JP2799700B2 - Stainless steel wire for spring - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel wire for a spring having excellent coil formability used for a coil spring.

[0002]

2. Description of the Related Art Conventionally, when a stainless steel wire for a spring is automatically formed (coiled) into a coil spring,
As shown in FIG. 1, the wire is straightened by a forcing roller 1, sent to a guide tool 3 (a precision wire guide called a quill) by a supply roller 2, then subjected to plastic working by a coiling pin 4, and in the case of a compression spring, After being slightly twisted by the pitch pin 6 to give a pitch, the mandrel 5 and the cutting blade
To complete one compression coil spring.

[0003] When the wire 8 is formed into a spring SP in such a coiling process, the wire 8 and the coiling pin 4 as a tool, as shown in FIG. Inclined groove 4 ₁
As a result, very heavy friction processing is performed, and as shown in the figure, "lubrication" L between the tool and the wire is important. The quality of the lubrication directly affects the dimensional variation of the coil spring (for example, a change in the free length of the spring), and appears as a change in the defective rate of the spring.

However, in the production of "stainless steel wires for springs" specified in JIS G4314, the steel type (SUS 304, SUS316, etc.), wire diameter, and temper classification (WPA, WPB) specified by the user are required. According to, wire manufacturers make wires using their own manufacturing methods (coating film for drawing, lubricant for drawing, die shape, number of drawing passes, drawing speed, etc.) Finished within tolerance. The shape of the wire coil (free coil diameter fd, hanging open δ in Fig. 3) and the presence of a nickel plating film before wire drawing are not specified in the JIS standard, which are important factors in coiling molding of the spring. It is well known that this has a great effect on the variation in the coiling dimensions of each of them, so each company has been focusing on their management.

[0005]

SUMMARY OF THE INVENTION Among the prior art,
Regarding Ni coating, which greatly affects the dimensional variation (formability) of springs other than the shape of the wire coil (see Fig. 3), the wire drawing method using a nickel-plated stainless steel wire developed 27 years ago was developed. (Japanese Patent Publication No. 44-14572) It is disclosed that a stainless steel wire is nickel-plated to facilitate wire drawing lubrication, but the thickness of the Ni film, the relative thickness between the material and the Ni film, is disclosed. Of the mechanical strength difference (hardness ratio) and the amount of lubricant that penetrated into the Ni coating by wire drawing have not been optimized for coiling performance, and a comprehensive analysis combining these three factors has been eagerly awaited. I was

[0006] By the way, when friction processing is performed with a material and a tool as shown in FIG.
It is well known that it can be expressed by ontons' law (F = A · τ A: true contact area, τ: shear yield stress of the material in contact with the tool) (Bauden, Tiber, translated by Norimune Soda, Solid Friction and Lubrication ”, p.88, Showa-36, Maruzen). As shown in FIG. 4, when a metal film S softer than the work is interposed thinly on the surface of the hard work H as in the case of Ni plating on a stainless steel wire for a spring, τ is small because the film is soft. A is small because the material is hard, and F = Aτ is a small value. Unlike the case where A in the hard workpiece H is small and τ is large when the soft metal film S is not interposed,
The law of ns does not hold. Further, in this case where Amontons' law is not satisfied, if a lubricating component is present on the soft metal film S, the frictional force F is expected to be extremely small. According to the conventional data, it is shown in FIG. 4 that the optimum thickness of the soft metal S for minimizing F is to coat indium with 1 μm on the tool steel (P102 mentioned above). , An expensive special precious metal comparable to gold, Ni on stainless steel wire
The optimum value for plating was unknown. In addition, the effect of the soft metal strength (particularly the relative strength ratio with the workpiece) and the amount of the lubricant adhering between the tool and the soft metal film have what effect and what optimum value exists. It is an unknown field to do.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned point, and has been developed in order to develop a technology for optimizing the coiling performance of a stainless steel wire in the production of a stainless steel wire for a spring. Dimensional variation (defective rate) such as free length during molding, Ni coating thickness of Ni-plated spring stainless steel wire, relative hardness between Ni coating and fabric wire, and lubricant penetrated into Ni plating An object of the present invention is to provide a technique for optimizing the three factors for obtaining the relationship with the amount of adhesion and minimizing the dimensional defect rate of the spring.

