CA2022235A1 - Steel drawing sheet with metal coating - Google Patents
Steel drawing sheet with metal coatingInfo
- Publication number
- CA2022235A1 CA2022235A1 CA002022235A CA2022235A CA2022235A1 CA 2022235 A1 CA2022235 A1 CA 2022235A1 CA 002022235 A CA002022235 A CA 002022235A CA 2022235 A CA2022235 A CA 2022235A CA 2022235 A1 CA2022235 A1 CA 2022235A1
- Authority
- CA
- Canada
- Prior art keywords
- sheet
- range
- drawing sheet
- sheet according
- cut
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000576 coating method Methods 0.000 title claims abstract description 27
- 239000011248 coating agent Substances 0.000 title claims abstract description 25
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 25
- 239000002184 metal Substances 0.000 title claims abstract description 25
- 229910000831 Steel Inorganic materials 0.000 title claims description 12
- 239000010959 steel Substances 0.000 title claims description 12
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 12
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 12
- 239000011701 zinc Substances 0.000 claims abstract description 12
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 6
- 229910001297 Zn alloy Inorganic materials 0.000 claims abstract 2
- 238000000034 method Methods 0.000 claims description 15
- 238000005096 rolling process Methods 0.000 claims description 7
- 238000000151 deposition Methods 0.000 claims description 5
- 238000007598 dipping method Methods 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910000611 Zinc aluminium Inorganic materials 0.000 claims 2
- 229910045601 alloy Inorganic materials 0.000 claims 2
- 239000000956 alloy Substances 0.000 claims 2
- HXFVOUUOTHJFPX-UHFFFAOYSA-N alumane;zinc Chemical compound [AlH3].[Zn] HXFVOUUOTHJFPX-UHFFFAOYSA-N 0.000 claims 2
- 229910000838 Al alloy Inorganic materials 0.000 claims 1
- 238000009792 diffusion process Methods 0.000 claims 1
- 235000019592 roughness Nutrition 0.000 description 16
- 238000010422 painting Methods 0.000 description 6
- 150000002739 metals Chemical class 0.000 description 4
- 230000008021 deposition Effects 0.000 description 3
- 238000000227 grinding Methods 0.000 description 3
- 239000003921 oil Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005246 galvanizing Methods 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 235000008247 Echinochloa frumentacea Nutrition 0.000 description 1
- 240000004072 Panicum sumatrense Species 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 210000003298 dental enamel Anatomy 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000001962 electrophoresis Methods 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 239000010687 lubricating oil Substances 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000004439 roughness measurement Methods 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 108010003641 statine renin inhibitory peptide Proteins 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 238000012345 traction test Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B1/227—Surface roughening or texturing
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/26—After-treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
- B21B2001/383—Cladded or coated products
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Coating With Molten Metal (AREA)
- Metal Rolling (AREA)
- Shaping Metal By Deep-Drawing, Or The Like (AREA)
Abstract
A B S T R A C T
Drawing sheet with a metal coating on at least one side has on this side a roughness constituted by regularly distributed isolated wells. The wells have a depth of 5 to 25 µm and a base diameter of 80 to 200 µm; they are distributed with a density of 50 to 150 wells per linear inch in at least two perpendicular directions.
The coated side has an arithmetic mean roughness Ra at the 0.8 mm cut-off of 0.5 to 2 µm, and the arithmetic mean roughness Ra of this side at the 8 mm cut-off differs by not more than 0.3 µm from the value of the arithmetic mean roughness at the 0.8 mm cut-off. The coating may consist of zinc, aluminum, or a zinc alloy.
Drawing sheet with a metal coating on at least one side has on this side a roughness constituted by regularly distributed isolated wells. The wells have a depth of 5 to 25 µm and a base diameter of 80 to 200 µm; they are distributed with a density of 50 to 150 wells per linear inch in at least two perpendicular directions.
The coated side has an arithmetic mean roughness Ra at the 0.8 mm cut-off of 0.5 to 2 µm, and the arithmetic mean roughness Ra of this side at the 8 mm cut-off differs by not more than 0.3 µm from the value of the arithmetic mean roughness at the 0.8 mm cut-off. The coating may consist of zinc, aluminum, or a zinc alloy.
Description
2~2223~
S~EL DRAWING SHEE~ NI~H ME~AL COA~ING
BACKGROUND TO THE I NV~NTI ON
Field of the Invention This invention relates to drawing sheet with a metal coating. It also relates to a process for the manuf~cture of such shest.
The sheets to which the invention relates include sheets coated with zinc or aluminum, whether by dipping or by electrodeposition, and sheets coated with an allot of zinc with another metal, particularly aluminum, nickel, or iron. Such sheets are intended particularly for the manufacture of visible parts in motor vehicle bodywork.
They generally have a thickness between 0.6mm and lmm.
In order to fix ideas and by way of a single example intended purely to illustrate the invention, the description which follows will make more particular reference to steel sheet with a dip-galvani~ed zinc coating, referred to for the sake of simpIicity as galvanised sheet.
What is desired is a sheet of this type which has good resistance to binding or seizing during drawing and : . :
-: .:. .
