Resin curing question,

[stevers]

Ok folks, got a question for you. I cast a set of label blanks last night, about 7:00. Today at 2:45PM they are still very tacky and the tube actually moved in one of them as I tried to trim it.
Question is, is this because of the temp change in the area? Went from around 110-115 to 95 in a few days.
Should I increase my MEKP a drop or two to account for this? The resin is only a month or two old. (as far as how long I have had it) It's Mr. fiberglass. I believe it's the temp, but want to confirm first.
By the way, for 3 ounces I use 8 drops.

 

[toolcrazy]

Tacky is normal, I did the same and it took about a week for everything to set. I used 3 drops per ounce. I may try a bit more next time. But you gotta be careful, increasing the MEKP will make the blanks more brittle.

 

[alamocdc]

I typically use 4 drops per ounce and it still takes mine two days to set. But I don't mind b/c they are much less brittle this way.

 

[gketell]

8 drops for 3 ounces is too low. The lowest I have heard anyone using is 3/ounce.

GK

 

[neon007]

Using more mekp will NOT make the blank any more brittle. It just increases the temp and speed of the chemical reaction. Yes temp effects the amount of mekp needed. I use about 4-5cc for 4 ounces of resin.

 

[stevers]

Thanks folks, thats what I thought. When it was 115, it cured OK. I even took them out of the mold and would set them in the sun to dry the outside. Usually only took a few minutes. I'll try altering my MEKP on the next batch.
Thanks All.

 

[dalemcginnis]

Regarding temperature curing faster, could you put it in an oven set on low to help cure?

 

[Fred]

Dale, I would imagine the taste of future food 'might' be different if you use the wife's oven. You just may be eating out a bit more often as well! []

 

[alamocdc]

Originally posted by neon007
<br />Using more mekp will NOT make the blank any more brittle. It just increases the temp and speed of the chemical reaction. Yes temp effects the amount of mekp needed. I use about 4-5cc for 4 ounces of resin.

Not trying to be argumentative, Keith, but the one time I used too much mekp (resin from same can as before and after, and same bottle of mekp), the blanks were MUCH more brittle than any of my others. I suppose it could have been an anomaly, but I'm not risking it again.

 

[mick]

I'm with you Billy, The times I've used more than 3-4 drops per oz I end up with brittle blanks. I noticed that when using more MEKP you get a faster reaction and maybe even a little more heat altho it's hard to tell in the ice molds I use. Whenever I've done this I've usually had almost unturnable blanks. I'm no chemist and we've talked about this back when I was still able to voice chat, but I think that the faster reaction time and higher temp causes the brittleness. This is just MHO but it's what I've noticed.

 

[jack barnes]

Ok not having done any casting yet is there a difference in MEK? I work with MEK in large quainties but I've never heard of MEKP.

 

[stevers]

Don't know, all I know is the P is peroxide.

 

[dalemcginnis]

Originally posted by Fred_erick
<br />Dale, I would imagine the taste of future food 'might' be different if you use the wife's oven. You just may be eating out a bit more often as well! []

Actually, I was thinking of an old toaster oven set at about 150 degrees with the door left open so there was no build up of fumes.

 

[neon007]

I know that when the pieces get brittle people like to blame it on to much MEKP. It is a fact that it does not effect the hardness. I have been doing casting for almost 6 yrs. and I have tried every amount of MEKP imaginable and weather I use 3 drops per oz. or more. It still is the same hardness. Im not trying to start an argument, This is fact. I was given this answer by an engineer who works with polyester resin for the Formica corp. The reason for using different amounts of MEKP is for adjusting for temp, humidity, and different additives, such as colors.

 

[Firefyter-emt]

http://en.wikipedia.org/wiki/Methyl_ethyl_ketone_peroxide []

I knew the Methyl ethyl part, I could not remember the "K" though..

 

[polarbear1]

I have had a casting stay tacky and unable to use for days one time I never did figure out what I did wrong, I would guess it was the mek and temp, or not mixed well enough.

 

[stevers]

Could have been color too. So I hear.