US3515599A - Process for treating ferrous surfaces - Google Patents

Description

J i 2,1970 LA VERN RQCONNELLY .-3:,-5 15','599

v A PROCESS FOR TREATING FERROUS'SURFACES Filed March 14, 1968 CAM BLANK Draassme DEeQEAsme HEATNG DHosDHomc Acm ETcHme QlNSiNG HEATKNG ADHEQNG MANGANESE PHOSPHATE QINSING SOLUBLE OIL. DIP

ASSEMBLY INVENTOR. LA VEEN Q. CONNELLY ATTOQNEYS.

United States Patent 3 515 599 PROCESS FOR TREAiIN FERROUS SURFACES La Vern R. Connolly, Marshall, Mich., assignor to Eaton Yale & Towne Inc., Cleveland, Ohio, a corporation of Ohio Continuation-impart of application Ser. No. 414,695, Nov. 30, 1964. This application May 14, 1968, Ser.

Int. Cl. (32st 7/10 U.S. Cl. 148-615 Claims ABSTRACT OF THE DISCLOSURE A process for treating the bearing surface of ferrous bodies to increase the resistance to wear thereof including the deposition of a polyvalent metal phosphate on the surface which has previously been machined smooth and etched with an aqueous solution of mineral acid.

This invention relates, as indicated, to an improved process for treatment of ferrous bodies, and more particularly to a process for conferring an ability to resist wear upon ferrous surfaces which in their ultimate use are to be operatively contacted over metallic surfaces of the same or similar nature as disclosed in application Ser. No. 414,695, filed Nov. 30, 1964, now abandoned, of which this application is a cont-inuation-in-part.

With relatively moving ferrous bodies or work pieces, for example, cams, gears, rollers, shafts journalled for rotation in beaings, relatively slidable members, e.g. pistons, or piston rings, in sliding contact with cylinder walls, or shafts sliding axially relative to a bushing, some means of lubrication of such relatively moving parts is normally prvided. Under conditions of elevated load, elevated temperature, shock loading conditions, or initiating relative motion from rest, the relatively moving metal parts are frequently forced into metal-to-metal contact due to displacement of the normal lubricating film. In certain circumstances, for example, the normal lubricating film may be a fluid passing through a pump. This material may have fairly good dynamic lubricating characteristics, but relatively little if any film strength of the type which would be able to resist displacement when the parts are at rest or when the parts are forced into dynamic contact by virtue of the impression of heavy loads or shock loading conditions. Under these circumstances, the relatively moving metal parts, the surfaces of which are not truly smooth as is apparent from microscopic examination, are brought into dynamic abrasive relationship causing wear. The surfaces of such relatively moving contacting metal parts contain asperities or promontories of microscopic size. Even though the pressure under which the parts themselves may be operated is relatively light, when a promontory of one part dynamically engages a promon tory on the relatively moving part the pressures become enormous causing a local increase in temperature sufficient to cause the promontories to melt. Prevalence of this condition for any substantial period of time results in scoring or welding and eventually seizure of the relatively moving parts whereby further relative movement is pevented.

The process of the present invention provides a method of treating the surface of ferrous parts which are intended for operatively contacting relative movement with respect to coacting parts whereby the life of the parts may be increased or operating pressures increased thus reducing replacement and maintenance costs.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means herein after fully described and particularly pointed out in the appended claims, the following description and annexed flow sheet setting forth in detail certain illustrative embodiments of the invention, such disclosed means constituting, however, but a few of the various forms in which the principle of this invention may be employed.

Briefly stated the present invention is in a process for the surface treatment of a ferrous body to improve the ability of such body to resist wear while operatively contacting another relatively moving surface. The process includes essentially the steps of dressing the surface of the body, for example, by machining, broaching, shaping,

single point return, grinding, or honing, or otherwise abrading the surface to round off the asperities by reducing the height and size thereof. Thereafter, the body is etched with an aqueous solution of a mineral acid. Thereafter, a polyvalent metal phosphate e.g. iron phosphate, zinc phosphate, manganese phosphate, lead phosphate, or the like, is deposited on the surface of the article. Thereafter the article may be rinsed in water, although the rinsing step is not essential. The invention hereof is illustrated by specific example of a process outlined in the annexed drawing which is a flow sheet of a process for treating pump cams.

