WO2007137346A1

WO2007137346A1 - A drum for a mixer assembly

Info

Publication number: WO2007137346A1
Application number: PCT/AU2007/000740
Authority: WO
Inventors: Michael Kelly
Original assignee: Cesco Australia Limited
Priority date: 2006-05-29
Filing date: 2007-05-29
Publication date: 2007-12-06

Abstract

A drum for a mixer assembly is disclosed. The drum (1) comprises a drum body (2) for rotatable mounting on a support. The drum body (2) has a wall forming an internal surface (10) and defining an interior space within which a material to be mixed is received. A coating (15) comprising ceramic particles and a support material that bonds the particles into the coating (15) and bonds the coating (15) to the internal surface (10) of the drum body (2), is applied to the internal surface (10) of the drum body (2). The ceramic particles are regular in shape, for example spherical, and have a Rockwell hardness of at least 90. The support material is a polymeric material that has a tensile adhesive strength of about 13700 kPa. A mixer truck for mixing and transporting cementitious materials having the drum (1) is also disclosed. The drum has blades (11) and flights (12) and these are also coated with the same material (15) that coats the internal surface (10) of the drum (1).

Description

A DRUM FOR A MIXER ASSEMBLY

FIELD OF THE INVENTION

This invention relates to a drum for a mixer assembly. • The invention also extends to a mixer assembly incorporating the drum. Further the invention also extends to a mixer truck including the drum.

This invention relates particularly but not exclusively to a drum for a mixer assembly used for mixing a settable cementitious material on a concrete transport truck. It also relates particularly to a mixer truck for mixing and transporting settable cementitious material, It . will therefore be convenient to hereinafter describe the invention with reference to this example application. However it should be clearly understood that the invention is capable of broader application. It needs to be borne in mind that mixing is a widely practiced unit operation in process plants around the world in all industries and this invention may be applied to many if not all of these industries. The Applicant clarifies that the invention applies equally to mixer assemblies for materials other than cementitious materials

BACKGROUND TO THE INVENTION

Settable cementitious materials such as cement and concrete are building materials that are widely used around the world. The materials are widely used in building structures and also general engineering structures such as bridges, walls, tunnels and the like. The advantages of using cementitious material in these applications including its strength have been well documented in the literature.

In use a cementitious material is broadly mixed in a plant and then loaded onto a so-called concrete mixer truck which transports the cementitious material to the site where it is to be poured. In one form the cementitious material is charged into the mixer truck as a dry mix at the plant and water is then added to the dry mix before the truck sets out on the road. The concrete is then mixed in the mixer truck while it is on route to the pour site. In another form the cementitious material is mixed with water in a batch plant and the wet mix or wet mixed cementitious material is then charged into the truck. This mix is then agitated and also further mixed in the mixer truck on the route to the pour site.

A concrete mixer truck comprises broadly a drum that is rotatably mounted on a support for rotation about a substantially horizontal axis. The support in turn is fixedly mounted on the chassis of the truck. The drum comprises broadly a cylindrical mid-section with frusto- conical end sections at each end of the mid-section. The drum further includes a port towards one end of the drum through which dry or wet material is charged into the drum • and through which wet cementitious material is discharged from the drum.

The drum has a wall defining an internal surface which faces into an interior of the drum. The drum also includes internal blades and flights mounted on the internal surface within the drum that in use assist in lifting cementitious material within the drum as the drum rotates.

The Applicant has become aware of some shortcomings of existing prior art drums.

Firstly the drum which has been typically made of steel is subject to high levels of abrasive wear by cementitious material that is mixed within it in use. This problem is particularly acute when coarse or hard aggregates are mixed within the drum. It is further exacerbated when dry aggregates as distinct from wet mixed aggregates are mixed within the drum. The reality is that water helps to lubricate the movement of the aggregate over the internal surface and frictional wear is greater when water is not present.. This has the effect of shortening the service life time of the drum and maintenance or replacement of the drum is required at least once during the life time of the truck. This is expensive and causes service downtime of the truck which also attracts a cost.

Secondly the steel drum is required to have a gauge thickness of typically 4-8mm. This represents the gauge thickness required to confer the requisite mechanical strength on the drum and also some additional thickness to cater for abrasive wear during use. The weight of the drum constitutes a significant weight component of a truck without a load. Road regulations limit the gross or maximum weight of a truck allowed on the road depending on the type of truck. For example for a typical mixer truck seen on Australian roads the gross weight of the truck including load is limited to about 28-32 tons. Clearly therefore if the weight of the drum could be reduced by reducing the gauge thickness of steel from which it is fabricated the weight of the truck without its payload could be reduced. This in turn would enable the weight of the payload of cementitious material being carried by the truck on each trip to be increased by a corresponding amount. This in turn would increase the productivity of the mixer truck.

Clearly therefore it would be advantageous if a drum could be devised that resisted abrasive wear of its internal surface at least to some extent. This would increase the service life time of the drum. It would also be advantageous if the weight of the drum could be reduced as would enable a correspondingly greater payload to be carried by the truck on each trip.

SUMMARY OF THE INVENTION

According to one aspect of this invention there is provided a drum for a mixer assembly, comprising: a drum body for a wall forming an internal surface and defining an interior space within which a material to be mixed is received; and a coating that is applied to at least part of the internal surface of the drum body, the coating comprising ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the internal surface of the drum body.

In this specification the term coating is to be interpreted broadly and to include all forms of coating applied to the surface. Further the coating is not to be limited in any way in terms of its thickness. Further in this specification the terms coating and lining may be used interchangeably and shall be interpreted to mean the same thing.

Thus the internal surface of the drum body is lined with a coating containing ceramic particles that adheres to the drum body and makes contact with the material being mixed within the interior space of the drum body. The ceramic coating shields the internal surface of the drum body from contact with material being mixed within the drum body.

The ceramic coating thus reduces wear of the wall and thereby prolongs the service life of the drum body. Further the ceramic lining can enable the overall weight of the drum body to be reduced.

The drum body may be adapted for rotatable mounting on a support.

The coating may be applied to substantially the full internal surface of the drum body.

