(19)
(11)EP 3 353 331 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
04.11.2020 Bulletin 2020/45

(21)Application number: 16849384.9

(22)Date of filing:  19.09.2016
(51)International Patent Classification (IPC): 
C21D 9/00(2006.01)
F27D 5/00(2006.01)
C21D 1/62(2006.01)
(86)International application number:
PCT/US2016/052408
(87)International publication number:
WO 2017/053215 (30.03.2017 Gazette  2017/13)

(54)

SYSTEM FOR SUPPORTING CASTINGS DURING THERMAL TREATMENT

SYSTEM ZUR UNTERSTÜTZUNG VON GUSSSTÜCKEN BEI DER WÄRMEBEHANDLUNG

SYSTÈME POUR LE SUPPORT DE PIÈCES COULÉES PENDANT LE TRAITEMENT THERMIQUE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 23.09.2015 US 201562222407 P

(43)Date of publication of application:
01.08.2018 Bulletin 2018/31

(73)Proprietor: Consolidated Engineering Company, Inc.
Kennesaw, GA 30144 (US)

(72)Inventors:
  • CRAFTON, Scott, P.
    Marietta, GA 30064 (US)
  • SUBRAMANIAM, Shanker
    Marietta, GA 30062 (US)
  • FAUTEUX, Paul
    Douglasville, GA 30135 (US)
  • TURNER, Andrew
    Marietta, GA 30064 (US)

(74)Representative: Hofstetter, Schurack & Partner 
Patent- und Rechtsanwaltskanzlei PartG mbB Balanstrasse 57
81541 München
81541 München (DE)


(56)References cited: : 
WO-A1-2005/033345
DE-U1-202009 015 250
FR-A1- 2 296 156
US-A- 5 186 764
US-A1- 2004 108 092
US-B1- 6 224 693
DE-A1- 2 641 421
DE-U1-202015 102 175
US-A- 4 427 379
US-A- 5 271 967
US-A1- 2010 236 669
US-B1- 6 401 941
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD



    [0001] The present invention relates generally to trays and fixtures for supporting castings during thermal treatments such as solution heat treatment, quenching and aging.

    BACKGROUND



    [0002] Historically, the thermal treatment of thin wall aluminum alloy castings that have been formed in high pressure die cast (HPDC) process is problematic and often results in defective parts and high scrap rates. For example, these types of castings often have complex shapes, surface features, apertures, and variations in their cross-sectional thickness that make it difficult to apply thermal treatments to the castings in a uniform manner. It has been found that unevenly-applied thermal treatments can often create large temperature gradients through the thickness or across the expanse of the alloy material during thermal treatment, resulting in dimensional distortions that remain set within the casting material after the thermal treatments are completed and the casting has returned to an ambient equilibrium temperature. In addition, the thin wall sections of the casting can also be particularly prone to distortion if not properly supported during thermal treatments that raise the temperature of the casting to highly-elevated levels, such as those applied during a solution heat treatment, that soften the alloy material and allow portions of the part to deflect or sag under its own weight. Whether caused by temperature gradients or sagging, if the dimensional distortion of the casting after thermal treatment exceeds predetermined tolerances, the casting is generally scrapped.

    [0003] Previous attempts to control the sagging created during solution heat treatments include full position fixtures, not shown but known to one of skill in the art, that are tightly or with close tolerances clamped around the castings shortly after their removal from the die, and which then travel with the castings throughout the thermal treatments to rigidly constrain the castings to reduce sagging and other thermal distortions that could pull the metallic parts out of dimensional tolerance. By their very presence, however, the full position fixtures can often impede or block the flow of thermal fluids to portions of the casting material, thereby exacerbating the temperature gradients across the expanse of the part. This can lead to the formation of internal stresses that cause the castings to spring out of shape when the full position fixtures are removed after the thermal treatments are completed.

    [0004] DE 26 41 421 A1 and DE 20 2015 102175 U1 disclose systems for supporting castings during thermal treatments comprising the features as mentioned in the preamble of claim 1.

    [0005] Further systems for supporting castings during thermal treatments are described in WO 2005/033345 A1, US 5 186 764 A, FR 2 296 156 A1, and DE 20 2009 015250 A1.

    SUMMARY



    [0006] The present invention is directed to a system for supporting castings during thermal treatments with the features of claim 1. Briefly described, one embodiment of the present disclosure comprises a system for supporting castings during thermal treatments, such as solution heat treatment, quenching and aging, and the like, that includes a tray defining a horizontal base plane and having a plurality of tray openings therethrough. The system further includes a fixture extending over at least one of the tray openings and comprising a plurality of support plates oriented vertically with lower portions extending across the tray opening, and top edges extending above the tray opening having shaped profiles along the lengths thereof. In addition, the plurality of support plates form an open lattice having a plurality of top edges that together define an open support surface that is substantially complementary with an underside surface of a casting, and that is configured to loosely support the casting atop the lattice and orientate the casting in space above the tray opening.

    [0007] Another embodiment of the disclosure includes a system for supporting castings during thermal treatments that includes a tray having a perimeter frame comprising a pair of side bars joined together by a pair of end bars to define a horizontal base plane, with at least one crossbar extending between the side bars intermediate the end bars to form a plurality of tray openings interior to the perimeter frame. The system further includes a fixture comprising a plurality of support plates oriented vertically, with lower portions that extend across a tray opening to engage at either end with the perimeter frame or with the at least one cross bar, and with top edges that extend above the tray opening with shaped profiles along the lengths thereof. In addition, each support plate intersects with at least one other support plate to form an open lattice having a plurality of top edges that together define an open support surface that is substantially complementary with an underside surface of a casting, and that is configured to loosely support the casting atop the lattice and align the casting in space above the tray opening

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0008] 

    FIG. 1 is a perspective view of a casting support system and castings, in accordance with a representative embodiment of the present disclosure.

    FIG. 2 is a perspective view of the casting support system and a casting shown in outline, in accordance with another representative embodiment.

    FIG. 3 is a cross-sectional side view of the casting support system and casting of FIG. 2, as viewed from section line A-A.

    FIG. 4 is a perspective view of the casting support system of FIG. 2, as viewed from the opposite side.

    FIG. 5 is a close-up of one end of the cross-sectional side view of FIG. 3.