This invention will be illustrated, therefore, with respect to rotary pump rolls which are carried by a rotary member and adapted for radial movement with respect to the axis of rotation and in contact with a cam surface. These rolls are formed from hardened steel and are adapted to be maintained in operative contact with the internal surface of the cam, which may be contoured according to a predetermined pattern, either by hydraulic means or mechanical means, such as springs. The combined force of centrifugal force and hydraulic and acceleration forces urging the rolls into contact with the inner cam of the housing imposes conditions of wear on the rolls which have been found to be materially lessened by the process of the present invention. In other applications imposing wear conditions on ferrous parts, the present process has been found to reduce wear in such alloy steels as molybdenum, chromiumand nickel, and irons including cast powdered iron.

As indicated above, the process of the invention includes at least three essential steps:

(1) Dressing the surface of the body;

(2) =Etching the dressed surface with an aqueous solution of a mineral acid, e.g. phosphoric acid; and

(3) Depositing a polyvalent metal phosphate e.g. iron,

zinc, lead and/or manganese phosphate, on the etched surface. While a product can be made which demonstrates improved wear characteristics by a process involving only these three steps, best results are obtained by the inclusion of additional steps as hereinafter more particularly described. Referring now more particularly to the annexed drawing, the cam blanks which have been shaped pursuant to conventional procedures are, as an essential step of the process, first dressed. By the term dressed or any of the various forms of the word, as used herein, it is meant that the surface has been smoothed by any of a number of conventional procedures for imparting a smooth surface to the cam member. These procedures may include, for example, finish grinding with a bonded garnet wheel, vapor blast, honing, liquid honing, etc. This is to be distinguished from rough grinding or rough shaping. The purpose of such dressing" is to round off the asperities by decreasing their height and size whereby said asperities are more uniform on the metal surface.

In accordance with conventional procedure, these bodies, for example, the cam of the specific example are heat treated to a Rockwell hardness of from 45 to 52 prior to the dressing operation. Following dressing the cam is degreased by any suitable conventional procedure, e.g. vapor degreasing.

Following the degreasing operation the temperature of the body is elevated by any suitable means to from about 160 F. to about 200 F. For this purpose an infrared oven, a hot air oven, or immersion in hot Water may be used. Since a large portion of the balance of the process involved immersion in aqueous media, it is convenient to utilize a hot water bath maintained at a temperature of about 190 F. and at a pH or near 7. The time of imrnersion may vary from 15 to 60 seconds, or more if desired.

It will be understood that the reason for raising the temperature of the article to be treated is to decrease the amount of time involved in the chemical reactions which are to take place subsequently. These reactions are timetemperature reactions, and follow the general rule that the higher the temperature the lower the time requirement, and its converse. It is desirable to raise the temperature of the article to at least about 160 to 200 F. to reduce the amount of time required for subsequent operations. Any suitable means for achieving this objecti've may be employed. It will be understood, however, that if the temperature of the article is not raised above room temperature, the chemical reactions which occur will require a longer period of time.

The next, and an essential step, is treatment of the surface of the article or body with an aqueous mineral acid solution which will remove no more than .001 inch of surface metal within 15 seconds to 15 minutes. Any suitable method of exposing the surface to the action of phosphoric acid, sulphuric acid, nitric acid, hydrochloric acid or any aqueous acid solution of comparable reaction rate, may be employed, for example, immersion in a body of acid solution or suspension in a spray of acid solution. Again, for convenience immersion in an aqueous phosphoric acid bath is preferred.

The purpose of the treatment with the aqueous acid solution is to etch the surface and to remove at least in part asperities and smeared over metal resulting from the dressing operation.

It is further believed that the acid etch not only removes the amorphous layer but also preferentially attacks the grain boundaries of steel, and the cell boundaries in the case of irons. If the ferrous body to be treated is carbon-containing, the etching treatment also exposes structural crystals of graphite or carbon. This procedure further provides pits of microscopic size which are available as receptors and reservoirs for phosphate salts later to be deposited. The phosphoric acid solution of the process exemplified in the flow sheet is, as indicated, an aqueous medium conveniently formed from available tap water and phosphoric acid, H PO of a commercial grade. Any phosphoric acid may be used whether ortho, meta or pyro. The concentration of the acid is desirably maintained at that level which is equivalent to from 10% to 25% by volume of ortho phosphoric acid. These concentrations are not critical, merely desirable, and concentrations from 5% to 50% would appear to be commercially feasible. Any concentration sulficient to induce etching or pitting of the surface and to further expose graphite embedded therein or preferentially attack cell and grain boundaries is sufficient. The lower the concentration, the greater the exposure time required. With the preferred solution the immersion time is within the range of from 2 to 15 minutes, and specifically it has been found that 8 minutes immersion time is sufficient with an aqueous phosphoric solution having the above concentration and at an elevated temperature between 135 and 175 F. Again, the higher the temperature of the solution, the shorter the required immersion time.

