Comparison of composite strapping with woven polyester cord strapping

Comparison of Woven And Composite Polyester Strapping

Loading Plans Using Dunnage Bags

1) Loading Plans
It is recommended that a loading plan be drawn up before loading the container and installing the dunnage bags.This will ensure that the cargo loads are correctly placed and the dunnage bags installed in the right locations.Any potential problem would have been highlighted and resolved at the planning stage resulting in smooth container loading operation.The same loading plan can be re-used for similar cargo loads.
It is also recommended that a few photographs be taken of the container stuffing at the half-way stage and final stage.One of the photograph should be with one of the container doors closed displaying the container no. These should be filed with the loading plan together with relevant information such as date, time, cargo type ,lot no. and loading staff involved. These pictures and information are available for review in case of any problem at the destination and also for study and future improvement .

2) Typical Loading Plans

2.1)Loose Carton Boxes And Tins

       Example 1 – Loose Carton Boxes

Loading Plan for Loose Cartons 220311

Dunnage Bag Holding The Carton Boxes Inside The Container

Securing Loose Cartons In Container With Dunnage Bags

                                                                                                                                                                                                                                                            

          Example 2 – Securing Loose Tins Inside the Container Using Dunnage Bags

          Loading Plan for Tins 220311

         

Securing Loose Tins Inside The Container Using Dunnage Bags

        

Securing Loose Tins Inside A Container

                                                                                                                                                                                                                                           2.2)Palletised Cargo Load

       Example 1

       Cargo Securement Plan For Palletized Cargo Load 230311          

       Example 2

       Cargo Securement Plan For Palletized Cargo Option 2 230311

       Example 3

       Cargo Securement Plan For Palletized Cargo Option 3 230311

       

Securing palletised cargo loads with dunnage bags

 

Securing palletised cargo loads with dunnage bags

                                                                                                                                                                                                                                            

2.3) Cargo Loads In Crates

         This is similar to palletised cargo except that the cargo load is very heavy or fragile and so need extra protection from the crates.

        

 

Securing crated cargp loads with dunnage bags

                                                                                               

Heavy crates secured with dunnage bags

                                                                                                                                                                                                                                           2.4) Big Bags

        Normally these are palletised before loading into the container .

        Example:

        Loading Plan for Big Bags 240311

       

Securing big bags with dunnage bags

                                                                                                                                                                                                                                                        2.5) 25-kg Bags

       If these are palletised , then this category of cargo load can be treated like palletised cargo. Sometimes , these bags are manually stuffed into the 20-footer container. In this case, the stacking method is also important .It pays to make full use of the alternating stacking pattern together with dunnage bags to ensure the cargo loads are safely secured inside the container.

      Example:

      Loading And Securement Plan For 25kg bags 280311 

      

     

Securing 25-kg bags with dunnage bags

     

     

       

     

    

                                                                                                                                                                                                                                           2.6) Cargo in roll form

         Example:

       

Securing rolls of plastic waterproofing sheets with dunnage bags

     2.7)  Jerrycans

                Example:

               

Securing jerrycans with dunnage bags

3.0) Conclusion

          There is no one best method to secure the cargo loads inside the container.It depends on the weight, shape, quantity and how the cargo loads are bundled together.  Just remember that the dunnage bags can be installed: a)between cargo loads  b)at the sides between the cargo loads and the sides of the container and c)at the top between the cargo loads and the roof of the container. The only forbidden place to install the dunnage bag is between the cargo loads and the doors . Installing a dunnage bag here is difficult and dangerous to the person opening the door at the destination.

Paper Dunnage Bags Versus Woven Polypropylene Dunnage Bags

There has always been an ongoing debate as to which is better. To answer this, we need to look at the background of the development of the dunnage bags.
The paper dunnage bag was introduced in the 1950′s and was a big advancement over the 1st generation rubber dunnage bag. It is lighter,easier to use, and much cheaper so it can be discarded after each use. There is no need to collect back the dunnage bags at the  destination for re-use.
In step with the advancement of plastic technology , plastic has quickly replaced paper in most areas . So in the 1990′s the 3 rd generation woven polypropylene (WPP) dunnage bag was introduced. The WPP dunnage bag quickly gain acceptance and has since grabbed the lion’s share of the dunnage bag market.It’s  advantages over the paper dunnage bag are lighter, stronger, waterproof and cheaper .

The paper dunnage bag supporters have put up the following major arguments :

1)We have used paper dunnage bags for decades and have no problem with them.

2)The paper dunnage bag is thicker and heavier so it can resist puncture better.

3)The surface of the wpp dunnage bag is smoother so it can easily slip out during transportation .

