Bottle Conveyor System for Glass Bottles: Type and Speed

The right conveyor for a glass bottle is whichever conveying principle keeps that particular bottle standing at the required speed along the actual route, so the choice is made from three inputs read together: the bottle, the speed and the route. Round, flat-based bottles of moderate weight run well on flat-top slat chain; light bottles on long, fast runs are usually hung by the neck ring on an air conveyor; slopes need a flighted belt and buffering needs a low-speed accumulation table. No speed in metres per minute or rail clearance in millimetres is given here, because both have to come from the confirmed bottle drawing and a loaded test on the real line.

Start from the bottle, the speed and the route

An empty glass bottle on a chain is an unstable object. Its centre of gravity sits high above a small contact area, nothing but friction holds it up, and the push that moves it arrives at the base while the mass resists further up. Whether it reaches the next machine upright depends on how those facts meet the geometry of the track, which is why a conveyor cannot be picked from a catalogue of machine types.

Each of the three inputs contributes something specific:

• The bottle gives the body diameter, height, empty weight, centre-of-gravity position, base shape and the surface condition of the glass.
• The speed sets how much time is available at every curve and transfer. A bottle that is steady at one speed can become unsteady once its dwell time at a rail shortens.
• The route is the series of straights, curves, inclines, transfers, accumulation zones and stops the bottle must get through between two machines.

Most conveyor trouble starts when one of these inputs shifts after installation. The brand takes weight out of the bottle. A shoulder sleeve is added, moving the centre of gravity and altering surface friction. A second format arrives and the rails are re-set by eye. A downstream machine is slowed and accumulation appears that nobody planned for. The conveyor is still doing what it was set to do; the bottle changed and the settings were not re-derived.

The remedy is to write the bottle's constraints down before equipment is ordered. A line specified from the machine list outward, with the conveyor treated as whatever fills the space between machines, gets commissioned by trial and error and then loses bottles at a rate no one can account for.

Conveyor types compared by format, speed and first failure

The comparison below is arranged by conveying principle, not by supplier or machine. For each one it shows the formats it handles well, the speed band it suits, what really holds the bottle upright, where it gives way first and which settings shift at a format change.

A figure published without the bottle, its surface condition and the route would end up copied onto a setting sheet and cause the next fall. That is the reason the table stays qualitative.

How bottle shape, neck and decoration narrow the choice

A format that is acceptable on body, neck and decoration can run on a wide range of equipment. A problem on any one of them restricts it.

Body and base

A round body offers the rails the same radius however it rotates, so it behaves predictably in a single lane. Square and oval bodies offer corners, and every corner that passes a rail nudges the bottle slightly; the next bottle inherits that nudge. With fluted or ribbed panels the effective diameter depends on where the rail happens to land, and a base with a pronounced push-up has less contact area than a flat one. Non-round formats generally call for a wider clearance band, lower speed through curves, or guides placed higher up where the cross-section is constant.

Neck and finish

Air conveying and some neck-handling transfers carry the bottle by its neck ring. This is efficient and takes base friction out of the picture, but the finish must bear the bottle's load without deforming and the neck ring needs enough defined surface for the rails to grip. An unusual finish, or a light-weight container with a thin neck, may not be suitable for suspension. It is one of the few points where closure interface and conveyor layout affect each other directly, so confirm it before committing to a neck-handling route. The choice of container itself, meaning capacity, profile and finish family, is made upstream of all this, from the glass bottle ranges.

Decoration

Decoration is the factor most often overlooked. A spray coating alters body friction at the rail contact, and matte and glossy finishes can differ. A full-body sleeve puts a plastic layer over the glass: the rails now see a diameter larger by the film thickness, and friction changes on base and sides alike. A sleeve ending at the shoulder can be scuffed by a rail that used to touch bare glass. Direct print raises the same concern with more fragility.

When decoration is added after the conveyor has been set, re-check rail height and rail material. Sometimes a low-friction rail is fitted so that the decoration is not marked.

