- 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.
- 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.
- 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 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.