GB2180179A

GB2180179A - Abrasive throwing wheel

Info

Publication number: GB2180179A
Application number: GB08624345A
Authority: GB
Inventors: William Robertson Macmillan; James Matheson Smith
Original assignee: MASSEY ALEXANDER
Current assignee: MASSEY ALEXANDER
Priority date: 1983-12-03
Filing date: 1986-10-10
Publication date: 1987-03-25
Also published as: GB2180179B; GB8624345D0

Abstract

An abrasive throwing wheel comprises a single backplate, a plurality of equi-angularly spaced radially-extending, throwing or paddle blades 11 and a central impellor 12, all formed as an integral unit, and with opposite sides of the blade identical so that, in use, the throwing wheel can be rotated in either the clockwise or anti-clockwise directions operationally bi-directional. The blades are progressively tapered in a direction away from the backplate to permit the throwing wheel to be used as a manufacturing core during casting.The throwing wheel may be cast from "hard" metal generally a high chrome content alloy; or it may comprise a metallic core with a plastics coating (preferably an elastomeric polyurethane locating) moulded therearound; or it may be formed wholly of plastics, preferably an elastomeric polyurethane coating. <IMAGE>

Description

SPECIFICATION A machine part This invention relates to an abrasive throwing wheel for use in shot blasting machinery.

It is an object ofthe present invention to provide such a throwing wheel which is cheaper and simpler to manufacture than existing throwing wheels and which requires less power to drive than an equiva- lent sized existing throwing wheel operating under the same conditions.

According to the present invention there is provided a reversible abrasive throwing wheel comprising a single backplate having integral therewith and projecting from the same surface thereof a plurality of equi-angularly spaced throwing or paddle blades, each having identical opposed throwing faces whereby the abrasive throwing wheel can be rotated in either direction during operation, and each being of progressivelytapered configuration in the direction away from the backplate, whereby the throwing wheel can be used as a manufacturing core.

The throwing wheel may be cast from "hard' metal, a term wellh known to those skilled in the shot blasting art, and generally a high chrome content alloy.

The throwing wheel may also comprise a metallic core with a plastics coating moulded therearound.

The meta I lic core may com prise the backplate and the throwing or paddle blades. Preferably, however, the metallic core also includes the central impellor.

The metallic core is preferably a fabricated steel plate core. It may alternatively be cast in hard metal.

The plastics coating is preferably an elastomeric polyurethane coating, preferably molecular bonded.

The elastic polyurethane preferably has a hardness within the range of A50 Shore to D50 Shore on the IRHD (International Rubber Hardness Degree) scale.

The throwing wheel may be formed wholly of elastomeric polyurethane having a hardness within the aforesaid range on the IRHD scale.

The hardness factor of the elastomeric polyurethane employed will depend, interalia, to the duty to which the throwing wheel is subjected, to the kind and/orsize of abrasive employed, to its operational environment and the centrifugal forces to which it is subjected.

Preferably, the backplate has integral therewith an impellorcomprising equi-angularly spaced vanes defining a tapered inlet for the abrasive to the wheel and projecting from the same surface ofthe backplate as the blades. The impellorvanes, preferably, define an inwardly reducing tapered abrasive receptacle. Such tapering serves to assist uniform distribution of the abrasive to the throwing blades or paddles by directing the abrasive back from the backplate or inner end ofthe impellortowardsthe inletthereof and so out through the inter-vane spaces to the blades.

The impellor preferably comprises an outwardlydirected central conical formation which serves to assist return ofthe abrasive towards the impellor inlet and so the aforesaid uniform distribution ofthe abrasive.

Preferably, the junction line between each blade side and the backplate is radiussed, which radius in- creases from the inner, impellor-adjacent end ofthe blade to the tip ofthe latter. This increasing radius assists spread ofthe abrasive across the throwing face of the blade and consequently improves uni formity of wear ofthe blade.

Preferably, each blade increases in thickness from its inner impellor-adjacent end to its tip which thus reduces the overall weight ofthethrowing wheel while presenting more metal at the area of the blade where g reatestwear by the abrasive tends to occur.

The blades also taper across the width of their faces and this together with the lengthwise taper assists in inducing spread of abrasive across the blade thus obviating straight-line grooving which is a customary wear pattern in such throwing blades or paddles.

The backplate between throwing blade or paddle regions may be chordally cut-away or of reduced dia meterto reduce weight.

