INTRODUCTION TO CONVEYORS
Conveyor Fabrication
How chain drive roller conveyors are made
Forward
Section One: Gravity Conveyors
Section Two: Powered Belt Conveyors
Section Three: Live Roller Conveyors
Section Four: Chain Conveyors
Section Five: Supports
Section Six: Couplings
Section Seven: Accessories
Section Eight: Useful Formulas
Section Nine: Essential Information Required
Section Ten: A Brief History of Conveyor
The package conveyor business has been in existence for almost one hundred years. Simplified, material handling engineering consists of determining "how a product should be moved from one place to another, within the shortest allowable period of time, for the least cost and with the least amount of manual effort". We hope that this publication will help to guide you to the best possible solution to the many material handling problems, which you may encounter. It is extremely difficult to put in to writing the many years of problem solving experienced by "old-timers" in this industry, no two solutions are identical. This publication will merely give you an idea of the uses of the many different types of conveyors available, and, it will be up to you to sift through to determine the best conveyor for your particular 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.
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:
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.
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.
The average roller conveyor line handling 40 to 45 lb. packages and equipment with ball bearing rollers requires a pitch of about 1/2" 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.
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.
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.
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.
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 Hytrol 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 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.
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.
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.
Some frames are of steel galvanized, heat-treated aluminum, and powdercoat painted steel. Hytrol green is our standard color.
You will at times, receive a 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.
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.
A. Slider or roller bed
B. Horizontal - Reversing and non-reversing
C. Incline/Decline - reversing and non-reversing
D. Powered Feeder
E. Brake and Meter Belts
F. Metal "Piano Hinge" Belts
G. Portable
Belt conveyors are used for the controlled movement of a large variety of both regular and irregular shaped products. They can move light, fragile to heavy, rugged unit loads on a horizontal, inclined or declined path within the limits of product stability and the conveyor component capacities. The items being conveyed are carried by the top surface of the belt.
The Hytrol General Catalog contains recommended uses for each model of powered conveyor. This general catalog also lists standard specifications as well as optional equipment for each model. Study the Hytrol General Catalog carefully and often. There is a world of good information to be gained from this practice.
Slider Bed is a belt conveyor, which utilizes a smooth surface bed as the carrying surface for the belt. In the Hytrol General Catalog this is a steel bed. In other applications, you may find the carrying surface for the belt to be Masonite or other solid bed surface.
Roller bed is a belt conveyor, which utilizes rollers as the supporting surface of 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 a gravity or powered conveyor transferring a package. This is a smooth transition such as packages transferring from the discharge end of a gravity or powered conveyor to the infeed end of this belt conveyor. If packages are hand loaded onto the belt, there is a strong possibility that the packages might be thrown and dropped onto the belt. We might consider more rollers (twice the number normally supplied), heavier duty rollers or slider bed in the area of impact only.
How do we select whether to offer the slider or roller bed conveyor? If we have light loads within the load parameters outlined in the Hytrol General Catalog, then, since cost is usually an important factor, we would select the slider bed conveyor. For heavier loads, again within the load parameters outlined in the Hytrol General Catalog, we recommend the selection of roller bed conveyor. 1.9" or 2" dia. rollers should not be used at belt speeds in excess of 150 F.P.M. Also, very wide conveyors require special consideration because of the possibility of axle deflection within the rollers.
Special conditions, such as high or low temperature conditions, and dirty or wet conditions should be brought to the attention of your Master Hytrol Distributor prior to quoting. Relatively heavy packages should not be transferred onto the middle of a belt conveyor say one 20 feet or longer in length. Continual transfer of the relatively heavy packages would have a tendency to push the belt to the one side of the conveyor, and if these packages were to enter the belt conveyor as a continuous flow, then could push the belt over to the extent that the edge of the belt could possibly be damaged at the drive or tail ends. The best type of transfer described above would be with the use of 1ive roller conveyors. However, if for some reason, the use of live roller conveyors is not practical, then we should consider the use of the three-pulley device normally furnished with the integral powered feeder, at each side of the junction of the push-on or push-off location. This provides a tight belt in the strategic location. A thin strip of wood, plastic, or steel, along the one edge of the belt opposite the push-on or push-off would also be helpful in retaining the belt in the proper tracking position. The solutions suggested herein are not to be construed as approval to accomplish a specific described action, these are merely recommendations for alleviating a non-recommended condition.