~2223~
excellent appearance after painting, the latter property applying both to the sheet in the undeformed state and to drawn components.
Tests which we have carried out have demonstrated that the behavior of a coated sheet during drawing is substantially different from the behavior of an uncoated steel sheet. Although the reason for this has not been clearly e~tablished at present, it would appear that the difficulties encountered are due at least in part to the fact that the coating metals are appreciably less hard than cold rolled steel.
It is in fact found that these sheets, and in particular galvanised sheets, are very much more susceptible to binding than steel sheets.
Also the drawing of a galvanised sheet gives rise to powdering.
Description of Prior art Binding and powdering are well known. A~ a brief remlnder, both conslst o~ the detachment of met~l partlcle~ from the surface of ths sheet by the drawing tool as a re~ult of the frictlon force~ cau~ed by drawlng. These are thersfore two phenomana of the ~ame . .
type, which differ es 9 entially in the siz 8 of the metal particles torn off. They occur to a greater extend with galvanised sheets than with steel sheets.
In the case of galvanised sheets they cause a build-up of particles at the base of the drawing tools, i.e. in places where binding of steel sheets generally does not occur; this results in additional defects in the drawn components. Finally, defects in galvanised sheets cannot be repaired by grinding as in the case with steel, as this would result in loss of the corrosion protection provided by the coating.
It has already been proposed, particularly in BE-A-870 609, that a relief consisting of regularly distributed plateaus and valleys should be imprinted onto the surface of the sheet to provide a specific roughness by means of a suitably treated finishing roll. These valleys form a reservoir in which the lubricating oil flows as it carries the particles torn off in the process of drawing. The application of this method to sheets coated with metals such as zinc or aluminum nevertheless runs into the difficulties which have been mentioned above, because of the very much lesser hardness of these metals. Torn off particles cannot be completely removed by the oil flowing in ths valleys of the rough surface; as a consequence they stick to the :
tools and damage he surface of the sheets.
It is also known, particularly through LU-A-86 784, that small isolated wells, i.e. wells which do not communicate with each other, can ~e imprinted onto the surface of sheets. This arrangement makes it possible to work with higher drawing pres~ures than in the case of communicating valleys, because the small wells act a~ "oil pockets~ prsventing exae~lvely rapid expul~ion of the lubricant under high pres~ures. It has been found, however, that this arrangement cannot be ussd directly with sheets coated with metals such as 2inc or aluminum; not only is roughness not regularly imprinted on the coated sheet, but the sheet is still particularly susceptible to binding.
DISCLOSURE OF THE INVENTION
The ob~ect of thl~ lnventlon 1~ to provide a coated sheet whloh doea not hava the aforementloned disadvantage3 and whlch through approprlats roughness ensures satl~f~ctory rasi3tance to blnding and excellent appearance after palntlng.
According to thls lnventlon a steel drawing ~heet provided wlth a metal coatlng on at lea~t one ~lde ha~ a roughness on that 31de oon~l~tlng of regularly .
s distributed isolated wells, the said wells have a depth of between 5 ~m and 25 ~m ancL a base diameter of between 80 ~m and 200 ~m, the said wells are distributed with a density of between 50 and 150 wells per linear inch in at least t:wo perpendicular directions on the said side of the sheet:, the said side has an arithmetic mean roughness Ra at the 0.8 mm cut-off between 0.5 ~m and 2 ~m and the arithmetic mean roughness ~a of the said side at the 8 mm cut-off does not differ by more than 0.3 ~m, from the value of the arithmetic mean roughness at the 0.8 mm cut-off.
According to preferred embodiment, the depth of the wells lies preferably between 7 ~m and 20 ~m, and their base diameter lies preferably between 100 ~m and 150 ~m.
In this respect it is appropriate to state that the base diameter considered here is the diameter of the cross-section of a well in the plane of the sheet surface. Similarly the base diameter of a boss on a roll in a rolling mill is the diameter of the cross-section of that boss at the surface of the roll, this cross-section being likened to a plane cross-section because its dimensions are very small in comparison with the diameter of the roll.
It is also to be noted, in the context of this ;,'` :. ~.
2~2~23~
invention, that the cross-sec:tion of a well and boss respectively is not necessarily circular or capable of b~ing directly likened to a circle; for a cross-section of any shape, the diameter wi.ll be the diameter of tha best possible circle circumscribed about the cross-section.
Finally it should not be forgotten that the cut-off exprssses the cut-off wavelength used for the roughness measurement; this expression means that, when measuring surface roughness, surface undulations having a wavelength greater than the value indicated, for example 0.8 mm and 8 mm in this case, are not taken into account.
Preferably, the density of the wells advantageously lies between 90 and 120 wells per linear inch, in at least one of the aforementioned directions.
Furthermore the arithmetic mean roughness Ra at the 0.8 mm cut-off prsferably lies between 0.8 ~m and 1.4 ~m.
The metal coating on the same side preferably has a thickness of between 7 ~m and 25 ~m.
Likewise in a preferential manner the said metal coating may be a zinc coating deposited by dip galvanising.
.
.
