Large amounts of lint inside the duct work prevents proper exhaust flow from your dryer resulting in excess heat backup in the dryer housing. Consolidated with the heat presently being generated by the dryer can contribute to significant temperature increase. Thermal overload fuses are blown with temperatures over 309 degrees.
Your duct work should definitely be checked ever so often, perhaps even annually, and either cleaned out thoroughly or replaced. There are wands with cleaning head attachments sold at big box stores and online that you can screw together and make a long flexible shaft to clean the duct work interior.
If you do reinstall new duct work, make certain that you do not leave any sags in the line during the installation underneath your house. Snug it tight and try to prevent it from sagging too much, the best you can. Use either pipe hangers designed for this purpose or either lightweight webbing cut and stapled to the side of the floor joists. Either of which can be used to prevent sagging in the line.
I would highly suggest the silver metallic foil type, which is essentially a coil encased in what appears to be a silver wrapper. It is a great duct that will withstand the heat from the dryer and will last many years without breaking down and developing holes or tears. This kind here below
Even better still, is to have solid duct work installed in the straight runs and short pieces of this flexible duct to make the connections at your dryer and exterior vent. This solid slick wall duct has a reduced potential to accumulating dust inside.
-chris
