JP2008307092A - Method of manufacturing stainless steel made rinse tank for dishwasher dryer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a large stainless steel made rinse tank for a dishwasher by one process of warm forming. <P>SOLUTION: Austenitic stainless steel directly provided on its surface with a resin film is used as material and the material is subjected to deep drawing using a die adjusted to a die temperature of 140-250°C and a punch temperature of 20°C or below, thus the stainless steel made rinse tank is manufactured. The resin film is formed from one or more kinds selected from among polyvinyl alcohol resin, urethane resin and acrylic resin, wherein: a ratio of molecular weight of an OH-group to the total molecular weight of the resin is 0.02 or larger; and it is preferable that 1 to 20 pts.mass of polyethylene fluorocarbon polymer powders in which fluorocarbon polymer powders is combined onto powder surfaces of the polyethylene resin is added to 100 pts.mass of the film resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of deep-drawing a water-washing tank for a dishwasher having large vertical, horizontal, and high dimensions in one step.

Conventionally, synthetic resin molded products have been used in washing tanks for desktop dishwashers for general households (for example, Patent Document 1). A synthetic resin molded product is also used in a washing tub of a dishwasher incorporated in a system kitchen (for example, Patent Document 2). Furthermore, a method for forming a washing tank by welding two U-shaped and L-shaped plate members made of stainless steel has been proposed (see, for example, Patent Document 3).
Thus, in the past, resin injection molded products or metal plates were welded and used, but from the viewpoint of durability and design, stainless steel steel deep drawn products have recently been used. It has become.
JP 2002-165743 A Japanese Patent No. 3740115 JP 2003-61887 A

By the way, the washing tubs of recent dishwashers are becoming larger. Although it is made of resin, for example, a resin having a size of a short side width of 400 mm × long side width of 600 mm × aperture height of 330 mm has been proposed. If resin injection molding technology is adopted, it is a size that can be produced without problems, but if you want to secure strength, you have to increase the thickness of the resin, and there is a problem of space .
In this respect, it is possible to manufacture a desired water rinsing tank including an increase in size by using a stainless steel plate as a raw material and employing various forming and joining techniques.

  However, the use of a welding method as a joining method is useful from the viewpoint of simplicity, but a problem remains from the viewpoint of design. That is, image degradation due to the presence of a weld line. For this reason, it is necessary to polish and remove the welded portion, and it is difficult to employ the welding method due to cost increase due to an increase in the number of processes. In addition, as a method of obtaining a water washing tank without polishing the welded part, it is assumed that a water washing tank in which the outer bent part of the box bending flange is seam welded is constructed. Contamination, odor, and hygiene impacts due to the invasion and breeding of the animals are concerned.

It is also assumed that the caulking joint method will be constructed, but the caulking joint method is also affected by the deterioration of the image due to the presence of the caulking part, the contamination and odor due to the invasion and breeding of germs into the caulking part, and the effect on hygiene. Legal is also difficult to adopt. Moreover, both the welding method and the caulking method are not suitable for mass production because of low productivity.
The molding method adopted there is the deep drawing method. If a stainless steel plate is used as a material and deep drawing is performed without adopting a welding method, it will be difficult to manufacture. It is more difficult to obtain a deep-drawn product with a reduced punch shoulder radius, die shoulder radius, and corner radius. Deep drawing products having extremely small corner radii and extremely high molding heights must be performed by dividing the deep drawing process into a plurality of times, which is problematic in terms of design.

For example, a dishwasher washing tank with a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, a corner radius of 40 mm, a short side width of 400 mm, a long side width of 600 mm, and a drawing height of 330 mm is manufactured by drawing using a stainless steel plate as a raw material. Then, if the short side width is 400 mm and the corner radius is 40 mm, a processed product having a drawing height of 330 mm cannot be drawn in a single process, and thus must be drawn in a plurality of press processes. However, when press molding in multiple deep drawing processes, shock lines appear on the surface of the product and mold galling occurs, resulting in deterioration of the appearance of the product and failure to obtain high design. The flatness of the water is impaired and water leakage may occur.
For this reason, a multi-drawing deep-drawn product is not used in a water-washing tank of a table-type dishwasher, which is mainly made of stainless steel plate.

