CA1068174A - Galvanizing steel strip of partial or one side by pretreatment thereof with silicone resin - Google Patents
Galvanizing steel strip of partial or one side by pretreatment thereof with silicone resinInfo
- Publication number
- CA1068174A CA1068174A CA247,625A CA247625A CA1068174A CA 1068174 A CA1068174 A CA 1068174A CA 247625 A CA247625 A CA 247625A CA 1068174 A CA1068174 A CA 1068174A
- Authority
- CA
- Canada
- Prior art keywords
- steel strip
- silicone resin
- metallic
- coating
- resin
- 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.)
- Expired
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Classifications
-
- 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
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
-
- 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
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0224—Two or more thermal pretreatments
-
- 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
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Coating With Molten Metal (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of continuous galvanizing a steel strip partially or one side, which comprises applying silicone resin to a part or of one side of the steel strip which is to be left non-plated in a subsequent continuous molten zinc coating, baking the silicon resin coated steel strip at a temperature ranging from 300 to 800°C in an oxidizing atmosphere, and subjecting the steel strip to heat treatment in a reducing atmosphere and introducing the heat treated steel strip to a zinc coating bath.
A method of continuous galvanizing a steel strip partially or one side, which comprises applying silicone resin to a part or of one side of the steel strip which is to be left non-plated in a subsequent continuous molten zinc coating, baking the silicon resin coated steel strip at a temperature ranging from 300 to 800°C in an oxidizing atmosphere, and subjecting the steel strip to heat treatment in a reducing atmosphere and introducing the heat treated steel strip to a zinc coating bath.
Description
-~ 1068174 The present invention relates to a method of continuous galvanizing steel strlp on partial or one side, In recent years, in automobile and electric industries, for example, demands have been increasingly made for partially ~ or one side coated steel sheets as a steel materiaI having good corrosion resistance on one side and good weldability and paintability on the other side.
To meet these demands, it has been in practice to produce such partially or one-side galvanized steel sheets by electroplating. However, the thickness of coating normally obtained by electroplating is small, and therefore it is necessary to increase the coating amount with sacrifice of pro-~f `
ductivity in order to obtain satisfactory corrosion resistance.On the other hand, a thick coating can be obtained by a hot dipping method, and for production of partially or one side galvanized steel sheets, it has been proposed to apply a phosphoric acid treatment partially or to one side of the sheet and then galvanize the sheet as disclosed in Japanese Patent Publication Sho 42-24966, or it has been proposed to apply water glass partially or on one side of the sheet so as to prevent the coat-ing deposition as disclosed in Japanese Patent Publication Sho 39-7112, and other various methods have been proposed. These prior arts, however, are applicable and effective only for a galvanizing method where no pretreatment by heating is applied just before the hot dipping, such as in Cook-Norteman method, and these prior arts cannot be applied to a galvanizing apparatus such as the Sendzimir type or a no-oxidizing furnace type in which the heat treatment is done in the production line to obtain ~ ~.
required surface and material properties, because the treating agents such as phosphate and water glass are denatured and decom-~ posed and peeled off during the heating for removing the steel ; :
'' ` ~ ~
~ 106817~
surface contamination and during the heating above recrystalliza-tion temperature for ~nnealing the steel strip, which heatings are normally done in such a plating process, and thus it is impossible to prevent galvanizing.
-~ One of the objects of the present invention is to provide a method for partially or one side coating effectively and advantageously even in a galvanizing line having a heat i treatment furnace, such as the Sendzimir type coating line and ; the no-oxidizing furnace type coating line.
- 10 One of the features of the present invention is that silicone resin is applied partially or on one side of a steel strip and thus silicone resin applied steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing atmosphere, ; then subjected to a heat treatment in a reducing atmosphere and is introduced to a galvanizing bath.
. Another feature of the present invention is that one ; or more of metallic oxides, metallic hydroxides, metallic nitrides, metallic carbides, metallic carbonates, metallic - phosphates, metallic silicates, etc. is added to the silicone .,~ , resin.
As for the silicone resins used in the present invention, polysilalkylene polymers having the formula:
CH3 ~CH3 , 3 CH3 - Si [~CH2~si~]n CH2 , 3 CH3 CH3 CH3 ;
; .... ..
: .
.~. . `'' "'', ''~ '; , ,:
. ..: . . ' .
'; '~ :.
