Strapping
Encyclopedia
Strapping, also known as bundling and banding, is the process of applying a strap
to an item to combine, hold, reinforce, or fasten it. The strap may also be referred to as strapping. Strapping is most commonly used in the packaging industry.
or various plastic
s.
es for steel strap include: paint
, paint and wax
, bluing
or zinc and wax. The wax is used to better transmit the tension around the bundle and for use with certain types of tensioners. Common applications include steel coils, bundles of metal, baling wire
, brick
s and pavers
, and roll end-binding.
What is not generally known to end users is that polypropylene strapping will lose about 50% of the applied tension within one hour, and that this tension loss is accelerated with increases in ambient temperature, consequently although suitable for packs with a degree of stored energy that will take up any relaxtion that occurs in the strap, unacceptable strap slackness may occur after time if used on product that is 'Solid' such as bricks or concrete. Further more polypropylene strapping is susceptible to UV degradation and can quickly degrade if left outside exposed to the elements.
There are specialized types available for specific applications. For instance, in cold climates a strap bonded in hot melt glue is used because it is weather-proof.
of the three plastics, however it is rarely used due to its high price. In the past nylon strap used to be very popular, but over time polyester has replaced almost all of its use. One application that still uses this type of strap is cold room applications, because it does not creep
as much as the other types of plastic.
strap is used to strap paper products between industrial processes. This allows the bundle to be introduced into the process without the need to cut the straps, which can lead to the product falling apart prematurely.
Strapping is most often used in complete horizontal or vertical bands. Edge protectors are used to help spread the load at corners and reduce damage to the load by the tensioned strap. Strapping can also be used in loops attached to holding locations on rail cars, skids, etc.
. Seals come in various shapes depending on the application; some can be put on after the strap is tensioned, while others must be installed before tensioning. To create the seal, the seal and strap are notched on both sides; if one set of notches are created then it is called a single notch joint, if two sets of notches are created then its called a double notch joint. Crimp joints also use a seal, but crimp undulations are used instead of formed notches. These crimps form great frictional forces which keep the joint from seeping. Seal-less joints are created by forming interlocking keys into the middle of the strap.
Plastic strap is most commonly joined by melting the straps together by adding heat to the joint. For lighter gauge strap, usually 16 mm (0.62992125984252 in) and narrower, heat is introduced with a hot knife
system. First, the hot knife moves in between the straps. Then a platen
comes up and compresses the straps and hot knife against an anvil on the order of tens of milliseconds. The platen then drops and the hot knife is removed. After the hot knife is completely clear of the straps the platen comes back up and compresses the joint so that the melted portions of the strap mix together and harden.
For thicker plastic strap, usually 9 mm (0.354330708661417 in) and wider, friction is used to create heat within the joint. The process starts with the strap compressed between the platen and the anvil. There is a vibrator built into either the platen or the anvil, which has teeth; there are also teeth on the opposite component that does not move. The vibrator is quickly vibrated, which creates enough heat to melt the interface between the two strap, because of friction. To complete the weld the vibrator is stopped and the pressure held until the joint has solidified.
It may also be joined manually by crimping a seal or via a buckle.
The joint is the weakest part of the system, therefore the type of joining method used is very important if strength is an issue. The strength of a joint is defined as the force required to break the strap in uniaxial tension. This is then compared to the uniaxial strength of the strap and recorded as the percent difference (e.g., a sample of steel strap may have a 5000 lb (2,268 kg) break strength and the seal may fail at 3000 lb (1,360.8 kg), so the seal is said to have a 60% strength). Hot knife welds have a minimum break strength of 55%. Friction welds have a minimum break strength of 65%. Metal clips 33%.
to stop the inertia
of the coil to keep the strap from over-running onto the floor. Dispensers used on strapping machines have multiple pulleys to act as a way to store strap in a way that can be quickly dispensed. This is required otherwise the strapping machine will draw the strap faster than the dispenser can pay off.
Within hand tools there are manual and automatic tools. Manual tensioners and crimping systems are available for low volume applications. Automatic hand tools are used for higher volume applications. Automatic tools are available using a battery
power source or compressed air
. Both manual and automatic tools are available as combination tools, which perform the tensioning, sealing and cutting, or as separate tensioners, sealers, and cutters. Manual sealers for plastic strap always use a seal and a crimp joint. Manual and automatic hand sealers for steel can use a seal or a seal-less joint. Automatic hand for plastic strap use a friction weld.
Strapping machines, also known as bundlers, are used for high volume applications or special applications. They are available in horizontal and vertical orientations, however the vertical orientation is far more common. They are also available in bottom seal, side seal, and top seal orientations, which define where the joint is located on the bundle. They are available in semi-automatic and automatic varieties. The automatic versions are designed to be used inline with conveyor systems. A photoeye is used to detect when the bundle is in the correct location, stop the conveyors, and activate the strapping machine.
Strap
A strap, sometimes also called strop, is an elongated flap or ribbon, usually of fabric or leather.Thin straps are used as part of clothing or baggage, or bedding such as a sleeping bag. See for example spaghetti strap, shoulder strap...
to an item to combine, hold, reinforce, or fasten it. The strap may also be referred to as strapping. Strapping is most commonly used in the packaging industry.
