Schach increases sensor performance, reduces sensor costs with SICK

Improved
processes at a fraction of the current costs attributable to sensors – for Industrieservice
Schach, working with SICK as a one-stop supplier is paying dividends both
technically and financially. Based in Nürtingen, Germany, the company uses
state-of-the-art sensor technology in its membrane filter winding machines. This
includes high-precision thickness and position sensors, opto-electronic
detection and rotative displacement sensors, easy-to-integrate pressure and
temperature sensors, as well as certified safety door switches and light
curtains.

Industrieservice Schach’s machines and plants for
manufacturing tubular membranes demonstrate just how strong an impact a broad
portfolio of innovative sensors for automation engineering and safety technology
can have. “With SICK’s help, not only were we able to identify improved
technical solutions for several machine applications, but we were also able to
reduce costs attributable to sensors in machinery by around 75 percent overall
through better product selections,” explains company owner Hans Schach. “And
that’s not even factoring in the new safety technology. What’s more, everything
now comes from a single source. Comprehensive advice is provided for all the
machinery’s automation functions, which in some cases enables significant optimisations
and substantially reduces the risks associated with delivery logistics.” For
Schach, the reliability of the sensors is another decisive advantage, since
manufacturing tubular filter elements – used for turbidity filtration in waste
water treatment or in the production of beverages, for example – is a process
that demands the very highest standards of quality from the end product.

Industrieservice
Schach: Special mechanical engineering a forte

At Industrieservice Schach, the design and
implementation processes go hand in hand. The company’s range of services
covers everything from sealing tools, eccentric clamps, and mounting equipment,
to joining, tightness testing, and assembly machines, all the way through to machinery
and entire plants designed for spiral-wound technology. It is in the last of
these areas that the company has built up a real stock of specialist knowledge:
designing and producing plants intended for manufacturing tubular supporting
bodies made from non-woven fabrics, with membrane filter technology in mind. At
the forefront of its work is its winding machine, on which non-woven webs from
0.1 to 0.3 millimetres in thickness and 12 to 25 millimetres in width
can be processed in both single and double layers. The tubular supporting body,
which accommodates diameters ranging from five to 25 millimetres, is
formed along a winding mandrel. Finely dosed, heated membrane polymer is
applied to the body and dried, and the overlapping non-woven webs are then welded
ultrasonically. Following this, the filter tube in the crosscut module is cut
to a customisable basic length using a flying saw.

“Around 380 filter tubes measuring five millimetres
in diameter are inserted in bundles inside 10″ pipes made from fibre-reinforced
plastic. This is carried out by the manufacturer of the filter elements for the
process plants,” explains Hans Schach. “It only takes a single defective tube
to stop the entire cross-flow filter module from working, and this, in turn,
leads to rejects.” That is why Schach believes it is vital to use not only
automated tube production techniques but, also quality methods that are
automated and can be documented – covering both machine processes and the
finished product.

“Some examples of particularly critical areas are
keeping the thickness of non-woven material constant or controlling pressure
and temperature with precision when applying polymer,” says Hans Schach. “In
addition to the burst pressure or tensile test benches that can potentially be
integrated, various sensor types are able to provide quality assurance in the
process itself.” At the same time, it is important to deliver solutions for
various detection, positioning, and measuring tasks, which enable the machine
to adapt automatically to the product being manufactured. As a result, almost a
dozen sensors with a variety of operating principles and functions are used in
the machinery.

Through
thick and thin: Monitoring materials with displacement and fork sensors

The principle of osmosis forms the basis for filtering
particles, foreign matter, and impurities out of liquid using membrane filters.
The membrane produced in the machine is semipermeable, meaning that it is only
porous to certain substances. As the membrane carrier, the thickness of the
non-woven material (among other factors) has a bearing on the diffusion behaviour.
“In the material infeed for the winding machine, we, therefore, monitor the
non-woven material for points where it may be thicker or thinner. This makes it
possible to cut out the damaged area in question automatically before it
reaches the winding unit.” Displacement sensors from the OD Mini product family
are used for detecting the material thickness. They can sample the material web
with a measuring frequency of 2 kHz and a resolution of 6 µm, which
means that the material thickness is very accurately monitored – and a
potentially damaged area can be localised with such precision that there is no
unnecessary loss of material when it comes to cutting it out. Looking back on
the situation as it was before, Hans Schach notes: “The solution that we
previously had from another manufacturer was ten times more expensive and was
neither as precise nor as easy to integrate. Particularly in this area, optimising
the product selection in line with SICK’s application advice has really paid
off.”

In the next stage of processing, WFM30 optical fork
sensors at the sonotrodes perform winding monitoring. Within a response time of
125 µS and with accuracy in the sub-millimetre range, they detect whether
the material leaving the winding mandrel is being pushed together or twisted –
in other words, becoming thicker. If this happens, the material cannot be
welded by the sonotrodes and must be cut out as a damaged area.

