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parts are available, they may 81.0 find wide use in building projects where the number of their points of use will ju3tify the cost of a mold. Thus, a hotel, hospital, or large apartment development might economically have its own distinctire molded knobs fabricated to order economically. The laminat'ed plastics, most widely used of all the group in the building field, have found their principal applications t,o date in instances where the alternative materials were comparatively expensive. Thus, scarcely a large city can boast of less than one theater with a laminated plastic lobby, Hundreds of doors and many wall surfaces were made of laminated plastics in the Philadelphia Savings Society Building, Store fronts, running into the many hundreds, have been spread the length of the land. In Chicago, a large group of outmoded theat'ers were remodeled with laminated plastics as the principal material used, and this is true of many other cities. SVit>hthe advent of repeal, hundreds of bars, grillrooms, and night-clubs have called upon laminated plastics for interior decorative surfaces as \vel1 as for table and bar surfaces. Notable among these are the Casino Club of Chicago, the Vendome Hotel of Buffalo, the Park Plaza Hotel of St. Louis, the Brevoort Hotel of Chicago, the Carlton Hotel of Washington, and the Plaza and Sherry-Netherlands Hotels of Piew York. Transluscent urea-formaldehyde laminations were used in the Chicago fair for signs and for a number of mural decorations as well as in the Deshler-SVallick Hotel of Columbus, Ohio. A more recent development has been the application of
VOL. 27, 50.10
cast phenolics to interior decoration and outdoor signs. This material, familiar to the general public in the form of Catalin costume jeivelry and as clock cases and other small accessories, has been used in a very ambitious manner in decorating the French Casino, a New York theater converted to night club purpojes. Two large bars, numerous lighting fixtures, and a large marquis sign have here been imtalled. The transluscence of the material has been taken advantage of for indirect lighting by means of hidden neon tubes. In the elevators of Radio City, another cast phenolic material, RIarblette, has been used for large ceiling lights, the light weight and freedom from brittleness was a major factor in the choice over glass in this instance. An installation is now in the process of fabrication for the Italian Building in Radio City consisting of four immense plaques illustrative of the Italian Line's coat of arms. Here, color and light reflection mere major factors. Another large installation will shortly be made in a New Jersey theater, where the entire front of the building will be constructed of cast plastics. Thus, plastics have passed beyond the laboratory stage. Definite characterist'ics of all these materials-their workability, their appearance, their wearing qualities, etc., have been proved by actual installations. It is now up to the architect, the engineer, and the builder to multiply the number of applications, and to do this he has a broad background of experience to serve as a guide. RECEIVED April 27, 1935.
(Previous symposium gapers appeared in August and September issue*, and others ~ 1 be1 printed i n
Preparation of Iron and Steel for Painting
November issue.)
V. RI. DARSEY Parker Rust-Proof Company, Detroit, SIich.
QP
RESEST-DAY demands for increased
corrosion-resistant finishes on iron and steel products have resulted in more durable organic coatings and improved scientific methods for preparing iron and steel for painting. In general, the useful life of any paint finish depends on two major factors-the durability of the organic coating film it-elf and the adherence of the film to the surface to which it is applied.' Providing metal with a nonmetallic coating of the proper texture adapted to inhibiting corrosion and increasing the adhesion to the final organic finish are the primary factors in the preparation of iron and steel for painting. Permanent adhesion iq clearly the primary requisite for improving practice in painting metal. The cleaning of metal for painting is so common and familiar that it is apt to receive but minor consideration with regard to the paint coating itself, and the fact that it has a definite function in relation to the useful life of the paint finish is often overlooked by the manufacturer. The importance of proper preparation of ferrous surfaces before painting has been more fully appreciated in the past two years than ever before, because of the increasing use of cold-rolled or cold-reduced steel and the use of synthetic organic finishes. The tremendous pressures used by the pres1
Hunt, J. K , and Lansing, K, D , IND ENG CREW.,27, 26-9 (1935)
ent-day methods of cold reduction produce steel impregnated with grease and oil to a n extent that makes their removal by old methods of metal cleaning very difficult. To obtain the maximum protection from the synthetic organic finishes, they should be applied over comparatively greasefree surfaces. It is not within the scope of this paper t o present in detail all methods used in the preparation of iron and steel for painting. The methods most widely used are classified into three groups as follows : I. Methods vhich do not change the surface of the metal. 11. Methods which change the surface of the metal either by mechanical or chemical processes. 111. Methods which transform a ferrous surface to a non-
metallic coating.
