Crack detection in razor blades

1. A method of inspecting razor blades for cracks comprising:

providing a plurality of razor blades in a stack,

inducing a current in the stack, and

measuring a parameter that is related to the current and indicative of the presence or absence of cracks in the razor blades.

2. The method of claim 1 wherein the inducing step comprises placing an induction coil adjacent the stack and delivering alternating current to the coil.

3. The method of claim 2 wherein the inducing step comprises placing the induction coil around the stack and causing relative movement between the induction coil and the stack in a direction parallel to a long axis of the stack.

4. The method of claim 1 wherein the measuring step comprises measuring the temperature of at least one of the razor blades in the stack.

5. The method of claim 4 further comprising monitoring the measured temperature for localized areas of relatively higher temperature, indicative of cracks.

6. The method of claim 4 further comprising obtaining a set of temperature profiles of the blades along the length of the stack.

7. The method of claim 1 wherein the measuring step comprises measuring infrared radiation emitted by at least one of the blades of the stack.

8. The method of claim 7 wherein the measuring step comprises using an infrared camera to generate a set of temperature profiles of the blades along the length of the stack.

9. The method of claim 1 or 8 further comprising fanning the blades during the measuring step.

10. The method of claim 9 wherein the fanning step comprises applying an air jet to a surface of the stack.

11. The method of claim 10 wherein the applying step comprises directing an air knife at the surface.

12. The method of claim 11 wherein the air knife includes a dual air nozzle assembly.

13. The method of claim 8 comprising operating the infrared camera at a speed of at least 250 frames/second.

14. The method of claim 8 wherein the razor blades are of uniform blade length and blade thickness, and the method further comprises using the infrared camera to generate an infrared image having a length at least equal to the blade length and a width at least equal to twenty times the blade thickness.

15. The method of claim 1 further comprising recording a sequence of thermal images of the blades along the stack.

16. The method of claim 1 wherein the measuring step comprises measuring the induced current.

17. The method of claim 16 wherein the induced current is measured using a second coil.

18. The method of claim 16 further comprising monitoring the measured current for areas of reduced current, indicative of cracks.

19. The method of claim 1 further comprising focusing the induced current.

20. The method of claim 19 wherein the focusing step comprises positioning counter-rotating field cancellation coils on both sides of the current-inducing coil.

21. The method of claim 20 wherein the ratio of the current in each of the field cancellation coils to the current in the current-inducing coil is from about 1:5 to 3:5.

22. The method of claim 1 wherein the providing step comprises stacking the blades so that their cutting edges are in substantially parallel alignment with one another.

23. The method of claim 11 wherein the blades each have a thickness of less than about 85 microns.

24. The method of claim 11 or 23 wherein the air jet has a width that is less than or equal to the blade thickness.

25. A method of inspecting razor blades for cracks comprising:

providing a plurality of razor blades in a stack,

inducing a current in the stack, and

measuring infrared radiation emitted by at least some of the blades of the stack to determine the presence or absence of cracks in the razor blades.