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How to Analyze Conveyor System Loads
Great systems rely on load and application information
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"Count on us to help guide you to the right solution -- one that achieves your goals and makes your work day easier. We'll work to understand everything about your load and application. What will be conveyed - a box, a pallet, an envelope, a barrel? What does it weigh? What are its dimensions? How fast does it need to convey? What are its sort rates? What's the conveyor's role in the operation? We'll help you sort out these questions so you get exactly the conveyor system you need."
Kevin, Employee-Owner
Systems Integration Group
Understanding the relevant factors
System productivity and is directly related to the proper material handling equipment selection and in-depth understanding of the application. Before hardware can be selected properly, the following criteria must be studied and defined carefully:
- Load data (physical properties of the product to be handled)
- Objectives of the application (what is to be accomplished with the equipment?)
Probably the most common error in selecting transfer mechanisms like conveyors is the fact that load data and application objectives are not understood in enough detail. In many cases, they are ignored completely and hardware is selected on an arbitrary basis or, worse yet, on a "lowest cost" basis. This is the point where rework happens and systems fail to meet the needs of the operation.
Load characteristics are critical
To specify the right equipment, you must understand the load and its characteristics. You must understand how it interacts with the conveyor, integrated machinery, other load types, and the inputs/outputs of the system. What do you need to know first?
- Shape or form. The load must be defined as pallet, box, drum, wire container, engine block, beer bottle, envelope, automotive body, or other item.
- Dimensions. If the load is a container such as a pallet, box, or tote, its length, width, and height must be known.
- If it is a unit item, the dimensions of the interface between product and conveyor -- such as the load bearing surface -- are critical.
And, in the case of a product on a container -- such as a pallet load of beer cases -- the dimensions of both the carrier and the load on the carrier must be known in order to provide for such factors as overhung clearance.
Load characteristics
Finally, if the load consists of bulk materials, such factors as density and flow rate must be identified.
- Weight. Maximum and minimum, filled and empty, weights of the load must be known if it is a container.
- Flow rate. The rate of flow or capacity of a system is usually stated in units per minute if a unit handling conveyor is used. Normal measurements of rate or capacity in bulk handling applications are cubic feet per minute or tons per hour.
Be specific with terminology
Ambiguous terms such as average rate or throughput capacity should be avoided. The rate usually varies in different areas of a material handling system. However, there is always one point -- usually an intersection or junction -- that acts as a bottleneck, and controls the rate of the entire system. This point must be identified, because it is a controlling factor in overall system design and hardware selection. The speed of an individual conveyor may have nothing to do with the rate or capacity of a system, except that the conveyor must be capable of handling the maximum required total load-feet per minute.
- Orientation. The position of the load on the conveyor must be established. A load length may actually become a height when the item is placed on a conveyor, tow line, or monorail carrier.
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Footprint. The bottom configuration, or footprint, of a load can
have a strong bearing on the design and cost of a conveyor system. The
following questions should be asked about footprints of different types
of loads:
- Pallet -- Are there block feet or runners? In which direction? Are there any broken boards, protruding nail heads, or straps?
- Drum -- Are there chines? Does the bottom bulge outward?
- Carton -- Is there a soggy bottom? Are there protruding staples?
- Casting -- Does it have irregular shapes? Is the surface machined? Does it have sharp edges or burrs?
- Steel shape -- Is the bottom surface flat, or is it warped? Is weld splatter present?
- Container -- Does it have feet? Is there a full-faced bottom? Is it flat or does it have sharp edges? Are ribs or runners used? Is weld splatter present?
- Bag -- Is the bottom flat, or is the shape like that of a bag of water?
Objectives of the system should be evaluated on a step-by-step, component-by-component basis. The purpose of each item of hardware should be questioned.
For example, is transportation the primary purpose of a certain conveyor, or is it accumulation and surging? Is the conveyor to be used as a moving assembly work table? Can it be combined with an adjacent conveyor to eliminate a separate drive?
Other typical questions
- If a turntable is being considered, can a right-angle transfer be used instead, to eliminate one drive mechanism? Can a roller gravity bed be used instead of a power conveyor? Why is the load to be turned or rotated in the first place?
- In a towline application, is the system strictly for transportation, or must accumulation take place at some point? Are accumulation areas absolutely necessary, or are they merely "nice to have"? Can switches and spurs be combined in some cases to reduce the number of separate elements?
- The same questions can be asked for a power-and-free system. An additional question to be asked is, "Is a power-and-free system really necessary?" Perhaps a combination of several trolley conveyors with interfacing transfers could do the same job.
The overall system should be reviewed after individual hardware components have been evaluated. In most cases, the scope of the system will be changed somewhat after the hardware analysis.
Frequently, the layout will be simplified, the number of transferring mechanisms reduced, and nonessential operations eliminated. This results in cost savings and improved conveyor performance.
