The pre-treatment tunnel, also called “cleaning tunnel” or “degreasing tunnel”, is the ideal solution to prepare the components for the subsequent processing stages, particularly coating. An effective pre-treatment phase improves the adhesion of the paint product, preventing the degradation of the parts and maintaining their functional and aesthetic characteristics over time. Verona Impianti 2002 designs, builds and installs pre-treatment tunnels suitable for all metal materials, including iron, steel and aluminium.
We offer pre-treatment tunnels consisting of several stations designed to achieve clean surfaces ready to be powder or liquid-coated. Each tunnel can be customised to specific requirements, precisely calibrating the number of stages and the type of action required on the parts.
For more than forty years, we have been collaborating with experts in the chemicals and pre-treatment industry to offer efficient and functional chemical pre-treatment solutions, minimising energy and water wastage without sacrificing the quality of our cleaning and pre-treatment results.
Pre-treatment tunnel stations
The standard pre-treatment tunnels offered by Verona Impianti can range from a minimum of 3 stages (e.g. for unrefined parts such as cast iron castings) to a maximum of 9 stages (specially designed for aluminium components with high aesthetic quality and intended for highly corrosive environments).
Each element of the pre-treatment tunnel is made of reliable and durable materials adapted to the chemicals used and the cycle performed.
The main stages in a pre-treatment cycle include as follows:
Active baths
- DEGREASING - The first stage of the process, which removes impurities from the surfaces by spraying a cleaning solution containing the degreasing product.
- HOT PHOSPHODEGREASING - This stage not only cleans the parts further but also performs a chemical conversion process to increase paint adhesion. Water is heated by a boiler outside the tunnel, reducing energy consumption and facilitating maintenance.
- PHOSPHATING - Another hot stage fed by a separate heating system can be inserted to meet special requirements, dividing degreasing from phosphating. Additional rinsing stages with mains water can also be added between degreasing and phosphating.
Rinses
- 1st rinse with mains water: a room-temperature stage that removes most impurities and detergent residues left by the previous degreasing stage.
- 2nd rinse with mains water: a stage similar to the first one, ensuring more thorough cleaning. If necessary, a third rinse can be added.
- Rinse with demineralised water: it effectively removes chemical residues and reduces the salinity of the parts, using water with low electrical conductivity produced by an anionic/cationic resin or reverse osmosis demineraliser.
Spraying technologies
The chemical solutions for efficient pre-treatment are sprayed through nozzles arranged on pipes that are fed by a hydraulic circuit pressurised by a centrifugal electric pump. After cleaning the components, the product falls back into the collection tank below, from where it is recirculated via an electric feed pump.
The top feeding of the spraying bars, i.e. from a manifold at the top of the tunnel, ensures that the pipes can empty naturally by gravity when the tunnel is not in operation.
That prevents the formation of limescale and sludge, which could clog the nozzles and cause them to malfunction. This system guarantees a much more uniform pressure in the nozzles and easier maintenance operations thanks to the absence of manifolds on the walkway grating.
Filters
Each chemical pre-treatment station has a tank equipped with a double filter through which the degreasing product and water flow before being sucked in by the pump to optimise process effectiveness and yield.
Heating of cleaning solutions
The cleaning solutions used in the hot stages are heated through a shell and tube heat exchanger fed by a burner or electric heating elements, located in a tank separate from the tunnel. This system offers numerous advantages:
- Increased heat output, as energy consumption is reduced.
- Improved cleanliness of the heat exchanger, which is not contaminated by impurities removed from the parts.
- Simplified cleaning and maintenance of the tanks.
- Longer service life of the tunnel and boiler.