Semi-sealed blast hole bit and method for drilling

1. A drill tool, comprising:

a bit body;

at least one bearing shaft extending from the bit body;

a cone mounted for rotation on the bearing shaft;

a first sealing system comprising a first annular seal gland formed in a cylindrical surface of the cone and a seal ring retained within the first annular seal gland and compressed against a cylindrical surface of the bearing shaft;

a second sealing system comprising a second annular seal gland formed in a radial surface of the cone and a sealing structure retained within the second annular seal gland and compressed against a radial surface surrounding the bearing shaft; and

a set of non-pressure compensated lubrication channels configured to supply lubricant to an interstitial volume defined between the cone and bearing shaft, the lubricant retained within the interstitial volume by the first and second sealing systems, the lubrication channels further supporting open air circulation through the bearing when the sealing systems fail and lubricant is lost.

2. The tool of claim 1 , wherein the sealing structure of the second sealing system comprises a Belleville spring.

3. The tool of claim 2 , wherein the second sealing system comprises a first corner formed between the radial surface surrounding the bearing shaft and a first cylindrical surface, wherein an inner circumferential surface of the Belleville spring is positioned at the first corner.

4. The tool of claim 3 , wherein the first cylindrical surface is offset from the bearing shaft by an offset radial surface surrounding the bearing shaft.

5. The tool of claim 3 , wherein the second sealing system further comprises a second corner formed between the radial surface of the cone and a second cylindrical surface, wherein an outer circumferential surface of the Belleville spring is positioned near the second corner.

6. The tool of claim 5 , wherein compression of the Belleville spring causes movement of the outer circumferential surface of the Belleville spring towards the second corner.

7. The tool of claim 2 , wherein the Belleville spring comprises a sealing material attached to an outer periphery of a surface of the Belleville spring, the sealing material extending out to the outer circumferential surface.

8. The tool of claim 7 , wherein the sealing material is in contact with the radial surface of the cone.

9. The tool of claim 7 , wherein the sealing material comprises a polytetrafluoroethylene ring mounted to the outer periphery of the surface of the Belleville spring.

10. The tool of claim 7 , wherein the sealing material comprises a ring mounted to the outer periphery of the surface of the Belleville spring, the ring comprising a material selected from the group comprising leather, packing foam, silicone, rubber, wire mesh, wax, clay, nitrile buna rubber, highly saturated nitrile buna rubber, fluoroelastomers, and perfluoroelastomers.

11. The tool of claim 1 , wherein the sealing structure of the second sealing system comprises a mesh screen ring.

12. The tool of claim 11 , wherein the second sealing system comprises a first corner formed between the radial surface surrounding the bearing shaft and a first cylindrical surface, wherein an inner circumferential surface of the mesh screen ring is positioned at the first corner.

13. The tool of claim 12 , wherein the first cylindrical surface is offset from the bearing shaft by an offset radial surface surrounding the bearing shaft.

14. The tool of claim 12 , wherein the second sealing system further comprises a second corner formed between the radial surface of the cone and a second cylindrical surface, wherein an outer circumferential surface of the mesh screen ring is positioned near the second corner.

15. The tool of claim 1 , further comprising a one-way fluid passage isolation structure mounted in one of the non-pressure compensated lubrication channels between an interior of the lubrication channel and an exterior air region of the tool.

16. The tool of claim 15 , wherein the isolation structure permits fluid flow into the interior of the lubrication channel from an inner air flow chamber of the tool.

17. The tool of claim 16 , wherein the isolation structure permits injection of lubricant into the set of non-pressure compensated lubrication channels to deliver lubricant to the interstitial volume defined between the cone and bearing shaft.

18. The tool of claim 16 , wherein the isolation structure permits, following failure of at least the first sealing system to retain lubricant within the interstitial volume, air to enter into the set of non-pressure compensated lubrication channels from the inner air flow chamber of the tool.

19. The tool of claim 18 , wherein the entering air assists in evacuating lubricant from within the interstitial volume.

20. The tool of claim 18 , wherein the entering air supports the open air circulation through the bearing when the sealing systems fail and lubricant is lost.

21. A method for rock drilling, comprising:

providing a non-pressure compensated rock drill bit with a bearing sealed to contain lubricant;

using the rock drill bit in an initial drilling mode with the lubricant supporting bearing operation;

continuing the initial drilling mode until seal failure and loss of the bearing lubricant; and

further using the rock drill bit in a secondary drilling mode, after loss of bearing lubricant, with an open air circulation supporting bearing operation; and

wherein providing comprises providing a first o-ring type sealing system and providing a second Belleville spring type sealing system to seal the bearing and contain lubricant.

22. The method of claim 21 , wherein lubricant is supplied to the bearing through lubricant channels, and where the lubricant channels support open air circulation during the secondary drilling mode.