The present invention relates to a method and apparatus for manufacturing tubes by rolling.
From the U.S. Pat. No. 4,876,870, there is known a method for manufacturing tubes of a non-ferrous metal, where a continuously cast billet is cold worked for instance by planetary rolling, so that owing to the influence of deformation resistance, the temperature of the worked material rises to the recrystallization range. In said publication, cold working generally means a process where the temperature of the billet under operation is normal when starting the working, but rises along with the process essentially higher than in an ordinary cold working operation, i.e. up to the recrystallization range of the material. A planetary rolling arrangement is disclosed in the U.S. Pat. No. 3,735,617, where three conical rolls are arranged at angles of 120° with respect to each other. The rolls rotate both around their own axis and around the center of the planetary housing. In said arrangement, the mainly conically narrowing shape of the rolls is essentially narrowed in the proceeding direction of the material to be rolled. There are also known corresponding arrangements where the rolls are arranged in a reversed position with respect to the proceeding direction of the rolled material, in which case their conical shape is narrowed against the proceeding direction of the material to be rolled. The U.S. Pat. No. 4,510,787 introduces a method for manufacturing hollow rods, where one possibility is to employ mainly conical rolls that are narrowed in an opposite direction than the proceeding direction of the rolled material. From the GB application 2019281 A, there also is known a planetary mill where the axes of the rolls are parallel with the proceeding direction of the tube billet to be rolled. Yet another arrangement known in the prior art is illustrated in FIG. 1.
Copper tubes have been manufactured extremely successfully by using the method of the prior art. However, if production capacity should be increased, the current method and particularly the employed equipments have some drawbacks. An increase in the production capacity reguires an increase in the rolling speed. The structures of current planetary rolling mills, particularly the structures of the roller heads, are ill suited to increasing the rolling speed and the rolling mill rotation speed. This is due to forces required to hold the roller heads in position during their rotation, among others.
The object of the invention is to realize a method whereby production capacity can be increased economically. Another object of the invention is to realize an apparatus whereby the drawbacks of the prior art can be avoided and production capacity increased according to the method of the invention.
The invention is based on the observation that the working resistance of copper is diminished to a fraction after recrystallization. This enables an extremely economical further rolling, with an equipment that is remarkably more economical than in the first working step.
The method according to the invention has several remarkable advantages. The division of the working process into two steps enables, among others, after the first working step, a larger wall thickness of the tube billet than in the prior art, which results in an increase in the production capacity. By means of the method and apparatus of the invention, production rates can be increased even two or three times in comparison with the prior art. The working of the tube billet—which is in the first working step recrystallized and softened mainly due to rolling—by rolling immediately after the first working step only requires a slight amount of power in the second working step. When both working steps are carried out in a protective gas chamber, harmful effects of oxidation, particularly in a copper-containing tube billet, are prevented during the working process.
In the present application, a conical roll generally means a rolling mill roll with a diameter that is at the first end of the rolling surface larger than at the second end. The true shape of the conical roll does not necessarily have to be conical or frusto-conical, but it can be varied according to the particular embodiment. Planetary rolling generally means rolling where the rolls rotate both around their own axis and around the billet to be rolled.
The invention is explained in more detail below by way of an example and with reference to the appended drawings, where
Essentially immediately after the first working step F1, the tube billet is subjected to a second working step F2, typically by rolling with a second set of conical rolls 7. At least during the first working step F1 and the second working step F2, and advantageously also between said working steps, the tube billet 1 is kept in non-oxidizing conditions. Said non-oxidizing conditions are created for instance by means of a protective gas space 9, where the conditions are adjusted in order to at least partly prevent the oxidation of the tube billet. The employed protective gas can typically be for example nitrogen or argon.
According to a preferred embodiment of the method according to the invention, in the second working step F2 the wall thickness s of the tube billet 1 is diminished. Typically the wall thickness of the tube billet (1) is diminished for about 50-70% in the second working step F2. The second working step F2 may comprise several successive rolling steps. In a typical embodiment, in the second working step F2 the tube billet 1 is worked by planetary skew rolling or planetary cross-rolling with conical rolls. In another embodiment, in the second working step F2 the tube billet 1 is worked by stretch reducing. In a third embodiment, the tube billet is worked by applying sizing rolling. The second working step may comprise several successive rolling operations. Different types of working processes can also be combined in succession.
