Vol. 22
January Issue
Year 2021


in Vol. 22 - January Issue - Year 2021
Rotary Solutions For Castings And Stampings Save Time, Space And Costs

Die-castings embedded in the media mix

The CB 5 rotary vibrator from Walther Trowal

The work pieces are transferred into the machine from the side with a conveyor belt

A CB rotary vibrator equipped with a magnetic separator that removes ferromagnetic work pieces from the media mix and feeds them into a drier (visible on the right side of the photo)

A CB vibratory vibrator equipped with a vibrating bunker for batch processing of work pieces.

Jointly conducted processing trials in the test lab in Haan so far have always produced practical and economic solutions.

When it comes to surface finishing of die-castings and stampings, the optimized CB rotary vibrators from Walther Trowal combine the technical features of linear continuous flow systems with the advantages of rotary vibrators. The CB machines are ideal for processing of work pieces, which merely require a light deburring operation. For example, die-castings containing only small metal flashes or stampings demand just a slight edge deburring. Since they allow feeding the work pieces individually into the machines in a continuous flow, the CB rotary vibrators can be very easily integrated into interlinked manufacturing operations.

A pronounced trend: Shorter processing times for surface finishing 

Compared to just a few years ago, the on-going technical improvement of key production methods has resulted in significantly shorter cycle times for deburring and light edge radiusing: This trend is especially prevalent in the field of aluminium, zinc or magnesium die-casting but can also be observed with stampings, which have only light burrs. Likewise, the slight rounding of sharp edges nowadays can be achieved in just a few minutes of “trowalizing”. 
For example, based on improved production methods, a renowned die-casting company was able to reduce the cycle times for de-flashing and surface homogenization of the raw die-castings to merely five to six minutes. Since the capacity of the existing linear continuous flow vibratory finishing systems was no longer needed, the company was looking for a more economical finishing solution. 
In principle, rotary vibrators could have handled the job; however, since the workpieces had to be loaded into the machines in batches, it was not possible to integrate the rotary vibrators into the interlinked manufacturing operation existing at this die-casting company. 
For this reason, in close cooperation with the customer, Walther Trowal implemented some technical changes that allowed processing the workpieces in continuous flow mode, and therefore made it possible to integrate the rotary vibrators directly into the manufacturing flow. The result: A surface finishing operation that is perfectly adapted to the processes in the die-casting department, requiring less space and emitting less noise. 

From linear finishing equipment to rotary vibrators

For the “trowalizing” process the raw workpieces are fed into a work bowl containing abrasive processing media. Through the oscillating bowl movement, induced by vibration, the mix of media and workpieces is put in motion, causing the media to constantly rub against the workpieces. This causes a slight removal of material from the workpiece surface. 
New is that the workpieces are no longer loaded into the work bowl in complete batches but are continuously fed into the rotary vibrator in single-piece flow. For example, in die-casting operations, this allows linking a rotary vibrator directly to the die-casting machine, thus finishing the raw castings immediately after they have been ejected from the die-casting machine.
Contrary to the rectangular work bowl in linear continuous flow systems, rotary vibrators have a spiral processing channel with a steady incline towards the machine discharge section. The movement of the workpiece/media mix can be controlled by the RPM of the vibratory motor and the setting of the imbalance weights. This allows to precisely adjust the intensity and duration of the finishing process. Even though the processing channel has a continuous incline, the kinetic energy of the vibratory motor induces a spiral forward motion of the mix of media and workpieces towards the so-called separation zone. A welcome side-effect of this unique vibratory equipment design is that the media exerts additional pressure on the castings resulting in a higher intensity, and therefore faster processing times. 
The discharge section is equipped with a screen that permits the separation of the media from the finished workpieces. While the workpieces are being discharged from the machine, the abrasive media is falling through the separation screen back into the processing bowl. Ferromagnetic workpieces can then be separated directly from the abrasive media with a so-called magnetic separator. 

Perfect integration into the production flow

Operating the rotary vibrator is extremely simple: All that needs to be done at the beginning of a shift is turn on the machine, and it then runs continuously without the need for any other operator intervention. The switch from linear continuous flow machines to rotary CB vibrators has consistently improved and simplified the overall production flow. Now the shop floor personnel can focus on the casting process, because the surface finishing operation is running by itself and requires very little attention. 
Since the CB rotary vibrators are equipped with a media undersize screen at the machine exit, the media operating mix is always optimal. As soon as individual media pieces wear below a defined size, the undersize screen automatically discharges them from the machine. This makes certain that the media mix in the processing bowl remains within a specified size range. Loose burrs and dirt particles also fall through the undersize screen so that the media always stays clean, so this also minimizes the required time for maintenance. 
During the finishing cycle, the work bowl is covered with a sound absorbing lid, and this reduces the noise emission to a point where no additional noise protection equipment is needed.  
For the first time, it is now possible to integrate the rotary vibrators of the CB model range into interlinked manufacturing processes. To date this was only possible with linear continuous flow vibratory systems. Especially in case of manufacturing operations with a high degree of automation, the CB rotary vibrators can be a significant factor for improving the overall productivity of the complete manufacturing line. 
Surface finishing requirements will no doubt become stricter in the future, and for this reason, the equipment must be adaptable for the challenges of the future. Whenever companies are faced with challenges that cannot be met with existing configurations of equipment, media or compound, they can contact the experts at Walther Trowal.  Jointly conducted processing trials in the test lab in Haan so far have always produced practical and economic solutions to these challenges.

First testimonials from customers

Several customers have already made the switch from the linear continuous flow AV systems to CB rotary vibrators. With a fraction of the capital expenditure,s they achieve the same throughput as the much larger AV machines … and with surface finishing qualities that are alike or even better.
The experience from actual customer installations has shown that with CB 400 optimal finishing, results can be achieved with a cycle time of four minutes whereas the cycle time in the much bigger CB 800 amounts to seven to eight minutes. 
One user, who operates seven vibratory finishing systems from Walther Trowal, has confirmed that with a cycle time of five to six minutes, all material flashes are consistently removed from his aluminium die-castings. At the moment, he is in the process of replacing his linear continuous flow systems with CB rotary vibrators, and this will help the company to reduce its capital expenditures and operating costs and, at the same time, save space in the die-casting facility. 
Christoph Cruse, sales director at Walther Trowal, identifies significant advantages for his customers: “Only four minutes for ‘trowalizing’ of aluminium die-castings? Until recently this would have been considered impossible, but our customers have refined their manufacturing methods to the point where such short cycle times for de-flashing and light deburring are fully sufficient. Naturally, we have adapted our rotary vibrators to this changed production environment, but we are also continuously improving our linear continuous flow AV machines, as they still represent the best finishing solution, whenever longer processing times are required”. 
When it comes to “trowalizing” of die-castings and stampings, Walther Trowal can now offer two processing alternatives to its customers: For work pieces with minor burrs, the CB rotary vibrators are the right choice. They can be easily integrated into interlinked manufacturing processes and, because of their compact design, require a minimum of space. 
Whenever a high processing intensity and/or a higher throughput is needed, the linear continuous flow AV machines are still the optimum solution, allowing practically any processing time that might be required for more difficult applications. 

For Information: 
Walther Trowal GmbH & Co. KG
Georg Harnau
Rheinische Str. 35-37, 42781 Haan, Germany
Tel. +49.2129.571-209
E-mail: g.harnau@walther-trowal.de