PROJECT 02/2014 - Conversion of a cleaning basin for cathodic dip paint shuttles at the BMW plant in Regensburg
Kunde: BMW-Werk Regensburg
DESCRIPTION OF A SHUTTLE FOR BODY TRANSPORT IN THE CDP PROCESS
A shuttle is particularly suitable for high throughput since it enables efficient coating due to the combination of the shuttle system and suspension technology - and that with a high surface quality. It consists of two freely programmable axes: a travel axis and a rotation axis. A frame is mounted to the rotation axis, which is connected at each of both ends to the skid and bodywork by a non-motorised pendulum.
This pendulum frame enables a flat and compact system design, since the stroke axis is completely saved. The compact design is also supported in that the swivel frame on the return path can be folded. Furthermore, coupling the shuttle system with a pendulum technique enables the use of shorter tanks.
Image: Shuttle for body transport in the CDP process
Nowadays, body parts are almost exclusively primed using cathodic dip-paint (CDP). Here, the work piece to be coated is negatively connected (cathode). Either a stainless steel sheet or the coating tank itself can be used as a counter electrode (anode). A voltage of from 320 to 360 volts is applied. The bath temperature is 28 to 32 °C and the (paint) solid content is about 40%.
Image: Cathodic dip-painting (CDP)
1. PROJECT OBJECTIVES - CUSTOMER REQUIREMENTS (PRODUCT SPECIFICATION)
In the CDP process line, the shuttles - on which the vehicle bodies are coated in the CDP tank- are first dipped in a special cleaning tank with cleaning solution. This pretreatment is used for easier detachment of CDP residue for subsequent high-pressure cleaning. BMW’s requirement is to improve the efficiency of cleaning effect - by increasing the concentration of the cleaning medium. This also means significantly higher costs. However, since the immersion depth of the shuttle is limited by design, approximately two thirds of the previous filling volume is superfluous. The challenge lies in a solution in which the volume is reduced and access is under the new tank is guaranteed at the same time. In addition, it must always be possible to return to the original condition at any time.
Image: Existing steel tank for shuttle cleaning
2. CONCEPT FOR SOLUTION (PERFORMANCE SPECIFICATION)
Our concept consists of a holistic system solution from a single source - from planning to the structural analysis, through to the complete installation of all system parts. The material is selected according to the product specification requirements of our customer BMW.
- Planning & design, development and construction of components, sheets made of PP plastic and a substructure of stainless steel
- Structural analysis, project management
- Production of individual prefabricated components & assembly
- Installation, commissioning, quality assurance
When selecting materials, we decided on polypropylene PP light grey (-5 °C to 80 °C).due to the high strength and chemical resistance compared with a concentrated cleaning solution. The individual components and plates were measured on-site to produce tailor-made components made of plastic and stainless steel, so that they can later be installed quickly and easily on-site.
Image: Planning, design, development and construction of the modified cleaning tank
3. PRACTICAL IMPLEMENTATION
All necessary parts were first prefabricated as custom-made in our plastics workshop according to their own design plans. We first build a stable stainless steel substructure in the existing tank on-site. It must be possible to screw this construction because of the limited possibilities of introducing it, in order to then mount it flexibly on-site. The new substructure must support the weight of the complete cleaning medium of about 20 tonnes, see structural analysis.
On this sub-structure, we then create a new tank made of PP-plastic plates, which are partly pre-fabricated on site and tightly sealed in the extruder welding process. A waterproof descent is also built in the cleaning tank, which allows for a descent under the new tank. A particular challenge was that the existing stainless steel cleaning tank could not be drilled, altered or compromised in any way. Our system solution ensures that the cleaning tank can be built back to its original state again at any time.
Image: Installing the stainless steel substructure and the tank liner by extrusion welding of the prefabricated PP plates
4. CUSTOMER BENEFITS
- Material damage due to aggressive cleaning agents are excluded
- Assurance of sustainable cathodic dip-paint process safety
- Improvement in paint quality through more efficient shuttle cleaning process
- High functional reliability and durability due to selection of resistant PP material
- Desired flexibility through subsequent dismantling to original state