AU2002300967B2 - Improvements to Mill Roll Surface Coatings - Google Patents

Description

P/00/011 Regulation 3.2 COMMONWEALTH OF AUSTRALIA Patents Act 1990 COMPLETE SPECI/FCA TON FOR A STANDARD PATENT Name ofApplicant" Actual nventorfs): Address for Sev'ice: Invention Title: The Track Shop Ptv Ltd Timothy Stuart Falkenhagen AHEARN FOX Patent Trade Mark Attorneys GPO Box 1149 Brisbane Queensland 4001 =IMPROVEMENTS TO MILL ROLL SURFACE COATINGSO The following statement is a full description of this invention, including the best method of performing it known to us: "IMAPROVEMENTS TO MILL ROLLER SURFACE COATlINGS" g~FLQyNTON THIS INVENTION relates to mill rollers and abrasion resistant surface coatings for mill rollers, as well as methods of adapting mill rollers to receive abrasion resistant surface coatings and forming abrasion resistant surface coatings on mill rollers. The invention has particular application to sugar mill rollers and for illustrative purposes, reference will be made to such application. However, it is to be understood that the invention is not limited to this field of use.

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In the sugar industry, sugar cane is typically crushed between rollers arranged in pairs or in groups of three.

Generally, the rollers have a plurality of machined ridges extending circumferentially about the roller forming a surface of alternate ridges and valleys. The grooves are typically evenly spaced along the roller, however, it will be appreciated that in some applicatiols, it may be desirable to have unevenly spaced grooves. The grooved arrangement provides for gripping of the sugar cane fibre as it passes between the rollers, the grooves of an upper roller being operatively in register with the ridges of its opposing lower roller or rollers. Moreover, the grooved arrangement seems to have particular advantages in tworoller systems where the bagasse is fed vertically between two rollers counter-rotating about axes which are substantially level with one another.

One method of hardf acing a sugar mill roller was sometimes used in Brazil in which a layer of weld was wrapped around the ridge profile by removing the roller from its normal mounting, inclining the roller up to close to vertical for a layer of chromium carbide alloy weld to be applied to one side of the -2ridge by laying beads of weld side-by-side one another circumferentially about the roller, successive beads in the layer of weld being adjacent one another in the radial direction outwards from the axis, and then inclining the roller with the lower end up to repeat the process for the other side of each ridge. Finally, a series of "dots" of weld were added to the tips of the ridges with the roller in the horizontal attitude.

In this method, weld was "sputtered" or "sprayed" on to the side of the ridge. Although the authors of the technique referred to the beads of weld as "layers", the present inventor believes that the technique involved a series of passes of weld to build up a single layer of weld. A modified version of this technique was used in Australia in which the mill roller was left in the normal horizontal attitude, and successive passes of chromium carbide alloy was applied in a sputtering process.

One of the problems of the traditional process and the hardfacing resulting therefrom was that chromium carbide wore smooth after a few days, weeks or months, depending on the duty demanded of the rollers. The rollers were "re-roughened" by a re-application of the chromium carbide hardfacing. However, this caused problems in itself due to arcing across the bearings of the roller, and significant fume problems.

In our co-pending Australian Patent Application No.

58482/98, the specification of which is incorporated herein by reference, an abrasion resistant surface coating and method of forming same are disclosed in which a sugar mill roller is provided with an abrasion resistant surface coating. The sugar mill roller has a substantially cylindrical roller body having a plurality of circumferentially running, substantially parallel, machined ridges spaced along a substantial part of the roller body, is provided such that each machined ridge has one or more land portions. The abrasion resistant surface coating is in the form of ridge capping including a plurality of layers of composite weld comprising a weld matrix supporting therein a wear resistant material on each ridge. The ridge is pre-machined to provide the one or more land portions upon which the ridge capping is supported. Even though the abrasion resistant surface coating was vastly superior to the traditional hardfacing, the typical ridge capping does not cover the entire profile of the machined ridge, and in such form, the abrasion resistant surface coating may, in some environments, be prone to undercutting beneath the ridge capping due to a range of possible mechanisms including corrosion, erosion, wear, or a combination of these effects, referred to herein as "attrition".

