CA1196235A - Process for producing pre-painted steel sheets - Google Patents
Process for producing pre-painted steel sheetsInfo
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- CA1196235A CA1196235A CA000402193A CA402193A CA1196235A CA 1196235 A CA1196235 A CA 1196235A CA 000402193 A CA000402193 A CA 000402193A CA 402193 A CA402193 A CA 402193A CA 1196235 A CA1196235 A CA 1196235A
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Abstract
Abstract of the Disclosure Process of producing pre-painted. steel sheets in one production line, comprising metal coating, paint coat-ing, curing of the paint coating by means of a plurality of near infrared lamps arranged above and below the running strip. The curing is controlled by regulating the number of the lamps to be turned on in accordance with the inform-ations of the sheet thickness, width, the line speed and the paint coating.
Description
The present invention relates to producing a pre-painted steel sheet at low production cost by combin-ing metal coating and paint coating steps in one produc-tion line.
In recent years, not only in the field of con-struction materials but also in the fields of automobiles, electric appliances, steel furniture and containers, there has been an increasing tendency that cold rolled steel sheets are replaced by metal coated steel sheets and further by paint coated steel sheets. Particularly in the applications where the steel sheets are paint coated, there are various public pollution problems caused by the paint coating process, and most users of paint coated steel sheets are more and more inclined to switch over ~rom performance of paint coatings at their own shops to procurement of already paint coated steel sheets (pre-painted steel sheets).
Xowever, there exists one hindxous factor against this ten~ency. 'hat is the high production cost of the pre-painted steel sheets. This is more prominent and serious in the case of production of pre-painted steel sheets ~sing metal coated steel sheets as sub-strates.
Thus, ~or production of pre-painted steel sheet by using metal coated steel sheets as substrates, it has been a conventional practice to electroplate a cold rolled steel sheet as a substrate in a continuous steel coil electroplating line to obtain a metal coated steel coil, and this metal coated coil is paint coated, cured in a separate coil paint coating line to obtain a pre-painted steel sheet coil. There~ore at least two separate pro-duction lines, electroplating line and paint coating line are required in the conventional production o~ pr~-painted steel sheets.
Therefore, one of the objects of the present inven-tion is to provide a process for producing pre-painted steel sheets in which the metal coating (plating) and the paint coating, which have been continuously per-formed in separate production lines, are performed in thesame production line, namely an in-line coating process.
By performing the metal coating and the paint coating in the same production line, various wastes of labour and time required by the conventional arts of passing the steel coil throuyh separate two production lines can be sa~ed, Specifically, transportation of the steel coil between the two lines, packing of the steel coil for prevention of rust during intermediate storage, repetition of coiling and uncoiling, and material loss caused by cutting the leading and rear ends of the coil required for jointing or division of the steel coil can be eliminated by successively performing the metal coat-ing and the paint coating in the same production line.
However, there are various problems to be solved in performing the metal coating and the paint coating in the same production line.
As the metal coated steel sheets used for pro-duction of pre-painted steel sheets, zinc coated sheets, zinc alloy coated sheets, tin coated sheets, tin-free steel sheets, aluminwm and aluminum alloy coated sheets, and nickel coated sheets and so on are used, which all can be produced by an electroplating or hot-dip coating process. These metal coated sheets which are used with-out further treatments in wide applications other than as substrates for the pre-painted sheets are produced in a great amount. Therefore, the metal coating process must be adapted for the mass production at low cost, reaching a production rate as high as more than lO,000 ton per month in one production line, On the other hand, demands for the pre-palnted sheets are rather small as compared with the production of metal coated sheets, although production of pre-painted sheets has been increasing, so that it is not necessary to paint coat the whole of the met~l coated sheets produced in one production line, but rather it is necessary to manage so as to obtain a certain amount of pre-painted sheets and a certain amount of metal coated sheets in one production line~ Further, it is necessary to select paints to be coated on the metal coated sheets depending on the final applications of the pre-painted sheets, and it is most common to change the curing conditions in view of the paints to be used.
However, the conventional axt of curing paint coated coils which is most commonly practiced is nothing more than the so-called hot blast curing method which comprises blasting a high-temperature hot blast to cure the paint by the heat transferred by the blast. According to this hot blast curing method, it is possible to control the curing condition on the basis of the final sheet temper-ature, and the temperature of the hot blast is adjusted so as to obtain an optimum temperature for the paint to be coated, and the line speed is adjusted so as to control the travelling time of the coil through the furnace.
In recent years, not only in the field of con-struction materials but also in the fields of automobiles, electric appliances, steel furniture and containers, there has been an increasing tendency that cold rolled steel sheets are replaced by metal coated steel sheets and further by paint coated steel sheets. Particularly in the applications where the steel sheets are paint coated, there are various public pollution problems caused by the paint coating process, and most users of paint coated steel sheets are more and more inclined to switch over ~rom performance of paint coatings at their own shops to procurement of already paint coated steel sheets (pre-painted steel sheets).
Xowever, there exists one hindxous factor against this ten~ency. 'hat is the high production cost of the pre-painted steel sheets. This is more prominent and serious in the case of production of pre-painted steel sheets ~sing metal coated steel sheets as sub-strates.
Thus, ~or production of pre-painted steel sheet by using metal coated steel sheets as substrates, it has been a conventional practice to electroplate a cold rolled steel sheet as a substrate in a continuous steel coil electroplating line to obtain a metal coated steel coil, and this metal coated coil is paint coated, cured in a separate coil paint coating line to obtain a pre-painted steel sheet coil. There~ore at least two separate pro-duction lines, electroplating line and paint coating line are required in the conventional production o~ pr~-painted steel sheets.
Therefore, one of the objects of the present inven-tion is to provide a process for producing pre-painted steel sheets in which the metal coating (plating) and the paint coating, which have been continuously per-formed in separate production lines, are performed in thesame production line, namely an in-line coating process.
