Tray Formers and Tray Formats for Glass Bottle Packs

A tray former erects a shallow corrugated tray from a flat blank, and specifying one means settling four things in writing: the tray format, the board grade, the closing method, and whether the volume on each format justifies a machine at all. Fix the format in this order: footprint from the pallet, wall height from the contents, closure interface from the closing method, and board grade last, against the load and the transit. A project that begins with the board grade has begun with the final question.

Cycle rates, tooling costs and delivery dates are not given here for any plant. They depend on the tray actually run and the machine actually installed, and are confirmed per project.

The five dimensions that make up a tray format

For glass bottles, a tray is a self-supporting corrugated base with low side walls. A group of bottles, or a row of smaller inner packs, goes into it before film, a lid or the pallet build stabilises the unit. It is neither a display tray nor a full shipping case unless it is deliberately specified to do one of those jobs. Mixing the two up costs money in both directions: a tray drawn like a case carries board it does not need, and a case drawn like a tray gives way inside the container.

A drawing that fully describes the format states five things.

• Footprint. External length and width across the base. The tray is the unit stacked on the pallet, so this dimension sets the pallet pattern and, through it, how well the container is used. The bottle count per tray is whatever fits inside with a workable clearance.
• Wall height. How far the erected walls rise above the base. A wall only a few centimetres high stops bottles sliding in handling and is normal for a tray that will be shrink-wrapped and stacked. Raise the wall and it starts to act like a case, taking stacking load through the board, which raises the grade requirement.
• Blank layout and scores. The blank is one piece of board, scored and slotted for folding. Score positions define footprint and wall height. Flutes are crushed at every score so the fold can happen, which makes each score a local weak point; a blank with more scores than the format requires is weaker than its grade suggests. The corner construction (glued, lock-tabbed or stitched) governs how much corner load the tray passes on.
• Board grade. Flute type, number of walls and liner weight or grade, all three stated. A thickness on its own describes one part of a three-part choice.
• Closure interface. The geometry the closing method needs. Shrink film needs walls and corners that will not cut it and a footprint it can bridge. A separate lid needs a rim it can grip. Hot melt or tape needs flaps designed for that method.

Two of these cause most late trouble. Wall height is the dimension most often revised near the end, because it has to absorb a taller cap or bottle, and any revision alters the blank and so the tooling. The closure interface is the one most often missing from the drawing, which is how a tray qualified with one closing method turns out to be unusable with another.

The format is an output of a wider document. What the pack must survive, what the customer wants on the outer and how many units go in a pack are set in the packing specification for the bottle; if that document does not exist yet, write it first.

Setting the footprint from the pallet

A pallet has a fixed length and width. The tray footprint must divide both into a whole number of trays, otherwise the remainder turns into overhang, an air gap, or a strip that needs stabilising by other means. That is why the footprint is worked backwards from the pallet. Set it from the bottle count and check the pallet later, and the overhang or wasted strip usually shows up at the first container loading.

Three rules apply to the pattern:

1. Overhang is zero or negative. An overhanging corner is unsupported, and it is the same corner a strap or wrap bears on, so it is where the pack fails first.
2. No tray bridges a gap between pallet boards. Spanning air, the base works as a beam, a load case it was never designed for.
3. Rotated layers are checked separately. Turning trays in alternate layers helps interlocking but moves the contact points between layers, so the format has to work in the rotated pattern as well as the straight one.

The pallet format is an input, and an easy one to forget. The standardised footprint families described in the ISO 3394 framework, such as the 1200 by 1000 millimetre and 1200 by 800 millimetre groups, subdivide differently, so a tray that tiles one cleanly leaves a remainder on the other. If the destination market prefers one of them, feed that into the footprint from the start. If one product ships to two markets with different pallets, there are two honest answers: a footprint that suits one market and carries a known inefficiency in the other, or two tray formats and the changeover burden that comes with them.

Height completes the sum. Footprint gives units per layer, the pallet height limit gives layers, and together they give units per pallet. The container loading calculation runs on that figure, and so does the number of trays the former must produce each day. A wrong footprint therefore changes the output asked of the machine and the quantity of blank the plant buys, as well as the fit.

Board grade, flute direction and moisture

Two trays cut from the same nominal grade can behave differently, and the cause is nearly always geometry and not material.

What a grade consists of

Corrugated board is described by flute profile, number of walls and liner combination. In glass bottle packs the profiles run from a fine flute a little over a millimetre thick, through a mid flute of about three millimetres and a coarser one of about four millimetres, to double-wall board that pairs two profiles and reaches seven millimetres or more. For a given liner weight a taller flute bends less, so coarse profiles go where the tray carries load or spans a gap, and fine profiles where print quality or a tight fit counts for more than stiffness.

