This article describes the following types of conveyors:
Belt drives can be divided into two groups: friction drives and positive drives. As their names imply, ''friction drives'' transmit power through the friction that exists between the belt and the pulley, while ''positive drives'' rely on the engagement of the belt’s teeth with grooves on the pulley. Positive drive belts are also known as ''synchronous belts''. Two of the other types, flat belts and V-belts, are friction-powered.
Flat belts provide high strength and friction levels as a result of the reinforced, rubberized material of which they are made. As a result, they are capable of transmitting up 150 hp/in (horsepower per inch) at speeds exceeding 20,000 fpm (feet per minute. Because of the flat belt’s lower bending losses, low creep, and high modulus of elasticity traction layers, they can provide an efficiency of nearly 99%, placing them ahead of V-belts. Overall, the performance of flat belts is not overly impacted by misalignment but, of course, they perform best when properly aligned. Although they do not have teeth, flat belts are inlaid with grooves, the design of which depends upon the speed, configuration, and environment of the equipment. Generally, they work best on drives that operate at speeds above 3,000 fpm with a continuous, smooth running motion.
Though slightly less efficient, V-belts are nonetheless an industrial staple due to their relative low cost, ease of installation and wide range of sizes. The surface of the V-belt is designed to stay wedged into its track grooves, an arrangement that multiplies the low tensioning force to increase friction on the pulleys. This increased friction makes alignment less of a critical element. As a result, V-belts are better suited for severe duty applications, including shock and high starting loads.
One particular type of V-belt that should be mentioned is the link-type. This belt type consists of removable links joined to adjacent links by shaped ends twisted in each. Because of their configurable design, link belts can be made up of any length. They can also be used to create matched sets and, because power transmission machinery does not need to be dissembled in order to fit them on, they are also very quick to install.
Synchronous belts have a toothed surface that corresponds with grooves in the pulleys, providing a positive engagement similar to gears or chains. The standard tooth shape is trapezoidal, but variations such as curvilinear teeth have come out in the last few years, each with a particular strength depending on the operation required. A recent modification has produced a belt and pulley that use a V-shaped, instead of straightedged, tooth shape. This configuration does not require pulley flanges and makes less noise. Overall, synchronous belts are ideal for applications that require indexing, positioning, or a constant speed ratio.
One of the most common causes of premature belt failure is misalignment. This problem gradually reduces belt performance by increasing wear and fatigue and, depending on its severity, can destroy a belt in a matter of hours. For the record, sheave alignment should not exceed a 1/2 degree of center distance on V-belts and 1/4 degree on synchronous belts. Angular misalignment can result in accelerated belt and sheave wear and potential stability problems with individual V-belts. Its effect on synchronous belt drives is even more severe. Symptoms such as high belt tracking forces, uneven tooth wear, edge wear, high noise levels and potential failure due to uneven cord loading are possible. Parallel misalignment, which can also result in accelerated belt and sheave wear and potential stability problems with individual belts, is more of a problem for V-belts. This is because V-belts run in fixed grooves and cannot drift between flanges like synchronous belts. Parallel misalignment is generally not a critical concern with synchronous belts as long as the belt doesn’t become trapped or pinched between opposite sprocket flanges and the tracks on both sprockets.
Tension is an especially important element in belt-drive performance. The amount of total tension that a belt drive requires depends on the type of belt, the design horsepower, and the drive speed. Since running tensions cannot be measured, it is necessary to measure the tension on a drive while the belt remains static. The force/deflection method is most often used. Once a calculated force is applied to the center of a belt span to obtain a known deflection, the recommended static tension is established. Force and deflection formulas can be found in most design catalogs.
With too little tension in a V-belt drive, slippage can occur and lead to spin burns, cover wear, overheating of the belt, and possibly overheating of the bearings. Not enough tension in a synchronous belt causes premature tooth wear or possible ratcheting that can destroy the belt and break a shaft. When installing a new belt, installation tension should be set higher, anticipating that drive tension will drop rapidly during the seating-in process. This extra initial tension does not affect bearings because it decays rapidly.
Belt conveyors ('''Figure 1''') are used for the controlled movement of a large variety of both regular and irregularly shaped products that can vary in weight. Unit loads travel on a horizontal, inclined, or declined path within the limits of product stability and the conveyor component’s capacities. The items being conveyed are carried by the top surface of the belt. The manufacturer’s General Catalog contains recommended uses for each model of powered conveyor. This general catalog also lists standard specifications and optional equipment for each model.
'''Figure 1: Belt Conveyor'''
The belt conveyor uses a belt riding on top of either a smooth metal bed or on top of rollers. The roller version is best suited for longer runs because it reduces the belt’s riding friction.
