METHOD AND ARRANGEMENT FOR PROCESSING ARTICLES

Abstract

A method (100) for pressing at least one article in an arrangement as well as a pressing arrangement (500). The method comprises providing an article inside a load compartment and feeding a pressure medium into the pressure vessel and increasing (140) the pressure in the load compartment; increasing (120) the temperature and maintaining (150) the increased temperature and the increased pressure for selected periods of time (t.sub.1, t.sub.2); changing (170) the temperature from the first predetermined temperature level to a second predetermined temperature level (T.sub.2); feeding (180) a carbon-containing gas into the pressure vessel; maintaining (190) the second predetermined temperature level for a selected period of time (t.sub.3); reducing (200) the temperature in the load compartment; and discharging (210) the pressure medium from the pressure vessel and reducing (220) the pressure in the load compartment.

Claims

1. A pressing arrangement, comprising a pressure vessel, a furnace chamber provided inside the pressure vessel, a load compartment arranged inside the furnace chamber, a pressure medium feeding device for feeding pressure medium into the pressure vessel, and a gas feeding device, separate from the pressure medium feeding device, for feeding a carbon-containing gas into the pressure vessel, wherein the pressing arrangement is configured to: perform hot isostatic pressing by the following steps: receive at least one article to be processed inside the load compartment; feed a pressure medium into the pressure vessel and increase the pressure in the load compartment; increase the temperature in the load compartment; maintain the increased temperature at a first predetermined temperature level (T.sub.1) for a selected period of time (t.sub.1); maintain the increased pressure at a first predetermined pressure level (P.sub.1) for a selected period of time (t.sub.2); and thereafter, perform case hardening by the following steps: change the temperature from the first predetermined temperature level to a second predetermined temperature level (T.sub.2); feed a carbon-containing gas into the pressure vessel; maintain the second predetermined temperature level for a selected period of time (t.sub.3); reduce the temperature in the load compartment; and discharge the pressure medium from the pressure vessel and reduce the pressure in the load compartment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0039] FIG. 1 is a schematic diagram of a method for processing at least one article according to an embodiment of the present invention,

[0040] FIG. 2 is a schematic block diagram of a temperature reducing process according to an embodiment of the present invention,

[0041] FIG. 3 is a schematic diagram of a sintering process of at least one article according to an embodiment of the present invention,

[0042] FIG. 4 is a schematic diagram of a tempering process of at least one article according to an embodiment of the present invention, and

[0043] FIG. 5 is a schematic view of a pressing arrangement according to an embodiment of the second aspect of the present invention.

DETAILED DESCRIPTION

[0044] FIG. 1 is a schematic diagram of a method 100 for processing at least one article in a (pressing) arrangement. The arrangement, comprising a pressure vessel, a furnace chamber provided inside the pressure vessel, and a load compartment arranged inside the furnace chamber, may constitute a hot isostatic pressing (HIP) arrangement. It will be appreciated that the ordinate (y-axis) in FIG. 1, as well as in FIGS. 3-4, only schematically indicates (levels of) temperature, pressure and/or carbon concentration, and is not to scale. Analogously, the abscissa (x-axis) in the mentioned figures only schematically indicates time, and is not to scale.

[0045] According to the method 100 of the present invention, one or more articles to be processed by the method of the present invention are provided (arranged) inside the load compartment of the arrangement. A pressure medium, e.g. argon (Ar), is fed into the pressure vessel such that the pressure P in the load compartment increases 140. The temperature T is thereafter increased 120 in the load compartment by means of the furnace chamber. It will be appreciated that the gradients of the increasing temperature T and pressure P in the load compartment are only schematically indicated.

[0046] The increased temperature T is thereafter maintained 150 at a first predetermined temperature level T.sub.1 for a selected period of time t.sub.1. The first predetermined temperature level T.sub.1 may be 800-1500 C., preferably 1000-1300 C., and more preferably ca. 1150 C. Furthermore, the selected period of time t.sub.1 for maintaining the first predetermined temperature level T.sub.1 may be 0.1-6 hours, preferably 0.5-4 hours, and more preferably 1-2 hours. The increased pressure P is maintained 160 at a first predetermined pressure level P.sub.1 for a selected period of time t.sub.2. The first predetermined pressure level P.sub.1 may be 20-500 MPa, preferably 50-200 MPa, and more preferably 80-150 MPa. Furthermore, the selected period of time t.sub.2 for maintaining the first predetermined pressure level P.sub.1 may be 0.1-8 hours, preferably 1-5 hours, and more preferably 2-3 hours. As an alternative, the selected period of time t.sub.2 for maintaining the first predetermined pressure level P.sub.1 may be approximately the same as the selected period of time t.sub.1 for maintaining the first temperature level T.sub.1. For example, if the first predetermined temperature level T.sub.1 is decreased to the second predetermined temperature level T.sub.2, the first predetermined pressure level P.sub.1 may decrease as a result of this temperature reduction. It will be appreciated that the first predetermined temperature level T.sub.1, the time t.sub.1 for maintaining the first predetermined temperature level T.sub.1, the first predetermined pressure level P.sub.1 and/or the time t.sub.2 for maintaining the first predetermined pressure level P.sub.1 may be dependent on several factors such as the article material used.

