US2647847A - Method for interfitting machined parts - Google Patents

Description

Aug. 4, 1953 M. 5. BLACK ET AL METHOD FOR INTERFITTING MACHINED PARTS Filed Feb. 28 1950 W J J 3nventors M/LLA RD 5. BLACK a M 7 k 6 r d R 5 A Gttorneg Patented Aug. 4, 1953 METHOD FOR INTERFISTTING MACHINED ART Millard s. Black, Huntington Park, and Albert G. Satterla, Jr., Whittier, Califi, assignors to Fluid Packed Pump Company, Los Nietos, Calif., a

partnership Application February 28, 1950, Serial No. 146,764

11 Claims.

' This invention relates to a method for tightly interfitting machined parts. For a better understandin of the present method, the pump barrel, such as in pumps conventionally employed in wells, will here provide the basis in respect to which the method will be described. It should-be understood, however, that the barrel is intended as an exemplary device.

. For reasons of durability, pump barrels essentially comprise a jacket and a suitable number of sleeves or liners therein, the latter having the I required hardness to resist wear of the piston operating in the barrel and also having the required resistance to corrosion.

At the present time there are two generally conventional methods for obtaining a tight fit of the liners in a barrel jacket. Both entail machining of the outer diameter of the liners to a dimension slightly greater than the machined internal diameter of the jacket. Since the barrels and, therefore, the jackets are frequently fifteen feet long and seldom less than six feet long, and the liners have a length in the nature of ten to twelve inches, it will be evident that to attempt to drive or press the liners into the jacket would be unsatisfactory. One of the mentioned conventional methods entails heating the jacket to a degree sufiicient to cause the same to expand to a size freely admittin the liners and then allowing the jacket to cool and shrink over the liners to tightly grip the same. The other conventional method entails subjecting the liners to low temperatures to cause them to shrink to a size whereby they Will freely slip into the jacket. When the liners are restored to normal temperatures, they will expand to their original size and tightly fit the jacket. Thus, in one case, the jacket is temporarily expanded, and in the other, the liners are temporarily shrunk or contracted.

In both cases, unless the interference fit of the jacket and liners is initially accurately gauged, the jacket is normally under considerable stress which is increased under working conditions wherein the temperature of the barrel, due to friction and for other reasons, rises above normal.

In contradistinction to, the above-described methods, the present method entails effecting a tight interfit of liners in a jacket by subjecting the entire assembly thereof to sub-zero temperatures to cause the liners to exp-and or grow to a size greater than theirinitial size, it being an object of, the present invention to provide a method, as indicated, in which an entire assem bly is subjected to abnormal temperatures rather than subjecting one or the other components of the assembly to abnormal temperatures, as in the old methods here given.

We have found that certain iron alloys have the property of growing when subjected to sub-zero temperatures and that the growth is permanent. While other metals expand only under heat and then contract when the heat is dissipated, and contract temporarily when subjected to sub-zero temperatures, iron alloys containing nickel and chromium permanently grow when subjected to sub-zero temperatures. After growth, such alloys are stabilized in the same manner as other metals, and return to the size to which the same have grown after normal expansion and contraction as will other metals.

Accordingly, another object of the invention is to provide a method for producing a tightly interfitted assembly of elements that makes use of the permanent growth characteristics of certain metals, thus enablin machining of the elements for an initialfree orloose interfit which becomesv a tight interfit when the assembly is subjected to sub-zero temperatures.

Of importance also is the fact that the hardness of alloys, as mentioned, increases after growth, a material advantage where such increased hardness is desired. Also of importance is that such alloys are highly corrosion-resistant.

Under tests which we have conducted, it has been found that 5% Ni and 2% Or with 93% Fe provides an alloy having desired properties with respect to hardness and resistance to corrosion. and that the same is easily machineable. The given formula is suitable for producing barrel liners that are approximately two inches in diameter and ten to twelve inches long. Should less hardness and corrosion-resistance be satisfactory, the nickel content may vary between 3.5% and 4%, and the chromium between 1.4% and. 1.6%.

