Guide to Conveyor
Every warehouses or distribution center faces the same primary challenge; to move product in and out as quickly and efficiently as possible. There are many means to this never-ending end, but the primary one utilized across most industries is with a simple piece of material handling equipment called a ‘conveyor’. Similarly, in a manufacturing or assembly environment, conveyors are used to move materials to their single or multiple points of assembly until the finished product is produced. In simple terms, conveyors are mechanical systems used for transporting materials, loads, and products from one point to another. They may be horizontal, vertical, or inclined to facilitate the movement of the load. Usually, the load moves atop belts or rollers fixed to a frame traversing the designated start and end points of the process. Conveyor systems can be either powered or non-powered with the main benefit of reducing the non-value travel time between workstations to lower labor costs and increase throughput capacity. Although the concept of a conveyor is easy to understand, there are so many different types and configurations of conveyor, some more suitable for specific applications than others, that understanding the basics of this type of material handling equipment could prove to be extremely beneficial for your operations.
As the name implies, this type of conveyor is non-powered and relies on gravity. As such, this is usually the most economical type of conveyor to procure, but at the same time, typically requires the most amount of manual labor to operate. Many times, gravity conveyor is often set at a slight declining pitch in order to let the force of gravity aid in the movement of the load. Since there are no motors, which require conduit and wiring, these conveyors are easy to install and relocate as necessary in order to support the operations. Gravity conveyors may be rollers, composite chutes, or skate wheel conveyors. Chute conveyor has a solid metallic or plastic made surface inclined at an angle down in a straight or spiral manner.
For a skate wheel conveyor, it is often ideal for use when handling light loads having flat bases. This conveyor has a series of skate wheels on axles installed on a frame to facilitate movement of the load, along with a gentle push. The frame can be fixed or flexible and the common use is typically on the inbound side of the warehouse unloading trailers or on the outbound side when loading freight for shipment.
This conveyor is powered by a motorized system and loads are transported on belts made from fabric, rubber, leather, metal or plastic. The most common type of belt conveyors are roller bed and slider bed belt conveyors. Roller bed belt conveyor has the belt being supported by rollers located in between the conveyor frames. Typically, these rollers are spaced every 6”, but they can be closer or further apart if necessary, based on project budget and the specific application. Belt over roller conveyors usually can extend lengths much longer than belts over a slider bed as there is less friction induced on the belt, which means less torque that the motor drive has to produce. As such, roller beds are commonly used on incline belts since the conveyor also has to overcome the force of gravity associated with the change in elevation, which induces additional torque on the motor drive.
Slider bed belt conveyor is much like roller bed belt conveyor, but instead of rollers being the supporting surface for the belt, the belt is supported by the flat surface of sheet metal, typically called a pan, that joins the conveyor side frames. This keeps the belt running smoothly with minimal bouncing of the product, which happens a lot with roller bed belt conveyor. As such, slide bed belt conveyor is used on scanning, weighing, labeling or other applications where the product on the belt must be very stable. Slider beds are also used in declining belts since the force of gravity is actually assisting the motor drive and the product is more stable compared to a roller bed decline.
Typical applications where belt conveyors are used are inclines and declines or where long runs of simple transportation is required. Belt conveyor is not used for accumulating packages prior to a merge or sort operation, but instead, are best used to simply span long runs of basic transportation conveyance.
Live Roller Transportation Conveyor
Another motorized conveyor type that is also basic in nature is the live roller conveyor. Like the belt conveyor, live roller conveyor is meant to transport packages from point to point with no intended accumulation along the path. The carrying surface are the rollers and they are typically spaced every 3”, although they can be closer or spread further apart if necessary, with the main rule of thumb being that the smallest planned package must always be supported by at least three rollers. As such, it is not common to use roller conveyor for bags, envelopes or other flimsy and light packages. Those types of packages, typically used in a parcel application, is conveyed on either standard slider bed belt conveyor or parcel belt conveyor.
On a live roller conveyor, there are a few ways to cause the rollers to rotate in synchronicity. Every manufacturer has its own proprietary method, but, in general, use of either a belt in contact with the underside of the carrying rollers or use of a long rotating shaft located underneath the rollers with spools spaced in the same manner as the rollers and connected with rubber o-rings that transmit the force to the rollers and cause them to rotate.
Live roller transportation conveyors are often used where long runs of simple conveyance is required. Many times, cartons or packages introduced onto roller conveyors are from the side, either with people pushing onto the conveyor or possibly another conveyor merging onto it. Live roller conveyor is better than belt conveyor for this type of merge or take-away process because lateral forces on a belt conveyor will cause the belt itself to track to the side and damage some of the components over time. Plus, the steel rollers have less friction than most belts, which also helps the merge process.
Live Roller Accumulation Conveyor
Accumulation conveyors have the benefit of providing both transportation of packages as well as their accumulation at the end of the line ahead of a specific process. This queuing of loads is most applicable prior to a complex and controlled operation, such as merging, sorting, scanning, strapping, wrapping, palletizing or other processes typically found in fulfilment centers, distribution or manufacturing facilities. They provide buffer zones to allow for a steady flow of the load where it can be oriented as it is held back on the line until the process is ready.
