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  • The thickness of the strapping material expressed in inches.
  • "Nominal" refers to the target thickness.
  • The "maximum" and "minimum" establish the tolerance or "leeway for variation from a standard."
  • Example: 0.016" + or - 0.002"

Polypropylene Strap and Polyester Strap Width:

  • Strap width is expressed in both inches and millimeters (1mm = 0.0394 inch).
  • Polypropylene sheet widths are 5, 6, 9, 10.5, and 12mm
  • Polyester sheet widths are 9, 10, 12, and 15.5mm.

Break Strength:

  • The level of strength in which a strap will fail when pulled apart (expressed in pounds).
  • "Tensile Strength" is the resistance of a material to a force tending to tear it apart.
  • This value is properly determined using a tensile tester
  • Break strengths vary according to product gauge and widths.

Slip (Surface Friction):

  • Proper lubrication enables the poly strap to slide easily around an object, corner, or on the strap itself.
  • Strap surface friction (or slip) is expressed in Newton or Meters.
  • Polypropylene Strapping Sheet Products: Maximum 10 NM, Minimum 3 NM.
  • Polyester Sheet Products: Maximum 10NM, Minimum 4 NM.
  • A lower number means a more slippery strap surface.

Slip (Surface Friction): Referring to Polypropylene Strapping

  • A slip additive is mixed with virgin PP pellets in the extruder. Finished coils of PP strap dwell in a chamber heated to 120 degrees for 48 hours. This causes the additive to "bloom" thereby providing proper surface friction.

Slip (Surface Friction): Referring to Polyester Strapping

  • Polyester surface friction is achieved by applying a coating of wax to the sheet. After annealing the polyester sheet is immersed into a wax/water mixture just before it is and wound onto a "slip spool."

Flame Treatment: Polypropylene Strap

  • Both sides of the sheet are exposed to flame treatment which "de-orients" the surface of the strapping material. This is needed to assure a good friction weld seal by reducing hairs and filaments that would otherwise interfere with the welding process.


  • Characteristics that enable a strap to resist lengthwise splitting.
  • Spit sensitive strap can get hung up in chutes, jam feed wheels, or not weld properly.
  • Polyester strap sheet specification: 1 of 10 split samples will be no more than 1 inch in length.
  • Polypropylene sheet specification: varies according to the width of the strap.


  • The increase in length of a poly strap stressed in tension.
  • The Signode test uses a tensile testing machine that stretches the strap until it breaks.
  • Elongation is expressed as a percentage at break.
  • Polypropylene sheet elongation specification is 20% to 40% with a nominal of 30%
  • Polyester sheet products have lower nominal elongation compared to Signode polypropylene. Depending on the strapping product, the elongation range is 10% to 25% with a nominal of 14%.


  • Camber is the characteristic of strap that, when laying on a flat surface, curves continuously to one side.
  • Excessive camber can cause miss-feads, and improper welds.
  • Polypropylene strapping should not exhibit camber of more than 6 inches in an 8 foot sample.
  • The specification for "Thin Strap" polypropylene products is 10 inches in an 8 foot sample.


  • Curl is the characteristic of strap that, when laying on a flat surface, curves upward.
  • Polyester sheet strap has a curl specification of 0.5 to 7.0 inches of curl in a 4 foot sample.
  • Polypropylene sheet specifications vary by product.

Edge Condition:

  • Sheet strap is slit into the finished width. A slit strap that is rough, ragged, or has "hair-like" filaments may cause miss-feeds and excessive dusting.

Weld or Joint Strength:

  • The level of strength that a weld will fail when pulled apart.
  • Sheet strap weld or joint strength values are expressed in pounds
  • Signode specifications satisfy A.S.T.M. minimum requirement for strapping material (at least 45% of the minimum break strength of the strap).


  • Pulldowns refers to straps that have "pulled down" between the side of the coil and the dispenser wall. This may be caused by improper winding tensions, a "saddled" or otherwise miss-wound coil, or improper setup of the coil on the dispenser.


  • Miss-wound refers to coils that do not have a uniform winding pattern.
  • There are a number of examples of miss-wound coils that may cause pull-downs, short feeds, miss-feeds

Crushed Cores:

  • Crushed cores is the result of miss-handling of strapping materials. Dropping strapping coils or tipping over full skids of material will cause the paper cores to crush, making it impossible to set the coil up on a dispenser.


  • Delamination is a condition that occurs in polypropylene strapping products whereby the strap peels apart.
  • Delamination is more likely to occur when black concentrate is added or when exceedingly high levels or "regrind" are included in the mix.


  • Scuff is a defect caused by insufficient flame depth that becomes evident when strap passes through the feed-wheel system of a power strapping machine.

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