Empty PET Bottles From the Depalletiser to the Filler: Static, Fallen Bottles and the Gap That Eats Them

The depalletiser pushes a layer of 24 bottles onto the take-away conveyor at 04:10. Each weighs 10 g, stands 210 mm tall, and carries its centre of gravity nearer the shoulder than the base. The layer sweeps into one lane over two metres, accelerates to meet a filler running 24,000 bottles an hour, and reaches the combiner. One bottle, fifth from the front, catches its base on the gap between two slats, leans, and goes down. The line stops for eleven seconds, the filler starves, and an operator stands the bottle up with a gloved hand that leaves a scuff on the shoulder — visible on the shelf, invisible in the report.

Forty of those in a shift is six minutes of filler time, which is the difference between hitting the week's target on Thursday and explaining it on Friday.

1. The Moment the Depalletiser Pushes

2. What an Empty Bottle Is, Physically

3. Where Conveying Sits Between Depalletiser and Filler

4. Three Places It Goes Wrong

5. Why This Conveyor Form Rather Than That One

6. The Numbers That Decide the Design

7. Changeover and Cleaning

8. One Sentence for the Line

A layer arrives as a block, not a stream. The take-away conveyor receives 24 bottles at once, each touching three neighbours, and has to turn that block into a single lane within a few metres without letting any of them fall. The bottles are at their lightest and their most unstable here: no product weight to settle them, no cap, no label, and a base that has just been pushed sideways across a pallet.

The combiner is where the block becomes a queue, and where the first fallen bottle of the shift usually happens.

· Weight: 8–12 g for a 0.5 L still-water bottle, 20–28 g for 1.5 L, heavier for carbonated formats. The bottle weighs less than the air it displaces in a draught.

· Geometry: 200–330 mm tall, 60–90 mm diameter, wall thickness 0.15–0.4 mm in the body and thinner in the panel recesses. The base is petaloid or champagne form: stiff in compression, useless in shear.

· Mass distribution: the centre of gravity sits high, near the shoulder. Tipping angle on a dry slat surface is often 12–15°, less than the tilt a bottle reaches when it rides up on a rail.

· The neck: the only rigid part, and the part that carries the whole bottle in a neck-handling conveyor. Its dimensions are set by the cap, so the conveyor fits what the cap has decided.

· Surface: dry, smooth, highly resistive — PET holds static, and dust holds on to PET.

The empty side is short in metres and long in decisions. Four to six stages, each with its own failure mode:

The two stages that decide the day are the combiner and the elevation, and both are usually drawn as straight lines with no dimensions.

The gap at the combiner. A bottle approaching a merge nose is leaning on a guide rail, so it is already at 5–8° of tilt. The gap between the moving slats and the fixed nose plate is typically 10–25 mm — enough for the base to bridge while the bottle is upright, and enough to swallow the leading edge once it tilts past that. The bottle goes down, the queue behind compresses, and the compression turns one fallen bottle into a jam rather than a pause. The mechanism is geometry, not speed: at 24,000 bph the bottles travel at walking pace, and the gap does not care how fast the base arrives.

Static, in two directions at once. A dry PET bottle sliding against a rail generates charge, and at 30% relative humidity in February that charge does not drain. Charged bottles repel each other, so a queue that was touching becomes a queue with 5 mm gaps, and a combiner that works by bottles pushing bottles loses its timing and double-feeds. The second effect is invisible until the customer finds it: a charged bottle attracts dust, film fragments and cap slivers, and the mouth is open. The filler fills a bottle that was clean when it was blown and is not clean when it arrives.

Accumulation pressure on a flexible panel. An empty bottle is designed to flex: the vacuum panels on a still-water bottle let the body breathe after capping. Under sustained side load in a queue, that flexibility becomes creep. Twenty bottles pushing on the front one at 30 °C for ten minutes leaves a permanent flat on the panel and a body that is no longer round. Nothing fails at the empty side. The bottle is filled, capped, labelled and cased, and the defect surfaces as a wrinkled label, a fill height that reads low, or a bottle that will not sit flat.

A flat-top slat chain carries bottles on their bases, with low-friction chain and guide rails doing the steering. It is quiet, needs no compressed air, handles mass flow without pitch control, and takes a format change with a rail adjustment. Its cost is contact: every bottle touches the chain and at least one rail, so scuffing, static and rail wear all happen here, and the bottles in a queue carry the load of everything behind them.

An air conveyor carries bottles by the neck ring, body free. It runs faster than any base-carrying conveyor, produces no scuffing, and cannot crush a panel because nothing pushes on the body. Its costs are energy and noise, and the neck ring now carries the whole bottle plus the acceleration — so a worn or mis-set rail wears the finish, and a worn finish is a cap leak six stations downstream.

Most plants end up with both: slat chain for the mass flow and the combiner, air for the long overhead run, and a Bottle Gripper Elevator where the bottle changes level.

The number that decides the most and gets measured the least is humidity. A line that runs clean in August can jam twice an hour in February on the same bottles, speed and rails, because charge that drained through humid air now stays on the bottle. Ionising bars at the combiner are the usual answer.

The empty side is a dry area, and treating it as a wet one creates more problems than it solves. Cleaning here is brush, vacuum and air: rails wiped, chain brushed, the tray under the combiner emptied of fallen bottles and cap slivers, a blow-off at the filler infeed where dust would otherwise enter the mouth. Water here leaves residue in the rail slots, which transfers to every bottle shoulder for a week.

Format changes are the real work: rail width, rail height, combiner guide positions, star wheel at the filler. A changeover measured in minutes rather than in a shift is decided by how many bolts sit between the operator and the rail.

The empty side gets treated as the cheap end of the line, and it is where availability is actually set — in the gap at the combiner, the charge on a dry bottle, and the queue quietly flattening the panels of everything in it.

About us. Shanghai Xisheng Taolan Intelligent Equipment Co., Ltd. builds custom conveying equipment for food and beverage plants. On an empty-bottle run the first things worth measuring are the gap widths at each transfer and the humidity in the hall.

Contact: Orange Zhou, Technical Sales Manager · orange@xstlconveyor.com