US3382557A - Means for manufacturing blanks for cast iron piston rings - Google Patents

Description

y 1968 E. s. NICKOLAENKO ETAL 3,382,557

MEANS FOR MANUFACTURING BLANKS FOR CAST IRON PISTON RINGS Filed May 28. 1964 United States Patent 3,382,557 MEANS FOR MANUFACTURING BLANKS FOR CAST IRON PISTON RINGS Evgeny Grigorjevich Nickolaenko, Dolja Josifoviclr Jassky, Evgeny Emeljanovich Mikotin, Georgy Grigorjevich Tsarev, and Petr Georgievich Kalashnikov, Odessa, and Filipp Mikhailovich Belykh, Georgy Mikhailovich Shevchenko, and Sergei Andreevich Mikulin, Stavropol, U.S.S.R., assignors to Tsentralnoe Konstruktorsko-Tei-:hnologicheskoe Bureau, Odessa, U.S.S.R.

Filed May 28, 1964, Ser. No. 370,955 2 Claims. (CI. 29-33) ABSTRACT OF THE DISCLOSURE Apparatus for producing piston ring blanks from liquid cast iron in which the liquid iron is cast into strips between rolls and means being provided for the cold-roll sizing of the strip thickness. The cold-roll strips are cut into narrow strips having a thickness approximating the radial thickness of a piston ring and such narrow strips are wound into a continuous helical spiral with such winding being combined with a longitudinal translational movement of the spiral. The spiral is cut along the cylinder generatrix into piston ring blanks and the blanks are heat treated.

The present invention relates to methods of manufacturing blanks for cast iron compression, oil control and other kinds of piston rings and to devices therefor.

Various modifications are known of the widely spread method of producing blanks for cast iron piston rings by individual casting in sand and other moulds made with patterns having the shape of a ready ring in a free, inoperative state.

However the method of individual casting of blanks for cast iron piston rings does not provide for producing blanks which both in size and shape would be similar to those of the ready rings.

The disadvantages of the known method of casting iron blanks for piston rings are as follows.

(a) Low percentage of metal utilization. For instance, when casting automobile piston rings the percentage of metal utilization does not exceed percent whereas in case of tractor rings it comes nearly to percent with about 80 to 90 percent of the metal running to shavings, scrap, rejects, runners and other wastage.

(b) Considerable size discrepancy of blanks and manufactured piston rings owing to great finishing allowances usually of the order of 50 to 60 percent of the weight of the blanks. From 60 to 70 percent of total labour is spent on removal of these allowances.

(c) Non-uniformity of metal structure and differences in the mechanical properties of blank metal across the ring plane section, conditioned by the one-sided feed of metal adopted in conformity with the existing pouring technology, that brings about a decrease of the piston ring service life.

(d) High percentage of foundry faults mainly due to the presence of cavities and other defects often reaching from 30 to 40 percent of the total number of cast blanks.

The above-described and other disadvantages inherent to all the modifications of the method of individual casting of iron blanks for piston rings make it impossible to automate the process of manufacturing piston rings.

It is also almost impossible to organize manufacture of rings with the required tolerance. In the bulk of the manufactured cast iron piston rings the permissible clearance of less than 0.02 mm. on the ring arc of 30 usually is not provided which leads to great annual overconsumption of fuel and lubricants and also to shut down time of motor vehicles because of the wear of engine cylinders.

The improvements proposed hitherto for the method of individual casting of blanks for cast iron piston rings actually did not eliminate said disadvantages of this particular method.

Another method also known in the art envisages manufaoture of piston rings from a cold, flattened steel strip, which are wound within the limits of elastic deformations with no mandrel between the rollers, placed at a certain angle, into a space spiral with the diameter equal to that of the piston ring in its operative (compressed) condition. Such a spiral has been manufactured in compliance with the method of bending of a bar disposed on two supportrollers by means of a third roller. The metal utilization factor for the piston rings wound from a steel strip sharply increases whereas the need in (the equipment for their further mechanical treatment substantially decreases.

However this method has not received wide application in manufacturing piston rings, because of the high cost of flattened steel strips and high percentage of rejected rings due to the non-uniformity of metal strength and structure resulting in an uneven curvature of the piston ring.

Such rings do not fit closely in the piston grooves so that the permissible clearance between the cylinder and the ring (no more than 0.02 mm.) is not observed and therefore normal operation of the engine is not provided. Besides, the creep-resistance of the piston rings made from a steel strip is lower than that of cast iron rings.

