Accumulation
Conveyors | Belt Conveyors | Heavy Unit Load Conveyors
Roller Conveyors | Wheel Conveyors | Wheel
and Roller Conveyors
Product Data Applicable to Multiple Conveyors | Product Specifications
Product Testing | Conveyor Angle Chart
Products To Be Handled
Accumulation of Products Separated by Gaps
Tapered products and those with handles or rims may create gaps between the bottom surfaces. With APC, accumulation sensors in the gaps are not depressed, resulting in a line pressure buildup. If products are of uniform or predictable length, positioning of a stop may prevent this problem; otherwise, double sensors are required.
When accumulating on APC units, lay out irregularly shaped and tapered products, and those with projections, to determine whether the gaps will result in non-depression of sensors.
Controls When Products Buckle
Also, when tapered products are accumulated end-to-end, or where there is a change in pitch, the products tend to lift off the carrying surface or buckle from the pressure of accumulated products. Non-APC accumulators are particularly prone to these problems. Further, the shock of products hitting those already accumulated causes buckling and toppling of loads.
Under these conditions, wheel or roller type limit switch controllers are ineffective, because the buckled or lifted products will sometimes permit the controller to travel to the "up" position. Instead, consider using special controllers; hold-downs to prevent the product from lifting, if loads permit; or photoelectric eye controllers.
Product Width Vs. Belt Width
Normally, the conveyable can be as wide as the belt. Occasionally, light products which are of such shape as to remain in contact with the belt can be wider than the belt. Long, narrow packages may require a wider belt for clearance around horizontal curves. To determine the proper width required to convey an item through a curve, see the Product Application section for the curve required.
Runners on Bottom of Products
If the runners are parallel to product flow, the belting must be wider than the runners, and guard rails must be designed to prevent any part of a runner from dropping off the belt and hanging up on the bed.
If the runner are perpendicular to product flow, the end-of-unit pulley positions must be carefully evaluated, because the product could hang up at these positions.
Condition of Pallet Bottoms
Warped bottom boards can cause the advancing pallet to nose into the next rollers, which interferes with conveying progress. Bottom surfaces must generally not be warped or bent more than 1/8 inch, especially when conveying wood pallets with up to 500 pound loads. Large volume pallet users must be encouraged to implement a repair facility to replace excessively worn or damaged pallets.
Guiding Pallets
If it is necessary to guide pallets or other heavy unit loads down the conveyor, use guide wheels instead of guard rails.
High Speed Conveying
Conveying at the higher speeds available must be carefully evaluated before implementing -- loads must be prevented from shifting at transfers and stops.
Load Distribution
Plywood pallets do not distribute the load well; the load will be concentrated in the same pattern as the products being carried on the pallet.
Banded loads can result in poor load distribution.
Loading Orientation
Pallets must be loaded straight and well-centered onto the conveyor, to avoid excessive pallet skewing.
Product Overhang
As a general rule, a product must not overhang a pallet more than 2 inches.
Roller Centers vs. Pallet Condition
For conveying pallets, check roller centers vs. condition of the pallet, and verify that a sufficient portion of the pallet will always be supported by rollers.
Shock Loading
If the product is loaded by fork lift, or if conveyor is subject to other types of shock loading, it is recommended that the conveyor be spring-mounted. The springs must be pre-loaded so that "at rest" height remains constant.
Unstable Loads
Watch for loads which are leaning, opening-up, becoming wobbly, or bulging. Remedies for unstable loads include steel or plastic stripping and plastic foil wrapping.
Further Information
For more information on Heavy Unit Products to be handled, see the PRODUCTS Tab in the Heavy Unit Load Handling Guide.
Roller conveyor is particularly suited to conveying products that have one firm, free-running surface.
Diverting Shrink-wrapped Cases
Follow these practices in applications where shrink-wrapped cases (dry grocery systems) are being diverted on live roller conveyor.
Furniture Cartons
When a chair or similar item has its four feet resting in the four corners of the carton, the carton may tend to misshape, causing potential hang-up on roller conveyors. Check condition of such cartons before conveying on rollers. Prolonged conveying of this type of carton is not recommended.
Narrow Products
Roller conveyors have no minimum product width, but guard rails are recommended when conveying unusually narrow products. This is necessary in order to keep the products longitudinally oriented, to prevent them from rotating while being conveyed, and to prevent side-by-side product conveying.
Orientation of Products
Products must be handled with their longest dimensions parallel to the direction of flow. When so oriented, products should be aligned square to the conveyor to avoid skewing. Apply an alignment device if products enter the conveyor in a badly misaligned state.
Product Length vs. Number of Rollers
Product to be conveyed on roller conveyor must have at least three rollers under the carrying surface. Products with soft or unusual bottoms, such as drums, wooden crates or cans with chimes will require more rollers to convey properly.
Product Width vs. Roller Width
Rollers should normally be at least 4 inches wider than the widest product to be conveyed. This provides support under the total product width and allows on each side a 2 inch clearance between the product and the frame or guard rails. Firm-bottomed products with even weight distribution have, however, been conveyed successfully on a conveyor narrower than the product.
If the conveyor will contain curves, determine the over-all conveyor width by the width of the required curves. Using curves in a system limits and determines maximum product length and width. Long narrow items may require a greater bed width for clearance around horizontal curves. To determine the proper width required to convey an item through a horizontal curve, refer to the Product Application section for the curve required.
Runners on Bottom of Products
If the runners are parallel to product flow, carefully consider the relationship between the runner, roller, and frame. When the product is against the guard rail or side channel, make sure that the runner cannot drop between the roller and frame.
