Material benefits

Using Nimalike in the production and reconditioning of two-stroke components provides outstanding product properties.

It is 7:30 in the morning in the assembly shop at the Märkisches Werk in Halver (MWH) and a lift-truck places a wooden box full of used two-stroke exhaust valve spindles in front of the inspecting technicians. One valve spindle is examined according to the specified procedure, and it is found that it can be reconditioned without any difficulty. After reconditioning it will look like new, and can be expected to offer a service life equal to that of a new Nimonic spindle. About 80 % of the valves that come in can be repaired.

For nearly 60 years, the Westphalian company has specialized in the manufacture of gas exchange components for four-stroke engines. For the past 15 years the Halver engineers have also devoted their attention to the optimization and servicing of two-stroke exhaust valves.

This work involves the manufacture of new, fully assembled units, as well as reconditioning second-hand valve spindles and units. The specialists at MWH have been using Nimalike for more than eight years. The material properties of this alloy are similar to those of the very expensive Nimonic 80A, in some respects even better. Yet machining Nimalike for the manufacture of new units costs only 75% of the price of a Nimonic valve.

Quite apart from its cost benefits, however, the material also offers something that many MWH customers have learnt to value highly: Nimalike is ideally suited to the subsequent addition of properties like those of Nimonic to a standard valve. A special PTA welding procedure is used to apply Nimalike to standard valves, allowing them to acquire properties comparable to Nimonic.

Reconditioning

“Here we most often see the typical wear that results from the action of sulfur and vanadium oxides from the heavy oil. The statistics show that seating problems are relatively rare. The base of the valve disk, in particular, is affected by high temperature corrosion,” says Fellmann.

The option of creating a product comparable to one manufactured with Nimonic out of a used, standard valve spindle is usually open. The high quality with which it can be machined also makes Nimalike ideal for reconditioning original Nimonic valve spindles.

From time to time these specialists also see valve spindles that have been incorrectly treated in the past. Fellmann confirms that the procedure followed with Nimonic valve spindles is unequivocal. “In these cases we will not carry out reconditioning, because the valve spindles have been wrongly welded and heat-treated. This usually results in catastrophic valve spindle breakage, and that sometimes causes massive engine damage,” he explains.

MWH takes a different attitude to standard valves that have been incorrectly reconditioned. “In the case of standard valves, everything depends on the individual case. Standard valve spindles are more robust when it comes to welding and heat treatment, and can withstand significantly more than Nimonic valve spindles,” says Fellman.

Which of the incoming valves are reconditioned and which are not is decided on the basis of the incoming goods inspection that ensures that all the necessary parameters and geometric limits are examined using a computer-aided and tightly specified inspection plan. Fellmann goes on to explain: “This makes it possible to give our customers a binding price quotation. If the operator so wishes, we can even specify limits on the turnaround time.” The spindles are then individually processed using a PTA welding procedure, specially adapted and optimized at MWH.

Manufacturing

The Märkisches Werk does not confine itself to repairing two-stroke valve spindles with Nimalike, but also produces new parts from the same material. For Holger Fellmann this was a logical decision: “We decided to use Nimalike because it offers a service life twice as long as that of a standard valve spindle, but only involves 75% of the costs generated by Nimonic 80A.”

The company?s engineers make use of existing geometries, and improve the valve spindles through the application of Nimalike. For the most common MAN-B&W engines in the MC series, new parts are held in stock, and this means that even the urgent inquiries can be answered immediately. In more difficult cases, MWH will manufacture the desired number of the parts required within eight weeks. Worldwide delivery is assured through the service centers in Rotterdam, Los Angeles and Singapore.

A great future

With the Märkisches Werk having used Nimalike for manufacture and for reconditioning since 1995, the experts at MWH are unanimous on the future potential of the material. Excellent quality figures are said to have been achieved, particularly on the valve disk base. Consequently, confidence in this material has grown to a high level.

MWH says that almost all of the customers won over the years are staying with Nimalike, having put their trust the recommendations they received. This has resulted in continuous growth for the company.

This is reinforced by the fact that increasingly more operators are said to be no longer satisfied with the conventional practice followed in standard repair shops. “Very few are informed about the normal service life to be expected from valves. As a rule, the valve spindles only go for repair when they are already defective,” says Fellmann of the situation he describes as “all too common”. “If we explain to the operators that they can save both time and money by having reconditioning done according to a schedule, before a fault occurs, they most often understand this straight away and stick with it.”

This is hardly surprising, if for no other reason than that unscheduled repairs involve not only the repair costs themselves but also the expense of a docked ship. In such cases, the Märkisches Werk can also be of service, as marketing manager Torsten Ludwig explains: “Our database gives us accurate knowledge of when each ship has logged how many operating hours on which cylinder. We not only can tell the operator in advance when reconditioning would be appropriate, we can even supply him with a replacement part at the next dockside, so that the component can be exchanged. We take the used exhaust valve spindle in part exchange, and only charge the difference.”

Prospects

Holger Fellmann’s team, therefore, has big plans for the coming years. The medium-term goal is to make a marketing approach to the whole of the existing fleet with standard valve spindles for reconditioning and exchange. Consequently he aims to double the volume of business with Nimalike by 2006.

“Even though we know, of course, that after we have overhauled a standard valve spindle with Nimalike it will be years before we see it back in Halver again for another overhaul,” he says. “This may well reduce the possible quantity of our service business, but the increased long-term benefit our customers get from Nimalike sets us apart from the standard repair work offered elsewhere.”