To meet these demands, it has been in practice to produce such partially or one-side galvanized steel sheets by electroplating. However, the thickness of coating normally obtained by electroplating is small, and therefore it is necessary to increase the coating amount with sacrifice of pro-~f `
ductivity in order to obtain satisfactory corrosion resistance.On the other hand, a thick coating can be obtained by a hot dipping method, and for production of partially or one side galvanized steel sheets, it has been proposed to apply a phosphoric acid treatment partially or to one side of the sheet and then galvanize the sheet as disclosed in Japanese Patent Publication Sho 42-24966, or it has been proposed to apply water glass partially or on one side of the sheet so as to prevent the coat-ing deposition as disclosed in Japanese Patent Publication Sho 39-7112, and other various methods have been proposed. These prior arts, however, are applicable and effective only for a galvanizing method where no pretreatment by heating is applied just before the hot dipping, such as in Cook-Norteman method, and these prior arts cannot be applied to a galvanizing apparatus such as the Sendzimir type or a no-oxidizing furnace type in which the heat treatment is done in the production line to obtain ~ ~.
required surface and material properties, because the treating agents such as phosphate and water glass are denatured and decom-~ posed and peeled off during the heating for removing the steel ; :
'' ` ~ ~
~ 106817~
surface contamination and during the heating above recrystalliza-tion temperature for ~nnealing the steel strip, which heatings are normally done in such a plating process, and thus it is impossible to prevent galvanizing.
-~ One of the objects of the present invention is to provide a method for partially or one side coating effectively and advantageously even in a galvanizing line having a heat i treatment furnace, such as the Sendzimir type coating line and ; the no-oxidizing furnace type coating line.
- 10 One of the features of the present invention is that silicone resin is applied partially or on one side of a steel strip and thus silicone resin applied steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing atmosphere, ; then subjected to a heat treatment in a reducing atmosphere and is introduced to a galvanizing bath.
. Another feature of the present invention is that one ; or more of metallic oxides, metallic hydroxides, metallic nitrides, metallic carbides, metallic carbonates, metallic - phosphates, metallic silicates, etc. is added to the silicone .,~ , resin.
As for the silicone resins used in the present invention, polysilalkylene polymers having the formula:
CH3 ~CH3 , 3 CH3 - Si [~CH2~si~]n CH2 , 3 CH3 CH3 CH3 ;
; .... ..
: .
.~. . `'' "'', ''~ '; , ,:
. ..: . . ' .
'; '~ :.
- 2 - ~
' ' :
: ' .. . ~ .. . . .
- ~ 1061 317~ :
..
. - si - ~ - si -CH3 o , 3 ;~-, - si - ~- si - '~.'' ' ~ '''' normal chained or ringed polysiloxene polymers such as ~ .
R R R
R - Si - O [-Si ~ ~n ~ Si - R
R R R
,~ 10 or ~(R)2sio3n , or further, condensation polymers of organo silanol such as ~ HO - [SiR2O]n - H (in which R is methyl, ethyl, butyl, phenyl ; or benzyl radical, etc.) are particularly useful.
The above silicone polymers may be used in single or in combination.
;' However, for obtaining a completely partial or one side galvanized steel sheet, it is desired to improve heat resis-tance of the resin coating. For this purpose, metallic oxides such as SiO2, A12O3, MgO, TiO2, metallic nitrides such as SiN4, carbides, phosphates and silicates such as WC, CaCO3, NaCO3, Ca3(PO4)2, AlPO4, CaSiO3 can be added to the silicone resin in ; single or in combination.
The amount of these additives to be added to the silicone resin is less than 50% by weight, and more than about 50% it is difficult to coat the resin uniformly and the coating peels off often during the galvanizing.
As for the method for coating the above silicone resins on the steel strip, a spray coating, a roll coating and . ~ . . .
'~ a squeeze coating, for example, may be applied to apply a uniform - 30 coating on the surface to be treated.
~ And the silicone resin is dissolved in an organic .. . .
:
'7~ ~
,~ .
~ solvent such as carbon,tetrachloride, benzene, ~oluene, and ; xylene so as to adjust the viscosity of the resin to meet the coating conditions.
Silicone resins which are in the liquid form having a viscosity of 10 to 1000 centistokes at ordinary temperature can be applied by themselves, and it is preferable that silicone resins having a higher viscosity are dissolved in an organic 'A solvent.
As for the silicone resin used in the present inven- ;
tion, KF 96, KM 722, KS 66, KE 45 RTV, KR 255 (all are trade-marks) produced by Shinetsu Chemical Industries Co., Ltd. of Japan and SH 200 (trademark) produced by Toray Silicone Co., Ltd. may be used.
. .
