Epoxies (two part)

Not necessarily. See 3M Scotch-Weld.

In very general terms, yes.

Of the consumer-grade polyamine-cure epoxies (most of the stuff you're likely to encounter), expect a 48-hour time at room temperature for full cure, and about a week to get really hard.

You need at least 0.005" for a high-strength bond, metal-to-metal. A little more is better.

That's how many aircraft wing skins are assembled. The epoxy provides sheer strength, and rivets resist peel failure. It's called rivet-bonding.

Ordinary amine-cure epoxies lose strength in the mid-200s F. Some of the industrial products are good up to 350 F or more.

Using epoxy for assembling metal parts is not a trivial thing, if you want decent performance. It's time to get on the phone with Devcon, or 3M, etc., engineers.

The heat effects seem to vary a lot from one mfg. to another. All the ones I examined give the maximum heat they will stand up to. I was looking for an epoxy to use in assembling fiberglass pallets to carry circuit boards through the solder reflow oven. The pallets are made from circuit board strips salvaged from panels of curcuit boards. I needed an epoxy to withstand 250-260 degree C. The only one available at reasonable prices is JB weld.

It does turn dark over time - many months. A few times it has eventually lost it's ability to hold onto the fiberglass board material. The pallets have been through the oven perhaps a thousand timed and still are ok. I recently had to rebuild some pallets because the circuit board epoxy was delaminating the layers of FR4 material. But the JB Weld was still holding and had to be cut away and sanded down to the bare board material.

JB Weld takes up to 12 hours to cure. I speed it up with a heat gun. Then about 1/2 hour.

Hope that helps some.

Paul

I'm not picturing exactly what you're doing, but Loctite makes some close fit "annular space" compounds, I used one once to set a brass sleeve for a diesel injector.

The Loctite line of retaining compounds for cylindrical parts are more suited to bonding bearings than epoxy. They also withstand higher temperatures. There are several types to choose from.

If you do use epoxy, you are correct that it needs a healthy gap. One way to keep a cylindrical part centered in an oversize hole when bonding is to use three small shims in the gap and let the cement fill the rest of the gap.

BTW there are a lot of 1-part epoxies that cure with heat.

I was thinking that. I think of the common Loctite formulations green is sleeve and bushing locker. That's what I used on the transmissions input shaft bushing where it goes into the primary case on my wife's old Fatboy anyway. Never looked at the heat rating. That shaft is constantly splashed with primary oil so it doesn't get to hot, but its also what I used for a press in sleeve for the cooling system on a truck engine. Never had a problem with either one.

We found that the 5 Minute 2 part, and under the 5 too, are not well suited to water even after full set. The boats sank. The more conventional times were fine.

Brian Lawson, Bothwell, Ontario

As someone mentioned, there are single-part epoxies, like scotchweld

2214 which cures at 350f, I think. Very hard when cured, very temp resistant. also expensive and hard to get in small qtys.

Loctite etc. cure in the absence of air, which is why they don't set until hidden away in a gap. anaerobic, is it? words fail me at the moment.

I've been looking for a sub for above 2214 to bond piezo wafers to my ultrasonic cleaning tank. Some idiot ran it dry and two of the wafers shattered.

Amazingly, the hardest stuff I've found so far is used for attaching golf club heads. Not sure if it will hack the temperatures. Only one way to find out, I guess. Sigh...

I did some side-by-side trials of epoxies and for steel-to-steel I like JB Weld best of the commonly available ones.

I have changed some of my joints so that there is mechanical advantage making the epoxy joints stronger (e.g. recessing a cylinder into a flat plane even slightly makes the joint much stronger than just gluing the flat of the cylinder to the said plane). I think it is worth looking at what forces will be present and how to minimize them in any particular design.

I made a few stone statues for the garden. The epoxy joints were strong indoors but all fell apart in the hot sun outside. Not all of them were exposed to UV light so I assume heat was the primary factor.

In addition to Ed's excellent response, I would like to add that the old technique of casting mounts and bearings in place is alive and well. This was done for years using lead alloys. The lead alloys have been taken over by epoxies. However, as bearings require service, it is usually the bearing boss that gets epoxied. An excellent example of this usage is the positioning of engine supports in large ships. These engines are very often built into the ships during construction. The engine mounts are optically aligned with laser and cast in place with a product called "Chalk Orange". The advantage of using this epoxy is that when it cures, there is no shrinkage. I actually used this myself when I positioned my oil bearinged propeller shaft/tube in my sailboat several years ago, as welding would have disturbed the shaft bearing alignment. Steve

Intuitively, I would think the longer the stronger.

I have 90 minute epoxy.

waiting forever to cure. Altho I have also found that

to encounter), expect a 48-hour time at room

big players, with big-time industrial uses, such

believe DevCon stated that epoxying bearings is in

good bonding. So a slip-fit for epoxy would be

more is better.

epoxied pins, or just epoxy -- typically nominal 7/8

goddamm, you gotta pick yer poison, it seems. I

applications.

strength, and rivets resist peel failure. It's

heat. I think boiling water, or at least not that

industrial products are good up to 350 F or more.

decent performance. It's time to get on the phone

technique of casting mounts and bearings in place is

s have been taken over by epoxies. However, as bearings

ellent example of this usage is the positioning of engine

s during construction. The engine mounts are optically

. The advantage of using this epoxy is that when it

ed my oil bearinged propeller shaft/tube in my sailboat

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? Intuitively, I would think the longer the stronger.

