2015

Trenchers used in construction and other tasks where heavy equipment is needed are much larger. They may be designed as attachments for tractors, or as standalone pieces of heavy equipment. In both cases, the trencher is controlled by a heavy equipment operator who sits inside the cabin of the equipment and controls the trencher from there, driving the equipment over the ground being trenched and manipulating the depth and speed of the trencher as needed.

Heavy equipment trenchers include wheel trenchers and chain trenchers. Wheel trenchers are used in relatively soft soil, while chain trenchers are capable of cutting into hard ground, operating much like a chainsaw. Both can be dangerous to operate, and special precautions must be observed by the operator and people on the work site to avoid injuries. This type of specialty trenching equipment can also be quite costly.

For those who have been reading novels set in the medieval era and won-

НОrТЧР аСКЭ СОКvв ЛЮТХНТЧР ОqЮТpЦОЧЭ аКs НШТЧР КЭ ЭСО ЭКЛХО, ЭСО ЭОrЦ “trencher” is also used in a food and dining sense, to refer to a platter used to hold food. The original trenchers were pieces of partially stale bread which were carved into bowls and eaten after the meal, eventually being replaced by wooden plates. Each diner was typically expected to bring his or her own trencher and knife for cutting

and manipulating food to the table. Both senses of the word come from the same rШШЭ, аСТМС ЦОКЧs “ЭШ МЮЭ.”

http://www.wisegeek.com/what-is-a-trencher.htm

1.What work does a trencher make?

2.АСКЭ НТН ЭСО ЭОrЦ “ЭrОЧМСОr” ЦОКЧ ТЧ ЭСО ЦОНТОvКХ ОrК?

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in Fresno, California, USA he had recognised the dependence of the Central San Joaquin Valley on irrigation, and the need for a more efficient means of constructing canals and ditches in the sandy soil. In perfecting the design of his machine, Porteous made several revisions on his own and also traded ideas with William Deidrick, Frank Dusy, and Abijah McCall, who invented and held patents on similar scrapers. Porteous bought the patents held by Deidrick, Dusy, and McCall, gaining sole rights to the Fresno Scraper.

The design of the Fresno Scraper forms the basis of most modern earthmoving scrapers, having the ability to scrape and move a quantity of soil, and also to discharge it at a controlled depth, thus quadrupling the volume which could be handled manually.

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Prior scrapers pushed the soil ahead of them, while the Fresno scraper lifted it into a C-shaped bowl where it could be dragged along with much less friction. By lifting the handle, the operator could cause the scraper to bite deeper. Once soil was gathered, the handle could be lowered to raise the blade off the ground so it could be dragged to a low spot, and dumped by raising the handle very high.

This design was so revolutionary and economical that it has influenced the design of modern bulldozer blades and earth movers to this day. Between 1884 and 1910 thousands of Fresno scrapers were produced at the Fresno Agricultural Works which had been formed by Porteous, and used in agriculture and land levelling, as well as road and railroad grading and the construction industry. They played a vital role in the construction of the Panama Canal and later served the US Army in World War I.

It was one of the most important agricultural and civil engineering machines ever made. In 1991 the Fresno Scraper was designated as an International Historic Engineering Landmark by the American Society of Mechanical Engineers. It is currently on display at the San Joaquin County Historical Society & Museum.

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pumps: the two main pumps are for supplying oil at high pressure (up to 5000 psi) for the rams, swing motor, track motors, and accessories, and the third is a lower pressure (700 psi) pump for Pilot Control, this circuit used for the control of the spool valves, this allows for a reduced effort required when operating the controls.

The two main sections of an excavator are the undercarriage and the house. The undercarriage includes the blade (if fitted), tracks, track frame, and final drives, which have a hydraulic motor and gearing providing the drive to the individual tracks, and the house includes the operator cab, counterweight, engine, fuel and hydraulic oil tanks. The house attach-

es to the undercarriage by way of a center pin, allowing the machine to sХОа 360° ЮЧСТЧНОrОН.

