Homebrew PCBs

Hi Everybody,

Have you tried Sodium Perborate in place of Hydrogen Peroxide??

Please inform.

Cheers.

On Sat, 12 Mar 2005 21:18:13 -0000, jamalzaghal <jzaghal@...>  
wrote:

>
>
>
> Hi Everybody,
>
> Have you tried Sodium Perborate in place of Hydrogen Peroxide??
>
> Please inform.
>
> Cheers.
>


No, but according to

<http://www.pcbfab.com/iepart5.html>

you can use Sodium Chlorate. I wonder which advantages it would provide.

I tried the pool-chlorine a while ago and it doesn't seem to work.

ST

hi,


I'm going to buy 5mm Lexan to make the tank, it seems the least prone to  
shattering and i hope to me able to machine it without pulling my hair out.
Please let me know if Lexan is unsuitable for CuCl, it takes up water but  
it is only the enclosure so...
The same supplier doesn't have PTFE but i'm going to get HDPE for  
"temporary" bearings.


For the sprayer itself i have found some 50mm inner dia, 3mm wall PVC  
piping.
It is rather large diameter but i hope to keep RPM low this way. I have  
found several lower diameter pipes i could try later.

I will try different ways of making "nozzles", and i also want to work out  
in some way which total "hole" size (or number of smaller ones) the  
sprayer can drive.

ST

ok, time for maths.

according to a formula i found on the web a 50mm dia tube spinning at  
1000rpm experiences 274m/s^2 or 28g on the inside edge.
so if there is, say 1cm high water over 1cm^2 that weighs 1g it should  
produce about 28g of pressure on the wall.
1 bar is 1kg per square cm, so the pressure created by the spinning tube  
is .... nothing?

According to my calculations one would need around 6000rpm to create 1bar.

HELP my maths is usually FAULTY.

Please, someone with some grasp of simple maths, do a rough calcuation and  
tell me that my result is wrong and what it should be.

It would be very important to get that about right, otherwise i do a lot  
of experimenting with the nozzles for nothing.
(my plan is to use compressed air to drive water through the nozzles in a  
water-filled tube because i can conveniently set compressed air to 1bar  
with the regulator. But i must be sure i can reach 1 bar with rotating the  
tube. thanks.)


ST

>
>
>   From: "Stefan Trethan" <stefan_trethan@...>
>Subject: Re: Sprayer pressure
>
>ok, time for maths.
>
>according to a formula i found on the web a 50mm dia tube spinning at  
>1000rpm experiences 274m/s2 or 28g on the inside edge.
>so if there is, say 1cm high water over 1cm2 that weighs 1g it should  
>produce about 28g of pressure on the wall.
>1 bar is 1kg per square cm, so the pressure created by the spinning tube  
>is .... nothing?
>  
>

Stephan

Just as a quick estimate,  your not producing NO pressure, just .28 
bar.  :^)
You need to generate at least (1000/2.5) = 400 Gs to make 2.5 cm fluid 
height give you one bar.
This is giving you credit for a constant G with depth (which you don't 
get, you either get linear increase with r or even r^2).
If it is linear, you need 2kG at the rim to get 1 bar.

American ignorance - Is bar an atmosphere, or does it just work out close?
Stupid Richard - it just works out close - 10 meters is ~32.8 ft H2O, 1 
atm is ~ 35 ft H2O



 - REMEMBER -  the following is all first order approximation, so my 
numbers are only order of magnitude! (at best)

1000 RPM is only 16&2/3 per second
A 0.05 meter diameter circle only has a 0.157 meter circumference.
16.67*0.157 is only 2.62 mps velocity at the inside rim.
Rotating  around the Z axis, a point on the rim gets accelerated (in the 
X axis) from V=0 to V=2.62 to V=0 to V=-2.62 to V=0 in 1 revolution.
This means as a lower bound, (I'm only dealing in one axis, not two, as 
I should be) the point gets accelerated from 0 to 2.62mps 4 times per 
revolution. so, 2.62 mps * 16.67 rps * 4 per revolution = 174.5 mps^2    
divide by 9.8 mps^2 = 17.8 G.
This tells me the 28G you calculated is the right order of magnitude. 
I guess if I were better at the Calculus, I'd have whipped out the right 
answer.

