Glass Bottle Strapping: Strap Spec, Tension and Audit

What the Buyer Is Actually Auditing When They Ask About Strapping

The question that opens most strapping conversations is which strap is used, and that question cannot be answered honestly without the load in front of the person answering it. A strap specification is a system rather than a product: a material, a format, a number of positions, a tension, a joint and a sequence, all chosen against a particular case format, pallet format and layer pattern. The practical result is that the useful audit is not a check of the strap itself but a check of whether the specification exists, whether it is written down, whether it is applied consistently and whether there is any record of it having been applied on the load in question.

Six questions do most of the work in that audit. The first is whether each load type the supplier ships has its own written strap specification, or whether one strap is used for every load because it has always been used. The second is how the tension is set and measured, by what instrument, at what point, and by whom, because tension is the variable that decides whether the strap does anything at all. The third is which joint type is used, how the joint is formed, and how its strength is verified, because the joint is the weakest element in the system and it is the element most often assumed rather than checked. The fourth is where the straps are positioned relative to the pallet and to the layer pattern, and why those positions were chosen. The fifth is whether the strap is applied before or after the film or hood, and who made that decision, because the order changes how the load behaves when the film is cut. The sixth is what happens on the loading dock when the machine stops, the strap runs out or a load is found with a slack strap, because that is where an undocumented process turns into a photograph at destination.

There is a diagnostic reason for asking those six rather than starting with the strap material. A load that arrives with a broken strap is almost never a load that was held by a strap which was too weak. It is far more often a load whose tension was set by feel, whose strap crossed a bare edge or a pallet gap, whose compressible pads settled after the strap was applied, whose joint was welded through a damp strap, or whose strap was hooked by a clamp truck during handling. All five of those causes produce the same symptom and all five are specification failures rather than material failures, which is why the audit has to reach past the strap to the process behind it.

Strap Material First: Polypropylene, PET and Why Steel Band Is Rarely Right for Glass

Three materials account for nearly all strapping in a glass supply chain, and the differences that matter are not only strength. They are how much the strap recovers its length after the load has settled, how it behaves over time under a sustained load, and what happens to it in heat and moisture.

Polypropylene is the common light duty strap. It has a moderate breaking strength, a comparatively high elongation and a tendency to creep, which means that under a load held for weeks it gradually extends and the tension with which it was applied falls away. It is inexpensive, it is available in a very wide range of widths and colours, and it is the normal choice for light loads, case level bundles and loads where the strap is a secondary aid rather than the primary restraint. It becomes brittle in cold conditions, where it can snap at the joint, and it is easily cut, which some buyers prefer at destination and some do not.

PET strap, often described as polyester strap, has a breaking strength approaching that of steel band at a fraction of the weight, with a much lower elongation and far better tension retention over a long voyage. It does not rust, which matters in a container that cycles between condensation and heat, it is safe to cut at destination, and it is recyclable. It is the usual choice for a palletised load of glass where the strap is doing real work, and it is the material that pairs well with compressible pads, because a low creep strap keeps its tension after the pads have settled.

Steel band is the material buyers most often reach for on the reasoning that more strength must be better, and on a load of glass it is usually the wrong answer. Steel has very high strength and almost no elongation, which means it cannot accommodate any settling at all. A few tenths of a millimetre of compression in the pads, a tray corner yielding slightly, or a carton settling under a stack is enough to leave a steel band slack, and a slack band is free to be moved by the load until it snaps tight against the pack edge during handling, which is the point at which it cuts. It also rusts in a container with condensation cycling, which stains labels and cartons, it demands the heaviest tensioning equipment and the most robust edge protection, and it is a genuine handling hazard when it is cut at destination because it releases stored energy. The material has legitimate uses on very heavy, dense, rigid loads where the customer’s own practice requires it, and where it is used it should always be paired with corner and edge protection. For a pallet of glass bottles on pads, PET is normally the sensible default and steel is the exception that has to be justified.

