Method and apparatus for forming a steel pressure container, such steel pressure container and a preform therefor

1. A method for forming a steel container having a curled open end, comprising the steps of:

i) providing a steel cup;

ii) deep drawing the steel cup into a drawn container preform;

iii) drawing and ironing the body of the drawn container preform; and

iv) curling an open end of the drawn container preform by forming a precurl and by curling the precurl into an elongated curl,

wherein the method further includes a step of pinch trimming a free end of the drawn container preform, and

wherein the pinch trimming step comprises:

engaging the free end of the drawn container preform with an inner tool, an outer tool, and at least one stepped edge provided on at least one of the inner tool and the outer tool;

moving the free end of the drawn container preform and the inner tool relative to the outer tool such that a portion of the free end of the drawn container preform is pinched between the inner tool and the outer tool at the at least one stepped edge; and

removing the pinched portion from the drawn container preform,

wherein the inner tool is a punch and the at least one stepped edge is provided on the punch.

2. The method as claimed in claim 1 , wherein the steel cup is provided by forming from steel plate.

3. The method as claimed in claim 1 , wherein the deep drawing step ii) comprises several deep drawing steps.

4. The method as claimed in claim 1 , wherein the container preform is provided with a concave bottom form during or after the deep drawing step ii).

5. The method as claimed in claim 1 , wherein the method further comprises a step of necking the free end of the drawn container preform.

6. The method as claimed in claim 5 , wherein the necking step includes mandril necking.

7. The method as claimed in claim 1 , wherein the steel is coated at least one side with a coating.

8. The method as claimed in claim 7 , wherein at least the free end zone to be necked, is subjected to a heating treatment.

9. The method as claimed in claim 8 , wherein the heating treatment comprises induction heating.

10. A method for forming a steel container having a curled open end, comprising the steps of:

i) providing a steel cup;

ii) deep drawing the steel cup into a drawn container preform;

iii) drawing and ironing the body of the drawn frawn container preform; and

iv) curling an open end of the drawn container preform by forming a precurl and by curling the precurl into an elongated curl,

wherein the method further includes a step of pinch trimmimng a free end of the drawn container preform, and

wherein the pinch trimming step comprises:

engaging the free end of the drawn container preform with an inner tool, an outer tool, and at least one stepped edge provided on at least one of the inner tool and the outer tool;

moving the free end of the drawn container preform and the inner tool relative to the outer tool such that a portion of the free end of the drawn container preform is pinched between the inner tool and the outer tool at the at least one stepped edge; and

removing the pinched portion from the drawn container preform,

wherein the method further comprises a step of necking the free end of the drawn container preform,

wherein the necking step includes a step of mandril necking, and

wherein the pinch trimming step is performed at the same time as the mandril necking step and the mandril necking step also includes moving the drawn container preform and the inner tool relative to the outer tool.

11. The method as claimed in claim 10 , wherein the inner tool is a mandril, the outer tool is a necking ring, and the at least one stepped edge includes at least one stepped edge provided on the mandril.

12. The method as claimed in claim 11 , wherein the at least one stepped edge further includes at least one stepped edge provided on the necking ring and the at least one stepped edge on the mandril cooperates with the at least one stepped edge on the necking ring to form the pinched portion.

13. An apparatus for forming a steel container, comprising:

i) a unit for deep drawing a steel cup into a drawn container preform;

ii) a unit for thin drawing the body of the drawn container preform; and

iii) a unit for curling an open end of the drawn container preform, which curling unit comprises a precurl forming sub unit and an elongated curl forming sub unit,

wherein the apparatus further comprises a trimming unit for pinch trimming a free end of the drawn container preform,

wherein the trimming unit comprises an inner tool, an outer tool, and at least one stepped edge provided on at least one of the inner tool and the outer tool, and

wherein the inner tool, the outer tool, and the at least one stepped edge engage the free end of the drawn container preform such that moving the free end of the drawn container preform and the inner tool relative to the outer tool causes a portion of the free end of the drawn container preform to be pinched between the inner tool and the outer tool at the at least one stepped edge,

wherein the inner tool is a punch and the at least one stepped edge is provided on the punch.

14. The apparatus according to claim 13 , further comprising a unit for forming the steel cup from steel plate.

15. The apparatus according to claim 13 , wherein the deep drawing unit comprises several deep drawing sub units.

16. The apparatus according to claim 13 , further comprising a unit for forming a concave bottom in the container preform.

17. The apparatus according to claim 13 , further comprising a necking unit for necking the free end of the drawn container preform.

18. The apparatus according to claim 17 , wherein the necking unit comprises a mandril necking unit.

19. The apparatus according to claim 13 , further comprising a heating unit for heating at least the free end zone to be necked.

20. The apparatus according to claim 19 , wherein the heating unit comprises an induction heating unit.

21. An apparatus for forming a steel container, comprising:

i) a unit for deep drawing a steel cup into a drawn container preform;

ii) a unit for thin drawing the body of the drawn container preform; and

iii) a unit for curling an open end of the drawn container preform, which curling unit comprises a precurl forming sub unit and an elongated curl forming sub unit,

wherein the apparatus further comprises a trimming unit for pinch trimming a free end of the drawn container preform,

wherein the trimming unit comprises an inner tool, an outer tool, and at least one stepped edge provided on at least one of the inner tool and the outer tool, and

wherein the inner tool, the outer tool, and the at least one stepped edge engage the free end of the drawn container eform such that moving the free end of the drawn container preform and the inner tool relative to the outer tool causes a portion of the free end of the drawn container preform to be pinched between the inner tool and the outer tool at the at least one stepped edge,

wherein the apparatus further comprises a necking unit for necking the free end of the drawn container preform,

wherein the necking unit comprises a mandril necking unit, and

wherein the mandril necking unit includes the inner tool and the outer tool of the trimming unit.

22. The apparatus according to claim 21 , wherein the inner tool is a mandril, the outer tool is a necking ring, and the at least one stepped edge includes at least one stepped edge provided on the mandril,

23. The apparatus according to claim 22 , wherein the at least one stepped edge further includes at least one stepped edge provided on the necking ring and the at least one stepped edge on the mandril is configured to cooperate with the at least one stepped edge on the necking ring to form the pinched portion.