The most popularly reason why your blades heat up quickly is because clippers run faster now than they did 15-20 years ago. Most clippers then use to run at 2,000 spm (strokes per minute) but now they have doubled in speed to around 4,000 spm. With added speed you always get more heat.
The secret to keeping your blades cool is Lubrication, Lubrication, and Lubrication!!
Lubrication is done by placing clipper blade oil onto your clipper blade before you clip, while you clip and after you clip. A spray that offers cooling, lubricating and cleaning at the same time is not intended to take the place of regular cleaning and oiling. Their purpose is to get you through clipping that animal quickly and efficiently.
Spray lubes hardly contain any oil. A majority of the product is made up of alcohol and less than 1% disinfectant. A lot of groomers tend to use them thinking their doing the best thing for their blades, but in fact the spray lube is drying the blade out. The blade will start to slow down from the increased friction and with the grime and dirt building up this will put undue tension onto your clipper.
As a blade gets hot the metal heats up and expands, which creates more friction. It then appears to be dragging and gives a feel of being blunt. You then send the blade to Clipit Grooming for sharpening with a note explaining your problems. On examination we test it and it works!
If you experience any of these problems you are probably not oiling enough. Firstly, the blade guide (which is the plastic piece on the top blade) needs oiling. Sprays will dry out the plastic and then you will get a squeaking from the plastic. Secondly the blade needs oiling in the following points, as outlined in the diagram.