[0001] The present invention relates to a method of straightening and calibrating a railway
bogie frame by means of induction heating.
[0002] As known, railway bogie frames are made by reciprocally connecting, by means of electric
welding, metal portions shaped by means of previous production cycles; during the
electric welding operations, the metal material (typically Fe 510 D1) undergoes a
thermal cycle from ambient temperature to melting temperature and from melting temperature
to ambient temperature in a relatively short time.
[0003] The above-mentioned rapid thermal cycle creates residual strains in the metal material
of melted zones and thermally altered zones, indeed introduced by rapidly heating/cooling
the metal. The residual strains are also introduced by the use of fasteners which
are arranged on the metal portions to be welded to prevent the structure from being
excessively deformed during the welding operations.
[0004] The presence of residual strains may negatively affect the mechanical and functional
features of the railway bogie.
[0005] In order to eliminate and/or reduce the aforesaid residual strains, the railway bogie
frames undergo a strain-relieving process by arranging the whole bogie in a electric
furnace having a controlled temperature.
[0006] However, after heating the frame in the furnace, some parts of the frame itself (specifically,
some surfaces) may not be aligned with respect to the nominal shape.
[0007] In order to return the frame to its nominal shape and allow the subsequent mechanical
machining operations, a straightening and calibrating procedure is carried out by
using specific calibration tools (e.g. screw jacks) adapted to generate loads on the
frame itself, and by heating some zones of the frame in a localized manner.
[0008] The heating operations (named "hot shrinkage") should be carried out at a temperature
of 650° C in order to maximize its effects.
[0009] In particular, the heating operation is carried out by using an oxy-acetylene blowpipe,
the flame of which reaches very high temperatures (2500-3000° C) which are much higher
than the optimal heating temperatures (650° C).
[0010] Under the operative conditions shown above, the fundamental parameters for the success
of the straightening and calibrating process are: the distance of the flame from the
zone subjected to heating and the movement speed of the flame.
[0011] Such parameters are manually and empirically controlled by an operator, who indeed
carries out the heating process on the basis of his/her experience.
[0012] For this reason, the straightening and calibrating process is not always successful
because the actual difficulty in controlling the temperature of the flame may result
in metallurgic defects and/or incipient melting in the zones subjected to heating.
Such defects or such a melting must severely compromise the mechanical futures of
the railway bogie. Furthermore, the use of naked flames is potentially dangerous and
produces harmful gases.
[0013] For such a reason, indeed due to the objective difficulty of controlling the process,
the local heating operations must be limited to the minimum.
[0014] It is the object of the present invention to implement a method of straightening
and calibrating a railway bogie frame, which solves the drawbacks of the known methods.
[0015] The method consists in applying induction heating technology, which is based on the
generation of a medium frequency, variable intensity magnetic field, in a specific
device, commonly named inductor.
[0016] Induced currents (eddy currents) are generated when a metal conducting body is placed
within the magnetic field, which currents cause the heating of the piece by Joule
effect.
[0017] This result is obtained by the present invention because it relates to a method of
straightening and calibrating a railway bogie frame wherein said frame is made by
reciprocally connecting, by means of electric welding operations, metal portions shaped
by means of previous production cycles; during the electric welding operations, the
metal material undergoes a thermal cycle which produces melted zones and thermally
altered zones in which residual strains introduced by rapidly heating/cooling the
metal are present, said frame being subjected to a step of heating in a furnace which
does not completely eliminate the distortions in the frame because some parts thereof
may not be aligned with respect to the nominal shape; said straightening and calibrating
method by heating comprising the step of applying loads to said frame and punctually
heating at least one portion of the frame,
characterized in that said step of heating comprises the steps of: arranging an inductor facing said portion
and feeding an alternating current to the inductor so as to generate induced currents
in the metal portion facing the inductor; such induced currents close in the metal
portion which is heated in a concentrated, punctual manner by Joule effect.
[0018] The invention will be explained with specific reference to the accompanying drawings
which represent a preferred, non-limiting embodiment thereof, in which:
- figure 1 shows a perspective view of a railway bogie frame subjected to a straightening
and calibrating method made according to the dictates of the present invention;
- figure 2 shows a perspective view, on enlarged scale, of an inductor used according
to the method of the present invention;
- figures 3 and 4 show alternative embodiments of the inductor shown in figure 2;
- figures 5 and 6 show a further embodiment of the present invention.
