Method of manufacturing cylinder structures

Application filed April 10

My invention relates to a method or process of manufacturing cylinder structures, and particularly cylinder structures adapted for use in internal combustion engines and it has 6 for an object to provide a novel and improyed method or process of the foregoing character which shall be susceptible of easy and practical accomplishment and at the same time capable of producing a cylinder ¹⁰ structure having improved physical properties. ' It has for a further object to provide an improved process or method of manufacture capable of producing a cylinder structure ¹⁵ which shall be less subject to wear than cylinders heretofore manufactured and which shall be non-corrodible.

It has for still another object to provide a • method or process of the foregoing character which shall be capable of producing a cylinder structure having an inner or bored surface of such a character that the amount of sliding friction created by a working piston reciprocating therein shall be materially less ⁵ than the amount created in cylinders constructed in accordance with the methods or processes of the prior art.

It has for still another object to provide a process or method of manufacture of the ³⁰ foregoing character which shall be capable of producing a cylinder of the water-jacket type wherein the interior surfaces of the jacket contacting with the cooling water shall ₃₅ be of such a character as to effectively resist corrosion thereof.

It has for still another object to provide a method or process of-the foregoing character wherein the cylinder structure shall be 40 composed of a steel which may have its sur-_ faces hardened by the absorption of nitrogen and wherein the cylinder structure may be hardened by a nitriding process.

These and other objects are effected by my ¹⁵ invention, as will be apparent from the following description and claim taken in connection with the accompanying drawings, forming a part of this application, in which: _w Fig. 1 is a view, in sectional elevation, of a finished air-cooled type of cylinder structure , 1929. Serial No. 354,112.

constructed in accordance with my improved method or process of manufacture;

Fig. 2 is a view, in sectional elevation, of the cylinder shown in Fig. 1 during a step of its process of manufacture; and, 65

Fig. 3 is a view, in sectional elevation, of a finished cylinder structure of the water cooled type constructed in accordance with my improved method or process of manufacture.

It is well known that the cylinders of in- 60 ternal combustion engines wear continuously in their bores because of the friction which takes place as a result of the rubbing action created between the bore of the cylinder and the piston and its piston rings. As the wear 65 increases, the bore of the cylinder becomes more and more deformed, resulting in objectionable leakage of lubricating oil past the piston and piston rings and ultimately requiring that the cylinder be either rebored 7u or discarded. In addition, the exterior surfaces of the cylinder and particularly, if it is of the air-cooled type, are subject to intensive corrosive action because of dampness' · prevailing in the atmosphere or because of M its use in the propulsion of aircraft of the marine type.

I have, therefore, conceived of a process or method of manufacture, whereby cylinders of the foregoing character may be readily 80 manufactured having both their interior and exterior surfaces hardened to a very high degree. As a result, because of the very hard character of the cylinder bore, the friction created between the piston and the cylinder 85 wall is materially lessened and consequently excessive wear or deformation of the cylinder bore is avoided. In addition, the exterior surface of the cylinder, being also very hard, is preserved and is not subject to corrosion ⁸⁰as in the ordinary cylinder.

In accordance with my invention, I form the cylinder of a steel which may be hardened by nitriding, that is, by the absorption of nitrogen. In this way, ή desired, all of ⁸⁸the surfaces of the cylinder may be hardened and, because of the relatively low temperatures involved and the avoidance of any quenching operation in the hardening process, any danger of warping or distorting the ^lno

1,853,562 cylinder structure is entirely avoided. Various kinds of alloy steels may be employed in the method herein proposed. Steels containing aluminum, chromium, manganese, 6 silicon or molybdenum, either separately or in any desired combination, may be considered to be nitridable. Preferably, I employ a steel known in the trade as Nitralloy and embodying the following constituents:

Per cent

C____________________________0.20 - 1.30

Mn__________________________0.40 - 0.60

P_________ 0.025-Max.

S______________________:______ 0.025-Max.

¹⁵ Si___________________________0.50 -Max.

Ni___________________________0.20 -Max.

Or___________________________0.75 - 1.50

Mo___________________________0.15 - 0.25

A1__l________________________0.50 - 1.25

Such a steel may be hardened for use in cylinder structures by placing it in a retort, raising the temperature of the retort sufficiently, for example, between 900° and 1050° 25 F., and disposing some substance capable of giving off nitrogen such as, for example, ammonia gas, into the retort for a sufficient length of time to obtain the depth of surface hardness required. In this way, a cylinder 30 structure is easily and readily produced which, obviously, has improved wearing qualities.

