Exactly what Don said. If you are shearing dirty sheep, you need to be using a shearing machine like this. These are designed to shear long, dirty wool. Combs and cutters have to be sharp though. Once they get dull, they are useless.
Clippers like these are designed to shear clean sheep with shorter wool. As in slick shearing for show. Note the difference in the head and blades. You have to wash the sheep before using them or they won't cut well and the blades will dull quickly.
For cleaning blades, I remove them from the clippers and simply rinse in hot water. An old toothbrush works to get the grime out from between the teeth.