Urethane to Steel Epoxy Suggestions

[lucky-guesser]

Repost from the chemistry -> adhesives section that didn't get any replies:

Hello all, we are currently using J-B Weld # 8280 (aka 8281) two component epoxy to bond small pieces of urethane to zinc plated mild steel. These urethane pieces are not critical in any way to the function of the assembly, more of just a minor convenience so if they fall out off in the field, obviously we don’t want that but it’s not the end of the world. Issue is, we are getting complaints that the urethane pieces are falling off on the way to the customer, not even getting out to the field before having issues.

We have a reference model on hand from 2017 and when I compare it to current production models I can see a substantial difference in quality over how the epoxy was applied. In this particular case there was much more epoxy than what was needed, but with the labor situation we all deal with today, the next batch could just as easily not have enough epoxy.

All that to say, this is likely operator error, however I still want to cover all my bases. After doing a quick look on the J-B Weld website, it looks like their 8265S may be better for our needs. Looking for thoughts on if you all would agree with that, as well as any products from other companies that may be better than that. I’m sure the purchasing dept would like it if we stayed with a J-B W product but they will change if we need them to.

Completed assemblies will likely be outside 24/7 in assorted weather, but no unnatural hot/cold situations. Will be subject to repeated light impacts but for relatively short periods of time.

 

[SWComposites]

with all bonded joints, surface preparation is critical. start investigating that first.

 

[lucky-guesser]

with all bonded joints, surface preparation is critical. start investigating that first.

There may be a time delay where parts collect a little dust but process wise parts are fresh out of the zinc plating tank. Otherwise no additional prep is done. Small parts + some awkward geometry would make any sort of surface roughing all but impossible. They could make a trip to the degreaser if they were oily but there's really no reason why they would have any oil on them.

 

[EdStainless]

I would go to 3M for double stick tape.

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P.E. Metallurgy, consulting work welcomed

 

[Jboggs]

There are several urethane custom molding shops around. Over the years I have designed several components that consisted of both steel and urethane. In all these the steel body was included in the urethane mold itself, so the metal and urethane were actually bonded as part of the molding process. You might consider that approach. If you need a shop recommendation reach out to me.

 

[hendersdc]

Pictures would help, are these getting knocked off due to shipping and handling and you would just like them to stand up to a little more abuse or are they failing so badly that if left alone in a room for 1 month they would all fail on their own?

 

[lucky-guesser]

Pictures would help, are these getting knocked off due to shipping and handling and you would just like them to stand up to a little more abuse or are they failing so badly that if left alone in a room for 1 month they would all fail on their own?

My boss probly wouldn't appreciate me posting pictures of the issue so I'm going to refrain. As to your question, the part is actually held in place under light spring pressure when at rest so even without adhesive I don't think it would fall out just sitting there. One of the pieces that is holding it in place gives it that small impact stress when rotating so I would suspect that it is happening when someone rotates the assembly, either on accident when the assemblers are putting them into the shipping boxes or the customer messing with them when the arrive.

I don't know that anyone on our end has seen the failures first hand as to my knowledge this is all based on customer reports, but just based on the geometry that would almost have to be the case.

 

[3DDave]

Many elastomers have close to zero elastic compression capacity; this is seen when Poisson's ratio is close to 0.5, so when contained in certain ways applied deflection can cause extremely high confinement or shear forces.

Thin pieces of material with relatively large areas to spread the load are especially prone to this. If one manages to get a sufficient adhesive bond, the next failure will be in the material. Each cycle will debond or shear more until nothing is left in place.

If the material becomes more stiff when cold and cold temperatures are encountered, the situation becomes worse.

Curing the urethane in place on a properly cleaned surface is likely the best, followed by a mechanical retainer.

 

[GregLocock]

I vaguely remember some bushings use a cyanoacrylate to bond the two materials together. I'd guess that surface prep is crucial.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[SnTMan]

I don't suppose it is worthwhile to bother the adhesives applications engineers with the problem

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[dvd]

Design for assembly - eliminate the adhesive and have features on the urethane part with press-in mating to the steel part

 

[TugboatEng]

Elastomers are one of the more easily bonded materials. Polyurethane, especially. Zinc is one of the more difficult metals to adhere to due to its rapid oxide formation. A light glass bead blast immediately prior to bonding will do a great deal to improve adhesion.

Do the most basic failure analysis the adhesive connection. Is the adhesive separating from the rubber or is it separating from the metal?