[0019] In figure 1, numeral 1 shows as a whole a railway bogie frame made according to a
known process.
[0020] Specifically, the frame 1 was made by reciprocally connecting, by means of electric
welding, metal portions shaped by means of previous production cycles; during the
electric welding operations, the metal material (typically Fe 510 D1) underwent a
thermal cycle which took it from ambient temperature to melting temperature and from
melting temperature to ambient temperature in a relatively short time.
[0021] In the illustrated embodiment, frame 1 further comprises two side-members 3, connected
to each other by means of a pair of rectilinear cross-members 4. Each side-member
3 comprises two vertical walls 8 (only one of these delimiting one side facing outwards
is visible in figure 1) and two upper/lower flange plates 10,11 and a predetermined
number of internal ribs (not shown). The rectilinear cross-members 4 have a structure
similar to that of the side-members 3.
[0022] Each side-member 3 comprises a rectilinear central portion 3_a and a pair of raised
end portions 3_b which extend integrally upwards from opposite ends of the rectilinear
central portion 3_a.
[0023] The flat wall 8 is connected by welding S to the upper flange plate 10, which delimits
an upper side of the side-member 3 and to a lower flange plate 11 which delimits a
lower side of the side-member 3.
[0024] Side edges 10_a, 11_a of the upper/lower flange plates 10 and 11 protrude over the
plane defined by the side wall 8, as clearly visible in figure 2.
[0025] The frame 1 further underwent a thermal treatment in a furnace (not shown) under
controlled temperature.
[0026] According to the present invention, a local heating of a zone Z of the frame 1 is
obtained by arranging an inductor 20 facing a metal portion of the frame 1 and feeding
a medium frequency, alternating current (10-30 KHz) to the inductor 20, so as to generate
induced currents in the metal portion facing the inductor 20; such induced currents
close in the metal portion which is heated in a concentrated, punctual manner by Joule
effect, thus introducing geometric deformations in the zone Z, which contribute, along
with the action of specific calibration tools of the known type which act on the frame
1 (e.g. screw jacks, not shown), to straighten and calibrate the frame.
[0027] A straightening and calibrating process is thus carried out, consisting in locally
heating a zone Z of the frame in which an optimal temperature (approximately 650°
C) is reached, which does not damage the frame itself and does not modify the features
of the metal.
[0028] Such an optimal temperature is reached in a relatively short time (5, 6 minutes according
to the tests carried out by the applicant). The tests carried out by the applicant
have shown that the heated metal portion appears without surface/structural defects
after the local heating process, thus demonstrating that excessive local temperatures
have not been reached.
[0029] The process is implemented without requiring the use of flames and without producing
harmful gases.
[0030] The provided thermal contribution may be easily controlled by adjusting the features
of the current fed to the inductor 20.
[0031] For this purpose, the inductor 20 may be fed by the feeder (frequency converter)
known under the trademark MINAC® 50/80 from EFD INDUCTION and adapted to provide an
output power in the range of 50-80 KW and a variable frequency between 10 and 40 KHz.
[0032] The feeder may be provided with a feedback temperature control in the heated zone
Z in order to ensure the repeatability of the straightening and calibrating strain-relieving
process.
[0033] With specific reference to figure 2, the inductor 20 consisting of a tubular copper
element having a rectangular section - made according to a first variant
- comprises a plurality of turns formed by:
- a first flat, rectilinear, metal element 25a having a rectangular (or quadrangular)
section which has a first end portion connected to a first U-shaped bridge element
26a connected to a first feeding terminal 27 of the inductor 20 - the first rectilinear
element 25a having a rectangular section has a second end portion connected to a second
U-shaped bridge element 28a;
- a second flat, rectilinear, metal element 25b having a rectangular (or quadrangular)
section, having a first end portion connected to a first U-shaped bridge element 26b,
connected to a second feeding terminal 29 of the inductor 20 - the second rectilinear
metal element 25b having a rectangular section has a second end portion connected
to a second U-shaped bridge element 28b; and
- a rectilinear, metal bridge element 30 (transparently shown by dotted lines) which
is transversal to the first/second element 25a/25b which reciprocally interconnects
the first U-shaped bridge element 26a and the second U-shaped bridge element 28b.