Thus, piston rings made of steel strip also failed to find Wide application. At best they are inserted into the lower grooves of the piston or in worn out cylinders. The upper piston grooves still should be provided with cast iron piston rings.

The proposed method of manufacturing blanks for cast iron piston rings provides utilization of favorable properties of cast iron as a mate-rial for making piston rings and, moreover, eliminates the disadvantages characteristic for the method of individual casting of iron blanks.

It has been proved that cheap blanks of high grade cast iron piston rings can be produced by an automatic process of their manufacture.

The proposed method of manufacturing blanks for piston rings from liquid cast iron, claimed in the present specification comprehends a well-known method of casting (rolling) the liquid cast iron into sheets between revolving rollers. (Authors certificates of the U.S.S.R. Nos. 57,902, 67,458, and others, 1940).

The main object of the invention is to provide a simple, reliable and cheap method of manufacturing cast iron blanks for piston rings which would be as close as pos sible to the ready piston rings in both shape and size.

Another object of the invention is to provide a method of manufacturing cast iron blanks for piston rings by which both metal expenditure and labor consumption of the process would be considerably reduced, a method that would provide uniform structure of the metal, improve mechanical characteristics of the rings and increase their wear-resistance without any negative influence upon the service life of the engine in which said rings operate.

One of the objects of the invention is to provide a method of manufacturing cast iron blanks of which thin piston rings could be made so that upon inserting tWo or four rings in one piston groove (instead of a single cast ring) their contact with the cylinder would be tight and practically without any clearance during the whole service life.

One more object of the invention is to provide means for manufacturing blanks for piston rings from liquid cast iron.

The aforementioned objects can be achieved due to the novel features of the proposed method of manufacturing blanks for piston rings from liquid cast iron and to the proposed embodiment of means for producing said blanks.

Blanks for piston rings are produced by combining such known procedures as casting strips of liquid cast iron; sizing strip thickness by cold rolling, cutting the strip into narrow ones and winding said narrow strips at the temperature of elastic deformation onto a revolving mandrel which shapes them into helical spirals, with the winding being combined with the spiral translational travel along the mandrel axis, and simultaneous cutting of the spiral along the generatrix of the cylinder. Then, the blanks for piston rings are subjected to heat treatment for obtaining the optimum structure of the cast iron and for thermofixation of the rings. After being wound the blanks do not require heat treatment.

The heated strip is wound on a mandrel which has an elliptical cross-section corresponding to the shape of the piston ring in its free inoperative state, or it is wound on a round mandrel of the same diameter as the inner diameter of the piston ring in its operative (compressed) state.

The proposed means for manufacturing blanks for piston rings from liquid cast iron is a complex of devices for casting (rolling) cast iron strips between rollers for sizing of the strip thickness by cold rolling, for cutting the strip into narrow ones; it comprises a complex of heating devices; a machine for winding the narrow strip into a continuous helical spiral wherein winding is combined with the translational travel of the spiral along the mandrel axis; it includes a device for cutting the spiral into blanks for piston rings along the cylinder generatrix and also a device for heat treatment of the blanks for piston rings and for their thermofixation.

The spiral winding machine is provided with a fixed face-plate through the center of which passes the shaft of the mandrel drive. Radially movable brackets each bearing two rollers are mounted on the faceplate. The rollers rotate about axes normal to each other and with the operating surface of the mandrel they form a cavity for shaping the spiral.

The novel features and advantages of the proposed method of manufacturing blanks for cast iron piston rings from liquid cast iron and of the means therefor will become apparent from the following description of the operations, in conjunction with the accompanying drawing of the machine which being a part of the whole means is intended for winding the cast iron strip, into a continuous spiral, with said winding taking place simultaneously with the spiral travel along the mandrel axis.

In the drawings:

FIG. 1 is a view partly in elevation and partly in section of a winding machine according to the present invention, and

FIG. 2 is an end view looking from the left in FIG. 1.

The process of manufacturing blanks for piston rings from liquid cast iron conducted under the same conditions as the testing ones is described below.

The process comprises the following stages. A strip of the required thickness is cast (rolled) between rollers from liquid cast iron obtained in a cupola furnace with a receiver, To manufacture piston rings of high-strength, additions are introduced into the liquid cast iron stimulating the formation of the spheroidal graphite.

The strips cast in accordance with said method is characterized by its chilled structure. To obtain metal of the ferrite structure with the spheroidal graphites the strip should be annealed at a temperature of 950 to 980 C.