By performing the metal coating and the paint coating in the same production line, various wastes of labour and time required by the conventional arts of passing the steel coil throuyh separate two production lines can be sa~ed, Specifically, transportation of the steel coil between the two lines, packing of the steel coil for prevention of rust during intermediate storage, repetition of coiling and uncoiling, and material loss caused by cutting the leading and rear ends of the coil required for jointing or division of the steel coil can be eliminated by successively performing the metal coat-ing and the paint coating in the same production line.
However, there are various problems to be solved in performing the metal coating and the paint coating in the same production line.
As the metal coated steel sheets used for pro-duction of pre-painted steel sheets, zinc coated sheets, zinc alloy coated sheets, tin coated sheets, tin-free steel sheets, aluminwm and aluminum alloy coated sheets, and nickel coated sheets and so on are used, which all can be produced by an electroplating or hot-dip coating process. These metal coated sheets which are used with-out further treatments in wide applications other than as substrates for the pre-painted sheets are produced in a great amount. Therefore, the metal coating process must be adapted for the mass production at low cost, reaching a production rate as high as more than lO,000 ton per month in one production line, On the other hand, demands for the pre-palnted sheets are rather small as compared with the production of metal coated sheets, although production of pre-painted sheets has been increasing, so that it is not necessary to paint coat the whole of the met~l coated sheets produced in one production line, but rather it is necessary to manage so as to obtain a certain amount of pre-painted sheets and a certain amount of metal coated sheets in one production line~ Further, it is necessary to select paints to be coated on the metal coated sheets depending on the final applications of the pre-painted sheets, and it is most common to change the curing conditions in view of the paints to be used.
However, the conventional axt of curing paint coated coils which is most commonly practiced is nothing more than the so-called hot blast curing method which comprises blasting a high-temperature hot blast to cure the paint by the heat transferred by the blast. According to this hot blast curing method, it is possible to control the curing condition on the basis of the final sheet temper-ature, and the temperature of the hot blast is adjusted so as to obtain an optimum temperature for the paint to be coated, and the line speed is adjusted so as to control the travelling time of the coil through the furnace.
2~ In connection with the ~bove conventional art, there are various problems.
One problem is that it is necessary to stop the line until the temperature o* the hot blast in the curing furnace reaches a predetermined temperature or it is neces-sary to wait until the furnace temperature lowers to sucha degree as that no adverse effect is produced on the quality of metal coated substrates. This is particularly necessary when the production is changed over in one pro-duction line between the metal coated sheets and the pre-painted sheets, more particularly when the production of pre-painted sheets is started or when the production of pre-painted sheets is terminated and changed over to the production of metal coated sheets.
The waste time caused by the above change-over, normally ranges from 30 minutes to one hour, and causes the lowering of the production rate, hence increased pro duction cost.
A second problem is caused when it is required to change the final sheet coil temperature due to the change of paints to be coated. In this case, it is possible to obtain a predetermined final sheet coil temperature by changing the line speed without changing the furnace temperature in principle, but in many cases, it is impossible to take such procedure in view of the metal coating conditions or, if possible, such procedure will lower the production efficiency. Explanations will be made referring to the electroplating process. In view of requirements for increasing the production as high as possible, namely the production amount per unit hour, the electroplating is performed by passing the current up to the limi~s o~ the capacity of current sources for rectifiers for the electroplating so that the line speed is automatically determined by the sheet widths of coils, the plating thicknesses and the capaci-ties of rectifiers. Therefore, if the line speed is tobe determined from the curing condition of the paint coating, the capacity of the rectifier is not sufficient so that a re~uired plating thic]~ness cannot be obtained or the operation is compelled to be done at a lower line speed than the proper line speed.
For solving the second problem, it may be con-templated to change the furnace temperature, but 10 to 30 minutes are wasted for the change of the furnace temper-ature and the line must be stopped for this period o~
time.
~62~5 A third problem is caused when the coil width, sheet thickness or plating thickness are changed. Thus, when the coil width or the plating thickness is to be changed, it is re~uired to change the line speed due to the limited capacity of the rectifier as mentioned in connection with the second problem, so that the furnace temperature must be changed accordingly, This change of the furnace temperature requires 10 to 30 minutes during which the production line must be stopped, thus, lowering the productivity. Also when the coil thickness is to be changed, it is necessary to change the furnace temperature so as to assure to obtain a desired same final sheet temperature even at the same line speed, or to change the line speed at the same furnace temperature so as to ob-tain the same final shee-t temperature. Therefore, similar problems as above are caused.
The second ar,d third problems mentioned above are confronted with also in the cases of metal coatings by hot dipping in molten metal baths, in which the condi-tions of pretreatments, such as oxidizing and ~he heattreatment in a reducing, depend on the sheet thickness and width, and in some cases this situation cannot be compatible with the situation ~here the paint curing condition depends on the sheet thickness and the type of paints to be coated.
The present inventors have made various investi-gations and studies to solve the problems in the conven-tional in-line coating art combining the metal coating and the hot blast curing of paint coating, and have found that a novel in-line coating art utilizing a curing system by means of a near infrared radiation is very effective and advantageous. According to this novel art, it is not only possible to obtain immediately the same curing condi-tion, namely the same final sheet temperature, despite changes in the line speed, sheet thickness and width, but ~6235i also it is completely unnecessary to stop the production line at the time of change over from the metal coated products to the pre-painted products or from the pre-painted products to the metal coated productsO The present invention has been co~pleted on the basis of the above discovery.
