JP4334963B2 - Surface treated steel pipe for hydrofoam with excellent electrodeposition paintability - Google Patents

Description

The present invention relates to a surface-treated steel pipe for hydrofoam that is excellent in electrodeposition coating properties for use in hydroforming .

  In hydroforming, a steel pipe is inserted between the upper mold and the lower mold, and a solution or emulsion processing fluid is filled inside the steel pipe, and then high pressure is applied to the processing fluid to create a complex shape. This is a molding method in which a steel pipe is pushed into a mold. Therefore, it is possible to integrally mold complex shaped parts, so there are advantages in the manufacturing process such as reducing the number of molds and abolishing welding, and at the same time, since there are no welds, it is possible to increase the rigidity and weight of the parts. It is a molding method.

  As described above, hydroforming is a processing method having an excellent feature capable of manufacturing integral molding of complex-shaped parts, but lubrication becomes more difficult as the shape becomes more complicated. In other words, the internal pressure of several hundred to several hundreds of atmospheres applied to the machining fluid acts on the steel pipe, and when the material flows into the mold hole, friction occurs between the die hole and the material, and the material is processed continuously. And scratches on the mold. Repair of a die having scratches not only reduces the production efficiency but also increases the maintenance cost of the die. If the friction is too strong, the material will not easily flow into the die hole, and a crack or break will occur at the top of the raised portion, resulting in failure to obtain a predetermined shape.

  For this reason, liquid lubricants such as press oil are used when lubrication is not so severe, while waxes, resins, metal soaps and paint paints that exhibit even higher lubricity than oil are used in severe lubrication. A solid lubricating film such as is applied. However, a solid lubricant film is not necessarily an optimal lubricant when considering welding and painting, which are post-treatments of hydroformed parts.

  Taking an automobile part as an example, a hydroformed part is electrodeposition-coated, but a phosphate treatment which is a kind of chemical conversion treatment is performed as a pre-coating treatment. At the time of this phosphate treatment, it is necessary to remove rust preventive oil and press oil adhering to the surface of the part by degreasing and cleaning. However, the resin, wax, and the like, which are the above-described solid lubricant film, are very difficult to degrease and clean after processing as compared with liquid lubricating oil, which adversely affects the coating performance. Therefore, a lubricant that has excellent coating performance and can withstand severe processing is desired.

Patent Document 1 states that “at least the outer surface of the steel pipe is provided with a film made of an inorganic substance having an adhesion amount of 0.1 to 10 g / m ² ” as different from the above lubricating oil, resin, or wax. "Surface-treated steel pipe for hydraulic bulge processing". Examples of the film made of an inorganic substance include films made of various metal oxides and metal salts, oxide scales, and the like, and reactive type and coating type various chemical conversion treatment films having particularly good adhesion are preferred. Specific examples thereof include a chemical conversion treatment film such as a chromate, phosphate, oxalate, borate, and zirconia salt. If it is a steel pipe provided with the chemical conversion treatment film, it can be performed continuously from cutting of the steel pipe to hydraulic bulge forming. In addition, after processing, it can be used as a product as it is, or it can be used after further necessary coating.

However, according to the research by the inventors, in the case of severe hydroforming, it cannot be said that all the chemical conversion coatings in Patent Document 1 described above satisfy the lubricity, and are performed after hydroforming. When electrodeposition coating is considered, it cannot be said that all the chemical conversion coatings described above can be a coating base coating. Therefore, a lubricant that satisfies both the lubricity in hydroforming and the paintability that is the subsequent process is desired. Especially when applied to automobile parts, the paintability is very important.
Japanese Patent Laid-Open No. 10-137865

In view of the above problems, the present invention provides a surface-treated steel pipe for hydrofoam that prevents seizure in hydrofoaming and reduces friction, and at the same time has no problem with electrodeposition coating properties after machining.

  The present invention solves the above-mentioned problems, and the gist thereof is as follows.

(1) The outer surface of the pickled steel pipe is provided with a zinc phosphate film having a P ratio (P / P + H) of 0.3 or more and less than 0.6, and a lubricating oil having antirust performance is applied thereon. This is a surface-treated steel pipe for hydrofoam with excellent electrodeposition coating characteristics.