The main boom attaches to the house, and can be one of several different configurations:

Most are mono booms: these have no movement apart from straight up and down.

Some others have a knuckle boom which can also move left and right in line with the machine.

Another option is a hinge at the base of the boom allowing it to

СвНrКЮХТМКХХв pТvШЭ Юp ЭШ 180° ТЧНОpОЧНОЧЭ ЭШ ЭСО СШЮsО; СШаОvОr, ЭСТs Тs

generally available only to compact excavators.

There are also triple-articulated booms (TAB).

Attached to the end of the boom is the stick (or dipper arm). The stick provides the digging force needed to pull the bucket through the ground. The stick length is optional depending whether reach (longer stick) or break-out power (shorter stick) is required.

On the end of the stick is usually a bucket. A wide, large capacity (mud) bucket with a straight cutting edge is used for cleanup and levelling or where the material to be dug is soft, and teeth are not required. A general purpose (GP) bucket is generally smaller, stronger, and has hardened side cutters and teeth used to break through hard ground and rocks. Buckets have numerous shapes and sizes for various applications. There are also

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many other attachments which are available to be attached to the excavator for boring, ripping, crushing, cutting, lifting, etc.

Before the 1990s, all excavators had a long or conventional counterweight that hung off the rear of the machine to provide more digging force

and lifting capacity. This became a nuisance when working in confined areas. In 1993 Yanmar ХКЮЧМСОН ЭСО аШrХН’s first Zero Tail Swing excava-

tor, which allows the counterweight to stay inside the width of the tracks as it slews, thus being safer and more user friendly when used in a confined

space. This type of machine is now widely used throughout the world. TСОrО КrО ЭаШ ЦКТЧ ЭвpОs ШП “CШЧЭrШХ” configuration generally use in

excavators to control the boom and bucket, both of which spread the four main digging controls between two x-y joysticks. This allows a skilled operator to control all four functions simultaneously. The most popular configuration in the US is the SAE controls configuration while in other parts of the world, the ISO control configuration is more common. Some manufacturers such as Takeuchi have switches that allow the operator to select which control configuration to use.

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tandem roller

steam roller

ballast roller

vibrating roller

pneumatic roller

static roller

roller passage

grid roller

tractor-mounted roller

The first road rollers were horse-drawn, and were probably just borrowed farm implements.

Since the effectiveness of a roller depends to a large extent on its weight, self-powered vehicles replaced horse-drawn rollers from the mid19th century. The first such vehicles were steam rollers. Single-cylinder steam rollers were generally used for base compaction and run with high engine revs in a low gear to promote bounce and vibration from the crankshaft through to the rolls in much the same way as a vibrating roller. The double cylinder or compound steam rollers became popular from around 1910 onwards and were used mainly for the rolling of hot-laid surfaces due to their smoother running engines, however both cylinder types are capable of rolling the finished surface. Steam rollers were often dedicated to a task by their gearing as the slower engines were for base compaction whereas the higher geared models were often referred to as 'chip chasers' which followed behind the hot tar and chipping laying machines. Some road companies in the United States used steamrollers through the 1950s, and in the UK, some remained in commercial service until the early 1970s.

As internal combustion engine technology improved during the 20th century, kerosene-, gasoline- (petrol), and diesel-powered rollers gradually replaced their steam-powered counterparts. The first internal-combustion powered road rollers were very similar to the steam rollers they replaced. They used similar mechanisms to transmit power from the engine to the wheels, typically large, exposed spur gears. Some users did not like them in their infancy, as the engines of the era were typically difficult to start, particularly the kerosene-powered ones.

Virtually all road rollers in commercial use now use diesel power.

1.What were the first road rollers?

2.What does the effectiveness of a roller depend on?

3.What is the difference between a steam roller and an internalcombustion powered road roller?

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