[0008]

In order to achieve the above object, a nickel-plated stainless steel wire for a spring according to the present invention is used as a technique for optimizing the above three factors, as a nickel plating thickness of a wire after final drawing. but 0.2 to 2 .mu.m, hardness ratio matrix of the plating layer is 0.2 to 0.83, the amount of lubricant deposited is characterized in that it is a respective values of 0.05~0.80g / ^{m 2} . This makes it possible to reduce the molding failure rate of the spring to as low as 10% or less.

In this case, the range of the three factors was determined as follows. First, a basic manufacturing process of a stainless steel wire for a spring will be described below. In the manufacturing process, the above three factors were changed, and the relationship between the rejection rate of the free length and each factor was examined.

[0010] Regarding the change in the thickness of the Ni plating film. When the current density and the concentration of the sulfamic acid bath were changed, the properties of the plating film changed. Therefore, the plating thickness was changed by changing the line speed and changing the plating time. Then, the plating thickness of the final stainless steel wire for spring was obtained by calculation from the thickness before drawing. For example, stainless steel wire is 4φ → 2φ
In the case of (75% processing), 3φ → 1φ (89% processing), it was found that the plating thickness was 1/2 and 1/3 of the thickness before wire drawing, respectively. In addition, this calculated value is also calculated using an optical microscope (X100
It was also measured and confirmed in 0). That is, in this measurement, the thickness of the plating film when a 1.7φ3μm Ni-plated wire was drawn to 0.7φ before drawing (the workability was 83% and the wire diameter was reduced to 41% before drawing). Regarding the change, it was recognized that the plating thickness was 1.2 μm as in the case of the decrease in the wire diameter. Stainless steel wire for spring with Ni film thickness changed in this way
0.7mm diameter using an automatic coiling machine PC-15 manufactured by Itaya Seisakusho Wire diameter 0.7mm Free length 38.0mm Coil average value 12.0mm Effective number of turns 10.5 Spring index 17.1 (Coil average value / wire diameter 1,500 compression coil springs were molded. Then, the free length is automatically measured one by one during spring molding, the free length control width is set to ± 0.10 mm, and the number of springs outside this limit is counted to calculate the free length rejection rate. Then, the relationship with the Ni plating thickness was determined (see FIG. 6).

[0011] Change in hardness of Ni plating film. As shown in FIG. 4, in the case where F becomes small such that Amontons' law is not satisfied, a soft metal film having a small thickness is required. However, there is no definition of “soft” and a high strength for a spring is used. It was completely unknown how hard the stainless steel wire should have to improve coilability. Accordingly, nickel carbonate is added to a nickel sulfamate bath as described below to adjust the pH of the solution to 1 to 5.5 to change the hardness of the plating layer, and to determine the free length defect rate at the same plating thickness. (See FIG. 7). Nickel sulfamate 800 g / l Boric acid 25 g / l Nickel bromide 6 g / l PH 1 to 5.5 (changed by adding nickel carbonate) Current density 13 A / dm ² Wire drawing of stainless steel wire for spring At
The change in hardness between the nickel plating film and the stainless steel material was obtained by changing the Vickers hardness of the plating layer from HV180 to HV510 and drawing the wire from 1.7φ to 0.7φ. Although the hardness of the fabric increases and the hardness of the nickel film tends to decrease, what is related to the spring formability is the relative hardness ratio between the stainless steel material and the nickel film after the final wire drawing. Will be. The hardness of the nickel plating layer was measured at a load of 1 g, as in the case of the stainless steel base material, by selecting a white flat portion called a boundary lubrication portion on the drawn surface (by an optical microscope).

