Stress free steel and rapid production of same

Abstract

A method of producing steel with reduced internal stress concentrations is disclosed. In an embodiment, hot steel is shaped by a rolling mill. The resultant steel product is bundled as soon as practicable and the bundle is allowed to cool. Vibration energy is applied to the bundle of steel product so that internal stress concentrations within the steel product are relieved. In an embodiment, a plurality of bundles are stored on a rack and the rack is vibrated, the vibrations being transmitted to the plurality of bundles so that undesired internal stress concentrations within the steel products are relieved. Thus, improved steel is produced as well as improved steel that can be produced more rapidly than known techniques.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 60/526,243, filed Dec. 2, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of production of steel, more specifically to a method of making steel with reduced internal stress concentrations.

2. Description of Related Art

Methods for ferrous metallurgy are known, perhaps the most common method being the production of steel. Typically, iron ore and other various raw materials such as coke, limestone and dolomite are heated in a blast furnace to a sufficient temperature to melt the raw materials and allow them to mix. Slag is separated from the mixture and the remaining molten metal is transferred to a steel melting shop where further refining is done. The resultant crude steel can then be further refined with the addition of alloys that give the particular steel the desired properties. As is known, some of the above processes can be supplemented with the inclusion of scrap steel or iron. The resultant product is typically continuously cast into billets, blooms or slabs, sometimes referred to as “semis”, and these semis are then processed to form the final product. In some plants the product is cast directly into strip on strip casters. In others, the semis can be beam blanks or near-net-shapes to reduce rolling requirements.

During the processing of semis, the semis are typically heated to a temperature sufficient to allow the semis to be worked, a typical such temperature being 1200 degrees Celsius. The semis are then processed by a rolling mill, the design of the rolling mill dependent on the desired shape of the finished product. The rolling mill, through the application of heat and pressure, forms the steel product. Thus, significant energy is used to shape the semis into the steel product.

Steel product, in a final form, can be a variety of shapes and configurations. Steel product includes, for example, flat rolled steel, steel strip, bars, beams, wires, rods, sheets, plates, bands, channels, tubes, pipes, tracks, and rails. If the steel product is a bar or a beam, for example, it may be stored in bundles. When steel product is shaped into flat rolled steel, for example, it is often rolled into round coils. Steel product, when shaped into wire or rod, for example, is also often typically rolled into round coils. For ease of reference, coils of steel product will also be referred to as bundles unless otherwise noted.

In general, there is a significant desire that the steel being produced have relatively constant dimensional straightness. Thus, significant resources are exerted in controlling the rolling mill process so that the finished product has the correct dimensions and straightness. Steel product with poor dimensional straightness control must be either sold at a lower cost, be reworked, or be reprocessed. The designation for out of tolerance straightness is referred to in the trade as camber or sweep; herein it will be called warp or warpage. Part of the process of producing steel product involves cooling the hot shaped steel to a temperature where the steel is dimensionally stable and/or can be stored. As is known, the rate at which steel cools has a significant affect on the properties of the steel due to, in part, the affect the rate of cooling has on the grain structure of the resultant steel product. Uneven cooling tends to produce stresses in the steel and such stresses may cause the steel product to warp or crack or otherwise suffer damage. When some coils are produced, it is necessary to retard the rate of cooling to prevent damage from stress. Special furnaces or other devices such as covers are used to control the rate of heat loss and temperature reduction.

Therefore, substantial resources are devoted to ensuring the hot shaped steel cools at a desired rate. Often the hot shaped steel is controllably cooled on a cooling bed. Cooling beds, depending on the dimensions of the steel product, and the desired rate of cooling, can be quite long and can add significant cost to the production of steel because of the upfront capital expenditures required to create the necessary facilities. Sometimes the size of the cooling bed is a limiting factor in determining the rate at which the steel production facility can operate. In addition, the time needed to cool the steel increases the amount of work in process. Naturally, increasing the amount of work in process increases the necessary level of inventory, which in turn decreases the efficiency of the plant operation. In addition, higher levels of inventory make the steel production facility less flexible and potentially less able to respond quickly to variations in the quality of the steel product. Thus, a decrease in the level of inventory would tend to make a steel production facility more profitable while potentially increasing the quality of the steel product produced.

For example, as is known in the art, when the steel product is a steel bar, the steel bars are first sufficiently cooled and then bundled together via straps and removed from the production line and typically placed in a storage facility until the steel product is transported to the customer. If the steel bars are bundled too soon, the interior portion of the bundle will cool at a slower rate than the exterior portion of the bundle. Also, the portion of the steel bar that is exposed to the outside air will cool more rapidly than the portion of the steel bar that is in contact with other bars. Thus, the exterior steel bars of the bundle will have internal stresses as a result of the disparate cooling rates. These stresses can cause the steel bars to warp once the straps holding the bundle together are removed, potentially making the steel bars unusable.

