Careful consideration has to be given to the selection of equipment when conveying materials that pack, cake or smear.
Causes of Packing, Caking and Smearing
Packing, caking and smearing are usually the result of particle binding within a material. This may be caused by the presence moisture, fats or oils within the material, the presence of electrostatic forces, or the result of binder hardening. Whatever the cause, the tendency of a material to pack, cake or smear can impede or block product flow through a conveyor, requiring clearing of the blockage to restore flow and throughput.
Materials prone to caking, packing and smearing include pigments, chemical powders such as titanium dioxide, food ingredients such as besan flour and cake mixes, and products which contain moisture, fats and oils.
Successfully Conveying Materials that Pack, Cake or Smear
To overcome the difficulties associated with conveying materials that pack, cake or smear, UniTrak usually recommends a TipTrakTM bucket conveyor as the equipment of choice. TipTrakTM equipment is suitable for both intermittent and continuous conveying, and the equipment design and operating principle surmounts many of the problems encountered when using flexible screw or aeromechanical conveyors to move materials that cake, pack or smear.
The operating principle of TipTrak conveyors, where material is gently conveyed in spillage-free buckets, lessens the risk that material to pack or cake as it moves through the conveyor. In contrast, when a flexible screw or aeromechanical conveyor is employed, material may tend to pack or cake as it is drawn through the conveyor.
Here is a test that we did a few years ago of a proprietary material that was prone to packing. Check out our video!
Materials which are hygroscopic in nature may tend to cake or pack should they absorb moisture from the atmosphere. When handling these materials, it may be advisable to use a fully sealed bucket conveyor, such as a TipTrakTM Monocoque unit. The fully sealed design of a TipTrakTM Monocoque helps reduce the risk of hygroscopic absorption which may lead to packing and caking. In addition, because some materials which cake and pack can also be dusty, the fully sealed design of TipTrakTM Monocoque conveyor completely controls any fugitive dust emissions which could coat and cake the equipment.
While a bucket conveyor such as TipTrakTM lessens the risk of packing and caking, it may still be wise to employ flow aids at the infeed and discharge ends of the conveyor.
At the infeed end of the conveyor, when infeed hoppers are used, these should be designed with a steep-wall conical geometry which creates sufficient shear force to overcome the tendency of material within the hopper to cohere and stick. In addition, hoppers could be electro-polished to a mirror-like finish which promotes good material flow from the hopper into the conveyor. In particularly challenging applications, flow promotion aids, such as feeders may need to be employed to overcome material packing and caking.
Similarly, at the discharge end, the use of a bucket discharge assist device can effectively release any material which has cohered within the buckets.
Should you have an application that requires conveying materials that pack, cake or smear, UniTrak is your preferred equipment partner. We have over 45 years’ experience in helping our customer to solve their bulk materials handling challenges, including the conveying of difficult-to-handle materials. To find out how we can help address your requirements, please contact our sales department.