Within any of the three materials, the specification is not only the material name. Strap is quoted by width and thickness, and the two together with the material determine the breaking strength, while the material determines how much of that strength survives as tension after a month at sea. Recycled content changes the elongation and the creep, so a strap bought on price alone can behave differently from the one the machine was set up for. The joint strength also follows the material, since a weld that works on PET does not necessarily work on polypropylene. And the strap itself has storage requirements that are easy to overlook: a strap stored in a cold place becomes brittle and welds poorly, and a damp strap produces a weak weld, so storage and handling belong in the specification alongside the material.

One interaction is worth naming because it links two consumables. The strap and the layer pad are chosen together, not separately. A compressible pad under a strap of low creep is a stable combination, because the strap holds its tension as the pad settles. A compressible pad under a strap that creeps is a load that quietly loses its restraint in the first week of the voyage, which is the reason a soft pad and a soft strap should not be specified together on a long route. The separation behaviour of the pads themselves is set out on the glass bottle layer pad page, and the strap specification has to be read against it.

Manual, Semi-Automatic and Automatic Strapping: Where the Volume Threshold Sits

The machine class is a bigger commercial decision than the strap material, and it is usually taken late, after the palletizer and the wrapping machine have been bought. That order is a mistake, because the strapping station sits at the end of the dock cycle and its capacity sets the pace at which finished loads can leave the building.

Manual strapping means a hand tensioner and a sealer, or a dispenser that feeds the strap by hand. It suits low volume, mixed formats, awkward load shapes and any situation where the load is not square enough for a machine to handle. Its weakness is consistency rather than speed: tension is set by the operator’s judgement, so two apparently identical loads can leave with different restraint, and the variation only becomes visible when a particular load fails. Its costs are the labour per strap, the consumables and the physical effort, and its advantage is that it can be used anywhere on any format without a setup.

Semi-automatic strapping means a machine with an arch, where the operator positions the load and the machine tensions, seals and cuts the strap at the press of a control. It is a large step in consistency, because the tension is set at the machine rather than by the operator, and the cycle time per strap becomes predictable. It still needs an operator, and it needs the load to be presented at a consistent height and within a footprint the arch can accept, which is where the quality of the palletizing operation starts to matter more than the strap itself.

Automatic or in-line strapping removes the operator from the cycle. The load arrives on a conveyor or a pallet truck and the machine straps it without intervention, often with a rotating arm that applies several straps in one cycle. The requirement is a consistently square load at a consistent height on a consistent pallet format, and the top surface has to be predictable if a strap has to cross it. An automatic strapper cannot compensate for a palletizer that produces a leaning load or a pack with a variable height, which is why the strapping decision should be read against the stacking station rather than in isolation from it. That station and the layer pattern it builds are described on the glass bottle palletizer page.

The volume threshold between these three classes is not a single number and it should not be quoted as one, because it depends on the number of straps per load, the shift pattern, the labour rate and how much format variety the line has to absorb. What can be stated is the direction. As volume rises and formats settle down, the case for a machine strengthens, because the labour saved per strap rises with volume and the consistency benefit applies to every load. Where volume is modest but formats vary, a semi-automatic arch machine with an operator is usually the sensible intermediate step, because it buys consistent tension without demanding format standardisation. And where the load is handled by clamp truck after strapping, the tension consistency of a machine is often the cheapest way to reduce breakage, because a clamp squeezes the pack and an over-tensioned strap cannot absorb the extra load. The strongest argument for automating a strapping operation is frequently the breakage reduction rather than the labour saving, and that is a claim which can be measured on the actual load rather than assumed.

Strap Tension and Joint Type: What Has to Be Tested and Recorded

Tension is where a strapping programme is won or lost, and it fails in both directions. A strap that is too tight crushes what it crosses: the top edge of a carton collapses, a pad corner is pressed out, a bottle shoulder is chipped, and in the worst case a crack opens at the shoulder or the heel. A strap that is too loose does nothing at all: it fails to develop the friction between layers that resists shear, it does not hold the load onto the pallet, and it can simply fall away during handling. The working principle is that the strap should still be in contact after the load has settled, and it should be tight enough to develop restraint without being tight enough to damage the top edge of the pack. That is a band rather than a number, and the band is different for every load type.

