Vacuum and pressure kit (not high vacuum)?

[Edward Rosten]

I've been doing some silicone casting recently, and have received many helpful suggestions, such as degassing the mixed silicone by putting it in a vacuum chamber before pouring it and/or curing it under pressure.

I gather there is a bit of low vacuum kit and/or pressure vessels with detachable lids knocking around which may serve for this purpose. Does anyone have any idea what's around and in working order? I gather there's a vacuum former project in the works. The pump should be suitable for dual use in this kind of thing if that's an acceptable use.

-Ed

[Peter "Sci" Turpin]

There's 3 vacuum projects.

* The vacuum former, which Hipster made. Don't know if the heaters
currently work.

* The high vacuum station, which is for high energy physics and space
environmental simulation. Not to be used for resins, foods or liquids of
any kind. Ultraclean work only. Under construction.

* The vacuum degasser, which is what you're after. There is the
home-made degassing chamber I donated, but it's not been well looked
after. It may still work but I doubt it. Sadly someone stole the chamber
that was going to become the new one.
The tatty chamber is a modified fire extinguisher beside the vacuum station.

If anyone has an old gas cylinder that is *exactly* 12" in diameter and
over a foot tall to the shoulder, we can build a new one. 12" L-seals
are about �30 and I need to buy one myself for my next degasser so we
could save on postage.

Pressure casting is something I've looked into, but the chambers aren't
something you can safely build at home and they're pretty expensive in
the UK. And I don't think I'd trust one being left in the space either.
I don't think our record of tool care is up to possessing unrestrictable
equipment that can explode if misused.

Also the pump on the vacuum former is a vacuum cleaner motor. The
figures I can find for vacuum cleaners say they'll have an air pressure
of about 800mb at the nozzle (atmosphere is about 1000mb). The pressure
level needed for resin degassing is an order of magnitude lower. I
usually see final degassing of my resins & silicones around the 50-10mb
mark. Refrigeration service pumps and lab-grade vacuum sources are what
get to that range.
Vacuum cleaners are also not meant to run in closed systems. They rely
on air-cooling. Trying to keep a closed chamber down at vacuum pressures
with one for the 10 minutes or so you'll need.. well without airflow
over the motor it'll probably overheat and catch fire while being
incredibly noisy.
Degassing requires a rotary vane pump. We have a couple of them.

Be happy to do a talk about it if need be, but basically we need parts
again to make a proper resin degasser for the space. I'm happy to do
that since I'm already making a new one for myself, and it would save
making the special cutting jig twice.

12" cylinder, L-seal, some 20mm clear polycarbonate, a few 1/4"BSP
fittings, some recycled angle-iron, vac-gague.. Probably under �60 total
and a day worth of grinding & welding. A little more if we add a safety
catch-pot to stop overflows getting ingested by the pump, which is a
good idea.

[Edward Rosten]

On Monday, 23 September 2013 14:59:07 UTC+1, Sci wrote:

* The vacuum degasser, which is what you're after. There is the
home-made degassing chamber I donated, but it's not been well looked
after. It may still work but I doubt it. Sadly someone stole the chamber
that was going to become the new one.
The tatty chamber is a modified fire extinguisher beside the vacuum station.

If anyone has an old gas cylinder that is *exactly* 12" in diameter and
over a foot tall to the shoulder, we can build a new one. 12" L-seals

are about �30 and I need to buy one myself for my next degasser so we

could save on postage.

Pressure casting is something I've looked into, but the chambers aren't
something you can safely build at home and they're pretty expensive in
the UK. And I don't think I'd trust one being left in the space either.
I don't think our record of tool care is up to possessing unrestrictable
equipment that can explode if misused.

OK, that pretty much eliminates pressure casting.

 

Also the pump on the vacuum former is a vacuum cleaner motor. The
figures I can find for vacuum cleaners say they'll have an air pressure
of about 800mb at the nozzle (atmosphere is about 1000mb). The pressure
level needed for resin degassing is an order of magnitude lower. I
usually see final degassing of my resins & silicones around the 50-10mb
mark. Refrigeration service pumps and lab-grade vacuum sources are what
get to that range.

Ah, ok, it's that kind of vacuum former. Trouble is with that sort is that it kind of (doesn't) suck.

The sort I was thinking of has a vacuum chamber that's evacuated to perhaps 0.1bar. When it comes to forming, you flip a valve and it connects the vacuum to the underside of the plastic and sucks the air out very hard and very fast. At the end you probably have maybe 0.5 bar left in the chamber. I've mildly refurbished and used a machine like that. They are very good.


