Common Casting Questions

Yigal Sharaby

<div class="jnlc-container" id="jnlc-container"> <img src="http://static1.shopify.com/s/files/1/0014/5692/files/CastingQA1.jpg" width="360" height="200" class="floatLeft" /> common casting questions Q: What causes water marks on castings? A: The most common cause of water marks is due to inadequate mixing time of an investment slurry. If the water and powder are not properly incorporated by mixing for precisely four minutes the result is "free water" separating from the mixture and running on or around the wax or plastic pattern, leaving subsequent water marks on the burned out mold. Q: I have mixed the investment slurry for precisely four minutes and I am still getting watermarks. What is the cause of this? A: There are two known reasons that this problem continues, even after proper mixing. The water is being driven out of the mixture by the force of sedimentation due to the long gloss-off. This occurs due to too cold of a water temperature in the mixture or a water quality of two high or low of a pH. Solutions to these two occurrences are: <ul> <li class="JNLC-copy">If the problem persists after proper mixing times, one should time the gloss-off. If the gloss off exceeds twelve minutes, it is necessary to heat the water used in the mix to speed the gloss-off. Water temperatures between 76Â°F and 78Â°F commonly give excellent results for this problem. </li> <li class="JNLC-copy">Distilled or de-ionized waters are preferable over tap water, due to the neutral pH of these treated waters. When using tap water, it should be left to sit for no less than thirty minutes to allow the chlorine and other chemical treatments to dissipate. </li> </ul> Q: Why does it take so long for platinum investments to set-up? A: Platinum investments are generally 98% silica sand, with the remaining percentage ingredient giving the material strength by sintering the investment in the burnout process. A high percentage of sand, with no chemical binders produces a sedimentary investment. Therefore, the investment particles have to slowly settle by gravitational force, to the bottom of the flask, slowly displacing the water content of the mixture. Due to the size of the particles this process usually requires 12 to 15 hours to complete. <a href="/pages/other-techniques"><img src='http://static1.shopify.com/s/files/1/0014/5692/files/Back1.png' alt='' /></a> </div>

2008-10-10T21:43:04-04:00

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2008-10-10T21:43:04-04:00

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Common Casting Questions 2008-11-04T12:10:14-05:00 <notextile> <div class="jnlc-container" id="jnlc-container"> <img src="http://static1.shopify.com/s/files/1/0014/5692/files/CastingQA1.jpg" width="360" height="200" class="floatLeft" /> common casting questions Q: What causes water marks on castings? A: The most common cause of water marks is due to inadequate mixing time of an investment slurry. If the water and powder are not properly incorporated by mixing for precisely four minutes the result is "free water" separating from the mixture and running on or around the wax or plastic pattern, leaving subsequent water marks on the burned out mold. Q: I have mixed the investment slurry for precisely four minutes and I am still getting watermarks. What is the cause of this? A: There are two known reasons that this problem continues, even after proper mixing. The water is being driven out of the mixture by the force of sedimentation due to the long gloss-off. This occurs due to too cold of a water temperature in the mixture or a water quality of two high or low of a pH. Solutions to these two occurrences are: <ul> <li class="JNLC-copy">If the problem persists after proper mixing times, one should time the gloss-off. If the gloss off exceeds twelve minutes, it is necessary to heat the water used in the mix to speed the gloss-off. Water temperatures between 76Â°F and 78Â°F commonly give excellent results for this problem. </li> <li class="JNLC-copy">Distilled or de-ionized waters are preferable over tap water, due to the neutral pH of these treated waters. When using tap water, it should be left to sit for no less than thirty minutes to allow the chlorine and other chemical treatments to dissipate. </li> </ul> Q: Why does it take so long for platinum investments to set-up? A: Platinum investments are generally 98% silica sand, with the remaining percentage ingredient giving the material strength by sintering the investment in the burnout process. A high percentage of sand, with no chemical binders produces a sedimentary investment. Therefore, the investment particles have to slowly settle by gravitational force, to the bottom of the flask, slowly displacing the water content of the mixture. Due to the size of the particles this process usually requires 12 to 15 hours to complete. <a href="/pages/other-techniques"><img src='http://static1.shopify.com/s/files/1/0014/5692/files/Back1.png' alt='' /></a> </div> </notextile>