Alumilite white and aluminum mold issue

[Anzomcik]

I am casting blanks of alumilite white into aluminum molds. Once cured and demolded the blanks have a shallow snowflake like voids that cover 10-30% of the blank. No two blanks have the same arangment, and the size and location are different.

I know the resin is filling the void because it leaves a thin skin over the void that is easly wiped off.

Any insite on why this would is happeneing. I have tried several thing at atempting to better the problem with little success. Thanks

[Anzomcik]

http://i487.photobucket.com/albums/rr24 ... hoto-1.jpg

I have tried different amounts of mold release, no mold release, warming the mold to 85 deg-130 deg (several attempt in that range) warmed the alumilite white from 80-120 deg (several attempts in that range). I can not figure out why it is doing that. It seems no matter what I change i can not get it to stop doing it. I have not noticed any improvment with anything i changed either.

[Mike - Alumilite]

Sorry for the slow response as I've been away for a few days but am now back in the swing and online. To me, it looks like the material is shrinking. To solve the mystery, use 50% microballoons and cast one. I may have missed this, but I'm sure you've poured one at room temp. I've had this happen to me with Alumisol lately ... I pour my part and the sprew cools very quickly and the material is then not able to draw (shrink) from my reservoir about my pour hole (sprew) and the material is forced to shrink in on itself from inside the mold. If the temp of the mold is warm enough, the thinner sprew you have may be curing first and not allowing the material to "shrink" from the draw point which is your sprew and reservoir where you pour from.

Just a thought but to confirm the "shrink" theory, I'd first load up a cast with at least 50% and maybe even 100% microballoons which will negate any shrink to test the theory. Then if that is the case, I'd go back to a room temp mold and see if that keeps the thinner sprew area liquid longer than the bigger mass of the thicker body to see if it will then draw from the sprew/pour hole/reservoir to eliminate the problem.

Please keep us posted and lets get this mystery solved.
Mike

[Anzomcik]

To start fresh i poured a blank this morning. Temp was 70 degrees (microballon, mold, and A,B side of the White all at room temp.), I used 42 grams of A, 42 Grams of B, and 90cc of microballons.

The blank was pulled and it still had the snowflake shaped depressin spots. It was better that previous attempts but still enough to warrent further investigation.

Generally my pour is 45grams of A, 45 grams of B, and 70 CC of micro ballons.

The pour when setting up volcanos out of the spru, like normal, so i know it is expanding, does the resin shrink that much after setting up?

[Mike - Alumilite]

If the material was volcanoing out of the sprew, the microballoons perhaps contained a little moisture. If that is the case, I don't believe the material was shrinking but do feel as though we are trapping air in the mold. Are you pouring it vertically? How many vents are there?

Mike

[Anzomcik]

I am pouring vertically. I store the MB in the same sealed cabnet as all my other casting chemicals. So is the possibility there, yes, but its somthing i feel isnt likely. They show no outward sign of moister.

I just poured a blank from my prototype RTV mold and one for the aluminum mold and the blank from the AL mold had the same depressions randomly on the blank, while the RTV blank came out perfect.

I only have one vent it is the spru (i pour the resin in a slow steady stream), I have not had issue doing that with rtv. But i may try putting in a few small vents.

Has you experenced any issues with AL molds before?

[Mike - Alumilite]

No. We even have some automtive applications that use aluminum tooling with no issues whatsoever. RTV's shrink rate is a fraction of what the urethanes are.

When you pour down the sprue hole in a thin stream allowing air to vacate at the same time, is the resin cascading all the way down to the bottom of the mold or is it hitting the side and slowly rolling down similar to the way you would tilt a glass when pouring a beer?

This really has me baffled and wish you were near Kalamazoo.
Mike

[BassinK9]

Anzomcik...... maybe you could send Mike one of your castings for him to analyze?

[Anzomcik]

I will post more photos in the next day or so showing the mold and the bait.

Mike I pour the bait through the "tail" and the stream falls all the way to the nose of the bait, I am very confident that the air is getting out. Reason for my confidence is I am doing the same exact process on the same bait in a silicone mold with no issue. I got aluminum molds made for faster production (3 cavity vs 1 cavity) and easier ejection with the 2 piece mold.

[Anzomcik]

I made molds off of my aluminum molds (because i am in a pinch) The new RTV molds preform great, I am not getting the shallow snowflake all ove the baits like i did with the aluminum. It is the same exact bait I am still baffled why the aluminum was doing that.

Attached is photos of the aluminum mold. it shows the spru in the tail and how the mold will fill. Then i have a few more photos of the markings i was getting when using the aluminum molds. Keep in mind the RTV mold was not doing anything like this, the baits were coming out very clean, with minor parting line missmatch (to be expected when compaired to machinged aluminum mold)

http://i487.photobucket.com/albums/rr24 ... k/mold.jpg

http://i487.photobucket.com/albums/rr24 ... /mold3.jpg

http://i487.photobucket.com/albums/rr24 ... /mold2.jpg

[Mike - Alumilite]

For kicks and giggles, pour only 1/2 full of resin that is required and allow it to start curing. Once the first pour hits approx the 7-10 minute mark, pour another batch on top of it. Maybe even do a three pour bait. I still believe shrink or the material expanding as it heats up during the exotherm and shrinking while cooling as it cures has something to do with it. The aluminum mold has no forgiveness and does not have any capability to flex like a silicone rubber mold and maybe causing the issue. Its worth a triple pour to see if it affects the way it cures. This would simply rule out a factor for us.

I have customers pouring large baits ... some in upwards of 17" that are the same basic shape in aluminum molds with no issues. The only factor that is different is the number of vents/sprues.

Mike

[bassfencing]

hey mike What mold material should I use for pouring lead into mold (which one will be better to handle hot lead pour?).Thanks

[Mike - Alumilite]

Mold Putty is typically my choice. Its fast, easy to use, and holds up decent to the temp of low melt metals. Will not last forever but will last awhile depending on the size of the pour. Big, deep pours take longer to cool and typically break the molds down faster.

Mike