US3707034A

US3707034A - Method of producing steel cylinder barrels having bonded bronze valve plates

Info

Publication number: US3707034A
Application number: US93129A
Authority: US
Inventors: Martin J Alger Jr; Nelson H Dunn
Original assignee: General Signal Corp
Current assignee: SPX Technologies Inc
Priority date: 1970-11-27
Filing date: 1970-11-27
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26
Also published as: AU464403B2; AU3606371A; CA956778A; JPS5016298B1

Abstract

The disclosure concerns a process for providing the steel cylinder barrel of a piston pump or motor with an adherent, bronze valve plate. The finished valve plate is machined from a bronze member which is cast in place against one end of the cylinder barrel blank under conditions which effect a sound metallurgical and mechanical bond between the steel and the bronze.

Description

United States Patent Alger, Jr. et a1.

[54] METHOD OF PRODUCING STEEL CYLINDER BARRELS HAVING BONDED BRONZE VALVE PLATES Martin J. Alger, Jr.; Nelson H. Dunn, both of Watertown, N.Y.

Assignee: General Signal Corporation Filed: Nov. 27 1970 Appl. No.:'93,129

Inventors:

References Cited UNITED STATES PATENTS 3 ,169,488 G allig e r u n gg/i'l 1 Dec. 26, 1972 3,280,758 10/1966 Leeming ..91/499 853,716 5/1907 Monnot ..164/1l2 2,066,247 12/1936 Brownback ..L ..164/8 0 2,207,150. 7/1940 Hirsch et al. ..164/8O X Primary Examiner-.JohnF. Campbell Assistant Examiner- Donald C. Reiley lll Attorney-George Vande Sande, Harold S. Wynn & Jeffrey S. Mednick [57] ABSTRACT,

The disclosure concerns aprocess-forproviding the steel cylinder barrel of a piston pump. or motor with an adherent, bronze valve plate. The finished valve plate is machined from a bronze member which is cast in place against one end of the cylinder barrel blank under conditions which effect a sound metallurgical and mechanical bond between the steel and the bronze.

' 8 Claims, 4 Drawing Figures METHOD OF PRODUCING STEEL CYLINDER BARRELS HAVING BONDED BRONZE VALVE PLATES 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 subtend angles slightly less than 180, 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 ofa satisfactory process for producing a bond between the steel and the bronze. v

The object of this invention is to provide a practical and reliable process for producing an adherent bronze valve plate on the valving end ofa steel cylinder barrel. According to the invention, the new process is characterized initially by the formation of an assembly including a steel cylinder barrel blank, amold which receives the valving end of the barrel and is shaped to define with an annular end face thereon a cavity in which a rough valve plate is to be cast, and a charge of bronze in the solid state which is adapted to flow into and fill the cavity when melted. The assembly is heated in a non-oxidizing atmosphere to a temperature between l,900 and 2,000F to melt the bronze charge, effect filling of the mold cavity, and to produce an intimate bond between the bronze and the steel end face of the cylinder barrel. Thereafter, the assembly is cooled in the controlled atmosphere to solidify the bronze and then air cooled to room temperature/ Finally, the finished valve plate is machined from the rough cast bronze plate. This procedure creates a true metallurgical, as well as a mechanical, bond between the bronze valve plate and the steel cylinder barrel, and the shape of the mold cavity and the cooling rate of'the cast bronze member are controlled so that shrinkage, if any, occurs in a region of the casting which is subsequently machined away. The combined effect of these factors makes the process a practical and reliable production technique.

BRIEF DESCRIPTION OF THE DRAWING The preferred process is described herein in detail with reference to the accompanying drawing in which:

FIG. 1 is an axial sectional view of the barrel blankmold-bronze charge assembly as it appears prior to the heating cycle.

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

FIG. 3 is an axial sectional view of the finished cylinder barrel.

FIG. 4 is a view of the valving face of the finished cylinder barrel shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The initial step of the preferred process concerns formation of the assembly 11 (see FIG. 1) which includes a steel cylinder barrel blank 12, a mold 13 and a bronze charge 14. Blank 12, which is rough machined from SAE 52100, 1045 or 4l50 steel stock, hasa circular cross section, contains a through axial bore 15, and is provided with a flat annular end face 16 towhich the bronze valve plate is to be bonded. Face 16 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 fact 16. After machining, blank 12 is cleaned to remove chips and then vapor degreased. Degreasing is not essential because any adherent oil or grease film will be burned off before the bronze-steel bond is effected. However, since these volatiles may leave a residue on face 16 which could cause localized impairment of the bond, it is considered best to remove them initially.