Longer cooling beds relieve this problem but, as discussed above, are costly and inefficient to implement. As can be appreciated, general storage facilities are somewhat less costly to install and maintain as compared to cooling beds. And the storage facilities are usually a necessary requirement anyway. Thus, storing the steel in a storage area while the steel cools would be less costly from a facility investment perspective and this decreased cost could significantly benefit the profitability of the steel production facility. Therefore, it would be beneficial to be able to bundle the steel bars sooner (i.e., while still quite hot) without having to later rework the steel bars due to warpage caused by internal stress concentrations affecting the dimensional straightness of the steel bars.

Once the steel product is delivered to the customer, the steel product is typically further processed to make finished goods. The processing can include machining the steel, drilling, punching, grinding, cutting, welding, cold working the steel, and various other known methods of processing steel into finished goods. During this process of working the steel, the initial internal forces are often unbalanced in the steel product. These forces tend to create localized stress concentrations in the finished good. As can be appreciated, a particular grade of steel can only withstand a particular level of stress before the steel deforms in an undesirable plastic manner. Thus, it is undesirable to have excessive internal stresses in the steel product prior to the steel product being processed into the finished good, because this additional processing can cause the internal stresses to distort the final product.

Depending on the desired properties, even the localized stresses created by the processing of the steel product into the finished good may be undesirable. Therefore, various methods of relieving the stresses of finished goods are known. One method is to let the finished good sit for a substantial time so that the excessive internal stress concentrations have time to relax. Another method is to heat the finished good so that the internal stress concentrations can more quickly be relieved. Another method is to vibrate the finished good in a known manner, the vibrations providing energy that allows the stress concentrations to more quickly dissipate. While these methods of reducing the resultant stresses in the finished product are sometimes necessary, it is undesirable for significant variations in the stress concentrations to exist prior to the processing of the steel. Therefore, it would be advantageous to ensure the steel product, before being further processed, is essentially free of internal stresses or at least has a relatively constant internal stress level throughout the steel product.

BRIEF SUMMARY OF THE INVENTION

In an embodiment, the process of making steel bars includes the shaping of semis with a rolling mill. The bars, after being shaped by the rolling mill, are directed via a conveyor to a shearing, straightening and bundling station. The bars are then bundled while still at an elevated temperature. In an embodiment, the cut-to-length and bundled bars can be removed from the bundling station and allowed to cool in a separate location such as in a storage facility. Once sufficiently cooled, bundled bars are then vibrated to reduce internal stresses. The bars can then be unbundled without concern that internal stresses will cause the bars to warp. Thus, it is possible to reduce the size of the cooling bed so that the cost of building a steel production facility can be reduced.

With the invention, in an embodiment, the rate of production through an existing steel production facility is greatly increased by allowing steel to move more quickly across the existing cooling bed because the requirement to wait for cooling to take place is reduced or eliminated by ignoring the stresses and then relieving those stresses at a later time. In this way, the cooling bed capacity is not the limiting factor on the rate of steel production, as is sometimes the case.

With the invention, in yet another embodiment, the coils of steel strip are allowed to cool and then vibrated so that stresses are relieved. These stresses ordinarily cause the edges of the coiled strip to cool and contract more than the center of the strip, thus the edges can crack or the center of the strip can tend to bulge, when the coil is opened. Coils are often slowly cooled or even annealed and slow-cooled to help alleviate this situation.

In still another embodiment the coils are vibrated while cooling to dissipate stresses that would otherwise form. This allows for a faster cooling rate.

With the invention, in the case of coiled steel rod or wire, the coils are cooled in a series of loose loops as they pass along a cooling conveyor and sometimes through a quench tank of liquid coolant. The loose loops are then coiled on a mandrel and wire tied or strapped together. These coils also have stress concentrations where the loops are resting on each other as they move along the cooling conveyor line. The stresses can be relieved by vibration techniques and methods of the invention as described herein, after cooling.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which:

FIG. 1 depicts a block diagram of a typical production of steel product.

FIG. 2a illustrates a side view of a bundle of steel bars.

FIG. 2b illustrates an end view of the bundle of steel bars depicted in FIG. 2a.

FIG. 3 illustrates a side view of the bundle of steel bars as shown in FIG. 2a, depicting an embodiment of a method of vibrating a bundle of steel bars.

FIG. 4 illustrates an alternative embodiment for vibrating a bundle of steel bars.

