system fnds defects in
Vision inspects the surfaces of hot rolled steel long products as if they were cold, even
though the inspection takes place at a temperature of over 1,000°C.
Antonio Cruz-Lopez, Alberto
Lago, Roberto Gonzalez, Aitor
Alvarez and José Angel
To produce seamless steel tubes, a steel billet
is transported into a furnace where it is frst
heated. Next, the billet is pierced to form a
thick-walled hollow shell, after which a mandrel bar is inserted into the shell. The shell then
undergoes elongation rolling in a mandrel mill.
Following the elongation process, the billet is
conveyed to a push bench, where it is pushed
through a series of roller cages. The result is that
a hollow length of steel tubing with consecutively smaller wall thicknesses is formed.
As effective as the hot rolling process is,
the roller cages in the push benches can
sporadically produce marks and defects on
the surface of the steel that are extremely diff-
cult to detect in hot conditions. Hence, in their
quality improvement programs, many manu-
facturers look to identify such defects as early
as possible to avoid producing tons of defective
material at considerable expense.
To resolve those issues, engineers at Tecna-
lia (Derio, Bizkaia, Spain; www.tecnalia.
com) have developed a machine vision system
dubbed Surfn’ that can enable steel manufac-
turers to detect such defects as the steel ema-
nates from the push bench (Figure 1). The de-
tection of such defects provides manufacturers
with an indication of any issues in the produc-
tion process, enabling them to perform pre-
ventative maintenance on the push benches at
an early stage and preclude any defective steel
tubes from being delivered to their customers.
The typical defects found on the surface
of such tubes generated by the roller cages
usually follow a repetitive pattern and con-
tinue to appear until the rolling stands are
changed. They can include tears or rips in the
Antonio Cruz-Lopez, Alberto La-
go, Roberto Gonzalez, Aitor Alvarez and
José Angel Gutiérrez Olabarria, Machine
Vision Engineering Team, Tecnalia, C/
Geldo 700, 48160 Derio, Bizkaia, Spain
Figure 1: Engineers at Tecnalia have developed a vision system called Surfn’ that can
enable steel manufacturers to detect defects
in steel tubing as the steel emanates from a
push bench at over 1000oC.