If an all-belt conveyor system is used, in order for product to get around corners, a powered conveyor with a concentric shaped belt ('''Figure 2''') is called for. This equipment is needed because it travels less on the inside than it does on the outside.
'''Figure 2: Curve and Belt Conveyor'''
This section describes the following types of belt conveyors:
A belt conveyor uses a smooth surface bed as the carrying surface for the belt. This surface is normally a steel bed, but in some applications, you may find the carrying surface for the belt to be Masonite or other solid bed surface.
A roller bed is a belt-type conveyor that uses rollers as the supporting surface for the belt. A good rule of thumb is to have at least two rollers under the belt supporting the shortest item being conveyed. This will give the item a reasonably smooth ride. The selection of the size of the carrying rollers is a function of the weight of the item being conveyed, the belt speed, and the manner in which the items are placed on the belt. Normal loading would simply be from a gravity or powered conveyor transferring a package. This is a smooth transition; packages transferring from the discharge end of a gravity or powered conveyor to the infeed end of this belt conveyor do not cause a mechanical shock to the roller bed. If packages are hand loaded onto the belt, there is a strong possibility that the packages might be thrown and dropped onto the belt, causing damage. We might consider more rollers (twice the number normally supplied), heavier duty rollers, or a slider bed in the area of impact only.
Horizontal belt conveyors usually consist of the following components:
Incline and decline conveyors consist of the same components listed above, except this unit would include a single or double noseover, possibly a feeder section, and a "rough" surface belt on the incline (decline) instead of a friction surface belt.
The brake belt is used as a stop at the end of an accumulation (live roller) conveyor and the meter belt is used as the speed-up belt to obtain case separation. The meter belt would normally have the drive, while the brake belt would be slave driven from the meter belt through a power take-off similar to that used at the chain-feeder section of an inclined belt conveyor. Meter belts normally run 1 1/2 to 2 times faster than the brake belt. Both meter and brake belts are normally provided with "rough" top type belting, such as "Hilltopper." As a rule of thumb, the total length of the combination of brake and meter belts should be about 1/7 the total length of the accumulation conveyor with the brake and meter belts. The length of the meter belt, based on the belt width, would be the same as a powered feeder section. For example, if the total length of an accumulation conveyor with brake and meter belts were 84 feet, then the total length of the combination brake and meter belts would be 12 feet; then, subtracting the length of the meter belt would give us the length of the brake belt portion.
This is a hinged steel belt, ideal for carrying hot and oily parts from punch presses, forging machines, etc. This type of conveyor may be level, horizontal, or inclined "S" shaped, as required.
This type of belt conveyor, because of the open mesh permitting the free flow of air, is excellent for conveying hot or cold materials that are too hot or too cold to handle on standard duck or PVC belts. The wire mesh belt can travel on rollers or longitudinal runners covered with a dense plastic material. The pulleys are generally cast with multiple teeth to grip the mesh of the belt. Under some circumstances, the pulleys can be standard rubber or neoprene lagged to grip the underside of the wire mesh belt. Since it carries no load, the return strand can also be supported by return idlers or by longitudinal runners.
A portable conveyor can be rolled from one position to another on caster wheels. Manufacturers offer a large variety of skatewheel conveyors or 1 ⅜" diameter roller conveyors with tripod stands and portable castered supports. There are catalogs that list various extendible portable gravity conveyors.
A reversible belt conveyor has been and will, no doubt, continue to be an item where the operating results will be in question until the conveyor is installed and tested under no load and load conditions. Theoretically, a belt conveyor will not operate reversibly unless all revolving surfaces in contact with the belt are square with the frame or the belt tracking devices are properly adjusted. When a reversible belt starts to give belt-tracking trouble, even after it has worked for a number of years, random adjustments should not be made. It could easily get out of hand if someone who does not know the proper procedure tries to correct the trouble by making adjustments. If, after operating satisfactorily for a number of years without problems, it begins giving belt-tracking trouble, it must be assumed that something must have happened to cause the belt to run off to one side.
Before trying to make any adjustments, the following points should be checked:
It is quite possible, if all of the above items are carefully checked and any corrections properly made, that the belt will then track in its original squared up position in both directions. The belt tracking conditions should be approached by correcting those things which may have gone wrong due to the age of the conveyor components, thus returning it as near as possible to its original condition.
The practice used in tracking a one-direction belt cannot be applied to a reversible belt conveyor. All moving parts in contact with the belt must be squared up with one another and all with the frame for the single direction only. Do not class a reversible belt conveyor in the same category as a single or one direction belt conveyor so far as installation time is concerned. The reversible belt conveyor does take considerably longer because of all the variable conditions to install it properly.
