Direct Answer
Paper bag machine faults repeat across a short list of families — bottom pasting failures, creases, knife and cut-off defects, tension drift, and speed-linked rejects — and each family has a defined check sequence. Start with the consumable most likely to drift: glue temperature and viscosity for pasting faults, left-to-right tension balance for creases, blade and anvil condition for cut quality. Speed-linked rejects are a timing problem, not a speed problem: the station that cannot follow the web is the fault, so correct it before pushing output. Diagnose in that order and most bag line faults resolve without guesswork.
Opening Hook
A bag plant's rejects doubled every time the line ran above 80% speed — and the operators blamed the machine. The fault log told the real story: the glue roller gap had drifted, so at higher web speed the paste film thinned and bottoms opened. One gap reset and a doctor blade change restored full-speed output. At yoco-group, our belief is unchanged — most bag machine faults are a short list of drifting settings, and the plant that checks them in order fixes them fast. Here is the troubleshooting guide.
The Fault Families
Nearly all bag line rejects belong to five families.
| Fault Family | Primary Cause Domain | First Check |
|---|---|---|
| Bottom pasting failure | Glue temperature, viscosity, film thickness | Glue system |
| Creases and folds | Tension balance, folder geometry | Left-to-right tension |
| Knife / cut-off defects | Blade wear, anvil condition, timing | Cutting station |
| Tension drift | Brakes, dancers, reel splice | Unwind system |
| Speed-linked rejects | Station timing lagging the web | Timing at speed |
Data: Lean Enterprise Institute's quality lexicon grounds fault work in the same discipline as any process problem — define the defect, trace it to a cause, and fix the cause rather than adjusting output around it.
Judgment: Classify the fault before touching the machine — a fault named by family points to its own check sequence, and the misdiagnosed fix is usually the expensive one.
Source: Lean Enterprise Institute — Lean Lexicon: Quality Terms (2023)
Fixing Bottom Pasting Failures
The most common bag fault — and usually the cheapest to fix.
| Check | Symptom If Wrong | Fix |
|---|---|---|
| Glue temperature | Weak bond, stringing | Set to glue spec |
| Roller gap / doctor blade | Thin or uneven film | Reset gap, replace blade |
| Paste timing | Glue off the fold position | Retime against folder |
| Glue age and quality | Inconsistent bond | Rotate stock, verify spec |
Data: TAPPI's paper and packaging test methods provide the standardized basis for checking paper, coating, and bond behavior — the reference frame that lets a bag plant verify whether a bonding fault is glue-side or paper-side.
Judgment: Split the fault at the material boundary — check glue film and paper surface separately, because a bonding fault blamed on the machine while the glue or paper drifted is a fault that will keep returning.
Source: TAPPI — Paper and Packaging Test Methods (2024)
Creases, Knife Wear, and Tension Drift
Three faults, three defined sequences.
- Creases — check left-to-right tension, then folding geometry, then scoring depth.
- Knife defects — inspect blade and anvil wear, verify cut timing against the web mark.
- Tension drift — check the unwind brake, dancer response, and reel splice quality.
Data: ISO's quality management framework (ISO 9001 family) requires documented corrective action — record the fault, analyze the cause, act, and verify — which is precisely the discipline that stops the same bag fault from recurring every shift.
Judgment: Write the fix down as a standard — a bag line where the same knife or tension fault recurs is a line where fixes are being done but not recorded.
Source: ISO — ISO 9001 Quality Management (2023)
The Speed-Link Problem and the Safety Rule
Speed does not cause rejects; a station that cannot follow speed does.
- Confirm the limiting station — slow down and watch which station cleans up.
- Fix the station, not the speed — timing, glue, or transfer, corrected at speed.
- Guard every fix — clearing jams and adjusting stations happens on a stopped, locked machine.
Data: OSHA's machine guarding standards require that maintenance and jam-clearing access be protected — the safety frame for any troubleshooting routine that sends hands near knives, rollers, and folding stations.
Judgment: Troubleshoot with the machine safe first — the fastest fix in the world is not a win if it is done against the guarding rules; lock out, clear, adjust, then run.
Source: U.S. OSHA — Machine Guarding Standards (2024)
The Bottom Line
Paper bag machine troubleshooting is a short, ordered discipline: name the fault family — pasting, creases, knife, tension, or speed-linked — then run that family's check sequence from the most drift-prone setting first. Glue temperature and film lead the pasting checks; tension balance leads the crease checks; station timing leads the speed checks. Record every fix as a standard so the same fault stops returning. The bag line with low rejects is the one whose faults are classified, checked in order, and written down.
For the machine-side context, our paper bag making machine types guide explains the configurations these faults appear on, and the paper bag machine guide: types, cost and ROI covers the buying side. Maintenance context lives in the paper machinery preventive maintenance guide.