FIG. 5a illustrates a side view of another alternative embodiment of a method for vibrating a bundle of steel bars.

FIG. 5b illustrates a front view of the embodiment depicted in FIG. 5a.

FIG. 6 depicts yet another alternative embodiment of a method for vibrating a steel product.

DETAILED DESCRIPTION OF THE INVENTION

The production of steel is a costly endeavor involving significant capital investment. Therefore, the amount of steel produced by a production plant needs to be quite large for the return on the capital investment to be positive. Thus, significant effort has been exerted to make the production of steel as streamlined and cost efficient as possible. It should be noted that while steel production is likely to enjoy the largest benefit from this invention given the volume of steel being produced, the production of other materials, including non-ferrous materials, having similar stress concentration issues could likewise benefit from this invention.

Turning to FIG. 1, a block diagram of a typical steel production facility is depicted. In step 10, the liquid steel is refined and the various other additives are introduced so as to produce the desired alloy. As is known, steel can have a varied composition. For example, stainless steel typically requires the addition of nickel and chromium.

Once the liquid steel is ready, it can be cast into semis, such as billets, in step 20. In step 30, the hot semis, are shaped by a rolling mill. Typically, the semis are reheated in a reheat furnace and a series of inline rolling mills are used to form the steel product. In an exemplary embodiment, the semis are shaped into long lengths of shaped bars. The bars can be in the shape of an angle, channel, beam, round, flat, oval, railroad track rails or any other suitable specialized shape for use in a final end product.

After being shaped, the hot shaped steel passes through a cooling bed in step 40; the cooling bed typically includes notched walking beams called rakes. The notched rakes help confine the bars to keep them from warping as they cool. Forced air or water can be used to increase the rate of cooling, with necessary attention given to metallurgical properties that may be altered by cooling.

In step 50, the long lengths of shaped bars are cut to the desired length and then run through a straightening machine to ensure the steel product is not warped. The steel product is then bundled is step 60. In step 70, the bundles are placed in storage until needed. Finally, in step 80, the bundles are transported, often to the customer. Transportation can be over short or long distances. Common means of transporting steel product over long distances include trucks, trains, and ships.

As discussed above, the term “bundle,” is not limited to bundles of bars of steel product but also encompasses other shapes such as rolled coils of steel product and also stacks of plates and sheets. In general, the term “bundle” is used to reference an amount of shaped steel that can be conveniently held together. As used herein, the term “steel product” includes any bar, rod, strip, sheet, plate, band, hot-band, beam, channel, tube, pipe, track, rail, wire, and structural and special shapes (such as, bed rails, window frames, fence posts, and so forth), of any shape and configuration, and made of any type of metal.

FIG. 2a depicts an exemplary embodiment of a bundle 100 of steel bars. FIG. 2b illustrates a close up end view of bundle 100. As can be readily appreciated, if the bars are still hot, the exterior bars along the outer edge 105 of the bundle 100 will cool quicker than the interior area 110. Thus, the bars on the outer edge 105 of bundle 100 will be especially likely to have localized stress concentrations. In addition, the act of rolling the bars will tend to create internal stress concentrations within the bars. Thus, bars created via a rolling mill are quite likely to have unwanted localized stress concentrations.

FIG. 3 depicts an exemplary embodiment of the invention and includes the step of vibrating a bundle 100. A support frame 120 is mounted to the bundle 100 via a clamp 125. Connected to the frame 120 is a vibration generating device 130. The bundle is supported by a plurality of support blocks 140.

As depicted in FIG. 3, the vibration generating device 130 is portable. Thus, the system can be moved from bundle to bundle as desired.

Turning next to FIG. 4, an alternative exemplary embodiment of the present invention is depicted. A bundle 200 travels down a conveyer system 202. The bundle travels over a plurality of rollers 245 that are mounted on a conveyer roll support 240. As the bundle travels along, the bundle passes through a conveyer vibration section 212.

The vibration section 212 acts to vibrate the bundle while the bundle passes through the vibration section 212 so as to aid in reducing the internal stresses in the bars that make up the bundle. As depicted, the vibration section consists of a vibration isolator 215 that supports a support frame 220. Mounted on the support frame 220 is a force cylinder 225. The force cylinder 225 exerts a force on the movable support frame 250 that in operation exerts a force on a roller 245. In turn, the roller 245 mounted to the movable support frame 250 prevents independent vertical movement of the bundle 200 by restraining the bundle 200 between two opposing rollers 245. Mounted to the frame 220 is a vibration generating device 230. The vibration generating device 230 provides a vibration energy that is transmitted through the support frame 220 and the rollers 245 into the bundle 200.

