Choosing the right magnetic conveying system
February 7, 2006
Magnetic soft-belt conveyors can feed presses and transport parts from one workstation to another or from production to inspection, storage, or packaging operations. If you work with ferrous metal coils or sheets, a magnetic system may help improve plant efficiency, safety and reduce costs.
|Incline and vertical magnetic conveyors are designed to conserve valuable floor space.|
Soft-belt magnetic conveyors feed presses and transport parts from one workstation to another or from production to inspection, storage, or packaging operations.
Magnetic conveyors can be configured to move ferrous materials vertically over aisles and above work areas to save floor space. They also can convey parts between floors, which can reduce part damage caused by other handling techniques.
In finishing operations, magnetic conveyors separate ferrous and nonferrous material, and some can change the direction of part travel. Other setups can flip parts over for visual inspection or secondary operations. Some conveyors are specially designed to maintain part spacing during transport, and by stabilizing parts and conveying at controlled rates, they become an essential part of automated production lines.
Common sheet and blank applications include cut-to-length lines, stamping operations, part transfer between presses and workstations, coating, and oiling.
Metal-frame, soft-belt magnetic conveyors can boost output from workstations by moving material to and from production machinery. Press loading, a time-consuming process if performed without any mechanical assist, can be more efficient, as well as transfers from stamping equipment.
Magnetic skate rails can be added to conveyors to support especially wide material. Photo courtesy of VIL.
Magnetic conveyors also can drive sheet stock and blanks horizontally or up inclines and correctly position them for automated punching and stamping lines. To increase quality control, sensors can detect double or defective blanks, then reverse-convey or route problem sheets to a separate conveyor line.
Modular Conveyors. These systems, sometimes called pre-engineered or standard-frame conveyors, are compatible with conventional conveying equipment and fit together like custom conveyors.
Modular units can be combined to construct horizontal and incline runs designed to transport, feed, accumulate, elevate, orient, and sequence ferrous sheets, blanks, and parts. To handle large sheets and blanks of any width, consider adding skate rails on either side of the layout (see Figure 1).
Depending on their magnetic strength, modular conveyors can move a range of parts and scrap up inclines as steep as 90 degrees. They provide positive, continuous control of conveyed materials, which may reduce labor costs, save floor space, and increase productivity (see lead photo).
Low-profile Conveyors. Space-saving, low-profile belt conveyors are designed to operate in confined spaces around production machinery. Some are built less than 2 inches high to fit between the stamping press bolster plate and the bottom of the die where clearance is extremely tight.
Low-profile conveyors can streamline part and scrap removal from presses.
Low-profile magnetic conveyors capture fast-moving parts and scrap and keep them from flying off the belt (see Figure 2). They can reduce labor and maintenance costs by preventing ferrous material from ricocheting and filling up the press pit or falling under the belt or under the press. Even on inclines, low-profile magnetic models provide continuous control of ferrous parts and scrap.
Punch press and automated applications require conveyors that can handle heavy loads, high belt speeds, and heavily oiled materials. Look for models with frames, motors, belts, and magnets that are right for the job. Useful options include gang drives for multiple units, specialized belts, floor supports, and side guards.
For moving heavier loads in confined spaces, medium-frame conveyors take up less space than conventional conveyors. The frames of these in-between units are slightly wider than their belts, which normally are from 2 to 36 in. wide. They have optional portability and offer a choice of frame lengths, magnetic elements, drive motors, and height and incline adjustments.
Magnetic incline conveyors elevate parts to feed hoppers, bowl feeders, and secondary operations. Hoppers with vibratory feed trays feed magnetic conveyors to provide continuous movement of product for tasks such as feeding heat-treating operations.
Special double-slope combination units—horizontal conveyors that feed incline conveyors within a single frame—can be used to remove parts and scrap from behind straight-side presses and open-back inclinable presses. They eliminate the need for tote pans that require a halt in production as workers remove the pans.
Beltless conveyors are designed to handle abrasive parts and demanding environments.
Beltless Conveyors. These conveyors have no belt and feature magnets that move under the slider bed via a chain-and-sprocket setup to transport ferrous material over the slider bed. Beltless conveyors are built to handle parts and scrap with sharp, jagged edges that can cut and damage belts. They hold ferrous material firmly against the smooth metal slider bed, which is made of stainless steel to avoid magnetization.
Beltless conveyors move parts at various speeds and can be stopped, started, or conveyed at angles. If the magnets are matched in grade and size to handle the parts, a product can be transported up steep inclines without significant product slippage (see Figure 3).
