BORGOGNO, Alessandro (Viale Fulvio Testi, Milano, I-20162, IT)
PORTO, Gianluca (Via Valle 9, Borgaro Torinese, I-10071, IT)
GIUDICI, Raoul (Via Monza 41, Giussano, I-20034, IT)
BASSI, Stefano (Via Sant'Anna 22, Nerviano, I-20014, IT)
BORGOGNO, Alessandro (Viale Fulvio Testi, Milano, I-20162, IT)
PORTO, Gianluca (Via Valle 9, Borgaro Torinese, I-10071, IT)
GIUDICI, Raoul (Via Monza 41, Giussano, I-20034, IT)
CLAIMS
1. A lubrication process for a die for press-forging metal products made, in particular, with non-ferrous alloys, characterised in that it provides for the injection of nitrogen and of a lubricating fluid and for the introduction into the die cavity of a stream of said nitrogen and lubricating fluid.
2. A process according to claim 1, characterised in that said lubricating fluid is of a mineral and/or synthetic and/or graphitised type.
3. A process according to claim 1 or 2, characterised in that said nitrogen is injected in gaseous form, at a pressure between 7 and 30 bars, preferably in the range of 10 to 15 bars.
4. A process according to anyone of the preceding claims, characterised in that said nitrogen is injected at a temperature between the ambient temperature and 50 0 C below the ambient temperature, preferably about 15-20° C below the ambient temperature.
5. A process according anyone of to the preceding claims, characterised in that before the introduction of said stream of nitrogen and of lubricating fluid onto said die, nitrogen is injected to displace the oxygen and to create an inert atmosphere.
6. A lubricating system for a die for press-forging metal products made, in particular, with non-ferrous alloys, comprising at least an injector (7) connected to fluid delivery means to inject a lubricating fluid into the die cavity, characterised in that it comprises nitrogen supply means (80, 81, 82, 83) to deliver a nitrogen stream towards said injector (7) into which it is injected with the lubricating fluid.
7. A system according to claim 6, characterised in that said nitrogen supply means comprise a cryogenic tank (80) containing liquid nitrogen and a vaporiser (81) in which the nitrogen is vaporised to be sent to the injector (7) at a suitable temperature and pressure for the injection with the lubricating fluid.
8. A system according to claim 7, characterised in that said vaporiser (81) is connected to the injector (7) by means of a delivery line (82) provided with solenoid valves (83) controlled by a control panel (84) to regulate the nitrogen pressure and flow rate. |
LUBRICATING SYSTEM AND METHOD FOR A PRESS-FORGING DIE
DESCRIPTION
The present invention refers to a lubrication system for a die for press-forging metal products made, in particular, with non-ferrous alloys such as brass, bronze and the like for the production, for example, of valve bodies, connectors and the like.
With reference to Figure I 5 the technology for press-forging metal products according to the prior art is shown diagrammatically. A press 100 comprises a die 1 integral with a fixed table 2 and a movable counter-die 3.
Step 1 : A billet 4 to be press-forged, generally hot (pre-heated by means of a furnace alongside the press), is placed (normally by hand) between the die 1 and the counter-die 3 of the press.
Step 2: The counter-die 3 is closed on the die 1 and, thanks to the high-pressure it exerts on the billet 4, it deforms said billet so as to take on the shape of the final forging 5. In this step, a heat plastic deformation of the billet 4 therefore occurs.
Step 3: When the press-forging operation is completed, the counter-die 3 is removed from the working area, then the forging 5 is picked up and placed in a suitable container. During this step, the counter-die 3 reaches high speeds.
Step 4: The die 1 is cleaned and lubricated by spraying thereon through nozzles a stream 6 based on a lubricant fluid (typically mineral-based and/or synthetic-based), through the use of compressed air, generally taken from a company pneumatic network; the cycle then begins again from the step 1.
This known process presents some drawbacks, especially in the lubrication step 4 of the die, in which the simultaneous presence of a combustible, of a comburent and of a trigger gives rise to combustion in suitable temperature and pressure conditions.