The ceramic particles may comprise particles that have substantially the same basic shape and the particles may also have a shape that is a regular shape. For example the particles may be spherically shaped, egg shaped, cylindrically shaped, oval shaped, disc shaped or rectangular shaped. The ceramic particles within the coating may have substantially the same size. By this is meant that particles that are arranged relative to each other and proximate to each other in the coating are of the same size.

The particles may be artificial in the sense that they are manufactured as distinct from being recovered from the environment and then comminuted or broken down to a suitable size.

In particular the particles may be prills and the prills may have a substantially spherical shape. For example the spherical shape may be formed by solidifying a drop of liquid of the material from which the particle is formed.

The coating of the internal surface may comprise more than one region, and each region may have particles which have substantially the same nominal diameter, e.g. the particles in any region are of substantially the same size. However in different regions of the coating the particles may have different particle sizes, e.g. different nominal diameters.

The particles may generally have a size in the range of 0.4 mm to 3.0 mm. By this is meant that they are sized to pass through a mesh or screen having openings of 3.1 mm. The particles may be substantially spherical prills and the prills may have a nominal diameter of 0 4 mm to 3.00 mm.

In some applications of the invention the prills may have a nominal diameter or size of 0.5 to 1.0 mm. In other applications the prills may have a nominal diameter of 1.0 to 1.5 mm. In other applications the prills may have a nominal diameter of 1.5 mm to 2.0 mm.

The particles may comprise aluminium oxide, e.g. alumina.

The ceramic particles may have a Rockwell hardness that is greater than 90. For example the particles may have a Rockwell hardness of 94 to 98. In some instances the prills may have a Rockwell hardness of greater than 100. This level of hardness helps to confer the requisite hardness and abrasion resistance on the coating.

The prills may be arranged side by side in the coating. The proximate surfaces of adjacent prills may be side by side with each other, e.g. they may be in side by side abutment. The coating may have two or more prills in its direction of depth or thickness. In some applications the coating may have two to four prills arranged in the direction of thickness of the coating. Thus the coating may generally have a multi- layer of prills across substantially its full extent.

The prills in adjacent layers of prills in the direction of depth of the coating may be off-set relative to each other. That is a prill in one layer is positioned intermediate the two closest prills in the adjacent layer. This way the prills in one row or layer fills in the spaces between the spherical prills in the adjacent layer thereby to achieve a substantially continuous cover of ceramic particles when viewed from the direction of depth.

The support material may be a polymeric material. The polymeric material may be elastomeric at least to some extent and the polymeric material may be described as a mastic material.

The support material may be a polymeric material that is caused to cure by the addition of a curing agent. For example the polymeric material may be cured by aliphatic compound.

The support material must bond the ceramic particles into the coating with a high degree of efficacy. The support material must also bond the coating including the particles to the internal surface of the drum body with a high degree of efficacy, e.g. to resist delamination of the lining from the drum body in use.

The binder material may have an adhesive tensile strength of at least 2000 psi.

The lining may conveniently be referred to as a ceramic reinforced polymeric composite.

The drum body may be made of a metallic material, e.g. a metal alloy material such as steel.

The wall of the drum body may have a thickness of 2 to 5 mm, e.g. about 3 to 4 mm.

The drum may be a drum for a . concrete mixer truck for mixing or agitating settable cementitious material while it is being transported on the road to a pour site. In particular the drum body may be mounted for rotation about a substantially horizontal axis, and the drum body may have a closed end and an open end at the other end through which material is discharged from the drum body, both ends being positioned on the horizontal axis. In some forms the closed end is at the front of the mixer truck and the open end is at the rear of the mixer truck. However the drum body is not always oriented in this way.

The drum body may have a broadly cylindrical central body section and one frusto-conical section towards the closed end of the drum and a further frusto-conical section towards the discharge end.

The ceramic and binder material from which the lining is formed may be a material that is manufactured and sold by. I MATECH PTY LTD of Unit 7, 6 Gladstone Road, Castle Hill, 2154, in the State of NSW₁ in Australia, under the general trade mark REDSKIN™. The product is sold in several different grades namely REDSKIN-97™, REDSKIN-85™, and REDSKIN-55™. In a preferred embodiment of the invention, the coating is formed from a product also obtainable from lmatech Pty Ltd, which product is sold under the trade name REDSKIN A97™ which has been developed to be applied to the inside surface of the drum by way of spraying it onto the surface of the drum. Further, the invention can also be carried out by forming the coating with a product available from lmatech Pty Ltd, which product is sold under the trade name BXSR™. The most suitable grade for any particular application is a matter of design choice for any given application and depends on the abrasive conditions and the manner in which the material is to be applied to the interior surface.

According to another aspect of this invention there is provided a mixer assembly, comprising: a support; and a drum rotatably mounted on the support as defined in the first aspect of the invention described above.

The coating may include any one or more of the optional features of the coating defined in the first aspect of the invention described above,

The drum body may be made of steel and the coating may comprise ceramic prills that are of substantially the same shape and the same size, and a support material that is a polymeric material that bonds the particles to each other and bonds the coating to the drum surface.

The polymeric material may be elastomeric and may be a resin mastic material.

The mixer assembly may further include drive means for driving the bowl to rotate.

According to yet another aspect of this invention there is provided a mixer truck, comprising: a chassis; a drum support mounted on the chassis; and a drum body rotatably mounted on the support, the drum body having a wall forming an internal surface and defining an interior space within which an aggregate material to be mixed is received, and a coating that is adhered to at least part of the internal surface of the drum body, the coating comprising ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the internal surface of the drum body.

The coating may include any one or more of the optional features of the drum defined in the first aspect of the invention described above.

In particular the coating may comprise ceramic particles of aluminium oxide that are of substantially the same size and have a substantially even and consistent shape. The support material may be a polymeric material.'

The drum body may comprise a substantially cylindrical middle section and frusto-conical end sections disposed at each end of the middle section. The coating may be applied to substantially the full internal surface of the middle section and the end sections.

The drum body may further include blades mounted on the internal surface of the drum body and extending from the internal surface radially inward into the interior space, and the coating may be applied to the surfaces of the blade as well as the internal surface of the drum. The drum body may further include flights disposed on the ends of the blades and the flights may also be coated with the coating that is applied to the internal surface of the drum.

