Product Overview

A traveling bridge sludge collector is a machine mobilized by high-torque, slow-speed drive system that must operate in difficult conditions. The distance between the supporting trucks can exceed 80 feet, the distance traveled can exceed 200 feet. The concrete structure and rail system supporting this mechanism are generally not perfectly level or straight. Thermal expansion of the bridge frame and rail system can be a problem. Loading on the scraper mechanism can be uneven and unpredictable. As the bridge alternately traverses the basin, stopping and restarting in the opposite direction, high starting torques are developed. Traveling bridge collectors have a high probability of experiencing overloads and of being inadvertently jammed. Additionally, these machines are in a wet and corrosive environment, and are expected to run continuously 24 hours a day in all weather conditions with only occasional operator attention.

Smooth and reliable operation of a traveling bridge collector is difficult to achieve. One approach to this problem is to strive for perfection of the installation and absolute synchronization of the drive trucks. Generally, this is done with some form of rigid mechanical system such as a solid line shaft extending from a central, high-ratio gear reducer. Double-flanged wheels are usually applied to one or both end trucks in an attempt to maintain the bridge position on the tracks.

The result is a mechanical system that is over constrained and too rigid. It is difficult to achieve perfect synchronization. For example, line shafts can twist and flex, drive chains can stretch, wheels can slip an rack teeth are usually misaligned. The system is too constrained to adapt to imperfections and unbalanced loads, and the devices applied to keep the bridge on track give a false sense of security. The following symptoms can be observed: the drive is easily damaged by unbalanced or excessive loads; wheels grind, and rails and rack plates are forced out of alignment; oilers are installed to prevent screeching; wheel flanges and bearing housings can crack; drive chains snap; axle and bearing failures occur; the trucks can jump off of the track; expensive high ratio gear reducers are damaged; and, finally, constant operator attention is needed to keep the system tuned-up and working properly.

A better approach to this problem is to release some of these constraints while tightening others, so that the components of this complex mechanism can adjust to load variations and imperfections without working against each other. IN applying this concept, it is important to understand that the rail anchorage, support rails, wheels, bearings, truck weldments and drive components represent an integrated mechanical system.

Due to the large distance separating the drive trucks, it is impractical to use a common drive system. Each truck should be driven independently so that it can better adapt to load conditions. At the same time, the trucks can not be totally independent. To a large degree, the trucks are maintained in alignment by the general stiffness of the connecting bridge frame. However, to prevent crabbing, the truck and wheels must be maintained parallel to the rails and must be designed to effectively react to side thrust. The traditional tapered rail wheel with a single inside flange will track on a line of contact generating a horizontal thrust component. Unlike the double-flanged wheel, which depends on the flanges acting as physical stops, which allows substantial side movement due to clearances, the tapered wheel allows the machine to seek a specific line of action. This works by providing a rate of travel differential. If on truck gets ahead of the other, the lagging truck tends to have the wheel surface running closer to the flange. Because this is a larger diameter, the lagging truck will travel farther for one revolution of the wheel bringing it back into alignment. Wheel noise is eliminated because the wheel flanges do not normally rub on the rail. To support the tapered wheel, heavy-duty combined radial and thrust load carrying bearings are required and the truck weldment must be very stiff. To react against the side thrust generated by the wheel and truck assembly, the rail system must be well supported laterally with closely placed heavy anchor plates.

The trucks must also be synchronously driven, but in a way that allows for some flexibility and load variations. In addition to other advantages, such as being well adapted to low speed, high use of a pressure compensated flow divider to meter equal fluid flow to each drive truck regardless of load. This provides constant speed with a variable torque as needed to accommodate unbalanced loads. A system flow regulator can be used to adjust the speed of all fluid motors simultaneously.

If 4-wheel drive is used for improved traction, the tow motors on each truck are connected in series so that the output of the first motor becomes the input to the second. This locks the two motors so that if one wheel loses traction, it will not over speed and assures that the drive torque is transferred to the wheel taking traction. The use of fluid power drive motors also allows stall torque without damage. This feature can be used to perfectly align each truck against rail stops at each end of travel if this degree of precision is needed.

Benefits

• 4 wheel hydraulic drive
  • Movement of our traveling bridges is provided by fluid power drives rather than line shaft and rack and pinion drives found on other units.
  • Built-in overload adapted to low speed, high torque, and outdoor specifications
  • Prevents “crabbing effect”
  • Eliminates the line shaft, drive chain and associated bearings found on conventional units
  • Low maintenance
• Single flanged tapered wheels
  • Superior to rack and pinion design because the tapered wheels force the bridge to seek a specific line of action, therefore preventing “crabbing”
  • Tapered wheels eliminate any wheel noise because the wheel flanges do not normally rub on the rail
• Festoon electrical system
  • Power to the traveling bridge is provided though a festoon system
  • An aluminum track located about 8-ft above the operating wall and plastic cars with rollers carry the flat power cable
  • All materials are corrosion resistant.

Applications

Rectangular clarifiers basins are generally chosen because of plant site constraints that dictate the use of a long narrow basin design. Multiple circular clarifier basins is not the most efficient layout at achieve maximum clarifier surface area in a constricted land site. When the value of the land per square foot is high enough the efficient use of a rectangular basin might offset the often times more costly “Traveling Bridge” style sludge collector. Water treatment plants are also good applications because the sludge generated isn’t affected by longer life on the basin floor, and scum is generally not a factor to deal with. Therefore the equipment might not have to be subject to continual use, as in an activated sludge process. The largest disadvantages of “Traveling Bridge” style collectors are initial cost, power supply, and increased maintenance.