Reference is now made to the drawing in which: i

Fig. 1 is an elevational view of a pump barrel, partly in longitudinal section and partly broken away.

Fig. 2 is an enlarged longitudinal sectional view, showing the interfit of the parts before the assembly is subjected to sub-zero temperatures.

Fig. 3 is a similar View after application of cold.

In a conventional manner, the barrel that i illustrated comprises a metal jacket 5 towhich is fitted end connections 6, the latter affording end shoulders. 1 between which a series of liners '8 reside within the jacket 5.

According to the present method, the length of the barrel between shoulders I is made to be somewhat larger than the total length of all of the liners 8 when the latter, after machining, are at normal temperatures. In practice, it has been found that ten to twelve inch long liners of an iron alloy, as above, will permanently elongate some .015 inch. Consequently, if there are ten liners 8 in the jacket, the total length of all of the liners is made to be some .150 inch less than the distance between shoulders I. Some variation is permissible providing the expanded total length of the liners closely approximates the distance between shoulders l to insure tight joints where the liners abut.

The internal diameter 9 of the jacket is machined to be slightly greater than the machined external diameter 10 of the liners. In practice, it has been found that the liners expand or grow diametrally some .002 inch per one inch diameter, a two inch diameter liner, growing approximately .004 inch. Thus, if the external diameter of the liners is machined to a dimension .002 inch smaller than the internal diameter of the jacket, the liners can readily be slipped, with suitable clearance, into the jacket, as suggested in Fig. 2, in which the clearance is exaggerated for illustrative purposes. The mentioned .020 inchdifference in length of the liners and the distance between shoulders I is also indicated at H in Fig. 2.

With the jacket 5 and liners 8 machined as above, and assembled with the easy facility permitted because the liners are smaller than the bore of the jacket, the assembly is subjected to sub-zero temperatures. Under actual test conditions it has been found that a two inch diameter liner having an eighth inch Wall, temporarily contracts to 1.9995 inches at 32 F., grows to 2.002 inches at between 60 and l00 F.,

and continues to grow to 2.004 inches during the L period approximating two hours or until the CO2 has completely evaporated. Under such deep freeze, the liners are permanently grown, expanded or enlarged, as stated, and the jacket is temporarily shrunk, returning to its initial size at room temperature. When the assembly has been restored to such normal temperature, an approximate .002 inch interference fit between the inner diameter of the jacket and the outer diameter of the liners is effected, the liners thereby being tightly and permanently fitted to the jacket as shown in Fig. 3.

Stress relief of the assembly may be effected with a 400 F. draw without change in the assembly except to realign the molecules of the liners to relieve stress therein. The normalizing temperature may vary, as desired.

It will be evident that the greater the differences of the machined diameters of the jacket and liners, the easier it is to slip the liners into the jacket. Accordingly, while higher temperatures than are obtained with solidified CO2 may be employed, the wider machining tolerances afforded when l00 F. is used, make CO2 an at present preferred medium for the instant method.

4 With respect to hardness, cast iron containing 5% Ni and 2% Cr has a hardness of Rockwell C which, when the alloy is deep frozen, as above, increases to C60. This increase in hardness is a material advantage for liners and like wear parts. It will be seen that the increased A hardness is obtained after the liners are maneeded.

chined, a further advantage since the machining is performed when the liners are relatively softer. While the metalurgy need not be discussed in detail, it may be stated that, in the iron alloy given, the nickel and chromium are the agents which harden the alloy as a casting thereof cools. No special hardening process is The increase in hardness observed under deep freeze is thought to result from an austenitic change in the combined carbon or iron carbide contained in the iron.

After the assembly has been restored to normal temperatures, the inner diameter of the lined barrel is honed, to insure a uniform bore in the barrel.

The assembly thus provided will expand and contract in the normal manner of metals, thereby insuring retention of the tight fit that is achieved according to the present method.

The present method may be employed to interfit other parts than jackets and liners, providing the inner part is formed of an alloy as above given.