The mixer truck may be of the type that is used for mixing settable cementitious materials, e.g. concrete or cement, and transporting these materials from a supply site to a pour site.

According to another aspect of this invention there is provided a method of manufacturing a drum having a drum body with an internal surface for a mixer assembly, the method comprising the following steps: preparing an internal surface of a drum body for application of a coating; applying a coating material comprising ceramic particles and a settable support as a layer across the internal surface of the drum; and causing the settable support to set to bond the particles to each other and to the internal surface to form the coating on the drum body.

The method may further include the step of fabricating the drum body prior to preparing the internal surface of the drum body for coating. The body may be fabricated from a plurality of discrete sections of steel plate that are welded together.

Further the drum may also include blades and flights mounted on the internal surface of the drum body and the method may also include fabricating the blades and flights and mounting them on the internal surface of the drum body once the drum body has been fabricated.

The ceramic particles of the material may include any one or more of the optional features of the ceramic particles defined in the first aspect of the invention described above.

The settable support may include any one or more of the optional features of the support material defined in the first aspect of the invention described above.

Thus the surface is first prepared and then the material is applied to the surface in a movable or flowable form. Thereafter the material is caused to set thereby to form a coating of ceramic particles bonded to the surface of the drum body by the support material. The step of preparing the internal surface of the drum may comprise roughening the internal surface of the drum, e.g. by blasting with a particulate material. The step of preparing the surface may comprise blasting the internal surface of the drum with an irregular particulate material. The surface may be blasted with a grit.

The step of preparing the surface may comprise blasting the internal surface to a surface finish of at least Class 2.5, e.g. Class 2.5 to 3.0.

The step of preparing may also include blasting the surfaces of the blades and flights at the same time that the internal surface is blasted.

The step of preparing may also include applying an oxidation retardant to the surface after it has been blasted and before the coating is applied to the surface.

The step of applying the material to the prepared internal surface may comprise spraying the material onto the surface in the form of a flowing slurry through a nozzle.

Instead the material may be in the form of a paste that is applied to the surface by means of a hose and which is smoothed off by means of a hand tool. '

The step of applying the material may comprise applying the material within 20 minutes of the surface treatment being completed.

According to another aspect of this invention there is provided a mixer member for a mixer assembly having a mixer drum, comprising: a flattened body having two major surfaces opposed to each other and defining a peripheral edge; and a coating applied to at least part of the major surfaces of the flattened body, the coating comprising ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the surfaces of the flattened body.

The coating may be applied substantially fully across the major surfaces of the body and the coating may also be applied over and around those parts of the peripheral edge of the body. The body may have a base at one end for mounting to the mixer drum and an opposed end that is free. The base may include a flange at said one end for mounting to the mixer drum.

The peripheral edge of the body at said opposed end may define a rounded peripheral edge, e.g. a bull nose edge.

The rounded edge may be formed by a bar, e.g. a round bar, mounted along the edge at said opposed end and a said coating over said bar. The thickness of the coating formed over the edge along said opposed end may be thicker than the coating applied over the major surfaces of the body. For example the thickness of the coating applied over the bull nose edge may be 5 to 8 mm and the thickness of the coating applied over the major surfaces may be 2 to 4 mm.

The mixer member may comprise a blade extending away from the base and a flight extending from the blade to the opposed end which is free.

The blade may extend substantially perpendicularly to the surface to which it is mounted. The flight may extend diagonally to the blade.

According to another aspect of this invention there is provided a method of making a mixer member for a mixer assembly having a mixer drum, the method comprising:

providing a flattened body having two major surfaces opposed to each other and defining a peripheral edge, the body having a base at one end for mounting to the mixer drum and an opposed end that is free; positioning a bar mounted on the peripheral edge along said opposed end; folding a sheet of mesh material over the bar such that it extends across part of a said major surface, around the bar, and then across part of the other major surface; and applying a material containing ceramic particles and a settable support over the major surfaces and the opposed end of the peripheral edge including the bar and allowing it to set.

The material may form a coating as defined in the first aspect of the invention. The coating may comprise ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the surfaces of the flattened body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION A drum for a mixer assembly of the type that is mounted on a mixer truck in accordance with this invention may manifest itself in a variety of forms. It will be convenient to hereinafter describe at least two embodiments of the invention in detail with reference to the accompanying drawings. The purpose of providing this detailed description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. However it is to be clearly understood that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the drawings:

Fig. 1 is a schematic three dimensional view of a mixer truck for mixing cementitious material that is known in the prior art;

Fig. 2 is an external schematic three dimensional view of a drum for a mixer truck in accordance with one embodiment of the invention;

Fig. 3 is a schematic three dimensional view of an internal surface of the drum of

Fig. 2 (with part of the drum omitted for clarity) showing the application of a coating to the internal surface;

Fig. 4 is a longitudinal sectional view through the drum of Fig. 3 showing different regions of the drum body;

Fig. 5 is a schematic three dimensional view from one side of part of the blade or mixing member on the drum of Figs 2 and 3 and showing the coating applied to the internal surface of the drum body;

Fig. 6 is a schematic three dimensional view from above of the part of the blade shown in Fig. 5;

Fig. 7 is a schematic sectional view through the mixing member at a point along its length showing how the coating is applied thereto; Fig. 8 is a schematic series of drawings showing the steps involved in preparing a surface for the application of the settable material forming the lining and then the application of the material to form the coating; and

Fig. 9 is a schematic three dimensional view of an internal surface of the drum of

Fig. 2 (with part of the drum body omitted for clarity) showing the application of a settable material in the form of a flowing slurry to the surface by means of nozzle.

Fig. 1 is a schematic three dimensional view of a prior art concrete mixer truck. ^•

The drawing shows the basic features of the mixer truck including the chassis on which the mixer assembly is mounted. The mixer assembly includes a support mounted on the chassis and a drum that is rotatably mounted on the support. The drum is formed by a wall that can be made of a metallic material and which defines an interior space within which a settable cementitious material can be received and mixed or agitated.

Typically some prior art drums have been manufactured with a wall thickness of 5-8 mm. The drum is rotated in use to mix or agitate the settable cementitious material within the drum and to resist the cementitious material from setting. The drum also includes a port towards its rear end through which material is charged into the drum and from which cementitious material is discharged from the drum.