Five variables move the tension that is appropriate for a given load. The first is how compressible the load is. Pads and cartons settle after they are loaded, so a load with pads will lose tension in the first hours after strapping, which means the initial setting has to account for the settlement, or the load has to be checked and re-tensioned after it has settled rather than at the moment it is strapped. The second is what the strap bears on at the top of the load. A carton corner or a tray edge needs a protector to spread the compression, and a load whose top layer is bare glass should not have a strap run directly across the shoulders at all, because the glass is the part that will be damaged first. The third is the creep behaviour of the strap material, which decides how much of the tension survives the voyage rather than just the handling. The fourth is the temperature over the route, since a load strapped in a cold yard and then held in a hot container experiences a different strap behaviour from one strapped and shipped in a stable climate. The fifth is the handling after strapping, because a clamp truck squeezes the load and a forklift can hook a strap that sits proud of the pack.

Measurement is what turns tension from an opinion into a specification. A strap tension meter, held against the strap and read at a defined point, is the only way to make the setting repeatable, and the record should state the unit and the point at which the reading was taken. A joint pull test on the samples from a run is the practical check on the joint, because the joint rather than the strap is the weak element. Where a load is strapped against a compressible layer, a second reading after the load has settled is more informative than the first, and it is the reading that shows whether the setting was correct or merely convenient.

The joint itself comes in two families. A friction weld, or heat seal, joins the two strap ends by melting them together. It is fast, it needs no consumable, and it is used by most arch machines and automatic strappers. Its strength depends on the cleanliness and dryness of the strap, the condition of the sealing elements and the setting of the machine, so a damp strap or a dirty strap produces a joint that looks acceptable and pulls apart under load. A metal buckle or seal clamps the two ends together mechanically. It tolerates a poor strap surface, it is easy to inspect by eye, and it costs a consumable and adds a metal item to the pack that can catch on handling equipment and that has to be disposed of at destination. Both are reliable when the machine is maintained and the process is specified, and both should be verified by pulling samples rather than by looking at them, because a weak weld and a strong weld look the same on a finished pallet.

Two path rules complete the tension picture. A strap should not be tensioned against a sharp edge, which in practice means the edge of a pallet deck board, the fold of a tray and the cut edge of a pad; a protector is what the strap bears on, and the protector is part of the specification rather than an improvised detail. And a strap should not be run across a gap in the pallet deck, because the strap will either crush the deck edge or deform across the gap and lose tension, so the strap positions should be chosen to land on deck boards or on the blocks rather than on the openings.

Audit and Documents: What a Strapping Specification File Has to Show

A strapping programme that works is a programme that can be audited, because the only way to tell whether a strap was applied correctly is to look at the record rather than at the finished pallet. The file that supports it has eight parts, and each one answers a question that a buyer or an inspector will eventually ask.

The first is a strap specification for each load type, naming the strap material, its width and thickness, the number and positions of the straps, the tension setting and the joint type. One document covering several load types is acceptable only if each load type is listed separately, because a specification written around a single load type and applied to a different one is the most common root cause of a failure. The second is the machine record: what machine is used, what maintenance interval it is on, and when the tension setting was last calibrated against a meter. The third is the tension and joint record: what was measured, on which load, by whom and when, kept as a running log rather than as a one-off sheet. The fourth is the material declaration for the strap, including whether it is virgin or recycled, because that is what determines the creep behaviour the machine was set up for.

The fifth is the strap storage condition, since a strap stored in a cold store or in a damp place does not behave as specified. The sixth is a set of photographs of the finished load, taken at the point of strapping, showing the strap positions relative to the pallet and the layer pattern and showing the corner treatment, because a photograph converts a statement into evidence. The seventh is the handling method used on the load after strapping, recording whether the load is moved by clamp, by fork or by hand, since a clamp truck applies a load that the specification has to anticipate. The eighth is a failure log: any load that arrived with a broken, slack or missing strap, together with what was changed as a result.

