This usually crops up when the two stages are not matched in output. The best solution is to install a pressure-adjusting valve at the discharge end of the extruder.
Every processor should get hold of the viscosity curves for the polymers they use or contemplate using in their operations, and learn how to read them.
Since many plastic products are made of a combination of materials with very different melting points, careful consideration must be given to designing screws when it comes time to recycle these products.
Coronavirus pandemic has made extrusion processors curious about entering the face-mask market. But melt-blown fiber is very different from most other extrusion processes and requires specialized equipment.
Very small screws have become more common with the growth of additive manufacturing. Designing such screws requires balancing their output requirements with their torque strength.
You might be able to reduce purging times and save money by scheduling processing jobs in order of the increasing material viscosity. But to get started, you'll need shear rate/viscosity curves for your polymers.
Processors need to “engineer” feeding properties similar to virgin pellets into their regrind to efficiently and economically utilize more of their scrap.