    FIG. 6 is a top view of a casting support system, in accordance with another representative embodiment.

    FIG. 7 is a schematic cross-sectional side view of the casting support system of FIG. 6, as viewed from Section Line B-B.

    FIG. 8 is a schematic cross-sectional side view of the casting support system of FIG. 6, as viewed from Section Line C-C.

    FIG. 9 is a schematic illustration of the dimensional distortions that may be present in a casting after thermal treatment.

    FIG. 10 is a cross-sectional schematic illustration of a flow of thermal fluid impinging on a casting that is carried by the casting support system of the present disclosure during a thermal treatment, in accordance with yet another representative embodiment.

    FIG. 11 is perspective view of a multi-level casting support system and castings, in accordance with yet another representative embodiment of the present disclosure.

    FIG. 12 is close-up perspective view of the multi-level casting support system and castings of FIG. 11.



    [0009] Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings may be expanded or reduced to more clearly illustrate the embodiments of the present disclosure described herein.

    DETAILED DESCRIPTION



    [0010] The following description is provided as an enabling teaching of exemplary embodiments of a system for supporting castings during thermal treatments, also known as a casting support system. Those skilled in the relevant art will recognize that changes can be made to the embodiments described, while still obtaining the beneficial results. It will also be apparent that some of the desired benefits of the embodiments described can be obtained by selecting some of the features of the embodiments without utilizing other features. In other words, features from one embodiment or aspect may be combined with features from other embodiments or aspects in any appropriate combination. For example, any individual or collective features of method aspects or embodiments may be applied to apparatus, product or component aspects, or embodiments and vice versa. Accordingly, those who work in the art will recognize that many modifications and adaptations to the embodiments described are possible and may even be desirable in certain circumstances, and are a part of the invention. Thus, the following description is provided as an illustration of the principles of the embodiments and not in limitation thereof, since the scope of the invention is to be defined by the claims.

    [0011] Illustrated in FIGS. 1-12 are several representative embodiments of a system for supporting castings during thermal treatments such as solution heat treatment, quenching and aging. As described below, the casting support system of the present disclosure can provide several significant advantages and benefits over other trays, fixtures or support systems that support and/or constrain castings, and in particular thin wall aluminum alloy castings formed in a high pressure die cast (HPDC) process, during thermal treatments. However, the recited advantages are not meant to be limiting in any way, as one skilled in the art will appreciate that other advantages may also be realized upon practicing the present disclosure.

    [0012] Illustrated in FIG. 1 is one embodiment of the casting support system 10 of the present disclosure that includes a base frame or tray 20 having a thickness and top surfaces 22 that define a horizontal base plane 24. The tray 20 also includes a plurality of vertically-aligned tray apertures or openings 26 through the thickness 28 of the tray that allow for thermal fluids such as heated air, cooling air, water, oil, and the like to pass unobstructed through the base plane 24 of the tray to impinge upon one or more castings 90 that are supported above the base plane 24. The thermal fluids can pass through the tray openings 26 before or after encountering the castings 90, depending on whether the thermal fluids are applied from below, from above, or laterally inward toward the sides of the castings. In one aspect the tray 20 can comprise a perimeter frame 30 having a pair or pairs of side bars 32 that are joined together by a pair of end bars 34 and one or more crossbars 36 extending between the side bars intermediate the end bars 34, and which together define the tray openings 26 interior to the perimeter frame 30. The various components that form the tray 20 can be manufactured from any suitable material, such as structural steel or another suitable material.

    [0013] It will be appreciated that the tray 20 is generally configured to ride on chains, a roller conveyor, or similar transfer mechanism while carrying the castings 90 through one or more thermal treatment zones, such as a furnace, a quench system, an oven, or the like, to expose the castings to the thermal treatments. In some embodiments the tray 20 can be used within a continuous process in which multiple trays 20, each supporting a group of castings 90, are carried in sequence through the thermal treatment zones. In some aspects the tray 20 can ride directly on the rollers or chains, while in other aspects the tray can include an underlying support structure (not shown) that provides an interface between the transfer mechanism and the tray 20. In other embodiments where the thermal treatments are applied in discrete batch-type furnaces or quench systems, the trays 10 may be adapted for conveyance by robotic arms, fork lift trucks, shuttle carts, or similar manipulators that move the trays and groups of castings between thermal treatments.

    [0014] The casting support system 10 further includes one or more fixtures 40 attached to the tray 20 that support and align the castings 90, such as the exemplary automotive vehicle shock towers 92 shown in the drawing, in space above one or more tray openings 26. Each fixture 40 generally comprises a plurality of support plates 42 that are oriented vertically with lower portions 44 that extend across the tray opening 26 and top edges 46 that extend above the tray openings 26, with the top edges 46 of the supports plates 42 having shaped profiles that extend along the lengths of the support plates. In one aspect each of the support plates 42 can intersect with at least one other support plate to form an open lattice 50 having a plurality of top edges that together define an open support surface that is substantially complementary or conforming with the underside surface of the casting 90, as shown in the drawing. In one aspect, the support plates 42 can include support plates 52 extending parallel to the longitudinal axis 12 of the base tray 220 and support plates 256 extending parallel to the width axis 16 of the base tray 20. However, in other aspects (not shown) the support plates may not intersect with one another, and instead can be aligned in another configuration, such as parallel, non-intersecting rows that are coupled together with beams or brackets, to define the open support surface. The various components that form the fixture 40, and especially the top edges of the support plates 42 that contact the casting 90, can be made from any suitable material, such as stainless steel or another suitable material.

    [0015] Although not limited to any particular type of casting, the casting support system 10 of the present disclosure may be particularly suitable for supporting thin wall aluminum alloy castings that have been formed in a high pressure die cast (HPDC) process by reducing many of the problems associated with the thermal treatment of these parts. For instance, as described above, thin wall aluminum alloy HPDC castings often have unique and highly-complex shapes, surface features, apertures, and variations in their cross-sectional thickness in multiple directions that make it difficult to apply thermal treatments to the castings in a uniform manner. It has been found that unevenly-applied thermal treatments can often create temperature gradients through the thickness and/or across the expanse of the alloy material, resulting in dimensional distortions that remain set within the casting material after the thermal treatments are completed and the casting has returned to an ambient equilibrium temperature. Moreover, the thin wall sections of the casting can also be particularly prone to distortion if not properly supported during thermal treatments that raise the temperature of the casting to highly-elevated levels, such as those applied during a solution heat treatment, that soften the alloy material and allow portions of the part to deflect or sag under its own weight. Whether caused by temperature gradients or sagging, if the dimensional distortion of the casting after thermal treatment exceeds predetermined tolerances, the casting is generally scrapped.