The silicone resin is applied to the steel strip surface in advance of a pretreatment equipment, and then the resin coated steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing atmosphere, then subjected to a heat treatment in a reducing atmosphere and introduced in the hot dipping bath to be applied with the zinc coating on the non-resin-coated surface. In some cases, a very small amount of metal coating attaches infragments on the resin coated steel strip surface. Therefore, it is desirable to apply brush-ing to the resin coated surface of the steel strip coming out from the hot dipping bath to remove the coated metal as well as to remove the silicone resin coating~
As described hereinbefore, the feature of the present invention lies in that the silicone resin coated steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing ~ -atmosphere, and then subjected to a heat treatment in a reducing atmosphere. This is the indispensable feature of the present invention as is understood from the following example in which di-methylpolysiloxane is used.
. ~-, . .
: ~:
.
~ ;
.: .
; The di-methylpolysiloxane is thermally decomposed in a reducing atmosphere (H2 : 5%, balance: N2) as below.
', . ' CH l ',CH3 1 CH3 CH3 ,CH3 , 3 CH3 - Si _ O Si - o ~ Si - CH3 ~ CH3 - Si - o - Si - - Si - CH3 -~ CH3 ~CH3 ,, n CH3 CH3 CH3 1 4 and vapourizes as low-molecular siloxane, which fills the furnace inside, and adheres not only on the silicone resin coated side ~, but also on the other side to be plated. In this way, the side ~'~ to be plated will show locally bad plating adhesion and in the 10 worst case will not be plated at all, while the side to be left ;
non-plated will be locally plated due to the loss of the silicone resin coating by its vapourization. In some cases, this non-, plating or bad plating adhesion problem will exist even after completion of the one-side plating until the low-molecular ;..
silicone resin remaining in the furnace is replaced by the atmosphere gas.
Whereas, when the heating is done under the presence .. .
of oxygen, the dimethylpolysiloxane takes the following reaction:
.
2 - Si - O - ~ 2 - Si - O - ~ 2 - Si - O - +HCHO
, .
:.' ' ' ~ - Si - O - Si - O - + H2O ~ 2 SiO2 .,~, ' ' :
O O
In an oxidising atmosphere (oxygen not lower - than 100%) the dimethylpQlysiloxane begins to decompose near 300C, completes endothermic reaction near 600C and finally decomposes into SiO2. This reaction causes a weight ~ 106B174 decrease of about 1.9% theoretically, but about 90~ or more ~ weight decrease is mea,sured by a thermobalance due to increasing : tendency of vapourization through decomposition into a low- -. molecular substance. ~ :.
. When the baking of the silicone resin in the oxidizing atmosphere is not enough, the formation of SiO2 film through the resin decomposition on the stee.l strip surface is not .. satisfactory and a lar~e amount of residual non-decomposed :: silicone resin is brought into the reducing furnace so that . 10 thermal decomposition is caused in the reducing atmosphere and the low-molecular siloxane resin is formed as mentioned before - and this low-molecular siloxane brings forth undesirable phenomena ~ :
such as local plating on the side to be left non-plated, local non-plating on the side to be plated, and existance of bad plating adhesion until after the one-side plating. ~
When the baking of the silicone resin in an oxidizing ::
atmosphere is done excessively, most of the coated resin . .
... .. . .
vapourizes so that the steel strip is not fully coated by the , residual SiO2 film alone, and thus the steel strip is activated .; 20 in the reducing furnace so that contact between the steel strip - -and the molten zinc is caused in the molten zinc bath and thus the zinc plating takes:place on the resin coated side. Further, the steel strip surface is oxidized beyond the capacity of the ~:
.. reducing furnace so that the bluing phenomenon takes place. :
. In order to obtain good one-side zinc plating, it is important that in the reducing furnace the SiO2 film covers the silicone resin coated side of the steel strip and protect the ~ surface from activation while a small amount of the low-molecular silicone resin covers the steel strip surface so as to avoid the ~
30 non-plating on the other side, and that in the molten zinc bath .~ .
:~ the strong SiO2 film prevents the contact between the molten . ' . .
- 6 - ~:
~ ~0ti~174 .', ':` . .
'~ zinc and the steel strip. For this purpose, it is necessary ;~ that the baking tempe~ature for the silicone resin under the ~, presence of oxygen is not lower than 300C but not higher than 800C.
The thermal decomposition of the silicone resin com-`' pletes near 600C, but in a commercial production line as the heating rate is higher, the resin decomposition delay so that the decomposition reaction sometimes continues up to 800C.
For actual practice, an optimum baking temperature '~ ' -~ 10 should be determined within the range from 300C to 800C taking into consideration operational conditions such as the line speed, the condition of the reducing furnace, the presence of an oxidizing heating furnace or a non-oxidizing heating furnace prior to the reducing furnace and the like.
