Difference between revisions of "Steel sheet in coils"
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This type of steel may eventually be sheared into short lengths of plate and made up into bundles to be sold to the fabrication industry. On the other hand, it can be destined for re-rolling in order to produce cold rolled steel sheeting.<br><br> | This type of steel may eventually be sheared into short lengths of plate and made up into bundles to be sold to the fabrication industry. On the other hand, it can be destined for re-rolling in order to produce cold rolled steel sheeting.<br><br> | ||
==Shipment/storage/usage== | ==Shipment/storage/usage== | ||
| + | ===Cold rolled steel sheeting=== | ||
| + | The effects of [[contact]] with moisture | ||
| + | Cold rolled steel sheeting can in a certain sense be considered a finished product. Any rust on the plating is not acceptable. In consideration of these facts, during loading or transport and discharge of the material, it must be kept completely dry at all times. Damage, resulting in heavy claims, can arise through contact with rain during loading and/or discharge from the ocean carrier. On voyage, ship and especially cargo sweat have been responsible fro heavy losses. Likewise, penetration of sea water into cargo compartments can be particularly devastating. Free moisture flowing across the outer metal envelope can pass beneath the overlaps of the packing and eventually penetrate the contents. As explained in similar circumstances with hot rolled coils, but with more serious results, through capillary action, moisture, which has penetrated and contacted the goods, is drawn between the turns of plating. | ||
| + | So called protection or strengthening rings, which consist of an angle iron placed around the outer and inner circumference edges of the packing, have proved to be an innovation which promotes rather than reduces the incidence of damage. Strengthening of the edge packing does provide greater protection against handling damage, but the benefits to be derived from this are far outweighed when the packing comes into contact with free moisture. The moisture trickles or runs across the surface of the packing to be caught up and accumulated in the edge protections. This water seeps through, penetrating the inner packing and eventually contacts the plating of the coil. | ||
| + | |||
| + | Rust | ||
| + | In the event of the plating developing a rust condition, whereby part of the coil so affected will be rejected and considered unusable for its originally intended purpose, loss in value will result. Depending upon the degree and overall extent of the rust, a decision will have to be made as to whether the plating qualifies as second choice material or whether it should be degraded to the value of scrap. One thing is certain, such material affected by rust cannot, in most instances, be reconditioned. | ||
| + | |||
| + | Handling damage | ||
| + | Depending upon the extent of this damage, claims can be forthcoming. A type of handling damage often encountered with cold rolled steel coils is often referred to as ovalisation, which can be caused by lowering a coil at such a speed that it lands heavily. This can result in the unit being forced out of the round so that it becomes oval in shape. In such a condition the coil will not fit into the decoiling machines. | ||
| + | |||
| + | Packages | ||
| + | To suit customer’s requirements cold rolled coils are often cut into short sections, in general measuring roughly 1.000 x 2.000 mm. The stack of sheets is wrapped in moisture-resistant paper and finally fitted with an outer metal envelope. Each package is then secured with flat metal strapping bands placed longitudinally and transversely around each unit. Beneath each package there is usually a framework of strong wooden bearers, which impart to the package rigidity and facilitates manipulation by fork-lift trucks. | ||
| + | |||
| + | Hold rolled steel sheeting | ||
| + | Packing | ||
| + | Hot rolled steel coils are not usually wrapped for protection against contact with moisture and the development of rust. They are secured with a number of flat metal strapping bands transversely through the eye or core of the coil, and securing bands are fixed around the outer circumference of the coil. There are instances when hot rolled coils are pickled and then oiled for protection, after which they are wrapped in moisture-proofed kraft paper and completely enfolded in a metal envelope, all secured with flat metal strapping bands. | ||
| + | |||
| + | Pre-shipment storage | ||
| + | Unwrapped hot rolled steel coils are often stored in the open, uncovered and exposed to the elements. Therefore, it is not unusual for such material to be partly or completely rusty in appearance at the time when it is shipped. Wrapped hot rolled steel coils pickled and oiled (H.R.P.O.) should be kept dry as any rust on the plating is inadmissible. H.R.P.O. coils should be given the same consideration as cold rolled coil. | ||
Revision as of 11:25, 6 August 2012
| Infobox on Steel sheet in coils | |
|---|---|
| Example of Steel sheet in coils |  |
| Facts | |
| Origin | Trade in steel and steel products primarily flows:
|
| Stowage factor (in m3/t) |
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| Humidity / moisture | Relative humidity: < 40 - 50% |
| Ventilation | (See also text) Steel sheet in sheets requires particular humidity/moisture and possibly ventilation conditions. Steel corrosion accelerates rapidly at relative humidity > 60%. If possible, relative humidity should be reduced to below 60% by appropriate ventilation measures. |
| Risk factors | (See also text) Seawater damage, contamination and mechanical damage |
Steel sheet in coils
Contents
Description
Cold rolled steel sheeting
This material is manufactured by re-rolling and cold reduction of hot rolled steel sheeting. The first step taken in the process is when a hot rolled steel coil is unwound and passed through rolls which flex the plating in such a manner as to break and fragment the mill scale. The plating is then pickled in an acid bath for the purpose of removing the mill scale completely, as well as rust and other extraneous matter which might be present. Thereafter, the material is washed to remove any traces of acid so leaving the surface of the sheet clean, fairly smooth and dull grey in colour.
