US2072170A - Elements for use in the electrodeposition of chromium - Google Patents

Description

March 2,` 2,072,l7

ELEMENTS FOR usElN THE ELEcTRoDEPoslTioN oF CHROMIUM vc5, K. HERZOG Filed NOV. 20, 1934 ,imp

nani/murs ron 'osu in 'run Etneo n nnrosrrion or nunon/univr e George K. llierzog, New Rochelle, N. Y., assigner to lilnited Chromium, incorporated, New orlt, N. Y., a corporation of Delaware 'appiieauon inventer to, 193i, senat no. 'Itasca n,` l Claims.

y\ *I This invention relates toa method,papparatus and elements thereof for use in the electrodeposition of chromium and provides improvements therein..

insulator which would be highly resistant to plating solutions containing chromic acid and be more satisfactory and serviceable than those heretofore used.. Insulators, or coatings thereof'are usedA p in the artof chromium plating, for example,` to

hold conducting parts of opposite polarity in` spaced relation in or above the solution, to insulate parts of conductors and racks immersed in the solution, to stopi4 or inhibit the flow of plating current' to parts of cathodes on which it is `desired not to have a plate, for lining containers to hold the plating solution, etc. The most satisfactory insulators heretofore discovered and now used are glass, ceramics, certain rubber prod- The word Bakelite is understood to be a trade-mark of the. corporation making and sellingl the resin, which resin is a. condensation product forme from phenol and ormaldehyde.

ose products. Glass and. ceramics are of limited application because they are dimcult to work, and l re fragile. Rubber reacts with the plating soluion, disturbing its compositionin several ways, the rubber reducing the chromic acid to various trivalent chromium compounds and fouling kthe solution, and the .sulphur increasing the acid- `radical contentby being oxidized to sulphuric acid radical. Bakelite is very brittle, dimcult to work and therefore of limited application. When fillers are incorporated in the Bakelite to reduce brittleness and increase workability, the

resulting product is readily attacked by the plating solution. causing fouling of the solution and destroying lthe insulator. Films of Bakelite or oi cellulose compounds 'resulting from the drying of liquid coats of the dissolved materials also react with the plating solution, reducing'the chromic acid and fouling the solution; the lms are brittle and swell and, increase in brittleness after exposure tov chromic acid solution, and the parts of conductors` and racks to whichthese coatings are applied have to be recoated. at frequent intervals, the practice inmany plants being` to applycoats of the solution on weakened p areas of theracksat Ythe end of each day preparatorv to use the next day. Furthermore, it

lms of grease or` dirt on` articles to be chro mersing the racks containing the work to be cleaned into hot alkaline solutions. Bakelite lms break down very rapidly `when immersed in hot alkaliner solutions.` Cellulose products and ucts, Bakeliteml condensation-resin, and cellu-` mium plated by iirstracking them and then infrfilms thereof behave similarly to Bakelite and have the same shortcomings.

The most satisfactory containers heretofore usedior plating solutions containing chromicacidare lead or lead-alloy lined containers, and glass or ceramic containers. The lead-lined containers are conducting and some current will flow to them resulting in objectionable stray current edects. A disadvantage of stray currents, for instance, ls the shading eect which occins when an article is placed too close to the conducting lining, some of the current intended for plating going to the lining, and not enough going to the article, so that the part'of the article adjacent to the lining is not plated or is improperly plated., Lead is also very heavy and is subject to attack by the solution, lead chromate bel ing formed, which results in failure ofthe linings and in the formation of Aan undesirable sludge in the solution. lCertain lead-alloys overcome the attack to a considerable extent. Glass and ceramic containers are heavy, fragile, and expensive, and they are principally used where the bath is of small capacity.

By the present invention I provide apparatus and elements thereof of an insulating character, or havinginsulating parts, which are highly resistant to attack by warm or cold chromium .plat- 'ing solutions containing chromic acid, which give superior service as insulation in the special use with these chromium-plating solutions, and which allow the plating process to be carried out without the composition of the solution being aleeted .or the solution fouled; and the invention also provides a method of applying such insulation.

