AJAX Unique Design of Ribbon Screws.
A leading UK Bioscience company bought an off the shelf screw conveyor for feeding a filter cake from a belt to fill kegs and IBCs. Like many filter cakes the product was damp and sticky. Unfortunately when the system was put into operation the screw flight surfaces built up with filter cake. Transfer capacity was soon reduced and the inlet hopper arched with product. Eventually complete blockage in the screw conveyor resulted in downstream equipment being starved of feed and production stopped. The problem was the form of screw. The standard construction of full face flights offered too much surface area for the product to adhere to. The design and construction of the inlet hopper was also poor. The combination of shallow wall angles and mismatched fabrication of the hopper joint to the conveyor casing created a ledge for the filter cake to build up on. These detailed features of construction are often overlooked with off the shelf equipment yet they provided the initial key for product hang up and led ultimately to complete blockage. The original supplier failed to deliver a solution to the problem. The user was a multi national and multi local company who sought advice from their centralised technical centre. Ajax have a reputation for making solids handling problems go away and the technical centre quickly identified that Ajax was well suited to take on this particular challenge.
A site visit was undertaken to scrutinise the actual equipment and process needs as well as detailed discussions with site engineers and operators. Samples of the filter cake were taken for laboratory testing at Ajax Equipment where wall friction tests quantified the frictional and adhesive characteristics of the filter cake. These are the key measurements required for establishing reliable hopper, chute and screw flight angles for slip and provide a design basis for the strategy to inhibit product build up and clogging. The newly developed LynFlow™ Ribbon Flights have unique geometry which minimises the surface area available for build up yet still provides a positive transfer capability with even the most tenaciously sticky materials, such as this damp filter cake and various pigments and pastes. Careful selection of the support shaft dimensions and attention to detail in construction and polishing of contact surfaces was all part of the design strategy for reliable performance. The hopper geometry was improved and detailed attention to interfacing with the screw feeder included adopting diverging side walls to ensure there were no dead zones (for filter cake to build up) by design.
Ajax Equipment completed the fabrication in house to their usual high standards within a short lead-time and the equipment was put to the test on plant. The customer was very satisfied with the Ajax solution and reported that performance capacity was completely achieved. Blockages and manual intervention are now a thing of the past. Production targets are being fully met and plant up time is now maximised. The lesson for users is to have the flow characteristics properly examined and make sure you source equipment from a reputable supplier. Above is a photograph of the replacement machine at Ajax Equipment works in Bolton just prior to despatch.