Project needs a freezer box.

[NC-Joey]

Hi all, thanks for the opportunity to get some help.

I`m building a CNC Machine to produce 3D Models made from ICE, using a micro-dispensing valve to spray a very fine water jet and building the 3D shape from 2D layers.

I know virtually nothing about refridgeration and could do with some help in designing and building a suitable freezer box. The ideal outside dimensions are 420 x 350 x 250 mm high.
The freezer box will be bolted to the machine table and will move in one direction only, with the X Axis (180mm total travel front to back)
The valve nozzle will be mounted on the end of a 12mm dia steel rod, and will be connected to the machine`s Y (200mm total travel side to side)and Z Axis (90mm total travel up and down)which is housed above the freezer box `roof`.

(Now this will be a major challenge) This rod must poke thru the `roof` of the freezer box. I`ll need to create a fancy sliding system that allows the X and Y movement but still keeps a seal within the box.

Can cold air blown into the freezer box be enough to create a -20C environment ?

I hope some of that made sense, please could you guru`s offer some help in designing a small compact freezer circuit. (phew that`s not asking for much :D )

many thanks

[Samarjit Sen]

Could you please make a drawing of what exactly you require. One thing I hope I understand that the box should be able to move 180 deg and maintain an inside temperature of -20oC. If you can put it on a drawing it may help.

[NC-Joey]

Box will move 180 in X.
Fancy seal arangement on the top face of the freezer box will allow movement in Y and Z.

Pic attached. thanks

[Paulajayne]

Hi
X and Y can be done with a large disc fitted around pipe.

The injector pipe will require a heater for startup.

Paula

[Samarjit Sen]

The pipe through which you propose to supply the cold air will be fixed to the top of the body or would it be moving.

The second thing is that you are not taking out the cold air from the chamber ( I presume) The cold air is going to be 100% fresh air cooled down to - 20oC. Or is it that you propose to leak out the cold air from the chamber and let the air - 20oC air come in.

If that be the case, what is the ambient temperature.

The reason for my asking so many questions is simply that first I am trying to understand your requirement, visualise it and then find a suitable system. I do not believe that in refrigeration anything is impossible.

[NC-Joey]

Hi Paula
tnx for your input.
I`ve attached a 2nd pic to show the opening required to cover any machine movement. I know it`s all over to one side of the freezer box. haha it`s a long story - basically my original machine design which would have put everything in the center was changed when I was forced to use Ballscrews and Stepper Motors for the linear movement.
I could extend the length of the freezer thru the back end, and also increase the width by about 30mm to allow a bit more room for adding a sealing system.

I`m not sure what you mean "The injector pipe will require a heater for startup"

[Samarjit Sen]

From your second drawing some more information has been achieved. Do you require a temperature of -20oC inside the air or the cold air has to be supplied in movement.

From what I can understand that the main thing is the movement of the pipe . Please correct me if I am wrong.

[NC-Joey]

Hi Samarjit Sen
Ideally it would be nice to have a flexible pipe feeding cold air into the chamber. This pipe could be placed at the back of the machine out of sight but yes it would have to move with the X Axis.
I guess this would mean the existing air in the chamber would have to leak out.
The ambient temperature, well this is `sunny` England we`re talking about ! No seriously this whole build is taking part in my little office- come workshop- come dumping ground ;) attached to the house. In fact it does`nt even have central heating.

[Samarjit Sen]

As stated by you, should I presume that you agree to have a flexible pipe fixed to the back of the box, and the cold air is to be leaked out. The problem inhaving the pipe at the top is making an arrangement to seal the space when the box is in movement.

[NC-Joey]

How does this look ?
The Freezer components (compressor etc) are housed in a box below the machine. The only thing attached to the freezer box is the flexible hose shown.

[Paulajayne]

"
I`m not sure what you mean "The injector pipe will require a heater for startup"

As the pipe will contain water and the container will be precooled down to operating temp then the injector/pipe will freeze so a defrost will be required.

Paula

[NC-Joey]

oh ok thanks Paula.

I have an oldish fridge lying about here (actually It`s been left outside to the elements for the last 2 mnths) the kind that has a small freezer box in the top section. Could I strip this down and obtain any usable parts for my new machine ?

[NC-Joey]

Well curiosity got the better of me - it had to come apart.
At times during stripping it down I did catch a pretty strong smell which I`d presume is the refrigerant, so it must have a leak.
Anyhow it`s all good learning for me, what surprised me was there is no compressor or motor, it seems to have an electrical heating element.

I was expecting to see a seperate unit cooling the freezer box in the top of the fridge but the whole lot came out as one piece.
Any chance one of you could Identify the different parts for me plz.

If it helps it is an Electrolux, Model RA510B, Prod No. 9263731

[Paulajayne]

Hi

Looks like this is wahat you have:-

http://en.wikipedia.org/wiki/Gas-absorption_refrigerator

Though yours will be powered by electrickery.

I would not think it will do what you require.

You will require a compressor type system as it will pull down and hold temp better, though I doubt that a small household unit will do it.

Lateral thinking. ---

1. What if you place the whole machine in a cold store/room?
2. Have a look at a chest freezer as an option. (local paper second user section)
3. If it is a trial system that you are working on them maybe look to rent some time/ space in a cold store.

HTH


Paula

[NC-Joey]

Hi Paula
Thanks for clearing that up me.

Chest Freezer...
funny you should mention that, early on in the machine build I bought a chest freezer and have made the machine to fit into it.
I am virtually ready to place it into the freezer and do some tests, but hmmm I`ve suddenly got cold feet (bad pun :rolleyes:) and am worried about trying it.
I fitted digital readout scales that give an accurate display of the machine`s position in X Y and Z.
I placed one of these scales into the freezer and after giving it time to cool down I looked to see what the effect was. Well it stopped working.. but luckily still worked after returning to room temp. I`m really worried about placing the whole machine into the freezer, in case the motors and ballscrew slides freak out.
It was then I put the brakes on and decided to seek help in making a freezer box to sit on the machine table.