TITLE OF THE INVENTION Method And Apparatus For Improved Solution Heat Treatment Of Metal Castings FIELD OF THE INVENTION The present invention describes a method and apparatus for producing metal castings with an improved standardization when are treated in a solution heat treatment furnace. More specifically, the invention relates to a solution furnace that provides the same treatment for all castings, thereby achieving a high productivity yet with consistent properties while removing sand cores therefrom, especially as applied to aluminium castings (such as engine heads and blocks).

BACKGROUND OF THE INVENTION The aluminium castings used in internal combustion engines usually comprise blocks and/or cylinder heads as their main components, thus requiring strict quality levels and a high standardization of the products.

The production of an aluminum casting for intemal combustion engines commonly involves a step called solution heat treatment to improve its mechanical properties, such as hardness and machinability. Several methods have been used over the years to perform this operation while also simultaneously removing from said castings the therein-contained sand cores (normally used to form the cavities required by such castings).

U. S. Patent No. 5,829,509 (issued November 3,1998) to Crafton describes a furnace that performs the solution heat treatment and also removes the sand core. This and the other patents cited herein are incorporated by reference. Crafton proposes heat treating and ageing the casting just after the extraction from the mold with the sand core still inside and at the same time recovering the core sand for reuse. This process uses a furnace with a working chamber for receiving the casting, a heating means to increase the temperature of the working chamber such that the casting and its sand core are heated to a temperature sufficiently high to burn out the binder, and, after the binder has been burned, a flow of air directed to the heated castings to dislodge the unbound sand from the casting. Any clumps of sand core material dislodged from the casting are retained within the furnace in order to permit the binder to be thoroughly combusted,

such that the sand essentially free of binder is suitable for reuse. As it can be seen in figure 1 A, Crafton preferably provides a furnace having two levels along either of which levels respective castings can be treated. Even though this method and structure by combining heat treatment and decoring into a simultaneous operation increases significantly the productivity of the furnace and requires less floor area over the prior art furnaces, this figure lA embodiment of the furnace with its two independent bi-level processing lines does not produce acceptable uniformity in the resulting products (i. e. there is a lack of the high quality standardization required by the automotive company customers).

The applicants have determined that main reason for this disadvantage is that the castings treated only in the upper level are exposed to a higher velocity of gas and with a better temperature and quality than that of the gas when it finally reaches and contacts the separate castings which traverse only the lower level. Since the upper level castings and the rolling system cause a pressure drop in the gas from the overhead gas and heater source, the castings at the lower level do not receive a resulting gas flow as turbulent as on the higher level and since the time for the treatment is essentially the same in both levels, the castings in the lower level contain higher amounts of sand if compared with the castings processed in the higher level. In other words, by the time sand essentailly completely removed from the upper castings, it is not yet adequately removed from the lower castings. Prolonging treatment for the lower castings would help some, but would add to production costs by unnecessary overtreatment of the upper castings.

This difference becomes apparent when the castings are subsequently quenched after the solution treatment. Since quenching is required to be performed rapidly, the different amount of sand present in the castings results in different cooling profiles and, as a result, in different properties for the casting.

See also the Crafton et al. Patent No. 5,551,998 (issued September 3,1996) and its several priority-related applications listed therein.

The applicants of the present invention, without suggesting any rule, have observed that the number of castings having to be reprocessed is much higher in the castings treated in the lower level than the castings processed at the higher level.

After reviewing the drawbacks of the prior art, applicants have perceived a need for a process which takes advantage of the improved capacity of the better improved prior art furnaces but additionally produces castings having a uniform quality and a high efficiency.

Another object of the invention is to have a process where all the castings are passed through the same treating conditions and thus complying with the standardization required by the automotive industry, yet with increased furnace compactness and increased productivity.

These above-mentioned objects and other objects related to the invention will be evident to those skilled in the art, without departing from the scope of the invention.

SUMMARY OF THE INVENTION The objects of the present invention are generally achieved by providing a method and apparatus where the castings are fed to the furnace at its lower level conveyor and then, after passing through the length of the furnace, the castings are moved up to the higher level conveyor to pass back through the furnace in the opposite direction along the furnace until the solution treatment and decoring is completed.

