Westweigh Systems has successfully commissioned a locally developed, multimillion rand automatic bag handling machine in the manufacturing facility of a local pet food manufacturer.
"After we exported the first machine to Botswana, manufacturers across the southern African region started expressing interest," reports Westweigh representative, Bill Binckes. "In addition to the second unit that we have just installed, we will also deliver one to a flour mill in Frankfort in the Free State in a few weeks time. This means that we are already starting to see a return on the rather significant investment we made in developing a South African alternative to machines that have traditionally proved very costly to import and maintain."
Offering significant cost benefits, Westweigh designed its original concept utilising every component on offer from Tectra Automation, local specialists in linear, pneumatic, servo-drive and control systems. Software engineers from Tectra Automation also coded the automation logic behind the concept.
A Rexroth CL200 Profibus Master PLC (programmable logic controller) with local/on-board input/output 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. The decision was made to employ Profibus as the communication protocol, thereby minimising cabling. 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 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. The choice of extruded aluminium resulted in remarkable advantages with regard to weight, hygiene and durability.
Tectra also provided Rexroth linear guides and ball screw drives. The new covered ball screw drives allowed the direct attachment of the servo motors and also provided a sealed unit that minimises the ingress of dirt. The pneumatic actuators used for the various stations for bag pick up, opening, closing, folding and heat-sealing 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.
"For the pet food manufacturer, we had to introduce two electronically controlled volumetric weighing feeders, with vibrating plates for smooth product flow," says Binckes. "The machine was specified to handle bags ranging from 1,4 kg to 4 kg, at a reduced speed of 8 bags a minute. The reduction in speed allows for nitrogen to be injected into each filled bag for long-term product preservation. Our ability to easily adapt the machine from the requirements of a flour mill to that of a pet food producer not only demonstrates the flexibility of our concept, but our in-house technical capabilities. We have changed the way in which the bag pick-up mechanism functions, which can allow speeds of up to 15 bags a minute if the operation allows it. Bag change-over times have been greatly improved and the ability to use multibag magazines further adds to the advantages this concept offers."
Westweigh also supplied a standalone automated bag placing machine incorporating drives and controls from Tectra Automation to the pet food producer, who has expressed interest in further automation solutions to be investigated.
"The ease-of-use of our concept, as well as its relatively low purchase cost and the high flexibility that allows bags of various sizes to be handled by the same machine, with minimum change-over time, gives us reason to be very optimistic about the future of this product line in both the local and export markets," says Binckes.
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