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Re: NEON- Sintering and burning

On 09/01/96 18:52:41 you wrote:
>
>Ed (eduzuzio, that is) wrote:
>>I am going to lean in Dirk's direction and guess the coating or binder is
>>>helping the staining. Could be that the binder was not sintered at the
>>factory >or the units were bombarded to the extent of burning the coating.
>>I suppose the >rest of the box of glass would provide a few clues. While
>>bombing post coated
>>glass you can tell during the pocess if the tubes were baked properly.
>>Tubes >that have been coated with suspension and not properly baked yield
>>similar >results. At the very least the light from the tubes is sort of
>>gray...
>>Peace
>
>I know this post was a while ago, but I had it on my list to respond to.
>I'm interested in hearing more.  While visiting the Dutchies and Neon Lewa
>and watching them pump, I noticed a difference between the dry powder units
>being pumped and the liquid suspension ones.  You could almost watch the
>difference in pressure increase with the dry powder units since they'd not
>been baked out.
>
>That is what the sintering process is, right; the tube is heated just below
>the melting point to fuse the phosphor particles to the glass?  If so, is
>that what I saw with the dry powder units; more than usual gasses being
>released as the phosphor particles become fused by the heat and pressure?
>Is it the binder outgassing or a pressure build up from all that activity
>(or is that one and the same)?
>
>At any rate, Ed's post made me wonder about seeing that in precoated
>tubing.  He seemed to imply that it does happen if the tubes aren't baked
>out sufficiently.  I've never really noticed anything in precoated tubes
>that I can compare to watching this happen at the Dutch shop.  At Neon
>Lewa; it was such a contrast between the oven baked tubes and the dry
>powdered, it was subtle, but I could tell.
>
>Ed also mentioned burning the coating during bombing.  I know that I've
>done this on occassion and am curious if anyone could speak to this.  At
>what temp. does this happen.  I know that when I've made the error and done
>this, it's a result of bringing the glass temp. up too fast and then having
>to heat the electrodes after the glass has reached temp.  So, the glass
>ends up getting hotter than it should.  What's the upper temp. limit for
>damaging the phosphor in precoated tubes, does it vary by manufacturer,
>phosphor, etc.  I'd say from my experience I've seen it happen around a
>tight window within 250-275C, yes/no/higher/lower?
>
>Thanks,
>
>Tom U.
  
The sintering process I was refering to is just that. Baking the coated glass to bind the coating to the wall 
of the glass tube and remove any trace of the binder itself. I am pretty sure that if the glass is not 
outgassed in the oven it will take the bombarding procedure as oppurtunity to further outgas and/or sinter.

Indeed I am implying and that precoated neon glasswork will bomb much better if baked the evening 
before bombing. I have done this many times in Holland and the results are amazing. I'd bet the cow, not 
the whole farm, that this procedure makes a much cleaner tube. Once the tube is baked the only other 
potential moisture and contaminents come from attaching the electrodes and condensation. Compared to 
the moisture from bending these are minimal. If are are fortunate enough to know the Dutch Technique you 
can easily see the advantage of baking any neon glasswork prior to bombing. The process of American 
practices allows so many contaminents into the tube. For example, many will take glass out of a box and 
slide it onto the bending table. This alone allows any and all particles on the table to be introduced into 
the tube. Now put your first bend in that tube and the moisture and condensation lock those particles in 
place. (By particles I mean dust and similar components). Although this may also happen with other 
techniques washing and baking the tubes balances the scale.In the future of my company one goal is to 
employ an oven. At this point I think I would still use pre coated tubes, I would rinse them with distilled 
water after bending, gently air dry them and bake them prior to troding and bombing. However a more 
realistic goal is climate conrol and air quality in the shop. Has this been discussed yet? I hate bending 
glass when it is humid...not good for the glass coating or the glassworker.
 
Peace.