Melting and Freezing Aluminum
Melting
It will take ~2-3 hours.
Add maintenance log record when finished describing melting conditions, e.g. power, temp, any trend chart features
Procedure
The first step is to ramp to 600C at 10C/min. We are starting from 400C (Eurotherm in Auto)
Set Eurotherm to manual.
Record the output, temperature, Sorenson voltage and current. Record this every 0.5% output increase or more often as needed (such as when Al ingots start melting)
Go through (it's more of to) the melting point at ~1 C/min, which occurs between 620 - 670 C
Each ingot should have a temperature jump when it melts (or a sustained higher ramp rate)
Once one melts there is a conductivity improvement, which helps melts the others, and lowers the risk of refreezing (why we do in manual)
Ramp rate will be between ~2-6 C/min
There should be no need to increase the output while the ingots melt and the temperature continues to rise
But don't let the power or temperature dip (it shouldn't but just don't)
Once the melt has finished (or nearly so), the ramp rate will slowly decrease and the temperature will still increase
Ramp rate will be between ~1.5-3 C/min
If ramp rate goes down to ~1 C/min, increase the output power by 0.1
Go to 700 C like this (above method)
Set cell temperature to 750 in Amber, with ramp rate of 10, and put Eurotherm in auto
Go to 750 at 10 C/min.
Let the cell soak at 750 C for about 30 minutes to stabilize (monitor it)
Set the interlock box and test it: Follow the Aluminum Interlock Wiki
Then we have to set the Eurotherm minimum output power and double-check the interlock (steps in Aluminum Interlock)
Set the cell to 800 C and we are done (also in Aluminum Interlock)
Add maintenance log record when finished describing melting conditions, e.g. power, temp, any trend chart features
Setting the interlock box
Sample Data from Al melting
May 21, 2015
This is an example, your numbers might vary. Large differences are noteworthy-- call someone
Output/Note | Temperature [C] | Voltage [kV] | Current [A] | Note |
10.1 | 602 |
|
| 10:52 AM |
10.4 | 609 |
|
| 10:55 AM |
10.6 | 611 | 8.2 | 4.7 |
|
11 | 614 | 8.6 | 4.8 |
|
11.5 | 618 | 9.0 | 5.0 |
|
11.8 | 622 | 9.3 | 5.1 |
|
12.0 | 627 | 9.4 | 5.1 | First ingot melted, temp spiked by 3 C. Don't change power, monitor melting. |
12.0 | 632 |
|
| Second ingot melted |
|
|
|
| 5 ingots melted, temp went from 624 to 650 C at 12% OP in 4 minutes |
|
|
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| Last two ingots melted at 11:17 AM. Power stayed at 12%, temp continued to rise. |
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| Get temp to 700 C, switched to Amber control; 11:46 AM |
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| Increase Al temp and set interlock box as prescribed. |
13.0 | 750 | 10.3 | 5.3 | These Sorenson values needed to be transferred to the backup Sorenson. |
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| When done, we raised the temperature to 800 C with Eurotherm in auto. |
14.3 | 800 | 11.3 | 5.7 | Final numbers |
Freezing
Add maintenance log record when finished describing freezing conditions, e.g. power, temp, any trend chart features
Important (upon freezing): Most of the charge/crucible stress occurs at lower temperature. To relieve built-up stress, John English recommends holding the cell at 400C for a number of hours.
First, it is important to disable the Al interlock. This is done by inserting the key into the Al interlock box and turning it to disable.
Set the Eurotherm minimum output to 0.0%. Do this by:
setting the Eurotherm to Full mode in the Access menu
Going to the Output menu oP
Setting OP.Lo to 0.0
Going to the Output menu SP
Setting SP.Lo to 10
It's ok to cool the Al cell down to 700 at 10C/min before starting the recipe. This will dramatically cut down on recipe time, and Al won't free at this temperature. If you start the recipe at 800C, it will take ~24 hours, so be prepared.
Once it freezes, set the output high on the Eurotherm to 0.0 to prevent a re-melt, and set the Amber setpoint max limit to 10.
Constant Power
With the Al Eurotherm in Manual mode, load the Al Freezing recipe and modify the starting values in steps so that it ends at 0.0% power. Start and monitor the recipe. The Al Base will go down at 0.1% per 10 minutes, which results in a decrease of about 1 C per 3 minutes, at first, then up to 1 C per 2 minutes. On April 6, 2016, it took 4 hours to go from 800 to 700 C, and 7 hours to go from 800 to 610 C. The Al froze over the span of ~40 minutes, starting at about 7.25 hours into the freeze recipe. The temperature plateau'd then kept dropping, briskly at first then to the same rate as before.