In addition to cylinders of the air cooled type, my method or process of manufacture 35 is equally applicable to cylinders of the water cooled or water-jacketed type wherein, not only may the bore of the cylinder and its exterior surfaces be made relatively hard, but the entire interior surfaces of the jacket space 40 may also be hardened so that the cooling water passing through the jacket cannot corrode the same. This constitutes a very important feature of my invention because of the fact that, although the interior surfaces of the 45 water-jacket space or spaces may be relatively inaccessible, nevertheless, by my improved method or process of manufacture, the entire surfaces of such spaces may be readily hardened.

One of the advantages of my improved method or process of manufacture res’ les in the fact that the temperatures involve.! in the process of nitriding are relatively low, that is, substantially lower than the tempera60 tures ordinarily involved in such heat treating. operations as, for example, case hardening. In addition, no quenching or drawing operation is involved so that the entire cylinder structure, when completed, may have its 60 surfaces hardened without any danger of distorting or warping the same.

Referring now to the drawings for examples of cylinders which may be constructed in accordance with my improved 65 process of method, I show in Fig. 1, a cylinder structure composed of a cylinder or barrel portion 10 provided with a series of annularly-extending cooling fins 11. Secured to the upper end of the cylinder or barrel portion 10 in any approved manner, as by shrinking and screw threads 12, is a cylinder head 13 generally composed of aluminum or some aluminum alloy. Disposed within the cylinder 10 is a piston 14 reciprocable therein in a manner well under- 75 stood in the art.

Referring now to the process of manufacturing the foregoing cylinder, it is noted that first of all a steel is selected for the cylinder barrel 10 which has such properties 80 that it may be readily hardened by nitriding. Preferably, the steel mentioned heretofore and known in the trade as Nitralloy is employed. Such a steel may, if desired, be so heat-treated as to have physical properties 85 equivalent to those of chrome nickel steel and hence a very light cylinder, consistent with the strength thereof, may be produced. In accordance with my improved method, the cylinder 10 is rough machined from a piece 80 of steel of the foregoing character. Thereafter, I may, if I so desire, heat treat it to relieve it of any internal strains or stresses. It is then machined to finish size and is preferably fitted with a cap 15, Fig. 2, in order ⁰⁵to prevent the threads 12 from being nitrided.

It is then disposed in. a closed retort, the temperature of which is raised, for example, to between 900° and 1050° F., and ammonia . gas is allowed to flow into the retort. This constitutes the process of nitriding and it continues until such time as the steel has absorbed sufficient of the nitrogen given off by the ammonia to provide the depth of hardness required. In other words, the longer ¹⁰⁵the cylinder is retained in the atmosphere of ammonia, the greater the depth of hardness. I have found that with a steel of the foregoing character, suitable cylinders may be produced by subjecting them to the fore- ¹¹⁰going hardening process for a period of from 24 to 90 hours, the length of time being dependent upon the size, design and service requirements of the cylinder.

Upon completion of the hardening process ¹¹⁸the cylinder is removed from the retort after which the cap 15 is removed from the cylinder and the head 13 fitted thereto in a mam ner well understood in the art.

From the foregoing description, it will be apparent that, by my process of manufacturing, a cylinder may be produced having both its inner surface or bore as well as its exterior surface hardened to a very high degree so that friction in the cylinder bore is lessened, excessive wear of the cylinder bore is avoided and any tendency for the exterior surfaces to corrode is eliminated. Such a form of cylinder may be said to have a maxi- .,θ mum length of useful life.

1,853,662

In the foregoing embodiment, I have assumed that all of the hardened surface portions have been provided with an equal depth of hardness. However, in some instances, I 5 may desire to provide one portion of the cylinder structure with a depth of· hardness greater than another portion and this may be readily accomplished in accordance with my improved process. For example, assum10 that it is desired to provide a greater depth of hardness for the bore of the cylinder structure than the exterior surface of the cylinder structure, I may cover the exterior surface, leaving the bore of the cylinder ex15 posed, and submit the cylinder structure to the nitriding process. After the nitriding process has continued for the proper length of time, the cylinder structure may be removed from the retort and the cover removed 20 from the exterior surface of the cylinder structure. Thereafter the cylinder structure may - be again disposed in the retort whereupon hardening of the exterior surface is effected and additional hardening of the 25 bore is also effected. After final removal of the cylinder structure from the retort, it will be obvious that the depth of hardness of the bore of the cylinder structure will be greater than that of its exterior surface. It 30 will, therefore be apparent that, in accordance with my improved process of manufacture, it is possible to produce cylinder structures wherein different depths of hardness are provided for different portions of the ³⁵ structures, as required.