Single direction non-reversing belt conveyor of reasonable length, may use a standard end drive with the 4" dia. drive pulley. A reversing belt conveyor should use a center drive, generally, with a larger than 4" dia. drive pulley, particularly with longer conveyor lengths or heavy loads on the belt. See the Hytrol General Catalog.
Horizontal belt conveyors usually consist of the following listed components:
Incline and decline conveyors: Consists of the same components listed above except this unit would include a single or double noseover, possible a feeder section, one of the two types offered, and a "rough" surface belt on the incline (decline) instead of 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 and 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 a "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 accumulation conveyor with the Brake and Meter belts. The length of the Meter belt, based upon the belt width would be the same as a powered feeder section. As an example: If the total length of 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.
Metal "Piano Hinge" conveyor: 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. The design and dimensional information is described in the Hytrol General Catalog.
Wire mesh belt conveyor: This type of belt conveyor, because of the open mesh, permitting the free flow of air, is excellent for conveying hot or cold materials 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.
Portable conveyors: The Hytrol General Catalog lists a large number of portable belt conveyors. A portable conveyor is one, which can be rolled from one position to another on caster wheels. In addition, Hytrol offers a large variety of skatewheel conveyors or 1 3/8" diameter roller conveyors with tripod stands and portable castered supports. The catalog also lists various extendible portable gravity conveyors, the descriptions of which are well covered in the Hytrol General Catalog.
Caution areas for belt conveyors: A reversible belt conveyor has been and will, no doubt, continue to be an item with which the operating results will be in doubt 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 unless the belt tracking devices are properly adjusted. Conveyors & Casters employs capable Millwrights who have had extensive experience in installing and testing the reversible belt conveyors.
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 various adjustments. If, after operating satisfactorily for a number of years, 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 herein described to install properly.
Belting: Belting manufacturers have come a long way in the manufacture of excellent quality belting. For example, most belting for level conveyors furnished by Hytrol will probably be PVC (poly vinyl chloride) machine woven 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. Check with the Hytrol Master Distributor for belt recommendations for specific special applications.
Motors: Hytrol Conveyor Company manufacturers their own gear reducers for most conveyor applications. The integral width gear reducer for "V" built variable speed drives and the "C" face reducer to receive any "C" face electric motor. Motors are available in open drip proof and totally enclosed, either single or 3 phase. In the Western States, we mostly use totally enclosed motors. Hytrol reducers are available in commercially standard speed ratios of 10 to 1, 20 to 1, etc. Hytrol Conveyor Company can provide variable speed motor drives at additional charge. They have one which is.2.7 to 1 ratio and another, which is 6 to 1 ratio. As an example, this means that the 2.7 to 1 ratio can have, lets say, a low speed range down to 10 F.P.M. and can be adjusted up to a maximum of 27 F.P.M. On the 6 to 1 ratio we can have, the low speed at 10 F.P.M. and the maximum speed at 60 F.P.M. We can adjust the low speed instead of using 10 F.P.M. to say 15 F.P.M. with the high-speed range greater than that stated above, within the speed capacity of the rollers, if the conveyor is a roller bed.
Many Hytrol portable conveyors are normally furnished with single phase motors and with reversing drum switch all for 115 volts. This reversing drum switch has no overload protection. When 3 Phase motors are used, then the push-button controls operating on.115 Volt single phase which in turn actuates a 3 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, which, in turn, interrupts the electrical current to the motor. The motor stops undamaged and the condition which 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, Hytrol does not normally furnish electrical controls unless specifically requested to do so, at additional charge. Limit switches, photo cells and other controls can also be furnished at additional charge.
Conveyors & Casters is proud to report they have "in house" capabilities to prepare sophisticated electrical wiring schematic drawings, at additional charge and can arrange with qualified local electrical contractors in order to provide a turn-key installation.
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
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:
For more information, please visit Joyroll.
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.
There is a wide variety of chain conveyor classified into four separate types:
A. Sliding chain conveyors
B. Rolling chain conveyors
C. Pusher Bar chain conveyors
D. Vertical chain conveyors
Sliding chain conveyor: 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 co efficient friction 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 and the bottom of the chains are in low frictional contact with the track.
