The Gold Star Quiz in Springmaking Answers

2. False. Flat springs have relatively small deflections when compared to normal variations in their free state. This, coupled with the fact that loads vary with the third power of material thickness, contributes to substantially greater load variations. This is particularly true of thin material applications where normal mill tolerances can account for more than ±20 percent variation due to the material alone.

3. False. Stainless steel Type 302 uncoils during stress relief. The hooks, then, would be closer to right angles.

4. a.

5. b.

6. b. While all three characteristics are important, it is generally agreed that ovality and size tolerance is the critical property for uniform coiling.

7. c. Must be passivated to prevent rust.

8. False. 302 stainless steel is nonmagnetic only in the annealed condition.

9. True.

10. False. The edge condition is very critical. A spring made with slit, deburred edge material will fatigue much faster than a spring with a smooth, round edge.

11. a. When two loads at two heights are defined, the rate is defined by Hooke’s Law (load = rate × deflections). It can also be expressed as R = (P2 – P1) ÷ (L1 – L2). Therefore, the number of coils would have to be changed as well as the free length. Also, the stated rate of 30 lb./in. would be changed to meet the load requirements.

12. Free length = 10.50 in. Free length tolerance = ± 0.150 in.

13. d. While all of the choices, a-e, will contribute to premature breakage, the single greatest cause of failure in extension springs is tool marks caused by the forming of the ends.

14. False.

15. True. Tooling should be designed so that any burrs that occur in critical or functional areas are on the compressively stressed side of the spring member.

16. True.

17. b.

18. c.

19. Lower. In the case of stainless steel wire, torsion straightening causes the tensile strength of the drawn wire to decrease by about 10%.

20. c.

21. c.

22. False. A 4-1 ratio is only good for ground ends. Springs with unground ends may buckle at a ratio greater than 2.630-to-1.

23. b. The torque deflection curve for a power spring is not linear. Therefore, at 25% unwind, the anticipated torque will be 95% of the fully wound torque, or 50 × 0.95 = 47.5 in. lb.

24. Setup time or rejections.

25. False. A close-coiled spring may be fitted with inserts that thread into the end coils. By adjusting the inserts farther in or out, the number of active coils (N) becomes variable and increases or decreases the rate per inch in the inverse proportion of the change.

26. b.

27. c.

28. False. Wire producers prefer to test tempered wires for tensile strength. Rockwell hardness is difficult to test for, except in the heaviest diameters.

29. a.

30. False. Pitch is measured from the center of the wire of adjacent coils, not from the coil opening.

31. b. 50 percent. Using less material or more material will decrease the available deflection.

32. False. Through Design of Experiments, it has been determined that the main culprit in variation is the setup. Raw material comes in second when machine capability is known.

33. True.

34. b.

35. a. Reduce the coil diameter to increase the rate per inch and then reduce the initial tension to center the loads.

36. b.

37. False. As temperature increases or decreases from 70oF, modulus changes by 1% to 2% per 100oF.

38. False. Type 301 stainless steel is self-passivating.