Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1997-03-19
2000-06-20
Ip, Sikyin
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148645, 148646, 148670, C22F 118, B21D 312
Patent
active
060773693
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of straightening bent wire rods of titanium and titanium alloy into the precisely straight rod products. More particularly, the present invention relates to a method of straightening titanium alloy wire rods appropriate for materials applied for engine valves.
BACKGROUND ART
Titanium and titanium alloy rod products are widely used for automobile parts such as engine valves and tools, because the specific strength and corrosion resistance of titanium and titanium alloy is excellent.
Because centerless grinding finish is required for such use of automobile parts materials, it is necessary to straighten the wire rod product to straightness less than 1 mm/m, i.e., the level of which centerless grinding can be conducted.
Since Young's modulus of titanium or titanium alloy is approximately a half of that of carbon steel or stainless steel, it is necessary to give a twice strain to straighten titanium and titanium alloys, comparing with carbon steel or stainless steel.
Therefore, when a wire rod made of titanium or titanium alloy is straightened at room temperature by using a conventional type of straightening apparatus used in the steel industry, the bend of the wire rod tends to remain. When a large amount of strain is given to the wire rod so as to remove the bend from it, cracks and flaws are likely to occur.
For example, a stainless steel wire rod is commonly straightened as follows. After the wire rod has been rolled, it is subjected to cold drawing and shaving in which the surface of the wire rod is shaved by an inverse die. After the surface of the wire rod has been finished, it is formed into a coil-shaped wire rod. Next, the wire rod is straightened by using a rotary housing type wire straightener and cut into a straight rod product.
When a wire rod made of titanium or titanium alloy is straightened by using the method described above, the following problems may be encountered. In order to straighten the wire rod of titanium or titanium alloy into a precise straight rod that can be subjected to centerless grinding, the straightening work of the wire rod of titanium or titanium alloy must be conducted at a higher accuracy than that of a stainless steel wire rod. Even if straightening work is conducted with high accuracy, problems of bend, cracks and flaws occur. As a result, the yield of the products becomes poor to cause the production cost higher.
Concerning a method of suppressing the occurrence of bends, cracks and flaws so as to enhance the yield of the products, the following methods have been disclosed. With respect to a deformed cross-section shape made of titanium alloy or super alloy, tensile straightening method in a movable radiation furnace is disclosed in Japanese Unexamined Patent Publication No. 2-187216. With respect to a sheet foil made of tungsten or molybdenum, tensile straightening method in a movable radiation furnace is disclosed in Japanese Unexamined Patent Publication No. 62-220220.
Most of straight rods of titanium or titanium alloy, which have been straightened, must be subjected to centerless grinding so that the surfaces of the rods can be finished. Therefore, the size, the amount of bend and scale thickness on the surfaces of the rods must satisfy small tolerances compared with that of shape steel and others.
Therefore, when the tensile straightening method mentioned above is applied to the straightening work in which a wire rod is straightened so as to make a straight rod, the wire rod is partially heated. As a result, it is difficult to provide a uniform contract of cross section in the longitudinal direction of the wire rod. Accordingly, the accuracy of the size in the longitudinal direction is lowered in one wire rod, and the ratio of defect rod increases in the straightening process.
Further, according to the above methods, only a predetermined tension is given to the wire rod, but an elongation caused by straightening is not stipulated. Accordingly, fluctuation of the target size increases according to the
Kimura Kinichi
Kusano Akihiko
Ohguro Haruo
Sadano Yutaka
Takayama Isamu
Ip Sikyin
Nippon Steel Corporation
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