Belting manufacturers have come a long way in the manufacture of excellent quality belting. For example, most belting for level conveyors will probably be PVC (polyvinyl chloride), machine woven, and nearly impervious to most liquids and ambient temperatures. The "hilltopper" belt has a rough surface bonded to the PVC base. Other belts, some impervious to food oils and some approved by USDA (US Department of Agriculture) for food handling, are also available. See '''Figure 3''' for standard belts.
Many conveyor companies manufacture their own gear reducers for most conveyor applications, such as the integral width gear reducer for "V" built variable speed drives and the "C" face reducer to receive any "C" face electric motor. Open drip proof and totally enclosed motors are available, either single or three-phase. Totally enclosed motors are generally used. Many reducers are available using commercially standard speed ratios of 10 to 1, 20 to 1, etc. Conveyor companies can provide variable speed motor drives at additional charges. They have one with a 2.7 to 1 ratio and another with a 6 to 1 ratio. For example, this means that the 2.7 to 1 ratio can have a low speed of 10 FPM and can be adjusted up to a maximum of 27 FPM. On the 6 to 1 ratio, we can have the low speed at 10 FPM and the maximum speed at 60 FPM. We can also adjust the low speed, instead of using 10 FPM, up to 15 FPM with the high-speed range greater than that stated above, and within the speed capacity of the rollers, if the conveyor is a roller bed.
Many portable conveyors are normally furnished with single-phase motors and with reversing drum switches for 115 volts. This reversing drum switch has no overload protection. When three-phase motors are used, then the push-button controls operating on 115 volt single-phase actuate a three-phase magnetic starter, which does have overload protection in the form of heater coils. If the motor, for any reason, is overloaded and starts to heat up in excess of its rated capacity, the heater coil automatically will be destroyed, interrupting the electrical current to the motor. The motor will top undamaged, the condition that caused the heater coil to be destroyed can be corrected, a new coil replaced in the starter, and the system started up once again. It is extremely important that the proper coil size be used. Other than portable conveyors, most companies do not normally furnish electrical controls unless specifically requested to do so, usually at an additional charge. Limit switches, photocells, and other controls can also be furnished at additional charges.
A live roller is just that, meaning the driving source of the roller is either a friction belt, V-belt, round belt, or chain, and the roller actually sits on top of the driving source so that when the driving source runs, the roller spins. This is the most cost effective way to get packages from point A to point B.
Live roller conveyors, because of the relatively low coefficient of friction between the bed rollers and the items conveyed, are used in preference to belt conveyors where:
Belt driven live rollers use regular friction surface and rubber filled belting and are not recommended for use in high environmental temperature extremes. Rubber can become sticky and soft at temperatures exceeding 150 degrees Fahrenheit, and can stiffen considerably and crack in temperatures less than zero. PVC or cotton belting is a considerable improvement in the range described above. Keep in mind that the belt travels in a direction opposite to the items being conveyed, unlike a belt conveyor where the items are being carried directly on the belt in the same direction.
A V-belt driven live roller is a conveyor where a single strand of V-belt is under the roller bed on one side of the rollers, adjacent to the side-frame. It is powered in a direction opposite to that of the items being conveyed. This type is recommended for light and medium duty loads. This type of conveyor is not recommended for use where moisture or oily conditions may exist. A very light contact with the underside of the bed rollers is all that is required to keep the items being conveyed in motion. This type of conveyor may also be reversible.
A belt-driven tapered roller curve generally gives good package conveying action. The tapered roller presents a true conveying surface on a curve, giving the correct radial speed along the full length of each roller. The curve radius, along with the taper on the roller, which comes to a common focal point, causes the package to leave the curve in much the same position in which it entered. For best results, there should be live rollers a minimum of 2/3 of the package length at the entry and at the discharge ends of the curve.
Two rail curves with straight rollers that are normally not recommended for use as a live roller curve because both rows of rollers must be powered separately and with a different speed to obtain some semblance of differential action. Under some conditions, the center rail may be moved off center, closer to the outer rail with the longer powered rollers.
A conveyor type with a flat width of belt under the roller bed, generally in the center of the conveyor, but can also be mounted off-of-center adjacent to the side frame if required. There is a greater contact surface at the underside of the roller bed, which allows this type of conveyor to be recommended for handling medium to heavy duty loads where moisture, hot, dirty or oily conditions do not exist. The pressure rollers that snub the driving belt to the underside of the bed rollers are set at a minimum, or just enough to convey the load, yet still allow belt slip without undue wear or stress on the gear motor when the loads are momentarily blocked.
