Excavator

Excavators  are heavy construction equipment, consisting of a boom, stick (or dipper), bucket, and cab on a rotating platform known as a «house». The house stands on a chassis with caterpillars or wheels. They are a natural evolution of the steam shovels and are often erroneously referred to as backhoes. All movements and functions of a hydraulic excavator are performed by hydraulic fluid, with hydraulic cylinders and hydraulic motors. Due to the linear actuation of hydraulic cylinders, their mode of operation is fundamentally different from cable-driven excavators, which use winches and steel ropes to perform movements.

Terminology

Excavators are also called diggers, power shovels, or 360-degree excavators (sometimes simply abbreviated as «360»). Crawler excavators are sometimes referred to as «track shovels» by analogy with a backhoe. In the UK and Ireland, wheeled excavators are sometimes referred to as «rubber ducks».

Usage

• Digging trenches, pits, foundations
• Material handling
• Shrub cutting with hydraulic saw and mower
• Forestry work
• Mulching the forest
• Demolition with hydraulic grippers, cutting and breaking attachments
• Mining, especially but not only open pit mining
• River dredging
• Hydroextraction to access fragile underground infrastructure using high pressure water
• Pile driving together with a pile driver
• Drilling shafts for foundations and blasting using an auger or hydraulic drilling rig.
• Snow removal with snow plows and snow plows
• Aircraft recycling

Configurations

Modern hydraulic excavators come in a wide variety of sizes. Smaller ones are called mini or compact excavators. For example, Caterpillar’s smallest mini excavator weighs 2,060 pounds (930 kg) and has 13 hp; their largest model is the largest excavator available (designed and manufactured by Orenstein & Koppel, Germany, before being taken over in 2011 by Caterpillar under the name «RH400»), the CAT 6090, which weighs over 2,160,510 pounds (979,990 kg), has 4500 hp, and the bucket volume reaches 52.0 m³.

Hydraulic excavators typically transfer engine power to (usually) three hydraulic pumps, rather than to a mechanical transmission. Two main pumps supply high pressure oil (up to 5,000 psi, 345 bar) for the booms, swing motor, track motors and accessories, while a third low pressure pump (~700 psi, 48 bar) is used for pilot control of spool valves; this third scheme allows you to reduce physical effort when working with controls. Typically, the 3 pumps used in excavators consist of 2 variable displacement piston pumps and a gear pump. The location of the pumps in the excavator assembly varies with different manufacturers using different formats.

The three main parts of an excavator are the undercarriage, the body, and the boom (a boom is also used). The undercarriage includes tracks, a track frame and final drives, which have a hydraulic motor and gear drive to drive individual tracks. The undercarriage may also have a moldboard, similar to that of a bulldozer. The house includes an operator’s cab, counterweight, engine, fuel and hydraulic oil tanks. The house is attached to the chassis with a central pin. High-pressure oil is supplied to the hydraulic motors of the tracks through a hydraulic pivot on the pin shaft, which allows the machine to turn 360° unimpeded and thus allows left and right movement. The hand provides up-down and closer-further (or digging) movement. The arms usually consist of an arrow,

The boom is attached to the house and provides movement up and down. It can be one of several different configurations:

• The most common are mono-arrows; they have no movement other than a direct up and down movement.
• Some others have a swivel boom that can also move left and right with the machine.
• Another option is a hinge at the base of the boom that allows hydraulic rotation through 180° independent of the house; however, this is usually only available to compact excavators.
• Angle adjustable booms have an additional pivot in the middle of the boom to change the curvature of the boom. They are also called tri-jointed arrows (TAB) or three-piece arrows.

Attached to the end of the arrow is a handle (or hilt). The arm provides the digging motion needed to pull the bucket across the ground. Stick length is optional depending on whether reach (longer stick) or breakout force (shorter stick) is required. The most common is a mono-stick, but there are, for example, telescopic ones.

At the end of the stick is usually a bucket. A wide, roomy (mud) bucket with a straight cutting edge is used for cleaning and leveling or where the material being dug is soft and no teeth are required. A General Purpose Bucket (GP) is generally smaller, stronger, and has hardened side cutters and teeth used to break through hard soil and rocks. Buckets come in many shapes and sizes for a variety of applications. There are also many other attachments that can be attached to the excavator for drilling, loosening, crushing, cutting, lifting, and more. Attachments can be attached with pins similar to other parts of the boom, or with a variety of quick couplers. Excavators in Scandinavia often have a tilt-and-turn mechanism.

An illustration of the controls of a hydraulic excavator, the color of the controls matches the moving part.

Until the 1990s, all excavators had a long or conventional counterweight that hung from the rear of the machine to provide greater digging force and lift capacity. This created inconvenience when working in a limited space. In 1993, Yanmar launched the world’s first zero tail turn excavator, which allows the counterweight to stay within track width when turning, making it safer and more user friendly when used in confined spaces. This type of machine is currently widely used throughout the world.

There are two main types of «Control» configuration commonly used in excavators to control the boom and bucket, both of which distribute the four main dig controls between two xy joysticks. This allows an experienced operator to control all four functions at the same time. The most popular configuration in the US is the SAE control 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.

Attachments for excavators

The capabilities of hydraulic excavators have gone far beyond earthworks using a bucket. With the advent of hydraulic powered attachments such as hydraulic hammer  ,  grapple or auger  , an excavator is often used for many other purposes besides excavation. Many excavators are equipped with a quick coupler to make it easier to mount attachments, making the machine more efficient on the job site. Excavators are commonly used in conjunction with loaders and bulldozers. Most wheeled, compact and some medium (11 to 18 tons) excavators have a backfill (or dozer) blade. This is a horizontal dozer blade attached to the undercarriage and used to level and push the removed material back into the hole.