GB2372721A - Throwing wheel - Google Patents

Abstract

A back plate for a throwing wheel has a plurality of back plate sectors (10 figure 4) mounted on a core 2, the core 2 is releasably mountable on the drive shaft of an abrasion machine. The back plate sectors (10) extend generally radially from the axis of the drive shaft and each terminate in an arcuate band (12, figure 2). Together, the sectors form a generally continuous circumferential band which encircles the core 2. The use of a plurality of sectors allows the arcuate bands 12 only to be case hardened to resist abrasion in operation. This allows the mass of the assembled throwing wheel to be reduced and also reduces the distortion caused by case hardening of the whole wheel as carried out in the prior art.

Description

THROWING WHEEL

This invention relates to a throwing wheel and a backplate for a throwing wheel.

Throwing wheels are used in connection with abrasion machines to propel particulate abrasive material onto a surface or surfaces. Although the term"abrasive"is used, the abrasive material may in some instances have an effect other than a primarily abrasive effect, for example, a cleaning effect. Such machines may be static, in which case an article to be treated is placed in an enclosure into which material is propelled or mobile, for example, as shown and described in GB-A-1575477, GB-A-1575478 and GB-A1542495.

The throwing wheels to which the invention relates are mounted to a machine and are driven for rotation by a drive motor of the machine. The wheels have blades which act to propel the particulate abrasive material.

Known throwing wheels include wheels with parallel spaced front and back plates, between which individually de-mountable blades are secured; see, for example, GB-A1328417 and US-A-3785105. One-piece cast wheels having a single back plate are also known; see, for example, GB-A-2150471.

The throwing wheels of the prior art are typically manufactured from steel castings which are then case hardened. The hardening is used because the throwing wheels are themselves abraded by the particulate abrasive material in operation. However, the case hardening (carried out in the conventional manner; using heating and quenching techniques) causes distortion of the castings which then require precision machining in order to restore balance to the wheel. Thus typically a throwing wheel is cast, machined, hardened and then re-machined. This means that the wheel is a relatively expensive component of an abrasion machine.

Furthermore, since the wheel is cast either as a complete steel casting or as separate component steel castings, the finished wheel has a high mass. Thus large motors and high currents are required to accelerate the wheel to its operating rotational speed.

This means that abrasion machines are relatively expensive to run.

According to a first aspect of the invention there is provided a backplate for a throwing wheel comprising a plurality of backplate sectors mounted on a core, the core being adapted for releasable mounting on a drive means of an abrasion machine for rotation about an axis, and the backplate sectors extending generally radially from the axis and each terminating in an arcuate band which together form a generally continuous circumferential band which encircles the core.

In this arrangement, only the backplate sectors need be made from abrasion resistant material (such as case hardened steel). The circumferential band protects the core from abrasive materials. Thus the core may, for example, be made from a mild steel casting (which since it is not hardened does not need re-machining after the hardening process) or even a plastics material such as nylon (for example that marketed under the name"Nylotron"). In this way, not only may the machining requirements be reduced but also the mass of the wheel may be reduced thereby providing reductions both in the cost of manufacture and operating costs.

In accordance with a second aspect, the invention provides a throwing wheel for an abrasion machine comprising a backplate having a plurality of backplatte sectors mounted on a backplate core, the backplate core being adapted for releasable mounting on a drive means of the abrasion machine for rotation about an axis, and the backplate sectors extending generally radially from the axis and each terminating in an arcuate band which together form a generally continuous circumferential band which encircles the backplate core, the throwing wheel further comprising a frontplate spaced apart from and generally parallel with the backplate, the frontplate including a plurality of frontplate sectors mounted on a frontplate core, and the frontplate sectors extending generally radially from the axis and each terminating in an arcuate band which together form a generally continuous circumferential band which encircles the frontplate core, the throwing wheel further including a plurality of throwing blades extending generally radially and extending between the inner surfaces of the frontplate and backplate respectively.

The invention will now be described by way of example with reference to the drawings in which:

Figure 1 is a plan view of a throwing wheel in accordance with the invention ; Figure 2 is a sectional view along line 11-11 of Figure 1 ; Figure 3 is a plan view of a backplate sector in accordance with the invention; Figure 4 is a sectional view along line IV-IV of Figure 3; Figure 5 is a perspective wire diagram showing a backplate sector; Figure 6 is a second perspective wire diagram of a backplate sector; and Figure 7 is a perspective view of a backplate sector.

With reference to Figure 1, a throwing wheel backplate has a core 2 which is a generally planar disc and which (in this embodiment) incorporates a hub 4 which is adapted for releasable mounting on the drive shaft of an abrasion machine. In an alternative embodiment, the hub 4 may be fixed to the core 2 using fastenings such as bolts.

The core 2 has a plurality of pairs of apertures 6; each pair being arranged to extend radially from the centre of the hub 4. Other numbers and arrangements of apertures may instead be used. Also, other locating arrangements may be used which do not require apertures.