The present invention aims to provide a mill roller having a wear resistant surface coating and method of forming same which alleviate one or more of the above disadvantages of the prior art. Other aims and advantages of the invention may become apparent from the following description.

DISCLOSURE OF THE INVENTION With the foregoing in view, this invention in one aspect resides broadly in a sugar mill roller including: a roller body of substantially circular cross-section having a plurality of circumferentially running machined ridges formed to be substantially parallel and spaced along a substantial part of said roller body, each said machined ridge including a plurality of land portions, and a ridge capping on said one or more land portions, each said ridge capping including an attrition resistant portion comprising one or more layers of attrition resistant weld supported by one or more of said land portions, and

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an abrasion resistant portion including a plurality of layers of composite weld comprising a weld matrix supporting therein a wear resistant material supported by the one or more layers of attrition resistant weld and/or the remainder of said land portions.

suitably, the lowermost layer or layers of the attrition resistant portion are supported by one or more of the lowermost land portions, and the lower most layer or layers of the abrasion resistant portion are supported on the uppermost layer or layers of the attrition resistant portion. Preferably, each machined ridge includes two or a multiple of two land portions, separated by a wall portion and one or more of the layers of weld are supported on respective ones of the land portions against the wall portion. It is also preferred that the roller body be formed of grey cast iron, and the attrition resistant portion be formed of stainless steel weld. In such form, it is preferred that the stainless steel be 309 or 309L stainless steel.

In our earlier abovementioned patent application No.

58482/98, a "butter layer" of stainless steel was disclosed for facilitating the placement of the abrasion resistant weld material onto cast iron. However, none or very little of the butter layer being exposed, the butter layer did not provide an attrition function.

In another aspect, this invention resides broadly in a method of applying hardfacing to a sugar mill roller, including: providing a roller body of substantially circular crosssection having a plurality of circumferentially running ridges on said roller body, said ridges being substantially parallel and axially spaced along a substantial part of said roller body; machining a plurality of land portions onto or into each of at least some of said ridges to provide a plurality of machined ridges; applying a plurality of layers of weld comprising attrition resistant material on one or more of the innermost land portion or land portions of each said machined ridge by successively applying weld on the previous layer; applying a plurality of layers of an abrasion resistant material including a composite weld comprising a weld matrix having particulate wear resistant material supported therein to the outermost layer or layers of the attrition resistant material and to the remainder of said land portions until a ridge capping of desired profile is formed substantially all the way round said roller body.

Preferably, a wall portion is machined on each ridge so as to provide one or more land portions on each side of the wall portion, and weld is applied against each side of the wall portion in successive layers until the height of the wall portion is substantially reached. One or more further layers of weld are preferably applied to each respective ridge to substantially encapsulate the wall portion.

The weld may be applied by any suitable welding process, however metal inert gas (mig) welding or tungsten inert gas (tig) welding is preferred. The weld pool first applied to the or each said land portion on each side of the wall portion is formed from a stainless steel welding rod without any wear resistant material added thereto to provide the attrition resistant portion of the ridge capping as hereinbefore described, and successive layers are formed from a mild steel welding rod, with a particulate wear resistant material being impinged into respective successive weld

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-6pools to form the abrasion resistant portion as hereinbefore described.

The layers are laid up until the ridge capping is formed to a desired ridge profile substantially all the way round each ridge, that is, circumferentially around the roller body. The weld is applied to the uppermost point of the roller as it is rotated so that the land portion or previous layer of weld is substantially horizontal whilst the weld pool is in the molten state, but the welding parameters are selected such that the weld pool has sufficiently solidified as weld laid down moves to an oblique angle as the roller is rotated.

In another aspect, this invention resides broadly in a sugar mill roller including a roller body formed in accordance with the method as hereinbefore described.