Fig. 2 shows a three dimensional view of a drum for a mixer truck for mixing cementitious material such as concrete in accordance with the invention.

In the drawings reference numeral 1 refers generally to a drum.

The drum 1 comprises a broadly cylindrical drum body or drum container 2 as shown that in use is mounted on a support with its rotational axis extending broadly in a horizontal direction. The drum body 2 comprises a circular cylindrical central or middle body section 5 and inwardly tapering frusto-conica) sections 6, 7 disposed at each end of the central body section 5. The drum 1 also includes an opening or port 8 towards its rear end through which cementitious material is introduced to and discharged from the drum 1.

The drum body 2 is formed from a wall that is made out of a metal alloy material such as carbon steel defining an internal surface 10. In the Fig. 2 embodiment the wall has a thickness of about 2 mm to 3 mm. It is envisaged that the wall thickness will usually be kept below the thickness of prior art drum bodies of 5-8 mm described above. The drum body 2 also has an access opening with a removable cover 11 releasably mounted over the opening to provide worker access to the interior of the drum body 2, e.g. for engineering or technical work. It can also be used to pass cables or pipes for services and materials into the interior space of the drum body 2.

Fig. 3 shows part of the interior surface of the drum body 2. This has been achieved by omitting part of the structure of the wall on the near side from the drawing.

As shown in Fig. 3 the drum 1 also includes a mixing fin or mixing member comprising a blade and a flight. The blade is shown generally by numeral 11 that is mounted onto the internal surface 10 of the wall. The blade 11 projects up from the interior surface 10 in a direction that is broadly orthogonal to the surface 10. The drum 1 also includes a flight 12 mounted on the blade 11 at the end thereof remote from the wall surface 10 and which is inclined relative to the blade 11. The blade 11 and flight 12 together assist with mixing cementitious material in the drum body 2. The blade 11 lifts up the cementitious material and causes it to be turned. In addition the diagonally extending flight 12 also directs it in a longitudinal direction towards the closed end 6 of the drum body 2 thereby to affect some mixing of the material in a longitudinal direction as well.

Further the blade 11 and flight 12 in their direction of length extend along the internal surface 10 of the wall in the form of a helical spiral from one end of the drum body 2 to the other. Figs. 5 and 6 in particular show some structural features of the blade 11 and flight 12.

The interior surface 10 of the drum body 2 which is formed by the wall is lined with a coating 15 (hereinafter called a coating or lining) that broadly comprises ceramic particles 16 fixed or embedded or bonded onto a support material. The support material bonds the ceramic particles 16 into the coating 15 and also bonds the coating to the internal surface 10 of the drum body 2. At a functional level the coating 15 is characterized by the fact that it resists abrasive wear due to aggregate particles scouring its surface during normal use.

The ceramic particles 16 which are shown only schematically in Figs. 3 to 7 comprise particles having a regular and even shape that is substantially spherical. Further all of the ceramic particles 16 may be of substantially the same size, certainly within any given or certain region or zone of the internal surface 10 of the drum body 2.

In this form of the invention the ceramic particles 16 are prills that are made of aluminium oxide, e.g. alumina. In particular the ceramic prills may be formed artificially by solidifying droplets of liquid in an apparatus and then collecting the solidified particles. The manufacture of the prills 16 is engineered such that they have a Rockwell hardness of at least 90. Some embodiments may have a Rockwell hardness of at least 96.

The ceramic particles 16 can have a diameter selected from the range of 0.5mm to 3.0 mm. In some applications a prill size of 0.5 mm to 0.8 mm is used. These prills are typically used to form a coating or lining having a thickness of about 1.5mm. These prill sizes are typically used to line regions of a surface that are exposed to a less aggressive or less abrasive environment.

In other applications where a more wear resistant surface is required a prill size of 1.0 mm to 1.5 mm can be used. This prill size can be used to form a lining having a thickness of 2 mm to 3 mm.

In yet other applications where an even more resistant wear surface is required a prill size of 1.5 mm to 2.00 mm can be used. This prill size can be used to form a lining having a thickness of 3 mm to 4 mm.

It should be noted that the prills 16 are closely packed and are in side by side abutment with each other in the coating 15. Further the coating 15 is applied to the internal surface

10 with a thickness that provides at least two layers of prills 16 in a direction of depth.

One prill layer lies against the internal surface 10 and at least one other layer overlays this one layer. The prills in the second layer are offset relative to the prills in the first layer so as to lie between two adjacent prills. In this way when the coating 15 is viewed from above the surface, a substantially continuous covering of prills extends across the surface

10 and none of the surface 10 can be seen. :

Applicant believes that two or more layers of prills arranged in this fashion contributes to achieving a high level of wear resistance with the lining. In other applications where even more abrasive environments are encountered larger prill sizes may be used. For example prill sizes of 2.5 mm to 3.0 mm can be used to form a lining of about 4.5 mm to 6 mm.

The support material is a settable polymeric material that sets on the application of a curing agent when the lining is applied to the internal surface during manufacture of the drum. The polymeric material may in particular be elastomeric and may be cured by an aliphatic curing agent.-

The polymeric material may have an adhesive tensile strength of at least 2000 psi (about 13790 kPa in SI UNITS). The internal surface 10 of the drum body 2 is exposed to harsh abrasive working conditions inside the drum body 2 in use. It will therefore readily be appreciated that a high tensile strength is required to effectively bond the coating 15 to the steel surface 10 of the drum body 2 and also to bind the ceramic particles 16 into the remainder of the coating.

In Australia an example support material for use in carrying out the invention can be obtained from lmatech Ry Ltd (IMATECH) based at Unit 7, 6 Gladstone Road, Castle Hill, 2154, in the State of New South Wales. The product is sold under the trade mark REDSKIN™ (™ being a trade mark owned by lmatech). The product is sold in various grades for example REDSKIN -97™, REDSKIN -85™, and REDSKIN -55™. In a preferred embodiment of the invention, the coating is formed from a product also obtainable from lmatech Pty Ltd, which product is sold under the trade name REDSKIN A97™ which has been developed to be applied to the inside surface of the drum by way of spraying it onto the surface of the drum. Further, the invention can also be carried out by forming the coating with a product available from lmatech Ry Ltd, which product is sold under the trade name BXSR ™.

