US3715790A

US3715790A - Method of reinforcing piston ring grooves

Info

Publication number: US3715790A
Application number: US00106279A
Authority: US
Inventors: W Reinberger
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1971-01-13
Filing date: 1971-01-13
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13
Also published as: IT946505B; FR2122224A5

Abstract

Method of making an aluminum alloy piston with a ring groove reinforcement wherein a grooved piston blank is cleaned to remove any oxide films, and a bonding metal is sprayed over the surface of the groove while the blank is at a temperature of from about 330* to 390* F., and thereafter a wear resistant metal is sprayed into the groove while the blank is still at a temperature within the aforementioned range to thereby fill the groove.

Description

United States Patent 1191 Reinberger 1451 Feb. 13,1973

[54] METHOD OF REINFORCING PISTON 3,031,330 4/1962 Homick ..117/50 X NG GROOVES 3,033,705 5/1962 Hanink et a] ..1'17/50 3,04l,l l6 6/1962 Rosen et al ..277/189.5 [75] Inventor: William C. Reinberger, lndepen- 3,295,198 1/1967 Coan 1 1 ..29/l56.5 R X dence, Ohio 3,405,610 10/1968 Hill et al. ..29/l56.5 R X [73] Assrgnee: TRW Inc., Cleveland, Ohio Primary Exami'ier charles w Lanham [22] Filed: Jan. 13, 1971 Assistant Examiner-Victor A. Dipalma [2]] Appl NW 106,279 Attorney-Hill, Sherman, Meroni, Gross & Simpson Related US. Application Data ABSTRACT [63] Continuation-impart of Ser. No. 762,720, Sept. 26, Method of making an aluminum alloy piston with a 1968, abandoned, ring groove reinforcement wherein a grooved piston blank is cleaned to remove any oxide films, and a [52] 0.8. CI. ..29/ 6.5 R, 117/50, 117/105, ing metal is pr y r h Surface f h 277/1395 groove while the blank is at a temperature of from [51] Int. Cl. .1523, 15/10 ut 3 to 3 and thereafter a wear resistant [58] Field at Search. ..29/156,5, 5212,5274, 527 6; metal is sprayed into the groove while the blank is still 117/50, 31, 92/223, 222; 277/ 189.5 at a temperature within the aforementioned range to thereby till the groove. 56 References C't d 1 I e 6 Claims, 4 Drawing Figures UNITED STATES PATENTS 2,833,668 5/1958 Dailey et al. ..l17/5O METHOD OF REINFORCING PISTON RING GROOVES CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application entitled Method of Reinforcing piston Ring Grooves U.S. Ser. No. 762,720 filed Sept. 26, 1968, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is in the field of reinforcing ring grooves in aluminum alloy pistons by a sequence of operations including preheating the piston blank, grit blasting the blank in the area of the grooves to remove any existing oxide film and to roughen the surface, after which the temperature of the blank is adjusted to a value between about 330 and 390 F., whereupon a bonding metal is sprayed into the grooves, followed substantially immediately by spraying a wear resistant metal such as stainless steel into the grooves.

2. Description of the Prior Art Heavy duty internal combustion engines using aluminum alloy pistons are subject to the difficulty that the walls of the piston ring groove are liable to deformation in use so that reinforcement of the ring groove area has become a necessity. In some cases, this reinforcement has taken the form of an insert which is usually metallurgically bonded to the metal of the piston head. Examples of this type of structure will be found in Stevens US. Pat. No. 2,550,879; Daub US. Pat. No. 3,118,712; and Christen et al. US. Pat. No. 3,183,796.

Other attempts at reinforcement have centered on the technique of spraying a reinforcing metal into the preformed groove. An example of this type of procedure will be found in Dailey et al. U.S. Pat. No. 2,833,668.

,The present invention is concerned with the second of the techniques mentioned above, that of spraying a wear resistant metal into a groove which has been preformed in the head of the piston. With the sequence of operations to be described more fully in a succeeding portion of this disclosure, it has been found possible to provide such a reinforcement at'a significantly lower cost than heretofore encountered, and at the same time it is now possible to increase the strength of the bond between the piston alloy and the sprayed metal.

