Sheet steel is normally classified into two categories. It can either be hot rolled or cold rolled. The manufacturer can produce several of material characteristics by varying the amount of carbon in the steel sheet. Mild steels that are used in sheet metal work have a less content of carbon than the steel that is used to make tools. The process of hot rolling is less costly but it results into depositing of slag on the surface and this is not good of it. Hot roll steel that has been oiled has a better surface appearance because most mill oxide in the sheet is removed.
Cold rolling steel is mostly used in making precision metal sheet applications because of its excellent condition of the surface, thickness accuracy and consistency. The steel metal material with maximum carbon content is known as ASTM-A366. This material has got a carbon content of 10 and is used for improved welding. The material in ASTM-A366 is very soft enabling the sheet to bend back on itself easily and on any direction without cracking. Typical applications of cold rolling include stamped parts, furniture, shelving, panels, truck bodies, refrigerators, washing machines and ranges.
Steel sheet rolling into a thin sheet is done in long rolling mills. The sheet passes through a number of steps, one after another. It is reduced in thickness as it follows o e stand after another. This process increases the length of the sheet steel. The process commences with a hot rolling mill and a roughing stand while the plate is still left to glow. After that, some plates that have been hot rolled are then cold rolled into smoother and thinner sheet steel. The following is an overview of the process of making sheet steel which involves hot rolling, hardening, cold rolling, heating and quenching, coating and cutting of the sheet steel to length.
The heating of the steel slabs takes place in two furnaces. Oil or Lp gas is normally used as a source of energy for the heating purposes. There is roughing of the slab as the second step. The product is then wound into a coil and then it is transferred into an adjacent strip of hot mill. After that, the material is passed through six stands. This results into reduction in thickness hence leading to expansion of the plate.
At this stage the material is quenched. The rate of quenching depends on the grade of the sheet steel that is required. Some grades require higher quenching rate while others require low rates. The sheet passes through a cleaning path. In hardening, the sheet is passed through pickling baths so as to clean and remove mill scale that is formed when the product is at the rolling stage. A large proportion of sheet steel material that is sold to the clients is in the form of a hot rolled sheet.
This process is carried out for those customers who order for thinner sheet steel than the one that is obtained in hot rolling. This stage produces a smoother with accurate thickness material. The sheet is passed through five stands for cold rolling. This stage makes the sheet to harden and become brittle at the initial point of this stage. The material is heated to make new grains to grow so as to compensate those that may be deformed hence restoring the formality of the sheet.
Heating and quenching
This is done to make the sheet steel hard. There is fast cooling after heating so as to modify the atomic structure of the grains of steel. A displacement that makes the carbon atoms not to move takes place through the cooling.
This is done in order to provide additional protection against corrosion. The strip is painted with a number of paints. This is done by rollers which apply the paint to moving strips.
A greater proportion of the sheet is cut to length with the aim of meeting the specifications of the customer. The sheet metal runs through a slitting line and this narrows its length.
One of the main pros of sheet steel over aluminum sheet is its easiness to resistances spot welding. Steel is also less costly as compared to aluminum. However, protection of plating and painting is added to sheet steel, the costs of steel over-weighs those of aluminum. There is a variety of pre-finished products that are made of sheet steel including primered, galvanized and paint. Most of the sheet steel companies plate the finished parts of products of steel sheet so as to ensure that all the bends and perforations are adequately covered.
Stainless steel alloys includes of the following;
1. Alloy 410
This alloy is mostly used in areas where corrosion resistance is not such severe, for example in fresh water, air and in some specific chemicals. It is a heat treatable stainless alloy. The alloy is frequently used in the manufacture of cutlery. It is magnetic, hot rolled, pickled and magnetic in nature.
2. Alloy 316
It has a better pitting and corrosion resistance. It also has a higher strength at high temperature as compared to T304. The alloy is used for manufacturing valves, pumps, textile, chemical equipments, and paperwork plus machine applications. The steel sheet is pickled, annealed and cold rolled.
3. Alloy 304
It is the mostly used heat resisting stainless steel. This type of steel provides a good corrosion resistant to many chemicals that are exposed to corrosion effects. It can be easily be welded by most common welding methods.
It is used for automatic applications of machines unlike This stainless steel sheet provides good corrosion resistance to foods, nitric acids, most dyes, most organic and many inorganic chemicals, heat resisting, sterilizing solutions and atmospheric exposures.
During the rolling process which results into the sheet stock, some amount of bowing takes place resulting to the sheet being wider at the center than at the edges. Sheet stock that is from the rolling meal is found in a wide range of finishes. A static PVC film may be applied so as to protect the finish. The part is polished by grains and DSM after all the perforations has been completed.