BASIC INTRODUCTION TO CONVEYORS

SECTION ONE
GRAVITY

APPLICATION
Probably no other type of conveyor is applied to so many gravity materials handling uses as roller and wheel conveyor, handling various packaged materials efficiently for distances as short as 2 ft. or as long as 100 ft. or more. Any item from light bulbs to bagged cement to heavy castings can be moved on gravity.

Most items are best handled on roller conveyor, however, wheel conveyor may be substituted where a portable type gravity conveyor is required, where light weight containers (38 lbs. per ft. in steel, 18 lbs. per ft. in aluminum) are to be handled and where semi-rigid filled multi-wall paper bags or bales are to be handled. In general, roller conveyor 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 type of material mentioned has 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 conveyor 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 the travel on conveyor.

Supports should have some height adjustment and should be selected for convenient height for personnel.

CONVEYOR SELECTION
Skatewheel conveyor, as a rule, is 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 conveyor. 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 conveyor is not recommended for handling cans with chimes, open bottom crates, cleated containers or damp, soft, soggy cartons. It is further 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 conveyor.

From the Hytrol Catalog, you will note that skatewheel conveyor is available in varied widths and varied wheels per foot patterns. The selection of wheel conveyor is based upon the rigidity, size and weight of package to be conveyed. The denser the wheel pattern, the greater the range of cartons that can be handled on such wheel conveyor.

Roller conveyor 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 a level push line or down grade 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 and the same conveyors handle heavier boxes of dishes and appliances. The selection of rollers is tailored to fit the application.

Roller conveyor is 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 will vary depending on whether the bearings are dry or grease packed, on the ambient temperature (if outdoors) and, in some areas, on 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 followed shortly, would benefit from this rotation and would 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.

A few elementary rules in the selection of roller conveyor are offered as follows:
(1.) Packages to be handled should, in general, have smooth firm bottom riding surface.
(2.) For normal conveying, at least three (3) rollers should be under the package being conveyed at all times.
(3.) To select the proper roller, divide the weight of the package by the number of rollers supporting the package. The load capacity charts in the Hytrol General Catalog will help in your selection.

Other important areas to be considered are the actual items to be conveyed as well as their size. While the load capacity chart indicates that 50 lb. empty oil drums could be conveyed on 1.9" Dia. x 16 Ga. rollers, we would recommend the use of 2" Dia. x 12 Ga. rollers because of the greater wall thickness in handling a steel drum.

The tolerances of the various components, which make up a roller conveyor, may be such as to not present a perfect conveying surface. Uniformly loaded packages, with some flexibility, will distribute the weight approximately to each roller supporting the package, whereas rigid packages may impose their entire load on a reduced number of rollers. Wood or steel pallets may actually be supported by only 50 per cent of the rollers under them. Select from the Hytrol General Catalog a roller to suit the required load capacity, taking into consideration the type of product being handled, so that in the event the load is actually supported by one-half of the rollers under the product. The rollers selected will actually support this type of load. When roller lengths exceed the catalog lengths, the axle deflection may be the limiting factor in place of ball bearing capacity. Package roller conveyors are not normally considered to be precision equipment, and past experience indicates that the tops of all of the rollers in the conveyor may not be at exactly the same height. Where an excessive impact might occur in the loading area of a conveyor, it is advisable to consider providing twice the number of rollers normally required for conveying the package in this loading area only.

Nominal roller length is determined by the maximum width of the commodity to be conveyed. Ordinarily, rollers would be two to three inches longer than the widest package within the standards listed in the Hytrol General Catalog. It is, however, permissible, in certain package handling situations, for the package to extend beyond the ends of the rollers if the rollers are mounted in a high position in the side frames and provided the bottom of the package does not flex and make contact with the side frames.

Grades
While it is difficult to recommend specific grades for various materials to be conveyed on wheel or roller conveyer, we offer the following suggested grades based upon average conditions. The actual grade for a specific requirement should be determined by test. Grades required for roller conveyer 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 fig. 7.

