High vacuum chamber

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hi

Yeah vacuum technology is a new learning curve for most , UHV chambers go down to <math>10^-</math><math>^1</math> <math>^1</math> torr, these chambers are tricky, we nee to get to <math>10^-</math><math>^4</math> Torr this is much less demanding on skills of welding and machining, you can even use glue sealants for leaks on these <math>10^-</math><math>^4</math> chambers.

For the bootstrap prototype using the old fashioned tried and tested simple TIG welded H 0.8m x W0.8m x Depth 0.4m plate chamber with 0.80m long electron gun tube diameter 0.32m on top in 25mm thick aluminum , cost of materials purchased in small quantity is approx 3000 euro plus fittings and welding.


Eventually thes fittings will be self printed and the chamber may be half this size but for now that's the challenge. Test instruments will also required creativity for price reduction.

So get playing, you can do an approx self test by filling a chamber with steam then sealing it and putting ice round the chamber and see if it crushes and make sure you post the videos, Remember if you are not using copper or aluminum or stainless you will need to coat the inside before use so that significant out-gassing is avoided [url=http://outgassing.nasa.gov/cgi/uncgi/search/search_html.sh]

As far as we know all existing commercialized vacuum products are based round permanently sealed designs, and those people who want to have pump down chambers have traditionally had million euro budgets Labs etc, so this is where the creativity comes in to get below this 3000 euro plus fittings and welding.

kind regards

MetalicaRap team


New Ideas to save cost

Free standing bolt together structure put inside chamber so use thinner plate, no virtual leaks problems as no welds on free standing structure. hack existing pressure chambers?

Task list

Research which vacuum device supplier catalogs are best information wise! ( we need to help each other up the learning curve) high vacuum 10^-5 Torr Limited outgasing required [1][2]units Torr Liters Per Square Cm. Per Second,

Design build & test conventional manufacturing and Self print manufacturing route ;

CF or KF or Bimetal flange - to be welded on stainless plate, Consisting of two parts plus copper ring seal a) Short pipe and flange, b)an end CF flange fitting [3]( holding ; windows or electrical connectors or pipes to pumps or electron gun or etc...)*** TOP Priority ( as expensive to buy so need to design and a challenge to self manufacture) pump pipes, 3x electrical feed through , 3 rotational feed through, window, arm glove hatches/ port, (9) no special heat treatment can be 304 or 319

vacuum chamber rotational motion feed-through magnetic type with inner wall ( not seal type or ferra fluid type too unreliable) See here[4] - or solid shaft O ring types leaky but high torque See page 21 Thread Mount Solid Shaft–KJLC Standard example [5] *** TOP Priority

air filter subµ- to protect roughing pump and turbo pump from metal powder

pipe fittings to pumps & gauges normal guage baritron ( down to 10 -4, ) cold cathode guages( 24 Volt supply cathode chamber with anode inside 2.7Kv chamber, powerful magnet or micro pirani element ( no magnet) ). flexible hose to connect roughing pump so avoid vibration viton ring conectors KF 16 flange .


valves- to close electron guns from main chamber inner diameter min 12mm- and on connections to pumps. kf16 falnge both ends,

low voltage electrical connectors / electrical conductor feedthroughs optical passthrough[6] , High-vac electrical feed-through glue name check ceramic name check TOP priority

leaded window Min diameter 12cm ( should be equivalent X ray shielding to 2mm lead or 6mm stainless, but could bodge with stainless shutter if too expensive.)Example window[7]

door locks ( Door will be whole front side of chamber, ie H 1.6m x W 1m) *** TOP Priority

Viton O ring Main door seal or alternatives

Solenoid casings to avoid the need for tefelon coated wire.

approx total wieght. 25 kg fittings, 25 kg pipe 2K Euro to 4K euro.

later

Special case of for sub 15µ powder active metals i.e.Titanium, Nitrogen use reduced oxygenated cleanup. See nitrogen separation tube here[8] also needs compressed air supply, and an atmospheric pressure (1 Bar) arm glove entry lockable port holes, for sand blast & suction/vacuum cleaner clean up (using metal powder not sand in blaster & Vacuum cleaner) Sieve metal back to metal powder hopper from vacuum cleaner and needs compressed air supply here.


Use airlock for build while pump down contained in vacuum chamber door,


Cleanup external Arm glove Inner door Port hole- So for 1µ size active metals (aluminum , Titanium ) - after print flood chamber with nitrogen and Sandblast/hoover parts inside chamber via arm gloves ( to avoid exothermic reactions as the nuclear industry refer to them.).

Vacuum airlock so print while repump

pumps initially purchase


guages purchase



General Advice

Essential reading before you weld/construct your vacuum chamber, "Basic Vacuum technology" workbook version is best by Varian

Maths behind vacuum processes ( Not for the faint hearted )[9]


All parts should be made of low out-gassing materials see here [10] Stick to this list / or materials with values like these and you won't go far wrong. High vacuum 10^-5 Torr or high Vacuum , This will be achieved through Diffusion pump or turbo pump system, along with a roughing vane pump The connection order is first gauges then turbo pump or oil diffusion pump next to chamber and then roughing pump last. ( Oil diffusion pump is cheap but slower pump down See pump down time discussion[11] and with oil vapor back-stream that can affect some build metals ) ( maybe later upgraded to CRYO pumped systems for solar deposit modes as no back-streaming but requires regeneration / can cause contamination from helium oil , and difficult to self print)