According to the present invention, the curing conditions can be optionally selected in accordance with desired line speeds for metal coating, and it is possible to perform or stop the paint coating and the curing at any desired time, while the metal coating is continuously performed without stopping the line. This is the second feature of the present invention A third feature of the present invention is particularly important for production of one-side metal coated or one-side paint coated steel sheets used as rust-preventive materials for automobile Thus, according to the present invention, a chemical conversion treatment is intentionally applied to the back side of the one-side coated sheet ox a thin metal coating is applied to the back side at the time of the coating-curing step so that rust and bluing are effectively prevented If the chemical conversion treatment is to be ~5 applied only to one side of the sheet, the paint coating method is limited to a roll coating and the like, but if the thin metal coating is applied and then, after the chemical conversion treatment and the paint coating and curing, the thin metal coating is mechanically removed,
One problem is that it is necessary to stop the line until the temperature o* the hot blast in the curing furnace reaches a predetermined temperature or it is neces-sary to wait until the furnace temperature lowers to sucha degree as that no adverse effect is produced on the quality of metal coated substrates. This is particularly necessary when the production is changed over in one pro-duction line between the metal coated sheets and the pre-painted sheets, more particularly when the production of pre-painted sheets is started or when the production of pre-painted sheets is terminated and changed over to the production of metal coated sheets.
The waste time caused by the above change-over, normally ranges from 30 minutes to one hour, and causes the lowering of the production rate, hence increased pro duction cost.
A second problem is caused when it is required to change the final sheet coil temperature due to the change of paints to be coated. In this case, it is possible to obtain a predetermined final sheet coil temperature by changing the line speed without changing the furnace temperature in principle, but in many cases, it is impossible to take such procedure in view of the metal coating conditions or, if possible, such procedure will lower the production efficiency. Explanations will be made referring to the electroplating process. In view of requirements for increasing the production as high as possible, namely the production amount per unit hour, the electroplating is performed by passing the current up to the limi~s o~ the capacity of current sources for rectifiers for the electroplating so that the line speed is automatically determined by the sheet widths of coils, the plating thicknesses and the capaci-ties of rectifiers. Therefore, if the line speed is tobe determined from the curing condition of the paint coating, the capacity of the rectifier is not sufficient so that a re~uired plating thic]~ness cannot be obtained or the operation is compelled to be done at a lower line speed than the proper line speed.
For solving the second problem, it may be con-templated to change the furnace temperature, but 10 to 30 minutes are wasted for the change of the furnace temper-ature and the line must be stopped for this period o~
time.
~62~5 A third problem is caused when the coil width, sheet thickness or plating thickness are changed. Thus, when the coil width or the plating thickness is to be changed, it is re~uired to change the line speed due to the limited capacity of the rectifier as mentioned in connection with the second problem, so that the furnace temperature must be changed accordingly, This change of the furnace temperature requires 10 to 30 minutes during which the production line must be stopped, thus, lowering the productivity. Also when the coil thickness is to be changed, it is necessary to change the furnace temperature so as to assure to obtain a desired same final sheet temperature even at the same line speed, or to change the line speed at the same furnace temperature so as to ob-tain the same final shee-t temperature. Therefore, similar problems as above are caused.
The second ar,d third problems mentioned above are confronted with also in the cases of metal coatings by hot dipping in molten metal baths, in which the condi-tions of pretreatments, such as oxidizing and ~he heattreatment in a reducing, depend on the sheet thickness and width, and in some cases this situation cannot be compatible with the situation ~here the paint curing condition depends on the sheet thickness and the type of paints to be coated.
The present inventors have made various investi-gations and studies to solve the problems in the conven-tional in-line coating art combining the metal coating and the hot blast curing of paint coating, and have found that a novel in-line coating art utilizing a curing system by means of a near infrared radiation is very effective and advantageous. According to this novel art, it is not only possible to obtain immediately the same curing condi-tion, namely the same final sheet temperature, despite changes in the line speed, sheet thickness and width, but ~6235i also it is completely unnecessary to stop the production line at the time of change over from the metal coated products to the pre-painted products or from the pre-painted products to the metal coated productsO The present invention has been co~pleted on the basis of the above discovery.
According to the present invention, the curing conditions can be optionally selected in accordance with desired line speeds for metal coating, and it is possible to perform or stop the paint coating and the curing at any desired time, while the metal coating is continuously performed without stopping the line. This is the second feature of the present invention A third feature of the present invention is particularly important for production of one-side metal coated or one-side paint coated steel sheets used as rust-preventive materials for automobile Thus, according to the present invention, a chemical conversion treatment is intentionally applied to the back side of the one-side coated sheet ox a thin metal coating is applied to the back side at the time of the coating-curing step so that rust and bluing are effectively prevented If the chemical conversion treatment is to be ~5 applied only to one side of the sheet, the paint coating method is limited to a roll coating and the like, but if the thin metal coating is applied and then, after the chemical conversion treatment and the paint coating and curing, the thin metal coating is mechanically removed,
3~ the chemical conversion ~ilm can be removed together with the metal coating so that the non-paint coated surface provides a fresh surface, on which users can advantageously apply a phosphate treatment, for example.
When one-side metal coated steel sheets are used as substrates and paint coatings are applied thereon, there :~9i~2~5 is no means to remove the chemical conversion film adher-ing on the steel sheet, and if this film is removed by mechanical grinding, it is very difficult to do so as compared with the present invention where the film is removed all together with the metal coating, so that users are confronted with troubles ~hen they apply phosphate treatrnents.
According to the present invention, pre-painted steel sheets and metal coated steel sheets are produced in a production line comprising uncoilers, pretreatment equipment, metal coating equipment, chemical conversion treatment equipment (pre-treatments for paint coating), paint coating equipment, near infrared radiation curing e~uiprnent, coilers~ etc.
1~ According to one ernbodiment of the present invention, steel coils may be used without cutting, and according to another embodiment, cut sheet products can be obtained by substituting the coilers with shears and pliers. Also by substituting the uncoilers and coilers respectively with cut sheet feeders, and cut sheet pliers, constituting a cut sheet production line, the present invention may be applied to cut sheets.
