JP2007333186A - Screw fastener and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw ensuring high corrosion resistance while using a material not containing hexavalent chromium. <P>SOLUTION: A surface treated layer 12 is formed on a basis material 11. The surface treated layer 12 comprises three layers which are an iron-zinc alloy layer 13, a metallic base coat layer 14 and a silicon-based top coat layer 15 in this order from the basis material 11. The base coat layer 14 is a water or glycol solution containing micro flake-like zinc, aluminum and a silicon-based inorganic binder as main components. The iron-zinc alloy layer 13 and the base coat layer 14 are metal-based to attain integration, and the top coat layer 15 is inorganic to ensure markedly high corrosion resistance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a screw-type fastener and a manufacturing method thereof. Here, the screw type fastener refers to a fastener having a male screw or a female screw, and examples thereof include screws, bolts, and nuts. Furthermore, for screws, a milled screw with a sharpened tip and self-drilling capability, a drill screw with a tip made of a drill with a cutting edge, a tapping screw with a self-tapping function for metal materials, a tip There are various forms such as a small screw formed flat. The present invention is particularly suitable for a self-drilling screw (screw) of a chopping type or a drill type. Needless to say, a tapping screw is also available in a chopping type (see JIS B1115).

  As a method of improving the corrosion resistance (rust prevention performance) of screws, it is roughly divided into using a material that does not rust and applying rust prevention treatment (surface treatment). The latter surface treatment includes plating. It is done. However, sufficient corrosion resistance may not be ensured by plating alone. For example, it is a case where it is exposed to the outside air, such as when a building exterior material is fastened.

As a method for improving the corrosion resistance, Patent Document 1 discloses a surface treatment method for a steel drill screw, in which zinc, tin, or solder is plated on a base (iron) and then heated to heat the plated metal and iron. It is described that an alloy layer is formed and a surface film for rust prevention is further formed on the surface of the alloy layer. And as an example of the processing agent that forms the surface film, Patent Document 1 mentions “Dacrozide” sold by Dacro Shamrock Co., Ltd.
Japanese Patent No. 2776484

  Now, environmental pollution caused by metals has become a global problem, and in particular, chromium (especially hexavalent chromium) that has been used extensively in plating and surface treatment has been pointed out, and basically it will be completely abolished. It can be said that it is moving.

  On the other hand, “dacrozide” is a kind of paint in which aluminum and zinc flake-like fine powder and chromic binder are dissolved in a solvent as a main component. For example, this is applied to the surface of a screw and then heated. By baking, for example, a rust preventive film is formed on the surface of the screw. “Dacrozide” is an excellent product from the viewpoint of rust prevention alone, but it has been pointed out that it may cause environmental pollution because it contains chromium.

  This invention is made | formed in view of such the present condition, and makes it a subject to provide the safe screw type fastener which does not have a possibility of polluting an environment, ensuring high corrosion resistance.

  As described above, as a means for obtaining a screw-type fastener excellent in corrosion resistance, there is a method of using a material that does not rust (such as stainless steel) that does not rust, such as stainless steel, but this has a problem that the material cost increases. In addition, there are cases where high hardness is required for the screws, and therefore, it may be required to be hardened as a condition of the material, but also in stainless steel, martensitic stainless steel that can be hardened is inferior in corrosion resistance, There is also a dilemma that austenitic stainless steel with excellent corrosion resistance cannot be quenched.

  Accordingly, there is a demand for a surface treatment technique that uses a steel material that is inexpensive, excellent in workability, and can be hardened, such as carbon steel, to maintain high corrosion resistance. The present invention meets this need.

  The present invention includes a screw-type fastener and a manufacturing method thereof. As described in claim 1, the screw-type fastener has a surface treatment layer formed on the entire surface or a part of the surface. In order from the base, apply an iron-zinc alloy layer, aluminum or zinc or both fine powder as the main metal component, a non-chromium base coat layer that is baked through an inorganic binder, and a silicon-based water-soluble coating liquid. And a top coat layer formed by drying or baking. The metal fine powder is preferably flakes (scale-like).

  The invention of the manufacturing method is a process of manufacturing an intermediate product formed into a fastener shape by applying machining to a steel material, as described in claim 2, and heating the intermediate product after galvanizing the intermediate product. A step of forming an iron-zinc alloy layer on a substrate, and a metal base coat layer by baking a non-chromium base coat solution mainly composed of metal fine powder and an inorganic binder on the intermediate product on which the iron-zinc alloy layer is formed. And a step of forming a topcoat layer by applying a silicon-based topcoat solution to the intermediate product on which the basecoat layer has been formed, followed by drying or baking, and the basecoat solution. As a main metal component, zinc fine powder or aluminum fine powder or both are used.