Maybe the outflow of the fluid is the result of it moving tangentially 
at 2.6 mps, not because it's squirting out under pressure.
It kind of makes sense if you look at the numbers. 
I wish I remembered half of what I've forgotten in fluid mechanics, I 
could understand it better and give a better explanation.
As far a nozzles go, in the US, Home Despot has started carrying 1/2 and 
1/4 inch irrigation equipment, mass produced plastic (not sure what 
kind), with all sorts of nozzles - mist, 45, 90 180 and 360 sprayers, 
all for 5 for two dollars kind of prices.  They screw right into 1/4 
inch tubing, and are made to screw into the side of 1/2 inch tube.  If 
you are interested, and can't get it over there (I hope the EU is not as 
obsessive about their lawns as we are), I'd be willing to mail you an 
assortment.  I think that USPS has an international 3 day for less than 
$20, and these things don't weigh much.
LMK
Thanks
Richard.


[Non-text portions of this message have been removed]

Thanks for your reply Richard.

We can not assume 2.5cm filled height, no.
There are holes on the bottom of the tube, to let etchant in, and if there  
is more etchant in the tube than the OD of this ring of holes it will flow  
out again there.
I assumed 1cm of etchant "skin" inside the tube, which probably is a  
rather high estimate.

A bar is fixed, the athmosphere isn't, i think the atmhosphere is off by a  
small bit but it not important for the estimation here.

Did you also try 6000RPM? i got approx. 1Bar with 6000RPM and 1cm "skin".
I found calculators on the web for lab centrifuges and they seem to agree.

I don't know how many rpm a pipe this diamter can take, and what sort of  
motor power one would require.

> Maybe the outflow of the fluid is the result of it moving tangentially
> at 2.6 mps, not because it's squirting out under pressure.
> It kind of makes sense if you look at the numbers.
> I wish I remembered half of what I've forgotten in fluid mechanics, I
> could understand it better and give a better explanation.
> As far a nozzles go, in the US, Home Despot has started carrying 1/2 and
> 1/4 inch irrigation equipment, mass produced plastic (not sure what
> kind), with all sorts of nozzles - mist, 45, 90 180 and 360 sprayers,
> all for 5 for two dollars kind of prices.  They screw right into 1/4
> inch tubing, and are made to screw into the side of 1/2 inch tube.  If
> you are interested, and can't get it over there (I hope the EU is not as
> obsessive about their lawns as we are), I'd be willing to mail you an
> assortment.  I think that USPS has an international 3 day for less than
> $20, and these things don't weigh much.
> LMK
> Thanks
> Richard.


I think you may be right there and the rotational speed is contributing.
I was already considering that. I was wondering which direction the  
nozzels would be best, straight outwards or maybe angled towards the  
tangent, i dunno. It seems straight is easiest.
I appreciate your offer with the home depot nozzles, but i'm not very sure  
they would be suitable. Generally irrigation nozzles create a big amount  
of mist, and ideally i would have "fan" type nozzles.
If someone had built a sprayer and the nozzles are known to work, there  
would be no question, but this way the chances that they are useless in  
the end for some reason are high.


I will have some time again today to try around with the nozzles, i have  
rigged up the static pressure test i described. I know it may not reflect  
true spray pattern when turning but better than nothing. I have looked at  
photos of industrial fan nozzles and one type seems to be a staight round  
hole with a small slit milled in the front. i can try that. Also, a single  
nozzle leaves something like a 4mm "ring" in the bucket, so if i space  
even round nozzles at 2mm it cold work. that would be 250 holes total and  
i'm not sure if the sprayer can supply that much.


Another worry is how to glue the lexan tank. I may just use silicone which  
i know how to use, but there might be better methods. I have made the  
supplier send me some scraps so i can try a few things beforehand... Let  
me know if any of you have experience with working Lexan/polycarbonate  
please.

thanks

ST