Under such a background, a system kitchen dishwasher that requires a deep box shape (punch shoulder radius 30 mm, die shoulder radius 10 mm, corner radius 40 mm, short side width 400 mm × long side width 600 mm × drawing height 330 mm) In this water washing tank, since a drawn product cannot be obtained in one step, the formation of a stainless steel plate does not progress, and a resin water washing tank having a thick wall is still used to ensure strength.
Therefore, the present invention has been devised to solve such a problem, and an object of the present invention is to provide a method for producing a large washing plate made of stainless steel plate for dishwashers by one-step warm processing. And

  In order to achieve the object, the stainless steel dishwasher / water washing tank manufacturing method of the present invention is a resin film formed from one or more selected from polyvinyl alcohol resin, urethane resin, and acrylic resin. An austenitic stainless steel plate provided with a resin film having a molecular weight ratio of OH groups in the total molecular weight of the resin of 0.02 or more directly on the surface is used, and the die temperature is set to 140 to 250 ° C. In addition, a deep drawing process using a die whose punch temperature is adjusted to 20 ° C. or lower is performed.

The resin film preferably has a polyethylene-fluororesin powder in which a fluororesin fine powder is bonded to the surface of polyethylene resin particles at a ratio of 1 to 20 parts by mass with respect to 100 parts by mass of the film resin.
When a die having a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, and a corner radius of 40 mm is used, as shown in FIGS. 1 and 2, the short side width is Ws, the corner radius is Rc, and the drawing height is H. It becomes possible to manufacture a dishwasher / water washing tank with /Ws≧0.8 and Rc / Ws ≦ 0.1.

In the present invention, an austenitic stainless steel plate having excellent drawing workability is used as a base material, a steel plate coated with a resin film having high ductility and high viscoelasticity is used as a material, and a warm deep drawing method is employed. ing. For this reason, softening of the film and seizure to the mold are suppressed, and as a result, it is possible to prevent mold galling and dents, etc., so that the required amount of ultra deep drawing water washing tank can be manufactured at low cost. Become. Also, the realization of warm drawing in one process not only generates shock lines, but also provides a highly-designed water washing tank with excellent surface properties, as well as high-flatness processing by softening the flanges by heating. Since the product is obtained, it is also effective in preventing water leakage.
According to the method of the present invention, it becomes possible to produce a dishwasher with high precision while maintaining a high precision and high design in the dishwasher water washing tank where high flatness of the flange portion is required. It can contribute to the spread of water washing tanks.

The inventors of the present invention have been studying a method for manufacturing a washing tub with a large size dishwasher as much as possible by adopting a deep drawing technique using a stainless steel plate as a raw material. In such a washing tank, it is not sufficient to simply increase the short side width and deepen the drawing height. In order to obtain a deep-drawn product with a large working space as a washing tank, a narrow installation area for the washing tank and good flatness at the top flange, the punch shoulder radius, die shoulder radius and corner radius should be set. It is preferable to make it small. If these values are reduced, it becomes difficult to manufacture a product with a deeper drawing height.
Using a die with the punch shoulder radius, die shoulder radius, and corner radius as small as possible, deep punch products with small punch shoulder radius, die shoulder radius, corner radius, short side width, long side width, and deep drawing height The present invention has been achieved by earnestly examining the measures obtained in a single drawing process.
Details will be described below.

First, a stainless steel plate having excellent corrosion resistance is employed as the substrate.
The stainless steel plate used is preferably austenite. An austenitic stainless steel sheet has a property that when austenite is strained at room temperature, austenite becomes martensitic transformations more easily as the austenite becomes unstable, so that the austenitic stainless steel plate becomes hardened by transformation hardening together with work hardening. For this reason, if the material of the punch head is cooled to maintain high strength and the material of the flange portion is heated to suppress hardening due to martensitic transformation of austenite, drawing workability is greatly improved.

In addition, the austenitic stainless steel sheet coated with a resin film that does not decrease viscoelasticity and ductility with increasing temperature, described later, is a metal contact between the stainless steel sheet and the mold caused by film melting or film breakage during warm working. Therefore, excellent slipperiness can be maintained.
By the way, in warm working, steel grades with a greater strength difference between the punch and the flange exhibit better workability. For example, if the punch temperature is the same, the higher the flange temperature, the deeper the drawing process is. There is.
In addition, since the austenite is difficult to undergo martensitic transformation by heating the flange part that shrinks and deforms in warm working, hardening of the flange part is greatly suppressed and the deformation resistance of the flange is greatly reduced. This facilitates material inflow into the die and reduces the strain applied to the flange, which has the advantage of obtaining a deep-drawn product having a high flatness flange.