2~222~
It has also been found that constancy of the thickness of the metal coating is an important factor in obtaining the desired roughness. In this respect it is advantageous in accordance with the invention that ~ha sum of the thicknesses of the metal coatings on the two sides of the sheet, measured at the sama point, should not differ by more than 30% and preferably ~y not more than 15%, from the sum of the nominal values of these two thicknes 8 e8 .
It has also been found that the best performance in finishing rolling, as regards compliance with reduction ratios and coating thicknesses, was obtained with steels which have no or virtually no drawing plateau. In this respect ultra-low carbon steels micro-alloyed with titanlum have proved particularly useful. Typically these steels have a carbon content of between 0.005% and 0.030% and a titanium content of between 0.050% and 0.150% by weight.
Another aspect of the invention relates to a process for the manufacture of a drawing sheet having the characteri~tics described above. In accordance with the invention the metal coating i~ deposited on at least one side of the said sheet and the coated sheet is rolled using rolls in which at least one roll corresponding to the said coated side has on its æurface a pluralit~ of isolated bosæes regularly di-stributed with a density of between 50 and 150 bosses per linear inch in at least two perpendicular directions, and preferably b~tween 90 and 120 bosses per linear inch in at least one of the aforesaid directions, the said bosses having the shape of spherical segments of a helight between 15 ~m and 30 ~m and a base diameter lying between 100 ~m and 150 ~m, the surface of the said roll also having an arithmetic mean roughness Ra of less than 0.4 ~m and preferably less than 0.2 ~m at the 0.8 mm cut-off between the said bosses.
In accordance with a particular embodiment of this process the said sheet is rolled with a reduction ratio of less than 1%, preferably between 0.4% and 0.8%.
The rolls used for finishing rolling are advantageously treated by means of a high energy beam, such as a laser beam or an electron beam, in accordance with processes which have been developed previously.
Prefer~bly, the said metal coating is daposited by dipping the sheet in a bath of zinc and the thicXness of the said coating is adjusted to a value lying between 7 ~m and 25 ~m, the sum of the thicknesses of the metal coatings on the two sides of the sheet measured at the same point differing by no more than 30% and preferably by not more than 15% from the sum of the nominal values of these two thicknesse~.
%~0 ~ 3`5 Other features and advantages of this invention will be revealed by the example embodiments described below and illustrated by the accompanying drawings.
BRIEF DFSCRIPTION OF THE DRANINGS
Figures 1 a-c show three photomicrographic views on different scales, of the surface of a galvanised drawing sheet according to the invention in its initial condition;
Figures 2 a-c show three photomicrographlc views on the same scales as in Figures 1 a-c, of the same sheet after it has been subjected to a friction test by drawing between planar jaws;
Figures 3 a-c show three photomicrographic views on the same scales as in Figures 1 a-c and 2 a-c, of the same sheet after it has been subjected to a friction test by passage through a device called a "bead simulator"; and Figure 4 is a graph which illustrates the distinctness of image (DOI) of a sheet according to the invention after painting by conventional means.
The photomicrographs are scanning electron microscope , - :
7~ 3 ~
photographs.
DETAILED D~SCRIP~ION OF PREFERRED EMBODIMEN~
The sheet used in this examp:Le was a deep drawing steel of the St 14 type. It was galvanised on both sides by dipping in a lead-free bath, with 140 g/m2 of 7inc on each side. The thickness of the zinc layer was from 8 ~m to 10 ~m on each side. Fini3hing rolling wa~
by means of rolls which had been dressed so as to have a roughness of less than 0.2 ~m at the 0.8 mm cut-off.
The rolls had then been textured by means of a laser beam so that their surface had bosses in the form of spherical segments of a height between 16 ~m and 20 ~m and a base diameter between 100 ~m and 120 ~m. The bosses were distributed in accordance with a predetermined pattern with a density RL = 90 bosses per linear inch in the circumferential direction of the roll and a density ~d = 120 bosses per linear inch in the axial direction of the roll. Finishing rolling was performed with a reduction ratio of 0.8%. After this operation the sheet had a total thickness of 0.76 mm.
Figure 1 shows the surface of the sheet at the time of acceptance, i.e. after galvanising and finishing rolling. Figure la shows the regularity of the surface distribution of the pattern, each unit of which consists 2`(~2`2~3`~
of a well and a plateau. Figure lb shows a portion of the surface of the sheet on a larger scale. The wells correspond to the darker part of each pattern unit. The lighter part of these pattern units represents the plateau, whose height does not exceed 5 ~m. Finally Figure lc illustrates the shape of a well, which in this case can be likened to that of a circle, and the base diameter D of the well.
In this condition the sheet has an effectively planar surface in which wells of a depth of some 12 ~m and a base diameter of some 100 ~m are formed. The distribution density of these wells is 120 and 90 per linear inch in the transverse and longitudinal directions of the sheet respectively. The sheet has an arithmetic mean roughness Ra, measured at tha 0.8mm cut-off, of the order of 1.2 ~m. A useful feature i8 that this roughness is not greatly affectsd by the level of the cut-off. Thus is does not excsed 1.5 ~m at the 8 mm cut-off.
