AU2009100047A4

AU2009100047A4 - Shredder hammer tip

Info

Publication number: AU2009100047A4
Application number: AU2009100047A
Authority: AU
Inventors: John Camuglia
Original assignee: Bradken Resources Pty Ltd
Current assignee: Bradken Resources Pty Ltd
Priority date: 2002-11-28
Filing date: 2009-01-20
Publication date: 2009-02-19
Anticipated expiration: 2011-11-06
Also published as: AU2003261479B2; AU2003261479A1; AU2002952971A0

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant(s): BRADKEN RESOURCES PTY LIMITED Invention Title: SHREDDER HAMMER TIP The following statement is a full description of this invention, including the best method for performing it known to me/us: -2- Field of the Invention THIS INVENTION relates to a shredder hammer tip, and to a method of manufacturing the tip and to a shredder hammer provided with at least one of the tips.

While the shredder hammer is particularly suitable for the comminution of sugar cane billets, the hammer may be used for the comminution/fracturing/shredding of other materials.

Prior Art The Australian raw sugar industry delivers billet cane to the factory for comminution prior to milling. The incoming material includes a percentage of trash (including soil) and other foreign debris such as steel components picked up by the harvester. The sugar industry employs heavy-duty swing hammer shredders to comminute the billet cane at the factory. Billets, trash and other foreign debris are fed into a vertical chute and generally fall under gravity into the shredder. The incoming material is struck by shredder hammers, which are pinned at the eye region. The cane is then further comminuted as it is dragged past a fixed grid-bar. A typical prior art shredder hammer is illustrated in FIG. 1.

A hammer is defined as a composite assembly consisting of an eye region, shank, long-life tip and tip holding mechanism.

High levels of comminution are crucial to good extraction performance during subsequent crushing. This is achieved by impacting the cane against heavy hammers (typically 20 kg), which are subjected to centripetal body forces with a tip speed of near 100 m/s. The hammers are sufficiently massive to resist any local rotation due to impact with incoming material. The level of -3comminution is influenced by several parameters but two important parameters are hammer tip speed and rake angle the local cutting angle between in-coming material and the top surface of the tip). The rake angle is dictated by the centre of gravity (CG) of the hammer assembly. For good shredding performance, the CG must be defined to ensure a positive rake angle. Some tip suppliers have introduced butterfly tips with the view of improving the cutting angle. These tips have been placed on conventional hammers and the CG of the assembly has not been taken into account. The resulting rake angle has been negative.

The shredder tip is designed to offer a hardwearing surface, which resists wear from particles of dirt trapped in the cane supply and some resistance to other debris such as pieces of steel. There are several categories of tips but most could be defined as consisting of a hard wearing surface atop a mild steel backing block. The "white iron" tip white-iron is vacuum brazed to mild steel) offers minimal wear resistance to dirt but offers excellent resistance to steel items and does not fracture). A "tungsten carbide" (WC) tip typically consists of nominally rectangular blocks of WC brazed (via a tri-ply system) to either white-iron, as an intermediate layer, or directly onto the mild steel backing block. A WC tip offers good resistance to dirt, but poor resistance to steel impact the tip can fracture under transient impact loads). Increasing the hardness of the WC reduces tip wear. Unfortunately, increasing hardness generally reduces the fracture toughness and makes materials more brittle.

SUMMARY OF THE PRESENT INVENTION The present invention relates to a shredder hammer tip with the geometry of a tungsten-carbide (WC) tip directed to providing resistance to wear due to dirt, and damage due to impact with steel (or other debris).

In one aspect the invention provides A shredder hammer tip including: a mild steel base having mounting means to mount the tip on a shredder hammer; and at least one tile fixed to the base, the or, each tile having a body comprising tungsten-carbide, a front face operable to engage material to be shredded (or otherwise treated) and a top wall of smooth convex profile, in side view, interconnecting the front face with a rear face of reduced height, and wherein the mild steel base has a substantially planar upper face to mount each tile, and at least one spigot extending from its lower face to releasably mount the tip on the hammer.