Some answers should raise a question rather than close it. A supplier who says that one strap is used for everything is describing a habit rather than a specification. A supplier who says that tension is set by feel is describing an uncontrolled variable. A supplier who says that the strap is only there to hold the film is describing a load whose restraint has not been thought through. A supplier who says that steel is used because it is stronger is applying a material reasoning that does not hold for a brittle product on a compressible base. And a supplier who reports no strap failures at all is either operating a genuinely well controlled process or not receiving the failure information, and the way to distinguish the two is to ask how the destination reports a problem back to the plant.

Load Type and Strap Specification: Reading the Table

The table below sets the common load types in a glass bottle supply chain against a starting strap specification and against the evidence a buyer should ask to see for that load type. It is a technical starting point rather than a quotation, and the row that matches the actual pack will normally narrow the answer to one or two configurations rather than settling it completely. Two warnings belong with it. A specification that works for a tray based load does not transfer automatically to a load of loose bottles, because the tray is a structural element that the strap can bear on and bare glass is not. And a load whose pack changes, through a new bottle, a new tray, a new pad or a taller stack, has changed the load type even if the strap has not changed, so the row has to be re-read rather than reused.

Four reading notes belong under that table. First, the material column is a starting point and the real specification depends on the breaking strength required, which follows from the load weight and the number of straps rather than from the material name alone. Second, position matters at least as much as material, so a table that answers the material question and leaves the positions unstated has answered half the question. Third, the strap interacts with the container loading operation, where the load is braced against movement inside the box, and that bracing is a separate restraint system with its own rules; it is treated on the glass bottle container loading page, and the two systems should not be asked to do each other’s work. Fourth, the strap specification should be re-read whenever the pack changes, and the change should be recorded, because an unchanged strap on a changed load is the most common way a working programme stops working.

Strap Position Against Pallet Format and Layer Pattern

Two families of strap position are in use, and they do different work. A vertical strap runs over the top of the load and down the sides, through the pallet, so it ties the load to the pallet and the load cannot slide off. A perimeter strap runs horizontally around the load above the pallet, so it binds the layers together as a unit without tying the load down. The choice between them follows from what the risk actually is. Where the load could slide off the pallet during handling, vertical straps are the answer. Where the load has to be bound as a unit but cannot be tied to the pallet, because the base is a slip sheet or a pallet format without strap openings, perimeter straps are the answer. Many loads use both, with vertical straps holding the load on the pallet and perimeter straps binding the upper layers.

Position relative to the pallet is not a detail. A vertical strap should pass through the pallet’s own strap openings, or through the gaps between the top deck boards, and it should land on a deck board or on a block rather than across an opening. A strap pulling across an opening either crushes the board edge or deforms across the gap and loses tension, and the load path through the pallet is weaker at exactly the point where it is loaded hardest. On a block pallet the strap is best aligned with the blocks, so the compression travels down the strongest part of the structure rather than through the unsupported span between them. The number of straps follows the load weight and the layer pattern rather than a fixed rule: a lighter load can be held on the pallet with two vertical straps, a heavier one normally needs four, and a load with a large footprint or an irregular top surface may need the pattern varied so that every strap bears on a structural element rather than on the middle of a layer.

The layer pattern decides how much the strap has to do. An interlocked pattern, where each layer is rotated against the one below, spreads lateral force through the stack and is comparatively stable on its own, so the straps are mainly holding the load onto the pallet. A column stack, where each bottle sits directly on the one below, is efficient in compression and less stable laterally, so it relies on the straps and on the pads for its resistance to movement and is the pattern most likely to lean if the restraint is inadequate. A divided layer pattern with pads is usually the most stable of the three, because the pads add friction at every interface, and that is the configuration in which the strap specification can be lightest. Layer pads, which are the subject of the layer pad page, are also where the strap compression lands at each layer, so a strap positioned over a pad corner compresses the pad rather than the glass, and a strap positioned over a bare shoulder compresses the glass rather than the pad.

Edge protection is the element that decides whether a correctly tensioned strap is harmless or destructive. Where a strap crosses a carton or a tray edge, a corner board or an edge protector spreads the compression over an area and prevents the edge from collapsing. Where the top of the load is bare glass, there is no edge to protect and the strap should not cross it at all: the specification should either use a rigid top frame or board that the strap bears on, which then has to be removed before the load is unloaded, or use perimeter straps only and accept that the load is not tied to the pallet. A strap run directly across the shoulders of the top layer of bottles is a breakage waiting for the first hard braking event, and it is also the single most common strapping mistake on a load that does not use a tray.