Types of strap
Strap is a flexible flat material, most commonly made from steelSteel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
or various plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
s.
Steel
Steel is the oldest and highest tensile strength strapping. It is available in a variety of widths and thicknesses as well as variations in the grade of steel. Steel is used for heavy duty holding where high strength and minimal stretch are desired. Surface finishSurface finish
Surface finish, also known as surface texture, is the characteristics of a surface. It has three components: lay, surface roughness, and waviness.-Lay:...
es for steel strap include: paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
, paint and wax
Wax
thumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...
, bluing
Bluing (steel)
Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface...
or zinc and wax. The wax is used to better transmit the tension around the bundle and for use with certain types of tensioners. Common applications include steel coils, bundles of metal, baling wire
Baling wire
Baling wire, otherwise known as "farm wire" or "soft wire," is used in an agricultural setting and industrial setting for everything from mending fences to manually binding square bales of hay, straw, or cut grass...
, brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...
s and pavers
Paver (flooring)
An interlocking concrete paver is a pre-cast piece of concrete or brick commonly used in exterior hardscaping applications. Pavers were developed in Europe and introduced into the United States in the early 1970s....
, and roll end-binding.
Polypropylene
Polypropylene strap (oriented or tensilized) is an economical material designed for light to medium duty unitizing, palletizing and bundling. It is available in various widths, thicknesses, and polymer variations (e.g., copolymers). Some polypropylene is embossed or printed. This product offers high elongation at break but tends to have irrecoverable dead stretch with constant stress.What is not generally known to end users is that polypropylene strapping will lose about 50% of the applied tension within one hour, and that this tension loss is accelerated with increases in ambient temperature, consequently although suitable for packs with a degree of stored energy that will take up any relaxtion that occurs in the strap, unacceptable strap slackness may occur after time if used on product that is 'Solid' such as bricks or concrete. Further more polypropylene strapping is susceptible to UV degradation and can quickly degrade if left outside exposed to the elements.
Polyester
Oriented or tensilized polyester and nylon are the strongest plastic strapping products and are used as a viable alternative to steel strapping in the some industries. Polyester provides excellent retained tension on rigid loads. Its excellent recovery properties help a load absorb impact without strap breakage.There are specialized types available for specific applications. For instance, in cold climates a strap bonded in hot melt glue is used because it is weather-proof.
Nylon
Nylon strap has the greatest specific strengthSpecific strength
The specific strength is a material's strength divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity is the usual measure of specific strength...
of the three plastics, however it is rarely used due to its high price. In the past nylon strap used to be very popular, but over time polyester has replaced almost all of its use. One application that still uses this type of strap is cold room applications, because it does not creep
Creep
Creep may refer to:* CREEP, the Committee for the Re-Election of the President, associated with the Watergate scandal of U.S. president Nixon's administration....
as much as the other types of plastic.
Corded and woven
Corded and woven strapping are available in several constructions, primarily involving polyester and rayon. Some types are reusable. Because this system uses a buckle for a joint, corded and woven strapping can have a larger system strength than steel banding. Corded polyester strapping also has a higher elongation than other strapping systems, which gives it an ideal memory for sea and rail shipments. Because corded and woven polyester is light and soft, it is also a safer alternative to steel banding.Paper
PaperPaper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
strap is used to strap paper products between industrial processes. This allows the bundle to be introduced into the process without the need to cut the straps, which can lead to the product falling apart prematurely.
Composite
Composite strapping has filaments embedded in it. In the load securing industry it is often referred to as “synthetic steel”. It is very abrasion resistant and has the highest joint efficiency when used with a buckle. Both advantages are not affected by climate.Uses of strapping
Examples include:- Bundling items together for handling and shipment: newspapers, pipe, lumber, concrete block, etc.
- Attaching items to palletPalletA pallet , sometimes called a skid, is a flat transport structure that supports goods in a stable fashion while being lifted by a forklift, pallet jack, front loader or other jacking device. A pallet is the structural foundation of a unit load which allows handling and storage efficiencies...
s, skids, and crateCrateA crate is a large shipping container, often made of wood, typically used to transport large, heavy or awkward items. A crate has a self-supporting structure, with or without sheathing. For a wooden container to be a crate, all six of its sides must be put in place to result in the rated strength...
s - Reinforcing wooden boxWooden boxA wooden box is a container made of wood for storage or as a shipping container.Construction may include several types of wood; lumber , plywood, engineered woods, etc...
es, crates, and corrugated boxes, such as gaylords - Attaching items to flatcars, flatbed semi-trailerSemi-trailerA semi-trailer is a trailer without a front axle. A large proportion of its weight is supported by a road tractor, a detachable front axle assembly known as a dolly, or the tail of another trailer...
s, - Securing a unit loadUnit loadA unit load combines individual items or items in shipping containers into a single "unit" that can be moved easily with pallet jack or forklift truck...
of bricks, packaged glass, metal parts, etc. - Closing corrugated boxes and shipping containerShipping containerA shipping container is a container with strength suitable to withstand shipment, storage, and handling. Shipping containers range from large reusable steel boxes used for intermodal shipments to the ubiquitous corrugated boxes...