Metal coating equipment useable in the present invention may be classified into two groups' electro-2~ plating equipment and hot-dip metal coating equiprnent, and appropriate pretreatrnent equipment are selected for these metal coating processes. As for the types and kinds of metal coatings, the present invention is not limited to specific metal coatings and can be applied to various metal coated sheets, such as zinc coated, zinc alloy coated, tin coated, tin-free, alumini~n coated, aluminum alloy coated and nickel coated steel sheets. Also the pxesent invention is not limited to specific metal coating processes.
As the pretreatments for paint coating, the present inver.tion is not limited to specific pretreat~
ments, but any pretreatment useful for paint coating, suc~ as phosphate treatment, chromate treatment, passivation treatment (oxide film formation treatment) can be used, and these treatments can be performed by any suitable method, such as spraying, immersion, roll coating and electrolysis.
The paint coating in the present invention can be applied by various methods, such as roll coating, spray coating, curtain flow coating, immersion coating, and electrodeposition coating, but from the points of uniformness and stability of the coating, the roll coating is most preferable when sheet`coils are treated, ~5 and the curtain flow coating is most preferable when the cut sheets are treated.
Further, the present invention is not limited to specific types or kinds of paints, but various paints such as thermal setting resins can be advantageously selected depending on final applications~
The near infrared radiation lamp used in the present inven~ion is a bar-shaped electric heating lamp which emits a near infrared radiation having its energy peak at a wave length o* 1 to 2 ~m, and characterized in that the density of output energy is very high and the time required for reaching the constant output is only about one second. These characteristics cannot be ob-tained by the conventional infrared lamp, far infrared lamp or ultraviolet lamp. ~s commercially available near infrared radiation lamps they are available from Nippon Phillips Corporation, Research Inc., Shinku Ricoh Co., Ltd. in Japan.
The products obtained by the process according to the present invention include pre-painted steel sheets for indoor and outdoor building materials, pre-painted ~6Z~3~
sheets for working into containers, electric appliances and furniture, pre-painted sheets for manufacturing of various cans including food cans and other cans, and pre-painted sheets for rus-t prevention purpose in auto-mobile. mus, the products obtained by the presentinvention can be used in very wid~ applications requir-ing different qualities.
The invention will now be described with reference to the accompanying drawings which show a pre-ferred form thereof and wherein:-FIGURE 1 schematically shows a production linefor the present invention.
FIGURES 2 and 3, respectively, illustrate arrangements of near infrared lamps, in which si~ lamps constitute one unit lamp house.
The present invention will be described in more detail as applied to the production of pre-painted sheets *or rust prevention in automobile by combining zinc-alloy electroplating and weldable paint coating with reference to Figure 1.
In Figure 1, a cold rolled steel sheet or a hot rolled steel strip to be treated is mounted o~ an uncoiler 13 and the strip uncoiled therefrom is introduced to a group of pretreatment equipments 1 - 4 through shears, jointing machines and pliers (nGt shown).
m e pretreatment equipment comprise a de~reas-ing tank 1, a washing tank ~ and an acid pickling tank, a washing tank 4, in which the strip surface is washed and activated by spraying, immersion, ~rushing or electrolysis, whichever suitable as pretreatment for the metal coating.
The principal object of the pretreatment is to assure the adhesion of the metal coating on the sub-strate, and the adhesion of coatings and corrosion _ g _ ~g~Z35 resistance of final products, and so far as this objectis achieved, the present invention is not limited to specific methods and conventionally known additional treatments other than the above treatments can be applied without departing from the scope of the present in~ention, The steel strip after the pretreatment is led to a plating tank 5 where it is applied with a desired thickness of a desired metal coating appro,priate to the final application, As for the metal coating useable in the present invention includes zince coating and zinc-alloy coating, such as zinc-nickel alloy coating, zinc-nickel-cobalt alloy coating, zinc-nickel-~hrome alloy coating and zinc-nickel-bron alloy coating. The present invention is not limited to the above coatings and various other metal and alloy coatings can be used.
Regarding the amount of metal coatings to be applied to the strip, it may be selected depending on the final applications and the desired corrosion resistance of the final products, but in order to assure desired effects of the metal coatings, it is desirable to apply the metal coatings in amounts not less than 1 g/m , prefer-ably not less than 3 gJm , and more preferably not less than 5 g/m2 and in amounts not larger than 15 g/m2.
When the metal coatings are applied by electro-plating, the electrolyte may be acid or alkaline and there is no specific limitation. The metal coating is performed in a suitable bath under suitable conditions depending on the desired ~uality of the final products and in view of the productivity. Further, the electro-plating tank may be of any desired type and shape, such as vertical and horizontal tanks, and the number of electroplating tanks may be selected depending on the desired production rate.
~6~35 According to the present invention, two-side paint coated products and one-side paint coated products can be obtained. In the former case, the amounts of the coatings on both sides may be selected depending on the desired qualities In the latter case, only one side on which the paint coating is to be ~pplied i5 metal coated, or for the purpose of preventing rust formation in the production line and temper color during the curing a thin metal coating not larger than 3 g/m is applied to one side of the strip on which the paint coating is not to be applied, and this thin metal coating may be or may not be chemically or mechanically removed immed-iately before the coiling or during other suitable steps to obtain a final product.
After the metal coating, the strip is washed in the washing tank 6 and led to the chemical conversion tank 7, where it is subjected to phosphate treatment, chromate treatment, passivation treatment or other pre~
treatments.
The chemical conversion ma~ ba performed by any conventionally known method, such as immersion, spraying electrolysis, roll coatin~ and by means of reaction cells.
