CA2519764A1 - Method for producing helical springs or stabilisers - Google Patents
Method for producing helical springs or stabilisers Download PDFInfo
- Publication number
- CA2519764A1 CA2519764A1 CA002519764A CA2519764A CA2519764A1 CA 2519764 A1 CA2519764 A1 CA 2519764A1 CA 002519764 A CA002519764 A CA 002519764A CA 2519764 A CA2519764 A CA 2519764A CA 2519764 A1 CA2519764 A1 CA 2519764A1
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- Prior art keywords
- rods
- temperature
- transformation
- starting material
- skew rolling
- Prior art date
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- 239000003381 stabilizer Substances 0.000 title claims abstract description 12
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 10
- 238000000034 method Methods 0.000 claims abstract description 55
- 238000005096 rolling process Methods 0.000 claims abstract description 33
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 22
- 239000010959 steel Substances 0.000 claims abstract description 22
- 238000001953 recrystallisation Methods 0.000 claims abstract description 20
- 238000010438 heat treatment Methods 0.000 claims abstract description 14
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 8
- 230000009466 transformation Effects 0.000 claims description 36
- 239000007858 starting material Substances 0.000 claims description 14
- 238000005496 tempering Methods 0.000 claims description 7
- 238000009826 distribution Methods 0.000 claims description 5
- 238000003303 reheating Methods 0.000 claims description 5
- 238000004804 winding Methods 0.000 claims description 5
- DYRBFMPPJATHRF-UHFFFAOYSA-N chromium silicon Chemical compound [Si].[Cr] DYRBFMPPJATHRF-UHFFFAOYSA-N 0.000 claims description 4
- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
- 229910000639 Spring steel Inorganic materials 0.000 claims description 2
- 238000005452 bending Methods 0.000 claims description 2
- 238000010791 quenching Methods 0.000 claims description 2
- 230000000171 quenching effect Effects 0.000 claims description 2
- 230000001131 transforming effect Effects 0.000 claims description 2
- 229910000742 Microalloyed steel Inorganic materials 0.000 claims 1
- 238000000844 transformation Methods 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 16
- 230000008569 process Effects 0.000 abstract description 14
- 230000003068 static effect Effects 0.000 abstract description 4
- 229910001566 austenite Inorganic materials 0.000 description 7
- 230000000930 thermomechanical effect Effects 0.000 description 5
- 238000001816 cooling Methods 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 239000010955 niobium Substances 0.000 description 2
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
- B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F3/00—Coiling wire into particular forms
- B21F3/02—Coiling wire into particular forms helically
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21F—WORKING OR PROCESSING OF METAL WIRE
- B21F7/00—Twisting wire; Twisting wire together
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/06—Surface hardening
- C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
- C21D1/10—Surface hardening by direct application of electrical or wave energy; by particle radiation by electric induction
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Thermal Sciences (AREA)
- Physics & Mathematics (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Articles (AREA)
- Springs (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
Abstract
The invention relates to a method for producing helical springs or stabilisers consisting of steel. According to said method, the parent material is heated to a temperature in excess of the re-crystallisation temperature, the structure is austenitised, held at an equalised temperature and then formed and subsequently quenched to form martensite and tempered. Round steel bars, whose re-crystallisation temperature is adjusted over the bar length in a compensation furnace, constitute the parent material. The round steel bars are subsequently re-modelled by cross-rolling, remaining substantially straight and after the critical deformation degree has been exceeded are subjected to dynamic re-crystallisation processes. The round steel bars are then subjected to a post-heating process above the Ac3 temperature, in order to undergo a complete static re-crystallisation, are wound to form a helical spring or bent to form a stabiliser and are finally quenched from the austenitic state to form martensite and tempered.
Description
METHOD FOR PRODUCING COIL SPRINGS OR STABILIZERS
The invention relates to a method of fihe introductory portion of claim 1 for producing coil springs or stabilizers from the steel.
A method for continuously hardening and tempering steel wire is disclosed in DE 43 40 568 C2 and contains the following steps:
~ rapidly heating the wire to a temperature in the austenite range at a rate of between 85° and 100°C/second;
~ holding the steel wire in the austenite range for a period of I 0 to 60 seconds;
~ quenching the steel wire to room temperature at a rate of more than 80°C/second;
~ rapidly heating to the to the tempering temperature at a rate of 85°
to 95 °/secand;
~ holding at the tempering temperature for a period of 60 to 100 seconds;
~ cooling the wire at the rate of more than 50°C/second, which is customary for water cooling.
Between steps 2 and 3, the wire can be rolled closely above the Ac3 temperature. At the same time, the wire is ovalized in a first roll pass, rolled round in the second roll pass and subsequently drawn through a calibrating die.
In the DE 195 46 204 C1, a method is described for producing objects of high-strength from a quenched and tempered steel and for using this method for producing springs. The steel with (in weight percent) 0.4 to 0.6% carbon, up to 1 silicon, up to 1.8% manganese, 0.8 to 1.5% chromium, 0.032 0.10% niobium and 0 to 0.2% vanadium, the remainder being iron, is produced in the following manner:
~ the raw material is solution annealed in the austenite region at temperatures from 1050° to 1200°C;
.. immediately afterward, the raw material is deformed hot in a first step at a temperature above the recrystallization temperature;
~ immediately afterward, the raw material is deformed hot in a second step at a temperature below the recrystallization temperature but above the Ac3 temperature;
~ the rolled material subsequently is maintained at a temperature above the Ac3 temperature for carrying out further transforming and processing processes and then ~ cooled to below the martensite temperature, ~ whereupon it is tempered.
