Causes of Pneumatic Air Leakage on Automatic Molding Machines

Pneumatic molding machines are core equipment for sand casting. They complete the full processes of jolt compaction, squeezing, pattern drawing and stripping by compressed air. The tightness of the air circuit directly affects molding accuracy, production energy consumption and equipment service life.

Air leakage is the most frequent fault of molding machines in actual production. Minor leakage will lead to insufficient air pressure, unqualified sand mold compactness and casting defects such as blowholes and shrinkage porosity. Severe leakage will cause equipment shutdown and sharp increase of energy consumption, which greatly raises casting production costs.

Combined with frontline operation and maintenance experience, the main causes of air leakage of molding machines are summarized as follows.

I. Aging and Wear of Sealing Parts – Primary Cause of Air Leakage
The sealing rings and dust-proof rings inside air cylinders, reversing valves and compaction cylinders are vulnerable parts with high air leakage incidence.
Casting workshops suffer heavy dust and dramatic temperature changes. Molding sand dust easily adheres to sealing contact surfaces and scratches rubber rings during reciprocating movement. Long-term reciprocating operation under high pressure will harden, deform and crack sealing rubber rings.
In addition, the air supplied by workshop air compressors contains water and oil. Water vapor corrodes sealing materials and accelerates seal failure, resulting in air leakage at cylinder piston rods and valve gaps. Such hidden leakage is hardest to detect and accounts for more than 60% of all air leakage faults.

II. Assembly and Wear Failures of Pneumatic Pipelines
The external air pipes and high-pressure hoses of molding machines are pulled by equipment vibration for a long time, which easily causes pipe wall cracking and loose joints. In low-temperature environments, rubber and plastic air pipes become brittle and tend to crack at bending positions, resulting in air leakage.
Non-standard on-site assembly is a common problem: loosely fastened pipe clamps, incompletely inserted quick connectors, and threaded joints without PTFE tape sealing will cause rapid air leakage after pressure rise upon startup.
Besides, long-term collision and wear will form tiny pinholes on pipeline outer walls, causing continuous slow air leakage that is easily ignored by maintenance staff.

III. Improper Operation and Maintenance Conditions Triggering Air Leakage
If air compressors are not drained in a timely manner, accumulated water and oil in compressed air will corrode valve cavities and pipeline inner walls and damage sealing structures.
Lack of routine maintenance, such as failing to regularly clean dust in air circuits and fasten pipeline joints, will lead to loose joints due to accumulated vibration.
Over-adjusted supply air pressure leads to long-term overload high-pressure operation, which squeezes and deforms sealing parts, shortens the service life of accessories and causes persistent air leakage.

In conclusion, air leakage of molding machines is mostly not an abrupt fault, but the combined result of material wear, careless assembly and inadequate maintenance.
Casting workshops must strictly control the quality of pneumatic accessories, implement maintenance regulations including daily drainage, monthly air leakage inspection and quarterly sealing part replacement, reduce air leakage faults fundamentally, stabilize casting quality and save production energy consumption.

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