After the chemical conversion treatment, the strip is washed and subjected to chrome-sealing (not shown), if necessary, and led to a drying furnace 8u Then the strip is applied with a weldable paint coating in a paint coater 9. l'he coating may be performed by spray coating, curtain coating, etc. although the roll coating is most common.
~s the weldable paint, powder zinc paint is known, but the following paint com~ositions are more suit~
able for the present invention:
~g6~3S
a) paint composition comprising a vehicle mainly composed of resins such as epoxy, polyester, acryl, vinyl, etc., not less than 8~/o by weight (with respect to non-volatile matters) of powdered zinc and optionally powdered aluminum, magnesium and carbon, b) mixed powder paint composition comprising a vehicle mainly composed of resins such as epoxy, polyester, acryl, vinyl, etc. at least one of iron, nickel, chrome, cobalt, manganese and their alloys in the powder form, and powdered carbide of at least one of tita~ium, zirconium, hafnium, vanadium, niobium, tantalum, chrome, tungsten and their mixtures, not less than 5% hy weight, preferably 40 to 80% by weight of powdered zinc, and optionally a small amount of at least one of powdered aluminum, magnesium and carbon.
Naturally, the above paint compositions may further comprise small amounts of rust preventive pig-ment, coloring dye and pigment, and other additives within a range which is not hinderous to the desired weldability~
The thickness of paint coatings may be determined depending on the final applications and the re~uired qualities, but normally it ranges from 3 to 20~, Although the paint coating may be applied outside the above range without departing from the scope of the present invention, paint coatings less than 3~ are generally insufficient for assuring the desired corrosion resistance of the paint coating, and paint coatings beyond 20~ generally tend to deteriorata the weldability.
The zinc powder contained in the paint composi-tion synergetically functions with the metal coating su~-layer and selfsacrifyingly prevents the corrosion of the base steel sheet~ For this purpose and in view of 3.~L9~235 the weldability, at least 80% by weight of zinc powder is required in the zinc-powd~r-straight paint composition. In the case of the mixed powder paint composition, at least 5% by weight, preferably at least 4~/O by weight of zinc powder is added for the purpose of assuring the desired corrosion resistance. The upper limit is determined mainly from the point of workability, but greatly influenced by the kind and amount of other powder additives to be added together the zinc powder. There-fore, the upper limit of 80% serves merely as astandard.
In the curing furnace 10, the near infrared lamps are arranged above and below the strip. The arrangement of the lamps may be done in a prallel direc-tion to the running direction of the strip (Figure 3),or in a perpendicular direction to the running direction of the strip (Figure 2)~ In the latter arrangement, as the energy density at the socket portions 16 and 17 of the lamp 15 lowers, it is desirable to arrange the lamps in a zig-zag manner. In the former arrangement in which the lamps are arranged in the parallel direction, to the line direction, and the low energy zone of the socket portions 16 and 17 is distributed uniformly in the width direction, the pro~lem is much less. Normally, 4 to 8 lamps constitute a unit of lamps, and these units of lamps are arranged in the lamp house provided with a reflection plate. The reflection plate is desirably in such a shape as that the energy density of the lamp house in the width direction is maintained to be almost uniform, Regarding wirings for the lamps, one independent wiring is provided for each unit of lamps or each lamp so as to turn on only the required number of lamps in accordance with the line speed, the sheet thickness and width. This operation can be automatically controlled ~y means of a process computer and the like by measuring the Z3~;
sheet thickness, width and the line speed or by inputting necessary informations. Against possible damage or dis-order of the lamps, auxiliary lamps may be provided and automatically turned on by detection of the damage or disorder.
The strip cured under predetermined conditions in the curing furnace 10 is cooled in air and water, dried in the dryer 12, ground in a one-side grinding machine, if necessary, cut by a shear, looped by a looper, oiled by an oil coater, etc~ (not shown) and finally coiled on the coiler 14 to obtain coil products, or it is cut into predetermined lengths and piled to obtain cut sheat products.
In order to promote the evaporation cf the solvent in the paint coating prior to the irradiation by the near infrared lamp~, a near infrared furnace or the like may be arranged.
The present invention will be more clearly understood from the following embodiments.
EXAMPLE 1:
A cold rolled steel sheet coil of 0.7 mm thick and 1000mm width is applied with zinc coating by electro-plating, and coated with a zinc-base paint in the apparatus as shown in Figure 1. Ihe electropla-ting tank is a horiæontal type with a total effective length of 19 m (1.5 m x 16) using an electroplating bath contain-ing 400 g/~ zinc sulfate, 25 g/~ ammonium sulfate with pH at 1Ø The zinc-base paint composed of 85% zinc powder and epoxy resin (Epicote OL-55) is applied in l0~ by a roll coater.
As shown in Figure 3, 42 near infrared lamps of 2 kw/30 cm (made by Nippon Phillips CorpO) are arranged above and below the strip in the parallel direction of the line and similar 30 lamps are arranged above and below the strip in the width direction of the 23~
line at intervals of S cm. The lamps are spaced 5 cm from the strip. The zinc coating is applied on the strip to an amount of 20 g/m at a current density of 50 A/dm which is the upper limit of the capacity of the rectifier for the electroplating. The line speed is 90 m/min.
The curing is performed by the near infrared lamps in such a manner that only 25 lamps in the width direction which corresponds to the strip width are turned on and only 25 lamps in the line direction are turned on to obtain a strip temperature of 260C, and the qualities of the resultant paint coated sheets are shown in Table lA.
Then in order to increase the zinc coating to 40 g~m , the line speed is changed to 45 m/min. and the electroplating is performed at 50 A~dm . Along this, only 12 lamps in the line direction are turned on to obtain a strip temperature of 255C without stopping the line.
This strip temperature is almost same as that obtained in the case of the zinc coating of ~0 g~m . The resul-tant qualities are shown in Ta~le lB.
