Review of plasma powder surfacing technologyPlasma powder surfacing is an advanced surfacing technology, which uses argon plasma arc as heat source and powder alloy as filler.Compared with the traditional surfacing methods such as electric welding and argon arc welding, plasma powder surfacing has the characteristics of good surfacing forming, controllable penetration, high adhesion, good density and easy automation. Therefore, it is also the necessary equipment required by the relevant certification departments when valve enterprises apply for special equipment manufacturing license (TS) A-level certification.
1.Working process of plasma powder surfacing equipment
(1) Arc generation
There are two kinds of arc generating devices inside the equipment, which supply non transfer arc and transfer arc respectively.The negative electrodes of the two power supplies are connected in parallel and connected to the tungsten electrode (negative electrode) of the stack welding gun through a cable.The positive pole of the non transfer arc power supply is connected to the nozzle of the stack welding gun through the cable, and the positive pole of the transfer arc power supply is connected to the workpiece through the cable.The cooling water is led to the welding gun through the water-cooled cable to cool the nozzle and electrode.Argon enters the welding torch through solenoid valve and rotameter.After the power is turned on, the non transfer arc is ignited by high frequency spark.Then the transfer arc is ignited by the conductive channel between the tungsten electrode and the workpiece caused by the non transfer arc flame.After the transfer arc is ignited, the non transfer arc can be retained or cut off.It mainly uses transfer arc to produce molten pool on the surface of workpiece.
(2) Solder powder output
The alloy powder is continuously supplied by the powder feeder according to the demand, and is sent into the welding gun with the aid of powder feeding gas (generally argon) and blown into the arc.The alloy powder is heated in advance in the arc column, in a molten or semi molten state, and sprayed into the molten pool of the workpiece, where it is fully melted, and the gas and slag are discharged.
(3) Parameter adjustment
By adjusting the transfer arc and non transfer arc current, powder feeding amount and other process parameters, the heat transferred to the workpiece and melted alloy powder can be controlled.With the relative movement of the welding gun and the workpiece, the alloy pool gradually solidifies and the required alloy deposit layer is obtained on the workpiece.
2.Process characteristics of plasma powder surfacing
Compared with other surfacing methods, plasma surfacing has many advantages because it uses plasma arc as heat source and alloy powder as filler metal.
(1) High cladding speed and high productivity.
(2) The penetration is controllable and the dilution rate is low.
Dilution ratio mainly refers to the overlap and fusion of surfacing layer and substrate, and its function is to control the bonding strength of surfacing.If the dilution ratio is too small, the strength will be low (and metallurgical bonding will be changed into mechanical bonding). If the dilution ratio is too large, the performance of the surfacing layer will be affected and the shrinkage stress of the surfacing layer will be large, resulting in cracking.It is generally controlled at about 5% - 10%.
(3) The surfacing surface is flat and smooth with high density, and the surfacing surface of 0.5-5mm can be completed at one time.
(4) The stable surfacing layer can be obtained continuously for a long time, and the surfacing surface has no quality problems such as porosity and trachoma.
(5) The alloy powder is easy to prepare and can be used in a wide range of materials. Cobalt based, nickel based, iron-based and copper based powder welding materials can be selected, and the formula can be directly formulated according to the working conditions.
(6) It can be equipped with special machine, robot, etc. according to the demand, which is easy to realize automation and reduce labor intensity.
(7) The utilization rate of powder is high, and the utilization rate can reach more than 75%.