"there is a gap of a few second 4-5 seconds in between the product coming out. "

If you get this kind of gap between each rolled profile, then the method outlined by Kai with a specific model of IR sensor could be a practical one to implement.

Also the inductive metal detector as proposed by Erik is a good one. But you will have to work out the mechanics of building the coil and placing it safely in the path of the profiles that are coming out.

In such mills there will defenitley be a shear somewhere in the line to cut the profiles and most of these are fitted with a counter that counts each "cut". And some of these are equipped with RS232 or 485 ports. Can't you use THAT if available to get one part of the data - which is number of pieces cut ?

Maybe all of us are just giving probable solutions and much will depend on the actual set up that exists at your client's place.

Have fun and just ensure you don't stand in front of the profile that is coming out ;-)

Cheers

Raghu