Further, the zinc coating is changed to 10 g~mIn this case, the capacity of the rectifier is well sufficient as contrary to the case of 40 g/m zinc coat-ing so that the line speed is increased to its upper limit of 150 m/min, and the electroplating is performed at 30 A/dm . Along this, 42 larnps in the line direction are turned on to obtain a strip temperature of 260C
without stopping the line. This strip temperature is almost same as that obtained at 20 g/m2 zinc coating, and the qualities of the resultant products are shown in Table lC.
EXAMPLE 2:
Using the similar apparatus as used in Example 1, a steel strip of 0.7 mm x 1000 r~m is applied with a zinc coating of 20 g/m2 and with a weldable paint - 15 ~
~ lL9~;~3S
coating (same as in Example 1) of 10~ and cured by means of near infrared lamps~
Then a steel coil of 0.5 mm thick and 1000 mm wide is welded to the above coil for the purpose of producing coated sheets with 20 g/m zinc coating and 10~ paint coating under the same electroplating condltion.
In this case, however, only 18 infrared lamps in the line direction ar~ turned on for curing the paint coating to obtain a final strip temperature of 260C as desired without stopping the line, and the qualities of the resultant products are shown in Table lD~
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When one-side metal coated steel sheets are used as substrates and paint coatings are applied thereon, there :~9i~2~5 is no means to remove the chemical conversion film adher-ing on the steel sheet, and if this film is removed by mechanical grinding, it is very difficult to do so as compared with the present invention where the film is removed all together with the metal coating, so that users are confronted with troubles ~hen they apply phosphate treatrnents.
According to the present invention, pre-painted steel sheets and metal coated steel sheets are produced in a production line comprising uncoilers, pretreatment equipment, metal coating equipment, chemical conversion treatment equipment (pre-treatments for paint coating), paint coating equipment, near infrared radiation curing e~uiprnent, coilers~ etc.
1~ According to one ernbodiment of the present invention, steel coils may be used without cutting, and according to another embodiment, cut sheet products can be obtained by substituting the coilers with shears and pliers. Also by substituting the uncoilers and coilers respectively with cut sheet feeders, and cut sheet pliers, constituting a cut sheet production line, the present invention may be applied to cut sheets.
Metal coating equipment useable in the present invention may be classified into two groups' electro-2~ plating equipment and hot-dip metal coating equiprnent, and appropriate pretreatrnent equipment are selected for these metal coating processes. As for the types and kinds of metal coatings, the present invention is not limited to specific metal coatings and can be applied to various metal coated sheets, such as zinc coated, zinc alloy coated, tin coated, tin-free, alumini~n coated, aluminum alloy coated and nickel coated steel sheets. Also the pxesent invention is not limited to specific metal coating processes.
As the pretreatments for paint coating, the present inver.tion is not limited to specific pretreat~
ments, but any pretreatment useful for paint coating, suc~ as phosphate treatment, chromate treatment, passivation treatment (oxide film formation treatment) can be used, and these treatments can be performed by any suitable method, such as spraying, immersion, roll coating and electrolysis.
The paint coating in the present invention can be applied by various methods, such as roll coating, spray coating, curtain flow coating, immersion coating, and electrodeposition coating, but from the points of uniformness and stability of the coating, the roll coating is most preferable when sheet`coils are treated, ~5 and the curtain flow coating is most preferable when the cut sheets are treated.
Further, the present invention is not limited to specific types or kinds of paints, but various paints such as thermal setting resins can be advantageously selected depending on final applications~
The near infrared radiation lamp used in the present inven~ion is a bar-shaped electric heating lamp which emits a near infrared radiation having its energy peak at a wave length o* 1 to 2 ~m, and characterized in that the density of output energy is very high and the time required for reaching the constant output is only about one second. These characteristics cannot be ob-tained by the conventional infrared lamp, far infrared lamp or ultraviolet lamp. ~s commercially available near infrared radiation lamps they are available from Nippon Phillips Corporation, Research Inc., Shinku Ricoh Co., Ltd. in Japan.
The products obtained by the process according to the present invention include pre-painted steel sheets for indoor and outdoor building materials, pre-painted ~6Z~3~
sheets for working into containers, electric appliances and furniture, pre-painted sheets for manufacturing of various cans including food cans and other cans, and pre-painted sheets for rus-t prevention purpose in auto-mobile. mus, the products obtained by the presentinvention can be used in very wid~ applications requir-ing different qualities.
The invention will now be described with reference to the accompanying drawings which show a pre-ferred form thereof and wherein:-FIGURE 1 schematically shows a production linefor the present invention.
FIGURES 2 and 3, respectively, illustrate arrangements of near infrared lamps, in which si~ lamps constitute one unit lamp house.
The present invention will be described in more detail as applied to the production of pre-painted sheets *or rust prevention in automobile by combining zinc-alloy electroplating and weldable paint coating with reference to Figure 1.
In Figure 1, a cold rolled steel sheet or a hot rolled steel strip to be treated is mounted o~ an uncoiler 13 and the strip uncoiled therefrom is introduced to a group of pretreatment equipments 1 - 4 through shears, jointing machines and pliers (nGt shown).
m e pretreatment equipment comprise a de~reas-ing tank 1, a washing tank ~ and an acid pickling tank, a washing tank 4, in which the strip surface is washed and activated by spraying, immersion, ~rushing or electrolysis, whichever suitable as pretreatment for the metal coating.
The principal object of the pretreatment is to assure the adhesion of the metal coating on the sub-strate, and the adhesion of coatings and corrosion _ g _ ~g~Z35 resistance of final products, and so far as this objectis achieved, the present invention is not limited to specific methods and conventionally known additional treatments other than the above treatments can be applied without departing from the scope of the present in~ention, The steel strip after the pretreatment is led to a plating tank 5 where it is applied with a desired thickness of a desired metal coating appro,priate to the final application, As for the metal coating useable in the present invention includes zince coating and zinc-alloy coating, such as zinc-nickel alloy coating, zinc-nickel-cobalt alloy coating, zinc-nickel-~hrome alloy coating and zinc-nickel-bron alloy coating. The present invention is not limited to the above coatings and various other metal and alloy coatings can be used.
