How do I clean dyeing machines and pipework in place?

Direct answer

Machine and pipework cleaning falls into two kinds: cleaning between batches and cleaning in place, where the machine is not opened up and production is not stopped, and the cleaning liquor is pumped right through the circuit. Thiourea dioxide is odourless, safe in the dry state and can be circulated with alkali, so it suits the reducing component of a CIP programme. But it needs enough temperature to release, so a quick cold flush does nothing.

1. Four conditions for cleaning in place

2. Starting cleaning liquor

• Thiourea dioxide: 2 to 3 g/L
• Caustic soda: 2 to 5 g/L
• Surfactant: 0.5 to 1.5 g/L, anionic or non-ionic
• Temperature: 85 to 95 C, circulated for 30 to 60 min

3. Three dead spots to cover

1. Filters and screens: colour deposits build up here first, so clean them or raise the flow before circulating

2. Heat exchangers: scale reduces heat transfer, so compare inlet and outlet temperatures after cleaning

3. Pipe ends and branches: confirm the valves are open so a circuit actually forms, otherwise the far end is never reached

4. After cleaning

• Drain and rinse to neutral; residual alkali contaminates the next batch
• Run a blank fabric batch to confirm there is no staining or rust spotting before returning to production
• Record flow resistance and temperature difference before and after as the basis for the next cleaning interval

5. Two things not to do

• Do not use a cold bath with a large dose of reducer: without heat it will not release reducing power, so the extra chemicals only add effluent load
• Do not mix it with oxidising cleaners: in the same bath as a peroxide-based cleaner the two simply consume each other

Sources

Parameters are the recommended ranges from our technical data sheet and published literature. Machine construction and deposit type vary widely, so confirm the concentration and time on your own equipment.