US3604819A

US3604819A - Impeller shaft assembly

Info

Publication number: US3604819A
Application number: US866312A
Authority: US
Inventors: Francis J Krahe; Lawrence J Serena
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1969-10-14
Filing date: 1969-10-14
Publication date: 1971-09-14
Anticipated expiration: 1988-09-14

Abstract

An impeller shaft assembly for a fan operating at high temperatures in the range from ambient temperature to a highoperating temperature is disclosed. The impeller shaft assembly has a metal shaft having at one end a connector portion of reduced nonround cross section. The reduced cross section has rounded corners. The shaft has a tapered portion provided with a taper toward the one end adjacent the connector portion. The shaft has a first coefficient of expansion. A ceramic impeller is disposed on the shaft and is provided with a connector aperture adapted to receive and frictionally engage the connector portion with a predetermined cold clearance. The impeller is provided with a tapered aperture adjacent the connector aperture, is adapted to receive the tapered portion with one cold clearance (of a cold clearance greater than the first predetermined cold clearance, a cold clearance equal to the first predetermined cold clearance and a cold clearance less than the first predetermined cold clearance) and defines an impeller shoulder with the connector aperture. The impeller shoulder is engageable with the shaft shoulder. The impeller has a second coefficient of expansion less than the first coefficient of expansion. Drive means are connected to the shaft to cause rotation of the shaft and the impeller at high speed. The shaft and the impeller are rotated by the drive means at the high speed and at the high temperature so that the predetermined cold clearance and the one cold clearance are reduced to a limit which approaches but never reaches zero.

Description

United States Patent (72] Inventors Francis J. Krahe Frazier Township, Allegheny County; Lawrence J. Serena, Washington Township, Westmoreland County, both of, Pa. [211 App]. No. 866,312 [22] Filed Oct. 14, 1969 [45] Patented Sept. 14, 1971 [73] Assignee United States Steel Corporation [54] IMPELLER SHAFT ASSEMBLY 11 Claims, 9 Drawing Figs.

[52] US. Cl 416/204, 287/53, 4l6/l88,4l6/244 511 im. Cl ..B60h 27/06, F0 l d 5/04 [50] Field of Search 263/40, 49; 287152.08, 53; 416/204, 223, 241, 244

[56] References Cited UNITED STATES PATENTS 337,072 3/1886 Montgomery 287/53 R 1,816,687 1 1/1929 Marron 287/53 R 2,297,508 9/ 1942 Schutte 416/244 2,479,102 8/1949 Dailey 263/40 2,558,088 6/1951 Hoop..... 263/40 2,751,188 6/1956 Rath 416/241 3,061,342 10/1962 Feller 287/53 R 3,443,792 5/ 1969 Moss 4161241 Primary Examiner-Martin' P. S chwadron Assistant Examiner-C. Schimikowski Attorney-Robert .l. Leek, .lr.

ABSTRACT: An impeller shaft assembly for a fan operating at high temperatures in the range from ambient temperature to a high-operating temperature is disclosed. The impeller shaft assembly has a metal shaft having at one end a connector portion of reduced nonround cross section. The reduced cross section has rounded comers. The shaft has a tapered portion provided with a taper toward the one end adjacent the connector portion. The shaft has a first coefiicient of expansion. A ceramic impeller is disposed on the shaft and is provided with a connector aperture adapted to receive and frictionally engage the connector portion with a predetermined cold clearance. The impeller is provided with a tapered aperture adjacent the connector aperture, is adapted to receive the tapered portion with one cold clearance (of a cold clearance greater than the first predetermined cold clearance, a cold clearance equal to the first predetermined cold clearance and a cold clearance less than the first predetermined cold clearance) and defines an impeller shoulder with the connector aperture. The impeller shoulder is engageable with the shaft shoulder. The impeller has a second coefficient of expansion less than the first coefficient of expansion. Drive means are connected to the shaft to cause rotation of the shaft and the impeller at high speed. The shaft and the impeller are rotated by the drive means at the high speed and at the high temperature so that the predetermined cold clearance and the one cold clearance are reduced to a limit which approaches but never reaches zero.