[0047] Hence, the method 100 of the present invention maintains the temperature 150 at the first predetermined temperature level T.sub.1 and maintains the pressure 160 at the first predetermined pressure level P.sub.1, at least during the time t.sub.1 as exemplified, whereby the article(s) in the load compartment of the (pressing) arrangement are subjected to hot isostatic pressing. In other words, the exemplified settings of the temperature and the pressure of the method achieves a relatively high densification of the article(s) arranged in the arrangement, leading to an increase of the service life and/or (fatigue) strength of the processed article(s). It will be appreciated that the first predetermined temperature level T.sub.1 may be reached before, simultaneously or after the first predetermined pressure level P.sub.1 has been reached.

[0048] After performing hot isostatic pressing of the article(s), the method 100 of the present invention comprises changing 170 the temperature T from the first predetermined temperature level T.sub.1 to a second predetermined temperature level T. In FIG. 1, T.sub.2 is indicated as being lower than T.sub.1, i.e. T.sub.2<T.sub.1, but it will be appreciated that T.sub.2 alternatively may be the same or higher than T.sub.1, i.e. T.sub.2T.sub.1. As an example, T.sub.2 may be 600-1200 C., preferably 750-1050 C., and more preferably ca. 950 C. As previously indicated, the (levels of) temperature T and/or pressure P are only schematically indicated, and are not to scale.

[0049] The method 100 of the present invention thereafter comprises feeding 180 of a carbon-containing gas into the pressure vessel of the arrangement. It will be appreciated that the carbon-containing gas may be substantially any gas comprising carbon (C), such as methane, acetylene, carbon dioxide and/or carbon monoxide. The carbon concentration C of the pressure medium within the pressure vessel is schematically indicated in FIG. 1. At first, the carbon concentration C of the pressure medium increases rapidly as the carbon-containing gas is fed 180 into the pressure vessel of the arrangement. Then, the carbon concentration C of the pressure medium decreases as carbon diffuses into the material of the article(s), modifying the chemical composition of the surface of the article(s). The process of the method 100 of the present invention hereby comprises a case hardening of the article(s), which in turn comprises an initial carburizing process of the article(s) arranged in the load compartment of the arrangement. The pressure level in the (pressing) arrangement during the carburizing process of the method may be substantially the same as during the hot isostatic pressing process, i.e. P.sub.1, which may be 20-500 MPa, preferably 50-200 MPa, and more preferably 80-150 MPa, such as approximately 100 MPa. The pressure of the carbon-containing gas fed into the pressure vessel may be 10 kPa-4 MPa (0.1 bar-40 bar). It will be appreciated that the diffusion depth of carbon of the article material is dependent on several factors, such as the chemical composition of the article material, the carbon concentration C in the surrounding pressure medium, the surrounding pressure P and temperature T, the holding time, etc. Hence, the skilled person realizes that the pressure P, temperature T, carbon concentration C and/or holding time to which the article(s) is (are) subjected may be varied in the method of the present invention to achieve a desired diffusion depth of carbon of the article material. A desired concentration of carbon at the article surface may be approximately 0.8 AD. However, it will be appreciated that the desired carbon concentration at the article surface is dependent on several factors, such as the article material.

[0050] After the method 100 of the present invention has performed the carburizing of the article(s) in the case hardening process, the temperature T is reduced 200 in the load compartment. Hence, the temperature T is reduced from the second predetermined temperature level T.sub.2 to a significantly lower temperature T, e.g. ambient temperature. It will be appreciated that the reduction 200 of the temperature T in the load compartment may be relatively fast. For example, the temperature may be decreased by a rate of 200-2000 C./min in the temperature interval of 800-500 C. in the load compartment. The relatively fast temperature reduction (quenching, cooling) step of the method 100 of the present invention contributes to the formation of martensite of the high-carbon surface layer of the article(s), thereby providing article(s) comprising a wear and fatigue resistant case.

