Guide to Diagnosis and Quick Troubleshooting of Common Mechanical Malfunctions in Paper Bag Machines

As the mainstream choice for environmentally friendly packaging, the stable operation of the paper bag machine, the production equipment for paper bags, is crucial. However, complex mechanical structures are prone to various malfunctions during long-term high load operation, resulting in downtime, waste, and even affecting order delivery. Mastering the diagnostic methods and quick troubleshooting techniques for common mechanical faults is the core ability to ensure production efficiency and equipment lifespan. This guide is based on years of frontline maintenance experience, systematically sorting out the high-frequency mechanical failure points of paper bag machines and their response strategies.

1、 High frequency basic faults: identifiable operation and preliminary handling

Poor paper transportation/frequent paper jams:
Phenomenon: Paper accumulates, tilts, and cannot smoothly enter the forming section at the feeding end, or gets stuck at the conveyor belt/drum in the middle.
Diagnostic points:
Suction/blowing system: Check whether the suction head and blowing nozzle are blocked (paper powder, dust), whether the air pressure is stable (pressure regulating valve setting, air leakage in the air path), and whether the suction cup is worn, aged, and has lost its suction force.
Paper feeding roller/wheel: Check whether the pressure is uniform and moderate (too tight can damage the paper, too loose can cause slipping); Whether the surface rubber layer is worn, hardened, stuck with glue or foreign objects; Whether the bearing rotates flexibly.
Paper guide/baffle: Check if the position is offset or loose, causing the paper to deviate; Whether the edges are smooth and free of burrs to prevent scratching the paper.
Paper itself: Check whether the weight and humidity meet the equipment requirements; Whether there is adhesion (static electricity or moisture); Whether the stack of paper is neat and the height is within the specified range.
Quick exclusion:
Cleaning: Thoroughly clean the suction/blowing pipes, suction cups, paper feeding rollers, and paper guides from paper scraps, dust, and adhesive stains.
Adjustment: Correct the position of the paper guide gauge to ensure it is parallel to the direction of paper feeding; Adjust the pressure of the paper feeding roller to a uniform and moderate level (usually based on the paper being able to be pulled steadily and without obvious indentation).
Replacement: Replace severely worn suction cups and aged paper feed roller rubber sleeves.
Check the air source: Confirm that the air compressor is working properly and the main air path pressure meets the standard (usually 0.6-0.8MPa), check the filter drainage, and eliminate the air path leakage point.
Standardize paper application: Ensure that the paper is stacked neatly and at an appropriate height. If necessary, use a paper beater or tap to eliminate static adhesion.
Poor molding (bottom opening, uneven folding, skewed molding):
Phenomenon: Asymmetric and unstable opening of the bottom of the paper bag; The side creases are unclear and not in place; The overall bag shape is skewed.
Diagnostic points:
Molding molds (such as bottom inserts, molding plates): Check for wear, deformation, looseness, or inaccurate installation positions.
Folding device (such as folding rod, folding wheel, pressure plate): check whether the position, angle, and pressure are accurate; Whether the relevant bearings and guide rails are worn and causing shaking.
Correction device: Check whether the photoelectric eye (electric eye) is clean, accurately aligned, and the sensitivity setting is reasonable; Whether the response of the actuator (such as cylinder, servo motor) is timely and in place.
Transmission synchronization: Check the synchronization of each conveyor belt/chain to see if slipping or unsynchronization is caused by improper tension or wear.
Quick exclusion:
Calibrate the mold: Strictly recalibrate the installation position and angle of the molding mold according to the equipment manual to ensure it is centered and level.
Adjust the folding mechanism: finely adjust the angle, height, and pressure of the folding rod/wheel, and tighten the fixing screws. Check and lubricate the relevant moving parts.
Cleaning/Calibration of Electric Eye: Clean the electric eye lens to ensure there is no obstruction; Re calibrate the position and detection points of the electric eye; Adjust sensitivity based on paper color.
Check synchronization: Check and adjust the tension of the conveyor belt/chain; Check whether the synchronous belt/sprocket is worn or loose; If necessary, recheck the phase angle of the main drive shaft.
2、 Key institutional failures: require in-depth investigation and maintenance