The six dimensions a conveyor is set by

Nearly every adjustment made to a bottle conveyor changes one of six dimensions. Knowing what each controls separates adjusting a line from guessing.

• Track width and rail clearance. The gap between the guide rails, taken at the height where they touch the bottle, matters more than any other number. Set too narrow, the rails grip the bottle: it slows, the decoration scuffs and eventually the glass chips. Set too wide, the bottle leans, reaches the next rail already displaced, and the lean adds up down the line. The correct value is a band worked out from body diameter and its tolerance, and it is measured with the real bottle, not from the drawing.
• Rail contact height. Guides belong on a cylindrical, structurally stiff part of the body, ideally below the label band and above the moulded base. A rail on a tapering shoulder pushes into a slope, turning a horizontal push into vertical lift, and that lift is a frequent reason bottles climb rails on curves and at transfers.
• Chain or belt pitch and surface. Pitch governs how smoothly the carrying surface passes under the base; surface governs available friction. A large-pitch chain with a worn top plate lets the bottle drop a little as each link goes by, felt at high speed as constant jitter.
• Transfer gap and dead plate geometry. Wherever one conveyor hands over to another there is a gap and a stationary plate. The gap must be too small for the base to drop into yet large enough that the two surfaces do not rub, and the plate must support the bottle until the next surface carries it. A disproportionate share of falls happen here.
• Curve radius and inner wedge. A curve is its centreline radius plus the geometry of the inner wear strip. On a tight radius every bottle loads the outer rail heavily while the inner rail stops the base sliding outward. A curve too tight for the diameter runs acceptably slow and fails when the line is sped up.
• Incline angle. The angle fixes how much friction is needed to stop the bottle sliding back; the belt or chain surface and the state of the bottle base fix how much there is. A lubricated chain that is fine on the flat may not hold a bottle on even a shallow incline, and a chain that holds a dry bottle may lose it once condensation forms on the base.

What the glass must deliver before it rides the line

The conveyor is the first place a glass delivery is tested under load. A batch can pass goods-in inspection and still misbehave, and four conditions account for most of that gap.

1. Base flatness. A domed base, or a bearing surface that is not annular and continuous, leaves a small contact patch under a high centre of gravity. Such a bottle falls on a line that carries a flat-based one without trouble.
2. Straightness. A lean you cannot see in a carton turns into lateral drift on the move, because the bottle no longer has neighbours propping it on every side.
3. Surface condition. Condensation, washing residue and lubricant all shift the friction between base and carrying surface. A line set with dry bottles may lose stability when a wet batch arrives.
4. Temperature. A bottle coming from a warmer or cooler stage than the rest of the line brings a different surface condition with it, and behaviour often changes at that transition and not along the run itself.

Conveyor settings and bottle specification therefore have to be agreed together. When we check a drawing for a project that involves light-weighting, a new sleeve or a coating change, we flag that the conveyor is affected even though no machine has been touched. Spotting that link early costs less than re-setting an entire line after a redesign.

On-site checks for rail clearance and tolerance

Rails are set to a bottle, not a drawing, so the checking routine carries more weight than the nominal setting. Five checks cover it.

1. Rail gap at contact height, measured at several points on a straight and again through each curve, with a physical gauge or the bottle.
2. The same measurement with the largest and smallest bottle in the delivery. Glass arrives with a spread of body diameters inside an agreed band. Rails that fit only the average bottle let the smallest lean and grip the largest. How wide that band is, and how a batch is judged against a stated dimension, is the subject of our guide to tolerance bands for glass bottles; a setter needs that input before touching a rail.
3. Loaded run against empty run. A chain at the right speed unloaded can slow noticeably under a full lane. Where two conveyors have separate drives, their speed difference under load is what pulls a bottle out of shape at the transfer.
4. Stop test. Run into a stopped downstream machine, let accumulation build to the level production will really see, and watch where bottles begin to lean. No measurement tells you as much, since this reproduces the condition the line handles worst.
5. Format-change verification. Once rails are re-set for a new bottle, repeat the first four checks instead of assuming them. A few millimetres' difference in body diameter moves the contact point and can land a rail on a shoulder or on the label band.

