Steel Cylinder Barrel Having Bonded Bronze-iron Valve Plate

Abstract

The disclosure concerns steel cylinder barrels for piston pumps and motors having bonded non-steel valve plates. The valve plate comprises a sintered iron powder matrix which is impregnated with bronze and is metallurgically and mechanically bonded to one end of the steel cylinder barrel. The valve plate is made from a porous sintered iron blank which is mounted in contact with one end of a steel barrel blank in an assembly which includes a mass of bronze in the solid state. The assembly is heated in a non-oxidizing atmosphere to a temperature between 1900.degree.F and 2000.degree.F to melt the bronze and cause it to infiltrate the sintered valve plate blank and bond to the steel. Thereafter, the assembly is cooled in the non-oxidizing atmosphere to solidify the bronze, followed by air cooling to room temperature. Finally, the finished valve plate is machined from the bronze-impregnated sintered preform.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

In hydraulic pumps and motors of the rotary cylinder barrel, longitudinally reciprocating piston type, oil usually is transferred to and from the cylinder bores through a rotary valve at one end of the cylinder barrel. This valve comprises a stationary element containing arcuate high and low pressure ports which angles slightly less than 180.degree., and an element which rotates with the cylinder barrel and contains a circular series of small arcuate ports, each of which communicates with one of the cylinder bores in the barrel. Since the valving elements are in continuous sliding engagement with each other during operation, it is desirable, if not a practical necessity in the case of high speed, high pressure hydraulic units, to make one of the two elements of bronze. This arrangement can be incorporated in several ways, but it is evident that the best approach for units which employ steel cylinder barrels is to use a bronze rotary valving element and to bond it directly to the end of the cylinder barrel. However, use of this design has been limited by the lack of a satisfactory process for producing a bond between the steel and the bronze.

The object of this invention is to provide a practical and reliable process for producing a valve plate which is intimately bonded to the steel cylinder barrel, and which also provides a valve plate having superior properties. According to the invention, the new valve plate comprises a matrix of sintered iron powder which is impregnated with bronze and is metallurgically and mechanically bonded to the end of the steel cylinder barrel. This type of valve plate affords an excellent bearing surface having greater strength than the bronze and better bearing characteristics than the iron. And, the intimate bond with the steel affords the absolute seal against leakage and the resistance to errosion required in a high performance pump or motor.

The process for making the new valve plate commences with the formation of an assembly including a porous, sintered iron valve plate blank, a steel cylinder barrel blank having an end face which bears against the valve plate blank, and a charge of bronze in the solid state having a volume sufficient to completely fill the pores in the sintered iron blank. The assembly is heated in a non-oxidizing atmosphere to a temperature between 1,900.degree.F and 2,000.degree.F to melt the charge and cause the bronze to infiltrate the valve plate blank and bond to the steel face of the cylinder barrel blank. Thereafter, the assembly is cooled in the controlled atmosphere to solidify the bronze, and then it is air cooled to room temperature. Finally, the finished valve plate is machined from the bronze-impregnated blank. The bond produced by this process has a true metallurgical character inasmuch as the region of the interface between the valve plate and the end face of the cylinder barrel contains an alloy of the constituent metals.

BRIEF DESCRIPTION OF THE DRAWING

The preferred embodiment of the invention and several alternatives are described herein with reference to the accompanying drawing in which:

FIG. 1 is a plan view of the blank-slug assembly.

FIG. 2 is a sectional view taken on line 2--2 of FIG. 1.

FIG. 3 is a sectional view taken on line 3--3 of FIG. 2.

FIG. 4 is an axial sectional view of the finished cylinder barrel.

FIG. 5 is a face view of the finished valve plate shown in FIG. 4.

FIG. 6 is an axial sectional view of an alternative blank-slug assembly.

DESCRIPTION OF THE EMBODIMENT OF FIGS. 1-5

The initial step of the preferred process concerns formation of the assembly 11 (see FIGS. 1-3) which includes a steel cylinder barrel blank 12, a sintered iron valve plate blank 13, a plurality of bronze slugs 14, and a dry sand support 15. Cylinder barrel blank 12 is rough machined from SAE 52100, 1045 or 4150 steel stock and is formed with a through axial bore 16, a circular series of parallel cylinder bores 17, and a flat, annular end face 18. Face 18 is left in the rough turned state since surface irregularities aid, rather than hinder, the bonding process. Moreover, it has been found that the process is not adversely affected by the formation of rust on face 18. After rough machining, blank 12 is cleaned to remove chips and then vapor degreased. Degreasing is not essential because any adherent oil and grease films will be burned off before the bronze-steel bond is effected. However, since these volatiles may leave a residue on face 18 which could cause localized impairment of the bond, it is considered best to remove them initially.