PATENTED SE?! 419?:

SHEET 3 0F 4 HON! 83d SJHON/ as ||l I III NVQQ I Rm 9k QQ 0N INVENTORS FRANCIS J. KRAHE 8 LAWRENCE J. SERENA A f fomey PATENTEDSEPIMQYI 3,604,819

- sum u (If 4 INVENTORS FRANCIS J. KRAHE' 8 LAWRENCE J. SERENA Attorney IMIELLER SHAFT ASSEMBLY 7 BACKGROUND OF THE INVENTION Heretofore, impeller shaft assemblies have been of the type shown in the following patents. US. Pat. No. 2,875,997 to Blackman, issued Mar. 3, 1959; 3,082,996 to Elrick et al., issued Mar. 26, I963.

The base of a coil annealing furnace is centrally apertured for retention of a vertically disposed metal fanimpeller encased in a circular hard brick wall. The fan provides circulation of a protective atmosphere within the inner cover and around the coiled strip during the annealing cycle. The protective atmosphere gas, such as hydrogen, nitrogen, or the like, is introduced into the base. The base fan motor is bolted to the base and the fan impeller is attached to the end of the metal base motor shaft.

The conventional metal impeller has a keyway by which it is connected to the straight motor shaft. A tight fit is critical in this attachment since the forces resulting from the combination of high operating temperature, rotation, time exposure and impeller weight (of about 60 pounds acting on the impeller) causes the impeller to go out of balance. The imbalance of the impeller is transmitted along the motor shaft and results in shaft distortion and bearing failure to the extent that the shaft becomes frozen and will not rotate. The base motor must then be removed and dismantled so that the shaft can be remachined and straightened. During a typical year, there were about 154 motor changes for about 44,000 tons annealed, with about 4.6 heats per motor change. This dismantlement and repair of the motor costs approximately $350 per occurrence. Due to the high cost of the conventional alloy steel impeller (about $300 each), they are reused until the imbalance is excessive and the occurrence of motor failure is accelerated (after approximately 100 heats). It is impractical to attempt to rebalance the impellers after each annealing cycle.

The replacement of the heavy alloy metal impeller with a ceramic unit has not been previously successful because of the brittleness of the ceramics and their poor thermalshock resistance. Due to this brittleness, a ceramic impeller cannot be keyed to the motor base shaft since the shaft expansion during an annealing cycle would immediately fracture the impeller.

A typical annealing charge consists of about six IO-ton coils (total-about 60 tons) on the three stools of a base. The steps of the annealing cycle are as follows:

Approximate Time required Operation 60 Hours Time to Reach Soak Temperature of about 2,075 F.

30 Soak Time at about 2,075 F.

20 Cooling to about L400" F. for Furnace Removal 48 Cool to about 350 F. for lnnercover Removal I50 Hours-Total Average Cycle OBJECTS OF THE INVENTION It is the general object of this invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of an improved impeller shaft assembly which:

a. operates continuously at high speeds of about 1,800 r.p.m. instead of conventional redliced speeds of about 900 r.p.m.; I I I b. reduces the total coil annealing cycle by about 2 hours;

0. avoids fracture of the impeller during the operating cycle;

d. provides a lightweight impeller suitable for high-temperature operation up to about 2,07 5 F.; I I

e. eliminates any lifting effect by fluid flow;

f. provides an adequate operating life at a reasonable cost;

g. allows for the difference in the coefficient of expansion of the shaft and the impeller; and I I l h. substantially eliminates impeller drive motor failure.

