The faults of hot melt adhesive pumps (used for conveying, measuring, and spraying hot melt adhesive, widely used in packaging, printing, woodworking, electronics, and other industries) are often related to "hot melt adhesive characteristics (high temperature, high viscosity, easy curing)", "equipment structure (pump body, sealing, drive system)", and "operation and maintenance". Common faults can be divided into four categories: "abnormal conveying, leakage, overheating overload, and adhesive blockage". The specific manifestations, causes, and preliminary investigation directions of the faults are as follows:
1、 Core Fault 1: Abnormal Conveyor - Insufficient Glue Quantity, No Glue Output, or Unstable Output
Abnormal delivery is the most common malfunction of hot melt adhesive pumps, which directly affects production efficiency. The main manifestations are "significant reduction/intermittent absence of adhesive output" and "large fluctuations in adhesive output". The core reasons are related to "adhesive state, pump body sealing, and drive system":
1. No adhesive output or severe insufficient adhesive quantity
Common reasons:
Insufficient melting of hot melt adhesive: Insufficient temperature in the glue tank (not reaching the melting temperature of hot melt adhesive, such as 150-180 ℃ for EVA hot melt adhesive, low temperature causes the adhesive material to be solid/semi-solid and unable to enter the pump chamber); Or the amount of glue in the cylinder is too low (lower than the pump suction port, causing the pump chamber to suck in air).
Blockage of pump chamber/suction channel: If not cleaned in time after shutdown, residual hot melt adhesive will cool and solidify in the pump chamber, suction tube or filter screen, blocking the flow channel of the adhesive material; Impurities (such as metal shavings and foreign objects) may be mixed into the hot melt adhesive, causing the pump core to get stuck.
Failure of pump body sealing: The pump shaft seal (such as mechanical seal, oil seal) is worn or aged, causing air to enter the pump chamber (forming "air resistance") and unable to establish effective negative pressure suction; Or the sealing gasket at the connection between the pump chamber and the pump cover is damaged, resulting in air leakage.
Drive system failure: Insufficient motor power, damaged reducer or slipping transmission belt, resulting in insufficient pump core speed and inability to effectively transport rubber material.
Preliminary investigation: First check the temperature of the glue cylinder (confirm with a thermometer that it has reached the melting temperature of the hot melt adhesive) and the amount of glue; Disassemble the suction filter again to check if it is clogged; Finally, check if there are any signs of air intake at the seal (such as bubbles).
2. The amount of glue produced fluctuates greatly (sometimes more and sometimes less)
Common reasons:
Uneven melting of rubber material: Local damage to the heating tube of the rubber cylinder leads to large temperature differences in the rubber material inside the cylinder (some areas become thinner due to overheating, and some areas become thicker due to insufficient melting). Fluctuations in the viscosity of the rubber material result in unstable conveying volume.
Wear of pump core: After long-term use, the gears of the gear pump (or the plunger of the plunger pump) wear out, causing an increase in the internal clearance of the pump chamber and an increase in "internal leakage" (the rubber material flows back from the clearance instead of being pressed out), and the output fluctuates with the change of clearance.
Improper pressure regulation: The outlet pressure valve (overflow valve) is set too high or the valve core is stuck, resulting in unstable system pressure; Or the nozzle of the external spray gun may be blocked or the caliber may be uneven, causing back pressure fluctuations and affecting the output of the pump.
Preliminary investigation: Observe whether there are "lumps" (not melted) in the rubber material inside the cylinder; Check whether the outlet pressure is stable (monitored with a pressure gauge); If used for a long time, the wear of the pump core should be checked (after disassembly, observe whether there are scratches or dents on the gear tooth surface).
2、 Core Fault 2: Leakage Fault - Rubber Leakage or Lubricating Oil Leakage
Leakage not only wastes adhesive and pollutes equipment, but may also cause safety hazards (such as high-temperature adhesive burns), mainly divided into two categories: "hot melt adhesive leakage" and "drive end lubricating oil leakage":
1. Leakage of hot melt adhesive (leakage of adhesive at pump body, interface or seal)
Common reasons:
Aging/damage of seals: Failure of pump shaft seals (wear of dynamic/static rings of mechanical seals, hardening of O-rings due to high temperature aging), and sealing gaskets between pump cover and pump body (deformation and cracking under high temperature), resulting in rubber leakage from the sealing gap.
Loose pipeline connection: The interface between the suction hose/outlet hose and the pump body (such as threaded connection, flange connection) is not tightened, or the sealing gasket of the pipe joint is damaged, and high-temperature rubber material leaks from the interface gap.
Pump body crack: During long-term high temperature use or low temperature start-up (sudden rise and fall of pump body temperature), the material of the pump body (such as cast iron, aluminum alloy) cracks due to thermal stress, and the rubber material seeps out from the crack.
Preliminary investigation: Observe the location of the leak (focus on checking the sealing area and pipeline interface); Check if the touch seal has hardened or deformed; If there are oil stains or adhesive marks on the pump body, it is necessary to check for cracks (which can be wiped with cleaning agent and observed).
2. Lubricating oil leakage at the drive end (oil leakage at the motor/reducer end)
Common reasons:
Bearing seal damage: The bearing oil seal of the motor or reducer is aging and worn, causing lubricating oil to seep out from the bearing end, which may contaminate the rubber material (if the leakage location is close to the pump chamber).
Overfilling of lubricating oil: exceeding the oil level line, high oil pressure during equipment operation, and lubricating oil overflowing from the breathing valve or sealing gap.
Cracks in the reducer housing: Long term vibration (such as pump core jamming causing motor overload vibration) leads to cracking of the reducer housing and leakage of lubricating oil.
Preliminary investigation: Check the lubricating oil level (whether it is within the specified range); Observe whether there is oil contamination on the motor/reducer end and whether the oil seal is damaged when touched; If the vibration is obvious, check whether the pump core is stuck.