While we have disclosed what we now regard as the preferred method of our invention, we do not wish to restrict ourselves to the particular method described but desire to avail ourselves of all modifications that may fall within the scope of the appended claims.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

l. A method for interfitting two metal parts one within the other that consists in providing the outer part with a seat that is sli htly larger than the inner part to receive said inner part with sliding clearance, forming said inner part of a ferrous metal that includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, and subjecting the assembled parts to a sub-zero temperature that is sufficiently low enough to cause said inner part to permanently grow to a size larger than the seatit occupies and to tightly fit said seat.

2. A method for interfitting two metal parts one within the other that consists in providing the outer part with a seat that is slightly larger than the inner part to receive said inner part with sliding clearance, forming said inner part of a ferrous metal that includes approximately 5% of nickel and approximately 2 of chromium, and subjecting the assembled parts to a subzero temperature that is sufficiently low enough to cause said inner part to permanently grow to a size larger than the seat it occupies and to tightly fit said seat.

3. A method for interfitting two metal parts one within the other that consists in providing the outer part with a seat that is slightly larger than the inner part to receive said inner part with sliding clearance, forming said inner part of a ferrous metal that includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, and subjecting the assembled parts to a temperature ranging between 60 F. and I00 F. to cause said inner part to permanently grow to a size larger than the seat it occupies and to tightly fit said seat.

4. A method for lining a cylindrically tubular jacket with wear and corrosion resistant liners that consists in providing a jacket of metal that contracts when subjected to subzero temperatures and returns to its initial size when returned to normal temperatures, providing a set of liners for the jacket of a metal that expands permanently when subjected to sub-zero temperatures, the inner diameter of the jacket and the outer diameter of the liners having such relative size that the latter slidingly fit into the former, and then subjecting the assembly of jacket and liners to sub-zero temperatures sufficiently low to cause the outer diameter of the liners to expand to a size greater than the initial diameter of the jacket.

5. The method according to claim 4 in which the sub-zero temperatures range below 60 F.

6. The method according to claim 4 in which the liners comprise a metal including 3.5 to 5% nickel, 1.4 to 2% chromium and the remainder iron.

'7. A method for interfitting metal parts that consists in providing one part with a seat that is slightly larger than the other part to receive said other part with sliding clearance, forming said other part of a metal that has the characteristic of permanently growing under subzero temperatures, and subjecting the assembled parts to a sub-zero temperature that is low enough to cause said other part to permanently grow to a size larger than the seat it occupies and to tightly fit said seat.

8. A method for forming an internally lined elongated tubular assembly that consists in providing an outer, elongated tube jacket of a metal that temporarily shrinks under sub-zero temperature and with an inner diameter that constitutes a seat slightly larger than the outer diameter of at least two liners, assembling said liners in the jacket by freely sliding the same into said seat, forming said liners of a ferrous metal that includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, and subjecting the assembled parts to a sub-zero temperature that is low enough to cause said liners to permanently grow to a diametral size larger than the diameter of said seat to thereby tightly fit said jacket seat.

9. A method for forming an internally lined elongated tubular assembly that consists in providing an outer, elongated tube jacket of a metal that temporarily shrinks under sub-zero temperature and with an inner diameter that constitutes a seat slightly larger than the outer diameter of at least two liners, assembling said liners in the jacket by freely sliding the same into said seat, forming said liners of a ferrous metal that includes 3.5 to 5% of nickel and 1.4 to 2% of chromium, and subjecting the assembled parts to a sub-zero temperature that is low enough to cause said liners to permanently grow to a diametral size larger than the diameter of said seat to thereby tightly fit said jacket seat, and to cause said tube jacket to temporarily shrink over the liners while the latter grow.

