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cmd15 (Electrical) (OP)
29 Sep 03 18:39
Hello,

I have a conveyor system used to transport large (1220W x 3660L x 550H) pallets of wood planks, weighing approx 1 - 1.5t. The problem we are experiencing is "jerky" conveyor travel that is causing nuisance tripping on a light curtain for our automatic wrapping machine. I have had very little experience in material handling with chain conveyors and would like some advice on what can affect the smoothness of chain conveyor operation. The chain is fenner C2080H, 2 inch pitch. The sprockets are actually for a 1 inch pitch chain and have slight ridges half way up the tooth. Generally sprockets for our other conveyors have a pitch matching the chain pitch, and are machined with smooth tooth surfaces. The chain guides are slightly (5mm) higher than the top of the sprocket, causing the chain to be pulled down as it leaves the guide to join the sprocket.

Any help or advice would be greatly appreciated.

Thanks,

Craig
dvd (Mechanical)
11 Oct 03 23:13
Your 2080 chain will run fine on the RC80 sprockets. If the sprocket has an odd number of teeth then the teeth on the sprocket will encounter a chain roller on every other revolution of the sprocket, thus doubling the life of the sprocket. If it is an even number of teeth then you will have to advance the chain one tooth to wear the unused set of sprocket teeth.

Don't know how many pallets you are conveying at 1.5 tons per pallet or is that total load? But you may have an overloaded system and your chain and sprockets are worn out. 2080 chain may be too small.

5mm is quite a bit (~0.200 in) to be above the sprocket pitch diameter on 2080 chain. As the chain encounters the sprocket the chain pitch line is well above the sprocket pitch line and thus will move faster but then slows down as the chain roller eventually finds it's way to the pitch center. Depending on the pitch diameter of the sprocket this will cause a large speed difference.

Are there high and low spots in the chain guides which cause the load to shift from one side of the conveyor to the other? For long strands of chain this will result in chain stretch which will be recovered when the load evens back out. You will also notice jerkiness if the conveyor head shaft is too small.
PeterCharles (Mechanical)
7 Feb 04 11:21
Chain 'jerk' is a well known phenomenon with chain conveyors.

I don't know the chain you are using, but if it is a roller type chain (like a bicycle chain but bigger), does the chain run on the rollers or on the side links?

If the chain runs on the sidelinks it's probably associated with the friction between the sidelinks and track.  You can easily check this by putting a little oil on the track and observing the result.

Chain drives all suffer from the 'polygon' effect of sprockets.  The drive shaft may rotate at a constant speed but the action of the sprocket driving the chain is to produce a varying linear speed due to the variation in the radius to the line of the chain.  The smaller the number of teeth, the greater is the variation.

The combination of variations in linear speed, difference between static and dynamic friction of the chain on the track and slack in the chain joints can all combine to produce chain 'jerk'.
unclesyd (Materials)
7 Feb 04 14:29
I think you have a condition known as "hooked teeth". This is a state of wear on the sprocket teeth that causes the chain to jump in and out of the sprocket when exiting.  You need to install a new sprocket of the proper size.
DigilubeJay (Mechanical)
18 Sep 05 9:48
The jerky action of the chain, or "Chain Surge" is normally attributed two things. Lack of proper lubrication, and poor design.

As mentioned above, the chain will experience a slight variation of speed due to the action of the roller meeting with the working face of the tooth. During this meeting, the chain is being put through "chordal action". The extent of the chordal action is relative to the number of teeth in the driver sprocket. The more teeth, the less vertical chordal action the chain encounters.

It is possible that the elevated guides are taking the chordal action of the chain into account, and if designed properly, would be correct to do.

Many time a drive that experiences lots of motion due to chordal action can relive some of the surge by replacing the driver with a larger diameter sprocket.

In my experiences, the main contributing factor to chain surge of roller chain conveyors, or for any type of endless conveyor for that matter, is lack of proper lubrication.

Roller chains demand lubrication. A roller chain conveyor should have automatic lubrication equipment mounted. Periodic manual lubrication normally does not provide the lubrication frequency that the chains require.

Even when the chains are being lubricated, often times the drive chain is neglected, and can be a major source of chain surge once it has elongated past rec. limits (>2-3% of original pitch)
And with that said, it is also possible, as mentioned above, that your chains have elongated more than 3% past original pitch length. This causes the chains to have a mismatch of pitch with the sprockets. If you measure a ten foot section of the chain and compare the original pitch length with that of what it is today, you will know the percentage of elongation the chain has experienced.
If your chain is indeed longer than 3% of original length, both the conveyor chain and the sprockets need to changed out.

One more point I might add...if there is a tensioning take-up unit on the chains, it is possible that it has reached it's workable limit and needs to be adjusted. Or, it may be mechanically damaged or blocked from working correctly. Sometimes addressing this is all that is needed to smooth the run of a chain out.

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