Strapping/Banding Machine Ejecting Strap
The machine feeds strap into the arch and then ejects it back out instead of tensioning. In most cases it's an arch sensor issue or strap that isn't completing the loop - both are diagnosable before opening the machine.
Common symptoms
How much strap ejects, and when it ejects in the cycle, tells you where to start looking.
Strap feeds in then immediately comes back out
The machine fed strap, didn't detect arrival at the arch sensor, and ran the eject cycle. Either the strap didn't reach the sensor position or the sensor didn't trigger when it arrived.
Arch alarm shows after every cycle
The machine is confirming it couldn't detect strap completion in the arch. The arch sensor is the first component to look at.
Large amount of strap loops in front of the machine
The feed ran its full length then reversed. The arch sensor is the likely cause - the strap fed successfully but the sensor didn't register its arrival.
Strap ejects before reaching the end of the arch
The strap isn't completing the loop. A partial obstruction inside the arch, or strap with too much curl, will stop it reaching the sensor position.
First cycle after re-threading works, then fails on the next
The strap left in the machine after the previous cut is too short to reach the arch sensor on the next feed. The machine ejects what it has.
Fault appears with one strap spec but not another
Strap that's marginally too wide, too stiff or with too much coil memory may not navigate the arch path correctly. Spec changes - even to a nominally equivalent product - can introduce this.
Typical causes
Arch sensor fault or misalignment
The sensor that confirms strap arrival at the end of the arch isn't triggering. If the sensor can't see the strap, the machine concludes the arch loop failed to complete and runs the eject cycle. Contamination on the sensor face and physical misalignment are the most common reasons.
Strap not completing the arch loop
The strap is stopping short of the sensor position. Debris inside the arch, a damaged inner guide wall or strap with too much coil curl will all prevent it reaching the sensor. A visual inspection of the arch interior usually shows the cause.
Strap specification outside arch tolerance
Strap that's too wide, too stiff or with significant coil memory may not navigate the arch path on the machine. This is especially common when switching strap grades or suppliers.
Previous cycle cut strap too short
If the previous cycle cut the strap short, there may not be enough strap remaining in the feed path to reach the arch sensor on the next cycle. The machine ejects what it has rather than attempting a tension on insufficient strap length.
What to check first
Start with the arch sensor. It's the most common cause and the easiest to rule out.
Check the arch sensor
Locate the arch sensor - usually at the end of the arch where strap arrival is detected. Clean the sensor face and check it's correctly positioned and undamaged. Manually trigger it if the machine allows and confirm it responds as expected.
Inspect the arch interior
With the machine isolated, look inside the arch. Any debris, a deformed inner guide surface or a section that's bent will catch the strap before it reaches the sensor. The location where the strap stops usually tells you exactly what's causing it.
Check the strap spec against the machine
Confirm the strap width and stiffness are within the machine's operating range. If you've changed strap supplier or grade recently, try a short test with the previous strap if you have any available.
Check the cut strap length from the previous cycle
After a normal cycle completes, measure the cut tail length. If it's shorter than the machine's minimum required feed length, there won't be enough strap left to reach the arch sensor on the next cycle.
If any of these apply, don't wait
- The arch sensor has been cleaned and checked but still isn't triggering on strap arrival
- There's visible damage inside the arch that can't be safely cleared without disassembly
- The machine is ejecting on every cycle regardless of strap spec or threading
- Wasted strap is affecting production output significantly
Arch sensor faults and internal arch damage both need hands-on access to diagnose properly. If the basic checks above haven't resolved it, call us rather than running through more reels of strap.