The mysteries of auto-body painting
Issued on 29 April 2015
Bernard Derelle retired in 2010 after nearly 40 years working as an engineer in the field of auto-body paint and rust-proofing for Peugeot, which later became PSA.
Today at the General Auto-Body Methods department, Paint division, and before he writes a book on these subjects, should his retirement activities allow it, he gives us a first glimpse of a few mysteries surrounding auto-body painting.
Paint’s mission is to magnify the beauty of auto bodies. The style must be shown to its best advantage by its shine,
and the reflections on the elegant colored shapes. So, the history of paint is linked to that of auto bodies.
In the beginning, automobiles were based on a horse-drawn carriage body, onto which a combustion engine was grafted. While the internal framework was still made of wood, the outer skin was soon made out of sheet metal, out of concerns for costs and serial production.The painting technique also stemmed from that used on horse carriages: brush application. Then, an increasingly rapid pace and concerns about production costs led to a search for faster techniques.
Reading technical reports from the Doubs factories tells us a lot about the evolution of these techniques. They contain the foundations of Peugeot policy:
* listening to criticism by the customers,
* that criticism being taken into account by a manager selected by the bosses,
* the proposal of solutions,
* trials and costings before application in production,
* following up on the issue through a series of reports,
* the constant focus on lowering production costs.
You have to keep a watchful eye out in any given paragraph for comments by this or that director who gives us insights into the evolution of techniques. It is noted that gun painting has been used for bike frames in 1919 at the Beaulieu plant.
In Mandeure plant, which manufactured auto bodies in the former Gauthier coach factory, applied paint by “vaporization” as early as January 1920.
At the same time, management was complaining of the lack of expert painters… and farther along stated that the development of the DeVilbiss “devices” (doubtless spray guns) was to be speeded up to make up for the lack of painters. That indicates that the experts in question were “brush” painters and that spray-gun application was expected to hire less-qualified personnel, who could certainly be trained more quickly.
What are they talking about?
This technique is explained in a German publication from the late 1920s, a translation of an English work by Charles E. Oliver. It consists of “giessen” and “flow-coating” in English, hence the term FLOCO seen above!
The paint arrived by gravity onto a device from which it flowed between two correctly spaced lips. The surplus flowed off by gravity and was recovered in gutters in the lower portion, then recycled.
this picture shows a worker using this tool. It “seems” that this shows the application of varnish on the body of the model 177B which had already received a coat of black paint.
The applicator, which looks like a clothes iron, extrudes the paint, which literally washed over the body and… the surplus flowed into the gutter set in the lower portion.
In 2013, we wonder about the upside of this process. The only advantage must be the lack of mist, because there was no spray. You will also note that the body being painted has a backseat! As for the rest, there are only disadvantages:
– paint or varnish drips causes visual flaws requiring touch-ups which results in high labor costs,
– flowing varnish picks up dust which creates further flaws during renewed application.
The archives make no further mention of it, and no other photo shows this bizarre instrument. From then on, only the spray gun was used.
Thomas DeVilbiss invented the spray gun in 1907 in the United States, but France didn’t get left behind. In May 1925, technical reports mention: “the flat-spray LEBARON paint guns, Chromographe N°9 model, have a yield 20% greater than DeVilbiss guns…” Profitability, then and always, profitability!
Here it is in use on a 172BC body in 1924 in Audincourt.
The next article will be devoted to the foreign terms used in auto body construction and painting, and whose origin has been lost over time.