In sugar milling applications, the ridge profile is selected to be similar in size and shape of cross-section to the ridge profile of cast sugar mill rollers, that is generally between mm and 80 mm pitch, but more commonly, either 25 mm, 37.5 mm or mm pitch.

Preferably, the ridge profile includes an elongate projection and one or more land areas on each side of the elongate projection such that successive layers of weld may be applied sequentially, allowing sufficient time between the respective layers for cooling of the weld. suitably, the first layer of weld on each side of the projection is applied to the respective land areas closest to and along the base of the projection. The elongate projection is of a suitable thickness to perform as a dam preventing the weld applied on one side of the projection from falling onto the land area or land areas on the other side of the projection. The land area is necessarily elongate in form around the circumference of the roller, and is of a width sufficient to support one or more beads of weld to form a layer. The weld layers are applied in such manner as to produce a ridge profile which, when solidified, is of substantially triangular cross-section.

The combination of welding torch angle, machined ridge profile, rotational speed of the roller (weld surface speed), raw materials, preheat specific welding consumables and selected welding procedure provides the finished ridge profile for a sugar mill roller to be used in an as-welded condition. This is advantageously done whilst the roller is rotated with its longitudinal axis in the horizontal plane. Each said layer of weld is a stratum of weld material consisting of one or more weld beads laid side-by-side. It will be appreciated that the plane of the stratum is not flat, as in most circumstances where weld is deposited in "layers". In the present invention, the plane of the stratum may be interpreted as a stratum parallel to the horizontal plane parallel to both the longitudinal axis of the roller and the tangent of the uppermost point of the roller radius as the weld is being laid down.

Considered in the static sense, the stratum may be considered as a stratum which wraps around the surface which has been coated, so that it lies in a curved plane which at all points remains substantially parallel to the surface which has been coated. Accordingly, the layers may be defined either by their height above the surface being coated or the thickness perpendicular to the original machined surface at any given point. In the present invention, the layers or weld are added on top of a respective land and/or a previously laid down layer of weld. Advantageously, the layering technique of the present invention permits the ridge profile to be built up unidirectionally onto the lands of the machined ridge profile in a similar fashion to our abovementioned patent application. If the layers are made up of more than one bead of weld, then the lands may be machined to be wider to accommodate the extra lateral width of the layer.

Preferably, the abrasion resistant hardfacing is formed by using ARM-2 weld as manufactured and supplied by Abrasion Resistant Materials Pty Ltd, at a suitable current, typically 200 to 260 amps, and a suitable potential, typically 22 to 26 volts in a mig atmosphere at a linear rate sufficient to coat the required net area required for the weld. This wire conforms to BS2901 Part 1 1970A18 and AWS A5.18 E70S-6. The grit may be added into the molten weld pool during the welding process, by any suitable means, and is preferably to mesh size 12/35.

BRIEF DESCRIPTION OF THE DRAWINGS In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:- Fig. 1 is a diagrammatic sectional view showing the ridge profile of a single ridge having abrasion resistant material applied thereto to form a ridge capping according to the invention; and Fig. 2 is a diagrammatic sectional view showing the ridge profile of a single ridge of a sugar mill roller which has abrasion resistant material applied thereto to form a ridge capping according to the prior art, and which has been partly eroded or corroded under the ridge capping.

DETAILED DESCRIPTION OF THE DRAWINGS The ridge profile 10 is formed onto the ridge 20 of a sugar mill roller by forming the ridge capping 21 from a plurality of layers of weld, each layer comprising a single bead of weld applied to the lands machined onto or into the ridge. There are seven pairs of lands, being two lowermost lands 11, two second lands 12, two third lands 13, two fourth lands 14, two fifth lands 15, two sixth lands 16, two seventh lands 17, and a top flat 18 which may be considered to be a land. The lands form a machined ridge 22, the lands and flat being separated radially from one another in a stepped fashion by seven wall faces 31 to 37, the reference numerals corresponding to the respective lands 11 to 27. The wall faces are provided in outward facing pairs corresponding to risers of the stepped profile of the machined ridge with the lands corresponding to the treads of the steps.

