Gravimetric Feeding in Pet Food Production

Three feeding duties sit in the same plant and they are not alike. The meal side handles coarse, fibrous, low density material at high rates; the micro side doses vitamins, minerals and sometimes a veterinary additive in grams; the coating side handles fat and palatant, which stick to everything.

The meal is a flow problem. Fibrous material with a wide particle size range bridges over a hopper outlet and hangs on a screw, and a feeder that will not discharge steadily cannot control a rate however good its load cells are.

The micro side is an accuracy problem, and the accuracy that matters is at the bottom of the range. A feeder sized for convenience has no useful precision at a few kilograms an hour, and the ingredients in question are the ones with regulated inclusion levels.

The coating side is a maintenance problem. Fat builds on the screw and the tube, the volumetric relationship drifts, and gravimetric control compensates until it runs out of screw speed.

A pet food plant doses across a range that spans a tonne an hour and a few grams, and the regulated inclusions sit at the bottom of it.

Each duty on a machine configured for it, with the micro feeders sized for their own rate rather than for the plant standard.

Hoppers and discharge devices that keep fibrous meal moving without working it into a different density, and build up on fat contact surfaces controlled by a checked interval rather than by hope.

Cleaning and changeover that fit the number of recipe changes the plant actually runs, with the regulated ingredients traceable through the feeder.

For pharmaceutical production accuracy is measured on the actual active rather than taken from a catalogue, and the process residence time decides how much short term error the line forgives.

Meal feeding is designed around flow. A steep hopper, flexible walls with external massage, or a live bottom, and a twin screw that will not let the material pack. Agitation is set to maintain flow and no more, because working a fibrous meal changes its density and therefore the feed factor.

Micro feeding is sized small and often duplicated. Separate feeders for separate ingredients, each at its own scale, with the accuracy stated at the real rate and the real sample time. Where a veterinary additive is involved the feeder enters the traceability record, not just the control system.

Fat and liquid addition is metered rather than fed by screw, and the surfaces that fat touches get an inspection and cleaning interval based on measurement: a feed factor check after a known running time shows how fast the drift is, and that number sets the interval.

Changeover is then specified honestly. Quick release hoppers, screws and tubes, and a sequence that runs from restricted products downwards so cleaning does not have to do work that sequencing can.

• Separate machines for meal, micro ingredients and liquids, each configured for its duty.
• Meal hopper designed for flow, with agitation limited to avoid density change.
• Micro feeders sized for their own rate, with accuracy stated at that rate.
• Regulated additives recorded through the feeder for traceability.
• Feed factor drift on fat contact surfaces measured, and the cleaning interval set from it.
• Quick release contact parts and a production sequence from restricted to unrestricted.

• Rate range across duties, which usually means several feeder sizes rather than one.
• Flow behaviour of the meal, including bridging and the effect of agitation on density.
• Regulated inclusion levels for additives and the traceability that follows.
• Fat and palatant contact, which decides the feed factor drift rate and the cleaning interval.
• Changeover frequency and the time allowed, which decides quick release construction.
• Dust explosion characteristics of the meal and premix dusts.