The above described conveyor design cannot be incorporated into a roller bed curve. Another type of live roller curve must be used where a curve is necessary.
A conveyor that uses a belt that varies in thickness at regular intervals along the full length of the belt. It is set so that the thicker portions of the belt make contact with the underside of the bed rollers. If the ripples are relatively far apart, only a few are in contact with the bed rollers. This makes for a fairly inexpensive live roller with reduced line pressure under blocked load conditions.
A type that is similar, in construction, to flat belt or V-belt driven live roller conveyors, except that the conveyor is sloped at a grade just sufficient to allow the items to convey by gravity. On the flat belt conveyor, the snubbing rollers are spaced further apart than the standard horizontal live roller. Since gravity is the driving force of the items being conveyed, the snubbing pressure is light enough to simply prevent the rollers from turning at excessive speeds, particularly when trains of items come one after another.
A conveyor that has a full-length drive shaft arrangement with each thread roller driven by a longitudinal drive roller. It is designed for applications that require accumulation of products without a build-up of line pressure. In most zero-pressure live rollers, the conveyor length is divided into zones where the length of each zone is greater than the maximum package length. Zero-pressure is achieved since the packages never touch one another.
A medium duty live roller conveyor that is ideal for conveying hot or oily items, or items subject to wash down. In this type of live roller, "Type A" plate sprockets are welded to one end of each roller. Care must be taken that the dimension from the end of each roller is identical to keep the roller chain in a straight path. In this type of conveyor, the roller chain which powers each roller only makes contact with one or two teeth of the sprocket. The sprockets and the chain are completely enclosed by the chain guard, which sometimes acts as a hold down for the upper strand of chain. Rack tooth sprockets must be used for this type of conveyor. If rollers used are a large diameter and would necessitate greater roller spacing than desired, idler (non-powered) rollers may be spaced between each driven roller.
The chain guard on chain driven live roller conveyors forms a guardrail on one side of the conveyor, causing items to only be transferred to and from the opposite side of the conveyor. Some manufacturers have developed a chain crossover, which simply crosses the chain over to the opposite side on a slave driven arrangement when items must be transferred to or from the driven side. Access is available from the one non-powered side only.
Single strand chain driven live roller curves can also be supplied using a side bow chain specially designed to bend around a curve.
A heavy-duty live roller conveyor that is used under the same conditions as single strand live rollers. In this instance, two type "A" sprockets are welded to one end of each roller. The roller chain then makes a complete loop around each pair of adjacent roller sprockets. With a greater number of sprocket teeth in contact with the roller chain, more power can be transmitted to and through each roller. Rack tooth sprockets must not be used on this type of conveyor.
Roll-to-roll chain driven live roller curves can also be supplied. A heavier duty roll-to-roll chain driven live roller conveyor utilizing two "B" type sprockets attached to the extended shaft on the outside of one side frame accomplishes the same as described above and permits the use of smaller drive sprockets, thus enabling us to keep the rollers to reasonably closer centers. This type of live roller can also allow access from either side of the conveyor, provided the chain guard which covers the outboard row of sprockets does not project above the top of the conveyor’s side frame.
A type of conveyor that uses extended pitch bushed roller chains with oversize rollers rolling in tracks adjacent to the outer rails. This kind of conveyor uses ball bearing rollers with the hexagon axles longer than normal; these axle ends pass through the hexagon broached bushings of the chain and are generally cottered at both ends on the outside of the chain.
On a blocked load, the conveyor continues to run, and the ball bearing rollers simply roll under the blocked load. This keeps the line pressure to a reasonably low level.
The roller slat conveyor is an extremely heavy type of conveyor. It must be assembled at the job site, as the assembled conveyor rollers in the chain are much too heavy to handle as an assembled unit. This is also a fairly expensive type of live roller and is used only under special conditions; such as heavy duty type used for filled oil drums or perhaps for newspaper mail rooms, where the blocked load of newspapers permits the roller slat to run under the newspapers without damage.
There is a wide variety of chain conveyors, which are classified into four types:
This is the type of conveyor consisting generally of two parallel strands of chain. For light unit loads and for short distances, the chain can be a double pitch roller chain with the standard small rollers running in a track lined with high density, low friction coefficient plastic material. For heavier loads, it is best to consider a heavy-duty cast pintle chain which will also run in a channel track lined with a high density, low coefficient of friction plastic material, of which there are many available today. The sliding chain conveyors carry the loads on the chains. The bottoms of the chains are in low frictional contact with the track.