10. A method for interfitting two tubular metal parts one within the other that consists in casting the inner part of a ferrous metal that includes 3.5% to 5% of nickel and 1.4% to 2% of chromium and which metal hardens when subjected to sub-zero temperature, machining the outer surface of said part while the same is at ordinary room temperature and While relatively soft, forming a seat in the outer part that is slightly larger than the machined inner part while said outer part is also at ordinary room temperature, assembling the inner part with sliding clearance into the seat of the outer part, and subjecting the assembled parts to sub-zero temperature at least as low as F. to cause said inner part, by reason of its composition, to harden and to permanently grow to a size larger than the initial size of the seat in the outer part and to, thereby, tightly fit said seat after the parts have been returned to room temperature.

11. A method according to claim 10: the step of honing the inner surface of the inner tubular part to make the size of said inner surface uniform.

MILLARD S. BLACK. ALBERT G. SA'I'IERLA, JR.

References Cited in the file of this patent FOREIGN PATENTS Number Country Date 475,244 Great Britain Nov. 16, 1937 436,961 Great Britain Oct. 21, 1945 OTHER REFERENCES P. 94 Steel, Nov. 6, 1944, Reclaims Undersize Pins.

P. 445 Alloys of. Iron and Chromium, vol. Kinzel and Crafts, pub. 1937, McGraw-Hill Book Co., New York, N. Y. (Copy in Div. 3.)

P. 678 Effect of Temp. on Metals, pub. by Americ. Society of Mech. Eng, 29 W. 39th St., New York, N. Y. (Copy in Div. 3.)

Cold Treating Practice With Deep Freeze, pub. in 1946 by Deep Freeze, 2301 Davis St., Chicago, 111., pp. 5, 7, 24, and 30. (Copy in Div. 14.)

Claims (2)

1. A METHOD FOR INTERFITTING TWO METAL PARTS ONE WITHIN THE OTHER THAT CONSISTS IN PROVIDING THE OUTER PART WITH A SEAT THAT IS SLIGHTLY LARGER THAN THE INNER PART TO RECEIVE SAID INNER PART WITH SLIDING CLEARANCE, FORMING SAID INNER PART OF A FERROUS METAL THAT INCLUDES 3.5 TO 5% OF NICKEL AND 1.4 TO 2% OF CHROMIUM, AND SUBJECTING THE ASSEMBLED PARTS TO A SUB-ZERO TEMPERATURE THAT IS SUFFICIENTLY LOW ENOUGH TO CAUSE SAID INNER PART TO PERMANENTLY GROW TO A SIZE LARGER THAN THE SEAT IT OCCUPIES AND TO TIGHTLY FIT SAID SEAT.

10. A METHOD FOR INTERFITTING TWO TUBULAR METAL PARTS ONE WITHIN THE OTHER THAT CONSISTS IN CASTING THE INNER PART OF A FERROUS METAL THAT INCLUDES 3.5% TO 5% OF NICKEL AND 1.4% TO 2% OF CHROMIUM AND WHICH METAL HARDENS WHEN SUBJECTED TO SUB-ZERO TEMPERATURE, MACHINING THE OUTER SURFACE OF SAID PART WHILE THE SAME IS AT ORDINARY ROOM TEMPERATURE AND WHILE RELATIVELY SOFT, FORMING A SEAT IN THE OUTER PART THAT IS SLIGHTLY LARGER THAN THE MACHINED INNER PART WHILE SAID OUTER PART IS ALSO AT ORDINARY ROOM TEMPERATURE, ASSEMBLING THE INNER PART WITH SLIDING CLEARANCE INTO THE SEAT OF THE OUTER PART, AND SUBJECTING THE ASSEMBLED PARTS TO SUB-ZERO TEMPERATURE AT LEAST AS LOW AS -60* F. TO CAUSE SAID INNER PART, BY REASON OF ITS COMPOSITION, TO HARDEN AND TO PERMANENTLY GROW TO A SIZE LARGER THAN THE INITIAL SIZE OF THE SEAT IN THE OUTER PART AND TO, THEREBY, TIGHTLY FIT SAID SEAT AFTER THE PARTS HAVE BEEN RETURNED TO ROOM TEMPERATURE.

Images