In fact, during the step 4, there is the presence of a combustible (the lubricating fluid), of a comburent (the oxygen contained in the compressed air) and of a trigger (the hot die, at
a temperature greater than 300°C), in favourable pressure and temperature conditions (in this case, the ambient conditions are sufficient). Even in the case of dies cooled on the inside by means of a water system, the temperature thereof, though cooled, nevertheless remains above the ignition threshold of the stream of compressed air and of lubricating fluid and a combustion is therefore triggered.
This combustion leads to the oxidation of a part of the lubricating fluid, with subsequent formation of black carbon residues which, when the press-forging process is repeated, tend to increase in volume and to aggregate, forming very hard carbon residues. These hard carbon residues remain on the die 1 and, at each press-forging, rub on the die, tending to cause a damage thereof by wear. Moreover, these hard carbon residues do not allow the hot billet 4 to take on the exact geometry of the die, producing wastes among the forgings 5 produced under these conditions (the perfect heading of the shape formed by the die and by the counter die is prevented).
As a result, it becomes necessary to stop the press, to replace the die and to clean it. In any case, in this cleaning step the die is subjected to a cooling cycle, which is necessary because it is not possible to intervene at press-forging temperatures, and to a cleaning with chemical means (aggressive solvents) and/or with mechanical means (sand blasting or grit blasting), which attack its surface, damaging it at each cleaning. Afterwards, the die has to be mounted on the machine again, subjecting it to a new heating cycle to prevent the difference in temperature between the billet and the cold die from damaging the die structure, creating cracks.
Thus, besides the long machine downtimes to replace the die, two phenomena that shorten the life of the die also occur, namely the heating cycle and the cleaning.
Moreover, during the lubrication step 4 of the die, in which a stream of air and of lubricant is directed into the die, the personnel manning the press run the risk of burns due to a possible ignition of the air-lubricant mixture. This risk cannot be eliminated except by a costly inertisation of the whole working area of the press. Fans are known for this purpose that serve to direct onto the press, and thus onto the die, a high flow of air to prevent the ignition of the air-lubricant mixture.
Object of the present invention is to overcome the drawbacks of the prior art by providing a lubrication system for a die for press-forging metal products that is able to allow a
better cleaning, lubrication and cooling of the die, which are reflected in a higher quality of the product and in an increased average life of the die.
Yet another object of the present invention is to provide such a lubrication system for a die for press-forging metal products that allows a fast production cycle, cutting to a minimum the machine downtimes for the cleaning and the cooling of the dies.
Another object of the present invention is to provide such a lubrication system for a die for press-forging metal products that is safe and practical for those operating it.
These objects are achieved in accordance with the invention with the characteristics listed in appended independent claims 1 and 6.
Advantageous embodiments of the invention are apparent from the dependent claims.
The applicant has surprisingly discovered that, instead of using a stream of air and of a lubricant for the lubrication of the die, the compressed air could be replaced with pressurised nitrogen, by modifying only the lubrication system of existing dies and no other part of the machine and/or of the manufacturing process.
The lubrication system for a die for press-forging non-ferrous alloy products, according to the invention, presents the following advantages: an improvement in the die cleaning (or rather a reduction in the operating and maintenance costs of the press), an increase in the production, a lengthening of the die life and a general improvement in safety conditions.
The use of a stream of nitrogen and of lubricant drastically reduces the formation of carbon residues, in that it eliminates one of the factors giving rise to these residues, namely the presence of oxygen. The nitrogen, being an inert gas, does not allow the combustion to be triggered between the lubricant and the hot die, protecting it from the combustion phenomena; it is thus possible to reduce drastically the number of die cleanings.
By reducing the formation of the carbon residues, the frequency of maintenance is reduced, reducing the number of interventions during the manufacturing cycle.
The present invention, by reducing the frequency of machine downtimes for maintenance, allows the potential of the production line to be exploited better, obtaining a greater yield therefrom and ensuring an increase in production deriving from the reduction in downtimes with no production. The reduction in the machine downtimes for maintenance can be quantified in the order of 50-60% as a rule.
