Lets put this in simple terms.
Coolant is basically a mixture of oil in water. Approx 5-20% oil and the rest is water.
The oil is called "soluble" but does not actually dissolve in water, per se. It forms an emulsion which is stable (the oil and water do not separate).
An analogy is olive oil and water mixed as a salad dressing. Normally the oil separates as an upper layer quite quickl
y (Other examples might be the way engine oil becomes milky if water leaks into the sump, or hydraulic oil becomes contaminated with water). E
nter an 'additive' which causes the mixture to not separate after shaking. Now you can make salad cream with the oil, water and additive. Clearly not the same ratios of oil to water for cutting fluid coolant, but the same principle.
For coolant, the oil is chosen for the properties required – like cutting oil. Other additives prevent microbe growth which would otherwise send the oil rancid (like old cooking oil).
The emulsifying agent is a compound that is soluble in both oil and water to some extent. We describe the two parts of the compound (responsible for the activity) as either hydrophilic (water loving) and hydrophobic (water hating!). In simple terms, the additive molecule combines loosely with water at one end and oil at the other, thus not allowing the two components to separate.
Lecithin is a common emulsifying agent used in cooking, but eggs also have this property.
I hope that simplifies coolant for cutting duties – the oil prevents the machine from rusting and provides some assistance for cutting, while the water is basically a coolant. Of course, there is a wide range of suitable products on the market and all can have different claims for their particular recip
e.
Edited By not done it yet on 20/12/2017 21:40:17