Valve plate blank 13 is a flat annulus having a thickness on the order of 5/32 to 3/16 inch and provided around its periphery with a series of uniformly spaced radial slots 19 which define the dynamic pads 21 (see FIG. 5) of the finished article. It is centered with respect to barrel blank 12 by a pair of sintered iron pins 22 which extend through it and into the small diameter lower ends of two of the bores 17. Blank 13 and pins 22 are made from the fine iron powder normally used in the powdered metal industry and have a density between 4.5 and 6.0 gms/cc, and preferably on the order of 5.6 to 5.8 gms/cc. In other words, these parts are porous, and, based on a pure iron density of about 7.9 gms/cc, each includes 24 to 43 percent and preferably 27-29 percent voids. These voids are distributed uniformly throughout the mass of each part and define capillary passages which permit complete infiltration by molten bronze. Except for their low density, blank 13 and pins 22 are formed and sintered in the same manner as any conventional powdered iron part.

The bronze slugs 14 are placed on the drill point surfaces at the lower ends of the large diameter portions of bores 17 so that, when melted, the bronze can flow downward onto valve plate blank 13. The slugs are of uniform size and, in the aggregate, contain enough bronze to completely fill the pores in blank 13 and pins 22. Various bronzes can be used, but experience shows that the composition should be free of zinc and nickel because these metals tend to separate from the other constituents and form a brittle interface which may crack under the service conditions encountered by the completed cylinder barrel. The composition should also have as low a lead content as possible because this metal will "bleed out" during heat treatment of the driving splines of the finished cylinder barrel. Bronzes having the following compositions, by weight, have proven acceptable:

a. 80% copper, 10% tin, 10% lead

b. 89% copper, 11% tin

c. 90% copper, 10% tin

However, the preferred slugs 14 are made of a bronze containing 85 percent copper, 10 percent tin and 5 percent lead which is purchased commercially in the nickel-free form. Although the slugs may be bronze castings, it is considered better to use sintered masses of bronze powder because this permits better control of composition.

After assembly 11 has been completed, it is placed in a furnace and supported in the illustrated upright position. The furnace should contain a non-oxidizing atmosphere, such as the filtered natural gas product commonly employed to control decarburization of the steel in blank 12 during heat treatment, and, in a typical case, it would be at a temperature of about 1,600.degree.F at the time assembly 11 is introduced. Furnace temperature is then raised to an elevated level above the melting range of the bronze and held there long enough to insure that all parts of assembly 11 reach a temperature which will produce a good metallurgical bond between the bronze and the steel. Although bonding can be effected at an assembly temperature on the order of 1,900.degree.F, experience indicates that a temperature of 1,950.degree.F is needed in order to provide the degree of bonding reliability required for a production process. The furnace temperature and length of time this temperature must be maintained in order to achieve the required assembly temperature must be determined empirically because these factors vary with furnace design and loading, i.e., the number of assemblies 11 being processed at the same time. The final selection involves a compromise since higher temperatures shorten holding time but also cause excessive evaporation of bronze and, because of localized hot spots, involve some risk of melting portions of steel blank 12. Our studies show that furnace temperature above 2,000.degree.F are too risky and are not really demanded by practical production considerations. For example, using a standard heat-treating furnace capable of holding thirty assemblies 11, we found that acceptable bonds were produced reliably at a furnace temperature of 1,990.degree.F which was maintained for one hour.

During the heating cycle just mentioned, the slugs 14 melt, and the molten bronze either migrates into blank 13 through sintered iron pins 22 or flows directly onto the blank through the open bores 17. In any case, this metal is distributed throughout the mass of blank 13 by capillary action. The combined effects of the heat and the infiltration renders the blank 13 somewhat plastic; therefore, the weight of steel blank 12 is sufficient to cause blank 13 to conform to any irregularities in the face 18. As a result, the bronze which wets the upper face of blank 13 can migrate into and form a true metallurgical and a mechanical bond with the steel over the entire interface between the two blanks.

