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General: EWI jointing/fixing

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      CommentAuthorfostertom
    • CommentTimeSep 20th 2012 edited
     
    Posted By: Phil.Chaddah-DukeWhat kind of glue is being used In these videos
    Which video? Talking about the back joint, or the edge joints?
  2.  
    I was talking about the back joint compound they use, they are troweling on white/grey gunk but then watching the Sto video, I see they use PU foam adhesive which seems pretty quick method, either seem to give some working time before going off. Anyone any preferences who has actually used these products? None of the video use a edge joint adhesive do they, just the foam in event of a gap?
  3.  
    Posted By: fostertomAFAIK any gap even fag paper thickness is a bypass heat-leak route, with quite strong convection forces causing constant (if slow) circulation of air from wall to surface and back.


    On the basis that an air filled glazing unit performs better with slightly larger spacings, why is a 'cigarette paper' gap between the EPS sheets for EWI so bad?

    What are the pros and cons of rockwool compared to EPS for EWI? Are the edges easier to fit tightly?
    •  
      CommentAuthorfostertom
    • CommentTimeSep 21st 2012
     
    The fag paper dimension between EPS sheets measures width of the route of the heat flow, from hot to cold - whereas an air gap in DG units measures the length of the heat flow.
    • CommentAuthoran02ew
    • CommentTimeSep 22nd 2012
     
    Posted By: spoonandforkWhat are the pros and cons of rockwool compared to EPS for EWI? Are the edges easier to fit tightly?


    1 con and its a deal breaker for me, the stuff is nasty to work just handling the stuff creates a day of painfull itching let alone cutting sticking screwing and fixing. rrruuughh im itching just thinking about it.:devil:

    Also i have never seen it thicker that about 100mm i think it would get heavy even in 1200x600 size in anything thicker?

    Thats 1 vote for EPS. any other votes?
    • CommentAuthornikhoward
    • CommentTimeSep 26th 2012
     
    love the hot knife

    and as i already have a framing bench in workshop, a 12v charger, plenty of off cuts, should cost me £0 to make

    what is the best wire to 'recycle' for the wire?
    • CommentAuthoran02ew
    • CommentTimeSep 26th 2012
     
    Posted By: nikhowardwhat is the best wire to 'recycle' for the wire?


    Its a bit trail and error, depending on your charger amps, for my 10amp i need 22swg. but whatever size you try it needs to be Ni-chrome wire, its not that expensive try amazoni got 1M lenghts of about 4/5 different guages.
    • CommentAuthorTimSmall
    • CommentTimeOct 2nd 2012
     
    Doesn't need to be trial and error...

    an02ew is sinking approx 10 amps at 12 volts into his 400mm length of wire.

    10 amps at 12 volts = 120 watts (watts = volts x amps).

    So, he finds 30 watts per 100mm to be about right.


    So for a car battery charger (nominally for a 12v battery), the rating in amps will determine what length of wire you can drive at 30 watts per 100mm. e.g. for a 4 amp charger, power is 4 * 12 = 48 watts, so you can do 100mm x (48/30) = 160mm

    OK, so now you've got the approx wire length (I should think you can vary this a bit tho - a slightly longer wire will just give you a slightly slower cut).


    ... now to work out which thickness of wire you need.

    Going back to Andrew's 10 amp set-up - in order for the current to go to 10 amps at 12 volts (ish), he needs the wire resistance to be about 1.2 ohms

    voltage drop (across a resistor) = current (in amps) x resistance in ohms
    12 = 10 * resistance

    so resistance = 12 / 10 = 1.2 ohms

    so for his 400mm length of wire, the resistance per meter needs to be 1.2 * (1000/400) = 3 ohms per metre.

    Since a car battery charger is a constant-current (or rather current-limiting) device, you can get away with something a little lower, and sure enough, if you look up 22swg ni-chrome wire (0.7mm approx) , it's spec is 2.7 ohms per metre.


    If you were going for the 4 amp charger instead, you'd then need 12 / 4 = 3 ohms of resistance in your 160mm wire, so you'd want something like 3 * (1000 / 160) = 18.7 ohms per metre nichrome wire. So .28mm wire would do it.

    If on the other hand you think that .28mm wire sounds a bit skinny+fragile, then you might need to invest in a beefier charger!

    If on the other hand, your 4 amp charger has a setting for a 6 volt scooter batteries as well as for 12 volt ones (mine does), then you can use thicker wire to get the same result...