SUMMARY OF THE INVENTION In the method of the present invention, an aluminum alloy piston is first provided with a peripheral groove of a stepped configuration. Next, the grooved piston is preheated at a temperature of about 400 F., but below the softening temperature of the metal of the piston alloy blank. While the piston blank is still at a moderately elevated temperature by virtue of the preheat, the groove is subjected to grit blasting to remove any oxides which would otherwise interfere with the bonding operation and to simultaneously roughen the surface. The next step consists of spraying on a bonding metal over the surface of the groove while the blank is still at a temperature of about 300 to 390 F. 1m mediatelythereafter, a wear resistant metal such as stainless steel is sprayed into the groove over the thin BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 is a fragmentary view of a portion of the head of the piston blank with a peripheral groove machined therein;

FIG. 2 is a somewhat schematic illustration of the manner in which the groove is grit blasted;

FIG. 3 is another somewhat schematic view illustrating the manner in which the metal spraying operations can be used to provide both the bonding metal and the wear resistant metal in the groove; and

FIG. 4 is a view similar to FIG. 1, but showing the head of the piston after the machining operation has been completed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 indicates generally a piston blank composed of an aluminum alloy. The head of the piston is first provided with a peripheral groove 11 which in the form of the invention illustrated, has a stepped profile. While the configuration of the groove can take various forms, there are certain considerations which dictate the use of the stepped-type profile. For one,'the cost of the sprayed meta'l inlay should be kept as low as possible, so that the volume and the maximum thickness of the sprayed metal should be held to a minimum consistent with the required physical properties. By holding the thickness of the deposit to .a minimum, the residual stress level in the deposited metal is also minimized.

The minimum thickness of sprayed metal on each side of the ring groove must be great enough to support the loads imposed by the piston ring. The sprayed metal must extend into the groove to a depth that will provide a wear resistant surface over the area where the'ring loading is most severe. From experience, it has been determined that pistons for heavy duty engines require a sprayed metal reinforcement with a minimum thickness of about 0.060 to 0.100 inch over the outer one-half to two-thirds of the ring groove depth.

The groove should be so shaped as to avoid tension loads on the bond between the sprayed metal and the piston alloy. Since the gas pressure loads and the friction loads on the piston ring are parallel to the axis of the piston, the groove should be designed with surfaces both parallel to and perpendicular to the center line of the piston. The resulting perpendicular surfaces of the groove should be joined by a small radius since sprayed metal particles tend to bridge across a sharp corner and leave an undesirable void.

In the ideal situation, sprayed metal would be applied normal to the surface of the aluminum piston alloy to insure the best possible bond. However, because of the other requirements mentioned, this ideal situation is not capable of realization. Consequently, the groove width with respect to its depth should therefore be established to permit the sprayed metal particles to impinge upon all surfaces of the stepped groove at an angle of approximately 45 from the normal.

After the peripheral groove 11 had been machined into the head of the piston blank, the piston blank is washed to remove all oils and residue. Various degreasing solvents such as trichlorethylene can be used for this purpose. The washing prevents contamination of the grit and grit blasting equipment used in the subsequent operation, and insures a clean surface for receiving the sprayed metal.

The next step in the process consists in preheating the workpiece to a temperature of about 400 F., but below the softening point of the metal to remove all residual moisture and to prevent the formation of a condensate in the subsequent operation. For aluminum alloy pistons, this preheat temperature is preferably in the range from about 400 to 420F.

The next step of the process, illustrated in FIG. 2 of the drawings, consists in grit blasting the surfaces of the groove. Asillustrated in FIG. 3, the grit may be applied through a pair of nozzles 12 and 13 disposed on opposite sides of the blank. During the grit blasting operation, the piston blank is mounted on a suitable turntable rotated at a relatively slow speed about 75 revolutions per minute. The piston blank groove is blasted on both sides simultaneously at an angle of 45 from the normal to all surfaces of the stepped groove. The blast is continued until a satiny finish of maximum uniform roughness on all surfaces of the groove is achieved.