If the runners are perpendicular to product flow, carefully evaluate roller spacing and evaluate gaps at the end of each unit.
Speed of Products
High flow rate causes product speed to increase, because the rollers keep turning between products.
Empty Cartons
Empty cartons conveyed on gravity conveyor require a high degree of pitch -- typically about 10-12 inches of pitch per 10 foot section.
Product Length vs. Rows of Wheels Required
Any product to be conveyed on wheels must have at least three rows of wheels under the carrying surface.
Product Speed on Gravity Conveyors
Greater pitch and product weight causes an increase in speed, which is not a function of rate with wheel conveyor.
Wheel Pattern
For corrugated cartons and other products that may indent, select a wheel pattern with at least six wheels under the product at all times.
Bags which are sometimes Conveyable
Multi-wall paper bags containing flour, cement, sugar, and similar firm, stiff products can occasionally be conveyed on roller or wheel by increasing the pitch and keeping the runs short. Laned wheels and/or close axle centers also increase conveyability.
Non-conveyables with Irregular Conveying Surfaces
Products such as flimsy parcels or wood cases, with irregular conveying surfaces, are non-conveyable on wheel or roller. Indentation of rollers or wheels into the bottom of products can cause the product to be non-conveyable. Products such as the following are usually too soft to convey on wheel or roller:
Product Data Applicable to Multiple Conveyors
Handles or Upper Rims on Products
In addition to the accumulation concern stated earlier, handles and rims tend to "lock" and cause jams. This is especially true when transferring from a horizontal or declined gravity run to an inclined belt unit. On live rollers, such locking can cause lack of pressure roller contact. Carefully evaluate the product's tendency to lock, and apply the conveyor accordingly.
Incline/Decline Suitability
With the product positioned at the desired level of incline, draw a vertical line through the product's center of gravity (not necessarily the geometrical center). This line must fall within the middle 1/3 of the product's base length if the product is to withstand this degree of incline/decline conveying (see below).
Overhang of Tapered Product or Open Flaps
If the bottom of a tapered product is rubbing against a guard rail, guide, or channel frame, the top edge of the container will overhang. This could permit the top of the product to contact support or ceiling hanger vertical members or other interferences and possibly products on adjacent conveyors. Open flaps on cartons can cause the same problems. This condition will require a combination of the following design features:
Plastic or Metal Product -- High Noise Levels
When conveying metal or plastic totes or similar containers, acceptable noise standards will sometimes be exceeded. Determine whether noise levels are critical for the application and evaluate possible methods to keep noise at acceptable levels. One possible solutions is reduction of conveyor speed.
Plywood/Hardboard Tote Bottoms
Plywood or hardboard bottoms on totes often becomes warped, thus causing improper flow on gravity and power roller and wheel conveyors.
Product Contact with Guard Rail
Product should never contact guard rail under normal circumstances. Guard rail is designed to keep the product from falling off the conveyor and is not intended as a guide.
Product Load Distribution
Distribution of load in products and relative location of the center of gravity must be studied and analyzed for all systems. Not only must the center of gravity height be determined to establish incline and decline angles, but the distance from the container's front or leading edge (or trailing edge) must be established and considered. This is necessary even when the center of gravity is low.
For optimum conveying, the load in totes or similar containers must be evenly distributed. If the center of gravity is near the front of the container, it tends to rotate when contacting a diverter arm. If the center of gravity is near the rear of the container, the front edge tends to lift off the conveyor, particularly with roller conveyors. This can cause the container to ride up and over a diverter arm that is positioned low on the conveyor.
Product Retention Netting
As an alternative to a guard rail, netting can used to contain accidental product spillage for protection of personnel below a conveyor.
For details on netting methods, including side guard netting, box shape netting, L-shape netting, gap netting, and double spillage protection, see the Product Retention Netting Application Guide in the Systems Engineering Standard Instructions.
Projections on Product Bottoms
Check the bottom of conveyable products for projections, which can cause conveying problems. For example, tiny rivet heads on product bottoms can cause the following:
Runners on Bottom of Products
Transfers: Pay special attention to all transfers when handling products with bottom runners. The product must always be square before activating the transfer.
Limit Switch Controllers: Check all possible positions of the product to verify that limit switch rollers cannot pop up between the runners. When in doubt, use photoelectric controls.
Shifting Loads
Products with partial or fluid loads that can shift should be analyzed carefully for movement, control, and transfer throughout the system. Shifting from impact on gravity wheel or roller lines can cause breakage. Shifting on inclines or declines (particularly when traveling over a nose-over from horizontal to decline) can change the center of gravity location and result in tumbling, spilling, and breakage.
Thin Bottoms on Products
A conveyable product with a thin bottom can "give" and form an uneven bottom surface when a concentrated, heavy article is placed in it.
Tote Characteristics
When totes or similar containers have been used for several years, the containers must be checked when applying a conveyor. The specifications of all the containers may appear identical, but small differences in tote condition or construction can cause significant conveying problems. For example, the containers may have some of the following inconsistencies:
Ordering totes at different times and/or from different suppliers is the typical cause of such inconsistencies.
For product-to-be-handled specifications in addition to those stated here, see the Product Handling Specifications table in the Conveyor Selection section at the beginning of this manual.
If a specific product has characteristics which may make it difficult to convey, test it on the selected conveyor to confirm suitability.
This chart may be used for quickly determining the horizontal distance between supports or vertical change in height. From the intersection of conveyor length and conveyor angle, go straight left or right for the net lift value (vertical change in height) and go straight down for the horizontal distance between supports.
