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New Valve Technology extends Maintenance Intervals for Selective Roll Cooling

On tandem stand 6 at thyssenkrupp Rasselstein, Evertz Hydrotechnik has increased the maintenance intervals of the valves and nozzles from a few weeks to several years by replacing the valve technology for the selective roll cooling system and has significantly reduced maintenance costs.

thyssenkrupp Rasselstein GmbH produces around 1.5 million tons of tinplate per year at the world's biggest packaging steel production site in Andernach. The main production equipment at the cold rolling mill includes a tandem mill with six rolling stands. In this plant, the rolls are cooled in accordance with the flatness control specifications in 56 zones distributed across the width of the strip with up to 10,000 liters of water per minute. Selective control of the individual nozzles is used in particular when a thermal bale forms on the work rolls and the flatness is to be corrected. It is also generally used for cooling the rolls. The multi-zone cooling system installed in 1998 had reached the end of its economic life after years of reliable operation. One reason for this was that the cooling water contained iron abrasion which had attacked the nozzles, valves and seals over time. The intervals for replacing individual nozzles became shorter. The water boxes above and below the belt with a total of four rows of nozzles had also been washed out over the years. In addition, it would not have been economical to repair or weld on the holes for the valves.
would not have been economical. A special feature of the Andernach plant is that palm oil is used for lubrication. Parts of this oil accumulate in the cooling water. This led to the old valves, which had seals, gumming up and sticking together - they had to be replaced and repaired every six to eight weeks. In order to significantly extend the maintenance intervals and minimize costs,
Rasselstein decided to invest in a new roll cooling system. In contrast to a repair, this offered the opportunity to incorporate the experience gained from operating the old system as well as new findings into the new construction. Since it was planned to modernize the strip press on stand 6, it was decided to also modernize the strip cooling system as part of this measure.

The solution

Evertz Hydrotechnik proposed replacing the piston valves previously used with Phragmspray® diaphragm spray valves, which the company developed for heavily contaminated cooling media and which are known in the industry as "Dirt Specialist". Among other things, they are proving their worth in the two hot strip mills of an aluminum rolling mill, where more than 2,000 membrane spray valves have been successively installed since 1999 and are being used there with great success.

An important design feature of the patented Phragmspray® valves is the multilayer stainless steel diaphragm, which acts as a hermetic seal separating the spray medium from the compressed air serving as the control medium. The patented i-Jet® nozzles produce a homogeneous spray pattern with a stable spray jet. Long-term tests at Evertz have shown that the valves precisely maintain response times of less than 100 milliseconds and a switching frequency of up to 2 Hertz even after 25 million switching cycles. Safety features such as the monitoring of pressure and wire breakage as well as the automatic draining of the spray system in case of standstill also contribute significantly to the high operational safety of the system.

The project

However, due to the special properties of the cooling water at the Andernach plant, there were initially reservations about the new valves. Due to the good, trusting cooperation over many years, the decision was finally made in favor of Phragmspray® technology from Evertz Hydrotechnik. The revamp order included the installation of a completely new cooling system with a total of 112 valves in four rows.
a total of 112 valves in four rows, new water boxes and a pneumatic control cabinet. After successful pre-commissioning at Evertz Hydrotechnik in Betzdorf and a workshop for the operators, the new system went into operation in January 2018 - at the same time as the new belt press. The integration into the process control system could be used to the greatest possible extent. The new system has been running smoothly
The new system has been working trouble-free from day one, and the experience gained during operation has been very positive without exception. All the features assured by Evertz Hydrotechnik have been met, and the availability of the new cooling system is 100 percent.
at 100 percent. The original expectations regarding the serviceability of the new spray valves have been clearly exceeded: While the goal was to extend maintenance intervals from six to eight weeks to six months, the new diaphragm spray valves have been operating extremely reliably for three years now. The function of the system is routinely checked at every program change with the so-called nozzle test, in which all nozzles are individually cycled before the first belt is threaded. In November 2019 - ten months after commissioning - the valves were inspected for the first time: There were no complaints to report. The new system is also much easier to handle from a maintenance perspective. The spray valve, the nozzle, and the cover have been structurally
unit. If replacement is necessary, the complete valve unit, including the nozzle, is pulled out of the water box. The larger screws compared to the old system are captive and are loosened with a simple removal tool. Thus, the design is excellently adapted to the adverse environmental conditions that cannot be avoided at the outlet of a tandem scaffold. Due to the significantly reduced maintenance effort, the maintenance department no longer needs to schedule an eight-hour maintenance shutdown of the scaffold every six weeks, as was previously the case, which is accompanied by a corresponding reduction in costs and an increase in the availability of the scaffold. Based on this experience, Evertz Hydrotechnik recommends that a minor maintenance visit involving inspection, cleaning and replacement of the static seals be carried out every two years, and a major one every six years involving the installation of new diaphragm pistons. The new connection with the MK31 type multi-coupling between the control cabinet and the water boxes has also proven its worth. Unlike the old system, the compressed air is not supplied in individual hoses, but in an armored flexible hose that is connected to the control cabinet and the water boxes with the multi-coupling. They are much more robust, can be plugged in without twisting thanks to the clear indexing, and are easier to handle than the individually routed plastic hoses used previously.

The future

Following the great success of the project, the team at Evertz Hydrotechnik is already thinking ahead: for other plants requiring faster reaction times and a switching frequency of up to 5 Hz, the purely electric spray valves of the Coolectro®pro series are currently being tested in continuous operation, also with the aggressive emulsions typical of the Rasselstein plant. To stand up there, my performance-optimized, hermetically separated solenoid drive is being used. The first results are expected in mid-2022.