Preferably, the backplate on its face opposite to that with which the throwing blades or paddles are integral is cast with a plurality of equi-angularlyspa- ced bosses into which bolth receiving steel inserts are cast, these inserts being adapted to receive bolts securing a drive hubtothethrowing wheel.

These bosses and corresponding inserts can, during manufacture ofthe throwing wheel, be cast in different radial spacings from the throwing wheel centre to suitthe particular hub configuration to which thethrowing wheel istobesecured.

The steel inserts which stand proud of the bosses have a diameter machined in them for hub location.

Thus, no machining ofthe hard metal bosses or backplate is necessary.

Instead of steel inserts the bosses or the backplateperse, i.e. no bosses provided, may have screwthreads casttherein where the backplate is of hard metal.

Where the backplate is of steel plate it may be tapped to receive the hub securing bolts.

An annularsteel boss drilled and tapped at appropriate angular locations to receive hub securing bolts may be fitted or cast into the backplate.

Preferably, a control cage is provided to surround the impelloras is customary,thecontrol cage being of differential diameter at its abrasive entry end to provide an internal annular locating seatforafeed spout spaced outwardly of the impellor inlet relative to the backplate.

Where the throwing wheel is a plastics, metalcored throwing wheel the control cage is preferably formed wholly of plastics material. The latter is preferably a polyurethane which may be molecular bonded.

The elastomeric polyurethane constituting the control cage preferably has a hardness greaterthan that forming the coating around the metal core ofthe throwing wheel.

Embodiments ofthe present invention will now be described, byway of example, with reference to the accompanying drawings, in which: Figure lisa front view of an abrasive throwing wheel according to the invention; Figure2 is a fragmentary sectional view on the line ll-ll of Figure 1; Figure 3 is a fragmentary sectional view on the line Ill-Ill of Figure 1; Figures 4and 5are respectively sectional views of one ofthe blades on the lines IV-IV and V-V of Figure 1; Figure 6is a diametral sectional view ofthethrowing wheel of Figure 1 with a control cagefitted thereon and a hub and feed spout indicated in dot dash lines; Figure 7 is a front view ofthe control cage;; Figure 8 is a front view of a plastics covered, metalh cored throwing wheel according to the invention; Figure 9 is a section along the line IX-IX of Figure8; Figure loins a section along the line X-X of Figure8; Figure 17 is a section along the line Xl-XI of Figure 8; Figure 12 isa view in the direction of arrowXII of Figure 8; and Figure 13 is a fragmentary sectional view of the throwing wheel of Figure 8 with associated control cage, feed spout and hood assembly.

Referring to Figures 1 to 7, the abrasive throwing wheel is cast in one-piece from "hard' metal (forexample a high chrome content alloy).

The throwing wheel comprises a single circular backplate 10 having integral throwing blades 11 and an integral central impellor 12.

The backplate 10 also has on its rearfacefour integral radial bosses 13 into each of which is cast a bolt receiving insert 1 4 formed with a tapped hole 15.

The inserts 14 are made of steel, and a diameter D is machined in these inserts for hub location. This diameter D is determined by the hub configuration to which the throwing wheel isto be bolted.

It is to be noted that in Figure 6the angularposition ofthe inserts 13 is shown incorrectly merelyforthe purpose of showing as much detail of the inserts 13 as possible.

In Figure 6 it can be seen that the throwing wheel is secured to a driving hub 16 by bolts 17 which screw- engagethetapped holes 15.

The th rowing wheel of this em bodiment has four throwing blades or paddles 11 spaced 90" apart and it will be seen from Figure 1 inparticularthateach throwing face 1 1A is identical which means that the throwing wheel is operationally bi-directional.

Each blade or paddle 11 is thicker at its tip 11 B than at its inner end 1 1C. In fact, it is doublethethickness at its tip 1 1Bthan it is at its innerend.The blade 11 thushasagreateramountofmetal in the area where greatest abrasive wear occurs, say the outer half of the blade, but also allows the overall weight ofthe throwing wheel to be reduced by permitting thinning ofthe blade over the inner half, say.

Each blade 11 also tapers across the width of its face as can be seen bestfrom Figures 1,4 and 5.

Each blade 11 where it joins the backplate 10 is radiussed and this radius R1 gradually increases from the inner end 1 Cto radius R2 atthetip 11 B.

This increasing radius and the lengthwise and widthwise tapering ofthe blade assists flow of the abrasive across the width ofthe throwing face ofthe blade which serves to assist uniformity of wear of the blade by the action of the abrasive and to avoid straight line groove wear.

