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INDlJSTRTAL AND ENGINEERING CHEMISTRY Acknowledgment
tory.
Vol. 23, No. 12
Literature Cited
(4) Wnlker and Thompson, Proc. Am. SOC. Testing. Materials, 22, Pt. 1 1 , 465 (1Q22)i
Automobile Coatings' H. C. Mougey and R. J. Wirshing RESEARCH LABORATORY, GENRRAL MOTORS CORPORATION, DETROIT, MICHIGAN
T
The materials used and typical finishing systems for ,HERE are only two restill leads the field, although bodies, fenders, wheels, and chassis are described. quirements for autosome lacquers as well as synDisadvantages of the present materials and systems mobile finishes-good thetic-resin materials are beare discussed. The following improvements, given in appearance that is retained in ing used in small quantities. the order of their importance, are desired: rustservice, and low cost. For wood and wire wheels, resistant fender enamel; lacquer with better chalkBy good a p p e a r a n c e is old-fashioned v a r n i s h m a resisting properties; increased resistance to chipping meant not only the initial apterials are still in use, but it from stones thrown up by tires, etc.; a surfacer or pearance on the showroom a p p e a r s that the syntheticsurfacing system that will give a surface ready for floor, but the appearance durresin materials will soon relacquer or the color coats at lower cost, counting both ing the life of the car. Replace them, except in the case material and labor; a lacquer or color material or sistance to cracking and reof black wire wheels where painting system that will give the desired final appeartention of luster are recogblack baking enamel may be ance at lower cost, counting both material and labor; nized as necessary qualities, desirable under certain cona material or system for producing colored fenders at a but resistance to mechanical ditions. cost comparable to that of the present black enamel injury is just as important. For chassis, baking enamels fenders; a material or system for finishing chassis at a A finish might show satisfacof the oil-asphalt type appear cost comparable to that obtained at present but with tory properties when tested to be best suited for the primer much greater resistance to rust and chipping from on an exposure-test panel, and coats with oil-asphalt, synstones, etc. yet it might be entirely unthetic resins, or lacquer for the suited for automobile use. If top coats. Typical schedules the finish mars by being scratched with dust when the car is for finishing with these various materials are given below, cleaned, its other desirable properties will not be appreciated On account of commercial conditions these schedules must be considered as typical only, with variations in the number of by the owner. By low cost is meant a total low cost for time, labor, and coats, drying schedules, etc., in different plants. material. A certain finishing material might have a low cost Schedule for Finishes per gallon, and yet, because of time required for application, high cost of labor, etc., the resulting finish might be very BODY-(^) Metal is cleaned with Sunoco spirits or phosexpensive. The effect of high-labor cost appears a t once in phoric acid, and dried. the cost records, but the time factor is much more intangible. (2) Primer (usually oil type) is sprayed and baked 1 hour Cost of floor space, interest on work in process, etc., are a t 180" to 200" F. (82.2"to 93.3" (3.). regular items in the books of the cost accountant, but these (3) Surfacer (usually oil type) is sprayed on and baked 1 items are not the important ones from the standpoint of time. hour a t 180" to 200" F. (82.2' to 93.3' C.). The real reason why a short finishing time is important is that I n some cases the primer is not baked but allowed to air-dry i t gives the car manufacturer the ability to produce cars when for a few minutes, after which the surfacer is applied and then the public is willing to buy them. Cars are very bulky and baked an hour at 180' to 200" F. (82.2" to 93.3" C.) cannot be stored in large numbers, and even if they could be The PX type primers and surfacers are not in wide use at stored, the rapid improvements made in cars might make the the present time. The PX primer does not adhere to the ones in storage obsolete. The rapidly changing ideas of the metal as well as the oil-type primer under production condipublic in regard to color, etc., are even more important in tions here. The PX type surfacer does not offer advantages their effect on the possibility of storing cars before sale. to offset its increase in cost. Many times in the history of the automobile industry it has (4) The surfacer is websanded and then dried. been necessary to withdraw cars from storage and repaint (5) Formerly japan ground coat was applied before the them in different colors in order to sell them. Some times finishing lacquer. However, trouble due to lack of adhesion this change was from somber colors, such as a black or gray, of the lacquer to the ground coat and "pinholing" of the to red or other bright colors, and at other times the reverse lacquer caused the use of japan ground coats to be diswas true. continued. At present, when a ground coat is used, a coat of These requirements for automobile h i s h e s appear to be the finishing lacquer is applied as a ground coat and forcevery simple, but, on account of production conditions, entirely dried for 30 to 60 minutes a t 125" F. (51.7" C.). different types of materials must be used for bodies, fenders, The finishing lacquer, properly thinned, is sprayed, usually wheels, and chassis. For the top coats on bodies, nothing has in 3 or 4 double coats. Force-drying between coats from 5 to appeared on the market to dispute the supremacy of lacquer, 15 minutes a t 100" to 125" F. (37.8' to 51.7" C.) is helpful in although the primer and surfacer coats are usually oil type, producing a smoother finish. with or without synthetic resins. For fenders, black enamel The application of a certain number of coats of lacquer with a high percentage of thinner is preferable to a fewer number of 1 Received September 10, 1931.