At the end of the heating cycle, i.e., after all parts of assembly 11 have reached the selected bonding temperature, the furnace is allowed to cool so that the temperature of assembly 11 reduces below the melting range of the bronze. Typically, this phase of the process consumes one hour, furnace temperature decreases to about 1,400.degree.F, and the temperature of assembly 11 drops to a level below 1,500.degree.F. These conditions insure solidification of the bronze and permit opening of the furnace without risk of explosion of the controlled atmosphere. Therefore, assembly 11 is now removed from the furnace and allowed to air cool to room temperature. When the bonded blanks 12 and 13 have cooled sufficiently, they are removed from sand bend 15, sand blasted, and then transformed into the finished cylinder barrel shown in FIGS. 4 and 5. The finishing steps include:

1. Machining the inner and outer peripheral surfaces 23 and 24, respectively, and the front face 25.

2. Cutting and heat treating driving splines 26.

3. Boring and honing cylinder bores 27, and end milling the arcuate port 28 at the valve plate end of each bore.

4. Machining bonded valve plate 29 to form land 31.

5. Grinding and lapping the faces of dynamic pads 21 and land 31.

Although the foregoing description treats only the process steps of the invention, it should be understood that, in the complete commercial process, bonding of valve plate 29 is effected simultaneously with the cylinder liner bonding step of our application Ser. No. 93,130, or Ser. No. 93,298, both filed concurrently herewith.

DESCRIPTION OF THE FIG. 6 EMBODIMENT

It will be noticed in FIG. 4, that a portion of the arcuate port 28 at the end of each cylinder bore 27 is formed in the barrel blank 12, and therefore is surrounded by a steel web. The strength afforded by this arrangement is needed in high performance pumps which operate continuously at pressures on the order of 5,000 p.s.i. and at speeds around 4,000 r.p.m. However, in the case of low performance units, e.g., those which operate at pressures of 1,500-2000 p.s.i. and at speeds below 3,000 r.p.m., real advantages can be realized by eliminating the steel web. The assembly 11a shown in FIG. 6 may be used for producing cylinder barrels for this type of service.

As shown in FIG. 6, the bores 17a are drilled through barrel blank 12a with a constant diameter, and the sintered iron valve plate blank 13a is formed with a series of integral circular projections 32 which fit into the bores 17a and contain the arcuate ports 28a. This design offers the important advantages that it eliminates step-drilling of bores 17a and end milling of the arcuate ports 28a. The blanks 12a and 13a are bonded together in exactly the same way as in the embodiment of FIGS. 1-5, but here, a bond is also effected between the projections 32 and the wall of bore 17a.

The assembly 11a of FIG. 6 also is designed to effect simultaneous bonding of bronze-iron liners in the bores 17a in accordance with the teachings of application Ser. No. 92,298, mentioned above. For this purpose, each bore is equipped with a porous sintered iron sleeve 33 and a charge 34 of bronze of sufficient size to effect complete impregnation of the sleeve. The lower end of each sleeve 33 abuts the face of the associated projection 32, so, during the bonding operations, these parts will be intimately joined. This is an added advantage because, as study of FIG. 6 will show, the arrangement affords a lined and faced cylinder barrel in which all contact between high pressure oil and the bronze-steel interfaces is precluded. Thus, the design affords even better insurance against leakage than the prior proposal of U.S. Pat. 3,169,488, granted Feb. 16, 1965.

Claims

We claim:

1. A steel cylinder barrel for a piston pump or motor characterized by a valve plate which comprises a sintered iron powder matrix which is completely impregnated with bronze and is metallurgically and mechanically bonded to an end face of the cylinder barrel, there being an alloy of the constituents in the region of the interface.

2. A cylinder barrel as defined in claim 1 in which the valve plate comprises, by volume, 24 to 43 percent bronze.

3. A cylinder barrel as defined in claim 2 in which the valve plate comprises, by volume, 27 to 29 percent bronze.

4. A cylinder barrel as defined in claim 1 in which the bronze contains, by weight, 85% copper, 10% tin and 5% lead, and is free of nickel.

5. A cylinder barrel as defined in claim 2 in which the bronze contains, by weight, 85% copper, 10% tin and 5% lead, and is free of nickel.

6. A cylinder barrel as defined in claim 3 in which the bronze contains, by weight, 85% copper, 10% tin and 5% lead, and is free of nickel.

7. A cylinder barrel as defined in claim 1 in which

a. the cylinder barrel contains a circular series of cylinder bores which open through said end face; and

b. the valve plate has a series of integral projections which extend into said bores, are metallurgically and mechanically bonded to the bore walls, and each of which is pierced by a port.