Preservation lines – for improved quality, productivity and cost efficiency

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In such diverse industries like steel fabrication, steel trading and ship building the temporary corrosion protection of steel plates and beams is critical for producing high quality end products. Preservation lines are key in providing such corrosion protection coatings. With numerous innovative technical features, preservation lines from Rösler offer significant operational and cost benefits.

Turnkey preservation lines usually consist of special transport systems for loading/unloading steel plates, beams and pipes. In addition, they incorporate a pre-heater, a roller conveyor shot blast machine, an automatic paint booth with overspray separation and paint drier with slat conveyor. All of these components are interlinked for  fully automatic operation with little or no operator involvement. If the work pieces are stored outside, a blow-off station in front of the pre-heater removes loose contaminants and moisture from the plates and beams. The use of solvent based paints requires the exhaust air from the drier to be guided to a thermal regenerative oxidation station. Critical for the overall quality, productivity and cost efficiency of any preservation line is an equipment concept that is best suited for the respective work pieces and technically sound design of the individual system components. Rösler preservation lines can be custom-engineered to process work pieces with different heights and widths. Numerous innovative technical features guarantee high throughput at relatively low costs.  This is reflected in transport speeds of up to 8 meters/min (27 feet/min) with unmatched coating qualities.

Pre-heating that is fast and saves energy
The newly developed high convection pre-heater, with its 250 mm (10”) thick insulation, quickly heats the work pieces to a temperature of 20 to 40°C (68 to 104° F) ensuring optimum paint adhesion and short drying times. In contrast to conventional pre-heaters the Rösler convection system incorporates multiple fans equipped with frequency inverters for quick adjustment of the fan speed. This allows adaptation of the heat output to the work piece mass (for example, thickness) and the transport speed. At the same time, the air circulation ensures that all work piece areas are equally exposed to the hot air. This not only contributes to quickly bringing the work pieces to the required operating temperature but also helps to reduce energy consumption.  

Significantly higher blast performance and turbine uptimes
From the pre-heater, the work pieces are transported to the roller conveyor shot blast machine. The blast chamber is always made from manganese steel. In addition, the direct blast area is lined with overlapping, easily replaceable plates, also made from manganese steel. The shot blast machine itself is equipped with Gamma 400 G turbines available with different power options, which allows the turbine’s performance to be tailored to the respective machine size. Compared to conventional blast wheels the Gamma 400 G turbines produce a 15 – 20% higher blast performance with at least 100% higher uptimes. The turbines are placed in the upper and lower section of the blast chamber at an incline so that the blast media hits the work pieces at a defined angle. Compared to turbines hitting the work pieces at an angle of 90 degrees, this inclined turbine arrangement results in a 15 – 20% higher de-scaling/de-rusting effect, which significantly reduces the required cycle times. The integrated cleaning system for removing residual blast media from the work pieces consists of a rotating brush and a targeted high velocity air stream. It is equipped with a work piece recognition system and automatic height adjustment. This ensures that the work pieces are leaving the blast chamber free of blast media and dust. At the same time it eliminates the need for lengthy manual adjustment and minimizes the wear of the rotating brush. The capacity of the blast media cleaning and recycling system and dust collector are, of course, tailored to the machine size. Both can be placed on top of the machine resulting in an extremely small overall machine footprint. Large doors allow easy access to the blast chamber for maintenance work.

Material-saving paint process with effective overspray separation

A critical cost factor in any preservation line is the paint and primer usage. For this reason, the automatic paint booth is equipped with sensors precisely measuring the work piece dimensions. The system controls then guide the paint gun movement, which precisely follows the work piece contours. This guarantees that the paint is only applied at the required thickness. The result is significant paint savings and a minimum of overspray. Practically all solvent or water based paints with 1, 2 or 3 components can be utilized. For applications requiring different types of paint, the automatic paint booth can be equipped with multiple independent paint delivery systems. The cabin exhaust air system features an innovative trapezoidal, flow-optimized arrangement, which prevents air turbulence and safely transfers the exhaust air mixed with paint mist to the standard dry separation unit, consisting of a patented brush pre-separator with slowly rotating brush rollers. Once they are dry, the paint particles stick to the brush and fall to the bottom. This pre-cleaning stage is followed by a sinter-plate filter, which reduces the residual dust load significantly below the legal requirements. The brush pre-separator reduces the filter load dramatically so that uptimes of around 15,000 hours for the sinter-plate filter can be achieved. Another benefit of this optimized air cleaning system is that minimal paint particles are deposited on the Teflon coated inner walls of the cabin resulting in reduced cleaning times and lower operating costs.

Excess heat eliminates energy requirements for paint drying
Special steel slat conveyors are used to transfer the work pieces, which are still wet with paint, to the paint drier. They have only six contact points per square meter (about ten square feet) keeping the risk of disturbing the paint at an absolute minimum. For heating of the paint drier to be between 40 and 80° C (104 to 176° F) the exhaust air from the pre-heater is utilized. This eliminates the need for any additional energy input for the paint drying stage. Recirculating fans and special air guides ensure an even, all-around drying of the painted work pieces.