In order to manufacture the washing tank of the present invention, it is preferable to use an austenitic stainless steel plate such as SUS304J2 which is excellent in deep drawability.
For example, even in a dishwasher / dryer made of stainless steel having a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, a short side width of 400 mm, a long side width of 600 mm, a height of 330 mm, and a corner radius of 40 mm, the plate thickness is 0.8 mm, for example. If a SUS304J2 stainless steel with a blank size of 980 × 1100 mm is selected and the resin film of the present invention that does not cause a decrease in viscoelasticity and ductility with the increase in temperature described below is applied, the warm working condition is, for example, a punch temperature of 0 When the press working is performed at a temperature of 140 ° C. to 250 ° C. and a pressing speed of 50 mm / sec, the washing tank having a desired shape can be processed by one-step drawing.

Next, the coating resin that coats the surface of the austenitic stainless steel sheet will be described.
Although it does not specify as a resin film, what was formed from resin which has a structure like polyvinyl alcohol is preferable when the point which viscoelasticity, intensity | strength, and ductility are acquired easily is considered. Resins containing many hydroxyl groups in the molecular structure, such as polyvinyl alcohol, form a network through the progress of hydrogen bonds between OH groups even when the temperature rises to 100 ° C. or higher. Resin film that does not soften or fall off easily even under the influence of heat during warm drawing. As a result of investigating the influence of the OH group on the film strength, when the molecular weight of the OH group in the total molecular weight of the resin is set to 0.02 or more, a resin film imparting excellent warm drawing workability is formed. understood.
As the resin containing a large number of hydroxyl groups in the molecular structure, resins such as urethane and acrylic can be used in addition to polyvinyl alcohol. If the molecular weight of OH groups / total molecular weight is modified to 0.02 or more by modification with an OH group-containing compound such as glycol, resins such as urethane and acrylic can also be used as the resin film of the present invention.

  The ratio of the molecular weight / total molecular weight of the OH group is an important requirement for imparting appropriate heat resistance and adhesion to the resin film. OH group molecular weight / total molecular weight: When the molecular weight is less than 0.02, the number of hydrogen bonds between OH groups is small, and the resin film is easily softened by the heat effect during warm drawing. However, as the number of OH groups increases, the intermolecular distance between the OH groups approaches and hydrogen bonds are likely to occur, and free OH groups contributing to adhesion to the surface of the stainless steel plate decrease, so the molecular weight / total molecular weight of the OH groups. The upper limit is preferably 0.40.

When a lubricant is added to a resin film formed from a resin having a molecular weight / total molecular weight of OH group adjusted to 0.02 or more, warm drawing workability is further improved. Polyethylene resin powder, which is often used as a lubricant, has a melting point in the range of 100 to 130 ° C., although it varies slightly depending on the resin type and molecular weight, and it melts due to the thermal effect during warm drawing and falls off the resin film. It is difficult to demonstrate lubricating ability.
On the other hand, since the fluororesin powder has a high melting point of 300 ° C. or higher, it retains excellent lubricity without melting even under the influence of heat during warm drawing. However, since the fluororesin powder has a large specific gravity, it is inferior in dispersion stability to the resin treatment liquid. Uniform dispersibility in the resin treatment liquid can be achieved by making the fluororesin fine powder, but if it is made too fine, the fluororesin fine powder may concentrate at the interface between the resin film / stainless steel plate and may not contribute to improvement of lubricity.

  Therefore, by using polyethylene-fluororesin powder in which fluororesin fine powder is bonded to the particle surface of polyethylene resin as a lubricant, dispersion stability is ensured and the high lubricity inherent in fluororesin is utilized. By using polyethylene-fluororesin powder, the fluororesin fine powder can be concentrated on the surface layer of the resin film, and excellent warm drawing workability is imparted to the stainless steel plate.

  Resin constituting the film: When the polyethylene-fluororesin powder is added in the range of 1 to 20 parts by mass with respect to 100 parts by mass, the required lubricity is obtained. If the addition amount is less than 1 part by mass, the lubricating action at the time of warm drawing tends to be insufficient. However, excessive addition exceeding 20 parts by mass hinders stable dispersion of the resin powder in the treatment liquid, and processing unevenness is likely to occur during coating, causing the appearance to be impaired.

  The resin treatment liquid is 0.1 to 5.0 masses of defoaming agent such as polyether type, polysiloxane type, acetylene diol type, glycerin fatty acid ester type, etc. for the resin treatment liquid: 100 parts by mass. Part, water dispersible silica sol for improving the heat resistance of the film: 1.0 to 20 parts by mass with respect to 100 parts by mass, amino type, ureido type, vinyl type for improving the adhesion between the film and the steel plate, Silane coupling agents such as methacrylic, epoxy-based, mercapto-based, and isocyanate-based can be included at a ratio of 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the resin.

