METHOD OF PRODUCING HOLLOW OBJECTS AND AN ARRANGEMENT FOR SUCH METHOD

Abstract

A method of, and arrangement for, producing shaped hollow metal objects by a hot process. A metal hollow semi-finished-product with at least one opening is heated to a forming temperature and placed into a cavity, whose shape corresponds to the desired final external shape of the hollow object. Then the cavity is sealed and water and/or steam is introduced therein. After the final shape of the semi-finished-product is achieved, the semi-finished-product is removed. The cavity is formed by a split mould, whose opening's entry edge has an expanded portion, against which a sealing feature is oriented. The outer surface of the sealing feature is arranged to close against this expanded portion. The sealing feature is also provided with a means of supply of water and/or steam, and a tube through which the water and/or steam is supplied. This tube extends into the interior space of the semi-finished-product, and can be provided with nozzles.

Claims

1. A method of producing shaped hollow objects of metals by a hot process, wherein a hollow semi-finished metal product (P) which is provided with at least one opening is heated to a forming temperature and placed into a cavity (D), whose shape corresponds to the desired final external shape of the hollow object, after which the opening in the semi-finished product (P) is sealed and water and/or steam is introduced into the cavity (D), and after the final shape of the semi-finished product (P) is achieved, the cavity (D) opens and the semi-finished product (P) is removed.

2. The method of producing shaped hollow objects of metals by a hot process according to claim 1, wherein after the temperature of the semi-finished product (P) becomes equal to the temperature of the mould (F), the semi-finished product (P) is removed from the mould (F), kept at this temperature for no less than 5 minutes and then cooled in air to ambient temperature.

3. An arrangement for implementing the method according to claim 1, wherein the cavity (D) is formed by a split mould (F), whose opening's entry edge has an expanded portion (Z), against which a sealing feature (U), is oriented, the outer surface (B) of said sealing feature being arranged to close against this expanded portion (Z), and this sealing feature (U) is provided with a means of supply of water and/or steam.

4. An arrangement for implementing the method according to claim 3, wherein the sealing feature (U) is provided with a tube (T) which includes a means of supply of water and/or steam, which tube extends into the interior space of the semi-finished product (P).

5. An arrangement for implementing the method according to 4, wherein the tube (T) is provided with nozzles (T).

Description

OVERVIEW OF FIGURES IN DRAWINGS

[0012] FIGS. 1 and 2 show a schematic depiction of a forming device for making hollow objects prior to the process and with a semi-finished product of the initial and final shapes, respectively.

EXAMPLE EMBODIMENT

[0013] A metal hollow semi-finished product P provided with one opening is made of the 25SiCrB material (Tab. 1). This semi-finished product P is heated approximately to its austenite temperature of 950 C. in an electrical furnace. Immediately after that, the semi-finished product P is transferred by means of tongs into a forming device. The forming device comprises a split mould F and a sealing feature U. A cavity D is created by bringing both parts of the mould F together, with their opening's entrance edge being provided with an expanded portion Z, against which the sealing feature U is oriented, whose outer surface B is arranged to close against this expanded portion Z. Bringing the sealing feature U into contact with the expanded portion Z seals the cavity D. In the gap between the expanded portion Z and the outer surface B of the sealing feature U, part of the semi-finished product P becomes trapped which thereby perfectly seals the cavity D. The sealing feature U is provided with a tube T and a means of supply of water by which it extends into the cavity D of the mould and into the semi-finished product P. On its circumference, the tube T is provided with nozzles T. In this case, the forming process in the forming device takes place with the aid of steam which creates internal pressure. The steam is generated by supplying water through nozzles T in the tube T, as a consequence of the contact of water with the heated semi-finished product. By means of the internal pressure, the semi-finished product P is deformed into the final hollow object shape at temperatures in an interval of approximately 920 C. to 500 C. The final shape is obtained by filling the internal contour of the cavity D in the forming device. The sealing feature U is pressed against the mould F via a spring A, which rests on the outer surface B of the sealing feature. When the maximum pressure is exceeded, said spring moves the outer surface B, which is arranged to close against the expanded portion Z of the entrance edge of the opening of the mould F, away from this expanded portion Z and the gap thus provided enables part of the pressurized steam to be released to the surrounding space. Thus, the spring A fulfils the function of a pressure relief valve. After the desired temperature and pressure have been achieved, the cavity D is opened, both parts of the mould F are drawn apart and the resultant hollow object D is removed from the forming device and is subsequently cooled to the ambient temperature. After the forming process, when the temperature of the hollow object D becomes equal to the temperature of the mould F, which is heated to approximately 250 C., the hollow object D having the final shape is removed from the mould F and transferred into a heating device. In this case, the heating device comprises a continuous furnace at the temperature of 250 C. This temperature enables carbon redistribution, austenite stabilization and relieves stress in the microstructure. The hollow object is kept at 250 C. in the furnace for about 6 minutes. In the last step, the hollow object D is removed from the heating device and cooled by means of a cooling device in still air to ambient temperature or to room temperature, in this case 20 C. In this case, the cooling device has the form of a cooling conveyor.

TABLE-US-00001 TABLE 1 Chemical composition of the material 25SiCrB (wt. %) C Si Mn Cr Mo Al Nb P S Ni Cu B 0.25 2.0 0.5 0.8 0.03 0.008 0.03 0.01 0.01 0.08 0.07 0.005

INDUSTRIAL UTILITY

[0014] This invention can be used in the production of metal parts, namely in the metallurgical industry in making semi-finished products, in particular for the automotive industry.