As can be appreciated, the time it takes the bundle 200 to travel through the vibration section, along with the amount of vibration energy supplied by the vibration device 230 determines the effectiveness of relieving internal stress concentrations.

Another exemplary embodiment of the present invention is depicted in FIG. 5a and FIG. 5b. As depicted, a plurality of bundles 300 is held in a storage rack 305. The rack includes a frame portion 340. The frame portion 340 is supported by vibration isolators 315. As depicted, mounted to the frame portion 340 is a plurality of vibration generators 330, each having the capability of providing different vibration forces or energy to the rack, or that the vibration force of one generator is not ordinarily aligned with the vibration force of a second generator, unless it is desired to augment the vibrations from the second. In between the plurality of bundles 300 are support blocks 345. Support blocks 345 facilitate the addition and removal of bundles 300 and also serve to transfer vibration energy between adjacent bundles 300.

In an embodiment, a plurality of bundles of hot steel product is placed on the rack. The bundles are then cooled. The cooling can be via application of a cool liquid or a blast of air. In an alternative embodiment, the bundles can be cooled by allowing them to reach near ambient temperature through conventional heat transfer between the hot bundles and the cooler ambient air and surroundings. Vibrations are then applied to the frame portion 340 via the vibration generators 330. In an embodiment, the level of vibration being applied to the frame portion 340 is lower than the vibration energy being applied during the conveyer method. Metal castings, for example, typically are allowed to age for an extended period of time so that the stress concentrations have time to be naturally relieved by seasonal changes in temperature and the like. The above embodiment allows for similar stress relief but on a much faster scale, such as within hours or days instead of months or a year.

FIG. 6 depicts another exemplary embodiment of the present invention. As depicted, a bundle 400 is supported by a crane 420 via a cable 424 or chain or rigid member. A vibration generating device 430 supports the cable 424. The vibration generating device is supported by a cable 425 which is in turn supported by crane 420. A vibration isolator, similar to the vibration isolators described above, is located between the crane and the vibration generation device to protect the crane from unwanted vibration. Thus, the vibration generating device 430 can be used to vibrate the bundle 400 while the bundle 400 is being transported. In this manner, the bundle 400 can experience stress relief without the need to separately vibrate bundle 400 at some other location. Naturally, when vibrating the bundle 400 during transportation between a first and a second location, it is preferable that the bundle 400 be sufficiently cooled so as to avoid further accumulation of internal stress as a result of later cooling. Other types of cranes or mobile carriers would use a similar arrangement to that shown, including cranes such as overhead traveling cranes, or specialized mobile carriers as typically used in steel mills and steel warehouses. Vibrators and isolators would be suitably mounted to the transporter to allow the bundles to be vibrated in transit.

The present invention has been described in terms of preferred and exemplary embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure.

Claims

1. A method of producing steel product with reduced internal stress, comprising the steps of:

processing a semis with a rolling mill to create a steel product;

preparing a bundle of the steel product while the steel product is still hot;

cooling the bundle of steel product; and

vibrating the cooled bundle of steel product so as to relieve unwanted internal stress concentrations present in the steel product.

2. The method of producing steel product of claim 1, wherein the semis is a billet.

3. The method of producing steel product of claim 1, wherein the steel product is a steel bar and the bundle is a bundle of steel bars.

4. The method of producing steel product of claim 1, wherein the steel product is steel strip or sheet.

5. The method of producing steel product of claim 1, wherein the steel product is selected from the group consisting of a bar, rod, strip, sheet, plate, band, hot-band, beam, channel, tube, pipe, track, rail, wire, and structural and special shapes.

6. The method of producing steel product of claim 1, further comprising the steps of:

preparing at least a second bundle of steel product; and

vibrating the at least two bundles of steel product simultaneously.

7. The method of producing steel product of claim 6, wherein the step of vibrating the plurality of bundles of steel product comprises the steps of:

placing the at least two bundles of steel product on a rack that is supported by a vibration isolator; and

vibrating the rack, whereby the at least two bundles of steel product are simultaneously vibrated.

8. The method of producing steel of claim 7, wherein the step of vibrating the rack includes the steps of applying a vibration force with a first vibration generator mounted on the rack and applying at least a second vibration force with a second vibration generator mounted on the rack, the second vibration generator mounted so the vibration force of the second vibration generator is not aligned with the force of the first vibration generator.

9. The method of claim 8 wherein the vibration forces are aligned.

10. A system for holding and vibrating bundles of steel product, comprising:

a frame, the frame configured to support a plurality of steel bundles;

a vibration isolator supporting the frame;

a first vibration generator mounted on the frame, the first vibration generator providing a first vibration force;

a second vibration generator mounted on the frame, the second vibration generator providing a second vibration force not aligned with the first vibration force of the first generator.

