Preservation Lines

Pre-heater

This is used to remove residual moisture. It is normally positioned upstream from the blast machine, in order to ensure that the workpieces are dry before they enter the blast chamber. The products are also heated, in order to reach the necessary temperature to ensure quick drying of the primer. 

The positioning of the pre-heater ahead of the blast machine means that it takes longer for the sheets or profiles to reach the entrance to the spray chamber.

This balances out unavoidable temperature spikes and avoids primer damage.

Benefits

• Maximum heat transfer to the material with minimal gas consumption: Combination of direct impact on workpieces with gas flames from long tubular burners (burner bars running straight through the pre-heater with hundreds of individual flames) and simultaneous high-speed hot-air circulation (approx. 250°C) via high-temperature fans
• The variable number of controllable long tubular burners makes it easy to adjust heating performance and therefore avoid excessively long pre-heaters

The Blast Machine

The roller conveyor shot blast machine is the key piece of equipment in the preservation line. The workpieces (plates, profiles or tubes) pass through the blast machine to remove rus t and scale. All machines are equipped with maintenance-friendly and highly efficient TITAN wheels. The wheels and their position, which can be varied depending on specific requirements, allow workpieces to be cleaned comprehensively on all sides in a secure process, ensuring a surface finish in line with the internationally recognised preparation grades of ISO 8501-1.

For high-level corrosion protection, blast cleaning to preparation grade Sa 2.5 is normally required. Sa 3 may be needed in some cases, which requires a significant reduction in working speed (approx. 50%).

Round steel grit abrasive is usually used to achieve a surface roughness of approx. Rz 40-80μm.

Type HD Roller Conveyor

This high-performance machine with angled wheels for metal plates, pipes and steel structures is used in the steel construction and steel preparation industries, with high passage speeds and long maintenance intervals.

Type S Roller Conveyor

This machine was designed purely as a plate blast machine and is used almost exclusively in large shipyards or rolling mills, where maximum blast performance and ease of maintenance are absolute necessities. 

Sheet widths of up to 5000mm can be processed, with passage speeds varying from 1.0m/min to 8.0m/min.

We use special large-volume airless pumps. The significant displacement volume of the pumps ensures a low pump frequency and therefore the least possible amount of wear on sealing elements.

This paint coating is by far the most expensive sub-process in the entire preservation line, but the ability to precisely control the coating process can result in annual savings running to 6 figures for a major preservation line.

Even the slightest reduction in coating thickness tolerance means a major saving for paint use. Wheelabrator spray systems can implement plate tolerances of an incredible 2μm.

Workpiece Recognition

The operator selects the correct setting for the piece (which is pre-programmed for the specific customer). This determines whether a spray pulling process or a push process is better for the workpiece variety. Workpieces are then recognised by a reflection light sensor that oscillates with the spray bridge. The height of the workpiece is measured at the same time by a high-resolution horizontal light grid.

Unlike other systems, the drives for the spray bridges and workpiece recognition sensors are positioned ahead of the actual spray chamber, in a clean area. This ensures that the sensors do not get contaminated with the paint spray mist over time, and their function is not compromised.

Spray technology

The recognised workpiece data (position, width, height etc.) is saved in the spray system SPS. A wide range of spray programs can then be used, based on this intelligent workpiece recognition.

This is the only way to incorporate extremely tight tolerances into the homogeneity of coating thickness.

The upper and lower spray bridges in Wheelabrator’s high-performance systems are often equipped with 4 spray nozzles each in order to cover a wide spray zone. The spray bridges can move up to 2m/s, brake at the deviating point and accelerate back in the other direction, often 24 hours a day.

Handling Overspray

Wheelabrator uses a spray chamber, with oscillators mounted upstream of the chamber. This means that the chamber largely consists of smooth, straight walls. They are coated entirely with Teflon film and dried overspray can simply be swept off this film. Depending on the size of the machine, the overspray can be removed from one or both sides by a pre-filter coated with Teflon film. This innovative system means that long sessions of machine downtime to clean the walls are avoided.

It is only then that any remaining (largely dry) paint dust can pass into the filter system. The system is equipped with special Tefloncoated cartridges to ensure long-term dust removal from waste air to a residual dust content of ≤ 2mg/m3³.

If solvent-based paints are used, these release gases that can naturally not be filtered out by a dust filter. Thermal, catalytic or activated carbon filtration systems can be used here (VOC systems).

Drying Chamber & Slat Conveyor

The preserved steel plates and profiles are dried continuously here. The drying chamber can be heated by the exhauste air from the pre-heater, so that even paints with long drying times (such as water-based paints) can be dried quickly. Additional circulation of high quantities of air accelerates the drying process. If a pre-heater does not need to be operated all year round, you can also use a self-sufficient heating system as an alternative or addition.

Workpieces are transported through the drying chamber on a slat conveyor. The greatest possible distance between the spray zone and the slat conveyor reduces unavoidable contamination with overspray. To prevent the bending of thin plates, an elevating roller is positioned upstream in order to balance out height differences and ensure that the plates are transferred smoothly onto the conveyor cross slats. The plates only rest on the support points of the conveyor cross slats, which means there are very few points of contact with the workpiece. The wet primer remains largely undamaged as a result.

The length of the drying chamber varies depending on the type of paint, coating thickness and passage speed.

It is vital to select the correct drive as the load on this can be very high. The right layout of the drive shaft, drive and gear ratio will ensure the even running of the slat conveyor. 

Outlet Roller Table

The last section is the outlet roller table. The preserved steel plates and profiles are discharged here.

The outlet roller table can be equipped with a cross transfer conveyor to optimise efficiency or connect it to a logistics system.