  As described in claim 3, the present invention includes a shaft on which a thread is formed and a head portion provided at a base end portion thereof, and sharpens a tip portion of the shaft or forms a drill portion. Therefore, it is preferable to use the screw having the self-drilling function. Examples of the material used in the present invention include carbon steel, chrome molybdenum steel, chrome steel, molybdenum steel, and the like, and may be selected according to required characteristics.

  The surface treatment layer of the screw type fastener according to the present invention is composed of three layers of an alloy layer, a base coat layer, and a top coat layer, and has high corrosion resistance, and chromium is used for both the base coat layer and the top coat layer. Because there is no problem of environmental pollution. Furthermore, since it is made of a steel material such as carbon steel, it is excellent in terms of cost and excellent in workability and quenching characteristics (it can also be applied to a non-quenched fastener).

  Therefore, the present invention is particularly suitable for fasteners that are used in an environment where they are exposed to the outside air or are humid, such as screws or bolts that fasten building exterior materials.

  Next, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the example of the form of the screw | screw (screw) to which this invention was applied, and the usage example are shown. The screws shown in (A) and (B) are chopped self-drilling screws, which are provided with a shaft 1 and a head 2 provided at the base end thereof, and the tip portion of the shaft 1 is the tip. The shaft 1 is formed with a single thread 3 that starts (rises) from the tapered portion 1a.

  The head 2 has a substantially trapezoidal shape, and as shown in (D), a cross hole 4 as an example of an engaging portion into which a driver bit is fitted is formed on the top surface. A large number of cutting edges 5 generally called flex are formed so as to extend radially. Needless to say, the number and pitch of the threads 3, the angle of the threads, the shape of the head 2, and the like can be freely set according to the application.

  As an example of use of the present embodiment, the screw is used to fasten the ceramic-based outer wall material (siding) 6 to the plywood inner wall plate 7. In the example shown in (B), the inner wall plate 7 overlaps the vertical frame 8 made of a thin steel plate having a substantially U-shaped cross section, and the screw is also screwed into the vertical frame 8. A counterbore 9 is formed in the outer wall material 6. When the vertical frame 8 is thin, for example, 0.8 mm or less, it is possible to enter the threaded screw as it is, but when using the threaded screw even in a thicker state, the vertical frame 8 (and It is advisable to make a pilot hole in the inner wall plate 7) in advance.

  The screw shown in (C) is a drill screw in which a drill portion 10 is formed integrally with the shaft 1. The drill portion 10 includes a pair of cutting edges 10 a and vertical grooves 10 b, and the length L of the drill portion 10 is larger than the total thickness T of the inner wall material 7 and the vertical frame 8. When the vertical frame 8 is thick and the pilot hole is not formed, if the drilling into the vertical frame 8 and the screwing into the inner wall material 7 are performed simultaneously, the vertical frame 8 floats between the inner wall material 7 and the vertical frame 8. If this occurs, it may be configured as shown in (C).

  (E) schematically shows a cross section of the screw. As shown in this figure, the screw has a cross-sectional structure in which a surface treatment layer (rust prevention treatment layer) 12 is provided on a substrate 11, and the surface treatment layer 12 is composed of an iron-zinc alloy layer 13 and a base coat layer in order from the substrate 11. 14 and the top coat layer 15. The base coat layer 14 is a layer (film) in which a group of flaky aluminum and zinc is baked with an inorganic binder, and therefore does not contain chromium (hexavalent chromium). The top coat layer 15 is made of a silicon salt-based film (paint film).

  Although there is no limitation on the thickness of each layer, it can be said that the iron-zinc alloy layer 13 is about 5 μm, the base coat layer 14 is about 8 μm, and the top coat layer 15 is about 1 to 3 μm because of the relationship between cost and effect. . Next, details of the surface treatment layer 12 including the manufacturing method will be described.

(2). Manufacturing method of screw FIG. 2 shows an example of a manufacturing process of a chopped screw. In this manufacturing method, a wire material (for example, a SWCH-based carbon steel wire for cold heading) is prepared, a head 2 is first formed with a header, and then a thread 3 is formed by rolling using a die. The tapered portion 1a is formed, thereby producing an intermediate product in which the form as a screw is completed (note that the cutting of the wire is performed simultaneously with the processing of the head 2).

  Next, the intermediate product is quenched, galvanized, and then tempered to adjust the hardness and form the iron-zinc alloy layer 13, and then the base coat solution is applied and then baked to form the base coat layer 14 is formed, and then the top coat liquid 15 is applied and then dried or baked to form the top coat layer 15. This completes a surface-treated screw having a high rust prevention function.

  When the screw is a drill screw, the drill part 10 is processed by forging or cutting before the thread 3 is processed. If there is a quenching / tempering step, it is possible to form the iron-zinc alloy layer 13 by galvanizing and further heating to temper, but the iron-zinc alloy layer 13 can be formed by tempering as shown in FIG. -Forming the zinc alloy layer 13 has an advantage that the process can be simplified.

