Engineering Properties of Roller Chain Pins 1

[BelchFire]

We use a machined element in a #80 roller chain to move a heavy load. We simply remove one link and insert the "dog" in the chain and use two 5/16" grade 8 bolts to complete the assembly. Grade 8 bolts aren't holding up too well. Does anyone know the engineering properties of the roller chain pins that I'm trying to replace? Tensile strength, hardness, material grade, etc.....

Thanks in advance

 

[3DDave]

Use Google to search for "roller chain pin hardness"

I saw hits from Timken and U.S. Tsubaki.

 

[Jboggs]

Have you contacted the chain mfr about inserting that "dog" for you? They make all kinds of special chains with a wide variety of special attachments. I have used several different types over the years.

 

[CoryPad]

A typical pin would be case hardened, so the surface would be ~ 60 HRC and the core would be similar to your grade 8 bolt.

 

[btrueblood]

Roller chain pins are probably ground to a more precise diameter and surface finish than a typical grade 8 bolt. Can you not design the dogs around standard attachment links (see

http://www.mcmaster.com/#roller-chain/=rrga78

)?

 

[BelchFire]

btrueblood, You've hit on my next approach. The dog is wide; 2.125" overall. I'm wondering if I can modify the dog to use a triple strand master link.

Until I get that far CoryPad made me wonder; what would happen if I tried to case harden a grade 8 bolt? Would it lose its native hardness? I'm guessing it would. Could I substitute a dowel pin?

 

[btrueblood]

I'm guessing the bolts are a slightly "sloppy" fit within the chain bearing holes, so that you can easily make the connection. Think of how hard it is to press the links out when repairing regular links. This likely results in a lot of "working" of the bolt within the female link bearing hole, and rapid wear of the bolt. Yes, a dowel pin will probably hold up better if it is a tight press fit into the female link bearing hole.

But, I think you will also find that even with precise fit between link pins and the mating bearing holes, that the dog link pins still wear quickly. This is because of the extra loads carried by the links due to bending moments from the loads on whatever the dog is pushing/lifting, and the extra flexing those pins see. You'll probably also begin to see some excessive wear on the female links. So, have plenty of spare female links as well as the pins on hand and replace both.

 

[Tmoose]

"Grade 8 bolts aren't holding up too well. "

Bending, breaking, wearing?

I'd think about making a "lug" that engags the chain roller full width and with some curvature, like a sprocket tooth does, and use larger bolts to secure the "lug" to the load.

 

[BelchFire]

btrueblood; I was wondering the same thing about the slop in the assembly. I'll have to make new dogs if I do this; the ones we have in inventory have 0.315" holes.

Tmoose, the bolts are breaking near the edge of the chain. I think it's all about the offset load. The load is off to the side of the chain; not on top of it. That puts a hard bending moment on the bolts. I'm going to try to fit a double strand master link through the dog and see if that helps. If I'm interpreting the dimensions I found on-line correctly, the inside dimensions of a double strand master link should be 2.250" and the dog is 2.125" wide. The link plates are 0.125" thick, so that works out perfectly! I'm going to try that before I try a dowel pin b/c I'd have a sloppy fit on the dowel and no good way to hold it in place.

I really appreciate all the input; you guys are great!

 

[CoryPad]

Do not try to case harden a grade 8 bolt, the result could lead to cracking or other problems. Since the shape is relatively simple, just buy some 8620 steel bar and machine/form to size, then carburize it. Assuming the part diameter is < 25 mm, you should have a core strength similar to a grade 8 bolt and a hard, wear resistant surface. A dowel could be manufactured (or maybe purchased) in a similar condition.

Do not use a large preload on a carburized fastener, that can result in delayed fracture due to hydrogen assisted cracking.

 

[handleman]

Please note... A 5/16 pin has an effective diameter of 5/16. A 5/16 bolt has an effective diameter somewhere considerably less than 5/16. Unless you're using a full-shank bolt with only a little bit of thread at the end.

-handleman, CSWP (The new, easy test)

 

[BelchFire]

Good catch, handleman! The dog is designed with through-holes and we use a lock nut on the end of the bolt, so it doesn't tighten up and bind on the chain. It's also 2.125" wide and we use a bolt long enough that the threads begin only after it has passed through the chain links. But to add to your point, the chain pins are 0.312", a 5/16" bolt (body) is usually under that by some "fit-function" factor so that it'll pass through a 5/15" hole. But that's not much.....

I appreciate the help everyone. I'm going to try the double strand master link. If that doesn't work out, I may make some custom fasteners with Corypad's 8620 suggestion.

 

[Timelord]

Have you tried a shoulder bolt? They have controlled diameters on the shank. You can cut the shoulder back to correct for the width if necessary.

Timelord

 

[Compositepro]

I would suggest using dowel pins or shoulder bolts.

 

[btrueblood]

Machinery's Handbook lists pin sizes for standard roller chain. For #80 chain, the pin diameter is listed as 0.312 +.0005/-.0000; you won't get those tolerances with a bolt. Even a "tight tolerance" shoulder bolt has looser tolerances of .3125 +0/-.001. I'd use a dowel pin, and cut retaining ring grooves on each end. Note the handbook also lists min. roller (female) hole i.d. as pin size +.0015, but doesn't list a max. I'd check the female holes where you have been attaching links, and replace them if the holes are more than a thou or two over the min.

 

[btrueblood]

"I'm going to try to fit a double strand master link through the dog and see if that helps. If I'm interpreting the dimensions I found on-line correctly, the inside dimensions of a double strand master link should be 2.250" and the dog is 2.125" wide. The link plates are 0.125" thick, so that works out perfectly! I'm going to try that before I try a dowel pin b/c I'd have a sloppy fit on the dowel and no good way to hold it in place."

I'm not following you here - are you saying your drive dog plates are thick enough to take up all the slack between the ~1-1/8 wide single strand side plates and the width of a double-strand master link?