Poor heat sealing, scalding or uneven sealing:
Phenomenon: Insufficient sealing strength leads to easy opening of the adhesive, paper at the sealing area is burnt and perforated, and the sealing line wrinkles or bubbles.
Diagnostic points:
Temperature control: Check if the thermocouple is in good contact, damaged, or calibration failure; Is the temperature controller parameter (PID) reasonable; Whether the heating plate/heating rod is aging and some areas have failed, resulting in uneven temperature.
Pressure system: Check whether the pressure of the heat sealed cylinder/cylinder is sufficient and stable (insufficient air pressure or leakage); Whether the pressure plate/silicone pad is flat, aged, or damaged; Is the pressure balancing mechanism functioning properly.
Time setting: Whether the heat sealing time (holding time) matches the current speed and material (if it is too fast, it will not melt through, and if it is too slow, it will easily burn).
Sealing material: Is the application of hot melt adhesive uniform and appropriate? Does the glue model and performance (opening time, curing time) match the paper and speed? Is the quality of the sealing strip (PE film, etc.) qualified?
Quick exclusion:
Calibration temperature: Use a contact thermometer (such as an infrared thermometer gun, pay attention to emissivity) to measure the actual temperature of the heat sealing knife/plate at multiple points, compare the displayed value of the temperature controller for calibration or replace the thermocouple. Ensure that the heating element is working properly.
Check pressure: Measure and adjust the working pressure of the cylinder (usually 0.4-0.7MPa); Check if there is any leakage in the air circuit; Replace aged and deformed silicone pads; Ensure that the pressure plate is clean and flat.
Optimize parameters: Based on paper weight, adhesive properties, and machine speed, retest and set the optimal temperature, pressure, and time combination.
Check the glue/material: Ensure that the glue gun nozzle is unobstructed and the temperature is appropriate; Adjust the amount and position of glue application; Verify whether the glue and sealing strip meet the process requirements.
Knife malfunction (continuous cutting, uneven cutting, abnormal noise):
Phenomenon: The paper cannot be completely cut, leaving continuous threads; The incision is rough and skewed; The cutting blade emits a piercing friction and impact sound.
Diagnostic points:
Cutting edge: Check whether the cutting edge of the upper/lower blade (rolling cutter or flat blade) is worn, broken, or curled.
Tool clearance/pressure: Check whether the clearance between the upper and lower blades is too large (continuous cutting) or too small (accelerated wear, noise); Is the pressure sufficient (flat blade).
Tool installation: Check if the tool shaft is bent or deformed; Whether the blade installation is firm and not loose; Is the blade seat bearing severely worn and causing radial runout.
Synchronization: Check whether the synchronization between the cutting blade action and the bag length conveying is accurate (phase angle setting).
Quick exclusion:
Grinding/blade replacement: Timely grind to restore sharpness (pay attention to maintaining the original angle), and replace the blade with a new one if it is severely worn or broken.
Precise adjustment of clearance/pressure: strictly follow the manual requirements and use a feeler gauge to adjust the clearance between the upper and lower knives (usually 0.03-0.08mm); Adjust the flat blade pressure to a moderate and even level.
Tighten and replace bearings: tighten all fixing screws; Replace the damaged blade shaft bearing.
Calibration synchronization: Re calibrate the phase angle of the cutting blade through the equipment control system to ensure accurate cutting position.
Abnormal transmission system (vibration, abnormal noise, overheating):
Phenomenon: Significant overall or local vibration during machine operation; Abnormal noise (creaking, clattering, sharp whistling) is emitted from the gearbox, bearing seat, and chain; The temperature of the motor and gearbox casing is too high.
Diagnostic points:
Bearings: are the main source of noise. Check whether the main drive shaft, guide roller shaft, and bearings inside the gearbox are worn, lacking oil, or damaged (using a stethoscope or long screwdriver to assist in listening and positioning).
Gear: Check whether the meshing gear (especially the gearbox) is severely worn, broken teeth, tooth surface pitting, and poorly lubricated.
Chain/sprocket: Check whether the chain is excessively loose, worn, elongated, or lacks oil; Check for wear and poor alignment of the sprocket teeth.
Coupling: Check whether the elastic coupling rubber ring is worn, aged, or broken; Is the alignment of the rigid coupling out of tolerance.
Foundation/fastening: Check if the anchor bolts are loose; Is the rigidity of the rack insufficient; Whether the installation of the motor and reducer is firm.
Quick exclusion:
Lubrication: Immediately add the correct grade and amount of lubricating grease or oil to the designated points (bearings, gears, chains) according to the equipment lubrication chart. Mixing is strictly prohibited!
Tensioning and centering: adjust the chain to a proper tension (usually the mid point depression is 2% -3% of the chain center distance); Check and calibrate the coaxiality between the motor and reducer, as well as between shafts.
Tightening: Conduct a comprehensive inspection and tighten all visible bolts and nuts, especially foundation bolts and major structural connections.
Replacement: Replace severely worn chains and sprockets; Replace damaged bearings (requires professional tools for disassembly and installation); Replace the failed coupling rubber ring.
3、 Complex system failures: require comprehensive analysis and professional intervention

