JP2697488B2 - Manufacturing method of steel pipe for rack bar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a steel pipe for a rack bar to be incorporated in a rack and pinion type steering device of an automobile.

[0002]

2. Description of the Related Art As shown in a perspective view in FIG. 2, a steel pipe 21 for a rack bar incorporated in a rack-and-pinion type steering device of an automobile is provided with a rack part 22 having a certain length in a part of a steel pipe 21. It is a thing.

[0003] As a conventional method of manufacturing the above-described rack bar steel pipe 21, there is the following method. (1) As disclosed in JP-A-59-209421, a method of cold-pressing a portion of a steel pipe to be formed with a rack to form a flat portion, and then forming a rack on the flat portion. (2) A method of shaving a thick steel pipe to form a rack. (3) A method in which a roll having a caliber portion raised up flat is used as a roll of a final stand of a stretch reducer (3-roll system) described in Japanese Patent Application No. 4-107472.

[0004]

However, the above-mentioned conventional method of manufacturing a steel pipe for a rack bar has the following problems. (1) Manufacturing method based on Japanese Patent Application Laid-Open No. 59-209421 It takes much time and increases manufacturing cost. (2) Manufacturing method for shaving from thick steel pipe The weight of the product increases.

(3) Method described in Japanese Patent Application No. 4-107472 As shown in FIG. 3A, a roll diameter of a roll 23a in which a part of a caliber is raised to form a flat portion for a rack on a steel pipe. Is not the same as the diameters of the other rolls 23b and 23c, the steel bar 21 for a rack bar having the flat portion 21a as shown in FIG. 3B cannot be obtained. FIG. 4 (a) is a cross-sectional view of a long steel pipe 24 shown in FIG. 4 (a), in which a part of a circular shape is cut away as shown in FIG. A plurality of rack bar steel pipes 21 are continuously formed by alternately forming a complete circular cross section (24b) as shown in FIG. If the rack length of the rack of the bar steel pipe 21 l ₁ and a circular portion and a length l ₂ will be uniquely determined, since the length of the total of both L also becomes constant, in some cases The circular cross section may be cut off to a certain extent, and the yield will be reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has a low production cost, a low product weight, and a low yield because no labor is required. An object of the present invention is to provide a method for manufacturing a steel tube for a rack bar.

[0007]

According to the present invention, a method for manufacturing a steel tube for a rack bar according to the present invention is characterized in that, in the reduction rolling of a steel tube by a three-roll type stretch reducer, only the last stand of the stretch reducer is a two-roll type. A steel pipe is rolled by using a roll in which a part of a caliber is raised flat to a two-roll type roll.

[0008]

In the method for manufacturing a steel tube for a rack bar according to the present invention, only the final stand of the three-roll type stretch reducer is set to the two-roll type, and a part of the caliber is raised flat to the two-roll type roll. In this way, when the steel pipe is drawn and rolled, a notch having a circular cross-section and a straight part for forming a rack partially circular is formed in the long steel pipe that has emerged from the final stand of the stretch reducer. Cross sections are formed alternately. Then, the long steel pipe is cut into a unit of a continuous body of the circular cross-section and the notched cross-section adjacent to each other, thereby obtaining a plurality of rack-bar steel pipes.

[0009] When the steel pipes for rack bars having the same length of the notched cross-section forming the rack of the steel pipe for rack bars but having different circular cross-sections must be manufactured, a part of the caliber is flattened. By appropriately changing the roll diameter of the roll raised, the desired steel pipe for a rack bar can be obtained, so that unnecessary portions are not cut off and the yield does not decrease.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a steel pipe for a rack bar according to one embodiment of the present invention will be described with reference to FIG. In the method of manufacturing a steel tube for a rack bar according to one embodiment of the present invention, as shown in the perspective view of FIG. 1A, only the final stand 2 of the stretch reducer 1 is a two-roll system. And FIG.
As shown in the front view of the roll of (b), a part 3b having a flat bottom is formed on a part of the semi-circular caliber 3a of the upper roll 3. Then, a steel pipe is passed between the upper roll 3 and the lower roll 4 consisting of only a normal circular caliber 4a, and a circular cut cross section as shown in the cross sectional view of FIG. Bar Bar Steel Pipe 21
To roll.