The drawability of the sheet was evaluated in relation to the most critical problem encountered with galvanised products, namely friction behavior and tendency to bind.
Friction behavior was evaluated on the basis of a traction test between two planar jaws gripping the ;
.
~ 2-2/.3~;
sheet; the sheet was slightly lubricated with protective oil. The sheet showed very satisfactory behavior: the depth and diameter of the wells wera not affected; the height of the plateaus became less than 3 ~m. Figures 2 a-c show the surface of the sheet after this test.
A test was also performed in a device called a bead simulator. This test consists of drawing the sheet across a set of three succe~sive rollers in such a way that it is bent in two opposite ways, under traction and wi.h friction. This test caused no change in the shape or dimensions of the wells was illu~trated in Figures 3 a-c. The arithmetic mean roughness Ra at the 0.8 mm cut-of fell to 0.9 ~m.
As far as the tendency to binding is concerned, the sheet was subjected to a U forming test, i.e. the drawing currently performed by the user. 15 blanks were drawn in succession without any sign of binding, whereas with a conventional galvanised sheet only 5 to 6 blanks can be drawn.
The sheet was also subjected to a painting test, performed under conditions typical of the process for the manufacture of motor ~ehicle coachwork sheets:
deposition of a layer of paint having a thickness of some 30 ~m by cataphoresis followed by stoving at 2a~235 for 30 minutes; deposition of a surface coat having a thickness of some 20 ~m followed by stoving at 150-C
for 30 minutes; and finally deposition of a coat of enamel some 45 ~m thick followed by stoving at 125-C
for 30 minutes.
The distinctness of image, DOI, was determined by means of a standard procedure well-known to those skilled in the art under the name of the Ford test. This index varies appreciably in relation the undulation of the surface before paint is applied. This undulation can in particular be expressed by the quantity W = (Raa~ 8mm _ RaC-o 0.8 mm) which represents the difference between the arithmetic mean roughness Ra at the 8 mm and 0.8 mm cut offs respectively, these roughnesses being measured on the unpainted galvanised sheets.
Figure ~ shows the change in the Ford distinctness of image index (DOI) for the painted sheet in relation to the undulation W of the surface of the sheet before painting. The two straight lines (a) and (b) bound a zone in which the values (square points) corresponding to a series of conventional sheets are scattered. It can be seen that among the best of these the ~2~
distinctness of image index l.ies between 8 and 9 for an extremely small undulation (W = 0.2).
Values obtained with sheets in accordance with the invention have besn plotted on this diagram as round points (I and II).
In its acceptance condition, i.e. galvanised and rolled, the sheet has an undulation W = 0.25, and ater painting by the process described above its Ford distinctness of image index is 10 (point I).
A painting test was also performed with a sheet according to the invention deformed by 10% by expansion along two axes in order to simulate drawing. The surface undulation of the sheet increase slightly, to W = 0.4; the Ford distinctness of image index nevertheless remained greater than 9 (point II).
The galvanised sheet according to the invantion thus has remarkable friction behavior as well as a very small tendency to bind; also it ha a very high Ford distinctness of image index, both in the undeformed and the deformed state. These properties makes it particularly useful for the manufacture of visible parts of vehicles, in particular motor vehicle bodywork sheets.
.. , , - ~ ~
S~EL DRAWING SHEE~ NI~H ME~AL COA~ING
BACKGROUND TO THE I NV~NTI ON
Field of the Invention This invention relates to drawing sheet with a metal coating. It also relates to a process for the manuf~cture of such shest.
The sheets to which the invention relates include sheets coated with zinc or aluminum, whether by dipping or by electrodeposition, and sheets coated with an allot of zinc with another metal, particularly aluminum, nickel, or iron. Such sheets are intended particularly for the manufacture of visible parts in motor vehicle bodywork.
They generally have a thickness between 0.6mm and lmm.
In order to fix ideas and by way of a single example intended purely to illustrate the invention, the description which follows will make more particular reference to steel sheet with a dip-galvani~ed zinc coating, referred to for the sake of simpIicity as galvanised sheet.
What is desired is a sheet of this type which has good resistance to binding or seizing during drawing and : . :
-: .:. .
~2223~
excellent appearance after painting, the latter property applying both to the sheet in the undeformed state and to drawn components.
Tests which we have carried out have demonstrated that the behavior of a coated sheet during drawing is substantially different from the behavior of an uncoated steel sheet. Although the reason for this has not been clearly e~tablished at present, it would appear that the difficulties encountered are due at least in part to the fact that the coating metals are appreciably less hard than cold rolled steel.
It is in fact found that these sheets, and in particular galvanised sheets, are very much more susceptible to binding than steel sheets.
Also the drawing of a galvanised sheet gives rise to powdering.
Description of Prior art Binding and powdering are well known. A~ a brief remlnder, both conslst o~ the detachment of met~l partlcle~ from the surface of ths sheet by the drawing tool as a re~ult of the frictlon force~ cau~ed by drawlng. These are thersfore two phenomana of the ~ame . .
type, which differ es 9 entially in the siz 8 of the metal particles torn off. They occur to a greater extend with galvanised sheets than with steel sheets.