Fig. 4 is a longitudinal section through the drum body.

As described above with reference to Fig. 2 the body comprises a forward frusto-conical end section 6, a cylindrical middle section 5, and a further frusto-conical end section 7 at the rear with a port 8.

The coating 15 is applied to substantially the full internal surface 10 of the drum body 2. It thus extends across the full extent of internal surface 10 shown in Fig. 4. These different regions 5, 6, and 7 undergo different levels of wear. The closed end section 6 of the drum body 2 is a region of high wear. This is because the most intense mixing occurs within this region 6 of the body 2. The cylindrical middle section 5 of the drum body 2 is a region of intermediate wear. The other end section 7 of the drum body including the discharge opening 8 is a region of relatively lower abrasive wear. .

Thus, the coating 15 applied to the different regions has a different composition depending on the level of wear that that particular region is exposed to. The internal surface 10 of the drum body 2 comprises a plurality of different zones or areas corresponding respectively to end section 6, middle section 5, and end section 7.

In the illustrated embodiment the different grades of coating described above with differently sized prills 16 are applied to the different zones or areas, 5, 6 and 7 of the interior surface 10. In particular prills 16 having a size of about 1.5 to 2mm are used in the closed end section 6 which is a region of high wear. Prills 16 having a size of about 1 to 1.5 mm are used in the middle section 5 which is a section that undergoes medium wear. Prills 16 having a size of about 0.8 to 1.0 mm are used in the rear end section 7 which is an area of lower wear.

Figs. 5 to 7 illustrate the blade and flight of the drum shown in Fig. 3 in more detail.

As shown in Fig. 7 in addition to the internal surface 10, the blades 11 and flights 12 within the drum body 2 are also coated with the same coating 15 that is applied to the internal surface 10.

The coating on the blade 11 and flight 12 is subjected to very high levels of abrasive wear when compared with other regions on the wall of the drum body 2. As such the blade 11 and flight 12 may have a coating 15 with prills of larger size applied thereto. For example the prills 16 used in the coating applied to the blade 11 and flight 12 may have a diameter of 1.5 mm to 2.0 mm. This corresponds broadly to a thickness of the multilayer coating of 2 or 3 prill thickness of about 2.5 mm to 3.0 mm.

Further as is clearly shown in the drawings the free or terminal end of the flight 12 has a rounded bull nose 20. The bull nose 20 of the flight 12 provides additional thickness to the coating 15 in this region which is exposed to high levels of abrasive wear. The rounded bull nose 20 also helps to direct aggregate within the drum body 2 past the major surfaces of the flight 12. The manufacture of this bull nose 20 on the flight is described in more detail below together with the manufacture of the rest of the drum 1.

In another embodiment that has been made by the Applicant but has not been illustrated, the prills used in the coating are of the same size for all the regions notwithstanding the different wear rates to which the different sections or^'regions of the surface are exposed.

In the manufacture of the drum 1 , the drum body 2 is first fabricated from steel. The drum body 2 is formed from several discrete panels of steel that are welded together, e.g. with fillet welds. Most of the panels will have a steel gauge thickness of about 3-4 mm.

However there is one panel that will usually be of thicker gauge steel than the rest of the panels. This is the panel that forms a rounded front end of the end section 6 of the drum body 2 to which the output flange of the drive system, e.g. the output flange of the gearbox, is bolted. This panel is made of thicker gauge as it bears a higher mechanical load, e.g. the thrust load of driving the drum body when it is filled with aggregate material.

An access opening as shown in Figs. 2 and 3 is cut in the drum body 2 once if is fabricated. A removable closure 11 is then removably mounted over the opening. The closure 11 can be removably mounted on the drum body 2 by means of a plurality of bolts that are spaced apart around the edge of the closure 11.

The blades 11 and flights 12 are then formed from steel and welded onto the steel surface 10 of the drum body 2 by means of fillet welds in the general configuration shown in Fig. 3. In earlier times the blade 11 would be mounted on the drum surface 10 first and then the flight 12 would be formed and be welded onto the free end of the blade 11. However in more recent times it has become more usual to form the blade 11 and flight 12 from the same piece of steel and to bend an outer region of this piece backward so that it extends diagonally relative to the blade to form the flight 12. However it will be appreciated that this invention is equally applicable to either of these techniques.

The first step in the process is to structurally prepare the blades and flights for being coated by mounting a round bar 22 over the free edge of the flight 12 along its full length.

The round bar 22 may be welded to the free edge of the flight 12. Thereafter a mesh material 24 of sorts is applied from one surface of the flight 12 around the round bar 22 and back over the other surface of the flight 12. This round bar 22 and mesh 24 is shown clearly in Fig. 7,

The following steps involve treatment of the fabricated drum 1 to coat the internal surface thereof and the blades and flights with coating material. These treatment steps are shown schematically in a sequence of drawings in Fig. 8.

The next step in this process is to perform a surface treatment of the internal drum surface and the blades and flights to ready them for the application of the surface coating. This is done by blasting the steel surface with non uniform particles as the blasting medium: A grit for blasting may be used to achieve a surface finish of class 2.5 - 3.0 with near white metal. This finish is a rough finish that produces some peak heights of at least 0.75 mm. This treatment step removes metal oxide from the metal surface. This is necessary because the polymeric support material bonds more effectively to a metal surface that is free of oxide.

After this surface treatment the internal surface 10 of the drum body 2 and the major surfaces of the blades and flights 11 and 12 are treated with an oxidation resisting agent to resist oxidization of the treated surface in the period after the blast and prior to the application of the coating material. This agent may be in the form of a liquid that covers the surface and thereby prevents it coming into contact with air and which evaporates off when the coating material is applied. The material forming the coating must then be applied within about 30 minutes, preferably within 20 minutes, of the surface treatment.

In parallel with the surface treatment of the surface to be coated, or even prior to this, the settable coating material with ceramic prills and polymeric binder is mixed up so that it is ready for application. The coating material is typically mixed up in batch form in a mixer, e.g. a batch mixer. The polymeric binder is in the form of two parts one of which is a curing agent. Once the rest of material has been well mixed the curing agent, e.g. an aliphatic curing agent, is added to the mixer and then shortly thereafter the coating material must be applied to the surface to be coated.