With reference also to Figures 3 and 4, the apertures 6 are positioned and dimensioned to receive locating fingers 8 formed on the underside of a plurality of backplate sectors 10.

Each backplate sector 10 has an arcuate band 12 formed at its periphery. When a plurality of the sectors 10 (in this embodiment seven sectors) are mounted on the core 2, the arcuate band 12 forms a continuous circumferential band around the core 2.

Each sector 10 is typically made from an abrasion resistant material such as case hardened steel. Thus the band 12 forms an abrasion resistant shield around the core

2. This allows the core 2 to be made from lightweight and/or relatively soft materials such as plastics or mild steel. The essential requirement of the core 2 is that it be sufficiently rigid in use, to locate the sectors 10.

With particular reference to Figure 3, each sector has a recess 14 formed at its edge.

As will be seen from inspection of Figure 1, when the sectors 10 are abutted, the recesses 14 of adjacent sectors form slots 16 into which throwing blades (not shown) may be inserted. The core 2 forms a base for the slot.

It will be noted that in the prior art such slots are typically machined from a solid billet of steel. Thus in the prior art, since the slots are difficult if not impossible to cast, the entire slot must be machined from the solid billet. However, in the invention, the sectors 10 may be cast and little or no post-machining is required. This is because the castings are relatively easy to make and also heat treatment of such components (if required) does not introduce significant distortion relative to heat treatment of a core and wheel formed from a solid single casting. Furthermore, since the band 12 is relatively thin, the hardening effect occurs through most if not all of the thickness of the material which assists in lengthening the operating life of the wheel.

With reference to Figures 5 and 6, it will be seen that the sectors 10 may themselves have hollow areas 18 and 20 which assist in reducing the weight of the assembled wheel.

In an alternative embodiment, a throwing wheel may be assembled using two of the backplates of the present invention spaced apart and axially aligned, with blades positioned between the confronting surfaces of the two places. In this arrangement, both the plates may be of the construction outlined above. In this way, the wheel may be reversibly mounted on a drive shaft of an abrasion machine in the manner described in our own patent publication GB-A-2285938. Alternatively, one of the plates may omit the portion of the hub 4 marked A in Figure 2. This further reduces weight.

Additionally, the throwing blades (not shown) may be hollow castings which further saves weight.

Thus in summary, the present invention provides the potential for a throwing wheel which is easy to manufacture since it uses simple castings, which does not require so many machining steps (because the castings are smaller and easier to case harden and also because many of the parts do not require to be hardened). Furthermore, the assembled wheel is lighter than the prior art wheels which provides operational savings.

Claims (13)

Claims

1. A backplate for a throwing wheel comprising a plurality of backplate sectors mounted on a core, the core being adapted for releasable mounting on a drive means of an abrasion machine for rotation about an axis, and the backplate sectors extending generally radially from the axis and each terminating in an arcuate band which together form a generally continuous circumferential band which encircles the core.

2. A backplate according to claim 1, wherein each backplate sector includes blade attachment means for releasably holding a throwing blade.

3. A backplate according to claim 2, wherein the adjacent edges of each backplate sector cooperate to form a generally radially extending slot which is arranged to engage the foot of an upstanding throwing blade.

4. A backplate according to any preceding claim, wherein the core has apertures or recess adapted to receive a respective, axially extending locating finger formed in each backplate sector.

5. A backplate according to any preceding claim, wherein the core has a separable hub for engaging the said drive means.

6. A backplate according to any preceding claim, wherein the core is made substantially from a non-metallic material.

7. A backplate according to claim 6 wherein the core is made substantially from a plastics material.

8. A throwing wheel for an abrasion machine comprising a backplate having a plurality of backplate sectors mounted on a backplate core, the backplate core being adapted for releasable mounting on a drive means of the abrasion machine for rotation about an axis, and the backplate sectors extending generally radially from the axis and each terminating in an arcuate band which

together form a generally continuous circumferential band which encircles the backplate core, the throwing wheel further comprising a frontplate spaced apart from and generally parallel with the backplate, the frontplate including a plurality of frontplate sectors mounted on a frontplate core, and the frontplate sectors extending generally radially from the axis and each terminating in an arcuate band which together form a generally continuous circumferential band which encircles the frontplate core, the throwing wheel further including a plurality of throwing blades extending generally radially and extending between the inner surfaces of the frontplate and backplate respectively.

9. A throwing wheel according to claim 8, wherein the frontplate core is adapted for releasable mounting on a drive means of the abrasion machine for rotation about the axis whereby the throwing wheel may be reversed on the drive means to allow both faces of the blades to be used.

10. A backplate sector for use with the backplate of any of claims 1 to 9.

11. A frontplate sector for use with the throwing wheel of claim 8 or claim 9.

12. A throwing wheel constructed and arranged as described herein with reference to the drawings.

13. A backplate or frontplate sector constructed and arranged as described herein with reference to the drawings.