relative to a radial line drawn between the vane spindle and the vertical axis of the mill) determines the extent of classification and hence the quality (i. e. fineness) of the pulverized product.

The classifier vane setting in some installations is fixed and non-adjustable, while in other pulverizers adjustment is carried out by rotating the individual vane spindles one at a time by hand, in which case a pointer is fitted to each vane spindle to indicate vane position on an adjacent graduated scale mounted on the mill top. Each vane is locked in position when the required setting has been achieved.

There has not heretofore been provided a vane adjust- ment system having the features and advantages provided by the present invention.

Disclosure of Invention In accordance with the present invention there is provided a slewing ring classifier vane adjustment system which overcomes the disadvantages and limitations of the previous methods for adjusting the individual vane positions. In a preferred embodiment, the slewing ring classifier vane adjustment system comprises: (a) a plurality of vanes supported on vertical spindles; (b) a lever secured to each spindle for pivotably moving each spindle relative to its axis; (c) an annular ring attached to every said lever; and (d) means for angularly moving said ring in a manner such that each lever and associated vane is pivoted simultaneously.

The features and advantages of the adjustment system of the invention will be apparent from the following detailed description and the accompanying drawings.

Brief Description of Drainas The invention is described in more detail hereinafter with reference to the accompanying drawings, wherein like reference characters refer to the same parts throughout the several views and in which:

FIGURE 1 is a perspective view of a preferred embodiment of a slewing ring classifier vane adjustment system of the invention; FIGURE 2 is a top view of the system shown in Figure 1 ; FIGURE 3 is a cross-sectional view taken along line 3- 3 in Figure 2; and FIGURE 4 illustrates a pointer and scale for indicating the angular position of the vanes in the embodiment of the adjustment system shown in Figure 1.

Best Mode for Carrying Out the Invention In accordance with the invention, the slewing ring adjustment system 30 has been developed to enable simultaneous adjustment of the complete ring 20 of classifier vanes 14 on a mill classifier in one operation.

Steel bearing housings 10 with bronze (or other) bearings, normally packed with high temperature grease, are fitted at each vane spindle 11 penetration instead of conventional glands or seals. This simplifies operation and manufacture and results in a very easy-to-adjust system. Each housing 10 may be secured in position to the mill either by bolting or welding.

Each lever arm 12 is secured to the external end of an individual vane spindle, such that movement of the arm rotates the spindle 11 and so alters the angular position of a vane 14. The opposite ends 12A of these arms 12 are drilled and slotted to accept a low friction, typically bronze bearing bush which can both rotate about, and slide along, the center line of the arm 12.

The key component of the system is the slewing ring 20 which is used to connect together all the vane operating levers. This ring is usually fabricated from mild steel flat bar drilled radially to match the classifier vane spacing. The ring is positioned over the top of, and central to, the classifier casing 40. Bearing bushes are fitted in the lever arm slots and pivot bolts 16 are passed through them and the slewing ring drillings, thus connecting all the vane operating levers together.

Finally, a leadscrew mechanism 22 (mounted on the mill top and connected to the ring by a pivot lever 24) is normally used to apply rotational movement about the mill center line CL to the slewing ring 20. Movement of the slewing ring is thus transmitted to the classifier vane spindles which rotate simultaneously to adjust all the vanes 14 to the required position in one operation, although a manual operating mode is also possible. A chain 25 extending around pulley 27 on leadscrew 22 facilitates rotation of the leadscrew.

Another preferred embodiment of the system of the invention is illustrated in Figure 4. It comprises a single pointer 28 and a scale 29 which gives an indication of the vane position. The scale and pointer are supported on brackets welded to the mill casing 40.

There are many advantages of the slewing ring vane adjustment system of the invention, including: (a) The complete ring of classifier vanes can be adjusted simultaneously by one operation to give an accurate, reliable and uniform setting throughout-indicated by a single pointer on an associated scale.

(b) Due to constraints imposed by original mill design, spindles may need to be offset from the vane center lines, giving an imbalance at their bearings which results in wear and difficulty in conventional vane adjustment. The slewing ring and associated lever system of this invention can normally be installed such that it counter- balances the vanes and hence alleviates this problem.

(c) Friction is reduced and leakage of mill product- laden air at vane spindle casing penetrations is eliminated by use of bronze bearings packed with high temperature grease.

Though the system of the invention is"low friction" and requires minimal force to operate, the mechanical slewing ring actuator is rigid and robust and can apply vane movement in either direction by hand and/or with a handwheel or from floor level using a chain as illustrated in the drawings. The actuator could easily be converted for conventional servo-motor operation, if desired.

Other variants are possible without departing from the scope of this invention.