    [0016] The casting support system 10 of the present disclosure can overcome these problems by supporting each casting at key locations during high temperature solution heat treatments while still providing direct access by the thermal fluids to nearly all of the surfaces of the casting. In this way the casting support system 10 can prevent sagging while facilitating uniform and evenly-applied thermal treatments that reduce the internal temperature gradients across the treated part as the overall temperature of the part is being raised or lowered.

    [0017] For example, as shown with another representative embodiment illustrated in FIG. 2, the fixture 140 of the casting support system 110 can be individually customized to securely engage with and support a uniquely-shaped casting 190 (such as another thin wall aluminum alloy HPDC shock tower 192, shown in outline) in space above the tray opening 126. As stated above, the fixture 140 can support the casting 190 in a manner that allows the thermal fluids to have direct access to nearly all of the surfaces of the casting 190, and especially the underside surfaces 196 that might otherwise be blocked by the tray 120 or the fixture 140. In addition, the fixture 140 can also orientate the casting 190 in the space above the tray opening 126 to align portions of the casting's topside surfaces 194 and/or underside surfaces with the flow of the impinging thermal fluids, so as to better impart heat into or extract heat away from the alloy material of the casting 190 in a uniform manner.

    [0018] As illustrated in the cross-sectional side view of the casting support system 110 and casting 190 provided in FIG. 3, in some applications the casting 190 can include a highly-irregular and complex shape, as shown by the irregular profiles of the topside surface 194 and underside surface 196 along the length of the cross section. In addition, the thickness of the casting 190 between the topside and underside surfaces can also vary considerably along the cross section, resulting in thin-wall portions 193 that can be rapidly heated or cooled, and relatively thicker-walled portions 195 or structurally-dense and heavy portions 197 that require more heat input or extraction to achieve a targeted change in temperature. It will be appreciated that when a similar part is simply placed on a standard flat heat treatment tray having multiple small apertures formed therethrough, the heavier thick-wall portions of the casting can often be elevated and supported by thin-wall portions. Consequently, when the yield strength of the alloy material is reduced in a heat treatment process because of softening at solution temperature, the thin wall portions may not be sufficiently strong to support the weight of the heavier portions of the casting without deflection and deformation.

    [0019] The casting support system 110 of the present disclosure can overcome this difficulty by independently supporting each section of the casting, including each of the heavy portions 197 or thick wall portions 195 as well as the thin wall portions 193, at key locations 148 across the underside of the casting 190. This can be accomplished by providing the top edges 146 of the support plates 140 with irregular shape profiles along their lengths that are at least partially complimentary with the irregular underside surfaces 196 of the casting. Once the support plates are assembled, and optionally interconnected, together to form the lattice 150, the plurality of top edges 146 of the lattice 150 define an open support surface that is substantially complementary with, although not necessarily conforming to, the underside surface 196 of the casting. As will be understood one of skill in the art, the support surface is "open" because it is not continuous, and instead is only defined by the top edges 146 of the support plates 142 that form a pattern or grid of narrow contact lines underneath the casting. The remainder, majority portion of the "surface" is imaginary and open to the polygonal-shaped flow areas or channels defined by the vertical support plates, and that can guide separate flows of thermal fluid upward from the tray opening 126 to the underside surface 196 of the casting 190.

    [0020] The support surface defined by the plurality of top edges 146 of the support plates 142 can be substantially complimentary with the underside surface 196 of the casting 190 in that the casting may only fit atop the lattice 150, or become securely engaged by the lattice, in a single position. This engagement with the lattice can include multiple contact locations 148 having both vertical components that bear the weight of the castings and horizontal components that prevent the casting from moving or shifting laterally. Thus, once the casting 190 is settled into position atop the fixture 140, it can be securely maintained in that position as the casting tray 120 is moved through one or more thermal treatment sections and subjected to a variety of applied loads by the impinging thermal fluids. For example, the casting support system 110 can facilitate the use of directed streams of high velocity thermal fluids during thermal treatments, including but not limited to jets of high pressure air or water during a quench cycle, that would tend to reposition or shift parts that are less securely supported on a casting tray.

    [0021] Nevertheless, even though the support surface defined by the plurality of top edges 146 of the support plates 142 may be substantially complimentary with the underside of the casting 190, it need not be exactly conforming with the underside surface 196 along the length of the support plates 142. The support surface can instead include discrete contact locations 148 separated by gaps 147 where the top edges 146 are spaced from the underside surface 196 by a distance that is sufficient to allow thermal fluids to flow between the two surfaces. In one aspect the contact locations 148 between the lattice 150 and the underside 196 of the casting 190 can be judiciously located at predetermined key locations across the expanse of the underside surface that would otherwise be prone to sagging or distortion if not directly supported by the fixture 140. In this way the casting 190 can be supported in space above the opening 126 using a reduced number of key contact locations 148, while leaving the remainder of the casting surfaces directly accessible by the thermal fluids.

    [0022] Also shown in FIG. 3 is a stationary thermal treatment zone having an upper plenum 104 having downwardly-directed nozzles 105 or outlets for creating one or more downwardly-directed flows 106 of a thermal fluid (e.g. heated air in a heat treatment zone or cooling air in a quench zone) that impinge on the exposed topside surfaces 194 of the casting 190, as well as a lower plenum 107 having upwardly-directed nozzles 108 or outlets for creating one or more upwardly-directed flows 109 of the thermal fluid that impinge on the exposed underside surfaces 196 of the casting 190. In addition, the fixture 140 that supports the casting 190 is itself coupled to a tray 120 that is carried on the rollers 102 of a roller conveyance system through the thermal treatment zone. In one aspect both the downwardly-directed flows 106 and the upwardly-directed flows 109 can be substantially aligned with the thick-walled portions 195 and the structurally-dense portions 197 of the casting 190 so that more heat can be imparted into or extracted from these portions of the casing than the immediately adjacent thin-wall portions that require less heat transfer to achieve the same change in temperature. Furthermore, in one aspect the support surface defined by the plurality of top edges 146 of the support plates 142 can position and orientate the casting 190 in space to align the thick-walled portions 195 and the structurally-dense portions 197 with both sets of nozzles 105, 108. In addition, the upwardly-directed flows 109 of thermal fluid can pass substantially unimpeded through both the tray opening 126 and the lattice 150 of intersecting support plates 142 to impinge against the underside surfaces 196 of the casting 190.

