Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1998-10-23
2000-08-29
Batten, Jr., J. Reed
Metal founding
Process
Shaping liquid metal against a forming surface
148541, 148546, 164477, B21B 146, C21D 804
Patent
active
06109336&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the manufacture of a steel strip or sheet which is suitable as deep-drawing steel for the manufacture of for example steel can bodies by deep-drawing and ironing. Ironing is also sometimes called wall-thinning.
DESCRIPTION OF THE PRIOR ART
To be suitable as deep-drawing steel, a grade of steel must fulfil a number of requirements, several important ones of which are discussed in the following.
To obtain a closed, so-called two-piece can, the first piece of which comprises the body including the base and the second piece is the lid, a flat blank of deep-drawing steel is taken for the first piece which flat blank is first deep-drawn into a cup with a diameter of, for example 90 mm and a height of, for example 30 mm, and which cup is then ironed into the can with a diameter of, for example 66 mm, and a height of, for example 115 mm. Indicative values for the thickness of the steel material in the different production stages are: starting thickness of the blank 0.26 mm, base thickness and wall thickness of the cup 0.26 mm, base thickness of the can 0.26 mm, wall thickness of the can at half height 0.09 mm, thickness of the top edge of the can 0.15 mm.
As this example shows, for making cans deep-drawing steel must have good formability and must retain this property over time too, to allow for storage and transport. In other words, deep-drawing steel must not be susceptible to ageing. Ageing leads to high forming forces, cracking during forming and surface defects from stretcher strains. A way of countering ageing is so-called over-ageing, wherein carbon, that contributes to a great extent to ageing symptoms, is separated in a controlled manner and can no longer diffuse to dislocations in the steel.
The desire to save material by being able to use increasingly lighter cans also acts on the requirement for high formability in order, from a given starting thickness to the blank, to be able to achieve the smallest possible finished thickness of the can wall and also of the top edge of the can. The top edge of the can places particular requirements on the deep-drawing steel. After the can has been formed by ironing, the top edge is reduced in diameter, so-called necking, in order to enable use of a smaller lid and so save on lid material. After necking, a flange is applied along the top of the top edge to enable the lid to be attached. The necking in particular and applying the flange are processes which place high requirements on the additional formability of the deep-drawing steel that was already formed earlier when the body was being made.
Besides the formability the purity of the steel is important. Purity is taken to mean the degree of absence of mainly oxidic or gaseous inclusions. Such inclusions occur in steel making in an oxygen steel plant and from the casting powder that is used in the continuous casting of the steel slab which is the base material for the deep-drawing steel. In the case of necking or forming of the flange, an inclusion can give rise to a crack which itself is the cause of a later leak in the can when filled with contents and closed. In the case of storage and transport, contents leaking out of the can may cause damage, in particular by contamination, to other cans or goods in its vicinity exceeding many times the value of the leaking can and its contents. The more the thickness of the edge of the can is reduced, the more becomes the risk of a crack as a consequence of an inclusion. Therefore, deep-drawing steel must be free from an inclusions. In as much as inclusions are unavoidable with the present method of steel making, these should be small in size and occur only in very small amounts.
Another requirement relates to the degree of anisotropy of the deep-drawing steel. In the manufacture of a deep-drawn/ironed or wall-thinned two piece can, the top edge of the can does not extend in a flat plane, but rather it displays a wave pattern around the circumference of the can. In the industry the wave peaks are known as ears.
REFERENCES:
patent: 4885041 (1989-12-01), Den Hartog et al.
patent: 5042564 (1991-08-01), Van Perlstein et al.
Den Hartog Huibert Willem
Pronk Cornelis
Batten, Jr. J. Reed
Hoogovens Staal BV
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