Vacuum chamber material see page 5 for AL SST Cu comparison [12] this is Ultra high Vacuum we only need High Vacuum for 3D printer. Example high Vacuum chamber[13]

Construction tips ; Welding; avoid dirt accumulation nooks and crannies, weld from inside full depth ( i.e. not both sides leading to trapped internal air pocket). Can use Brazing ( little local differential heating , as heats whole part therefore less leaks from residual stress cracks) , TIG welding (a argon) Ideally only inside / vacuum side See weld speed caculator[14], If must weld both sides only intermittent welds on the outside, So no empty trapped voids at plate joints. Avoid gaps between plates inside on the bottom surfaces and corners of the chamber , where dirt could accumulate leading to virtual leaks ( virtual leaks are created by out-gassing of trapped dirt or voids behind screws or voids between double sided welds, this type of leak is recognized by a change rate of leaking overtime (curved time vs log pressure plot) , normal leaks have a constant leak out rate within stable pressure situations ( straight line on log plot).

Avoid grease touching metal, all inner screws must have venturi vent holes ( ie hole down middle of screw axis)

Seals 1)stainless steel knife into OFHC copper plate ( relocation on reseal creates leaks) , 2)Aluminum gasket with ridge pressed on flat stainless steel seat( only low temp),3)gold or silver plated ridge pressing on stainless flat plate( can bake to 400C and position changes uncritical and most robust solution).

Sealing force ; via bellows, roller ramp mechanism, Varian elastomer-sealed gate design.

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding. Alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone. Ferritic chromium stainless steels do require preheating to prevent cracking in the heat-affected zone. . A DCEN power source is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases.

Can use nitrogen for venting chamber as thick easy to pump out, ( unlike water argon oxygen difficult to pump out) High vacuum sealant leaks spray [15]

list of traditional high vacuum chamber machining methods [16]

Calculations Step 1 - Required thickness approximation

I've calculated plate thickness, constrained by maximum deflections of 0.01 & 0.03 inches = 0.254 & 0.762 mm and pressure differential of 1 atm sea level for the largest dimension plates, ie electron gun tube length 0.80 diameter .032 on top ; H 0.8 x W0.8 x Depth 0.4 (assuming smaller plates will have less deflection)

Online calculator for fixed rectangular plate (Bypass calculation limit by clearing your cookies)[17]



Simple just plate chamber with electron gun tube length .080 diameter 0.32 on top ; H 0.8 x W0.8 x Depth 0.4 area 2.56

Material

Stainless Steel 304 (check this)

Youngs modulus E GPa Stainless Steel 207

Poissions ratio v 1 0.3

Uniform loading p Pa 101325

Individual plate sides of chamber given 0.253097 mm max plate deflection

Width Lx mm 800

Length Ly mm 800

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Individual plate sides of chamber given 0.761671615 mm max plate deflection

Width Lx mm 800

Length Ly mm 800

thickness needed 15.8 ( 15.8mm ( 5/8inch)( deflection 0.683mm) 2098 euro per m sq.)2.56 x 2098 do again BAD PRICE? = 5370 euro(( do we need to go up to 316 stainless?)

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Material

Aluminium

Youngs modulus E GPa 62.053

Poissions ratio v 1 0.3

Uniform loading p Pa 101325


Individual plate sides of chamber given 0.253097 mm max plate deflection

Width Lx mm 800

Length Ly mm 800

thickness needed

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Individual plate sides of chamber given 0.761671615 mm max plate deflection

Width Lx mm 800

Length Ly mm 800

thickness needed 25 Aluminum plate (deflection .583mm) 2.56 m sq. 2000 euro[18]

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA



another possible chamber with no electron gun tube.

Simple just plate chamber no electron gun tube ; H 1.6 x W0.8 x Depth 0.4

Material

Stainless Steel 304 (check this)

Youngs modulus E GPa Stainless Steel 207

Poissions ratio v 1 0.3

Uniform loading p Pa 101325

Individual plate sides of chamber given 0.253097 mm max plate deflection

Width Lx mm 800

Length Ly mm 1600

thickness needed 40.6 do again

Width Lx mm 400

Length Ly mm 1600

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA


Individual plate sides of chamber given 0.761671615 mm max plate deflection

Width Lx mm 800

Length Ly mm 1600

thickness needed 28.2 do again ( 1inch 25.4mm 1200 euro per m sq.) so 6.4m x 1200 = 7680 euro(( do we need to go up to 316 stainless?)

Width Lx mm 400

Length Ly mm 1600

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA

Material

Aluminium

Youngs modulus E GPa 62.053

Poissions ratio v 1 0.3

Uniform loading p Pa 101325


Individual plate sides of chamber given 0.253097 mm max plate deflection

Width Lx mm 800

Length Ly mm 1600

thickness needed 59.3

Width Lx mm 400

Length Ly mm 1600

thickness needed TBA

Width Lx mm 400

Length Ly mm 1080

thickness needed TBA

Individual plate sides of chamber given 0.761671615 mm max plate deflection

Width Lx mm 800

Length Ly mm 1600

thickness needed 41.1 40mm Aluminium plate 6.4 m sq 4708 euro[19]

Width Lx mm 400

Length Ly mm 1600

thickness needed TBA

Width Lx mm 400

Length Ly mm 800

thickness needed TBA


next steps - Material prices ?? - using next larger standard dimensions ?? - factoring in compressive stresses from edge loading (buckling)

6mm plate with internal bolted structure

Further reading ; Vacuum chamber principles; Essential reading before you weld/construct your vacuum chamber, Basic Vacuum technology by Varian