Keep a short written record for each format: rail gap, rail height, transfer plate position and chain speed. It removes most of the setting time from the next changeover and makes the settings repeatable from shift to shift.

How line pressure causes falls behind a stopped machine

Back-pressure, or line pressure, is the force passed along a row of touching bottles when something downstream slows or stops while the upstream keeps feeding. On a line that runs perfectly until it accumulates, it is the commonest cause of unexplained falls.

The failure does not occur where people look. The first bottle to reach the stopped machine halts and those behind press into it. Load builds through the row and lands on the front bottle, which is why the bottle at the stop is the one usually found damaged. The falls, though, happen several bottles further back. Every bottle in the row is being pushed at its base while its mass, and any lean it has picked up, act higher. At some level of accumulated load one bottle loses lateral stability and tips, and the bottles behind follow it into the space.

The cure is to stop pressure building, not to ask for stronger bottles. Three measures do this:

• slow the infeed whenever the discharge slows;
• divide the line into sections with independently controlled drives;
• add accumulation zones where bottles are deliberately left to sit apart without contact.

The design rule is that a bottle should be pushed by a small number of bottles behind it, never by the whole length of the line.

Over-correcting loses bottles the other way. With too much clearance, a bottle free to wander across the track reaches a curve or transfer already leaning, and gaps between bottles let bases slide sideways. The target is a band: enough contact for the row to track in a line, but not so much stored force that the row acts as a rigid column carrying a stop all the way back to the infeed.

Why bottles fall at curves, inclines and transfers

Bottles seldom fall on a straight. They fall where the track turns, changes level or passes the bottle to another surface, and each has its own cause.

Curves

The outer rail supplies the side force that turns the bottle, and that force grows with speed. A bottle that enters leaning is already loaded against one side, so the curve can only supply the correction it was designed for. Typical faults are a radius too tight for the diameter, an inner wedge worn until the base is no longer guided, and a rail gap right on the straight but wrong on the radius because it was set at one point only. Measure the gap at entry, apex and exit.

Inclines

Here the question is friction, not side force. Going up, base friction must exceed the component of gravity along the slope. Going down, bottles must be spaced so they do not run into each other and recreate the accumulation of a stopped machine. Both directions react to surface condition and to whether the belt or chain has been lubricated. The top and bottom of the slope are a separate hazard: the bottle crosses between two surfaces at different angles and for a moment neither supports it properly.

Transfers

The bottle crosses a stationary plate from one chain to another, and the controlling parameter is the relative speed of the two surfaces. If the receiving conveyor is faster, the base is dragged ahead while the mass still travels at the earlier speed, and the bottle leans forward at the discharge. If it is slower, the base decelerates first and the bottle leans back. A well-set transfer has matched surface speeds, a dead plate placed for continuous support, and a gap too small for the base to drop into. Judge every transfer by those three checks, including the one into the machine.

Fault-finding order for falls and jams

When bottles start going over, the temptation is to tweak the nearest rail. A fixed sequence finds the true cause sooner and avoids a line that has been adjusted everywhere and now fails in a new way.

1. One position or many? A repeating position means a local mechanical cause: rail gap, worn wedge, shifted dead plate, obstruction. Random positions mean something systemic such as speed, back-pressure or the bottle.
2. Only during accumulation or stops? Falls clustered behind a stopped machine are line pressure. The answer lies in infeed control and accumulation design, not the rails.
3. Has the bottle changed? Confirm the batch has the same format, weight and decoration the line was set for. A sleeve or coating change is easily missed and alters diameter and friction together.
4. Has the surface condition changed? Wet bottles, a different lubricant, higher humidity or a new cleaning regime can each remove friction the line relied on, especially on inclines.
5. Has the speed changed? Above its set speed a line loses bottles at curves and transfers first.
6. Is the mechanical condition still as set? Chain tension, worn top plates, stretched mesh, worn wedge strips and loose rail brackets drift gradually; the symptom shows up suddenly when wear crosses a threshold.
7. Is the conveyor to blame at all? An out-of-round bottle, a foreign object or a mis-timed machine can cause a jam. Adjusting the conveyor to mask it creates a second problem.