Regarding the change in the amount of lubricant attached. In the case where the Amontons law shown in FIG. 4 does not hold, if the lubricant that reduces the friction coefficient is interposed between the tool and the soft metal thin film, it is considered that the above-mentioned F = Aτ is further reduced. By the way, in wire drawing, the powder lubricant J is drawn into the die D as shown in FIG.
A state in which the material is softened by the friction and processing heat to be in a liquid state and interposed between the die D and the wire 8, and a part of the material is cut into the wire 8 and strongly adheres appears. At this time, a portion bites lubricant J into the wire 8 fluid lubrication unit L _f, can no longer fit bite that boundary lubrication portion L _b. Lubrication unit L _f of the flat boundary lubrication portion L _b and black parts of the white portion when this situation observation using an optical microscope are irregularly mixed. When the fluid lubricant portion L _f of the black portions is large, and bite many lubricant to the wire, the lubricant coating weight increases (Heijiro Kawakami: lubricating Vol. 32 No. 2, 1986 P111, Nakamur
a, Y .: Wire Jowrnal Vol. 13, No. 6, 1980, p. 54). The fact that the lubricant has penetrated into the fluid lubrication part can be confirmed by the line analysis of the stainless steel wire for spring by a microanalyzer.
It is clear from the fact that is detected.

Therefore, the conditions such as the nickel plating thickness, the hardness ratio between the stainless steel base material and the plating film are fixed, the die angle is 7 to 18 °, the drawing speed is 50 to 300 m / min, and the conditions such as the use of a pressure roller are combined. Thus, the amount of lubricant attached to the wire was changed (the fluid lubricating portion was changed), and the relationship with the defect rate during spring molding was determined (see FIG. 8). Incidentally, the measurement of the amount of the lubricant attached was performed in the first stage by degreased by ultrasonic vibration in acetone for 3 hours, and then immersed in normal hexane for 20 hours, and the change in weight was measured to obtain g / m ² . displayed.

The relationship between the three factors obtained from the above test and the spring free length defect rate is as follows. Influence of Nickel Plating Thickness on Spring Failure Rate As shown in FIG. 7, the failure rate tends to increase when the plating thickness is small and when the plating thickness is large, and tends to decrease at an intermediate value. A good range is about 0.8 μm to 1.0 μm. Effect of hardness ratio between stainless steel wire base material and nickel plating on spring failure rate As shown in FIG. 7, the hardness ratio has a very strong dependence,
The defective rate is high whether the plating is soft or hard, but plating that is too hard has an adverse effect. Effect of Lubricant Adhesion Amount on Spring Defect Rate As shown in FIG. 8, the defect rate is high when the adhesion amount is small or large, but when the adhesion amount is particularly large, the wire guide shown in FIG. Since the groove diameter is very precisely made with a thickness of about 1.01 to 1.015 times the wire diameter d, it is not good because the lubricant is clogged and an accident such as coiling stop occurs.

From these results, the defect rate is 10% or less (total
(The rating is 90% or more) The range of the above three factors is: Nickel plating thickness: 0.2 to 2.0 μm Hardness ratio: 0.20 to 0.83 Lubricant adhesion amount: 0.05 to 0.80 g / M²  The range in which the defective rate is 5% or less (the pass rate is 95% or more) is as follows: Nickel plating thickness: 0.3 to 1.6 μm Hardness ratio: 0.30 to 0.81 Lubricant adhesion amount: 0.1 to 0 .70 g / m²  Becomes

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on the following examples. First, Fe-0.07% C-18.72
% Of _{C r -8.51% Ni-1.20%} M n -0.40% S i SUS304 stainless steel wire 5.5φ with ingredients were heated at 1120 ° C., After quenching was performed pickling coating. After that, with continuous wire drawing machine, speed 200m / min.
Wire was drawn to φ. Then, it is heated to 1130 ° C in a bright annealing furnace using ammonia decomposition gas to perform solution annealing treatment, then coated, stretched 5 times at a speed of 200m / min to 1.7φ, and processed 53.8%. Carried out. Then, as a final step, wire is formed in the following steps to finish the stainless steel wire for spring, and the thickness of the nickel plating film, the hardness ratio, and the amount of lubricant attached are changed, and the comparative material and the product of the present invention are changed. And performance comparison.