The impellor 12 is centrally ofthe backplate 10 and a pitch circle defined by the inner ends 11 B of the bla dell.

The impellor 12 is disposed radially inwardly ofthe blade inner ends 11 B to permit location of a control cage 18therebetween (see Figure 6).

The impellor 12 comprises four equi-angularly spaced vanes 1 2A defining four inter-vane passages 12B forcentrifugal egress of abrasive from the impellor 12. The innerfaces 12C of the vanes 12 define a mouth which reducingly tapers from the impellor inlet towards the backplate 10.

Centrally ofthe impellor 12 is a conical formation or boss 19 reducingly tapering from the backplate 10 towards the impellor inlet.

The innertapering ofthe impellorvanes 12Aand the provision of the conical boss 19 serve to directthe incoming abrasive away from the backplate 10 to ardsthe impellor inlet and so uniformly out ofthe inter-vanespaces 12Btowardsthe blades 11.These inter-vane spaces 1 2B are defined by the side faces 12D of adjacent vanes 12A and it isto be noted (see particularly Figure 1 )thatthese spaces arewiderat the impellor inlet than at the backplate 10. This outward widening of the inter-vane spaces 12B assists uniform centrifugal egress of abrasive out of the impellor 12 outwardly ofthe backplate 10.

The control cage 18 is ofthe generally known construction and is dual handed. It is inwardly stepped as indicated at 18Ato provide an annular seat spaced from the mouth ofthe impellor 12to locate the outlet end of an abrasive feed spout 20.

It is to be noted that in manufacturing an abrasive throwing wheel as described above, the wheel can be used as its own core, that is each side or face ofthe wheel is simply pressed into the moulding sand without the need to provide any ancillary core elements. Manifestly this makes the manufacture of this throwing wheel easier and cheaper than existing throwing wheels.

Reference is now made to Figures 8to 13which again is of one piece construction and which has all the characteristic construction features ofthe throwing wheel of Figures 1 to 7.

This throwing wheel may be formed wholly of elastomeric polyurethane but, in this instance, is constituted by a metal core 20 preferably of fabricated steel plate covered by an elastomeric molecularh bonded polyurethane coating 21, the elastomeric polyurethane having a hardness within the range A50 Shore to D50 Shore ofthe IRHD scale.

More specifically, the backplate 22, the throwing blades or paddles 23 and the central impellor24are all constituted buy a unitaryfabricated steel plate core wholly covered with an elastomeric coating having a hardness within the range A50 Shore to D50 Shore of the IRHD scale.

The elastomeric polyurethane coating 21 is moulded (injection orcompression mouldingforexample) around the metal core 20.

The backplate 22 in this instance is chordally cutaway as indicated at 25 between throwing blades or paddles 23 to assist in weight reduction.

As aforesaid, the characteristic constructional features ofthe cast, hard metal, throwing wheel of Figures 1 to 7 are all to be found in the metal-cored elastomeric polyurethane throwing wheel of Figures 8 to 13 butforthe avoidance of doubt, the latterwill now be described in more detail.

The backplate 22 has on its rearface an annular steel boss 26 which is drilled and tapped as indicated at 27 to receive hub securing bolts 28.

In Figure 13 it can be seen thatthe throwing wheel is secured to a driving hub 28 by the bolts 28 which screw-engage in the tapped holes 27.

The throwing wheel ofthis embodiment has four throwing blades or paddles 23 spaced 90 apart and it will be seen from Figure8 in particularthateach throwing face 23A is identical which means that the throwing wheel is operationally bi-directional.

Each blade or paddle 23 is thicker at itstip 23B than at its inner end 23C. In fact, it is double the thickness at its tip 23B than it is at its inner end. The blade 23 thus has a greater amount of metal in the area where greatest abrasive wear occurs, say the outer half of the blade, but also allows the overall weight ofthe throwing wheel to be reduced by permitting thinning ofthe blade over the inner half, say.

Each blade 23 also tapers across the width of its face as can be seen best from Figures 8,11 and 12.

Each blade 23 where itjoinsthe backplate 22 is rad iussed andthisradiusRl graduallyincreasesfrom theinnerend23Cto radiusR2atthetip23B.

This increasing radius and the lengthwise and widthwise tapering ofthe blade assists flow of the abrasive across the width ofthe throwing face of the blade which serves to assist uniformity of wear of the blade by the action of the abrasive and to avoid straight line groove wear.

