Information
on Strapping

To help you understand strapping and choose the right product, you may find the following information usefulStrapping was
originally made of steel, which is extremely strong, has low stretch and is
heat- and UV-resistant, but also has limitations. It is heavy, easily corrodes,
has poor stretch recovery and when it is cut under tension, presents a safety
risk. Its applications were therefore limited.

Just over
fifty years ago, plastic strapping began to emerge as an alternative to steel
and as it was developed so its potential uses increased. Friction welding made
it possible to seal strap without having to manually apply a separate buckle or
seal, and automated strapping systems could be integrated within high-speed
production lines. Expensive nylon strap was replaced with more economical
polypropylene and stronger polyester became a viable alternative to steel. Woven
polyester cord strapping became popular for applications where the harsher
surface of extruded plastic strapping could cause damage.

Let’s take a
look at the types of plastic strapping now available, their pros and cons and
the applications they’re most suited to.

Polypropylene

The majority
of plastic strapping used today is oriented polypropylene – cheap and suitable
for most light- to medium-duty strapping, compatible with a wide range of
manual tools and automatic or semi-automatic tools and machines.

Polypropylene
strapping
has relatively poor UV resistance and so should be
avoided for outdoor storage. UV resistance is reduced if the strap is a lighter
colour, so most strap is black or blue.

It should
also be noted that polypropylene loses 50% of its tension within two hours of
being applied, more quickly in warmer ambient temperatures. It also has poor
memory and will not recover its original dimensions when placed under
additional tension. This makes it unsuitable for heavy materials such as brick
and block, or for pallet loads that are inclined to shift during transport.

Polyester also called PET

Oriented
polyester strapping
may appear similar to polypropylene, but it
has quite different characteristics that make it more suitable for heavier
applications and a preferable alternative to steel. It is lighter, doesn’t
corrode or stain, is safer when cut under tension and has a good memory that
retains tension and will continue to securely hold a load even after movement
or impact. It is also considerably cheaper than steel.

Polyester is
also suited to a wide range of manual tools and some automatic and
semi-automatic tools and machines. It is suitable for most applications where
steel has formerly been used, such as construction materials, shipping crates
and the like.

Polyester
cord

Strands of
polyester fibre, either woven or bonded together, create straps that are
flexible yet strong, soft yet abrasion-resistant. These fall into three
categories:

Woven cord
strapping
is a cost-effective and safer alternative to steel
strapping, offering bi-directional strength and split-resistance for harsher
environments and suitable for securing heavy loads.

Composite
cord strapping
lacks some of woven cord’s bi-directional
strength and split-resistance but is coated with clear polypropylene. This
coating enhances its water resistance and makes it more rigid – a boon when
feeding it through pallet frames and through metal buckles.

Hotmelt cord
strapping
is an inexpensive product for general purpose use.
Bale press strapping is a variation of hotmelt cord used in automatic bale
press machines for bundling waste materials destined for recycling.

Unlike
oriented polypropylene and polyester strapping, which is secured with a crimped
seal or friction weld joint, polyester cord straps use a plastic or metal
buckle. Both ends of the strap are fed through opposite sides of the buckle and
tension is applied manually or with a hand operated tensioner. The buckle locks
onto the strap to prevent it from loosening, but if the strap stretches or the
load contracts, additional tension can be applied without having to re-strap
the load.

Cord
strapping also has another unique feature – system strength. All strapping has
what we call break strength, or break strain; this is the maximum force that
strap will sustain under tension before breaking. The break strain of cord
strapping is lower than that of oriented strapping, but the combination of the
strap and the buckle (system strength) almost double the break strain of the
strap alone. That’s why, when you are choosing corded strapping, you should
compare system strength as well as break strain.National Packaging Supplies can offer a wide range of strapping systems suitable for a variety of applications.If you have any questions please contact us through e mail, sales@nationalpackagingsupplies.com, or by phone, 087 181 1173.

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