Automated Sack Emptying in Food Production

Sack tipping is the dustiest operation in most food plants and the one with the most human contact.

An operator lifts twenty five kilograms, cuts it open and shakes it out, several hundred times a shift. Every one of those movements releases dust at face height, and the empty sack carries product back out of the station.

Automating it removes the lifting and most of the exposure, but introduces the problems of handling a sack mechanically: sacks vary, they tear, and the cutting has to separate paper or film from product reliably.

Sacks emptied without an operator in the dust, with the product free of packaging fragments and the empty sacks compacted and removed.

The figures that matter are residual product in the discarded sack and packaging fragments in the product, both measured rather than assumed.

An enclosure that is included in the allergen changeover, not just the hopper below it. The cutting chamber, the sack inversion area and the compactor all hold product dust from whatever ran last, and none of them is visible from the operator position.

A realistic sack rate. A station that cannot keep up with the line will be helped by hand, and a station being helped by hand has none of the exposure benefit it was bought for.

For mineral processing the governing figure is the respirable silica fraction, and capture judged by how clean the station looks passes while the dangerous part is still in the air.

Sacks are fed from a pallet onto an infeed conveyor, usually by a de-palletiser or by hand onto a magazine.

The machine opens the sack by cutting or by ripping, inverts it over a screen and shakes or beats the remaining product out. The screen catches packaging fragments and any foreign body, which is the food safety function of the station as much as a product one.

Extraction runs at the cutting point and at the discharge, because both release dust. The empty sack is compacted and discharged into a closed container rather than being handled again.

Everything downstream of the screen is a food contact surface and has to be cleanable in the plant's changeover window.

The screen is the food safety function of the station. Sacks bring staples, string, paper fragments and occasionally something from the pallet, and the screen after inversion is where those are removed. Its mesh is chosen for the packaging fragments rather than for the powder, which usually means a different aperture from the process sieve downstream.

Residual product in the discarded sack is worth measuring. It is a yield loss that runs continuously, it is an allergen leaving the station in a compactor, and it is the simplest indicator of whether the beating stage is specified correctly.

• Cut, invert, beat, screen.
• Extraction at the cut and at the discharge, not at the room.
• Empties handled mechanically, never a second time by hand.
• Screen mesh chosen for packaging fragments, which is not the process sieve aperture.
• Enclosure, cutting chamber and compactor included in the allergen changeover.
• Residual product in the empties measured as a yield and an allergen figure.

• Sack construction: paper, film or laminate all cut and tear differently, and a mixed supply is the hard case.
• Product cohesion, which decides how much beating is needed to get the last of it out.
• Allergen matrix, which decides whether the station can be shared and how it is cleaned.
• Throughput in sacks per hour, measured at the realistic rate rather than the peak.
• Explosion characteristics of the powder, since the station contains a dust cloud by design.
• Residual product target in the empties, which indicates whether the beating is right.
• Cleaning access to the enclosure, since the cutting chamber is not visible from outside.
• Realistic sack rate, because a slow station invites manual help.