Gourmets think of Gouda as a cheese paradise, but specialists from the oil and gas industry value this city for the special valves that are produced there: There is much talk in the industry of the high-pressure control and stop valves from Mokveld that are manufactured on special machine tools. The Dutch specialists are particularly proud of their new "quiet machine".
"Normally, the hydraulics make a terrible amount of noise. We didn't want our employees to have to put up with that anymore", says Bart van den Bosch, Manager of Production Engineering at Mokveld Valves BV in Gouda. "But now there's almost no noise". The ergonomic answer to this problem is a vertical turning lathe (Dörries Contumat VCE 2000 / 200 MC FC So) from Dörries Scharmann Technologie GmbH in Mönchengladbach, Germany. Mokveld also had all auxiliary units enclosed in a housing by the subsidiary of the Swiss-based Starrag Group. It is not unusual for the valve manufacturer to go to extra expense for the benefit of workers. This is evidenced by the working environment, which is very clean for this type of production. "We always have two people cleaning the shop floor here", explains the Manager. "Cleanliness and quality simply go hand in hand".
The machine has been in use since 2013. The unusual tower structure is noticeable upon first glance. The machine table (60 kW drive capacity; 19,300 Nm torque) can be used to process workpieces that weigh up to 12 tonnes, with a maximum height of 2450 mm and a diameter of up to 2000 mm. "This design is very unusual for a vertical turning lathe", says van den Bosch. "The machine is also very special in other ways: The special pallet table with separate straightening table and motor-driven alignment stand is extremely important to us". This extra feature on the VCE 2000 makes the setup process for the next workpiece more ergonomic and productive, allowing it to be completed while another workpiece is still being processed.
Tall, quiet and productive
Dörries CONTUMAT VCE 2000 lathe in valve production
The Dutch company uses the VCE 2000 predominantly to machine cast steel, chrome steel, duplex, super duplex, Inconel and occasionally titanium. Two round valves, each weighing around 5.5 tonnes with 80-mm flange holes, were produced from Inconel in a complete machining process. The integrated tool magazine with 90 pockets also plays an important role in the complete machining process. As around 80% of the machining operations are allotted to turning, the magazine contains 50 lathe tools that Mokveld has transformed into 300 lathe tools using a technological trick with special holders. However, the percentage of milling and drilling operations also plays a crucial role: The Dutch valve specialists appreciate the fact that bores can now also be manufactured on the machine in a single clamping position. This reduces the long machining times, as well as costs and energy consumption.
The expenditure on measuring devices is remarkably high: Both the aligning station and the machine room are equipped with a Renishaw probe and automatic calibration device. This function is important in a turning and machining centre that roughs down, finishes, mills and drills in a single clamping position. There is even a finishing process of exactly 30 µm for very large workpieces, whereby grinding is omitted. "For safety reasons, precision and quality are very important to us", says the expert. "After all, our valves work at high pressures of 20 to 900 bar". "Our customers expect a high level of performance from us in every respect", adds Marketing Manager Chris van Assem. "The requirements have increased in the standards that we need to observe".
Another special feature is the extended retraction and stopping function, which Mokveld ordered for two reasons: Firstly, if there are impending collisions, then the tool is directed out of the machining area and into a safe position. The Siemens 840 D sl control system controls the movement of one or two drive axles during this extended retraction. These drive axles provide various individual retraction distances depending on the situation at hand. Secondly, Mokveld responds with the extended retraction and stopping function in the event of a power failure. The necessary energy comes from the DC bus of the drive system, which is controlled in a way that ensures the energy does not fall below or exceed the voltage limits. Thanks to this clever control, drives do not spin out and can be brought to a standstill.
But what are the aspirations of an experienced production expert who machines challenging valves on a daily basis? Bart van den Bosch: "I hope that one day we will also machine small housings on a machine tool in a complete machining process".
