Material Handling Systems

Excavators

Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform (known as the "house"). The house sits atop an undercarriage with tracks or wheels. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the steam shovels and often called power shovels. All movement and functions of a hydraulic excavator are accomplished through the use of 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-operated excavators.

Backhoe

What is a Backhoe Loader?

Backhoe loaders have a very unique appearance -- they have components sticking out every which way. It's obvious what adump truck does just by looking at it; but what are the different appendages of a backhoe used for?

A backhoe loader is an interesting invention because it is actually three pieces of construction equipment combined into one unit. A backhoe loader is:

• A tractor
• A loader
• A backhoe

Each piece of equipment is suited to a particular sort of work. On a typical construction site, the backhoe operator usually uses all three components to get the job done.

The Tractor

The core structure of a backhoe loader is the tractor. Just like the tractors that farmers use in their fields, the backhoe tractor is designed to move easily over all kinds of rough terrain. It has a powerful,turbocharged diesel engine, large, rugged tires and a cab with basic steering controls (a steering wheel, brakes, etc.). Backhoe cabs are either completely enclosed or have an open canopy structure to give the operator protection.

The Loader

The loader is attached in the front and the backhoe is attached in the back. These two components serve very different functions.

The loader can do several different things. In many applications, you use it like a big, powerful dustpan or coffee scoop. You usually don't dig with it; you mostly use it to pick up and carry large amounts of loose material. It's also used to smooth things over like a butter knife, or to push dirt like a plow. The operator controls the loader while driving the tractor.

The Backhoe

The backhoe is the main tool of the backhoe loader. It's used to dig up hard, compact material, usually earth, or to lift heavy loads, such as a sewer box. It can lift this material and drop it in a pile to the side of the hole.

Basically, the backhoe is a big, extremely powerful version of your arm or finger. It has three segments:

• The boom
• The stick
• The bucket

This arrangement is very similar to your arm. Your arm has three segments -- your upper arm, forearm and hand.

The backhoe segments are connected by three joints, comparable to your wrist, elbow and shoulder. The backhoe moves in pretty much the same way as your arm. In a Caterpillar® backhoe, the boom is bent upward to make it easier to dig with obstacles in the way. This design also provides extra space for the bucket when the operator curls it in with a full load.

The backhoe can dig all sorts of holes, but is especially suited for digging ditches. To use the backhoe, the operator has to park the tractor and turn the seat around.

So what do the tractor, loader and backhoe have to do with each other? The tractor component is for moving the other two components from place to place, and the operator also maneuvers it when using the loader. The loader and backhoe components are a natural combination for all sorts of jobs. When you dig up a lot of dirt to make a ditch or any other sort of hole, you generally need a loader to either move the dirt out of the area or to fill the dirt back in once you've got the pipes, power lines, etc. in position. The most common application for a backhoe loader is this basic job -- digging a trench with the backhoe and then back-fillingit with the loader.

The Stabilizer Legs

The other appendages you'll typically notice on a backhoe loader are the two stabilizer legs just behind the rear wheels. These legs are crucial to backhoe operation because they take the brunt of the weight when a backhoe is digging. Without the stabilizer legs, the weight of a heavy load or the downward force of digging into the ground would strain the wheels and tires, and the whole tractor would bounce constantly. The stabilizers keep the tractor steady, minimizing the jostling effect of digging with the backhoe. They also secure the tractor so that it won't slip into the ditch or hole.

The stabilizer legs have two types of "shoes," so that they can be planted securely on both dirt and pavement. The grouser shoe side digs into the dirt for a better grip, but would tear up the pavement if you were to use it on a road. For a good grip on asphalt, the operator simply flips the rubber-padded shoe into position.

Hydraulic Power

If you've ever watched a backhoe at work, you know that it is an extraordinarily powerful tool. An experienced operator can dig a 5-foot-deep, 10-foot-long ditch in less than 15 minutes. Just think how long it would take you to do that with only a shovel! Amazingly, all of this work is done withhydraulics -- pumping liquid to move pistons.

The concept of hydraulic machinery may seem pretty bizarre -- how can pumping liquid give you such power? -- but it's actually very simple. First, let's look at the basic idea of a hydraulic system, and then we'll see how a backhoe uses these systems to dig and load such huge amounts of dirt.

Hydraulic systems simply transmit forces from point to point through fluid. Most systems use anincompressible fluid, a fluid that is as dense as it can get. This sort of fluid transmits nearly all of the original force instead of absorbing some of it. The most commonly used incompressible fluid in hydraulic machinery is oil.

In the very simple hydraulic machine shown below, the operator pushes on the oil with one piston so that the oil pushes on another piston, raising it up.

