Daily Maintenance of Screw Compressors for Blow Molding Machines: Carbon Deposit — Causes and Routine Cleaning

With the growing popularity of blow molding machines, many customers have begun equipping their machines with screw air compressors. The routine maintenance of the screw compressor directly affects the service life of the machine. In particular, carbon deposit in the air compressor causes severe damage to the compressor itself. Therefore, understanding the causes of carbon deposit and how to clean it is the top priority in screw air compressor maintenance and care.

How carbon deposit damages the air compressor When a large amount of carbon deposit builds up in the automatic exhaust valve and exhaust piping of a screw air compressor, the automatic exhaust valve becomes sluggish or fails to close tightly. This causes the discharged gas to flow back into the cylinder and be compressed repeatedly (i.e., secondary compression), rapidly raising the gas temperature. The high gas temperature in turn intensifies the oxidation reaction of the lubricating oil, and since the reaction products cannot be discharged in time, the temperature inside the exhaust piping rises rapidly. When the temperature reaches the auto-ignition point of the lubricating oil, the oil accumulated in the lubricant gradually ignites. The incomplete combustion products, oil decomposition products, and welding fumes in the gas combine with air to form an explosive gas mixture, resulting in an explosion. For this reason, fires and explosions caused by carbon deposit pose a huge threat to the safe operation of the compressor. After purchasing and putting an air compressor into use, routine maintenance must be performed on schedule as specified. If the compressor is not properly maintained, carbon deposit is inevitable in its oil passages and main unit, which endangers the operation of the air compressor unit and creates significant safety hazards.

How is carbon deposit generated, and how should it be cleaned?

1. Air filtration: Fine particulate matter drawn in with the intake air thickens the oil, which extends the time for oil oxidation reactions, thereby accelerating the rate of carbon deposit formation. Therefore, proper installation of the air filter must be ensured; if damage is found during cleaning, the filter must be replaced.

2. Temperature: Lubricating oils of different grades and types have different oxidation onset temperatures. Air compressors operating in high-temperature environments for extended periods accelerate the oxidation of the lubricating oil. For compressors equipped with a cooler, it is recommended to use treated or impurity-free cooling circulating water to prevent water circuit blockage.

3. Lubricating oil quality: There are currently many channels for purchasing lubricating oil, and quality inevitably varies. Some users choose substitute products, and in such cases, carbon deposit problems are common.

4. Extended use of lubricating oil beyond its service life: After the lubricating oil exceeds its specified service life, its service time may be appropriately extended depending on its appearance condition. Some users continue to use the oil after its color changes (turns black). In such cases, the air compressor may fail to operate within a very short period due to carbon deposit.

Routine carbon deposit cleaning: Having analyzed how carbon deposit forms during air compressor maintenance, the methods for inspecting and cleaning carbon deposit in the oil passages and the main unit become clearer. Specialized cleaning agents (carbon deposit cleaners or bearing cleaners) can be used for the oil passages and main unit, and the main unit can be cleaned without disassembly. For small units, soak the unit in the cleaning agent and rotate it several times during soaking; for large units, seal the inlet/outlet pipes and oil lines, then pour in the cleaning agent and soak. The soaking time should follow the specifications indicated on the cleaning agent, generally 8–12 hours; some cleaning agents are highly corrosive, so their specified soaking times must be strictly observed. After soaking, rinse with cold water under pressure, then blow dry with compressed air.