This is the type of conveyor which generally uses two parallel strands of double pitch roller chains (sometimes three strands), with the rollers running on key stock material of the width to fit between the side plates of the roller chain. This design is used for fairly light loads and for short conveyors. For heavier loads, we can use the double pitch chain with oversize rollers, where the rollers are greater in diameter than the width of the chain side plates, causing the rollers to project below the side plate of the chain. This rolling friction design uses a lower horsepower requirement, so they can be used for longer runs of chain driven conveyors. The loads are carried on attachments, which raise the load above the chain rollers.
An A-slat or apron conveyor type uses steel or wood slats, or even ball bearing conveyor rollers, between the two parallel strands of roller chain (which actually fits the category description for roller slat conveyor previously described). In the use of steel or wood slats, heavy loads can be carried under such conditions where perhaps PVC or a rubber belt could not possibly be used.
This is also another type of sliding chain conveyor that uses single strand link chain riding in a plastic-lined track in the center of the conveyor. Outboard of this center track on both sides to the outer frame rails are gravity rollers or wheels spaced on suitable centers compatible with the containers being handled.
The link chain, which is powered, projects slightly above the side rollers and is the driving force that carries the containers, while the side rollers or wheels merely balance the load. Some advantages of this conveyor:
Some disadvantages are that it can only be used satisfactorily for fairly light loads and inclines, and declines cannot be too steep (probably not more than 15 degrees).
These types are similar in design to the horizontal slat conveyor in that we have two outboard strands of roller chain adjacent to the side frames. We can use an attachment on the chain to which we can fasten an angle, a flat bar, or a round rod. This angle, flat bar, or rod is the pusher bar. Under the chain track and between the side frames we have a slider bed. The units to be conveyed will slide on the slider bedplate and will be pushed by the pusher bars. The spacing of the pusher bars must permit the conveyed items to fit in between them. Some advantages of this type of conveyor are:
Some disadvantages are:
This type of conveyor can be designed to handle individual cartons as well as full pallet loads. The design can be similar to a dumbwaiter style, where the unit is a reciprocating lift, handling one unit at a time; or it can be a continuous lift with flights attached to side roller chains. Each flight can handle one unit; therefore the flight spacing vertically depends upon the maximum height of the unit being conveyed.
Accumulation conveyors provide a way to hold product on the conveyor until given a signal to release the product. Typical applications include feeding product to a machine such as a case sealer at a specified rate, or to hold all items to be shipped on a given truck until that truck is ready to be loaded. Accumulation conveyors have a distinct advantage over live rollers since they can allow boxes to "back up" without hurting the product.
There are three basic kinds of powered accumulation conveyor:
This type of conveyor ('''Figure 4''') accumulates product with a build-up of backpressure. While the rollers under the stopped packages are not turning, the system used to power the rollers is still engaged and moving. This system could be a V-belt, a flat belt, or a rotating shaft. With the drive engaged, pressure builds up over distance; therefore, when accumulation is required over long distances, pressure relief controls, like brakes and pop-up roller stops, must be employed. Generally, product can be accumulated for about 20 feet without special controls. Product to be conveyed needs to be relatively uniform in size and weight.
This type ('''Figure 5''') accumulates product by completely dropping out power to a zone of rollers when product is stopped in that zone. Product can be detected with a pneumatic sensor roller, or with a photoelectric eye. Sensor roller technology involves the use of linkages, springs, and mechanical valves, so it can become difficult to maintain in working order over time as the mechanical parts loosen and wear. Sensor roller zero pressure is best applied with relatively heavy packages of like weights and sizes. Because it is electronic, photoeye technology is more reliable over time. Photoeye zero pressure works well with varieties of product weights and sizes. It is well applied when very reliable accumulation is necessary, for instance, in overhead situations, or for accumulating and then releasing slugs of singular product through a sorter.
'''Figure 5: Zero Pressure Roller Conveyors'''
This type accumulates product by indexing it onto a belt, one box at a time, using a clutch/brake assembly, photoeye sensors, and a sophisticated computer-operating program. Indexing belts are not as efficient in filling up a line as other types of accumulation, but they don’t care about varieties of product weights and sizes. An operating programmable logic controller (PLC) is required to apply this technology. Also, air operated clutch/brakes are recommended over electronic clutch/brakes because of their reliability.
Gravity conveyors provide an economical means of transporting product where the conveyor does not need to be powered. Probably no other type of conveyors is applied to so many gravity material handling uses as roller and wheel conveyors, which are capable of handling various packaged materials efficiently for distances as short as 2 feet or as long as 100 feet. Items ranging from light bulbs to bagged cement to heavy castings can be moved by gravity.
