Патент USA US2111377код для вставки
March 15, 1938. ` F, A, WALES 2,111,377 ART oF GOATING ALUMINUM Filed Nov. 14, 1935 @L 2 Sheets-Sheet. l 5, A TTORNEYÖ. March 15, 1938. F. AQWALES 2,111,377 ART OF COATING ALUMINUM Filed Nov. 14, 1935 2 Sheets-Sheet. 2 n "„Iun“u a l/ INVENITOR. „ai /Z Mles. BY ATTORNEYâ. 2,111,377 Patentedl Mar. 15, 1938 UNITED STATES PATENT OFFICE 2,111,377 ART, oF ooA'rlNG ALUMINUM Fred A. Wales, Detroit, Mich. Application November-14, 1935, >serial No. 49,647 3 Claims. 'I‘he present invention relates to the art of coating aluminum or aluminum alloys or ar ticles formed therefrom, and particularly to improvements in the method of and apparatus for 5 forming such coatings, particularly coatings of Óthe so-called "oxide” type. Such coatings on aluminum or aluminum alloys are commonly recognized as being formed chiefly of A1203, S03, and H2O, and are formed as a 1n plurality of laminated layers which vary. as to thickness, hardness and porosity. Such coatings (Cl. 204-1) a protective coating on aluminum or aluminum alloys, or articles formed therefrom, which is particularly, but not exclusively, adapted to pro-` duce the improved coatings on. pistons formed of aluminum or aluminum alloys ~for use in_in- 5 ternal combustion engines or similar purposes. A `further object of the present invention is ' to provide a process for the production of pro tective coatings _on aluminum or aluminumalloys, or articles formed therefrom, in which the cost 10 of operation and of the equipment has been re duced over similar costs of prior art processes have been formed by processes heretofore known . to the art by making the aluminum or aluminum - and equipment, and which, while being more eco alloy an anode in an electrolytic cell having sul nomical than processes and equipment of the 15 phuric acid asthe electrolyte. The coatings are prior art, produces coatings which are superior 15 formed upon the passage of direct current elec to the coatings produced by the prior art. trical energies through the cell and are formed It is a further object of the _present invention on the aluminum or the aluminum alloys which to provide an apparatus for use in forming pro form the anode in the cell. The direct current tective coatings on aluminum or aluminum al 20 used in such processesI is of the order of twelve loys, or articles formed therefrom, which is a 20 to eighteen volts and of from six to twenty am portable self-contained unit. peres per square foot of material undergoing Other objects of the present invention will ap treatment. A cathode,` electrically connected in the circuit, forms the other contact with the pear 'in the following description and appended «- electrical circuit and is placed in the electrolyte. bodying the present invention is shown by Way of example Vin the accompanying drawings form ing a part ofthis speciñcation wherein like ref erence characters designate corresponding Darts In certain embodiments, such cathode frequently was the tank, and the current ñowed between the cathode and the anode through the electrolyte and caused the growth of the sor-called “oxide”'coat 30 ing at the anode. In using such processes for the formation of the oxide coatings on aluminum or aluminum alloy articles, 'such for example as pistons for use in internal combustion engines, I have discovered that the coating formed by the 35 processes of the prior art was not'satisfactory in such fields due particularly to the large var iations in ñneness of grain structure, the irregu larity asto size and distribution of p'ores, the extreme variations in hardness between the re ¿0 spective layers, and the relatively high` cost of `processing and of the apparatus for use there with. ‘ « claims. One preferred form of apparatus em-. in the several views, and in which , Fig. 1 is a view in perspective of an apparatus 30 which is adapted to be used in connection with the present process and embodied in the form of a self-contained portable unit. ' Fig. 2 is a front view in elevation of the ap paratus of Fig. 1 showing the enclosing cover in 35 closed position. ' Fig. 3 is an end view in elevation of the appa ratus shown in Fig. 2. . Fig. 4 is a sectional view taken along the line 4-4 of Fig. 2 in the direction of the arrows. Before explaining in detail the present inven 40 tion it is to be understood that the invention is The process and apparatus of the present in- ` not limited in its application to the details of . vention has as its principal object to provide a 45 coating for aluminum or aluminum alloys, or ar construction and arrangement of parts illus trated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various Ways. Also, it is to be understood that the phraseology or terminology employed herein is for the pur pose of descriptionv and not of limitation, and it 50 is not intended to limit the invention claimed ticles formed therefrom, the coating being su perior to coatings