Accumulation conveyor can be either contact or non-contact, meaning that the packages come in contact with each other as they accumulate and come to rest or they don’t come in contact with each other and they come to rest each in a defined “zone” along the conveyor section. There are benefits to both methods, but there are also many drawbacks, too. So careful consideration must be taken when determining the details of the accumulation and release strategy, especially considering the process it serves and the types and characteristics of the packages being conveyed.
Non-contact accumulation conveyor is also called zero pressure photo-eye accumulation conveyor. The method to ensure that packages do not come in contact as they accumulate is done by the photo-eye sensor in each zone that sends product presence signal to the adjacent zone controller. In the event that a product is stopped in an adjacent downstream zone, the zone controller maintains the drive rollers from activating. And when the adjacent downstream zone is cleared of the product, the drive rollers are activated to convey the load to the next zone. This is the basic operation of a photo-eye accumulation conveyor, but there are also many different settings with most zone controllers that can be utilized. Multiple adjacent zones can be programmed to allow for a “slug” release of a train of products in adjacent zones, products to coast to stop in a zone, or delay start in a zone, or many other settings that might help optimize the process that the accumulation conveyor serves.
In addition to the traditional 480VAC motorized photo-eye accumulation conveyor, there is also a 24VDC powered zero pressure photo-eye accumulation conveyor option which uses a decentralized drive system made of a 24V motor at each accumulation zone. The motors at each zone can run based on adjustable speeds and other settings. This conveyor type is compact in design, energy efficient, does not require pneumatics (air), and operates with minimal noise levels. Most conveyor manufacturers offer this in their suite of products in the same configurations as the traditional 480VAC models and is extremely popular when the product being conveyed is not significantly heavy or required to be conveyed at a significantly high speed.
Belted Zone Accumulation Conveyor
In applications where the material being conveyed includes small packages, envelopes, bags or has flimsy packaging, a belted zone accumulation conveyor is used. Similarly, belted zone accumulation conveyor can also be used on inclines and declines since standard roller conveyor does not have the friction on the steel rollers to convey at a pitch that is greater than a couple of degrees. The zones on a belted zone accumulation conveyor range in length from 18” to 48” and use photo-eyes and zone controllers in the same manner to sense and accumulate packages as the photo-eye accumulation roller conveyor. The main difference is that there is a rubber belt that is wrapped around the entire set of rollers in the zone and it covers the full width of the zone. In between zones, it is common to find a small transition piece so that small products smoothly convey from zone to zone. In addition to applications where the accumulation of small packages, envelopes or bags is necessary, belted zone accumulation conveyor is also being used in gapping and scanning prior to a sortation operation, gapping and label application operation and gapping and check-weighing operation.
Although many distribution centers, especially those that distribute to retail or wholesale stores, ship out pallet loads, most of the pallet conveyor in the industrial market is found in high volume production plants. Pallets built for shipment in distribution centers are forklifted or pallet jacked into the truck and do not use pallet conveyor for transportation. Pallets built in high-volume production facilities are usually stored into inventory before shipped out. Most of the time, the pallets are unitized by way of an automatic or robotic palletizer at the end of the production line. Then, the pallet is conveyed through an automatic stretchwrapper and then finally conveyed to the pickup point for an associate in a forklift to pull the load off of the conveyor and place into pallet rack or other storage medium. This process is continuous and thus, the pallet conveyor usually includes an accumulation buffer prior to the pick off point so that the production process does not have to shut down and wait, which is never good at a high-volume facility.
When the runners on the pallet being conveyed are short edge leading, then the most applicable type of pallet conveyor to be used is simply a wider and heavier duty type of live roller transportation or accumulation conveyor. The rollers are driven by use of a chain and sprocket, with the sprockets welded to the rollers on one side. Chain driven live roller conveyors or CDLR, find their application in high load capacity pallet transportation and other heavy unit loads. Another application of this type of conveyor is on dirty and oily environments since the chain and sprocket drive transmission does not require friction like a belt and roller does. If the runners on the pallet being conveyed are long edge leading, then a roller conveyor will likely not work very well. In this circumstance, a two or three strand drag chain conveyor is most suitable. Conveying pallets can be extremely tricky as there are many details that must be considered and is not as simple as normal case conveyor layout. Additionally, since the loads are tall and extremely heavy, there is a higher level of safety concern that impacts the system design.
With ecommerce and direct to consumer fulfillment continuing to grow exponentially, the conveyor type required to support this market has evolved rapidly as well. Parcel packages come in all types of sizes, shapes and materials. And since the volume of this market is increasing, parcel sort centers have adapted to a new type of conveyance; bulk flow. Packages are not singulated, one after another neatly organized on a conveyor system. Instead, a parcel carrier could have a large gaylord of packages dumped onto the system and a huge wave of items are immediately conveyed to manual or automatic scan and sort stations. Therefore, heavy duty belt conveyor is needed. Heavy gauge steel slider beds, heavy duty drives units and high tensile strength belting are required. Also, no gaps or catch points along the conveyor path is allowed. These conveyors are typically wide, either 49” or 60”, and have high solid side pans to keep packages from falling off the sides. Great consideration to elevation changes are required in the system layout design as bulk flow of packages have unique characteristics, especially when inclining or declining. Also, changes of direction of conveyance has its own nuance with bulk flow of parcels as this is an area where jams can occur, causing catastrophic results.