` By the present invention I furthermore provide containers, etc. which are highly resistant to attack by warm or vcold plating solutions containing chromic acid, which are of reduced weight as compared with metal, glass or ceramic containers, and which enable the process of plating to be carried out without the disadvantages of stray current effects.

v One of the usually given properties ci chroniic:

acid is that of its attack on, and reduction. by, organic substances* It is therefore a surprising pound polymers which I have found suitable are those which from the physical standpoint are solid and tough. As most of the polymerizationproducts of the common vinyl compounds are either too soft or too brittle, the desired physical properties may be obtained in the conjoint polymerization product of two different vinyl compounds (by which is meant polymerization of two or more compounds while in mutual contact); one compound (a vinyl halide, as vinyl chloride, for example, or vinyl benzene (styrene), for example) being one which, when separately polymerized, forms a hard resin, and the other compound (an ester of a lower aliphatic acid, as vinyl acetate, vinyl propionate, vinyl butyrate, for example) being one which, when separately polymerlzed, forms a soft resin.

'I'hese conjoint polymerization products or resins are made and sold by Carbide & Carbon Chemicals Corporation, 30 East 42nd Street, New York city. However, those conjoint polymerization products in which the proportion of the vinyl ester of the soft resin forming type is too great, may tend to hydrolyze, or are less resistant for some other reason, and therefore the vinyl ester of the soft resin forming type should be about equal to, and preferably less than, the vinyl compound of the hard resin forming type. That is, the range of the proportions of the two types of cornpounds in the conjoint polymerization product (calculated as the monomeric compounds however present in the resin) should be 50 to 95 parts of the vinyl compound of the hard resin forming type to 50 to 5 parts of the vinyl ester of the soft resin forming type. The optimum conjoint polymerization resin is one having 85 to 87 parts, of a total of D parts, of the vinyl compound of the hard resin forming type, and to 13 parts of the vinyl ester of the soft resin forming type, calculated as explained above; and when parts of one or the other vinyl compounds are referred to herein, the word will be understood as being used in the sense explained above.

According to my invention, I make apparatus and elements, and the insulating parts thereof, to be used in contact with chromium plating solutions of a conjoint polymerization resin as herein described.

Embodiments of the invention are illustrated in the accompanying drawing, wherein;

Fig. 1 is a view principally in side elevation, but with parts in section, illustrating the invention in the form of a rack with an auxilary anode.

Fig. 2 is a view partly in side elevation and partly in section, illustrating the invention in the form of a rack or xture for plating an article with stops applied thereto.

Fig. 3 is a view in side elevation illustrating the invention in the form of a rack for holding a number of articles to be plated.

Fig. 4 is a view in cross-section of a plating tank according to the present invention.

Referring to said drawing, numeral I0 designates insulation of conjoint polymerization resin according to the present invention applied in a variety of ways to apparatus and elements, and to parts thereof.

Referringto Fig.` l, numeral I2 designates an auxiliary anode (conducting) which may be, as here shown, connected to the same anode bus-bar as the normal anode I4. I6 designates a conducting-rod which is connected to the cathode busbar and which supports the article C to be plated, the article being illustrated as a part of an icecream scoop, and as connected to a threaded stud I8 projecting from the rod I6. The position of the auxiliary anode I2 with relation to the cathode-article C is a more or less precise one, and so as to avoid the labor and care of positioning the auxiliary anode I 2 for each plating operation, Vthe auxiliary anode I2 and the cathode-rod I6 are mounted in fixed relation in a blockZD. The block 20, connecting the parts I2 and I6 of opposite polarity, is made of insulation of the herein described kind. 'I'he rack or xture shown in Fig. 1, when used for plating in a chromium plating installation, projects partly below the surface of the plating bath, the immersed part being below the solution level indicated in the gure. The parts I2 and I6 being conductors having opposite polar-,l

ity, the parts below the solution level should beinsulated so that current will not ow directly from one part to the other. To prevent such current flow, insulation of the herein described kind in the form of a tube or sleeve 22fis applied to the vertical length of the auxiliary anode I2, and insulation of the herein described kind in the form of a tube or sleeve 24 is applied to the rod I6. The parts of the rack above the solution level also come into contact with the solution, als the gas arising from the bath as a spray carries with it some of the plating solution which wets the parts of the racks above the solution-level of the bath.