The method according to the invention provides wider possibilities for working than the prior art. In the second working step F2, the (inner) diameter d of the tube can be maintained essentially constant. In another preferred embodiment, the tube diameter d is enlarged in the second working step F2 (FIG. 3). The tube diameter d is enlarged by using, when necessary, a mandrel 5 inside the tube billet. In
In the method according to the invention, the (inner) diameter d and the wall thickness s of the tube billet 1 can be adjusted to the desired measures in a way that is remarkably more flexible than those used in the prior art.
When necessary, the temperature of the tube billet 1 is adjusted, either prior to the first working step, during it, prior to the second working step or during it. Heating can be carried out for instance by using an induction coil. Naturally the billet can also be cooled in order to obtain the desired processing temperature in the tube billet.
The apparatus according to the invention for working the tube billet comprises in the first working step F1 a rolling mill arrangement with at least one conical roll element 2. Essentially immediately after the rolling arrangement of the first working step F1, in the proceeding direction 6 of the tube billet 1, there is arranged the rolling arrangement of the second working step F2. The apparatus includes means for creating non-oxidizing conditions that protect the tube billet 1, said means being for example a protective gas space 9, at least at the first working step F1 and the second working step F2 of the rolling arrangement and advantageously also therebetween.
Typically the protective gas space 9 surrounds, at least partly, the rolling arrangement of both the first and the second working step, and also the space provided in between, at least in the vicinity of the tube billet 1. Obviously the apparatus typically also comprises means for conducting the protective gas to the protective gas space and for maintaining a sufficient protective gas content in said protective gas space.
In a typical embodiment, the diameter of the roll element of the rolling arrangement of the first working step F1 is larger on the input side of the tube billet than on the output side (as is seen in FIG. 1). According to another embodiment, the diameter of the roll element 2 of the first rolling arrangement is larger on the tube billet output side than on the tube billet input side (according to FIG. 2). Typically the first rolling arrangement is a planetary mill with at least three conical roll elements 2 provided as the employed rolling elements.
In the embodiment of
In a preferred embodiment, the rotary axis 8 of the roll 7 of the rolling arrangement of the second working step is parallel to the longitudinal axis 4 of the tube billet 1.
Typically the rotary axis 8 of at least one roll 7 of the rolling arrangement of the second working step forms an angle with the longitudinal axis 4 of the tube billet.
In an embodiment, the rotary axis 8 of at least one roll 7 of the rolling arrangement of the second working step is essentially perpendicular to the plane that is tangential to the longitudinal axis 4 of the tube billet 1.
Thus the roll arrangement of the rolling apparatus of the second working step can consist of conical roll elements, or roll elements with rotary axes that are perpendicular to the proceeding direction of the tube billet, or of a combination of these.
The apparatus comprises at least one mandrel element 5. The shape and size of said mandrel element depends on the embodiment in question.
The invention is mainly suited to the manufacturing of tubes made of a non-ferrous material. In particular, the invention is designed to the manufacturing of copper or copper alloy tubes.
Number | Date | Country | Kind |
---|---|---|---|
20002797 | Dec 2000 | FI | national |
This is a national stage application filed under 35 USC 371 based on International Appplication No. PCT/FI2001/01075 filed Dec. 11, 2001, and claims priority under 35 USC 119 of Finnish Patent Application No. 20002797 filed Dec. 20, 2000.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FI01/01075 | 12/11/2001 | WO | 00 | 6/11/2003 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO02/05522 | 7/18/2002 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4318294 | Yoshiwara et al. | Mar 1982 | A |
4578974 | Pozsgay et al. | Apr 1986 | A |
4722209 | Mankins | Feb 1988 | A |
4727747 | Naud et al. | Mar 1988 | A |
4738128 | Staat | Apr 1988 | A |
4928507 | Staat et al. | May 1990 | A |
6651473 | Roller | Nov 2003 | B2 |
Number | Date | Country |
---|---|---|
2929401 | Feb 1981 | DE |
Number | Date | Country | |
---|---|---|---|
20040035165 A1 | Feb 2004 | US |