I need – I need a really good adhesive…

I have another “pet project” in my brain – a stainless steel gadget with three pieces that need to be joined together. I want this thing to be seamless to the touch – I can’t use fasteners. I have played with brazing and soldering with limited success – surface preparation is crucial to a good join, and any void or other flaw in the braze or solder eventually leads to corrosive failure from inside the join. So, I turned to adhesive technology – I need a really good adhesive…

I thought this would be a simple problem to solve.  I contacted 3M and Henkel (Loctite) – I figure I need a notch or two below the exotic, and these two companies should be able to help me. These companies have comprehensive product lines, tech support staffs are accessible, and there are plenty of publications from these companies to refer to. Now, have you ever called the IRS with a complicated question? And you called back to see if the second answer you got matched the first answer? They didn’t? Well, it seems that adhesives are a little like taxes…

Here is the problem description:

  • Substrates: 316L stainless steel to 316L stainless steel;
  • Static Forces: 100Kg of sheer force and 10Kg cleavage force (like bell peel) – pulling and twisting, in other works – no compressive force;
  • Dynamic Forces: Occasional impulses of force that double and triple the sheer and cleavage stress – no vibration;
  • Ordinary Physical Environment: 35C to 45C, 95% humidity (noncondensing – slightly acid from sea salt) – no submersion; may be exposed to water, detergent and drying heat to clean every month or so;
  • Color: Colorless, off-white, tan, light grey would be good – not black;
  • Join #1: Plate to plate (flat to .1mm) 1cm x 1.5 cm;
  • Join #2: Wire to plate – 3mm diameter wire with 1 cm over the plate.
  • Working time: At least several minutes – almost anything will work – not an issue…;
  • Cure time: over night, but up to 3 days will work – can heat cure if necessary – also not an issue;
  • Non-sag (viscous): not an issue for Join #1 – a high viscosity adhesive may be helpful for Join #2;
  • Production: several per week maximum; adhesive budget for up to $50/week.

With all that, I would have thought that someone would have said, “You obviously need product A for Join #1 and B for #2.  Those are obviously your best choices.” But, I got a different answer every time I talked to someone. How frustrating. No one who was accessible had any experience using the adhesive products they were discussing. These companies were not paying for experience that was facing the customer! Dad-gum-it. Experience for products with a broad range of critical applications is crucial, and it wasn’t there.

To 3M’s credit, I eventually got indirect access to a chemist, but I couldn’t talk to this employee directly. To Henkel’s credit, I eventually got direct access to the product line manager who knew the product line frontwards and backwards. These individuals were ultimately helpful. To the credit of both of these companies, they sent me several free samples of a variety of products (in lieu of a definitive answer) to play with and determine for myself what would work best. 3M sent me a dispensing gun, and Loctite made sure I had plenty of hard to get 10:1 static mixing nozzles. These companies did everything possible to get their products in my hands.

So, I still have a few unanswered questions:

  1. What material is 316L stainless most similar to with regard to surface bonding? Aluminum or cold-rolled steel (these two materials are commonly tested for manufacturer test data)? Is there a different answer for epoxies and for acrylic adhesives?
  2. What is the optimum bond thickness for each candidate adhesive for Join #1 (not always stated on the tech data sheet)?
  3. What is the optimum surface preparation technique for epoxies and for acrylic adhesives (there is a difference of opinion between companies)?
  4. What is the effect of monthly thermal cycling from 40C to 120C to 40C on the bond lifetime?
  5. What is the typical viscosity of a paste? A light paste?

Here are the products I have to trial – anyone recognize a winner:

3M – for Join #1 – VHB Transfer Tape, DP420, DP460; for join #2 – DP460NS (three epoxies);

Devcon – Metal Welder (an acrylic);

JB Industries – JB Weld;

Loctite H4710, H8500, H8600 (three acrylics for Join #1), E-60HP, E-214HP (two epoxies for Join #2); E-60HP may also work for Join #1.

LORD – 310 (medium viscosity, general purpose epoxy).

This will be a fun Thanksgiving project! I’ll report back… Anyone know answers to my questions???

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2 Responses to “I need – I need a really good adhesive…”

  1. Brian Says:

    Most of my buddies reading this blog comment directly to me in e-mail. A quick query from two readers:

    – What is the range in price for the Loctite solutions? What premium would you pay for a good solution vs. a best solution? Did you look at MasterBond?

    That is a good question and a frustration I had with the Loctite folks. The price range for all their epoxy and acrylic products is from $10 to about $15 from specialized distributors for 35ml or 50ml dispensers (Grainger is twice that price). The premium for good vs best is just a few dollars per week. Loctite initially was trying to give me the cheapest good solution, and it was difficult to tell them I didn’t care about a few dollars.

    MasterBond was extremely expensive – priced out of the market at 10x Loctite’s price. I suspect they have better product control and superior chemistry – but maybe not…

    – What is the lifetime you want from these adhesives? How will you do accelerated lifetime testing?

    Well, I want at least 10 years of lifetime, and I have no idea how to do accelerated lifetime testing… If anyone known, please comment!

  2. Brian Says:

    Another e-mail this morning:
    “There’s always a magazine to glean tid-bits from.”

    And I found this link today:

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