The DB 196 37 968 C2 discloses a method for the high temperature, thermomechanical production of spring leaves for leaf springs andlor leaf spring linkages. The method is based on a two-step thermomechanical, production of parabolic springs and comprises the following steps:
~ the starting material is heated at a rate of between 4°C/second and 30°C/second to the austenitizing temperature;
~ the austenitizing temperature is 1100° + 100°C;
~ the material is cooled from the austenitizing temperature to the temperature of the first rolling step at a cooling rate between 10°Gs and 30°C/s.
~ Then, in the first rolling step, at a temperature of 1050° ~
100°C, with a non-constant changing of shape between 15% and 80%, it is roughed down in one or more passes.
~ It is cooled from the temperature of the first rolling step to the temperature of the second rolling step at a rate of between 10°C/secand and 30°CJsecond.
~ In the second rolling step, it is finish-rolled with rolls adjustable under load, at a temperature of 880° + 30°C with a change of shape, constant over the length of the spring leaf, of between 15% and 45%.
Finally, the DE 198 39 383 C2 discloses a method for the thermomechanical treatment of steel for tarsionally stressed spring elements, wherein the starting material is worked at a temperature above the recrysta7.lization temperature and then reshaped at such a temperature above the recrystallization temperature in at least two transformation steps, that a dynamic andlor static recrystallization of the austenite results. The austenite of the converted product, so recrystallized, is quenched and annealed. A silicon-chromium steel is to be used, which has a carbon content of 0.35 to 0.?5% and is microalloyed with vanadium or other alloying element.
The methods to be taken from the state of the art for the thermomechanical treatment of objects consisting of steel are based essentially on multiple converting steps, repeated cooling and heating of the starting material being necessary in order to produce the parameters obtained later on in the end product.
It is an object of the invention to make a method available for the production of coil springs or stabilizers of steel of the introductory portion of claim 1, the method permitting a targeted improvement in the property parameters directed to the loading profile of the end product.
This objective is accomplished by a method with the distinguishing features of claim 1.
Advantageous developments and embodiments of the method are described in claims 2 to 21.
The invention relates to a method of fihe introductory portion of claim 1 for producing coil springs or stabilizers from the steel.
A method for continuously hardening and tempering steel wire is disclosed in DE 43 40 568 C2 and contains the following steps:
~ rapidly heating the wire to a temperature in the austenite range at a rate of between 85° and 100°C/second;
~ holding the steel wire in the austenite range for a period of I 0 to 60 seconds;
~ quenching the steel wire to room temperature at a rate of more than 80°C/second;
~ rapidly heating to the to the tempering temperature at a rate of 85°
to 95 °/secand;
~ holding at the tempering temperature for a period of 60 to 100 seconds;
~ cooling the wire at the rate of more than 50°C/second, which is customary for water cooling.
Between steps 2 and 3, the wire can be rolled closely above the Ac3 temperature. At the same time, the wire is ovalized in a first roll pass, rolled round in the second roll pass and subsequently drawn through a calibrating die.
In the DE 195 46 204 C1, a method is described for producing objects of high-strength from a quenched and tempered steel and for using this method for producing springs. The steel with (in weight percent) 0.4 to 0.6% carbon, up to 1 silicon, up to 1.8% manganese, 0.8 to 1.5% chromium, 0.032 0.10% niobium and 0 to 0.2% vanadium, the remainder being iron, is produced in the following manner:
~ the raw material is solution annealed in the austenite region at temperatures from 1050° to 1200°C;
.. immediately afterward, the raw material is deformed hot in a first step at a temperature above the recrystallization temperature;
~ immediately afterward, the raw material is deformed hot in a second step at a temperature below the recrystallization temperature but above the Ac3 temperature;
~ the rolled material subsequently is maintained at a temperature above the Ac3 temperature for carrying out further transforming and processing processes and then ~ cooled to below the martensite temperature, ~ whereupon it is tempered.
The DB 196 37 968 C2 discloses a method for the high temperature, thermomechanical production of spring leaves for leaf springs andlor leaf spring linkages. The method is based on a two-step thermomechanical, production of parabolic springs and comprises the following steps:
~ the starting material is heated at a rate of between 4°C/second and 30°C/second to the austenitizing temperature;
~ the austenitizing temperature is 1100° + 100°C;
~ the material is cooled from the austenitizing temperature to the temperature of the first rolling step at a cooling rate between 10°Gs and 30°C/s.
~ Then, in the first rolling step, at a temperature of 1050° ~
100°C, with a non-constant changing of shape between 15% and 80%, it is roughed down in one or more passes.
~ It is cooled from the temperature of the first rolling step to the temperature of the second rolling step at a rate of between 10°C/secand and 30°CJsecond.
~ In the second rolling step, it is finish-rolled with rolls adjustable under load, at a temperature of 880° + 30°C with a change of shape, constant over the length of the spring leaf, of between 15% and 45%.
Finally, the DE 198 39 383 C2 discloses a method for the thermomechanical treatment of steel for tarsionally stressed spring elements, wherein the starting material is worked at a temperature above the recrysta7.lization temperature and then reshaped at such a temperature above the recrystallization temperature in at least two transformation steps, that a dynamic andlor static recrystallization of the austenite results. The austenite of the converted product, so recrystallized, is quenched and annealed. A silicon-chromium steel is to be used, which has a carbon content of 0.35 to 0.?5% and is microalloyed with vanadium or other alloying element.