Position
detection for drum modules and dancer roller controls material replenishment

The winding machines from Industrieservice Schach are
capable of producing tubular membranes at a speed of up to eight meters
per minute. To enable continuous and autonomous operation over several hours, a
drum module with automated splicing is responsible for replenishing the
material as necessary. As soon as a roll of material nears its end, this is detected
by a GTB6 photoelectric proximity sensor in a space-saving rectangular housing
– thanks to background suppression, this is a highly reliable process that is
not affected by interference stemming from the machine environment. The optical
pushbutton signal activates the splicing process. This clamps, cuts, and welds
the material webs on both rolls.

C-slot cylinder sensors from the MZC1 product family,
made from high-strength special VISTAL plastic, are used for detecting the
position of the clamping cylinder when it is either retracted or extended. Hans
Schach praises the ease with which these sensors can be installed and their
secure fastening method: “The sensor can be inserted into the C-slot simply by
dropping it in – without having to remove the cylinder end cap and even in
cases where the cylinder has already been installed. Not only that, but the
captive eccentric screw also guarantees that the interlocking mechanism for the
MZC1 remains resistant to shocks and vibrations in the slot.” IME12 inductive
sensors, meanwhile, provide a solution for end position monitoring and
detecting the dancer roller position in the non-woven material infeed. During
the automated process of changing the rolls and splicing the new non-woven web
with the old one, the buffer module ensures that the non-woven material infeed
required over this time is delivered. “The IME12 sensors stood out due to their
space-saving, metric short variant, the option of installing them flush in
metal, plus the sensing range of four millimetres,” says Hans Schach. “This
allowed us to provide a detection solution that delivered maximum performance
with minimum space requirements.”

Rotative
measuring technology for web infeed and flying saw

Non-woven webs of various widths and material
thicknesses can be processed on the winding machines. To be used for this
purpose, the angle of the non-woven material infeed and the machine’s winding
belt module must be adjusted automatically. Singleturn absolute encoders from
the ACS36 product family are used for path measurement and positioning. With
their resolution of 2,979 increments, they enable modules to be adjusted as
precisely as is required to ensure optimum infeed and processing of the
non-woven webs. As well as this, the control can recognise the exact setting
for the non-woven material infeed and winding belt even when the machine has
been switched off and back on again – with no reference run necessary. A DBS60
incremental encoder with a friction wheel fixed to the solid shaft is used for
measuring the length of the membrane-coated supporting bodies following ultrasonic
welding. The system detects the feed speed of the finished filter tube and
controls the flying saw used for cutting the material to a flexibly adjustable
basic length.

Safe
process control, safe machine operation

The speed and quality of membrane production depend
directly on certain factors present in the process: the temperature, pressure,
and dosing of the polymer being used. Optimum processing temperatures range
between +20 °C and +60 °C, depending on the type of polymer. The
ideal value for the process in each case is monitored using a TSP resistance
thermometer. Alongside the temperature sensor, a PTB pressure sensor – which is
also compact and easy to install – is used to detect the polymer pressure.
Together with the winding machine’s special dosing principle, this technology
ensures that the end product meets consistently high processing standards.

In both the winding machine itself and the connected
drum module, hazardous movements present a potential risk of accidents
involving people. A physical guard is used on the winding unit. The access door
– providing entry to the machine to remedy faults or performing maintenance –
is equipped with a non-contact STR1 transponder safety switch. This fulfils the
highest safety requirements: SIL3 in accordance with IEC 61508 and SILCL3 in
accordance with EN 62061, as well as PL e in accordance with EN ISO 13849.
What’s more, the transponder safety switch is effectively protected against the
risk of tampering thanks to its unique coding. To allow simple and ergonomic operation,
a deTec4 safety light curtain with a height of 1.35 meters is installed on
the drum module; this also meets the criteria of the aforementioned standards.
Through the use of two deflector mirrors, all three accessible sides are
monitored in a non-contact manner. The distance between the beams used for
monitoring is 30 millimetres. Not only does this resolution ensure
reliable protection for hands in the event of unauthorised access to the
machine while it is still running, but it also makes it possible to remove the
non-woven material web located between two single beams and leading through to
the machine without the safety device responding.

Membrane
filter technology ready for yet more innovations

Industrieservice Schach’s machines and complete plants
used for manufacturing tubular membranes have been met with great interest in
the field of waste water technology. With sensor technology that is both
innovative and deployed in intelligent ways, filter element production is
guaranteed to be not only technically efficient and cost-effective, but also a
high-quality, transparent process that can be documented. What’s more, the
Nürtingen-based company is already looking ahead to two areas that will become
vital in the future. One of these involves implementing layer thickness
measurement inside tubes, which will enable the company to provide a fully
rounded quality concept. The other will see it processing new polymers into
membranes – which, for the first time, will enable hormones and antibiotics to
be filtered out of waste water along with other impurities. The right machine
technology – including the ideal sensors from both a technical and financial
perspective – is already at hand. All that remains is to adapt it for these
tasks.

By Eyüp
Ergün, Field Sales, SICK Vertriebs-GmbH, Düsseldorf

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