The diameter D ₂ of the upper roll 3 shown in FIG.
The length l ₁ of the rack portion and the length l _{2 of the} circular portion shown in FIG.
And the diameter D ₀ of the semi-circular caliber 3a (ie, the outer diameter of the steel pipe to be rolled), as follows. Assuming that the roll diameter at the bottom of the caliber is D _2n , the roll diameter D ₂ and the caliber diameter D ₀ are in the relationship of equation (1). D ₂ = D _2n + D ₀ (1) Further, l ₁ , l _2, and D _2n are in the relationship of equation (2). l ₁ + l ₂ = πD _2n (2) From the expressions (1) and (2), D ₂ can be expressed by the expression (3). D ₂ = {(l ₁ + l ₂ ) / π} + D ₀ (3)

That is, a roll for rolling a flat portion for forming a rack of a steel pipe for a rack bar (an upper roll in FIG. 1B).
Is determined from the length l _{1 of} the flat portion for forming the rack of the steel pipe for the rack bar, the length l ₂ of the circular cross section, and the outer diameter D _{0 of the} steel pipe to be rolled.

As described above, by changing the roll diameter of the roll for rolling the rack forming flat portion of the rack bar steel pipe, the rack bar steel pipe of various lengths (L) is continuously formed on the long steel pipe. However, it is not necessary to change the roll diameter on the side where the flat portion for rack formation is not rolled. Then, the roll diameter is different between the upper and lower rolls, and there is a possibility that the circumferential speed of the rolls is different and the steel pipe slips. However, as shown in FIG. with driving the lower roll 4 at the drive shaft 5, the driving force it is sufficient as a mechanism for transmitting to the upper roll through the diameter of the pinion 6 and the diameter of the gear 7 of d ₂ of d _1. By doing so, the peripheral speeds of the upper and lower rolls can be made equal by setting the diameters d ₁ and d _{2 of} the pinion 6 and the gear 7 to be as shown in the expression (4), so that slip occurs. Absent. D ₁ × d ₁ = D ₂ × d ₂ (4)

Example 1 A flat portion having a length of 180 mm was formed on a steel pipe having an outer diameter of 30 mm by forming an upper roll having a diameter of 300 mm and a lower roll having a diameter of 300 mm.
mm. Overall length of obtained steel tube for rack bar = 850 mm Pinion diameter: gear = 1: 1

Example 2 A flat portion having a length of 180 mm was formed on a steel tube having an outer diameter of 30 mm by forming an upper roll having a diameter of 200 mm and a lower roll having a diameter of 300 mm.
mm. Overall length of the obtained steel tube for rack bar = 534 mm Pinion diameter: gear = 2: 3

[0016]

According to the present invention, steel pipes for rack bars having different lengths can be manufactured with good yield and at low cost.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a method of manufacturing a steel tube for a rack bar according to one embodiment of the present invention, wherein (a) is a perspective view showing an installation location of a two-roll stand, (b) is a front view of a roll, and (c). () Is a cross-sectional view of the roll.

FIG. 2 is a perspective view of a steel tube for a rack bar.

FIG. 3 is an explanatory view of a conventional method for manufacturing a steel tube for a rack bar, in which (a) is a perspective view showing a configuration of a three-roll stand;
(B) is a cross-sectional view of the roll.

FIG. 4 is an explanatory view showing a state in which a steel tube for a rack bar is formed on a long steel pipe, (a) is a longitudinal sectional view of the long steel pipe,
(B) is a view on arrow AA of (a), and (c) is a view of B- on (a).
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stretch reducer 2 Final stand 3 Upper roll 4 Lower roll 5 Drive shaft 6 Pinion 7 Gear

Claims (1)

(57) [Claims] In the rolling reduction of a steel pipe by a three-roll type stretch reducer, only the last stand of the stretch reducer is a two-roll type, and a roll obtained by raising a part of a caliber to the two-roll type roll flat. A method for producing a steel pipe for a rack bar, comprising rolling a steel pipe using the method.