Mass and stability
Weight, footprint, centre of gravity, packaging strength and whether the product can tolerate contact.
Air blast, pusher, sweep, flap and diversion
Conveyor reject methods for automatic inspection systems.
Choose a reject mechanism around the product, speed, spacing and failure consequence—not simply the inspection machine that sends the signal.
Direct answer
Which automatic reject method should you use?
The correct method removes only the failed product at the required line speed without damaging it, upsetting adjacent good product or creating a new blockage. Air blast suits light packs; pushers suit stable containers and cartons; sweep or diversion handles larger products; drop flaps and retracting belts suit products that should not be pushed sideways.
Final selection must be proven against actual product samples, speed range, spacing and conveyor conditions.
Reject mechanism comparison
| Method | Often suited to | Why it is selected | Key design checks |
|---|---|---|---|
| Air blast | Light pouches, sachets, flow wraps and small cartons | Fast, non-contact removal with few moving parts | Pack mass, air supply, spacing, open product and adjacent-pack disturbance |
| Pneumatic or servo pusher | Bottles, jars, cartons, trays and stable packs | Positive side transfer for medium-weight products | Stability, pusher face, stroke, return time, reject-side clearance and guarding |
| Sweep arm or lane diverter | Cases, multipacks, larger cartons and continuous diversion | Moves product onto a reject lane or secondary conveyor | Product footprint, centre of gravity, line width, speed matching and recovery path |
| Drop flap or retracting belt | Fragile packs, open trays, loose product and items unsuited to side impact | Allows the failed product to fall through a controlled opening | Available length, space below, cycle time, cleaning and safe access |
| Stop on detect | Heavy, awkward, low-speed or tightly spaced products | Stops the line so the failed item can be removed in a controlled way | Production interruption, operator procedure, reset control and removal confirmation |
Selection criteria
Five facts control the reject-method decision.
Speed and spacing
The reject must fire and recover inside the available product window across the full speed range.
Reject frequency
Expected reject rate affects cycle life, air demand, bin size and the risk of product accumulation.
Environment
Washdown, dust, temperature, hygiene and product-contact requirements affect construction.
Failure consequence
The risk determines verification, containment, line-stop logic and authorised recovery.
What information is needed to select the mechanism?
Provide the smallest and largest product, weight range, minimum product gap, normal and maximum speed, conveyor width and height, travel direction, inspection trigger, available reject length and photos or video of the line.
Do not overlook product presentation
A mechanism that works with evenly spaced upright bottles may not work when bottles touch, lean or arrive in groups. Trials should include normal variation and the least stable product condition expected in production.
Common questions
Practical reject-method answers.
The mechanism is one part of a complete tracked and verified reject sequence.
Is air blast suitable for bottles or jars?+
Usually not as a first choice because container mass and stability can make the result inconsistent. A pusher, sweep or guided lane transfer is often more controllable, subject to trials.
Can a pusher reject flexible pouches?+
It can in some applications, but the pusher face, product support and spacing must prevent folding, snagging or multiple-pack rejection.
What is the gentlest reject method?+
That depends on the pack. A controlled diverter, retracting section or low-drop transfer may avoid the sudden side impact associated with a pusher.
Can one system handle several product sizes?+
Often, yes. The design may use adjustable guides, recipe-controlled timing, interchangeable contact parts or a mechanism sized for the full product range.