The impellor24 is centrally ofthe backplate 22 and a pitch circle defined by the inner ends 23B ofthe blades 23.

The impellor24 is disposed radiallyinwardlyofthe blade inner ends 23B to permit location of a control cage26therebetween (see Figure 13).

The control cage 30, in this embodiment, is formed wholly of elastomeric polyurethane of a hardness withintheA50shoreto D50Shorerangebutwitha greater hardness value than the aforesaid elastome- ric polyurethane coating 21. This is considered necessary since the control cage 26 does not have are inforcing metallic core and due to centrifugal forces may lose its physical stability and/or configuration.

The impellor24comprisesfourequi-angularly spaced vanes 24A defining four inter-vane passages 24B for centrifugal egress of abrasive from the impellor24. The innerfaces 24C ofthe vanes 24 define a mouth which reducing Iy tapers from the im pellor inlet towards the backplate 22.

Centrally ofthe impellor 24 is a conical formation or boss 31 reducingly tapering from the backplate 22 towards the impellorinlet.

The innertapering of the impellorvanes 24Aand the provision of the conical boss 31 serve to direct the incoming abrasive away from the backplate 22 towardsthe impellor inlet and so uniformly out ofthe inter-vane spaces 24B towards the blades 23. These inter-vane spaces 24B are defined by the side faces 24D of adjacent vanes 24A and it is to be noted (see particularly Figure 8)that these spaces are wider at the impellor inlet than at the backplate 22. This outward widening ofthe inter-vane spaces 24B assists uniform centrifugal egress of abrasive out ofthe im pellor 24 outwardly ofthe backplate 22.

The control cage 30 is ofthe generally known construction and is dual handed. It has a flared mouth or inlet 32 with an outwardlyh directed flange 33 engagable in a recess 34 in the wall of a hood 35 lined, as is conventional, with wear plates 36.

Theflange33 is clamped inthe recess34bya flange 37 of an abrasive feed spout 38.

The relative thickness of metal core and elastome ric coating are determined mainly bythe particular duty to which the throwing wheel is to be subjected, the abrasive employed, the working environment of the throwing wheel and the centrifugal forces applied to the throwing wheel.

Athrowing wheel moulded from elastomeric polyurethane with orwithout a metal core can conveniently be used in applications where the use of a conventional all-metal throwing wheel or even an allmetal throwing wheel according to the present invention is not desirable but where until now has been imposed on the user. For example, in the production of airframe components an allah metal wheel is preferably not employed (but has hitherto out of necessity been used) in case, for whatever reason, it broke up since the resulting shrapnel from the disintegrating throwing wheel could do hundreds ofthousands of pounds damage. This is less likely with a plasticscoated wheel or an all-plasticsthrowingwheel.

Moreover, a metal-cored plastics throwing wheel or all-plastics throwing wheel can be employed to throw abrasives not usable with all-metal wheels due to their extremely severe wear characteristics. Such abrasives are well-known to those skilled in the art.

Further, a metal-cored plastics or all-plastics throwing wheel can be used where hitherto air blast abrasive cleaning is usually employed but with far superior results. For example, a selected metal-cored plastics orall-plasticsthrowing wheel can throw 70lbsweightofabrasive per minute employing a power factor of 1.5 horsepower while a 1/2 inch dia meter air blast nozzle can only impel 61bs wieghtof abrasive per minute with the power factor necessary to provide the compressed air carrier being 50 horsepower.

Various modifications may be made. For example there could bean odd numberofthrowing blades or paddles; the bosses need not be equi-angularlyspaced; instead of bolts, set screws or studs could be employed to secure the hub to the backplate ofthe throwing wheel; instead of having bolt-receiving holes, the backplate may have studs welded thereon for hu b secu rement; the th rowing blades or paddles need not be twice the thickness attheirtips, it is only preferred that they increase in thickness from inner end to tip.

The impellor inlet may be parallel and the impellor may be a flat bottom, i.e. no conical formation. The junction line between each blade and the backplate need not be radiussed, or, if radiussed, uniformly radiussed. The blades need not be lengthwise and/or widthwisetapered. The control cage may be of uniform diameter and is of plastics may be metal cored.

It will be manifest that either of the two embodiments ofthrowing wheel described above can be (a) cast in hard metal; (b) a fabricated metal (e.g. steel plate) core with an elastomeric polyurethane coating; (c) a cast hard metal core with an elastomeric polyurethane coating; (d) a wholly elastomeric polyurethane wheel.

