After struggling with the problems with gravity feeding molten glass though a small nozzle (inherent with MIT’s glass printer design), we have decided to redesign our hotend to forcefully extrude molten glass (and other materials). Before we share details of the new design, the next several posts will be covering what we are building so that we can build everything we need for the new design in-house. To that end, our 15KW induction generator is capable of melting most anything at a flip of a switch. It’s seriously like magic! Here are the results from our first run.
SiC Heater Rod Rewire
This post has been a while in the making; my apologies. It turns out that it is one thing to run an electric load at room temperature, and quite another altogether to operate in the confines of a super compact, 2000F furnace that itself is intended to operate inside a toasty 800F furnace – continuously. In other words; the wiring to service our SiC heater rods was vastly underrated for its operating conditions. With sorrow it became clear that we had to strip down the whole furnace and rewire each and every rod. For our last attempt we ran 8 strands of 18 gauge stainless steel wire. Since oxidization is our enemy, we went with solid 6-gauge (or better) stainless steel rod. It is worth noting at this point, that a typical furnace of similar capability would be much larger. Every effort has been made to keep it compact as possible since it will be mobile and takes from our usable print area.
Also, the connection contacts to the rods where the weakest point in wiring system, so we painstakingly tapped out each end of the SiC rod to accept 3/8″ stainless steel bolts. This alone will allow our cool ends to operate much much cooler, and since it eliminated the need for connection clamps, it doubled the length of undersized cold ends. Win/Win!
While it took tremendous effort to completely rewire our furnace, I am hopeful that it should last the life of the SiC heater rods themselves which are designed for many thousands of hours of operation. So I hope we don’t have to take it apart again anytime soon.
First Glass Melt!
On a much more uplifting entry; we succeeded in melting glass (Studio Nuggets 96) on our machine for the first time last night! We got the crystal clear stuff up to 1100 Celsius (over 2,000F) and was nearly fluid as water! However, our thrifty SCR used to control the nozzle heater was not up to par for the current it wanted to draw (it is a low voltage high current monster) so we had to reluctantly ladle the glass out. We need to redo some minor things but all in all it was a success!
We are looking forward to the next run!
Murphy and his Law. ZAP!
Evidently in my last post I was reckless enough to challenge Murphy by taunting: “Looks like we should be printing our first glass tomorrow!”. It turns out that a couple of seemingly insignificant mistakes met for one big 7,000 watt ZAP setting us back weeks. Our machine’s (once perfectly working) sensitive motion controller took way more than it was designed for cooking components all the way up to the PCI card in the computer. We are mostly back to operation now with three of our four axes on the machine fully operational (X, Z and A). We have Y narrowed down but at the time it is not operational yet.
The “insulation” of our wire made unintentional contact with our 240 volt 30-amp service, but only because we wanted to see how the crucible furnace behaved before insulating it. That said, we have learned from our mistake and as a result the machine is much safer for it. Now for critical things we say “that shouldn’t happen” we have it covered at least once or twice it the event it does happen!
We have ignition! Our printer’s crucible was fired up for the first time (and on the machine) tonight with flying colors. She’s running 1,600F+ in open air (no lid), at about 2/3 power and using only a fraction of the planned insulation.
Looks like we should be printing our first glass tomorrow!
A naked furnace frame wouldn’t run very efficiently, so time for some fluffy 2600F-rated spun alumina (industrial sapphire) blanket.
Furnace Frame Rebuild
Once the furnace was re-designed (prior post), of course the next step is to implement it.
1500C Furnace Redesign
As much as I would prefer to only report success we are learning a lot which means of course means making some mistakes along the way.
The first design of our glass melting furnace relied on a 2KW wire heater. After installing the wire we found that it only deliver 1.3KW at best. In addition, burying the metal wire in castable refractory was likely a fatal mistake, because I now suspect that the wire needs to be able contract and expand each operating cycle. Even if it didn’t there is a chance that at operating temperatures the refractory (which is a good insulator at room temperature) could have become conducive at working temps — potentially shorting out the entire heater coil.
In addition, even if the coil had operated at 2KW for any length of time (ignoring the above) it would have taken a long time to heat up and likely struggle to maintain the desired temperatures. In other words, it was vastly underpowered.
The new design is based a 7KW system comprised of Silicon Carbide (SiC) heating elements (ED shape). In addition to heating up rapidly, the new setup will allow us to operate continuously 1500C. This will allow us to print borosilicate (Pyrex®) and possibly interesting things like (fired) ceramics and de-composed granite (that is what the “dirt” we are sitting on top of is mostly comprised of).
So while it has been a bit of a misstep, it will only be for the better. Our set of custom SiC rods are currently being fabricated in China and will hopefully ship to us this week. All other aspects our massive printer have been tried and verified to work. More soon.
We now have our heat electronic control box installed on our great big printer and starting to test things out. Here our annealing oven is heating up for one of the first times.
Print Chamber Installed
We now have the print chamber finished and installed on our massive machine. The chamber will be operated at a toasty 800F during printing glass (it will be put to use for pizza firing undoubtedly after a days run) that allows the inter-printed layers to adhere (and at optical quality), grow without warping and or cracking and to anneal so a printed piece doesn’t self-implode at some time in the future.
Nozzle Rack & Pinion
In order to control our stainless steel nozzle actuator from a more reasonable room temperature, where standard stepper motors merrily step to and fro, we needed to transfer the power to outside our 800F print chamber. For that purpose it seemed that good old rack and pinion was the ticket.
Being able to actively control the nozzle should allow us much greater control (it can actively restrict the flow rate), allow us to print any form without restriction (other than support restrictions inherent to the FDM process), and we think it should be able to print molten metals (aluminum, copper, etc) in a similar fashion as glass.
Our precious crucible cart has undergone its final transformation into what will likely become the key element of our glass printing machine. Unlike portland, refractory does not use good ol’ H20 for its chemical bound, so for refractory, firing is a key step.
Next time you see our crucible cart it should be mounted on our machine!
Final Refractory Work
One last chapter before we can begin our crucible cart’s dryout schedule: the top. We need a bomber top to handle ladling of molten glass blobs into the crucible as well as way to fix the loose electrical terminals. The insulating refractory won’t cut it in these departments so its time for some more 3000F rated refractory to coat on top.
After its fired we can get it mounted to the machine and should be showtime!
Insulating Refractory Installation
Now that we have that big (potentially) hot heater coil wrapped about our crucible, its time to give her some insulation to keep those precious BTUs where we want it – melting glass (or whatever else we may find ourselves melting with our new contraption – mooohahaha).
Alright, so now after carefully placing our crucible cart onto our vibrating table we clamped forms around the sides ready for filling. In all places where there was potential wood contact, we covered said wood with plastic bags to prevent it from adsorbing an unfair of moisture from the curing refractory.
Then we get to flip it over and finish the top side – next episode.
Crucible Heater Coil Packed
With each post, our excitement grows!
Of course, if we are to melt glass, we are going to need some heat, a whole lotta’ heat indeed! So we are pleased to finally outfit our crucible a 220V 2KW heat coil and packed in a jacket of 3200F rated refractory.
Next up – fill this baby with some insulating refractory to keep our needed heat in.
We got the cart all built today. The crucible isn’t much good if we can’t steer it around, and that is the the cart’s primary task. The secondary task is to provide a frame that will fill with high temperature insulation (refractory).
The third task is to provide a thermal heat break from the 2000F crucible. We selected stainless steel for that task and in addition, the stainless doesn’t make full contact with the steel it will be mounted to. So the stainless is about 1/4″ away and only make contact where it is bolted.