BRIEF SUMMARY OFTI- IE INVENTION The aforesaid objects of this invention, and other objects which will become apparent as the description'proceeds,are achieved by providing an impeller shaft assembly fora fan operating at high temperatures in therange from ambient temperature to a high-operating temperature. The imp'eillfer'shaft assembly has a metal shaft having at 'oneend'a connector portion of reduced cross section. The reduced cros's seiction has rounded comers. The shaft has 'a tapered portionjprovided with a taper toward the one end adjacent the connectorportion and defining a shaft shoulder with the connec o -portion. The shaft has a first coefficient of e'xpa nsioni A ceramic impeller is disposed on the shaft and ispro vide d with swimmer aperture adapted to receive and frictionally engage th e connector portion with a predetermined cold clearance. The impeller is provided with a tapered aperture adjaceritthe connector aperture, is adapted to receive the tapered portion with one cold clearance (of a cold clearance greater than thc fi'r st predetermined cold clearance, a cold clearance etjual to the first predetermined cold clearance and a cold clearanceless than the first predetermined cold clearance) anddetine'san impeller shoulder with the connector aperture. The impeller shoulder is engageable with the shaft shoulder. Theirnpeller has a second coefficient of expansion less than thefirst coefficient of expansion. Drive means are'connected to the shaftto' cause rotation of the shaft and' the impeller at high speed. The shaft and the impeller are rotated by the drive means at the high speed and at the high temperature so thattliepredetermined cold clearance and the one cold clearance are reduced to a limit which approaches but never reaches'aerol I I I BRIEF DESCRIPTION OFTHE SEVERAL v ews or T RAWINGS For a better understanding of this invention reference should be had to theaccompanying drawings, wherein like numerals of reference indicate similar parts throughout the several views and wherein: I I I FIG. 1 is a side elevational view, partially in section of a coil annealing furnace; I I

FIG. 2 is an enlarged plan view of the improved impeller shaft assembly; I

FIG. 2A is an enlarged fragmentary plan view showing the frictional engagement between the shaft and theimpeller; I

F IG. 3 is a vertical sectional view' taken along the line of FIG. 2 in the direction of the arrows; I I

FIG. 3A is a graph showing the thermal expansion of the ceramic impeller; I

FIG. 4 is a view similar to FIG. 3 of an alternative embodiment showing the impeller shaft assembly utilized in the down position; and I FIG. 5 is a view similar to FIGS. 3, 4 of another alternative embodiment showing the impeller shaft assembly employed in the side position; I I I I FIG. 6 is a view similar to FIG. 2, showing a polygonalshaped connector portion on the shaft and a poygonal-shaped connector aperture in the impeller; and I I FIG. 7 is a view similar to FIG. showing the use of spacer means between the shaft and the impeller to compensate for the permanent growth deformation of the shaft after a plurality of heating cycles.

Although the principles of this invention are broadly applicable to impeller shaft assemblies for high speed, high temperature use,-this invention is particularly adapted for use in conjunction with a coil annealing furnace and hence it has been so illustrated and will be so described.

DETAILED DESCRIPTION With specific reference to the form of this invention illustrated in the drawings, and referring particularly to FIG. 1, an annealing furnace is indicated generally by the reference numeral I0.

This annealing furnace I has a base 12 (FIG. 1) and a coil support I4 upstanding from the base 12. Such coil support 14 has a hard brick wall 16 (FIG. 1) suitably of the Varnon type manufactured by Harbison-Walker Co., Pittsburgh, Pa., or the like, a refractory wall 18 (FIG. I), suitably a Castable Refractory of the type LWI manufactured by Plibrico Co., Chicago, Illinois, or the like and a metal baseplate 20 (FIG. I) on which a coil 22 (to be annealed) is disposed. Varnon is the trade name of Harbison-Walker Co., Pittsburgh, Pennsylvania for a refractory brick. An inner refractory plug 24 (FIG. 1), suitably type K23 manufactured by Babcock and Wilcox Co., Atlanta, Georgia or the like, defines a shaft cavity 26 (FIG. 1) and is supported on an annular plate 28 (FIG. 1) projecting from the hard brick wall 16. Above the refractory plug 24, the hard brick wall 16 and baseplate 20 define an impeller cavity 30.

