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-기계기술영어- 5.7.1 FACING AND TURNING Facing and turning are operations that are performed on the lathe. Usually, in the operation of a lathe, the piece to be worked is held and turned by a rotating vise called a chuck, and the metal is removed by a nonrotation cutter. When the cutter moves perpendicular to the axis os the workpiece, the operation is known as facing; when it moves parallel to the workpiece axis, the operation is called turning. 5.7.2 MILLING Milling machine operations are among the comprehensive accomplished in a machine shop. Gear cutting and shaping are perhaps the most common jobs done on a milling machine. The milling machine cutter is usually shaped to the desired appearance of the cut required and it turns until the cut is completed. The work is then moved to the next position for the succeeding cutting operation. 5.7.4 REAMING Drilled holes are rarely absolutely straight, cylindrical, or accurate in size. To "true" them they are reamed out by a tool that removes the riflings left by drill. This operation can be performed on any machine that can be used for drilling. 5.7.5 GRINDING This operation, intended to bring surfaces to a fine finish, is accomplished by the removal of a very small amount of the material as both the work and the grinder wheel turn at high speed, or as the grinder turns while the work is moved only at intervals. Grinding machines fall into four groups known as surface, cylindrical, tool, and centerless grinders. 7.1 ACCIDENTS Accidents do not happen, they are caused. There is not a single accident that could not have been prevented by care and forethought on somebody's part. Accidents can and must be prevented. They cost millions of pounds every year in damage and loss of premises, plant and lost business. They cost millions of lost working hours each year, but these are of little importance compared with the immeasurable cost in human suffering. In every eight-hour shift nearly 100 workers are the victims of industrial accidents. Many of them will be blinded, maimed for life, or confined to a hospital bed for months. At least two of them will die. Fig. 7.1 shows the main causes of accidents. 7.2.1 SHARP TOOLS Sharp tools protruding from the breast pocket can cause severe wounds to the wrist. Since the motor nerves of the fingers are near the surface in the wrist, these wounds can paralyse the hand and fingers. 7.2.2 BUTTON MISSING Since the overall cannot be fastened properly, it becomes as dangerous as any other loose clothing and is liable to be caught in moving machinery. 7.2.6 LIGHTWEIGHT SHOES The possible injuries associated with lightweight and unsuitable shoes are: Severe puncture wounds caused by treading on sharp objects. Crushed toes caused by falling objects. Damage to the Achilles' tendon due to insufficient protection around the heel and ankle. In addition to body protection, it is necessary to protect the head, eyes, hands and feet. Let's now consider suitable protective clothing. 7.3 HEAD PROTECTION Long hair is a very real hazard in any workshop. Long hair is liable to be caught in moving machinery, particularly drilling machines and lathes. When the hair and scalp are torn away, the resulting wound is both extremely painful and dangerous. Brain damage may also occur. Long hair is also a health hazard, as it is almost impossible to keep it clean and free from infection in the workshop environment. If your hair becomes entangled in a machine (Fig. 7.3), you are very likely to be scalped a very painful and serious injury. If a fitter or machinist persists in retaining a long hairstyle in the interests of fashion, then the hair must be contained within a close-fitting cap. This also helps to keep the hair and scalp clean and healthy. 7.4 EYE PROTECTION Although it is possible to walk on a wooden leg, nobody has ever seen out of a glass eye. Therefore eye protection is possibly the most important safety precaution to take in the workshop. Eye protection is provided by wearing suitable goggles or visors(Fig. 7.4). When welding, special goggles have to be worn with coloured lenses to filter out harmful rays. Gas welding goggles are not suitable when are welding. Eye injuries fall into three main categories: Pain and inflammation due to abrasive grit and dust getting between the lid and the eye. Damage caused by exposure to ultraviolet radiation (arc welding) and to high-intensity visible radiation. Particular care is required when using laser equipment. Loss of sight due to the eyeball being punctured or the optic nerve being severed by flying splinters of metal (swarf, or by the blast from a jet of compressed air). 