WO2009116005A1

WO2009116005A1 - Method and machine for manufacturing spring-guide sections

Info

Publication number: WO2009116005A1
Application number: PCT/IB2009/051159
Authority: WO
Inventors: Bruno Gili
Original assignee: Oreiller, Mariella
Priority date: 2008-03-21
Filing date: 2009-03-19
Publication date: 2009-09-24
Also published as: EP2257396A1; ITTO20080221A1

Abstract

Method and machine for manufacturing semicircular arc-shaped spring-guide sections (G), wherein flat strips (B) of hardened and tempered non-alloy carbon steel are dimensionally controlled, induction heated to austenitising temperature, and then moulded to form a semicircular arc-shape and simultaneously cooled martensitic temperature.

Description

"Method and machine for manufacturing spring-guide sections"

* * *

Field of the invention The present invention refers to the manufacturing of generally semi-circular arc-shaped spring-guide sections, of the type used in torsional dampers of automobile friction clutches, generally known to the art by the name DMFW ("Dual Mass Fly Wheels") . State of the prior art

The current method of manufacturing spring-guide sections thus made traditionally provides for the use of flat strips (one of which is represented in figure 1) obtained by cutting an annealed strip of extra mild steel Fe₃O₄. These strips are cold deformed to obtain the final semicircular arc-shaped configuration with concave transverse section, as represented in figure 2. The section thus deformed is then subjected to a stress relieving treatment process, followed by a mechanical finishing and by a surface hardening thermochemical treatment, called "Nitrotec NQ15".

As known to those skilled in the art, such treatment provides for four subsequent steps:

- carbonitroration, - oxidation,

- quenching,

- impregnation with organic substances.

A hardened layer, usually having a maximum thickness of 0.15 mm, structured from the surface towards the core in four zones is made in such manner on the surface of the spring-guide section: Fe₃O₄ oxide layer connection layer: nitrides, nitrites, carbonitrites, _ nitrogen and austenite layer, diffusion zone rich with nitrogen.

With such treatment the maximum surface hardness attainable by the section is of about 650 HV, due to which an enhanced resistance to wear of the spring- guide section during use is attained, specifically regarding the effects of the mutual sliding of the surfaces at contact between the spring-guide and springs .

However, such conventional method leads to a series of problems.

Firstly, the core of the sections thus made is relatively soft (the maximum hardness is in the order of 200 HV) and characterised by the low mechanical properties of the selected steel, which is optimal for making pipes for transporting fluids but it is actually unsuitable in applications where there might be the presence of high stresses amounting to millions of cycles, as in the case of spring-guide sections this invention refers to. As a matter of fact, these sections thus treated using the conventional methods are subject to yielding under stress, which leads to the consequent failure of the clutch friction leading to the reparation costs related thereof.

A further problem of the conventional method is related to its insufficient productivity, in that each piece must necessarily remain in a thermal treatment oven for a considerable period of time, generally not lower than at least one hour. Summary of the invention The object of the present invention is that of overcoming the abovementioned drawbacks, and providing a method for manufacturing spring-guide sections of the type defined above capable of ensuring excellent mechanical properties of the produced pieces, and more in particular in particular high surface and core hardness, with lower cycle times.

The method according to the invention is essentially characterised in that the flat strips for manufacturing arc-shaped spring-guide sections are of hardened and tempered non-alloy carbon steel, particularly C55 steel, which are controlled dimensionally and thus subjected to a quick induction heating up to an austenitising temperature, immediately followed by moulding by means of a press and simultaneous cooling to martensitic temperature.

The heating temperature is typically comprised between 900 and 950⁰C, reached in an induction oven within a period of rime normally comprised between 15 and 30 seconds. Subsequently to the cooling step, the sections can be further conveniently subjected to a stress relieving, typically at a temperature of 180⁰C.

According to another aspect, the invention also has the object of a machine for continuously actuating the abovementioned method, wherein the step of pressing the induction heated strips and simultaneous cooling of the moulded sections is conveniently performed in a protected atmosphere, typically under nitrogen, with the advantage of not requiring further surface finishing operations for the sections exiting from the machine .

Brief description of the drawings

The invention shall now be described in detail with reference to the attached drawings, strictly provided for exemplifying and non-limiting purposes, wherein:

- figure 1 is a perspective view which shows an initial strip for manufacturing a spring-guide section through the method and the machine according to the invention, - figure 2 is a perspective view which shows the arc-shaped spring-guide section obtained at the end of the manufacturing process, and

- figure 3 is a perspective schematic view which shows the essential components of the machine for implementing the manufacturing method according to the invention .

Detailed description of the invention Figure 2 schematically shows a spring-guide section G made using the method and the machine according to the invention. The spring-guide section G is generally semicircular arc-shaped with a concave transverse section having a cylindrical surface and - as mentioned it is made starting from a flat steel strip, indicated with B in figure 1, typically having a length in the order of 25 cm and a width of 1 mm.

