Bent channel shaping method

FIELD: plastic working of metals, namely production of bent channels of increased strength steels.

SUBSTANCE: method for shaping bent channels of high-strength steels with thickness 7 = 8 mm comprises steps of successively from one transition to other bending up flanges of shape at predetermined bending radiuses; setting bending radiuses in each of two first passes equal to 1 - 2 mm; in third and in each of three last passes setting bending radius depending upon thickness of shape and in each intermediate pass reducing bending radius according to given relation.

EFFECT: improved rigidity of bent shapes.

1 ex

 

The invention relates to rolling production, in particular to technology profiling of cold-formed equal channels.

These profiles are manufactured in high grade roll forming mills by consecutive passages bended form of boundary elements being formed of a strip of the workpiece at defined angles and with predetermined radii of bends to produce the final section. Technology features profiling of these channels is described, for example, in the book Apekisheva and Webclicker "the Bent profiles of car", M.: metallurgy, 1975.

The total number of forming passes (and the values of the corners of the aisles), and the magnitude of the bending radii depend on the thickness of the workpiece and its plastic properties, in particular, on the value of the temporary resistance σinmaterial. Typically, the radii of bends consistently reduced during profiling, and the maximum value of the final radius is directly proportional to the thickness of the cast strip (see GOST 8278).

There is a method of profiling bent bars in rolls with equal radii of curves, in which the values mijalkovic gaps in each pass is determined by the given dependencies (see U.S. Pat. Of the Russian Federation No. 2164186 class. 21D 7/00, publ. in BI No. 8, 2001). The disadvantage of this method is the inability to increase the rigidity (bearing capacity)of the channel, in particular, from high strength steel.

The closest analogue to the claimed method is profiling technology equal of channels described in the book edited by Istoricheskogo "Calibration rolls for the production of roll-formed profiles rolled, Kyiv: Kyiv, 1980, p.48-54.

This technology is consistent across the aisles Podlipki shelves profile with the given values of the radii of bends and is characterized by the fact that the radii sequentially decrease from the first passage (draft) to final passage, which establishes the magnitude of the radii of the finished profile. A disadvantage of the known technology is the inability to increase the rigidity of channels, including from high strength steel.

Indeed, one of the criteria for determining the rigidity of the channel (more precisely, the magnitude of the moment of resistance to bending of its cross section), is the radius of the bend between the wall and shelves profile, and the value of the moment resistance (ceteris paribus) increases with decreasing of the radius. However, there is a critical value of the bending radius for channel specific parameters, the reduction of which inevitably leads to cracking of the bends.

That is why GOST 8278 sets of different sizes of bending radii for varying the thickness of the channels, and, in addition, for bars of different grades of steel: the values of the radii should be greater for high strength steel, which affects the carrying capacity of the channel.

The technical task of the present invention is to improve operational properties of cold-formed sections made of high strength steel by increasing their rigidity.

To solve this problem in the way of profiling bent bars of high strength steel, including consecutive passes of pogibko shelves profile with the given values of bending radii riunlike the closest analogue, when profiling the channel thickness, S, is equal to 7...8 mm, the bending radii riin each of the first two passages is equal to 1...2 mm, in the third (4,1 4,3...) S, in each of the last three are the same and equal to (1,25 1,4...) S, and each of the intermediate passages reduce for dependencies:

,

where ri- the value of the radius in the previous passage.

The mathematical dependences obtained by processing the experimental data and are empirical.

In practice, to obtain in the first and second passages values: ri=1...2 mm of the edge of the upper rolls in place of the pair of cylindrical and conical elements dull, controlling the obtained values of ri.

With mnost of the proposed technical solution is in roughing (I and II) passes through a significant reduction (more than an order of magnitude) values of the bending radius decreases and the contact surface of the moldable billet with rollers in the bending zones. This leads to a significant reduction of friction forces in these areas, which, apparently, helps to reduce residual stresses in the profile. Because it reduces the probability of crack formation, it becomes possible to reduce the value of the final (finished profile) bending radii.

