For centuries, people relied on manual labor to move large quantities and heavy, cumbersome items from point-to-point. This time-consuming process was eased around 1900 when conveyors were invented. One of the first applications was by Henry Ford's engineers to transfer parts from production to the assembly area. This eliminated scores of runners, saved hours of work, and improved production rates.
For as common as conveyors are, however, they are often an after-thought in the design process. The primary question most engineers face is whether to build or buy their conveyors. Experience insists that it's usually best to let a conveyor expert help make that decision.
Build or buy
Many integrators and OEMs choose to build conveyors in-house. Although this initially appears to save money, several drawbacks exist. For one, considerable time is spent locating and purchasing parts, designing the system, and physically building it. Another disadvantage is that conveyors manufactured in-house usually contain parts from various suppliers, making it difficult to quickly find a replacement. If a supplier discontinues a part or goes out of business, there may be no replacement.
Another is personnel. If the designers leave the company, a knowledgeable back-up may not be available to take responsibility for the equipment. And, there is no guarantee that a conveyor built in-house will compare in quality to a supplier-built conveyor.
Suppliers who specialize in building conveyor systems can devote 100% of their time to design and construction, unlike in-house personnel who typically multi-task the project with other assignments. Supplier lead times can also be as little as a few days. One more advantage is the assurance of a conveyor built for a specific application.
Another benefit to supplier-built conveyors is customizing them for unique applications such as handling heavy parts or assisting quality-assurance inspections. Professionally built conveyors also eliminate replacement part issues, as suppliers service their own products and parts. Additionally, several people in a supplier setting can readily provide technological support.
Conveyors are more than just belts wrapped around two spindles; they are integral components of an application, an extension of a plant's equipment and machinery. Recent trends in conveyor design and accessories increase throughput and productivity. While the most common type of conveyors are straight-line, many other designs — now considered to be standard — result from customization for specific applications.
Backlit conveyors use light fixtures installed at certain sections in the frame to illuminate items traveling on a translucent belt. These conveyors incorporate in-line vision sensors for visual-system interface and inspection. Contrast between passing parts and the belt is created by light, which allows inspection. Parts can stop directly over the lighted section or pass by uninterrupted, depending on the application.
Some applications require inspecting products for metal shavings and, therefore, employ a metal-free design. In these conveyors — which also contain a metal-free belt — part of the steel bedplate is removed and replaced with a Delrin (inflexible polymer that resists heat) bedplate over the inspection area. As a result, the metal-scanning device checks passing products without receiving false readings from the bedplate.
Single-drive multiple belts employ a common drive or shaft coupled to a single gearmotor and move two or more conveyor belts. Multi-belt conveyors can mount two or more individual belts onto a single frame. These conveyors are commonly used in stamping parts, scrap removal, and accessing the underside of components by spanning wide items across multiple belts, creating multiple lanes. Their advantages include minimizing motor quantity, reducing space requirements by remotely mounting drives, and achieving the same belt speed with multiple side-by-side conveyors.
Using permanent ceramic magnets placed in the bed, magnetic conveyors hold ferromagnetic parts to the belt during processing (including upside down applications) and accommodate changing elevations. Magnets are one inch wide and are normally spaced at half the product's width; strength and size of the magnetic field are application-specific. In general, two rows of magnets are installed: one oriented as north and one as south. However, multiple rows can be used for larger products or additional strength.
Vacuum conveyors are made by perforating the belt and drawing air, using a regenerative vacuum blower, through grooves in the bed of a standard conveyor. The vacuum blower's size is determined by the total area of vacuum holes open during product running, as well as the pressure to hold the product and its seal to the conveyor belt. Belt types are usually high friction or electrically conductive and can reach speeds of 264 fpm. Vacuum conveyors hold parts securely to the belt for inspection and assembly/feeding applications, move items on an incline, and maintain control of flimsy parts or moving material.
Mounted to a base, pivot conveyor s swing out of the way to provide walk-through line access and only pivot upon sensing that no product is on the transfer point. Interlock switches and a timer clear the conveyor before the gate opens, preserving full product control. Product flow automatically resumes once the conveyor returns to its in-line position.