, Then the steel strip is introduced to the reducing furnace where the steel strip surface to be plated is reduced and activated and is introduced to the plating bath.
.,:
~'`' The above ,heating within the range from 300 to 800C
is done for 2 to 30 seconds, more desirably for 4 to 20 seconds.
",' 20 The heating for 2 seconds or shorter, the reaction of dimethyl-; siloxane does not fully progress and in the subsequent treatments ;'- in the reducing furnace etc. non-decomposed dimethylsiloxane is thermally decomposed into a low-molecuIar substance and vapourizes in the furnace.
Thus, many non-plated portions appea,r on the zinc-plated side, and zinc adheres on the side to be left non-plated.
Even when the heating time exceeds about 30 seconds the result will be same as obtained by the heating for about 20 seconds in case of a heating temperature up to about 400C, and no economical advantage is obtained by a longer heating time.
When the heating is done at a temperature within a . .
' - ' , , . , - 10681'7~
.: :
range from 500 to 800C for 30 seconds or longer, the film composed mainly of SiO'2 formed during the heatlng is embrittled by the heat and becomes less effective to prevent the contact between the steel strip and the molten zinc in the bath.
As for the removal of the remaining (metal resin) coating, mechanical removal such as brushing, acid pickling such as by HCl or H2S04, or etchiny by a chromate treating liquid ;-which is applied as a~ after-treatment is effective ~or the removal.
As for the above-mentioned chromate treating liquid, a chemical conversion treatment liquid commonly used for pre venting white rust of zinc coated steel plates, namely a chromate treatment liquid is useful, and typical examples ; includes, a) CrO3 - fluorine compound:
Example: CrO3 15 g/l , Na2SiF6 2g/1 '~r b) CrO3 - inorganic acid:
; Example: CrO3 lOg/l , H2S04 2ml/1 c) CrO3 - inorganic acid - fluorine compound:
; 20 Example: CrO3 15g/1 , NaF lg/l : H3P04 5ml/1. ;~
Further, the steel strip may be pre-coated with the silicone resin and coiled in a separate line and then the -steel strip is uncoiled while galvanized in the hot dipping line.
The amount of the resin coating to be applied on the metal surface is 0 5 _ 50 g/m2 as the silicone resin content `~ for effectively prevention of metal coating.
;; In this way, partial or one side galvanizing can be attained advantageously even in a continuous galvanizing line equipped with an oxidizing furnace and a subsequent reducing furnace as a pretreatment equipment.
As for the above-m~ntioned continuous galvanizing line, ':
.: .
- - : , - . - . . . . .
.. . . . .
81~
a conventional apparatus, such as of Armco-sendzimer type, Selas direct-fired heating type, United States Steel type, may be used. The steel strip which has been applied with silicone resin coating partially or on one side of the strip in the heat treating furnace of the continuous galvanizing line is heated to a temperature between 300 and 950C for about 20 seconds to 9 minutes, and then dipped in the molten zinc plating bath, so that the steel strip is plated with zinc partially or on one side only. For the heating, it is effective to heat the strip in an oxidizing atmosphere at a temperature 300 - 800C. Thus, the silicone resin coating on the steel strip is oxidized in the heat treating ~urnace to form a thin SiO2 film on the surface ` of the strip so that when the steel strip is dipped in the molten zinc plating bath, the bath is protected from contamina-tion.
Further, since the silicone resin coating can be ."4 ' easily removed after the galvanizing, the primary object of the present invention to assure weldability can be attained with any sacrifice~
Also, the productivity of the ordinary coating can be maintained.
In accordance with a specific embodiment, a method of continuous galvanizing a steel strip partially or one side, comprises applying silicone resin in a liquid form or in a dissolved form in an organic solvent to a part or on one side of the steel strip which is to be left non-plated in a sub-sequent continu~us molten zinc coating, baking the silicone resin coated steel strip at a temperature ranging from 300 to 800C in an oxidizing atmosphere, and subjecting the steel strip to heat treatment in a reducing atmosphere to clean the uncoated part or side of the steel strip and introducing the heat treated steel strip to a zinc coating bath.
_ , ~ .
.
' Next, one example of the apparatus ~or practising the present invention will be described referring to the attached drawing.
In Fig. 1, the steel strip 2 is uncoiled from the steel strip coil 1, one side of the steel strip 2 is applied with the silicone resin by means of the coating roll 3 ( a spray - may be used also), then the resin coated steel strip 2 is baked , . . .
at a temperature ranging from 300 to 800C in the oxidizing furnace 7, then annealed in the reducing pretreatment equipment 4 and introduced into the hot dipping bath 5 where it is coated with zinc on the other side, the amount of the zinc coating is controlled, and finally the silicone resin coating lS removed from the strip furnace by means of the brushing roll 6 and the strip is coiled.
