GB2419556A

GB2419556A - A blade for a throwing wheel with an inner ceramic member

Info

Publication number: GB2419556A
Application number: GB0324042A
Authority: GB
Inventors: Tony Philippson
Original assignee: SURFACE PREPARATIONS Ltd
Current assignee: SURFACE PREPARATIONS Ltd
Priority date: 2003-10-14
Filing date: 2003-10-14
Publication date: 2006-05-03
Also published as: GB0324042D0; WO2005039826A1

Abstract

A blade for a throwing wheel, comprising an inner ceramic strengthening member 6; where the ceramic member may have an outer metallic frame 8, such that the relatively soft metallic frame 8 is locally abraded away, in use, to reveal the ceramic abrasion-resistant member 6. The ceramic material may be of cellular construction and an impeller with an enclosed core of ceramic material (figure 5, 10) may be provided.

Description

ThROWING BLADES AND THROWING WHEELS This invention relates to throwing

blades for a throwing wheel, to a throwing wheel and to methods of manufacturing a throwing blade.

Throwing wheels are used in connection with abrasion machines to propel particulate abrasive material on to 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-i 575478 and GB-A-1542495 The throwing wheels to which the invention relates are mounted to a machine and are driven for rotation by a drive rotor 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 in between which individually demountable blades are secured with a demountable central impeller which directs the abrasive material onto the blades. Examples of this type of throwing wheel are shown in GB-A-1328417 and US-A-3785i05. One- piece cast wheels are also known with integral blades and an impeller such as that shown in GB-A-218179 The blades and impellers of such throwing wheels are subject to wear in use.

Accordingly, these components require periodic replacement and it is desirable therefore to minimise wear in order to extend the working life of the machine between periods of maintenance. Typically the blades and impellers are manufactured using a casting process using 25% chrome iron. In order to extend the life of such components, these components may also be manufactured using tungsten carbide. However, this material is very brittle, having a low tensile strength, and at the same time is expensive. Thus machines using components made from this material have a limited and relatively narrow use since they may only be used in environments in which the blades are safe from impact from foreign materials which would cause the blade to shatter.

Accordingly, there is a need for a hard, relatively cheap and relatively shatter-proof blade for throwing wheels.

In accordance with a first aspect of the invention there is provided a blade for a throwing wheel comprising an outer metallic frame and an inner ceramic strengthening member.

In a second aspect there is provided a method of manufacturing an improved blade for a throwing wheel comprising casting a metallic blade around a ceramic core.

In a third aspect there is provided a throwing wheel including a plurality of the blades of the first aspect radially mounted around a generally central hub.

In a fourth aspect there is provided an impeller for a throwing wheel including an enclosed core of ceramic material.

Embodiments of throwing blades and impellers in accordance with the present invention will now be described by way of example with reference to the drawings in which:- Figure 1 is an elevation of a throwing blade in accordance with the invention; Figure 2 is a section along line B-B of Figure 1; Figure 3 is a section along line A-A of Figure 1; Figure 4 is a section along line C- C of Figure 1; Figure 5 is an elevation of an impeller for receiving the blade of Figure 1; Figure 6 is a section along line A-A of Figure 5; Figure 7 is a section along line C-C of Figure 6, and Figure 8 is a section along line B-B of Figure 7.

With reference to Figure 1 a blade has a face 2 upon which abrasive material impacts as the throwing wheel rotates. The blade acts to direct the abrasive material radially outwardly from the wheel.

The blade also has a foot 4 which is adapted to engage the hub or impeller as is known in the art.

With reference to Figures 2, 3 and 4, the blade has a central ceramic core 6 which is harder than the material of an outer metallic frame 8 within which the core 6 is contained.

The frame 8 acts to strengthen the ceramic core 6 so that it does not shatter or fracture. Correspondingly, the ceramic core 6 is harder wearing than the material (for example chrome iron) used to manufacture the frame 8. Thus in use, the face 2 is abraded by the abrasive material as is known in the art. This typically removes the thin layer of metallic material covering the ceramic core while still leaving structurally significant portions of the frame 8 intact. Abrasion of the ceramic core is much slower than the metallic frame and is therefore much slower than that of a conventional throwing blade.

Thus, in effect, there is a symbiotic relationship between the ceramic core 6 and metallic frame 8; the frame supports the ceramic core to make it resistant from damage, and the ceramic core protects the frame from rapid wear.

Blades of this type may be used with the multi-part throwing wheel of our co-pending application published as GB-A-2372721.

Alternatively, the blade described above may be used with a more conventionally shaped impeller as shown in Figure 5. In this case also, the use of a ceramic core 10 helps prevent wear on the impeller. Impellers typically have slots allowing the egress of abrasive material from a central feed at the point marked 12. The slots are aligned with the face 2 of the blades so that material is thrown out of the impeller and then directed by the blade in a generally radial direction. However, the pillars which separate the slots (marked 14 on Figure 6) are themselves subject to wear and thus these may also be made more wear resistant by incorporating ceramic material within.

The ceramic material is preferably of a cellular or matrix form and is sufficiently heat resistant to maintain its shape at the casting temperatures of the metallic frame.

This means that the impeller and/or blade may be made using casting techniques by inserting the ceramic material ready formed in shape, into the mould prior to casting.

An examples of a suitable ceramic is alumina (A1203).

In this way, a blade and impeller may be manufactured which provides similar resistance to tungsten carbide but at reduced cost and increased resistance to shattering.

It will be appreciated that it is not necessary to have the ceramic core wholly enclosed. For example, in the case of the blade, the ceramic material may be positioned in the mould such that even before use of the blade, the ceramic blade is present on the surface of the blade. A similar approach may be taken with the impeller.

Claims

Claims 1. A blade for a throwing wheel comprising an outer metallic frame

and an inner ceramic strengthening member.
2. A blade according to claim 1, wherein the strengthening member is wholly encased in the frame before use.
3. A blade according to claim 1 or claim 2, wherein the relatively soft metallic frame is locally abraded away in use to reveal the relatively abrasion resistant strengthening member.
4. A blade according to any preceding claim wherein the ceramic strengthening member is a generally planar member having a major face generally aligned with the major faces of the blade.
5. A blade according to any preceding claim, wherein the frame is adapted to engage a hub of a throwing wheel.
6. A blade according to any preceding claim, wherein the ceramic material has a cellular construction.
7. A method of manufacturing an improved blade for a throwing wheel comprising casting a metallic blade around a ceramic core.
8. A method according to claim 7 wherein the ceramic core has a cellular construction.
9. A throwing wheel including a plurality of the blades of any preceding claim radially mounted around a generally central hub.
10. An impeller for a throwing wheel including an enclosed core of ceramic material.
11. A throwing blade constructed and arranged as described herein and as shown in the drawings.
12. A method of manufacturing a throwing blade as described herein.