Featured and proven values of these radii in 2,50...2.57 times less than the values recommended GOST 8278 (table 2) for channels of high-strength steel.

Experimental validation of the proposed method was implemented on the varieties of the roll forming mill "2-8" of OJSC "Magnitogorsk iron & steel works".

With this purpose, the profiled channels 280×80×8 mm from stty (procurement had σin=590...620 MPa) and 250×120×7 of sths (procurement had σin=510...540 MPa)used, respectively, as spar for trucks and construction designs, varied the radius of the bend in the aisles (there were 9) when continuously bended form: 0°→10°→20°→32°→44°→58°→70°→80°→88°→90°. The results of the experiments were evaluated on the quality of the seam is larow: their geometry and the absence (presence) of crack formation in the bends.

The best results (qualitative profiles of not less than 99.4% of in the absence of cracks) obtained using the proposed method. Deviations from the recommended values of the radii worsened the results.

Thus, when the bending radii in roughing passes of more than 2 mm could not obtain profiles with finite radius of less than 15 mm (on the part of the channel was observed cracks). At different values of the bending radii in three finishing (last) aisles (r8>r9>r10) up to 1.5% of the channels had increased Deposit-collapse" at the ends of the rods, i.e. the deviation from a right angle was exceeded (1°30′) for a length of up to 0.8 m

When riin the third pass over 4.3's had to increase the radii in subsequent passes, resulting in target radius (finished profile) was 12...13 mm

Reduction of this value to (...4,0 3,8) S caused by separate rods (especially derived from the ends of the slit strips) cracks.

When bending radii in intermediate passageshad to reduce the number of forming passes (for the last passages ri=(1,25...1,40)S, worsened the geometry of the finished profiles. The increase of the radii toled to the opposite result: the increase in the share of the Islands forming passages, that has increased the consumption of the rolls.

Control profiling technology, taken as the closest analogue was not possible to obtain channels with finite bending radii in the range (1,25 1,400...) s

Thus, experimental validation confirmed the acceptability found technical solutions to achieve this goal and its advantages over the known object.

According to the data sheet-rolling shop №7 OJSC MMK and the Central laboratory of the plant using the proposed method for the production of bent channels of high-strength steel will reduce the metal consumption of products from these profiles (by increasing their carrying capacity) is not less than 10%.

Specific example

1. Channel 280×80×8 mm steel FU with σin=610 MPa profiled in nine stands from the original workpiece width 407 mm and a thickness of S=8 mm

The angle bended form on passes:

0°→10°→20°→32°→44°→58°→70°→80°→88°→90°

The bend radius on the finished profile: r=1,33 S≅10,5 mm

In the first and second pass: ri=1.5 mm, and in the last three (VII...IX) - ri=1,33S≅10,5 mm

The radius of the bend in the third passage - ri=4,2S=4,2·8≅34 mm

The radii in the IV VI...passes:

IV - ri=340,085≅23 mm; V - ri=230,885=16 mm; VI - ri 0,885≅12 mm

2. Channel 250×120×7 of STRs with σin=530 MPa profiled in nine stands from the original workpiece width 455 mm and a thickness of S=7 mm

The angle bended form on passes:

0°→10°→20°→32°→44°→58°→70°→80°→88°→90°

The bend radius on the finished profile: r=1,33S≅9.5 mm

In the first and second pass: ri=1.5 mm, and in the last three (VII...IX) - ri=1,33S≅9.5 mm

The radius of the bend in the third passage - ri=4,2S=4,2·7≅29 mm

The radii in the IV VI...passes:

IV - ri=290,885≅20 mm; V - ri=200,885=14 mm; VI - ri=140,885≅10,5 mm

Method profiling bent bars of high strength steel, including consecutive transitions of pogibko shelves profile with the given values of bending radii ri, characterized in that the profiling of the channel thickness, S, is equal to 7...8 mm, the bending radii riin each of the first two passages is equal to 1...2 mm, in the third (4,1 4,3...) S, in each of the last three are the same and equal to (1,25...1,40)S, and each of the intermediate passages rireduce over dependence:where ri- the value of the radius in the previous passage.



 

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