In some instances it may be commercially practicable to utilize an aqueous phosphoric solution having a 5% to 50% concentration and immersion times ranging from 2 minutes to 60 minutes at 100 F. to 210 F. In any event, with any of the solutions involved herein, temperai tures above the boiling point of the solution at the prevailing pressure (normally atmospheric), will be avoided. Super-atmospheric pressures and sub-atmospheric pressures may be employed in the treating steps of this invention if desired, but they are not necessary.

Following the etching step, the article is rinsed, preferably in clean rinsing water, which may be hot or cold, for a short period of time e.g. 15 to 30 seconds. The rinsing step is not essential but has been found to be desirable to prevent premature destruction, contamination, or aging of the subsequent treating bath.

Following the rinsing step, the temperature of the cam member or work piece is again increased as in the previous heating step, preferably by immersion in hot water for 15 to 30 seconds. For this purpose, the same bath as used in the previous heating step may be employed although in a continuous operation it may be found convenient to employ a separate heating bath.

The next, and an essential step in the present process, is the treatment of the cam by a process which is similar to that known in the trade as lubriting. This is a conventional procedure and contemplates treatment of the surface by a chemically reactive solution which contains dissolved therein, manganese dihydrogen phosphate. Preferably, the concentration of the solution is such that the amount of manganese dihydrogen phosphate is chemically equivalent to a concentration of from 7% to 10% by volume of phosphoric acid, H P0 although concentrations ranging from 5% to 20% have been found satisfactory. Instead of manganese dihydrogen phosphate, any polyvalent metal hydrogen phosphate soluble in hot or cold water or solubilizable therein, e.g. in phosphoric acid solution, may be used. Such phosphates include for example the hydrogen phosphates of iron, lead and zinc. These phosphates are also designated as metal phosphates, monobasic or dibasic signifying the amount acidic hydrogen replaced by the polyvalent metal. All these materials contain an excess of acidic hydrogen not replaced by a polyvalent metal.

As indicated above, it is desirable to maintain the temperature of this immersion bath at an elevated temperature, preferably from 190 F. to 210 F. Again, the chemical reaction resulting upon immersion is a timetemperature reaction; the higher the temperature the less time required. Temperatures as low as F. may be commercially feasible in some circumstances. In general, it is desired to deposit a coating including manganese phosphate on the surface of the ferrous article. Under the microscope this coating appears discontinuous, that is, the surface is not completely covered by manganese phosphate and the usually present iron phosphate crystals. This is evident because under such microscopic examination, particles of graphite embedded in the surface and exposed by the phosphoric acid treatment are visible. So also are areas which have been identified as manganese phosphate and/0r iron phosphate. There is no bond between the graphite and the phosphate coating.

Following the lubriting" step, the article is rinsed in a cold rinsing water of 15 to 30 seconds and may be dried or, as is frequently desirable, dipped in hot oil for a period of about 30 seconds. Neither of these last two steps is essential to the production of the product, although each leads to an improved, more satisfactory product.

The nature of the chemical reaction which takes place between the acid treated ferrous surface and the man ganese dihydrogen phosphate reactant is not well understood.

It is known that there is much less iron phosphate and a greater percentage of manganese phosphate on the surface if the surface has been etched prior to the lubriting process, and that the manganese phosphate provides superior wear characteristic and has greater adherence to the surface. This may be explained at least in part by the preferential grain and cell 'boundary attack mentioned herein before. It is also theorized that the phosphoric acid etch provides a very thin iron phosphate coating on the ferrous material, on the order of -30 mg. per

6 parts formed from SAE 1015 carburized steel which have been treated according to indicated procedures and tested for pick-up, and operation at pressures in excess of the normal 1200 psi pressure.

square foot, which acts as a nuclei for the subsequent manganese phosphate reactions.

By way of attempted explanation of the reactions, it is theorized that the phosphoric acid in the presence of TABLE I Total No. Cam Phosoi cams acid, phate, treated mins. mins. Wheel Treatment Condition 62 8 8 Std Lubrite Excellent.