Rolling chain conveyors: This is the type of conveyor, which utilizes generally, two parallel strands of double pitch roller chains (sometimes three strands), with the rollers running on key stock material of width to fit between the side plates of the roller chain. Again, 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 thus the rollers do project below the side plate of the chain. This rolling friction design utilizes a lower horsepower requirement and thus can be used for longer runs of chain driven conveyor. The loads are carried on attachments, which raise the load above the chain rollers.
A slat or apron conveyor using steel or wood slats or even a ball bearing conveyor rollers between the two parallel strands of roller chain 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 a PVC or a rubber belt could not possibly be utilized.
Also another type of sliding chain conveyor, which utilizes single strand of 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 container being handled. The link chain, which is powered, projects slightly above the side rollers and is the driving force which carries the containers while the side rollers or wheels merely balance the load. Some advantages of this conveyor are:
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.
Pusher Bar Conveyors 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 be such as to permit the conveyed items to fit in between. Some advantages of this type of conveyor are:
Some disadvantages are:Vertical chain conveyors can be designed for use to handle individual cartons as well as full pallet loads. The design can be similar to a dumb waiter style where the unit is a reciprocating lift handling one unit at a time or 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 handled.
Types of supports are listed as follows:
A. Tripod stands.
B. Portable castered supports.
C. Stationary floor supports.
D. Polytier supports.
E. Ceiling hangers.
F. Under trussing.
Tripod Stands are used for temporary installations. It consists of a "T" shape upper top which fits under the cross brace of wheel conveyor or SSR/SAR roller conveyor. The bottom part of the "T" slips into a 3-legged tripod and is held in the height position by a friction grip.
Portable castered supports utilizes the "T" portion of the tripod stand which slips into a vertical pipe with a flat cross piece at the bottom to which are attached casters for portability.
Stationary/Floor supports consists of two pivot plates attached to the underside of the conveyor section, to which are attached formed steel channel legs. Adjustable feet are attached to the bottom of the legs. The feet are provided with holes for fastening the support to the floor. Stationary floor supports may also be fitted with castered supports.
Polytier supports are designed to provide sturdy supports for multi-level conveyor lines, utilizing formed steel channel uprights with 1 1/2 inch diameter pipe cross braces to which the conveyor lines are attached with "U" shaped brackets. Knee braces, which are angled between the upright leg and the underside of the conveyor frame, provide increased longitudinal rigidity.
Ceiling hangers consist of 5/8 inch diameter painted steel rods fastened to the 1 1/2 inch diameter cross pipe mounts on the underside of the bed sections and the upper portion is fastened either to ceiling beams or metal clips which in turn are fastened to ceiling beams.
Types of couplings are as follows:
A. Hook and rod normally used on conveyors at temporary installations. These are only provided on wheel or SSR/SAR roller conveyors. Hook and rod couplings can be used in fixed installations with stationary floor supports.
B. Butt Couplings used in fixed installations and are attached to each corner of the bed section for bolting the sections together.
A. The traffic cop is a mechanical device with spring loaded arms and cams located at the junction of two powered conveyor lines and prevents the flow of carton traffic on one line from interfering with the flow on the adjacent line. In other words, it eliminates collision of cartons arriving at the junction simultaneously. If possible, the two conveyors should be of the live roller type.
B. Case stops of blade and roller type are available as hand operated and foot operated. The air cylinder operated type is available as the roller type only. The blades or rollers are located between the rollers on the live roller or gravity conveyors only. They cannot be used in the middle of a belt conveyor, for obvious reasons.
C. Turning wheels are used at the junction of a branch line to a main line to insure proper carton orientation and to prevent cartons from falling off the conveyor during the course of the transfer.
D. Angle end stop is mounted to the ends of the conveyor side frames to prevent the continued flow of cartons on the conveyor from falling off of the conveyor.
E. Guard rails are available in many shapes and sizes. Their purpose is to prevent cartons from falling off the conveyor and they must be used on all overhead conveyors.
F. Ball transfers consist of a large steel ball riding on a bed of smaller balls all contained within a steel stamping to hold and support the configuration together. We utilize a pattern arrangement of ball transfers on a steel bed in a conveyor line to permit cases to be manually positioned or rotated easily.
G. "Y" Switch of skatewheel design provides a simple method of converging or diverging cartons. Consult the Hytrol General Catalog for a description and photo.