    [0023] FIG. 4 is a perspective view of the casting support system 110 of FIGS. 2-3 without the casting, and illustrates the fixture 140 that is formed by, in this case, four intersecting vertical support plates 142 mounted to the tray 120 above the tray opening 126. As can be seen, in this embodiment the perimeter frame 130 of the tray 120 can include multiple pairs of side bars 132 with cylindrical cross-sections, that are coupled at their ends to end bars 134 or crossbars 136 with rectangular cross-sections, and which together define a plurality of tray openings 126 interior to the perimeter frame 130. In one aspect the side bars 132, end bars 134 and crossbars 136 can be sized and configured together to form a standardized tray 120 that can serve as a base frame with standardized dimensions, so that a variety of differently-configured fixtures 140 can be removably and interchangeably mounted over the tray openings 126. In addition, the underside surfaces of the perimeter frame 130 and cross-bars 136 can ride directly atop the rollers 102 of the conveyance system (FIG. 3), and in one aspect can be removably coupled to each other to form a modular tray 120 that can be lengthened or shortened according to a desired application, and in which a damaged side bar or end bar/crossbar can be individually removed and replaced with an undamaged component without having to replace the entire tray 120

    [0024] The fixture 140 of representative support system 110 can comprise four support plates 142 that are oriented vertically with lower portions 144 that extend across the tray opening 126 and top edges 146 that extend above the tray opening 126 and together form a lattice structure 150 in which the top edges 146 define the open support surface for the casting. In one aspect the support plates 142 can be substantially aligned with the major horizontal axes 112, 114 of the perimeter frame 130, with the lower edges 144 extending across the length or the width of the tray opening 126. In another aspect (not shown) the support plates can be aligned on the diagonal or at another angle relative the major horizontal axes of the perimeter frame 130. For the two support plates 152 of representative fixture 140 that are aligned parallel with the longitudinal axis 112 of the perimeter frame 130, the lower ends can terminate with notches 153 that engage the inner edges of the rectangular end bars 134 and crossbars 136, and may not extend across the centerlines of the crossbars 136 so as to not interfere with a fixture overlying the adjacent tray opening. For the two support plates 156 that are aligned parallel with the width axis 116 of the perimeter frame 130, the lower ends can extend outward past the side bars 132 and can include notches 157 formed into their lower edges that engage with mounting bars 138 that extend upward from the upper surfaces of the cylindrical side bars 132.

    [0025] In one aspect the support plates 142 can intersect and connect with each other at predetermined locations defined by upwardly-opening half-slots formed into a lower pair of support plates 152 that mate with downwardly-opening half-slots formed into an upper pair support plates 156, as known in the art. In this way the support plates 142 of the fixture 140 can become interlocked together to form the lattice 150 prior to attachment to the tray 120. Furthermore, and as described in more detail below, the positions of the interlocking support plates 152, 156 within the lattice 150 can be modified relative to each other and to the surrounding structure of the tray 120 to position the contact locations 148 of the top edge 146 underneath the portions of the casting that require the most support. In the illustrated embodiment this can be accomplished by adjusting the locations of the half-slots along the lengths of the support plates, with the ends of the support plates being moved a corresponding distance along the end bars 134 or crossbars 136 or along the mounting bars 138 atop the side bars 132. Nevertheless, it will be appreciated that other connection methods or mechanisms for connecting the support plates 142 to each other and to the tray 120 are also possible and considered to fall within the scope of the present invention, which is defined by the appended claims.

    [0026] Also visible in FIGS. 2-4 are the plurality of apertures 145 that can be formed through the thickness of the support plates 142 that allow the thermal fluid to flow crossways through the support plates. As shown in FIGS. 2 and 4, in one aspect the apertures 145 can be elongated in the direction of the vertical axis 118 of the support system 110. This can result in a lattice support structure 150 that is largely "transparent" to the upwardly-directed flows of thermal fluid due to the minimal amount of flat surface areas and corners oriented perpendicular to the path of the thermal fluid that could obstruct its passage and diminish its velocity. In another aspect of the fixture 140 shown in FIG. 3, however, the apertures 145 in the vertically-aligned support plates can be elongated in the direction of the major horizontal axes 112, 116 of the support system 110. This can result in a support structure 150 with a much larger amount of flat surface area and corners oriented perpendicular to the path of the thermal fluid, thereby creating a greater degree of obstruction to the upwardly-directed flow of thermal fluid that can reduce its velocity while increasing its turbulence and mixing. It will be appreciated by a person of ordinary skill in the art that, depending on the application, both options could be used to provide for an improved transfer of heat into or away from the underside surfaces of the casting.

    [0027] Castings 190 that are similar to the thin wall aluminum alloy HPDC shock tower 192 shown in FIGS. 2-3 can often include thin-wall projections of alloy material that project outwardly to define an outer edge 199 or flange (FIG. 3). These thin wall structures that are unsupported along one side can often be more susceptible to deflection or deformation during thermal treatments, and can therefore require a greater degree of support or constraint than other thin-walled internal sections of the casting that are substantially surrounded by alloy material. To provide this extra support, in one aspect the ends of the support plates 142 can include upwardly extending projections 149 that bound the outer edges 199 of the casting.

    [0028] FIG. 5 is a close-up view of the left-side end of the support plate 142 of FIG. 2, and illustrates the upwardly extending projection 149 that bounds one outer edge 199 of the casting 190. In one aspect the lower inside edge of the projection 149 can include a notch 155 that is sized to receive the outer edge 199 of the casting after accounting for the thermal growth of both the casting and the support plate during a heat treatment. In addition, the top edge 146 of the support plate 142 can provide an extended line on contact at the contact location 148 along the underside surface 196 of the thin-wall portion 193 of the casting proximate the outer edge 199. It will be appreciated that both the extended line of contact that defines the proper position of the thin-wall portion 193 and/or the notch 155 that constrains the outer edge 199 from pulling upward during heat treatment can serve to maintain the alignment and prevent deformation of the outer edge portions of the casting during a plurality of thermal treatments.