Constant Temperature
With the Al Eurotherm in Auto mode, start cooling down the cell using setpoints and a very slow ramp. Go very slow, 1C/min from 50C above freezing to 50C below freezing. If you need to save the crucible, go as slow as you can afford after that (like 2C/min). Aluminum keeps contracting as it cools but gets stiffer, so you can't go fast.
Freezing Notes
The first time we froze Al in Bravo's 200g Al SUMO, the Al crucible was overloaded with source material (something like 60 grams instead of the max of 25 grams). The crucible did not break, but because of the amount of Al left in the crucible it got bent along the long axis and got wedged in the source. It took a lot of force to pull the crucible out. Thus, it is probably wise to avoid freezing Al if most of the charge is still unused (especially if the crucible is overloaded). (July 2012 HPN)
Freezing Recipe
Updated as needed
title (Bravo Al Freeze Recipe 20170510)
comment (Al crucible Freezing)
! ****************************************
! Grower: SDM/NTS
! Description: Freeze Al
! Date: 20170510
! Al crucible is empty !
! ****************************************
! Before starting....
! Disable the Al interlock
! Change the minimum output of the Eurotherm to 0%
! Set the Al cell to 700 C ramp 10 C/min in auto mode and let stabilize
! Adjust the starting Al_Sub_Out to today's value
! Adjust the number of repeats/loops to be 10x Al_Sub_Out starting value
waitop (complete the comments at the top of this recipe)
! change starting value
! Starting value at 700 C between 11.2 and 11.6
! Setting start point to lower value as the cell is there most often
eval Al_Sub_Out = 11.2
! change number of repeats/loops
! Important (upon freezing): Most of the charge/crucible stress occurs at lower temperature. To relieve built-up stress, John English recommends holding the cell at 400C for a number of hours.
! Note on 20170510 we are "freezing" an empty crucible we will try to re-use, so we will manually pause the recipe around 400 C for 2-3 hours
! It is good practice to do this manual pause every time to prevent crucible deformation or damage that makes crucible handling more difficult
comment (Consider pausing recipe around 400 C for hours)
repeat 112
eval Al_Sub_Out = Al_Sub_Out - 0.1
setparameter Output AlBase=Al_Sub_Out
wait 00:10:00
er
comment (End Al Freeze recipe)Melting at Stanford
Unmodified from Stanford MBE lab... Please modify
It is very important that you know what temperature aluminum will freeze at, both for emergencies (Did aluminum freeze in that power failure, or not?) and also for when it's time to freeze the cell before an opening. The freezing point will vary from one loading to another, so the only way to be sure is to measure the actual melting point.
Start at moderate temperature (200-400C). Set Eurotherm switch to High voltage and let it stabilize for a few minutes. Ramp to 600C, let it stabilize again. Ramp up by 1C/min, checking every 2-3C until melted; you may need to turn up the current limit. Record the initial & full melt temperatures with comments in /mbe/sources/mbe4sources. TC temp may be wrong by 50C or more in either direction, so don't just let it go. You may also find it useful to record the Eurotherm temperature and output power every 10-20 seconds. Sometimes the melting point can be discerned from a small increase in power. (Note: Mike DeBruzzi at Veeco says the majority of stress in aluminum is below the freezing point, so you should ramp slowly even if the aluminum is solid.)
To set power limits: (backup power, minimum power, minimum temperatures, and the %power if the input thermocouple breaks)
After full melt, ramp both cells (Al1/Al2, or Al/In) to ~50C above the melting temperature. Set both Eurotherms to manual power. Plug in the backup power supply. Have someone else briefly pull the "normal" 120V power from the blue & white backup supply so it trips, and watch Al & In temperatures to see if they go up or down, and hit little red Reset button on front of the backup supply. Adjust the backup supply with a small screwdriver and repeat until temperature is stable when going to and from backup power. Set Eurotherm low temp limit to this temperature. Also set the minimum temperature in /mbe/sources/mbe4sources for each cell.
"I/P break %" is the amount of power which the Eurotherm should provide in case the input thermocouple breaks (i.e. once a year!). Set it to a large value to start with, 70-100% depending on how high the current limit of the Eurotherm is set (use 100% if it's barely high enough to maintain the cell at this temp). Set idle temperature in /mbe/sources/mbe4sources at least 20C higher.
After outgassing cell, ramp back down to idle temperature, let stabilize, set to manual power, and record the power %. Set "I/P break %" to this value.
At idle, verify that the low-temperature switch on the backup power is
functioning correctly... Flip the switch on the blue & white box to Armed (not Override). Set Alarm 1 on the Eurotherm to a temperature just above the idle temperature, and make sure the blue & white box trips the cell to backup power. This is necessary in case the Eurotherm or its power supply fails but the building power is still okay (like happened to System 1). If it's working okay, set Alarm 1 to 20C below the idle temperature.