Hydraulic systems represents a large proportion in machinery but still today, many problems relate to hydraulics and they are not often visible to operators and it may be hard to connect hydraulic problems as a cause to runnability or profile problems. Anyway, fixing of the problems found can be priorised in maintenance operations and for future shutdown planning will be easier. At best, production efficiency, energy efficiency and / or product quality can be improved. Likewise, the nip loading test gives a good knowledge about the operational condition of the hydraulic systems and it gives valuable information on a moisture profile problem, caliper profile problem, too short changing interval of nip rolls or fabrics,... The possible causes of an incorrect nip loading could be from many causes like for e.g. friction in pivots or loading cylinders, faulty pressure transmitter or meter, wrong loading curve (due to structural changes or mistake in a control) or wrong roll crown compensation or internal pressure. PMPRO in cooperation with ProTest Engineering, specialize in hydraulic, pneumatic and automation / control systems, have introduced different kind of products / services to help and support our customers which depend on the case and difficulty they are facing.
The aim of the study is to find out existing condition of loading system. The nip testing and tuning includes: • Shutdown pressure measurements for loading hydraulics and crown control roll hydraulics including pumps • Nip force measurements • Tuning of the loading system • Nip profile measurements. / The service could be applied to press, size press, machine calender.
Shutdown pressure measurements (multichannel pressure analysis) for loading and CCR roll hydraulic system components are needed to identify problems and for the system tuning. All pressure measurements are done in time domain and will be also transferred to frequency domain to do more precise root cause analysis.
Nip force measurements are very important in this case, because uneven nip profile is visible. Problems in nip load are the most common reason for these kind of problems. Nip force measurements will reveal actual linear load vs. setpoint, difference between TS and DS, the condition of the loading mechanics and the need for possible mechanical service. With nip force measurements, loading curves to machine control system are optimized to have even nip load and to match the actual nip load to setpoint.
Nip profile measurements are done to have the needed information about the crown control roll adjustable crowning functionality. With nip profile measurements, crown control roll internal pressure difference will be optimised for straight as possible CD pressure profile. Crown control roll pressure difference curve is programmed in PLC and new optimized values can be updated. Nip profile measurements is made using Fujifilm paper. With nip paper is possible to obtain information about the profile across the entire nip width. Nip profile measurements and the tuning of the internal roll pressure difference control curve are normally the final steps in optimisation after everything else has been inspected and tuned.