The methods to be taken from the state of the art for the thermomechanical treatment of objects consisting of steel are based essentially on multiple converting steps, repeated cooling and heating of the starting material being necessary in order to produce the parameters obtained later on in the end product.
It is an object of the invention to make a method available for the production of coil springs or stabilizers of steel of the introductory portion of claim 1, the method permitting a targeted improvement in the property parameters directed to the loading profile of the end product.
This objective is accomplished by a method with the distinguishing features of claim 1.
Advantageous developments and embodiments of the method are described in claims 2 to 21.
For the inventive method, the starting material is first heated to a temperature above the recrystallization temperature and subsequently the temperature is equalized over the entire length of the rod. Furthermore, the temperature, to which the rod is heated, is kept constant virtually up to the entry of the rod into the roll gap.
With these working steps a highly uniform structure of the rod is sought, both over its length and over its cross section, before it enters the roll gap. This is of advantage for the transformation process that follows. On account of the process-specific peculiarities of the skew rolling and due to a targeted establishment of the rolling parameters, a predetermined twisting of the material in the marginal area of the rods and a transformation gradient over the cross section of the rod set in during the one-step transformation process. Since the direction of transformation during the skew rolling is at an angle to the axis of the material rolled and the maximum of the transformation is in the marginal region of the rods, the structural stretching in this marginal zone, caused by the transformation, is especially greatly pronounced and the structural alignment corresponds to the transformation direction and also extends at an angle to the axis of the rolled material. After the critical degree of transformation is exceeded, the dynamic recrystallization process takes place with special intensity in this marginal zone, so that a gradient of the degree of recrystallization from the outside to the inside may be noted over the cross section of the rod. In the reheating following the transformation process to a temperature above Ac3, the static recrystallization is completed and leads to the formation of fme-grained austenite, especially in the marginal zone. After hardening followed by tempering, the marginal zone is characterised by a fine martensite structure of great strength.
The invention has considerable advantages over the solutions known from the state of the art. As a result of the combination of a targeted, one-step transformation by means of skew rolling and a heat treatment coordinated therewith, the treated rods have a strength profile over their cross section, which reaches its maximum values in the marginal area. The direction of the twist of the structure produced by the skew railing in the marginal region of the round rods corresponds to the main direction of stress of a component subjected to torsion, and the property features developed by the rods as a result thus provide optimum prerequisites for their use especially in the spring industry. The distribution of structures over the cross section of the rod produced by the inventive method results in a property profile in the completely processed round rods, which is adequate for the stress profile over the cross section of the rod during bending and torsional stresses. Stabilizers or coil springs, produced from such a steel, may have a lesser weight for the same load.
Since only a transformation step is necessary for the development of these advantageous strength effects, and the working steps that follow are performed essentially at an elevated temperature, only a heating process for the starting material is therefore necessary. This leads to considerable savings of energy and time resulting from the procedure itself. The inventive method is distinguished therefore from known methods not only by an improvement in the stress-oriented strength and toughness properties of the finished product, but also by economic advantages offered by the minimal number of process steps.
Advantageously, the starting material, in the form of round rods, is heated inductively at a rate of 100° to 400°K/s to a temperature between 700° and 1100°C. Subsequently, the heating temperature of the rod is equalized over its length during a period of at least 10 seconds. With that, it is ensured that the temperature difference does not exceed 5°K over the length of the rod. By means of suitable reheating equipment, the heating temperature of the rod is kept constant until it enters the roll gap, The transformation itself is performed by skew rolling in a single step, in which the rods run through the roll gap, remaining straight. Depending on the quality of the starting material, the transformation is carried out preferably at a temperature ranging from 700° to 1150°C. The ratio of the starting diameter to the finished diameter is selected so that the skew rolling of the rods is performed with a mean degree of stretching 7~ of more than 1.3, and so that the maximum transformation amounts to ~y = 0.3. By the targeted setting of the rolling parameters, such as the rotational speed of the rolls and the rate of feed, and by the special selection of roll contours with specific angular relationships, it is brought about that the maximum transformation in the marginal region is between 0.65 and 1.0 of the diameter of the rods, and that a desired transformation gradient is established over the cross section of the rod. Preferably, the skew rolling process is controlled so that a maximum local temperature increase of 50°K is not exceeded in the rolled material.
Due to the transformation, after a critical degree of transformation degree is exceeded, dynamic recrystallization processes take place, which, on account of the maximum transformation, are more strongly pronotmced in the marginal zone than m the core region of the rods. The targeted influencing of the formation of a transformation gradient over the cross section of the rod has the result that the fast indications of a differentiated structure distribution appear across the cross section of the rod akeady in the course of the dynamic recrystallization. Thus, metallographic studies of rods in the recrystallized state, which have been rolled pursuant to the invention, show that the proportion of fuse austenite crystals decreases clearly from the marginal zone toward the core region.
The differentiated structural formation across the cross section of the rolled material is furthermore additionally intensified by a typical peculiarity of skew rolling. Since the direction of transformation runs at an angle to the axis of the rolled material in skew rolling, a striking stretching of structure occurs especially in the marginal areas of the material rolled due to the greater degree of transformation corresponding to the direction of transformation. The structure is also stretched at an angle to the axis of the rolled material and leads to a twisting of the material in the marginal zones. In the course of the inventive process, the direction of the twisting of the structure in the marginal region of the rods is 35 to 65 degrees of angle with respect to the longitudinal axis of the rod and thus corresponds to the main direction of stress of a component subjected to torsion.