Furthermore, embodiments are aimed at resisting damage due to compressive contact stresses.

With advantage embodiments can provide a tip where the centre of gravity of the hammer assembly has a positive rake angle, and may be designed to maximise the cross-sectional moment of inertia while minimising mass.

Embodiments may provide a tip which has bevelled edges to resist, or minimise, fracture from edge hits.

5 White iron laminate, preferably vacuum brazed to the upper lace of the mild steel base, may be interposed between the mild steel base and the tungsten-carbide tiles. Preferably, the white iron has a hardness of at least Rockwell C.

The tiles can be fixed to the upper surface of the mild steel base, or to the white iron, via a tri-ply foil. (Tri-ply is a composite foil consisting of a copper layer coated both sides with silver). When heated to 6500, the silver wets both surfaces (the base of the tungsten-carbide tiles) and the top of the mild steel or white iron) and following cooling to ambient conditions, acts on an elastoplastic io bonding interface.

The tungsten-carbide tiles can be manufactured from tungsten-carbide specified to have a hardness in the range 1200 to 1600 Vickers and a transverse rupture strength in the range 2600 to 3900 MPa.

In a second aspect, the present invention resides in a shredder hammer fitted with the tip hereinbefore described.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, reference will be made to the accompanying drawings, in which: FIG. 1 is a side view of a typical layout of a prior art hammer shredder; FIG. 2 is a perspective view of a shredder hammer fitted with a tip in accordance with a first embodiment of the present invention; FIG 3. is a perspective view of a tip in accordance with a second embodiment; FIG. 4 is a perspective view of the tip of FIG. 2 on a larger scale; and 6 FIGS. 5, 6 and 7, are respective front, rear and side elevational views of one of the tungsten-carbide tiles.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a typical (prior art) hammer shredder 100. The shredder 100 has a housing 101 with an inlet 102 and outlet 103.

A rotor 104, driven by a suitable motor (not shown) has a disc 105, on which are pivotally mounted 12) hammers 10, which co-operate with fixed grid bars 106 to shred the sugar cane billets as they pass from the inlet 102 to the outlet 103.

As shown in FIG. 2, each hammer 10, fitted with a tip in accordance with the present invention, has a shank 11 interconnecting an eye-region 12 and a head 13 on which is releasably mounted the tip 20. The eye-region 12 has a bore 14 to receive a pivot pin (not shown) to mount the hammer 10 on the disc 105 of the hammer shredder 100.

As shown in more detail in FIG. 4, the tip 20 has a mild steel base with a spigot 31 releasably engageable in a socket (not shown) in the head 13 of the hammer A white iron laminate 40 of 60 Rockwell C hardness) is vacuum brazed to the top of the mild steel base 30. (If the white iron laminate 40 is omitted, the thickness of the mild steel base 30 is increased to fill the gap.) Four tungsten-carbide tiles 60, to be hereinafter described in more detail, are fixed to the white iron laminate 40 (or mild steel base 30) via a tri-ply foil 50. The tri-ply foil 50 is a composite foil of a copper layer coated on both sides with silver; and when heated to 650°C, the silver wets the bases of the 7 tungsten-carbide tiles 60 and the white iron laminate 40 (or mild steel base and on cooling to ambient conditions, provides an elasto-plastic bonding interface therebetween.

In the embodiment of FIGS. 2 and 4, four tiles 60 have been shown on the tip 20, in back-to-back pairs. However, the number can vary from 1 2, 4, 6, etc.) depending on the intended application.

The tiles 60 are manufactured from tungsten-carbide specified to have a hardness in the range of 1200 to 1600 Vickers and a transverse receptive strength in the range of 2600 to 3900 MPa.

As shown in more detail in FIGS. 5 to 7, each tile 60 is substantially rectangular in plan view, with a front face 61, rear face 62, side faces 63 and 64 and bottom face 65, all of which are substantially planar.