[0034] The inductor 20 is arranged with the rectilinear elements 25a, 25b facing each other
and coplanar to the flat wall 8 and with the U-shaped bridge elements 26a,26b and
28a,28b, respectively, accommodating the edges 10_a, 11_a of the flange plates 10
and 11.
[0035] In this manner, the inductor 20 has shaped turns so as to make a profile which mimics
the profile of a section of the portion subjected to heating by forming an air gap
having a constant value (typically of 3-5 mm).
[0036] With specific reference to
figure 3, the inductor 20 - made according to a second variant - comprises a plurality of
turns formed by:
- a first flat, rectilinear metal element 35a having a rectangular (or quadrangular
section), which has a first end portion connected to a first U-shaped bridge element
36a, connected to a first feeding terminal 37 of the inductor 20;
- a second flat, rectilinear metal element 35b having a rectangular (or quadrangular
section), which has a first end portion connected to a first U-shaped bridge element
36b connected to a second feeding terminal 39 of the inductor 20; and
- a rectilinear metal element 40 which reciprocally interconnects the end portions of
the first/second flat rectilinear element 35a,35b.
[0037] The inductor 20 is arranged with the rectilinear elements 35a, 35b and 40 facing
each other and coplanar to a flat wall 42 of the frame 1 and with the U-shaped bridge
elements 36a,36b accommodating the edges 42_a of the wall 42.
[0038] Also in this case, an air gap having a constant value (typically of 3-5 mm) is formed.
[0039] With specific reference to
figure 4, the inductor 20 - made according to a third variant - is shaped so that it may be
used with a cylindrical tubular portion 44 of the frame 1 and comprises a plurality
of turns formed by:
- a first arch-shaped, metal element 50 having a rectangular section provided with end
portions 50a,50b connected to metal conductive spacer elements 51a, 51b;
- a second arch-shaped, metal element 52 having a rectangular section provided with
a first end portion, connected to the spacer element 51a, and with a second end portion,
connected to a first feeding terminal 53 of the inductor 20, which extends in a radial
direction; and
- a third arch-shaped, metal element 54 having a rectangular section, provided with
a first end portion connected to the spacer element 51b, and with a second end portion
connected to a second feeding terminal 55 of the inductor 20, which extends in a radial
direction.
[0040] In this manner, the turns lay on a cylindrical surface with is arranged at a constant
distance from the cylindrical tubular portion 44 for making the air gap having a constant
value.
[0041] A channel 60 is made, which extends through the turns and the terminals belonging
to the inductor 20 (in such a case, the turns may be formed by a rectangular-section
tube); such a channel 60 has a feeding opening in which cooling water from a feeding
circuit (not shown) is introduced, and a discharge opening. The forced flow of water
from the feeder (e.g. the frequency converter MINAC® 50/80 is adapted to generate
a cooling water flow) allows to cool the inductor 20 thus preventing a possible damage
thereof due to an extended use.
[0042] It is finally apparent that changes and variations may be made to the inductor described
and illustrated herein without therefore departing from the scope of protection defined
by the appended claims.
[0043] In particular, as shown in figures 5 and 6, an inductor 50 comprises first and second
terminals 51 and 52, connected to a system of turns made by means of the same rectangular-section,
tubular conductor used for the inductor 20. The system of turns comprises an inlet
segment 53 connected to the terminal 51, an outlet segment 54 connected to the terminal
52, a fixed branch 55 connected to the inlet segment 53 and an oscillating branch
56 connected between the fixed branch 55 and the outlet segment 54.
[0044] More in general, an inductor 50 has more than 1 branch, according to the geometry
of the cross section on which the straightening and calibrating interventions should
be carried out.
