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Chariot élévateur ( English )
Un chariot élévateur est un engin de manutention destiné au transfert de charges dans les usines ou les halles de stockage. Ses domaines d'activité sont principalement la reprise des produits finis des chaînes de fabrication vers les lieux de stockage, le chargement ou déchargement des moyens de transport tel les wagons ou camions , l'aide au chargement ou déchargement dans les cales des navires, mais sa grande souplesse lui permet beaucoup d'usages.
Manutention d'un conteneur de 40"
Les premières versions ont été des chariots à fourches fabriqués en 1917 par l'industriel anglais installé aux États-Unis, Eugene Clark . La renommée de Clark dans le domaine a fait de ce nom de marque un nom commun , c'est toutefois aussi vrai de Fenwick qui fut le premier à construire de telles machines en France.
Le chariot élévateur est connu pour sa compacité et son aptitude à la manutention de palettes . Il existe toute une variété de modèles pouvant transporter des charges de 1,5 tonnes (palettes) à plus de 40 tonnes ( conteneurs ), et pouvant gerber sur des hauteurs considérables (plus de 10 mètres). Il est équipé naturellement de deux fourches, mais il peut être aussi équipé de pinces hydrauliques pour la prise de bobines ou de rouleaux de papier, de palonniers à conteneurs, de pieux horizontaux pour les pièces cylindriques à axe évidé etc.
Ces machines fonctionnent généralement avec des moteurs thermiques alimentés au gaz pour les petites et moyennes et au gasoil pour les grosses. Les petites unités peuvent aussi être à moteur électrique avec une alimentation par batteries.
Description technique
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Les éléments d'un chariot élévateur (agrandir)
Un chariot élévateur typique est généralement composé des éléments suivants :
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Le chariot lui-même, est une machine mobile avec des roues et/ou des chenilles dirigées par un train directionnel. Pour une plus grande sécurité et stabilité de l'engin, celui-ci peut être équipé de « pneus » pleins, évitant les risques liés à une crevaison au cours d'une opération de chargement, manutention ou déchargement.
- Un moteur à combustion interne alimenté par du GPL , de l' essence ou du gazole , ou un moteur électrique à courant continu ou à courant alternatif alimenté par une batterie d'accumulateurs ou par des piles à combustible .
- Le mât est l'assemblage vertical qui permet de lever, de baisser et de pencher la charge. Le mât peut être actionné hydrauliquement : il se compose d'un ou plusieurs vérin et de rails emboîtés les uns dans les autres qui servent pour soulever, baisser et pour la stabilité latérale. Le mât peut aussi être actionné par des chaînes par un moteur hydraulique fournissant la puissance motrice. Dans tout les cas, le circuit hydraulique est équipé d'un limitateur de vitesse de descente.
- Le porte-charge, sur lequel sont fixées la ou les fourche en métal ou les équipements optionnels, se déplace le long du mât au moyen de chaînes, ou en étant fixé directement au vérin hydraulique. Généralement, le porte-charge qui est monté sur roulement , est guidé par, et se déplace entre les deux rails du mât.
- Une ou plusieurs fourches , qui sont les bras en forme de L qui retiennent la charge. La partie verticale arrière de la fourche est le plus souvent accrochée au porte-charge au moyen d'un crochet ou d'un loquet (fourches de classe I à IV). Quelques fourches sont montées sur un axe . La portion horizontale des fourches est effilée pour faciliter l'insertion dans ou sous la charge, on peut les déplacer horizontalement et verticalement au moyen de vérins hydrauliques. Pour des utilisations particulières, un chariot à fourches peut être équipé avec toute une variété d'autre équipements, incluant les pinces, les pinces pour carton, les boucliers racleurs, les manipulateurs de poteaux, les manipulateur de container, les pinces pour rouleaux et d'autres. Ces équipements se déduisent généralement de la charge admissible du chariot. Cette réduction est provoquée par l'agrandissement de la dite distance de priorité de fret .