A load that will be unloaded by a vacuum head needs a further adjustment, because a strap crossing the top surface changes the top surface. The strap compresses the top pad at the corners, so the top of the load is no longer flat, and the vacuum cups no longer seal evenly across the layer. The strap also physically obstructs the head, which means it has to be cut before the head descends, and the cut ends have to be controlled so they do not catch in the machine. The cleanest specification for such a load is perimeter straps only, with the top surface left flat and free, supplemented where necessary by a wrap or hood for weather protection. Where a vertical strap is unavoidable, the top frame that it bears on has to be a rigid removable element, and the cutting and end handling become part of the unloading process rather than an afterthought at the machine.

Strapping and Wrapping in Sequence, and Which One Solves Which Problem

The order in which the strap and the film or hood are applied is decided by what each one is doing, and the distinction is worth restating because the two are frequently described as alternatives. A strap is a tensile member with a defined breaking strength and a tension that can be measured. It resists the layers moving relative to one another, and it resists the load moving relative to the pallet when it is a vertical strap. A stretch film or hood is a barrier and a light unitising aid: it keeps dust and rain off the load, it holds a load together through the cling and tension of the film, and it loses a substantial part of that restraining force as the film relaxes and as the temperature rises. The protective and weather side of that subject belongs to the glass bottle stretch hood page, and this page treats only the tensile tie.

From that difference the usual sequence follows: strap first, then wrap. The strap is applied while the load is still on the strapping station, which is the moment when the load is square and the pads are freshly laid, and the film or hood that goes on afterwards then protects the straps and stops them being hooked by handling equipment on the way to the container. This is the sequence that gives the most restraint for the least risk, and it is the default for pallet loads that will be moved by forklift or loaded into a container.

The reverse sequence, wrap first and strap over the film, is used deliberately in some situations and should be an explicit decision rather than an accident. It is chosen where the customer needs to see and cut the strap at destination, for example where a numbered or coloured strap functions as a security seal or where the receiving site inspects the load before accepting it, and where the film is genuinely only a dust cover. The trade-offs are real. A strap lying outside the film is exposed to snagging, it can abrade and tear the film at the corners, and it hides the film defect that would otherwise be visible. It also means that cutting the strap releases the outer film, so the two cannot be inspected independently.

There is a third case worth naming because it is the one that produces damage. A load that is wrapped but not strapped, and whose only restraint is the film, becomes unrestrained the moment someone cuts the film. In a container, in a yard, or at a destination where the film is opened with a knife along the side, the layers above the cut are free to move. That is not an argument against wrapping, which does its own job well. It is an argument for specifying what holds the load if the film is cut, and for stating in the packing document whether the load is restrained by straps or only wrapped, so that the person cutting the film knows which of the two they are dealing with.

Two related methods sit outside this page but are often raised in the same conversation. Anti-slip sheets raise the friction between the load and the pallet or between layers, which is a restraint route that adds friction rather than a tie, and it belongs with the layer and surface question rather than here. Shrink hooding and stretch hooding differ in how the film is fitted and heated, and both belong to the hood page. What belongs here is the narrow point that a strap and a film are not substitutes for one another, and that a load which uses both should specify both, including which one is expected to hold the load if the other is removed.

Where the Strapping Operation Bites the Loading Schedule

Strapping sits at the very end of the dock cycle, after the load is complete, and that position makes it the step that absorbs every delay from upstream. If the stacking line is short a pallet, if the pads have run out, if a load has been built to the wrong height or is not square, the consequence arrives at the strapping station, and the strapping station is the one that has to wait. That is why the strapping capacity should be sized against the peak rather than the average of the daily pallet count, and why a strapping machine that is exactly matched to the average will be a bottleneck on the days that matter.