According to a first aspect of the invention, the steel of which the strip B is made is a hardened and tempered non-alloy carbon steel typically -though not exclusively- a C55 steel. Other hardened and tempered non-alloyed steels useable for making the band from which the strips B are cut can be C50, C68 and C70.

The strip B is obtained by cutting a quenched and tempered band and it is possibly subjected to a preliminary finishing treatment, which however is not deemed strictly necessary.

Now, referring to figure 3 following are detailed descriptions of the steps of the method for manufacturing the section G starting from the strip B, as performed by the automatic machine whose essential components are schematised in figure 3.

The treating process is substantially performed in continuous supplying the strips B to a rotating holder

1, for example provided with a lifting and sorting device . From the holder 1 the strips B are picked by means of a vacuum manipulator 2 and deposited one at a time on a guide 3 at which the dimensional control is performed, through generally known methods, to verify whether the length, width and thickness of each strip B fall within the preset tolerances.

The non-conforming strips B are thus unloaded by the manipulator 2, while those ascertained suitable are transferred one at a time, by means of a suitable pusher not illustrated in that it is known to a man skilled in the art, into an induction oven 4, also of the generally conventional type.

Each strip B is subjected to quick heating, typically within a period of time comprised between 15 and 30 seconds, until the austenitising temperature of the steel is reached, usually comprised between 900 and 950⁰C.

Possibly, but not necessarily, the strip B inside the inductor 4 may be subjected to a first heating followed by a stabilisation and by a subsequent heating at austenitising temperature: however, a single heating cycle up to the temperature indicated above is considered preferred, in that more advantageous for production purposes.

At the end of the induction heating the strip B is thus subjected to a cooling at martensitic temperature, to complete the tempering treatment, while it is simultaneously shaped to acquire the final arc-shape. This is attained by means of a press 5, preferably vertical, with an immobile mould 6 and mobile counter- mould 7 both cooled, typically by means of circulation of a cooling liquid therein.

The induction heating oven 4 and the press 5 for moulding and simultaneous cooling are conveniently enclosed in a protected atmosphere environment, typically under nitrogen. At the end of the moulding and cooling step, the spring-guide sections G are sent to an unloading section .

The cycle thus performed by the machine according to the invention is entirely automatic and substantially performed continuously, within considerably shorter periods of time with respect to the conventional methods, described previously, currently used for making the same sections. The sections G can may thus be subjected to a final stress relieving treatment, at a temperature un the order of 180⁰C, performed for example by means of an oven with external resistors with respect to the machine, and it does not require further finishing operations.

The spring-guide sections G thus made have excellent mechanical and control properties for the deformations, alongside a high surface and core hardness (above 650 HV) . Experimental tests performed by the Applicant show that such spring-guide sections G thus made are capable of excellently overcoming resonance tests and fatigue tests of over 1.5 millions of cycles at 3000 rpm.

Obviously, the construction details of the machine for implementing the method may be widely varied with respect to that described and illustrated, without departing from the scope of protection of the present invention as defined by the following claims.

Claims

1. Method for manufacturing a semicircular arc- shaped spring-guide section (G) for torsional dampers of automobile clutch frictions, characterised in that it comprises the following operations:

- providing a flat strip (B) made of hardened and tempered non-alloy carbon steel, subjecting the strip (B) to quick heating by means of induction up to the austenitising temperature, - subjecting the strip (B) to moulding under a press (5) simultaneously cooling it to a martensitic temperature .

2. Method according to claim 1, characterised in that the induction heating temperature is generally comprised between 900 and 950⁰C.

3. Method according to claim 1 or 2, characterised in that the induction heating time is generally comprised between 15 and 30 seconds.

4. Method according to any one of the preceding claims, characterised in that it further includes the step of dimensionally controlling the flat strip (B) before the induction heating thereof.

5. Method according to one or more of the preceding claims, characterised in that the arc-shaped spring- guide section (G) is further subjected to a final stress relieving operation at a temperature in the order of 180⁰C.

6. Method according to one or more of the preceding claims, characterised in that the hardened and tempered non-alloy carbon steel is selected from among C50, C55, C68 and C70.

7. Machine for manufacturing a semicircular arc- shaped spring-guide sections (G) for torsional dampers for automobile friction clutches, made according to one or more of claims 1 - 6, characterised in that it comprises :

- means for induction heating said steel strips (B) to austenitising temperature, - means (5) for moulding the heated strips (B) for semicircular arc-shaping (G) thereof and simultaneous cooling to martensitic temperature.

8. Machine according to claim 7, characterised in that said moulding and simultaneous cooling means include a press (5) with cooled mould and counter- mould (6, 7) .

9. Machine according to claim 7 or 8, characterised in that it further comprises means (3) for dimensionally controlling said flat strips (B) upstream of said induction heating means (4) .

10. Machine according to any one of claims 7 - 9, characterised in that it further comprises means (2) for automatically supplying strips (B) from a rotating holder (1) to said induction heating means (4) .

11. Machine according to one or more of the preceding claims, characterised in that said induction heating means (4) and said moulding and simultaneous cooling means (5) are enclosed in a protected atmosphere environment (8) .