Industrial vehicles/trucks is one of the most common groups of materials handling equipment used in industry as well as in day to day distribution of goods in warehouses, large stores, transport depots, etc. The basic operation and construction features of some of the common types of industrial trucks will be discussed here. The adjective ‘‘industrial’’ used before this group of vehicles/trucks is to distinguish these from other groups of vehicles like buses, lorry, trucks, etc. used for transportation of men, livestock, or goods.
The entire range of industrial vehicles/trucks are generally sub-classified into two groups viz. non-powered trucks, (also called hand trucks) and powered trucks.
The powered trucks can be further subdivided into the following three subgroups, for convenience of discussion:
(a) Power Truck.
(b) Forklift Truck.
1.1.1 HAND TRUCKS
Hand trucks, as the name implies, have no source of motive power, these are generally moved manually or are attached to other powered moving equipment/units. Hand trucks are classified into three subgroups:
(i) 2-Wheel hand truck,
(ii) multiple-wheel hand truck and
(iii) Hand lift truck.
1.1.2 Two-wheel Hand Trucks
These are generally used for moving unit or unitized loads like bags, barrels, boxes, cartons, bales, cylinders, etc. by pushing the truck manually.
Basically, it consists of two long handles fixed by a number of crossbars which form the frame to carry the load. Two wheels mounted on an axle are fixed on the far end of the frame. Two short legs are generally fixed to the two handles at the other end to allow the hand truck to stay in a horizontal position during the loading and unloading of the truck. The Construction feature of a common 2-wheel hand truck is shown in the below figure.
Different varieties of 2-wheel trucks are in use based on the type of loads to be handled. Some of these, which are variations of the basic design, is illustrated in Figure 5.1.2 below indicating the type of load they are used for.
Pry trucks having a crowbar nose, pry up a heavy load, and roll it away. These are used for loads too heavy for ordinary 2-wheel trucks. They are often used in pairs by two men. Multiple-wheel Hand Trucks These trucks generally consist of a platform or framework mounted on 3 or 4 or more wheels. The truck is generally provided with a handle for pushing or pulling the platform. Certain trucks are provided with no handle or detachable handle.
2. Side rail
4. Leg brace
5. Top crossbar
6. 3rd crossbar
7. 2nd cross-bar
8. 1st crossbar
10. Axle brace
12. Pressed steel wheel
Dollies: These units consist of a wooden or metallic low platform or frame of different shapes (rectangular, triangular, or circular) and sizes depending on the load to be carried. The frames are provided with different numbers of wheels and fixed and/or swivel caster types. No handle is provided. These are moved by pushing the load itself. Fig. 5.1.3 shows some of the different designs of dollies.
1.1.3. Different designs of dollies
Platform Trucks: These are basically larger versions of dollies in which metallic frames are generally of rectangular shape and produced in many sizes in light, medium, and heavy-duty construction. Handles at one or both ends are provided for pushing. There are two basic chassis constructions from the point of view of wheel arrangement: (a) tilt or balance type which have rigid wheels at the center of the platform and a set of one or two swivel casters located at two ends of the platform permitting maneuverability. (b) the non-tilt type where the rigid wheels are at one end and the swivel casters, usually smaller in size, are located at the other end so that all the wheels are always active (Fig. 5.1.4). The platform may be provided with corner posts or various types of steel slat racks and frames to avoid slippage/spilling of the load (Fig. 5.1.5). Platform trucks may be built with extra reinforcement and provided with a suitable coupler so that they may be used for light-duty trailer service or towline conveyor systems.
Semi-live skid platform: These are basically flat platforms with two load wheels on one end and two legs at the other. The skid platform with load is activated by a lift jack, which is a long handle with a pair of wheels and a hook. The hook engages with a coupling at the leg end of the platform and gives a jacking or prying action to lift the legs from ground/floor. The unit thus becomes a 3 wheel platform truck. Fig. 5.1.6 illustrates a semi-live skid platform.