Referring now to Fig. 3, this shows a cylinder of the water cooled type having an inner cylindrical sleeve 21 and an outer jacket sleeve 22 defining therewith an intervening 40 cooling jacket 23. Cooling fluid, for example, water may be supplied to the cooling jacket 23 through an inlet 24 and discharged through an outlet 25.

Although my invention is applicable to ⁴⁵ any type of water cooled cylinder, I have shown, for purposes of illustration, a cylinder of the opposed piston type provided with longitudinally spaced scavenging fluid inlet ports 26 and exhaust outlet ports 27. Lo⁵⁰ cated intermediate of the ends of the cylinder are circular, fuel inlet ports 28 and disposed within the cylinder are opposed pistons 29 and 31 arranged to reciprocate therein in a manner well understood in the art.

As disclosed and claimed in a copending application of mine, Serial No. 331,809, Patent No. 1,820,069 issued on Aug. 25,1931 entitled Method of manufacturing an engine cylinder and assigned to the Westinghouse Electric & Manufacturing Company, the sleeve 21 and the jacket sleeve 22 of a cylinder structure of the type shown in Fig. 3 are preferably first formed from separate pieces of material after which the jacket sleeve 22 is secured upon the cylinder sleeve by a shrinking process. In order to insure thorough water-tightness of the cooling jacket, the end-portions of the jacket sleeve may be welded to the cylinder sleeve as at 32 and 33. In addition, the jacket sleeve 70 may be welded to the cylinder sleeve in the vicinity of the cylinder ports, as at 34, 35 and 36.

Referring now to my improved, process or method of manufacturing a cylinder of the 75 .. foregoing character, it is noted that first of all the cylinder sleeve 21 and the jacket sleeve 22 are separately machined from a steel of the character heretofore mentioned, that is, a steel that may be hardened by nitriding. 8® Thereafter, the jacket sleeve may be fixedly secured upon the cylinder sleeve by a shrinking process after which' the welding of the jacket sleeve to the cylinder sleeve may be effected. In the welding process, a welding 85 steel is utilized having properties similar to that of the jacket sleeve and the cylinder sleeve, in that it is susceptible of hardening by nitriding.

After assembly of the jacket sleeve upon ⁹⁰the cylinder sleeve, the entire cylinder structure may be disposed in a retort and heated m the presence of ammonia gas in order that all of the surfaces of the cylinder may absorb the nitrogen given off by the ammonia ⁹³gas and become hardened. The flanges 37 may be utilized to protect the threads 38 from the nitriding process.

Upon completion of the nitriding process, the cylinder structure may be removed from ¹⁰⁰the retort and¹ there is thus produced a cylinder of the water cooled type having a hardened bore, having a hardened exterior surface resistive to corrosion or the influence of dampness in the atmosphere, and an inte- ⁷⁹³rior jacket space, all surfaces of which are very hard.

Attention is especially invited to the fact that my method permits of hardening the entire, relatively inaccessible, surfaces of the ¹¹⁰jacket space 23, the ammonia gas having ready access thereto through the cooling water connections ordinarily provided in the cylinder structure.

While I prefer to use the nitriding proc- ¹¹⁵ess for hardening those portions of the cylinder structure required to be hardened because of the peculiar adaptability of the nitriding process on account of the low temperatures involved and the absence of chang- ¹²⁰ing the physical properties of the element hardened, nevertheless it will be understood by those skilled in the art that my invention, in its broader aspects, contemplates hardening by any suitable medium. That is, the ¹²⁶invention, considered from a broad point of view, consists in providing a suitable cylinder structure having portions to be hardened, and, in some cases, portions not to be hardened, in covering the portions not to be ¹³⁰

1,863,662 hardened by some suitable material, and then in subjecting.the cylinder structure to the influences of a suitable hardening agent and under proper conditions. ,

From the foregoing, it will be apparent that I have evolved a novel method or process of manufacturing cylinder structures of both air and water cooled types whereby the surfaces of the cylinders are readily hardened 10 to a very high degree so as to resist wear and corrosion and that the method proposed is susceptible of ready accomplishment and capable of producing cylinder structures having improved physical qualities.

While I have shown my invention in several forms, it will be obvious to those skilled in-the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specificially set forth in the appended claim.