Questions to ask when considering Powered Conveyors
WHAT is being handled.
– Sizes, weights and rates?
– How is the item loaded and unloaded on conveyor?
– What is the physical characteristics of conveying surface?
– Is it a lever “push system” or a gravity free-flowing system?
-Is the load evenly distributed in the container or pallet?
Where is it being handled (environmental conditions)?
Why do they want a conveyor?
– Who identified the problem, you or the customer?
Portable Belt Conveyors:
Portable Belt conveyors are pre-engineered power driven units. They are specially designed to move cartons, cases, boxes, bags etc… up an incline. They can be used with or without supports. The following is a list of a few applications.
– Loading and unloading trucks and railroad cars.
– As a booster in a gravity line
– On a stairway (not too long or too steep)
– Horizontally (when short and portable units are needed)
-Floor to floor conveyor, when vertical lift required is not too great.
When selecting a PORTABLE CONVEYOR consider the following:
1. To keep material when conveyor is inclined, RUBBER ROUGH TOP BELT is used.
2. The maximum recommended ANGLES of incline for portable belt conveyors with rubber rough top belt and without cleats is 30 degrees or lesss. With cleats, unit can be inclined up to 45 degrees. Keep in mind the CENTER OF GRAVITY of the material being covneyor, base on height and length (i..e: if carton is higher than it is long, it will topple back)
3. Portable conveyors can also be used horizontally if lengths suffice. In this case a smooth type belt can be ordered.
4. Material can moved can be wider than belt if it has a solid, rigid conveyable surface. For example, an 18 inch wide carton can easily be moved on a 12 inch wide belt (minimum belt width= 2/3 product width.)
5. Undercarriage supports are available for standard units. These supports are ADJUSTABLE and PORTABLE and should be utilized when quick adjustment and easier portability are desired.
The belt conveyors that will be considered are:
– Horizontal Belt Conveyors
– Incline/Decline Belt Conveyor
– Brake Belt
– Meter Belt
– Brake/Meter Belt
Note: The minimum overall conveyor length is equal to the belt width x 3
Horizontal Belt Conveyors:
Horizontal Belt conveyors are pre-engineered units and are usually designed for stationary use. However, with certain conditions, they are also used as portable units when equipped with portable supports.
When selecting a Horizontal Conveyor consider the following:
1. Horizontal Belt conveyor design is such that they can be quickly installed, economically operated and easily maintained. They lend themselves to many types of operation such as:
– Assembly Lines
– Order Packaging
– Transferring parts from one operation to the next.
2. Because the conveyor is horizontal, a less expensive smooth type belting is used. In most cases, Black PVC belt is ideal. Other belt types are available. Other belt types for applications such as food handling, higher temperatures, lower coefficient of friction are also available.
3. Material can be wider than belt when packaged items with flat solid bottoms are conveyed. However, loose parts, odd shaped sub-assemblies, etc. should be handled in trays or tote pans if they are wider than the belt.
4. Horizontal belt conveyors can be reversing. However a center drive take-up must be used
5. Permanent and adjustable supports are most frequently used for horizontal units. Hanger brackets are available for overhead support mounting.
Incline & Delcine Belt Conveyors:
Model “I” conveyors are also made up of pre-engineered standard sections, but are designed for permanent installation only.
When selecting an incline or decline conveyor consider the following:
1. Incline conveyors are normally equipped with a noseover at the top end. This enables the product to level off to a horizontal position before even being discharged. A noseover is particularly desirable if the product is fragile because the noseover eliminates the tendency for the front end of the package to drop when it reaches the top. It is suggested that any angle of 10 degrees or greater have a noseover. A noseover is a MUST for angles over 15 degrees.
2. Incline conveyors are used to move product from one level to another.
3. Rough top belt is used on the incline length of the conveyor.
4. Material wider than the belt can be conveyed satisfactorily if it has a flat, solid bottom. The general rule of thumb for inclines is the width of the material should not exceed the overall width of the conveyor.
5. An incline conveyor normally requires center drive and take-up. A center drive and take up is a must when reversing the unit or a power feeder is used.
6. Permanent and adjustable supports are most frequently used for incline and decline units. Hanger brackets are available for overhead support mounting. For floor-to-floor units, permanent supports are nomrally used at the top and bottom of the conveyor.
Power Feeder Belts:
Power feeder belts are used to provide a positive and smooth transition from horizontal to incline or from decline to horizontal.
1. When using a POWER FEEDER, set the feeder pulley height in relation to the incline pulley to allow a smooth transition of th eload.
– On an incline conveyor the feeder pulley should be slightly higher than the incline pulley.
– On a decline conveyor the feeder pulley should be slightly lower than the incline pulley.
2. There are other methods of making the transition. While being less expensive they are limited. Power feeder belts will usually solve the problem when other devices will not…
– They are positive because of the simultaneous “push-pull” action of both the power feeder and the incline belts.
– They result in a smooth transition because the load is under powered conveyor control at all times.
– They are adaptable to reversing applications whereas a gravity feeder is not.
3. It is sometimes desirable to separate the product at the transition point between a horizontal power feeder and the incline bed by a belt speed change. This will prevent the top of the product from being subject to a crushing point.
Gravity Tail Feeder to Incline Belt Conveyor
Under controlled conditions, gravity conveyors can discharge directly onto an inclined belt conveyor. There are some variables to consider.