While the piston blank is still hot from the preheat, and at a temperature in the range from about 330 to 390 F., the bond coat is sprayed onto the groove by means of a metallizing gun 14 while the blank is oscillated to fill the groove completely, as illustrated by the dashed lines in FIG. 3. I particularly prefer to use a bond coat consisting of nickel aluminide since this material forms a non-porous coating which is resistant to gaseous atmospheres up to about 3,200 F.

The preferred coating thickness for the bonding layer is about 0.004 to 0.006 inch.

Nickel aluminide coatings can be produced from commercial materials which are formed of composite particles in the form of a wire. The composite particles are formed by chemically depositing nickel onto aluminum particles. When fused and sprayed, there is an exothermic reaction with the formation of nickel aluminide. The nickel aluminide is self-bonding to properly prepared surfaces, and no subsequent fusion treatment is required.

The next step consists in spraying the wear resistant metal to fill the groove 11 while the piston blank is still hot. In this operation, the workpiece should still be a temperature of about at least 330 to 390 F. to minimize the residual stress level in the sprayed metal inlay when thermal equilibrium is established. The application of the wear resistant inlay can be made with the same type of apparatus as illustrated in FIG. 3m

provide complete coverage throughout the depth of the groove. During the spraying of the wear resistant metal if it becomes necessary to cool the piston blank to avoid exceeding 390 F., a cooling air jet can be directed on the inner surfaces of the piston.

Finally, the piston is machined to remove excess reinforcement metal and to trim the piston to final dimensions. The final step consists in machining a groove 16 in the reinforcement metal for receiving the piston ring.

The following specific example illustrates with more particularity the process conditions under which the process of the present invention can be best carried out.

EXAMPLE An aluminum alloy piston blank is provided with a groove of the type shown in FIG. 1 of the drawings. After washing to remove oils and residue, the piece was preheated to a temperature of 400 F. to remove all residual moisture and prevent the formation of condensate.

While the piece was hot, it was grit blasted using a cast iron grit at a pressure of 80 pounds psi while the piece was rotated on a horizontal turntable at a speed of 75 revolutions per minute. The piece was fixtured on the turntable so that both sides of the groove could be blasted simultaneously at an angle of 45 from the normal to all surfaces of the stepped groove. The blasting was continued for 8 seconds at a spacing of 3 inches between the nozzles and the workpiece at point of contact.

Immediately after the grit blasting, and while the temperature of the piece was still above 325 F., a nickel aluminide bond coat was applied. The workpiece was mounted in the fixture and rotated at 125 rpm. A standard Metco" metallizing gun was used, using a one-eighth inch diameter wire. The gun was positioned 4 inches from the surface to be coated. The acetylene pressure was set at 17 psi and the oxygen pressure was set at 50 psi. Gun settings for the metallizing gun were adjusted to provide air at psi and 43 cubic feet per hour, oxygen at 40 to 42 psi and 42 cubic feet per hour, acetylene at 12 to 14 psi and 34 cubic feet per hour, using a wire speed of 3 feet per minute. The workpiece was oscillated from side to side through an included angle of for 9 seconds at approximately I second intervals causing the sprayed metal to impinge on first one side of the groove and then on the other. The bond coating thickness which resulted averaged about 0.005 inch.

