CA2297917A1

CA2297917A1 - A roll assembly for use at high temperature and method of making same

Info

Publication number: CA2297917A1
Application number: CA002297917A
Authority: CA
Inventors: Arthur L. Huckelbridge; Stewart P. Hawk; John F. Wallace; John C. Rogers; Warren L. Mehnert
Original assignee: Sandusky International Inc
Current assignee: Individual
Priority date: 1997-09-22
Filing date: 1998-09-21
Publication date: 1999-04-01
Also published as: JP2003517537A; WO1999015305A1; WO1999015305A8; KR20010024234A

Abstract

A roll assembly (20) for high temperature applications comprising a roll body (22) and trunnions (30) on opposing ends (24) thereof is disclosed. The roll body and supporting trunnions are comprised of alloys having dissimilar coefficients of linear thermal expansion. The trunnions are attached to the roll body so that there is a predetermined gap (40) at room temperature that decreases or closes at a desired operating temperature. The gap decreases due to the dissimilar thermal expansions between the roll body and the trunnions.
In certain embodiments, the distance of the gap is determined so there is a tight predetermined interference fit between the trunnions and the roll body for roll assembly integrity and load transfer. In other embodiments, the distance of the gap is determined so that a plurality of mechanical connectors (44) extending between the roll body and the trunnions provide the roll assembly with integrity and provide load transfer between the roll body and the trunnions.

Description

DESCRIPTION
A ROLL ASSEMBLY FOR USE AT HIGH TEMPERATURE
AND METHOD OF MAKING SAME
Background of the Invention Roll assemblies are used in a variety of high-temperature applications such as steel manufacturing including, for example, a steel mill furnace roll which is used to move steel slabs through a heat treatment furnace. The roll assemblies include a generally cylindrical roll body and heads or trunnions at opposing ends of the roll body. The trunnions are rigidly attached to the roll body by weld fabrication or standard mechanical methods. Figure 1 is a schematic diagram of a prior art welded roll assembly 10. A roll body 12 has trunnions 14 and 16 attached by welds 18 to the roll body 12. The roll body 12 is supported and rotated by the trunnions 14 and 16 which act as a transition shape from the roll body 12 to supporting roll shafts. The trunnion attachments are intended to be rigid, high strength connections. Typically the trunnions and the roll body are the same material. However, it would be advantageous to have the roll body made of a different material than the trunnions in order to place the appropriate materials in locations where they are needed to meet certain technical requirements while still maintaining an economical roll assembly.
While it would be advantageous to use dissimilar materials for the roll assembly, the dissimilar materials may have different coefficients of linear thermal expansion. The dissimilar materials expand different amounts when heated to a desired operating temperature. As a result, the stresses from the dissimilar thermal expansion cause high design stresses which, in turn, lead to early failure of the roll assembly. It would be particularly advantageous to have the roll body made of a high heat resistant alloy such as an expensive nickel aluminide alloy, while the trunnions are made of a different, more economical material.
Nickel aluminides alloys are nickel-aluminum (Ni3 AI) intermetallic alloys which were developed for high temperature commercial applications such as forging dies and heat treatment furnace fixtures (Sikka, V., "Commercialization of Nickel and Iron Aluminides, International Symposium on Nickel and Iron Aluminides: Processing, Properties and Applications, Proceedings from Materials Week'96, ASM
International, 1996, pp 361-375). Nickel aluminide furnace rolls are an improvement over rolls made from standard heat resistant metals. The nickel aluminide furnace rolls do not develop a defect called a "blister,"
they do not distort in service, they do not scratch the steel slab that passes over the top of them, and they do not cause oxide pick-up on the steel slabs. As a result, the nickel aluminide rolls improve product quality, increase furnace productivity, reduce maintenance downtime and reduce maintenance costs. A comparison of the approximate chemical compositions of some nickel aluminide alloys and conventional heat resistant chromium-nickel-iron alloys are listed in Table I below.
TABLE I

(Values in weight percent) AI Cr Mo Zr B Ni Fe IC-396M 8.0 7.7 1.4 1.7 0.005 81 ---(nickel aluminide) IC-221 M 8.0 7.7 3.0 0.8 0.005 81 ---(nickel aluminide) HK --- 26 --- --- --- 20 bal.