Strap supply is the second schedule risk and it is easy to underestimate because the item is cheap. A strapping machine is built around a specific strap format, including the width, the thickness and the core size, so a substitute strap bought by appearance rather than against the machine may not run at all, or may run badly and produce weak joints. A strap that has run out stops the dock just as effectively as a machine that has broken, so the buffer held at the plant should be sized from the daily pallet count and the supplier’s lead time for the exact format, and the specification should be on file so that a replacement can be ordered against the machine rather than from memory. The same logic applies to the consumables of the joint: where a metal seal is used, the seal is a second stocked item that can run out independently.

Machine downtime has a specific shape at the end of a shift. A strapper has a tensioning wheel, a cutter, a sealing element and a control that all wear, and the failure usually appears as a joint that pulls apart or a strap that does not tension rather than as a machine that stops dead. A load discovered with a weak joint at the dock has to be opened, inspected, re-strapped and re-wrapped, and the re-work costs more than the strap by a wide margin, which is the argument for a service interval and for keeping a manual tensioner and sealer as a genuine fallback rather than as a formality.

The third schedule interaction is the one that is hardest to see and easiest to fix. Because the strapping step is last, it is where the quality of everything before it becomes visible: a load that is not square, a stack built to the wrong height, a pad missing from a layer, a tray with a collapsed corner. Measuring the dock cycle including the strapping step, and recording the reason each re-work happened, turns those upstream defects into data. The specification for the load, including the number of straps and the tension, should be re-checked whenever the pack changes, because a new bottle, a new tray or a new pad changes the settlement behaviour of the load and therefore changes the tension that should have been set.

Where the Strap Specification Ends and the Rest of the Pack Starts

This page has covered the strap as a restraint system: the audit questions that establish whether a specification exists, the three strap materials and why steel band is rarely the right default for glass, the split between manual, semi-automatic and automatic strapping and the direction in which volume and format consistency move the decision, the way tension and joint type have to be measured and recorded, the document set behind a strapping specification, the load types mapped against a starting specification, the positioning of vertical and perimeter straps against the pallet format and the layer pattern, the sequence between strapping and wrapping, and the way the strapping step affects the loading schedule.

The adjacent subjects are handled elsewhere and are not repeated here. The document that records the whole packaging requirement for an order, of which the strap specification is one line item, is the glass bottle packing specification. The film and hood side of load protection, including the weather and dust barrier and the condensation question, belongs to the stretch hood page. The separator between layers, which is the surface the strap compresses at each interface, belongs to the layer pad page. The forming of the tray, and the board grade that decides how much edge compression the strap can apply, belongs to the tray former page. The bracing of the load inside the container is a separate restraint system and belongs to the container loading page. And the treatment and marking of the wooden pallet itself is a phytosanitary and customs subject rather than a restraint one, and is treated on the wood packaging fumigation page, which is where the question about the wood should be asked rather than here. What remains here is the strap and the way it is applied.

Questions Buyers Ask About Glass Bottle Strapping

Is strapping enough on its own, or is wrapping still needed?

They solve different problems, so the honest answer is that a load usually needs both unless the requirement is clearly one sided. Strapping provides the tensile restraint that stops the layers moving and stops a vertical strapped load sliding off the pallet, and its tension can be measured. Wrapping provides the barrier that keeps dust and rain off the load and a limited unitising force from the tension and cling of the film. A load that is wrapped but not strapped is restrained only until someone cuts the film, which in a container or at a destination it eventually does. A load that is strapped but not wrapped is restrained and exposed. Where the route is dry and the load is fully enclosed in cartons, a wrap may be dispensable; where the route involves humidity, rain or an open yard, it is not.

Why is steel band not recommended for glass bottles?

Because it cannot accommodate movement. Steel has very high strength and very little elongation, so a small amount of settling in the pads, a tray corner yielding or a carton compressing leaves the band slack, and a slack band is free to shift until it snaps tight against the pack edge and cuts. It also rusts in a container where condensation cycles with heat and stains the labels and cartons around it, it needs the heaviest tensioning equipment and the most robust edge protection, and it stores energy that is released when it is cut at destination. PET strap reaches a comparable breaking strength at a fraction of the weight and keeps its tension far better, which is why it is the usual default for a palletised load of glass. Steel has legitimate uses on very heavy rigid loads where the customer’s own practice requires it, and there it should always be used with edge protection.