Logging which of these seven conditions applied each time a fault occurs usually reveals the pattern within two or three occurrences.

What to put in a conveying brief

A sound recommendation needs three inputs that only the buyer holds, sent together:

• Bottle format: body diameter with tolerance, overall height, empty weight, whether the body is round, oval, square or fluted, and any coating, sleeve or direct print.
• Line speed: what the section must deliver, and whether it is constant or follows the machine it feeds.
• Route: the order and length of straights, curves, inclines, transfers and accumulation zones between the two machines, with the direction of each change of level.

These narrow the principle before hardware is discussed. Format settles whether base conveying is viable or neck handling is safer. Speed settles whether a single lane will do or throughput demands a wider lane arrangement. Route shows where the risk lies, because a line with several inclines and tight curves poses a different problem from a straight run of equal length.

Say also whether the bottle is likely to change during the life of the line: a weight reduction, a closure change that moves the fill height, an added decoration step. A layout planned around a known range of formats is far easier to set and re-set than one built around a single bottle. A request that arrives as a machine list alone tends to come back as a layout drawing and a schedule, with transport settings left for commissioning.

Transport is only one link. Standing empty bottles up and singling them into a stable lane is the task of the bottle unscrambler, and the conveyor is set to the lane it delivers, not the reverse; depalletising before that is a separate handling decision. Fill valves, nozzle timing and the closing sequence at the far end are covered in the glass bottle filling line guide, the place to begin when the question concerns the machine and not the track.

Frequently asked questions about bottle conveyors

Which conveyor type suits a light glass bottle at high speed?

Base-driven conveying becomes the limit, because the little friction at the base has to accelerate and steer a body with small mass and a high centre of gravity. Air conveying on the neck ring is the usual answer for long runs, as long as the finish has a well-defined neck ring and the neck carries the container without deforming. If the bottle must travel on its base, flat-top slat chain with rails on a stiff part of the body comes next, with curves and transfers run slower than the straights.

How much back-pressure is too much?

No single figure exists; the limit depends on bottle weight, base contact area and how much lean the row already has. Use the stop test at production-level accumulation. If bottles tip several positions behind the stop instead of at it, the stored force already exceeds what the format tolerates, and the pressure has to be reduced at source through sectioned drives and an infeed that slows with the discharge.

What must be adjusted at a format change?

Four settings normally move: rail gap, rail contact height, transfer dead plate positions and chain or belt speed. Curve elements may need adding or removing where the new diameter alters what the radius can carry, and the number of lanes opened at an accumulation table may change. Record the settings per format when the line is first set so a changeover repeats a known state, then re-check with the largest and smallest bottles of the new delivery, not a single sample.

When should a line go from one lane to several?

When a single lane cannot give the downstream machine its throughput at a speed the bottle survives, or when the accumulation required cannot be held in one lane without excessive back-pressure. Extra lanes raise throughput and buffer bottles without pushing them together, but they bring two problem points: the diverter that splits the lane and the combiner that closes lanes back into one. Both must be designed for the format, because a diverter that suits a round bottle can lift a corner on a square one.

Can empty glass bottles travel by air without touching a belt?

Yes. Air conveying is widely used between halls. The bottle hangs from its neck ring and is driven by air, so light weight, base shape and decoration have almost no effect on stability. It rules out some light-weight and unusual finishes, since the neck must carry the container and the ring must give the rails a defined surface. The critical points shift to the entry and exit of the air channel, where the neck passes between suspension rails and the base-supported section; treat both as transfers and check them as such.