Most items are best handled on roller conveyors; however, wheel conveyors may be substituted where a portable gravity conveyor is required, where light-weight containers (38 lbs. per feet in steel, 18 lbs. per feet in aluminum) are to be handled, and where semi-rigid filled multi-wall paper bags or bales are to be handled. In general, roller conveyors should not be used for conveying burlap bags of coffee beans, paper or cotton bags of rice, cotton bags of flour, or freshly filled paper bags of cement because the types of material mentioned have a tendency to drape over rollers.
Conveyors, when properly applied, confine the flow of materials, thus conserving valuable production and storage space. Frequently, as in storage racks and production assembly lines, roller or wheel conveyors are used for storage, providing accessibility and easy movement for processing or production. Breakage or damage is generally minimized when the products are supported and restricted during their travel on the conveyor.
Supports should have some height adjustment and should be selected for convenient height for personnel.
Skatewheel conveyors, as a rule, are generally used for handling smooth bottom, wood, fiber or plastic containers. Semi-rigid smooth bottom bags or bales may also be conveyed on some wheel conveyors. If there is any doubt, the product and container should be tested on an appropriate wheel conveyor. Such testing can help determine the suitable grade.
Skatewheel conveyors are not recommended for handling cans with chimes, open bottom crates, cleated containers, or damp, soft, soggy cartons. Further, they are not recommended for conveying flexible filled bags or articles too small to span at least three rows of wheels. Extremely heavy or soft-bottomed cartons may fold around wheels and are therefore also not recommended for use on wheel conveyors. The selection of wheel conveyor is based upon the rigidity, size, and weight of the package to be conveyed. The denser the wheel pattern the greater the range of carton that can be handled on such a conveyor.
Roller conveyors are also used for handling smooth bottom, wood, fiber, or plastic containers, crates (without wire binding), drums and cans with chimes, kegs, and long, narrow packaged materials.
Gravity conveyors are used as level push lines or downgrades by utilizing the natural force of gravity. The use of gravity to convey the selected class of packages to move by their own weight on a bed of rollers or wheels is, perhaps, the most widely used means for conveying in industry. The weights to be conveyed may vary from a few ounces to several tons. For example, in department stores, conveyors are used for handling light-weight boxes of hosiery; the same conveyors also handle heavier boxes of dishes and appliances. The selection of rollers is tailored to fit the application.
Roller conveyors are not recommended for conveying soft-bottom cartons or bags which will flex and fold or wrap around the upper carrying portion of the roller and thus deter the free motion of such containers.
The degree of decline required varies depending on whether the bearings are dry or grease packed, the ambient temperature (if outdoors), and, in some areas, the humidity. The degree of decline also depends on the specific application. The first package will start rotation of the rollers. The second package, if it follows shortly, will benefit from this rotation and travel a bit faster than the first package, and the third package even faster. In the course of the day’s production, trains of packages could be traveling very fast on a degree of decline originally defined to start package movement from rest. Retarding devices to help control this situation are available.
Roller and wheel conveyor curves are made to match the straight conveyor. The radii of any curve are dependent upon the length and width of the packages to be conveyed. The length and width of the packages also determine the width (between rails) of the curve and, generally, the width of the curve determines the width of the adjacent connecting straight conveyor. If a package is exceptionally long, as for florescent light tubes or cut flowers, the adjacent straight conveyor might normally be excessively wide, a condition which, of course, creates a costly conveyor. The imbalance in this type of situation can be corrected by using a narrower width curve and offset guard rails, thus permitting the package to overhang the rollers on the curve but still keep the adjacent straight conveyor to a satisfactory width and help keep the price of the required conveyor within competitive limitations.
Wheel curves, because of the multiple rows of individual ball bearing wheels, perform an excellent job of conveying rectangular packages, as the individual wheels apply the necessary differential action to keep the package centered as it traverses the curve. Hytrol wheel curves are available in standard overall widths to join to adjacent straight sections, with 45 degrees and 90 degrees of curvature as standard.
Straight roller curves are generally better for handling cylindrical packages than rectangular packages, because of the lack of the differential action required on this type of roller conveyer. Since a package has a longer distance to travel adjacent to the outer rail, the package in this type of curve has a tendency to slip to the outer frame.
Double roller curves (curves with a center frame midway between the two outer frames which splits the roller length) will convey a square or rectangular package better than the single straight roller curve because of the differential action of the two separate lanes of rollers.
For best results, gravity curves should have a straight gravity roller conveyor section at the in-feed, and discharge ends of the curve of minimum length equal to approximately 2/3 of the length of the packages.
Gravity curves are not recommended for accumulation of square or rectangular packages. The line pressure will prevent the packages from maneuvering the gravity curves and generally will force the packages against the outer guard, thus blocking the free flow of further packages.
