High velocity oxy fuel process is a thermal spray process which is used to spray a variety of powders ranging from chrome to tungsten carbides to name a few.
The HVOF spray process works by mixing liquid or gas fuel with oxygen flowing into a combustion chamber where the fuel and gas is ignited. This result in a high temperature flame (2700 – 3100 °C) which under pressure accelerated through a nozzle to reach subsonic speeds (1500 – 2000 m/s).
The high velocity creates characteristic shock waves in the flame which is visible as a diamond pattern in the flame.
Powder, specific for the type of application is fed into the centre of the flame which then partially melt on the surface while in the flame. These particles are then through the flame deposited onto the component surface to form a mechanical bond with the base material.
These coatings are low in porosity <1%, low oxide inclusions and have high bond strengths which provide low wear properties, high corrosion and high temperature resistance in various applications.
Electric arc spray is a process in which two wires (various material types) are fed through a push or a push/pull feeder system into a spray gun.
The system uses DC power to energize two conductive wires (one positive and one negative). These wires then in the gun arc against each other resulting in melted material. This melted material is then transferred onto a component substrate with clean compressed air which blows through the centre of the arc of the two wires, atomizing the molten material into fine droplets. These droplets of material coming into contact with the substrate flattens and form splats. These splats form one on top of the other to form a strong mechanical bond.
Different coatings of zinc, aluminium, chrome steels, copper, bronze can be sprayed for corrosion protection, surface modification and decoration as well as for engineering reclamation.
Plasma spray utilize a high energy heating source to melt and accelerate fine powder particles onto a prepared substrate. During impact, the molten particles or droplets cool down and solidify instantly by heat transfer to the underlying substrate and therefor form, by accumulation a coating consisting of thin layers.
For plasma spraying, the creation and utilization of plasma as the high temperature source are legalized in the plasma torch. The plasma torch or gun consist of a cone-shaped thoriated tungsten cathode and a cylindrical copper anode.
Gasses (for forming plasma) flow through the annular space between two electrodes and an arc is initiated by high-frequency discharge. A stream of gas which flows between the electrodes stretches the arc, so that in its course from one electrode to the other, the arc loops out of the nozzle of the torch as a plasma flame.
Gasses that are mainly used on the plasma spray process is He, H2, N2 and Ar and are mainly used as the plasma forming gasses.
The temperatures in the plasma flame are normally 10 000 – 15 000 °C. For this reason, we can spray almost any metal or ceramic including refractory metals or oxides by melting and deposit to form plasma sprayed coatings.
PTA process, Plasma Transferred Arc, is a melting welding process suitable for hardfacing on mechanical workpieces subject to wear and/or corrosion with super alloy metal powders.
The powder filler metal is continuously projected on the piece through the plasma arc. The driven output of the PTA torch allows to keep the dispersion in flat below 5% and to deposit, in max efficiency conditions, beads from 1 to 4 mm and width from 3 to 30 mm.
The shape and the size of the coated layer change according to the welding parameters. The penetration control in PTA machines is obtained by varying the quantity of ionized gas and it is not conditioned by the process, unlike other arc welding systems.
The quantity of plasma gas is continuously adjustable by the operator and it is monitored by sophisticated feedback control. This is one of main features of PTA process in welding coatings, so that, in most cases, you can work with one layer only, obtaining a hardness closed to the nominal value of the alloy employed.
Precision welding that is used to join different minute parts together is known as micro welding. This is a careful type of welding. It is performed in a small area and it should be taken care of that the parts near welding are not damaged.
Micro welding is defined as a generic term for welding processes which are applied to the sections which, owing to the object for welding being extremely small and or fine, are affected by factors such as weldability, diffusion thickness, deformation amount and surface tension, particularly whose effect on dimension is to be taken into account.