Method of producing sectional strips and sectional sheets

Details Method of producing sectional strips and sectional sheets Method of producing sectional strips and sectional sheets

1997-12-18

2001-02-20

Ryan, Patrick (Department: 1725)

Metal fusion bonding

Process

Specific mode of heating or applying pressure

C228S205000, C228S206000

Reexamination Certificate

active

06189770

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of producing sectional strips and sectional sheets having different thicknesses over their widths and to sectional strips and sectional sheets produced by the method.
Sections produced by extrusion, particularly closed hollow sections, can be extruded with different wall thicknesses. But a minimum wall thickness of at least 1.2 mm is required in the thinnest regions. Sections with thinner wall thicknesses may be produced only from thinner sheets by folding or roll forming. But, they then have the same wall thickness throughout, which corresponds to the greatest required wall thickness.
For lightweight structural sections, the greatest wall thickness is often required only in specific regions, for strength, while lesser wall thicknesses are acceptable for use in other regions. Such lightweight structural sections are particularly desired in automotive engineering, to save as much weight as possible on the vehicle.
Cold rolling strips or sheets, in particular of aluminum or aluminum alloys, cannot produce different thicknesses, since the thinner regions suffer a considerably greater degree of deformation than the thicker regions and are therefore stretched considerably more in length than the thicker regions. This causes backward slip of material ahead of the roll groove in the thinner region, with consequent wave formation and finally leads to tearing of the strip or sheet passed through the rolling stand.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of producing sectional strips and sectional sheets of different thicknesses over the width of the sheet or strip, to be controlled in terms of rolling technology for producing sectional strips and sectional sheets of high quality and which are suitable for producing sheet sections by folding or roll forming.
The method of producing sectional strips and sectional sheets of different thicknesses over the width according to the invention comprises joining at least two overlaid strips or sheets of different widths, as measured across the roll direction, to each other by roll bonded cladding.
Roll bonded cladding is known for applying metallic coverings. Roll bonded cladding enables the widest variety of metals to be joined to one another after suitable pre-treatment. However, the known cladding method serves only for applying thick, impervious coverings to a base metal. Such coatings are intended, for example, as corrosion protection or as protection against chemical attack in chemical apparatus engineering or as lustrous material, for example in the lighting industry. By contrast, the roll bonded cladding method of the invention is used for joining at least two overlaid strips or sheets of prescribed, different widths to each other to obtain sectional strips and sectional sheets with a step change in thickness and which are then usable for further processing into sheet sections.
Tests have shown that a different backward slip ahead of the respective roll grooves caused by the deforming likewise occurs in roll bonded cladding. Surprisingly, the tests have shown that this backward slip is compensated by the different drawing in rate of the strips or sheets, whereby no wave formation and no tearing occurs ahead of the roll grooves.
So that the strips or sheets joined by roll bonded cladding are completely straight when they emerge from the roll groove, it is advantageous if the at least two strips or sheets are joined to each other symmetrically in the rolling direction with respect to the longitudinal center line of different thicknesses, i.e., either the narrower strip is rolled centrally onto the wider strip, or two or more narrower strips, which are spaced apart and symmetrical with respect to the longitudinal center line, are rolled on in line with the outer edges of the wider strip.
If a sectional strip or sectional sheet with only one change in thickness is required, the strips or sheets joined to each other by roll bonded cladding may be slit along the longitudinal center line after the roll bonded cladding. Of course, a plurality of sectional strips or sectional sheets may also be produced by multiple slitting.
Preferably, at least two strips or sheets can be rolled to the prescribed thickness by roll bonded cladding in one pass. It must be ensured that the degree of deformation caused by the roll bonded cladding is the same for the at least two strips or sheets, i.e., that the roll bonded cladding takes place, for example, with a degree of deformation of 60%. Accordingly, if the thinner region originally has a thickness of 3 mm, it is deformed to 1.2 mm. The thicker region, which comprises two strips or sheets lying one on top of the other and which may have an initial thickness of 5 mm, has to be deformed to 2 mm. This controllable ratio deformation is obtainable when the overlying strips or sheets are of the same material or have the same deformability under pressure.
When using strips or sheets of aluminum or aluminum alloys, their mutually facing surfaces may be freed of their oxide layers immediately before roll bonded cladding so that they can then be joined to each other homogeneously, since the thus activated surfaces of aluminum or aluminum alloy have a great affinity for each other.
Preferably, the roll bonding is performed between two cooperating rollers, profiled to produce the desired deformations and also to confine the widths of the strips or sheets, so that they will displace linearly upon being deformed.
Since there are linear displacements in the rolling direction between the strips in the roll groove during roll bonded cladding, this produces a bond which is equivalent to a bond carried out by means of friction welding.
The strips or sheets to be joined to each other by roll bonded cladding may have the same or different initial thicknesses and final thicknesses. As a result, sectional strips and sectional sheets can be produced which comprise strips or sheets of different widths and different thicknesses over the width joined by roll bonded cladding. Sectional strips or sectional sheets are particularly preferred which comprise two strips or sheets of different widths and each having a thickness of 3 mm and 2 mm, which are joined to each other by roll bonded cladding in such a way that, after roll bonded cladding, the thinner region has a thickness of 1.2 mm and the thicker region has a thickness of 2.0 mm.
These sectional strips or sectional sheets can be used for producing sheet sections as lightweight structural sections for vehicle construction if, for example, an age-hardening aluminum alloy, for example AlMgSi1F21, is used for both layers. After the roll bonded cladding, the sectional strips or sectional sheets are solution annealed, quenched and stretched and can be subsequently converted into sheet sections of different material thicknesses in different regions by folding or roll forming.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.


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