- Un support arrière de charge ou dosseret est installé quand la charge est plus haute que le haut du porte-charge ; c'est une extension semblable à un ratelier boulonné ou soudée au porte-charge pour empêcher la charge de se déplacer en arrière.
- La cabine, qui avec une place pour le conducteur ou cariste , contient les pédales de commande, le volant de direction, les boutons et les leviers de commande hydraulique pour diriger la machine, un tableau de bord avec les voyants et un diagramme de charge informant le conducteur du poids à ne pas dépasser en fonction des dimensions de la charge et de la hauteur d'élévation. La cabine peut être ouverte, ou fermée, mais est limitée par l'ensemble de protection semblable à une cage. Le cariste qui conduit les machines est protègé, de n'importe quel objet tombant, par un toit en métal soutenu par des poteaux
Exemple de plaque de charge d'un chariot élévateur
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Les chariot élévateurs en porte-à-faux ont un contrepoids d'équilibrage, qui est une masse en fer attachée à l'arrière de la machine, nécessaire pour compenser la charge. Dans un chariot de levage électrique, l'ensemble des batteries acide-plomb elles-même peuvent servir de contrepoids. Le fret maximum à soulever en fonction de la longueur de course, peut être lu sur un diagramme de charge admissible.
Marques
A forklift truck , a lift truck or a forklift is a powered industrial truck used to lift and transport materials, normally by means of steel forks inserted under the load. Forklifts are most commonly used to move loads stored on pallets . The forklift was developed in the 1920s by various companies including the transmission manufacturing company Clark (today known as Clark Material Handling Company ) and the hoist company Yale & Towne Manufacturing (today known as Yale Materials Handling Corporation) [1] . It has since become an indispensable piece of equipment in manufacturing and warehousing operations.
Design types Top
There are many national and/or continental associations related to the industrial trucks. The three major ones are the Industrial Truck Association (North America), the Fédération Européenne de la Manutention (Europe), and the Japan Industrial Vehicles Association (Japan). There are many significant contacts among them and they have established joint statistical and engineering programs. One program is the WITS (World Industrial Trucks Statistics) published every month to the association memberships. The statistics are separated by area ( continent ), country, and class of machine. While the statistics are generic, and do not count production from most of the smaller manufacturers, the information is significant for its depth. These contacts have brought to a common definition of the Class System , which all the major manufacturers adhere to. Following is the list of the more common truck types, from the smallest to the biggest:
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Hand pallet truck (a "pump truck" or a "chep truck", a simple mechanism whereby hand-pumped hydraulics raise or lower a single pallet simply to provide clearance from the floor for manual (hand) pulling; heavy loads are unwieldy or risk injury to operators.) (Separate article to follow with photographs.)
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Walkie low lift truck (powered pallet truck, usually electrically powered)
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Rider low lift truck
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Towing tractor
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Walkie stacker
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Rider stacker
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Reach truck (small forklift, designed for small aisles, usually electrically powered)
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Electric counterbalanced truck
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IC counterbalanced truck
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Telescopic handler
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Slip Sheet machine
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Walkie Order Picking truck
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Rider Order Picking truck (commonly called an "Order Picker"; like a small forklift, except the operator rides up to the load and transfers it article by article)
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Very narrow aisle truck (usually a reach truck designed for aisles less than five feet wide)
For a common (North American) reference, Home Depot , Lowes and Rona generally employ reach trucks inside the store and "traditional" forklifts when the store is closed. Most employees of such warehouse stores will happily explain the differences between the machines.
Characteristics Top
A typical forklift may be generally described as follows:
- The truck proper, which is a motive machine with wheels and/or tracks powered through a drive train.
- A liquefied petroleum gas –, petrol - or diesel fueled internal combustion engine , or an electric motor(s) either direct current or alternating current powered by either a battery or fuel cells .