s - Securing coils of steel or paper
- Holding bales of agricultural products or textiles
- Load securingLoad securingthumb|Cargo damage because of improperly secured cargoLoad securing, also known as cargo securing, is the securing of cargo for transportation. According to the European Commission Transportation Department “it has been estimated that up to 25% of accidents involving trucks can be attributable to...
items within intermodal containerIntermodal containerAn intermodal container is a standardized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system...
s, boxcarBoxcarA boxcar is a railroad car that is enclosed and generally used to carry general freight. The boxcar, while not the simplest freight car design, is probably the most versatile, since it can carry most loads...
s, and semi-trailers
Strapping is most often used in complete horizontal or vertical bands. Edge protectors are used to help spread the load at corners and reduce damage to the load by the tensioned strap. Strapping can also be used in loops attached to holding locations on rail cars, skids, etc.
Joining methods
After the strap is tensioned, the strap is often sealed to itself. Steel strap is sealed with a seal and notch joint, a seal and crimp, seal-less joint, or via weldingWelding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
. Seals come in various shapes depending on the application; some can be put on after the strap is tensioned, while others must be installed before tensioning. To create the seal, the seal and strap are notched on both sides; if one set of notches are created then it is called a single notch joint, if two sets of notches are created then its called a double notch joint. Crimp joints also use a seal, but crimp undulations are used instead of formed notches. These crimps form great frictional forces which keep the joint from seeping. Seal-less joints are created by forming interlocking keys into the middle of the strap.
Plastic strap is most commonly joined by melting the straps together by adding heat to the joint. For lighter gauge strap, usually 16 mm (0.62992125984252 in) and narrower, heat is introduced with a hot knife
Hot knife
Hot knife may refer to:* A tool with a heated blade, used to cut materials* Hot knife , a method of smoking hashish...
system. First, the hot knife moves in between the straps. Then a platen
Platen
A platen is typically a flat metal plate pressed against a medium to cause an impression in letterpress printing...
comes up and compresses the straps and hot knife against an anvil on the order of tens of milliseconds. The platen then drops and the hot knife is removed. After the hot knife is completely clear of the straps the platen comes back up and compresses the joint so that the melted portions of the strap mix together and harden.
For thicker plastic strap, usually 9 mm (0.354330708661417 in) and wider, friction is used to create heat within the joint. The process starts with the strap compressed between the platen and the anvil. There is a vibrator built into either the platen or the anvil, which has teeth; there are also teeth on the opposite component that does not move. The vibrator is quickly vibrated, which creates enough heat to melt the interface between the two strap, because of friction. To complete the weld the vibrator is stopped and the pressure held until the joint has solidified.
It may also be joined manually by crimping a seal or via a buckle.
The joint is the weakest part of the system, therefore the type of joining method used is very important if strength is an issue. The strength of a joint is defined as the force required to break the strap in uniaxial tension. This is then compared to the uniaxial strength of the strap and recorded as the percent difference (e.g., a sample of steel strap may have a 5000 lb (2,268 kg) break strength and the seal may fail at 3000 lb (1,360.8 kg), so the seal is said to have a 60% strength). Hot knife welds have a minimum break strength of 55%. Friction welds have a minimum break strength of 65%. Metal clips 33%.
Equipment
There are two major types of equipment available for strapping: hand tools and strapping machines. A dispenser is used with both types of equipment to dispense the strap. Some strapping machines have the dispenser built-in, others have a separate powered dispenser, which can automatically load or thread new coils. Non-powered separated dispensers have a pulley which releases and activates a brakeBrake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
to stop the inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
of the coil to keep the strap from over-running onto the floor. Dispensers used on strapping machines have multiple pulleys to act as a way to store strap in a way that can be quickly dispensed. This is required otherwise the strapping machine will draw the strap faster than the dispenser can pay off.
Within hand tools there are manual and automatic tools. Manual tensioners and crimping systems are available for low volume applications. Automatic hand tools are used for higher volume applications. Automatic tools are available using a battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
power source or compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....
. Both manual and automatic tools are available as combination tools, which perform the tensioning, sealing and cutting, or as separate tensioners, sealers, and cutters. Manual sealers for plastic strap always use a seal and a crimp joint. Manual and automatic hand sealers for steel can use a seal or a seal-less joint. Automatic hand for plastic strap use a friction weld.
Strapping machines, also known as bundlers, are used for high volume applications or special applications. They are available in horizontal and vertical orientations, however the vertical orientation is far more common. They are also available in bottom seal, side seal, and top seal orientations, which define where the joint is located on the bundle. They are available in semi-automatic and automatic varieties. The automatic versions are designed to be used inline with conveyor systems. A photoeye is used to detect when the bundle is in the correct location, stop the conveyors, and activate the strapping machine.
Further reading
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
Standards
- ASTM D3953 Standard Specification for Strapping, Flat Steel and Seals
- ASTM D3950 Standard Specification for Strapping, Nonmetallic (and Joining Methods)
- ASTM D4675 Standard Guide for Selection and Use of Flat Strapping Materials