BASIC INTRODUCTION TO CONVEYORS

SECTION THREE
LIVE ROLLER CONVEYORS FOR UNIT HANDLING ONLY

Types of Live Roller Conveyor:

A. V-Belt Driven
B. Flat Belt Driven
C. Zero-Pressure
D. Single strand roller chain driven
E. Roller to roller chain drive
F. Roller Slat Conveyor

Applications
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 conveyor where:
1. Temporary utilization of the items being conveyed is a requirement.
2. Items are stopped momentarily such as traffic control points.
3. Items must be turned, say 90° on the conveyor.
4. An air operated or manual stop is injected into the line so that the item may be inspected or some operation performed while the conveyor remains in motion.
5. Side loading or unloading is required involving a sliding motion across the bed rollers.

Belt driven live roller using regular friction surface rubber filled belting is not recommended for use in high environmental temperature extremes. Rubber can become sticky and soft at temperatures exceeding 150°F, and this belting can stiffen considerably and crack in the minus zero range. PVC or cotton belting is a considerable improvement in the range described above. Check with your Master Hytrol Distributor for special cold room applications.

Keep in mind, that the belt travels in a direction opposite to the items being conveyed. This is unlike a belt conveyor where the items are being carried directly upon the belt, so they both go in the same direction.

V-Belt driven live roller conveyor is that type where a single strand of V-belt is under the roller bed, on one side of the rollers, adjacent to the side-frame and is powered in a direction opposite to that of the items being conveyed. We recommend this type of conveyor 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.

Belt driven tapered roller curves generally give 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 package length at the entry and at the discharge ends of the curve.

Two rail curves with straight rollers are not normally recommended for use as a live roller curve because both rows of rollers must be powered separately and with a different speed in order to obtain some semblance of differential action. Under some conditions, the center rail may be move off center, closer to the outer rail with the longer rollers powered.

Flat Belt driven live roller conveyor is that type where a flat width of belt is under the roller bed, generally in the center of the conveyor, but can be mounted off-of-center adjacent to the side frame if required. Because of the greater contact surface at the underside of the roller bed, this type of conveyor is recommended for handling medium to heavy duty loads, where moisture, hot, dirty or oily conditions do not exist. Again, the pressure rollers which snub the driving belt to the underside of the bed rollers are set to a minimum, just enough to convey the load, yet 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, and another type of live roller curve must be utilized where a curve is necessary.

Ripple Belt conveyor is one utilizing a belt, which 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.

Controlled gravity live roller is similar, in construction, to flat belt or V-belt driven live roller conveyor, 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 coming one after another are being conveyed.

Hytrol Zero-Pressure Live Roller Conveyor is very completely described in the General Catalog under the headings 190-ACO and 190-ACOC. This is a full length drive shaft arrangement, with each thread roller driven by a urethane o-ring from a 1.9" diameter longitudinal drive roller. The 190-ACOC curves, which are slave driven from the adjacent 190-ACO, is designed for applications that require accumulation of products without a build-up of line pressure. In addition, Hytrol has developed the model 190-ACA, a flat belt drive zero-pressure conveyor. In all zero-pressure live roller, the conveyor length is divided into zones, the length of each is greater than the maximum package length. Zero-pressure is achieved since the packages never touch one another.

Single strand chain driven live roller is a medium duty live roller conveyor, 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 form 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 just one or tow 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 a greater roller spacing than desired, then idler (non-powered) rollers may be spaced between each driven roller.
Because the chain guard on chain driven live roller conveyor forms a guardrail on the one side of the conveyor, items can only be transferred to and from the opposite side of the conveyor. Hytrol has 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, especially designed to bend around a curve.

Roll to roll chain driven live roller is a heavy-duty live roller conveyor for use under the same conditions as for single strand live roller. 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 reasonable 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 side frame.

Roller slat conveyor utilizes extended pitch bushed roller chain with oversize rollers rolling in tracks adjacent to the outer rails. Using 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. The line pressure thus is kept to a reasonable low level.

This roller slat conveyor is an extremely heavy type of conveyor, and 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 for filled oil drums or perhaps for newspaper mail rooms where the blocked load of newspapers permit the roller slat to run under the newspapers without damage.

Except for Hytrol's Zero-Pressure 190-ACOC conveyor, under no circumstances should curves be used for accumulation of square or rectangular items. Cylindrical items only are permissible. The very nature of a square or rectangular conveyor would cause the corner of one container to dig into the corner of another.

Powered curves should not be warped because of the difficulty in providing power to the individual rollers of a warped curve.

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