The present invention will be more clearly under-stood from the following examples.
Examples of the present invention will be set forth under. These examplés were conducted using the above illustrated ~;~ production apparatus.
(A) ,; Examples Amount of Annealing Temp. of Amount Speëd of Silicone Condi- Hot Dipp- of Strip Resin tions ing Bath Coated Pass _ _ _ Coatinq __ Metal ~; 1 6 g/m740C 450C 183 g/m2 50 m/min.
(KM 722~
2 32 `' `' " "
, (KF 96)
' ' :
: ' .. . ~ .. . . .
- ~ 1061 317~ :
..
. - si - ~ - si -CH3 o , 3 ;~-, - si - ~- si - '~.'' ' ~ '''' normal chained or ringed polysiloxene polymers such as ~ .
R R R
R - Si - O [-Si ~ ~n ~ Si - R
R R R
,~ 10 or ~(R)2sio3n , or further, condensation polymers of organo silanol such as ~ HO - [SiR2O]n - H (in which R is methyl, ethyl, butyl, phenyl ; or benzyl radical, etc.) are particularly useful.
The above silicone polymers may be used in single or in combination.
;' However, for obtaining a completely partial or one side galvanized steel sheet, it is desired to improve heat resis-tance of the resin coating. For this purpose, metallic oxides such as SiO2, A12O3, MgO, TiO2, metallic nitrides such as SiN4, carbides, phosphates and silicates such as WC, CaCO3, NaCO3, Ca3(PO4)2, AlPO4, CaSiO3 can be added to the silicone resin in ; single or in combination.
The amount of these additives to be added to the silicone resin is less than 50% by weight, and more than about 50% it is difficult to coat the resin uniformly and the coating peels off often during the galvanizing.
As for the method for coating the above silicone resins on the steel strip, a spray coating, a roll coating and . ~ . . .
'~ a squeeze coating, for example, may be applied to apply a uniform - 30 coating on the surface to be treated.
~ And the silicone resin is dissolved in an organic .. . .
:
'7~ ~
,~ .
~ solvent such as carbon,tetrachloride, benzene, ~oluene, and ; xylene so as to adjust the viscosity of the resin to meet the coating conditions.
Silicone resins which are in the liquid form having a viscosity of 10 to 1000 centistokes at ordinary temperature can be applied by themselves, and it is preferable that silicone resins having a higher viscosity are dissolved in an organic 'A solvent.
As for the silicone resin used in the present inven- ;
tion, KF 96, KM 722, KS 66, KE 45 RTV, KR 255 (all are trade-marks) produced by Shinetsu Chemical Industries Co., Ltd. of Japan and SH 200 (trademark) produced by Toray Silicone Co., Ltd. may be used.
. .
The silicone resin is applied to the steel strip surface in advance of a pretreatment equipment, and then the resin coated steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing atmosphere, then subjected to a heat treatment in a reducing atmosphere and introduced in the hot dipping bath to be applied with the zinc coating on the non-resin-coated surface. In some cases, a very small amount of metal coating attaches infragments on the resin coated steel strip surface. Therefore, it is desirable to apply brush-ing to the resin coated surface of the steel strip coming out from the hot dipping bath to remove the coated metal as well as to remove the silicone resin coating~
As described hereinbefore, the feature of the present invention lies in that the silicone resin coated steel strip is baked at a temperature ranging from 300 to 800C in an oxidizing ~ -atmosphere, and then subjected to a heat treatment in a reducing atmosphere. This is the indispensable feature of the present invention as is understood from the following example in which di-methylpolysiloxane is used.
. ~-, . .
: ~:
.
~ ;
.: .
; The di-methylpolysiloxane is thermally decomposed in a reducing atmosphere (H2 : 5%, balance: N2) as below.
', . ' CH l ',CH3 1 CH3 CH3 ,CH3 , 3 CH3 - Si _ O Si - o ~ Si - CH3 ~ CH3 - Si - o - Si - - Si - CH3 -~ CH3 ~CH3 ,, n CH3 CH3 CH3 1 4 and vapourizes as low-molecular siloxane, which fills the furnace inside, and adheres not only on the silicone resin coated side ~, but also on the other side to be plated. In this way, the side ~'~ to be plated will show locally bad plating adhesion and in the 10 worst case will not be plated at all, while the side to be left ;
non-plated will be locally plated due to the loss of the silicone resin coating by its vapourization. In some cases, this non-, plating or bad plating adhesion problem will exist even after completion of the one-side plating until the low-molecular ;..
silicone resin remaining in the furnace is replaced by the atmosphere gas.
