The system design must start with a device for supporting the product from the conveyor. Usually, the end user will specify the position in which he would like the product suspended. Also, the processing equipment through which the conveyor passes will tend to influence the type of product hook required.

In figure #6, a paint finish system is shown. The presence of the spray washer demands that the part be suspended in a way that will permit direct sprays of fluids to reach the part while at the same time providing drainage. It will also be noted that the rather simple product hook is attached to a #2035-17 swivel fixture which allows the part to be automatically rotated through the two Ransburg paint booths. In addition, the part is purposely positioned well below the conveyor track to minimize the amount of paint and washer over spray reaching the track.

In Figure #5, the product being carried is a tote pan. A simple ski type carrier is adequate in that it permits easy loading and unloading.

The carrier layout is also used to fix the conveyor height at the load and unload points. To reduce operator fatigue in handling, the center of the product should be about 3'6" from the floor. Referring to Figure #5, it will be noted that the top of the track is 6'6" from the floor. This allows clearance below for the operators, as specified by plant safety rules.

The carrier assembly drawing also provides valuable dimensional information for the washer, spray booth and oven manufacturers as well as determining track elevations at conveyor crossovers and interference points such as pipes, ducts, etc.

In most Zig-Zag conveyor installations there are usually a great number of product carriers, and since this item affects so many of the operating functions, it is advisable to provide a sample to the user for testing and approval prior to fabricating the entire lot.

LOAD CLEARANCE

Next in importance is the determination of load spacing on the conveyor. In most instances the user prefers minimum load centers for full utilization of all equipment. This is especially true in paint finishing systems where close product spacing is mandatory to minimize the size of the paint bake oven.

In Figure #5 a plan view, to scale, of a 180° horizontal 2'-0" R. track curve is shown with loads placed on 24" centers. It will be seen that at the closest point there is a clearance of approximately 4". If the loads were placed 6", or one pendant spacing, closer together or 18" apart, there would be a load interference of about 2".

Also in Figure #5 a side elevation of a track incline is shown. This is also drawn to scale, and it will be seen that the 24" load centers do allow sufficient clearance.

SYSTEM LAYOUT

Resolution of the product carrier design and load spacing clears the way for the system layout, providing all information is at hand as indicated in Step #1.

Using field dimensions or the customer's numbering and lettering of the columns since this fixes the location of the conveyor system with respect to the building. However, it is necessary to show only that portion of the building in which the conveyor is to be located.

Next in order, washers, spray booths, ovens and other equipment to be tied together by the conveyor are drawn in to scale and should be shown in phantom lines. Phantom lines merely indicate that equipment shown thus is not included in the conveyor sales engineers proposal.

The conveyor may now be sketches in heavy lines, starting at the load point. (See figure #6) and continuing on through the washer, dry off oven, spray booths, oven cool down area and on to the unload area.

INCLINES AND DECLINES

Next, the inclines and declines are shown to indicate elevation changes. It will be noted that track rises or dips, in plan view are shown as a heavy line at either side of the track line with the track elevations noted at top and bottom. In Figure #1, it will be seen that for a rise of 6'0" @ 45°, the length between curve and tangents (x to x) is 7'8". This dimension may be determined by calculation, a scale layout such at Figure #1, or it may be found in the Zig-Zag catalog chart. In any case, all elevation changes must be located on the drawing to scale.

CONVEYOR GUARDS

Conveyor guards are next for consideration. Most plant safety rules specify that the guards must be placed under the conveyor in all locations where the bottom of the guard is to be 7'-0" or more from the floor. The height of the bottom of the guard is equal to the distance from the top of the conveyor track to the bottom of the carrier or product plus the height of the product, plus 3". for further clarification, refer to Figure #6 in which the bottom of the part to the top of the track is 5'-0". If the part should fall from the conveyor it would lie horizontally and would occupy 5" of height. to be sure that the parts on the conveyor pass over the part without interference, a clearance of 3" is allowed. Therefore, from the top of the track to the bottom of the guard is equal to the sum of 5'-0" + 3" (clearance) + 5" (product) or 5'-8". Consequently, any point in the system where the track is 12'-8" (5'-8" + 7'-0" clearance) from the floor, guarding is required.

