Lekce 1: Belt Conveyor
Kapitola 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.
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
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
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Belt Conveyor powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you briefly describe belt conveyors?
- How do they operate?
- Can you give some examples of their application?
Kapitola 4: Autotest
- What is the powered pulley called?
- What is the unpowered pulley called?
- Which type of belt conveyor is usually used for transporting e. g. grain?
- What are elevator belts used for?
- What can the under layer (carcass) of belts used in general material handling be made of?
Lekce 2: Screw Conveyor
Kapitola 1: Screw Conveyor
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
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Screw Conveyor powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe screw conveyors?
- How do they operate?
- Can you give some examples of materials, which they can transport?
Kapitola 4: Autotest
- Where are screw conveyors usually used?
- How can you influence the capacity of the conveyor at the given speed?
- How is it driven?
- How are they used?
- What sort of material do they usually transport?
Lekce 3: Hydraulic Jack
Kapitola 1: Hydraulic Jack
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 jacks 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
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
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Hydraulic Jack powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe hydraulic jacks?
- How do they operate?
- Can you compare them with screw jacks?
Kapitola 4: Autotest
- Hydraulic jacks can lift
- How is their capacity usually indicated?
- What do they use for their operation?
- How is the fluid pumped into the cylinder?
- How does the pressure in the cylinder change when lifting the loads?
Lekce 4: Screw Jack
Kapitola 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
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
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Screw Jack powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe screw jacks?
- What are they used for?
- How do they have to be maintained?
Kapitola 4: Autotest
- What do the screw jacks usually consist of?
- What is the typical shape of the teeth of its thread.
- What does the base of the tooth typically look like?
- Why are they considered very safe?
- What is thei biggest disadvantage of acme threats?
Lekce 5: Rack and Pinion
Kapitola 1: Rack and Pinion
A rack and pinion is a type of gearing, consisting of a pair of gears, which are used to convert rotational motion into linear movement. It can be used to lift loads as well. One of the gears is a circular pinion, which rotates and meshes its teeth with the teeth of a flat bar, called the rack. As the pinion rotates, the rack is moved to the side, or (if the rack is fixed) the pinion moves along it.
Application
The rack and pinion gearing can be often seen in various steering mechanisms of cars or other vehicles. For this purpose it was improved by an American engineer Arthur E. Bishop, who wanted to improve the vehicles response to the drivers’ manoeuvres with the steering wheel, especially at high speeds, which had always made steering very difficult. Since that time it has become the most commonly applied steering mechanism in modern vehicles.
Rack railway
Another very frequent usage of the rack and pinion system can be found in a rack railway (also called rack-and-pinion railway or cog railway), where it enables the train to move up or down a very steep slope, without a danger of slipping wheels. The rack and pinion mechanism was first adopted for locomotives and patented by English mining engineer John Blenkinsop in 1811. The train is equipped with one or more cog wheels (pinions) that mesh with a rack rail. This mechanism allows the trains to move on steep gradients and therefore they are used especially in mountains.
Vocabulary
Rack and pinion – hřebenový převod
Rack – ozubnice
Pinion – ozubené kolečko, pastorek
Gearing – převod
Gear, cog – ozubené kolo
Convert – převést
Rotational motion – rotační pohyb
Linear movement – lineární pohyb
Rotate – otáčet se
Mesh – prolínat se
Bar – tyč
Fixed – upevněný
Steering – řízení
Vehicle – vozidlo
Manoeuvres – ovládání
Steering wheel – volant
Speed – rychlost
Applied – používaný
Rack railway, rack-and-pinion railway, cog railway – ozubnicová železnice
Steep – prudký
Slope – svah
Slipping – prokluzování
Wheel – kolo
Mining engineer – důlní inženýr
Equipped – vybavený
Rail – kolej, kolejnice
Gradient – sklon
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Rack and Pinion powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe the rack and pinion system?
- Can you give some examples of its application?
- What is a rack railway?
Kapitola 4: Autotest
- Rack and pinion systems are used to
- How is the cog wheel called?
- What happens, if the rack is fixed?
- Can this be used in steering mechanisms of cars?
- What is the biggest advantage of a rack railway?
Lekce 6: Scissor jack
Kapitola 1: Scissor jack
Description
The main difference from other screw jacks is that the leadscrew of a scissor jack is in horizontal position (typical screw jack has the leadscrew positioned vertically). The leadscrew operates two metal arms, which are usually of equal length. The term “scissor“ is derived from its shape, because the two arms resemble the letter X.
Operation
When turning the screw, the arms can move nearer or farther from each other, and thus the crossing pattern is elongated and the load is lifted. The force that is necessary to apply to the leadscrew can be calculated from the following scissor jack equation:
Where:
F is the force provided by the leadscrew
W are combined weights of the load and the load platform
Wa is the combined weight of the two scissor arms
φ is the angle between the scissor arms and the horizontal
If the lift consists of several pairs of scissors combined in a series, then the force (F) has to be multiplied by the number of scissor mechanisms. The equation can be applied only to the scissor jacks with equally long arms.
Vocabulary
Scissor jack, scissor lift, scissor mechanism – nůžkový zvedák
Screw jack – šroubový zvedák
Screw – šroub
Leadscrew – vodící šroub
Metal – kovový
Arm – rameno
Equal – stejný
Shape – tvar
Resemble – podobat se
Pattern – vzor
Elongate – prodloužit
Lift – zvednout; zvedák
Force – síla
Apply – použít
Calculate – vypočítat
Equation – rovnice
Weight – hmotnost
Load – náklad, zatížení
Platform – plošina
Angle – úhel
Horizontal – horizontála
Multiply – násobit
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}.
Kapitola 2: Cvičení
- Studenti zpracují na téma Scissor Jack powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you briefly describe scissor jacks?
- How do they operate?
- How can you calculate the force that is necessary to apply to the leadscrew?
Kapitola 4: Autotest
- Scissor jack is a type of
- What is the typical position of the leadscrew?
- Can the arms of the scissor jack have different lengths?
- What happens with the position of the arms, when the load is lifted?
- Can scissor jacks consist of several pairs of scissors?