Araldite repair failing in dishwasher

[Lobster]

I mended a broken Magimix foodprocessor bowl lid with 2-part Araldite
epoxy adhesive a few months ago (I think it was Araldite Rapid?); all
has been well until yesterday when I found it in bits again in the
dishwasher - the glue was quite flexible and the remnants pulled off
quite easily. (I assume that since the repaired bowl must have been
through the dishwasher many times sucessfully, the glue must goes rigid
again with time.)

Anyway, was quite surprised, as I've put Araldited repairs through the
dishwasher countless times over the years with no problems; but I assume
it's not an appropriate adhesive to use here.

Any suggestions for a better repair or glue?

The item concerned looks a bit like this:
<http://www.amazon.co.uk/Lid-for-Magimix-Food-Processors/dp/B004EEKB6Q>
and it's the retaining lug at bottom right which has broken off.

Realistically it needs to be dishwasher-proof; and it has to be able to
sustain a fair amount of force.

Thanks
David

[Andy Dingley]

On Thursday, 23 August 2012 11:26:19 UTC+1, Lobster wrote:
> I mended a broken Magimix foodprocessor bowl lid with 2-part Araldite
> epoxy adhesive a few months ago (I think it was Araldite Rapid?); all

Araldite isn't great - other epoxies like West System are much better, as they aren't pre-thickened, so you can mix them up to exactly what you need.

If it's Rapid though, this is well known for not standing up to even boiling water temperatures.

[Jethro_uk]

I bought some epoxy to try and fix a leaky rad (so far it seems to have
done the trick). It was Plumbers Mait Quick leak repair putty. It's
supposed to be ok at 150 C ....

[The Natural Philosopher]

very bad glue to use for styrene.
If there is no gap filling try plastic model plastic cement instead.

I think they also do a sort of body putty for plastic models That could
be used to fill gaps

Epoxies typically soften when they get hot and dont in any case adhere
very well to styrene. The key to a heatproof epoxy is to stove it
hotter then the part will ever get, so I repair china by putting it in
the oven while the epoxy sets. THAT then goes brittle hard and clear.

Half the problem is getting exact 50:50 mixes and mixing them totally -
heating which renders the epoxy liquid helps mix things much more
thoroughly, which is probably why it sets harder.


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

[The Natural Philosopher]

it will if you heat it to about 140C as it sets.

[The Natural Philosopher]

car body filler is the best cheapest option.

Because its a catalysed reaction, you don't get such severe problems of
inadequate mixing that you do with epoxies, so it always sets rock hard.
It probably does stick to styrene better as well.

[djornsk]

One method which I have had some success with is welding with a
soldering iron which involves stiring up the plastic from both sections
in the region of the break, and even transplanting plastic from another
part of the item for reinforcement. Though I have never tried it one
could perhaps embed wire in the plastic, but not necessarily in this
particular repair.

This technique I have found particularly useful in repairing trims in
cars where usually there is a side which is not seen with plenty of
plastic which can be moved around at the same time achieving a near
perfect finish on the visible side.

The motor trade was and no doubt still is a great place to learn how to
bodge - ISTR in my first week seeing a Hillman Imp cylinder block
repaired with plastic padding by the service manager. It never ceases to
amaze me what people can get away with by what I suppose might be called
thinking outside the box.

j

[dennis@home]

"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:k157su$8rv$2...@news.albasani.net...

> Because its a catalysed reaction, you don't get such severe problems of
> inadequate mixing that you do with epoxies, so it always sets rock hard.
> It probably does stick to styrene better as well.

Epoxy is catalysed.

[Tim+]

Actually, I suspect that neither is "catalysed" as a true catalyst is not
consumed by the process. In car body filler a peroxide supplies oxygen
that speeds up the hardening process and in epoxy resins the components
chemically combine.

Tim

[The Natural Philosopher]

Er no,. it isn't.

"Epoxy, also known as polyepoxide, is a thermosetting polymer formed
from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has
a wide range of applications, including fiber-reinforced plastic
materials and general purpose adhesives."

(wiki)


In fact polyester resins aren't catalysed either,

"The use of unsaturated polyesters and additives such as styrene lowers
the viscosity of the resin. The initially liquid resin is converted to a
solid by cross-linking chains. This is done by creating free radicals at
unsaturated bonds, which propagate in a chain reaction to other
unsaturated bonds in adjacent molecules, linking them in the process.
The initial free radicals are induced by adding a compound that easily
decomposes into free radicals. This compound is usually and incorrectly
known as the catalyst[citation needed] . Substances used are generally
organic peroxides such as benzoyl peroxide or methyl ethyl ketone peroxide."

(wiki)

But the action is quite different with polyesters. a chain reaction is
propagated through the mixture by addition of a small quantity of the so
called catalyst or hardener. Not by direct chemical reaction between two
(more or less equal*) chemical components.

This is worth repeating in full (wiki)

"While it is common to associate polyester resins and epoxy resins,
their properties are sufficiently different that they are properly
treated as distinct materials. Polyester resins are typically low
strength unless used with a reinforcing material like glass fibre, are
relatively brittle unless reinforced, and have low adhesion. Epoxies, by
contrast, are inherently strong, somewhat flexible and have excellent
adhesion. However, polyester resins are much cheaper.