H. Spur curve switch of skatewheel design also provides a simple method of converging or diverging cartons. Again consult the Hytrol General Catalog.
I. Carton push-offs come in various sizes and designs. All push-offs simply push a carton at right angles to the original direction of flow. The overhead push-off is a high speed air cylinder actuated unit which can cycle up to 40 times per minute and can push carton with weights up to a maximum of 150 lbs. The medium duty horizontal push-off can push up to 300 lbs. and the heavy duty over 300 lbs. A horizontal push-off will cycle considerable less than the 40 cycles per minute available with the overhead unit.
J. Pop-up wheel diverter is specifically designed for use in the 190-ACC Accumulating conveyor. It provides for high speed automatic diverting of cartons onto a 30 degree spur. It consists of three rows of 2 1/2 inch diameter powered wheels, the mechanism of which is raised and lowered pneumatically. It can handle cartons of 150 lb. maximum weight up to 40 cycles per minute maximum. A description and photo is in you Hytrol General Catalog.
K. High speed diverter uses a powered diverting belt and can handle maximum weight cartons of 200 lbs. each. It is best used for rapid singulation and diverting. See the Hytrol General Catalog.
L. The powered turn-table is used when two parallel lines must be close together. The minimum turning radius is much less than our standard roller or even powered curves.
M. The manually operated turn-table simply consists of a given length of conveyor on a revolving mechanism, which allows the conveyor to be manually turned and positioned for "inline" flow of products. It is used where curves are unable to fit into the system. Pneumatic and motor indexing turntables are also available.
N. Plows can only be used to divert to a 30 degree spur from a main line. In addition to the manual1y positioned plow, Hytrol has the pneumatic positioned plow as well as the V-belt motorized and pneumatic positioned unit.
O. Manual Vertical Gates for gravity lines are available and the maximum length of gate is determined by the weight of the conveyor to be lifted. Gates are used to provide access through a conveyor line.
P. Spring Balanced Gate allows the use of heavier gates than with manual gates with the use of tension springs adjusted to provide a minimum weight lift.
Q. Horizontal Swing Gates with castered supports can also be supplied. The conveyor in this instance may be powered as well as gravity.
R. Jump transfers are devices set between rollers of gravity or live roller conveyor to transfer the product at right angels from the conveyor. They perform the same function as the push-offs under more controlled circumstances. Hytrol has available the skatewheel transfer, the powered V-belt transfer and the powered chain transfer. In most instances, air bags are used to raise and lower the transfer.
To determine the horsepower required for a belt conveyor, it is first necessary to determine the total belt pull. The belt pull, in turn, is based upon the live load plus the weight of all moving parts, multiplied by the coefficient of friction. The information required is listed as follows:
A. Live Load
The live load is the actual load on the conveyor at a given time. First we multiply the weight of each package times the number of packages per minute; we divide this total by the belt speed in feet per minute. This gives us the live load per foot which when multiplied by the total length of conveyor results in the total live load.
B. Weight of Belt
This includes the actual weight of both the TDP and bottom runs, in other words, the belt on top of the slider bed or carrying rollers and the return strand. See attached belt length formulas
How To Obtain Approximate Belt Lengths For Various Conveyors
NOTE: These formulas are for calculating horsepower only, not for determining replacement lengths of belts. *OAL = Overall Length
C. Weight of Rollers: Include the total weight of all bed rollers and return idlers. When slider bed construction is use, include only the weight of the return idlers.
ROLLER WEIGHTS (IN POUNDS) Roller Length 6" 12" 18" 24" 30" 36" 42" 48" Roller Diameter 13/89 0.7 1.2 1.8 2.6 - - - - 1.9 x 16 Ga. 1 1.8 2.7 3.6 4.5 5.4 6.3 7.2 1.9 x 9 Ga. 2.1 3.8 5.4 7.1 8.8 10.5 12.1 13.8 2 1.6 2.8 4.3 5.7 7.2 8.6 10 11.5 2 1/8 2 3.2 4.9 6.5 8.1 9.7 11.3 12.9 2.5 2.4 4.1 6.1 8.2 10.2 12.2 14.3 16.3 2 5/8 3.5 5.9 8.8 11.8 14.7 17.6 20.6 23.5
D. Coefficient of Friction: Use the coefficient of friction which corresponds to one of the sketches pictured below. The percentages shown are for all types of belting on roller conveyor. Rubber covered belting is not normally recommended for slider bed construction, except for short lengths and light loads.