1.1.4. Semi-live skid platform
1.1.5 Hand Lift Trucks
These hand trucks are provided with a mechanism of lifting its platform, which can be rolled under a pallet or skid, and raised to lift the pallet or skid with load to clear the ground and then move this load from one place to another. Depending on the lifting mechanism, these are grouped into hydraulic or mechanical types. Hand lift trucks are widely used in small to medium-sized manufacturing industries using pallets, skids and/or containers.
Hydraulic lifting mechanism: This consists of a hydraulic ram (single-acting cylinder), an oil storage vessel, and a plunger pump. The handle of the truck is connected to the plunger of the pump through a suitable mechanism, such that when the handle is moved up and down, the pump forces a certain quantity of oil into the ram which through a suitable linkage mechanism raises the platform with the load. The capacity range of hydraulic hand lift trucks varies between 1⁄2 tons to 10 tons. The platform is lowered by releasing a flow control valve to allow the pressurized oil to go back to the tank, and the ram is retracted by the load itself.
Mechanical lifting mechanism: This mechanism is operated by a system of levers. The platform is raised by actuating a handle, which in turn, raises a pawl that falls into a slot or groove. Lowering is accomplished by releasing the pawl. There is single stroke, and low-lift mechanisms also. The capacity of mechanical hand lift trucks is generally limited to 1 ton.
Both hydraulic and mechanical hand lift trucks are further classified, based on general constructional features, into:
(a) pallet, (b) platform and (c) special types.
(a) A hand pallet truck is used for handling pallets. It consists of two strongly built metallic fingers, popularly called forks, connected at one end to give a U-shape. The lifting mechanism is housed at this end. At the outer ends of each fork, a wheel is provided, which acts in accordance with the lifting system. The connected end is mounted on a pair of large-sized wheels that can be steered. Fig. 5.1.7 shows a photographic view of hydraulic hand pallet trucks. Fig. 5.1.8 shows the typical operation of the truck where the forks are introduced inside a pallet and the forks are raised with the pallet. Fig. 5.1.9 shows a line diagram with important dimensions of such a truck. IS:5007-1988 lays down recommended dimensions of fingers (forks) of hand pallet trucks in line with recommended pallet dimensions.
(b) Platform lift truck is similar to a pallet truck except that instead of two forks it has a platform, which can be raised. The platform may be solid or of an open frame structure. These trucks are generally used with skids. Load capacity and nominal sizes of standard trucks of this kind vary within ranges: 1⁄2 ton to 3 tons, 450 mm to 680 mm width, 750 mm to 1800 mm length and lift heights from 150 mm to higher values (see Fig. 5.1.10).
(c) Lifting feature has been utilized in designing various types of lifting trucks for handling various specialized loads in industries. All these are called special hand lift trucks as a group. A coil (reel) handling hydraulic lift truck is an example.
When a vehicle/truck contains its own source of motive power, it is called a power truck. Power
trucks are divided into several categories of equipment. The wide varieties of powered industrial trucks have been classified into the following six groups in BIS specification number IS 7217:1990 and IS 4660:1993:
(i) mode of action
(ii) power source
(iii) type of wheel
(iv) mode of control
(v) height of lift
(vi) mode of travel
Functions with sketches of different classes of fixed and lift-powered trucks have been described in specification no. IS 4660:1993, while various nomenclatures pertaining to powered industrial trucks are available in the other specification IS 7217:1990.
Fixed Platform Truck (powered)
These are powered (battery, diesel or gas-operated) industrial trucks having a fixed level, a non-elevating platform for carrying the load. Materials to be moved have to be loaded and unloaded to and from the platform by hand, hoist or crane. The capacities of these trucks can go up to 40 tons. Smaller capacity models are called load carriers. The operator normally stands on the truck and runs it. Platform trucks are particularly useful for the occasional handling of heavy loads.
Variations of normal platform trucks are
(i) drop platform trucks, and
(ii) drop center baggage trucks in which the central platform between two sets of wheels is very close to the floor.
Fig. 5.2.1 shows photographic views of different types of powered platform trucks.
Platform Lift Truck (powered)
This equipment is a particular type of powered platform truck, whose platform can be raised and lowered to handle loads on skids. The range of lift of the platform may be ‘‘low-lift’’, up to 300 mm, or ‘‘high-lift’’, over 300 mm.