The next step is to line the internal surface 10 of the drum body 2 with the settable coating material containing the ceramic prills and also the support that bonds the prills into the coating and binds the coating to the surface. In addition to the drum surface TO the blades 11 and flights 12 are also coated with the coating material. Fig. 9 shows an application of the coating.

In Fig. 9, the material is transferred from the mixer to the interior space of the drum body 2 by means of a flexible pipe 26 coupled in line with a pump leading into the drum body 2 and having a spray nozzle 28 at its remote end. The nozzle 28 is directed and operated by a workman 30 in a similar way to a nozzle used to direct concrete slurry onto a rock wall. The application of the material onto the drum internal surface in this way is shown in

Fig. 9. The workman 30 applies the coating material onto the internal surface 10 such that there is a multi layer of prills 16 across the full surface area 10. That is the coating material will have a thickness of at least 2 prills across the full surface area of the coating

10.

Further while the nozzle 28 directs the material directly onto the internal wall surface 20 the work man 30 has a hand tool such as a trowel 32 which they use to spread and even out the application of the material onto the surface 10. The settable coating material sets within a relatively short time after it has been applied to the surface and forms the hard abrasion resistant coating 15.

Further while the coating 15 will only be as thick as is necessary to perform its coating and abrasion resistance along major expanses of the wall surface, it will inevitably be thicker in corner regions of the internal surface 10. For example the work man will use the trowel to radius the layer of material in the corner regions and smooth the transition from one wall region to another.

As is shown in Fig. 7 the settable coating material is also applied to the blades and flights 11 and 12. Broadly this is carried out in the same way as it is applied to the wall surface 10 using the nozzle 28 to spray the material onto the blade and flight surfaces and then having the worker 30 smooth the coating 15 with the hand tool 32.

The settable material is applied over the major surfaces of the flight 12 and also over the round bar 22 at the end of the flight 12 where it forms the bull nose 20 at the free end of the flight 12. This bull nose 20 is important to provide a layer of the settable materia! over the free end of the flight 12 to protect this from abrasion wear as well. In another form of the invention shown in Fig. 3 the settable material is applied as a thick paste that issues from a pipe head. The paste has a much higher viscosity than the slurry that is pumped out of the nozzle at high velocity. The paste form of the material is spread across the internal surface as it issues from the head by the work man.

As shown in Fig. 3 the workman 30 smoothes off the paste material -with a trowel 32 to form a coating 15 with the requisite finish across the full internal surface 10. Applicant believes that the application technique shown in Fig. 9 might be easier to use in a production environment. However the invention can be equally implemented with the application technique shown in Fig. 3.

A mixer assembly in accordance with the invention is formed by the drum shown in Figs. 2 to 7 in combination with the other structural features of a mixer. These include a support, e.g. in the form of a support frame, on which the drum is mounted and also a drive means for driving the drum to rotate. While a full mixer assembly in accordance with the invention has not been illustrated its structure and function would be readily be discernible by a skilled addressee equipped with the information provided in this specification.

A mixer truck in accordance with this invention is equipped with the drum shown in Figs. 2 to 7. While an overall mixer truck in accordance with the invention has not been specifically illustrated in the specification the drum 1 is mounted onto the mixer truck in the same way and operates in the same way as prior art drums on mixer trucks subject of course to the key structural differences conferred by the coating of the invention described above. Consequently the mixer truck does not look unlike the mixer truck shown in Fig. 1 from the outside to a casual observer.

In use the drum body 2 of the mixer truck is charged with a dry mix of material and a separate volume of water and the mix is mixed during travel of the truck to the pour site. The dry cementitious material is charged into the drum 1 through the opening or port 8 defined therein as is the separate volume of water. The drum body 2 rotates during this time and the blades and flights 11, 12 lift the cementitious material and this causes it to mix. The flights 12 also displace the cementitious material in a longitudinally direction towards the closed end of the body 2 to promote some displacement of the material in a longitudinal direction as well as the lifting and falling displacement. The aggregate within the cementitious material rubs against the coating 15 on the drum body 2 as the drum 1 turns. This particularly occurs before the water is added and only dry aggregates are being mixed within the drum body 2. However the coating described above with the ceramic prills that extends across the internal surface of the drum body is very hard and resists abrasive wear. Therefore even though the materials have high levels of abrasive wear they do not excessively wear away the coating 15.

Broadly there are two types of mixer trucks for cementitious materials in the world. One type receives a dry aggregate of cementitious material in the drum and then a separate amount of water is added. The cementitious material is only mixed in with the water within the drum body to form the settable cementitious material. Typically this occurs while the mixer truck is being driven from the supply site to the pour site. Thus this type of mixer truck can fairly be said to mix the material during transport. The mixing does not take place in a mixing plant prior to it being loaded onto the truck. These types of mixer trucks are widely used in Australia. One characteristic of these trucks is that the mixing of dry aggregates in the drum prior to the introduction of water exposes the internal surface of the drum to very high levels of wear.

The other type of mixer truck receives a wet mix of cementitious material from the supply site. That is, the cement and water are mixed with each other in a batch plant prior to the material being charged into the drum body. Thus this type of mixer truck further mixes the cementitious material while it is being transported to the pour site. These types of mixer trucks where the material is wet when it is charged into the drum are subjected to lower levels of abrasive wear than the first type above where a dry mix is charged into the drum. These second types of mixer trucks are widely used in the USA.

In some applications the drum may be used on a mixer truck for the construction industry.

In this application the aggregate is fairly consistently sized and is not overly harsh on the lining.

However the drum of the invention also has potential application in the mining industry.

Specifically it has great potential for application on mixers in mines and in particular underground mines. For example mixers are used in mining environments to mix up shot- crete and fibre-crete for lining the walls of mine tunnels. The mixers are also used at mines to mix mine fill which is waste or gangue material with modest amounts of cementitious material which is then poured down disused shafts and holes to fill them up. Very often the aggregates used in mine fill are very harsh materials with widely differing sizes and are very harsh on the internal surface of the drum in which they are mixed.