Older beltless designs have housings filled with oil for lubrication. Newer designs use oil-impregnated guides that wrap around the chains that move the magnets. This type of magnetic conveyor is also used in hostile environments, such as with oily and razor-sharp scrap, and where maintenance is difficult to perform.
Stacking/Destacking Conveyors. Magnetic stacking/destacking conveyors are a key component of many conveying systems. They are designed to take sheets from a cut-to-length station and transfer, index, and stack them at preselected drop sites (see Figure 4).
Magnetic stacking/destacking conveyors can take sheets from a cut-to-length station and transfer, index, and stack them at preselected drop sites.
These conveyors come in a variety of configurations, can be used in a range of automated setups, and provide an alternative to manual handling of sheet metal parts as they come off the production line. Simple controls direct stacking conveyors to position blanks and parts in predetermined places and quantities, ready to be transferred to another production area, warehouse, or shipping station.
Magnetic stacking/destacking systems also can be fitted with a variety of sophisticated sensing devices to monitor blanks and parts and redirect those that have defects. Stackers can be configured to transfer rejected parts to alternate locations for special handling.
Timing-belt Conveyors. This type of conveyor is designed to provide speed control. Throughout transport, sheets and parts stay in lock-step order for further processing and robotic manipulation. Precise belt timing maintains the spacing of sheets, blanks, and parts from initial placement until they are processed, removed by robotic devices, transferred to another conveyor, or stacked (see Figure 5).
Timing-belt conveyors keep ferrous parts accurately positioned for placement and processing. Photo courtesy of VIL.
Timing-belt conveyors can save time and labor by allowing you to perform production operations as materials are transported, and by allowing conveyor indexing and multiple pickup options along a production line. Conveyed items are separated and avoid contact damage. Just as with standard conveyors, skate rails can be added to support extra-wide material.
Once you've determined the type of conveyor you need, you're ready to decide how it should be specified and equipped to handle the size, weight, and volume of the parts and scrap produced. Work with a manufacturer to select the proper drive motors with power ratings matched to conveyor size and your anticipated loading, convey speed range, and output.
Also consider end drives, center drives, and gang drives for parallel conveyors. Various belt materials, thicknesses, and surface textures are available to complement the materials you convey at different stages in your operation. Cleats, ribbed cleats, antistatic polyesters, and oil-resistant urethanes are some of the choices.
Electromagnets sometimes are used in conveyors, but this design is not common. Although electromagnets produce strong magnetic fields, they depend on an electric power source.
Permanent magnets are the common source of holding power for most conveyors. They are shaped or machined pieces of magnetic materials, such as ceramics, alnico alloys, or rare-earth elements, which are magnetized through exposure to intense electric fields.
Once magnetized, these materials maintain their magnetic energy over a range of environmental conditions. They are self-contained and require no electrical hookups or outside power supply. Magnet type and grade determine characteristics like strength and resistance to demagnetization from high temperatures and physical shocks.
Ceramic magnet material is the energy source used in most magnetic conveyors. Alnico is used for high-temperature applications more than 300 degrees F, and rare-earth magnets are used in demanding applications. All magnet materials come in several grades and can be sized to meet most strength requirements.
The type of materials conveyed influence what magnets and belt options you require. These characteristics include surface materials, which can be flat, irregular, or round; oily or wet; and smooth or rough. The larger the absolute mass of metal and the greater the air gap or coatings between the magnet and metal, the more magnetic energy is required to hold the material properly on the conveyor belt.
Conversely, the greater the contact area, the less energy is needed to do the job. The magnetic properties of the material also must be factored in. The more conductive or magnetic the material is, the less energy is required to hold it.
Increasing the angle of incline requires more magnetic force to elevate the parts or scrap. Steeper inclines reduce required floor space, but heavy parts may require shallower inclines for better product control and reduction in stress on belts and drive systems. To prevent round shapes such as cylindrical parts from rolling downhill on inclined conveyors, cleated belts can be used in addition to high-energy magnets.
If you work with ferrous metal coils or sheets, a magnetic system may help improve plant efficiency, safety, and reduce costs.
Mike Wilks is director of marketing and sales with Bunting Magnetics Co., 500 S. Spencer Ave., P.O. Box 468, Newton, KS 67114-0468, 800-835-2526, fax 316-283-4975, email@example.com, www.buntingmagnetics.com.