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The Swedish BT Products company has been coating forklift truck parts for more than 20 years. The brilliance and robustness of the surface achievable with powder coating plus the statutory clean air regulations are the main reasons for the user to invest further in powder coating.
To continue to be competitive in the international market the intention was to invest in a fully automatic coating plant. To allow them to satisfy themselves of WAGNERs capabilities, BT were invited to visit a reference installation in Germany. The visitors were especially impressed by the powder feed using DDF-Technology and the precise, fully automatic coating of complex parts.
The aim of the investment was to increase the previous throughput of 28,000 product carriers (units) per year to 38,000 and up to a maximum of 55,000 units. The parts being coated (Size: W = 1300 mm; H = 2000 mm) were to pass through the plant virtually untouched by human hands, which was achieved as follows:
The equipment invested in was an electrostatic powder coating system consisting of a plastic booth with 2 extraction belts, operated as a self-contained unit. (See Illustration 2).
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Illustration 2: When coating, the booth doors are closed completely automatically. After-coating by hand is not necessary. The booth is only entered by the operating personnel for maintenance purposes or for major colour changes. |
The fully automatic coating of the work-piece components is done by 4 WAGNER Twin Gun with flat jet nozzles, which run on 2 ABB robots (LKN/SCS = Swedish system provider) (see Illustration 3). The short build of the electrostatic powder guns allows optimal penetration into edges, undercuts and cavities; so no manual after-coating is required.
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Illustration 3: Thanks to 2 Perspex windows integrated in the booth wall, the fully automatic coating process can be observed from outside. |
The special feature here is the integral robot cleaning unit. At regular intervals a joint blowing off of the spray equipment (gun blow off function) takes place. The over-spray is taken directly to the recovery system (cyclone with filter, extraction power 24,000 m3/h) by 2 extraction belts located on the booth floor. This ensures that only a minimum quantity of powder is in circulation. (See Illustration 4)
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Illustration 4: The 2 extraction belts ensure continuous transport of the powder out of the booth, directly to the recovery unit. This means less powder in circulation and care for the whole circulation. |
Due to the continuous transport of the over-spray out of the booth, the integral blow-off function and the sandwich construction of the plastic booth walls (hardly any accumulation of powder thanks suppression electrode effect) the cleaning times - even with extreme colour changes - only amount to 30 minutes at the most. With only 3 main colours (black, red; orange) the downtimes caused by cleaning are limited.
Powder feed & colour changing time
The use of DDF-Technology (Digital high Density Feed) has provided convincing benefits for this plant. It ensures a gentle powder feed and precise quantity dosing of the powder to the guns. With very long powder hoses (in BTs case up to 28 metres!) a uniform economical powder feed to the spray systems is assured - thanks to DDF. Due to the low flow velocities of the powder (approx. 3 to 5 m/s) there is a high efficiency, a particularly soft powder cloud and all at minimal powder consumption.
The uniform feed to the spraying apparatus also gives a distinctly better spray pattern and a better surface finish. The integral ultrasonic sieving ensures the best sieving results and coating quality. Over and above this, there are potential savings due to a minimal requirement for feed air (the total air consumption per Twin Gun only amounts to 2,45 Nm3/h at a powder feeding rate of 360 g/min) and the lower powder consumption resulting from the higher efficiency.
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Illustration 5: The plant at BT is equipped with a PMC (Powder Management Centre) with 8 DDFs and 2 transfer pumps. |
Control technology
The complex control of the plant is overseen by the Profitech switch cabinet (S 265 controller) plus 4 AFC-modules and can be operated simply, though a Touch Screen. Due to real time visualisation, the plant operator always has an up-to-date overview of the ongoing coating status. In this way even complex control relationships can be shown and controlled easily and simply. From simple operation by setting parameters, exact fault diagnosis, right up to data saving and process data recording, the system provides everything at a glance. The fully automatic program control is achieved through hanger coding. The coating programs for the individual work-pieces are stored in the PLC controller and are called up via the hanger coding.
The main arguments for BT deciding on WAGNER:
- A powder coating booth with 2 powder extraction belts on the booth floor and integral viewing windows on the outer sides of the booth; ideal for observing the coating process.
- Due to the long powder hoses from the powder pumps to the robot-controlled guns, the best result is achieved with the DDF-Technology.
- Due to the special geometry of the electrostatic Twin Gun it is very much easier for the robot to solve complex coating problems in the best possible way.
Summary
The new powder coating plant now replaces the old coating line, where the manual coating booth did not have a recovery system and because of the large accumulations of powder, even in the automatic booth, problems constantly occurred.
Thanks to the new powder coating plant, BT is calculating on powder savings alone of up to 70%, so it is estimated the plant will be amortised in 1 to 2 years.
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WAGNER-Group
