Today, I’m going to show you how to measure roller chain for wear elongation.
First, let’s all the components so we’re all speaking the same language.
When I’m talking chain. Roller link. pin link. Roller link. Pin link.
The roller links The narrow link.
So we break that chain apart. This would be a roller link consisting of a roller, a bushing, and a side plate. And this would be a pin link.
So a pin connects a series of roller links together
Roller diameter. This is the roller that engages the sprocket.
Inside width. Talking the inside width of the roller link because that’s where your sprocket goes.
That would be this distance right here.
Link plate. You need link plate thickness and height.
And the last thing and most important is the pitch.
Pitch is the distance from pin center to pin center.
It’s hard to measure the pitch in the field because you’re trying to go from pin center to pin center.
So what I like to do…I try to use a digital caliper and I like to measure from outside a pin. Provided the pin has a nice edge on it. You don’t want it pinned over or rust on it. You want a nice clean edge.
You want to measure outside, outside, and then subtract the pin diameter from it.
Now I’ll give you the same thing as measuring from the center pin to center a pin.
Once you have the chain measured compared to the catalog to determine the size, some chain will have a number stamped on the side plate. For instance, this one says 100. So I know this is 100 chain.
Now you know your chain size. So now let’s discuss wear, what is wear?
Wear occurs when the chain articulates, bends, around a sprocket while under load.
As the idea, the bushing and the od of the pin wears as it articulates, it causes the chain to grow in length or elongate.
So what I’m referring to is the roller link pin link as this pin rotates inside of that bushing.
Over time it causes wear and the chain will elongate chain elongates too much. The chain won’t engage with the sprocket correctly, and it could have severe downtime.
If you know your chain size, look at the machine and determine if it has a chain take up or raise a fixed center that will determine which side of this elongation ruler you will use. I’ll get into that in a little bit.
I have a demo rig set up that I use for an example.
If it has a K-Cup, which means the chain can be tightened. We recommend replacing the chain when it has elongated 3%.
So what I mean by that is typically the bearings will be slotted to where you can move your sprockets back and forth. Or it will have some type of mechanical take-up. That will keep the chain tight.
If it has fixed centers, which means the chain cannot be tightened. We recommend replacing the chain when it’s elongated one and a half percent. And I’ll show you how to measure all that in a minute.
These percents are what we call a rule of thumb. So your equipment may be different.
Remember, Make sure the machine is turned off and locked out and tagged out before you take any measurements.
Ideally, it is best to remove the chain from the system and put a predetermined amount of load on it, and then measure the pitch.
Remember pitch is center pin to center pin.
But very few people have time to do that.
Most will need to measure the chain while still in the equipment.
You will always want to take your measurements from a tight side of the chain, which is typically right before the drive sprocket.
So in this example, this is your drive sprocket and the chain is moving in this direction as you see, the chain is tight.
The top side, the bottom side, we consider the loose side.
A quick disclaimer, the elongation gauge I’ll be using it just for quick reference. It’s always best to measure as many pitches as you can with a tape measure.
What I prefer to do is take a tape measure on the beginning edge of the pin. Then measure, as long as you can as many pitches as possible to a corresponding pin to the beginning of another pin. Write down that dimension, then divide it by the number of pitches. That way you have a good average.
I also like to take the equipment, measure it, rotate it by a third, and measure it again. Rotated by a third, measure it again. I take the average of those three measurements.
Now we have a good, good example of the full length. The chain.
The chain I’m measuring is the number 50.
We already determined the demo unit has slotted bearings, which means it’s adjustable, which means we can use the 3% max elongation part of the ruler.
The 1.5% max elongation is for fixed centers. Because you can’t let the chain elongate as much. Because there’s no adjustability. Because it could cause sprocket to chain interaction issues.
If you look over here at our diagram, we show where to connect it. So here we’re connecting to a pin link.
Remember, make sure your chain is tight. This demo unit’s kind of hard because there’s no break in the system. Even on your own piece of equipment, you may need help making sure the chain is tight.
So remember, you want to count 15 pitches for number 50 chain.
So remember, a pitch is from the center of pin to center. PIN, right.
So that’s one pitch, two, pitch three, pitch four, pitch five, pitch six, pitch seven, eight, nine, ten, 11, 12, 13, 14, 15.
There’s the 15th pitch. Chains pulled tight. You’ll see that the edge of that pin is not to the 50 line, which means there’s a lot of life left in that chain.
Once the edge of that pin reaches that 50 line, the chain will need to be replaced.