An impeller-type fan 32 (FIG. 1) has its drive means or motor 34 (FIG. 1) secured as by bolts 36 and nuts 38 to the annular plate 28. Its metal shaft 40 (FIGS. 1, 2, 2A, 3, 4, 7) projects through the shaft cavity 26, carries a ceramic impeller 42 on its upper end, as viewed in FIG. I, and rotates such impeller 42 in the direction of the arrows (FIG. I) in the impeller cavity 30. Such shaft 40 and impeller 42 form the improved impeller shaft assembly of this invention and circulate (in the direction of the arrows shown in FIG. I) a protective atmosphere, such as hydrogen, nitrogen, or the like through holes 44 (FIG. I) in the hard brick wall 16, ducts 46 in the refractory wall 18, the heating cavity 48, FIG. 1, (defined by the radiator-type metal inner cover 50 (FIG. 1), the coil support I4 and the coil 22) and down the eye 52 (FIG. 1) of the coil 22. The inner cover 50 is sealed by sand 51 (FIG. 1) to the base 12. An outlet pipe 54 (FIG. I) transports the protective fluid or atmosphere to a first turbine, refrigeration unit and first drier (all not shown) where such gas is dried and an inlet pipe 56 (FIG. 1) introduces the dried gas from a second turbine and second drier (also not shown).

7 IMPELLER SHAFT ASSEMBLY The metal shaft 40 has at one end (the upper end shown in FIGS. 1-3) a connector portion 58 (FIGS. 2, 2A, 3, 4, 5, 7) of reduced nonround cross section, the reduced cross section 58 having rounded comers and desirably having an elliptical cross section (FIGS. 2, 2A). The shaft 40 has a tapered portion 60 (FIGS. 2, 4, 5, 7) provided with a taper (of less than about a=20, FIG. 3) toward the upper end and adjacent the connector portion 58 and defining a shaft shoulder 62 (FIGS. 3, 4, 5, 7) with the connector portion 58.

The shaft 40 may be formed of the type 22H stainless steel manufactured by the National Alloy Division of White Industries, Cleveland, Ohio or the following nickelchromium steels, all of which have the following coefi'icients of expansion shown in table 1 below:

The ceramic impeller 42 is disposed on the shaft 40 and is provided with a connector aperture 584 (FIGS. 2, 2A, 3, 4, 5, 7) adapted to receive (and frictionally engage at 59, FIG, 2A, when rotated) the connector portion 58 with a predetermined cold clearance of about 0.030-0.040 inch at about F. The impeller 42 is provided with a tapered aperture 600 (FIGS. 3, 4, 5, 7) adjacent the connector aperture 58a and is adapted to receive the tapered portion 60 of the shaft 40 with one cold clearance of a cold clearance which is greater than the first cold coefficient of expansion of, for example, about 0.0350.050 inch, a cold clearance which is equal to the first cold coefficient of expansion of, for example, about 0.0350.050 inch and a cold clearance which is less than the first cold coefficient of expansion of, for example, about 0.0350.050 inch.

The tapered aperture 600 defines with connector aperture 580 an impeller shoulder 62a (FIGS. 3, 4, 5, 7). The impeller shoulder 62a is engageable with the shaft shoulder 62. The impeller 42 has a second coefficient of expansion less than the first coefficient of expansion of the metal shaft 40, which second coefficient of expansion is less than about 7.92 millionths of an IN/IN/ F. for the examples of the shafts 40 recited above.

The ceramic impeller 42 may be formed of a high alumina brick having the following approximate composition shown in table II.

The thermal expansion of the ceramic impeller 42 is shown in FIG. 3A.

Assuming an impeller thickness t=2.5 inches (FIG. 3) for the impeller 42 and a diameter d=3.0 inches (FIG. 3) for the shaft 40, then =l0.0 (10")X3.0 inchX( 2,075-20) =0.060 inch where E =expansion of the shaft 40 in inches;

C coefficient of expansion of the shaft 40 in inch/inch! D diameter of the shaft 40 in inches;

t temperature differential in F E,= expansion of the impeller 42 in inches;

C, coefficient of expansion of the impeller 42 in inch/inch at 2,075 F. (FIG. 3); and

At= thickness of the impeller 42 in inches.

Assuming a hot clearance of about 0.005 inch the hot temperature diameter of the shaft 40 is 3.065 inch. Subtracting the expansion E =0.0l8 inch for the impeller 42 gives a cold temperature IP=3.047 inch for the impeller 42.