Moreover, the system according to the invention uses a gas at a higher pressure than that of the factory compressed air system (5-6 bars). By so doing, the gas delivered from the nozzles will be colder thanks to the greater pressure jump (δP) that is obtained on passing from 10-12 bars to the ambient pressure. Assuming that the nitrogen behaves similarly to a perfect gas, it can be calculated that the heat jump will be proportional to the pressure jump according to the formula:
δT = k-δP
Consequently, the final temperature of the nitrogen-lubricant stream will be lower than that of the air-lubricant stream. In fact, the nitrogen will be injected with the lubricant at a temperature about 15-20 °C below the ambient temperature. The low temperature of the nitrogen-lubricant stream leads to the following advantages:
- it contributes to keeping the temperature of the dies under control, avoiding a sudden cooling thereof and preserving the temperature range at which they work optimally; - it allows a more even and less marked wear in the critical points due to thermal and mechanical stresses (also attributable to the rubbing of the carbon deposits on the dies); and
- it allows an appreciable increase in die life.
The nitrogen used in the die lubrication process is under different pressure conditions than those of the air in the company pneumatic network (compressed air: 5-7 bars; pressurised nitrogen: 10-12 bars).
Using the nitrogen at appreciably higher pressures than those normally used with the compressed air allows the lubricating fluid to be nebulised better and conveyed more evenly onto the surface of the die, improving the lubrication thereof. Lastly, the continuous use of an inert gas allows a surface cleaning of the dies that is reflected in a greater cleanness of the components.
It should be considered that the die maintenance operations carry the risk of accidents to the operators. The contact with heated and possibly moving parts and the use of abrasive
mechanical means or of chemical means for the cleaning thereof are possible sources of danger for the safety of the personnel involved. The possibility of significantly reducing the number of maintenance interventions required means that the ensuing level of risk can be lowered. As a result, the production lines are easier to run.
Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplifying and therefore non-limiting embodiment thereof, illustrated in the appended drawings, in which:
Figure 1 is a diagrammatic view of a press according to the prior art, illustrated during four steps in the press-forging process for metal products;
Figure 2 is a diagrammatic view of the lubricating system according to the invention.
With reference to Figure 2, the lubricating system according to the invention, indicated as a whole with the reference numeral 8, comprises a cryogenic tank 80, a vaporiser 81 and at least one injector 7 adapted to inject a lubricating fluid onto the die.
The nitrogen in liquid form is stored in the cryogenic tank 80 and sent to the vaporiser 81 in which it is vaporised under pressure and temperature conditions suitable for the process. The nitrogen leaving the vaporiser 81 is at a pressure between 7 and 30 bars, preferably in the range of 10 to 15 bars, and a temperature that can range between the ambient temperature and 50 °C below the ambient temperature, preferably about 15-20 0 C below the ambient temperature.
A delivery line 82 provided with solenoid valves 83 controlled by a control panel 84 to regulate the pressure and the flow rate of the nitrogen is situated at the outlet from the vaporiser 81.
The injector 7 has a first inlet 71 connected to the nitrogen delivery line 82 and a second inlet 72 connected to the machine hydraulic system delivering the lubricant. A nitrogen and lubricant fluid 73 thus flows out from the injector 7.
Said lubricant can be of mineral and/or synthetic and/or graphitised type.
It is possible to manage the introduction of the nitrogen a certain time in advance of that of the lubricant fluid so as to displace the oxygen present in that area. Instead of starting a flow of nitrogen and of lubricant at the same time, it is possible to start the introduction
of the nitrogen into the injector 7 - and thus onto the die - a fraction of a second earlier so as to remove the air in the area above the die. In this manner the nitrogen sprayed without lubricating fluid displaces the oxygen of the air from the die and prepares an inert or almost inert environment on the die for the stream of nitrogen and lubricant.
Numerous changes and modifications of detail within the reach of a person skilled in the art can be made to the present embodiment of the invention without thereby departing from the scope of the invention, as set forth in the appended claims.