The groove was filled with a stainless steel spray coating using the same fixture and spray gun as used in providing the bond coat. The workpiece at this stage should still have a temperature of at least 330 F., but not more than 390 F. The gun was positioned 4 inches from the surface to be coated. The gun settings were such that the air pressure was 55 pounds psi and 40 cubic feet per hour. The oxygen setting-was such that the pressure was 30 to 34 psi with a volumetric rate of 37 cubic feet per hour. The acetylene was introduced under a pressure of 15 pounds psi with a volume rate of 37.5 cubic feet per hour. The wire speed was 4.5 feet per minute for a one-eighth inch wire diameter. The workpiece was oscillated through an included angle of 60 starting with spraying the left side of the groove for 5 seconds followed by the right side of the groove for 5 seconds. This sequence was repeated for two additional 5 second intervals. Then the left side was sprayed for 30 seconds, followed by spraying the right side for the same interval of time. Then the spray was allowed to dwell on the center of the groove for a period of 100 seconds. Next, the left side was sprayed for seconds followed by an equal amount of spraying on the right side. The spraying was completed by training the gun on the center of the groove for 35 seconds or as long as required to completely fill the groove. During this spraying of the stainless steel, a cooling air jet was played on the inner surfaces of the piston to prevent the temperature of the piston from exceeding 390 F.

FInally, the piston was given a finished machining operation in the usual way, using a relatively light cutting tool pressure to machine the piston ring groove in the sprayed metal inlay.

Operation of the process in the manner stated in the example has been found to reduce the cost of applying the sprayed metal, and also has resulted in a 30 percent increase in the strength of the bond between the piston alloy and the sprayed metal, as compared with previous practices.

A series of tests was run to determine the tensile strength of stainless steel inlays versus blank temperature at the start of the metal spray operation. In one series of tests, spraying of the blank while the blank was at a temperature of about 120 F. resulted in a tensile strength of about 17,800 psi. When the temperature of the blank at the time of spraying was increased to 190 F., the resulting tensile strength was 18,100 psi. However, when the blank temperature was raised to 330 F., the tensile strength rose to 22,700 psi. When the blank temperature was increased to 365 F., the tensile strength was 24,000 psi. When the blank temperature was 390 F., the resulting tensile strength was 23,300 psi. At blank temperatures in excess of 400 F., specifically at 420 and 470 F., the tensile strength dropped to below 21,500 psi.

In another series of tests, using a different type of aluminum alloy blank, maintaining the blank at a temperature of F., resulted in a tensile strength of 20,400 psi for the stainless steel inlay. When the blank temperature was increased to F., the tensile strength increased only to 21,000 psi. At a blank temperature of 330, however, the tensile strength rose sharply to 23,200 psi, while using a blank temperature of 360 F., resulted in achieving a tensile strength in excess of 26,500 psi. At a blank temperature of 390 F., the tensile strength was still in excess of 25,000 psi. However, when operating at a blank temperature of 460 F., the resulting tensile strength fell below 24,000 ps1.

I claim as my invention:

1. The method of making an aluminum alloy piston with a ring groove reinforcement which comprises providing a piston blank having a peripheral groove formed therein, heating said blank to a temperature in the range from 330 to 390 F., spraying a bonding metal over the surface of said groove while the temperature of the blank is in said range, and thereafter spraying a wear resistant metal into said groove to fill the same while said blank is at a temperature within said range.

27 The method of claim 1 1n Wl'lllCh said wear resistant metal is stainless steel.

3. The method of claim 1 in which said wear resistant metal is nickel aluminide.

4. The method of claim 1 which includes the steps of heating said blank to an elevated temperature between 400 F. and the softening point of the blank, and grit blasting said groove while said blank is at said elevated temperature prior to spraying on said bonding metal.

5. The method of claim 1 in which said groove has a stepped profile.

6. The method of claim 1 in which said blank is oscillated during applicationof said bonding metal and said wear resistant metal.

Claims

1. The method of making an aluminum alloy piston with a ring groove reinforcement which comprises providing a piston blank having a peripheral groove formed therein, heating said blank to a temperature in the range from 330* to 390* F., spraying a bonding metal over the surface of said groove while the temperature of the blank is in said range, and thereafter spraying a wear resistant metal into said groove to fill the same while said blank is at a temperature within said range.

2. The method of claim 1 in which said wear resistant metal is stainless steel.

4. The method of claim 1 which includes the steps of heating said blank to an elevated temperature between 400* F. and the softening point of the blank, and grit blasting said groove while said blank is at said elevated temperature prior to spraying on said bonding metal.

5. The method of claim 1 in which said groove has a stepped profile.