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Feasibility of DIY Glass Molding Set-up? (primarily for tube-making)

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krfkeith

Mon Apr 15 2013, 08:24AM

Registered Member #10924 Joined: Mon Mar 11 2013, 04:02AM
Location:
Posts: 5

Hello folks!
I'm interested in trying to make my own tubes of various sorts. While I am by no means underestimating the difficulty of this project, I have, what I think is, a fairly good understanding of how to go about this. The one area where I am a little uncertain of how to go about is conceptually the most simple: making the glass envelope. Now, I know that I could use a glass lathe (or god forbid, do it by hand) but the problem I see here is that it is very hard, and takes a lot of skill and a steady hand, to shape the glass evenly and consistently across runs. While I realize that this endeavor is going to be expensive, acquiring or building a lathe would add significant expenditure to an already costly project. One idea I had, that seems relatively simple, would be to simply blow mold the glass. This however brings with it a new set of questions. To be clear as well, my intent is to use borosilicate.

1) Is this harder than I am giving it credit? Should I just stick with a glass lathe? I don't know a whole lot about glass work and I don't have too much direct experience, but I like to think I am a quick learner. Nevertheless, is the threshold to entry higher for molding than it is for lathe-ing?

2) Is this process suitable for making glass envelopes? I have seen tubes made from pretty shoddily formed envelopes, and I would imagine that molding would tend to better. However, is there some problem I am overlooking?

3) How do I make the mold itself? What do I make it from? My initial thought was of course graphite. There are plently of tutorials online on how to make graphite crucibles, which could easily be adapted. The problems I see with this are whether I could produce a smooth enough surface, and whether the graphite would rub off and contaminate the glass. Another idea I had was glassy carbon. I've read a few patents on this, and while it seems promising, getting ahold of the precursors seems to be rather hard. I'm farily certain that tungsten carbide is used industrially, but that is obviously beyond my capabilities. Metals such as steel seem to have the problem of wetting/sticking to the glass, so that's out. Do you guys have any suggestions?

4) Are there any suggestions anyone here has in general? Should I try something that I haven't even thought of?

Please let me know your thoughts on this, I greatly appreciate it!

Thanks!

Ash Small

Mon Apr 15 2013, 09:45AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, glass bottles are generally made in a two part mold which I assumed was steel. A 'slug' of molten glass is just blown in by compressed air, then another blast of air cools it, then the mold is opened, and the bottle released. The process takes no more than a second or two.

You may be correct about tungsten carbide, but the molds used look like steel to me, although I never examined them that closely.

Sulaiman

Mon Apr 15 2013, 12:21PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I have no idea what your application is but unless you are going into mass production
can't you just buy glass tubes of suitable diameter?
glass tubes can be cut, shaped, welded/melted together fairly easily.
The setup cost would be much higher than buying a few glass tubes (or test-tubes etc.)

krfkeith

Mon Apr 15 2013, 06:08PM

Registered Member #10924 Joined: Mon Mar 11 2013, 04:02AM
Location:
Posts: 5

Thanks for the replies!

Ash Small wrote ...

Well, glass bottles are generally made in a two part mold which I assumed was steel. A 'slug' of molten glass is just blown in by compressed air, then another blast of air cools it, then the mold is opened, and the bottle released. The process takes no more than a second or two.

You may be correct about tungsten carbide, but the molds used look like steel to me, although I never examined them that closely.

I could be totally off base here, but it was my understanding that steel is not generally used because molten glass has the tendency to stick to it.

Sulaiman wrote ...

I have no idea what your application is but unless you are going into mass production
can't you just buy glass tubes of suitable diameter?
glass tubes can be cut, shaped, welded/melted together fairly easily.
The setup cost would be much higher than buying a few glass tubes (or test-tubes etc.)

Haha! Definitely not doing mass production! You're absolutely right that I could use glass tubing, and that was my original plan, but this would require the use of the aforementioned glass lathe. As I understand it, it is non-trivial to put the "domes" on the tubes without one. In addition, molten glass obviously has the tendency to sag, so the centripetal force acting on the tube in the lathe can be used to counteract this. Finally, I would also like to try and make more complex shapes than just a simple cylinder, and while this is surely possible using a lathe, it is not something that I have anywhere near the skillset to do.

Ash Small

Mon Apr 15 2013, 08:01PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

It looks, from this link, like it's OK to use iron molds:

This link mentions cast iron as well:

And this link states that stainless steel is better than iron, it also lists a few other options as well:

This link states 'cast iron and bronze':

krfkeith

Mon Apr 15 2013, 08:41PM

Registered Member #10924 Joined: Mon Mar 11 2013, 04:02AM
Location:
Posts: 5

Ash Small wrote ...

It looks, from this link, like it's OK to use iron molds:

This link mentions cast iron as well:

And this link states that stainless steel is better than iron, it also lists a few other options as well:

This link states 'cast iron and bronze':

I appreciate the links! Casting iron/steel/bronze is definitely something I could do. I'll have to look into that. Thanks!

If anyone else here has any experience or recommendations, those are of course welcome too.

Carbon_Rod

Tue Apr 16 2013, 12:40AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

It takes a lot of practice:

...getting wire that matches the thermal expansion of the specific glass you are using that will also 'wet' glass is probably the hardest thing to find.

Best of luck,
Rod

Patrick

Tue Apr 16 2013, 05:20PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

we draw sodium glass, in chemistry and physics classes al the time, its pretty easy. other glass types can be harder, map pro flame is cheap and more than adequate.

Dr. Slack

Tue Apr 16 2013, 06:54PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Carbon_Rod wrote ...

...getting wire that matches the thermal expansion of the specific glass you are using that will also 'wet' glass is probably the hardest thing to find.

Best of luck,
Rod

The easiest way to get glass/metal seals for DIY use is to carefully break an old filament lamp, or old tube or CRT, and fuse the liberated seals into your new glassware.

Sigurthr

Tue Apr 16 2013, 08:45PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I know they used to use uranium (vasoline glass) glass to make the seal between glass and metal because it spans the thermal expansion gradient best. You can get rods of uranium glass on eBay, but it isn't really cheap.

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