home mating apparatus. uniform temperature

[RiccDS]

Hello, they laugh here. I've been stuck on something for weeks. I am attempting to make pairs of polypropylene sheets (1mm and 0.5mm thick). I am using a home oven(I know I know) from the large size. in practice we buy these sheets between two 1.5cm aluminum plates. to give pressure use four tightened screws with dynamometer key and a 5mm aluminum plate(I will replace soon with steel) making as a spring. The pressure seems to be fine. the problem is that from the observed result I think there is a seemingly uneven temperature field so that in the center of the coupling we observe characteristic undulations and without shadow of doubt ugly. I think it is very probable that the center of the plate is exceeded the temperature of 165-170°c and in practice the slag pp. What I don't want. I attach a photo of the oven (ventilated, upper and lower heating); the plates for now rest almost on the 3 lower resistances, on those steel sleighs specially built.
Do you have any idea how I could uniform the temperature in the plates without raising them? I think this disuniformity is due to the closeness to resistors, which go to much higher temperature than that set. I thought I'd use a copper plate to put under but I don't know if that's enough.

Thank you.

 

[RiccDS]

or even a barrier to irradiation?

 

[TECNOMODEL]

I guess you have no way to put any resistance on the plates, right?

can you put thermocouples on the plates and check the oven through these?

 

[RiccDS]

we say that I have thought about more resistances placed on the plates, but too late I thought about it, now I have taken this oven specially and having tight times I would like to solve without overturning the approach to which I arrived.
as from photo I have 4 thermocouples available with which to see the temperature where I like (also wanting to the interface between the pp sheets encapsulating them). I have verified that at least on the side of the ruined pp zone the temperature is higher than other areas not ruined. from which my idea that t is not uniform, and the pp in a couple of degrees, about from 165-170 °c has a collapse of viscosity. check the oven through the thermocouples, I wouldn't know I should open it and see a little. What would you check? we say that to try I can also keep under eye the monitor temperatures and change through the oven knobs (general temperature, ventilation, activation of upper and lower resistances).

 

[meccanicamg]

I think you'll have the problem if you don't get a couple of positions in the oven. the ventilated is used to uniform but there must be space to wrap everything at constant temperature.

 

[rinato]

hello riccds, excuse if I ask a trivial question, but: the temperature of the oven is set at 165-170°c or at 210-220°c as you owe on the reader of the thermocouples?
because I would also try to keep it as close as possible to the limit temperature of the pp, and to better exploit the ventilation of the oven, as they have already suggested.
almost certainly the times of the "thermal treatment" stretch, but to this you will think after.

that I didn't understand one thing: do you want to "shade" the pp sheets without foundation? Can you? It seems to me a contradiction in terms, but of organic chemistry or I know very little.
does not develop strange "odoris"?

Then I say another (sweet) just: use a thermal camera and look literally, even through the glass, how does the piece warm, would it be likely?

Good luck,
Reborn.

 

[RiccDS]

Mechanicalmg, that's something that worries me. It is true that I can climb a little more but I'm afraid that I will continue to collide with this problem since the apparatus is designed to mate dozens of sheets. therefore the height will become much and undoubtedly remains not much space for the recirculation. I hope in the conductivity of aluminum to uniform the temperatures. I think that the gradient of t in x and y is mainly due to the fact that resistors (presumably nicr) should have a high radiative emissivity that obviously close to the lower plate heats it strongly, especially in the back where the profile of steel (which bases on the sleigh) prevents recirculation and makes from sponge for heat. to overcome this I have interposed, between the resistors and the lower plate and leaving intercapedins, a thin glossy aluminum foil (low emissivity) which should be barrier to thermal radiation. I am sending a test now and between the front and the back I mix a difference of t of about 1-2 degrees, which does not seem bad to me. We'll see if it goes well.