[0051] After performing the case hardening process of the method 100 of the present invention, the pressure medium is discharged from the pressure vessel and the pressure is reduced 210 in the load compartment. Eventually, after the pressure P has reached a relatively low pressure (e.g. ambient pressure), the processed article(s) may be removed from the arrangement. Consequently, the method 100 of the present invention may perform hot isostatic pressing and case hardening (including carburizing) of article(s) in the same arrangement, thereby conveniently providing article(s) comprising a wear and fatigue resistant case superimposed on a tough core.

[0052] FIG. 2 shows a schematic block diagram of the reduction 200 of the temperature (i.e. the quenching or cooling) shown in FIG. 1 in the load compartment of the (pressing) arrangement, in which one or more articles are arranged, according to an embodiment of the method of the present invention. The reduction 200 of the temperature comprises moving 250 pressure medium having a temperature at the second predetermined temperature level from the load compartment, e.g. to a space outside the load compartment. Then, pressure medium is provided 260 having a temperature below the second predetermined temperature level, and the provided pressure medium is mixed with the moved pressure medium. The thus obtained mixed pressure medium is thereafter led 270, e.g. from the space outside the load compartment, into the load compartment of the (pressing) arrangement. It will be appreciated that these steps of the embodiment of the method of the present invention may be repeated continuously during the cooling of the load compartment for an efficient cooling of the article(s) arranged therein.

[0053] FIG. 3 is a schematic diagram of a sintering process 300 of at least one pre-pressed article according to an embodiment of the present invention. The pre-pressed article(s) to be processed in the load compartment of the (pressing) arrangement may be formed from at least one (metal) powder. For example, the at least one powder may comprise water atomized metal powder and/or gas atomized metal powder. The embodiment 300 of the method of the present invention comprises increasing 310 the temperature T in the load compartment in which the pre-pressed article(s) are arranged and maintaining 320 the increased temperature at a third predetermined temperature level T.sub.3 for a selected period of time t.sub.4. It will be appreciated that the pressure P during the step of maintaining the third predetermined temperature level T.sub.3 for the selected period of time t.sub.4 may be relatively low, e.g. ambient pressure. The third predetermined temperature level T.sub.3 may, for example be 1000-1300 C., such as approximately 1150 C., and t.sub.4 may, for example, be 0.5-4 h, such as approximately 1-2 h. It will be appreciated that the third predetermined temperature level T.sub.3 and/or the time t.sub.4 for maintaining the third predetermined temperature level T.sub.3 may be dependent on several factors such as the article material used.

[0054] It will be appreciated that this sintering process 300 of the method of the present invention may take place in the same (pressing) arrangement before the hot isostatic pressing process and the case hardening process of the method of the present invention.

[0055] FIG. 4 is a schematic diagram of a tempering process 400 of at least one article according to an embodiment of the present invention. Here, the tempering process of the article(s) is performed after the hot isostatic pressing process and the case hardening process of the article(s) according to the method of the present invention, i.e. after the reduction 200 of the temperature according to FIG. 1. In the tempering process 400 of the method of the present invention, the temperature T in the load compartment is increased 410 and maintained 420 at a fourth predetermined temperature level T.sub.4 for a selected period of time t.sub.5. The fourth predetermined temperature level T.sub.4 may, for example, be 100-400 C., preferably 150-250 C., and more preferably 180-200 C. Furthermore, the selected period of time t.sub.5 for maintaining the fourth predetermined temperature level may be 0.1-4 hours, preferably 0.5-2 hours, and more preferably ca. 1 hour. It will be appreciated that the fourth predetermined temperature level T.sub.4 and/or the time t.sub.5 for maintaining the fourth predetermined temperature level T.sub.3 may be dependent on several factors, e.g. the article material used.

