Alternative to JB Weld???

[jeffgeraci]

I'm sick and tired of buying these piddlylittle tubes of JB Weld at $6 bucks a pop!!! Does anyone know of an alternative manufacturer who offers larger containers of a similar adhesive????? I can't believe that JB Weld would have a monopoly on high-temp epoxy.

 

[GregGleason]

I know there are alternatives for high-temp epoxy, such as Cotronics, 3M, and Wildman.

But nothing is as cheap and performs as well (at least regarding the advertised temps it can handle).

However, somebody may know of something out that is at least equal to JB Weld, which is why I have subscribed.

Greg

 

[AfterBurners]

Two part epoxy clay. Is resistant to heat and you can get in 1 lb tubs. It's called FIX IT epoxy clay.

 

[H_Rocket]

You can get it for slightly less than the blister packs at McMaster Carr. They have a 5oz tube that is $16 as opposed to the $6 for the 1oz tube. About half the price. Keep in mind that JB Weld really has limited applications (IMO) in rocketry. It is actually weaker than many other epoxies.

You can also make a fair approximation using regular epoxy and a mix of colloidal silica and fine iron dust. That is essentially what JB Weld is. The iron powder gives it better heat transfer capability that way the heat passes throgh the joint rather than melt it.

 

[GregGleason]

...You can also make a fair approximation using regular epoxy and a mix of colloidal silica and fine iron dust. That is essentially what JB Weld is. The iron powder gives it better heat transfer capability that way the heat passes throgh the joint rather than melt it.

That's interesting Al. Did you read that somewhere?

Hmmmm, thinking out loud: If the reason that iron dust is used as an additive because of its thermal conductivity (80.4 W·m^−1·K^−1), aluminum dust may be better as its thermal conductivity is higher (237 W·m^−1·K^−1). Although aluminum dust requires a bit more care to deal with. Then again, if it's mixed with silica which is not very conductive and with a high-melting point ...

Greg

 

[nh4clo4]

I buy my JB Weld from Amazon in the "professional size". Much much cheaper than what you get at Lowes or Home depot.


https://www.amazon.com/J-B-Weld-8280-Professional-Reinforced/dp/B000ALG8LO/ref=sr_1_2?ie=UTF8&qid=1336667669&sr=8-2

 

[H_Rocket]

No.

Just got peeved at the price and did some digging to find out what makes JB Weld. Found out it is thickener and Iron dust mixed in. Gave it a try with some West epoxy and so far...so good on two Aeropack mounts. They use Calcium Carbonate as the thickener and all I had was some silica.

 

[COrocket]

I'm sick and tired of buying these piddlylittle tubes of JB Weld at $6 bucks a pop!!! Does anyone know of an alternative manufacturer who offers larger containers of a similar adhesive????? I can't believe that JB Weld would have a monopoly on high-temp epoxy.

Something I am curious of - What are building that requires a bulk amount of high temp epoxy? The only necessary application that most people find for the stuff is bonding motor retainers to the back of rockets, in which case takes only a small amount out of the small tubes. That or minimum diameter rocket fillets.

If you need a bulk amount, the amazon deal that nh3clo4 looks like a good option. I've used the Cotronics stuff, which is good, but also pricey. It probably is cheaper per ounce than JB weld, but you will end up spending quite a bit to get a quart of it.

 

[GregGleason]

No.

Just got peeved at the price and did some digging to find out what makes JB Weld. Found out it is thickener and Iron dust mixed in. Gave it a try with some West epoxy and so far...so good on two Aeropack mounts. They use Calcium Carbonate as the thickener and all I had was some silica.

Thanks Al for the data-point.

I think you are on to something.

Greg

 

[CarVac]

What about the heat resistance? There has to be something different about the epoxy formula that makes it higher-temperature than something like West with fillers.

 

[llickteig1]

I buy my JB Weld from Amazon in the "professional size". Much much cheaper than what you get at Lowes or Home depot.


https://www.amazon.com/J-B-Weld-8280-Professional-Reinforced/dp/B000ALG8LO/ref=sr_1_2?ie=UTF8&qid=1336667669&sr=8-2

If you have an Autozone near you, they have the 10oz. Professional pack as well. 5X the JBWeld for 2X the price vs. the 2oz. packs.

JB Weld is good for gluing on motor retainers, bonding fins to airframes/motor tubes, and securing nuts inside altimetere bays (not a heat thing here, but the consistency and bonding to metal ability works for my usage). Not saying it is the ony or best solution for all these applications, but it works for me.

--Lance.

 

[jeffgeraci]

You can get it for slightly less than the blister packs at McMaster Carr. They have a 5oz tube that is $16 as opposed to the $6 for the 1oz tube. About half the price. Keep in mind that JB Weld really has limited applications (IMO) in rocketry. It is actually weaker than many other epoxies.

