Automated Sack Emptying in Chemical Plants

In a chemical plant the sack tipping station handles materials that are irritant, corrosive or toxic, and the operator is the exposed part of the system.

Manual tipping puts a person in a dust cloud of a material that may have an occupational exposure limit measured in milligrams. The sacks also vary across a wide material list, and some products attack the equipment that handles them.

Sacks emptied with the operator outside the dust and the exposure demonstrably below the limit for each material, with the station able to handle the full product list.

Empties that leave the station clean enough that the waste area is not the next exposure point, which means the beating out stage is specified for the residue target rather than for the cycle time.

A station that can handle the whole product list, with a documented answer for each incompatible pair: dedicated contact parts, a verified cleaning procedure, or a campaign sequence that keeps them apart.

In food production the machine is defeated by sack construction rather than by exposure: one slitting arrangement specified, and a mixed supply of paper and lined sacks delivered.

Sacks are fed to the machine, cut open, inverted and beaten out over a screen, and the empties are compacted into a closed container.

In a chemical plant the extraction is designed as an exposure control rather than as housekeeping: the volume comes from the opening and the required capture velocity, and the result is verified by measurement.

Material compatibility decides the contact parts. A station that handles both an acid and an alkaline powder needs either dedicated parts or a cleaning procedure that is verified rather than assumed.

Where the area is classified, the machine and its extraction need the corresponding ratings, and that is cheaper to decide before the equipment is chosen.

The exposure target drives the sizing. Capture volume follows from the open area at the tipping point and the face velocity needed to hold the dust in, and the result is verified by personal sampling rather than by looking at the station. For a material with a limit in milligrams per cubic metre, appearance tells you nothing.

The opening method then has to match the sack. A cutting knife suits a paper sack with a sewn top; a woven polypropylene sack with a valve behaves differently and can be torn rather than cut. Where the supply is mixed, which it usually is, the station has to cope with the whole range or the operator will start helping it by hand.

• Extraction as exposure control, verified by measurement.
• Contact parts for the whole material list.
• Area classification settled before selection.
• Opening method matched to the full range of sack constructions in the supply.
• Residue in the compacted empties measured, so the waste route is not the next exposure.
• Explosion characteristics measured for the worst material on the list, not the first one.

• Exposure limits of the materials, which set the capture requirement.
• Material compatibility across the full list, including the incompatible pairs.
• Area classification and the resulting equipment ratings.
• Sack construction and whether the supply is mixed.
• Dust explosion characteristics, since the station creates a cloud by design.
• Residue target for the empties, which decides the beating out stage and the waste handling.
• Throughput and sack rate, since a station that cannot keep up invites manual intervention.
• Cleaning agent compatibility for the contact parts, which is often harsher than the products.