In these mining applications with extremely harsh abrasive wear the coating applied to the internal surface has prills with a larger nominal diameter in the lining than those used in mixers for building industry applications, For example the coating could have prills having a nominal diameter of 2.5 mm to 3.0 mm.

Applicant has established that a coating with prills of this size has a greater abrasive wear resistance than the coatings described above with prills of lesser diameter.

Further very often the mines are based in remote locations far away from urban centers. As such mine operators do recognize that the mine equipment should have as long a service life as possible and should be built to require as little ongoing maintenance as possible. Applicant believes that these reasons may cause this invention to find particular application in mining applications in addition to the construction industry which has traditionally been the main market for the Applicant.

An advantage of the drum 1 described above with reference to the drawings is that the lining 15 significantly reduces the rate of wear of the internal surface of the drum body 2. This therefore increases the service life of the drum body 2 before it starts failing and therefore reduces maintenance costs and service downtime during the life of the mixer truck.

Another advantage of the drum 1 described above is that it can be used to coat the blade and flight 11, 12 within the drum 1 as well as the internal surface of the drum body 2. This is useful because it confers an increased abrasion resistance on these components which are also exposed to high levels of abrasive wear. If the lining 15 could not be applied to the flights and blades 11 , 12 then these components would have to be replaced at regular intervals and this would lead to service down time and expense even though the drum body 2 was not wearing excessively.

Another advantage of the drum 1 described above with the lining 15 on the internal surface is that when the lining 15 does eventually wear out the internal surface can have a fresh and new. lining applied thereto and then be used again. The drum 1 does not need to be thrown away. This has the potential to generate further significant savings through the use of this drum 1.

Another advantage of the drum 1 described above is that different regions 5, 6, 7 on the interior surface of the drum 1 can be coated with linings having different levels of abrasion resistance to correspond to the severity of the abrasion that it is exposed to in that particular region. Thus high wear regions of the drum 1 such as the blades and flights 11 ,

12 and sections of the drum body, e.g. the closed end section and the middle section, can be lined with a material having a larger prill size conferring greater abrasion resistance in that particular region.

A further advantage of the drum 1 described above with reference to the drawings is that the characteristics and properties, of the drum 1 can be varied to suit the application to which it is, being put. For example if the aggregate material to be mixed within the drum is very harsh then a lining with larger prills can be used in the coating. This then provides a lining with a superior abrasion resistance when compared with a lining with smaller prills. For example in mixer trucks where dry aggregate is added to the truck and then water is added separately at a later stage the abrasive wear is very high. This drum with its superior abrasion wear resistance is therefore potentially very useful in these applications. For example where mixer trucks are used in mining applications to mix mine fill, an aggregate of hard rock having high abrasive wear properties is mixed in the drum 1. By appropriate engineering of the coating the drum 1 described above with its superior abrasion wear resistance is potentially very useful in these applications to cater for this harsh environment.

Another advantage of the drum 1 described above with reference to the drawings is that the steel wall of the drum body on which the lining is applied can have a significantly thinner gauge thickness than a drum 1 with out the lining 15. For example a prior art drum body may have a cylindrical wall gauge thickness of 5 mm to 8 mm. The drum body described in this application can have a cylindrical wall gauge thickness of 2 mm to 4 mm in the same middle cylindrical section. The reduced thickness translates into a weight saving in the mixer truck. This then enables the mixer truck to carry a correspondingly higher pay load each time the truck carries a load of cementitious material to a pour site.

Another advantage of the drum 1 with lining 15 described above is that the lining 15 can be applied fairly easily to the interior surface of the drum body 2 by a workman. For example the material from which the lining 15 is formed can be mixed up in batch form on site and then pumped as a slurry through a pipe to a nozzle in the interior space of the drum 1. The nozzle can then be directed by a workman standing within the barrel onto the interior surface as a spray. The coating of material 15 on the interior surface can then be smoothed off by the workman using a hand tool such as a trowel before it sets and hardens to form the lining. Applicant believes that the material will be able to be applied to the interior surface fairly easily and cost effectively in a production environment.

Further the material that is applied to the wall is easy to handle and store and can be easily mixed up on the manufacture site in batch form. Further it can easily be pumped into the interior of the drum body 2. Yet further the material has a fairly rapid cure time and thus the coating process will not be unduly lengthy.

It will of course be realized that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

Claims

CUIMS:

I . A drum for a mixer assembly, comprising: a drum body having a wall forming an internal surface and defining an interior space within which a material to be mixed is received; and a coating that is applied to at least part of the internal surface of the drum body, the coating comprising ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the internal surface of the drum body.

2. A drum as claimed in claim 1 , in which the drum body is adapted for rotatable mounting on a support.

3. A drum as claimed in claim 1, in which the coating is applied to substantially the full internal surface of the drum body.

4. A drum as claimed in claim 1 , in which the ceramic particles comprise particles that have substantially the same basic shape.

5. A drum as claimed in claim 1 , in which the particles have a regular shape.

6. A drum as claimed in claim 1 , in which the particles are generally spherically shaped.

7. A drum as claimed in claim 1, in which the particles have substantially the same size.

8. A drum as claimed in claim 1, in which the particles are artificially manufactured.

9. A drum as claimed in claim 1 , in which the coating of the internal surface comprises more than one region, and each region has particles which have substantially the same nominal diameter unique to that region.

10. A drum as claimed in claim 1 , in which the particles have a nominal size of between 0.4 mm and 3.0.

I I . A drum as claimed in claim 1 , in which the ceramic particles is made from alumina.

12. A drum as claimed in claim 1, in which the ceramic particles have a Rockwell hardness that is greater than 90.

13. A drum as claimed in claim 1, in which the ceramic particles are arranged side by side in the coating.

14. A drum as claimed in claim 1, in which the ceramic particles is arranged to have at least two layers of ceramic particles in its direction of depth or thickness.

15. A drum as claimed in claim 1 , in which the ceramic particles are hexagonally stacked in the coating.

16. A drum as claimed in claim 1, in which the support material is a polymeric material.

17. A drum as claimed in claim 1 , in which the support material is elastomeric.

18. A drum as claimed in claim 1 , in which the. support material has elasticity to permit expansion and retraction of the coating as the drum expand, retract, and flex.

