The authoritative public forum
  for Metal Finishing since 1989
-----

Degreasing LM6 Aluminium in hot water

2003

We are currently using a hot water dip to remove soluble oil from the surface of machined Aluminium (LM6) castings.

The temperature of the water is 60 °C and the castings are submerged and agitated for approximately 30 seconds.

Upon drying they tend to discolor and will go black at higher temperatures. Does anyone know why this is? and could it be prevented by lowering the temperature of the dip. We are not currently using any detergents in the dip.

Scott Rowlands
Production Engineer - Cannock, Staffordshire, England

---

DEAR

This is because you are not using any chemical for cleaning. Use neutral Cleaner (non caustic non silicate based cleaner and through rinsing, or hot kerosine oil.

Rakesh Sharma
- Delhi, India
2004

---

Dear sir,

Water in any case affect aluminum because of its amphoteric behaviour. For heavy oil removal using detergent is useless. The best way to overcome the attacking of aluminum is to use steam . Try to locate your parts so that oil being dripped easily meanwhile suspending them over boiling water.

Hadi Khosravi
anodizing and plating - Tehran, Iran
2004

---

Hi,

A method worth consideration would be vapour phase degreasing, no detergents are used, only solvents. The system is closed and can operate at elevated temperatures and the solvent recovered, sludge removed. Solvents used can vary from white spirits, DiChloro Methane, NMP. These will not cause any discolouration and the last two are cold water soluble so you would first start with say petroleum solvent Kerosene, white spirits etc and finish with DCM or NMP.

Robert Fyfe
Audio Eng. - Wyoming, NSW, Australia
2004