previously known and charac terized by having a very dense ñne grained lami nated structure. The various layers exhibit sub 50 stantially uniform hardness characteristics and are permeated with very small and substantially uniform pores between the particles of the coat _ herein beyond the requirements of the prior art. The apparatus, shown in the drawings com 'It is a'further object of the present invention `prises a casing I0 which is mounted upon a sup 55 to provide a process and apparatus for producing porting rack Il, which may be provided with a ’ A 2 2,111,377 -plurality of casters I2 to permit moving the en. tire unit from place to place about a plant. The ‘ casing I0 is divided interiorly to form a rinse tank I3 anda tank I4, which is provided with a lead or other non-corrosive lining I5 and is adapted to contain the electrolytic bath. Mounted on one end of the framework II is a bracket I6 on which is mounted an electric motor I1 which drives a~ fan I 8 of the blower 10 type. An air pump IB, preferably of the pulsat ing type, is also driven by the motor Il and is connected by „means of the conduit 2l) with a A suitable control panel 3l is electrically con nected with the transformer 3i) and actsto pro vide the connections through which the current flows tothe electrolytic bath. Electrical connec tions are provided between the vtransformer 3i! through the control panel 3| with bus bars 32 which extend crosswise of the tank M. The ar-' _ticlers to be treated, such for example as alumi num or aluminum alloy pistons 33, are provided with a suitable clamp 34 which is electrically 10 connected with and engages one of the bus bars .32.110 suspend the article being treated into the series of perforated pipes 2I yextending across they .electrolyte in the tankV I4. In this manner bottom of the lead-lined tank I4. Air is sup articles to be treated 'are connected through electrolytic bath in a parallel series so that 15 plied to the pipes 2| and is discharged there through to keep the electrolyte agitated during flow of electricity is through the bus bars 32, operation of the apparatus. The fan or blower I8 is connected by means of a duct 22 with the hooded upper part of the tank I4 (Fig. 4) and 20 serves to ventilate the apparatus while in op eration. ‘ the the the 15 the clamps 34, the article 33, through the electrolytic bath to the article 33, its clamp 34, and the bus bar 32. This method of connection is contrary tovconventional >methods ln that the tank or bath remains neutral, whereas in prior known proc During the operation of the apparatus, a hood ¿ esses the, bath or tank forms the other connection or cover 23 is‘placed in the closed position, as with the electrical current and only the article shown in Fig. 4. 'I'he cover 23 prevents fumes 25 given olf during the carrying out of the process from escaping into the atmosphere, thus func tioning as a collection hood from which the' col lected fumes are drawn through the duct 22l and are thereafter discharged through a stack (not 30 shown),- which is connected with a discharge opening 24 on the blower I8.Í i ' As shown in Fig. 4, the lead lining I5 forming the tank I4 is spaced apart from the casing IU in such a manner as to provide a duct 25 which 35 extends about all sides of the lead lining I5 inside the casing I0. The duct 25 communicates with the -interior of the tank I3, into which may be placed a suitable temperature controlling fluid mass which will flow through the chamber I3 40 and around the duct 25 surrounding the lead,` lining I5 -of the tank I4. By varying the teme, perature of thefluid medium in the tank I3, the temperatures within the tank I4 may b_e con trolled within definite predetermined limits. 'I‘he ñuid is fed into the tank I3 through a 45 suitable conduit 26 which is operatively con nected with the source of ñuid supply and the level is maintained in the tank I3 by means of a waste or outlet pipe 21 which acts as an over 50 iiow pipe when the fluid reaches the top thereof. If water is used as the fluid temperature con trol medium in the tank I3, and its temperature is not sufficiently low to control the temperature of the tank I4, a cake of ice or other refrigerant may be placed therein and so refrigerate the iiuid which runs through the tank and around `the chamber 25. During the operation of the being treated forms the anode thereof. In the present apparatus, with the use of alternating 25 current, the articles 33 alternately form the anode and the cathode of the current flow and on the 11i) volt, 60 cycle, line this alternation oc curs sixty times each second, but will vary; how ever, with variations in the cycles of the a1ter-, nating current. A valve _35 is provided in the casing I El and communicates with the duct 25 to permit with drawal of fluid temperature control mediums therefrom. ' rThe foregoing described apparatuswhile be 35 ing particularly adapted to the process of the present invention, is also adaptable (with slight changes, particularly as to its electrical circuit) ' for -use in conventional processes known to the art, and as such, by reason of the temperature control provided in the electrolytic bath and in the portability of the unit, produces results which -are desirable and which are superior to the ap paratus previously known to the art, although lt 45 is my belief that using such apparatus with con ventional processes will not produce the satisfac tory results produced by the practice of my im proved process therein. 