The beads of weld forming the layers forming the ridge capping are allocated letters A through Z, AA, AB and AC. The sequence of adding the layers to the stepped profile generally is in pairs, such that the layers A and C are followed by B and D, then E and G, followed by F and H, I and K, L and J, M and O, N and P, all being of stainless steel 309 or 309L, the carbon content of the stainless steel being relatively unimportant.

Then layers Q and S are followed by R and T, U and W, V and X, Y and AA, Z and AB, and finally layer AC is added to the top of the weld profile. The layers Q through AC are mild steel with tungsten carbide grits added to the molten weld pool to solidify as a composite hardfacing abrasion resistant material comprising a wear resistant material supported in a mild steel matrix.

Although the machined ridge profile is shown as having a distinct interface between the material of the roller and the material of the beads or layers of weld, it will be appreciated that an indistinct interface develops as the molten weld is applied to the lands. Indeed, it is believed that the radiused edge between the wall faces and the lands above them undergoes a higher degree of fusion than the remainder of the substrate.

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Experience has shown that the lands retain sufficient structure for subsequent layers of weld to be applied, and the wall faces provide sufficient heat transfer away from the weld pool to prevent the wear resistant material added to the previous layer from dissolving in the layer being deposited. The stainless steel layers provide a smooth surface finish, as opposed to the rough, grippy surface of the composite hardfacing.

The ridge capping according to the prior art 40 shown in Fig. 2 has an undercut 42 beneath its lower edge. The undercut is where the material of the ridge substrate 43 has been eroded and/or corroded away due to the high pressure and velocity impingement of sugar cane juices as it is forced out of the mat of cane fibres under the high compressive forces generated in the nip between counter-rotating adjacent rollers. It is believed that this undercut is a by-product of the improvements in abrasion resistant surface coatings applied to sugar mill rollers according to the invention described with reference to our earlier patent application No. 58482/98. In the case of traditional chromium carbide hardfacing as applied to sugar mill rollers before our abovementioned invention, it is believed that this phenomenon was not manifested because the ridge profile wore away before the effect of such erosion and/or corrosion could take place.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to an example of the invention having the welding process specifications as follows: A sugar mill roller was provided having a plurality of circumferentially running substantially parallel ridges about its outer cylindrical surface, and was rotatable about a substantially horizontal axis. The machined ridge profile was -11cut into a triangular ridge to conform substantially to that shown in Fig. 1.

The rotating surface speed of roller to apply weld layers was in the range of from 21.7 mm to 22.3 mm per second for the stainless steel layers A through P and the hardfacing layers Q through AB, the weld beads in each layer being laid on the previous layer and/or the next available land. The rotating surface speed of roller to apply final capping weld layer AC onto the top of layers AA and AB was 19.35 mm to 20.02 mm per second.

The welding torch angle was 18 from the vertical when applied to the uppermost (that is, horizontal) perimeter of the roller, the angle in each case being towards the central axis of the ridge, being reversed one way or the other for each side of the ridge. The angle can be varied up to 25 to weld the bottom layers in pre-machined ridge profile as shown in and described with reference to Fig. 1.

The current used for the welding was in a range of from 200 A to 300 A and the voltage from 22 V to 26 V, using ARM 1 and 2 wires provided by Abrasion Resistant Material Pty Ltd. These wires are 0.9 mm wires which conform to BS2901 Part 1 1970A18 and AWS A5.18 E70S-6. The preheat temperature of the grey cast iron rollers was 100 0 C 5 0 C prior to welding. ARM 1 wire is mild steel and ARM 2 wire is 309L stainless steel. The first eight layers were welded using ARM -2 wire, and then ARM -1 wire with ARM STD 1 tungsten carbide grit was immediately welded onto the uppermost or outermost stainless steel layer weld beads 0 and P.

