How to Choose the Right Spray Arc Voltage

According to the features and demands of the arc spraying process, the main parameters of the arc spraying process can be categorized to the four: spray voltage, current, air pressure and distance. The choice of these parameters can directly affect the stability of the arc spraying process, the coating quality, the spraying speed and the deposition efficiency. Therefore, it is very important to learn how to apply the parameters reasonably. This article will discuss the spray voltage.

Spray voltage refers to the arc voltage between the two wires when spraying. When arc spraying, two wires are fed evenly and an arc is generated at the tip of the two wires at the front of the spray gun. To achieve a stable and reliable coating, a stable arc voltage is required. The arc voltage reflects the measurement of the distance between the wire tip. To control this parameter effectively can maintain the stability of the geometry of the atomization zone, so the commonly used arc spraying equipment requires a flat volt-ampere characteristic of electrical source.

The arc voltage affects the stability of the arc combustion, and each material has its own minimum value. The lower the arc voltage, the smaller the size of the melted particles, and the narrower the range. If the arc voltage is lower than the critical minimum arc voltage of the material, the arc cannot be burned stably. Hence the wire will be intermittently contacted, i.e. arc intermitted and ignited, and the block non-fully melt wire appears. Sometimes two wires can even be welded together in parallel. At this time the ammeter needle swings violently, sometimes even beyond the working range.

The critical arc voltage of the material is mainly related to the melting point of the material. In general, a low melting point of the material leads to a low critical arc voltage; On the other hand, the higher melting point, the higher critical arc voltage. Besides, the resistivity of oxide film of wire surface also affects the critical voltage of the material.

When the spray voltage exceeds the critical arc voltage, with the rise of the arc voltage, the distance between the tip of the wire increases, the angle of the spray jet grows, and the particle size range of the sprayed particles will also enlarge. The figure below shows the effect of arc voltage on the atomization and distribution of sprayed particles. As the arc voltage increases, the burnt tendency of the sprayed material elemental increases, especially those that are easily oxidized. Therefore, to obtain high-quality coatings, under the premise of ensuring the stability of arc combustion, we have to choose the lowest possible arc voltage.