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[Casting] vented gases


#1

Marc if you have not tried the plastic webbing that goes on the
inside of the flask to vent gases I would reccomend that you do.
I use them for centrifical as well as vaccume and will not cast
without them. They seem to really help solve gas porousity. I use
the vacu-cast product myself with great results.Frank


#2
       Thomas, When you say venting, what exactly do you mean?
Doyou mean using  the wax screens on the inside of your flask
or something similar? or do you  mean something else? let me
know.. 

Marc, Someone years ago showed me the way they said they
’vented’ gases(?) when vacuum casting, by adding a wax rod to
the
top of a wax pattern going toward the top of flask,(when inverted
in the caster, goimng towrd vacuum),presumably to have the gas
go
to the rod instead of being trapped in the wax model.?


#3

Hi Marc,

A vent is an off shoot of 18ga. or so sprue wax. I have seen
them done 2 ways. Firstly, the 18ga. or so sprue wax(s) can run
from the top of the casting out and down to the sprue former
just before the casting ring is in the former. These vents
allow all of the trapped gases that are not dissipated into the
investment to be forced out and down. Secondly, I have seen
’tails’ of 18ga sprue wax dead ended in the investment. These
’tails’ are supposed to collect the porosity and to give the
back pressure a place to go.

One helpful tip that I use is that I invert the ring, holes up,
for the last 10 min before I cast.

Regards,

Skip

Skip Meister
@Skip_Meister
Orchid Jewelry Listserve Member
N.R.A. Endowment
"No man’s life, liberty or fortune is safe…while our legislature is in session."
Benjamin Franklin


#4

Hi All, I’m unsure how to use the plastic webbing. The stuff I have
is only half as wide as my flasks. Do I put it near the bottom so it
would drain out when I steam dewax or toward the top so gases would
be drawn away as I cast with a centrifuge. I love orchid.


#5

FWIW,

 Marc if you have not tried the plastic webbing that goes on the
inside of the flask to vent gases I  would reccomend that you do. I
use them for centrifical as well as vaccume and will not cast
without them. They seem to really help solve gas porousity. 

If you want to try venting without purchasing the webbing or other
products made expressly for that application you can use soda straws.

To use soda straws, place a number of them in the flask before
pouring the investment. Place them in the flask so the bottom of each
straw is solidly on the bottom cap of the flask. The rest of the straw
should stand vertical & contact the inside of the flask all the way to
the top. If necessary, long straws can be cut off so the protrude a
little above the side of the flask. Double stick scotch tape can be
used to hold them in position until the investment is poured. Any size
straw can be used. If large diameter place them about 1 inch apart
around the inside of the flask. If small straws, link drink stirs, are
used place them closer together.

The plastic webbing or the straws provide surface area to the outside
of the investment that is exposed to the atmosphere. Any gases that
percolate through the investment have a shorter & unrestricted access
to the outside, they’re not held in by a solid metal sleeve (the
flask). Because part of the investment is still in contact with the
inside of the flask, it provides sufficient structural integrity to
prevent the investment from disintegrating when the vacuum is turned
on or the centrifuge is turning.

HTH
Dave


#6

The webbing should be placed so the bottom edge is about mid point of
the wax model and the top edge at the top of the investment. Frank


#7

I always put the wax web at the bottom (sprue hole is top) of the
flask and steam dewaxed with the web side down first. Then I turned
the flask over and steamed the sprue and injection wax out. Then I
put the flask in a preheated furnace sprue side up for burnout.
Ideally the web should be about 1.5-2 inches shorter than your flask.

Chris Maugham
Harrisburg, PA


#8

Hi Folks,

Another thought has occurred to me about ‘venting’ and mesh. When I
put my ring liner in the casting ring, I make sure that the ring is
exposed on both the top and bottom end and I flow pink base plate wax
to cover the liner (any wax will work), making a ‘poor mans’ vent.
This also allows the investment to expand so the coefficient of
expansion more easily matches the metal. This is important in
jewelry (ring sizes) and absolutely critical in dental technology.