Servo/stepper drive position abnormality (inaccurate positioning, step loss, overload alarm):
Phenomenon: Inaccurate correction, drifting cutter position, unstable paper feeding length; The drive panel displays alarms such as Overload and Following Error.
Diagnostic points:
Mechanical resistance: Check whether the motor-driven mechanisms (such as the correction frame and cutter seat) are stuck or have excessive resistance (such as oil shortage, deformation, foreign object obstruction, or bearing damage).
Transmission connection: Check if the coupling is loose, if the key pin is damaged or loose, and if the synchronous belt is slipping or too tight.
Feedback device: Check if the encoder connection wire is loose or damaged; Is the encoder itself damaged (rare but possible).
Electrical parameters: whether the driver gain (speed loop, position loop) parameters are set improperly; Is the current (torque) limit too low.
Power interference: Does the strong current line cause interference to the encoder signal line and communication line (non-standard wiring).
Quick exclusion (preliminary):
Disconnect load test: Under safe conditions, attempt to disconnect the mechanical connection between the motor and the load and run the motor independently. If it is normal, the problem lies on the mechanical side; If the alarm persists, it may be on the motor or drive side.
Check the machinery: manually rotate the driven mechanism and feel whether the resistance is uniform or abnormal; Check and lubricate the guide rails, screws, and bearings; Eliminate dead spots.
Check the connection: tighten the coupling screws; Check and tighten/replace the synchronous belt; Check the status of key sales.
Check the cables: Check if the encoder cables and motor power cables are securely connected and undamaged. Try unplugging again (power off operation!).
Reset after recording parameters: After recording the current drive parameters, attempt to reset the drive alarm. If it is frequently reproduced, it is necessary to contact the equipment manufacturer or professional electrical engineer to check the parameter settings, interference issues, and hardware status.
Pneumatic system failure (slow/weak/unresponsive cylinder, unstable pressure):
Phenomenon: The execution cylinder (such as heat sealing lifting, folding and pressing) moves slowly, has insufficient thrust, or even does not move at all; The pointer of the system pressure gauge fluctuates greatly.
Diagnostic points:
Gas source pressure: Has the main gas path pressure reached the set value (0.5-0.7 MPa)? Is the air compressor working properly? Is the pressure in the gas storage tank sufficient?
Air leakage: Check if there is any obvious air leakage sound in the trachea (especially the quick connector, solenoid valve interface, and cylinder interface) (soap water test).
Filter/pressure reducing valve/oil mist device (three piece): check if the filter element is clogged; Is the output pressure of the pressure reducing valve set correctly and stably; Whether the oil mist device has oil and whether the oil dripping speed is appropriate.
Electromagnetic valve: Check if the valve core is stuck (manual forced button test), if the coil is burnt (if it heats up or has magnetism when powered on).
Cylinder: Check whether the piston sealing ring is worn or leaking (which can be determined by the amount of air leakage at the exhaust port); Whether the cylinder is pulled or not; Is the guide bearing damaged or stuck.
Quick exclusion:
Check the air source: Ensure that the air compressor is running normally and the main air pressure meets the standard. Drain the condensate from the gas storage tank.
Dealing with leakage: Identify the leakage point and repair it (replace the joint sealing ring, tighten the interface, replace the damaged air pipe).
Maintain the three components: clean or replace clogged filter cartridges; Clean the pressure reducing valve (pay attention to protecting the diaphragm); Add specialized lubricating oil to the oil mist device and adjust the drip volume.
Test solenoid valve: Manually press the button to operate the solenoid valve and see if the cylinder action is restored. Replace the faulty solenoid valve (pay attention to the model and voltage).
Replace cylinder: Confirm that the cylinder is leaking or stuck inside and needs to be replaced (or professionally repaired).
4、 Preventive Maintenance: Building a Fault Line of Defense

No matter how efficient troubleshooting is, it's better to prevent faults from happening. Systematic preventive maintenance is the cornerstone of ensuring the long-term stable operation of paper bags

Strictly implement the lubrication system: lubricate according to the time, location, and grease grade specified in the equipment manual. Pay special attention to high-speed, heavy-duty bearings, and open gear chains.
Regular cleaning: Clean paper scraps, dust, and glue stains daily, especially for photoelectric sensors, paper feeding rollers, suction systems, heat sealing parts, and transmission components. Prevent dust from exacerbating wear and interfering with testing.
Key component inspection and fastening: Regularly inspect and tighten all bolt connections (especially the transmission and frame parts); Check the tension of the belt/chain; Check the sealing of the gas path; Check the status of vulnerable parts (suction cups, rubber rollers, blades, silicone pads).
Parameter backup and calibration: Regularly backup equipment control system parameters (PLC, servo drive, etc.). Regularly calibrate key sensors (temperature, photoelectric sensor), check mold positioning accuracy, and ensure transmission synchronization.
Spare parts management: Establish a safety stock of key vulnerable parts (such as suction cups, heating rods, heat sealed silicone pads, commonly used bearing models, specific types of solenoid valves, blades) to shorten downtime due to malfunctions.
Operation records and fault analysis: Detailed recording of equipment operating parameters, maintenance content, occurrence of fault phenomena, and handling process. Regularly analyze fault data, identify patterns and potential risk points, and improve maintenance strategies accordingly.
The diagnosis and troubleshooting of mechanical faults in paper bag machines is a process that closely combines theoretical knowledge with practical experience. Operators and maintenance personnel need to be familiar with equipment principles, carefully observe fault phenomena, follow a troubleshooting approach from simple to complex, from surface to interior, and make good use of basic methods such as listening, seeing, touching, and measuring (temperature, pressure, gap). Establishing and adhering to a scientific preventive maintenance system can effectively reduce failure rates, improve overall equipment efficiency (OEE), and ensure the continuity, stability, and economy of paper bag production. Remember, every successful quick elimination comes from careful daily maintenance and a deep understanding of the equipment. When encountering complex and difficult problems, promptly contact professional maintenance personnel or equipment suppliers to avoid blindly operating and causing greater losses.