Conveyors and Jacks
Conveyors and Jacks
1 Celkový obraz O modulu Pomůcky a nástroje Pravidla a konvence
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2 Obsah 1. Celkový obraz
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2. Obsah
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3. Belt Conveyor
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3.2 Belt Conveyor 4. Screw Conveyor 4.2 Screw Conveyor 5. Hydraulic Jack 5.2 Hydraulic Jack 6. Screw Jack 6.2 Screw Jack
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7. Rejstřík
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3 Belt Conveyor 3.1 Belt Conveyor Description A belt conveyor is a type of conveyor, consisting of at least two pulleys, around which a conveyor belt rotates. One of the pulleys, which is powered, is called the drive, the other one (unpowered) is called the idler. Sometimes both of the pulleys are powered. The rotating belt moves the material forward.
Application Two main types of belt conveyors are used in industry: conveyors for general material handling, which for example move boxes or products inside a factory, and conveyors for bulk material handling, which can transport various materials in loose bulk form, such as grain in agriculture, ore or coal in heavy industry, or mixed wastes. Belts used in general material handling have to consist of two layers. The under layer, called carcass, is usually made of cotton or plastic mesh and provides linear strength and shape. The over layer, called cover, can be made of various materials, depending on its application, such as silicone for heat or rubber, if it has to resist some traction.
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A special type of conveyor belts are elevator belts which have regularly spaced partitions, thanks to which they can transport loose materials, or even liquids, up steep inclines. Belt conveyors are used in self-unloading bulk freighters or hopper wagons and live bottom trailers. Various smaller commercial applications can also be seen, such as those at cash registers in supermarkets. Sometimes conveyor belts transport also people, such escalators in department stores or urban underground transit systems. Some ski areas use conveyor belts to transport skiers up the hill.
Vocabulary belt conveyor – pásový dopravník conveyor belt – dopravní pás 24.11.2009
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pulley – kotouč powered – poháněný general material handling – běžné nakládání s materiálem bulk material handling – nakládání se sypkým materiálem loose bulk form – volně ložený grain – zrno agriculture – zemědělství ore – ruda coal – uhlí heavy industry – těžký průmysl mixed wastes – směsný odpad under layer – spodní vrstva over layer – svrchní vrstva cotton – bavlna mesh – síťovina linear – podélný application – využití silicone – silikon heat – teplo rubber – guma resist – odolat traction – napětí elevator belt – korečkový dopravník partitions – příčky liquid – kapalina steep incline – prudké stoupání self-unloading bulk freighters – samovykládací nákladní lodě pro převoz volně loženého materiálu hopper wagons – samovykládací železniční vagóny live bottom trailers – samovykládací nákladní přívěsy cash register – pokladna v supermarketu escalator – pohyblivé schody underground transit system – metro exposed – odhalený 24.11.2009
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Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}.
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4 Screw Conveyor 4.1 Screw Conveyor Screw conveyors are a type of conveyors, which can be found in bulk handling industries.
Description Screw conveyors can have bigger pitch spacing, thanks to which they can have a higher capacity with the same rotation speed. They consist of a trough with a spiral coiled around a shaft. One end of the shaft is driven, the other is just held. Some screw conveyors contain a shaftless spiral, which is driven at one end, but the other is free. Operation Screw conveyors are often used horizontally or slightly inclined and they can efficiently move various semi-solid and non-coherent materials, such as ash, animal feed (such as meat and bone meal), food waste or municipal solid waste, wood chips or rubble. When they are inclined, they work as an Archimedes screw. Thus they can transport the material upwards. This can be very economical method how to convey and elevate material at the same time, but it needs enough space. The higher the angle of inclination is, the smaller is the allowable capacity of a given unit. Vocabulary screw conveyor – šnekový dopravník bulk handling – nakládání s volně loženým materiálem industry – průmysl, průmyslové odvětví 24.11.2009
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pitch spacing – rozteč capacity – kapacita rotation speed – rotační rychlost trough – žlab coil – vinout se shaft – hřídel drive – pohánět shaftless – bez hřídele inclined – nakloněný inclination – naklonění, náklon semi-solid – polotuhý non-coherent – sypký efficiently – účinně ash – popel meat and bone meal – masokostní moučka waste – odpad municipal solid waste – tuhý komunální odpad wood chips – štěpka rubble – kamenivo, hrubý štěrk Archimedes screw – Archimédův šroub upwards – směrem nahoru convey – dopravovat elevate – zvedat angle – úhel allowable – přípustný unit – jednotka Obrázky a fotografie použité v této kapitole pochází ze stránek {Wikimedia Commons XH http://commons.wikimedia.org}, kde byly zveřejněny pod licencí {GNU FDL XH http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License}.