Hydraulic multiplication

Because the second piston has a larger diameter than the first piston, the second piston moves a shorter distance but pushes up with greater force.

The basic concept at work is a trade between distance and force. The work you do in pressing down on the piston on the left has two components -- the amount of force you apply and how far you push the piston. This pushes down a certain amount of fluid. Since the fluid is incompressible, it can't absorb the force you apply, so it pushes up on the piston on the right. The fluid has the same pressure (pounds per square inch) at every point in the system. Since the pressure at the piston on the right is working on a larger area, that piston pushes upward with a greater force.

It's pretty easy to figure out the exact multiplication factor. Assume that the piston on the left has a 2-inch diameter (1-inch radius), while the piston on the right has a 6-inch diameter (3-inch radius). The area of each piston is Pi * r². The area of the left piston is therefore 3.14 (3.14 * 1²), while the area of the piston on the right is 28.26 (3.14 x 3²). The piston on the right is nine times larger than the piston on the left. This means that any force applied to the left-hand piston will be nine times greater on the right-hand piston. So, in the illustration above, the 100-pound downward force applied to the left piston creates a 900-pound upward force on the right piston. But, in keeping with the force-distance trade-off, you've moved the left-hand piston 9 inches and raised the right-hand piston only 1 inch.

In the backhoe loader shown above, the hydraulic system pumps oil at up to 3,300 pounds per square inch, and the cylinder pistons in the backhoe arm have a diameter of up to 5.25 inches. This gives each cylinder piston a force of 70,000 pounds!

Different Types of Material Handling Equipment

Material handling equipment  encompasses a diverse range of tools, vehicles, storage units, appliances and accessories involved in transporting, storing, controlling, enumerating and protecting products at any stage of manufacturing, distribution consumption or disposal.

Categories of Material Handling Equipment

The four main categories of material handling equipment include: storage, engineered systems, industrial trucks and bulk material handling.

Storage and Handling Equipment

Storage equipment  is usually limited to non-automated examples, which are grouped in with engineered systems. Storage equipment is used to hold or buffer materials during “downtime's,” or times when they are not being transported. These periods could refer to temporary pauses during long-term transportation or long-term storage designed to allow the buildup of stock. The majority of storage equipment refers to pallets, shelves or racks onto which materials may be stacked in an orderly manner to await transportation or consumption. Many companies have investigated increased efficiency possibilities in storage equipment by designing proprietary packaging that allows materials or products of a certain type to conserve space while in inventory.
 
Examples of storage and handling equipment include:
 

• Racks, such as pallet racks, drive-through or drive-in racks, push-back racks, and sliding racks

• Stacking frames

• Shelves, bins and drawers

• Mezzanines

Engineered Systems
 
Engineered systems cover a variety of units that work cohesively to enable storage and transportation. They are often automated. A good example of an engineered system is an Automated Storage and Retrieval System, often abbreviated AS/RS, which is a large automated organizational structure involving racks, aisles and shelves accessible by a “shuttle” system of retrieval. The shuttle system is a mechanized cherry picker that can be used by a worker or can perform fully automated functions to quickly locate a storage item’s location and quickly retrieve it for other uses.
 
Other types of engineered systems include:
 

• Conveyor systems

• Robotic delivery systems

• Automatic guided vehicles (AGV)

 
Industrial Trucks
 
Industrial trucks refer to the different kinds of transportation items and vehicles used to move materials and products in materials handling. These transportation devices can include small hand-operated trucks, pallet-jacks, and various kinds of forklifts. These trucks have a variety of characteristics to make them suitable for different operations. Some trucks have forks, as in a forklift, or a flat surface with which to lift items, while some trucks require a separate piece of equipment for loading. Trucks can also be manual or powered lift and operation can be walk or ride, requiring a user to manually push them or to ride along on the truck. A stack truck can be used to stack items, while a non-stack truck is typically used for transportation and not for loading.
 
There are many types of industrial trucks:

• Hand trucks

• Pallet jacks

• Pallet trucks

• Walkie stackers

• Platform trucks

• Order picker

• Sideloader

• Many types of AGV

 
Bulk Material Handling Equipment

Bulk material handling refers to the storing, transportation and control of materials in loose bulk form. These materials can include food, liquid, or minerals, among others. Generally, these pieces of equipment deal with the items in loose form, such as conveyor belts or elevators designed to move large quantities of material, or in packaged form, through the use of drums and hoppers.

• Conveyor belts

• Stackers

• Reclaimers

• Bucket elevators

• Grain elevators

• Hoppers

• Silos