A resin film suitable for warm drawing is formed on the surface of the stainless steel plate by applying a resin treatment liquid to the degreased and cleaned stainless steel plate, followed by heating and drying. The applied treatment liquid becomes a resin film even when it is naturally dried, but when heated, film formation is completed in a short time. However, high temperature drying exceeding 200 ° C. facilitates thermal decomposition and tends to impair the function of the resin film.
Further, when the surface of the stainless steel plate is hydrophilized by washing with a mixed acid aqueous solution containing phosphoric acid and / or a phosphoric acid compound and nitric acid, the adhesion of the resin film to the stainless steel plate is further improved. An aqueous solution of hydrochloric acid, sodium hydroxide, potassium hydroxide or the like can also be used as the hydrophilic treatment liquid.

  In order to function as a protective film completely coated with a stainless steel plate, it is preferable to apply the resin treatment liquid in a coating amount necessary for forming a resin film having a film thickness of 0.3 μm or more. If the film thickness is less than 0.3 μm, the surface of the stainless steel plate cannot be uniformly coated, and local wrinkles may occur at the location where the hot drawing is performed. However, if the film thickness is too thick, the quality improvement effect associated with increasing the film thickness is saturated and disadvantageous economically, so the upper limit of the film thickness is preferably 100 μm.

An embodiment in which warm deep drawing is performed using an austenitic stainless steel sheet having a resin film formed on the surface as a blank will be described.
As described above, an austenitic stainless steel sheet has a property that when austenite is strained at room temperature, the more austenite is more stable, the more austenite is martensite transformed, and thus it is hardened by transformation hardening together with work hardening. For this reason, it is preferable that the punch head material is cooled to maintain high strength, and the flange material is heated to suppress hardening due to martensitic transformation of austenite and to improve drawing workability.
Therefore, a means for deep drawing in a warm region using a mold in which a die is heated and a punch is cooled to a room temperature or less was adopted.

In the warm working, since the flange portion that shrinks and deforms is heated, the transformation of austenite to martensite is suppressed, so that the hardening of the flange portion is greatly suppressed and the deformation resistance of the flange is greatly reduced. Reduced deformation resistance facilitates material flow into the die and enables deeper deep drawing deformation and reduces strain applied to the flange, resulting in a deep drawn product having a high flatness flange. It will be.
The die heating temperature and die holding temperature when performing the warm deep drawing are based on experimental examples. Details will be given in the examples, but the short side width 400 mm × long side width 600 mm is made of an austenitic stainless steel plate provided with a resin film in which the ratio of the molecular weight of OH groups to the total molecular weight of the resin is 0.02 or more. × When trying to obtain a deep-drawn product with a drawing height of 330 mm, if drawing is performed with the die temperature adjusted to 140-250 ° C and the punch temperature adjusted to 20 ° C or less, the normal punch indentation A desired product can be obtained without causing cracks or deformation of the flange portion by pressing at a speed of 50 mm / sec.

If the die temperature is less than 140 ° C., the martensitic transformation generated in the flange portion cannot be sufficiently suppressed. On the contrary, when the die temperature exceeds 250 ° C., the film strength is remarkably lowered, so that linear marks and galling are likely to occur. When the punch temperature exceeds 20 ° C., it is difficult to sufficiently obtain an increase in the breaking strength of the punch portion due to martensitic transformation.
The heating of the die is preferably performed with an electric heater arranged around the die. The cooling of the punch is preferably performed by circulating cooling water inside the punch.

In order to increase the effective volume of the washing tank, it is preferable to reduce the punch shoulder radius, die shoulder radius, and corner of the die as much as possible. When actually manufacturing a washing tub to be incorporated in a dishwasher, it is preferable that the punch shoulder radius of the mold is 30 mm, the die shoulder radius is 10 mm, and the corner radius is 40 mm.
Further, when the long side width of the washing tank to be manufactured is Wl, the short side width is Ws, the corner radius is Rc, and the drawing height is H, H / Ws ≧ 0.8, Rc / Ws ≦ 0.1. For example, even in a washing tank having a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, a short side width of 400 mm, a long side width of 600 mm, a height of 330 mm, and a corner radius of 40 mm, the plate thickness is 0.8 mm and the blank size is 980 × It becomes possible to manufacture from a 1100 mm SUS304J2 stainless steel plate.