(conventional alloy) HP ___ 26 ___ ___ ___ 35 bal.

(conventional alloy) WO 99/15305 PCTlUS98/19697 Various prior art roll assemblies have the trunnions welded to the ends of the roll body. In the past, weld fabrication was considered necessary to manufacture an economical assembly. In one prior art roll assembly, a tC-396M nickel aluminide roll body was welded to nickel aluminide trunnions. However, the welds fractured after an unacceptably short-term service of one month and the roll assembly was removed from service. It was concluded in the industry from this failure that the nickel aluminide alloy was not suitable for welded fabrications.
However, since those skilled in the art still believed welding to be the preferred method of commercial fabrication, extensive welding development work was conducted to develop the nickel aluminide alloy IC-221 M, a more weldable alloy than the IC-396M alloy. A gas tungsten arc welding technique was developed to assemble roll bodies and trunnions of the IC-221 M alloy. (Santella, M., "An Overview of the Welding of Ni3 AI and Fe3 AI Alloys", Proceedings from Materials Week '96, ASM International, 1996, pp. 321-327y. However, three of the five rolls built using the gas tungsten arc welding technique for nickel aluminide rolls and trunnions failed due to weld cracking in unacceptably short service periods of 1 to 14 days. The long-term service of welded nickel aluminide fabrications is considered unreliable.
The industry has determined that even if nickel aluminide alloy components could be successfully weld fabricated for long-term service, the cost of the nickel aluminide roll assembly is prohibitive compared to conventional heat resistant alloys. A nickel aluminide roll assembly is 2.5 to 3 times more expensive than conventional rolls. However, the industry still desires to find a way to use the nickel aluminide roll body since the nickel aluminide roll body gives a superior performance needed in the heat treatment furnaces.
The industry has also determined that a roll assembly which is comprised of a roll body made of a first alloy cannot be welded to a trunnion made of a second alloy. The welds between alloys having dissimilar coefficients of linear expansion do not readily accommodate the stresses which occur due to the differential thermal expansion of the roll body and the trunnion. The weld also does not accommodate the stresses set up by the thermal gradient in the roll assembly.
Attempts to weld lower-cost conventional alloy trunnions to nickel aluminide roll bodies have been made. However, the differences of linear thermal expansion that exist between the conventional alloys and nickel aluminide alloy yielded an unacceptably high von Mises effective stress of 280 MPa (40,000 psi) at the weld joint at the temperature of furnace operation. One of two rolls made this way failed in the weld joint after an unacceptably short service of four months.
In a roll assembly comprised of a roil body and trunnions made from alloys having similar linear expansions, the weld filler metal still does not accommodate the stresses in the roll assembly. For example, the nickel aluminide weld has an extremely low ductility of less than 5%
elongation as measured in short-term high-temperature tensile tests in the range of 600°C-1000°C (1100°F-1830°F). The nickel aluminide weld filler metal is susceptible to brittle fracture and the weld filler metal is not satisfactory for long term performance.
Based on the past attempts to produce improved roll assemblies, the industry had determined that commercial roll assemblies required weld fabrication and dissimilar alloys could not be fabricated together in intimate contact to form the roll assembly.
Summary of the Invention The present invention relates to a roll assembly and a method for making the roll assembly. The roll assembly comprises a generally cylindrical roll body and first and second heads or trunnions which each engage the opposing ends of the roll body. The ends of the roll body have a first diameter. An end of each trunnion has a second or outside diameter such that the end of each trunnian engages the end of the roll body. It is within the contemplated scope of the present invention, that in certain embodiments, the ends of the roll body fit inside the trunnions, 5 while in other embodiments, the end of each trunnion fits inside the ends of the roll body.
A precisely determined or controlled gap exists between the diameter of the roll body and the diameter of the trunnion. The roll body is made of a first material having a first coefficient of linear thermal expansion and the trunnions are made of a second material having a second coefficient of linear thermal expansion.
The differences between the linear thermal expansions of the first material of the roll body and the second material of the trunnions are accommodated in different embodiments. In a first embodiment, the controlled gap is large enough at room temperature so that the size of the gap decreases as the roll assembly reaches its desired operating temperatures and a small gap remains at the operating temperature.
Thus, no stress is induced in the roll body from the expansion of the trunnion.
In a second embodiment, there is a controlled gap at room temperature and as the roll assembly reaches its desired operating temperatures, the gap closes so that there is a tight contact of the trunnion to the roll body. In this embodiment, a controlled interference fit is created at operating temperatures between the roll body and the trunnions, while still maintaining an acceptable von Mises effective stress for the roil assembly integrity during the useful service life of the roll assembly.
In both embodiments, the roll body and trunnions are mechanically connected together when the roll assembly is not at the high temperature operating conditions. The mechanical connection prevents the roll WO 99/15305 PC1'IUS98/19697 assembly from becoming unassembled at colder temperatures without restraining expansion of the materials of the roll body and trunnions when heated. In the embodiments where a gap intentionally remains at high operating temperatures, the mechanical connection also provides the means for transferring the load on the roll body to the trunnions. In the embodiments where a controlled interference fit develops at operating temperatures, the interference fit transfers the load and the reliance on mechanical connection is greatly reduced.
The present invention provides an improved and economically fabricated roll assembly for use at high temperatures. In one embodiment of the present invention, a nickel aluminide heat treatment furnace roll body is attached to trunnions made of less expensive alloys.
A controlled gap between the trunnion and roll body is manufactured at room temperature. Mechanical connectors, such as pins, are used to connect the roll body and trunnions at room temperature. At a desired operating temperature the trunnions expand more than the roll body. The difference in thermal expansion is accommodated in different embodiments. In one embodiment, a gap remains at operating temperature and the mechanical connectors are used to transfer all of the load. In another embodiment, a controlled interference is created between the roll body and the trunnions to transfer the load. However, in certain embodiments it is desired that when an interference fit is used, the mechanical connectors provide the roll assembly with an additional safety measure to accommodate the differential stresses between the roll body and the trunnions. Furthermore, at a desired operating temperature, the mechanical connectors are reasonably loose so that differential thermal expansion can take place without restraint.
The present invention is also useful with other high temperature materials and in situations where the material with the lower linear thermal expansion is used for the trunnions instead of the roll body.

