More info on viscosity of 7100

From: Miller, Michael W (
Date: Tue Mar 23 1999 - 02:57:32 EET

This is follow up information on comments I made some weeks ago on the viscosity increase of DuPont 7100 in our sla500.
Although the exact cause of the viscosity increase was not determined there are two factors that likely exacerbated the problem:

1) For an undetermined amount of time our sla500 had problems finding sensor 1 thus subjecting the resin to excessive scatter radiation.

2) We've never cleaned out the vat.

Any polymerized resin, either from failed builds or scatter gradually collects in the bottom of our vat. According to DuPont (technical bulletin #2, Stability of Epoxy Stereolithography Resins), polymerized resin acts as a catalyst via extraction on the resin in contact with it and will typically cause the viscosity to increase exponentially with time. Other situations which can cause instability are excessive draining of parts, light exposure, high temperature, and low humidity. Of course, with these new high speed resins, instability is even more likely.

I highly recommend you read the technical bulletin at , and clean your vat! I hear an aquarium net works. I would also appreciate some 3rd party feedback on BKP INTECH ( who makes a removeable screen. Thank you DuPont for resolving this issue in a timely and satisfactory manner.

Michael W Miller (
The Boeing Company MS 17-PE B-XT62
Propulsion Experimental Hardware 206-655-3289
Rapid Prototyping 655-4366 Lab 655-4365

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