- The mast , which is the vertical assembly that does the work of raising, lowering, and tilting the load; the mast is either hydraulically operated consisting of one or more cylinder(s) and interlocking rails for lifting and lowering operations and for lateral stability, or it may be chain operated with a hydraulic motor providing motive power.
- The carriage , which comprises flat metal plate(s) and is moved along the mast either by means of chains, or by being directly attached to the hydraulic cylinder.
- One or more forks , which are the L-shaped members that engage the load. The back vertical portion of the fork attaches to the carriage most often by means of a hook or latch (Class I to IV forks), while some forks use a shaft mount. The front horizontal portion (which is usually tapered for ease of insertion) is inserted into or under the load, usually on a pallet or skid . Alternatively, a variety of other equipment is available, including slipsheet clamps , carton clamps , carpet rams , pole handlers , container handlers , roll clamps and others.
- A load back rest is fitted when the load is higher than the top of the carriage, and is a rack-like extension either bolted or welded to the carriage to prevent the load from shifting backward.
- Rider operated machines have a driver 's overhead guard , which is a metal roof , supported by posts, that helps protect the operator from any falling objects.
- The cab, which may contain a seat for the operator, along with the control pedals , steering wheel , levers , and switches for controlling the machine and a dashboard containing operator readouts. The cab may be open, or closed, but is bounded by the cage-like overhead guard assembly.
- Counterbalance machines have a counterweight , which is a heavy iron mass attached to the rear of the machine, necessary to compensate for the load. In an electric forklift, the large lead-acid battery itself may serve as part of the counterweight.
Control and capability Top
Forklift trucks are available in many variations and load capacities. In a typical warehouse setting most forklifts used have load capacities of around one to five tons, though machines of over 50 tonnes capacity have been built and operated.
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. Some machines also allow the operator to move the tines and backrest laterally (side-shift), allowing easier placement of a load. To aid the handling of skids that may have become excessively tilted and other specialty material handling needs, some forklifts are fitted with a mechanism that allows the tines to be rotated. In addition, a few machines offer a hydraulic control to move the tines together or apart, removing the need for the operator to get out of the cab to manually adjust for a differently sized load.
Roll and barrel clamp attachments for handling barrels, kegs, or paper rolls also have a control to operate the clamp pads that grab the load, such attachments also usually have a rotate function so that a vertically stored paper roll can be inserted into the horizontal intake of a printing press.
In some locations (such as carpet warehouses) a long metal pole is used instead of forks to lift large rolls. Similar devices, though much larger are used to pick up 40 tonne metal coils.
Another variation, used in some manufacturing facilities, utilizes forklift trucks with a clamp attachment that the operator can open and close around a load, instead of forks. Products such as cartons, boxes, etc., can be moved with these trucks. The product to be moved is squeezed, lifted, and carried to its destination. These are generally referred to as "clamp trucks".
Skilled forklift operators annually compete in obstacle and timed challenges at regional forklift rodeos .
Forklift safety Top
Standards
Forklift safety is subject to a variety of standards world wide. The most important standard is the ANSI B56—of which stewardship has now been passed from the American National Standards Institute (ANSI) to the Industrial Truck Standards Development Foundation after multi-year negotiations. ITSDF is a non-profit organization whose only purpose is the promulgation and modernization of the B56 standard. The B56 standard is now a free download from the ITSDF website .
General
Forklifts are rated for loads at a specified maximum weight and a specified forward centre 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 many have rear-wheel steering. While this increases maneuverability in tight cornering situations, it differs from a driver's traditional experience with other wheeled vehicles 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 centre 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 will be designed with a load limit for the forks, which is decreased with fork elevation and undercutting of the load (i.e. load does not butt against the fork "L"). A loading plate for loading reference is usually located on the forklift. A forklift must not be used as a personnel elevator without the fitting of specific safety equipment, such as a "cherry picker" or "cage". Additional safety considerations are detailed in the applicable Occupational Safety and Health Administration (OSHA—United States) and Health and Safety Executive (HSE—United Kingdom) rules, and lift truck operators must be trained and certified.