The annealed strip is then sized on a cold rolling mill till its thickness becomes equal to the width of the piston ring, whereby the quality of the strip surface is simultaneously improved. After recrystallization annealing at a temperature of 550-650 C., the strip is cut endwise into narrow strips each of which has the same width as the radial thickness of the pis on ring y g g slitting shears with guides. The strips are then reeled into coils.

Strip coils are heated in a continuous-action drum furnace. The furnace is charged from one side and the mate rial gradually moves along its axis towards the furnace discharge end wherein a built-in device is provided for reeling the strips off and delivering the end of the heated strip to the winding machine.

The strip can also be heated by electric current.

The heating brings the strip to the plastic condition necessary for winding. The heating is carried on until a temperature of 650 to 700 C. is reached, cooling of the spiral being effected only for fixing the shape.

To avoid subsequent heat treatment of the strip, the latter should be heated in the austenite zone to up to a temperature higher than the critical point A Cooling (by an air flow or some other method) provides for the required structure and the necessary shape of the spiral which should be in strict compliance with the shape of the mandrel.

After one turn of the spiral has been wound, the next one shifts the shaped turn and the whole spiral along the mandrel. Upon completion of the winding, the spiral is delivered to a device which serves for its endwise cutting along the generatrix of the cylinder into ring blanks with the joints cut out. The cut piston ring blanks are subjected to heat treatment and to thermofixation of the joints at a temperature of 900 to 950 C. with subsequent cooling in a corresponding medium in order to obtain the structure of the sorbitic pearlite or troostite with the spheroidal graphite.

The produced blanks for piston rings have minimum allowances for the subsequent mechanical treatment which either consists only in outer finish turning (for oil control rings) or in both finish turning and grinding (for compression rings). The machine for winding cast iron strips into spirals which is a novel feature of the means for manufacturing of the blanks comprises a fixed face-plate 1 of a machine bed in the center of which, through a supporting journal 2, drive shaft 3 is passed, coupled with a mandrel 4 having a working profiling part 5.

On face-plate 1 four similar radially movable brackets 6 are fitted (only one of them being shown on the drawing). Each bracket is provided with spring 7 and screw 8 with the screw regulating the spring compression and with two shaping rolls 9 and 10. Roll 9 rotates on shaft 11 in the vertical plane whereas roll 10 rotates on shaft 12 in the horizontal plane. The shaped turn of strip 13 moves spiral 14 along the mandrel axis.

The mandrel has either an elliptical cross-section as illustrated in FIGURE 2 corresponding to the free, inoperative, and expanded state of the piston ring, or a round cross-section with the diameter equal to the inner diameter of the ring in the operative (compressed) state.

The operation of the machine for winding the cast iron strip into a spiral is as follows.

The front end of the strip 13 heated to the required temperature is placed with the butt end in a slot provided in the mandrel and wound on the working profiling part 5 of the mandrel 4 under the action of the spiral shaping rolls, when the mandrel is rotated by driving shaft 3.

Rolls 9 shape and flatten out the ring radially in the vertical plane with the implied pressure force being directed towards the center of the turn, while rolls 10 shape and flatten out the ring laterally in the direction parallel to the mandrel axis. As the spiral is being wound, the shaped turn of the spiral is moved aside by the next to come. The wound spiral is gradually moved towards the inoperative part of mandrel 4 and thereby the continuity of the process is provided.

To manufacture flat piston rings, rolls 10 should be made cylindrical whereas for disk-like rings the rolls should be tapered.

Since the strip in the process of winding is in a plastic state, the manufactured rings will be substantially identical as to shape and size irrespective of accidental variations in the properties or the cross-section of the strip.

The wound spiral at the end of the machine is cut by a special device into separate rings with joints, and the spiral is then heated for obtaining the optimum structure of cast iron and for thermofixation of the joints. The outer diameter of the manufactured rings should be ground.

The results obtained in thorough testing of both the proposed method of manufacturing blanks for piston rings and of the means therefor, as well as of the compression and oil control rings themselves establish that piston rings manufactured from liquid cast iron by the proposed method considerably excel the hitherto known cast iron rings in mechanical properties.

In the course of testing, the metal utilization factor reached 70 to 75 percent, and the newly manufactured rings turned out to be considerably cheaper than the former cast rings.

The data obtained in the control testings of the proposed method and means for manufacturing blanks for cast iron piston rings from liquid cast iron, carried out in collabora-.

tion with some scientific and research institutes are given below.

The charge was melted in a cupola with a receiver. The cupola output was 2.6 ton/hr.