Regarding the amount of metal coatings to be applied to the strip, it may be selected depending on the final applications and the desired corrosion resistance of the final products, but in order to assure desired effects of the metal coatings, it is desirable to apply the metal coatings in amounts not less than 1 g/m , prefer-ably not less than 3 gJm , and more preferably not less than 5 g/m2 and in amounts not larger than 15 g/m2.
When the metal coatings are applied by electro-plating, the electrolyte may be acid or alkaline and there is no specific limitation. The metal coating is performed in a suitable bath under suitable conditions depending on the desired ~uality of the final products and in view of the productivity. Further, the electro-plating tank may be of any desired type and shape, such as vertical and horizontal tanks, and the number of electroplating tanks may be selected depending on the desired production rate.
~6~35 According to the present invention, two-side paint coated products and one-side paint coated products can be obtained. In the former case, the amounts of the coatings on both sides may be selected depending on the desired qualities In the latter case, only one side on which the paint coating is to be ~pplied i5 metal coated, or for the purpose of preventing rust formation in the production line and temper color during the curing a thin metal coating not larger than 3 g/m is applied to one side of the strip on which the paint coating is not to be applied, and this thin metal coating may be or may not be chemically or mechanically removed immed-iately before the coiling or during other suitable steps to obtain a final product.
After the metal coating, the strip is washed in the washing tank 6 and led to the chemical conversion tank 7, where it is subjected to phosphate treatment, chromate treatment, passivation treatment or other pre~
treatments.
The chemical conversion ma~ ba performed by any conventionally known method, such as immersion, spraying electrolysis, roll coatin~ and by means of reaction cells.
After the chemical conversion treatment, the strip is washed and subjected to chrome-sealing (not shown), if necessary, and led to a drying furnace 8u Then the strip is applied with a weldable paint coating in a paint coater 9. l'he coating may be performed by spray coating, curtain coating, etc. although the roll coating is most common.
~s the weldable paint, powder zinc paint is known, but the following paint com~ositions are more suit~
able for the present invention:
~g6~3S
a) paint composition comprising a vehicle mainly composed of resins such as epoxy, polyester, acryl, vinyl, etc., not less than 8~/o by weight (with respect to non-volatile matters) of powdered zinc and optionally powdered aluminum, magnesium and carbon, b) mixed powder paint composition comprising a vehicle mainly composed of resins such as epoxy, polyester, acryl, vinyl, etc. at least one of iron, nickel, chrome, cobalt, manganese and their alloys in the powder form, and powdered carbide of at least one of tita~ium, zirconium, hafnium, vanadium, niobium, tantalum, chrome, tungsten and their mixtures, not less than 5% hy weight, preferably 40 to 80% by weight of powdered zinc, and optionally a small amount of at least one of powdered aluminum, magnesium and carbon.
Naturally, the above paint compositions may further comprise small amounts of rust preventive pig-ment, coloring dye and pigment, and other additives within a range which is not hinderous to the desired weldability~
The thickness of paint coatings may be determined depending on the final applications and the re~uired qualities, but normally it ranges from 3 to 20~, Although the paint coating may be applied outside the above range without departing from the scope of the present invention, paint coatings less than 3~ are generally insufficient for assuring the desired corrosion resistance of the paint coating, and paint coatings beyond 20~ generally tend to deteriorata the weldability.
The zinc powder contained in the paint composi-tion synergetically functions with the metal coating su~-layer and selfsacrifyingly prevents the corrosion of the base steel sheet~ For this purpose and in view of 3.~L9~235 the weldability, at least 80% by weight of zinc powder is required in the zinc-powd~r-straight paint composition. In the case of the mixed powder paint composition, at least 5% by weight, preferably at least 4~/O by weight of zinc powder is added for the purpose of assuring the desired corrosion resistance. The upper limit is determined mainly from the point of workability, but greatly influenced by the kind and amount of other powder additives to be added together the zinc powder. There-fore, the upper limit of 80% serves merely as astandard.
In the curing furnace 10, the near infrared lamps are arranged above and below the strip. The arrangement of the lamps may be done in a prallel direc-tion to the running direction of the strip (Figure 3),or in a perpendicular direction to the running direction of the strip (Figure 2)~ In the latter arrangement, as the energy density at the socket portions 16 and 17 of the lamp 15 lowers, it is desirable to arrange the lamps in a zig-zag manner. In the former arrangement in which the lamps are arranged in the parallel direction, to the line direction, and the low energy zone of the socket portions 16 and 17 is distributed uniformly in the width direction, the pro~lem is much less. Normally, 4 to 8 lamps constitute a unit of lamps, and these units of lamps are arranged in the lamp house provided with a reflection plate. The reflection plate is desirably in such a shape as that the energy density of the lamp house in the width direction is maintained to be almost uniform, Regarding wirings for the lamps, one independent wiring is provided for each unit of lamps or each lamp so as to turn on only the required number of lamps in accordance with the line speed, the sheet thickness and width. This operation can be automatically controlled ~y means of a process computer and the like by measuring the Z3~;
sheet thickness, width and the line speed or by inputting necessary informations. Against possible damage or dis-order of the lamps, auxiliary lamps may be provided and automatically turned on by detection of the damage or disorder.
The strip cured under predetermined conditions in the curing furnace 10 is cooled in air and water, dried in the dryer 12, ground in a one-side grinding machine, if necessary, cut by a shear, looped by a looper, oiled by an oil coater, etc~ (not shown) and finally coiled on the coiler 14 to obtain coil products, or it is cut into predetermined lengths and piled to obtain cut sheat products.