19. A drum as claimed in claim 1, in which the support material has an adhesive tensile strength of at least 13700 kPa.

20. A drum as claimed in claim 1 , in which the drum is formed from a metal alloy material.

21. A drum as claimed in claim 1 , in which the wall of the drum has a thickness of between 2 mm and 5 mm.

22. A drum as claimed in claim 1 , in which the drum is a drum for a concrete mixer truck for mixing or agitating settable cementitious material while it is being transported.

23. A drum as claimed in claim 1 , in which the drum body has a generally cylindrical central body section and one frusto-conical section towards the closed end of the drum and a further frusto-conical section towards a discharge end.

24. A drum as claimed in claim 1 , in which the drum includes a helical mixing fin attached to the inside surface of the drum and projecting into the drum interior, the coating being applied to a surfaces of the helical mixing fin as well as the internal surface of the drum.

25. A drum as claimed in claim 24, in which the mixing fin includes a blade portion having a base attached to the inside surface of the drum and projecting into the drum interior, the mixing fin further including a flight diagonally disposed on the radial inward end of the blade, the flight being coated with the coating. ^•

26. A drum as claimed in claim 1 , in which the coating is formed form a material that is manufactured and sold by IMATECH PTY LTD of Unit 7, 6 Gladstone Road, Castle Hill, 2154, in the State of New South Wales, Australia, which material is sold under the trademark selected from the group of trademarks comprising: REDSKIN -97™, REDSKIN -85™, REDSKIN -55™, REDSKIN A97™, and BXSR™.

27. A mixer assembly, comprising: a support; and a drum as claimed in claim 1.

28. A mixer assembly as claimed in claim 27,' which includes a drum as claimed in any one of claims 2 to 26.

29. A mixer truck, comprising: a chassis, a drum support mounted on the chassis; and a drum as claimed in claim 1.

29. A mixer truck as claimed in claim 29, which includes the drum as claimed in any one of claims 2 to 26.

30. A mixer truck as claimed in claim 29, in which the mixer truck is of the type that is used for mixing settable cementitious materials and for transporting these materials from a supply site to a pour site.

31. A method of manufacturing a drum having a drum body with an internal surface for a mixer assembly, the method including the steps of: preparing an internal surface of a drum body for application of a coating; applying a coating material comprising ceramic particles and a settable support as a layer across the internal surface of the drum; and causing the settable support to set to bind the particles to each other and to the internal surface to foam a coating on the drum body.

32. A method as claimed in claim 31 , which includes the prior step of fabricating the drum body prior to preparing the internal surface of the drum body for coating.

33. A method as claimed in claim 32, in which the drum body is fabricated from a plurality of discrete sections of steel plate that are welded together.

34. A method as claimed in claim 31 , which include mounting a helical mixing fin inside the drum, the helical mixing fin comprising a blade portion and a flight portion mounted on a radial inner edge of the blade, an surface of the mixing fin forming part of the interior surface of the drum.

35. A method as claimed in claim 31 , in which preparing the internal surface of the drum comprises roughening the internal surface of the drum prior to application of the coating.

36. A method as claimed in claim 35, in which the internal surface is roughened by blasting it with a particulate material.

37. A method as claimed in claim 35, in which the internal surface is roughen to a surface finish of at least class 2.

38. A method as claimed in claim 35, which includes applying an oxidation retardant to the surface after it has been blasted and before the coating is applied to the surface.

39. A method as claimed in claim 31 , in which applying the material to the prepared internal surface includes spraying the material onto the surface in the form of a flowing slurry through a nozzle.

40. A method as claimed in claim 39, in which applying the material to the prepared internal surface includes trowelling the coating onto the surface by means of a hand tool.

41. A mixer member for a mixer assembly having a mixer drum defining an interior in which the mixer member is mountable, comprising: a flattened body having two major surfaces opposed to each other and defining a peripheral edge; a coating applied to at least part of the major surfaces of the flattened body, the coating comprising ceramic particles and a support material that bonds the particles into the coating and bonds the coating to the surfaces of the flattened body.

42. A mixer member a claimed in claim 41 , in which the coating is applied substantially fully across the major surfaces of the body and the coating is also applied over and around those parts of the peripheral edge of the body.

43. A mixer member as claimed in claim 41, in which the body has base at one end for mounting to the mixer drum and an opposed end that is free.

44. A mixer member as claimed in claim 41, in which the base includes a flange for mounting to the mixer drum.

45. A mixer member as claimed in claim 44, in which the peripheral edge of the body at said opposed end define a rounded peripheral edge.

46. A mixer member as claimed in claim 45, in which the rounded edge is formed by a bar having a thickness thicker than that of the flattened body and mounted along the edge at said opposed end and a said coating over said bar.

47. A mixer member as claimed in claim 46, in which the thickness of the coating formed over the edge along said opposed end is thicker than the coating applied over the major surfaces of the body.

48. A mixer member as claimed in claim 47, in which the thickness of the coating applied over the edge along said opposed end is between 5 mm and 8 mm and the thickness of the coating applied over the major surfaces is between 2 mm and 4 mm.

49. A mixer member as claimed in claim 48, in which the mixer member comprises a blade extending away from the base and a flight extending diagonally away from the blade to the opposed end which is free.

50. A method of making a mixer member for a mixer assembly having a mixer drum, the method comprising: providing a flattened body having two major surfaces opposed to each other and defining a peripheral edge, the body having a base at one end for mounting to the mixer drum and an opposed end that is free; positioning a bar mounted on the peripheral edge along said opposed end;

folding a sheet of mesh material over the bar such that it extends across part of a said major surface, around the bar, and then across part of the other major surface; and applying a material containing ceramic particles and a settable support material over the major surfaces and the opposed end of the peripheral edge including the bar and allowing it to set.

51. A method as claimed in claim 50, in which the ceramic particles are spherical and the settable support material is elastomeric.

52. A method as claimed in claim 51 , in which the base includes a flange at said one end for mounting to the mixer drum.

53. A method as claimed in claim 52, in which the thickness of the coating applied over the free edge is between 5 mm and 8 mm, and the thickness of the coating applied over the major surfaces is between 2 mm and 4 mm.