    [0029] The fixture 140 illustrated in FIGS. 2-4 can engage with the casting 190 along both the underside surfaces 196 and the outer edges 199 to securely support the casting 190 in a single position and to prevent it from accidently becoming dislodged from the fixture during thermal treatment. In other embodiments, such as casting support system 10 illustrated in FIG. 1, the fixture 40 can engage with the casting 90 primarily along its underside surfaces to securely support the casting in a single position, without necessarily engaging an outer edge.

    [0030] FIG. 6 is a top view of another representative embodiment of the casting support system 210 that also includes a fixture 240 comprising four vertically-aligned and intersecting support plates, with two of the support plates 252 extending parallel to the longitudinal axis 212 of the base tray 220 and two support plates 256 extending parallel to the width axis 116 of the base tray 220. When assembled, the support plates 252, 256 together define nine polygonal shaped flow channels 260 that can guide flows of thermal fluid upward from the tray opening 226 to the underside surface of the casting (not shown). In this embodiment one or more support plates can also include a deflector 262, 266 that extends outward into a channel to redirect the flow of thermal fluid toward an opposing support plate. In one aspect the deflector 262 can extend outward and upward in the direction of the flow 263 to redirect the flow toward the opposite side of the same channel, as shown in the cross-sectional schematic view of FIG. 7. In another aspect the deflector 266 can extend outward and downward against the direction the flow 267 to redirect the flow through an aperture 268 in the support plate and toward the opposite side of an adjacent channel, as shown in the cross-sectional schematic view of FIG. 8.

    [0031] In addition to the above-described benefits and advantages, the casting support system of the present disclosure can provide the user with additional options and flexibility in optimizing the support of any particular casting, including those with highly-irregular and complex shapes, so as to substantially reduce or eliminate dimensional distortions during thermal treatment. For example, the development of a new HPDC aluminum alloy casting can often include a set up period in which prototype castings formed with the new dies undergo a variety of thermal treatments to determine a preferred thermal treatment protocol that results in the highest yield of parts that meet end-user specifications. These protocols can often include solutionizing heat treatment, quenching and aging. With reference to FIG. 9, in one aspect accurate three dimensional measurements of the surfaces of the castings 290 can be captured first after removal from the die, and then again after passing through the thermal treatments. FIG. 9 illustrates the combination of these measurements in the form a contour map of a casting 290, in this case a thin wall aluminum alloy HPDC shock tower 292, in which an affected portion 297 of a surface 294 of the castings has experienced a substantial dimensional distortion. If this distortion is identified on a prototype casting part during the set up period as being caused by sagging, the fixture for the casting can then be modified to include an addition contact location between the top edge of the support plate and the casting 290 to better support the affected portion 297 during production runs. This could be accomplished by relocating a support plate or adding a new support plate underneath the affected portion, and/or by reshaping the top edge of a support plate that was already located beneath the affected portion.

    [0032] Moreover, as shown in FIG. 10, in another aspect the casting 390, the casting support system 310, and a thermal treatment zone 302 could be modeled during development of the thermal treatment protocol to determine the flow pattern 306 of thermal fluids, such as heated hair or cooling air, around the casting 390 and the projected heat transfer rates across the surfaces of the casting. If it is determined that the heat transfer rates are improperly balanced between the thin wall portions 393 and thick wall portions 395 in a manner that would create temperature gradients through the thickness and/or across the expanse of the alloy material, then the fixture 340 for the casting 390 could be modified to adjust the position and/or orientation of the casting 390 within the flow pattern 306, or to improve or re-direct the flow pattern to the underside the casting using one or more deflectors. In this way the casting support system 310 can be used to facilitate uniform and evenly-applied thermal treatments that reduce the internal temperature gradients across the treated casting 390 as the overall temperature of the part is being raised or lowered.

    [0033] In yet another embodiment of the casting support system 410 shown in FIGS. 11-12, the trays 420 that support the castings 490 can be stacked one above the others using risers 425 that, in one aspect, can be coupled to the end bars 434 of the perimeter frames 430. In this way multiple levels of castings 490 can be supported one above the other during one or more thermal treatments. This can greatly improve the speed and efficiency of the casting manufacturing process, especially for batch-type thermal treatment processes.

    [0034] As shown in the drawings, the base trays 420 can be formed from the modular components similar to those described above, such as the side bars 432, end bars 434, crossbars 436, and mounting bars 438 that project upward from the upper surfaces of the side bars 432, and that together define a plurality of tray apertures 426 interior to the perimeter frames 430. The modular and interchangeable tray fixtures 440 formed from a plurality of support plates, such as the intersecting support plates 432, can be mounted to the trays 420 to extend over the tray openings 426, and to define polygonal-shaped flow areas for guiding thermal fluid upward from the tray openings to the underside surfaces of the castings. Due to the largely-open design of the stackable casting support system 410 that allows for the thermal fluids to readily flow between the rows the castings 490 in addition to flowing across or around nearly all of the surfaces of the individual castings, it will be appreciated that the casting support system 410 can facilitate uniform and evenly-applied thermal treatments that can also reduce the temperature gradients across rows of castings that have grouped together for one or more thermal treatments.

    [0035] In addition, in one aspect each fixture 440 can be configured to support a plurality of castings 490, such as the set of HPDC aluminum alloy housings 492 shown in FIGS. 11-12.

    [0036] The invention has been described herein in terms of preferred embodiments and methodologies considered by the inventor to represent the best mode of carrying out the invention. It will be understood by the skilled artisan, however, that a wide range of additions, deletions, and modifications, both subtle and gross, may be made to the illustrated and exemplary embodiments without departing from the scope of the invention as defined by the appended claims. These and other revisions might be made by those of skill in the art without departing from the scope of the invention that is constrained only by the following claims.