'I'he improved process of the present invention proceeds in part upon my discovery that a su perior type of coating may be formed either on aluminum or aluminum alloys or articles formed therefrom, and can be provided by using the aluminum or aluminum alloy or article formed therefrom as both the anode and the cathode of the electrical circuit flowing through the elec trolytic bath. The change from anode to cath-, apparatus, the tank I3 functions also as a rinse tank and the aluminum or aluminum alloys or 60 other articles which have been treated in the treating tank may be rinsed in the tank I3 after ode is preferably a successively occurring change which will be brought about in relatively rapidly the coating has been formed thereon. Electrical energy is supplied to the tank I3 by ceeds upon my discovery that such successively and rapidly alternating electrical changes in the ' means of a transformer 3D which is suitably 65 mounted on the framework II, preferably at a character of the aluminum or aluminum alloy alternating sequence. The process also pro during the coating operation can best be effected 65 point adjacentthe bottom of the tank I3. The by utilizing various voltages of 60 cycle alternat transformer operates on alternating electrical “ihg current, beginning at approximately 12.5 ` ~ current and in a preferred-embodiment has a volts and increasing'the voltage of the electrical rated capacity of 200 amperes and 24 volts. The flow düring the coating operation to 24 volts at 70 transformer is of a conventional design adapted a time when the temperature of the bath is defl 70 for use either on 110 volts or 220 volts, and is nitely controlled between limits of approximately - provided with a series of taps through which the current may be drawn to be passed to the bath, such current to have controlled and varying 75 voltages up to 24 volts. 69° to '74° F. ' In carrying. out the present process, I pro vide an electrolytic bath in the tank by using com mercial grades of sulphuric acid in concentrations 75 3 2,111,877 of 13% by weight in aqueous solution. At least y two pieces of the aluminum or aluminum alloy or article formed therefrom are electrically con nected, one with each side of the line supplying the electric current .to the electrolytic bath and from the anode and cathode respectively of the cell resulting from the immersion of the articles formed by means of the process herein disclosed than that of processes utilizing a ilow of direct current electrical energy. In a typical example, the coating formed by the process herein described is approximately twice as thick as the coating $1 formed by the conventional direct current proc esses treated for like periods of time. I believe this is due to the fact that the metal is not de The operation is started at a voltage of the composed and changed to the sulphate as is the 10 lower order, preferably from 9 to 121/2 volts, which case in all prior operations. A particular field in which the present inven is increased as the operationprcceeds, to the higher range `of voltages, preferably from 20 to 24 tion has great utility is in the iield of formed pro volts. The temperature of the bath is /preferably tective and oil bearing coatings onaluminum or maintained from approximately 69° F. to approxi- ' aluminum alloy pistons for use in internal combustion engines. In this field the coatings of the mately 73° F. by the use of a suitable circulat ing temperature control medium surrounding the present invention are -superiorto coatings formed tank in which the _operation is being carried on. by prior methods in that the coating is very much more closely knit, being formed of very much The treatment and processing is complete With in time intervals of about 20 to 40 minutes, the smaller particles than the coatings resulting from operation being carried on'approximately three-- the direct current process. The result is that the pores of the coating are very much smaller and quarters of the time at the higher range of volt much more uniformly distributed than in the prior ages, i. e. voltages in excessÍ of- 12.5 volts. In'coatings which are formed on the aluminum processes. This, in turn, increases the capillary in the electrolyte. ' or aluminum alloy, or the articles formed there 25 from, I have _found that »there is relatively no value of the coating so as to give a