    So on the 6 v setting, you want 6/4 = 1.5 ohms. ... so wire which is 1.5 x (1000/160) = 9.4 ohms per metre

    .375mm looks like it'd do the trick at 9.7 ohms per metre...
    • CommentAuthorEd Davies
    • CommentTimeOct 2nd 2012
     
    Posted By: TimSmall10 amps at 12 volts = 120 watts (watts = volts x amps).

    an02ew said he had a 10 A, 12 V charger but he didn't say it was operating at 12 V and 10 A. If the resistance of his wire was greater than 1.2 ohm it could be operating at less than 10 A and if less then at a lower voltage (than 14.8 or whatever, actually). Be worth checking before taking the calculations too seriously.
    • CommentAuthoran02ew
    • CommentTimeOct 2nd 2012
     
    i use a 12v 10 amp batery charger on full power, but i am currently cutting 225mm platinum EPS. i have used 20swg.22swg,and 28swg all work but i found 22 the best for my set up. however i do not use an old car battery, i use a charger.
    • CommentAuthornikhoward
    • CommentTimeOct 2nd 2012
     
    Posted By: TimSmallDoesn't need to be trial and error...

    an02ew is sinking approx 10 amps at 12 volts into his 400mm length of wire.

    10 amps at 12 volts = 120 watts (watts = volts x amps).

    So, he finds 30 watts per 100mm to be about right.


    So for a car battery charger (nominally for a 12v battery), the rating in amps will determine what length of wire you can drive at 30 watts per 100mm. e.g. for a 4 amp charger, power is 4 * 12 = 48 watts, so you can do 100mm x (48/30) = 160mm

    OK, so now you've got the approx wire length (I should think you can vary this a bit tho - a slightly longer wire will just give you a slightly slower cut).


    ... now to work out which thickness of wire you need.

    Going back to Andrew's 10 amp set-up - in order for the current to go to 10 amps at 12 volts (ish), he needs the wire resistance to be about 1.2 ohms

    voltage drop (across a resistor) = current (in amps) x resistance in ohms
    12 = 10 * resistance

    so resistance = 12 / 10 = 1.2 ohms

    so for his 400mm length of wire, the resistance per meter needs to be 1.2 * (1000/400) = 3 ohms per metre.

    Since a car battery charger is a constant-current (or rather current-limiting) device, you can get away with something a little lower, and sure enough, if you look up 22swg ni-chrome wire (0.7mm approx) , it's spec is 2.7 ohms per metre.


    If you were going for the 4 amp charger instead, you'd then need 12 / 4 = 3 ohms of resistance in your 160mm wire, so you'd want something like 3 * (1000 / 160) = 18.7 ohms per metre nichrome wire. So .28mm wire would do it.

    If on the other hand you think that .28mm wire sounds a bit skinny+fragile, then you might need to invest in a beefier charger!

    If on the other hand, your 4 amp charger has a setting for a 6 volt scooter batteries as well as for 12 volt ones (mine does), then you can use thicker wire to get the same result...

    So on the 6 v setting, you want 6/4 = 1.5 ohms. ... so wire which is 1.5 x (1000/160) = 9.4 ohms per metre

    .375mm looks like it'd do the trick at 9.7 ohms per metre...


    Hi Tim, thanks for that, good work. Are you a physics teacher? You will be giving steamy a run for his science money.
    • CommentAuthorTimSmall
    • CommentTimeOct 3rd 2012
     
    Thanks for the original design Andrew - my site carpenter and I knocked one up yesterday - seems to work very well (cutting 100mm thick EPS100). No polystyrene blizzard to annoy the neighbours!

    I didn't have a 10A battery charger available, so I used a power supply from a retired PC instead (always seem to have loads of those around in my line of business), and connected the wire across the 12v line (yellow) and 0v (black).

    BTW, it uses 8 amps or so for a 450mm odd length of 22SWG nichrome wire when it's up to operating temperature. I used some ceramic terminal blocks (40p from Toolstation I think - your local electrical suppliers should do some), and some old 4mm mains wire to complete the circuit.

    To add another data point regarding power, that'll be 8 * 12 / 4.5 = 21 watts per 100mm.

    We found getting the tension in the wire a bit tricky (snapped it once) due to the expansion on heating, so we switched to a counter-weight tensioner instead (using coach screws as the "pulleys"). About 1 brick seems about right, but I've only done one test cut since changing it over, so we might need to adjust that a bit.