The chromium plating solution is one containing chromic acid, and, to resist the action of the plating solution, I make the insulating block and tubes 22 and 24 of molded or extruded conjoint polymerization resin hereinbefore described. Blocks, tubes, and also the coatings hereinafter described, of the hereinbefore described conjoint polymerization resin are not attacked by chromium plating solutions containing chromic-acid, such conjoint polymerization resins having the characteristic of not being wetted by the platin solution, and hence do not require frequent re-v newals. They are also strong and non-brittle.

In Fig. 2 a xture 3U for re-plating the n'o-gof portion of a go no-go gauge is illustrated. Ther'. go portion of the gauge is stopped" by having applied thereto a moulded cap 32 of the hereinbefore described conjoint polymerization resin which is fitted closely over the go portion of the gauge. A sleeve 34 of the hereinbefore described polymerization resin is also preferably applied to the handle part of the gauge to stop plating thereon.

In Fig. 3 is illustrated a conventional form of rack 40 for holding a plurality of articles for chromium plating at one time. The rack 40 comprises the side-rods (conducting) 42 and 43, to which are connected a series of cross-rods (conducting) 45, 46, 41, 48, and on these cross-rods are sets of spring-fingers (conducting) 5U, 5I, which press and hold the articles (not shown) to be chromium plated. The rack 40 is suspended in the chromium plating solution from a cathode-bus-bar by hooks 55.F vInsulation I0' of the hereinbefore described kind is applied to the rods 42, 43, 45, 46, 41, 48, to prevent current from passing directly from the anodes to the said rods. The insulation I0 is here shown as a coating 60 resulting from the successive application of films or coats of the hereinbefore described conjoint polymerization resin in solution, and drying. In applying the coating 6I) to the metal surface (copper for example) the metal should rst be thoroughly cleaned. A priming coat should then be applied. The priming coat consists of a solution of the hereinbefore described conjoint polymerization resin containing a suitable pigment (as d 2,072,170 blue-lead) `for stabilizing the resin during subsequent baking.

i *See page 38, Useful information about lead published by Lead Industries Association, New York city, 1931.

The priming coat isthen baked on at a suitable Q. temperature.

" hereinbefore described conjoint polymerization `resin are applied by applying successive coats of iio Thereafter successive coats of the a solution of the aforesaid resin, anddrying.

An example of the method of applying the resin as "a built-up coating, is as followszi 1."A Spray one coat of primer consisting of a solutiorijpf the hereinbeiore described conjoint polymeization resin containing blueA lead as a stabilizer.

2( Dry 1/2 hour ln air, then bake onehour at 3. Apply one coat by dipping in aclear solution scribed conjoint polymerization resin dissolved in a suitable solvent.

4. Dry 1A; hour in air, then force dryone hour in an oven at 150 F. i if.

` 5. 'Apply one coat by dipping in said clear resin solution. 6. Dry 1/2 hour in air; then force dry one hour in an oven at 150 F. A

'1. Apply one coat by dipping in said clear resin solution.

` kindiapplied thereto in the form-of a lining or coating T4. The coating may be a coating which is built up by spraying or otherwise applying coats or lms of the hereinbefore described resin solution, and drying, as heretofore described, or it may be composed oi. moulded sheets of the coni joint polymerization resin hereinbefore described.

'The joints 'I6 may be closed in suitable manner,

as by heating the lapped portions of the sheets of the hereinbefore described conjoint polymerization resin to soften them somewhat and then pressing the lapped portions together; or the i, hereinbefore described conjoint polymerization i resin in the form of` a powder may be warmed and applied as a putty to the joint; or a thick solution of the hereinbefore described conjoint polymerization resin may be applied to the joint and subsequently dried. f The tank or tank-lining `fore described may also bea `molded monolith of the hereinbeconjoint polymerization resin.