better oil ab sorption of the coating than when the coating is formed by the prior processes. It is a known bath such as occurs in forming coatings by means phenomenon that capillary elevations and depres of conventional processes utilizing direct current sions, other circumstances being equal, are con-v electricity. This feature of the present process versely proportional to the diameters of the ca 30 permits the use of the electrolytic bath for a very pillary tubes so that, considering the pores of the 30 coating as capillary tubes having an añinity for much longer period of time, for once the acid con centration of- the bath has-been normalized it the oil or other ñuid medium, it will be seen -that the smaller size of the pores and the greater uni appears to continue at the normalized acidcon formity of placement of the pores in the coat centration during the entire operation for a con „ ,Y , ` ing resulting from the present invention, will ac 35 siderable period of time. precipitation of the metal into the electrolytic Utilizing direct current, the metal decomposes yand reacts with the bath to form sulphates. When the bathl contains 20 grams per litre, the count for the greatly increased capillary values of such coating. , Excellent oxide coatings are produced under the bath must be completely changed because 4of -the resultant decrease in electrical conductivity of the bath. The present process is characterized by the fact that little or none of the metal-is decomposed by the electrolyte and put into the bath in the form of va, sulphate. This is due to the use of the relatively dilute bath which is possi ble by the use of the alternating current electrical following conditions on pistons produced from a energy in the' process. connected to each electrode„.and the .12..volt alter nating current is‘ impressed'bn the "cell for a period ofV 3 minutes. The voltage is then in _creased to 24 volts and the treatment is con tinued for an additional 20 minutes, While main taining the bath temperature at between ap This particular feature is »one of theoutstax'iding defects of the- direct cur rent method now being used, as this sulphate is 50 insoluble in the bath and readily affects the con ductivity of the bath, and when it reaches the concentration of 20 grams per litre of electrolyte, the bath must be changed. V 'I'he efliciency of such low-aluminum high-silicon alloy which contains approximately 12% of silicon. An equal number 40 of pistons are placed in the electrolyte and act"4 as the electrodes. The electrolyte is composed of ap proximately 13% by weight of commercial sul phuric acid in aqueous solution. A l2 volt alter 45 nating current` is used, one side of the line being proximately 70° to 74° F. processes of the‘art is progressively lessened by Using this particular alloy, the thickness of the rapidly diminishing conductivity value in this the coating will be not less than .0004 inch in 55 bath up to the ultimate point of 20 grams per thickness and the abrasimeter values will read litre. 30 or more. -_ The coatings formed . by the process of the present invention as above described, will be found. 60 to have a substantially increased uniformity of ‘ hardness throughout the successive layers, which, ` f ' l For purposes of comparison, it is interesting -to note that similar coatings formeduby con yentional methods utilizing direct current and 60 a stronger electrolyte, where the article is treated ' when investigated by means of photomicrographs, for the same length of time, produces coatings will be shown to possess a very ñne grained crys . talline structure and very small and uniformly having an average thickness of .000327 inch as against the average thickness of the coatings distributed pores extending therethrough. -In an average'4 case, the variation between the softest- produced by the use of the alternating` current of .000746 inch; land the abrasimeter values layer and the hardest layer is inthe neighborhood of approximately 20%, Whereas in a characteristic coating formed by the processes of the prior art, will be less than 30. 70 utilizing direct current electrical energy and baths of the speciñed concentrations of acid, there is a variation of from 140 microcharacter to approxi mately 5,000 microcharacter between the hardest - layer and the softest layer formed. Also, there is a considerably thicker coating y In treating the aluminum o_r aluminum alloy articles by the4 present process, I ñnd that it is possible to dispense with ~the preliminary clean 70 ing and Washing processes which are common to the prior art, itbeing sufficient with the improved process of the present invention to merely dip thealuminum or 'aluminum alloy article in a hot water bath. This is possible, in my opinion, 75 4 2,111,377 because of the use of the alternating current in the present process which, in conjunction with the electrolyte, reacts in such a way as to in eii’ect clean the articles more completely and Cl thoroughly than it would be possible to do by previously suggested methods. This, I believe., is due to some extent at least to the action oi’ the alternating current in expelling the adhered surface oxygen. 