In the process of single-step skew rolling, the entire length of the rod being rolled runs through a roll gap of constant geometry. This procedure is selected whenever rods with uniform diameter over their entire length are to be produced. The inventive method furthermore makes an alternative variation of the process possible, in which the roll gap geometry is varied in the operating state while the rod to be rolled is passing though the roll gap. This flexible manner of operation is achieved with a skew roll stand, the rolls of which can be adjusted in the axial and/or radial direction as needed during the transformation. The inventive method thus permits round rods to be produced, the diameter of which varies over the length of the rods.
Immediately a$er they exit from the roll stand, the skew-rolled rods are subject~i to repeating at a temperature above Ac3 in such a manner, that the temperature difference over the length of a rod is limited to 5°K.
Depending on their later intended use, the rods, skew-rolled and repeated to the recrystallization temperature, are either coiled hot to form coil springs or bent to form a stabilizer.
The coiled or bent components are then hardened and afterward tempered.
Rods, which are intended for manufacturing torsion bar springs, are mechanically worked at their ends in the cold state after repeating, then heated to above Ac3, quenched and tempered.
Macro-examinations of the finished rods show a typical distribution of structures over the cross sections of the rods as a consequence of the inventive combination of skew rolling and heat treatment. The immediate marginal zone has fine-grained martensite structure of high strength. The marginal area has a continuous stretching of structure extending at an angle to the axis of the rod, the direction of twist corresponding to the main direction of tension of a torsionally stressed component. The mixed pearlite-martensite structures of the core zone are coarser than the structures in the marginal area and exhibit no twisting phenomena.
To provide optimum toughness and strength parameters in the finished product, round rods of spring steel, preferably silicon-chromium steels with carbon contents of less than 0.8%, are used as starting material in the inventive method.
Alternatively, these steels can be micro-alloyed with vanadium or niobium The inventive object is represented by an embodiment in the drawing and is described as follows.
The sole Figure shows the diagrammatic arrangement of a continuous working line for the inventive thermomechanical treatment of round steel rods of a silicon-chromium steel.
The rods to be treated are heated in an induction apparatus 1 to a temperature above the recrystallization temperature, while their structure is austenitized. In the present example, the round steel rods are heated at a rate of 130°Kls to a temperature of 980°C. In an equalization furnace 2 following the induction apparatus 1, the heating temperature of the rods is equalized over a period.
of I 5 s, so that the course of the temperature over the length of the rods has a gradient of 4°K.
In this state the round steel rods, now uniform by tempered, are brought into a holding oven 3 to keep their temperature constant until they enter the roll gap.
The heated rods are transported by means of gang rolls 6 and 7, both in the equalizing oven 2 and in the holding oven 3.
In a skew rolling stand 4, the rotmd steel rods, heated to 980°C, are shaped in a rolling step. At the same time the ratio of the starting diameter to the finished diameter is chosen so that the average degree of stretching ~, is 1.5 and that the maximum transformation ~y is at least 0.3. By the targeted setting of rolling parameters, such as the roller speed or the rate of feed and by the special selection of roller contours with specific angular relationships, the maximum transformation in the marginal region between 0.65 and 1.0 of the diameter of the rods is achieved and thus a desired transformation gradient is established over the cross section of the rod. The rolling parameters are coordinated with one another so that a maximum local temperature increase of 50°K due to the transformation process is not exceeded in the material rolled. The direction of transformation at an angle to the rolling axis during the skew rolling produces in the marginal regions of the material rolled a pronounced stretching of its structure because of the greater transformation.
Corresponding to the direction of transformation, this stretching of structure likewise runs at an angle to the axis of the rolled matexial and, in the marginal regions of the rods, results in a twisting of the material. In the course of the inventive process, the direction of the twisting of the structure, with respect to the longitudinal axis of the rods, amounts to 35 to 65 degrees of angle and thus corresponds to the main direction of stress of a component subjected to torsion.
After they exit from the skew rolling stand 4, the rolled rods pass into a repeating furnace 5 downstream from the stand, in which they are repeated above the Ac3 temperature to assure complete static recrystallization. The rods are transported through the repeating furnace 5 by means of a roller conveyor 8. After leaving the repeating furnace 5 the skew-rolled rods are transported further on a transfer roller conveyor 9. From this transfer roller conveyor 9, the rods are delivered to the rest of the intended processing steps.
Figure I diagrammatically shows a production line for producing wound coil springs. Accordingly, the rods are passed over the transfer roller conveyor 9 to a lift table 10 and pass from there into a CNC winding bench 11, where the hot winding to coil springs takes place after the recrystallization. After the winding process, the rods, now wound into coil springs, are transferred to a hardening vat 12, in which they are quenched and their structure is converted to martensite. The hardened coil springs are then subjected to a tempering treatment, which is not shown.
