Hollow forging process for main shaft of large wind turbine generator

1. A hollow forging process for main shaft of wind turbine generator, comprising the following steps:

a first step of cutting off the dead head and the bottom of an ingot; a second step of upsetting and punching a hole; a third step of drawing-out; and

a fourth step of local upsetting, drawing-out and shaping-up;

wherein, in the fourth step, the forged piece is shaped up by local upsetting and drawing-out through a turnplate; the turnplate comprises a circular turnplate base and a turnplate body connected to the turnplate base; a circular hole that matches the shape of the lower end of the main shaft to be processed is arranged on the turnplate body; a hole with a taper is arranged in the middle of the turnplate base, which ensures both excircle and inner hole of the main shaft will not result in eccentricity in combination with a core rod of the taper; the core rod is a conic cylinder; the head of the core rod is cylindrical; the fillet radius of the end of the core rod is 30-50 mm and the taper of the core rod is 1:100.

2. The hollow forging process for main shaft of wind turbine generator according to claim 1 , wherein, in the third step, the process of drawing-out is conducted by a drawing-out core rod; the drawing-out core rod is overall cross-shaped; the transverse core rod body that forms the cross-shape abuts against a flange plate face of the main shaft during drawing-out so as to prevent material escaping from a through-hole in the center of the main shaft.

3. The hollow forging process for main shaft of wind turbine generator according to claim 1 , wherein, in the second step, a plunger chip is used for punching the hole; the height of the plunger chip is greater than the depth of the punched hole after upsetting plus the necessary height allowing hanging tongs to remove a roughly processed ingot out of the plunger chip.

4. The hollow forging process for main shaft of wind turbine generator according to claim 3 , wherein, both the plunger chip and the turnplate are made of 5CrMnMo.

5. The hollow forging process for main shaft of wind turbine generator according to claim 1 , wherein, an outer gear ring is arranged around the periphery of the turnplate body; a gear is arranged to mesh with the outer gear ring; the shaft of the gear is connected to that of a motor that drives the gear to rotate; since the gear and the outer ring are engaged to each other, when the motor operates, the turnplate body will rotate to realize rotated upsetting.

6. The hollow forging process for main shaft of wind turbine generator according to claim 1 , further comprises a step of heating the ingot before the first step by directly putting a hot-charged steel ingot of above 600° C. into a furnace for heating up to 850° C.±20° C. and the temperature is maintained for 7 hours, and further reheating up to 1250° C.±10° C. and the temperature is maintained for 15 hours;

in the first step, the dead head and the bottom of the ingot is cut off under a forging temperature of 1200-1220° C. and the forging temperature is maintained for 5 hours;

in the second step of upsetting, the turnplate is adopted for rotated upsetting; and a plunger chip is adopted for punching the hole; hanging tongs are adopted for removing a roughly processed ingot out of the plunger chip after proper upsetting and punching so as to put it back into the furnace for reheating up to 1250° C.±20° C. and the temperature is maintained for 8-10 hours;

in the third step of drawing-out, the ingot is drawn out into an octagon shape with marks made; a roughly processed intermediate ingot is processed; the ingot is put back into the furnace for reheating up to 1240° C.±20° C. and the temperature is maintained for 6-7 hours;

in the fourth step of local upsetting, the ingot is drawn out to shape up under the temperature of 1230-900° C., and the roughly processed intermediate ingot is vertically inserted into a gasket group consisted of several folded gaskets that is placed on a movable turnplate formed with a lower tumplate and a upper gasket; while local upsetting, an upper junction plate and an upper anvil fixed on the upsetting plate are demounted and the upsetting plate on a movable cross beam is used for upsetting by 200 mm downward; then the upper junction plate and the upper anvil are mounted to reduce the contact area of upsetting; the methods of rotated upsetting and gradual rolling are adopted to reach the required size; after upsetting, the ingot is put back into the furnace for reheating up to 1230° C.±20° C. and the temperature is maintained for 5 hours.

7. The hollow forging process for main shaft of large wind turbine generator according to claim 1 , wherein, the main shaft is made of 34CrNiMo6.

8. The hollow forging process for main shaft of wind turbine generator according to claim 2 , wherein, the main shaft is made of 34CrNiMo6.

9. The hollow forging process for main shaft of wind turbine generator according to claim 6 , wherein, the hot-charged steel ingot is a steel ingot with a surface temperature of above 650° C. soon after pouring and demoulding, and the hot-charged steel ingot is placed into a heat preserving barrel for 4-5 hours; the heat preserving barrel has a steel plate-welded outer shell, a lining of mineral wool and a cover on the top.