Not long after the beginning of the 20th century, 1909 by his own account, Henry Ford made the famous statement, “Any customer can have a car painted any color that he wants so long as it is black.”
In reality, the Model T was offered in multiple colors as early as 1908, but he was experimenting with the assembly line and the resulting increase in production speed required a fast-drying paint – which, at the time, was only available in black.
Modern automotive paint finishing has come a long way
Automotive paint finishing has greatly evolved since then. In those days, the process was completed by hand. Now, it is almost fully automated. And modern paint formulations and curing technologies allow multiple paint colors to be applied (even to the same body) at a rate that can still be embedded into the manufacturing process – just as Mr. Ford originally envisioned!
The process has been diversified in other ways as well. Modern automobiles are composed of many different materials – steel, aluminum, plastics, composites – just to name a few. And many of these components come to the line pre-painted, yet they must match the body they are to be mounted on perfectly.
A more complex process
Automotive paint is generally applied according to the following steps:
- First, the body is cleaned and chemically prepped. This begins the anti-corrosion process and conditions the parts to accept the paint.
- Next, primer is applied. In essence, this prepares the surfaces for subsequent layers by filling in tiny imperfections and provides a good surface for subsequent layers to bond to.
- Then, the basecoat layer is applied. This provides the color. Basecoats come in many different looks and formulations. They can be a single solid color, or they can shift color as the viewing angle changes. They may be metallic, with a “glittery” appearance. They may be metallic with a color shifting property. They can be pearlescent where, as the name implies, they take on the variegated appearance of a pearl. They can be waterborne or solventborne chemistry. You get the idea – lots of options. We’ll discuss those in greater detail in a later blog.
- The final layer is the clearcoat, the thickest layer of the three, which creates a sort of protective armor for the basecoat. Small scratches and other relatively insignificant damage is more easily hidden by the clearcoat than they would be by the basecoat – and the heavier film also allows these to be “buffed out.” Some clearcoats today (on higher-end vehicles) are even self-healing. This layer also determines if the finish is matte or gloss – and to what degree.
But it’s still not perfect
In each of the steps outlined above, the paint automation is usually comprised of a combination of robots and reciprocators. These will utilize a combination of standard spray guns for “cut-in” and bell atomizers for larger surfaces. Furthermore, these applications are often electrostatic, which improves transfer efficiency and reduces paint waste.
The problem is that the performance of each layer is determined by the viscosity of the paint when it is applied. And it’s a constant tug-of-war between objectives. The paint must be low enough in viscosity to “flow out” to cover the surface with a smooth, even layer. But it must be high enough in viscosity to prevent sags and runs that create both aesthetic and functional issues.
Contemporary automotive paint operations are huge operations. It is often necessary to transport paint hundreds of feet, through pipes, from the mix room to the point of application. These pipes may be run overhead in the truss level where all of the heat in the manufacturing facility accumulates. Or, they may be run in trenches under the floor, where the temperature is cooler. And it’s hard to heat and air condition such large areas, so the ambient temperature in the facility is significantly affected by seasonal temperature changes.
By the time the paint reaches the applicator, its temperature may have changed greatly. And, if you’re a regular reader of this blog, you already know that changing the temperature of any fluid – especially paint – changes its viscosity.
Put simply, this means that your carefully planned and constructed process is not going to be able to achieve consistent results, and you may experience surface imperfections such as orange peel or runs, sags, or drips, inconsistent color, uneven surface coverage, and more.
These can lead to added rework (often called “finessing”), and potential customer rejections.
The solution to inconsistent paint results
Fortunately, there’s a solution. Modern automotive paint temperature control systems can help you control your paint temperature to within +/- 1°F, ensuring that your process can achieve consistent and repeatable finish quality. The best of these systems provide the ability to control your paint temperature where it matters most – at the point of application.
Best of all, these systems generally pay for themselves, providing an ROI of less than one year, with purchase cost offset by savings in paint and solvent consumption, reject and rework costs, and reductions in material waste streams, which is great news for your bottom line.
If you’re interested in learning more about how paint temperature control can benefit your automotive finishing application, contact Saint Clair Systems.