IO
List of Reference Numbers 1. Induction apparatus 2. Equalization furnace 3. Holding oven 4. Skew rolling stand 5. Reheating furnace 6. Gang rolls 7. Gang rolls 8. Gang rolls 9. Transfer roller conveyors 10. Lift table 11. CNC winding bench 12. Hardening vat
With these working steps a highly uniform structure of the rod is sought, both over its length and over its cross section, before it enters the roll gap. This is of advantage for the transformation process that follows. On account of the process-specific peculiarities of the skew rolling and due to a targeted establishment of the rolling parameters, a predetermined twisting of the material in the marginal area of the rods and a transformation gradient over the cross section of the rod set in during the one-step transformation process. Since the direction of transformation during the skew rolling is at an angle to the axis of the material rolled and the maximum of the transformation is in the marginal region of the rods, the structural stretching in this marginal zone, caused by the transformation, is especially greatly pronounced and the structural alignment corresponds to the transformation direction and also extends at an angle to the axis of the rolled material. After the critical degree of transformation is exceeded, the dynamic recrystallization process takes place with special intensity in this marginal zone, so that a gradient of the degree of recrystallization from the outside to the inside may be noted over the cross section of the rod. In the reheating following the transformation process to a temperature above Ac3, the static recrystallization is completed and leads to the formation of fme-grained austenite, especially in the marginal zone. After hardening followed by tempering, the marginal zone is characterised by a fine martensite structure of great strength.
The invention has considerable advantages over the solutions known from the state of the art. As a result of the combination of a targeted, one-step transformation by means of skew rolling and a heat treatment coordinated therewith, the treated rods have a strength profile over their cross section, which reaches its maximum values in the marginal area. The direction of the twist of the structure produced by the skew railing in the marginal region of the round rods corresponds to the main direction of stress of a component subjected to torsion, and the property features developed by the rods as a result thus provide optimum prerequisites for their use especially in the spring industry. The distribution of structures over the cross section of the rod produced by the inventive method results in a property profile in the completely processed round rods, which is adequate for the stress profile over the cross section of the rod during bending and torsional stresses. Stabilizers or coil springs, produced from such a steel, may have a lesser weight for the same load.
Since only a transformation step is necessary for the development of these advantageous strength effects, and the working steps that follow are performed essentially at an elevated temperature, only a heating process for the starting material is therefore necessary. This leads to considerable savings of energy and time resulting from the procedure itself. The inventive method is distinguished therefore from known methods not only by an improvement in the stress-oriented strength and toughness properties of the finished product, but also by economic advantages offered by the minimal number of process steps.
Advantageously, the starting material, in the form of round rods, is heated inductively at a rate of 100° to 400°K/s to a temperature between 700° and 1100°C. Subsequently, the heating temperature of the rod is equalized over its length during a period of at least 10 seconds. With that, it is ensured that the temperature difference does not exceed 5°K over the length of the rod. By means of suitable reheating equipment, the heating temperature of the rod is kept constant until it enters the roll gap, The transformation itself is performed by skew rolling in a single step, in which the rods run through the roll gap, remaining straight. Depending on the quality of the starting material, the transformation is carried out preferably at a temperature ranging from 700° to 1150°C. The ratio of the starting diameter to the finished diameter is selected so that the skew rolling of the rods is performed with a mean degree of stretching 7~ of more than 1.3, and so that the maximum transformation amounts to ~y = 0.3. By the targeted setting of the rolling parameters, such as the rotational speed of the rolls and the rate of feed, and by the special selection of roll contours with specific angular relationships, it is brought about that the maximum transformation in the marginal region is between 0.65 and 1.0 of the diameter of the rods, and that a desired transformation gradient is established over the cross section of the rod. Preferably, the skew rolling process is controlled so that a maximum local temperature increase of 50°K is not exceeded in the rolled material.
Due to the transformation, after a critical degree of transformation degree is exceeded, dynamic recrystallization processes take place, which, on account of the maximum transformation, are more strongly pronotmced in the marginal zone than m the core region of the rods. The targeted influencing of the formation of a transformation gradient over the cross section of the rod has the result that the fast indications of a differentiated structure distribution appear across the cross section of the rod akeady in the course of the dynamic recrystallization. Thus, metallographic studies of rods in the recrystallized state, which have been rolled pursuant to the invention, show that the proportion of fuse austenite crystals decreases clearly from the marginal zone toward the core region.
The differentiated structural formation across the cross section of the rolled material is furthermore additionally intensified by a typical peculiarity of skew rolling. Since the direction of transformation runs at an angle to the axis of the rolled material in skew rolling, a striking stretching of structure occurs especially in the marginal areas of the material rolled due to the greater degree of transformation corresponding to the direction of transformation. The structure is also stretched at an angle to the axis of the rolled material and leads to a twisting of the material in the marginal zones. In the course of the inventive process, the direction of the twisting of the structure in the marginal region of the rods is 35 to 65 degrees of angle with respect to the longitudinal axis of the rod and thus corresponds to the main direction of stress of a component subjected to torsion.
In the process of single-step skew rolling, the entire length of the rod being rolled runs through a roll gap of constant geometry. This procedure is selected whenever rods with uniform diameter over their entire length are to be produced. The inventive method furthermore makes an alternative variation of the process possible, in which the roll gap geometry is varied in the operating state while the rod to be rolled is passing though the roll gap. This flexible manner of operation is achieved with a skew roll stand, the rolls of which can be adjusted in the axial and/or radial direction as needed during the transformation. The inventive method thus permits round rods to be produced, the diameter of which varies over the length of the rods.
Immediately a$er they exit from the roll stand, the skew-rolled rods are subject~i to repeating at a temperature above Ac3 in such a manner, that the temperature difference over the length of a rod is limited to 5°K.
Depending on their later intended use, the rods, skew-rolled and repeated to the recrystallization temperature, are either coiled hot to form coil springs or bent to form a stabilizer.
The coiled or bent components are then hardened and afterward tempered.
Rods, which are intended for manufacturing torsion bar springs, are mechanically worked at their ends in the cold state after repeating, then heated to above Ac3, quenched and tempered.