The front face 61 is taller than the rear face 62, in the range of 110-140%, and the faces 61, 62 are connected by a top face 66 with a smooth convex profile. Preferably, the corners interconnecting the front/rear/side/bottom/top faces 61, 62, 63, 64, 65, 66 are bevelled with a bevel 67) to resist fracture from edge hits.

In a preferred example, the tip 20 will have the following dimensions: Length: L Height: H Depth: D The plan area of each tile 60 will be 0.5L x Preferably, the front face 61 of each tile has the approximate dimensions 0.27H x 0.5D; the rear face 61 has the approximate dimensions 0.21 H x 8 and the top face 66 has a convex radius of approximately 2.2H. (The actual dimensions can be varied to suit the particular intended application.) The front face 61, the face most likely to contract the cane billets and most likely to contact foreign debris, has maximum thickness to resist damage due to compressive contact stresses.

The top face 66 has the smooth convex profile to maximise the cross-sectional moment of inertia while minimising the mass of the tile The transition radius of the top face 66, connecting the front and rear faces 61, 62, forms an integral part of the preferred design to minimise fracture of the tile 60 due to bending-induced failure where cracks initiate from the bottom face 65 (near the centre) and propogate towards the top face 66; and cracks initiated from the top face 66 and propogated in a radial direction towards the outer faces 61-64.

When the front faces 61 of the leading pairs of tiles 60 have become worn, the tip 20 can be indexed through 1800 to bring the front faces 61 of the (formerly trailing) tiles 60 into operation.

In the embodiment of FIG. 3, the tip 120 has three tungsten-carbide tiles 160 mounted in a recess 141 in the white iron laminate 140, the latter mounted on a mild steel base 130 with a spigot 131 as hereinbefore described.

The shape/number/material of the tungsten-carbide tiles 60, 160 can be varied to suit the particular intended application.

A grade of tungsten-carbide should be chosen which has high tensile strength and high hardness. The tensile strength is important because it controls the onset of crack initiation at the base for a mid-side hit or at the top for a front-face hit. The high hardness is important to resist erosion due to dirt.

High fracture toughness can be of secondary importance provided the grade of tungsten-carbide has good reproducability minimal inherent flaws).

The shape of the tiles, and thereby the centre of mass of the tiles, ensures that the centre of gravity of the hammer assembly has a positive rake angle, to ensure high comminution of the incoming material. The centre of mass of each tile is closer to the front (impact) face than to the rear face.

Claims

1. A shredder hammer tip including: a mild steel base having mounting means to mount the tip on a shredder hammer; and at least one tile fixed to the base, the or, each tile having a body comprising tungsten-carbide, a front face operable to engage material to be shredded (or otherwise treated) and a top wall of smooth convex profile, in side view, interconnecting the front face 1o with a rear face of reduced height, and wherein the mild steel base has a substantially planar upper face to mount each tile, and at least one spigot extending from its lower face to releasably mount the tip on the hammer.

2. A tip as claimed in Claim 1 wherein: white iron laminate, vacuum brazed to the upper face of the mild steel base, is interposed between the mild steel base and the or each tile, the white iron having a hardness of at least 60 Rockwell C.

3. A tip as claimed in claim 1 or claim 2 wherein: the tiles are fixed to the upper surface of the mild steel base, or to the white iron laminate when provided on the base, via a tri-ply foil, being a composite foil consisting of a copper layer coated on both sides with silver.

4. A tip as claimed in any one of Claims 1 to 3 wherein: 11 the tiles comprise tungsten-carbide specified to have a hardness in the range 1200 to 1600 Vickers and a transverse rupture strength in the range 2600 to 3900 Mpa. A tip as claimed in any one of Claims 1 to 4 wherein: the tip has the following dimensions: Length: L, Height: H, Depth: D, and the plan area of each tile is substantially 0.51- x 0.5D, and the front face of each tile has the approximate dimensions 0.27H x 0.5D; the rear face has the approximate dimensions 0.21 H x 0.5D; and the top face has a convex radius of approximately 2.2H.