Point Loading Explained

In Diagram 1, a standard 2 ft. radius, 90 degree, horizontal track curve contains a chain with 8 -1/8 inch load wheel spacing. The section of track illustrated can accommodate 5 horizontal guide wheels also set on 8 -1/8 inch centres. Guide wheels roll against the sides of the track when traveling around horizontal curves, and take the full brunt of chain pull during the turn.  Assuming chain pull is the advertised maximum of 750 lb., the point loading on the track under each guide wheel is 150 lb. (750 lb. chain pull divided by 5 wheels).

 

 

In Diagram 2, a standard 2 ft. radius, 90 degree horizontal track curve contains a chain with 6 in. load wheel spacing. The section of track illustrated can accommodate 7 horizontal guide wheels also set on 6 in. centres. Again, assuming chain pull is 750 lb., the point loading on the track under each guide wheel in this chain is only 107 lb. ( 750 lb. chain pull divided by 7 wheels).

 

Compare that to the illustration in Diagram 4.  This chain does not employ a crude universal block. Instead, a smooth, machined, hour-glass shaped roller of hardened steel with a diameter at its narrowest point of almost 1/2 inch engages a strong, machine-honed, forged steel side link.  Point loading at this union of two links is an order of magnitude smaller than in the other chain.  Even if your company pays twice the price for this chain - which, in fact, it won't - it would still come out money ahead. Properly lubricated, this chain will last three or four times longer than the universal block type.

 

Extra Thick Track

How else might an enclosed track conveyor be improved in order to provide really long life and maximum return on investment?  Most enclosed conveyor track is made from 11 gauge, mild steel with an actual thickness of about 0.12 inch. Because track curves are formed by bending straight track, thickness must be kept down to allow for a viable bend.  Contrast that with track constructed of 7 gauge surface hardened steel with an actual thickness of 0.18 inch.  This track is so strong and thick that track curves can not be manufactured by stretch bending straight track. Instead, track curves are constructed of two roll-formed sections welded together and flame hardened for even greater durability.

 

 

 

Back to FastTrack systems here.

 

 

Why FastTrack?

 

 

Not Created Equal

Not all enclosed track conveyors are created equal.  Although they all look pretty much the same, there are some fundamental engineering considerations that put one type of enclosed track conveyor miles ahead of the rest.

 

The True Limit

Ask enclosed track overhead conveyor owners what they think the chief limiting factor to long conveyor life is, and they answer the chain. In fact, the main limiting factor to long enclosed track conveyor  life is the track.  While chain is readily replaced, a badly worn track means replacing the conveyor.

 

A Lesson From Our Highways

When the various highway departments around the country found their roads were being destroyed by trucks carrying overly heavy loads what did they do?  They legislated more wheels per truck. That decision was based on a concept called Point Loading. The weight of a  truck's load is transferred to the road through the wheels. The amount of load transferred to any individual point in the road is reduced when there are more wheels.  This same rule of spreading the load to avoid damaging or sinking through the supporting surface, is evidenced in snow shoes and in the large balloon tires often used on off-road bicycles.

 

The Source of Track Failure

It's well known that conveyor track starts to peen when point loads exceed 135 lb. That is, when any wheel is transferring more than 135 lb. of weight to any single point on the track.  Like hot asphalt under truck wheels, the conveyor track surface starts to bulge in front of the chain wheels and molecules are shifted permanently off to the sides. Eventually, that portion of track where the wheels consistently make contact, becomes so thin it fails.  The truly surprising thing about this phenomenon is that it is happening consistently on conveyors operating within the 750 lb. chain pull guidelines suggested by their manufacturers. This Point Loading problem is illustrated in the two small drawings which follow.

 

Spreading The Load

In Diagram 2, more wheels help to spread identical chain load over a greater area, such that point loading under these wheels is 40 percent lower.  Now, this same principle applied internally to the chain, also saves it from damage. Each wheel in Diagram 2 bears a smaller load and will last longer even if made of the same material.

 

Point Loading Inside The Chain

Let's focus now, on some point loading considerations inside the chain itself. That portion of a chain link which engages the adjoining link also warrants closer scrutiny.  Most enclosed track conveyor chains use a universal block and sliding holes to join the links and provide chain flex. (See Diagram 3)  The diameter of the pins engaging the chain side links is barely 5/16 of an inch.  This part is not machined, and still contains parting lines from the mold in which it was forged.  The physical area actually engaging the slotted side link is so small and rough that early chain wear is a certainty.