The carrier or product also requires a clearance at either side of 6" minimum. Since standard guard is available in widths of 2'-0" to 10'-0" and 8'-0" lengths with side heights of 1'-0" to 4'-0", the proper guard r the conveyor shown in Figure #6 would be 2'-0" wide and 2'-0" high sides. The 2'-0" high side would prevent a falling part from toppling over the guard sides.

CHAIN PULL CALCULATION

There are few, if any, short cuts in the process of determining the chain pull on an endless chain conveyor. Many factors, which vary greatly from system to system, influence the end result. Product carrier weight, product weight, coefficient of friction, track curves, inclines, declines, temperature and lubrication are some of the principle items affecting chain pull. However, by knowing the value of the various factors, the total chain pull may be determined by the point to point accumulation method of calculation.

ZIG-ZAG FRICTION FACTORS

The above friction factors were obtained from accurate laboratory tests with lubricated chain and have been verified by dynamometer tests of complete systems.

It will be seen that straight conveyor has friction factor of 1 1/2%. Therefore, if a conveyor did not have any vertical or horizontal curves, inclines or declines, the weight of the total live or moving load could be multiplied by 1 1/2% to determine the weight in pounds to move the conveyor. For instance, a 100'-0" conveyor with a 1 1/2# hooks and 6# loads on 1'-0" centers would be 10# per foot (including chain @ 2.5# per foot) x 100'0" or 1000# @ 1 1/2% = 15# chain pull. However, an endless conveyor chain must at least have horizontal curves, and each of these generate additional forces which must be taken into account as will be seen in Figure #2.

In Figure #2 a simple system about 116'-0" long is shown with four horizontal curves. The first item to be determined is the pounds in chain pull per foot of straight conveyor. the following formula provides a result of .45 pounds per foot.

In the following computation, it will be seen that the footage from the down stream end of the drive to the far tangent of the next curve (0 to 1) is multiplied by .45# and the 2% friction for the 90° curve is added. Next the footage from (1) to (2) is multiplied by .45#, added to the 2.75# resultant plus 2% for the 90° curve. The procedure of accumulating at each curve is followed back to "0" at starting point.

It will be noted that the spring take-up is just downstream from the drive. This arrangement ensures that the slack chain will not accumulate at point "0" to jam the drive. Introduction of inclines and declines in a system further complicates chain pull calculation by adding to the forces. In Figure #3, a conveyor is shown identical to Figure #2 except for the addition of an incline and decline.

Due to the elevations changes, the formula for finding the pounds per foot chain pull is arranged differently because it must be assumed that at some point the incline will be loaded and the decline empty. In systems having multiple rises and falls, this may be treated somewhat differently, depending on loading patterns.

Where the loads are spaced no more than 2'0" on centers, the formula of the total pounds per foot multiplied by the rise in feet can be used to determine the additional force in pounds for the inclined section. This can be seen in the chain pull calculation for the conveyor in Figure #3 from point #5 to #6. It is expressed as ' + (6.0' x 30#)' or 180# as the additional force induced by the rise.

In situations where the loads are more than 2'0" on centers, a more accurate result can be achieved by multiplying the total live load on the inclined portion by the sine of the angle of incline, as shown in Figure #4.

Trig tables will provide the sine of any angle, but the following angles of slope are most used.

Computation (Figure 4)

It will be seen that a maximum of four loads can be on incline from "X" to "X" at any one time.

If the other method of calculation is used the average load per foot would be 33.75# x 10 Ft. of lift or 337.5# chain pull. In both cases rolling friction of 1 1/2% has been omitted for simplification.

Figures #2, #3 and #4 provide several essential points:

#1
It was stated previously that in multi-plane conveyors it is well to allow for the extreme condition of a fully loaded incline with only the chain, pendants and product hooks on the decline. In many operations this situation occurs infrequently, but it must always be taken into consideration to eliminate any possibility of an overload drive which does result in drive, curve and chain damage.

As evident, inclined conveyor sections usually account for the major portion of the overall force required to move the chain and loads. Therefore, it is important that these forces always be included in the total chain pull.

In systems having two or more inclines and declines, all inclines must be calculated on a fully loaded basis. The first decline should be figured less product load only, the second decline with 50% product load and additional declines as fully loaded.

This procedure is predicted on the theory that not all inclines can be loaded while all declines are empty.

#2
In Figure #3, the drive unit is located a considerable distance from the decline at point #3. However, at point #3 the chain pull shows a minus 7.02#, which means that gravitational forces resulting from the decline will create some chain tension at point #3 to ensure the absence of slack chain in front of the drive.

