When analysing a painting process, most of the attention is often focused on the efficiency of the spraying equipment in terms of paint consumption. This applies both to liquid paints and to powder coating systems.
However, the same level of care should also be devoted to the pretreatment of the surfaces to be coated and to the curing oven.
In many plants, pretreatment stages are still managed mainly on the basis of the operator’s experience. Product dosing is often manual and process parameters taken from the technical data sheets are checked only approximately.
These considerations are supported by a real case study in which a more efficient product was selected and periodic process control procedures were introduced.
After six months, the following results were obtained
(we will call the product previously in use A and the new product B):
Phospho-degreasing tank capacity: 4500 l
| Product type | Bath concentration |
Bath renewal per year |
Consumption per bath renewal |
Consumption to maintain concentration |
kg/year | Annual consumption product (renewals + top-ups) |
|---|---|---|---|---|---|---|
| A | 3.5–4% | 6 times | 150 kg × 6 900 kg/year |
12 kg/day × 240 working days | 2880 kg | 900 + 2880 = 3780 kg |
| B | 1.5–2% | 3 times | 100 kg × 3 300 kg/year |
8 kg/day × 240 working days | 1920 kg | 300 + 1920 = 2220 Kg |
From this documented experience, it is clear that using product B results in a reduction in consumption of around 40% compared to product A, previously used in the same plant. Even though product B has a higher unit price than product A, the lower annual consumption leads to a significant overall saving over the year.
The greatest benefits were observed in the reduction in waste volumes to be treated and disposed of. Fewer bath renewals mean fewer tonnes of phospho-degreasing solution to manage, in a context where treatment and disposal costs for these solutions are increasingly relevant in the total operating cost of the line.
In the specific case, process water was removed and transported for disposal when the volume reached 18,000–20,000 kg of solution. Every renewal therefore involved a complete emptying of the tanks, followed by transport and treatment charges for these volumes.
In addition, for each tank emptying, cleaning and refilling, two operators typically spend around four hours, with a significant impact in terms of labour time and availability of personnel.
By reducing the number of renewals from six to three per year, not only is there less liquid to dispose of, but there is also a measurable saving in working hours devoted to these operations.
If tank renewals have to be carried out during normal production hours, it is also important to consider that fewer renewals generally mean higher effective productivity, because the plant is available for coating for a larger share of the time.
In this specific case, to avoid manual operations affecting the test results, a dosing pump was used to feed the pretreatment product into the tank.
To evaluate the new product, a weekly report was compiled, analysing the key process parameters: concentration, conductivity, pH and temperature.
Adjustments were also made to the product feed rate, to the spray ramps (optimising spray pressure) and to the process temperature.
In the end, it mainly takes time and the willingness to run trials and measure the results…