Hello reborn, on the readers of the thermocouples in that photo we actually read an almost ambient temperature, 21-22, because the test had just left. the temperature of the oven I keep it around 160 even if everything is relative: the resistors warm much more, so much so that I avoid measuring them with the thermocouple or I shake the sheath. In short, in the oven it is not that there is this uniformity of temperatures. I confirm that the times are very long unfortunately, on the hour and a half with these piastrones.
the pp I bring it to softening, not to melt. around 165°, from solid that it was, a reduction of viscosity occurs, it softens, probably the mechanisms of diffusion are activated. put the pressure on us and the job is done. It's something I did and saw doing. the sheets remain welded perfectly and if you do a section you do not notice any interdiffusion. if you further increase the t the pp has a collapse of viscosity and liquefa.
As far as the thermal camera is concerned (other than the price ), probably the upper plate I use as a spring would be a truthful reading.

 

[RiccDS]

ah acre odors yes, only if exaggerated with the temperature. but at 160-165 it is quiet.

 

[meccanicamg]

I use the oven to make the pizza....and if I put the pan leaning on the black plane down where there are the resistors I would burn everything. on the day-to-day instruction manual there are explained some reasons for the positions of the oven shelves and the use of the ventilated.
If you used the static oven you should raise the temperature to get the same result and also you would not have a homogeneous heat.

at this point, since you do not have many degrees of freedom you could wrap your play in aluminum paper trying to preserve it from the non-homogeneous thermal gradients as you do with the chicken in order not to cause it to dry up and eventually drop of temperature of some degree increasing the time of stay.

 

[exxon]

I agree with mechanicalmg on the use of aluminum sheet. prevents heating by irradiation and leaves only that by convection, which should be homogeneous due to ventilation. aluminum should be ripped and not smooth, leaving a minimum of space to the content.

I have doubts about the final result: These couplings are always done by compressing the laminates with rollers that provide progressive compression. It's hard for a flat compression to give appreciable results.

 

[RiccDS]

Mechanicalmg, you sure what happens to a chicken over the resistances is better not to try it. I was just wondering if there was a way to shield it from the resistances themselves. Informing me a little bit of the solution you said you should go well also for this species if the leaf does not go in contact with the acrocchio. I still do some tests and see. It is interesting that this thing should be uniform and protect against the irradiation of resistance.

exxon, should the aluminum foil say be increspato of superficial or rubbish finish? around I find that the smooth surface finish lowers radiative emissivity, this should prevent the sheet itself from ejecting on the big plate.
with thermal calandre I have seen making couplings between much more fine materials, film basically, is a standard thing. but on so many so no one told me to do it. on the floor I found only one producer in Italy who did it with a press, and some good coupling came, but other research costs on the pp in particular would probably rise beyond our possibilities. if you know someone who can do this is well accepted an indication.

Thank you.

 

[exxon]

I meant "stropicy." this to make sure that the sheet touches the plates only in single points and that the average distance is however consistent. If the sheet was smooth, with the flat plates, it would risk having whole areas with a very small distance between the two parts and loss of homogeneity in the heat transfer. another solution would be to interpose a thin cloth in rock wool or fiberglass retina to maintain the distance.
in any case, the sheet should not re-emitting for irradiation (local) towards the inside, because the external specular surface should heat only by convection and consequently in a homogeneous way.

talking about rollers, I wasn't referring to thermal calandre, but to compression rollers after heating. I designed and built machines that couple laminate fabrics in pp with thicknesses up to 4 kg/m^2 in which the rollers are cooled, not heated. the heating is for irradiation with linear resistances in the area immediately preceding the roller on which the compression and cooling of the coupling takes place.