The liners are the skins that take tension and compression; the flute holds them apart so they can work. In pure compression a heavy liner on a modest flute can beat a light liner on a tall flute. Specifying by thickness alone therefore pins down the least relevant property.

The two figures to ask a board supplier for

Ask for the edge crush resistance of the combined board, which drives the compression strength of the erected tray, and for a burst or puncture figure, which tells you whether the board survives a handling knock without tearing. Both should come with the test basis named. Offers stated that way can be compared with each other; offers stated as a thickness cannot.

Flute direction

Board is far stiffer along its flutes than across them, and this matters more on a tray than on a case. In the base, flutes should run the way that lets the base span between load points without sagging, normally along the longer side of the footprint. In the walls the fold and the corner fix the direction, and vertical flutes resist top load much better than horizontal ones. A drawing with a grade and no flute direction is incomplete: cut the same blank with the flutes turned and both base and walls behave differently.

Moisture margin

Compression strength drops substantially as the moisture content of the board rises, and the drop starts long before the board feels damp. A tray qualified in a dry plant, then shipped through a humid port inside a container whose climate cycles daily, arrives weaker than it left. The symptom is a collapsed corner layer on the pallet, with nothing obviously wrong with the tray. Specify a margin above what a bench test says is just sufficient.

Shrink-wrapped tray, lidded tray or closed case

Most tray projects end up as one of three forms. Cost per pack is only part of the comparison; stacking and the destination's requirements decide it.

The film-wrapped tray is the lightest and lowest in material cost, and its transparency lets the pack be inspected and the product seen. The lidded tray sits in the middle on both cost and protection; its real gain is stacking performance, plus a printing surface, which is why it appears where pallets are stacked high and footprints are large. The closed case belongs to a different pack family. It gives the most protection and is the form that meets markets or channels expecting an enclosed, printed, sealed shipping container. It normally runs on a case erector, not a tray former, so choosing it changes the machine as well as the format.

The decision usually falls out like this. Single-stacked pallets of modest height going to a destination that accepts an open or wrapped pack favour the lightest form. Several layers of stacking make the load path through board dominant, and a lid or a case earns its extra cost. A destination that demands an enclosed, printed, sealed outer ends the discussion in favour of the case whatever the cost comparison shows.

Settle the opening behaviour before fixing the format. Where the pack is opened in front of a customer, or becomes the shelf display, how it opens is a commercial requirement. The wider choice among wraparound, shrink bundling and retail-ready packs is set out in our guide to secondary packaging forms for glass bottles.

Closing the tray with hot melt, tape or the film itself

The closing method is picked together with the format, and the common options do different jobs.

Hot melt goes on as a bead or a row of dots at the flap or corner and sets in a second or two into a rigid joint. Because it bonds the board fibres, the joint carries load, and a hot-melt tray is stiffer than the identical tray taped. An opened joint is also plainly visible, useful where the customer expects evidence of pack integrity. In return it needs a maintained glue system and a machine able to hold the joint under compression for as long as the glue requires. Too short a compression produces a joint that looks shut at the machine and opens later. A hot melt joint is not a moisture barrier.

Tape lies across a seam and keeps the flaps in place without bonding the board. It is simpler, needs less attention at the machine and costs less to run, but adds no stiffness. Adhesion depends on the surface: high recycled content, dust or a coating can defeat a good tape, and the failure shows as lifted tape, not a broken pack. Strip placement is visible, so alignment becomes a quality signal the customer reads.

Film as the closure applies when the pack is shrink-wrapped. There is no flap joint, the format is designed round the film, and the closure question moves to the film specification. Wall profile and corner geometry still have to be chosen so that no edge cuts the film and the film bridges the tray properly, which keeps this a tray design decision.

Between hot melt and tape, three points settle it. If the tray is part of the load path, as it is whenever packs are stacked several layers deep, hot melt keeps the board's contribution. If a clean opening at destination matters, ask that customer whether cut tape or a broken glue joint is more acceptable. If the board is mostly recycled, qualify tape adhesion on the actual board; that test often closes the question.

Seven common tray formats and when each is wrong

The table is arranged by format, since the pallet, the content weight and the closing method select a format, not a machine configuration. No figures are given because the right ones depend on content weight, stack height, transit and closure, and have to be confirmed on your own pack.

Four checks on a formed tray, and two at start-up

A tray coming off the former looks ordinary, and the faults that cause trouble later rarely show at a glance. Check these on a defined sample.