Brief Description of the Drawinqs_ Fig. 1 is a schematic illustration of a prior art roll assembly.
Fig. 2 is a schematic illustration of a cross-sectional view portion of a roll assembly of the present invention.
Fig. 3 is a schematic illustration of an end view of a portion of a roll assembly of the present invention.
Fig. 4 is a schematic illustration of a cross-sectional view of a portion of a roll assembly of the present invention.
Fig. 5 is a view taken along the fine 5-5 in Fig. 4.
Fig. fi is an enlarged view of the area shown in Fig. 4.
Description of Preferred Embodiment The different linear thermal expansions for the roll body and the trunnions are accommodated by having a controlled gap between the roll body and trunnions at room temperature. Mechanical connectors are used to connect the trunnions to the roll body and to maintain the roll assembly integrity at room temperature. The mechanical connectors are loose enough to allow differences in thermal expansion to occur without restraint. The controlled gap decreases or closes on heating of the roll assembly to the desired operating temperature without creating unacceptably high von Mises stresses in the roll body or trunnions. In certain embodiments, the gap is manufactured so that, on heating, a small gap remains and the mechanical connectors transmit all of the service load. In other embodiments, the gap is manufactured so that, on heating, the gap closes and a tight interference fit develops between the roll body and the trunnions. The interference fit transmits the service load while the mechanical connectors act as a secondary means of load transfer. The compositions of the materials comprising roll body and the trunnions are selected to meet industry service requirements and to provide an economic roll fabrication. Examples of this invention are *rB

