Designing a Conveyor for Finishing

Automating material handling is one of the most important steps in planning a finishing operation. The right choice adds efficiency, adaptability and dependability, whether you are finishing household appliances, automotive parts, office products or aircraft components.

Where to begin. Any good plan begins by determining your material-handling objectives. An efficient conveyor system provides for repeatability and precision. It allows for a continuous flow of operations. It improves overall product quality and lowers costs. Also, the right system provides flexibility and versatility to grow with plant needs.

Power-and-free conveyor systems meet these objectives. However, several types of overhead conveyors are also available, including manual monorail and continuous power conveyors.

Conveyor types. Manual monorail conveyors consist of a steel channel from which a trolley is hung. To spread the weight of the load over the track, a loadbar and additional trolleys are used as needed. This type of conveyor is best suited for low-volume applications when plant personnel are available to manually move the load.

In a continuous power system, a chain is pulled by an electrical drive mechanism with the product attached directly to the chain. Continuous power conveyors work well in applications where a large volume of parts goes through identical processes. One drawback is that the system must be designed for the slowest process in the production loop.

For situations with variations in work flow, power-and-free conveyors offer the most flexibility. A power-and-free system combines the powered rail of a continuous power line with non-powered (free) rail that carries the weight of the products. Since the two can run independently, products are moved by the interface between the rails. The powered chain pushes the trolley on the free rail by means of a pusher dog.

The flexibility of a power-and-free conveyor system allows tracks to be arranged to carry product at different rates through various operations. This allows finishing equipment to be sized for optimum efficiency. Product carriers can be stopped in designated areas for loading, assembly or inspection; switched to other powered loops or manual spurs; or accumulated for meeting, sequencing or work-in-process storage.

In finishing operations, power-and-free allows for optimum throughput through ovens and spray booths. Long loads can be conveyed parallel to the main line, then turned for storage or sorting. To minimize booth size or allow for turning clearances, loads may be racked horizontally and travel through a paint booth parallel to the conveyor, then travel perpendicular while drying in the oven and moving through the rest of the system.

Products can also follow multiple routes, so a variety of parts requiring different processes can be sent through the same system. This feature is important when a large number of parts are finished using combinations of stripping, pretreating, priming and finishing. These conveyors can be linked to Computer Integrated Manufacturing (CIM) systems for routing and monitoring throughout the entire manufacturing process.

Designing the system. Once you have identified a power-and-free conveyor as the most practical means of material handling for your application, evaluate the characteristics of your operation. An efficient conveyor system design depends on a thorough consideration of your finishing processes.

What products will be carried? Consider your products before designing your conveyor. What types of components are involved? How much does each weigh? What are the dimensions? How much do components vary in size and shape? Can multiple parts be carried? Will loading and unloading be manual or automatic? The answers will help you specify the appropriate loadbars, attachments and carriers for the system.

Projecting production rates. The rate of production has a tremendous impact on system design. A power-and-free conveyor system is engineered to accommodate the different speeds needed for various functions. You need to calculate carrier rates, determine chain-dog spacing and conveyor speed for the overall production line.

Buffer storage space can also be incorporated into a system. For example, products can be sent into storage areas to await color or process changes. Buffer storage requires minimal handling by plant employees. Power-and-free systems can be arranged with storage located overhead on a second tier of conveyor lines, efficiently using otherwise wasted space above the production floor.

When production rates differ between finishing processes or functions, buffer storage provides an efficient way to handle materials. Components may move through anodizing much more quickly than curing and drying. Buffer storage takes up the slack without reducing system efficiency.

Finishing processes. Next, consider the processes involved in your finishing operations. What ovens, spray booths, degreasers and washers are involved? Depending on the type, variety and combination of paints, special considerations may be necessary. In one operation, for example, the finishing operation handles more than 160,000 components with 1,100 different combinations of paints, primers and coatings.

Power-and-free systems are quite adept at handling multiple functions. Some components may require a prime coat only, with the final coat applied to the assembled product. Other components may require multiple coats of paint. With a power-and-free system, both groups can be placed on the same conveyor. Carriers will be identified electronically, then routed through different processes. Procedures can even be repeated, such as applying multiple coats of paint. At the end of the line, components accumulate for assembly.

Plant layout. To design the most workable conveyor system, evaluate the layout of the plant carefully. Start with a plant layout that shows the location of building columns, walls, machines, aisles and service areas that the conveyor must negotiate. Changes in elevation and direction are important to consider. Power-and-free conveyors are adaptable to most situations, even when retrofitted into plants with multiple levels. Conveyors with enclosed tracks maneuver multiple turns and steep inclines better than I-beam conveyors. Enclosed track systems also require less headroom, fitting into tight spaces effectively.

Once you have decided that a power-and-free conveyor is right for your finishing application, consult a manufacturer to help you design the system and select the proper components for your specific operation. Used successfully in most industrial applications, power-and-free conveyors are noted for their reliable operation in paint booths, oily atmospheres and ovens. The right material handling system reduces finishing time, increases throughput and saves labor costs. Power-and-free conveyor systems are relatively simple, yet adaptable and flexible enough to adapt to changes in procedures and production volume.

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