Regards,

Skip

Skip Meister
@Skip_Meister
Orchid Jewelry Listserve Member
N.R.A. Endowment
"No man’s life, liberty or fortune is safe…while our legislature is in session."
Benjamin Franklin


#9
Marc if you have not tried the plastic webbing that goes on the
inside of the flask to vent gases I  would reccomend that you do. I
use them for centrifical as well as vaccume and will not cast
without them. They seem to really help solve gas porousity. I use
the vacu-cast product myself with great results.Frank 

Marc , Frank and anyone else doing vacuum or centifugal castings .
The wax web works ok, but check out the Tivac vacuum liners that are
available from The contenti Co. http://www.contenti.com or The
Gesswein co.They both carry the product . This liner increases the
vacuum /degassing of any standard flask and also has an extra 2
inches that extends beyond the flask to effectively stop investment
spillage and helps to keep the machine much cleaner, saves labor ,and
saves any kind of investment from going out of the flask while
investing.It is also inexpensive to use and can be shipped anywhere
in hot or cold climates without fear of breakage.I have used them
since 1988(before market availability ) and continue using them at
this time.If anyone has any questions on their use, please email me .
Please visit the “workshop” on my casting website to see what they
look like and how they are used … along with other ideas . We also
do model making,mold making , custom and production casting /
finishing in many different metals for designers and people in the
jewelry trade Daniel Grandi http://www.racecarjewelry.com (click
on “workshop”) 52 Glen Rd , Cranston, RI . 02920 Tel: /Fax
401-461-7803


#10

Why do you put the spru side up in burn out? I learn as I go and I
never have done it that way. Comments please. Thank you all so much!


#11

Dave, How do you get vacuum casting to work with the soda straws
running all the way to the top (in casting position) of the flask?
That would seem to me to break the vacuum. I can see how they would
work just like wax web for spin casting. For vacuum casting I don’t
even use wax web up to the wide part of the model like recommended,
usually cut it off a few millimeters short. Geo.


#12
The webbing should be placed so the bottom edge is about mid point
of the wax model and the top edge at the top of the investment.

Could you please restate this for those who haven’t used webbing
before. Is the bottom edge of the webbing midpoint between the wax
model and the top edge of the investment at the sprue button? I
thought the webbing was placed close to the end opposite the sprue
button opening or am I totally confused? I am having a difficult time
conceptualizing this and would like to try using it with a casting
class which is beginning on Monday night! (not my first casting
experience but I would like to limit the amount of porosity I get with
natural casting (casting from nature) Thanks! Shael


#13
   ... Place them in the flask so the bottom of each straw is
solidly on the bottom cap of the flask. The rest of the straw should
stand vertical & contact the inside of the flask all the way to the
top. 

If you are vacuum casting, putting in vents that go all the way
through the flask from top to bottom will destroy the vacuum pull on
the mold cavity. You want the straws to extend from the bottom
(closed end that sits on the vacuum pad) of the flask to no higher
than about the same level in the flask as the upper limit of the
model, leaving at least about a half inch of solid investment between
these vents and the upper (sprue cone) side of the flask. This way,
vacuum applied to the bottom of the flask will draw through the mold
cavity, as it needs to. With vents all the way through, you might as
well just be gravity casting without the vacuum. If you are venting a
flask used for centrifugal casting, then the vents can go all the way
through if you like, though they don’t need to.

Peter Rowe


#14

I always place the bottom edge of the webbing so that it is about
even with the middle of the wax model as it sets in the sprue base on
the sprue ,about 1 to 1.5 inches from the bottom edge of the flask,
depending on spure length and model size. hope that makes it clearer.
frank


#15

Hi, I burn out sprue side down, but, when I start to ready the casting
machine I invert the ring in the oven. It is in there for about 10
minutes in the inverted position. In dental technology I use many
palladium based alloys and generally the majority of each
crown(tooth), about 2/3 of it, is about 3 tenths of a millimeter
thick in order to have enough space to build up and fire the 7
separate veneers of porcelain that covers the casting. The metal
manufacturer recommended this but I had learned years earlier that it
reduced the number of crowns with ‘windows’ in them from incomplete
castings. I suspect it helps the gasses to escape easier.

Regards,
Skip

Skip Meister
@Skip_Meister
Orchid Jewelry Listserve Member
N.R.A. Endowment
"No man’s life, liberty or fortune is safe…while our legislature is in session."
Benjamin Franklin