Highly flexible and efficient solution for processing of zinc die-castings
Gjuteriteknik, a Swedish foundry specialized in zinc die-casting, was looking for a mass finishing system that allows the fully automatic and cost-efficient running of different finishing processes. With the mass finishing system R 420 2-CH Rösler was able to provide the ideal solution. This system allows the simultaneous dry or wet processing of two work piece batches, including the drying of the finished work pieces, with a high degree of process stability.
In the mid 1990’s the foundry Gjuteriteknik AB, founded in 1978, made the strategic decision to exclusively specialize in the production of zinc die-castings. This family-owned company, located in Värnamo, Sweden, and run by the second generation owners Jonas und Peter Abrahamsson, has successfully established itself in this field and produces about one million castings per day. The company’s services include the design phase for a product, the production, surface refinement and logistics. With this comprehensive portfolio the zinc die-casting specialist Gjuteriteknik is partner of a wide range of companies active in the fields of telecommunication, electronics, automotive, furniture and construction in Europe, Asia and South-America.
A recipe for success - flexibility, quality and automation
Jonas Abrahamsson comments: „Zinc die-casting is a relatively small segment in the foundry industry. To be competitive on an international level, as a Swedish company we must not only be highly flexible in the fulfillment of the customer requirements but must also be very cost-competitive. We have achieved this by the implementation of highly automated processes throughout our entire manufacturing operation”. Mr. Abrahamsson continues: „Our goal is to produce casting qualities that require no additional processing. However, if the work pieces had to be deburred, we did this predominantly in fully automatic shot blasting cells. One reason for this approach was that our old mass finishing system offered only very limited processing possibilities and required a lot of manual operations”. Therefore, when the company decided to purchase a new mass finishing system, its main requirements were flexible processing possibilities, an automated process from the loading of the work pieces to their discharge after the drying operation and a high capacity. Because of its excellent experience with the existing Rösler mass finishing and shot blast equipment, Gjuteriteknik decided to purchase a system that consists of a double-batch rotary vibrator, model R 420 2-CH, a hot air belt dryer and a centrifuge for cleaning and recycling of the process water. Another reason for purchasing the Rösler system was that it fully met the cycle time requirements of the customer.
Efficient, parallel wet or dry processing
At the center of the double batch system, allowing the parallel processing of two work piece batches, is a rotary vibrator with a gross volume of 420 liters that is suitable for wet as well as dry finishing operations. „We already had one project for dry finishing of the work pieces. And we knew that the demand for dry finishing would grow significantly. Therefore, it was very important for us to process the work pieces fully automatically, which so far had not been possible. For this reason, process flexibility had top-priority”, explains the managing director.
For the mass finishing operation customer-supplied bins with raw work pieces are placed into the lift and tip loading device that transfers the work pieces into a vibratory hopper. After the operator has entered the work piece identification into the PLC, the work piece specific processing program starts automatically. While the vibratory hopper transports the raw zinc die-castings into the rotary vibrator, the loading device moves back into its home position. This allows placing another batch of work pieces into the loader and selecting the respective program.
After the pre-programmed processing time an unload gate in the bottom of the rotary vibrator is opened, and the mix of media and finished work pieces is discharged onto a vibratory buffer with an infinitely adjustable vibration intensity. As soon as the processing bowl is empty, the unload gate is closed, and the processing bowl is filled with another batch of media and raw work pieces. At the same time the vibratory buffer gently transfers the mix of finished work pieces and media into the vibratory screen separation unit, where media and work pieces are separated. An undersize media screen ensures that during the separation operation media that has become too small, is discharged from the system. This ensures a high process stability. Within certain time intervals new media is manually added to the system.
The area around the vibratory separation unit was designed as a separate safety zone, which can be safely entered, while the rotary vibrator is running. This allows placing empty part bins for work pieces that were finished in a dry process and discharged through a movable vibratory cross conveyor. Work pieces that underwent a wet finishing process are transferred to the two meter long hot air belt dryer R 2000 BT.
Cleaning and recycling of the process water by centrifuge
During wet finishing processes a high water-compound flow through the rotary vibrator ensures a complete and safe flushing out of contaminants such as metal and media fines, etc. The water/compound mix flows into the rotary vibrator from the top, is discharged through bottom drains and then pumped to the semi-automatic centrifuge Z 800. To promote the separation of the solids from the process water in the centrifuge, flocculants are automatically dosed into the process water. The cleaned water is pumped to a clear water tank. As needed, compound is injected into the process water fully automatically. This guarantees a constant compound concentration and, therefore, absolutely repeatable, high-quality finishing results.
Jonas Abrahamsson concludes: „The new mass finishing system permits us to adapt our finishing processes to the work pieces and, thus, enables us to perfectly fulfill the requirements of our customers. We are very happy with the new equipment and feel that we are well prepared for any future finishing challenges”.