-----Original Message-----
发件人: Brent Hickel <hickelb@uswest.net>
收件人: Bradley VanDike <bvandike@yazaki-na.com>; DANIEL@proton.com.my
<DANIEL@proton.com.my>; SiderWhite@worldnet.att.net
<SiderWhite@worldnet.att.net>
抄送: rp-ml@bart.lpt.fi <rp-ml@bart.lpt.fi>
日期: 1999年4月10日 3:27
主题: Re: More info on freeze cast process (FCP), ATTN: Andy Scott
>Evaporation of water at increasingly lower pressures cools the remaining
>liquid to the freezing point.
>
>
>Temperature of vaporization lowers as the pressure decreases (Gas Law
>PV=nRT). Evaporation takes energy, which is passsed fom the liquid
>molecules of H2O to the evaporating molecule, thus cooling one and heating
>the other(Entropy). As the pressure decreases, the water vapor molecules
>are sucked out by the vacuum pump thus taking energy out of the system.
>Eventually the remaining liguid will freeze and begin to sublime directly
>from ice to vapor.
>
>BRENT
>-----Original Message-----
>From: Bradley VanDike <bvandike@yazaki-na.com>
>To: DANIEL@proton.com.my <DANIEL@proton.com.my>;
SiderWhite@worldnet.att.net
><SiderWhite@worldnet.att.net>
>Cc: rp-ml@ltk.hut.fi <rp-ml@ltk.hut.fi>
>Date: Friday, April 09, 1999 9:23 AM
>Subject: Re: More info on freeze cast process (FCP), ATTN: Andy Scott
>
>
>I have seen water freeze in a vaccum chamber. What takes place that causes
>that to happen? Does the extraction of air molucules cause the temperature
>of the vaccum chamber to drop?
>
>Brad Van Dike
>Yazaki North America
>Canton, Michigan
>e-mail: bvandike@yazaki-na.com
>phone: 734-844-6994
>
>>>> "Monica & Glenn Whiteside" <SiderWhite@worldnet.att.net> 04/09 12:12 AM
>>>>
>Dan:
>
>Your ideas would probably work OK. I think one of the toughest areas would
>be in designing the mold correctly, figuring out the "expansion factor"
>necessary to accomodate for the water-to-ice transition multidirectional
>growth.
>
>Regards,
>
>Glenn Whiteside
>
>>Glenn & Andy,
>>
>>I wonder if following will make for a repeatable process, without air
>>entrapment:
>>
>>1. place the mold and water in a vacuum casting machine (Kugelgen, MCP,
>>etc.)
>>2. degass the water in a vacuum chamber
>>3. after degassing, but before the water freezes, pour water into mold
>>4. contiune applying vacuum until frozen
>>
>>Any thoughts?
>>
>>---
>>Regards,
>>Dan Davis
>>PROTON Rapid Prototyping & Manufacturing Center
>>Hicom Industrial Estate, Batu Tiga, PO Box 7100
>>Shah Alam, 40918 Selangor MALAYSIA
>>+60 3 515-2380 phone/fax
>>http://www.protoncar.com/rapid/index.htm
>>
>>
>>> -----Original Message-----
>>> From: Monica & Glenn Whiteside [SMTP:SiderWhite@worldnet.att.net]
>>> Sent: Thursday, April 08, 1999 8:57 AM
>>> To: Rapid Prototype Mailing List
>>> Subject: More info on freeze cast process (FCP), ATTN: Andy Scott
>>>
>>> Andy:
>>>
>>> In reply to your question I have quoted some more information from the
>>> article that might answer
>>> some questions that people may have:
>>>
>>> "Fine-tuning the process:"
>>>
>>> "Not surprisingly, many problems were encountered during the
>>> development
>>> of the freeze cast process.
>>> Mold design was particularly challenging, because water expands as it
>>> freezes. Fortunately, ice exhibits the same linear expansion
>>> repeatability,
>>> if frozen at the same temperature. However, the expansion is
>>> multidirectional (I take this to mean that water is isotropic - GW).
>>> Therefore, the elastomer mold must be designed to provide enough extra
>>> volume to absorb multidirectional forces. Moreover, the thickness and
>>> consistency of the elastomer must be correlated with the different
>>> modules
>>> for the different shapes of the castings".
>>> "After conducting hundreds of tests and measurements, problems
>>> involving
>>> the morphology of castings and the induced stresses were resolved. A
>>> system
>>> was developed in which several basic geometries were designed, to
>>> which
>>> certain semi-constants could be applied in the design of a specific
>>> mold. A
>>> major breakthrough came when directional solidification was viewed in
>>> terms
>>> of expansion rather than shrinkage".
>>> "Another major problem was how to prevent the cracking caused by
>>> stresses induced in the ice pattern by constricted freezing. This was
>>> studied and attacked from three different directions: mold design, the
>>> freezing medium's velocity and temperature, and air content in the
>>> water/ice
>>> system. It was discovered that
>>> extremely low temperatures trigger cracking, particularly when the
>>> patterns
>>> are stripped at higher temperatures. This problem was adressed by
>>> "conditioning" the ice, just as wax is conditioned prior to being
>>> injected.
>>> Conditioning involves controlling the air content of the ice and
>>> regulating
>>> additives (amount and chemistry) in the water".
>>> "Warmer mold temperature was found to be crucial for fast, clean
>>> stripping of rubber molds. Parting sprays that do not freeze,
>>> pre-chilling
>>> the water solution, and higher temperatures are used for
>>> fast-stripping of
>>> the molds".
>>> "Air bubbles trapped on the surface of the ice were a recurring
>>> and
>>> persistent problem, in spite of molds designed to permit air bubbles
>>> to
>>> escape. Unfortunately, these bubbles would be reproduce on the
>>> surface of
>>> the casting. This problem was minimized by controlling turbulence and
>>> counter pressure within the mold, through proper mold design and
>>> venting. A
>>> vacuum was also applied in a sealed chamber, prior to and during the
>>> mold-filling procedure. A combination of these methods, along with
>>> special
>>> additives for the water, finally eliminated the air bubbles".
>>>
>>> Fascinating process!!
>>> Hope this additional information helps.
>>>
>>> Best Regards,
>>>
>>> Glenn Whiteside
>>>
>>>
>>>
>>> >In a message dated 99-04-05 19:39:55 EDT, SiderWhite@worldnet.att.net
>>> writes:
>>> >
>>> ><< Then water
>>> > (with "special" additives to minimize air bubbles) is poured into
>>> the
>>> rubber
>>> > mold and frozen. >>
>>> >Water expands when it freezes. Is it isotropic? Then you need to
>>> compensate
>>> >for the metal shrinkage as it cools. Sounds to me, it might take a
>>> few
>>> >iterations to get the numbers dialed in.
>>> >Andy Scott
>>> >Lockheed Martin Aerospace
>>> >
>>> >For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>>> >
>>>
>>>
>>> For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>>
>>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
>
>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
>
>
>For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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