In the case of galvanised sheets they cause a build-up of particles at the base of the drawing tools, i.e. in places where binding of steel sheets generally does not occur; this results in additional defects in the drawn components. Finally, defects in galvanised sheets cannot be repaired by grinding as in the case with steel, as this would result in loss of the corrosion protection provided by the coating.
It has already been proposed, particularly in BE-A-870 609, that a relief consisting of regularly distributed plateaus and valleys should be imprinted onto the surface of the sheet to provide a specific roughness by means of a suitably treated finishing roll. These valleys form a reservoir in which the lubricating oil flows as it carries the particles torn off in the process of drawing. The application of this method to sheets coated with metals such as zinc or aluminum nevertheless runs into the difficulties which have been mentioned above, because of the very much lesser hardness of these metals. Torn off particles cannot be completely removed by the oil flowing in ths valleys of the rough surface; as a consequence they stick to the :
tools and damage he surface of the sheets.
It is also known, particularly through LU-A-86 784, that small isolated wells, i.e. wells which do not communicate with each other, can ~e imprinted onto the surface of sheets. This arrangement makes it possible to work with higher drawing pres~ures than in the case of communicating valleys, because the small wells act a~ "oil pockets~ prsventing exae~lvely rapid expul~ion of the lubricant under high pres~ures. It has been found, however, that this arrangement cannot be ussd directly with sheets coated with metals such as 2inc or aluminum; not only is roughness not regularly imprinted on the coated sheet, but the sheet is still particularly susceptible to binding.
DISCLOSURE OF THE INVENTION
The ob~ect of thl~ lnventlon 1~ to provide a coated sheet whloh doea not hava the aforementloned disadvantage3 and whlch through approprlats roughness ensures satl~f~ctory rasi3tance to blnding and excellent appearance after palntlng.
According to thls lnventlon a steel drawing ~heet provided wlth a metal coatlng on at lea~t one ~lde ha~ a roughness on that 31de oon~l~tlng of regularly .
s distributed isolated wells, the said wells have a depth of between 5 ~m and 25 ~m ancL a base diameter of between 80 ~m and 200 ~m, the said wells are distributed with a density of between 50 and 150 wells per linear inch in at least t:wo perpendicular directions on the said side of the sheet:, the said side has an arithmetic mean roughness Ra at the 0.8 mm cut-off between 0.5 ~m and 2 ~m and the arithmetic mean roughness ~a of the said side at the 8 mm cut-off does not differ by more than 0.3 ~m, from the value of the arithmetic mean roughness at the 0.8 mm cut-off.
According to preferred embodiment, the depth of the wells lies preferably between 7 ~m and 20 ~m, and their base diameter lies preferably between 100 ~m and 150 ~m.
In this respect it is appropriate to state that the base diameter considered here is the diameter of the cross-section of a well in the plane of the sheet surface. Similarly the base diameter of a boss on a roll in a rolling mill is the diameter of the cross-section of that boss at the surface of the roll, this cross-section being likened to a plane cross-section because its dimensions are very small in comparison with the diameter of the roll.
It is also to be noted, in the context of this ;,'` :. ~.
2~2~23~
invention, that the cross-sec:tion of a well and boss respectively is not necessarily circular or capable of b~ing directly likened to a circle; for a cross-section of any shape, the diameter wi.ll be the diameter of tha best possible circle circumscribed about the cross-section.
Finally it should not be forgotten that the cut-off exprssses the cut-off wavelength used for the roughness measurement; this expression means that, when measuring surface roughness, surface undulations having a wavelength greater than the value indicated, for example 0.8 mm and 8 mm in this case, are not taken into account.
Preferably, the density of the wells advantageously lies between 90 and 120 wells per linear inch, in at least one of the aforementioned directions.
Furthermore the arithmetic mean roughness Ra at the 0.8 mm cut-off prsferably lies between 0.8 ~m and 1.4 ~m.
The metal coating on the same side preferably has a thickness of between 7 ~m and 25 ~m.
Likewise in a preferential manner the said metal coating may be a zinc coating deposited by dip galvanising.
.
.
2~222~
It has also been found that constancy of the thickness of the metal coating is an important factor in obtaining the desired roughness. In this respect it is advantageous in accordance with the invention that ~ha sum of the thicknesses of the metal coatings on the two sides of the sheet, measured at the sama point, should not differ by more than 30% and preferably ~y not more than 15%, from the sum of the nominal values of these two thicknes 8 e8 .
It has also been found that the best performance in finishing rolling, as regards compliance with reduction ratios and coating thicknesses, was obtained with steels which have no or virtually no drawing plateau. In this respect ultra-low carbon steels micro-alloyed with titanlum have proved particularly useful. Typically these steels have a carbon content of between 0.005% and 0.030% and a titanium content of between 0.050% and 0.150% by weight.
