Dear RP-World,
Thank you to all the people who responded with recommendations for our
rotor client. My original posting is repeated below. This posting is a
review of the responses received.
The neutral buoyancy is going to be the hardest property to satisfy
directly in a fabricator. Materials that are likely to be strong enough for
the rotor include:
-- Cibatool SL-5149 urethane-acrylate for SLA 250
specific gravity (SG) = 1.07, fully waterproof
-- DTM's Duraform for laser sintering
SG=0.97, needs coating to resist swelling in water
-- ABS for the Stratasys FDM, SG=1.05
-- Cubital's material for the Solider, SG=1.1
-- DTM's nylon composite for laser sintering, SG>1
Several people suggested placing small cavities in the rotor design or
drilling holes in the rotor to reduce the overall density. I think that
approach is needlessly complicated and defeats the purpose of prototyping
the actual desired geometry.
I have recommend to the client a "rapid tooling" approach, which was
suggested as an alternative by several respondents. In this approach, of
course, a fabricator is used to make a tool (mold) for the prototype rotor.
Then they can use either the production material or a polyurethane modified
to match the target specific gravity. For polyurethane, silicone rubber
tools can be cast from masters made in a variety of fabricators, and one
might expect to get a dozen or more prototype rotors from a single tool set.
For polypropylene, an epoxy tool could be used for injection molding. This
would allow them to run a much greater quantity, if this is interest, and it
should match the production characteristics most closely. I offered to
recommend a number of shops for these tooling procedures, or to manage the
project for them at Ennex. If they ask us for referrals or to work on the
project further, I will first consider for the job the people who responded
to my posting.
Best regards,
Marshall Burns
Marshall Burns wrote on October 14:
> Dear RP-world,
>
> We have a client that wants to prototype and test a water
> flow-measuring turbine rotor. They need a specific gravity of 0.9 +/-
> 0.02 for neutral buoyancy.
>
> What fabricator ("RP") materials can people recommend that
>
> (a) have specific gravity of 0.9 +/- 0.02
> (b) do not swell or degrade in water ("cold" tap water, 40
> to 75 F), and
> (c) will stand up to continuous free (ie propelled by the
> water, not powered) rotation of about 1850 rpm with short term exposures
> to 2400 rpm.
>
> The rotor has 16 blades 0.126 inches thick and 0.765 inches wide
> with root and tip diameters of 2.5 and 3 inches respectively and a 30
> deg twist. The production material currently is molded polypropylene,
> which has adequate properties.
>
> I know that Cubital has reported successful results with underwater
> rotor testing under much more challenging conditions. Does anyone want
> to recommend specific materials for this application on a Solider, SLA,
> Sinterstation, FDM, or other fabricator?
>
> I would be happy to hear from fabricator shops (service bureaus) on
> materials you work in. Helpful responses that indicate they offer
> fabrication services in the recommended material will be referred to the
> client. Third party recommendations of good shops for a project like
> this will be appreciated as well.
>
> Feel free to respond publicly or privately. I will post a summary of
> nonconfidential information received.
>
> Best regards,
> Marshall Burns
-- Marshall Burns Marshall@Ennex.com***************************************************************** ***** ENNEX(TM) CORPORATION ***** Fabbing the Future(TM) ***************************************************************** ***** 10911 Weyburn Avenue, Suite 332, Los Angeles, U.S.A. 90024 ***** Phone: +1 (310) 824-8700. Fax: +1 (310) 824-5185 ***** E-mail: fabbers@Ennex.com. Web site: http://www.Ennex.com ***************************************************************** ***** Copyright (c) 1998, Ennex Corporation
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:47:00 EEST