In order to promote the evaporation cf the solvent in the paint coating prior to the irradiation by the near infrared lamp~, a near infrared furnace or the like may be arranged.
The present invention will be more clearly understood from the following embodiments.
EXAMPLE 1:
A cold rolled steel sheet coil of 0.7 mm thick and 1000mm width is applied with zinc coating by electro-plating, and coated with a zinc-base paint in the apparatus as shown in Figure 1. Ihe electropla-ting tank is a horiæontal type with a total effective length of 19 m (1.5 m x 16) using an electroplating bath contain-ing 400 g/~ zinc sulfate, 25 g/~ ammonium sulfate with pH at 1Ø The zinc-base paint composed of 85% zinc powder and epoxy resin (Epicote OL-55) is applied in l0~ by a roll coater.
As shown in Figure 3, 42 near infrared lamps of 2 kw/30 cm (made by Nippon Phillips CorpO) are arranged above and below the strip in the parallel direction of the line and similar 30 lamps are arranged above and below the strip in the width direction of the 23~
line at intervals of S cm. The lamps are spaced 5 cm from the strip. The zinc coating is applied on the strip to an amount of 20 g/m at a current density of 50 A/dm which is the upper limit of the capacity of the rectifier for the electroplating. The line speed is 90 m/min.
The curing is performed by the near infrared lamps in such a manner that only 25 lamps in the width direction which corresponds to the strip width are turned on and only 25 lamps in the line direction are turned on to obtain a strip temperature of 260C, and the qualities of the resultant paint coated sheets are shown in Table lA.
Then in order to increase the zinc coating to 40 g~m , the line speed is changed to 45 m/min. and the electroplating is performed at 50 A~dm . Along this, only 12 lamps in the line direction are turned on to obtain a strip temperature of 255C without stopping the line.
This strip temperature is almost same as that obtained in the case of the zinc coating of ~0 g~m . The resul-tant qualities are shown in Ta~le lB.
Further, the zinc coating is changed to 10 g~mIn this case, the capacity of the rectifier is well sufficient as contrary to the case of 40 g/m zinc coat-ing so that the line speed is increased to its upper limit of 150 m/min, and the electroplating is performed at 30 A/dm . Along this, 42 larnps in the line direction are turned on to obtain a strip temperature of 260C
without stopping the line. This strip temperature is almost same as that obtained at 20 g/m2 zinc coating, and the qualities of the resultant products are shown in Table lC.
EXAMPLE 2:
Using the similar apparatus as used in Example 1, a steel strip of 0.7 mm x 1000 r~m is applied with a zinc coating of 20 g/m2 and with a weldable paint - 15 ~
~ lL9~;~3S
coating (same as in Example 1) of 10~ and cured by means of near infrared lamps~
Then a steel coil of 0.5 mm thick and 1000 mm wide is welded to the above coil for the purpose of producing coated sheets with 20 g/m zinc coating and 10~ paint coating under the same electroplating condltion.
In this case, however, only 18 infrared lamps in the line direction ar~ turned on for curing the paint coating to obtain a final strip temperature of 260C as desired without stopping the line, and the qualities of the resultant products are shown in Table lD~
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Claims (4)
1. A process for producing pre-painted steel sheets comprising metal coating, paint coating, and curing of the paint coating by means of a near infrared lamp, all being performed in one production line.
2. A process according to claim 1, in which the curing of the paint coating is performed under a pre-determined condition by controlling the number of the near infrared lamps to be turned on for irradiation.
3. A process according to claim 2, in which the control of the number of the near infrared lamps to be turned on is effected on the basis of informations of sheet thicknesses widths and line speeds.
4. A process according to claim 1, in which the paint coating is a weldable paint coating containing zinc powder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP56-68108 | 1981-05-08 | ||
| JP6810881A JPS57184473A (en) | 1981-05-08 | 1981-05-08 | Production of precoat steel sheet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1196235A true CA1196235A (en) | 1985-11-05 |
Family
ID=13364206
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000402193A Expired CA1196235A (en) | 1981-05-08 | 1982-05-04 | Process for producing pre-painted steel sheets |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS57184473A (en) |
| CA (1) | CA1196235A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1201321A1 (en) * | 2000-10-24 | 2002-05-02 | Sidmar N.V. | Method of producing painted metal sheets |
| AU776513B2 (en) * | 1999-03-31 | 2004-09-09 | Bluescope Steel Limited | A pre-coated metal sheet having enhanced thermal resistance properties |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04180868A (en) * | 1990-11-16 | 1992-06-29 | Setsuo Tate | Drying method for coating film |
| JP2533467B2 (en) * | 1991-06-07 | 1996-09-11 | 節男 楯 | drying furnace |
| KR20000011746A (en) * | 1998-07-17 | 2000-02-25 | 미야무라 심뻬이 | Method of drying copper foil and copper foil drying apparatus |
| JP4954589B2 (en) * | 2006-04-10 | 2012-06-20 | 新日本製鐵株式会社 | Method for producing surface-treated steel sheet and heat drying apparatus |
| JP4954758B2 (en) * | 2007-03-19 | 2012-06-20 | 新日本製鐵株式会社 | Method for producing plated steel sheet with excellent corrosion resistance and paint adhesion |
-
1981
- 1981-05-08 JP JP6810881A patent/JPS57184473A/en active Pending
-
1982
- 1982-05-04 CA CA000402193A patent/CA1196235A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU776513B2 (en) * | 1999-03-31 | 2004-09-09 | Bluescope Steel Limited | A pre-coated metal sheet having enhanced thermal resistance properties |
| EP1201321A1 (en) * | 2000-10-24 | 2002-05-02 | Sidmar N.V. | Method of producing painted metal sheets |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS57184473A (en) | 1982-11-13 |
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