Another aspect of the invention relates to a process for the manufacture of a drawing sheet having the characteri~tics described above. In accordance with the invention the metal coating i~ deposited on at least one side of the said sheet and the coated sheet is rolled using rolls in which at least one roll corresponding to the said coated side has on its æurface a pluralit~ of isolated bosæes regularly di-stributed with a density of between 50 and 150 bosses per linear inch in at least two perpendicular directions, and preferably b~tween 90 and 120 bosses per linear inch in at least one of the aforesaid directions, the said bosses having the shape of spherical segments of a helight between 15 ~m and 30 ~m and a base diameter lying between 100 ~m and 150 ~m, the surface of the said roll also having an arithmetic mean roughness Ra of less than 0.4 ~m and preferably less than 0.2 ~m at the 0.8 mm cut-off between the said bosses.
In accordance with a particular embodiment of this process the said sheet is rolled with a reduction ratio of less than 1%, preferably between 0.4% and 0.8%.
The rolls used for finishing rolling are advantageously treated by means of a high energy beam, such as a laser beam or an electron beam, in accordance with processes which have been developed previously.
Prefer~bly, the said metal coating is daposited by dipping the sheet in a bath of zinc and the thicXness of the said coating is adjusted to a value lying between 7 ~m and 25 ~m, the sum of the thicknesses of the metal coatings on the two sides of the sheet measured at the same point differing by no more than 30% and preferably by not more than 15% from the sum of the nominal values of these two thicknesse~.
%~0 ~ 3`5 Other features and advantages of this invention will be revealed by the example embodiments described below and illustrated by the accompanying drawings.
BRIEF DFSCRIPTION OF THE DRANINGS
Figures 1 a-c show three photomicrographic views on different scales, of the surface of a galvanised drawing sheet according to the invention in its initial condition;
Figures 2 a-c show three photomicrographlc views on the same scales as in Figures 1 a-c, of the same sheet after it has been subjected to a friction test by drawing between planar jaws;
Figures 3 a-c show three photomicrographic views on the same scales as in Figures 1 a-c and 2 a-c, of the same sheet after it has been subjected to a friction test by passage through a device called a "bead simulator"; and Figure 4 is a graph which illustrates the distinctness of image (DOI) of a sheet according to the invention after painting by conventional means.
The photomicrographs are scanning electron microscope , - :
7~ 3 ~
photographs.
DETAILED D~SCRIP~ION OF PREFERRED EMBODIMEN~
The sheet used in this examp:Le was a deep drawing steel of the St 14 type. It was galvanised on both sides by dipping in a lead-free bath, with 140 g/m2 of 7inc on each side. The thickness of the zinc layer was from 8 ~m to 10 ~m on each side. Fini3hing rolling wa~
by means of rolls which had been dressed so as to have a roughness of less than 0.2 ~m at the 0.8 mm cut-off.
The rolls had then been textured by means of a laser beam so that their surface had bosses in the form of spherical segments of a height between 16 ~m and 20 ~m and a base diameter between 100 ~m and 120 ~m. The bosses were distributed in accordance with a predetermined pattern with a density RL = 90 bosses per linear inch in the circumferential direction of the roll and a density ~d = 120 bosses per linear inch in the axial direction of the roll. Finishing rolling was performed with a reduction ratio of 0.8%. After this operation the sheet had a total thickness of 0.76 mm.
Figure 1 shows the surface of the sheet at the time of acceptance, i.e. after galvanising and finishing rolling. Figure la shows the regularity of the surface distribution of the pattern, each unit of which consists 2`(~2`2~3`~
of a well and a plateau. Figure lb shows a portion of the surface of the sheet on a larger scale. The wells correspond to the darker part of each pattern unit. The lighter part of these pattern units represents the plateau, whose height does not exceed 5 ~m. Finally Figure lc illustrates the shape of a well, which in this case can be likened to that of a circle, and the base diameter D of the well.
In this condition the sheet has an effectively planar surface in which wells of a depth of some 12 ~m and a base diameter of some 100 ~m are formed. The distribution density of these wells is 120 and 90 per linear inch in the transverse and longitudinal directions of the sheet respectively. The sheet has an arithmetic mean roughness Ra, measured at tha 0.8mm cut-off, of the order of 1.2 ~m. A useful feature i8 that this roughness is not greatly affectsd by the level of the cut-off. Thus is does not excsed 1.5 ~m at the 8 mm cut-off.
The drawability of the sheet was evaluated in relation to the most critical problem encountered with galvanised products, namely friction behavior and tendency to bind.
Friction behavior was evaluated on the basis of a traction test between two planar jaws gripping the ;
.
~ 2-2/.3~;
sheet; the sheet was slightly lubricated with protective oil. The sheet showed very satisfactory behavior: the depth and diameter of the wells wera not affected; the height of the plateaus became less than 3 ~m. Figures 2 a-c show the surface of the sheet after this test.
A test was also performed in a device called a bead simulator. This test consists of drawing the sheet across a set of three succe~sive rollers in such a way that it is bent in two opposite ways, under traction and wi.h friction. This test caused no change in the shape or dimensions of the wells was illu~trated in Figures 3 a-c. The arithmetic mean roughness Ra at the 0.8 mm cut-of fell to 0.9 ~m.
As far as the tendency to binding is concerned, the sheet was subjected to a U forming test, i.e. the drawing currently performed by the user. 15 blanks were drawn in succession without any sign of binding, whereas with a conventional galvanised sheet only 5 to 6 blanks can be drawn.