Macro-examinations of the finished rods show a typical distribution of structures over the cross sections of the rods as a consequence of the inventive combination of skew rolling and heat treatment. The immediate marginal zone has fine-grained martensite structure of high strength. The marginal area has a continuous stretching of structure extending at an angle to the axis of the rod, the direction of twist corresponding to the main direction of tension of a torsionally stressed component. The mixed pearlite-martensite structures of the core zone are coarser than the structures in the marginal area and exhibit no twisting phenomena.
To provide optimum toughness and strength parameters in the finished product, round rods of spring steel, preferably silicon-chromium steels with carbon contents of less than 0.8%, are used as starting material in the inventive method.
Alternatively, these steels can be micro-alloyed with vanadium or niobium The inventive object is represented by an embodiment in the drawing and is described as follows.
The sole Figure shows the diagrammatic arrangement of a continuous working line for the inventive thermomechanical treatment of round steel rods of a silicon-chromium steel.
The rods to be treated are heated in an induction apparatus 1 to a temperature above the recrystallization temperature, while their structure is austenitized. In the present example, the round steel rods are heated at a rate of 130°Kls to a temperature of 980°C. In an equalization furnace 2 following the induction apparatus 1, the heating temperature of the rods is equalized over a period.
of I 5 s, so that the course of the temperature over the length of the rods has a gradient of 4°K.
In this state the round steel rods, now uniform by tempered, are brought into a holding oven 3 to keep their temperature constant until they enter the roll gap.
The heated rods are transported by means of gang rolls 6 and 7, both in the equalizing oven 2 and in the holding oven 3.
In a skew rolling stand 4, the rotmd steel rods, heated to 980°C, are shaped in a rolling step. At the same time the ratio of the starting diameter to the finished diameter is chosen so that the average degree of stretching ~, is 1.5 and that the maximum transformation ~y is at least 0.3. By the targeted setting of rolling parameters, such as the roller speed or the rate of feed and by the special selection of roller contours with specific angular relationships, the maximum transformation in the marginal region between 0.65 and 1.0 of the diameter of the rods is achieved and thus a desired transformation gradient is established over the cross section of the rod. The rolling parameters are coordinated with one another so that a maximum local temperature increase of 50°K due to the transformation process is not exceeded in the material rolled. The direction of transformation at an angle to the rolling axis during the skew rolling produces in the marginal regions of the material rolled a pronounced stretching of its structure because of the greater transformation.
Corresponding to the direction of transformation, this stretching of structure likewise runs at an angle to the axis of the rolled matexial and, in the marginal regions of the rods, results in a twisting of the material. In the course of the inventive process, the direction of the twisting of the structure, with respect to the longitudinal axis of the rods, amounts to 35 to 65 degrees of angle and thus corresponds to the main direction of stress of a component subjected to torsion.
After they exit from the skew rolling stand 4, the rolled rods pass into a repeating furnace 5 downstream from the stand, in which they are repeated above the Ac3 temperature to assure complete static recrystallization. The rods are transported through the repeating furnace 5 by means of a roller conveyor 8. After leaving the repeating furnace 5 the skew-rolled rods are transported further on a transfer roller conveyor 9. From this transfer roller conveyor 9, the rods are delivered to the rest of the intended processing steps.
Figure I diagrammatically shows a production line for producing wound coil springs. Accordingly, the rods are passed over the transfer roller conveyor 9 to a lift table 10 and pass from there into a CNC winding bench 11, where the hot winding to coil springs takes place after the recrystallization. After the winding process, the rods, now wound into coil springs, are transferred to a hardening vat 12, in which they are quenched and their structure is converted to martensite. The hardened coil springs are then subjected to a tempering treatment, which is not shown.
IO
List of Reference Numbers 1. Induction apparatus 2. Equalization furnace 3. Holding oven 4. Skew rolling stand 5. Reheating furnace 6. Gang rolls 7. Gang rolls 8. Gang rolls 9. Transfer roller conveyors 10. Lift table 11. CNC winding bench 12. Hardening vat
Claims (21)
1. A method for producing coiled springs or stabilizers of steel, comprising the steps of: heating starting material in form of round steel rods to a temperature above the recrystallization temperature; austenizing; holding for equalization of temperature along lengths of said rods;
deforming thereafter and finally quenching to martensite and tempering; skew rolling said rods for transforming said rods while remaining substantially straight so that a predetermined twisting of the rods in a marginal area and a desired trans-formation gradient is achieved over cross-sections of said rods; exceeding a critical degree of transformation to produce dynamic recrystallization; reheating said rods to a tmperature above Ac3; winding said rods into coiled springs or bending into a stabilizer for finally hardening and tempering.
deforming thereafter and finally quenching to martensite and tempering; skew rolling said rods for transforming said rods while remaining substantially straight so that a predetermined twisting of the rods in a marginal area and a desired trans-formation gradient is achieved over cross-sections of said rods; exceeding a critical degree of transformation to produce dynamic recrystallization; reheating said rods to a tmperature above Ac3; winding said rods into coiled springs or bending into a stabilizer for finally hardening and tempering.
2. A method as defined in claim 1, wherein a twisting direction in said marginal area of said rods corresponds to a main direction of tension of the coiled springs or the stabilizer stressed by torsion.
3. A method as defined in claim 1, wherein a twisting direction in said marginal area with respect to the axes of sid rods corresponds to substantially 35-65 degrees.