Pallet Lift Truck (powered)
These are similar to platform lift trucks in which the platform is replaced by forks to work also with loads on pallets. These are basically for a number of fork-lift trucks. Low-lift models (Fig. 5.2.2) are used for the movement of materials only while the high-lift models are used for stacking of pallets/skids one over another or in storage racks. Different variations of the high-lift truck have been built. Some of these are:
(a) Reach truck: In this design, the forks can reach out on a pantographic mechanism that permits the forks to travel forward to engage load, lift it, and then retracts towards the mast before travel starts. These are of great use for warehousing and loading/unloading vehicles.
(b) Side loader truck: In this design, the operational direction of the forks is at right angles to the movement of the truck. The major benefit of the design is that the truck does need not turn into the load. The truck can move along a narrow aisle of a warehouse, and the fork can load/unload
This term implies different types of powered trucks described above when the operator walks with the truck and operates it by means of controls available
Walkie trucks are smaller, lighter, and slower than rider-types, generally powered by a battery. These are designed to fill the gap between hand trucks and powered rider-trucks in which the operator stands/sits on the truck.
This is a self-loading powered truck for the movement of long and heavy loads including shipping containers. The truck consists of an inverted “U” shaped frame having wheels mounted on the outside of the frame. The truck can straddle a load/loads, and pick it up with hydraulically operated load-carrying shoes, mounted inside the frame, and then move with the load and unload it very quickly at the desired location.
Capacities up to 40 tons are common
Amongst the powered industrial vehicle/truck family, the most versatile, useful and widely used equipment is industrial lift trucks, popularly called forklift trucks (FLT in short). These are self-loading, counterbalanced, powered, wheeled vehicles, with the operator seating on the vehicle, designed to raise, move and lower load on forks or other attachments fastened to a mast which is fixed in front of the vehicle to allow lifting and stacking of loads. forklift trucks are used for lifting, lowering, stacking, unstacking, loading and unloading and maneuvering of medium to large weight, uniform shaped unit loads, intermittently. However, the limitations of this equipment are
(i) usually requires pallet/skid/container,
(ii) requires a skilled operator,
(iii) equipment needs maintenance facility,
(iv) capacity of this equipment varies from 1 ton up to about 60 tons,
(v) slow travel speed (10-15 km) ,
(vi) suitable for short hauls (hundreds of meters).
Other features of a forklift truck are:
(i) The source of power is petrol/diesel or LP gas engine or a battery-driven motor.
(ii) The mast may be tilted forward or backward within a range, for better stability during movement with load and also to facilitate loading and unloading. In a particular design, the mast may be moved outboard and inboard on tracks laid over the chassis of the truck.
(iii) The mast may be a single mast or maybe telescoping in design which allows high lifting of the load for trucks that must run through limited headroom areas.
(iv) In certain designs, the forks are independently retractable outboard and inboard through a pantograph mechanism. Loads are picked up and placed while forks are outboard but are moved inboard for greater stability during movement.
(v) The operation of the mast and movement of the forks (or any other attachment) are through a hydraulic power pack.
(vi) The body of the truck is purposely built heavy which acts as a counter load while lifting loads on forks/attachments.
(vii) Solid rubber tires are provided for operation in different floor conditions. The rear two wheels are steered for manipulation of the forks/attachment fixed in front of the truck.
Fig. 5.3.1 is a line diagram showing the major parts of a forklift truck.
Drive axle, Chassis, Steer axle, Fork arms, Fork arm carrier, Mast Steering Wheel Overhead guard Counterweight Diesel operated FLT Single mast FLT, forks raised 12 tons tilting mast diesel Battery-operated FLT with single rear wheel Heavy duty FLT with two pairs of forks FLT with telescoping mast handling container FLT loading a container truck 5.3.1 Specifications of Fork Lift Trucks
There are different operating parameters or specifications based on which the suitability of a particular FLT is determined. The following is a list of major specifications from an operational point of view:
(a) Rated capacity (1000 kg, 2000 kg, etc.) at the specified load center.
(b) Power sources (gas, diesel, battery, etc.)
(c) Turning radius.