Mold 13 is formed to receive the end ofblank 12 and to cooperate with face 16 to define a mold cavity 17. The outermost region of cavity 17 is subdivided by a circumferential series of uniformly spaced, radial ribs 18 which define the dynamic bearing pads (see pads 19 in FIG. 4) of the finished valve plate. Inboard of these ribs, the bottom wall 21 of cavity 17 slopes downward toward the center so that the thickest portion of the bronze casting will lie adjacent the inner periphery of face 16..This arrangement is important because it enables the central portion of the casting to act as a riser and concentrate shrinkage in a region which is removed during final machining of the cylinder barrel. Because mold 13 usually has a relatively large surface area and low mass compared to blank 12, it tendsto cool much more rapidly than the blank. This differential cooling can cause shrinkage in the region of the bronze-steel interface and adversely affect the bond. In order to prevent this, mold 13 is equipped with a heat-insulating jacket 22 composed of a mass of asbestos fibers. Inclusion of the jacket tends to equalize the rates at which heat is transferred from the bronze through blank 12 and through mold l3, and thus minimizes the risk of shrinkage at the bronze-steel interface. Mold 13 preferably is made of ceramic material and carries a thin graphite coating 23 which serves as a release agent for the casting, but carbon molds or graphite-coated steel molds may be used. It also is possible to make the mold of core sand. However, this last alternative is not considered as reliable as the others because, during the heating cycle, the binder in the sand gives. off gases which may accumulate in the empty cavity 17 and impair the bond which is to be created.

The bronze charge 14 is in the form of a cylindrical body which has an enlarged portion that fits within axial bore 15, and a smaller portion that fits within a central-recess formed in mold 13. The charge, therefore, serves as a convenient means for centering blank 12 in the mold during make-up of assembly 11. The

charge may be a solid bronze casting, but preferably is a sintered mass of bronze powder because this form permits better control of composition. While various bronzes may be used, experience indicates that the composition should be free of zinc and nickel because these metals tend to separate from the other constituen'ts and form a brittle interface which may crack under the service conditions encountered by the finished 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 cylinder barrel. Bronzes having the following compositions, by weight, have proven acceptable: v

a. 80 percent copper, lOpercent tin, percent lead b. 89 percent copper, l 1 percent tin c. 90 percent copper, 10 percent tin However, the preferred charge 14 is made of a bronze containing 85 percent copper, 10 percent tin, and 5 lead, and which is purchased commercially in the nickel-free form.

It will be noted from FIG. 1 that the charge 14 is so positioned in assembly 11 that, when melted, the bronze will flow into mold cavity 17. The volume of metal in the charge is greater than the volume of the cavity so that the liquid level of the molten mass-will lie above the end face 16 of blank 12. This measure insures that cavity 17 will be filled completely and that the molten bronze will be in contact with face 16 throughout its whole area.

After assembly 11 has been completed, it is placed in a furnace and supported therein in a level position, i.e., in a position which is sufficiently level to guarantee that the liquidlevel of the molten bronze will lie above face i l6 throughout'the full extent of the latter. The furnace should contain a non-oxidizing atmosphere, such asthe filtered natural'gas product commonly employed to control decarburization of the steel in blank 12 during heat treatment. In a typical process, the furnace is at a temperature of about l,600F when assembly is inserted, so the temperature must subsequently be raised to an elevated level above the melting range of the bronze and held there long enough to insure that all parts of. assembly I] reach a temperature which will produce a good metallurgicalbond between the bronze and steel. Although bonding can be effected at an assembly temperature on the order of l,900F, experience indicates that a temperature of 1,950F 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 becausethese factors vary with furnace design and loading, i.e., the number of assemblies 11 being processed at the sametime. 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 temperatures above 2,000F are too risky and are not really demanded by practical production considerations. For example, using a standard heat treating furnace capable of simultaneously processing thirty assemblies, we found that acceptable bonds were produced reliably at a furnace temperature of 1,990F which was maintained for one hour.

During the heating cycle just mentioned, charge 14 melts and the bronze flows downward into mold cavity 17. Since the volume of bronze in the charge is greater than the volume of the cavity, some of the molten metal will rise upward into bore 15 and around the outer periphery of blank 1 2. In other words, the liquid level of the molten bronze mass will lie above the face 16 of blank 12. This is of vital importance because it insures that there will be contact between the bronze and the steel over the entire area of face 16. As a result, a sound metallurgical and mechanical bond will be effected over the entire interface. A

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 reduces below the melting range of the bronze. Typically, this phase of the process consumes about 1 hour, furnace temperature decreases to about 1,400F, and the temperature of assembly 11 drops to a level below 1,500F. Theseconditions insure solidification of the bronze and permit opening of the furnace without risk of explosion of the controlled atmosphere. Assembly llis now removed from the furnace and allowed to air cool to room temperature. Dur- I ing these cooling phases of the process, some shrinkage may occur in the cast bronze valve plate blank; However, as mentioned above, the enlarged central mass of bronze and the insulation afforded by jacket 22 to tend to confine this effect to the annular region adjacent the inner periphery of face 16, which is removed during final machining.