In order to prepare the steel for cold working by improving its grain structure, the plating is annealed by heating to a high temperature in a special type of furnace. It then passes on to the cold reduction mill, which consists of a number of sets of rolls, five strands in tandem where the plating is under tension between strands, progressively reduced in thickness to the required gauge.
In order to rectify the adverse effects of cold working, the coils are again annealed in sealed furnaces, into which a special oxygen free atmosphere is fed, to avoid the formation of scale upon the surface of the plating. Finally, the sheet is given a skin pass through a single strand of rolls, which is referred to as temper rolling. In this operation the sheet is further reduced, but only very slightly, and then re-coiled. The object of this is to produce the required mechanical properties and surface finish. In general, the purpose of cold rolling is to impart to hot rolled material a finer finish in the form of a fine smooth surface, accuracy of thickness and dimension and also improved tensile strength. As a rough guide, in general, plate thickness of 0,5 mm or even less are involved. Coil weights are between 5 to 15 tons per unit with a width of plating from about 900 to 1.300 mm. Coil diameters of from 1.000 to 1.400 mm are about average. Apart from being wound into coils the continuous strip, or band of steel, is also cut into separate sheets which are made up into oblong packages.
The finished coil, with a fine mirror like surface, is oiled for protection against the development of rust, secured with a steel strapping band applied around its circumference, completely wrapped in moisture-resistant paper packing, after which an outer metal cover is applied for further protection. Flat metal bands, usually not less than four, are passed transversely through the core piece of each unit and also not less than three additional bands around the circumference to secure the packing in place. The banding is also applied to ensure that the coil remains tightly wound.
Hold rolled steel sheeting
Ingots are placed in a soaking pit where they are reheated to a suitable temperature for further rolling into slabs, and then into steel sheeting in the form of a continuous strip. In some instances, slabs are taken from stock in which case the slab is placed in a reheating furnace. The ingot or slab is brought to intense white heat to ensure that the temperature is uniform throughout this initial rolling. Temperature will be in excess of 1.000ºC. During reheating, a layer of basic oxide forms on the slab, and in order to remove this, the slab passes through a scale breaker. The loosened scale is blown away by high powered jets of water. Onwards to the roughing train, where the slab passes through four to five sets of rolls in tandem which reduces the slab down to about one fourth of its original thickness, and at the same time squeezes the slab into becoming longer in length. Rolls, placed vertically, control the width of the slab as it reduces in thickness and lengthens into a continuous sheet of thin plating.
Finally, the hot plating, at a temperature of just over 800°C, passes to the finishing train where it passes through six or seven strands of rolls in tandem at great speed, and when the thickness of the plating if progressively reduced it emerges as a thin sheet of great length. Thereafter, the strip of sheeting, travelling at a speed of over 1.000 m. per minute, moves towards the coiling machine, before which it is sprayed with water to reduce it to a predetermined temperature. The entire operation is meticulously monitored by computer in order to ensure exact width and thickness of plating as well as a satisfactory cooling rate. The final product, in coil form, might consist of a plate thickness of about 1 mm to 5 mm, and 125 cm in width. Each coil usually weighs between about 7 to 15 tons depending on the length and thickness of the plating. Coils weighing up to 30 tons are not altogether uncommon.