Said improved method comprises a means for elevating the castings from the lower conveyor to the upper conveyor and also involves increasing the velocity of the castings travelling inside the furnace to at least reach the same overall productivity (but with better quality) of those furnaces with two separate treatment levels of the prior art (exemplified by Patent No. 5,829,509).

BRIEF DESCRIPTION OF THE DRAWINGS In this specification and in the accompanying drawings, some preferred embodiments of the inventions are shown and described. Various modifications and alternatives thereof have been suggested, but it is to be understood that they are not intended to be exhaustive, and that many changes and modifications can be made within the scope of the invention. The suggestions herein described are selected and included for illustrative purposes only, in order that others skilled in the art will more fully

understand the invention and the principles thereof and will thus be enabled to modify it in a variety of forms, each as may be best suited to the conditions of a particular use.

Figure 1 shows schematically a side sectional view of a preferred embodiment of the present invention, illustrating the solution heat treatment device feature of the inventive process and apparatus for removing sand cores from castings, with the elevator positioned to receive a casting from the lower level conveyor.

Figure 2 shows schematically the same solution and decoring device as in figure 1, when it is in a second working position after elevating the casting to the upper level conveyor and when it is ready to be delivered to said upper conveyor.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 shows schematically a vertically-sectioned longitudinal view of a preferred embodiment of the present invention, illustrating the solution heat treatment and decoring bi-level furnace with the elevator device positioned to receive a casting 12 (or a basket 12 containing a plurality of castings). The solution heat treatment and decoring furnace 2 has a lower conveyor level 4 and an upper conveyor level 6 wherein conveying means 14 transports baskets or castings 12. The furnace 2 also comprises fans or blowers 10 located at the top of said furnace 2 in order to provide a high velocity turbulent stream of gas properly heated by burners 8. The doors 22 and 24 are provided to be opened to feed or withdraw, respectively, the castings 12 from inside the furnace 2. When a casting 12 is fed to the furnace 2, the door 22 is opened and the casting 12 is set on the lower level conveyor 4 which conveys said castings through the furnace.

Rolls 14 can be used as conveying means, but any other means that preferably allows a low-pressure drop for the gas stream could be used. While travelling, the castings are contacted with the turbulent gas stream at high temperature and soon reach the solution heat treatment temperature. The binder contained in the sand core is also burned, promoting the erosion of said core and its removal from within the casting 12. The conveyors 4 and 6 are programmed to move at twice the usual speed relative to a prior art dual-level single-pass furnace in order to achieve the same required overall residence time for the castings. The productivity of the furnace 2 is thus maintained the same as in said prior art furnace of the same dimensions. Under this concept, the residence time of

a casting 12, while passing through the lower conveyor 4 is half the overall residence time required. When the castings 12 reach the opposite side of the furnace 2, an elevator 18 is set to receive the casting-to-be-elevated 12a. A set of conveying means 16 is operated apart from the rest of the rolls 14 to facilitate the operation. A piston 20 or any other suitable elevating means raises the casting 12a in the elevator 18 from the lower conveyor level 4 (as shown in Figure 1) to the higher conveyor level 6 (as shown in figure 2) to continue its treatment. Elevator 18 can be provided with a maintenance door 17, which can also be used advantageously when it is desired to empty the furnace, (i. e., the door 17 could be used to withdraw the castings travelling in the lower level conveyor 4). It is recommended to provide sand removing means 19 in order to prevent the excessive deposition of sand on the floor of the elevator 18. Thus, all the castings 12 are assured of travel through the upper level 6 in close contact with the more effective portion of the turbulent stream of gas provided by fans 10 to assure full decoring and effective even heat treatment prior to discharge from the furnace.

Having all the castings 12 in the furnace 2 follow the same path assures that all the castings 12 treated in the furnace 2 are processed under the same conditions and thus have the same required properties and characteristics when withdrawn through the exit door 24.

Figure 2 shows basically the same embodiment shown in figure 1, with the difference that the elevator 18 is positioned at the upper conveyor level 6 ready to deliver the casting 12a.

Even though the elevator 18 is shown in both figures 1 and 2 as an external elevator, this can be located inside the furnace 2, if desired.

The sand reclamation and/or classification mechanism taught by Patent No.

5,829,509, or other appropriate device for handling the decored sand, has not been shown but may be included as will be understood in view of the foregoing by those skilled in the art.