• Squareness. Measure the angle between adjacent walls at the corners. Beyond a small error, bottles do not seat against the intended wall, the pack sits askew in a pattern that assumes a rectangle, and the error adds up layer by layer until the top of the stack has visibly rotated. When a pallet starts to lean, look here first; the cause lies in the machine and the blank, not the bottles.
• Wall height consistency. Measure each wall at several points. Variation along one wall means a score folding unevenly; variation from tray to tray means a machine setting or board moisture. Either way the stack will not sit flat, because the high spot of one tray becomes the contact point for the layer above and concentrates load.
• Score quality. The flutes should be crushed enough to fold and not so far that the board delaminates. Too tight a score tears the outer liner, and the tear spreads under stack load. Too loose a score lets the wall spring back once the forming tool lets go. The blank supplier's rule and die and the moisture of the incoming board set this, so inspect the blank as it arrives and not only the formed tray.
• Glue bond or lock engagement. A glued corner must be bonded over the whole intended area, with the glue applied at an open time that suits the machine cycle. A cold or partial bond holds at the machine and lets go under load, so inspect trays after they have stood for a while. On locked or stitched corners, confirm the tabs engage fully and see whether a tab can be pulled out by hand with modest effort.

Add two functional checks to the start-up routine. Put the erected tray on a known flat surface: if it rocks it will not load properly, and the usual cause is a base distorted by the forming tool. Then lift it by two opposite walls and carry it. A sagging base points to a grade that is marginal for the content weight.

Matching the former to the loader and the palletiser

The former pulls a blank from a magazine, erects it, forms and seals the corners and hands an open tray to the loading station. That station may be a case packer head, a pick-and-place unit or a manual bench. The filled tray then passes to a film wrapper, a lidding station or a lid placer, and on to the palletiser. On a glass line the former is never the fastest machine and seldom the slowest, so its headline rate matters less than how it relates to its neighbours. Speed without squareness helps nobody: a slightly distorted tray simply hands the problem to the loading head.

Three conditions decide whether the group runs.

• A buffer of empty trays ahead of the loader. A short accumulation absorbs the fact that two machines do not stop together. Without one, each former stop halts the loader, and the stoppage spreads to the palletiser. Size it for realistic stoppages, which are mostly magazine reloads and glue system attention, not for the ideal cycle.
• Magazine capacity against reload interval. How often someone must load blanks shapes the effective rate as much as cycle time does. Frequent refills turn a good nominal rate into a poor effective one. The remedies are a bigger magazine, bundled blank presentation or loading planned during production, not a faster cycle.
• Layer timing at the palletiser. The palletiser works in complete layers of trays. If former and loader cannot complete a layer in a sensible time, the palletiser waits on a partial layer or a stock of filled trays builds up, occupying floor and adding breakage risk. Pallet pattern, units per tray and machine rates together fix how a layer is built; change one and the palletiser's operating point moves.

When comparing machine offers, two formers with the same nominal cycle are not equal if one magazine holds twice as many blanks or one glue system needs less attention. Ask for the effective rate across a shift, reloads and stoppages included. Few suppliers volunteer it. The station that places bottles into the tray, with its drop height, tooling and breakage controls, is specified separately in our page on case packing equipment for glass bottles.

What a second tray format really costs

A former that is plainly justified on one format can be the wrong purchase for a plant running several. Judge changeover by listing what physically changes and what must be proven again, not by counting minutes in the abstract.

The blank and its tooling. This is the largest item. A new footprint, wall height or corner construction means a new blank and a new tooling set: magazine guides, pick and erection tooling, fold tools and, on glued corners, glue nozzle positions. Changing only the grade on unchanged geometry is far smaller. Products meant to share a former should therefore share one tray geometry and vary the grade.

Loading, closing and palletising. A new footprint alters what the loading head presents to, the film width or lid size, and the pallet pattern. Plants often plan the changeover round the former and then find the palletiser's layer program needs rewriting too, and that is where the time actually goes.

Re-verification. New geometry or a new grade changes the compression performance of the pack, so stacking claims and transit qualifications made on the old pack do not carry over. A pack qualified against a transit test regime such as the ISTA series usually needs at least partial re-qualification, and that belongs in the changeover cost. A new bottle in an unchanged tray triggers the same work, since content weight, centre of gravity and load path all shift together.

The design consequence is that a plant expecting two or three formats usually does better by giving them a shared family of dimensions, so one machine runs them with minimal tooling change, than by optimising each for its own pallet pattern. The pallet inefficiency this introduces is often smaller than the changeover cost it removes. That only becomes visible if the changeover cost is written down as a number.

When hand erection or a semi-automatic former is the better choice

A former buys consistency and rate, and both are worth far less at low volume with frequent format changes. A hand-erected tray needs no tooling and no changeover, and at low volume that flexibility outweighs the cost per tray by a wide margin.