The composition of the charge was:

40 to 50 percent of foundry pig iron, trademark A'KO or AKl; 15 percent of open-hearth pig iron, trademark 61 or 62; 20 percent of steel scrap, trademark Al-l; 5 to 10 percent of return iron; 5 to 10 percent of packets of iron sheet shavings: 5 percent of furnace ferrosilicon, trademark CulO (trademarks are given in accordance with the U.S.S.R. standards).

Chemical composition of the melted cast iron for cast ing the sheet was as follows:

Percent Carbon 3.0 to 33. Silicon 1.40 to 1.75 Manganese 0.4 to 0.7 Phosphorus Up to 0.12 Sulphur Up to 0.1

Shaping of the cast iron strip in rollers was carried out at the temperature of pouring cast iron being 1300- 1320 C.

The rate of shaping with the strip thickness of 1.5 mm. was 0.7 m./sec. or 11.8 kg./sec. The width of the strip was 1400 mm. Capacity of the ladle was 3 tons. Pouring time was 7-8 min. Strip was obtained in rolls.

The cast iron strip was annealed in a gas-fired furnace with a capacity of 6660 kg./hr., the gas consumption being 400 cum. per hour.

Annealing conditions were as follows. Hot strip rolls with the temperature of 900 C. were heated to 950-980 C. and kept at that temperature for 6 hours (first stage of graphitization). Then they were placed in a furnace and cooled to 780 C. with subsequent temperature fall to 680 C. during 13 hours (second stage of graphitization). Finally the strip rolls were cooled in the open arr.

Before annealing, the structure of the strip was very similar to that of chilled cast iron. After annealing, its structure changed into the ferrite with the flaky or spheroidal graphite and pearlite (not more than 5 percent).

The annealed cold strip was rolled on a sheet mill with a deformation ratio of 20 to 30 percent.

Mechanical properties of 1.5 mm. thick strip were:

Before rolling Ultimate strength kg./sq. mm 28-32 Relative elongation --percent..- 5 to7 After rolling with deformation ratio of 20 percent Ultimate strength kg./sq. mm.. 30 Relative elongation percent 6 to 8 By means of gang slitting shears the strip was cut into narrow strips with a thickness equal to the piston ring radial thickness with an allowance of 0.2 to 0.3 mm. for turning.

Then, the strip heated to 630-650 C. was wound into a spiral on the machine described above provided with four pairs of shaping rolls.

After the spiral was cut into blanks, these blanks were arranged on a special mandrel with expanded joints heated to 920-940 C., kept at this temperature for 15 to 20 min. and then compressed to align the ends of the joints; after this treatment, they Were cooled in oil at a temperature of 230 to 250 C.

The structure of the blank metal after heat treatment was acicular troostite and residual .austenite, compact graphite (flaky or spheroidal).

This invention is not to be confined to any strict conformity to showings in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claims.

What we claim is:

1. An apparatus for manufacturing blanks for piston rings from liquid cast metal comprising means for casting liquid metal into strips between rolls; means for coldroll sizing of the strip thickness; means for cutting the cold rolled strips into narrow strips having a thickness approximating the radial thickness of a piston ring; heating means for heating said narrow strips; means for winding said narrow strips into a continuous helical spiral with the winding being combined with a longitudinal translational movement of said spiral; means for cutting the spiral along the cylinder generatrix into piston ring blanks, and means for heat treating said blanks and for thermofixation of the joints thereof.

2. The apparatus for manufacturing blanks for piston rings from liquid cast metal as claimed in claim 1 wherein said means for the winding and longitudinal displacement of the spiral includes a fixed vertical face-plate, mandrel drive shaft running through the center of said faceplate; a mandrel on said shaft, radially movable brackets mounted on said faceplate, each of said brackets carrying two shaping rolls said rolls rotating normally to each other and defining with the surface of the mandrel a cavity to receive and form the wound spiral in the mandrel.

References Cited UNITED STATES PATENTS 1,859,057 5/1932 Six 29-156.6 1,919,584 7/1933 Cords 29156.6 2,022,154 11/ 1935 Rothweiler 29156.6 2,183,358 12/1939 Six 29-156.6 2,279,133 4/ 1942 Cross 29156.6 2,349,372 5/1944 Phillips 29-156.6 2,748,453 6/ 1956 Haldeman 29156.6 2,453,330 11/ 1948 Marshall 29156.6

JOHN F. CAMPBELL, Primary Examiner. P. M. COHEN, Assistant Examiner.

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