Gravity roller or wheel conveyor spurs are used for merging and diverging packages onto or off of a main line transportation conveyor. The standard angles are 30 degrees, 45 degrees, and 90 degrees. The 45 degree diverging unit is not normally recommended for automatic diverging of packages but should be manually attended. Turning wheels should be used as shown in the ''Hytrol General Catalog'' where spurs are used in the converging application.
These switches, using skate wheels, provide a simple method of diverting or converging products from one line to another as described in the ''Hytrol General Catalog''.
These are hinged sections used as gates and are available for vertical movement of the section to provide access for personnel, lift trucks, or other equipment. They are available with or without springs. The springs provide some assistance in lifting the heavier gate sections. Horizontal gate sections with a pivot pin on one end and caster supports on the opposite end are also available.
Thin wall rollers are perfectly satisfactory for most package handling, but should not be used for handling extremely heavy packages with steel strapping or filled steel drums regardless of the indicated roller capacity. Thin wall rollers may be easily bent, dented, or cut, thus impairing their usefulness. The heavier rollers such as 2 1/2" dia. x 11 ga., 2 9/16" dia. x 7 ga., and 3 1/2" dia. x 9 ga. are much better suited for this latter application.
Spring-loaded axle construction is a standard for:
The spring-loaded construction, which requires no hog rings or cotter pins, permits the customer to easily remove and relocate or replace rollers.
Other than wheel conveyors and 1 ⅜" dia. roller conveyors, which have bar and hook type couplings, all other frames have butt couplings for bolting sections together.
Most overhead conveyors are usually required to be provided with guardrails on both sides. Curves may also be provided with guards at the outside rail. Consult the ''Hytrol General Catalog'' for various types.
Some frames are made of steel galvanized, heat-treated aluminum, and powder coat painted steel. Hytrol green is the standard color.
You will at times have to replace rollers in a frame. It is extremely important that exact information be furnished and used to determine the replacement roller. '''DO NOT GUESS'''.
While it is difficult to recommend specific grades for various materials to be conveyed on a wheel or roller conveyer, '''Table 1''' lists suggested grades based upon average conditions. The actual grade for a specific requirement should be determined by test. Grades required for roller conveyers may vary because light cartons with soft bottoms may require more grade than heavy packages with hard bottoms.
Grades on curves are based upon the length of the outside rail, and grades on straight roller curves should be increased 25 to 50 percent than charted in '''Table 1'''.
The average roller conveyor line handling 40 to 45 pound packages and equipment with ball bearing rollers requires a pitch of about 1/2" per lineal foot of travel, and for wheel conveyors, the pitch is about 3/8" per lineal foot of travel. The pitch will increase or decrease according to the riding surface and the weight of the commodity to be conveyed. Also, the use of sleeve (sanitary) type bearings will affect the conveyor pitch.
Skatewheels are mounted on axles to convey product. This is the most economical type of conveyor. It is frequently used for loading trucks, with the conveyor set up on removable stands or supports.
Gravity roller conveyors use rollers for greater weight carrying capacities than skatewheel conveyors.
Flexible, extendable gravity conveyors allow you to move, reshape, lengthen, and shorten gravity skatewheel or roller conveyors to match your application.
Sortation conveyors provide a means of diverting a product from one conveyor line to another. By using controls and multiple sortation conveyors, product can be sorted by diverting the product only to the appropriate conveyor.
The following sortation conveyor components are described here:
In this type of conveyor, stationary or movable arms deflect, push, or pull a product to the desired destination ('''Figure 6'''). Since they do not come in contact with the conveyor, they can be used with almost any flat surface conveyor. These arms are usually hydraulically or pneumatically operated, but also can be motor driven. These types of conveyors are simple and low cost.
'''Figure 6: Diverter'''
A pop-up devices is one or more rows of powered rollers or wheels or chains that pop up above the surface of the conveyor to lift product and guide it off the conveyor at an angle; wheels are lowered when products are not required to be diverted ('''Figure 7''').
'''Figure 7: Pop-Up Device'''
The sliding shoe sorter (aka, ''moving slat sorter'') uses a series of diverter slats that slide across the horizontal surface to engage product and guide it off the conveyor ('''Figure 8''').
'''Figure 8: Sliding Shoe Sorter'''
Trays or slats provide combined sorting mechanism and product transporter ('''Figure 9''').
'''Figure 9: Tilting Device'''
Cross-belt transfer devices are either continuous loop, where individual carriages are linked together to form an endless loop, or train style (asynchronous), where a small number of carriers are tied together with potential for several trains running track simultaneously ('''Figure 10''').
'''Figure 10: Cross-Belt Transfer Device'''
The following are examples of the different types of sortation systems.