 

[RiccDS]

I've made several attempts. various leaves of aluminum stropicciate have attenuated a little the thermal gradient but not enough. are probably too close to resistors as mechanicalmg said. I also tried to turn on only the higher resistance to the maximum. But I can't make the oven go to the temperature. I reach maximum 140°c at the interface. I also isolated the oven more externally with glass wool, but nothing yet. indeed even the glass wool has darkened for heat at certain points. What I didn't expect. and for this reason I would avoid putting it in the oven. before raising the whole structure I wanted to try to interpose between the resistors and the mallops an insulating material (and at this point also refractory). I just don't know what material to rely on. tiles should be fine, right? :

It's a shame we're out of money, otherwise I would have commissioned you the whole thing. 4 kg is a nice thickness. It's a slightly different procedure. In my case I do not know if it would be okay because it is to avoid an observable interconnection to the naked eye (they are two different colors) of the two sheets. then in section, when mating happened you should observe the two sheets as if they were glued

 

[exxon]

I think the oven is the weak point: It is strange not to be able to maintain a temperature that is not so high. if the job must be done in economics, consider the opportunity to build the oven from scratch. It's a little heavy work, but nothing impossible.

p.s. not all tiles are refractory. . .

 

[RiccDS]

with both resistors on it makes it seemingly, but with a no.
I will pass on the construction of the oven. apart from that I don't have the right place and instrumentation to work steel, my crushing colleagues have already rejected the idea given me the overcoming of the deadline they gave me. but some attempt that doesn't take me too long I still do it for a matter of principle and if I can maybe get back the idea. a little lack of experience makes you feel.

 

[exxon]

Then, at the limit, the oven puts it as a hat to colleagues, since they complain about the times for a project of this complexity. . .

 

[RiccDS]

It's a war.
Excuse me another question: about those aluminum plates and other plates that I took, as well as a polyethylene plate to work in cnc, there is one that is saved. They're all boarded and they've given me a lot of trouble. everywhere I always ask myself the same story. who should I address if I want materials with engineering precision?? Good luck choking a slab all boarded.

 

[exxon]

to set up an unsealed plate, you need a lot of experience. the problem is not to cut it, but to fix it in the car so that it stays flat even once pulled down. It's work for a few.

In addition to this, if the plate is extruded aluminum, there will not be to pull it flat because every time the brakes, cuts of the internal tension lines that free forces able to "until it" as soon as released from the clamp.

It is essential to start from cast aluminium plates, which already come with mirror finish and flat as a billiard. I don't think you need to specify that they cost "a little more" than those extruded.

Among other things, one of the reasons why you may have had those problems is precisely the poor flatness of the surfaces. industrially we use rollers not only for large formats, but also for small laboratory machines (one of my last works), precisely to ensure quality and consistency in results.

 

[RiccDS]

Thanks for the exxon answer. say that any tensions can cause problems with polyethylene (1.5cm)? because I'm about to try to rectify it. It's really very busy, so the idea would be to put it on the milling machine's plane and block the only x and y-long scorings with pins all along the perimeter, avoiding games. without tensioning it long z therefore. After that it is rather tender, therefore, that the mill should not bend or strain it in a sensitive way. made one side, the other should be a boy's game.

the big aluminum ones were flat enough and then preloading them I think I have a minimum reduced the problem. However we say that from a whole series of tests I have reason to believe that the main problem was temperature; in practice bubbles were formed (the real gaps inside the material), as well as redistributions of material. Unjustifiable aspects if the pp did not exceed 170°c. or at least I think.

on the rollers, the fact that the contact surface is linear, does not imply redistribution of material and therefore a thinning of the laminate? because in our case it was not acceptable to lose in thickness.

 

[exxon]

to rectify a boarded sheet, it must be glued with all the surface on a support that has the opposite side considered flat, using a filler (type black pece, for metal plates). the support must be mounted in the machine and the cutter will cut the plate that will not have undergone deformations from the untended state. the new surface will be that of assembly for the milling (or grinding) of the opposite side, after draining or milling also of the support and glue used. the operation must be repeated several times if the milling releases other tensions. barbino work.. .

spying on the pe should not be different (I have never done it...), but fresare the slab without fixing it completely I do not see a great idea (as well as a little dangerous...).

for roller rolling machines, you must consider that the position of rollers is micrometrically adjustable, both in reciprocal distance, and in axle angle (to ensure the straightness of the output product. the thickness is directly connected to the distance between the roller surfaces with very high precision and repeatability.