4. A method as defined in claim 1, wherein said skew rolling is carried out in one step.
5.A method as defined in claim 1, wherein said skew rolling is is carried out with an average degree of stretching of at least 1.3.
6. A method as defined in claim 1, wherein maximum transformation in said marginal area is between 0.65 and 1.0 times the diameter of said rods and is at least 0.3.
7. A method as defined in claim 1, wherein said starting material is heated at a rate between 100-400°K/s.
8. A method as defined in claim 1, wherein said starting material is heated to a temperature between 700-100 degrees C.
9. A method as defined in claim 1, wherein said heating is carried out inductively.
10. A method as defined in claim 1, wherein equalization of heating along said rods occurs for at least 10 seconds.
11. A method as defined in claim 1, wherein temperature difference along length of said rods is less than 5 degrees K.
12. A method as defined in claim 1, wherein heating of said rods is held constant substantially to entry between rolls of said skew rolling step.
13. A method as defined in claim 1, wherein a maximum local temperature increase of 50 degrees K is not exceeded.
14. A method as defined in claim 1, wherein said skew rolling is carried out in a temperature range of 700 - 1000 degrees Centigrade.
15. A method as defined in claim 1, wherein rolls in said skew rolling are adjusted in an axial and/or radial direction during transformation and said rods are produced with a diameter varying over lengths of said rods.
16. Amethod as defined in claim 1, wherein temperature over lengths of said rods is limited to a maximum of 5 degrees K
during reheating above Ac3 followed by skew rolling.
during reheating above Ac3 followed by skew rolling.
17. A method as defined in claim 1, wherein said~
starting material is spring steel.
starting material is spring steel.
18. A method as defined in claim 1, wherein said starting material is silicon-chromium steel.
19. ~A method as defined in claim 1, wherein said starting material is microalloyed steel.
20. ~A coil spring produced by the method of claim 1, wherein stress distribution is equal over cross-sections of said rods. when under load.
21. ~A stabilizer produced by the method of claim 1, wherein parts stressed under torsion have substantially equal stress distribution over cross-sections of said rods when under load.
-15-~
-15-~
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10315419.1 | 2003-04-04 | ||
| DE10315419A DE10315419B3 (en) | 2003-04-04 | 2003-04-04 | Production of screw springs or stabilizers made from steel comprises comparing the heating temperature over the rod lengths and maintaining between the rollers |
| PCT/EP2004/002280 WO2004087367A2 (en) | 2003-04-04 | 2004-03-05 | Method for producing helical springs or stabilisers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2519764A1 true CA2519764A1 (en) | 2004-10-14 |
Family
ID=32115629
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002519764A Abandoned CA2519764A1 (en) | 2003-04-04 | 2004-03-05 | Method for producing helical springs or stabilisers |
Country Status (13)
| Country | Link |
|---|---|
| US (1) | US20070074792A1 (en) |
| EP (1) | EP1613449B1 (en) |
| JP (1) | JP4518415B2 (en) |
| KR (1) | KR100776954B1 (en) |
| CN (1) | CN100385020C (en) |
| AT (1) | ATE556153T1 (en) |
| BR (1) | BRPI0408916B1 (en) |
| CA (1) | CA2519764A1 (en) |
| DE (1) | DE10315419B3 (en) |
| ES (1) | ES2386720T3 (en) |
| MX (1) | MXPA05009831A (en) |
| PL (1) | PL1613449T3 (en) |
| WO (1) | WO2004087367A2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110640398A (en) * | 2019-09-05 | 2020-01-03 | 安徽东华弹簧有限公司 | Processing technology of automobile electric tail gate spring |
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| DE102005038772B4 (en) * | 2005-08-15 | 2013-04-18 | Heraeus Materials Technology Gmbh & Co. Kg | Wire of oxide dispersion strengthened Pt-Ir and other alloys with improved surface for spark plug electrodes |
| DE102006010526A1 (en) * | 2006-03-08 | 2007-09-13 | Volkswagen Ag | Spring-elastic part e.g. coil spring, manufacturing method for use in passenger car, involves carrying out cross sectional variation of rod-shaped metallic workpiece during traction process under heating up with traction force |
| KR101075323B1 (en) * | 2009-05-19 | 2011-10-19 | 대원강업주식회사 | Manufacturing method of coil spring using helicoid reduction mill |
| DE102009036512B3 (en) * | 2009-08-07 | 2011-06-16 | Schomäcker Federnwerk GmbH | Method and apparatus for producing parabolic core and parabolic springs for in particular vehicle chassis, vehicle bodies and the like. |
| CN101786221B (en) * | 2010-02-24 | 2012-07-04 | 钱江弹簧（北京）有限公司 | Method for processing arc spring |
| US8912472B1 (en) | 2010-07-19 | 2014-12-16 | Barnes Group Inc. | Induction heating of springs |
