By relying on the single-source supply of holistic sensor technology from SICK, Industrieservice Schach is optimising manufacturing processes and driving down costs, paying dividends technically and financially. Based in Nürtingen, Germany, the company uses state-of-the-art SICK 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 used in the manufacture of tubular membranes demonstrate just how large 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 with comprehensive advice on machinery 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 wastewater treatment or in the production of beverages, for example – is a process that demands the very highest standards of quality from the end product.
Intelligent sensors for high-precision mechanical engineering
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 acquired 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. A 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 millimeters 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 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 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 are able to 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, 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.
High-precision detection with minimal space requirements
The winding machines from Industrieservice Schach are capable of producing tubular membranes at a speed of up to eight metres 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. 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 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 is able to 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 and safe machine operation
The speed and quality of membrane production depends 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 for the purpose of remedying 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 metres 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 wastewater 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 wastewater 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.