4)The paper dunnage bag is more resistant to chemicals.

Nothing can be done about Argument #1 so we move on to the other 3 arguments.

Paper Dunnage Bags Are More Puncture Resistant

All types of dunnage bags are filled with compressed air and so can be punctured by sharp objects . To minimise the risk , it is recommended that the user take the following precautions :

1. Remove or cover any sharp edges that may come into contact with the inflated dunnage bag during container stuffing.

2. Sandwich the dunnage bag between 2 sheets of cardboard , plywood or chipboard ( new or recycled) before installing it between the cargo loads. The boards also serve to distribute the pressure evenly onto the cargo loads.

The Surface Of The WPP Dunnage Bag Is Smoother So It Can Easily Slip Out

There are 2 possible scenario where the dunnage bag,whether paper or wpp, can slip out during transportation:

1. Installing 2 dunnage bags side-by-side as the void between the cargo loads is too big. This is a no-no in installing the dunnage bags as during transportation the rocking and vibrations will cause one of the dunnage bags to slip out. If the void is too big, user may need to install one dunnage bag on either side of the cargo load(s). Or use solid void fillers to reduce the void size before installing the dunnage bags.

2. Underinflation.If the dunnage bag is under-inflated , then it will slip out during transportation . It needs to be inflated until the cargo loads on both sides are pressing hard against it thus holding it in place even during transportation.

The Paper Dunnage Bag Is More Resistant To Chemicals

Both the paper and wpp dunnage bag contain an inner PE liner bag which holds the compressed air during inflation. This liner bag is about 1 micron thick.If the chemical is corrosive , both types of bag will be damaged .Anyway, there are special guidelines governing transportation of hazardous chemicals as there are great risk to the people handling them .

The WPP dunnage bag is the market leader by a wide margin and growing . So, the majority of the users must be onto something . It pays for us to take note of the trend. The end user has to look at his situation objectively and evaluate which  bag is most cost effective for him. Dunnage bags are added overhead cost and need to be managed as well.

Is lamination necessary for polywoven dunnage air bags?

Historical Background
The lamination process is a carry-over from the FIBCs and big bags which came into being in the 1960s.These bags were used to hold flowable materials like food grains, plastic resins, animal food pellets and powder like cement .The lamination helps to prevent the contents from leaking out and dirt & mosture from seeping in. In the process, a plastic film (PP or PE)of thickness from 0.02 – 0.06mm is laminated onto the surface ( inner, outer or both) of the bag using heat.

What does the lamination do to the dunnage bag?
It does not contribute anything to enhance the performance of the dunnage bag. On the contrary , it adds about 3-5% to the cost of the bag.
Some quarters claim that with lamination the polywoven dunnage bag is stiffer and therefore easier to hold in place during inflation .We have always recommended that the uninflated bag (both polywoven and paper types) be ‘sandwiched” between two pieces of cardboard ( used or new) before inflation . This will make it easier to hold the bag in place during inflation and also prevent the inflated bag from being punctured by any sharp edge or point from the pallet or cargo load.

Training On Using The Dunnage Bag

Dunnage Bag Training

Using Plastic Slip Sheets To Replace Pallets

1) What is a slip sheet?

 The slip sheet is used as a portable material handling base for storage and transportation of unitized goods. It is actually a thin sheet ( from 0.5mm to 2.5mm) made from solid fibre , corrugated board or plastic materials.

Typical solid fibre slip sheet

  Typical Plastic Slip Sheet

2) Background

After World War II , the wooden pallet has become the primary portable platform/base  for the movement and storage of goods  in the advent of containerization.

However , shippers are always looking for innovative ways to reduce cost and receivers are searching for ways to reduce trash disposal costs.The large US food processors were the first industry group to adopt slip sheets during the 1970′s .The slip sheet was developed by such companies as General Foods and Quaker Oats for shipment of their goods.

The first slip sheets were made from solid fibre and later corrugated kraft liner medium . A little later the plastic slip sheet made its appearance.

The “green” movement to reduce usage of wood and the implementation of the ISPM15 (Regulation of Wood Pacakaging Material in International Trade) has led to exporters shifting to other portable bases such as slip sheets, paper pallets, pressed wood pallets and plastic  pallets.

3) Construction of the plastic slip sheet

This can be made from any kind of combination of polmerized material , including but not limited to polyethylene or polypropylene that provide adequate tensile strength . Most of the plastic material used are recycled. The most common method of production is by extrusion.

