Pick tool and method for making same

1. A pick tool comprising an insert mounted in a steel holder, the insert comprising a superhard tip joined to a cemented carbide support body at an end of the support body, the support body comprising an insertion shank;

the steel holder comprising a bore configured to accommodate the insertion shank and a shaft configured for mounting the steel holder onto a tool carrier, the shaft being configured to inter-engage non-rotationally with the tool carrier;

the cemented carbide support body having a volume of at least 15 cubic centimeters (cm 3 ) and comprising cemented carbide material having fracture toughness of at least 8 megapascals times square root meter (MPa·m 1/2 ) and at most 17 MPa·m 1/2 ;

in which an inserted portion of the insertion shank is non-rotationally secured in the bore such that the insert does not rotate relative to the shaft when the shaft is engaged with the tool carrier, the inserted portion having an axial length of at least 4 centimeters (cm) and at most 8.5 cm, and a mean diameter of at least 1.5 cm and at most 4.0 cm.

2. A pick tool as claimed in claim 1 , in which the insertion shank is shrink-fitted within the bore.

3. A pick tool as claimed in claim 2 , in which the interference between the insertion shank and the bore is at least 0.002 percent of the diameter of the insertion shank and at most 0.3 percent of the diameter of the insertion shank.

4. A pick tool as claimed in claim 2 , in which the support body comprises cemented carbide material comprising grains of metal carbide having a mean size of at most 8 microns.

5. A pick tool as claimed claim 2 , in which the superhard tip comprises diamond material.

6. A pick tool as claimed in claim 2 , in which the superhard tip comprises a polycrystalline diamond (PCD) structure bonded to a cemented carbide substrate.

7. A pick tool as claimed in claim 1 , in which the interference between the insertion shank and the bore is at least 0.002 percent of the diameter of the insertion shank and at most 0.3 percent of the diameter of the insertion shank.

8. A pick tool as claimed in claim 1 , in which the support body comprises cemented carbide material comprising at most 10 weight percent metal binder material.

9. A pick tool as claimed in claim 8 , in which the support body comprises cemented carbide material comprising grains of metal carbide having a mean size of at most 8 microns.

10. A pick tool as claimed in claim 2 , in which the support body comprises cemented carbide material comprising at most 10 weight percent metal binder material.

11. A pick tool as claimed claim 10 , in which the superhard tip comprises diamond material.

12. A pick tool as claimed in claim 1 , in which the support body comprises cemented carbide material comprising grains of metal carbide having a mean size of at most 8 microns.

13. A pick tool as claimed claim 12 , in which the superhard tip comprises diamond material.

14. A pick tool as claimed in claim 1 , in which the ratio of the volume of the cemented carbide support body to the volume of the superhard tip is at least 30 and at most 300, and the volume of the superhard tip is at least 200 mm 3 and at most 500 mm 3 .

15. A pick tool as claimed in claim 1 , in which a surface area of the insertion shank abuts a corresponding inner side surface area of the bore, the surface area being at least 20 cm 2 .

16. A pick tool as claimed in claim 1 , in which a portion of the insertion shank is only partly surrounded by the bore of the steel holder.

17. A pick tool as claimed in claim 1 , in which the steel holder is provided with a seat for supporting an end of the cemented carbide support body, and the bore communicates with the outside of the steel holder through a passage provided through or adjacent the seat.

18. A pick tool as claimed claim 1 , in which the superhard tip comprises diamond material.

19. A pick tool as claimed in claim 1 , in which the superhard tip comprises a polycrystalline diamond (PCD) structure bonded to a cemented carbide substrate.

20. A pick tool as claimed in claim 1 , in which the superhard tip comprises diamond grains dispersed in a cemented carbide matrix.

21. A pick tool as claimed in claim 1 , in which the inserted portion has a mean diameter of at least 2 cm and at most 3.5 cm.

22. A method of making a pick tool, the method including

providing an insert and a steel holder for the insert, the insert comprising a superhard tip joined to a cemented carbide support body having an insertion shank;

the steel holder comprising a shaft configured to inter-engage non-rotationally with a tool carrier and the steel holder provided with a bore for receiving the insertion shank;

the insertion shank having a volume of at least 10 cm 3 ; and

shrink fitting the insertion shank into the bore of the steel holder to form the pick tool;

wherein the cemented carbide support body has a volume of at least 15 cubic centimeters (cm 3 ) and comprises cemented carbide material having fracture toughness of at least 8 megapascals times square root meter (MPa·m 1/2 ) and at most 17 MPa·m 1/2 ; and

wherein an inserted portion of the insertion shank is non-rotationally secured in the bore such that the insert does not rotate relative to the shaft when the shaft is engaged with the tool carrier, the inserted portion having an axial length of at least 4 centimeters (cm) and at most 8.5 cm, and a mean diameter of at least 1.5 cm and at most 4.0 cm.

23. A method of disassembling a pick tool, the method including

providing an insert and a steel holder for the insert, the insert comprising a superhard tip joined to a cemented carbide support body having an insertion shank;

the steel holder comprising a shaft configured to inter-engage non-rotationally with a tool carrier and the steel holder provided with a bore for receiving the insertion shank;

the insertion shank having a volume of at least 10 cm 3 ; and

heating the steel holder to expand the bore and withdrawing the insertion shank from the bore;

wherein the cemented carbide support body has a volume of at least 15 cubic centimeters (cm 3 ) and comprises cemented carbide material having fracture toughness of at least 8 megapascals times square root meter (MPa·m 1/2 ) and at most 17 MPa·m 1/2 ; and

wherein prior to the withdrawal, an inserted portion of the insertion shank is non-rotationally secured in the bore such that the insert does not rotate relative to the shaft when the shaft is engaged with the tool carrier, the inserted portion having an axial length of at least 4 centimeters (cm) and at most 8.5 cm, and a mean diameter of at least 1.5 cm and at most 4.0 cm.

24. A pick tool comprising an insert mounted in a steel holder, the insert comprising a superhard tip joined to a cemented carbide support body at an end of the support body, the support body comprising an insertion shank;

the steel holder comprising a bore configured to accommodate the insertion shank and a shaft configured for mounting the steel holder onto a tool carrier, the shaft being configured to inter-engage non-rotationally with the tool carrier;

in which an inserted portion of the insertion shank is non-rotationally secured in the bore such that the insert does not rotate relative to the shaft when the shaft is engaged with the tool carrier, the inserted portion having an axial length of at least 4 centimeters (cm) and at most 8.5 cm, and a mean diameter of at least 1.5 cm and at most 4.0 cm.

25. A pick tool as claimed in claim 24 , in which the inserted portion has a mean diameter of at least 2 cm and at most 3.5 cm.