During the latter part of 2002, Anadigi was approached by DPI Plastics to provide a quote for upgrading the additive dosing and mixing plant at its Roodekop factory. Having successfully automated the DPI plant in Cape Town in 1997, Anadigi leveraged its expertise to enhance the Roodekop plant.
Overview of Plant Operation
The facility processes raw extrusion PVC material (corvic), which is blown from storage silos into holding bins on the fourth floor of the mixing plant. Injection moulding corvic is manually debagged at designated stations before being transported to holding bins.
Additives are blended with the corvic to create specific formulations. The materials are weighed, mixed, and then further processed by adding waxes and pigments. Once mixed to a preset temperature, the product is cooled and transferred to finished-product silos or bulk bags for special orders.
Operators manage the entire process from a centralized control room on the first floor, where all plant status values are displayed. The control room also houses the main control PLC and mixer control panels.
The Upgrade Process
Initial Assessment
Anadigi conducted an initial site inspection to evaluate the scope of the upgrade. Key data points, such as cable lengths, motor sizes, solenoid operating voltages, and system functionality, were gathered. Meetings with stakeholders helped define customer requirements for the new system.
System Design & Components
- PLC Selection: The LG GM4 rack-mounted PLC was chosen as the system’s master controller due to its large memory, module variety, and flexibility.
- Network Architecture: The LG F-Net bus system, based on Foundation Fieldbus, was implemented to manage distributed I/O across the five-floor facility.
- Remote Stations: Three LG GM6 PLCs were installed as remote units, eliminating excessive hard-wired connections and reducing overall wiring by 70%.
- Operator Interface: A Pentium 4 PC running LG GLOFA software and an Adroit SCADA package provided enhanced plant visualization and reporting.
- Weighing Accuracy: New weight indicators were installed for PVC and additive scales, ensuring precise dosing.
- Improved Mixer Panels: LG GM7 PLCs were used in the two mixer control panels, operating in a master/master configuration for seamless integration.
Implementation Challenges & Execution
To minimize downtime, the upgrade was executed in multiple phases, primarily during monthly stock-take weekends. The first phase began in August 2003, despite an accelerated schedule. The plant remained operational, requiring all wiring to be handled as live connections. The process involved meticulous planning to avoid disruptions and ensure safety.
- Phase 1: Conversion of initial systems, re-establishing interlocking between old and new control panels.
- Phase 2: Complete integration of the new PLCs, SCADA enhancements, and removal of obsolete wiring.
- Phase 3: Replacement of old mixer panels, installation of new soft starters, and full SCADA integration.
Final Outcome
Upon completion in November 2003, DPI Plastics gained full control of the upgraded system. The new infrastructure allowed for increased production efficiency, improved accuracy, and greater flexibility in recipe management. The removal of outdated equipment, including the massive mimic panel, marked a significant milestone in modernizing the plant.
The collaboration between DPI Plastics and Anadigi ensured a successful transition, balancing the need for minimal disruption with the demands of production continuity. With its new control system, DPI Plastics is well-equipped to meet future production goals while maintaining high-quality standards in its manufacturing processes.