  As a quenching method, a method of curing to the core like oil quenching can be adopted, or a method of curing only the surface portion like carburizing quenching can be adopted. Which method should be adopted may be determined in consideration of mechanical properties required for the screw such as hardness and brittleness. Tempering is performed, for example, by heating at 300 to 350 ° C. for about 60 minutes and then air cooling.

  As the galvanizing method, either an electroplating method or an immersion method can be used. Zinc oxide is formed in the step of galvanizing and tempering, but this may be removed by shot blasting or the like.

  As the base coat solution, for example, one sold by Nippon Dacrosham Rock under the trade name “Geomet” can be used. This is a product in which aluminum and zinc flakes (fine powder) and a silicon-based inorganic binder (for example, silane) are used as main components and diluted with water or alcohol. After cutting, heat in a furnace and bake. Thereby, a base coat layer 14 made of a metal film mainly composed of aluminum and zinc is formed.

  The baking temperature is, for example, 200 to 230 ° C., and the time is 10 to 40 minutes, but is not limited thereto. Note that the base coat solution may contain a metal other than aluminum or zinc.

  As the topcoat liquid, an aqueous solution of a silicon-based material is used. Examples of silicon-based materials include colloidal silica and silicon salt-based materials. Further, the silicon salt material can be either inorganic or organic. Examples of the inorganic silicon salt material include sodium silicate, and examples of the organic silicate material include alkyl silicate such as ethyl silicate and alkoxy silicate such as ethylene glycol monoethyl silicate.

  After applying the top coat solution, the hard top coat layer 15 made of a silica component is formed by drying or baking at 60 to 170 ° C., for example. Examples of the drying method include a method of exposing to warm air or hot air using a tunnel furnace or the like. The drying or baking time may be about 10 to 20 minutes.

(3). Evaluation With respect to a milled screw having a nominal diameter of 4 mm and a length of 40 mm, the product of the present invention (“Geomet” was used to make the base coat layer 8 μm thick, and the silicate top coat layer. And a comparative product obtained by subjecting the iron-zinc alloy layer to surface treatment with the above-mentioned “dacrozide”, both were subjected to a salt spray test based on JIS-Z-2371. Then, it was confirmed that the product of the present invention has a corrosion resistance equivalent to or higher than that of the comparative product.

  Further, when the milled screw was used in the state shown in FIGS. 1A and 1B, a phenomenon such as an increase in screwing resistance or peeling of the surface treatment layer accompanying the screwing was not observed.

  In addition, when zinc is contained in the base coat layer 14, the integrity of the base coat layer 14 and the iron-zinc alloy layer 13 is strengthened, and it is presumed that the peel resistance and the corrosion resistance are excellent.

(A)-(D) is a figure which shows an example of the form of the screw to which this invention is applied, and an example of use, (E) is a figure which shows a part of cross section typically. It is a figure which shows an example of a manufacturing process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 axis | shaft 1a Constriction part 2 Head 3 Screw thread 6 Exterior material as an example of a workpiece 7 Plywood inner wall board as an example of a base material 8 Vertical frame made of a thin steel plate as an example of a base material 10 Drill part 11 Thread Base 12 Surface treatment layer 13 Iron-zinc alloy layer 14 Base coat layer 15 Top coat layer

Claims (3)

It is a steel screw fastener that forms a surface treatment layer on the whole or a part of the surface,
The surface treatment layer is, in order from the base, an iron-zinc alloy layer, aluminum or zinc or a fine powder of both, a non-chromium base coat layer that is baked through an inorganic binder, a silicon-based water-soluble layer It consists of a top coat layer that is formed by applying a coating liquid and then drying or baking.
Screw fastener. The process of manufacturing intermediate products in the shape of fasteners by applying machining to steel materials,
Forming an iron-zinc alloy layer on the substrate by heating the intermediate product after galvanizing,
A step of forming a metal base coat layer by baking a non-chromium base coat liquid mainly composed of metal fine powder and an inorganic binder on the intermediate product in which the iron-zinc alloy layer is formed;
A step of forming a topcoat layer by applying a silicon-based topcoat liquid to the intermediate product on which the basecoat layer has been formed, followed by drying or baking;
Each of the above steps, and as the base coat liquid, zinc fine powder or aluminum fine powder or those containing both as main metal components are used,
A method for manufacturing a screw-type fastener. The screw type fastener includes a shaft on which a screw thread is formed and a head portion provided at a base end portion thereof, and a self-drilling function is maintained by sharpening a tip portion of the shaft or forming a drill portion. Being crushed,
The manufacturing method of the screw type fastener described in Claim 1 or the screw type fastener described in Claim 2.

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