Noise and Vibration Page

Vibrations are a result of motion within the machining process. This motion naturally causes disturbances in the air, causing noise. This noise and vibration is generally an unwanted byproduct of manufacturing which has a significant effect on the capability of the manufacturing process, and also an environmental effect.

Many machine tools today are isolated from the floor with special mounting devices to limit their vibration transmission. This is primarily done to prevent disturbance of other machines. Machines are also enclosed by rigid structures lined with acoustic material to deaden sound transmission. This is primarily done to protect the workers from hearing loss. This is no small concern. Shops with high noise background levels must undertake steps to conserve the hearing of the workers. Measures include mandatory hearing protection usage, annual hearing examinations, and limited exposure to exceptionally high noise operations, such as some forging operations. Release of compressed air is of real concern, as it is one of the leading causes of high noise levels in many plants.

While noise and vibration effects are primarily limited to the confines of the plant, noise will travel outside of the plant and may have an effect on wildlife, making an area less hospitable for animals. Vibrations have an effect on machine tool and manufacturing processes, leading to scrap and worn out machine tools entering the waste stream.

Tin plate

  By far the most important coated product of the steel mill is tin plate for the manufacture of containers. The “tin” can is actually more than 99 percent steel. In some mills steel sheets that have been hot-rolled and then cold-rolled are coated by passing them through a bath of molten tin.

The most common method of coating is by the electrolytic process. Sheet steel is slowly unrolled from its coil and passed through a chemical solution. Meanwhile, a current of electricity is passing through a piece of pure tin into the same solution, causing the tin to dissolve slowly and to be deposited on the steel. In electrolytic processing, less than half a kilogram of tin will coat more than 18.6 sq m (more than 200 sq ft) of steel. For the product known as thin tin, sheet and strip are given a second cold rolling before being coated with tin, a treatment that makes the steel plate extra tough as well as extra thin.

Cans made of thin tin are about as strong as ordinary tin cans, yet they contain less steel, with a resultant saving in weight and cost. Lightweight packaging containers are also being made of tin-plated steel foil that has been laminated to paper or cardboard.

Other processes of steel fabrication include forging, founding, and drawing the steel through dies.

Open-hearth process

Essentially the production of steel from pig iron by any process consists of burning out the excess carbon and other impurities present in the iron. One difficulty in the manufacture of steel is its high melting point, about 1370° C (about 2500° F), which prevents the use of ordinary fuels and furnaces. To overcome this difficulty the open-hearth furnace was developed; this furnace can be operated at a high temperature by regenerative preheating of the fuel gas and air used for combustion in the furnace. In regenerative preheating, the exhaust gases from the furnace are drawn through one of a series of chambers containing a mass of brickwork and give up most of their heat to the bricks. Then the flow through the furnace is reversed and the fuel and air pass through the heated chambers and are warmed by the bricks. Through this method open-hearth furnaces can reach temperatures as high as 1650° C (approximately 3000° F).

The furnace itself consists typically of a flat, rectangular brick hearth about 6 m by 10 m (about 20 ft by 33 ft), which is roofed over at a height of about 2.5 m (about 8 ft). In front of the hearth a series of doors opens out onto a working floor in front of the hearth. The entire hearth and working floor are one story above ground level, and the space under the hearth is taken up by the heat-regenerating chambers of the furnace. A furnace of this size produces about 100 metric tons of steel every 11 hr.

History of Iron and Steel Manufacture The exact date at which people discovered the technique of smelting iron ore to produce usable metal is not known. The earliest iron implements discovered by archaeologists in Egypt date from about 3000 BC, and iron ornaments were used even earlier; the comparatively advanced technique of hardening iron weapons by heat treatment was known to the Greeks about 1000 BC.

The alloys produced by early iron workers, and, indeed, all the iron alloys made until about the 14th century AD, would be classified today as wrought iron. They were made by heating a mass of iron ore and charcoal in a forge or furnace having a forced draft. Under this treatment the ore was reduced to the sponge of metallic iron filled with a slag composed of metallic impurities and charcoal ash. This sponge of iron was removed from the furnace while still incandescent and beaten with heavy sledges to drive out the slag and to weld and consolidate the iron. The iron produced under these conditions usually contained about 3 percent of slag particles and 0.1 percent of other impurities.

After the 14th century the furnaces used in smelting were increased in size, and increased draft was used to force the combustion gases through the “charge,” the mixture of raw materials. In these larger furnaces, the iron ore in the upper part of the furnace was first reduced to metallic iron and then took on more carbon as a result of the gases forced through it by the blast. The product of these furnaces was pig iron, an alloy that melts at a lower temperature than steel or wrought iron. Pig iron was then further refined to make steel.