` With atank so constructed straying of current to the sides of the tank will beavoided and the shading" effect on articles suspended in the solution, near the si'des for plating, will be avoided.

` .Also there will be no attack on the lining by the i consequently no sludge formation such as results plating solution which contains chromic acid, and

from the attack of chromic acid onthe lead linings of lead-lined tanks. Moreover, with a tank, `such as here provided, there is no metal contamination of the plating solution, such as results when solutionsfcontaining chromicacid come into contact with iron, copper, etc. The tanks accordcon'tainlng about 20%.of the hereinbefore de-l ing to this invention are lighter in weight than heretofore, strong, and non-fragile.

The conjoint polymerization resins as herein described, applied as herein described, will hold their form, and'maintain their resistance tothe action of chromium plating solutions containing chromic acid in the usual warm baths (temperatures of 35-55 C.) as well as in the cold baths.

Chromium plating solutions usually contain from about 150 to 500 grams per liter of chromic acid (CrOa) and catalysts in the form of an acid radical or radicals, such asV sulphate-radical, iiuoride-radlcal (sllico-fiuorides, boro-fluorides), etc. Such solutions may also sometimes contain other radicals, such as the chloride-radical, etc. Reference is made to Fink Patent #1,581,188 and Fink & McLeese 1 Patents #11,844,751 and #1,928,284, concerning the composition, etc. of chromium plating baths and methods.

Racks provided with insulation according to this invention havefthe further advantage that they may be immersed in the usual hot alkaline cleaning solutions frequently employed preliminary to chromium plating, without being destroyed .by such solutions or liquids.

The invention may receive various other embodiments than those herein speciiically illus,- trated and described.

What is claimed is:

1. An element or part of a chromium plating `installation which is in contact with a solution containing chromic acid and has insulating properties, consistingessentially of a conjoint polymerization resin which does not hydrolyze and does not react with such a plating solution, containing a vinyl compound of the hard resin forming type (consisting of the group vinyl halformingtype, calculated as such however present.

3. A container for a chromium plating solution containing chromic acid, comprising a surface portion in contact with the chromic acid solution consisting essentially of a conjointpolymerization resin which does not hydrolyze and does not react with such a plating solution, containing a vinyl compound of the hard resin forming type (consisting of the group vinyl halides, styrene) and a vinyl compound of the soft resin forming type (consisting of the group of esters of a lower aliphatic acid) the range of the proportions of the two types of compounds in the conjoint polymerization product (calculated as the `monomeric compounds however present in the resin) being 50 to 95 parts oi vinyl compound or the hard resin forming type to 50 to 5 parts of the vinyl compound of the soft resin forming type. i

4. A container for a chromium plating solution containing chromic acid-according to claim 3, in which the range oi the proportions of .the am installation, according to claim 1,'ln which the sal two types of vinyl compounds is 85 to 8'? parts oi. the vinyl compounds of the hard" resin forminer type and l5 to 13 parts of vinyl compounds of the soft resin forming type, calculated as such however present. l

V5. A rack forming an element of a chromium plating installation, comprising insulation on parts thereof in contact with solutions containing chrornic acid consisting essentially of a conjoint polymerization resin which does not hydrolyze and does not react with such a plating solu tion, containing a vinyl compound of the hard resin forming type (consisting of the group vinyl halide, styrene) and a vinyl compound of the soft resin forming type (consisting of the group of esters of a lower aliphatic acid) the range of the proportions of the two types of compounds in the conjoint polymerization product (calculated as the monomeric compounds however present in the resin) being 50 to 95 parts of vinyl compound of the hard resin forming type to 50 to 5 parts of the vinyl compound of the-iso1ft" resin forming type.

6. A rack forming an element of a chromium plating installation, according to claim 5, in which the range of the proportions of the two types of vinyl compounds is 85 to 87 parts of the vinyl compounds of the hard resin forming type and 15 to 13 parts of vinyl compounds of the soit resin forming type, calculated as such however present. l

'7. A rack forming an element of a chromium plating installation, according to claim 5, in v'ihich the insulation consists of built-up films or layers of the said resin. i I' GEORGE K. HEazdLGf.v

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