RU2149726C1 - Method for making coils and branch pipes - Google Patents

Abstract

FIELD: plastic metal working, namely production of coils and branch pipes of tubular blanks by bending at acting upon them by cross and longitudinal efforts. SUBSTANCE: method comprises steps of bending tubular blank by cross efforts normal relative to its axis, selecting predetermined distance between acting lines of adjacent efforts directed one opposite to another. It allows to reduce degree of wall thickness difference and out-of-roundness until value less than 5 % and to eliminate step of preliminary heating of blank up to high temperature with use of sand and melt glass. EFFECT: enhanced efficiency. 4 dwg, 1 ex

Description

 The invention relates to the processing of metals by pressure and can be used in the manufacture of pipe billets by bending bends for the needs of a boiler and gas facilities and coils of various heat exchangers.

 A known method of manufacturing bends by bending a pipe billet as a result of rotation of one section of the billet relative to another (Romanovsky "Handbook of cold stamping, 1971, p. 432).

 The disadvantage of this method is the destruction of the workpiece along a convex surface or the loss of stability along a concave surface when bending along a radius less than the maximum permissible, which affects the quality of the products.

 A known method of manufacturing steeply curved thin-walled nozzles by stepwise displacing one flat section of the workpiece relative to the adjacent bend at a certain angle, followed by calibration of the cross section of the workpiece (AS USSR N 674312, class B 21 D 9/00 for 1977).

 The disadvantage of this method is that as a result of stepwise displacement and bending, a pipe facet is formed, which leads to a difference that cannot be removed by calibration (rubber pressure on the inner surface of the pipe), which affects the quality of the product.

 The closest in technical essence and the achieved positive effect (prototype) is a method of manufacturing coils and bends (AS USSR N 1581412, class B 21 D 11/02, 1990).

 The method includes bending the workpiece by forces acting in the transverse and longitudinal directions, and is carried out in two stages: first, the workpiece is given a wavy shape with mating radii greater than the calculated radius, then it is bent to the calculated radius.

The disadvantage of this method is that, despite the stepwise deformation of the bend of the workpiece with different radii, thinning at the top of the branch reaches 15%, which affects the quality of the product, and the need to preheat the workpiece to 1000-1100 ^o C with filling it with a mixture of sand and liquid glass increases the cost of the challenge. An object of the invention is to improve product quality by reducing the difference in pipe billet.

, (1)
где l - расстояние между линиями действия соседних сил, направленных навстречу друг другу, мм;
R_г - радиус гиба трубной заготовки, мм;
D_н - наружный диаметр трубной заготовки, мм;
α - суммарный угол двух гибов трубной заготовки на участке между линиями действия соседних сил, направленных навстречу друг другу, причем α = 2α₁; (2)
α₁ - численное значение угла одного гиба, исчисляемого в радианах, толщина стенки поперечного сечения трубной заготовки, мм.This task is achieved in that the billet is subjected to bending by transverse forces perpendicular to its axis, and the distance between the lines of action of adjacent forces directed towards each other is selected based on the ratio

, (1)
where l is the distance between the lines of action of neighboring forces directed towards each other, mm;
R _g is the bending radius of the tube stock, mm;
D _n - the outer diameter of the tube stock, mm;
α is the total angle of two bends of the pipe billet in the area between the lines of action of adjacent forces directed towards each other, and α = 2α ₁ ; (2)
α ₁ is the numerical value of the angle of one bend, calculated in radians, the wall thickness of the cross section of the pipe billet, mm

In FIG. 1 shows a diagram of the bending of a tube billet for one bending radius and angle α ₁ .

In FIG. 2 shows a diagram of the bending of a tube billet with two radii R _g and an angle α = 2α ₁ .

In FIG. 3 shows a diagram of the bending of a tube billet for two bending radii R _g , angle α = 2α ₁ , obtaining a coil and bends according to the proposed method.

 In FIG. 4 shows a diagram of the bending of a pipe billet for no more than two bending radii at the same time, obtaining a coil and bends according to the proposed method.

. (5)
Рассматриваемая площадь сечения тогда

. (6)
Результирующая сила:

(7).To derive the condition for the absence of a difference in the blank, we use FIG. 1. The normal reaction from the action of the force is P ΔN = σα • ΔF (3), where σα = σ _max sinγ. (4)
Normal stress in the considered section (at an angle to the neutral layer)

. (5)
Considered sectional area then

. (6)
Resulting Force:

(7).

, (8)
где σ_max - максимальное касательное напряжение;
σ_т - предел текучести материала при сдвиге, а главное напряжение.According to the theory of Tresca-Saint-Venant in uniaxial stress state (Elenev SA "Cold stamping", ed. Moscow, Higher School, 1981, p. 18, 19):

, (eight)
where σ _max is the maximum tangential stress;
σ _t - yield strength of the material under shear, and most importantly stress.

 Under conditions (8), tensile (compression) plastic deformation will not occur, but plastic shear deformation of the outer fibers of the preform will occur.