After assembly 11 has cooled sufficiently to be handled, blank 12 is removed from mold 13 and transformed into a completed cylinder barrel by the final finishing operations. These include: v

l. Machining the inner and outer

peripheral surfaces

24 and 25, respectively, and the front face 26.

2. Cutting and heat treating driving splines 27.

3. Drilling, boring and honing cylinder bores 28 and end milling arcuate ports 29. I v

4. Machining bonded valve plate 31 to form land 32.

5. Grinding and lapping the faces of dynamic pads 19 and land 32.

Although the foregoing description treats only the process steps of the present invention, it should be un-' derstood that, in' the complete commercial process, bonding of the valve plate 31 is effected simultaneously with the cylinder liner bonding step of our application Ser. No. 93,1 30, or Ser. No. 93,298, both filed concurrently herewith.

We claim: 1. A process for producing 'a bonded bronze valve plate on the end of a steel cylinder barrel for a pump or motor comprising the steps of a. fabricating a steel barrel blank (12) having an end provided with an annular face (16); I

b. fabricating-a mold (l3) equipped with a surrounding heat sink (22) and formed to receive said end of the blank and define with said annular face a cavity (17) having a thickened cross section adjacent the inner periphery of said face. 16);

c. preparing a mass (14) of bronze in the solid state which has a volume greater than the volume of said cavity (17);

. heating said assembly (11) in a non-oxidizing at- I mosphere to a temperature between l,900 and 2,000F to thereby melt the bronze and cause it to fill said cavity (17) and form a metallurgical and mechanical bond with said annular face (16);

. cooling said assembly (11) in the presence of the non-oxidizing atmosphere to solidify the bronze in said cavity;

further cooling the assembly (11) to room temperature; and

machining the final valve plate (31) from the bonded bronze member and, in the course thereof, removing an annular region of bronze adjacent the inner periphery of said annular face.

the assembly (11) is cooled in the non-oxidizing atmosphere to a temperature between 1,400 and 1,500F; and

b. said further cooling is effected in air. 5. The process defined in claim 1 in which a. the barrel blank (12) is made of SAE 52100, 1045 or 4150 steel; and

b. the bronze mass (14) is a nickeLfree composition containing, by weight, percent copper, 10 percent tin, and 5 percent lead.

6. The process defined in claim 5 in which the bronze mass includes a sintered slug of bronze powder.

7. The process defined in claim 1 in which a. the barrel blank (12) is formed with an axial bore (15) which is normal to and encircled by said annular face (16); and

b. the mass (14) of bronze is in the form of a cylinder which fits within said bore and has an integral portion which fits a central recess in the mold (13),

c. whereby the bronze cylinder serves to center the blank with respect to the mold in said assembly.

8. The process defined in claim 7 in which a. the mold (13) is made of ceramic and is coated with a graphite release agent;

b. the barrel blank (12) is made of SAE 52100, 1045 or 4150 steel;

0. the bronze mass (14) is a nickel-free composition containing, by weight, 85 percent copper, 10 percent tin and 5 percent lead;

d. the assembly (11) is heated to a temperature of e. the assembly (11) is cooled in the non-oxidizing atmosphere to a temperature between l,400 and 1,500F; and

f. said further cooling is effected in air.

Claims

2. The process defined in claim 1 in which the mold is made of ceramic and is coated with a graphite release agent.
3. The process defined in claim 1 in which said assembly (11) is heated to a temperature of 1,950*F.
4. The process defined in claim 1 in which a. the assembly (11) is cooled in the non-oxidizing atmosphere to a temperature between 1,400* and 1,500*F; and b. said further cooling is effected in air.
5. The process defined in claim 1 in which a. the barrel blank (12) is made of SAE 52100, 1045 or 4150 steel; and b. the bronze mass (14) is a nickel-free composition containing, by weight, 85 percent copper, 10 percent tin, and 5 percent leAd.
6. The process defined in claim 5 in which the bronze mass includes a sintered slug of bronze powder.
7. The process defined in claim 1 in which a. the barrel blank (12) is formed with an axial bore (15) which is normal to and encircled by said annular face (16); and b. the mass (14) of bronze is in the form of a cylinder which fits within said bore and has an integral portion which fits a central recess in the mold (13), c. whereby the bronze cylinder serves to center the blank with respect to the mold in said assembly.
8. The process defined in claim 7 in which a. the mold (13) is made of ceramic and is coated with a graphite release agent; b. the barrel blank (12) is made of SAE 52100, 1045 or 4150 steel; c. the bronze mass (14) is a nickel-free composition containing, by weight, 85 percent copper, 10 percent tin and 5 percent lead; d. the assembly (11) is heated to a temperature of 1,950*F; e. the assembly (11) is cooled in the non-oxidizing atmosphere to a temperature between 1,400* and 1,500*F; and f. said further cooling is effected in air.