    Claims

    1. A system for supporting castings (90, 190, 290, 390, 490) during thermal treatments such as solution heat treatment, quenching and aging, the system comprising:

    a tray (20, 120, 220, 420) defining a horizontal base plane and having a plurality of tray openings (26, 126, 226) therethrough; and

    a fixture (40, 140, 240, 340, 440) extending over at least one tray opening, the fixture (40, 140, 240, 340, 440) comprising a plurality of support plates (42, 142) oriented vertically with lower portions extending across the at least one tray opening (26, 126, 226) and top edges (46, 146) extending above the at least one tray opening (26, 126, 226) with shaped profiles along the lengths thereof, the plurality of support plates (42, 142) having a plurality of top edges that together define an open support surface that is complementary with an underside surface of a casting (90, 190, 290, 390, 490) and configured to loosely support the casting (90, 190, 290, 390, 490) atop the open support surface and orientate the casting (90, 190, 290, 390, 490) in space above the tray opening (26, 126, 226),

    characterized in that

    the top edges (46, 146) of the support plates (42, 52, 142, 152) define narrow contact lines underneath the casting (90, 190, 290, 390, 490) and have irregular shaped profiles along the lengths thereof and together define an irregular open support surface that is complementary with an irregular underside surface of the casting (90, 190, 290, 390, 490).


     
    2. The system of claim 1, wherein
    said tray (20, 120, 220, 420) includes a perimeter frame (30, 130, 430) having a pair of side bars (32, 132, 432) joined together by a pair of end bars (34, 134, 434) to define said horizontal base plane, and having at least one crossbar (36, 136, 436) extending between the side bars (32, 132, 432) intermediate the end bars (34, 134, 434) to form said plurality of tray openings (26, 126, 226) interior to the perimeter frame (30, 130, 430); and
    said fixture (40, 140, 240, 340, 440) comprises said plurality of support plates (42, 142) oriented vertically with lower portions extending across said tray opening (26, 126, 226) to engage at either end with the perimeter frame (30, 130, 430) or with the at least one cross bar, and top edges (46, 146) extending above the tray opening (26, 126, 226) with shaped profiles along the lengths thereof, with each of the plurality of support plates (42, 142) intersecting with at least one other support plate (52, 152) to form an open lattice (50, 150).
     
    3. The system of claim 1, wherein each support plate (42, 142) intersects with at least one other support plate (52, 152) to form a lattice (50, 150).
     
    4. The system of claim 1 or 2, wherein the plurality of intersecting support plates (42, 52, 142, 152) further define a plurality of channels having polygonal-shaped flow areas for guiding a flow of thermal fluid upward from the tray opening (26, 126, 226) to the underside surface of the casting (90, 190, 290, 390, 490).
     
    5. The system of claim 4, further comprising at least one deflector extending outward from a support plate for redirecting the flow of thermal fluid through a channel toward an opposing support plate.
     
    6. The system of claim 1 or 2, wherein the ends of the support plates (42, 52, 142, 152) include upwardly extending projections that bound at least two opposing outer edges of the casting (90, 190, 290, 390, 490).
     
    7. The system of claim 6, wherein the upwardly extending projections include notches formed into the inside edges thereof and configured to receive the outer edges of the casting (90, 190, 290, 390, 490) in a heated and thermally-expanded state.
     
    8. The system of claim 1 or 2, further comprising at least one additional tray (20, 120, 220, 420) having an additional fixture supported above the first tray and fixture to form a vertical rack for loosely supporting and aligning a plurality of castings (90, 190, 290, 390, 490) in space above one another and the at least one tray opening (26, 126, 226).
     
    9. The system of claim 2, further comprising apertures formed through the thickness of the support plates (42, 52, 142, 152) to allow a cross flow of a thermal fluid through the support plates (42, 52, 142, 152).
     
    10. The system of claim 9, wherein the apertures are elongated and substantially aligned with a vertical axis of the system.
     
    11. The system of claim 2, wherein the support plates (42, 52, 142, 152) are substantially aligned with the perimeter frame (30, 130, 430) with lower edges that extend across a width or a length of the tray opening (26, 126, 226).
     
    12. The system of claim 2, wherein the tray (20, 120, 220, 420) is made from a structural steel material and the support plates are made from a stainless steel material.
     
    13. The system of claim 2, wherein the fixture (40, 140, 240, 340, 440) is removably secured to the tray (20, 120, 220, 420); or wherein the fixture (40, 140, 240, 340, 440) is removably secured to the tray (20, 120, 220, 420) and the perimeter frame (30, 130, 430) further includes mounting bars (138, 438) extending upward from the upper surfaces of the side bars (32, 132, 432) and configured for engagement within complimentary notches formed into the lower edges of the support plates (42, 52, 142, 152).
     
    14. The system of claim 2, wherein the open lattice (50, 150) is adapted to support at least two castings (90, 190, 290, 390, 490) above the tray opening (26, 126, 226).
     


    Ansprüche

    1. System zum Abstützen von Gussstücken (90, 190, 290, 390, 490) während Wärmebehandlungen wie z. B. Lösungsglühen, Abschrecken und Aushärten, wobei das System umfasst:

    eine Ablage (20, 120, 220, 420), die eine horizontale Basisebene definiert und eine Vielzahl von Ablageöffnungen (26, 126, 226) durch diese aufweist; und

    eine Halterung (40, 140, 240, 340, 440), die sich über mindestens eine Ablageöffnung erstreckt, wobei die Halterung (40, 140, 240, 340, 440) eine Vielzahl von vertikal orientierten Stützplatten (42, 142) mit unteren Abschnitten, die sich über die mindestens eine Ablageöffnung (26, 126, 226) erstrecken, und oberen Kanten (46, 146), die sich oberhalb der mindestens einen Ablageöffnung (26, 126, 226) erstrecken, mit geformten Profilen entlang der Längen davon umfasst, wobei die Vielzahl von Stützplatten (42, 142) eine Vielzahl von oberen Kanten aufweist, die zusammen eine offene Stützoberfläche definieren, die zu einer Unterseitenoberfläche eines Gussstücks (90, 190, 290, 390, 490) komplementär ist und dazu ausgelegt ist, das Gussstück (90, 190, 290, 390, 490) oberhalb der offenen Stützoberfläche locker abzustützen und das Gussstück (90, 190, 290, 390, 490) im Raum oberhalb der Ablageöffnung (26, 126, 226) zu orientieren, dadurch gekennzeichnet, dass

    die oberen Kanten (46, 146) der Stützplatten (42, 52, 142, 152) schmale Kontaktlinien unterhalb des Gussstücks (90, 190, 290, 390, 490) definieren und unregelmäßige geformte Profile entlang der Längen davon aufweisen und zusammen eine unregelmäßige offene Stützoberfläche definieren, die zu einer unregelmäßigen Unterseitenoberfläche des Gussstücks (90, 190, 290, 390, 490) komplementär ist.