Alkali and Solvent Cleaning Group I includes various methods of alkali and solvent cleaning which constitute the simplest and most economical methods used in the preparation of metal for painting. These methods provide only for the removal of foreign matter, grease, and oil without imparting any surface change to the
OCTOBER, 1935
INDUSTRIAL AND EXGINEERISG CHEMISTRY
1143
does not provide for inhibiting corrosion; nietal bo prepared metal. The greatest possible succe3s obtainable from such must be painted immediately. Because of the increased surmethod. is an absolutely clean, plain metal 5urface which face area, metal cleaned by either of these methods tends to does not provide for inhibiting corroqion or for increa+ing the corrode more rapidly than ordinary plain steel. adhesion of the final organic fin1.h. Metal products are generally freed of oil and grease before Ferrous objects may be cleaned by immersion in an alkali they are sand- or shotblasted. This precaution prevents the solution in a still tank or by a similar solution in a washing abrasive material from becoming contaminated and the grease machine. In either method the time of cleaning, the confrom being driven into the metal. In shotblastingit is particucentration of alkali. and the teninerature of the cleaning solularly necessary t o avoid contamition are important factors. The’ -~ nating the shots Lo obtain a type of alkali cleaner used should grease-free surface wh i c h will depend upon t’lietype of drawing Several methods of preparing metal for provide good paint adhesion. I n compound or grease present on painting are briefly described. Many inobt cases such methoda of metal the object to be prepared for factors are to be considered before any preparation are expensive and painting. In general, 0.26 to 0.5 specific method of preparing iron and steel require considerable equipment ounce of alkali cleaner per gallon for application. for painting can be chosen. The quality of water is sufficient for cleaning Ordinary acid p i c kl in g remetal in a washing m a c h i n e . and useful life of the final paint finish is m o v e s s c a l e from metal and Alkali-immersion cleaning in a of first importance. Cost of application etches the surface. The operastill tank requires a s t r o n g e r and adaptability of the method for pret i o n s h o u l d be followed by a solution of alkali ranging from 2 paring all types of metal products for thorough water rinse t o insure to 4 ounce> of cleaner per gallon the removal of any adhering salts painting are major factors. -4ny method of water. The object after alkali from the metal. The primary cleaning should be thoroughly should provide for taking care of many factor in the pickling operation rinsed to remove all alkali, and different-sized objects and for eliminating, is to remove scale and to etch dried before painting. Experias far as possible, the human element in the metal surface and provide ments show that, if metal prodobtaining a satisfactory surface. Often b e t t e r a d h e s i o n for the final ucts are rinsed in water containpaint finish. it is impossible to paint metal immediately ing 0.01 per cent alkali, paint Acid cleaning of metal with coatings applied over such surfollowing the cleaning operation, and in p h o s p h o r i c acid and a grease faces may fail prematurely. It such cases it should be protected from solvent provides for the removal is not only economical to operate corrosion. In many instances metal prodof grease and the etching of the alkali cleaning solutions at the ucts are provided with a phosphate coating metal surface in one operation. lowest alkali c o n c e n t r a t i o n s The application of such cleaning and shipped to assembly plants before but is advantageous for obtainmethods is generally by hand, ing the best surface as a base painting. From the various available and the human element is a for painting. methods, the manufacturer should be able factor in the succetiful operation S o l v e n t c l e a n in g by either to choose one especially suitable for his of the process. Following the the immersion or vapor process requirements. acid c l e a n i n g operation, it is is rapidly increasing as a customary to rinse t h e m e t a l method for p r e p a r i n g metal and dry it thoroughly b e f o r e for p a i n t i n g . The vapor depainting. This method of metal preparation is extensively greaser forms an efficient and qatisfactory way of cleaning used for preparing