Belt Conveyors

Conveyors and Elevators
I am using Belt Conveyors and Belt Elevators By Frederic Valerius Hetzel published 1922 for reference. There is a great amount of information in the book for all kinds of conveyors but I will be focusing on what information I need for a specific use – moving coal from the Unwashed Coal Bin to the breaker.
Description
The elements of a belt conveyor are, therefore:

  1. A belt to carry the material and transmit the pull.
  2. Means to support the belt, usually rollers or pulleys.
  3. Means to drive the belt, usually a pulley or a pair of pulleys.
  4. (a) Accessories for maintaining belt tension, such as take-ups.
    (b) Accessories for loading the belt, such as a chute.
    (c) Accessories for discharging the material, such as a chute or a tripper.
    (d) Accessories for cleaning and protecting the belt, such as housings, decks, covers, cleaning brushes, etc.

The belt is a flexible jointless structure which runs quietly at any speed; it is not ordinarily harmed by the actual conveying of the material it carries. Since the material does not come into contact with the moving surfaces of pulleys and shafts in which there are friction losses, these losses are relatively small and the power required for the transfer of material is generally less than in other forms of conveyors. The belt with its rollers weighs less per foot of run than other types of conveyors doing the same or similar work, and hence frames, bridges and other supporting structures are relatively lighter and cheaper.

The text goes into some detail on the various materials used for belts – help was used to some extent in Europe but in the US cotton fiber was preferred. These are sub-divided into several forms – Rubber, Stitched canvas, Balata (hard rubber like material made by drying the milky juice produced by the bully tree) and Solid-woven belts. For modeling purposes it doesn’t really matter other than figuring out how to create them in 1:48.

Supports for the Belt
Figs.1-9(various rollers discussed in the text) – (…) For heavier work, the roller may consist of several cast iron pulleys mounted on a through shaft (Fig. 3), or the outer pulleys of the combination may be enlarged at their outside ends (flared idlers) in order to lift the edges of the belt slightly and prevent spilling (Fig. 4). When it is desired to increase the carrying capacity of a belt it may be bent into trough form by turning up the edges of the belt by troughing or ” concentrator” pulleys (Fig. 5), or by supporting the whole width of the belt on idlers in which two, three, four or five pulleys are set at various angles from the horizontal to trough the cross section of the belt (Figs. 6, 7, 8, 9).
Troughing or “concentrator” pulleys
Image1In the text above it mentions that – When it is desired to increase the carrying capacity of a belt it may be bent into trough form by turning up the edges of the belt by troughing or ” concentrator” pulleys (Fig. 5). With that in mind I found an example on page 11 of an 1893 installation at an ore concentrating plant of the New Jersey and Pennsylvania Concentrating Co. at Edison, N.J. The inclusion of both a side and frontal view were helpful in re-creating a version of the pulley in Sketchup. Heck .. a directional arrow even lets me know the direction of belt movement –
troughing_pulleyI think that whoever did the drafting of the troughing pulley must have been drinking at the time as the end and frontal views were not at the same scale. I made use of them though and came up with this in Sketchup.
troughing_pulley_wideFinally, I made the center roller wider to fit it to use in moving coal from the bin. This is as detailed as I wish for the moment .. a general design I can work around later. It would be nice if I could figure out how to make the darn thing from bits and pieces from the beading section at Walmart .. but I doubt that will happen!
On pages 9-10 it talks about the problems with the inclined concentrator pulleys. The earlier concentrator pulleys were inclined at 60°, but this lead to longitudinal cracking of belts. This angle was reduced to 45°, and then to 35°, which was most common when the book was written (1922). Concentrators with angles of 30° and 22° were also used to reduce the flexure of the belt edges. My design above uses a 42° concentrator angle. I may re-design mine to match that 35° – I’ll have to see if there is much difference visually .. after all it IS a model.

It is also mentioned that “it is customary” to use inclined concentrator pulleys at the loading point only, or at intervals along the length of the conveyor. They were specifically talking about loading grain and show them spaced at 15ft intervals – but when in the late 1800’s conveyors were used for handling coal, ore and other heavy materials heavier then grain, designers followed the handling practice for moving grain as to belts and idlers.

Fig.66The text returns to “Supporting and Guiding the Belt” in Chapter IV. Evidently, the design I have is similar to one referred to as a “three-pulley two-plane idler”. .. and “It is simple and strong, and there are no gaps between the pulleys where the belt may sag and be pinched. That is because the corners of the pulleys overlap as regards the run of the belt.” .. the difference being that the concentrating rollers have been moved up so .. as it says .. “corners of the pulleys overlap“. (Fig. 66)

Fig.67Next up in the text was the “Main Belting Co.’s three-pulley two-plane idler (Fig.67). It states that “The horizontal pulley has twice as much contact with the belt as each inclined pulley, and the inclination of the latter is adjustable to three positions – 10°, 15°, 20°“. This one caught my attention immediately as it is very similar to my original design .. but better! I really like this design and will replace the older design with this one (well .. modified as necessary).
Intermission
At this point I have to stop and pose some questions and then see if I can supply some answers. Someone is sure to state that .. as it has been done infamously .. “What difference does it make?” .. “… after all .. it’s only a model.”. I have no real answer to that since to me it is obvious that the closer the model approaches reality the better. Someone that can’t understand that need to stick with another hobby.

Questions/Statements etc.

  • How about taking up slack? [1]
  • How far apart should the rollers be placed?
  • The idler rollers along the bottom are straight, lacking the angled rollers. At what point is the transition?
  • In partial response to the last statement/question … the trough rollers would have to remain in place it seems to me until the aggregate is dumped .. in other words the trough needs to stay in place until that time. This seems to me to say that a transition to straight rollers needs to happen after that point.
Removing Slack in the belt
[1] There is some time spent talking about the various methods of removing slack from the belt. “At some point in the conveyor, a pulley is mounted on a shaft running in bearings which are adjusted either by a screw or by a weight“. (…) it goes on to show various places for this. If placed at the head end the tension required to pull the loaded side of the belt is transmitted through the take-up; the usual position for the take-up is at the foot where the belt is under less tension.

In this discussion there are illustrations of various methods on different arrangements of belts that is interesting, including changing the incline of the belts.

Loading/Discharging
Loading
Loading chutes may be used in connection with a gate controlled by hand (…)“. “The chief trouble at the Edison plant (and others doing similar work) was with the belts. The sharp pieces of ore cut the fabric and the stitching of canvas belts and loosened the piles; the same thing happened with rubber belts”. We now know that much of the difficulty was due to improper delivery of materials to the belts.”

Fig.30The text talks about delivering materials to the receiving belt with some velocity in the direction of travel. They were concerned with belts moving quickly. THat’s not my concern with my coal bin – but – they give an example from the Edison plant of a transfer between two belts (Fig. 30) as an example of not delivering materials in this method. What catches my eye is that this overcomes the ore beating the belts during transfer – and something like may prove useful.

Discharging
The simplest discharge is over the end of the pulley; sometimes a chute is required there, often it is not.“. Fig.30 is an example of this.

Chapter VIII – Discharging from the Belt — The simplest discharge from a belt conveyor is over the head pulley. The path of the material in leaving the belt is a parabola. (…)


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