An obsolete analogue drive on a critical item of production plant is
replaced by a modern digital dc drive to achieve superior accuracy,
flexibility and a fast payback on the retrofit investment
Increasing demand for its PVC products prompted compounder, Polycol to
boost capacity at its Stephanie works in Stalybridge. The company
acquired a Battenfield uniplex extruder, complete with analogue drive,
and added this large output unit to its existing line-up of eight PVC
extruders. The additional capacity was easily achieved - that is, until
the analogue drive failed, which also damaged the extruder's motor beyond
repair. Polycol electrical supervisor, Keith Chambers takes up the story:
We contacted the extruder manufacturer and were quoted three to four
months for a costly replacement. And this would have been analogue - old
technology. Fortunately, we knew of a drives and CNC specialist called
QRotek* who were not only able to engineer a better solution at half the
price, but also managed to get the extruder up and running again in under
three weeks. Moreover, the Control Techniques Mentor II digital dc drive
SCADA management system.
The extruder, a 130mm twin screw type with a capacity of 1,500kg/h, was
fitted with a 150kW M420R Mentor II digital dc drive, together with an
MD29 applications module and FMX5 field controller. QRotek technical
director, Andrew Stephens remarks that Control Techniques drives, both ac
and dc, meet the special needs of retrofitting because of their easy
on-board programming capability.
Polycol had tried to change analogue drives before, but had experienced
problems due to the lack of I/O. Using drives from other manufacturers,
it could only be done with the addition of a PLC - not so with the Mentor
and MD29 combination. QRotek added an I/O interface and programmed the
MD29 so that the Mentor emulated the analogue drive it replaced. Being a
digital drive, however, the Mentor II provides additional benefits,
including accurate control and better reliability, plus a serial
interface to the plant's central control system.
Mentor provides the platform for a range of applications through a series
of expansion boards, which can add functionality through many
off-the-shelf programs, as well as network communications. Designed with
easy commissioning in mind, the drive includes data displays, easily
assimilated function menus and a five-key control panel. It can also be
configured on a PC using Control Techniques' MentorSoft software, and the
program downloaded to the drive via the serial interface.
As far as Polycol is concerned, the new dc drive has brought a
considerable degree of accuracy to the process. The company produces a
range of compounds, including cable grade, shoe grade and window grade -
all being produced to different recipes, temperature gradients and work
rates. Mentor maintains the extruder screw speed to ensure that the
required work rate and product quality are achieved - these being a
complex function of temperature, crammer speed and screw speed.
QRotek, with bases at Wetherby and Stoke-on-Trent, specialises in the
maintenance, programming and retrofitting of CNC machine tools, automated
systems, drives, servos, robotics and special-purpose machines. The
company operates a UK-wide 24-hour response service, with onsite
diagnostics, free estimates and evaluation.