2 8 8 ..do None Do. 5 8 5 ..do Lubrite Slt. Pick-up. 10 8 do do Excellent.

6 15 8 Garnet do Do. 5 12 8 3 10 8 8 8 8 1 8 8 3 8 9 0 15 3 15 8 Garnet None Excellent. 1 5 5 Std do D0.

TABLE II Number Time Pressure Condition 1,200 Excellent. 1, 400 Do. 1,200 Do. 1 600 D0 heat breaks down into hydrogen and phosphate radicals:

The selected metal oxide, manganese oxide for example, combines wi th the phosphoric acid to form manganese phosphate, phosphoric acid and water:

The phosphoric acid reacts with the iron in the workpiece to form iron phosphate and water and to evolve gaseous hydrogen:

The manganese hydrogen phosphate also reacts with the iron in the workpiece in the presence of phosphoric acid to form manganese phosphate, iron phosphate and water:

The iron-dihydrogen-phosphate will also react with accelerators such as sodium nitrile which may be added to the metal phosphate solution in small quantities for example 2%:

It is believed that it is the insoluble metal phosphates formed in accordance with the above reactions which form protective coatings on the work piece. When the conditions of the relatively moving metal parts are sufficient to squeeze out all of the normal lubricant, e.g. lubricating oil, or fluid being pumped and to permit metalto-metal contact the temperatures and pressures prevailing are sufficient to cause the phosphates adhered to the metal surface to fuse. Even though present in small amounts, the fused phosphates provide a liquid film which effectively maintains the relatively moving metal surfaces spaced from each other. When the conditions giving rise to fusion of the phosphate salts have passed, the materials recrystallize in bonded relation with the metal surface and are available for substantially instantaneous fusion when the conditions conducive thereto again arise. This theory may serve to explain why substantially improved wear characteristics are observed in articles which have been treated in accordance with the foregoing process.

The following tables list specific examples of steel pump 1: 600 Very good.

The foregoing pressure tests were run using pumps including dressed rollers treated for 8 minutes in aqueous phosphoric acid and for 8 minutes with manganese dihydrogen phosphate with SAE 10W oil at 200 F. intake temperature and 2500 r.p.m.

In the foregoing series of tests, the pump units utilizing cams treated in accordance herewith, and rolls lubricated or not as indicated were run with automotive transmission fluid at a temperature of 200 F.:20 F. at a cycllized series of shaft speeds including 900 r.p.m.; 3000 r.p.m.; and 4500 r.p.m. for 20 minutes at each speed sequentially over a one hour period for a total of 21 cycles. The pressure at discharge was 50 p.s.i.:l0 p.s.i. with a shut off pressure of 1000 psi. After this test the pumps are disassembled and visually examined for wear. Pick-up refers to gain in weight of the roll. due to wear of the cam. Excellent indicates no appreciable pick-up.

As a result of this process, and as indicated in the above Table I, it has been found possible to improve roller and cam life and also to reduce torque. Prior to this process, there was obtained 70% cam carrier roll pick-up on endurance and cycle tests. On completed units, it has been found that these pumps have after being tested on intermittent operation over a long period of time have the appearance of never having been run at all. It has also been found that there is a torque re duction of approximately 10% by reason of treating the cams and rolls of certain pump units in accordance with this procedure.

Other benefits which have been achieved by treating cam and roll elements used in pump units in accordance with the procedure of this invention has been reduction in noise level and a reduction in the criticality of the nature of the finish grinding operation. Cams having a finish of up to 50 r.m.s. and heavy chatter have been evaluated. When treated in accordance with this invention cams have in all cases passed both operation and noise tests. Without the process of the present invention and utilizing only a lubriting step, the cams have failed both noise and wear tests.

Other modes of applying the principle of this invention may be employed instead of those specifically set forth above, changes being made as regards the details herein disclosed, provided the elements set forth in any of the following claims, or the equivalents of such be employed.