A 2D finished material of SUS304J2 stainless steel plate having a thickness of 0.8 mm and a size of 980 × 1100 mm was immersed in an alkaline degreasing solution having a pH of 12.5 and a liquid temperature of 60 ° C. for 5 seconds, and was used for a degreased and water-washed original plate. Moreover, as shown in Table 1, resin treatment liquids mainly composed of polyvinyl alcohol (PVA), urethane or acrylic having different OH group contents were prepared. As shown in Table 1, a resin to which various resin powders were added as a lubricant was also prepared.
The stainless steel plate after the degreasing and washing was coated with the resin treatment solution shown in Table 1 and inserted into an oven, and heated and dried at an ultimate plate temperature of 140 ° C. to form a resin film having a thickness of 2 μm. The OH group ratio in the resin is determined by analyzing the resin molecular weight of the resin film provided on the surface of the stainless steel plate by the GPC method, and analyzing the OH group amount in the resin by the terminal group quantification method. The ratio of molecular weight is calculated.

The stainless steel plate blank on which the resin film was formed was drawn at a processing speed of 50 mm / sec using a mold in which the temperature of the punch and die was variously changed. The size of the processed product was a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, a short side width of 400 mm, a long side width of 600 mm, a height of 330 mm, a corner radius of 40 mm, and was pressed in one step with a cushion pressure of 1600 kN. The obtained drawn product was visually observed, and “X” indicates that cracks, linear traces and shoulder galling were observed, and “◯” indicates that these were not observed. In particular, those having excellent surface properties were marked with ◎. The case where slight linear marks and shoulder galling were observed was evaluated as Δ. In addition, about the thing which crack generation | occurrence | production generate | occur | produced, the linear trace and the shoulder galling were not confirmed.
The results are shown in Table 2.

As can be seen from the results shown in Tables 2 to 4, an austenitic stainless steel plate coated with a resin having an OH group content ratio of 0.02 or more is used as a raw material, and the die temperature is set to 140 to 250 ° C. and the punch temperature. When a deep drawing process using a mold whose temperature is adjusted to 20 ° C. or less is performed, a desired deep drawing product free from linear traces and shoulder galling is obtained by a single press process. When a lubricant is added to the film resin, a deep-drawn molded product having excellent appearance characteristics is obtained.
On the other hand, when the OH group ratio of the resin is less than 0.02, hydrogen bonds effective for improving the adhesion cannot be expected, and the resin film is easily softened due to the heat effect during warm drawing. As a result, drawing workability is deteriorated. Even if the OH group ratio of the resin is 0.02 or more, if the die temperature is lower than 140 ° C., the hardening due to martensitic transformation of the flange portion cannot be sufficiently suppressed, and cracking occurs. As a result, the drawing process could not be performed.
When a large amount of lubricant was added so as to exceed 20 parts by mass, a molded product free from cracks, linear traces or shoulder galling was obtained, and there was no problem with moldability. The appearance was slightly impaired.

Plan view showing an example of the shape of a washing tub for a dishwasher Front sectional view showing an example of the shape of a washing tank for a dishwasher

Explanation of symbols

Wl: Flush tank long side width Ws: Flush tank short side width H: Flush tank squeeze height
Rc: Corner radius of washing tank

Claims (4)

  A resin film formed from one or more selected from polyvinyl alcohol resin, urethane resin and acrylic resin, wherein the ratio of the molecular weight of OH groups to the total molecular weight of the resin is 0.02 or more Using austenitic stainless steel sheet with a coating directly on the surface as a raw material, and subjecting the raw material to a deep drawing process using a die with a die temperature adjusted to 140 to 250 ° C. and a punch temperature adjusted to 20 ° C. or lower. A method for producing a stainless steel dishwasher water washing tank.   2. The stainless steel according to claim 1, wherein the polyethylene-fluorine resin powder obtained by bonding the fluororesin fine powder to the polyethylene resin particle surface is added to the resin film at a ratio of 1 to 20 parts by mass with respect to 100 parts by mass of the resin. Steel dishwasher water washing tank manufacturing method.   The method for producing a stainless steel dishwasher / water washing tank according to claim 1 or 2, wherein a mold having a punch shoulder radius of 30 mm, a die shoulder radius of 10 mm, and a corner radius of 40 mm is used.   4. The stainless steel according to claim 3, wherein H / Ws ≧ 0.8 and Rc / Ws ≦ 0.1, where Ws is the short side width of the washing tank to be manufactured, Rc is the corner radius, and H is the drawing height. Dishwasher / Dryer water washing tank manufacturing method.

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