     
    2. System nach Anspruch 1, wobei

    die Ablage (20, 120, 220, 420) einen Umfangsrahmen (30, 130, 430) mit einem Paar von Seitenleisten (32, 132, 432), die durch ein Paar von Endleisten (34, 134, 434) miteinander verbunden sind, um die horizontale Basisebene zu definieren, und mit mindestens einer Querleiste (36, 136, 436), die sich zwischen den Seitenleisten (32, 132, 432) zwischen den Endleisten (34, 134, 434) liegend erstreckt, um die Vielzahl von Ablageöffnungen (26, 126, 226) innerhalb des Umfangsrahmens (30, 130, 430) zu bilden, umfasst; und

    die Halterung (40, 140, 240, 340, 440) die Vielzahl von vertikal orientierten Stützplatten (42, 142) mit unteren Abschnitten, die sich über die Ablageöffnung (26, 126, 226) erstrecken, um an beiden Enden mit dem Umfangsrahmen (30, 130, 430) oder mit der mindestens einen Querleiste in Eingriff zu kommen, und oberen Kanten (46, 146), die sich oberhalb der Ablageöffnung (26,126, 226) erstrecken, mit geformten Profilen entlang der Längen davon umfasst, wobei jede der Vielzahl von Stützplatten (42, 142) mindestens eine andere Stützplatte (52, 152) schneidet, um ein offenes Gitter (50, 150) zu bilden.


     
    3. System nach Anspruch 1, wobei jede Stützplatte (42, 142) mindestens eine andere Stützplatte (52, 152) schneidet, um ein Gitter (50, 150) zu bilden.
     
    4. System nach Anspruch 1 oder 2, wobei die Vielzahl von sich schneidenden Stützplatten (42, 52, 142, 152) ferner eine Vielzahl von Kanälen mit polygonförmigen Durchflussflächen zum Führen einer Strömung von Wärmefluid nach oben von der Ablageöffnung (26, 126, 226) zur Unterseitenoberfläche des Gussstücks (90, 190, 290, 390, 490) definiert.
     
    5. System nach Anspruch 4, das ferner mindestens eine Ablenkeinrichtung, die sich von einer Stützplatte nach außen erstreckt, zum Umlenken der Strömung von Wärmefluid durch einen Kanal in Richtung einer gegenüberliegenden Stützplatte umfasst.
     
    6. System nach Anspruch 1 oder 2, wobei die Enden der Stützplatten (42, 52, 142, 152) sich nach oben erstreckende Vorsprünge umfassen, die mindestens zwei gegenüberliegende äußere Kanten des Gussstücks (90, 190, 290, 390, 490) begrenzen.
     
    7. System nach Anspruch 6, wobei die sich nach oben erstreckenden Vorsprünge Kerben umfassen, die in den inneren Kanten davon ausgebildet sind und dazu eingerichtet sind, die äußeren Kanten des Gussstücks (90, 190, 290, 390, 490) in einem erhitzten und wärmeausgedehnten Zustand aufzunehmen.
     
    8. System nach Anspruch 1 oder 2, das ferner mindestens eine zusätzliche Ablage (20, 120, 220, 420) mit einer zusätzlichen Halterung umfasst, die über der ersten Ablage und Halterung abgestützt ist, um ein vertikales Gestell zum lockeren Abstützen und Ausrichten einer Vielzahl von Gussstücken (90, 190, 290, 390, 490) im Raum übereinander und über der mindestens einen Ablageöffnung (26, 126, 226) zu bilden.
     
    9. System nach Anspruch 2, das ferner Durchlässe umfasst, die durch die Dicke der Stützplatten (42, 52, 142, 152) ausgebildet sind, um eine Querströmung eines Wärmefluids durch die Stützplatten (42, 52, 142, 152) zu ermöglichen.
     
    10. System nach Anspruch 9, wobei die Durchlässe länglich und im Wesentlichen auf eine vertikale Achse des Systems ausgerichtet sind.
     
    11. System nach Anspruch 2, wobei die Stützplatten (42, 52, 142, 152) im Wesentlichen auf den Umfangsrahmen (30, 130, 430) mit unteren Kanten, die sich über eine Breite oder eine Länge der Ablageöffnung (26, 126, 226) erstrecken, ausgerichtet sind.
     
    12. System nach Anspruch 2, wobei die Ablage (20, 120, 220, 420) aus einem Strukturstahlmaterial besteht und die Stützplatten aus einem Edelstahlmaterial bestehen.
     
    13. System nach Anspruch 2, wobei die Halterung (40, 140, 240, 340, 440) abnehmbar an der Ablage (20, 120, 220, 420) befestigt ist; oder wobei die Halterung (40, 140, 240, 340, 440) abnehmbar an der Ablage (20, 120, 220, 420) befestigt ist und der Umfangsrahmen (30, 130, 430) ferner Montageleisten (138, 438) umfasst, die sich von den oberen Oberflächen der Seitenleisten (32, 132, 432) nach oben erstrecken und zum Eingriff mit komplementären Kerben gestaltet sind, die in den unteren Kanten der Stützplatten (42, 52, 142, 152) ausgebildet sind.
     
    14. System nach Anspruch 2, wobei das offene Gitter (50, 150) dazu ausgelegt ist, mindestens zwei Gussstücke (90, 190, 290, 390, 490) oberhalb der Ablageöffnung (26, 126, 226) abzustützen.
     


