JPS5912389B2 - Overlay welding method for screw shaft blades - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of overlay welding on the blade surface of a screw shaft.

For example, in the treatment of sludge and sludge, so-called screw decanter-type centrifuges are used to separate solids suspended in water, but as their processing capacity has gradually increased in size, The inner screw shaft has come to be used with a length of about 3.5 m and an outer diameter of 1 m.

The blades of such screw shafts are easily corroded or worn out by sludge, sand, pebbles, etc. during use.
To prevent this, it is desirable to perform hard overlay welding on the lead surface of the blade.10 Also, repair areas that have been severely worn during use by overlay welding, or overlay welding on the entire blade. It may be played back.

However, such a large screw shaft is prone to deformation due to build-up welding, or cracks occur when applying 15 hard build-up, and it is difficult to cover a large area with arc welding using conventional methods. If overlay welding is attempted, there are some problems in construction, such as the number of man-hours required.

The present invention aims to provide a method for overlaying the blades of a screw shaft that solves the above-mentioned problems. The blade is locally heated with an induction electrode to melt the overlay metal powder placed on the surface of the blade, and the temperature of the molten pool is controlled, and the high-frequency induction electrode is vertically heated while rotating the screw shaft. The thickness of 30 blades of a screw shaft is characterized by moving the electrode along the blade surface to sequentially create a molten pool on the blade surface under the electrode and continuously hardening the blade. Concerning the welding method.

Next, the method of the present invention will be described with reference to the accompanying drawings, taking as an example the case of overlay welding on the lead surface of a blade.

Both ends of the screw shaft 1 are supported vertically by thrust bearings 2 etc. so that they can rotate freely, and a suitable binder is added to metal powder for overlay and applied to a predetermined range of the lead surface of the blade 3. Then, the coating layer 5 and the blade of the area are sandwiched from above and below with a gap between the electrodes 4 of a high-frequency welding machine, and when a high-frequency current is passed through the electrodes, the coating layer 5 of the metal powder for overlay and the coating layer 5 of the metal powder for overlay are sandwiched between the blades 3 sandwiched between the electrodes. An induced current is generated and heated. In this case, if the distance between the electrode 4 and the blade 3 is adjusted so that heat is concentrated on the surface layer of the lead surface of the blade and the coating layer 5, the surface layer of the lead surface and the coating layer 5 will melt first. The high-frequency electrode 4 is made to be movable up and down by, for example, rotation of the screw shaft 6, and the electrode 4 is moved upward while rotating the vertically supported screw shaft 1, so that the electrode is moved relative to the blade surface. If the metal powder coating layer 5 under the electrode 4 is moved to
The surface layer of the blade lead surface is sequentially melted and the molten pool 7 is solidified by the movement of the raw L electrode 4, so that overlay welding can be performed automatically and continuously. In this case, the molten pool 7 If the temperature is raised too high, the blade may deform or even the blade base material may be melted. Therefore, in order to continue stable overlay welding, the temperature of the molten pool 7 under the electrode 4 is constantly monitored using a non-contact pyrometer. For example, the radiation pyrometer 8 measures the temperature, and the measurement signal is input to the control device of the high-frequency welding machine.

When a high-frequency current is applied to the electrode 4 and the hardened overlay metal previously applied to the lead surface of the blade 3 begins to melt locally at one end of the screw to form a molten pool 7, the electrode moves. A radiation pyrometer 8, which is provided to move up and down along with the molten pool 7 and has been placed in advance to focus on this position, is connected to the molten pool 7.
The temperature is measured at a predetermined temperature (for example, 1050
℃), the detection signal causes the screw blade to immediately move relative to the high frequency electrode (for example, 100℃).
! ! The spread of the molten pool and the state of temperature rise between the time when the welding process starts (L/min) and the welding progresses are extremely delicate, so it is extremely difficult to manually adjust the power output by visual inspection. If No. 5 is connected to the output control device of the high-frequency power source to control the molten pool temperature, stable overlay welding becomes possible.Also, the electrode 4 moves relative to the blade 3 at a constant speed. If so, the molten pool 7
If the temperature of the molten pool 7 exceeds the set temperature, the high-frequency power supply will dynamically turn off for a short period of time to prevent overheating, and if the temperature of the molten pool 7 falls, the power will be turned on automatically. is prevented from rising too high.

The appropriate temperature of the molten pool 7 differs depending on the type of overlay metal, but is approximately in the range of 1050 to 1200°C. When hardfacing is performed using hardfacing metal powder, especially when using a large screw shaft. In such cases, cracks often occur, but in such cases it is better to weld the front and back of the molten pool while sequentially heating the weld with gas.

That is, as the electrode 4 moves relative to the blade 3 of the screw shaft to locally create a molten pool 7 on the blade surface and perform overlay welding in sequence, the process is indicated by an x mark in Fig. 3. The screw shaft is rotated while gas heating two locations 9 and 10 on the shaft side of the inside of the blade 3 at the front and back of the electrode 4 in the direction of movement, so that the molten pool 7 is heated before and after the electrode 4.
Overlay welding is performed while heating the front and back of the shaft. By doing this, it is similar to heating the welding area after preheating, and the heat rapidly moves from the molten pool to the shaft, resulting in overlay welding. This prevents cracks from forming in the metal layer and also prevents deformation of the blade.In order to prevent the molten overlay metal from flowing down from the edge of the blade 3 during welding, a band 11 is attached to the edge of the blade 3. It is best to temporarily attach it and remove it by cutting or grinding after overlay welding.

In addition, if the screw shaft is deformed due to overlay welding, the shaft can be prevented from bending by applying compressive force by hydraulic pressure from the top and bottom of the shaft in the axial direction and performing overlay welding.

As explained above, in the method of the present invention, metal powder for overlay is applied to the blade surface of the screw shaft to be overlaid, and the high-frequency electrode is moved relatively along the blade surface to sequentially locally create a molten pool. This method is easy to automate, as it is a method of making and overlaying welding, and it is also stable throughout as the temperature of the molten pool is measured and welding is carried out while controlling high-frequency induction heating. Can perform overlay work.

Furthermore, when hardfacing is performed, it is easy to automatically proceed with welding while heating the front and rear parts of the molten pool with gas, which has extremely large practical effects such as easily preventing the occurrence of cracks.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of one embodiment for explaining the method of the present invention, Fig. 2 is a sectional view of the main part, and Fig. 3 is a plan view of the main part. , 2・
...Bearing, 3...Blade, 4...
... High frequency induction electrode, 5 ... Metal overlay coating layer, 6 ... Screw shaft, 7 ... Molten pool, 8.
...Radiation pyrometer, 9,10...Heating position, 11...Band.

Claims (1)

[Claims] 1 In the method of overlay welding to the blades of a screw shaft, the screw shaft is supported in a rotatable manner, and the blades are locally heated using a high-frequency induction electrode that is movable in the vertical direction and placed on the surface of the blade. After melting the metal powder for overlay and controlling the temperature of the molten pool, the high-frequency induction electrode is moved vertically while rotating the screw shaft, and the electrode is moved along the blade surface to form the area under the electrode. A method for overlay welding of blades of screw shafts, which is characterized by sequentially creating a molten pool on the blade surface and performing hard overlaying continuously.