Delay element problem

[mobster1930]

I hope this it the right subforum for this topic, forgive me if it's not. I work in in the mining detonator industry and we have a problem with our delay element. The delay composition is made out of 60% Pb3O4, 30% Si and 10% Sb2S3. This delay composition for detonators has a delay of 500ms, +-12ms tolerance. When we test the batch right out of the production, it's fine and the tolerance is indeed +-12ms. However, after 7 or more days in storage, the delay seems to fluctuate quite a lot, increasing by 20% to 30% from the original 500ms.

What could be the possible reasons behind this ? What should we look into? Our chemics can't figure it out and they're saying "it was always like this", like it isn't a problem at all.

 

[Compositepro]

The first thing I would suspect is moisture in your raw materials or being absorbed during or after manufacture. Moisture can cause your materials to react slowly at room temperature and it will absorb some reaction heat which would slow the reaction after ignition.

 

[mobster1930]

We've taken a few detonators out of the series and put them in a humid environment. We'll see the results soon and I will let you know if that was indeed the cause.

 

[itsmoked]

We're all are seeing different weather.. Here, where I live, we maybe had one or two days a year we'd call 'humid'. We also would say we had about, oh, five or six notably windy days a year. This year we've probably had 40 days of high humidity and several months of windy days in a row.

I agree with Compositepro that it could be moisture and that if you're location is seeing different weather than 'before' research it for changes from last year and how they could affect your process this year.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

Another important factor is particle size of the powders. Finer particles can segregate from coarser particles in handling or while feeding from hoppers. This can cause variability within a batch. It is possible that your sampling plan is making variability within a batch appear to be variability with time. Just something to ponder.

 

[georgeverghese]

Could it otherwise be due to oxidation of antimony sulfide in air ? - Wiki says stibnite oxidises in air.