Attention is called to the location of the drive unit which is at the highest level and quite some distance upstream from the decline at point #3. Actually, it could be located much farther away since a force of 71# is generated at point #3, as a result of gravity on the slope. the 71# force is wasted because the chain cannot be pushed, and can only be pulled. If the chain did not telescope when pushed, the 71# of force could be utilized to help move the loaded chain up the incline between #4 and #5, which would then reduce the resultant of 333.32# at point #5. As it is, and due to the telescoping effect, the chain will need to pile up at point #3 if there is any looseness. For this reason, "0" lb. chain pull is shown at point #3.

As evident, the chain will always tend to gravitate to the lowest point in the system, and it is for this reason that the take-up unit it positioned at the lowest level. Also, when installed at the minimum height from the floor, adjustment of the take-up for removal of chain slack is facilitated.

MULTI-DRIVE SYSTEMS

In a system having a total chain pull in excess of 600#, it is necessary to use two or more drive units. The method of calculating chain pull is the same as previously described, except that all drives must pull about the same amount, or at least within 10%. It is sometimes difficult to achieve the necessary drive balance. In such cases, the Engineering Department of McGinty Conveyors, Inc. Indianapolis, Indiana should be consulted.

Chain Pull Calculation - Figure #6 Conveyor (#CH-1974-600# Chain)

A computer program has been developed for chain pull calculations. Consult factory for availability of a format for your computer.

ELECTRICAL FIELD WIRING

Field wiring for a Zig-Zag conveyor is a relatively minor cost since it usually involves only the drive motor, motor starter, two or more stop buttons and the Electro Brush Oiler or Electro Mist Spray Oiler. Normally, two electricians can complete this wiring in eight to twelve hours or sixteen to twenty-four hours total. To the labor prices the cost for conduit, wire, motor starter and push buttons must be added. However, most users prefer to supply the electrical controls, wire and conduit in addition to using their maintenance people to do the wiring.

Should the customer request a "Turn Key" job, a local electrical contractor will provide a price.

FIELD AIR PIPING

If the conveyor has a #LU-884A spray mist oiler, it is necessary to connect it to an 80# air supply line. An estimate of the labor hours and material can only be made after the site conditions are known. The latter has to do with the distance of the air supply line from the oiler. In any case, the user will furnish the material and labor for this item since the cost will be considerably less than an outside contractor would charge.

SHORT CUT METHOD OF CHAIN PULL CALCULATION

Using a 2 1/2% friction factor for the short cut method will cover most normal conditions. A large number of vertical and horizontal curves will create slightly higher friction.

Caution:

If calculated chain pull using this short method is in excess of 550 pounds per drive, you must use the long point-to-point accumulation method of calculation illustrated in the McGinty conveyors, Inc. Engineering Manual.

STEP #1 Determine number of carriers.

The required number of carriers is equal to the total conveyor length divided by the carrier spacing.

STEP #2 Determine number of loaded and unloaded carriers.

Establish distance from loading to unloading. Divide this distance by carrier spacing to determine number of loaded carriers.

STEP #3 Determine live load.

The live load on a conveyor is equal to the sum of weights of the chain, pendants, product hook or carrier, and the product.

A. Multiply weight of the chain (2.5#) by the number of feet of chain.
B. Multiply weight of pendants by required number of total pendants in system.
C. Multiply weight of empty product hooks or carriers by total number of carriers in system.
D. Multiply weight of product only by number of loaded carriers only as determined in Step #2.
E. Total of a, b, c, d = total live load on the conveyor system.

STEP #4 Determine lift load.

The lift load is the amount of force required to pull the live load upward along the vertical curves in the entire system.

To calculate this force, determine the difference in elevation of all the vertical curves traveling upward in the system. The net vertical rise (in feet) will be considered the total lifting height of the conveyor.

The lift load for the elevation changes of the conveyor is equal to the total lift height (in feet) multiplied by the individual product weight (in pounds), then divided by the load spacing centers in feet.

STEP #5 Determine the chain pull.

To determine the chain pull due to friction, multiply total moving load by selected friction factor.

A. Total live load for Step #3
B. Multiply (a) by fraction factor of .025.
C. Add lift load obtained in Step #4 to (b) above to obtain total chain pull.