The average roller conveyor line handling 40 to 45 lb. packages and equipment with ball bearing rollers requires a pitch of about ½" per lineal foot of travel, and for wheel conveyor 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.

CURVES
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 package to be conveyed. The length and width of the package also determines 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 for such a package, which condition, of course creates a costly conveyor. The imbalance of 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° and 90° of curvature as standard.

Hytrol also has available tapered steel rollers, which also apply the necessary differential action to keep the package centered as it travels through the curve.

Straight roller curves are generally more satisfactory for handling cylindrical packages rather 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 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 infeed and the discharge ends of the curve of minimum length equal to approximately 2/3 of the length of the package.

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 package against the outer guard thus blocking the free flow of further packages.

SPURS
Gravity roller or wheel conveyor spurs are used for merging and diverging of packages onto or off of a main line transportation conveyor. The standard angles are 30°, 45° and 90°. The 45° 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.

"Y" AND SPUR CURVE SWITCHES
These switches utilizing skate wheels provide a simple method of diverting or converging products from one line to another as described in the Hytrol General Catalog.

GATE SECTIONS
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.

ROLLER CONSTRUCTION
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 ½" Dia. x 11 Ga., 2 9/16" Dia. x 7 Ga., and 3 ½" Dia. x 9 Ga. are much better suited for this latter application.

AXLES
Spring-Loaded axle construction is a Hytrol standard for:
1 3/8" Dia. x 18 Ga. Rollers using ¼" Dia. Galv. steel axles 1.9" Dia. x 16 Ga. Rollers using 7/16" Hex. steel axles 2" Dia. x 12 Ga. Rollers using 7/16" Hex. steel axles 2 ½" Dia. x 11 Ga. Rollers using 11/16" Hex. steel axles 2 9/16" Dia. x 7 Ga. Rollers using 11/16" Hex. steel axles.
The spring-loaded construction which requires no hog rings or cotter pins permits the customer to easily remove and relocate or replace rollers.

COUPLINGS
Other than wheel conveyor and 1 3/8" Dia. roller conveyor, which have bar and hook type couplings, all other frames have butt couplings for bolting sections together.

SUPPORTS
Hytrol stationary supports are available in light, medium and heavy duty styles. Consult the Hytrol General Catalog for further information.
Poly-tier supports for support of multi-level conveyor lines are also described in the Hytrol General Catalog.
Ceiling hangers are 5/8" Dia. painted steel rods with threaded ends.
Tripod stands are useful in setting up temporary conveyor lines, using skatewheel and/or 1 3/8" Dia. x 18 Ga. roller conveyor.
For other types of supports, consult the Hytrol General Catalog.

GUARD RAILS
Most overhead conveyor are usually required to be provided with guardrails both sides. Curves as an option, may also be provided with guards at the outside rail. Consult the Hytrol General Catalog for various types.

FRAMES
Some frames are of steel galvanized, heat-treated aluminum, and powdercoat painted steel. Hytrol green is our standard color.

REPLACEMENT ROLLERS
You will at times, receive request to quote on replacement rollers even for frames, which may have been furnished by other than Hytrol. It is extremely important that exact information be furnished. DO NOT GUESS.
1. Obtain roller diameter and gauge.
2. Check axle size; i.e. ¼" Dia., 7/16" Hex, 11/16" Hex. etc. on 1 3/8" Dia. x 18 Ga. rollers, Hytrol furnishes ¼" Dia. Galv. steel spring loaded axles. Other conveyor suppliers may use 5/16" hex axles.
3. Check to see if bearings are dry, grease packed or re-greasable.
4. Measure the exact distance between existing frames.
5. Measure the frame thickness, i.e. 12 Ga., 10 Ga., 3/16", ¼" etc.
6. Some customers re-use their existing axles. Determine if axles should be furnished. If the customer uses rollers with spring-loaded axles, it is best that we furnish these complete.

QUESTIONS:
If you have questions, the answers to which are not to be found in Hytrol Catalogs, do not hesitate to call your master Hytrol Distributor. He will obtain the information for you. Do not place collect calls to your master distributor.

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