Hi,
Electrical pipe is not smooth due to the galvanized iron pipe (zinc coated) also you have two hard material.
Use a 280 or 320 mesh water sand paper and sand lightly the top pipe , that is nocostly but need work.
Another solution use a electrical tape and cover the top rail where the wheels run or you can use any smooth tape or vinyl
Another solution use both sand it and cover with tape like electrical or vinyl similar to sign business use.
A paint coating on galvanized pipe is not recommended.
Regards,
YR