(2) The crystal grain size of the zinc phosphate coating is 5 to ²⁰ μm, and the coating adhesion is in the range of ² g / m ² or more and 5 g / m ² or less. Surface treated steel pipe for hydrofoam with excellent electrodeposition paintability.

(3) The electrodeposition paintability according to (1) or (2), wherein the lubricating oil has a viscosity of 40 ° C. and is a rust-preventing lubricating oil of 10 mm ² / sec or more and less than 30 mm ² / sec. Excellent surface treated steel pipe for hydroforming.

  Here, P: Phosphophyllite and H: Hopite.

The surface-treated steel pipe for hydrofoam of the present invention can satisfy both the lubricity and electrodeposition coating properties at the same time. Therefore, the present invention is effective for increasing the number of processing steps and reducing workability due to insufficient lubricity or poor electrodeposition coating properties, which are conventional problems.

  The surface-treated steel pipe for hydroform of the present invention will be described in detail below.

The reason why the P ratio (P / P + H) in the present invention is specified to be 0.3 or more and less than 0.6 is that if it is less than 0.3, the cationic electrodeposition coating property is poor, and if it is 0.6 or more, the lubricity is poor. It is. P ratio refers to the (110) plane of phosphophyllite (iron zinc phosphate (Zn ₂ Fe (PO ₄ ) ₂ .4H ₂ O)) and hopite (zinc phosphate (Zn ₃ (PO ₄ ) The peak intensity of the (020) plane of ₂ · 4H ₂ O)) is P and H, respectively, and represents the peak intensity ratio of P / P + H.

  Moreover, as a method of forming a zinc phosphate film having a P ratio in this range on the outer surface of the steel pipe, surface adjustment is performed before the zinc phosphate treatment, and the condition of the zinc phosphate treatment solution is adjusted. They are achieved, for example, by bringing the zinc concentration in the chemical conversion liquid within the range of 2 g / L to 4 g / L.

  However, since only the zinc phosphate coating has a too high friction coefficient during hydroforming, it is essential to use a lubricant that lowers the friction coefficient. Furthermore, rust prevention before and after hydroforming is also necessary. Therefore, it is necessary to form a lubricating oil having antirust performance (hereinafter referred to as an antirust lubricating oil) on the phosphate coating. As a rust preventive lubricating oil, 50 kinds in total of one or two kinds of rust preventive additives such as barium sulfonate and calcium are added to one or more kinds such as mineral oil, natural fat and oil, and synthetic ester. It is preferable to use oil added in an amount of not more than mass%. Furthermore, for the purpose of improving lubricity, one or more of extreme pressure additives such as phosphorus-based and sulfur-based and oiliness improvers such as oleic acid and dimer acid can be applied as needed. You may add 50 mass% or less.

  In general, the larger the crystal grain of the phosphate film, the greater the amount of lubricating oil on it and the better the lubricity. Therefore, the crystal grain is preferably 5 μm or more. On the contrary, the adhesion of the paint is better as the crystal grains are smaller. One of the evaluation methods of coating film adhesion (paintability) is a gobang test (marking 100 squares of 1 mm square with a cutter blade and checking the remaining degree of the coating film after peeling the tape) However, in the phosphate film having crystal grains exceeding 20 μm, large crystals are likely to be partially broken by the scribing of the cutter blade. Therefore, the crystal size satisfying both the lubricity and the coating film adhesion is suitably 5 to 20 μm. The size of the crystal grains can be controlled by adjusting the surface, adjusting the phosphate treatment liquid composition, and adjusting the liquid supply (soaking or spraying).

Why the film deposition amount specified in 2 g / ^{m 2} or more 5 g / ^{m 2} or less, is less than 2 g / ^{m 2,} at the time of hydroforming, abrasion tends to occur, and when it exceeds 5 g / ^{m 2,} coating adhesion It is because it is inferior. As in the case of controlling the size of the crystal grains, the coating amount can be controlled by adjusting the surface, adjusting the phosphate treatment liquid composition, and adjusting the liquid supply (immersion or spraying).