1. Roller bed with return idlers Coef. of friction
a. Ball bearings 5%
b. Wood burning 10%
2. Roller bed with steel slider return Coef. of friction
a. Roller bed with slider return & F.S. x F.S. belt 30%
b. With PVC belt 25%
3. Steel slider bed with return idlers Coef. of friction
a. With F.S. x F.S. belt 30%
b. With PVC belt 25%
4. Steel slider bed with steel slider return Coef. of friction
a. With F.S. x F.S. belt 35%
b. With PVC belt 30%
E. Weights of All Pulleys: Include total weight of all drive and idler pulleys, snub rollers, end and take-up pulleys.
PULLEY WEIGHTS (IN POUNDS) Pulley Diameter 6" 12" 24" 30" 36" 42" 48" 4" 6 12 24 30 36 42 48 6" 9 16 33 42 50 58 67 8" 13 27 54 68 81 95 108 12" - - 108 135 162 189 216F. Inclines or Declines: When all or any part of a conveyor is inclined or declined, an added belt pull is applied. This additional belt pull is obtained by multiplying the total live load on the inclined (or declined) portion by the sine of the angle.
SINE OF ANGLES Angle Sine Angle Sine Angle Sine Angle Sine 2° 0.03 12° 0.21 22° 0.37 32° 0.53 4° 0.07 14° 0.24 24° 0.41 34° 0.56 6° 0.1 16° 0.28 26° 0.44 36° 0.59 8° 0.12 18° 0.31 28° 0.47 38° 0.62Belt pull for inclined portion = Live Load on incline times sine of angle or incline.
G. Two and Three Pulley Device: Add 5% of the Live Load preceding the device.
H. Deflectors: To accurately determine the total belt pull, add 30% of the weight of the heaviest package being diverted. We normally do not recommend diverting from belt conveyors except for light weight packages.
Belt pull equals weight of heaviest package times coefficient of friction for specific belting being used. Use only a smooth top belting.
I. Mechanical Traffic Cop: Add 30% of the weight of the maximum number of packages which will be held back by the traffic cop arm. The maximum weight of the total number of packages should never exceed 250 lbs.
J. Formula:
Horsepower = Effective belt pull x conveyor speed (feet per minute)
33,000 x .85 x .95
1. One horsepower is defined as the power required to move 33,000 lbs. A distance of one
foot in one minute.
2. .85 allows for 85% for worm gear efficiency. Hytrol gear boxes use worm gears.
3. .95 allows for the roller chain drive efficiency.
Example (Level RB Belt Conveyor)
1. Package weight = 45 lbs.
2. No. of packages per minute = 20
3. Belt speed = 65 FPM
4. Bed rollers = 12" CTRS. (Ball bearings)
5. Return idlers = 10' - 0" CTRS.
6. Belt width = 12" PVC 120
7. Conveyor width = 15" BR
8. Conveyor length = 100'= 0"
9. Drive 8" pulley = Center drive and take-up
Live load per foot = 45 x 20 = 14 lbs. Per foot
65
Live load = 100 ft. x 14 lbs. Per foot = lbs.
Bed rollers = 100 x 1.5 lbs = 150 lbs
Return idlers = 10 x 1.5 lbs. = 15 lbs.
Belting = 206 ft x .060 x 12 = 150 lbs.
Center drive and end pulleys = 77 lbs.
TOTAL WEIGHT TO MOVE lbs
Coef. of Friction 5% x .05
EFFECTIVE BELT PULL 90 lbs.
HP = 90 lbs. X 65 FPM = .20
33,000 x .85 x .95
Summary: Use the minimum horsepower offered by Hytrol: 1/3 hp (1/3 more than required).
LIVE ROLLER - HORSEPOWER CALCULATIONS
The same method for belt conveyors can be used for belt driven live roller conveyors. If the live roller is to accumulate a blocked load, simply calculate as though it were a moving load then double the horsepower.