Epoxy resins typically require a precise mix of two components which
form a third chemical. Depending on the properties required, the ratio
may be anything from 1:1 or over 10:1, but in every case *they must be
mixed exactly*. The final product is then a precise thermo-setting
plastic. Until they are mixed the two elements are relatively inert,
although the 'hardeners' tend to be more chemically active and should be
protected from the atmosphere and moisture. The rate of the reaction can
be changed by using different hardeners, which may change the nature of
the final product, or by controlling the temperature.

By contrast, polyester resins are usually made available in *a
'promoted' form, such that the progress of previously-mixed resins from
liquid to solid is already underway, albeit very slowly*. The only
variable available to the user is to change the rate of this process
using a catalyst, often Methyl-Ethyl-Ketone-Peroxide (MEKP), which is
very toxic. The presence of the catalyst in the final product actually
detracts from the desirable properties, so that small amounts of
catalyst are preferable, so long as the hardening proceeds at an
acceptable pace. *The rate of cure of polyesters can therefore be
controlled by the amount and type of catalyst as well as by the
temperature.*

As adhesives, epoxies bond in three ways: a) Mechanically, because the
bonding surfaces are roughened; b) By proximity, because the cured
resins are physically so close to the bonding surfaces that they are
hard to separate; c) Ionically, because the epoxy resins form ionic
bonds at an atomic level with the bonding surfaces. This last is
substantially the strongest of the three. By contrast, polyester resins
can only bond using the first two of these, which greatly reduces their
utility as adhesives and in marine repair."


There was a lot of discussion on epoxies on a model aeroplane site some
years back. Various experiments were done with mis-mixing epoxies and
testing the results. The conclusions were that the commonest mistake was
inadequate mixing of the two parts, and the second commonest mistake was
not having the correct ratio, Both produced soft low strength bonds.

Heating seems to actually promote mixing, as well as a faster set time.
If you have time, mix some 24 hour araldite and then play a hair dryer
or heat gun over it till it goes from milky to clear. It will set in a
less than 10 minutes and set rock hard.

Interestingly enough, the fraternity there also tested wood glues. Best
strength was bog standard cheap PVA white glue, worse was foaming
polyurethane. 'Yellow' or aliphatic glue was faster to set than white,
but less strong and more brittle. And heavier.





* there is in fact no reason for them to be more or less equal: But
domestic products are made that way because dumb shits can just about
get equal quantities out of two tubes

[The Natural Philosopher]

+1

[Andy Dingley]

On Thursday, 23 August 2012 13:41:42 UTC+1, dennis@home wrote:
> Epoxy is catalysed.

Nope. It's a two part mix for a reaction, but that's not the same as being catalysed, and not the same as curing styrene.

[Andy Dingley]

On Thursday, 23 August 2012 13:35:41 UTC+1, djornsk wrote:

> One method which I have had some success with is welding with a
> soldering iron which involves stiring up the plastic from both sections
> in the region of the break, and even transplanting plastic from another
> part of the item for reinforcement. Though I have never tried it one
> could perhaps embed wire in the plastic, but not necessarily in this
> particular repair.

Tried that loads of times as a kid, never got it to work for more than 5 minutes.

However borrowing a trick from car bodyshops, and how they repair bumpers, then hot-air welding of plastics can work pretty well. Not using a soldering _iron_, but rather a hot air gun for surface mount soldering. This seems to work pretty well on polypropylene and the other unglueable thermoplastics. Use an offcut of the same plastic as filler rod.

[Lobster]

On 23/08/2012 13:05, The Natural Philosopher wrote:
> Lobster wrote:
>> I mended a broken Magimix foodprocessor bowl lid with 2-part Araldite
>> epoxy adhesive a few months ago (I think it was Araldite Rapid?); all
>> has been well until yesterday when I found it in bits again in the
>> dishwasher - the glue was quite flexible and the remnants pulled off
>> quite easily. (I assume that since the repaired bowl must have been
>> through the dishwasher many times sucessfully, the glue must goes
>> rigid again with time.)
>>
>> Anyway, was quite surprised, as I've put Araldited repairs through the
>> dishwasher countless times over the years with no problems; but I
>> assume it's not an appropriate adhesive to use here.
>>
>> Any suggestions for a better repair or glue?
>>
>> The item concerned looks a bit like this:
>> <http://www.amazon.co.uk/Lid-for-Magimix-Food-Processors/dp/B004EEKB6Q> and
>> it's the retaining lug at bottom right which has broken off.
>>
>> Realistically it needs to be dishwasher-proof; and it has to be able
>> to sustain a fair amount of force.

>

> very bad glue to use for styrene.
> If there is no gap filling try plastic model plastic cement instead.

No gap filling needed; although there is scope for piling gunk on over
the repair to reinforce it. Is model cement really likely to provide a
strong enough repair? Or is a different (ie non-Araldite-Rapid) epoxy
likely to be better?

Thanks
David

[The Natural Philosopher]

if its styrene - and lots of that crappo kitchen gear is - then styrene
cement should make it as strong as new.

http://www.anticsonline.co.uk/1213_1.html

you can either use a pure solvent to weld it or a solvent plus styrene,
which is a bit gap filling.

If you have an 'airfix' style model shop nearby get a bit of each and
see what works.



> Thanks
> David

[Lobster]

Hmm... same stuff as for solvent-welding waste pipes, which I have
sitting on my shelf?

David

[Andrew Gabriel]

In article <e0b8dd33-0b37-4105...@googlegroups.com>,

I've done it using a gas burner to melt the two surfaces and push them
together to fuse.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]