' OPERATION The drive means or motor 34 causes rotation of the shaft 40 and the impeller 42 at a high speed of about 1,800 rpm. and at high temperatures of about l,075 F. for periods of about 3 0 hours. However, under such conditions, the predetermined cold clearance of about 0.035-0.050 inch and the one cold clearance (which is either greater, equal or less than about 0.0350.050 inch) are reduced to a limit which approaches but never reaches zero and desirably is maintained at about 0.005 inch.

During the high-speed temperature rotation of the shaft 40 and the impeller 42 the impeller 42 will tend to ride up the shaft 40 in the direction of the arrow (FIG 3).

, ALTERNATIVE EMBODIMENTS It will be understood by those skilled in the art that altematively an impeller shaft assembly (FIG. 4) may be used in the down" position. Retaining means are associated with the impeller 42 and the shaft 40 to retain the impeller 42 on the shaft 40 and have a washer 64 disposed between a bolt 66 (threaded into the connector portion 58) or the like and the impeller 42.

In FIG. 5 a cotter pin 68 or the like replaces the bolt 66 for use of the impeller shaft assembly in the side position.

FIG. 6 shows a generally polygonal connector portion 58 of the shaft 40 and having rounded comers 70 and a polygonal connector aperture 580 in the impeller 42 and also having rounded corners 700.

After a plurality of heating cycles (about five), a permanent growth deformation occurs in the shaft 40. In order to compensate for this growth deformation, the tapered portion 60 of the shaft 40 may be machined down about 0.005 inch or a spacer means, such as a washer 72 (FIG. 7) inserted between the shoulder 62 of the shaft'40 and the shoulder 62a of the impeller 42.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION It will be recognized by those skilled in the art that the objects of this invention have been achieved by providing an improved impeller shaft assembly which operates continuously at high speeds of about 1,800 rpm. instead of reduced speeds of about 900 r.p.m.; reduces the total coil annealing cycle by about 2 hours; avoids fracture of the impeller 42 during the operating cycle; provides a lightweight impeller 42 suitable for high-temperature operation up to about 2,075 E; eliminates any lifting effect on the impeller 42 by fluid flow; provides an adequate operating life at a reasonable cost; allows for the difference in the coefficient of expansion of the shaft 40 and the impeller 42; and substantially eliminates failure of the impeller drive motor 34.

While in accordance with the patent statutes a preferred and alternative embodiment of this invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

We claim:

I. An impeller shaft assembly for a fan operating at high temperatures in the range of ambient temperature to a highoperating temperature, said impeller shaft assembly having:

a. a metal shaft having at one end a connector portion of reduced nonround cross section; 1. said reduced cross section having rounded corners, 2. said shaft having a tapered portion provided with a taper toward said one end adjacent said connector portion and defining a shaft shoulder with said connector portion, 3. said shaft having a first coefficient of expansion, b. a ceramic impeller disposed on said shaft and provided with a connector aperture having a nonround cross section and adapted to receive said connector portion with a predetermined cold clearance, said connector aperture (58a) contacting said connector portion (58) along at least two contact lines (59); 1. said impeller being provided with a tapered aperture adjacent said connector aperture, adapted to receive said tapered portion with another cold clearance, and defining an impeller shoulder with said connector aperture, a. said impeller shoulder being engageable with said shaft shoulder, 2. said impeller having a second coefficient of expansion 7 less than said first coefficient of expansion,

c. drive means connected to said shaft to cause said shaft to frictionally engage said impeller thereby causing rotation of said shaft and said impeller at high speed;

d. said shaft and said impeller being rotated by said drive means at high speed and at said high temperature so that said predetermined cold clearance and said other cold clearance are reduced to a limit which approaches but never reaches zero.

2. The impeller shaft assembly recited in claim 1 wherein said reduced nonround cross section is generally elliptical.

3. The impeller shaft assembly recited in claim 1 wherein said reduced nonround cross section is generally polygonal and is provided with rounded comers.

4. The impeller shaft assembly recited in claim 1 wherein said metal shaft is stainless steel.

5. The impeller shaft assembly recited in claim 1 wherein said ceramic impeller has silica in the range of about 4.3 to 14.3 percent by weight; alumina in the range of about 85.0 to 95.0 percent by weight and trace quantities of titania, iron oxide, lime, magnesia and alkalies.