11. The system of claim 10, further comprising a support member for use in preventing the plurality of steel bundles from falling off of the frame.

12. The system of claim 11, further comprising a plurality of support blocks for use in transferring vibration between adjacent bundles of steel product.

13. The system of claim 10 wherein the vibration forces are aligned.

14. A system for vibrating a bundle of steel product, comprising:

a mobile carrier configured to support and move a bundle of steel;

a vibration isolator between the carrier and vibration generator;

a vibration generator supported by the carrier; and

a support member supported by the vibration generator, the support member configured to support a bundle of steel product.

15. The system of claim 14, wherein the support members are selected from the group consisting of cables, chains and rigid members.

16. The system of claim 14, further comprising a cable extending from the carrier to the vibration isolator, the cable configured to couple the vibration isolator to the carrier.

17. A method of producing steel product with reduced internal stress, comprising the steps of:

creating a steel billet via a continuous casting process;

processing the steel billet with a rolling mill to form a hot steel product;

preparing a first bundle of the hot steel product;

cooling the first bundle of the hot steel product, thereby allowing internal localized stress concentrations to form in the steel product within the bundle; and

vibrating the first bundle so as to reduce the internal localized stress concentrations of the steel product to an acceptable level.

18. The method of claim 17, wherein the step of vibrating takes place during the movement of the first bundle from a first location to a second location.

19. The method of claim 17, wherein the step of vibrating occurs during the step of transporting the first bundle.

20. The method of claim 18, wherein the step of transporting is done via a transporting device selected from the group consisting of a crane and mobile carrier.

21. The method of claim 17, further comprising the steps of:

preparing a second bundle of steel product; and

cooling and locating the second bundle in close proximity to the first bundle, wherein the step of vibrating the first bundle of steel product also vibrates the second bundle.

22. The method of claim 21, wherein the vibrating step is accomplished by vibrating a rack being used to store the first bundle and the second bundle.

23. The method of claim 17, wherein the vibrating step is accomplished by a vibrating conveyor.

24. A method of increasing the production rate of steel product, comprising the steps of:

processing a semis with a rolling mill to create a steel product;

preparing a bundle of the steel product while the steel product is still hot;

cooling the bundle of steel product; and

vibrating the cooled bundle of steel product so as to relieve unwanted internal stress concentrations present in the steel product,

whereby the rate of production of the steel is increased because the time consumed in waiting for the steel product to cool prior to bundling is reduced.

25. The method of claim 24 wherein the step of vibrating takes place at a location away from a steel production facility.

26. A method of producing metal product with reduced internal stress, comprising the steps of:

processing a semis with a rolling mill to create a metal product;

preparing a bundle of the metal product while the product is still hot; and

cooling and simultaneously vibrating the bundle of metal product so as to relieve unwanted internal stress concentrations present in the metal product.

27. A method of producing a metal product with reduced internal stress, comprising the steps of:

casting a metal on a continuous strip caster to create a product;

preparing a bundle of the product while the product is still hot;

cooling the bundle of product; and

vibrating the cooled bundle of product so as to relieve unwanted internal stress concentrations present in the product.

28. The method of claim 27 wherein the step of vibrating takes place at a location away from the metal production facility.

29. The method of claim 27, wherein the step of vibrating is accomplished by a vibrating conveyor.

30. The method of claim 27, further comprising the steps of:

preparing a second bundle of product; and

cooling and locating the second bundle in close proximity to the first bundle, wherein the step of vibrating the first bundle also vibrates the second bundle.

31. The method of claim 27, wherein the step of vibrating is accomplished by vibrating a rack being used to store the first bundle and the second bundle.

32. A method of producing steel product with reduced internal stress, comprising the steps of:

casting a steel strip on a continuous strip caster to create a product;

preparing a bundle of the steel product while the steel product is still hot; and

cooling and simultaneously vibrating the bundle of steel product so as to relieve unwanted internal stress concentrations present in the steel product.

33. A method of producing steel product with reduced internal stress, comprising the steps of:

casting a steel shape on a continuous caster to create a product;

preparing a bundle of the product while the product is still hot;

cooling the bundle of product; and

vibrating the cooled bundle of product so as to relieve unwanted internal stress concentrations present in the product.

34. A method of producing steel product with reduced internal stress, comprising the steps of:

casting a steel shape on a continuous caster to create a product;

preparing a bundle of the steel product while the steel product is still hot; and

cooling and simultaneously vibrating the bundle of steel product so as to relieve unwanted internal stress concentrations present in the steel product.