| JP5064590B1 (en) * | 2011-08-11 | 2012-10-31 | 日本発條株式会社 | Compression coil spring and method of manufacturing the same |
| DE102011112077B4 (en) | 2011-09-01 | 2013-04-11 | ThyssenKrupp Federn und Stabilisatoren GmbH | Production plant for the production of products from cylindrical metal bars |
| CN103949856B (en) * | 2014-04-25 | 2016-06-01 | 哈尔滨飞机工业集团有限责任公司 | A kind of method improving extension spring force value |
| MX2017002798A (en) | 2014-09-04 | 2017-06-15 | Thyssenkrupp Federn & Stabilisatoren Gmbh | Method for producing cold-formed steel springs. |
| JP5923155B2 (en) * | 2014-10-28 | 2016-05-24 | 日本発條株式会社 | Stabilizer manufacturing apparatus and method |
| CN106282520B (en) * | 2016-08-03 | 2018-07-10 | 浙江玛斯特汽配有限公司 | A kind of torsion-bar spring thermomechanical treatment process |
| PL445934A1 (en) * | 2023-08-29 | 2024-03-25 | Towes Spółka Z Ograniczoną Odpowiedzialnością | Method of producing springs, especially those with above-standard parameters |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2261878A (en) * | 1939-09-11 | 1941-11-04 | L A Young Spring & Wire Corp | Method of manufacturing coil springs |
| FR2477914A1 (en) * | 1980-03-17 | 1981-09-18 | Daido Steel Co Ltd | METHOD AND APPARATUS FOR MANUFACTURING CONICAL RODS |
| JP2913115B2 (en) * | 1990-10-03 | 1999-06-28 | 住友金属工業株式会社 | Manufacturing method of steel bars with ultrafine structure |
| JP2662122B2 (en) * | 1990-11-15 | 1997-10-08 | 新日本製鐵株式会社 | Manufacturing method of circular section material |
| DE4340568C2 (en) * | 1993-11-29 | 1996-04-18 | Sendner Thermo Tec Anlagen Gmb | Process for the continuous tempering of steel wire |
| EP0753595B1 (en) * | 1995-07-06 | 2001-08-08 | Benteler Ag | Pipes for manufacturing stabilisers and manufacturing stabilisers therefrom |
| DE19546204C1 (en) * | 1995-12-11 | 1997-03-20 | Max Planck Inst Eisenforschung | High strength steel object prodn.,esp. leaf spring |
| DE19637968C2 (en) * | 1996-09-18 | 2002-05-16 | Univ Freiberg Bergakademie | Process for the high-temperature thermomechanical production of spring leaves for leaf springs and / or leaf spring links |
| EP0904860A3 (en) * | 1997-09-30 | 2000-07-05 | Firma Muhr und Bender | Method and installation for manufacturing biconical wire |
| EP0974676A3 (en) * | 1998-07-20 | 2003-06-04 | Firma Muhr und Bender | Process for thermo-mechanically treating steel for torsion spring elements |
| DE19839383C2 (en) * | 1998-07-20 | 2001-04-19 | Muhr & Bender | Process for the thermomechanical treatment of steel for spring elements subject to torsion |
| JP3844622B2 (en) * | 1999-06-17 | 2006-11-15 | 新日鐵住金ステンレス株式会社 | Method for producing austenitic stainless steel bar wire |
| DE10030823C2 (en) * | 2000-06-23 | 2003-08-07 | Gmt Ges Fuer Metallurg Technol | 3-roll cross-rolling mill |
| JP4215413B2 (en) * | 2001-05-10 | 2009-01-28 | 高周波熱錬株式会社 | Manufacturing method of heat-treated deformed steel wire |
-
2003
- 2003-04-04 DE DE10315419A patent/DE10315419B3/en not_active Expired - Lifetime
-
2004
- 2004-03-05 CN CNB2004800093975A patent/CN100385020C/en not_active Expired - Fee Related
- 2004-03-05 KR KR1020057018840A patent/KR100776954B1/en active IP Right Grant
- 2004-03-05 CA CA002519764A patent/CA2519764A1/en not_active Abandoned
- 2004-03-05 MX MXPA05009831A patent/MXPA05009831A/en active IP Right Grant
- 2004-03-05 AT AT04717577T patent/ATE556153T1/en active
- 2004-03-05 EP EP04717577A patent/EP1613449B1/en not_active Expired - Lifetime
- 2004-03-05 WO PCT/EP2004/002280 patent/WO2004087367A2/en active Application Filing
- 2004-03-05 JP JP2006500053A patent/JP4518415B2/en not_active Expired - Fee Related
- 2004-03-05 ES ES04717577T patent/ES2386720T3/en not_active Expired - Lifetime
- 2004-03-05 PL PL04717577T patent/PL1613449T3/en unknown
- 2004-03-05 BR BRPI0408916-2A patent/BRPI0408916B1/en not_active IP Right Cessation
- 2004-05-03 US US10/551,538 patent/US20070074792A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110640398A (en) * | 2019-09-05 | 2020-01-03 | 安徽东华弹簧有限公司 | Processing technology of automobile electric tail gate spring |
Also Published As
| Publication number | Publication date |
|---|---|
| ATE556153T1 (en) | 2012-05-15 |
| KR20050122233A (en) | 2005-12-28 |
| JP2006522214A (en) | 2006-09-28 |
| WO2004087367A3 (en) | 2005-04-28 |
| MXPA05009831A (en) | 2005-12-05 |
| BRPI0408916A (en) | 2006-03-28 |
| WO2004087367A2 (en) | 2004-10-14 |
| JP4518415B2 (en) | 2010-08-04 |
| EP1613449A2 (en) | 2006-01-11 |
| DE10315419B3 (en) | 2004-05-19 |
| ES2386720T3 (en) | 2012-08-28 |
| PL1613449T3 (en) | 2012-10-31 |
| EP1613449B1 (en) | 2012-05-02 |
| US20070074792A1 (en) | 2007-04-05 |
| BRPI0408916B1 (en) | 2012-12-11 |
| CN100385020C (en) | 2008-04-30 |
| KR100776954B1 (en) | 2007-11-21 |
| CN1771342A (en) | 2006-05-10 |
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