How tight should a strap be?

Tight enough to still be in contact after the load has settled, and tight enough to develop restraint, but not tight enough to crush the edge it bears on. That is a band rather than a number, and it is different for every load type, which is why the setting belongs in a written specification and the reading belongs in a log. The practical method is to set the tension at the machine, record the reading with the instrument and the measurement point, and then check again after the load has settled, because pads and cartons compress in the first hours after strapping. A load whose only tension reading was taken at the moment of strapping has no evidence about the tension it actually travelled with.

Do straps run over the top of the load or around the perimeter?

Both are used and they do different work. A vertical strap runs over the top, down the sides and through the pallet, so it ties the load to the pallet and stops it sliding off. A perimeter strap runs horizontally around the load above the pallet, binding the layers as a unit without tying the load down, and it is the route used when the load cannot be tied to the pallet, for example on a slip sheet. Position matters as much as direction: a vertical strap should land on a deck board or a pallet block rather than across an opening, and it should bear on a pad corner, a tray edge or a corner protector rather than on bare glass. Where the top of the load is bare glass, a strap should not cross it at all without a rigid removable frame for it to bear on.

Can a pallet load be strapped if it will be depalletized automatically?

It can, but the specification has to change. A strap crossing the top surface compresses the top pad at the corners, so the top of the load is no longer flat, and a vacuum head needs a flat surface for the cups to seal evenly. The strap also obstructs the head, so it has to be cut before the layer can be lifted and the cut ends have to be controlled. The cleanest route is perimeter straps only, with the top surface left flat and free, and a wrap or hood for weather protection. Where a vertical strap cannot be avoided, the rigid top frame it bears on should be a removable element and the cutting step should be written into the unloading procedure rather than improvised at the machine.

What should a strapping specification contain?

Eight things: the strap material and its width and thickness, the number and positions of the straps, the tension setting with the unit and the measurement point, the joint type, the edge or corner protection used, the sequence relative to the film or hood, the storage condition for the strap, and the inspection rule that says when a load has to be re-strapped. Alongside the specification there should be a log that records the tension and joint checks with the date, the load reference and the person who set the machine, and a photograph of a finished load for each load type. A specification that names the strap material but not the positions and the tension has described a product rather than a process, and a product description cannot be audited.

How many straps does one pallet load need?

It follows the load weight, the layer pattern and what the strap is expected to do, so there is no single number. A light tray based load held on the pallet is commonly restrained with two vertical straps, a heavier load with four, and a load with a large footprint or an irregular top may need the pattern adjusted so that every strap bears on a structural element rather than on the middle of a layer. Where the load cannot be tied to the pallet, perimeter straps at one or two levels replace the vertical ones, and where a tall stack tends to sway, a second perimeter level reduces the movement of the upper layers. The number should be justified against the load rather than inherited from the previous pack, and it should be re-checked when the pack changes.

Send the Case Format, the Pallet Format and the Daily Volume

To get a strapping answer that can be audited rather than a general recommendation, send three things. The case format, meaning whether the load is loose bottles on pads, bottles in trays, full cartons, returnable crates or a mixture, together with the layer pattern and the weight of the finished load. The pallet format, including the deck footprint, whether the pallet has strap openings, whether the top of the load is bare glass or covered, and whether the load is moved by fork, by clamp or by hand. And the daily volume with the shift pattern, together with the number of straps the current process applies per load, because that combination is what decides whether the sensible route is a manual station, a semi-automatic arch machine or an in-line automatic strapper.

With those in hand, the reply can set out the strap material and format suited to the load, the number and positions of the straps with reference to the pallet and the layer pattern, the tension band and the joint type, the edge or corner protection required, the sequence relative to the wrap or hood, and the inspection rule and records that make the specification auditable. The load types and specifications in the table on this page are orientation for planning rather than a quotation, and the specification that governs an order is the one agreed against the actual pack, the actual pallet and the actual handling route.