6. The impeller shaft assembly recited in claim 5 wherein said first predetermined cold clearance is in the range of about 0.03 50.0 50 inch. 7

7. Theimpeller shaft assembly recited in claim 1 wherein said limit is greater than 0.005 inch.

8. The impeller shaft assembly recited in claim I and having space means between said shaft shoulder and said impeller shoulder to maintain said predetermined cold clearance.

9. The impeller shaft assembly recited in claim 1 and having retaining means on said connector portion and engageable with said impeller to retain said impeller on said shaft.

10. The impeller shaft assembly recited in claim 1 wherein said taper is less than about 20.

11. The impeller shaft assembly recited in claim 1 wherein I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,604 319 Dated September Q 1 91 Inven Francis J. Krahe, et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet in the ABSTRACT, line 8, after "portion" insert and defining a shaft shoulder with the connector portion Column 3, line 32, after "42" insert (Figs. l,2,2A,3,4,7) line 56, "2" should be 3 Column 4, line 50, "(10 should be (10- line 69, "IP" should be ID line 75, "1,075F" should be 2,075F

Signed and sealed this 17th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'ISCHALK Attesting Officer Commissioner of Patents RM USCOMM-DC 003164=d9 GOVEwNMENT PRINTNG OFFICE 9.9 O-355 33

Claims

1. An impeller shaft assembly for a fan operating at high temperatures in the range of ambient temperature to a highoperating temperature, said impeller shaft assembly having: a. a metal shaft having at one end a connector portion of reduced nonround cross section; 1. said reduced cross section having rounded corners, 2. said shaft having a tapered portion provided with a taper toward said one end adjacent said connector portion and defining a shaft shoulder with said connector portion, 3. said shaft having a first coefficient of expansion, b. a ceramic impeller disposed on said shaft and provided with a connector aperture having a nonround cross section and adapted to receive said connector portion with a predetermined cold clearance, said connector aperture (58a) contacting said connector portion (58) along at least two contact lines (59); 1. said impeller being provided with a tapered aperture adjacent said connector aperture, adapted to receive said tapered portion with another cold clearance, and defining an impeller shoulder with said connector aperture, a. said impeller shoulder being engageable with said shaft shoulder, 2. said impeller having a second coefficient of expansion less than said first coefficient of expansion, c. drive means connected to said shaft to cause said shaft to frictionally engage said impeller thereby causing rotation of said shaft and said impeller at high speed; d. said shaft and said impeller being rotated by said drive means at high speed and at said high temperature so that said predetermined cold clearance and said other cold clearance are reduced to a limit which approaches but never reaches zero.

2. said shaft having a tapered portion provided with a taper toward said one end adjacent said connector portion and defining a shaft shoulder with said connector portion,

2. said impeller having a second coefficient of expansion less than said first coefficient of expansion, c. drive means connected to said shaft to cause said shaft to frictionally engage said impeller thereby causing rotation of said shaft and said impeller at high speed; d. said shaft and said impeller being rotated by said drive means at high speed and at said high temperature so that said predetermined cold clearance and said other cold clearance are reduced to a limit which approaches but never reaches zero.

3. The impeller shaft assembly recited in claim 1 wherein said reduced nonround cross section is generally polygonal and is provided with rounded corners.

3. said shaft having a first coefficient of expansion, b. a ceramic impeller disposed on said shaft and provided with a connector aperture having a nonround cross section and adapted to receive said connector portion with a predetermined cold clearance, said connector aperture (58a) contacting said connector portion (58) along at least two contact lines (59);

6. The impeller shaft assembly recited in claim 5 wherein said first predetermined cold clearance is in the range of about 0.035-0.050 inch.

7. The impeller shaft assembly recited in claim 1 wherein said limit is greater than 0.005 inch.

8. The impeller shaft assembly recited in claim 1 and having space means between said shaft shoulder and said impeller shoulder to maintain said predetermined cold clearance.

10. The impeller shaft assembly recited in Claim 1 wherein said taper is less than about 20*.

11. The impeller shaft assembly recited in claim 1 wherein said stainless steel has a minimum nickel content of about 35 percent and a minimum chromium content of about 15 percent.