Tow tractors and trailers from Warehousing Equipment
Over recent years and particularly in the past two years, many articles have appeared in trade magazines regarding the safety issues associated with forklifts, in many cases to do with mixing them with pedestrians.
According to Warehousing Equipment, the simple answer is to seperate forklift trucks and people, however this is often not possible or is possible in part.
Warehousing Equipment points out that as well as this, recent safety innovations such as: limiting speed when tines are raised, seatbelt interlocks, immobilisers when operator leaves the drivers seat and stability control has helped to establish a safer workplace.
These design improvements still rely on the operator who must be trained and licensed. Another option has been developed involving the use of a tow tractor and and a train of trailers in conjunction with forklifts, to minimise exposure to pedestrians, and remove the margin for error as a result.
Many applications use three trailers in a train but much longer (up to 10 or more) trailers can effectively be coupled together.
Battery electric tow tractors are available with tow capacities from as little as 1 tonne up to 30 tonne.
The tractor operator drives from the front of the train giving an unimpeded forward and sideways view. This is often not possible with a forklift.
The operator of a forklift has restricted frontal visibility due to the mast and load being transported. The tractor provides an unrestricted frontal view, which, when driving in a busy, congested facility means a safer workplace.
Towing say, 3 trailers, 6 pallets can be delivered each journey; whereas using a forklift, only one pallet can be delivered each journey.
Assuming the travel speed is the same for forklift or tractor, a large saving in time can be achieved as well as providing a safer environment for pedestrians due to less frequent movements (a factor of 6).
One argument put forward against the use of trailers is that wider aisles are needed to accommodate the train of trailers, but this can be overcome simply and economically by using the correct configuration trailers.
There are three basic types of trailers and choosing the correct configuration is important for a particular site.
Caster steer:
Two swivel casters at drawbar end and two fixed wheels at rear.
Characteristics:
- Good tracking in a train
- Easy to manoeuvre by hand when disconnected
- Often fitted with push bar for manual handling
- Can be constructed in a square pattern (carry one pallet)
- Good stability as deck can be lower to ground and wheels can be placed at corners of chassis
- On uneven concrete or bitumen surfaces, caster wheels can “shimmy” causing premature wear and can also create noise
Two wheel steer:
Front axle on a turntable, rear wheels fixed.
Characteristics:
- Better tracking in a train than caster steer
- Can be reversed if single trailer only
- Needs to be a rectangular shape (2 pallets or more) to allow steer axle clearance
- Fixed rear axle provides good stability
Four wheel steer:
Front and rear axles are on turntables and are connected with a cross bar which steers the rear axle in opposite direction to front axle.
Characteristics:
- Good tracking in a train and little corner cutting even with multiple trailers in a train
- Stability not as good as other configurations particularly if loads are offset to one side
- Difficult to reverse, even if single trailer only
- Difficult to manoeuvre by hand
In all configurations, trailers can be built to suit individual crates, pallets etc and goods can be loaded directly onto the trailer without needing a pallet or skid
Wheels and tyres can be selected to suit a particular application. For two and four wheel steer, the most popular equipment is pneumatic tyres, optional foam filled for puncture proofing or solid cushion tyres.
For particularly heavy loads such as plasterboard packs of say 6 tonnes, urethane on cast iron wheels are used.
For caster steer, there is a wide range of wheels from pneumatic tyres to solid rubber tyres to urethane on cast iron to plain cast iron or nylon.
In all cases non marking tyres are available.
The motivation to minimise the use of forklifts in areas where people are working in conjunction with lean manufacturing practice has caused logistics designers to rethink the whole scene.
This has largely been driven by the motor manufacturers and consequently their suppliers.
Component parts from off site suppliers are now loaded into specific modules on wheels which are road trucked to the assembly site, lifted off by forklifts in a pedestrian free zone then towed in a train to the production line, where by definition people are working.
Empty modules are returned to lift on/lift off area, sometimes in knock down configuration for return to the supplier.
Considering the investment that the motor manufacturers have in existing crates, stillages etc and the traditional materials handling methods used to bring them to the production line via forklift, an improved safety regime needed to be found without breaking the bank. Enter the roll on/roll off trailer towed in a train.
Component parts packed into traditional stillages are unloaded from the suppliers transport and placed on a roller storage conveyor in a pedestrian free zone by forklift.
A tow tractor with a train of trailers fitted with rollers comes alongside the storage conveyor and stillages are pushed by hand or gravity onto the trailers.
The stillages are offloaded at a marshalling point or offloaded directly at the production line where there is a static roller conveyor.
Over recent years there has been a consistent trend by manufacturers and warehouses to minimise the use of forklifts to improve safety.
Forklifts will continue to be a key element in the movement of goods but a tractor and train of trailers can minimise the number of trips and therefore exposure to pedestrians and can produce more economical outcomes as well.
6-Jun-2007