TW201435142A - Process to produce a self-driving screw - Google Patents

Abstract

The invention relates to a method for producing a self-tapping screw, in which a blank consisting of a steel that can be hardened in a martensitic manner is provided. A screw form having a screw shank and a screw thread arranged on the screw shank is manufactured from the blank, and the screw form is then hardened in a nitrogen-containing gas atmosphere at a temperature greater than 900 DEG C. The invention further relates to a self-tapping screw.

Description

Method of manufacturing self-tapping screws

The present invention relates to a method of making a self-tapping screw, particularly for hard mineral substrates (especially concrete), and to such self-tapping screws.

Screws made of Worthian steel or fat steel or multi-phase steel are certainly more resistant to corrosion, but often the hardness is extremely resistant to wear and is not sufficient for hard and scratch-resistant substrates (such as concrete). Drill and/or cut threads yourself. For example, it is mentioned in EP 2 204 244 A1 to additionally provide an additional hard metal cutting edge in the thread which ensures the required cutting durability even in a hard substrate.

Certain types of granitic steel can achieve or require the hardness required for cutting concrete, but generally wear-resistant and corrosive, so for example, in WO 88/05991 A2, it is mentioned that different materials are combined into the same screw. The base shaft and the head are sufficiently resistant to abrasion, and on the other hand, there is sufficient cutting durability at the drill tip, but such a plurality of screws are required to be complicated and expensive to engage, and they also have an adverse effect on the product value in specific cases. .

EP 0 652 300 A1 teaches a heat treatment process to form a granulated iron-type edge layer which contains melted nitrogen in the near-end mold part, consisting of stainless steel, in a nitrogen-containing atmosphere between 1000 and 1200 ° C. The temperature is increased by nitrogen, and then cooled, and the cooling rate must be such as to prevent nitride precipitation.

The object of the present invention is to provide a method for manufacturing a self-tapping screw and a self-tapping screw, which is low in manufacturing cost and simple in manufacturing, and has excellent wear resistance and high reliability, and particularly ensures application properties and load. Remove the nature.

According to the present invention, this object is achieved by a manufacturing method having the features of the first application of the patent application, a manufacturing method having the features of the first application of the patent application, and a screw having the features of claim 11 of the patent application. The embodiments are shown in the dependent claims.

A method of manufacturing a self-tapping screw according to the present invention, wherein the step (1) provides a blank made of steel which can be hardened by means of a ram field, and the step (2) is a blank process screw type having a The dry shaft of the screw and the dry shaft of the screw are provided with cutting threads; in step (3), the screw is then hardened in a nitrogen-containing atmosphere at a temperature greater than 900 °C. In particular, it is greater than 1000 ° C, especially between 1000 ° C and 1200 ° C.

The basic idea of the invention is that when manufacturing a self-tapping screw, the steel hardened by the granulated iron method is hardened under a nitrogen atmosphere in a thermochemical procedure, which adds nitrogen to the edge region, thus The material has a higher hardness. In this respect, the self-tapping screws of the method of the present invention have two advantages: - compared to low temperature hardening (the resulting edge layer is thin), the high temperature method of the invention can be used to cause the edge layer thickness to be in the range of several hundred micrometers without Special additional costs. The resulting layer thickness can be measured in the cross-sectional dimension of a typical "cutting thread", thus resulting in a sufficient supply wear volume (typically > 0.2 mm). Therefore, when screwing in, the "cutting thread" can be avoided by knowing the deformation, so the application property is particularly good. The reason for the larger layer thickness is: this hair The temperature of the whole layer, on the surface of the whole layer, the molecular nitrogen is decomposed into monoatomic nitrogen, and it is preferably diffused into the steel by the process of rapid diffusion at high temperature; - the wear resistance of the basic material can be improved by the high temperature program of the invention This makes it possible to use a basic material which is generally wear-resistant and corrosion-resistant but harder, whereby the cutting property can be further improved. The reason why greater corrosion resistance can be achieved is that nitrogen is not in the form of a nitride but is dissolved in the iron lattice.

In particular, the present invention makes it possible to manufacture a self-tapping screw that is particularly resistant to corrosion and has a durable cutting capability for use in hard and/or scratch-resistant substrates. Here, the corrosion resistance is high enough for use in outdoor areas and wet indoor areas, and the cutting ability durability is sufficient for use in mineral substrates (eg, concrete, full brick, etc.) Or cut the thread on the steel substrate. According to the present invention, such a screw can also be integrally manufactured without a joint operation, that is, a "single-piece screw" method.