Horsepower for single strand chain driven live roller as well as roller-to-roller chain driven live roller is calculated as follows:
A. Determine the live load in the same manner as for belt conveyor.
B. Add the weight of the rollers (See chart under belt conveyor).
C. Add the weight of sprockets and roller chain.
D. Determine chain pull in the same manner as for belt pull under belt conveyor.
Chain Number Allowable Chain Pull Conveyor Speed F.P.M to 65 65 to 80 80 to 100 100 to 150 RC 50 875# 800# 750# 650# RC 60 # # # 850# RC 80 # # # #SERVICE FACTORS
Operation up to 24 hours
Continuous single strand: 1.0
Roller to roller: 1.2
Sudden stopping or reversing: 1.4
Dirty conditions: 1.4
COEFFICIENT OF FRICTION
Single strand 6%
Roller to roller 5%
The formula to use is:
HP = Effective chain pull x speed in FPM
33,000 x .85 x .95
Multiply the effective chain pull service factor to determine if it is higher or lower than the allowable chain pull.
Horsepower calculations for chain conveyors are more complex in that shaft torque and bending moments farther the picture. Suggest checking with your Master Hytrol Distributor on applications which require chain conveyor.
Below is a formula for determining sprocket ratio, motor RPM, or belt speed:
No. of teeth (motor spkt.) x Pulley Dia. (inches) x TT x Reducer shaft RPM = Belt speed (ft. per min)
No. of teeth (pulley spkt.) 12
Substitute known values and solve for unknown.
EXAMPLE:
Wanted number of teeth on motor sprocket:
Known values:
1. Drive pulley dia. = 8 inches.
2. Reducer output shaft = 48 RPM
3. Belt speed = 65 FPM
4. Number of teeth (pulley sprocket) = 32
Then: 65 x 32 x 12 = 21 teeth 8 P x 48
MORE MISCELLANEOUS USEFUL FORMULAS
RPM (pulley) = FPM (belt) x 12
Pulley dia. (in inches) x P
RPM (roller) = FPM belt x 12
Roller dia. (in inches) x P
RPM (pulley) = Motor sprocket (no. of teeth)
RPM (motor) Pulley sprocket (no. of teeth)
FPM = RPM (motor) x no. teeth (motor spkt.) x pulley (or roller) dia. x P
No. of teeth (pulley sprocket x 12)
HP = Torque (lb. -ft.) x RPM = Torque (lb - inch) x RPM 63,025
Torque = Effective belt pull x 1/2 dia. of drive pulley.
1. Type of Products to be conveyed:
A. Carton (corrugated) (glued, stapled or taped bottom).
B. Bag (multiwall paper, cotton or plastic).
C. Bundle or bale (tight, steel or plastic bonds).
D. Wood case (cleats on bottom).
E. Plastic tray (smooth or grip bottom).
2. Size of Products:
Length: Max/Min
Width: Max/Min
Height: Max/Min
Weight: Max/Min
3. How is product to be conveyed?
A. Lengthwise.
B. Widthwise.
4. How will product be placed on conveyor?
A. Manually.
B. Transferred from anther conveyor.
5. Method of Transport?
A. Gravity.
B. Power.
C. Combination of gravity and power.
6. How many hours per day will conveyor be used?
A. 8 hours (one shift).
B. 16 hours (two shifts).
C. 24 hours (three shifts).
7. Available electrical current?
A. Volt Phase Hertz
8. Maximum (not average) production rate?
9. Will conveyors be floor supported or hang from overhead?
10. Will conveyors be subjected to unusual conditions?
A. Wash down.
B. Extreme heat.
C. Extreme cold.
11. Will the customer require engineering services?
The conveyor industry actually started about 80 years ago [] in the Minneapolis-St. Paul area by a group of men unloading wood shingles from rail cars. The idea worked so well that part of the group decided to relocate to a steel tube mill location and selected Ellwood City Pennsylvania, the home of National Tube. This relocated group called itself Mathews Gravity Conveyer Company with Rufus P. Mathews as president.
The group that remained in the Minneapolis-St. Paul area also started a conveyor company named Standard Conveyor Company.
A Mr. Offutt was superintendent of National Tube in Ellwood City, Pennsylvania. At times, Mathews got into financial difficulty, and Mr. Offutt bailed them out and received stock in the company. He also secured employment for his son John in the Mathews engineering department. Also, Mr. Offutt's daughter was married to the Ellwood city bank president. Upon Mr. Offutt's death, John, his son, inherited all of the Mathews stock his father owned.