As in the case of the use of butter layers for laying of mild steel weld onto cast iron rollers, it is believed that dilution of the last layers of stainless steel by the initial layer of mild steel creates a unique matrix and weld metallurgy to affect the weld bead shape and cooling characteristics as well as the solidification (as opposed to melting) of the tungsten carbide -12in the weld pool. This is believed to produce a superior bond to grey cast iron and in particular reduces the problem of longitudinal underbead cracking in the heat affected zone.

However, the main purpose of the stainless steel is not to be a butter layer, but to perform an attrition resistant function as hereinbefore described.

The technique described above for one ridge capping was repeated for each machined ridge profile.

The embodiments described are for the purposes of illustration of one or more examples of the invention and it will be understood that any such modifications as would be apparent to persons skilled in the art are encompassed within the broad scope and ambit of the invention as defined by the following claims.

Claims (11)

1. A sugar mill roller including: a roller body of substantially circular cross-section having a plurality of circumferentially running machined ridges formed to be substantially parallel and spaced along a substantial part of said roller body, each said machined ridge including a plurality of land portions, and a ridge capping on said one or more land portions, each said ridge capping including an attrition resistant portion comprising one or more layers of attrition resistant weld supported by one or more of said land portions, and an abrasion resistant portion including a plurality of layers of composite weld comprising a weld matrix supporting therein a wear resistant material supported by the one or more layers of attrition resistant weld and/or the remainder of said land portions.

2. A sugar mill roller according to claim 1, wherein each machined ridge includes two or a multiple of two land portions, separated by a wall portion and one or more of the layers of weld are supported on respective ones of the land portions against the wall portion.

3. A sugar mill roller according to Claim 1 or Claim 2, wherein the roller body is formed of grey cast iron, and the attrition resistant portion be formed of stainless steel weld.

4. A sugar mill roller according to Claim 3, wherein the stainless steel is 309 or 309L stainless steel.

A method of applying hardfacing to a sugar mill roller, including: -14- providing a roller body of substantially circular cross- section having a plurality of circumferentially running ridges on said roller body, said ridges being substantially parallel and axially spaced along a substantial part of said roller body; machining a plurality of land portions onto or into each of at least some of said ridges to provide a plurality of machined ridges; applying a plurality of layers of weld comprising attrition resistant material on one or more of the innermost land portion or land portions of each said machined ridge by successively applying weld on the previous layer; applying a plurality of layers of an abrasion resistant material including a composite weld comprising a weld matrix having particulate wear resistant material supported therein to the outermost layer or layers of the attrition resistant material and to the remainder of said land portions until a ridge capping of desired profile is formed substantially all the way round said roller body.

6. A method according to Claim 5, wherein a wall portion is machined on each ridge so as to provide one or more land portions on each side of the wall portion, and weld is applied against each side of the wall portion in successive layers until the height of the wall portion is substantially reached.

7. A method according to Claim 6, wherein one or more further layers of weld are applied to each respective ridge to substantially encapsulate the wall portion.

8. A method according to any one of Claims 5 to 7, wherein the weld pool first applied to the or each said land portion on each side of the wall portion is formed from a stainless steel welding rod without any wear resistant material added thereto to provide an attrition resistant portion of the ridge capping, and successive layers are formed from a mild steel welding rod, with a particulate wear resistant material being impinged into respective successive weld pools to form an abrasion resistant portion.

9. A method according to Claim 8, wherein the layers are laid up until the ridge capping is formed to a desired ridge profile substantially all the way along each ridge circumferentially around the roller body.

A method according to any one of Claims 5 to 9, wherein the io welding parameters are selected such that the weld pool has sufficiently solidified as weld laid down moves to an oblique angle as the roller is rotated.

11. A sugar mill roller including a roller body formed in accordance with the method as hereinbefore described. Dated this i th day of September, 2002 THE TRACK SHOP PTY LTD By its Patent Attorneys AHEARN FOX