Whereas, when the heating is done under the presence .. .
of oxygen, the dimethylpolysiloxane takes the following reaction:
.
2 - Si - O - ~ 2 - Si - O - ~ 2 - Si - O - +HCHO
, .
:.' ' ' ~ - Si - O - Si - O - + H2O ~ 2 SiO2 .,~, ' ' :
O O
In an oxidising atmosphere (oxygen not lower - than 100%) the dimethylpQlysiloxane begins to decompose near 300C, completes endothermic reaction near 600C and finally decomposes into SiO2. This reaction causes a weight ~ 106B174 decrease of about 1.9% theoretically, but about 90~ or more ~ weight decrease is mea,sured by a thermobalance due to increasing : tendency of vapourization through decomposition into a low- -. molecular substance. ~ :.
. When the baking of the silicone resin in the oxidizing atmosphere is not enough, the formation of SiO2 film through the resin decomposition on the stee.l strip surface is not .. satisfactory and a lar~e amount of residual non-decomposed :: silicone resin is brought into the reducing furnace so that . 10 thermal decomposition is caused in the reducing atmosphere and the low-molecular siloxane resin is formed as mentioned before - and this low-molecular siloxane brings forth undesirable phenomena ~ :
such as local plating on the side to be left non-plated, local non-plating on the side to be plated, and existance of bad plating adhesion until after the one-side plating. ~
When the baking of the silicone resin in an oxidizing ::
atmosphere is done excessively, most of the coated resin . .
... .. . .
vapourizes so that the steel strip is not fully coated by the , residual SiO2 film alone, and thus the steel strip is activated .; 20 in the reducing furnace so that contact between the steel strip - -and the molten zinc is caused in the molten zinc bath and thus the zinc plating takes:place on the resin coated side. Further, the steel strip surface is oxidized beyond the capacity of the ~:
.. reducing furnace so that the bluing phenomenon takes place. :
. In order to obtain good one-side zinc plating, it is important that in the reducing furnace the SiO2 film covers the silicone resin coated side of the steel strip and protect the ~ surface from activation while a small amount of the low-molecular silicone resin covers the steel strip surface so as to avoid the ~
30 non-plating on the other side, and that in the molten zinc bath .~ .
:~ the strong SiO2 film prevents the contact between the molten . ' . .
- 6 - ~:
~ ~0ti~174 .', ':` . .
'~ zinc and the steel strip. For this purpose, it is necessary ;~ that the baking tempe~ature for the silicone resin under the ~, presence of oxygen is not lower than 300C but not higher than 800C.
The thermal decomposition of the silicone resin com-`' pletes near 600C, but in a commercial production line as the heating rate is higher, the resin decomposition delay so that the decomposition reaction sometimes continues up to 800C.
For actual practice, an optimum baking temperature '~ ' -~ 10 should be determined within the range from 300C to 800C taking into consideration operational conditions such as the line speed, the condition of the reducing furnace, the presence of an oxidizing heating furnace or a non-oxidizing heating furnace prior to the reducing furnace and the like.
, Then the steel strip is introduced to the reducing furnace where the steel strip surface to be plated is reduced and activated and is introduced to the plating bath.
.,:
~'`' The above ,heating within the range from 300 to 800C
is done for 2 to 30 seconds, more desirably for 4 to 20 seconds.
",' 20 The heating for 2 seconds or shorter, the reaction of dimethyl-; siloxane does not fully progress and in the subsequent treatments ;'- in the reducing furnace etc. non-decomposed dimethylsiloxane is thermally decomposed into a low-molecuIar substance and vapourizes in the furnace.
Thus, many non-plated portions appea,r on the zinc-plated side, and zinc adheres on the side to be left non-plated.
Even when the heating time exceeds about 30 seconds the result will be same as obtained by the heating for about 20 seconds in case of a heating temperature up to about 400C, and no economical advantage is obtained by a longer heating time.
When the heating is done at a temperature within a . .
' - ' , , . , - 10681'7~
.: :
range from 500 to 800C for 30 seconds or longer, the film composed mainly of SiO'2 formed during the heatlng is embrittled by the heat and becomes less effective to prevent the contact between the steel strip and the molten zinc in the bath.
As for the removal of the remaining (metal resin) coating, mechanical removal such as brushing, acid pickling such as by HCl or H2S04, or etchiny by a chromate treating liquid ;-which is applied as a~ after-treatment is effective ~or the removal.