You can also make a fair approximation using regular epoxy and a mix of colloidal silica and fine iron dust. That is essentially what JB Weld is. The iron powder gives it better heat transfer capability that way the heat passes throgh the joint rather than melt it.

I second what Greg said; aluminum powder. Aluminum powder, if I recall correctly, comes available at auto parts stores as a radiator leak plug. Has better heat transfer than iron, hmmmm. Time to experiment.

 

[MarkII]

JB Weld is good for gluing on motor retainers, bonding fins to airframes/motor tubes, and securing nuts inside altimetere bays (not a heat thing here, but the consistency and bonding to metal ability works for my usage). Not saying it is the ony or best solution for all these applications, but it works for me.

--Lance.

Thinned down with alcohol after being mixed up, then painted onto ejection baffles and areas on the interiors of booster stages that are exposed to exhaust during gap staging.

 

[edwinshap1]

It should be noted that while Mark's "mod" will not reduce it's heat capacity, or the temp it can go up to, it will lose much of its structural integrity, and will not be useful for bonding high stress components.

 

[MarkII]

It should be noted that while Mark's "mod" will not reduce it's heat capacity, or the temp it can go up to, it will lose much of its structural integrity, and will not be useful for bonding high stress components.

Eh?

I don't even understand what the first criticism is, and the second item is not anything that I ever claimed or even alluded to.

What did you think I was talking about in my post?

Why would I ever want to reduce a baffle's ability to tolerate heat (its heat capacity)?

How does applying a coating of epoxy cause a baffle (a short and simple bit of ducting) to lose its structural integrity? What level of "structural integrity" do you feel a baffle requires?

Where does "bonding high stress components" come into play, since I never mentioned using thinned-down JB Weld for any bonding?

 

[CarVac]

He is referring to your mixing alcohol with the epoxy reducing the strength of the epoxy, not the epoxy reducing the strength of the baffle.

 

[H_Rocket]

What about the heat resistance? There has to be something different about the epoxy formula that makes it higher-temperature than something like West with fillers.

The epoxy is pretty much a basic formulation. It is the iron filler that seems to increase the thermal resistance. Keep something in mind with JB Weld - people are forever saying it is better for fin roots, motor mounts, epoxying aardvarks to flagpoles, etc. It was invented to fix metal parts. It is not a real high strength epoxy.

 

[jeffgeraci]

epoxying aardvarks to flagpoles

HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!!!!!!!!:lol:

 

[McKailas Dad]

On a side note, I found that heating up JB Weld before mixing makes it much easier to work with.

I loosen or remove the caps, and place the tubes on top of an electric radiator type heater.

Max temp gets about 140 degrees.

I also use this method for thinning paint (in a can, not spray paint!) before spraying.


Old school farmer tricks work on rockets, too!

 

[GregGleason]

On a side note, I found that heating up JB Weld before mixing makes it much easier to work with.

I loosen or remove the caps, and place the tubes on top of an electric radiator type heater.

Max temp gets about 140 degrees.

I also use this method for thinning paint (in a can, not spray paint!) before spraying.


Old school farmer tricks work on rockets, too!

Along those same lines of heating, from what I have read most modern blow dryers for hair are limited to 140 F to avoid burns.

Greg

 

[stantonjtroy]

There is a comperable product we use in the aerospace industry. Loctite Hysol 9394. I think it may be available through Mc Master Carr. If not a general search will find it. Comes in a Qt can ( that's how we get it anyway). It's a 2 part but has an odd ratio, 10:1.7 by weight. I use it for all my Aeropack retainers. It's good stuff.

 

[GregGleason]

There is a comperable product we use in the aerospace industry. Loctite Hysol 9394. I think it may be available through Mc Master Carr. If not a general search will find it. Comes in a Qt can ( that's how we get it anyway). It's a 2 part but has an odd ratio, 10:1.7 by weight. I use it for all my Aeropack retainers. It's good stuff.

That's interesting stuff. According to this document, the tensile strength is actually less than Aeropoxy adhesive (Aeropoxy ES6209 at 55 MPa vs Loctite/Henkel at 46 MPa).

Greg

 

[stantonjtroy]

That's interesting stuff. According to this document, the tensile strength is actually less than Aeropoxy adhesive (Aeropoxy ES6209 at 55 MPa vs Loctite/Henkel at 46 MPa).

Greg

We use it primarily because it's MIL-SPEC. We're limited in that reguard. Mixes nice and we typically force cure it for an hour at 145dF. Otherwise it cures at ambient overnight. More of a broad spectrum material.

 

[David]

We use it primarily because it's MIL-SPEC. We're limited in that reguard. Mixes nice and we typically force cure it for an hour at 145dF. Otherwise it cures at ambient overnight. More of a broad spectrum material.

