Knuckle for a railway car coupler
A knuckle for a railway coupler system is made without internal voids or cores. Instead, external pockets are formed on the front face and tail portion surface to reduce weight. The knuckle is formed by investment casting, which permits a pulling face to be provided without a draft angle or parting line typical of a cast part. As a result of these innovations, the knuckle according to the invention has an improved fatigue life.
1. A method of increasing fatigue life in a knuckle for a railway car coupler system, comprising the steps of:
forming a destructible prototype of the knuckle, said prototype having a pulling face and including a plurality of ribs defining front external weight reduction pockets and a plurality of ribs defining rear external weight reduction pockets;
coating the destructible prototype with a semi-permanent coating to form a temporary mold;
removing the destructible prototype from the temporary mold;
casting a finished knuckle in the temporary mold without using a destructible core; and
destroying the temporary mold;
wherein the finished knuckle has a weight in a range of about 75 to about 90 lbs.
2. The method according to claim 1 , wherein the finished knuckle has a minimum fatigue life of 400,000 cycles as determined by AAR standard M-216.
3. The method according to claim 1 , wherein the pulling face has no draft angle.
4. The method according to claim 1 , further comprising the step of shot peening at least the pulling face of the finished knuckle to create residual compressive stress to improve the fatigue life profile of the pulling face under tension.
5. The method according to claim 1 , wherein the finished knuckle has a minimum average life of 600,000 cycles as determined by AAR standard M-216.
6. The method according to claim 1 wherein the finished knuckle is free of a parting line on the pulling face.
7. The method according to claim 1 , wherein the knuckle has a weight in a range of about 80 lbs to about 85 lbs.
8. The method according to claim 1 , wherein the temporary mold defines external weight reduction pockets in the surface of the knuckle having a cumulative volume in a range of about 50 in 3 to about 70 in 3 .
9. The method according to claim 1 , further comprising the step of preheating the temporary mold after removing the destructible prototype and before casting in the temporary mold to remove moisture from the temporary mold.
10. The method according to claim 1 , wherein the knuckle has a surface roughness in a range of about 120 microinches (RMS) to about 200 microinches (RMS).