1. The feeding gravity conveyor must discharge higher than the belt so that the package will contact the belt regardless of the position of the take-up pulley.
2. The forces that advance that load onto the belt is a combination of the friction between the belt at the leading edge of the package plus the gravity section of the feeding gravity conveyor.
3. If the angle of incline of the belt is too steep then the package will advance into a “bridging” position. The trailing edge of the package will tend to hold back the package rather than advance it onto the belt.
4. The following parameters must be considered before a satisfactory result can be expected.
– The angle of incline belt conveyor must be minimized. A general rule is to not exceed 12 degrees.
– The package must be reasonably stable.
– The variation in length between the longest and shortest package must be minimal.
– Loads must be able to withstand the “drop off” action without damage.
Gravity Discharge from Decline Belt Conveyor:
Under controlled conditions, powered belt conveyors can discharge directly onto gravity conveyor. There are some variables to consider that will have a direct bearing on the degree of success that will be obtained.
1. The packages have tendency to “nose” or “dig” into the space between the rollers or wheels. The package may hang up and be damaged at the point of transfer.
2. These factors must be considered.
– The angle of decline of the belt conveyor.
– The length and condition of the package.
– The position of the take-up pulley.
Take caution when applying gravity feeders and gravity discharge sections to or from powered conveyors. Many safety issues need to be considered including pinch points.
Motor brakes are an important control device. They are used to minimize “coasting” and or to hold a belt stationary against the force of gravity or push of the accumulated conveyor.
Without a brake, the momentum of the moving loads and the conveyor components (pulleys, belts, etc.) will cause the belt to drift after the power has been turned off. The amount of drift can vary from a few inches to a few feet as a result of one or more of the following:
– The moving weight.
– The conveyor speed.
– Friction factor of conveyor components (roller bed vs. slider bed)
– The angle of incline or decline.
– Friction factor of drive mechanism.
A brake motor may be desirable particularly on a decline conveyor or roller bed if you do not want the product to drift on the decline portion. Incline conveyors will drift less than decline conveyors.
Maximum Incline and Decline Angles:
Another consideration when choosing an incline or decline conveyor will be: Is the angle of incline shallow enough to prevent the load from tumbling back or sliding down the incline bed?
1. The maximum angle of incline or decline is a function of two facts:
– The type of belt being used.
-The condition of the load.
2. A general rule is to stay within 25 degrees. However solidly packed. Uniformly loaded packages may negotiate a particular angle, but non-uniformly loaded packages such as TV sets, or furniture may not.
3. We know that a load is most stable under “static conditions”. However a belt conveyor does not provide a static condition. The load must start and stop quickly and be able to absorb the forces of momentum and acceleration without rocking beyond its stability point and start tumbling.
– A short load is more vulnerable to tumbling than a long load.
– Acceleration and deceleration of higher speed belt conveyors will add to the problem more severely than do slow moving conveyors.
– The use of magnetic brakes for stopping the conveyor will accentuate the problem.
– The bottom of most cartons are not flat but, slightly bulged. This creates some rocking even on level conveyors.
– The spacing of carrier rollers on roller bed section will effect the amount of “bobbing” or “sway” in transit. The closer the roller centers the smoother the travel. Slider bed conveyors provide the smoothest travel.
– Plastic totes may become slippery with age and use should be tested.
The following are a few of the accepted methods of determining whether a load will negotiate a given angle of incline or decline without tumbling.
1. One method is the 1/3 Rule
– Under normal con, a load is considered stable if a vertical line from the center of gravity falls within the middle 1/3 of the base.
2. To determine if a load is stable:
– Draw a scaled diagram of the product at the angle of incline/decline.
– Draw diagonal lines from corner to corner of the load. They will intersect at the “theoretical” center of gravity.
– Divide the base of the load into 3 equal parts.
– Draw a vertical line from the center of gravity. The vertical line should fall within the middle 1/3 of the base.
A specer belt conveyor is nothing more than a horizontal slider bed belt conveyor and is used to produce a required space or “gap” between beeing fed to downstream devices such as transfers, belt sorters etc…
When applying a spacer belt conveyor consider the following:
1. A slider bed section should be used.
2. A belt with a high coefficient of friction such as rough top belting should be used.
3. The length of the space belt is 3 x the belt width, minimum.
4. The speed of the spacer belt portion is determined by the following formula.
Spacer Belt Speed (fpm) -= (CL+ S) x CMP
Where: CL= Carton Length (Ft.)
S= Gap space between each carton in feet.
CPM = Cartons Per Minute (in feet)
For example: a 2′ long product is being produced at a rate of 20 cartons per minute and requires a 1′ gap. The meter belt speed would be (2′ + 1′) x 20 (CPM) = 60 (fpm)
– A 15% safety factor should be add 60 (fpm) x 1.15 = 69 (fpm)
Brake belt conveyors are used to stop, brake or hold back product at the end of a powered or gravity accumulation line.
When applying a brake belt conveyor, consider the following:
1. A slider bed section should be used.
2. A belt with a high coefficient of friction, such as rough top belting should be used.
3. A motor with a brake should be used.
4 The length of the brake belt is determined by dividing the total length of the accumulated load by 6.
– For example: If you have a total lenght of accumulated loads of 60′, the length of the brake belt would be: 60/6 = 1′