Applications
Cold rolled steel sheeting
This type of steel sheeting is used extensively in the automobile industry for the manufacture of car bodies. It is used for household appliances such as refrigerators, bread bins, electrical home appliances, radiators, metal furniture, drums, etc. Also there is a growing demand for pre-coated cold rolled steel plating which has a diverse range of uses. To suit some customer’s requirements, coils are finished on slitting lines which cut the wide steel band down into narrow widths.
Hold rolled steel sheeting
This type of steel may eventually be sheared into short lengths of plate and made up into bundles to be sold to the fabrication industry. On the other hand, it can be destined for re-rolling in order to produce cold rolled steel sheeting.
Shipment/storage/usage
Cold rolled steel sheeting
The effects of contact with moisture Cold rolled steel sheeting can in a certain sense be considered a finished product. Any rust on the plating is not acceptable. In consideration of these facts, during loading or transport and discharge of the material, it must be kept completely dry at all times. Damage, resulting in heavy claims, can arise through contact with rain during loading and/or discharge from the ocean carrier. On voyage, ship and especially cargo sweat have been responsible fro heavy losses. Likewise, penetration of sea water into cargo compartments can be particularly devastating. Free moisture flowing across the outer metal envelope can pass beneath the overlaps of the packing and eventually penetrate the contents. As explained in similar circumstances with hot rolled coils, but with more serious results, through capillary action, moisture, which has penetrated and contacted the goods, is drawn between the turns of plating. So called protection or strengthening rings, which consist of an angle iron placed around the outer and inner circumference edges of the packing, have proved to be an innovation which promotes rather than reduces the incidence of damage. Strengthening of the edge packing does provide greater protection against handling damage, but the benefits to be derived from this are far outweighed when the packing comes into contact with free moisture. The moisture trickles or runs across the surface of the packing to be caught up and accumulated in the edge protections. This water seeps through, penetrating the inner packing and eventually contacts the plating of the coil.
Rust In the event of the plating developing a rust condition, whereby part of the coil so affected will be rejected and considered unusable for its originally intended purpose, loss in value will result. Depending upon the degree and overall extent of the rust, a decision will have to be made as to whether the plating qualifies as second choice material or whether it should be degraded to the value of scrap. One thing is certain, such material affected by rust cannot, in most instances, be reconditioned.
Handling damage Depending upon the extent of this damage, claims can be forthcoming. A type of handling damage often encountered with cold rolled steel coils is often referred to as ovalisation, which can be caused by lowering a coil at such a speed that it lands heavily. This can result in the unit being forced out of the round so that it becomes oval in shape. In such a condition the coil will not fit into the decoiling machines.
Packages To suit customer’s requirements cold rolled coils are often cut into short sections, in general measuring roughly 1.000 x 2.000 mm. The stack of sheets is wrapped in moisture-resistant paper and finally fitted with an outer metal envelope. Each package is then secured with flat metal strapping bands placed longitudinally and transversely around each unit. Beneath each package there is usually a framework of strong wooden bearers, which impart to the package rigidity and facilitates manipulation by fork-lift trucks.
Hold rolled steel sheeting Packing Hot rolled steel coils are not usually wrapped for protection against contact with moisture and the development of rust. They are secured with a number of flat metal strapping bands transversely through the eye or core of the coil, and securing bands are fixed around the outer circumference of the coil. There are instances when hot rolled coils are pickled and then oiled for protection, after which they are wrapped in moisture-proofed kraft paper and completely enfolded in a metal envelope, all secured with flat metal strapping bands.
Pre-shipment storage Unwrapped hot rolled steel coils are often stored in the open, uncovered and exposed to the elements. Therefore, it is not unusual for such material to be partly or completely rusty in appearance at the time when it is shipped. Wrapped hot rolled steel coils pickled and oiled (H.R.P.O.) should be kept dry as any rust on the plating is inadmissible. H.R.P.O. coils should be given the same consideration as cold rolled coil.