The export of a fully automated bag handling machine signals a marked shift in fortunes for a local equipment supplier to the milling industry, as the norm to date has been to import these sophisticated tools due to a lack of quality local alternatives. Not only has a world-class brick-pack machine now been developed in Midrand, but it is available at a significant cost benefit in comparison to units produced overseas.
Westweigh Systems, manufacturer of automatic, in-line weighing and bagging systems for over seven years, is proud to have exported its innovation to a Botswana mill this month at about a third of the cost of imported units, with the promise of several further orders. Making its success story even more unique is the fact that the design and manufacture of the new brick-pack machine included every component on offer from Tectra Automation, local specialists in linear, pneumatic, servo-drive and control systems. This was achieved in under two months.
"The project started merely as a request for a glue-sealer," recounts Westweigh representative, Bill Binckes. "After investigating the client's operation and surrounding needs, we realised that an automated bag-handling system would be of great benefit to them and proposed the design of such a system, as imported units have become simply too expensive."
Using software engineers from Tectra Automation to code the automation logic behind their concept, Westweigh set out to build a product for medium sized sugar, flour and other powder mills that would improve on existing machines while remaining affordable. The decision was made to employ Profibus as the communication protocol, thereby minimising cabling. A Rexroth CL200 Profibus Master PLC (programmable logic controller) with local/on-board I/O was selected for the main control panel, incorporating an NT 200 power supply module and ZE200-DP central processing unit that can control up to 64 DP slave units. A Sutron BT 20 HMI (human machine interface) was chosen to monitor and set up all the control functions of the machine, down to the Profibus servo drives. The Servo Drives are Rexroth EcoDrive 03s, delivering up to 40 A, controlling MKD090B motors with 12 Nm nominal and 43 Nm maximum torque with a maximum speed of 3000 rpm and fitted with an absolute encoder system for axis positioning.
The entire frame of the machine was constructed from Tectra's extensive range of extruded aluminium profiles and basic mechanical elements. Over 500 m of aluminium profile and about 4000 fastening elements were required. The choice of extruded aluminium resulted in significant advantages with regard to weight, hygiene and durability. More importantly, this also allowed the high levels of flexibility required in designing a new concept.
In addition to the aluminium profile, Tectra also provided Rexroth linear guides and ball screw drives. The new covered ball screw drives allowed the direct attachment of the servomotors and also provided a sealed unit that minimises the ingress of dirt.
Incorporating two auger filling devices with top feeders, the process employs a two stage volumetric measuring principle during filling of the bags to ensure the utmost repeatable accuracy. As no glue-sealer was available in South Africa that could form neat gussets, the experienced engineers at Westweigh developed a solution that quickly and precisely folds and cuts the bags for sealing. Ten to 12 bags a minute can be processed by the present machine, with the potential for this figure to be increased in future models. Bags will also vary in weight from 10 kg to 12,5 kg, with consistent presentation being a high priority. The pneumatic actuators used for the various stations for bag pick up, opening, closing, folding and gluing are all controlled by a single, 16-bank Rexroth HF03 pneumatic valve terminal system, interfacing with the Profibus protocol. The compact nature of the modular HF03 kept space requirements to a minimum.
Some of the features lauded by the client upon first inspecting the Westweigh brick-pack solution included safety doors, which would automatically shut down the operation the moment they are opened, as well as cutting-edge diagnostics and a dust extraction function. With about 1000 points on the machine being monitored, faultfinding has been designed to be quick and precise.
"The control panel that we put together produces production reports that can be downloaded to a PC for analysis and data storage," Bincke points out. "A further advantage specific to this mill is that all drives are auto-lubricated, with the additional option of an upgrade that would allow spillage to be recycled. I can confidently state that this is the first fully automated weighing and packaging machine manufactured in South Africa that can compete worldwide, and we are already receiving requests from various export markets. Depending on the speed of our expansion and related factors, we are also considering the development of downstream products, such as a fully-automated palletising solution."
For more information contact Emil Berning, technical director, Tectra Automation, 011 971 9400, [email protected], www.tectra.co.za
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