As for the above-mentioned chromate treating liquid, a chemical conversion treatment liquid commonly used for pre venting white rust of zinc coated steel plates, namely a chromate treatment liquid is useful, and typical examples ; includes, a) CrO3 - fluorine compound:
Example: CrO3 15 g/l , Na2SiF6 2g/1 '~r b) CrO3 - inorganic acid:
; Example: CrO3 lOg/l , H2S04 2ml/1 c) CrO3 - inorganic acid - fluorine compound:
; 20 Example: CrO3 15g/1 , NaF lg/l : H3P04 5ml/1. ;~
Further, the steel strip may be pre-coated with the silicone resin and coiled in a separate line and then the -steel strip is uncoiled while galvanized in the hot dipping line.
The amount of the resin coating to be applied on the metal surface is 0 5 _ 50 g/m2 as the silicone resin content `~ for effectively prevention of metal coating.
;; In this way, partial or one side galvanizing can be attained advantageously even in a continuous galvanizing line equipped with an oxidizing furnace and a subsequent reducing furnace as a pretreatment equipment.
As for the above-m~ntioned continuous galvanizing line, ':
.: .
- - : , - . - . . . . .
.. . . . .
81~
a conventional apparatus, such as of Armco-sendzimer type, Selas direct-fired heating type, United States Steel type, may be used. The steel strip which has been applied with silicone resin coating partially or on one side of the strip in the heat treating furnace of the continuous galvanizing line is heated to a temperature between 300 and 950C for about 20 seconds to 9 minutes, and then dipped in the molten zinc plating bath, so that the steel strip is plated with zinc partially or on one side only. For the heating, it is effective to heat the strip in an oxidizing atmosphere at a temperature 300 - 800C. Thus, the silicone resin coating on the steel strip is oxidized in the heat treating ~urnace to form a thin SiO2 film on the surface ` of the strip so that when the steel strip is dipped in the molten zinc plating bath, the bath is protected from contamina-tion.
Further, since the silicone resin coating can be ."4 ' easily removed after the galvanizing, the primary object of the present invention to assure weldability can be attained with any sacrifice~
Also, the productivity of the ordinary coating can be maintained.
In accordance with a specific embodiment, a method of continuous galvanizing a steel strip partially or one side, comprises applying silicone resin in a liquid form or in a dissolved form in an organic solvent to a part or on one side of the steel strip which is to be left non-plated in a sub-sequent continu~us molten zinc coating, baking the silicone resin coated steel strip at a temperature ranging from 300 to 800C in an oxidizing atmosphere, and subjecting the steel strip to heat treatment in a reducing atmosphere to clean the uncoated part or side of the steel strip and introducing the heat treated steel strip to a zinc coating bath.
_ , ~ .
.
' Next, one example of the apparatus ~or practising the present invention will be described referring to the attached drawing.
In Fig. 1, the steel strip 2 is uncoiled from the steel strip coil 1, one side of the steel strip 2 is applied with the silicone resin by means of the coating roll 3 ( a spray - may be used also), then the resin coated steel strip 2 is baked , . . .
at a temperature ranging from 300 to 800C in the oxidizing furnace 7, then annealed in the reducing pretreatment equipment 4 and introduced into the hot dipping bath 5 where it is coated with zinc on the other side, the amount of the zinc coating is controlled, and finally the silicone resin coating lS removed from the strip furnace by means of the brushing roll 6 and the strip is coiled.
The present invention will be more clearly under-stood from the following examples.
Examples of the present invention will be set forth under. These examplés were conducted using the above illustrated ~;~ production apparatus.
(A) ,; Examples Amount of Annealing Temp. of Amount Speëd of Silicone Condi- Hot Dipp- of Strip Resin tions ing Bath Coated Pass _ _ _ Coatinq __ Metal ~; 1 6 g/m740C 450C 183 g/m2 50 m/min.
(KM 722~
2 32 `' `' " "
, (KF 96)
3 47 " 1~ 1, 1, (KE 45 RTV)
4 17 " " " "
(KR 255) 0.7 1~ 1~ 1, 1, (SH 200) ... . .... . ..
-, . . . .
.. . .
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. O
." ' ~
1061~17~
o ~ rl o ~ ~ ~ ~ o ..
,: ~ o ,~ : ~
~ ~ ~ , ., .~ o ~ tq ~ ~ a~O ~, td R Q, . :~
:~;. ~ ~ ~ ~ (d O O o~ o ~ -.. ~ .~ . ...
~n . ... _ _.
.~'' ~ ~
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.''' '. $ ' .
,~ o = = = - . ,: .