As the rust preventive lubricating oil in the present invention, a commercially available rust preventive lubricating oil having a viscosity at 40 ° C. in a viscosity range of 10 mm ² / second or more and less than 30 mm ² / second may be used. The reason for defining the viscosity range is that the rust preventive oil having a viscosity at 40 ° C. of less than 10 mm ² / sec is inferior in lubricity, and if it is 30 mm ² / sec or more, it takes too much time for degreasing before chemical conversion treatment. .

  Examples of the present invention will be given together with comparative examples, and the effects will be described more specifically.

  A sequence of evaluation tests is shown in Table 1 in the order of processing.

  Table 2 shows the method of coating performance evaluation from phosphate film treatment.

  Table 3 shows the conditions of surface adjustment and chemical conversion treatment, and the characteristics of the formed zinc phosphate coating.

  Next, anti-rust lubricating oil PI-LUB500 (manufactured by Parker Kosan Co., Ltd.) was applied to steel pipes on which various zinc phosphate coatings shown in Table 3 were formed, and subjected to a hydroform test. The hydroform test method is shown in Table 4.

  Next, the steel pipe hydroformed according to the conditions shown in Table 4 was subjected to a phosphate coating treatment and electrodeposition coating as a coating base. Table 5 shows the processing conditions.

  Table 6 shows the commercial oil used in the test and the evaluation criteria of the test, and Table 7 shows the evaluation test results of the examples and comparative examples.

  In Examples 1 to 4, the size of crystal grains and the amount of coating film are controlled by the type and amount of the surface conditioner, and a zinc phosphate coating having a P ratio of 0.4 is formed. It is a steel pipe coated with anti-rust lubricating oil PI-LUBE500. The lubricity was significantly better than that of Comparative Example 5 in which PI-LUBE500 was simply applied, and the performance was similar to that of Comparative Example 6 coated with a Teflon (registered trademark) film. On the other hand, although the coating film adhesion tends to decrease with the increase of the crystal grains and the coating weight, it is not in a state in which peeling from the goby cut line is severe as in Comparative Example 6, and the coating film adhesion is not particularly problematic. It is.

  Comparative Examples 1 and 2 are steel pipes on which a zinc phosphate film having a P ratio of 0.2 was formed and PI-LUBE500 was applied. Although the lubricity is good, it is not as good as Teflon (registered trademark) -coated Comparative Example 6, but the coating film adhesion is poor. On the other hand, in Comparative Examples 3 and 4 in which a zinc phosphate film having a P ratio of 0.9 was formed and PI-LUBE500 was applied, contrary to Comparative Examples 1 and 2, coating film adhesion was good, but lubricity Is inferior.

Examples 5 and 6 are steel pipes in which two types of commercially available rust preventive oils having a viscosity of 5 mm ² / second and 50 mm ² / second are applied onto a steel pipe No 2 on which a zinc phosphate film having a P ratio of 0.4 is formed. is there. When oil with a low viscosity is used, lubricity is slightly inferior, and when it is a high viscosity oil, coating film adhesion is slightly inferior. However, Examples 5 and 6 can be sufficiently used in terms of lubricity and coating film adhesion.

Claims (3)

Lubricating oil that has a zinc phosphate coating with a P ratio (phosphophyllite / phosphophyllite + popite) of 0.3 or more and less than 0.6 on the outer surface of the pickled steel pipe, and also has anti-corrosion performance A surface-treated steel pipe for hydrofoam with excellent electrodeposition paintability, characterized by being coated with A grain size of 5~20μm zinc phosphate coating, and film coating weight, electrodeposition coating according to claim 1, characterized in that in 2 g / m ² or more 5 g / m ² or less of the range Surface treated steel pipe for hydrofoam with excellent properties The viscosity of the lubricating oil, 40 ° C. hydroformed surface treatment steel pipe excellent in electrodeposition coating of claim 1, wherein less than 10 mm 2 ^/ sec or more 30 mm 2 ^/ s at.