(d) Physical dimensions (length, width, height)
(e) Mast height
(f) Lift height.
(g) Mast specification (single or telescoping, tilting or non-tilting, retractable or not.)
(h) Travel speed.
(i) Lifting speed.
(j) Floor clearance.
(k) Free lift (movement of the fork without mast movement).
(l) Retractable fork or not.
(m) Fork size (length, width, the maximum gap between forks, etc.)
(n) Attachments provided.
Other important technical specifications are : (i) motive power (h.p. rating), (ii) power transmission system (disc clutch, fluid coupling etc.), (iii) tyre specifications, (iv) battery and charger specification etc.
5.3.2 Capacity rating of FLT
FLTs are specified for a rated capacity at a specified load center. The load center is the distance from the heel (vertical face) of the forks to the assumed c.g. of the load. However, if the actual c.g. of the load goes beyond the specified load center, the loading capacity of the truck has to be reduced accordingly, so that the moment of the load about the front wheel does not exceed that of the counter-loaded body of the truck, and the rear wheels do not lose contact with the ground. For example (see Fig 5.3.3), the rated capacity of the FLT is 2000 kg and the load center is 450 mm.
Let the distance between the front wheels to the heel of the fork (distance A to B) is 350 mm. Then true capacity of the FLT is =2000 × (load center + distance A to B) = 2000 × (450 +350) = 16 × 105 kg.mm.
Now, if a load is to be carried whose c.g. ‘‘C’’ is at a distance of 550 mm from the heel of the forks (distance B to C = 550), then the maximum safe weight ‘‘W’’ that can be carried is given by the equation:
W × (550 + 350) = 16 × 105 or W =5 16 10900×= 1777 kg
C B A
Fig. 5.3.3. Capacity rating of FLT
The stability of a fork lift truck at the rated capacity is of paramount importance from the point of view of safe operation. Indian standard number IS 4357:2004 titled ‘‘methods for stability testing of forklift trucks’’, specifies basic tests to verify the stability of counterbalanced forklift trucks, of rated capacity up to and including 50,000 kg.
5.3.3 Turning Radius and Aisle Width.
A FLT can move freely through an aisle having its width at least 300 mm more than the max-width of the load or the FLT, whichever is higher. However, if the FLT has to work across the length of an aisle, like stacking or unstacking into racks in a warehouse, the minimum aisle width requirement can be determined from the following factor, as illustrated in Fig. 5.3.4.
Fig. 5.3.4. Minimum turning radius of FLT
Let A = width of the aisle.
B = distance from center line of truck to the point about which truck turns when wheels are turned to extreme position (minimum turning radius condition). Centre of turning is designed to lie on front wheel center line TR = minimum turning radius
L = Length of weight resting on fork
X = distance between center line of drive (front) wheel to face of fork
C = clearance ( may be 150mm).
Then minimum aisle width A is given by the formula, A = TR + X + L + C
5.3.4 FLT Attachments Forks of a forklift truck are one of the most common attachments.
A pair of forks is used for working with skids, pallets, containers and box shaped loads resting on legs/ packers. However, a wide variety of devices have been designed for attaching to lift trucks to make them useful for many different tasks. Some of the common types of attachments are listed below with their names, short description of their special use and with some of their sketches.
(i) Boom: This attachment is fixed with respect to the fork carrier At the end of the boom, a chain pulley block is provided for lifting loads using the hook and slings.
(ii) Clamp: These are hydraulic devices for picking up loads like bales, barrels, cartons etc. by gripping them with opposing adjustable plates.
(iii) Drum grab: For drum-handling in a vertical position.
(iv) Crane: A crane mechanism is attached to FLT.
(v) Die handler: Platform for carrying heavy loads.
(vi) Drop-bottom container
(vii) Load inverter cum pusher
(viii) Load pusher (pallet unloader)
(ix) Ram: Fitted to the lift carriage for lifting cylindrical load with a hole (coil etc.)
(x) Roller platform
(xi) Shovel (scoop): A scoop fitted to the carriage for scooping and carrying loose loads.
(xii) Special forks: (a) brick, (b) block, (c) extended,(d) scissor,(e) retractable.