After Rufus P. Mathews, F.E. Moore became president. Then came Bill Dean, then Odd McLeary.
F.E. Moore set up Mailer-Searles in San Francisco as the west coast manufacturer of Mathews Conveyors and built a new plant in Port Hope, Ontario, Canada. Mailer-Searles sold the area west of the Mississippi River and maintained offices in Salt Lake City, Los Angeles, San Francisco, Portland Oregon, and Seattle.
Mathews Chief Engineer, Norton Meyer, and Chief Draftsman, John Offutt took Harry Harlick under their wings and taught him all about the application of conveyors to industry. In addition to Mathews, Mailer-Searles also acquired the Standard-Knapp line of packaging machines.
Bill Dean was jealous of Bill Jaenicke, president of Mailer-Searles because Jaenicke was offered the presidency of Mathews before Bill Dean, but, Jaenicke refused, saying he had been born and raised in San Francisco and did not care to relocate to Ellwood City.
Bill Dean decided to build a Mathews Plant in San Carlos and take the Mathews line back. He also appointed P.W. (Joie) Brown as President of Mathews-West Coast. The new plant had only 2 acres and quickly outgrew the San Carlos facility. They purchased 80 acres in Chico and built a new plant. P.W. Brown ultimately died of a heart attack and Bill Peppard was appointed Vice-President and General Manager.
When Mathews took the line from Mailer-Searles, Bill Jaenicke obtained the Alvey Conveyer line from Jack Alvey of St. Louis.
The Alvey Conveyor Company had started in the north barn of Anhuser-Busch in St. Louis, furnishing all the conveyor for the brewery. When Alvey solicited more work from other St. Louis breweries, he was politely told to move.
Alvey eventually passed away and Jack Alvey and Bob Mayer bought the company from his uncle's widow. Both Jack and Bob were standard Conveyor sales people in New York and specialized in brewery conveyors.
Meanwhile, Hartford-Empire, manufacturers of automatic blowmold glass making equipment bought Standard-Knapp. It was suggested that Mailer-Searles also sell to Hartford-Empire, later known as Emhart.
Bill Jaenicke later was told that Emhart was going to dissolve Mailer-Searles. Emhart formed a separate Standard-Knapp office in San Mateo and Harry Harlick was retained to finish up all outstanding Alvey business, after which he went to work for FMC corporation in Riverside, CA.
Now, Odd McLeary was President of Mathews and arranged a sale of Mathews to Rex-Chainbelt of Milwaukee Wisconsin. Rex also bought Nordberg a rock crushing equipment manufacturer and changed their name to Rexnord. The cost of Mathews to Rex was $9M with $25k per year retirement to Odd for a period of 5 years. Mathews had $9M in the bank, so the actual cost to Rex as zero.>
FMC set aside $10M for the Riverside Division to get into the conveyor business. Since they were furnishing practically all conveyor to the citrus industry, they had a good start. The Riverside Division could purchase a conveyor company or start one from scratch. The Riverside Division also manufactured about 7 different product lines; the bulk feed trucks which deliver cattle and chicken feed, egg machines which automatically grade and package eggs for producers, along with juicers and other equipment for citrus growers.
Also FMC purchased some Palletizer patents from an inventor in Los Angeles. The rest of the patents were purchased by Lamson Corporation, of Syracuse, New York. This caused a legal battle between FMC and Lamson which nearly bankrupted Lamson. Both companies manufactured Palletizers.
FMC head office in San Jose discovered the Riverside Division was diverting conveyor funds to other product lines and fired all product managers and demoted the division manager Mr. Sid Boucher, the conveyor sales manager Don Derricott was allowed to retire.
About the time Tom Loberg (Hytrol) designed the bale conveyor, Bill Jaenicke also designed a variable speed bale conveyor to elevate bales of hay to truck beds. E.W. Buschman (Buschman) was a Rapistan salesman in Cincinnati when he decided to go into business for himself.
There was a wheel conveyor manufacturer in, I believe, Buffalo, New York, who hired local housewives to assemble wheel conveyors at hours they chose and paid minimum wages. Their profits were rock-bottom. Mathews also used women to assemble wheel conveyors. They did a very good job in Chico.
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