The sheet was also subjected to a painting test, performed under conditions typical of the process for the manufacture of motor ~ehicle coachwork sheets:
deposition of a layer of paint having a thickness of some 30 ~m by cataphoresis followed by stoving at 2a~235 for 30 minutes; deposition of a surface coat having a thickness of some 20 ~m followed by stoving at 150-C
for 30 minutes; and finally deposition of a coat of enamel some 45 ~m thick followed by stoving at 125-C
for 30 minutes.
The distinctness of image, DOI, was determined by means of a standard procedure well-known to those skilled in the art under the name of the Ford test. This index varies appreciably in relation the undulation of the surface before paint is applied. This undulation can in particular be expressed by the quantity W = (Raa~ 8mm _ RaC-o 0.8 mm) which represents the difference between the arithmetic mean roughness Ra at the 8 mm and 0.8 mm cut offs respectively, these roughnesses being measured on the unpainted galvanised sheets.
Figure ~ shows the change in the Ford distinctness of image index (DOI) for the painted sheet in relation to the undulation W of the surface of the sheet before painting. The two straight lines (a) and (b) bound a zone in which the values (square points) corresponding to a series of conventional sheets are scattered. It can be seen that among the best of these the ~2~
distinctness of image index l.ies between 8 and 9 for an extremely small undulation (W = 0.2).
Values obtained with sheets in accordance with the invention have besn plotted on this diagram as round points (I and II).
In its acceptance condition, i.e. galvanised and rolled, the sheet has an undulation W = 0.25, and ater painting by the process described above its Ford distinctness of image index is 10 (point I).
A painting test was also performed with a sheet according to the invention deformed by 10% by expansion along two axes in order to simulate drawing. The surface undulation of the sheet increase slightly, to W = 0.4; the Ford distinctness of image index nevertheless remained greater than 9 (point II).
The galvanised sheet according to the invantion thus has remarkable friction behavior as well as a very small tendency to bind; also it ha a very high Ford distinctness of image index, both in the undeformed and the deformed state. These properties makes it particularly useful for the manufacture of visible parts of vehicles, in particular motor vehicle bodywork sheets.
.. , , - ~ ~
Claims (12)
1. Drawing sheet with a metal coating on at least one side, wherein said side has a roughness constituted by regularly distributed isolated wells, wherein said wells have a depth in the range of 5 µm to 25 µm and a base diameter in the range of 80 µm to 200 µm, said wells are distributed with a density in the range of 50 to 150 wells per linear inch in at least two perpendicular directions on said side of the sheet, said side has an arithmetic mean roughness Ra at the 0.8 mm cut-off in the range of 0.5 µm to 2 µm, and the arithmetic mean roughness Ra of the said sheet at the 8 mm cut-off does not differ by more than 0.3 µm from the value of the arithmetic mean roughness at the 0.8 mm cut-off.
2. Drawing sheet according to claim 1, wherein said metal coating consists of a metal selected from the group consisting of zinc, aluminum, and zinc alloys.
3. Drawing sheet according to claim 2, wherein said metal coating is a deposit obtained by dipping said sheet in a bath of zinc or a zinc-aluminum alloy.
4. Drawing sheet according to claim 1, wherein said metal coating consists of zinc and iron and is formed by hot diffusion.
5. Drawing sheet according to claim 1, wherein the thickness of said metal coating on said side is in the range of 7 µm to 25 µm.
6. Drawing sheet according to claim 1, wherein the sum of the coating thicknesses on the two sides of the sheet measured at the same point differs by a percentage difference of not more than 30% from the sum of the nominal values of the two thicknesses.
7. Drawing sheet according to claim 6, wherein the percentage difference is not more than 15%.
8. Drawing sheet according to claim 1, wherein the sheet consists of a steel which has substantially no drawing plateau.
9. Drawing sheet according to claim 1, wherein said walls have a depth in the range of 7 to 20 µm.
10. Drawing sheet according to claim 1, wherein said wells have a base diameter in the range of 100 to 150 µm.
11. Drawing sheet according to claim 1, wherein said well density is in the region of 90 to 120 wells per linear inch in at least one said direction.
12. Drawing sheet according to claim 1, wherein the arithmetic mean roughness at the 0.8 mm cut-off is in the range of 0.8 µm to 1.4 µm 12. Drawing sheet according to claim 1, wherein the thickness of said metal coating is in the range of 7 µm to 25 µm.
14. A process for the manufacture of drawing sheet according to claim 1, comprising the steps of depositing said metal coating on at least one side of said sheet and subjecting the coated sheet to finishing rolling using rolls in which at least the roll corresponding to the coated side has on its surface a plurality of regularly distributed isolated bosses having a density in the range of 50 to 150 bosses per linear inch in at least two perpendicular directions, said bosses being in the shape of spherical segments with a height in the range of 15 µm to 30 µm and a base diameter in the range of 100 µm to 150 µm, the surface of said roll between said bosses having an arithmetic mean roughness Ra at the 0.8 mm cut-off of less than 0.4 µm.
