Polyester Cord Strappings And Lashings

1)Background
The first US commercial polyester fiber production was by Dupont Company in 1953. At that time, the polyester fibers were primarily used for fabric production.There was a growing movement to develop plastic strappings to replace the steel strappings that were widely used then.
Some time later in the 1950′s , the glue bonded polyester cord strapping was developed .At the early stage , these cord strappings were used for simple bundling of goods .The woven strapping was also developed at about the same time frame.In the 1960′s , the composite strapping was developed .By the 1990′s ,  cord strappings have made major technical advances to largely replace steel strappings in most applications.

2) Types of Cord Strappings
There are 3 main types of polyester cord strappings depending on their manufacturing processes:

2.1 Glue-Bonded Cord Strappings

The linear polyester yarns are held in band by hot-melt glue .This strapping has a soft and tacky feel . Comes only in natural color.

 

2.2 Woven Cord Strappings

These are woven from high tenacity polyester yarns and can come in any colour. The woven strapping is soft ,lightweight and flexible .

Woven polyester cord strapping

  

  

2.3 Composite Cord Strappings

The linear polyester yarns are co-extruded with polyethylene to produce a stiff strapping band .Only comes in natural colour.

Composite cord strapping

    

The 3 types of cord strappings are interchangeable  in usage. It is just a marketing strategy by manufacturers to diffentiate themselves in order to compete better. Individual customers may have preferences for a particular type based on their individual  opinion. 

3) Properties

All polyester cord strappings and lashings share the same properties :

3.1 Safe

       It has no sharp edges and does not spring back when cut under tension .

3.2 Strength

       It is really strong as steel !

3.3 No damage to products

       As it is soft and flexible , it does not damage the product being bundled.

3.4 Rot-proof

        It does not rot or stain .

3.5 Lightweight

        It is at least 5 times lighter than the corresponding steel strapping.

3.6 Absorbs Shock Better

       With about 10% elastic elongation, it can absorb shocks very well .

3.7 High system Strength

       When used with a steel wire buckle it provide high system strength and can be retensioned at any time.

3.8 Creep Resistance

       Once tensioned it retains its tension.

4) Performance

     4.1 Linear Break Strength (Tensile Strength)

     The most common measure used is the linear break strength where a length of the strapping is pulled till failure .

     This is following the ASTM standard. 

     4.2 System Strength

     The Europeans decided that the system strength is a better measure as it tests the whole loop including the buckle

     which is how the strapping is used.The system strength shall be double the linear break strength if the buckle is

     100% efficient.

     system strength test

    4.3 Energy To Break

    The latest trend is that the energy to break is the most complete measure of strength . This measures the energy

     required to break the strapping . It is the area under the curve in the force-elongation graph.

     Energy to break graph

   4.4 Joint Strength

   In all applications , strappings have to be joined together into a loop. The joint is also the weakest link in the loop.

   The common jointing methods are heat seal, crimps , seals and buckles. For the polyester cord strappings , buckles

   are the only means of forming strong joints.There are two main types of buckles being used for cord strappings and

   lashings :

   i)Wire buckles are used for strappings up to 32mm width .

  ii) Welded rectangular buckles are used for lashings of width 32mm and above. Buckles with hooks or cam buckles

  may also be usedwhen lashings are used to tie down cargo loads for transportation.

 

Wire Buckles And Welded Buckles

   

    

     

  

 

   

   The joint strength is normally called the buckle efficiency which is the measured system strength divided by twice

    the linear break strength and given in percentage.

    Buckle Efficiency = (Measured system strength / 2 x Linear break strength)      x 100%

    The buckle efficiency normally range from 75%- 95% , depending on how well the buckle is designed and produced.

   4.5 Creep

   Strappings are expected to maintain its applied tension around the goods over time. Unfortunately, it is a natural

   phenemenon for tensioned strapping systems to lose strength over time and this is called creep . It has been shown

   that the corded polyester strapping with wire buckle system has less than 10% creep and is far superior to other

   strapping and jointing systems.

   Decrease of tension over time

  4.6 Shock Absorbency

  The polyester strappings have an elastic elongation of about 8-12 %. During the elastic elongation phase ,

  the tensioned strapping will return to its original state once the  tension is released. In application , this acts as a

  shock absorber to absorb sudden load and return to the normal state once the shock  is over.

  5) Accessories

  5.1 Tensioners

  A tensioner (either manual, pneumatic or automatic) is used to tension the strapping looped around the

  goods .Tensioners come in various sizes to suit the strapping width.

 

Manual tensioner

   

 

   5.2 Wire Buckles

   The buckles also come in various sizes to suit the width and breaking strength of the strapping .These buckles  have

   either galvanized or phosphate treament finishing. The phosphated buckles (  dull blackish color)are slightly more

   expensive but have better slip resistance as the phosphate treatment gives a rough finish to the surface of the buckle.                                            

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