7.5 HAND PROTECTION An engineer's hands are in constant use and they run the risk of handling dirty, oily, greasy, rough, sharp, brittle, hot and maybe toxic and corrosive materials. Gloves and palms in a variety of styles and materials are available to protect the hands, whatever the nature of the work. Gloves are sometimes inappropriate, e.g. for working precision machines, but hands still need to be protected from ail and grime, though not cuts and abrasions, by rubbing them in a barrier cream before starting to work. This is a mildly antiseptic, water-soluble cream which fills the pores of the skin and prevents the ingress of dirt and subsequent infection. The cream is easily removed by washing, which carries away the dirt and removes sources of infection. 7.6 FOOT PROTECTION Unsuitable footwear should always be discouraged. It is not only false economy, but extremely dangerous to wear lightweight casual or sports shoes in the workplace. They offer no protection from crushing or penetration. In safety footwear, protection is provided by a steel toecap (inside the boot or shoe) which conforms to a strength specification in accordance with BS 1870. Safety footwear is available in a wide range of styles and prices. It can be attractive in appearance and comfortable to wear. Fig. 7.5 shows sections through safety footwear. 7.7 LIFTING AND CARRYING As shown by Fig. 7.1. the movement of materials is the biggest single cause of factory accidents. Manual handling accidents can be traced to one or more of the following: Incorrect lifting technique. Carrying too heavy a load. Incorrect gripping. Failure to wear protective clothing. Fig. 7.6(a) shows the wrong technique for lifting, which can lead to ruptures, strained backs, sprains, slipped discs and other painful and permanent injuries. The correct technique is shown in Fig. 7.6(b). The back is muscles. Fig. 7.6(c) is a reminder that, to avoid falls and injury, the load being carried must not obstruct for-ward vision. 15.1 INTRODUCTION Aircraft is the name we use for flying machines. Most have wings to keep them in the air but helicopters and hot-air balloons are really aircraft as well. During the 19th century, short gliding flights were made in craft built by Sir George Cayley in England and Otto Lilienthal in Germany. However, it was not until 1903 that powered flight was achieved by the Wright brothers in the USA (Fig15.1). In 1909, Louis Bleriot flew across the English Channel. Ten year later, Alcock and Brown made the first non-spot flight across the Atlantic. Passenger flying developed after World War I. During the 1920s, passengers often flew aboard mail planes, sometimes with the mailbags on their laps! By the late 1930s, flying was a much more luxurious affair. People could travel between Europe and the Far East aboard large flying boats which took off and landed on water. The first jet aircraft, the Heinkel HE178, flew in 1939. However, jets were developed mainly after World War II. The first jet airliner, the De Havilland Comet, entered service in 1952. Today, nearly all long-distance international travel is by jet. 15.2 SHAPES Most aircraft have a central body called a fuselage, with wings near the middle and horizontal stabilizer and vertical stabilizer at back (Fig. 15.2) Straight wings work best for carrying heavy loads at low speed, but swept-back wings give a better airflow for fast flying. Some military jets, such as the Panavia Tornado, have swing wings' which swing further back for high-speed flight. Some aircraft do not have a tailplane. Instead, the wings form a triangular shape, called a delta, which goes all the way to the back. 15.3 POWER Most modern aircraft use jet engines in one form or another. Even where a propeller is fitted, the power may come from a turbo-prop engine which is based on the jet. Until the 1950s, most aircraft had propellers turned by piston engines. Some small aircraft still do. These engines work in the same basic way as a motor car engine. 15.4 THE CHANGING FACE OF DESIGN Concorde was designed in the 1960s. Nowadays, airlines are more interested in economy than speed, and other airliners travel at less than half Concorde's speed. Using computers, designers have developed wing which slip more easily through the air, and engines which are quieter and burn their fuel more dfficiently. A 'jumbo jet' can carry four times as many passengers as Concorde using only the same amount of fuel. Computers are an important part of a modern airliner. The autopilot is a computer which can navigate and fly the aircraft for most of its journey. On some aircraft, the pilot does not directly control the plane. Instead, the pilot's controls send instructions to a computer and the computer works out the best way to fly the plane.