[0056] FIG. 5 is a schematic view of a pressing arrangement 500 according to an embodiment of the second aspect of the present invention. The pressing arrangement 500 comprises a pressure vessel 501. Although not shown in FIG. 1, the pressure vessel 501 may be opened such that the contents of the pressure vessel 501 can be removed. A furnace chamber 502 is provided inside the pressure vessel 501, and a load compartment 503 is arranged inside the furnace chamber 502 for receiving and holding one or more articles 504 to be processed. The load compartment 503 may comprise a holding arrangement 505 for holding or supporting the articles 504. It will be appreciated that the holding arrangement 505 of the load compartment 503 in FIG. 5 is only schematically indicated, and that the holding arrangement 505 may take on substantially any other form or shape for holding the articles 504, such as a cylinder shape. In FIG. 5, gear wheels constitute the example of articles 504 to be processed by the present invention. It will be appreciated that the present invention is particularly suitable for the processing of articles 504 or components such as gear wheels, as the present invention results in gear wheels having teeth cases which are wear and fatigue resistant and which are superimposed on tough teeth cores. However, the present invention may be applied to substantially any other article(s) 504 or component(s) for improving its (their) the material properties, such as cam or ring gears, bearings or shafts, etc.

[0057] The furnace chamber 502 of the pressing arrangement 500 comprises heating elements for increasing the temperature of the furnace chamber 502 and, hence, the load compartment 503 in which the article(s) 504 are arranged.

[0058] The pressing arrangement 500 further comprises a pressure medium feeding device 506, which is schematically indicated in FIG. 5, for feeding pressure medium into the pressure vessel 501 of the pressing arrangement 500. The pressure medium may, for example, be argon (Ar), but it will be appreciated that substantially any other gas or gaseous medium which has a low chemical affinity in relation to the articles to be processed may be used. The pressure medium feeding device 506 may comprise one or more compressors for increasing the pressure within the pressure vessel 501. It will be appreciated that a more detailed presentation of the pressure medium feeding device 506 is omitted, since details of such a device are known to the person skilled in the art.

[0059] The pressing arrangement 500 further comprises a gas feeding device 507 for feeding gas into the pressure vessel 501, wherein the gas feeding device 507 is schematically indicated in FIG. 5. The gas supplied to the gas feeding device 507 and fed into the pressure vessel 501 by the gas feeding device 507 may be a carbon-containing gas such as methane, acetylene, carbon dioxide, carbon monoxide, or a mixture thereof. It will be appreciated that a more detailed presentation of the gas feeding device 506 is omitted, since details of such a device are known to the person skilled in the art.

[0060] Although the pressure medium feeding device 506 and the gas feeding device 507 are shown as two separate devices in FIG. 5, it will be appreciated that the pressure medium feeding device 506 and the gas feeding device 507 may alternatively constitute a single (combined) device of the pressing arrangement 500.

[0061] It will be appreciated that the pressing arrangement 500 as presented in this context may constitute a hot isostatic press (HIP).

[0062] The pressing arrangement 500 according to the present invention is configured to receive at least one article 504 to be processed inside the load compartment 503. The pressing arrangement 500 is further configured to feed the pressure medium into the pressure vessel 501 by means of the pressure medium feeding device 506 such that the pressure in the load compartment 503 is increased. The pressing arrangement 500 is further configured to increase the temperature in the load compartment 503 by means of the furnace chamber 502. The pressing arrangement 500 is further configured to maintain the increased temperature T at a first predetermined temperature level T.sub.1 for a selected period of time t.sub.1 and to maintain the increased pressure P at a first predetermined pressure level P.sub.1 for selected periods of time t.sub.1 and t.sub.2, respectively, according to the schematic diagram of FIG. 1. The pressing arrangement 500 is further configured to change the temperature T from the first predetermined temperature level T.sub.1 to a second predetermined temperature level T.sub.2, to feed a carbon-containing gas into the pressure vessel 501 by means of the gas feeding device 507 and to maintain the second predetermined temperature level T.sub.2 for a selected period of time t.sub.3, according to the schematic diagram of FIG. 1. The pressing arrangement 500 is further configured to reduce the temperature in the load compartment 503, and to discharge the pressure medium from the pressure vessel 501 such that the pressure P in the load compartment 503 is reduced.

[0063] Consequently, it will be appreciated that the pressing arrangement 500 is configured to perform hot isostatic pressing, carburizing and case hardening of article(s) in the same pressing arrangement 500, thereby conveniently providing article(s) comprising a wear and fatigue resistant case superimposed on a tough core.

[0064] Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims. For example, the diagrams of FIGS. 1, 3 and 4 for presenting the method of the present invention are merely schematically indicated, and are not to scale. Furthermore, any sizes and/or number of units, devices or the like of the schematically indicated pressing arrangement 500 in FIG. 5 according to the second aspect of the present invention may be different than those described.