Unit 3. A forklift truck. Design types
A forklift truck.General operations
A forklift truck (also called a lift truck, a fork truck, or a forklift) is a powered industrial truck used to lift and move materials short distances. The forklift was developed in the early 20th century by various companies. Following World War II the use and development of the forklift truck has greatly expanded worldwide. Forklifts have become an indispensable piece of equipment in manufacturing and warehousing operations.
Forklifts are rated for loads at a specified maximum weight and a specified forward center of gravity. This information is located on a nameplate provided by the manufacturer, and loads must not exceed these specifications. In many jurisdictions it is illegal to remove or tamper with the nameplate without the permission of the forklift manufacturer.
An important aspect of forklift operation is that most have rear-wheel steering. While this increases maneuverability in tight cornering situations, it differs from a driver’s traditional experience with other wheeled vehicles. While steering, as there is no caster action, it is unnecessary to apply steering force to maintain a constant rate of turn.
Another critical characteristic of the forklift is its instability. The forklift and load must be considered a unit with a continually varying center of gravity with every movement of the load. A forklift must never negotiate a turn at speed with a raised load, where centrifugal and gravitational forces may combine to cause a disastrous tip-over accident. The forklift are designed with a load limit for the forks which is decreased with fork elevation and undercutting of the load (i.e., when a load does not butt against the fork "L"). A loading plate for loading reference is usually located on the forklift. A forklift should not be used as a personnel lift without the fitting of specific safety equipment, such as a "cherry picker" or "cage".
Forklifts are a critical element of warehouses and distribution centers. It’s imperative that these structures be designed to accommodate their efficient and safe movement. In the case of Drive-In/Drive-Thru Racking, a forklift needs to travel inside a storage bay that is multiple pallet positions deep to place or retrieve a pallet. Often, forklift drivers are guided into the bay through guide rails on the floor and the pallet is placed on cantilevered arms or rails. These maneuvers require well-trained operators. Since every pallet requires the truck to enter the storage structure, damage is more common than with other types of storage. In designing a drive-in system, dimensions of the fork truck, including overall width and mast width, must be carefully considered.
Forklift control and capabilities
Forklift hydraulics are controlled with either levers directly manipulating the hydraulic valves, or by electrically controlled actuators, using smaller "finger" levers for control. The latter allows forklift designers more freedom in ergonomical design.
Forklift trucks are available in many variations and load capacities. In a typical warehouse setting most forklifts have load capacities between one and five tons. Larger machines, up to 50 tons lift capacity, are used for lifting heavier loads, including loaded shipping containers.
In addition to a control to raise and lower the forks (also known as blades or tines), the operator can tilt the mast to compensate for a load's tendency to angle the blades toward the ground and risk slipping off the forks. Tilt also provides a limited ability to operate on non-level ground. Skilled forklift operators annually compete in obstacle and timed challenges at regional forklift rodeos.
Unit 3. A forklift truck. Design types
The following is a list, in no particular order, of the more common lift truck types:
· Hand pallet truck - no on-board power system of any kind; the operator's muscle power is used to jack-up and move loads.
· Walkie low lift truck - powered pallet truck, usually electrically powered
· Rider low lift truck - usually electrically powered
· Towing tractor - may be internal combustion engine or electrically powered
· Walkie stacker - usually electrically powered
· Rider stacker - usually electrically powered
· Reach truck - variant on a Rider Stacker forklift, designed for small aisles, usually Electrically Powered, named because the forks can extend to reach the load. There are two variants, moving carriage, which are common in North America, and moving mast which are common in the rest of the world, and generally regarded as safer
· Electric Counterbalanced truck - comes in Stand on End Control, Stand on Center Control, and Sit Down Center Control, which is the most numerous
· Internal Combustion Engine Powered Counterbalanced Forklift- comes in Stand on End Control, Stand on Center Control, and Sit Down Center Control, which is the most numerous. Engines may be diesel, kerosene, gasoline, natural gas, butane, or propane fueled, and may be either two stroke spark ignition, four stroke spark ignition (common), two stoke compression ignition, and four stroke compression ignition (common). North American Engines come with advanced emission control systems. Forklifts built in countries such as Iran or Russia will typically have no emission control systems.
· Electric forklifts - powered by lead-acid batteries, several types of forklifts are electric: cushion tire forklifts, scissor lifts, order pickers, stackers, reach trucks and pallet jacks. Electric forklifts are primarily used indoors on flat, even surfaces. Electric forklift batteries last 6 consecutive hours or throughout an 8-hour shift with 2-3 breaks. Batteries prevent the emission of harmful fumes and are recommended for facilities in food-processing and healthcare sectors.
· Fuel cell forklifts produce no local emissions, can work for a full 8-hour shift on a single tank of hydrogen, can be refueled in 3 minutes and have a lifetime of 8–10 years. Fuel-cell-powered forklifts are often used in refrigerated warehouses as their performance is not degraded by lower temperatures.
· Sideloader - comes in Stand on End Control, and Sit Down End Control, which is the most numerous. It may be electrically powered, or have an internal combustion engine. Engines may be diesel, kerosene, gasoline, natural gas, butane, or propane fueled, and may be either two stroke spark ignition, four stroke spark ignition (common), two stoke compression ignition, and four stroke compression ignition (common). North American Engines come with advanced emission control systems. Forklifts built in countries such as Iran or Russia will typically have no emission control systems. Some sideloaders have hybrid drivetrains.
· Telescopic handler - comes in Stand on Center Control, and Sit Down Center Control, which is the most numerous. Usually has an Internal Combustion Engine. Engines are almost always diesel, but sometimes operate on kerosene, and sometimes use propane injection as a power boost. Some old units are two stoke compression ignition, most are four stroke compression ignitions (common). North American Engines come with advanced emission control systems. Forklifts built in countries like Iran or Russia will typically have no emission control systems. Some Telescopic handlers have Hybrid drivetrains.
· Walkie Order Picking truck - usually Electrically Powered
· Rider Order Picking truck - commonly called an "Order Picker"; like a small Reach Truck, except the operator rides in a cage welded to the fork carriage, while wearing a specially designed safety harness to prevent falls. A special toothed grab holds the pallet to the forks. The operator hand transfers the load onto the pallet one article at a time. This is an efficient way of picking less than pallet load shipments, and is popular for use in large distribution centers.