 

Vacuum cleaners are also not meant to run in closed systems. They rely
on air-cooling. Trying to keep a closed chamber down at vacuum pressures
with one for the 10 minutes or so you'll need.. well without airflow
over the motor it'll probably overheat and catch fire while being
incredibly noisy.
Degassing requires a rotary vane pump. We have a couple of them.

OK, that rules out the vacuum former pump. Good that we have some decent pumps. Those would otherwise be the expensive bit I think.

 

Be happy to do a talk about it if need be, but basically we need parts
again to make a proper resin degasser for the space. I'm happy to do
that since I'm already making a new one for myself, and it would save
making the special cutting jig twice.

 

12" cylinder, L-seal, some 20mm clear polycarbonate, a few 1/4"BSP

fittings, some recycled angle-iron, vac-gague.. Probably under �60 total

and a day worth of grinding & welding. A little more if we add a safety
catch-pot to stop overflows getting ingested by the pump, which is a
good idea.

Not sure I 100% understand the design. Do you have a photo or link to an example that you're basing your design on?




-Ed
 

[Peter "Sci" Turpin]

>
> 12" cylinder, L-seal, some 20mm clear polycarbonate, a few 1/4"BSP

> fittings, some recycled angle-iron, vac-gague.. Probably under �60

> total
> and a day worth of grinding & welding. A little more if we add a safety
> catch-pot to stop overflows getting ingested by the pump, which is a
> good idea.
>
>
> Not sure I 100% understand the design. Do you have a photo or link to an
> example that you're basing your design on?

Pretty standard "bucket" design. 12" wide cylinder with the cut top off.
L-shaped seal goes around the top edge, clear polycarbonate plate goes
on top to seal it and provide a window.
BSP gas fittings provide pump and UTA (up-to-air) valves, angle-iron
makes some legs for it to stand on so the pump can go underneath & make
it a discrete unit. Also gets used to make a hinge mount for the top
plate so it doesn't get lost and/or damaged.

Would be the sort of size that usually sells for �150-200.

[Edward Rosten]

Any idea where the rotary vane pumps are or roughly what these ones look like?


-Ed

On Tuesday, 24 September 2013 00:19:25 UTC+1, Sci wrote:

>
>     12" cylinder, L-seal, some 20mm clear polycarbonate, a few 1/4"BSP

>     fittings, some recycled angle-iron, vac-gague.. Probably under �60

>     total
>     and a day worth of grinding & welding. A little more if we add a safety
>     catch-pot to stop overflows getting ingested by the pump, which is a
>     good idea.
>
>
> Not sure I 100% understand the design. Do you have a photo or link to an
> example that you're basing your design on?

Pretty standard "bucket" design. 12" wide cylinder with the cut top off.
L-shaped seal goes around the top edge, clear polycarbonate plate goes
on top to seal it and provide a window.
BSP gas fittings provide pump and UTA (up-to-air) valves, angle-iron
makes some legs for it to stand on so the pump can go underneath & make
it a discrete unit. Also gets used to make a hinge mount for the top
plate so it doesn't get lost and/or damaged.

Would be the sort of size that usually sells for �150-200.

[Peter "Sci" Turpin]

I don't think either are currently configured to be connected to the
existing chamber. I believe the pump that was has been removed by it's
owner.

On 26/09/2013 16:58, Edward Rosten wrote:
> Any idea where the rotary vane pumps are or roughly what these ones look
> like?
>
>
> -Ed
>
>
> On Tuesday, 24 September 2013 00:19:25 UTC+1, Sci wrote:
>
>
> >
> > 12" cylinder, L-seal, some 20mm clear polycarbonate, a few
> 1/4"BSP
> > fittings, some recycled angle-iron, vac-gague.. Probably

> under �60

> > total
> > and a day worth of grinding & welding. A little more if we
> add a safety
> > catch-pot to stop overflows getting ingested by the pump,
> which is a
> > good idea.
> >
> >
> > Not sure I 100% understand the design. Do you have a photo or
> link to an
> > example that you're basing your design on?
>
> Pretty standard "bucket" design. 12" wide cylinder with the cut top
> off.
> L-shaped seal goes around the top edge, clear polycarbonate plate goes
> on top to seal it and provide a window.
> BSP gas fittings provide pump and UTA (up-to-air) valves, angle-iron
> makes some legs for it to stand on so the pump can go underneath & make
> it a discrete unit. Also gets used to make a hinge mount for the top
> plate so it doesn't get lost and/or damaged.
>

> Would be the sort of size that usually sells for �150-200.
>
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