. (9)
Приравниваем результирующую силу по формуле 5 к той же силе по формуле 8:

, (10)
откуда

, (11)
т.е. при

(12)
соответственно σ_max< σ_т для одного гиба - условие теории Треска-Сен-Венана выполнено, а следовательно, заготовка будет испытывать пластическую деформацию сдвига, т.е. без утонения (утолщения) стенок трубной заготовки. При одновременном выполнении двух гибов (фиг. 2)

. (13)
Так как отношение S/D_н составляет для тонкостенных труб порядка нескольких процентов (например, труба диаметром 109х4,5 - 4,5 х 100 % = 4,19%), то для практических целей можно считать l ≤ 2D_н. (14)
При отсутствии пластической деформации растяжения-сжатия в наружных волокнах трубной заготовки ее длина должна оставаться неизменной (присутствует деформация сдвига). При одновременном выполнении двух гибов радиусом 2π/360^° суммарный угол α = 2α₁ (фиг. 2),

, (15)
l₁ - длина заготовки после двух гибов на суммарный угол α = 2α₁.Maximum resulting shear stress force

. (9)
Equate the resulting force according to the formula 5 to the same force according to the formula 8:

, (ten)
where from

, (eleven)
those. at

(12)
accordingly, σ _max <σ _t for one bend - the condition of the Tresca-Saint-Venant theory is satisfied, and therefore, the workpiece will experience plastic shear deformation, i.e. without thinning (thickening) of the walls of the pipe billet. With the simultaneous execution of two bends (Fig. 2)

. (thirteen)
Since the S / D _n ratio is about several percent for thin-walled pipes (for example, a pipe with a diameter of 109x4.5 - 4.5 x 100% = 4.19%), for practical purposes, l ≤ 2D _n can be considered. (14)
In the absence of plastic tensile-compression deformation in the outer fibers of the tube billet, its length should remain unchanged (shear deformation is present). With the simultaneous execution of two bends with a radius of 2π / 360 ^{°, the} total angle α = 2α ₁ (Fig. 2),

, (fifteen)
l ₁ - the length of the workpiece after two bends on the total angle α = 2α ₁ .

, (16)
т. е. при данном условии будет отсутствовать разнотолщинность стенок трубной заготовки - следствие пластической деформации, а не растяжения - сжатия.Substituting the value from formula 15 into formula 13, we obtain

, (16)
that is, under this condition there will be no different thickness of the walls of the pipe billet - a consequence of plastic deformation, and not tension - compression.

Example (Fig. 3): manufacturing a coil for bends with an angle of 90 ^o in two steps, first the pipe billet 1 with two punches 2 and 3 simultaneously bends on two half-bends with bending angles α ₁ = 45 ^° , then the punches 2 and 3 diverge, the workpiece 1 moves forward by a step equal to l, and at the same time rotates around its axis by 180 ^o , then again there is a simultaneous double bending by two half-bends with bending angles α ₁ = 45 ^° (α = 2 • 45 = 90 ^° ).

The result is a coil consisting of one branch with an angle of 90 ^o and two semi-branches with bending angles of 45 ^o . Then the cycle repeats, the resulting coil is cut into bends with an angle of 90 ^o .

.At the pilot plant, a coil was made, and then bends from a pipe ⌀ 57x3.5 mm GOST 8734-75,

.

 According to the formula 14 l ≤ 2D ≤ 57x2 = 114 mm.

откуда R_г = 44 мм, подставляя в формулу 14, и проверяем:

т.е. 114 = 114,
формула справедлива.By formula 16, we determine the radius of the bend:

whence R _g = 44 mm, substituting in the formula 14, and check:

those. 114 = 114,
the formula is valid.

After cutting the coil into bends with an angle of 90 ^o , the following results were obtained: the difference in the bends from one tube billet was less than 4% (according to GOST 8734-75, the tolerance for a tube billet wall thickness of 1-5 mm is ± 10%).

 The ovality of the cross-sectional diameter of the tube stock was less than 5%.

According to OST 108.030.40-79:
when R _g > 2D _n - ovality 8-12%,
R _g <2D _n - ovality is less than 20%.

In FIG. 4 shows the manufacture of coils and bends with an angle of 90 ^o in one step with a shear step of the billet equal to 2l. As a result of the existing design, the cross sections of the punches 2, 3, 4 are made in terms of the outer diameter of the tube stock D _n , as well as the stops 5, 6, 7 located opposite the punches 2, 3, 4.

The manufacture of coils and bends according to the proposed method has the following advantages:
a) obtaining coils and bends with a minimum difference improves the quality of the product, and therefore, increases the reliability and durability of heat exchangers, heat and gas networks;
b) the use of cold plastic shear deformation in the manufacture of coils and tap reduces the cost and increases labor productivity, since it does not require additional energy and time to heat up the workpiece;
c) the proposed method has an extended scope:
so, in the manufacture of bends by heating the workpiece with high-frequency currents, it has its limits S / D _n = 0.03 - 0.06, R _g ≥ 1.5 D _n , low productivity 0.2-0.4 mm / s, high cost, thickens the walls of the workpiece; bending in stamps S / D _n ≥ 0.06 R _g ≥ (2-3) D _n ; the use of internal mandrels or additional tensile forces increases the thinning of the walls by 20-50% (Averkiev Yu. A., Averkiev A.Yu. Cold stamping technology, Moscow, Engineering, 1989, pp. 110-114).

In the proposed method, R _g <D _n , the difference and ovality is less than 5%.

Claims (1)

A method of manufacturing coils and bends, including bending the tube billet with transverse forces directed towards each other and perpendicular to its axis, characterized in that the distance between the lines of action of adjacent forces directed towards each other is selected from the ratio

where l is the distance between the lines of action of neighboring forces directed towards each other, mm;
R _g is the bending radius of the tube stock, mm,
D _n - the outer diameter of the tube stock, mm;
α = 2α ₁ - the total angle of two bends of the pipe billet between the lines of action of adjacent forces directed towards each other;
α ₁ is the numerical value of the angle of one bend, calculated in radians;
S - wall thickness of the cross section of the pipe billet, mm

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