provided for heat treatment furnace rolls operated at approximately 840°C-1010°C (1550°F-1850°F). However, it should be understood that the scope of this present invention is not to be limited to the examples given herein, and that these examples do not limit the present invention to this particular high temperature use.
When an IC-221 M nickel aluminide roll body that has a nominally 363.6 mm (14.313 in.) outside diameter and a 322.2 mm (12.688 in.) inside diameter is rigidly attached to an HK alloy trunnion, the von Mises effective stress is calculated using the coefficients of linear thermal expansion of IC-221 M and HK as shown in Table I1 below.
TABLE II
Coefficient of Linear Thermal Expansion from Room Temperature to 900°C, 10-B/°C (10-el°F) 1C-221 M roll body 15.8 (8.8) HK trunnion 18.1 (10.0) The difference in expansion between the HK alloy trunnion and the nickel aluminide alloy roll body, if each were tightly fabricated, is about 0.64 mm (0.025 in.). Also, allowing for differences in the modules of elasticity at the operating temperature, the von Mises effective stress resulting from the restrained expansion of the HK by the IC-221 M is approximately 280 MPa (40,000 psi). This exceeds the safe design stress levels and is not acceptable.
Figure 2 shows a schematic ilEustration of one end of a roll assembly 20 of the present invention which comprises a roll body 22 and a trunnion 30. It is to be understood that the roll assembly 20 generally comprises a trunnion 30 at each end of the roll body 22. For ease of illustration only one trunnion 30 is shown. It should be further understood, however, that the present invention contemplates the use of trunnions at each end of the roll body. The roll body 22 has a generally cylindrical shape and has opposing ends 24. For ease of illustration, only one end 24 of the roll body is shown. However, it should be understood that the opposing end (not shown) of the roll body 22 can have substantially the same or a different shape, c!epending on the end use requirements for the roll assembly. The end 24 of the roll body 22 is counterbored to a desired inside diameter 26.
The trunnion 30 has a first end 34 which is machined to a desired outside diameter 36. The first end 34 of the trunnion 30 fits within, or is axially positioned in, the counterbored inside diameter 26 of the roll body 22. In the embodiment shown in the Figures, the first end 34 of the trunnion 30 is axially positioned within the first end 24 of the roll body 22 and the inner diameter 26 of the end 24 of the roll body 22 is greater than the outer diameter 36 of the first end 34 of the trunnion 30.
However, it is also within the contemplated scope of the present invention that another embodiment can have first end of~the trunnion axially positioned outside of the first end of the roll body and the outer diameter of the end of the roll body is smaller than the inner diameter of the first end of the trunnion.
Referring now to Fig. 3, when the trunnion 30 is axially positioned on the end 24 of the roll body 22 at a cold or room temperature, a desired gap 40 exists between the inside diameter 26 of the roll body 22 and the outside diameter 36 of the trunnion 30. The length of the gap 40 is determined by the difference between the diameter 26 of the rol!
body 24 and the diameter 36 of the trunnion 30. In one embodiment, the roll body ends 24 of a roll body 22 made of the IC-221 M nickel aluminide alloy are counterbored to an inside diameter of 327.36 mm (12.888 in.). The outside diameter 36 of the HK trunnions 30 are machined to a smaller diameter of 326.90 mm (12.87 in.). There is a clearance of 0.46 mm (0.018 in.) between the overlapping inside diameter 24 of the roll body 22 and the outside diameter 36 of the trunnion 30 when the trunnion 30 is coaxially positioned in the roll body 22 and assembled in a cold or room temperature environment. Upon 5 exposure to the desired operating temperatures the roll body 22 and the trunnions 30 expand at different rates. The von Mises effective stress is less than 70 MPa (10,000 psi) which is within the safe design stress.
The 0.46 mm (0.018 in.) distance of the expansion is accommodated by the trunnion 30 expanding and decreasing the length of the gap 40. The 10 remaining 0.18 mm (0.007 in.) difference in expansion is calculated to provide the controlled tight interference fit at the operating temperature.
In another embodiment the roll body 22 and trunnions 30 are connected together without an interference fit such as for example, when the difference in expansion between the HK alloy trunnion 30 and the nickel aluminide alloy roll body 22 is about 0.64 mm (0.025 in.). When the gap 40 is manufactured to a minimum of 0.64 mm (0.025 in.) at room temperature, no interference fit will develop at operating temperature.
In certain embodiments, at room temperature the trunnions 30 are secured to the roll body 20 by a plurality of mechanical connectors 44 such as pins, as seen in Figs. 4 and 5. The end 24 of the roll body 22 has a plurality of radially extending openings 28 extending therethrough.