4) Specifications

4.1 Tensile Strength

This is the strength per unit cross-sectional area.It will determine how thick a slip sheet need to be in order to support a given payload. For practical purposes, it is given as thickness versus load capacity  . For example , a typical PE slip sheet will have the following load capacities versus thickness:

          Thickness (mm)                            Load Capacity (tonne)

                 0.7                                                    1.0

                 0.9                                                    1.2

                  1.1                                                   1.5

                  1.6                                                   2.0

                  2.2                                                   3.0

4.2 Coefficient Of  Friction

The side of the slip sheet where the goods sit on must have high slip resistance so that the goods will not slide off during loading, unloading or movement.However, the reverse side has to be smooth so that the loaded slip sheet can slide on the floor /pallet smoothly during loading and unloading . The standard measure of slip resistance is known as the coefficient of friction where the higher value signifies a higher slip resistance.

In practice ,one side of the slip sheet is embossed with a criss-cross pattern to increase the friction while the opposite side is smooth. Typical coefficient of riction values for plastic slip sheets are :

Side                                           Coefficient of friction

Embossed face(rough)                           0.5+

Smooth face                                       0.2 – 0.3

5.0) Pull Tabs 

Pull tabs are areas at the edges of  the slip sheet where the gripper clamps on during loading and unloading . More tabs will allow the handling equipment to approach the loaded slip sheet  from more sides (very much like the 1-way,2-way 4-way entry pallet concept).

Typical tabs & scoring for solid fibre slip sheets

        Typical Plastic Slip Sheet Dwg 140709

5.1 No. of tabs

There are 4 possible configuration :

i)   Single tab

ii)  Two opposite tabs

iii) Two adjacent tabs

iv) Four tabs

The typical tab width can range from 75 – 100mm .Unlike the solid fibre slip sheet, the tabs are not clearly defined as no scoring or cutting are necessary to form the tabs for the plastic slip sheet.

5.2 Scoring

Scoring is only necessary for solid fibre and corrugated slip sheets. As the solid fibre is stiff, scoring and cutting at the corners are necessary to allow the tab to bend upto 90 degrees. Otherwise , the stiff fibre will crack and the tab will tear when the gripper clamps on it and pull on it .

As the plastic slip sheet is very flexible , scoring or cutting at the corners to from the tabs are not necessary. A typical plastic slip sheet therefore appears as a rectangular sheet with no clear demarcation of the tabs. The user has the flexibility to assign the pull tab(s) during use when loading the goods onto it.

6.0 Unitizing

The common feature of using  pallet and slip sheet is that the goods need to be unitized.

Individual products are combined and shipped in larger unitized loads . These unitized loads can then be handled using mechanical handling equipment saving cost of manual labour and turn-around time . There is also less pilferage and less handling  damage so less costly protective packaging is needed. The load is unitized using the following methods or combination of methods :

i) Strapping

The goods are strapped together to form a single load.

Strapped Load

                        

Unitizing the drums using strappings

ii) Shrink wrapping

The plastic shrink film /bag is put over the goods and heat shrinked to form a unitized load.

Shrink wrapping

                                                     
 

                                             

iii) Stretch Wrapping

The stretch film is wrapped around the goods to form a unitized load.This can be done manually or by using a machine.

Stretch Wrapping

iv) Net Wrapping

The goods are wrapped with netting or  perforated film . Normally , done for goods that need to “breathe ” like fruits and vegetables.

Net Wrapping

                                                                            

Net wrapping of vegetable

v) Using adhesives

Each layer of products are glued onto the next so that they form a unitized load .

Load unitized by using adhesive Using adhesive to unitize the load

                         

Using adhesive to unitize the cartons

vi) Using hot-melts

This is similar to using adhesive except that hot-melt adhesives are used.

Hot melt guns used to apply the glue for unitizing the load.

viii) Rubber banding

Big rubber bands are used to tie the products together to form a unitized load.

Pallet banding

  

Unitized load using pallet band

7.0) Handling the Slip Sheets

It should be noted that the slip sheet handling equipment must be available at both the shipping and receiving stations for loading and unloading the goods shipped on slip sheets.

7.1 Push-and- Pull Attachment

This is an attachment for the forklift so that it can handle the loaded slip sheet . It basically has  a gripper which grips the pull tab and pull the loaded slip sheet onto its 2 platform arms for transportation. In unloading, it pushes the loaded slip sheet onto the pallet or floor.The attachment just fits onto the normal forklift (without need to remove the original forks) and it  takes only  a few minutes.  

Typical push pull attachment

 

Forklift with the push pull attachment

7.2 Rollerforks

This is also an attachment for the forklift . It has 2 sets of rollers on each arm which can roll the loaded slip sheet onto the arms for transportation. A specially designed pallet with extra slats(RF pallet) will greatly improve efficiency of handling the slip sheets when used with the rollerforks . The rollerforks can also be used with the normal pallets.