15. A process according to claim 14, wherein there are 90 to 120 bosses per linear inch in one said direction.
16. A process according to claim 14, wherein said coated sheet is rolled with a reduction ratio of less than 1%.
17. A process according to claim 14, wherein said roll surface between said bosses has an arithmetic mean roughness Ra at the 0.8 mm cut-off of less than 0.2 µm.
18. A process according to claim 14, wherein said depositing step comprises dipping said sheet in a bath of a metal selected from the group consisting of zinc, aluminum, and zinc-aluminum alloys.
19. A process according to claim 14, wherein said coating has a thickness in the range of 7 µm to 25 µm.
20. A process according to claim 14, wherein the sum of the coating thicknesses on the two sides of the sheet measured at the same point differs by no more than 30 from the sum of the nominal values of the two thicknesses.
14. A process for the manufacture of drawing sheet according to claim 1, comprising the steps of depositing said metal coating on at least one side of said sheet and subjecting the coated sheet to finishing rolling using rolls in which at least the roll corresponding to the coated side has on its surface a plurality of regularly distributed isolated bosses having a density in the range of 50 to 150 bosses per linear inch in at least two perpendicular directions, said bosses being in the shape of spherical segments with a height in the range of 15 µm to 30 µm and a base diameter in the range of 100 µm to 150 µm, the surface of said roll between said bosses having an arithmetic mean roughness Ra at the 0.8 mm cut-off of less than 0.4 µm.
15. A process according to claim 14, wherein there are 90 to 120 bosses per linear inch in one said direction.
16. A process according to claim 14, wherein said coated sheet is rolled with a reduction ratio of less than 1%.
17. A process according to claim 14, wherein said roll surface between said bosses has an arithmetic mean roughness Ra at the 0.8 mm cut-off of less than 0.2 µm.
18. A process according to claim 14, wherein said depositing step comprises dipping said sheet in a bath of a metal selected from the group consisting of zinc, aluminum, and zinc-aluminum alloys.
19. A process according to claim 14, wherein said coating has a thickness in the range of 7 µm to 25 µm.
20. A process according to claim 14, wherein the sum of the coating thicknesses on the two sides of the sheet measured at the same point differs by no more than 30 from the sum of the nominal values of the two thicknesses.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE8900820A BE1004324A6 (en) | 1989-07-31 | 1989-07-31 | Stamping sheet steel having a metal coating and method for producing a sheet as. |
| BE08900820 | 1989-07-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2022235A1 true CA2022235A1 (en) | 1991-02-01 |
Family
ID=3884267
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002022235A Abandoned CA2022235A1 (en) | 1989-07-31 | 1990-07-30 | Steel drawing sheet with metal coating |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0412073B1 (en) |
| JP (1) | JPH03271356A (en) |
| AT (1) | ATE95571T1 (en) |
| BE (1) | BE1004324A6 (en) |
| CA (1) | CA2022235A1 (en) |
| DE (1) | DE69003769D1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11559829B2 (en) * | 2017-08-29 | 2023-01-24 | Baoshan Iron & Steel Co., Ltd. | Metal sheet having low friction coefficient and low waviness |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2704070B2 (en) * | 1991-10-30 | 1998-01-26 | 川崎製鉄株式会社 | Alloyed hot-dip galvanized steel sheet with excellent press mold sliding properties |
| EP1323843A3 (en) * | 1993-06-30 | 2004-09-15 | Nkk Corporation | method for manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability |
| JP3779941B2 (en) * | 2002-01-09 | 2006-05-31 | 新日本製鐵株式会社 | Galvanized steel sheet with excellent post-painting corrosion resistance and paint clarity |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR333738A (en) * | 1903-06-04 | 1903-12-02 | Hubert Dachelet | Mechanical device for obtaining various patterns of zinc on galvanized surfaces by difference in crystallization |
| US3086879A (en) * | 1958-03-05 | 1963-04-23 | Frederic H Lassiter | Metallized products and foils and method of forming the same |
-
1989
- 1989-07-31 BE BE8900820A patent/BE1004324A6/en not_active IP Right Cessation
-
1990
- 1990-07-17 EP EP90870112A patent/EP0412073B1/en not_active Expired - Lifetime
- 1990-07-17 AT AT90870112T patent/ATE95571T1/en not_active IP Right Cessation
- 1990-07-17 DE DE90870112T patent/DE69003769D1/en not_active Expired - Lifetime
- 1990-07-30 CA CA002022235A patent/CA2022235A1/en not_active Abandoned
- 1990-07-31 JP JP2203748A patent/JPH03271356A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11559829B2 (en) * | 2017-08-29 | 2023-01-24 | Baoshan Iron & Steel Co., Ltd. | Metal sheet having low friction coefficient and low waviness |
Also Published As
| Publication number | Publication date |
|---|---|
| ATE95571T1 (en) | 1993-10-15 |
| EP0412073A1 (en) | 1991-02-06 |
| BE1004324A6 (en) | 1992-11-03 |
| EP0412073B1 (en) | 1993-10-06 |
| DE69003769D1 (en) | 1993-11-11 |
| JPH03271356A (en) | 1991-12-03 |
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| FZDE | Discontinued |