The end 34 of the trunnion 30 has a plurality of radially extending bores 38. The mechanical connectors 44 are positioned through the radially extending openings 28 in the end 24 of the roll body 22. Each opening 28 is in radial alignment with a corresponding radialfy extending bore 38 in the end 34 of the trunnion 30. The bore 38 may terminate at a distal end 39. The mechanical connector 44 is positioned in the opening 28 of the roll body 22 and in the bore 38 of the trunnion 30. The mechanical connector 44 has a distal end 46 which contacts the distal end 39 of the bore 38. It is also within the contemplated scope of the present invention that the bores 38 may extend through the end 34 of the trunnion 30. The mechanical connectors 44 may extend beyond the trunnion 30 and be fastened with a snap ring (not shown) or other locking device.
The mechanical connectors 44 have a desired diameter to provide a reasonably loose fit in the roll body 26 and in the trunnions 30 at room temperature so that any restraint of the intended thermal expansion is avoided during furnace heating and cool down periods. The mechanical connectors 44 are positioned in the openings 28 and bores 38 when the roll assembly 20 is at room temperature. There is no tight interference fit between the roll body 22 and the trunnions 30 at room temperature.
Rather, the mechanical connectors 44 loosely connect the roll body 22 to the trunnions 30. As the roll body 22 and trunnions 30 are heated, there is room for expansion of the roll body 22 and trunnions 30.
The mechanical connectors 44 maintain the alignment of the roll body 22 with the trunnions 30 and also support any stresses which may be present at room temperature. The mechanical connectors 44 in the openings 28 and the bores 38 also provide support to the roll body-trunnion joint when the roll assembly 20 is at room temperature. In addition, the mechanical connectors 44 may also accommodate any differential stresses which are not accounted for by the interference fit between the roll body 22 and the trunnions 30. However, it is also within the contemplated scope of the present invention that other methods for mechanically attaching the roll body 22 to the trunnions 30 at room temperature are possible.
The mechanical connectors 44 are designed to withstand all of the mechanical loads experienced by the roll assembly 30. The mechanical connectors 40 still allow for the difference in thermal expansion between the alloy trunnion 30 and the nickel aluminide roll body 22 to occur without restraint.
tn certain embodiments, the advantages of avoiding the interference fit are that the manufacturing tolerances of the controlled gap can be much broader thereby simplifying the machining processes prior to assembly, and any concern over the long-term integrity of an interference fit is eliminated. In the embodiments where no interference fit is used to join the trunnions to the roll body it is to be understood that the compositions and the sizes of the mechanical connectors are chosen 70 to be compatible with the compositions and sizes of the trunnions and roll bodies and that such variations are within the scope of the present invention.
Proper alignment of the roll body 22 and trunnions 30 during assembly is important to achieve. A relatively large gap 40 is required at room temperature in order to allow for placement of the trunnions and the roll body in an approximate coaxial relationship. However, there is a need to maintain concentricity (that is, coaxial alignment) between the ends 34 of the trunnions 30 and the ends 24 of the roll body 22 when the trunnions 30 and roll body are being assembled. The trunnions 30 are positioned in the ends 24 of the roll body 22 prior to the forming of the radially extending opening 28 in the ends 26 of the roll body 22 and the forming of the bores 38 in the trunnion 30.
As shown in Fig. 6, the concentricity between the roll body 22 and the trunnions 30 is maintained by placing at least one layer of a disintegratable material 50 circumferentially extending around at least portions of the end 34 of each trunnion 30.
In one preferred embodiment, the material 50 substantially circumferentially surrounds the end 34 of the trunnion 30 and/or the ends 24 of the roll body 22. However, it is also within the contemplated scope of the present invention that a plurality of sections of material 50 (not shown), which act as shims, can be circumferentially positioned on portions of the circumference of the ends 34 of the trunnion 30 and/or on portions of the interior diameters 26 of the ends 24 of the roll body 22 to maintain the roll body 22 and the trunnions 30 in a coaxial relationship. Also, in certain embodiments, a further piece 54 of disintegratable material can be positioned in the distal end 39 of the bore 38 to prevent the mechanical connector 44 from becoming stuck in the bore 38.
The material 50 maintains the uniform gap 40 between the trunnion end 34 and the roll body end 24 so that when the radially extending openings 28 and the bores 38 are formed, the openings 28 and the bores 38 are in radial alignment. When the roll body assembly is raised to its desired operating temperatures, the material 50 disintegrates and leaves the planned gap 40 which is necessary for 15 unrestrained expansion of the dissimilar metals of the roll body 22 and trunnions 30.
Having described the invention above, various changes from the specific materials, procedures and apparatus will occur to those skilled in the art. It is intended that all such variations are within the scope and 20 spirit of the appended claims.

