Polycarbonate/ABS blend to 304 Stainless Steel - Adhesive

[tomalway]

Hello,

I am working on a project where a polycarbonate/abs blend part and a 304 stainless steel part need to be joined together.
The parts are both tapered cylinders, open at only one end. The stainless steel part will fit into the PC/ABS part and there is a gap between the two surfaces of about 2.5mm.

The adhesive will also need to meet a set of requirements:
- The adhesive must not rely on air contact to cure. It is unlikely that UV curing will possible.
- The adhesive must be flexible/rubbery to allow for expansion and contraction between the materials at different temperatures. The adhesive will be exposed to temperatures up to 90°. It is also important that the adhesive has good impact resistance.
- Ideally the adhesive needs to be food safe but will be open to suggestions of adhesives that are not food safe.
- The colour should be as light as possible, trying to keep away from black adhesives.
- The adhesive must be low cost.
- The adhesive must have a reasonable cure time. (Not too fast or too slow)
- The adhesive must be viscous, an adhesive that is too runny will not work in this application.
- Finally, if the adhesive requires either material to have surface treatment, it must be treatment that is very quick and easy to do.

Looking forward to any help somebody can give!

 

[btrueblood]

epoxy

 

[berkshire]

Rubber modified epoxy.
B.E.

You are judged not by what you know, but by what you can do.

 

[tomalway]

Thanks very much for your replies. Are there any brands or grades of adhesives you could suggest?

 

[blakmax]

Please read my previous postings in other threads on the importance of surface preparation for bonding. Trust me, unless you get the surface preparation right, it does not matter what adhesive you use.

I'd recommend solvent degrease, grit blast at 80psi, blow dust off and use AC-130 to treat the stainless.

Regards

Blakmax

 

[tomalway]

Thank you for your reply but that kind of surface preparation will not be possible, it would just to too long. I am interested to find more out about rubber modified epoxy, could anyone suggest a brand or grade of rubber modified epoxy that could work in our application?

 

[blakmax]

Trust me! If you do not undertake surface preparation then you must anticipate the consequences of a 100% probability of failure and the selection of the adhesive will only change the colour of the failure surface.

Regards

Blakmax

 

[tomalway]

I appreciate your help but we have already tried various surface treatments. It has helped improve the strength of the joint but the failure has always depended more on what adhesive was used. There are many different kinds of adhesive and as you will see from the criteria I have written, the adhesive we are in search of is something quite specific. The comments regarding rubber modified epoxy seem to be what we want to be looking for and if anyone could suggest any brands or grades of rubber modified epoxy it would be greatly appreciated.

 

[CoryPad]

3M Scotch-Weld DP100

Henkel Loctite E-30CL Hysol

 

[tomalway]

Thanks very much, I will have a looking into those!

 

[blakmax]

Tomalaway

Surface preparation has a moderate effect on STRENGTH but it has a dramatic effect on longer term bond integrity. Almost any reasonable process will demonstrate short term strength. It is only processes which prevent hydration of the metal oxides that have any chance of long-term bond integrity. Try this: make two or three batches of specimens: abrade the surface of the metal with abrasive paper. Solvent clean it, then bond. Test one batch soon after bonding. Strength will be moderate to great, so you think that is adequate. Now place the rest of the specimens in the environment that the bond will be exposed to (Food product at 90º?) for a few months. Test the specimens, and then repeat the process after for a few more months. If the second batch show sufficient strength I will be amazed. If the third batch still shows any strength I am prepared to lower my trousers and walk backwards down the main street of your city for ten minutes.

What you fail to understand is that surface preparation is specific to the material being bonded. It is only indirectly of significance to the adhesive you select.

Please understand that bond integrity relies not only on initial strength but also the long-term ability of the interfacial chemical bonds to resist environmental degradation. Please read my postings elsewhere on Eng-Tips. You may actually save yourself from future legal actions, because you now have been made aware that the importance of surface preparation to long-term bond integrity is far greater than the selection of the specific adhesive.

Eng-Tips has been created to enable specialists like myself to provide reliable advice to engineers who may be dabbling in a field which is not within their primary knowledge base. It is not necessarily there to provide you with the answer you THINK you need.

I remain happy to help, but only if you are prepared to listen.

Kindest regards

Blakmax

 

[tomalway]

Blakmax

I appreciate what you're saying and I am prepared to listen. I do also thank you for your help. Could you please direct me to your postings elsewhere on Eng-Tips.

I understand what you suggest for the surface preparation of stainless steel. The more problematic material to bond to is the PC/ABS, are there any surface preparation methods you are aware of that would help to create a strong bond with integrity? The surface of the PC/ABS can be textured so what else can be done to help? The bond will want to last for years, exposed to temperatures reached by dishwashers and the chemicals associated with dishwashing.

I appreciate any help you will be able to give us.

Best regards

Tom

 

[blakmax]

Tom

The high temperatures and caustic nature of the operating environment in a dishwasher would be very challenging for any adhesive system, especially if you do not get the surface preparation right. I can tell you that a simple environment such as room temperature with a the presence of a neutral to slightly acidic moisture is sufficient to challenge the long-term survival of most adhesives even with the surfaces prepared using high level processes. I am a very strong advocate of adhesive bonding, but in this case I strongly suggest that you consider using mechanical fasteners for this task.

Happy to talk further

Max Davis
Adhesion Associates

 

[tomalway]

Max

If the adhesive did not come into contact with the chemicals and liquids involved in dishwashing, would you expect the bond to last longer? The adhesive itself would not come into direct contact with any chemicals and liquids, the adhesive would only be exposed to the temperature and the associated expansion and contraction of the materials.

I do understand your concerns but using a mechanical fastening would require changing the design of some parts which is something we want to avoid as it is not easy to make changes at this stage. If an adhesive could be used with appropriate surface preparations, that would be preferred.

Best regards

Tom