Interlinked, automated shot blasting system improves the quality and reduces costs

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When a Polish manufacturer of complex steel weldments was ready to invest in a new shot blast machine, quality, capacity, high equipment uptime and integration into the manufacturing flow were the key selection criteria. As an essential part of the pre-treatment operation for a cathodic painting line, the new shot blast system had to produce optimal surface preparation results within an interlinked work flow in a 3-shift operation. The company chose a Rösler RHBD 17/32-K continuous feed spinner hanger blast machine because of its wear-resistant design and favorable operating costs.

The specialty of the Stelweld Sp.o.o. is the production of complex steel weldments, including machining, laser and CNC cutting, bending as well as wet painting and powder coating. With this market philosophy the company, founded in 1997, has established itself as a key supplier for such diverse industries as automotive, agricultural and construction equipment, cranes, including all kinds of lifting equipment, renewable energy and rail transport. Among many other companies Stelweld also sells its products to Scania, Volvo, Bombardier and Cargotec.
In the year 2019 a new building was erected to provide space for a new, fully automated cathodic painting line (KTL) with 16 operating stations and a power & free transport system. Danuta Dobrzynska, project manager at Stelweld, comments: „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”.

Sturdy equipment design and convincing test results
A high capacity, excellent shot blasting results, an outstanding equipment uptime and a high cost efficiency were the other key selection criteria. Among the five shot blast equipment manufacturers who were considered as potential suppliers, the customer chose Rösler with its continuous feed spinner hanger blast machine RHBD 17/32-K. „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 the decision for Rösler and continues: „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 that ensure excellent results, outstanding efficiency and high uptime
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 that are in full compliance with the standards defined by Stelweld and its customers. This ensures an excellent paint adhesion on the work pieces. To achieve such demanding 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. This 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”, concludes the project manager.

Fully automatic, interlinked operation produces repeatable high quality
The power & free transport system 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 are closing, and the turbines, the blast media return system and dust collector are starting automatically. During the shot blast 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.
Danuta Dobrzynska concludes: „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”.