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epoxied pins, or just epoxy -- typically nominal 7/8

but goddamm, you gotta pick yer poison, it seems. =A0I

in some applications.

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e industrial products are good up to 350 F or more.

ant decent performance. It's time to get on the phone

Learned something new. Thanks Karl

This is good advice, as is the contrapositive: In really cold weather these epoxies can go for weeks without ever getting hard. Don't expect a repair made in an unheated garage in upstate New York in December, to be ready in March :-).

Tim.

As a further contribution to this thread, there are many applications coming on line in the shipbuilding,automotive and aircraft industry in the metal to metal bonding area. These epoxies are not available to the general public. An example is the chassis of the Lotus Elise. It is fully bonded aluminum without welds. In the ship building industry, the major detractor to adhesive use is not structural. It is insurance and IMO regulation issues relating to heat vulnerabilities during fires. Steve

Intuitively, I would think the longer the stronger.

have 90 minute epoxy.

waiting forever to cure. Altho I have also found that

big players, with big-time industrial uses, such

believe DevCon stated that epoxying bearings is in

good bonding. So a slip-fit for epoxy would be

pins, or just epoxy -- typically nominal 7/8 alum

goddamm, you gotta pick yer poison, it seems. I could

heat. I think boiling water, or at least not that

Dental epoxies are impressive as well. They have one now that cures under UV. It's very hard upon curing, enough to stand up to some pretty brutal teeth cleaning/gum surgery.

:-) Technically all epoxy adhesives/coatings are two-part. It's just that some have both the epoxide resin and the curative (or a catalyst---not the same thing) in a single component. As you say, most of these cure with heat. Consequently they may have a limited shelf life.

Example: a mixture of the 'standard' epoxy resin DGEBA and finely powdered dicyandiamide ("dicey") has a shelf life of six months or more. There is a reaction between the two components that is extremely slow to nonexistent at room temperature. At about 150 C the dicey breaks down and reacts in about 30 min.

Best -- Terry

Hi ExAn:

The pot life depends on the amount prepared, though this is of little consequence for the small amounts used for most home/shop repairs. The only things for which I use five-minute epoxy are repairs that need to be done NOW but for which strength is not a serious issue--- gluing marble chess pieces back together after the cat knocked 'em over, that sort of thing.

I use a fair bit of epoxy (quarts) in constructing large model rockets and rocket motors. Bought two gallons of the resin, one quart of "fast" curative, and a half-gallon of "slow" curative. But a cup of the prepared 'slow' mixture will cure faster than a teaspoon of the 'fast' mixture. The phenomenon is called "exotherm".

Any intermediate speed can be obtained by mixing the two curatives in the appropriate proportions, though it's rarely necessary.

The same stuff is used both to laminate fiberglass/carbon fiber and as an adhesive. I just add a thickener for adhesive work. Baby powder, very fine sawdust, quartz microballoons, etc.

A lot of epoxies have heat-distortion temps around 100 C but that doesn't mean that the parts come unglued at that temperature. The rocket motor casing can reach temps well above 100 C, but that seems not to affect the parts that are epoxied in the vicinity of that casing. Many epoxies actually see an increase in ultimate strength from a post-cure heating phase of around 150 C or even higher.

Yeah, I know, I rambled... :-)

-- Best -- Terry

On 8/7/2010 5:02 AM, Steve Lusardi wrote: The

"Chockfast Orange"?

Kevin Gallimore

Handy stuff. Thank you.

"Existential Angst" wrote in news:4c5c9162$0$4988$ snipped-for-privacy@cv.net:

For the last ~ 40 years, I've sworn by Hysol 0151 two part epoxy. It is clear enough that it is used on some optical applications, and I first learned about it when working on satellites. I figured it can't be too bad if it's used on really expensive hi rel applications like that. It has a 60 minute pot life, and takes overnight to cure reasonably well at room temperature.

The "Epoxi-Patch" kits are convenient & easy to use. You get a large tube of resin, and a smaller tube of hardener. You just lay down equal length beads & mix. It used to be sold under the Dexter brand, but it is now sold by Loctite. It's not the easiest stuff to find. Some electronics tool outfits sell it:

as does Aircraft Spruce:

They also sell a white "1C" version, which has a thickener in it that helps it stay put while it cures. We still use it at work to brace electronics parts that are subject to shock & vibration.

For quick jobs where strength isn't crucial, we use Hardman "Double Bubble" epoxy packs (typically the red 5-minute stuff)

The downside is that I haven't found any place that sells them in moderate quantities (like 10 or 20) for a decent price for home shop use. In 100's, it's less than a buck a pack. The places that sell them individually want close to twice that.

Doug White