Rösler Provides an Interlinked, Automated Shot Blasting System at Stelweld

Date: 11/10/2021
Categories: Success stories

Polish manufacturer of complex steel weldments, Stelweld, has chosen Rösler’s RHBD 17/32-K continuous feed spinner hanger blast machine to automate its pre-treatment operations.

Stelweld Sp.o.o, specialized in the production of complex steel weldments for the automotive, ACE, cranes, renewable energy and rail transport sectors, has installed a new shot blasting machine with the aim of improving quality, capacity, high equipment uptime and integration into the manufacturing flow.

As an essential part of the pre-treatment operation for a cathodic painting line installed in 2019, which counts 16 operating stations and a power & free conveyor, the new shot blast system had to produce optimal surface preparation results within an interlinked work flow in a 3-shift operation. Other key selection criteria were a high capacity, excellent shot blasting results, an outstanding equipment uptime and a high cost efficiency.

“Within the framework of this expansion we also wanted to automate the shot blasting operation and integrate it into the painting line. To date, the paint preparation process was predominantly done manually”, explained Danuta Dobrzynska, project manager at Stelweld.

Among the five shot blast equipment manufacturers who were considered as potential suppliers, Stelweld chose a Rösler RHBD 17/32-K continuous feed spinner hanger blast machine because of its wear-resistant design and favourable operating costs.

“I was familiar with Rösler through a project I dealt with, when working for another company. Rösler does not offer the lowest price. But with regard to quality and technical features this supplier offered many advantages. Compared to the competitive products all essential components of the Rösler shot blast machine consist of wear-resistant materials, such as the throwing blades of the turbines, which are made from forged tool steel”, explains Danuta Dobrzynska. “Another key factor for our decision were the results of the shot blasting trials that were conducted with some of our original components. In the Customer Experience Center at Rösler we achieved excellent shot blasting results, which provided valuable pointers for our actual shot blasting operation”.

Technical features of the system

The continuous feed spinner hanger blast machine RHBD 17/32-K allows the blast cleaning of a very wide spectrum of three-dimensional weldments with dimensions of up to 2,500 x 1,200 x 3,000 mm (L x W x H) and weights of max. 1,250 kg.

At cycle times of 6 to 8 minutes, the automatic shot blasting process produces a finishing quality of SA 2,5 on the entire surface of the steel weldments and surface roughness values in compliance with the standards defined by Stelweld and its customers. This ensures an excellent paint adhesion on the work pieces.

To achieve such results, the shot blast machine is equipped with 16 Gamma 400G turbines, each with a drive power of 15 kW. These high-performance turbines, developed by Rösler, are furnished with throwing blades in “Y” design. Compared to conventional turbines, the special blade geometry with its precisely calculated curvature produces a very high throwing speed with, at the same time, a lower energy consumption. This results in an up to 20% higher shot blast performance. Moreover, because of their symmetric design both sides of the throwing blades can be used resulting in a two-fold increase of the usable blade life. Thanks to a special quick-change system blade changes can take place without having to dismount the turbine. The turbine placement (position and angle) was determined with a special simulation of the shot blast process.

The highly focused blast pattern also contributes towards the high efficiency of the shot blasting process. In order to adapt the blast media throughput of up to 200 kg/min to the geometry of its steel components, Stelweld is utilizing three different shot blasting programs. The rotational speed of the turbines is adjusted by frequency inverters, which allows the precise control of the impact energy of the blast media on the work piece surface.

For optimum wear protection and, thus, a long equipment life, critical sections of the inlet and outlet chamber are fabricated from 6 mm thick manganese steel. The same material, this time 8 mm thick, is used for the blast chamber. Furthermore, the blast chamber is protected by overlapping, easy-to-replace wear plates made from high-strength materials. Sturdy rubber curtains in the inlet and outlet chamber, as well as the protection of gaps with multiple rubber seals and brushes, prevent any blast media spillage to the immediate environment.

“The turbines, the entire equipment design and the used materials guarantee a high uptime. This ensures a safe, trouble-free and energy-efficient operation”, says Danuta Dobrzynska.

The shot blasting process

The power & free conveyor transports the steel weldments, containing a QR code for the automatic selection of the respective shot blast program, to the shot blast machine. As soon as a trolley with one work piece has entered the inlet chamber, the double leaf doors close, and the turbines, the blast media return system and dust collector start automatically.

During the shot blasting process the work piece is passing through the blast chamber at a pre-defined speed. The 16 blast turbines ensure an intensive cleaning of all work piece areas with highly homogeneous and consistent shot blasting results. Two dropout boxes placed in the duct connection between shot blast machine and dust collector make sure that the generated dust is evacuated from the blast chamber, whereas re-usable blast media is returned into the shot blast machine.

The shot blast machine is accessible behind the outlet chamber. This allows the manual removal of residual blast media from the weldments, especially those with cup-shaped sections. An auger in the bottom returns the removed blast media to the media recycling and cleaning system consisting of two cascade air-wash separators. Subsequently the blast cleaned work pieces are transported to the KTL painting line.

“Compared to our previous manual shot blast operation the new shot blast machine achieves considerably better and much more consistent shot blast results in a much shorter time cycle. This allows us to employ our qualified personnel for more productive work, helping us to create more added value. Through savings in energy consumption and other operating costs the overall shot blasting operation has become considerably more economical”, concludes Danuta Dobrzynska.