Carbide coating devices - to meet the highest requirements for toughness, hardness and surface wear resistance

Toughness, hardnessand wear-resistant surfacesare the core objectives for tools, devices and machine parts. 

With the carbide coating devicesfrom joke Technology, you achieve all three objectives in an optimal combination.

Nowadays, three processes are mainly used:

• Galvanic coatingwith hard layers
• Plasma flame sprayingand
• Electro erosive tungsten carbide coatings.

The first two processes often fail to produce enough adhesive strengthfor the coatings applied. In contrast, with process three it is possible to apply tungsten carbideto a very wear-resistant surface at the highly stressed points of a workpiece.

Characteristics of the carbide coating

The applied coating combines perfectly with the steel, and adheres so that it can withstand almost any mechanical stress. Even impacts, bending, stretchingor compressioncannot dislodge the coating. It can only be removed by grinding or special sandblasting, however it can be lapped with diamond or silicon carbide. The underlying steel is not softened by the coating, instead the hardness of the upper zone increases. With certain steel alloys, the tungsten carbide coatingeven penetrates into the base material. The coating reaches a hardness of up to 82 HR 30N, without changing or deforming the workpiecebecause the deposition process is practically cold. The coating is highly heat resistant. The surface is evenand without directional structure.

Material and its pretreatment

For coating with tungsten carbide, any soft, temperedor hardened, alloyedor unalloyed steelis a suitable material . The surface must be clean and metallically pure. Scale and oxide layersmust be removed without fail. Ground, polished or bare machined parts must be degreased. If the tungsten carbide coating is applied to an unclean surface, the strength of adhesion is insufficient, the coating is uneven and has inclusions.

Procedure

The tungsten carbide is coatedusing the electro erosion principle. A tungsten carbide electrode is attached to the positive terminal of a direct current circuit with electronic current and voltage control, to which capacitors of different capacities can be connected. The electrode is clamped in a vibrator gun. The vibrator (gun) sets the electrode in vibration, and brings it into contact with the workpiece being treated. The workpiece is connected to the negative terminal. The electrode contact with the workpiece creates an ionised field, which ensures that the tungsten carbide fuseswith the base material without oxidation. The vibrator helps to rebuild this field continuously. With brief contact pulses of less than 1/100 second, particles are pulled out of the electrode and welded to the surface of the workpiece. Regular to and fro movement of the electrode creates a compact carbide coating. The preselected coating thickness (between 2 and 40 microns)cannot be exceeded, because after reaching saturation no further material is picked up. Therefore post-processing is not required with this method.