Routing Powder to Multiple Destinations in Plastics

A plastics plant routes from rail or truck unloading, or from an extruder, to a silo farm with a dozen or more destinations. The line is long, the material is valuable and each silo holds a specific grade.

The dominant risk is a misroute. Resin grades look alike, the destinations are numerous, and a diverter in the wrong position for an hour puts a grade into a silo it does not belong in. The cost is the contents of the silo, not the cost of the mistake, and a blended silo is often only usable as a lower grade or not at all.

The junction also damages product. Pellets striking a step or a sharp transition abrade and smear, and the frictional heat draws material into the threads that become angel hair. Those threads collect downstream at bends and screens and eventually block a line that worked for months.

Static runs through all of it. Pellets charge heavily in conveying, and a junction assembly with an unbonded actuator bracket or an isolated liner becomes the discharge point in a line that also carries explosible polymer dust.

Routing that cannot be set to a destination the recipe and the silo inventory do not allow, with the position confirmed by sensors before conveying air starts.

A flow path with no step, no lip and no abrupt change of bore, so the junction contributes as little as possible to streamer formation.

A fully bonded assembly with measured continuity, treated as part of the line grounding rather than as a separate component.

A power plant sets the same clearance against upset temperature, because a diverter adjusted cold binds once the ash line is hot.

The control design comes first here, which is unusual for a mechanical component. The destination is selected from the recipe and checked against what the silo already contains and what its level allows, and conveying cannot start until the position sensors agree with the selection. A diverter that reports only its command is the single most common cause of a contaminated silo.

The mechanical design then concentrates on smoothness. Matched bores either side of the junction, no gasket protruding into the flow, radii instead of angles and a seal face that sits flush. Plug and tunnel type diverters do this better than a flap with a step at its seat.

Grounding is designed as a system and tested. Every flange, the body, the actuator and the frame are bonded, continuity is measured at commissioning and re measured periodically, because the failure is invisible until it is not.

Regrind service is treated separately. It is angular, carries film and dust, and jams clearances that pellets pass, so the openings are larger and metal separation sits ahead of the junction.

• Destination selected from the recipe and interlocked against silo contents and level.
• Conveying air released only after position sensors confirm the selection.
• Matched bores, flush seals and radii to limit pellet damage at the junction.
• Full bonding and grounding of the assembly, measured and re measured.
• Larger openings and metal separation upstream in regrind service.
• Streamer accumulation points downstream inspected as part of the junction maintenance.

• Number of destinations and whether a multi port device or cascaded two way diverters carries the lower misroute risk.
• Consequence of a misroute, measured as the value of a silo rather than the cost of the hour.
• Streamer sensitivity of the downstream process and therefore how smooth the junction has to be.
• Material form: pellets, powder or regrind, which changes both the damage and the jam case.
• Static behaviour and the grounding concept for the whole assembly.
• Position confirmation and interlocks, which are the actual protection against the main risk.