The test is a ratio. The machine is a fixed cost recovered over the trays actually run on it, and the denominator is trays per year on each format, not total trays per year. One format run daily recovers the machine quickly. Four formats, each run one week per month, recover it four times more slowly, with four tooling sets and four changeovers to pay for meanwhile. Do this arithmetic with your own formats, not a round number.

Below the point where a machine pays, three options sit between a former and plain hand folding:

• A pre-glued or auto-bottom tray, supplied already jointed. It opens by hand into a square tray in a fraction of the time needed to fold a flat blank and removes the variation of hand-folded corners.
• A bench tool or jig that holds the tray square while someone folds and closes it. It costs a fraction of a machine and keeps most of the quality benefit.
• A different pack form, such as a wrap-around or a film-only bundle where product and destination permit, so that no tray is needed.

Above that point, the usual intermediate step is a semi-automatic former. It erects and glues while an operator manages the blank feed, taking the slowest and least consistent work (folding and gluing) off the person and leaving the flexible part. Most plants with moderate volume and a couple of formats settle here. The operator still paces the machine, so its effective rate depends on how well the feeding rhythm lasts through a shift.

Decisions that sit next to the tray

The tray former's contribution ends with a square, open tray arriving at the loading station. Several adjoining questions are answered elsewhere:

• Sleeves and labels on the bottle, as distinct from the film round the pack, are covered under shrink sleeve application.
• How many trays fit in a container is arithmetic that follows from pallet pattern and pack height. Loading mode, pallet position in the box and cushioning against movement are covered in container loading for glass bottles. Choose a container fill first and a tray format second, and you will normally end up re-specifying the tray.
• If your question concerns the gas inside the bottle and not the board round it, the filling-side counterpart to this page is nitrogen dosing in the headspace.

When we review a tray project, the inputs that move the answer most are the bottle type and filled weight, the units wanted per pallet, daily or annual volume, any pallet format fixed by the customer, the closing method, whether packs are stacked several layers high, and whether a transit qualification already exists for the current pack. The last three shift the board grade and the changeover plan more than anything else.

Frequently asked questions about tray forming for glass bottle packs

How does a tray differ from a case for glass bottles?

A tray is open and shallow and needs film, a lid or a strap to hold the contents. A case surrounds the bottles, shuts with glued or taped flaps and takes vertical load through its own walls. Trays are lighter, cheaper and easier to inspect; cases protect more and satisfy destinations that want an enclosed, printed outer. They also run on different machines: a tray former for one, a case erector for the other.

How do I choose the board grade for a tray?

Begin with the load and the transit, never a thickness. State flute profile, walls and liner combination, and request edge crush resistance together with a burst or puncture value, each with its test basis, since the two govern different failure modes. Add a humidity margin, then confirm the flute direction on the drawing.

Is shrink film enough to hold a tray pack together?

Yes for light contents on a low stack, where the film only has to keep bottles from moving on the tray. No once packs are stacked several layers deep, or where the destination wants a pack sealed against dirt and moisture. For a moderate stack, a lid under the film is a common middle answer.

Why does hand-folding trays limit line output?

One person folds a fraction of what a machine forms and cannot be paced by the line. Consistency also drifts over a shift: corner angles and wall heights vary slightly, so trays that look acceptable still misbehave at the loading station and on the pallet. The labour has to be found every time the line runs, which makes it a scheduling constraint as well as a cost.

Can a tray former run more than one tray format?

It can. A grade change on the same geometry is minor. A footprint or wall height change brings new magazine, erection, fold and glue tooling, a rewritten palletiser pattern and usually repeated compression or transit qualification. Formats planned around a shared family of dimensions generally cost less over the machine's life.

How should the tray footprint be matched to the pallet?

Derive it from the pallet so that whole numbers of trays fill the length and width with no overhang and no significant gap. Because the footprint also sets units per layer, and with the height limit units per pallet, it feeds straight into the container loading figure. Where two pallet formats are in use, decide deliberately which one the tray favours.

How do I know a formed tray is good enough?

Sample it for corner squareness, even wall height along each wall and between trays, clean scores that neither tear nor spring back, and a complete glue bond or full lock engagement. Judge the bond after the tray has stood, since a partial bond can survive the machine and fail afterwards.

When is an automatic tray former not worth buying?

When no single format runs at enough annual volume to recover the machine, its tooling and the changeover time. Several formats share one machine and pay it back more slowly. Under that threshold, consider a pre-glued tray opened by hand, a squaring jig at a bench, or a pack form that does away with the tray.