GB2267241A - Rotor for blasting apparatus - Google Patents

Abstract

A rotor for throwing particles centrifugally therefrom at a workpiece for blast cleaning and surface treatment comprises a rotor body and vanes mounted on the body. The body has outwardly directed grooves 12 each with under-cut edges 13 for receiving a vane and each vane has a root with correspondingly shaped edges adapted to engage in the undercut edges of the grooves to hold each vane in its groove. The bases 16 of the under-cut edges of the grooves are rounded with a substantial radius. This radius reduces wear at the bases of the under-cut edges. <IMAGE>

Description

ROTORS FOR THROWING PARTICLES CENTRIFUGALLY THEREFROM The invention relates to rotors for throwing particles centrifugally therefrom.

Such rotors are used for blast cleaning and surface treatment of work pieces. The particles, generally referred to as shot, are fed to a central region of such a rotor and are hurled out at high speed by centrifugal action. Eight such rotors may be arranged at fixed positions in a cabinet. A work piece is introduced into the cabinet with the rotors stationary and the supply of shot cut off. When the rotors are set in motion and shot is supplied, the shot impinges on the surface of the work piece. The shot blasting is intended for cleaning and similar surface treatment of work pieces. The shot is of necessity abrasive and it tends to abrade the vanes of the rotor. For this reason the vanes are made readily replaceable by mounting roots of the vanes in outwardly directed grooves in a rotor body.The grooves may have under-cut edges to provide a dove-tail arrangement and the roots of the vanes may be shaped correspondingly to engage them in the grooves.

Despite the use of a surface hardened rotor body, there is a tendency for the body to wear under the influence of the shot so that eventually it becomes necessary to replace the whole body and not just worn vanes. One particular region of wear is at the corners of the undercut edges of the grooves.

Rotors of this kind are known from UK patent specification 1,489,225 and this particular design of rotor has been used successfully for many years despite the tendency to wear of the rotor body as well as of the vanes and the consequential need to replace the rotor body.

An objective of the present invention is to provide a rotor for throwing particles centrifugally therefrom which has less tendency to wear under the influence of particles than the known rotor.

According to the present invention a rotor for throwing particles centrifugally therefrom comprises a rotor body and vanes mounted on the body; the body having outwardly directed grooves each having under-cut edges for receiving a vane and each vane having a root with correspondingly shaped edges adapted to engage in the under-cut edges of the grooves to hold the vane therein; the bases of the under-cut edges of the grooves having a substantial radius.

It is believed that the known rotor with a sharply angled under-cut is such that individual particles become wedged in a corner of the groove and that other particles then impinge on such a wedged particle and cause it to wear away part of the rotor surface. The under-cut tends to deepen in the conventional arrangement allowing more build up of particles and even greater wear. Eventually the rotor develops a substantial weakness or becomes incapable of reliably holding a vane by its root.

By providing a substantial radius at the under-cut edge, the tendency for particles to wedge is eliminated or diminished and the wear rate of the rotor is reduced dramatically. A radius of about 3 mm has been found to be particularly suitable. A smaller radius of 2 mm or even as low as 1 mm may be satisfactory in some circumstances, depending on other factors such as the size and shape of the particles, speeds employed and the material and surface treatment of the rotor. More recent tests have found that even larger diameters produce significant further improvements in wear rate. A radius of at least 3 mm and ideally between 10 mm and 20 mm is now preferred.

A conventionally shaped vane root would not fit in a groove in accordance with the invention due to interference of its sharp dove-tail edge with the additional material provided by the rounded edge of the groove. For this reason, part of the edge of each vane has to be removed as compared with the conventional vane design. A rounded edge of slightly larger radius than that of the groove has been found to be particularly beneficial because it simplifies insertion and removal of vanes by reducing a tendency for them to jam in the grooves.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view of part of a rotor in accordance with the invention; and Figure 2 is a cross section through part of the rotor and a vane fixed in the rotor.

The embodiment to be described corresponds generally to that described in GB 1,489,225. Thus it is not necessary to describe the complete rotor in detail. Those parts which are not described correspond to the aforesaid GB 1,489,225.

