Accurate mixing of raw materials is critical to product quality in many manufacturing processes. Good mixing depends in turn on reliable, accurate feeding and dosing of individual components. A flexible approach pays dividends when choosing conveying and weighing systems.
Depending on the needs of the process, especially whether it operates batchwise or continuously, engineers can choose between pneumatic conveying systems, container systems and hybrid systems to move products from storage to weigh stations and mixers. With no single best answer, manufacturers of automatic mixer feeding systems must maintain a broad base of expertise and strive to analyze their customers’ requirements accurately, while end-users need to remain open-minded. The energy efficiency of mixer feeding systems is an example of a measure that only a few years ago was considered unimportant, yet is now a significant criterion in equipment choice.
Vacuum Weighing Systems
Vacuum weighing systems are the obvious solution whenever many bulk solid components must be conveyed automatically to one or more mixers, kneading machines, stirrers, dissolvers, or extruders. We distinguish between three different types of vacuum weighing systems:
- With the single pipe system, one conveying line carries products to the conveying scale from all the product feed points, which may include hoppers, big bag dischargers, and silos. Process automation systems can increase accuracy by compensating for differences in product run-on resulting from the varying transport distances.
- With the multiple-pipe system, a conveying line runs from each product feed point to a multi-port valve connected to the conveying scale. This system has the advantage that downstream of the multi-port valve product run-on is very low, so it is more precise than the single-pipe system.
- A central weighing system is often the best choice when there are many feed and supply points. This combines the benefits of vacuum weighing and pressure conveying systems. Individual components are sucked from the appropriate feed point onto a central conveying scale equipped with an electromechanical weighing device. Once weighed, the batch is emptied into a hopper and transported from there to its final destination using pressurized conveying. High throughput is ensured by weighing the next component while the previous component is being conveyed from the central scale to its destination.
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