Silicone Sac

[Reefallo]

Tried my first repair this morning; didn't get very far. Did a "dry run," to see if I could stretch the sac enough to fit it over the section nipple.

 

Didn't work, because the sac tore instead.

 

Is that normal for silicone sacs? No give? Easier to work with a traditional sac?

 

BTW, this was me using just fingers...

[loudkenny]

I resacced my 1920´s Senior Duofold with a silicone sac about two weeks ago, and here´s what I learned...

 

1) The sac diameter is very important, and IMO isn´t meant to stretch. You must choose a sac with an ID very close to the section nipple OD, or the sac will not go on and stay there. If the sac is too tight either the sac will not stay on the section no matter what you do, or it rips.

 

2) Wash out the inside of the sac with alcohol and cotton swabs to remove any traces of mold release before you glue, or it doesn´t stick.

 

3) The glue you use is very important. I tried GE silicone that gave off methanol instead of acetic acid when it cured, and it stuck well once it dried. I also used shellac on another sac, and it seemed to work OK but the jury is still out on that one.

 

ken

Edited November 27, 2014 by loudkenny

[Ron Z]

Are we talking about silicone sacs from David Nishimura (vintagepens.com) or "silicone" sacs from Woodbin?

[loudkenny]

I get all my sacs from Brian @ Anderson Pens, which is only about 25 miles from me.

 

Mine have the mold lines, so I think they are originally from David N.

 

ken

[Reefallo]

The ones I bought were also from Anderson; also with mold lines. I was going to do the "heat test," until I got to the part where the sac tore.

[Ron Z]

Then you really do need to use silicone cement i.e. a non-corrosive RTV silicone to attach the sac. The sac will not stick to the silicone.

[adyf]

Are we talking about silicone sacs from David Nishimura (vintagepens.com) or "silicone" sacs from Woodbin?

 

Ron, what would be the difference? Are different adhesives required or are they different thickness?

[Ron Z]

The sacs from David are true silicone, injection molded. The sacs from Woodbin are really PVC. To test for PVC VS silicone, David did a number of tests with heat. Silicone doesn't melt or burn. The Woodbin sacs do. I sent David a couple to test, and the plasticiser in them lifted the laser printer type off of the note that I included with the sacs.

 

Not that I don't use them. They're the only thing that I will put in Sheaffer pneumatic fillers (snorkel, TD and PFM, and they can be used in hard rubber pens. But I avoid using them in celluloid pens and some other plastics. I don't think it's an issue in the modern acrylics though because many of these don't react to any solvent I've tried on them.

For a deeper discussion of the different sac materials take a look at my post titled No Silver Bullets.

 

With both types, the sac should be cleaned out with a cotton swap soaked in alcohol to remove any residual mold release compound. Different adhesives are required. You can use shellac with the PVC. Only silicone sticks to silicone, so an RTV (Room Temperature Vulcanization) silicone adhesive should be used. Standard RTV gives off acetic acid, which may or may not be harmful to celluloid. The amount is so small that it may not matter. Non-corrosive RTV gives off alcohol as the material cures. For best results you want a thicker compound though, not a potting RTV compound.

[adyf]

Thanks for the detailed explanation Ron. I guess you no longer use latex sacs on Sheaffer pneumatic fillers then.

[Reefallo]

I decided today I would just use a regular sac. All I was trying to do with the silicone sac was prevent future discoloration of the barrel on a celluloid Balance, but I figured for my first repair, I'll try the regular and see what happens.

 

The regular sac presented its own set of issues, but if you can't even stretch the silicone sacs over the nipple, that's a whole different kettle of fish.