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Report: INV5552 - 1 Client: XXXXX Attention: XXXX Order No: 0001 Date: 10 August 2006

Briquette Roll Failures

EXECUTIVE SUMMARY

An examination of several fractured and intact briquette rolls was undertaken to determine the mode of failure of these components. Although the fractured rolls were heavily corroded, examination of the fracture faces suggested fatigue failures had occurred from the keyway in the bores, as well as from the corner of the side face and OD of the rolls. The material properties of 4 rolls were examined, and the structures were all found to be castings made to D2 tool steel composition (with higher silicon to aid castablility) that had been hardened to a range of 55-62 HRC. Manufacture of these rolls from castings is considered to be inferior to forged material due to the poor carbide network, which embrittles the structure, so it is suggested that they be manufactured from forgings. It is recommended that in future, the fracture faces of any broken rolls be preserved from the elements and submitted for further examination to more accurately identify the source of the fatigue cracking. Author JXXX Senior Consultant Reviewed XXX Principal Metallurgist Distribution: Client XXXXX

On behalf of: XXXX Report No.: INV5552-1 Date: 10 August, 2006

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1 INTRODUCTION At the request of Mr M. XXXX, an examination of fractured briquette rolls was undertaken. Two intact used rolls were provided as well as 5 five sections of fractured rolls for inspection. The rolls were used for briquette manufacture and had suffered fracture during service. It was not known how long the fractured rolls had been in service at the time of the failure. The fractured rolls were heavily corroded and appeared to have been stored in the outside weather since the time of failure. A number of manufacturing drawings were provided to assist with the examination, see typical roll in appendix A. Photographs were also provided showing recently fractured rolls in the mill. The purpose of the investigation was to determine the material properties of the rolls, and to identify the mode of failure. 2 OBSERVATIONS AND INVESTIGATIONS 2.1 Visual Inspection A general view of the briquette rolls supplied for examination is shown in figure 1. The five fractured sections were heavily corroded, so the fracture faces were cleaned with inhibited hydrochloric acid prior to examination. Assembly of the fractured sections showed there were three separate rolls, and these were identified as #1, #2, #3 for the purposes of this examination. The intact rolls were identified as #4 and #5.

• Roll #1 A view of the assembled roll is shown in figure 2a. This roll did not have pockets machined on the OD, and had fractured transversely through the keyways at the bore. A view of the fracture faces of the roll is shown in figure 2b. The fracture face to the LHS of the view suggested fracture had initiated from the keyway, as can be seen by the apparent beach marks. A closer view of both sides of this fracture face is shown in figure 3. The arrows in the views identify the arrests of the beach marks. Fatigue propagation had travelled about 80% across the fractured section.

• Roll #2 A view of the assembled roll is shown in figure 4a. This roll had no pockets machined on the OD. It had fractured transversely at three positions, although only two

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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sections were supplied. A view of the fracture faces of the roll is shown in figure 4b. The fracture face to the RHS of the view suggested fracture had initiated from the corner of the side face and OD of the roll, as can be seen by the apparent beach marks. A closer view of both sides of this fracture face is shown in figure 5. The arrows in the views identify the arrests of the beach marks. Fatigue propagation had covered about 30% of the fracture face. • Roll #3 A view of the sole section from this roll is shown in figure 6. This roll had pairs of pockets machined on the OD. It had fractured transversely, at one location through the keyway in the bore. There were no obvious features on the fracture faces that could indicate the fracture path. A view of the fracture faces of the roll is shown in figure 6. • Roll #4 This roll contained pairs of pockets, and was in good condition. • Roll #5 This roll contained 3 pockets across the face, and was very clean indicating it had seen minimal service.

The presence of fatigue cracking in the rolls suggests there has been flexing of the rolls during operation. The original photographs submitted also indicated there may be the presence of fretting damage in the bores, which would indicate there had been relative movement on the arbours. The interference of the rolls on the arbours should be checked during manufacture.

2.2 Magnetic Particle testing Each of the rolls was subjected to magnetic particle inspection around the bores, keyways and side faces. There were no cracks detected on the rolls. 2.3 Hardness Hardness testing was performed on the rolls using a portable Equotip hardness tester. The side face to be tested were prepared by fine grinding, and the following results were obtained after conversion to HRC:

Roll # 1 2 3 4 5 HRC (HLD) 56 to 59 60 to 62 62 57 to 58 55 to 57

On behalf of: XXXX Report No.: INV5552-1 Date: 10 August, 2006

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2.4 Chemical Composition Samples removed from the rolls #1 and #2 were analysed using an atomic emission spectrometer. The results are tabled below:

C Mn P S Si Ni Cr Mo V Al #1 1.23 0.79 0.032 0.026 1.28 0.13 12.0 1.60 0.03 0.068 #2 1.32 0.85 0.030 0.029 1.25 0.15 12.3 1.49 0.03 0.004

The compositions were essentially consistent with grade D2 tool Steel. The high silicon indicated the material had been manufactured by casting. 2.4 Metallographic Examination Samples were removed from the #1 and #2 fractured rolls for preparation and examination under the microscope. The intact rolls #4 and #5 were also subjected to preparation in situ, and were examined using a portable microscope. The prepared locations were etched in 2% nital and the microstructures examined. The microstructures, shown in figures 7 to 10, consisted of a network of carbides associated with the cast dendritic structure, in a matrix of tempered martensite. Some pearlite was detected, notably in the sample from the #1 roll, see figure 7. Pearlite in the structure indicates the heat treatment was not completely effective at transformation to martensite. The network of carbides confirmed that all the rolls had been manufactured from castings. The carbides are normally present as globular spheroids in forged D2 material. Dissolution of these carbides during heat treatment is difficult in castings, compared with forged material. 3 CONCLUSIONS An examination of several fractured and intact briquette rolls was undertaken to determine the mode of failure of these components. Although the fractured rolls were heavily corroded, examination of the fracture faces suggested fatigue failures had occurred from the keyway in the bores, as well as from the corner of the side face and OD of the rolls. The material properties of 4 rolls were examined, and the structures were all found to be castings made to D2 tool steel composition (with higher silicon to aid castablility) that

On behalf of: XXXXXX Report No.: INV5552-1 Date: 10 August, 2006

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had been hardened to a range of 55-62 HRC. Manufacture of these rolls from castings is considered to be inferior to forged material due to the poor carbide network, which embrittles the structure, so it is suggested that they be manufactured from forgings. It is recommended that in future, the fracture faces of any broken rolls be preserved from the elements and submitted for further examination to more accurately identify the source of the fatigue cracking.

Disclaimer This report was prepared by XXXX expressly for the customer as nominated on the front cover. Neither XXXX nor any person acting on its behalf (a) makes any warranty, express or implied, with respect to the use of any information or methods disclosed in this report or (b) assumes any liability with respect to the use of any information or methods disclosed in this report. Any recipient of this document, by their acceptance or use of this document, releases XXXX and their affiliates from any liability for direct, indirect, consequential or special loss or damage whether arising in contract, warranty, express or implied, tort or otherwise, and irrespective of fault, negligence and strict liability. Email copies of this report are not official unless authenticated and signed by XXXXX td and are not to be modified in any manner without XX’s express written consent. Sample Disposal Test samples and off-cuts of client test samples sent to XXXX for investigation will be retained in a weatherproof area for approximately one month after the issue of this report and for a further two months in external storage before disposal. If these parts are required by you then you must contact XXXXX o arrange pick up before this term has elapsed.

On behalf of: XXXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 1 View of the rolls submitted for examination. The five broken pieces were heavily corroded.

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 2 Views showing the fractured roll #1. Fracture occurred through the keyways. Evidence of fatigue cracking was visible on the fracture to the LHS of figure 2b, see figure 3.

Roll #1

a

b

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 3 Views showing the mating fracture faces of roll #1. Beach marks radiating from the keyway are evident (arrowed), extending over about 80% of the fracture face.

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 4 Views showing the fractured roll #2. Evidence of fatigue cracking was visible from the OD of the fracture to the RHS of figure 4b, see figure 5.

Roll #2

a

b

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 5 Views showing the mating fracture faces of roll #2. Beach marks radiating from the corner of the side face and OD are visible (arrowed), extending over about 30% of the fracture face.

On behalf of: XXXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 6 Views showing the fracture faces of roll #3. There were no distinctive features on the fracture face to indicate the fracture origin.

a b

a

b

Roll #3

On behalf of: XXXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 7 x400 mag 2% nital etch Photomicrograph of roll #1. The structure consisted of a network of carbides associated with the cast dendritic structure, in a matrix of tempered martensite with some pearlite.

Figure 8 x400 mag 2% nital etch Photomicrograph of roll #2. The structure consisted of a network of carbides associated with the cast dendritic structure, in a matrix of tempered martensite.

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Figure 9 x250 mag 2% nital etch Photomicrograph of roll #4 taken using portable microscope. The structure consisted of a cast network of carbides in a matrix of tempered martensite.

Figure 10 x250 mag 2% nital etch Photomicrograph of roll #5 taken using portable microscope. The structure consisted of a cast network of carbides in a matrix of tempered martensite.

On behalf of: XXXXX Report No.: INV5552-1 Date: 10 August, 2006

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Appendix A