Claims

1. A reversible abrasive throwing wheel comprising a single backplate having integral therewith and projecting from the same surface thereof a plurality ofequi-angularlyspaced throwing or paddle blades, each having identical opposed throwing faces whereby the abrasive th rowing wheel can be rotated in either direction during operation, and each being of progressively tapered configuration in the direction away from the backplate,whereby the throwing wheel can be used as a manufacturing core.

2. Athrowing wheel as claimed in claim 1, cast from "hard' metal generally a high chrome content alloy.

3. Athrowingwheel as claimed in claim 1,comprising a metallic core with a plastics coating moulded therearound.

4. Athrowing wheel as claimed in claim 3, in which the metallic core comprises the backplate and the throwing or paddle blades.

5. Athrowing wheel as claimed in claim 4, in which the metalliccore also includesthe central impellor.

6. Athrowingwheel as claimed inanyoneof claims 3 to 5, in which the metallic core is a fabricated steel plate core.

7. Athrowing wheel as claimed in any one of claims3to 5, in which the metallic core is cast in hard metal.

8. Athrowing wheel as claimed in any one of claims 3 to 7, in which the plastics coating is an elastomeric polyurethane coating, preferably molecular bonded.

9. Athrowing wheel as claimed in claim 8, in which the elastomeric polyurethane has a hardness within the range of A50 Shore to D50 Shore on the IRHD (International Rubber Hardness Degree) scale.

10. Athrowing wheel as claimed in claim 1, formed wholly of elastomeric polyurethane having a hardness within the range of A50 Shore to D50 Shore on the IRHD (International Rubber Hardness Degree) scale.

11. Athrowing wheel as claimed in any one ofthe preceding claims comprising an impeller integral with the backplate and including equi-angularly spa cedvanes defining a tapered inletforthe abrasive to the wheel, and projecting from the same surface of the backplate as the throwing blades or paddles.

12. Athrowingwheel as claimed in claim 11, in which the impellorvanes define an inwardly reducing tapered abrasive receptacle.

13. Athrowing wheel as claimed in claim 11 or 12, in which the impeilorvanes have relativelywide inter-vane spaces between same to provide a relatively large circumferential abrasive outlet area in the impellorwall.

14. Athrowing wheel as claimed in any one of claims 11 to 13, in which the impellorcomprisesan outwardly-directed central conical formation which serves to assist return of the abrasive towards the impellor inlet and so the aforesaid uniform distribution of the abrasive.

15. Athrowing wheel as claimed in any one of claims 11 to 14, in which thejunction line between each blade side and the backplate is radiussed, which radius increases from the inner, impellorh adjacent end ofthe blade to the tip ofthe latter.

16. Athrowingwheel as claimed in anyone of claims 11 to 15, in which each blade increases in thickness from its inner impellor-adjacent end to its tip which thus reduces the overall weight of the throwing wheel while presenting more material (metal, metal and plastics or plastics) at the area of the blade where greatest wear by the abrasive tends to occur.

17. Athrowing wheel as claimed in any one of claims 1 to 16 in which the blades taper across the width oftheirfaces and this together with the lengthwise taper assists in inducing spread of abrasive across the blade thus obviating straight-line grooving which is a customary wear pattern in such throwing blades or paddles.

18. Athrowingwheel as claimed in anyone of claims 1 to 17, in which the backplate between throw- ing blade or paddle regions is chordally cut-away or of reduced diameter.

19. Athrowing wheel as claimed in any one of claims 1 to 18, in which the backplate on its face opposite to that with which the throwing blades or paddles are integral is provided with a plurality of equi-angularly spaced bosses into which boltreceiving steel inserts are cast, these inserts being adapted to receive bolts securing a drive hub to the throwing wheel.

20. Athrowing wheel as claimed in claim 19, in which the steel inserts which stand proud of the bosses have a diameter machined in them for hub location.

21. Athrowing wheel as claimed in any one of claims 11 to 20, in which a control cage is provided to surround the impellor as is customary, the control cage being of differential diameter at its abrasive entry end to provide an internal annular locating seat for a feed spout spaced outwardly ofthe impellor inlet relative to the backplate.

22. Athrowing wheel as claimed in claim 21 when dependent on any one of claims 1 and 3 to 9, in which the control cage is formed wholly of elastomeric polyurethane having a hardness factor greater than that of the polyurethane coating of the wheel.

23. An abrasive throwing wheel substantially as hereinbefore described with reference to Figures 1 to 7 or Figures 8to 13ofthe accompanying drawings.