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' . ~ ~ '~
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~ O E~
~ 3 ~ o ~ = = = = =
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;. , ~ ~ =` = = = = .. ';', ~ ~ ~ . ..
i. ............. ~ ~ ~ ~ . ... ~ .. ~
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;., ~ ~ = =, = :, , r~ .
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(KR 255) 0.7 1~ 1~ 1, 1, (SH 200) ... . .... . ..
-, . . . .
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.; . . ~:.
, ., ~ ~ C) o o :.' ~i o ~ = o ~. , .,` ~ .
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,,.' ~ .~ :
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a) R C) `.............. ~ ~ ~
a) m x ~9 1` 0 ~ o . . ' .
. O
." ' ~
1061~17~
o ~ rl o ~ ~ ~ ~ o ..
,: ~ o ,~ : ~
~ ~ ~ , ., .~ o ~ tq ~ ~ a~O ~, td R Q, . :~
:~;. ~ ~ ~ ~ (d O O o~ o ~ -.. ~ .~ . ...
~n . ... _ _.
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~ a L~ ~ `
.''' '. $ ' .
,~ o = = = - . ,: .
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N ~ ; - .
1~. ~ ~ o 'd~ - = , '~ ' . E~
' . ~ ~ '~
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~ O E~
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. .:
Claims (8)
1. A method of continuous galvanizing a steel strip partially or one side, which comprises applying silicone resin in a liquid form or in a dissolved form in an organic solvent to a part or on one side of the steel strip which is to be left non-plated in a subsequent continuous molten zinc coating, baking the silicone resin coated steel strip at a temperature ranging from 300 to 800°C in an oxidizing atmosphere, and subjecting the steel strip to heat treatment in a reducing atmosphere to clean the uncoated part or side of the steel strip and introducing the heat treated steel strip to a zinc coating bath.
2. A method according to claim 1, in which the silicone resin is coated in an amount of 0.5 - 50 g/m2 as the resin content.
3. A method according to claim 1, in which one or more of metallic oxides, metallic hydroxides, metallic nitrides, metallic carbides, metallic carbonates, metallic phosphates and metallic silicates is added to the silicone resin.
4. A method according to claim 3, in which the amount of the additive to the silicone resin is less than 50% by weight.
5. A method according to claim 1, in which the silicone resin is dissolved in an organic solvent selected from the group of carbon tetrachloride, benzene, toluene or xylene.
6. A method according to claim 1, in which the residual resin coating, after plating, is removed by acid pickling in one of HC1 or H2SO4.
7, A method according to claim 1, in which the residual resin coating, after plating, is removed by etching with chromate treating liquid.
8. A method according to claim 1, in which the residual resin coating, after plating, is removed by brushing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP50045420A JPS51119627A (en) | 1975-04-15 | 1975-04-15 | Method of producing steel plate zinccplated on one side |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1068174A true CA1068174A (en) | 1979-12-18 |
Family
ID=12718763
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA247,625A Expired CA1068174A (en) | 1975-04-15 | 1976-03-09 | Galvanizing steel strip of partial or one side by pretreatment thereof with silicone resin |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS51119627A (en) |
| CA (1) | CA1068174A (en) |
| DE (1) | DE2609968C3 (en) |
| GB (1) | GB1529634A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5310329A (en) * | 1976-07-15 | 1978-01-30 | Nisshin Steel Co Ltd | Oneeside molten plating method and apparatus therefor |
| DE102015101312A1 (en) * | 2015-01-29 | 2016-08-04 | Thyssenkrupp Steel Europe Ag | A method of applying a metallic protective coating to a surface of a steel product |
| DE102017120782A1 (en) * | 2017-08-07 | 2019-02-07 | Fontaine Holdings Nv | Hot-dip galvanizing process as well as carrying and / or holding means for hot-dip galvanizing |
| CN116162880A (en) * | 2022-12-20 | 2023-05-26 | 中国船舶重工集团应急预警与救援装备股份有限公司 | Hot galvanizing bridge equipment friction surface treatment method |
-
1975
- 1975-04-15 JP JP50045420A patent/JPS51119627A/en active Pending
-
1976
- 1976-03-09 CA CA247,625A patent/CA1068174A/en not_active Expired
- 1976-03-10 GB GB9477/76A patent/GB1529634A/en not_active Expired
- 1976-03-10 DE DE2609968A patent/DE2609968C3/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1529634A (en) | 1978-10-25 |
| DE2609968A1 (en) | 1976-10-21 |
| JPS51119627A (en) | 1976-10-20 |
| DE2609968C3 (en) | 1979-10-18 |
| DE2609968B2 (en) | 1979-03-01 |
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