Rollerforks attachment

8.0) Using the slip sheets

8.1 Inside the factory or warehouse, the slip sheet is placed on top of the pallet and the goods are loaded on top of it. The slip sheet is arranged on the pallet so that the desired pull tab(s) extend out from the edge(s) of the pallet . With this arrangement , the push pull attachment can easily grip the tab later on.

8.2 The goods are normally moved about within the premises using these captive pallets ( these pallets never leave the premises). Some organizations invest in high quality plastic captive  pallets .All movement of the goods within the premises is  done using the forklift and pallet just like normal.However, this movement can also be done using the slip sheet if so desired.

8.3 The goods on the pallet are unitized  ,either before storage or just before loading  into tthe container/truck for shipment. 

8.4 When loading the loaded slip sheet into the container or truck, the push pull or rollerforks attachment will be needed.

8.5 It is possible to retrieve   and save the slip sheet  when loading the goods into the container or truck  using a specially designed push pull attachment.In which case, the goods will have to be unloaded manually at the discharge destination.

Sheet Save push pull

9.0) References

9.1 http://en.wikipedia.org/wiki/slip_sheet

9.2 http://www.scotland.gov.uk/Topics/agriculture/plant/18273/potatoexpconds/ISPM15

9.3 http://rollerforks.com/pushpull.aspx

9.4 http://www.cascorp.com

9.5 ISO 12776:2008, Pallets-Slip sheets

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.                                            

Dunnage Bag Terms

Common Terms Used In Dunnage Bags
AAR                                                           American Association of Railroads
Air Bladder                                            The inner plastic bag holding the air . Also called liner.

Burst pressure                                      The pressure beyond which the bag may burst

Crosswise bracing                               The dunnage bag is installed with the length parallel to the floor

Deflate                                                      Air is released from the inflated bag

Effective contact area                       The area of the bag directly in contact with the cargo loads or walls. The inflated bag

                                                                    is rounded at the top and bottom so only the central portion is in contact with the

                                                                    cargo load 

Force                                                        The force generated by the inflated dunnage bag. It is proportional to the effective
                                                                     contact area and the inflation pressure.

Gap                                                            See void

GSM                                                          Refers to the weight in gram per square metre of the kraft paper or polywoven fabric

Inflate                                                      Fill the bag with compressed air

Install                                                      Place and inflate a bag in a void

Kraft paper                                            Special paper used to make the outer bag

Laminated paper                                Refers to kraft paper laminated with layer of polywoven fabric

Layer                                                       The number of separate layers of material making up the bag

Leak                                                         The inflated bag losing air over time

Lengthwise bracing                           The dunnage bag is placed with the length perpendicular to the floor

Level 1                                                    AAR classification of dunnage bag with working pressure of 2.5psi and burst pressure

                                                                   of 8psi 

Level 2                                                   AAR classification for dunnage bag with working pressure of 5psi and bust pressure of 

                                                                  17psi

Level 3                                                   AAR classification of dunnage bag with working pressure of 8psi and burst pressure of

                                                                 25psi

Level 4                                                 AAR classification of dunnage bag with working pressure of 10psi and burst pressure of

                                                               30psi

Liner                                                     See air bladder

One-way valve                                 The valve only allows compressed air to enter the bag but not out of it.As such, the bag

                                                                can only be inflated once.

Paper dunnage bag                        A dunnage bag with a paper outer bag

Ply                                                        Refers to the number of separate layers of paper in the outer bag

Polywoven dunnage bag             A dunnage bag made with a polywoven outer bag

Recyclable                                        The material making up the bag can be recyled into raw material for reuse.

Reusable                                           The bag can be used 2 or more times

RoHS                                                  This refers to the European Union directive on Restriction on use of Heavy Metal

                                                              substances

Size of bag                                         Refers to the length and width of the uninflated bag

Two-way valve                               The valve allows compressed air to be pumped into the bag and also allows the air

                                                               inside the bag to be released . This means the bag is reusable.

Void                                                     The empty space between cargo loads or between the cargo load and the wall where the

                                                               dunnage bag is installed.

Working pressure                          The  pressure that the bag can be safely inflated to.

WPP fabric                                         Woven propylene fabric is woven from polypropylene yarn

RoHS in Dunnage Bags

heavy-metals-in-plastic-dunnage-bags-60309

How Many Dunnage Bags To Use?

no-of-dunnage-bags-needed-for-standard-container1