Timing-belt conveyors replace standard belts and work in conjunction with a toothed conveyor pulley. While belts in a standard conveyor slip over time, a toothed pulley provides consistent movement on the belt. This is important for accurate placement of parts during indexing or assembly runs. Toothed pulleys also allow heavier torque transfer to the belt. As a result, excellent belt-movement control positions parts and fixtures accurately.
Accessories are also integral to successful conveyor operation. For example, manufacturers can mount shaft encoders to the conveyor's drive shaft to sense rotations, count pulley revolutions, and control the belt in feeding or indexing applications. Diverters and gates manage the product's continuous flow on the conveyor. Controlled by proximity switches, photo eyes, or counters, they guide and change product direction to single or multiple locations. In addition, diverters and gates meter flow to specific areas or separate products based on attributes.
Depending on the product and required stroke length, pushers mount overhead or on the conveyor's side to remove items flowing perpendicularly from the conveyor. Servo drives accurately stop the conveyor to provide precise part location. They help control acceleration and deceleration and assist in assembly operations.
Once equipment is up and running, routine maintenance is necessary to extend equipment and conveyor life, trim downtime, and catch potential problems. Belt speed, weight on the conveyor, surrounding environment, and the number of daily operating hours are some factors to consider when developing a maintenance program. Since a set maintenance standard does not exist for say, every 100 hours of operation, the conveyor types and application they're supporting should determine maintenance procedures.
Additionally, an inventory database aids in recording vital information. Pertinent criteria and headings include all facility conveyors, makes and models, dimensions (conveyor length and belt width), motor type, belt brand, manufacturer serial numbers, dates of last maintenance check and next inspection, type of maintenance performed, and the manufacturer's phone number. These criteria accurately track system problems and provide long-term reference for future conditions.
Furthermore, a bench stock of common conveyor replacement parts should be established, such as belts and bearings. A general rule for belts is to keep at least two replacements for each conveyor style in a plant. This way, if two fail in a matter of days, they can be replaced quickly. Some manufacturers also offer kits of commonly replaced parts for their conveyors.
When belts fray or rip, it's best to pull a conveyor off the line and replace them immediately. Although belt changes temporarily slow production, disregarding them may cause conveyor breakdown during production runs and damage other more expensive components.
When operating in harsh environments, routinely washing conveyors and spindles with hot water or a light chemical cleaner will remove built-up dirt, grease, and oil. While a conveyor is off the line, bearings should also be greased as needed and gearboxes lubricated. Many new conveyors are built with sealed bearings, eliminating grease. If, however, the conveyor's bearings have a grease zerk, they should be greased routinely. Bearings that are sealed should not have grease forced into them.
Fitting the application
Conveyor speeds vary depending on the application. Some operate at just a few feet a minute, while others run at several hundred feet per minute. Whatever the desired speed, conveyors can be programmed accordingly.
An application and its surrounding environment dictate conveyor and component lifespans. For instance, in the metal stamping industry, heavy sections are stamped out of large scrap metal and fall onto a moving conveyor. Here, belts regularly fray and rip, and pulleys can be damaged by constant conveyor installation and removal. Oils, lubricants, and chemicals that come in contact with the conveyor also harm longevity. Due to these rugged conditions, conveyors and components are frequently replaced.
Other applications, such as packaging, labeling, and sorting are lighter on conveyors, enabling them to last several years without major repairs.
When standard is better
Using standard and modified conveyors expands an integrator or OEM's efficiency. Autologik, a Hartland, Wis. distributor of automation solutions employs many supplier's standard conveyors to move, twist, turn, feed, identify, label, sort, and special-handle a variety of packages and parcels.
Upon identification, Autologik solutions monitor and track an item's movement through completion. Standard conveyors allow Autologik to focus its resources on the value-added facets of business, while assuring customers that service and spare parts are always available.
“Oftentimes, conveyors are installed as part of an overall process,” stated Terry Ball of Autologik. “While their main job is to move parts from point A to point B, they can accomplish much more.” For example, Autologik offers solutions where labeling occurs at up to several hundred items per minute. This process applies (or prints and applies) labels to the underside of items while moving on standard belt conveyors. “Conveyors' design flexibility allows us to increase our software capabilities and resources to provide world-class solutions,” Ball said. “As a result, we provide solutions more effectively, gaining a marketplace advantage.”