The repair and strengthening process of the extruder screw is as follows:
1. Surface cleaning of the extruder screw
Before spraying the screw, you should clean up the plastic attachments on the surface of the screw. The cleaning method is to install the extruder screw on the spraying machine to rotate it, and you should bake it with the neutral flame of a spray gun, and remove it with a spatula after it is plasticized. Then, you can use a sandblasting gun to further remove the oxide layer of the welded surface.
2. Preheating of the extruder screw
During preheating process, the screw head (transmission part) can be clamped by a spraying machine or a vibration surfacing machine. The machine speed should be adjusted below the minimum speed of 15r/nin, and a neutral flame from the muzzle to the twin screw extruder parts about 100mm to preheat the entire screw to about 270℃. The aim is to reduce the thermal stress of the shaft and ensure the quality of the spray welding layer.
3. Spray welding of the extruder screw
The one-step spray welding process can be used. Also, an SPH-1/h spray gun and nozzle No. 2 can be used. The oxygen pressure should be 0.25MPa while the acetylene pressure should be 0.06MPa.
The worn parts of the extruder screw should be repaired by spray welding during rotation, and the maximum screw wear is about 2-3mm. It is necessary to spray enough size in one operation, and the machining allowance must be considered. If the first time of spray is insufficient, special attention should be paid to the preheating temperature and preheating uniformity during the next repair welding to avoid cracks in the weld layer.
4. Trimming and straightening of the extruder screw
The surface quality of Ni60 self-fluxing alloy spray welding is good. Due to the technical requirements of the screw, that is, the straightness, the runout of the surface and the working side of the thread to the screw axis, etc., the screw should be trimmed after welding.
The trimming method is to process a mandrel with a central hole, and press it into the bearing hole of the extruder screw. One end has the three-claw top tightening mechanism while one end has a centering mechanism. It can be machined by turning or grinding, and the blending of the screw caused by spray welding will be eliminated. YMO53 is used for the cutting tool.
The hardness of the welded layer of the screw repaired with Ni60 self-fluxing alloy powder spray welding can reach HRC60, and the thickness of the welded layer is 2-3mm. The screw can be repaired and strengthened, and its service life can also be prolonged.
There may be slight diffusion between the coating and the roll neck to enhance their bonding strength. The bonding between the sprayed particles is mainly mechanical, and the diffusion bonding, metallurgical bonding, crystal epitaxy are supplemented by physical bonding.
5. Preheat the workpiece before spraying the extruder screw
As one of the leading extrusion screw manufacturers, we will tell you how to preheat the extruder screw. The preheating of the workpiece before spraying has great practical significance. It can remove the moisture on the surface and reduce the stress accumulation of the coating. The suitable preheating temperature is about 100°C. Aluminum-clad nickel composite powder F505 should be sprayed on the surface of the processed journal as the bonding layer. The thickness of the bonding layer is 0.10-0.15mm, there is no need to spray it too thick since it is only used for bonding. You can spray the working layer of G101 powder after spraying the bonding layer. The G101 powder must be preheated and baked at 105-250°C to ensure the fluidity of the powder spray and avoid agglomeration blocking the spray channel.
In the spraying process, the gas pressure, flame temperature, spraying distance, spraying angle, and moving speed should be strictly controlled to ensure uniform and smooth coating as well as firm bonding.
The specific control parameters are as follows: the coating position is outer arc surface, the preheating temperature should be 100-200°C, the spray distance should be 180-200mm, the spray angle should be 90°, the moving speed of the spray gun should be 6-12mm/min and the roller linear speed should be 8-12m/min.
A neutral flame is used when spraying the working layer, and the powder can be observed from the flame. If the powder at the end of the flame is bright white, it means the temperature is high. If it is dark red, it means the temperature is sufficient. At this time, it is necessary to adjust the size of the powder feeding airflow and the flame energy rate to heat the powder to bright white. The powder temperature is higher, the speed is faster, and the deposition effect is better.
6. Metal processing after spraying the extruder screw
After spraying, you can use asbestos to wrap the sprayed part with multiple layers to make it cool slowly to avoid cracks. When it is cooled to room temperature, rough turning can be carried out, and you should leave a grinding allowance (about 0.3-0.5mm) for grinding. The grind should be based on the size required by the drawing and the specified roughness. The repair of the roll is completed so far.