Figure l--Artlllery Wood Wheel Exposed Three Months on Florida
Tees Rack
coats of a mixture containing less thinner. This has a tendenoy to reduce the amount of orange peel. The lacquered job is force-dried 30 or 40 minutes a t 125' F. (51.7' C.) and is then rubbed and polished. I n some cases the job is mist-coated between the rubbing and poliabing operations. FEh.DERw%nders are cleaned usually hy passing through a washing machine, although in some cases they go through a "burn-off" oven before the cleaning operation. They are then dried, hung on the conveyor, tack-ragged, and passed into the dip tank of rubber enamel, and then into the oven. This is followed by the second dip tank and oven, the entire operation being done on the same conveyor chain. The number of coats applied varies from 2 to 4. The time of baking averages about 30 miriutes per coat, and the temperature is approximately 450' F. (232.2O C.). WAEELS-Wood wheels are filled and primed (oil-type primer) and forcedried an hour a t 150' to 180" F. (65.6" to 82.2' (2.). One or two color coats are applied, each forcedried an hour a t 125" to 150" F. (51.7°t065.60C.) A stripe is them applied, usually by spraying with the aid of a template, and then a coat of clear is sprayed over the entire wheel. I t isthenforcrdriedanhourat 125"to150°F. (51.7t085.6°C.). Wire wheels are primed and baked and the calor (syntheticenamel type), either by airdrying or baking, is then applied. FRAMES AND CnAsfim-Frames are usually received from the manufacturer with a coating of baked enamel. The requirements usually set up for this material are as follows: It must be rust resistant, gasoline resistant, and gravel resistant, and must take lacquer and other finishes. There seems to be no standard method for finishing chassis. In some case8 the various parts are enameled before assembly, and in others the entire job is assembled and then painted either with an air-dry material or low-bake enamel. Improvements Desired in Finishes for Automobiles Attention should be called to the fact that the materiala and systems in use in automobile finishing are in a state of flux. Most of them have been developed within the last ten years,
and since needs must he discussed in terms of known materials and in terms of present knowledge, it is difficult to say just what is wanted in the line of fmishing. The most important development would be rust-resistant fender finishes. Anyone who will examine cars parked along the curb will be struck by the difference in rust-resistance in the finishes used on the bodies and on the fenders. This is especially true at the seacoast and in cities where sodium chlorideisusedon the streetsto melt ice in winter. Of course, fenders can be finished in the same manner as bodies, with the same results, hut the cost would be prohibitive for all cars except those of the higher-price class. .4n increase of only 10 cents per car appears to he insignificant but on the produotion of one million cars per year it amounts to $100,000. If, by spending this amount or less on research, a rust-resisting finish can be developed at a price equal to the present price, then the aniiual expenditure of this amount of niouey is saved, and the added value is passed on to the car owner. The problem of rust-resisting fender fillislies can easily he solved by simply adding on euough cost, but the problem is to obtain a great improvement at little or no increase io cost, and it is not desirable to keep costs of the fi11al product the same by going forward in some respects and going backward in others. Observation and tests have shown that the principal cause of the rusting of fenders is the action of sodium chloride. When exposed to salt water, the enamel 6lm softens and peels, especially at the edges and areas where the film is thinnest. Rust then forms on the unprotected surface and gradually spreads beneath the enamel causing further peeling.
Figure Z-ReI3ecdans
in New Car Flnlsh
There have been two general methods suggested for overcoming this trouble: treating the surface of the steel so that it is more resistant to mting; and making the enamel so that it is less subject to the action of salt solutions. There is no question but that much proFe8s will be made along one or hoth of these lines in the near future. The next improvement in the order of importance is that of
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I.VD I;sTRIAL .1 s D .!3zVGI.V.!3BliI.VGC H E M I S TI1Y
vu1 23, No. 12
lines OF changes ni the cheniical composition and methods of manufacture of the oicments: usp of
Fipuro 3--Espurure-'re8t Fleld, Miami. Florida
chalk-resisting properties in both black enamel and lacquer By chalk reruisting is meant ability to ret,ain luster on exposure. Cracking of the finish, in craclis visible to the unaided eye, is no longer a problem in automobile finishing, except in a very few isolated cases. Chalking is a microscopic surface failure which results in loss of luster. This trouble due to chalking is more prevalent in the southern climates. I t is true that the luster can be restored to a chalked surface by polishing. but part of the film is removed in this operation, and frequent polishing results in tho film's being worn through. The desired finish will hold its luster without frequent polishing. Within the last few years lacquer has been improved so that it is much better in chalk-resisting properties than black enamel, hut a black enamel with greatly improved antichalking properties has recently been placed on the market,
improved methods in applying the finish. The hubs of the rear wheels, especially of the present wire-wheeldesign, aresubject to theaction of stones and gravel thrown by the front tires. Changes in design, so that more protection is afforded by the tires or hub caps, or projectiona from the rear fenders or the running boards, seem to be indicated in this case, for this sandblast action ia too severe for ordinary paint or enamel to withstand. The finish on the top sides of the fenders may be made more resistant to chipping by improvements in the enamel or in the method of baking. Roughening the steel does not make much improvement, and it has the disadvantage of interfering with luster. Conclusion
In this p a p r the subject of methods of testing has not been discussed since the authors are simply trying to point out what they believe to be the needs of the automotive industry in
Figure il-Re8ections of Plinted Cards on Car Fenders Shown how new bisck baking Enamel retains inate? BQ compared with old ty e of bakng enamel. affer fenders inere erpovd on D&zt test r o d lor JIX we&
and it is now in production on several makes of automobiles The authors believe that the material now generally known as black enamel will very rapidly become obsolete, and that it w!li. be replaced by antichalking black enamel at least as good as the antichalking material mentioned above. I n the case of lacquers, while there has been a great improvement in their chalk-resisting properties, much still remains to be done, and experiments now under way indicate that great improvements are possible. This work is along the
regard to finishing materials It is also felt that this subject of testing methods i s one of such imprtance that it should be discussed in a separate paper, which will be written in the near future. The authors have endeavored to present briefly what they consider the principal problems in the finishing of motor cars, and, although some of them may seem almost impossible of solution, there is reason for hope for the automobile industry has the reputation of demanding the impossible and getting it.