    Sorry for the poor photo quality - only have my camera phone with me at the moment (good phone, rubbish camera).

    https://plus.google.com/photos/112859335830186234298/albums/5795010856970048913?authkey=CN3ikcD-rrjhBg

    Might be better to hang the brick underneath, but there was a puddle of water under the table this morning, so I added it to the top connection instead!

    Tim.
    • CommentAuthorTimSmall
    • CommentTimeOct 3rd 2012 edited
     
    Posted By: nikhoward
    Hi Tim, thanks for that, good work. Are you a physics teacher? You will be giving steamy a run for his science money.


    Thanks. Not a physics teacher, but studied physics as far as A-level about 18 years ago... I'm a computer programmer, and do a bit of electronics and electrical work in my job and elsewhere. I've also done some IT work at a physics research establishment, and for a company which employed physicists too.

    Those calcs should get you to about the right place, and since a battery charger limits the current it puts out by varying the voltage it puts out, you shouldn't end up blowing its fuse.

    If you go for the PC power supply option instead (you could also use some 12v halogen downlighter "transformers" too I suppose), then you need to be a little more careful about not exceeding the rated max supply current (e.g. by making the wire a little longer if necessary).
    • CommentAuthoran02ew
    • CommentTimeOct 3rd 2012
     
    Hi Tim

    Great work,i love the counter weight design, as you say getting the tension right is the hardest part.

    Maybe you could help with my next problem? i am trying to think of a way to profile cut the EPS, so holding the wire in a simple arc to shape the corners of the eps around my window revels? any ideas?
  15.  
    an02ew, probably a daft idea but could you use a thin strip of tempered steel, similar to a saw blade or are the currents/voltages required too great to create a hot surface.
    • CommentAuthoran02ew
    • CommentTimeOct 4th 2012
     
    Posted By: Cav8andrewprobably a daft idea but could you use a thin strip of tempered steel, similar to a saw blade or are the currents/voltages required too great to create a hot surface.


    That was my idea too, but my electriction put his tester gadget thing across a spare blade and shook his head like a doctor. i think thats a no, too much resistance for the 10 amp charger?
    • CommentAuthorEd Davies
    • CommentTimeOct 4th 2012
     
    Posted By: an02ewi think thats a no, too much resistance for the 10 amp charger?

    I'd guess the opposite - too little resistance. The charger will limit at 10 amps but at a very low voltage (Ohm's law: V = IR) so not a lot of power will be transferred.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 4th 2012
     
    I visited Andy (an02ew) yesterday, saw his cutting table and the EPS-clad (before rendering/cladding) building (his own house) - all v impressive and a practical evolution of our prev building contracts together. Lots for us all to learn here.
    • CommentAuthordjh
    • CommentTimeOct 4th 2012
     
    Posted By: an02ewMaybe you could help with my next problem? i am trying to think of a way to profile cut the EPS, so holding the wire in a simple arc to shape the corners of the eps around my window revels? any ideas?

    Perhaps use several passes with your straight wire to make an approximate curve, then round it off with the render?

    Or use a much longer wire parallel to the surface to cut the whole edge at once. But you'd need to go much slower or use a lot more power.

    If you have access to James Bond's quartermaster, a CNC laser cutter could probably do the job.
  20.  
    Posted By: djh
    Posted By: an02ewMaybe you could help with my next problem? i am trying to think of a way to profile cut the EPS, so holding the wire in a simple arc to shape the corners of the eps around my window revels? any ideas?

    Perhaps use several passes with your straight wire to make an approximate curve, then round it off with the render?

    Or use a much longer wire parallel to the surface to cut the whole edge at once. But you'd need to go much slower or use a lot more power.

    If you have access to James Bond's quartermaster, a CNC laser cutter could probably do the job.


    Maybe go mechanical for this bit? ...
    I looked into the wire option for our corners but reverted to type for ours.
    (Pic shows the cutting plan)
    Our blade was two of this kind:
    http://www.wickes.co.uk/compound-mitre-saw-blade-60cm/invt/186774/
    soldered together to make the blade up to about 1m and then screwed to a 140cm-ish length of 2 by 2.
    The 60/15 blocks were clamped into the rig shown in second pic.
    After a couple of cuts with an old shoot-tooth panel saw the action was side-to-side shaving.
    Not that much "dust" in the end ... pretty much all falling in a neat pile, but this was EPS Platinum, so ....
      corner block cutting diagram.jpg
  21.  
    ...
      CIMG1892 50%.jpg
    • CommentAuthorTimSmall
    • CommentTimeOct 7th 2012
     
    I'd go for a scheme using a couple of ply "end-guides" like Mike's photo, but using a hot wire on a large hand-held "bow" to do the cutting (I've seen a YouTube video using a very similar set-up to cut a model aircraft wing out of XPS - can't find it at the moment tho'). If you need to increase the wire length (I'm assuming you will) then you'll probably need to move to a thicker wire that you still draw 10 amps out of the charger (see the "ohms per metre" figure for the various guages of nichrome wire on the suppliers' web sites - and the calcs above).