Lot's of good discussion about strength of epoxies, but do we know how strong the bond needs to be? Does anyone have an useful formula or a rule of thumb for the necessary bond strength of centering rings-to-airframe or to-MMT? Otherwise, how do we know 55 Mpa or whatever is enough (except empirically)?

 

[CarVac]

It always depends on the rocket design. If you have 10 centering rings, then the MMT-centering ring bond only needs to be 1/10 as strong. Different motor retainers have different contact areas: Giant Leap Slimlines us a full half of an inch, while PML HAMRs use only 3/8 of an inch, so a HAMR demands a stronger epoxy than Slimlines do.

Determining exactly how much, though, is a different story. It's difficult to determine the force that the ejection charge exerts on the motor retainers, and even harder to calculate the force caused by parachutes jerking on the booster. Also, motor mounts can be stressed by landing on the motor retainer, which might even be harder than some motors' thrust, but that would be extremely hard to determine.

 

[GregGleason]

Lot's of good discussion about strength of epoxies, but do we know how strong the bond needs to be? Does anyone have an useful formula or a rule of thumb for the necessary bond strength of centering rings-to-airframe or to-MMT? Otherwise, how do we know 55 Mpa or whatever is enough (except empirically)?

I think at the hobby level, it is more trial-and-error than a truly engineered rocket. For that reason, experience and gathering whatever information on what works (and doesn't work).

However, for most of what we do, epoxy is a good and reliable way to achieve a good bond between rocket parts, especially dissimilar parts.

Add to what has been said, the performance of epoxy is affected by:

• How well it is stored
• How well it is mixed
• How well the area has been prepped to receive the adhesive (roughed up to give it "tooth", free of oils and contaminates)
• The amount placed onto the work area (not too little or too much)
• The amount and kind of amendments added (milled fiber, chopped carbon, etc.)
• If and how a post-cure cycle was applied
• Time at or beyond the glass transition stage (such a thermal soaks from motor burn)

Greg

 

[GregGleason]

We use it primarily because it's MIL-SPEC. We're limited in that reguard. Mixes nice and we typically force cure it for an hour at 145dF. Otherwise it cures at ambient overnight. More of a broad spectrum material.

Sounds like it is good stuff. I figure if it's good enough to use in the "professional aerospace" arena then it's certainly good enough for us hobby folks!

Greg

 

[David]

Yes, but let's say we have a particular design, how would you determine the strength of bond needed?

 

[GregGleason]

Yes, but let's say we have a particular design, how would you determine the strength of bond needed?

That is the point where engineering comes in. As I understand it, the forces placed upon rocket components are shear, compression, tension, and perhaps (once in a while) torsion. Those loads are determined by the impulse of the motor, the aerodynamic loads, and whatever shock is placed upon the recovery system when it is deployed. Perhaps an engineer can give a more complete answer, and break it down in layman's terms. You can look at a rocket as a bunch of parts, but it always flies (or fails) as a system. That's where the answer to the question gets a bit complicated.

That said, there maybe "paper napkin" calculations that are out there that may be useful. I just haven't run across any.

Greg

 

[David]

That is the point where engineering comes in. As I understand it, the forces placed upon rocket components are shear, compression, tension, and perhaps (once in a while) torsion. Those loads are determined by the impulse of the motor, the aerodynamic loads, and whatever shock is placed upon the recovery system when it is deployed. Perhaps an engineer can give a more complete answer, and break it down in layman's terms. You can look at a rocket as a bunch of parts, but it always flies (or fails) as a system. That's where the answer to the question gets a bit complicated.

That said, there maybe "paper napkin" calculations that are out there that may be useful. I just haven't run across any.

Greg

We do need an engineer to weigh in. Until then, maybe we can muddle into it a bit, qualitatively. Let's imagine a simple system with two CRs, foreword and aft, holding a MMT within an airframe. Let's focus first on the climb phase, and leave recovery stresses aside for now.

The motor develops thrust and begins to move the MMT upward. The first stress point is the CR-MMT joint. The resistance to moving is the inertia of the CR and airframe; main factor is mass. So, the thrust is moving the MMT but the CR is resisting. The joint connecting the two is stressed as the MMT tries to move upward, with or without the CR. If that joint holds, then the second stress point is the CR-AF joint. Inertia is from the mass of the airframe.

Let's assume the CR material is strong enough and just focus on the joints.

Seems like the three major factors determining the strength of the MMT-CR and CR-AF joints are 1) how tight the physical joint is or the "squeeze" of the ring on the tube, 2) the "grip" of adhesive to the CR and MMT/AF materials (did you scuff enough?), 3) the strength of adhesive.

I'll propose a hypothesis: the strength of adhesive is the least important of the factors at play. If true, then the Mpa of West System verses JB Weld matters much less than a tight CR and proper surface prep.

What additions or corrections does this model need? Then, who can supply the math? Or better yet, the actual testing?