Scissor type fork
(xiii) Vacuum: For handling light and fragile objects by a set of suc-tion pods.
(xiv) Side-shifter: With this attachment, a load on truck can be moved from 100 to 150 mm on each side. This helps enormously in storing loads, without any damage to storage racks and mer-chandise.
(xv) Rotator: This is used in conjunction with a clamp or fork attachment to rotate load or for safer grip during movement with loads.BIS specification number IS 7570:1975 covers glossary of terms relating to fork arms and attachments, including their function, for forklift trucks.
5.3.5 Batteries for FLT Engine driven trucks are comparatively cheaper than battery operated trucks. Moreover, engine driven trucks can be used almost without the need of electricity. Despite all these, the number of battery trucks continues to increase, particularly for capacities up to 3 tons due to factors like overall lower maintenance cost and lack of smoke, fume and noise. Battery operated trucks are particularly suitable for warehousing and operations in confined areas. However, prerequisite to using battery-operated trucks is availability of electricity and battery charging facility.
Types of batteries: Batteries may be either of lead acid or nickel alkaline type of sufficient ampere-hour capacity to insure at least one full day’s operation. The advantages of lead-acid batteries are: lower cost, greater energy (kw-hr) capacity in a given space, lower internal resistance. Benefits of nickel-alkaline battery are: longer life, better mechanical strength, noncorrosive electrolyte(KOH) which does not freeze, shorter recharge period (7 Hrs) and noncritical control of the charging current.
Battery voltage: The battery voltage has largely been standardized by industrial truck manufac-turers. Table 5.3.1 below shows the types and capacities of battery operated trucks and average voltage employed for their operation:
Battery rating: It is essential that sufficient battery capacity be provided to allow uninterrupted operation of the truck during normal operation period. Capacity of a battery is rated in ampere-hour for a six hours discharge period. This rating, divided by six, gives the current draw in amperes, which, if continued six hours, will completely discharge the battery. The average voltage multiplied by the amperehours rating gives the total energy capacity of the battery in watt-hour. The battery sizes for trucks of various capacities have been standardized by the manufacturers.
Battery selection: Battery selection is based on energy rating for a proposed duty cycle of the truck within a given period between two battery changes. Energy calculations for different operations are based on certain charts and formulae adopted by the “Electrical Industrial Truck Association” in 1950 standardized through field study.
Energy calculation: Table 5.3.2 shows average watt-hours of energy required to accelerate and drive a truck over level distances. For intermediate distances, the data may be interpolated. The energy consumptions for other operations of FLT are given by following set of equations:
Example: A battery operated FLT weighs 4000 pounds including weight of battery and opera-tor. It is carrying a weight of 2000 pounds. The truck lifts the load to 2 ft and carries the load to a distance of 200 ft of which 170 is along level road and balances 30 ft on an upgrade of 6%.After discharging the load it returns over the same route. Calculate total watt-hours of energy spent by the truck.Select suitable battery if the truck has to make 200 such trips daily.The total energy can be calculated by summing up energy spent for the following elements of activity:
(i) Total run with load.
(ii) Extra power for 30 ft of inclined travel at 6% grade.
(iii) Return empty run deducting the downgrade run.
(iv) Lifting of load.
(v) Tilting of the mast.
(i) Energy for total run with load: Total weight of the truck with load is 6000 pounds. From
chart we find the energy required for a 200 ft run = 24 watt-hours.
For 200 trips, total energy requirement = 200 × 51.55= 10,310 watt-hrs. If we choose the voltage of the battery to be 36 volts, then total ampere hour capacity of the battery between two charges should be =10,310 ÷ 36 = 286.39.
Therefore, a 36 volts battery having an ampere-hour rating of the nearest figure above 286.39 should be the minimum size battery to be considered for the duty cycle.
Battery charging: Charging of used-up batteries is an essential facility for battery-operated FLTs. Industrial batteries used in forklift trucks are intended to be recharged approximately 300 times per year or once in 24 hours on average. More frequent recharges generally reduce the overall life of the batteries.