A particularly good point is that the steel of the blank (and the screw made by Yida) has a carbon content of less than 0.07%. Due to the use of this soft hemp field, it is particularly resistant to water embrittlement and can achieve extremely high core ductility (Kernduktilität). This in turn makes the load detachability (Lastabtrag) particularly good. According to the present invention, the edge hardness is increased due to nitrogen doping, so that the core hardness is small (for example, the core of the screw has a tensile strength of less than 1100 MPa - which is caused by a low carbon content) and does not significantly affect the cutting. Thread properties.

In addition, it is advantageous that the steel of the blank (which is also preferably made of screws) has a carbon content of more than 0.02%, in particular greater than or equal to 0.03%. The core hardness thus created ensures that the large torque generated by the screw being screwed into the concrete is reliably transmitted.

A further feature of the invention is that the chromium content of the steel of the blank is greater than 12% And/or the nickel content is more than 2.5%, so that even when the carbon content is low, a specially contained 麻田散铁 tissue structure can be caused. In addition, corrosion resistance and toughness are further improved.

It is also preferred that the steel of the blank (preferably also made of steel) has a copper content greater than 0.3%. The steel is alloyed to improve the corrosion resistance of the chlorine-containing environment. The amount of percentage in this case is specifically referred to as the mass percentage in the manner in which the practitioner is accustomed.

For example, the steel of the blank (preferably also made of screws) X3CrNiMo13-4 (1.4313), which combines good low temperature toughness and high strength, especially at -20 ° C, the low temperature toughness is greater than 20 J (ISO- V).

In addition, the screw type has a rotary fitting means for driving (in a shape fitting manner) to the screw shaft, the screw type should be combined with the rotary fitting means (especially at the temperature of the present invention and In the nitrogen-containing atmosphere of the invention, it is hardened, so that the screw should be designed in one piece, and in particular, the rotary fitting means can be provided, and the rotary fitting means can have a polygonal shape or an inner polygon in particular. For example, the rotary fitting means may have a screw head having a polygonal shape or an inner polygon.

This type of screw should be quenched quickly at the end of the hardening process (abschreckrn, English: quench) to avoid nitride precipitation. In this way, the strength and corrosion resistance can be further improved, and the quarry iron structure is also retained in a metasabil manner during quenching.

Further, according to the present invention, after hardening and quenching, the work is tempered immediately, and is preferably in the temperature range of 150 ° C to 450 ° C. By this tempering, the remaining Worth iron in the granulated iron is reduced, which also has a favorable effect on the strength. In addition, the ductility of the screw is improved.

For example, from the viewpoint of manufacturing cost, the screw type should be formed by cold deformation of the blank, and the "cutting thread" should be formed by rolling. This load fitting means and/or screw head can be forged For press forming, the blank can be in particular a wire segment.

In addition, before hardening in a nitrogen-containing atmosphere, a region of the screw type is covered with a non-diffusion barrier, and some areas of the screw are covered by the anti-diffusion barrier, which can be restricted to a specific area by the addition of nitrogen, so as to extend The properties and/or hardness can be further optimized. For example, the rotary fitting means (and preferably the dry shaft area directly below the rotary fitting means) is covered by the anti-diffusion barrier.

Surface hardness greater than 600 HV can be achieved using the method of the present invention, which corresponds to a draw strength greater than 1800 MPa. After the hardening according to the invention in the nitrogen-containing atmosphere, or before the hardening of the invention, a thermal conditioning procedure can be applied to the element or screw type.

The invention also relates to a screw manufactured using the method of the invention.

The ratio of the outer diameter of the cutting thread to the cutting pitch can be in the range of 1 to 2, in particular in the range of 1.2 to 1.45, which is the typical size of a screw for screwing into a mineral substrate such as concrete from a cutting thread. The term "pitch" refers in particular to the axial spacing of the threads following the thread phase.

According to the invention, the concrete substrate can also be provided with a hole into which the screw of the invention is screwed. Wherein the concrete substrate forms a negative mold shape, which is opposite to the cutting thread of the screw, whereby the screw is screwed into the hole in a self-cutting manner to form a pair of opposing threads.

The invention is described in detail below with reference to the preferred embodiments illustrated in the drawings.