Many operations require sort rates of less than 30 items per minute. Tote systems, smaller case distribution operations, service parts centers, and many other operations require cost effective, low rate sortation technologies.
The most cost effective sortation devices available are diverter arms. Some are shaped like "baseball bats" and come across the conveyor to deflect products at an angle, 30 degrees typically, onto a different conveyor. Other diverters are curved to divert the product onto a take away conveyor at 90 degrees while maintaining product orientation. Diverter arms can be manually activated, or they can be controlled automatically with scanning technology.
A right angle transfer operates by engaging the bottom of a unit-load, lifting it off the transportation conveyor, and transferring it onto another conveyor at a 90 degree angle. Transfer mechanisms can be chain transfers or belt transfers. Typical rates achieved are 8–20 sorts per minute depending on the size and stability of the product.
Pushers are used to divert products at right angles at slightly higher rates than transfers. Comprised of either an electrically or pneumatically activated pusher, the device moves across the conveyor, moving the product it contacts onto another conveyor at a 90 degree angle. Typical rates will be in the 15–25 sorts per minute range.
The work transporter is a good solution for work-in-process sortation. Totes or boxes are diverted to work stations set up alongside the conveyor, and a return belt underneath conveys product out of the work station. Rates can be from 2-15 products per minute.
As distribution operations grow in size and complexity, sortation requirements generally expand. Medium rate sortation technologies are available when rates between 30 and 100 items per minute are required to be sorted in a shipping or distribution operation.
Pop-up wheel sorters can be used when rates are moderate and the product has a flat conveying surface. Products must be fairly uniform in size, as products that are too long or short will not divert consistently. Typical rates are 20-60 sorts per minute. Products are diverted at a 30 degree or 45 degree angle on relatively close centers, allowing for compact location of divert lanes.
The multiple belt sorter falls between the pop-up wheel and shoe sorters in both rate and cost. Capable of sort rates of up to 100 products per minute, the multiple belt sorter can sort at either 30 degree or 90 degree angles. Thirty degree diverts are capable of higher rates, while 90 degree diverts allow for really close spacing of divert lanes to minimize floor space.
For distribution operations requiring over 100 cases sorted per minute, higher speed devices are required. Shoe sorters are most commonly used. Using a series of tubes or slats with sliding shoes, these sorters provide positive sortation at rates up to and exceeding 200 cases per minute. Critical to achieving high sortation rates are systems to properly space cartons before inducting onto the sorter.
In high-speed sortation systems, cases need to be properly gapped before being inducted into the sorter. Equipment can range from meter belts, to servo-induction conveyors, to multi-lane induction belts, depending on the rate.
Capable of 200 sorts per minute, shoe sorters come in a variety of configurations. The sorters can be tube or slat, single sided diverts or dual diverts, and 30 or 20 degree diverts. A careful analysis of the product and rates is required to provide the best solution.
In large-scale distribution markets where a significant amount of the overall volume is distributed by the piece, different types of sortation technology are required. Catalog, apparel, and shoe distribution are a few markets that use high-speed piece sortation equipment.
Carousel put systems work well when a fairly large number of SKUs need to be sorted to a large number of locations. Often used in retail distribution, carousel put systems can create an environment of one-touch sortation directly to the shipper while also accommodating a very large number of shippers.
Carousel sorters are used for manual piece sortation directly to a shipping container, the carousel sorter works well on high volume SKUs. Accommodating up to 500 locations on a single sorter, the carousel sorter can sort up to 4,000 pieces per hour per operator. The carousel sorter allows a flexible number of operators to man sort zones, allowing for total system rates to exceed 20,000 lines per hour for a single sorter. The equipment is inexpensive and simple, costing far less than other technologies.
A-frame sorters are used to facilitate the picking of small individual items, the A-frame is extremely popular with drug and pharmaceutical distribution facilities. As the name implies, individual items are loaded or stacked in two rows of dispensing magazines (one or more magazines per item) that are arranged side-by-side, forming an "A-frame." A belt conveyor passes through a long tunnel created by the A-frame. As orders are filled, one at a time, items automatically dispensed from the bottom of selected magazines are kicked onto the belt conveyor and then carried to the end of the tunnel where they fall into a tote.
Tilt tray sorters are used to sort a wide variety of loads, including parcels and envelopes, totes, cartons, individual articles, poly-bags, luggage, and other items. Sorting rates over 10,000 units per hour are possible. Tilt-tray sorters are applied in many industries, including general merchandise distribution, shoe and apparel distribution, specialty retail, catalog and direct sales operations, as well as parcel and freight operations and postal processing centers. Care must be taken with fragile products as tilt-tray sorters generally sort into chutes.