The lead-acid batteries, for 8-hrs. charging period requires a high rate (about 25amps per 100 amp-hrs of battery capacity) of charging at the beginning and a low finishing rate (20% of the initial rate) at the end. A nickel-alkaline battery with a 7-hrs. charging period needs a charging voltage of 1.5 times its normal voltage rating. Each size of nickel-alkaline cell has a specified current charging rate. At the beginning, it should be about 140% of this specified rate and gradually it should taper down so that the average charging rate is approximately equal to the specified rate of the cell.
The battery charging unit may be
(i) motor-generator type or
(ii) dry-plate rectifier type.
However, each of these is provided with the above charging sequence control features. The battery chargers may be suitable for a single battery or multiple batteries charging simultaneously. It should automatically stop charging when each battery gets fully charged.
The tractor is a vehicle, having its own source of motive power, used as a prime mover to haul i.e. to give motion to another or a group of other vehicles which do not have their own motive power, such as trailers, semi-trailers, transfer cars, etc. Tractors are used in a wide field of activities, starting from agriculture to earth-moving, municipal waste handling, construction, and industries. A tractor may be fitted with different attachments to do different jobs like sweeping sidewalks, plowing snow, excavating the ground, scoop loading, bulldozing, etc.
5.4.1 Industrial Tractor industrial tractors are generally grouped into
(i) wheel type which is primarily used for movement of one or more trailers for interplant or interplant transportation, and
(ii) crawler type which is mostly used in outdoor and storage yard service at slow speeds and for short hauls.
The most important specification of a tractor is its draw-bar pull rating. According to this rating, they are classified as small (100 kg normal to 500 kg), medium (250 kg normal to 750 kg), large (1.0 tons normal to 5 tons maximum), and extra large (up to 35 tons). Other specifications are physical dimensions, weight, horsepower, number of wheel drive, front or rear wheel-steer, walkie or rider type, etc.
The small and medium tractors are often battery-operated walkie types.
However, an ‘‘electronically guided type’’ of tractor requires no operator which follows a white line painted or a wire embedded in the floor. These are used for point-to-point pick-up and delivery of trailers. These may be programmed for the automatic decoupling of trailers and give signals of arrival at two ends. Large and extra-large tractors are powered by an internal combustion engine fueled by diesel or gas and are essentially rider-type. A two-wheel tractor depends on working in conjunction with the attachments or load carrier for balance. Steering of these tractors is done by pivoting about one of the two wheels, thereby resulting in a very small turning radius i.e., high maneuverability of these tractors. A coupler is secured to the rear of the tractor body for quick coupling and uncoupling of the trailers/transfer cars.
Tractors are preferred over FLT when a large volumes of materials of different types of loads which can be carried on specifically designed trailers, need to be handled.
In Fig. 5.4.1 the view of a few tractors is illustrated.
Trailers are load bearing wheeled vehicles or cars without any motive power, designed to be drawn by a tractor or truck. Trailers are classified as semi trailers and full trailers.
A semi trailer is a truck-trailer having one or more axles and constructed so that a part of its weight is carried by the truck/tractor. A full trailer is constructed to carry almost all its weight on its own wheels.Number of axles may be one or more. The tractor has to give only the pulling force for its motion.More than one trailer may be pulled at a time by a tractor when it is called as a tractor-trailer train.Trailers can be of different shapes and sizes. Figure 5.4.2 shows a few types of trailers:
REFERENCES AND BIBLIOGRAPHY
1. Bolz, H.A. and Hagemann, G.E. (ed.), ‘‘Materials Handling Handbook’’, Ronald Press.
2. Allegri, T.H., ‘‘Materials Handling: Principles and Practice’’, CBS Publishers & Distributors,N. Delhi.
3. Apple, J.A., ‘‘Material Handling System Design’’, John Wiley & Sons.
4. IS 7217:1990, Classification and Nomenclature of Powered Industrial Trucks, BIS.
5. IS 4660:1993, Powered Industrial Trucks—Terminology, BIS.
6. IS 4357:2004, Methods for Stability Testing of Forklift Trucks, BIS.
7. IS 7570:1975, Glossary of Terms Relating to Fork Arms and Attachments of Forklift Truck,BIS.