In my previous post, I mentioned the environmental challenges faced by the automotive sector today, including the major technological efforts to find alternatives that can improve management of production resources, such as water.
Water plays a very important role in manufacturing processes in the automotive industry (including cooling, steam production and production lines). However, there are several stages in which it is absolutely crucial, in terms of quality and quantity. These stages are the preparation of the bodywork and the paint process.
The preparation of the bodywork is a very important stage of vehicle manufacture, as the paint process has very strict quality requirements to guarantee the characteristics that clients want: a decorative finish and protection against corrosion.
It involves two clearly differentiated processes:
- Surface treatment of the bodywork (known by some vehicle manufacturers as the surface treatment line, STL)
- Cathode electrophoresis (KTL).
The main environmental problems caused by the surface treatment of bodywork are related to contaminated effluents and high water consumption (in bath formulations and solutions, refilling and washes), followed by the generation of waste and, to a lesser extent, atmospheric emissions.
Water from the degreasing stage is basic and oily, with high organic matter content (oils and grease).
In the phosphating stage, the water used for baths and rinsing accumulates phosphates, fluorides, manganese and metals such as nickel or zirconium (Zr) in the form of inorganic salts, as well as suspended solids and oils and grease from the sediments of previous baths.
The water from rinsing and washing accumulates these inorganic salts and organic matter content.
Once the surface of the parts has been prepared, they enter the KTL process, which involves electrophoretic deposition of anticorrosive paint on the metal surface. In this process, there are different stages in which paint and binder is applied and recovered.
The industrial process of painting bodywork involves the application of three coats (base, colour and finish), and requires the use of auxiliary water.
Specifically, the water is used to clean exhaust air from the chambers in which the paint is applied in stages. This is achieved by passing the exhaust air through a water curtain. The contamination remains in the curtain in a soluble, suspended, colloidal form.
As a high volume of water is required for this process, it is carried out in an almost closed circuit, in which each paint application area has an independent treatment system.
All the contaminated water from the different paint application chambers is collected in a treatment area, where it is subjected to physical and chemical treatment and dehydration via centrifuges.
Most of the treated water is returned to the circuit, although some is purged to remove soluble contaminants.
The rest of the water
Another kind of water is used in car manufacturing processes: ‘service water’. This water has less potential to contaminate but is used in greater volumes to produce steam, in cooling systems, to clean and sluice down lines, in sprinkler systems and greywater from staff hygiene in the factory.
Consequently, Aqualogy professionals should study and analyse each client in detail, and propose the most appropriate techniques and technologies for each case, taking into account criteria for selecting the best available techniques (BAT) that are economically viable. Occasionally, electrochemical technology is proposed as the best solution.
I will discuss this technology and its application in the automotive sector in my next post.