A rotor body 11 is generally in the form of a circular plate which in practice is mounted on a hub on a shaft for rotation about its own axis. The rotor body incorporates a series of outwardly directed grooves 12 which are set at an angle to a radial direction as explained in GB 1,489,225. Each groove is of dove-tail shape in that it has a generally flat base and under-cut edges 13. Figure 2 shows that a groove 12 carries a vane 14 which has a root 15 mounted in the groove 12. The root 15 has a dove-tail shape corresponding generally to that of the groove so as to be located in the groove.

The vanes are locked or wedged in the grooves as disclosed in GB 1,489,225.

The under-cut edges 13 of grooves 12 have a substantial radius at their junction with the base of the groove as shown at 16. In this example, a radius of 3 mm is chosen. As shown in Figure 2, the corresponding corners of the roots of the vanes 14 are similarly curved but to a slightly larger radius to provide a clearance. The rounded corners of the grooves do not make contact with the corresponding radius of the roots 15 of the vanes.

Location of the vanes in the grooves is provided by engagement of the flat portions of the dove-tail edges in conjunction with the wedging action between rotor body and vane.

The rotor body should be manufactured from a steel capable of surface hardening and should be hardened, for example to a depth of about 1.5 mm.

The vanes should be of cast iron which provides good wear resistance and in general the vanes can be used in the as cast condition.

In use, the complete rotor is rotated at high speed in a cabinet and particles such as shot to be projected at a work piece are fed in to the centre of the rotor. The particles impinge on and are flung out by the rotors at high speed. The particles impinge directly or after deflection from the surface of the cabinet on to a work piece within the cabinet and provide an abrasive action on the surface of the work piece. The action of the particles on the work piece may be to clean it or to improve the surface of the work piece in some other way.

The rotor is subjected to a high degree of abrasion which results in wear. The vanes themselves have a limited finite life due to wear and have to be replaced at regular intervals. It is for this reason that they are mounted detachably on the rotor body. The rotor body is also subject to some wear and tends to require replacement but less frequently than the vanes. One region where severe wear has taken place in the past with the rotors of GB 1,489,225 is at the lower corners of the edges of the dove-tail grooves. It is believed that this wear has come about by wedging of abrasive particles in these bottom corners, particularly in parts of the groove which are still exposed when a vane is positioned in the groove. The associated wear of this part of the rotor body is believed to be caused by impact of further particles on particles which are already wedged in position.The simple expedient of applying a substantial radius in place of a sharp corner at the base of the edges of the grooves has proved successful in alleviating wear and substantially improving the life of a rotor.

This can have significant commercial advantages by resulting in reduced down time of the equipment as well as reducing costs for replacement of the rotor body.

Although significant improvements over the prior art have been achieved with a radius of 3 mm and an even smaller radius might give useful results, later tests suggest that a still larger radius gives better improvements in wear rate. 15 mm is a particularly suitable radius and the preferred range is 10 to 20 mm.

With the arrangement of GB 1,489,225, there is a tendency for vanes to become jammed inadvertently in their grooves during removal and installation. A further advantage of the rounded corners is that they tend to reduce this inadvertent jamming of the vanes.

Claims (8)

1. A rotor for throwing particles centrifugally therefrom comprising a rotor body and vanes mounted on the body; the body having outwardly directed grooves each having under-cut edges for receiving a vane and each vane having a root with correspondingly shaped edges adapted to engage in the under-cut edges of the grooves to hold the vanes therein; the bases of the under-cut edges of the grooves having a substantial radius.

2. A rotor as claimed in Claim 1 wherein said radius is at least 1 mm.

3. A rotor as claimed in Claim 1 or Claim 2 wherein said radius is at least 3 mm.

4. A rotor as claimed in Claim 3 wherein said radius is between 10 mm and 20 mm.

5. A rotor as claimed in Claim 1 wherein the radius is sufficiently large to avoid wedging of particles thrown by the rotor in the base of the under-cut edge of a groove.

6. A rotor as claimed in any of the preceding claims wherein the roots of the vanes have radiuses to correspond to the radiuses in the grooves.

7. A vane for use in a rotor as claimed in Claim 6 having a root with rounded lower edges.

8. A rotor for throwing particles centrifugally therefrom substantially as described with reference to and as illustrated by the accompanying drawings.