A weak strap seal usually comes from one of four areas: strap material, machine settings and hardware, the strapping process, or the workplace environment. Check them in order. Do not replace parts before you find the actual cause.
Strap material
PP and PET straps have different melting temperatures. If the strap does not match the heater settings, the overlap will not melt evenly. Oil, release agent, dust, and other contaminants on the strap surface also block bonding. High crystallinity, moisture, and aging can cause the same problem.
The hot melt adhesive or buckle must match the strap material. A mismatch lowers seal strength even when the machine settings are correct.
Machine settings and hardware
The heating block or sealing head may have glue buildup or oxidation. This lowers heat transfer. If the temperature is too low, the overlap does not melt enough. PP usually needs 160 to 190 C. PET usually needs 220 to 250 C. If the temperature is too high, the strap burns and forms a carbon layer. That layer cannot bond.
Pressure and dwell time also matter. Normal dwell time is 3 to 5 seconds. Thicker strap needs a longer dwell. If the machine releases the strap before the melted layer bonds and sets, seal strength drops.
Check the heating head position. It must line up with the overlap area. Check the strap feed allowance. An overlap shorter than 50 mm does not meet the common industry requirement. A cutter burr can also stop the melted surfaces from fitting together. A tensioner fault leaves too little tension after the strap wraps the package, so the overlap cannot press tight.
When a heating block, tensioner, guide, or pressing part reaches its wear limit, Hansheng Automation can machine a replacement from customer drawings. We match material, tolerance, and surface treatment to the working conditions.
Strapping process
Misaligned overlap or too little overlap leaves a weak joint. Low tension keeps the strap from sitting tight against the package. Under load, the overlap can open.
A fast cycle also causes problems. If the machine starts the next cycle before the melted layer cools, the seal does not fully set. The package surface matters too. Oil, water, or a very smooth surface lets the strap slide. The overlap then takes uneven load.
Environment
Low temperature slows melting and speeds cooling. Both reduce seal strength. High humidity lets the strap absorb moisture. During heating, the moisture can form bubbles and break the bond. Dust in the workshop can settle on the strap surface and block contact at the overlap.
Before you check the machine
Cut power to the strapping machine first. Stay away from the heating head and moving parts. A trained maintenance technician should do the inspection and adjustment.
Hansheng Automation also machines custom precision parts beyond strapping equipment. Our drawing-based service covers yacht components, RC car components, tobacco packaging machinery parts, filling machinery parts, and non-standard parts for printing, food, and medical equipment. We work from customer drawings for single pieces and small batches.