It is therefore, particularly pointed out and distinctly claimed as the invention:

1. A process for the surface treatment of a ferrous (c) etching the surface of the body to remove up to .001 inch of surface metal and to microscopically pit the surface by immersing the body in an aqueous body to improve the ability thereof to resist wear while operatively contacting another relatively moving surface comprising the steps of:

(a) a fine dressing the surface of the body; (b) etching the surface of the body by immersing the solution of a mineral acid chosen from the group consisting of phosphoric, nitric, sulphuric and hydrobody in an aqueous solution of phosphoric acid chloric acids for a period of from 2 to 60 minutes at containing 5% to 50% by volume of phosphoric absolution temperature of between about 100 F. and acid, for a period of from 2 to 60 minutes at a solua tion temperature of between about 100 F. and about (d) ieposibting a polyvalelnt gngtal phosphate on said a 210 F,; d sur ace y lmmerslng t e o y in an aqueous so Vud iti man anese ho h t on id surface tion containing a polyvalent metal hydrogen phosifnmesing the fiih ii 2 1??? iii? 1335532333 3336 if?! iiiiiffii ihiillii taimng manganese y rogen p osp a in an amount chemically equivalent to from 5 to 20% fi liulvalentdtof from 5dto f222% by volune of phosby volume of phosphorloacid, for a period of from P one F 0! a Perlo 0 Tom to 3 mlomltes. at 4 to 30 minutes at a solution temperature of between absolliltil'a t g p of between abOllt 175 an about 175 F. and about 210 F. a on 2. A process for the surface treatment of a ferrous A P 10 Surface treatment of a fe1{01lS y body to improve the ability thereof to resist wear while Improve l ablhty thereof F Teslst f Whll p r operatively contacting another relatively moving surface FlY t li i 2 l'elatlvely movll'lg Surfacfi comprising the steps of: Prlslllg e 5 R 1 fi d i th surface f h b d '(a) fine fin1sh1ng the surface of the body to reduce (b) etching the surface of the body by immersing the (b th body body in an aqueous solution of phosphoric acid egfealng 6 containing 5% to 20% by volume of phosphoric )f g 3 y i hot Water at a temperature acid, for a period of from 2 to 15 minutes at a 2 5 32 123 31 the temperature of the ol ti t erature of between 135 F. and about i7; gg (d) etching the surface of the body by immersing the (c) depositing manganese phosphate on said surface 5 5 51 223; sglutlolll of g pl l i q by immersmg the body 111 an aqueous so ution confamlng d f f 0 32 23 P f 1; t?

taining manganese dihydrogen phosphate in an a i b 5 13 85 3 3 13 amount chemically equivalent to from 5% to 20% emgera ure o Ween a an cu by volume of phosphoric acid, for a period of from i- 3 e y in water 4 to 20 minutes at a solution temperature of between about 190 F. and about 210 F. 35 lgggt ga 1 body to elevate the temperature above 3. A process for the surface treatmet of a ferrous body to improve the ability thereof to resist wear while (3) g g s a polyvalelt g Phosphate on i operatively contactingfanother relatively moving surface z g gg g n g ;-5i; 5en2 glgl gyz ig ggg 5120 comprising the steps 0 (a) fine finishing the surface of the body to reduce 40 g gsgizg zgf fi g i g g f i m g sfz gl i vii aspenttes; were are up to arenas mustangs a on me o su ace me a an o rmcroo scopically pit the surface by immersing the body in an gigfifip of betwem about 175 nd a ut aqueous sloution of a suitable mineral acid for a h a th b d d period up to 60 minutes at an elevated solution tcmif i b g Wateri 1 perature up to about 210 F.; and (1) PPmg t e O Y m a so e 01 ,(c) depositing a polyvalent metal phosphate on said surface by immersing the body in an aqueous solu- References cued tion containing a polyvalent metal hydrogen phos- UNITED STATES PATENTS Phate selected from f gfoup 11sisfing 0f 2,191,435 2/1940 Ballard et al. 1486.15 lead, manganese and zinc in an amount chemically 2,266,379 12/1941 Floyd eqllllfalelljL to from 5 to 20% by Volume 9 P 2,29 ,344 9 1942 Glasson 5 phoricacid, for a penod of from 4 to 30 m nutes at 2,341,293 2/1944 Rives. a solution temperature of between about 175 F. and 2,343,569 3/1944 Neely et a1 X about 210 2,476,345 7/1949 Zavarella 1486.15

l. A process for the surface treatment of a ferrous body 2,375,110 2/1959 Rossander 148*615 to improve the ability thereof to resist wear wlnle opera- 3382316 3 [/1963 Halversen et tively contacting another relatively moving surface comprising the steps of:

(a) fine dressing the surface of the body to reduce asperities; (b) elevating the temperature of the body to above about F.;

50 RALPH S. ENDALL, Primary Examiner [1.5- CI. X.R.

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