Meaning
Material flow defects occur when bulk solids move unevenly through a storage vessel or drying hopper. During resin drying, hopper channeling describes the formation of a fast flowing core of resin pellets that leaves stagnant regions along the hopper walls. This phenomenon prevents uniform drying because the resin flowing through the center of the hopper does not spend enough time in contact with the hot, dry air.
The result is a mixture of wet and dry pellets reaching the molding machine.
Flow Pattern
Pellets in the center of the hopper move rapidly downward while those near the walls remain stationary for hours. This behavior is typical of funnel flow, which occurs when the hopper cone angle is too shallow or the resin coefficient of friction is too high. Hopper channeling is particularly problematic with soft or tacky regrind resin that resists smooth sliding.
Processing Defect
Underdried resin pellets entering the injection cylinder undergo hydrolytic degradation during melting. This degradation causes cosmetic defects like splay and drastically reduces the mechanical strength of the molded parts. When hopper channeling is present, the processor will experience sudden cycles of part failures interspersed with periods of normal production, making the process almost impossible to troubleshoot.
Mechanical Remedy
Installing a flow promotion insert or redesigning the hopper to ensure mass flow are effective solutions. Mass flow ensures that the entire volume of resin moves downward at a uniform rate, eliminating stagnant zones.
