Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
System for Producing One-Side Zinc Hot Dipped
Steel Sheets
BACKGROUND OF THE INVENTION
This invention relates to a system Eor producing one-side
zinc hot dipped steel sheets or strips used in automobiles
or the like.
It is well known in the motor industry that one-side
zinc plated steel sheets are widely used as automobile body
steel sheets which are substantially free of severe local
corrosion in the interior and give an excellent painting
appearance on the exterior of the vehicle body.
One-side zinc plated steel sheets are generally produced
either by hot dipping process or by electrodeposition process.
In general, the former process is advantageous in increased
plating speed and thickness while the latter is suitable for
producing thin coatings. Since the one-side plating, whether
it is by the hot dipping or electrodeposition, encounters
much technical difficulty as compared with usual both-sides
plating, the cost of plating is not necessarily low irrespective
of a one-half reduction in the quantity of zinc plated. Attempts
have been made to produce one-side zinc plated steel sheets at
low cost. Typical proposals include (1) one-side cutting process,
~2) meniscus process, and (3) the use of an anti-plating agent.
The one-side cutting process is by plating the both
sides of a steel sheet followed by cutting off a zinc plating
on one side. Apparently, this process is inefficient and
expensive, and the sheet surface from which the zinc plating
has been cut away is poor in quality. The meniscus process
is designed so as to contact only one surface of a strip with
molten zinc by the utilization of ultrasonic, electromagnetic
pump, or other means. Temper color appears on the cold rolled
surface of a strip since the strip is exposed to the ambient
atmosphere before the strip temperature is sufficiently lowered.
Pickling must be carried out to remove such temper color,
resulting in products of non-uniform quality. The temper
color is undesirably enhanced when the zinc plating must be
subjected to an alloying treatment. Removal of such enhanced
temper color is also a problem.
A number of proposals have also been made for the use
of anti-plating agents, but none of them have enjoyed successful
resul's in commercial production. Zinc remains in the form
of entrained particles on the surface of an anti-plating film
on a steel strip emerging from a molten zinc bath, resulting
in a limited line speed. The entrained zinc particles are
adhered or transferred to the surface of a carry/guide roll,
causing dents in the steel strip.
In these years, the likelihood of entraining zinc particles
was significantly reduced due to improvements in releasability
of an anti-plating film and the use of a flame wiper.
S~MMARY OF THE INVENTION
An object of this invention is, therefore, to provide
an improved system for producing one-side zinc plated steel
sheets in such a manner that dent formation is thoroughly
precluded even when a few zinc particles remain on the anti-
plating film surface.
This invention is directed to a system for carrying out
one-side zinc hot dipping process of the type wherein a steel
sheet having a film of an anti-plating agent formed on one
surface thereof is passed through a molten zinc bath to plate
the other surface of the steel sheet with zinc, and the anti-
plating film is then peeled and removed to produce a one-side
zinc plated steel shee-t. According to a novel feature of this
invention, the sytem is arranged such that the anti-plating
film on the steel sheet does not contact with any rigid member
while the sheet is moved from the molten zinc bath to the
anti-plating film peeling site.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages
of this invention will be more fully understood from the
following description when taken in conjunction with the
accompanying drawings, in which;
Fig. 1 is a schematic illustration of a prior art system
for producing one-side zinc hot dipped steel sheets; and
Fig. 2 is a schematic illustration of the one-side zinc
hot dipped steel sheet producing system according to this invention.
D CRIPTION OF TIIE PREFERRED EMBOD MENTS
In order to facilitate understanding of the invention,
reference is first made to a prior art system shown in Fig.
1. A strip or sheet 1 of steel which is previously cleaned
is transporated in the direction of an arrow to a roll coater
2 where an anti-platlng agent is applied to one surface of
the sheet. The steel sheet having the anti-plating agent
applied thereon enters an annealing furnace 3 where it is
heated for drying and baking to form an anti-platlng film
temporarily firmly adhered to the sheet. After cooling, the
steel sheet 1 is immersed in a molten zinc bath 4 for zinc
hot dipping. The steel sheet is turned around a sink roll
in the bath and emerges vertically upward from the bath.