Changes in Nickel Plating Film Thickness The plating solution composition and plating conditions are as follows. Nickel sulfamate 809 g / l Nickel carbonate 29 g / l Boric acid 25 g / l Nickel bromide 5.8 g / l Current density 12 A / dm ² Furnace length 26 m PH 3.8 Bath temperature Room temperature It was changed to 12 m / min.
The change in plating thickness before wire drawing was the same ratio as the change in wire diameter due to wire drawing, but was measured with an optical microscope. For a plating thickness of 0.5 μm or less, a plating layer was determined by an oblique cutting method.

Change in Hardness Ratio In order to change the hardness of the plating, the amount of nickel carbonate added to the nickel plating bath was changed to PH1 to 5.5. In the case of nickel, the plating hardness sharply increases at PH 4.8 or more.

Changes in Lubricant Adhesion The lubricant used was a Ca-based lubricant. (A) Die angle (full angle) changed from 7 ° to 18 ° to change lubricant adhesion amount, (b) Wire drawing speed changed from 50 to 300m / min. (C) Increase / decrease in the number of pressure rollers (lubricator) used (maximum) (D) Use of powder lubricant in the die box of three dies before drawing (no lubricant in the three die boxes up to three). Make wires,
A coiling test was performed.

The specifications of the spring processed to evaluate the coilability (formability) are as follows. Wire diameter: 0.7mm Free length: 28.0mm Coil average diameter: 12.0mm Effective number of turns: 8.5 Spring index: 17.1 Free length control width: ± 0.10mm Coiling speed: 20 pieces / min. It uses an automatic coiling machine PC-15 manufactured by Itaya Seisakusho.) During coiling, the free length is automatically measured for each spring, and the number of springs outside the control width can be counted by another route. It was calculated as a defective rate for 2000 springs and used as a formability index of the spring wire.

Table 1 shows the results of the coiling test. No
Nos. 1 to 17 are products of the present invention, and Nos. 18 to 26 are comparative materials.
The product of the present invention has a low rejection rate and shows very excellent moldability.

[0022]

[Table 1]

[0023]

According to the stainless steel wire for a spring according to the first aspect of the present invention, emphasis is placed on points such as tensile strength, wire diameter, and coil creep which have been conventionally performed in the production of a stainless steel wire for a spring. It is possible to control the characteristics of the wire in more detail, especially the three factors that have been clarified this time, namely the thickness of the nickel plating film and the hardness of the plating thickness relative to the base metal. By controlling the ratio and the amount of lubricant adhering to achieve the respective target range values, it is possible to make a great contribution to improving the efficiency of coiling of the spring.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional coiling mechanism.

FIG. 2 is an explanatory diagram showing a state of friction processing between a wire and a tool (coiling pin).

FIG. 3 is an explanatory diagram of a shape of a wire coil.

FIG. 4 is an explanatory view showing a state of contact between a hard workpiece having a soft metal film on a surface and a tool.

FIG. 5 is an explanatory diagram showing a state of lubrication during wire drawing.

FIG. 6 is a graph showing an effect of a nickel plating thickness on a defective rate of a spring.

FIG. 7 is a graph showing the effect of the hardness ratio between the stainless steel wire base material and the nickel plating on the failure rate of the spring.

FIG. 8 is a graph showing an effect of a lubricant adhesion amount on a spring failure rate.

[Explanation of symbols]

3 Guide tool (wire guide), 4 Coiling pin (tool), 6 Pitch pin, 8 Wire, fd
Free coil diameter, δ: hanging open, F: frictional force,
A: True contact area, τ: Shear yield stress of material, L:
Lubrication, J: powder lubricant, _Lb : boundary lubrication part, _Lf :
Fluid lubrication unit.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Lee Katsuzai 1-3-3 Kitahorie, Nishi-ku, Osaka-shi Within Course Japan Co., Ltd. (56) References JP-A-6-226330 (JP, A) JP-A Heihei 4-17616 (JP, A) JP-A-3-51537 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21C 1/00 B21C 9/00 B21F 35/00

Claims (1)

(57) [Claims] 1. A stainless steel wire for a nickel-plated spring
And the nickel plating thickness after the final drawing is 0.2 to
2 μm, and the hardness ratio of the plating layer to the base material is 0.2 to 0.1.
83, spring stainless steel wire, wherein the amount lubricant deposited is each value of 0.05~0.80g / ^{m 2.}