Claims

WE CLAIM:

1. A roll assembly for use in high temperature applications comprising a roll body comprised of a first material having a first coefficient of linear thermal expansion, the roll body having opposing ends, each end defining a first diameter, and at least one trunnion comprised of a second material having a second coefficient of linear thermal expansion, the trunnion having a first end defining a second diameter, a gap of a desired distance being present at room temperature when the first end of the roll body is positioned in the first end of the trunnion or when the first end of the trunnion is positioned in the first end of the roll body, the distance of the gap being defined by the difference between the first diameter of the roll body and the second diameter of the trunnion, a disintegratable material positioned in the gap, whereby the roll body and the trunnions are held in a coaxial relationship during assembly of the roll assembly, the gap decreasing between the roll body and the trunnion when the roll assembly is at a desired elevated temperature whereby no weldment is used to secure the trunnion to the roll body.

2. The roll assembly of claim 1, wherein the gap closes and the ends of the roll body and the ends of the trunnions engage due to an interference fit when the roll body and the trunnions are at the desired elevated temperature.

3. The roll assembly of claim 1, wherein the roll body is attached to the trunnions at room temperature by at least one mechanical connector.

4. The roll assembly of claim 3, wherein the ends of the roll body include a plurality of radially extending openings which are in alignment with a plurality of radially extending bores in the first end of the trunnion, and wherein the roll body is attached to the trunnions by a plurality of mechanical connectors positioned in the radially extending openings and bores.

5. The roll assembly of claim 4, wherein the mechanical connectors allow the roll body and the trunnions to engage due to an interference fit wherein the roll body and trunnions undergo linear thermal expansion without restraint of the roll body or the trunnions by the mechanical connectors.

6. The roll assembly of claim 4, wherein no interference fit develops and the roll body is attached to the trunnions at the desired elevated temperature by at least one mechanical connector.

7. The roll assembly of claim 3, wherein the mechanical connectors comprise pins.

8. The roll assembly of claim 1, wherein the end of the roll body has an inner diameter greater than an outer diameter of the first end of the trunnion, whereby the first end of the trunnion is axially positioned within the first end of the roll body.

9. The roll assembly of claim 1, wherein the end of the roll body has an outer diameter smaller than an inner diameter of the first end of the trunnion, whereby the first end of the trunnion is axially positioned outside of the first end of the roll body.

10. CANCELLED.

11. The roll assembly of claim 1, wherein the disintegratable material substantially circumferentially extends around the outer diameter of the first end of the trunnions and/or around an inner diameter of the ends of the roll body.

12. The roll assembly of claim 1, wherein a plurality of sections of the disintegratable material are positioned on at least a portion of the outer diameter of the ends of the trunnions and/or on at least a portion of the inner diameter of the ends of the roll body.

13. The roll assembly of claim 1, wherein the roll body comprises a nickel aluminide alloy and the trunnions comprise a heat resistant chromium-nickel-iron alloy.

14. The roll assembly of claim 1, wherein the nickel aluminide alloy comprises about, in weight percent: about 8.0% aluminum, about 7.7% chromium, about 1.4% molybdenum, about 1.7% zirconium, about 0.005% boron and about 81 % nickel.

15. The roll assembly of claim 1, wherein the nickel aluminide alloy comprises about, in weight percent: about 8.0% aluminum, about 7.7% chromium, about 3.0% molybdenum, about 0.8% zirconium, about 0.005% boron and about 81 % nickel.