[0045] The oscillating branch 56 is advantageously connected by means of a pair of hinges
57, 58 to the inlet segment 53 and the fixed branch 55, respectively. Each hinge 57,
58 is configured to ensure the diffusion continuity of electric current and cooling
fluid from terminals 51, 52, segments 53, 54, and branches 55, 56. In particular,
each branch comprises both a fluidic circuit and an electric circuit, and such circuits
are connected in series to each other. In particular, in order to ensure the continuity
of the cooling fluid flow, each hinge 57, 58 comprises first and second elements 59,
60, each of which has a through pipe for the cooling fluid. The fluidic connection
between the first and second elements 59, 60 is preferably carried out by means of
a flexible pipe 61 connected between the through pipes (dashed line in the figure).
[0046] For example, as shown in figure 5, the path of electric current and cooling fluid
from the terminal 51 is as follows: outlet segment 53, hinge 57, oscillating branch
56, hinge 58, fixed branch 55 and outlet segment 54.
[0047] A single inductor may be mounted by means of hinges 57, 58 on each portion to be
straightened, and thus the assembly/disassembly operation may be simplified. In particular,
by means of an inductor 50 having a complex geometry which at least partially reproduces
the cross section of the bogie portions to be straightened and calibrated, such a
cross section is processed in the best possible manner, thus ensuring the high quality
of the straightening and calibrating process.
[0048] The inductor 50 is mounted as described for the inductor 20, i.e. so as to have a
substantially constant gap with respect to the cross section of the bogie portion
to the treated.
1. A method of straightening and calibrating a railway bogie frame (1) wherein said frame
(1) is formed by reciprocally connecting, by means of electric welding operations,
metal portions shaped by means of previous production cycles; during the electric
welding operations, the metal material undergoes a thermal cycle which produces melted
zones (ZF) and thermally altered zones (ZTA) in which residual strains introduced
by rapidly heating/cooling the metal are present, said frame being subjected to a
step of heating in a furnace which does not completely eliminate the distortions in
the frame because some parts thereof may not be aligned with respect to the nominal
shape;
said straightening and calibrating method by heating comprising the step of applying
loads to said frame and punctually heating at least one portion of the frame,
characterized in that said step of heating comprises the steps of: arranging an inductor (20, 50) facing
said portion and feeding an alternating current to the inductor (20, 50) so as to
generate induced currents in the metal portion facing the inductor (20, 50); such
induced currents close in the metal portion, which is heated in a concentrated, punctual
manner by Joule effect.
2. A method according to claim 1, wherein the step of adjusting the current frequency
from 10 to 40 KHz is included.
3. A method according to claim 1 or 2, wherein the step of arranging shaped conductors
forming turns of said inductor (20, 50) at a constant distance from said metal portion
for making an air gap with a constant value is included.
4. A method according to claim 3, wherein the inductor (20, 50) has turns shaped so as
to make a profile which mimics the profile of a section of the portion subjected to
heating.
5. A method according to claim 3 or 4, wherein said air gap has a value in the range
of 3-5 millimeters.
6. A method according to any one of the preceding claims, wherein the step of arranging
said inductor comprises the steps of arranging at least one first flat, rectilinear
metal element (25a) facing and coplanar to a flat wall (8) of said frame.
7. A method according to any one of the preceding claims, wherein the step of arranging
said inductor comprises the step of adjusting the position of a U-shaped bridge element
(26a,26b; 28a,28b) with respect to said frame (1) so that said U-shaped bridge element
accommodates one end edge (10_a, 11_a) of a wall (10, 11) of said frame.
8. A method according to any one of the claims from 1 to 6, wherein said inductor comprises
a plurality of turns formed by metal elements which lay on a cylindrical surface;
said method comprising the step of adjusting the position of said turns so that said
cylindrical surface has a constant distance with respect to said portion of the frame.
9. A method according to any one of the preceding claims, wherein the step of cooling
said inductor is included.
10. A method according to claim 9, wherein the step of cooling said inductor comprises
the step of making a flow of cooling fluid in a pipe which extends through the turns
made by said inductor.
11. A method according to any one of the preceding claims, wherein the inductor (50) comprises
first and second branches (55, 56) hinged to each other.
12. A method according to claims 10 and 11, comprising at least first and second hinges
(57, 58) each of which is electrically conductive and defines a pipe for the cooling
fluid, said pipe being defined by a flexible portion (61).