(1) ‧‧‧Step 1 (providing blanks)

(2) ‧‧‧Step 2 (made into screw type)

(3) ‧‧‧Step 3 (screw type hardening)

(4) ‧‧‧Step 4 (screw type quenching)

(5) ‧‧‧Step 5 (screw type tempering)

(10)‧‧‧ screws

(15)‧‧‧ screw head

(20)‧‧‧ screw head

(21)‧‧‧ cutting thread

(28)‧‧‧Support thread

(50) ‧‧‧Mineral substrate

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic flow diagram of a manufacturing process of the present invention; Figure 2 is a schematic view of the screw of the present invention made by the manufacturing method of the present invention.

Figure 1 shows in a schematic manner the sequence of steps of the manufacturing procedure of the present invention. First, in step (1), a blank is provided, which is made of a steel which can be hardened by the ramie iron, and then formed into a screw type from the blank in the step (2), having a screw shaft (20), one set on the screw The cutting thread (21) on the dry shaft (20) is a rotary fitting means (15) provided on the screw shaft (20). Then, in step (3), the screw type is hardened in a nitrogen-containing atmosphere at a humidity of more than 900 ° C (especially greater than 1050 ° C) and rapidly quenched after the step (4) to avoid nitride formation. Finally, in the step (5), the screw type is tempered, and it is preferably in the temperature range of 150 ° C to 400 ° C.

An embodiment of a screw made in accordance with the present invention is shown in Figure 2, which is designed as a concrete screw.

The screw (10) has a cylindrical screw shaft (20) having a hexagonal screw head (15) at its end which forms a rotational fitting means. A cutting thread (21) has a smaller diameter support thread (28) along the screw shaft (20).

The screw shaft (20) of the screw is screwed into a hole in a mineral substrate (50), in particular a concrete substrate, wherein the cutting thread (21) is cut into a corresponding one in the substrate when screwed in The threaded, threaded stem (20) passes through a hole in a load (55) that is held by the screw head (15) on the substrate (50).

(1) ‧‧‧Step 1 (providing blanks)

(2) ‧‧‧Step 2 (made into screw type)

(3) ‧‧‧Step 3 (screw type hardening)

(4) ‧‧‧Step 4 (screw type quenching)

(5) ‧‧‧Step 5 (screw type tempering)

Claims (13)

A method of manufacturing a self-tapping screw (10), wherein the step (1) provides a blank made of steel hardened by the rams iron method; and the step (2) is a blank process screw type having a screw The dry shaft (20), the screw shaft (20) is provided with a cutting thread (21); in step (3) the screw is then hardened in a nitrogen-containing atmosphere at a temperature greater than 900 °C. The method of claim 1, wherein the steel of the blank has a carbon content of less than 0.07%. A method according to any one of the preceding claims, characterized in that the steel of the blank has a carbon content of greater than or equal to 0.03%. A method according to any one of the preceding claims, characterized in that the steel of the blank has a carbon content of more than 13% and a nickel content of more than 2.5%. A method according to any one of the preceding claims, characterized in that the steel of the blank has a copper content of more than 0.3%. A method according to any one of the preceding claims, wherein the steel of the blank is X3CrNiMo13-4. A method according to any one of the preceding claims, characterized in that the screw-shaped part has a rotary insert (15) for transmitting the torque to the screw shaft (20), and the screw type is The rotating insert portion (15) is hardened. A method according to any one of the preceding claims, characterized in that the screw profile is rapidly quenched at the end of the hardening process (step 4) so that the screw profile is tempered (5) after hardening, and The temperature range of 150 ° C ~ 400 ° C is tempered. A method according to any one of the preceding claims, wherein the screw profile is formed from the blank by cold forming. A method according to any one of the preceding claims, wherein at least a portion of the screw profile is covered with a barrier that prevents expansion prior to hardening in the nitrogen-containing atmosphere. A self-tapping screw which is manufactured by the method of any one of claims 1 to 10. For example, the screw of the 11th item of the patent application, wherein: the ratio of the outer diameter (d) of the cutting thread (21) to the pitch (p) of the cutting thread (21) is in the range of 1 to 2, especially 1.2 to 1.45. range. A concrete substrate (50) having a hole into which a self-tapping screw (10) as claimed in claim 11 or 12 is screwed, wherein the concrete substrate (50) is formed with a self-tapping screw ( 10) The cutting thread (21) is opposite to the female mold shape.