Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1999-02-09
2001-03-13
Pyon, Harold (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S124000, C164S125000, C148S543000, C148S545000
Reexamination Certificate
active
06199618
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a process for producing castings such as engine blocks, etc., out of cast iron with lamellar graphite.
2. Description of the Related Art
Castings find use in nearly every branch of industry such as in machine tool construction, in semi-finished products, in the construction of furnaces and heating systems, in engine construction, and finally also in the chemical industry. To save weight, it is desirable to produce castings with thin walls but still with sufficient strength, but this requires that the molten cast iron have good flow behavior. It is known that an elevated carbon content promotes the flowability of the molten cast iron. The carbon content of the cast iron can be controlled by the make-up of the charge and by the way in which the furnace is operated. Cast iron is usually melted in a cupola furnace. Nevertheless, the melting process can also be carried out in a rotary furnace or in an electric furnace. After the melt has been poured, the casting usually remains in the mold until it has cooled to about 300° C. The structural state achieved during this cooling process is usually accepted as is, even though it is known that effects can be exerted on the microstructural condition and thus on the mechanical properties of the casting by the use of certain cooling conditions. To achieve specific types of mechanical properties, it is conventional practice to produce alloyed cast iron by the addition of special additives such as copper, chromium, phosphorus, antimony, manganese, microalloys, etc.
For many types of castings, including especially the engine blocks of internal combustion engines, it is desirable for certain areas of the casting to be harder or to have higher strength values than other areas of the same casting.
SUMMARY OF THE DESCRIPTION
The task of the present invention is to produce castings with mechanical properties which, with respect to hardness and strength, can be influenced in a predetermined manner by the formation of appropriate microstructures. In accordance with the present invention, the carbon content of the cast iron is adjusted to approximately 3-4% carbon in the melt by control of the melting process through adjustments to the charge make-up and/or to the operation of the melting furnace. The melt is then poured into a mold in the sand-casting or lost-form method. The casting is removed from the mold at a temperature in the range of 1,100-800° C. Immediately afterward, the casting is subjected to a cooling treatment by a stream of air to remove all traces of mold material from the casting and selected areas of the casting are cooled to a point below the eutectoid range by short, aimed, intermittent blasts of air for obtaining improved mechanical properties. The cooling treatment is stopped after the temperature drops below the temperature of the eutectoid range. As a result of this treatment, there is no longer any need to add alloying materials to the charge or to the cast iron melt, because it is possible to give certain partial areas of the casting superior mechanical properties in the manner indicated without involving the entire casting. Thus, when the casting is machined later, only the areas which have the superior mechanical properties need to be cut with expensive tools. The other areas can be machined with simple, conventional tools. The increased hardness of certain areas of the cast iron is compensated by an increase in the carbon content to 3-4%, and preferably to a C content of 3.6-3.8%, which can be achieved by control of the melting process, i.e., by adjusting the make-up of the charge and/or the operation of the melting furnace and the subsequent pouring of the melt by the sand-casting or lost-form process. Thus the areas of the casting which have not been given extra hardness by additional intermittent air blasts can be machined in the simple, conventional way. Castings of through-alloyed cast iron or cast iron which has been hardened all the way through would be more expensive to machine as a result of the increased tool wear.
To eliminate internal stresses in the casting after the cooling treatment, it is advantageous, after the cooling treatment, to return the casting in steps to a small residual temperature in a holding furnace to avoid residual stresses.
To harden selected areas of the casting, separate blasts of air are directed onto the predetermined surface areas, these blasts being calculated in such a way as to produce a hardness of more than 220 HB. It is also preferable to calculate the cooling times of both the continuous, general air stream and the separate air blasts in such a way as to obtain a tensile strength of at least 250 N/mm
2
. The amount of cooling air for the continuous, general air stream, the amount of air for the separate air blasts, and the cooling times can be determined on the basis of experience, that is, empirically. To standardize the process with respect to reproducibility, it is advantageous from an economic standpoint to use an EDP system including a camera and a monitor to control and to program the cooling treatment of the casting with respect to cooling intensity, the continuous air stream, and the pulsating, individually directable air blasts. For this purpose, it is preferable to position the castings on a continuous conveyor, so that they can pass through the treatment line where they are subjected to the continuous air stream and the intermittent air blasts. Although various methods for conducting the castings through the treatment section can be imagined, it is advantageous to use a continuous conveyor in the form of an apron conveyor with insertable retaining edges for holding the castings in position. At least the settings of the nozzles which deliver the air blasts should be adjustable, and they should be able to move along with the apron conveyor at the same rate of speed.
To avoid the waste of energy, it is advantageous for the air which has been heated during the cooling process to be used for heating purposes and/or for the preparation of hot water. The heated air is preferably sent to a heat exchanger.
REFERENCES:
patent: 2019480 (1935-11-01), Campbell
patent: 4769092 (1988-09-01), Peichl et al.
patent: 4990194 (1991-02-01), Obata et al.
patent: 2461293 (1976-07-01), None
patent: 3442130 (1986-05-01), None
patent: 0538575 (1993-04-01), None
patent: 342334 (1931-01-01), None
patent: 5-104234 (1993-04-01), None
Patent Abstracts of Japan, vol. 013, No. 042 (C-564), Jan. 30, 1989 & JP 63-241112 A (Kawasaki Steel Corp), Oct. 6, 1988.
Mellon, Dale F., “Industrial Thermography”, Sep. 1988, Advanced Materials & Processes Inc. Metal Process, Metals Park, Ohio US.
Fenne Michael
Holtz Oswald
Kueffner Friedrich
Lin I.-H.
Pyon Harold
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