iron and steel for painting. certain types of metal products. It is obvious that objects so designed that they will “carry out” solvent cannot be Nonmetallic Coatings economically cleaned by such a process. Metal atampings which have previously been alkali-cleaned but not rlnsed, Group I11 includes those methods which traii>form a ferand used in some stage of the fabrication process, generally rous surface to a nonmetallic coating, such as an oxide or a cannot be satisfactorily prepared for painting by solvent phosphate. By far the most widely used method in this group cleaning unless followed by wiping. Certain compounds, consists in providing iron and steel products with a phosphate such as alkali, soaps, and oxidized oil films, are not removed coating. During 1934 over 390,000,000 square feet of metal from metal by solvent or vapor degreasing. Practice has were treated by the Bonderite proce-9 whirh converts a fershown that a solvent wipe on metal after alkali or degreaser rous surface to a finely crystalline phosphate coating, adapted cleaning is necessary t o remove these materials. Like alkali to inhibiting corrojion and increasing the adherence of the cleaning, solvent cleaning does not change the surface of final paint finish t o the metal. The process is carried out by the metal or inhibit corrosion, and products cleaned by dissolving the necessary Bonderite chemicals in hot water either method m u d be painted immediately to prevent (around 210” F.) and immersing the properly cleaned metal corrosion. in the solution for 2 minutes; this interval is sufficient to transform the metal surface to a crystalline phosphate coating. Surface-Roughening Rlethods The latest method of application consists in spraying the Bonderite solution under pressure onto the metal in order to In group I1 are various rnechanical methods of metal prepaaccomplish a cleaning and coating operation a t the same time. ration, such as sandblasting and shotblasting, which tend to The solution is maintained around 170’ F., and the processing confer on the metal a roughness to which paint will more time is 1 minute. Figure 1represents the equipment used by readily adhere. In tliib same group are chemical methods of this process. Following this operation the parts are rinsed metal preparation, such as a n ordinary acid pickle and other and dried, and can either be painted immediately, or be stored methods involving the use of an etching acid and a grease or shipped before painting. The processing solution contains solvent to clean the metal and etch the surface in order to free phosphoric acid, metallic acid phosphates, and an oxidizprovide better mechanical adhesion for the final paint finish. ing agent in the proper ratio t o produce a phosphate coating These methods impart a roughness on the metal surface which on metal in the shortest possible time. The concentration results in increased mechanical adhesion of the prtint film but
tlae solution i b n i ~ ~ t r o l l I,? r d titrating the turwinit OS acid present ill a zwnijilc iisiiig standard sodinnr Iiydruxide :ind plienol~ilitlinleiii a s iiidicatrr. A s rrietal is t,reiited i n the liath, tlie roiior?rit,rutii,iiriS tlie latter is reduced and must he rcplenislied from time to tiiiie with additional clreinicals to restore t.11~operating efficiency. The fortnation of a j~liospliatermting on iiiet,al depends lipon the fact ttiat pi ic, acid solittiow will dissolve ferrous plwqhate ~ i t l i i I definite lirniti iir direct imiiortimi to the concentration of t,lit: acid preserit. The additiori of iron or steel prudiicts in such solntinns results in the preripitation of Serroiw phosplrate on tlic rrietal snrface a t tho point of solution. The reactiiin taker glace with the c v d m tion of liyilrogcn nntil tlie nietal surface is conipletely covered witti a plhplrate eiinting. An oxidizing agciit capable of .ti film wliirll forins on tlie surface of tile .iiig iiperatimi is used to aeceleratr the forinatiorr of tlie phosphate coating. In ronvert,ing N ferrous surface to i i plioqiate mating, it is i,f
ntial to w m t , r d the t,extiire arid t,Ix: tliickiies lic ix,nt,iiig to d h i n tlic mo paint fiiiislt. 'file tautrirc of tile plioq~lratecoating s l m t l d i~ fill? grained, ~iiediuinhard, arid adlmcntly etrlieil i i i t i l t,lic nictnl surface. Tliese i~lia.rnct,crixtic~ are iilit,aiocd I iy inc:mporatiitg ill tire procesitig I x A r the necessary clieiiiicals to 11rodrii:e aiicli n c