    Revendications

    1. Système pour le support de pièces coulées (90, 190, 290, 390, 490) pendant des traitements thermiques tels qu'un traitement thermique en solution, une trempe et un vieillissement, le système comportant :

    un plateau (20, 120, 220, 420) délimitant un plan de base horizontal et ayant une pluralité d'ouvertures de plateau (26, 126, 226) à travers ceux-ci; et

    un dispositif de fixation (40, 140, 240, 340, 440) s'étendant sur au moins une ouverture de plateau, dans lequel le dispositif de fixation (40, 140, 240, 340, 440) comporte une pluralité de plaques de support (42, 142) orientées verticalement dont les parties inférieures s'étendent sur l'au moins une ouverture de plateau (26, 126, 226) et les bords supérieurs (46, 146) s'étendent au-dessus de l'au moins une ouverture de plateau (26, 126, 226) avec des profils profilés sur leurs longueurs, dans lequel la pluralité de plaques de support (42, 142) a une pluralité de bords supérieurs délimitant ensemble une surface de support ouverte qui est complémentaire avec une surface inférieure d'une pièce coulée (90, 190, 290, 390, 490) et configuré pour soutenir librement la pièce coulée (90, 190, 290, 390, 490) au-dessus de la surface de support ouverte et orienter la pièce coulée (90, 190, 290, 390, 490) dans l'espace au-dessus de l'ouverture de plateau (20, 120, 220, 420),
    caractérisé en ce que

    les bords supérieurs (46,146) des plaques de support (42, 52, 142, 152) délimitent des lignes étroites de contact en-dessous de la pièce coulée (90, 190, 290, 390, 490) et comportent des profils profilés irréguliers sur leurs longueurs et ensemble délimitent une surface irrégulière de support ouverte qui est complémentaire avec une surface irrégulière inférieure de la pièce coulée (90, 190, 290, 390, 490).


     
    2. Système selon la revendication 1, dans lequel

    ledit plateau (20, 120, 220, 420) comporte un cadre périphérique (30, 130, 430) ayant une paire de barres latérales (32, 132, 432) réunie par une paire de barres d'extrémité (34, 134, 434) pour délimiter ledit plan de base horizontal et ayant au moins une barre transversale (36, 136, 436) s'étendant entre les barres latérales (32, 132, 432) intermédiaires des barres d'extrémité (34, 134, 434) pour former ladite pluralité d'ouvertures de plateau (26, 126, 226) à l'intérieur du cadre périphérique (30, 130, 430); et

    ledit dispositif de fixation (40, 140, 240, 340, 440) comporte ladite pluralité de plaques de support (42, 142) orientées verticalement dont les parties inférieures s'étendent sur ladite ouverture de plateau (26, 126, 226) pour s'engager à l'une ou l'autre extrémité avec le cadre périphérique (30, 130, 430) ou avec l'au moins une barre transversale, et les bords supérieurs (46,146) s'étendent au-dessus de l'ouverture de plateau (26, 126, 226) avec des profils profilés sur leurs longueurs dont chacune des pluralités de plaques de support (42, 142) se croisent avec au moins une autre plaque de support (52, 152) pour former un treillis ouvert (50, 150).


     
    3. Système selon la revendication 1, dans lequel chaque plaque de support (42, 142) se croise avec au moins une autre plaque de support (52, 152) pour former un treillis (50, 150).
     
    4. Système selon la revendication 1 ou 2, dans lequel la pluralité de plaques de support (42, 52, 142, 152) qui se croisent délimitent en outre une pluralité de canaux ayant des sections transversales d'écoulement de forme polygonale pour diriger un débit de fluide thermique depuis le dessus de l'ouverture de plateau (26, 126, 226) vers la surface inférieure de la pièce coulée (90, 190, 290, 390, 490).
     
    5. Système selon la revendication 4 comportant en outre au moins un déflecteur s'étendant de l'extérieur d'une plaque de support pour rediriger le débit de fluide thermique à travers un canal vers une plaque de support opposée.
     
    6. Système selon la revendication 1 ou 2, dans lequel les extrémités des plaques de support (42, 52, 142, 152) comportent des saillies s'étendant vers le haut qui limitent au moins deux bords extérieurs opposés de la pièce coulée (90, 190, 290, 390, 490).
     
    7. Système selon la revendication 6, dans lequel les saillies s'étendant vers le haut comportent des entailles formées dans les bords intérieurs de celles-ci et configurées pour recevoir les bords extérieurs de la pièce coulée (90, 190, 290, 390, 490) dans un état chauffé et thermiquement expansé.
     
    8. Système selon la revendication 1 ou 2 comportant en outre au moins un plateau (20, 120, 220, 420) supplémentaire ayant un dispositif de fixation supplémentaire supporté au-dessus du premier plateau et du premier dispositif de fixation pour former un bâti vertical pour soutenir librement et aligner une pluralité de pièces coulées (90, 190, 290, 390, 490) dans l'espace les unes au-dessus des autres et l'au moins une ouverture de plateau (26, 126, 226).
     
    9. Système selon la revendication 2 comportant en outre des orifices formés à travers l'épaisseur des plaques de support (42, 52, 142, 152) pour permettre un écoulement transversal d'un fluide thermique à travers les plaques de support (42, 52, 142, 152).
     
    10. Système selon la revendication 9, dans lequel les orifices sont allongés et sensiblement alignés avec un axe vertical du système.
     
    11. Système selon la revendication 2, dans lequel les plaques de support (42, 52, 142, 152) sont sensiblement alignées avec le cadre périphérique (30, 130, 430) avec des bords inférieurs qui s'étendent sur une largeur ou une longueur de l'ouverture de plateau (26, 126, 226).
     
    12. Système selon la revendication 2, dans lequel le plateau (20, 120, 220, 420) est fabriqué à partir d'un matériau en acier de construction et les plaques de support sont fabriquées d'un matériau en acier inoxydable.
     
    13. Système selon la revendication 2, dans lequel le dispositif de fixation (40, 140, 240, 340, 440) est fixé au plateau (20, 120, 220, 420) de manière amovible ou dans lequel le dispositif de fixation (40, 140, 240, 340, 440) est fixé au plateau (20, 120, 220, 420) de manière amovible et le cadre périphérique (30, 130, 430) comporte en outre des barres de montage (138, 438) s'étendant depuis le dessus des surfaces supérieures des barres latérales (32, 132, 432) et étant configurées pour un engagement dans des entailles complémentaires formées dans les bords inférieurs des plaques de support (42, 52, 142, 152).
     
    14. Système selon la revendication 2, dans lequel le treillis ouvert (50, 150) est adapté pour soutenir au moins deux pièces coulées (90, 190, 290, 390, 490) au-dessus de l'ouverture de plateau (26, 126, 226).
     




    Drawing























    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description