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5 Hydraulic Jack 5.1 Hydraulic Jack Hydraulic jacks are a type of jacks which use hydraulic power to lift heavy loads. Comparison with screw jacks Jacks are mechanical devices, which are used to lift heavy loads and which are often capable to apply great forces. The most typical jacks use either a screw thread (these are called screw jacks) or a hydraulic cylinder (these are called hydraulic jacks). Although the screws jacs can also lift very heavy loads, really powerful jacks usually use hydraulic power, which enables them to provide the lifts over greater distances. They are usually designed with a certain lifting capacity, which is indicated by the manufacturers in tons (for example 2 tons). Way of operation A hydraulic jack uses a fluid, which is almost incompressible. Usually a piston pump is used to pump the fluid into a cylinder. Most manufacturers prefer oil, because it is very stable and self lubricating. First the piston goes backward and sucks the fluid (oil) out of the reservoir through an inlet valve into the pump chamber. Then the piston goes forward, the resulting pressure closes the inlet valve ball, opens the discharge valve ball and the piston pushes the fluid through the discharge valve into the cylinder. As a result, the pressure inside the hydraulic cylinder rises. Vocabulary jack – zvedák hydraulic jack – hydraulický zvedák screw jack – šroubový zvedák hydraulic power – hydraulický pohon load – náklad, zatížení mechanical device – mechanické zařízení lift – zvedat, zvednutí capable – schopný apply – aplikovat screw thread – šroubový závit cylinder – válec hydraulic cylinder – hydraulický válec powerful – silný 24.11.2009
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enable – umožnit provide – zajistit distance – vzdálenost design – navrhnout indicate – udávat manufacturer – výrobce ton – tuna fluid – kapalina compressible – stlačitelný incompressible – nestlačitelný piston – píst piston pump – pístové čerpadlo pump – čerpadlo, čerpat oil – olej stable – stálý self lubricating – samomazací suck – sát reservoir – nádrž inlet valve – sací ventil chamber – komora backward – nazpět forward – dopředu pressure – tlak valve ball – koule ventilu discharge valve – výtlačný ventil
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6 Screw Jack 6.1 Screw Jack Screw jack (sometimes also referred to as jackscrew) is a mechanical device used to lift heavy loads. It consists of a leadscrew combined with a lever. Thread Screw jacks usually have an acme thread with teeth in the shape of a trapezoid, 29 degree thread angle and with the height half of the pitch, but other types of thread, such as a square thread, are also possible. The tooth shape of acme thread has a very wide base which makes the screw stronger than for example an equivalent screw with a square thread. Thanks to this strength it is more convenient for heavy loads and it is not easily weakened by wear. Another big advantage is that they are self-locking. Thanks to this they are very safe, unlike hydraulic jacks, which need continual pressure to remain in a locked position. The biggest disadvantage of acme thread is that it is much less efficient. Safety Screws jacks are an important part of various equipment and therefore their safety is considered crucial. However, they require regular maintenance and have to be sufficiently lubricated with grease, otherwise they wear off much quicker and thus their safety decreases very much. An example of bad maintenance with fatal consequences was a crash of an American airplane in California in 2000, which was caused by a failure of a worn and insufficiently lubricated screw jack. Vocabulary screw jack – šroubový zvedák screw – šroub mechanical device – mechanické zařízení load – náklad, břemeno leadscrew – vodící šroub lever – páka acme thread – lichoběžníkový závit trapezoid – lichoběžník degree – stupeň thread angle – vrcholový úhel závitu pitch – rozteč square thread – plochý závit 24.11.2009
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tooth shape – tvar zubu base – základna convenient – vhodný weaken – oslabit wear – opotřebení wear off – opotřebit se worn – opotřebený advantage – výhoda disadvantage - nevýhoda self-locking – samosvorný hydraulic jack – hydraulický zvedák continutal pressure – stálý tlak efficient – účinný safety – bezpečnost equipment – vybabení, přístroj crucial – klíčový maintenance – údržba sufficiently – dostatečně insufficiently – nedostatečně lubricate – mazat grease – mazivo, kolomaz decrease – snížit fatal – smrtelný consequence – následek failure – selhání
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