10, A characteristic of the coating produced is that it is very smooth on the exterior surface so as to make possible the use of the article without using a buiiing machine for the purpose of re moving the chalk-like soft coating which is formed by the treatment of aluminum or its -alloys by The soft outer coating formed by conventional processes is a coating which consists, to a large extent, of the mate-~ rial which is precipitated into the bath as the 20 sulphate which has heretofore been described. The coating formed by the present process has no such soft outer coating and tests to date in _ conventional processes. dicate that there is not more than approxi~ mately 20% variation in the microcharacter val» ues from the outside skin of the coating to its base where it forms on the aluminum or the aluminum alloy. Due to the action of the alternating- current, less metal is taken away from the material un 30 dergoing treatment and thus the coating is oi greater strength than coatings produced by prior methods wherein more of the metal is taken away during the processing operation. While particular uses have been mentioned in the foregoing discussion of the apparatus and process of the present invention, it is to be un derstood that both the apparatus and the process are adapted to other uses than those herein par ticularly mentioned and'may be used success~ 40 fully to form protective coatings on articles which may >bejformed of some material other than aluminum or aluminum alloy but which may be coated with aluminum or aluminum alloy by such processes as calorizing, metal spraying, etc. I claim: ' ' 1_. A process of producing _a protective coat ing having a thickness ln excess of approxi-_ mately .0004 inch and a hardness in excess of approximately'30 grams’abraslmeter value, on an 50 alux'ninum-'silicon‘alloy which contains approxi the immersed articles in parallel with 'a source of alternating current electrical> energy and. uti lizing the immersed articles as both the anode and cathode of the circuit, and subjecting said articles to a flow of alternating current electrical energy in successive stages beginning at approximately 9 to 12.5 volts intensity for a period of approximately 3 minutes duration and increasing through successive stages to approxi-r mately 24 volts for a period of approximately7 20 minutes duration at the conclusion of the process. 2. A process of producing a protective coatingv on an aluminum-silicon alloy containing ap proximately 12% silicon having substantially increased uniformity of hardness throughout the successive layers, which comprises immersing the aluminum alloy in an electrolytic bath contain ing 13% by weight of sulphuric acid in aqueom solution, electrically- connecting the immersed alloy in parallel with a source of alternating cur alloy as both the anode and cathode of the cir cuit through the bath, and subjecting the said alloy to a flow of alternating current electrical energy- in successive stages beginning at ap proximately‘9 lto 12.5 'volts for a period of ap proximately 3 minutes and thereafter increasing“ to approximately 20 to 24 volts for a period of approximately 20 minutes while agitating the bath to maintain a substantially constant circu-l lation thereof and maintaining a substantially constant temperature of the bath between ap proximately 70° and 74° Fahrenheit. . 3. A process for forming a ñnished and smooth unbuffed protective coating having a thickness 35 in excess of .0004 inch and a, hardness inl excess , of approximately 30 grams abrasimeter value on an aluminum-silicon alloy containing ap proximately 12% silicon having substantially 1n creased uniformity of hardness throughout the successive layers, which comprises immersing said alloy in an-oxidizing bath containing 13% by weight of sulphuric acid in an aqueous solution and passing an electrical current therethrough for a period of approximately 3 minutes dura 45 tion at a potential of approximately 9 to 12.5 volts and thereafter for a period of approxi mately 20 minutes duration at a potential of ap proximately 24 volts, utilizing the said alloy in , the bath as both the anode and cathode of the 50 mately 12% of lsilicon having substantially in creased uniformity of hardness throughout the successive layers, which comprises immersing -stant temperature of between approximately 70° the farticles'formed of vsaid alloy in an electro a'ndf'l‘ì" Fahrenheit. lytic bath 'containing 13% by weight of sulphuric 'acid in aqueous solution, electrically connecting 20 rent electrical energy and utilizing the immersed circuit through the bath, while agitating the bath and maintaining therein a substantially con ' FRED A. WALES.