The zinc dipped sheet, which possesses the anti-plating film
on one surface 5 and a zinc plating on the other surface 7,
passes across a flame wiper 6 immediately above the bath for
wiping off zinc entrained on the anti-plating film 5, and
then across a plating thickness control 8 in the form of a
wiper for adjusting the thickness of the zinc plating 7.
Subsequently, the sheet is passed through an alloying furnace
9 and a cooling unit 10, and then introduced into a peeling
machine 1~ through a deflector roll 11 where the anti-plating
film is removed from the sheet by peeling. After washing,
a one-side zinc plated steel sheet is obtained. The steps
of coating and drying the anti-plating agent may, of course,
be previously carried out in a separate line.
Such a process of producing one-side zinc hot dipped
steel sheets has the likelihood that zinc particles deposited
or entrained on the anti-plating film 5 of the emerging hot-
dipped sheet will make dents in the sheet, as described earlier.
The inventors have found that such dent formation is caused by
the contact of the anti-plating film 5 on the sheet with the
deflector roll 11. As a result of such contact, zinc particles
remaining on the anti-plating film surface are captured by the
deflector roll 11 to form dent-causing projections on the
roll surface.
To eliminate the cause of dent formation, the present
invention guides the sheet 1 along a path from the molten
zinc bath 4 to the peeling machine 12 while keeping the anti-
plating film 5 on the sheet out of contact with any rigid member
such as a deflector roll.
One preferred embodiment for such guiding is shown in Fig.
2. The system shown in Fig. 2 also includes the same steps
applied to a steel sheet as described in connection with
the prior art system shown in Fig. 1, that is, steps of applying
an anti-plating agent to one surface 5 of a steel strip or sheet
1, drying and baking the anti-plating agent followed by cooling,
zinc plating in a molten zinc bath 4, wiping off zinc
entrained on the anti-plating film by means of a flame
wiper 6, controlling the thickness of a zinc plating
by means of a thickness controller 8, optionally effecting an
alloying treatment in an alloying furnace 9, cooling in a
cooling unit 10, and removing the anti-plating film from the
sheet by peeling through a peeling machine 12 followed by
a suitable post-treatment. The system shown in Fig. 2 includes
a reentrant way extending from the molten zinc bath 4 to the
peeling machine 12 where the sheet 1 is turned around three
guide rolls in the same direction. All the guide rolls are
in contact with only the zinc plating 7 on the sheet 1. Dif-
ferently stated, the system is arranged such that the anti-
plating film 5 on the sheet 1 does not contact any rigid member
such as a deflector roll while the sheet 1 is moved from the
outlet of the molten metal zinc bath 4 to the inlet of the
peeling machine 12. With this arrangement, formation of dents
on the sheet surface is thoroughly precluded since zinc particles
entrained on the anti-plating film 5 are no longer depressed
onto :he confronting sheet surface in the absence of any rigid
roll in a line leading to the film peeling-off stage.
The peeling machine may be of any desired type including
water cooling, mechanical bending, and brushing as well as
any combination of these types. The position in which the
peeling machine is disposed is not limited to the position
shown in Fig. 2, and it may be disposed in the position of
the cooling unit 10 or connected downstream of the cooling
unit 10. Such peeling machines per se are well known in the
q~
art and as such form no particular part of the present invention
except in combination with the other elements thereof. It
is critical for the present invention that the system is
arranged such that the anti-plating film 5 on the sheet 1
does not contact any rigid member such as a deflector roll
while the sheet 1 is moved from the molten zinc bath ~ to
the peeling machine 12.
Since an anti-plating film on a steel sheet does not
contact any rigid member such as rolls or experience any com-
pression by such rigid members during passage of the sheet froma molten zinc bath to a film peeling machine, the present
invention can effectively prevent dent formation even in the
presence of zinc particles or deposits remaining on the anti-
plating film. The prevention of dent formation is of great
advantage in the commercial manufacture of one-side zinc plated
steel sheets using anti-plating agents since significant improve-
ments are accomplished including increased line speed, mitigated
requirements for the flame wiper, and the use of a wider range
of anti-plating agents.
