1. Scraping or Grinding Sounds
Hydraulic Pump Issues
If the noise originates from the hydraulic pump area, potential causes include loose motor base or pump frame fixing screws, a loose motor coupling, or other faulty transmission components. Solution: Tighten and adjust loose components; replace faulty transmission parts promptly.
If the pump emits a low humming sound accompanied by inlet pipe vibration, air may be entering the system. Apply soapy water or grease to suspected leakage points on suction lines to locate and seal leaks .
Screw and Barrel Issues
A scraping sound during operation often indicates screw and barrel problems: the barrel center line may be bent; the barrel and screw may be misaligned; the cylinder inner wall or screw outer diameter cylindricity may be insufficient; or the screw may be distorted .
Solutions:
Adjust barrel center height
Check and correct alignment of barrel and screw
Inspect and replace components with insufficient cylindricity accuracy
Check and replace distorted screws
Foreign Objects in the Screw
Metal objects accidentally dropped into the feed hopper (screws, nuts, or stainless steel pieces) can become lodged between the screw and barrel, creating abnormal mechanical friction sounds. While magnetic separators can catch ferrous metals, non-magnetic materials like stainless steel may still pass through .
Prevention: Install strong magnetic devices in the feed hopper, use negative pressure material transport, and ensure raw material cleanliness. Consider using metal separation devices to remove metal particles from plastic raw materials .
2. Loud Exhaust Sounds
Abnormally loud exhaust noises typically indicate a problem with the high-pressure exhaust system. The most common cause is a damaged or missing exhaust muffler. If the muffler is cracked, loose, or has fallen off entirely, the high-pressure air release will produce a sharp, loud report with each cycle .
Solution: Inspect the high-pressure exhaust muffler immediately. Replace if damaged or reattach if loose.
3. Gear, Chain, and Transmission Noise
Abnormal noise from gears and chains, often accompanied by transmission jamming or motor overload alarms, points to mechanical transmission failures .
Causes:
Insufficient lubrication or severe wear on transmission parts
Installation accuracy deviation (misaligned guide rails, screw eccentricity)
Motor failure (bearing damage, winding short circuit) or excessive load
Solutions:
Regularly add lubricating oil; replace worn gears, chains, or belts
Recalibrate mechanical installation positions; adjust coaxiality of guide rails and screws
Repair motors, replace bearings or windings; check for excessive load causes (e.g., mold jamming)
4. Valve Body Noise
Vibration and noise from various valve bodies can have several causes .
Seal Damage
Damaged sealing rings allow air leakage, creating whistling or chattering sounds.
Electromagnet Malfunction
Faulty valve electromagnets may produce buzzing or clicking noises due to incomplete actuation.
Loose Fastening Screws
Loose screws on valves allow components to vibrate against each other, producing chatter.
If a solenoid valve, electro-hydraulic valve, proportional valve, or servo valve is suspected, check the power supply, fuses, relays, contactors, and input/output signals. Also verify control oil pressure and air supply pressure .
5. Pneumatic System Noises
Air Leaks
Leaks in pneumatic lines, fittings, or cylinder seals produce whistling or hissing sounds. These leaks waste energy and can affect machine performance.
Solution: Inspect all pneumatic connections, lines, and cylinder seals. Apply soapy water to suspected areas to locate bubbles indicating leaks. Replace damaged seals or tighten loose fittings.
6. Gripper and Bearing Noise
Abnormal noises from the gripping pliers that carry preforms into molds indicate potential bearing failure. The posterior bearings supporting the pliers are critical components that can degrade over time, producing unusual sounds during operation .
Research has shown that accelerometer-based monitoring can detect bearing faults in pliers mechanisms. The fault symptoms are most pronounced in specific operating quadrants where the damaged bearings are under load .
Solution: If unusual noises come from the gripper area during preform transfer, inspect the pliers mechanism and bearings. Replace damaged bearings promptly.
7. Pipe and Tube Vibration Noise
Vibration and noise can also originate from the machine's piping system .
Causes:
High oil temperature in the system
Air leakage in the oil suction pipe
Loose pipe clamps on high-pressure lines
Unreasonable component installation positions
Solutions:
Control system oil temperature within specifications
Check and seal any air leaks on suction lines
Tighten or replace loose pipe clamps
Re-evaluate and adjust component positioning if vibration persists
8. Siren or Alarm Sounds
Any siren or alarm sound from the machine or elsewhere in the plant demands immediate attention. These sounds indicate active fault conditions that have triggered the machine's safety or diagnostic systems. Do not ignore alarms—investigate and resolve the underlying issue before continuing production .
9. Sounds That Have Stopped
Interestingly, the absence of expected sounds can also indicate problems. If a normally present sound (such as a pump, loader, or cooling fan) stops, this silence may be the first warning of equipment failure. Check any silent component that should be operating .
Troubleshooting Process
When you hear an unusual noise:
Identify the approximate location of the sound
Note when the sound occurs (during specific machine actions?)
Check for any accompanying symptoms (vibration, quality defects)
Consult the machine manual for component-specific guidance
Perform systematic inspection of the suspected area
Repair or replace faulty components before continuing production
Preventive Maintenance
Regular preventive maintenance is the best defense against unexpected noise-related failures :
Follow the manufacturer's lubrication schedule for all moving parts
Perform regular inspections of bearings, gears, chains, and belts
Check and tighten all mounting bolts and fasteners periodically
Inspect pneumatic and hydraulic systems for leaks
Train operators to recognize and report unusual sounds immediately
Keep maintenance logs to track component life and replacement intervals
An alert operator who knows the equipment's normal sounds is the best defense against downtime and equipment failure .
