Valk Welding: 2003

Valk Welding has delivered two robot installations to Caltax Marine Diesel B.V. in Kruiningen, specialised in reconditioning of parts for marine diesel engines. The installations provide worn parts of valves, valve seats and piston heads with a new wearing layer. Set-up times can be largely reduced when replacing the semi-automatic welding process by completely automatic robot welding using the off-line programming system DTPS that is also supplied by Valk Welding. In doing so, Caltax Marine Diesel B.V. was able to further improve its position on the fierce competitive market.

Caltax Marine Diesel B.V., a part of the holding Traas van Houte, is active in the reconditioning of marine diesel engines for shipping companies. Thereto, Caltax disposes of a number of agents in Europe, Asia and the United States. The often very bulky engines (with ten to twelve cylinders and an engine power of sometimes up to 100,000 pk) are dismounted on the site. Partially worn valves, seats, pistons etc. are then transported to Kruiningen, where they undergo an intensive repair process. All in all, this is much cheaper than replacing them with new parts, providing the reconditioning process is carried  out by experts.

Caltax Marine Diesel B.V. has an excellent international reputation based on twenty years of experience, skilled collaborators and - not in the least - a high quality machine park. The company has among others ten installations for welding under powder cover and four weld-on units with which worn parts of valves and seats get a new cover of heat-resistant steel. Large machining units, turning machines and boring machines are being used for precision machining of valves, seats and pistons.

Critical heat-input
The reconditioning process starts with jet cleaning of the dismounted parts. Then the part is inspected and the critical measurements are taken to  determine the scope of the wear and to gain insight in the necessary repair measures to be taken. This is taken as a basis for the customer offer. The repair process then starts with removing the burned parts. By means of welding under powder cover and MIG-welding with solid wire, new layers of heat-resistant steel are applied to the valves and seats and to the upper part of the pistons (piston heads).

The valves are usually made of RVS 307. The weld-on layer consists of stainless steel type AISI 307 or Inconel 625. The latter material is highly heat-resistant. That is why this material is being used on request to weld-on the piston heads. In that case, a layer of steel is applied first; then follows rough-turning and then a layer of Inconel 625 of about  5 mm thickness is applied. When welding under powder cover, it is important that the heat-input does not exceed a certain limit. Excess heat supply will lead to excessive stress building and when the part is remounted in the engine, the large shock load might cause cracks with all the subsequent consequences.

When it comes to know-how and experience, controlling the heat-input is one of the critical points that will make the fundamental difference between one reconditioning firm and another. For pistons and cylinder covers, stress-free annealing is the following necessary step. Then, the parts are correctly sized by turning, boring, drilling of the cooling channels etc., followed by a final check. The last step includes remounting (that is applying of the studs etc) after which the parts are ready for transport.

Enormous gain of time
Recently, Caltax Marine Diesel B.V. has invested in two robot installations for welding-on new wearing courses so that the various parts of the marine diesel engine can start a second life. The installations are identical and consist of a Panasonic VR-006L robot and a manipulator for workpieces up to 2500 kg. With these installations, a new layer of stainless steel can be applied to valves and valve seats, says manager Jaap Weber; for pistons, a new layer of steel is welded-on to the top side.

Application of a layer of Inconel 625 on the piston heads is also done by robots. Before, this was done semi-automatically, using among others a Bug-O welding tractor and a turn table. Although the results of this process were of satisfactory quality, the process itself was quite labour-intensive. The setting for each new part was a time-consuming activity;  the part concerned had to be clamped in the clamping chuck several times for each treatment.

Weber: "For example, a valve is now scanned by means of a measurement arm to map its contour. In no time, the actual contour can be seen on the display. With the off-line programming and simulation system DTPS we define the new contour. Then, the welding programme is generated and sent to the robot. That is all: the valve will be completely welded in one action."

The short set-up time, just one clamping and the high welding duty (about 98% - with semi-automatic welding this was about 60%) mean an enormous gain of time, and hence an increase of competitive edge. Furthermore, the procedure, including off-line programming, is being experienced as a distinctive improvement of the labour conditions. That is why we will continue automation with robots in the future.

Weber: "The support by Valk Welding, in particular the practical application of the DTPS-software, is important and highly valued. The availability of this support has played an important role when choosing Valk Welding, although there were two other companies in the race for the order. If they had only sold us one or two robots and said: now you have to sort it out yourself, there would never have been a transaction. Now, we have the feeling that we work together on the project - also with wire and gas suppliers."

(Source: Roestvaststaal no. 2 / March 2003)