    You'll end up with a lower power-per-mm (so a slower cut) if you stick with the same battery charger power source, but that probably doesn't matter too much...

    HTH,

    Tim.
    • CommentAuthoran02ew
    • CommentTimeOct 7th 2012
     
    i was thinking more about trying to suspend/hold the wire in a set curve to enable to feed different lenghts of EPS, i have racked my brain, but just cant seem come up with a solution
  24.  
    an02ew, when I wer young I used what I knew as piano wire to build slot car chassis. This would take a curvature really well and was incredibly hard to cut, I assume it was a high tempered steel. I imagine it would take a charge and in the process heat up. Could you mount it on some for of guided trolley that could be fed across the board. Having said that I do like Mike's solution, could you not just make it wide enough to take the widest permutation or is it more the speed of feeding boards through.
    • CommentAuthorEd Davies
    • CommentTimeOct 7th 2012
     
    If you want to use a longer length of the same nichrome wire then the best thing to do is keep the current the same and use a higher voltage. Perhaps use two of the chargers in series (if their outputs are floating relative the mains earth - I assume they will be but worth checking) or put a battery which the charger has just charged in series with it.

    My first thought on using steel wire was "nah - the resistivity is totally different" but actually it's not that far off:

    http://en.wikipedia.org/wiki/Nichrome

    says nichrome is 1 to 1.5 × 10⁻⁶ Ω·m whereas:

    http://hypertextbook.com/facts/2006/UmranUgur.shtml

    says stainless is around 0.7 × 10⁻⁶ Ω·m.

    Both have a lot of chromium in them, after all.
    • CommentAuthordjh
    • CommentTimeOct 8th 2012
     
    I just came across an article:

    "Slicing Polystyrene Produces Problematic Particles
    Flame Retardants: When cut with hot wires, polystyrene foam releases nanoparticles bearing brominated flame retardants, possibly exposing workers to the compounds"

    "The team estimates that if a worker breathed in about two-thirds of the particles released during an hour of cutting, that person would inhale 13 µg of HBCD. On average, a person receives exposure to that much HBCD–through furniture foam, household dust, and food packaging—in about one to three months"

    http://cen.acs.org/articles/90/web/2012/10/Slicing-Polystyrene-Produces-Problematic-Particles.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+cen_latestnews+%28Chemical+%26+Engineering+News%3A+Latest+News%29

    Nothing's ever simple, is it? Best to do the job outside and stay upwind, I guess.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 8th 2012
     
    Posted By: djhif a worker breathed in about two-thirds of the particles released
    To capture that %age of the particles he'd need a vacuum cleaner attached to his nose.
    • CommentAuthordjh
    • CommentTimeOct 8th 2012 edited
     
    Posted By: fostertom
    Posted By: djhif a worker breathed in about two-thirds of the particles released
    To capture that %age of the particles he'd need a vacuum cleaner attached to his nose.

    Yes, I thought the way it is stated was a bit suspect. But on the other hand, somebody might do an awful lot more than one hour's cutting in a month or three. If s/he did ten hours cutting, they'd only need to breathe 7%. If they did it full time, only 0.03%. Then they'd be doubling their normal dose.
    • CommentAuthorMikeRumney
    • CommentTimeOct 13th 2012
     
    Posted By: an02ewi was thinking more about trying to suspend/hold the wire in a set curve to enable to feed different lenghts of EPS, i have racked my brain, but just cant seem come up with a solution


    Which dimension do you mean by "length"?
    When the block is on the wall I imagine you mean the long horizontal?
    (as opposed to the short horizontal "thickness")
    If that's the case then we cut to different lengths by simply starting in different places when clamping the block between the end guides.
    • CommentAuthormark_s
    • CommentTimeNov 4th 2012 edited
     
    I'd look at setting up a number of wires at different angles. Effectively have a overhang tunnel.

    Like the kids game thing - can;t remember what its called though - stringart?

    Like this

    http://www.ratemydrawings.com/tutorials/drawing/109-Straight_lines_make_a_curve.html

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