Why should you choose a grease rather than an oil, if you have the choice? There are some simple or practical reasons and some more chemical advantages.
First and foremost, a grease will ‘stay in place’. How good a grease is at staying where it has been applied is down to a number of factors such as the proposed device and application for the grease and also the grease type/chemistry and viscosity of the finished grease. The construction of a grease involves some type of ‘thickener’ (sometimes referred to as a gellant) which in simplistic terms acts like a sponge; maybe watch this video about the constituents/components of grease:
The first job of a grease is to keep the oil where it is applied but the microscopic way a grease works in a customer application will vary…is the application static or dynamic, is the application a mechanical or electrical application etc. For some applications (e.g. an unsealed bearing), choosing a grease is a no-brainer. The advantages of using a grease rather than an oil are numerous:
Formulating a grease is considered much like extreme cooking, the permutations of the finished grease properties are vast, the key properties normally highlighted are: