How do you choose a good vegetable oil for steel

By price:
Price per unit quantity has some bearing; however, the ratio of the amount consumed to work performed is critical. A more expensive fluid used in lesser quantities could be themost cost effective.

By colour:
The natural, pure, colours are a pale yellow to colourless. Adding any colouring contaminates the natural product, reducing its effectiveness. Since blue is the least contaminating colour it is often used by many suppliers. A more deep yellow colour could indicate that sulphur has been added to increase pressure properties.

By friction tests:
Although friction tests have some value, if performance in a machining operation is the objective, testing it in that operation is the only valid test. Friction test results may have little or no value in fluid machining performance characteristics.

By smell:
Almost all vegetable fluids are virtually odourless at room temperature. More commonly, an undesirable odour can be generated when the fluids become hot. Since normally they have a very high flash point, they can get extremely hot
before burning and emit an undesirable odour.

By feel:
Commonly, rubbing some fluid between the fingers is used to evaluate the "slipperiness" of a fluid. This has no bearing on what is transpiring at the interface of a warm cutting tool and the work piece.

By shelf life:
A truly pure vegetable product will have an infinite shelf life. Additives intended to increase performance and/or reduce cost could cause degradation of shelf life.

By environmental requirements:
Vegetable fluids are almost always very environmentally friendly in their neat state. Normally they are non-toxic and biodegradable. Once they are applied, they can 'break-down', and possibly react with the machined material and its chips, creating less desirable properties. Often if the fluid is atomized excessively, airborne particles result which can cause irritation. This normally results from excess fluid and/or excess atomizing air.

By compatibility with paint, subsequent processing, etc:
Most fluids require viton seal materials. Some fluids are compatible with pre-painted stock, but may have negative side effects. Some fluids can ruin anodizing fluids. Some fluids can become tacky, causing chips to adhere to each other, the tool and machine. This same property can cause a varnish type residue to form, which is not soluble in any other fluid.

By reliability of the source:
Most companies have many products available at differing prices. Check with your supplier on the properties of their products. Most often you get what you pay for, and a cheaper product may not be the most cost effective option.

By performance:
There is no better way than trying the fluid in the actual application of its intended use. Many fluids will initially give similar results. Many fluids will expose oxidation or polarization problems only after exposure to heat and pressure. The most notable evidence of negative properties is 'stickiness', which could eventually build into a hard varnish residue, creating unlimited problems. The less pure, and normally less costly, fluids fall into this category.

By viscosity:
Vegetable products are known for their good 'viscosity index' - that is viscosity changes very little with a temperature change. Viscosity at room temperature really tells very little about the effectiveness of a lubricant at the interface of a cutter and the work piece, the true behaviour of a lubricant under such pressures is not predictable and is best determined by experimentation. Penetration - or the ability of a fluid to migrate into the heat zone is a key to fluid effectiveness