15 Common Molds & Casting Errors

Yigal Sharaby

<div class="jnlc-container" id="jnlc-container"> 15 common mold & casting errors Error 1 Cut mold is warped and doesn't seal evenly: The usual causes for warping are when the rubber used in packing has begun to vulcanize. Under-packing the mold or over-packing the mold also causes this problem. Error 2 Voids in the mold due to air entrapment: There can be a number of reasons for this problem including: <ul> <li class="JNLC-copy">The model is not filled in with rubber. </li> <li class="JNLC-copy">The platens are not at the proper curing temperature. </li> <li class="JNLC-copy">The platens close down too quickly. </li> <li class="JNLC-copy">The mold is not cured for the recommended time. </li> </ul> Error 3 The mold delaminates after curing: This occurs when the surfaces of the strips are not clean. Use new strips when necessary and do not contaminate the surfaces with your hands or any extraneous dirt and dust. Error 4 The mold is soft and sticky in the center: This happens when the mold is underheated or when the cure cycle is too short. Be sure to cure 15 minutes for each ¼"/6 mm. Error 5 Overheating the mold: Overheating can cause a number of problems that will make the mold unusable. <ul><li class="JNLC-copy">The mold having a pebbly surface </li> <li class="JNLC-copy">The mold being sticky -Excessive shrinkage </li> <li class="JNLC-copy">Lack of flexibility in the mold These items can be avoided by checking the calibration of the vulcanizer. </li> </ul> Error 6 Shiny castings before pickling (without the use of deoxidizing investment): This is caused from incomplete elimination of wax. Carbon residue deoxidizes cast metal. Error 7 Porous castings, which will show a dispersion of fine cavities in the metal: This can happen when: <ul> <li class="JNLC-copy">The pattern is improperly sprued. </li> <li class="JNLC-copy">Incomplete wax burnout. -Metal overheated. </li> <li class="JNLC-copy">Mold too hot. </li> <li class="JNLC-copy">Too much "old" metal in cast. Never use more than 50% old. </li> <li class="JNLC-copy">Metal insufficiently fluxed. </li> <li class="JNLC-copy">Too much flux added to metal. </li> </ul> Error 8 "Non-fills" for incomplete castings: The pattern improperly sprued because they are either too thin, too long, or too few. There can also be incomplete wax burnout, the mold can be too cool when casting, the metal can be too cool when casting, or there may be insufficient ammounts of metal by weight. Error 9 Foreign particle inclusions in castings: There can be a number of reasons foreign particles are mistakenly introduced in casting. Such as... <ul> <li class="JNLC-copy">Sharp corners and bends in sprue system. </li> <li class="JNLC-copy">Flask placed in furnace with insufficient setting time. </li> <li class="JNLC-copy">Flask heated too rapidly. </li> <li class="JNLC-copy">Sprue hold not checked for particles after sprue base is removed. </li> <li class="JNLC-copy">Molten metal contained foreign particles. </li> <li class="JNLC-copy">Flask contained rust or is unclean from prior cast. </li> <li class="JNLC-copy">Crucible old and disintegrating or insufficiently fluxed. </li> </ul> Note: Graphite has a tendency to absorb moisture and break down if not properly dried. Error 10 Fins or Flash on castings: <ul> <li class="JNLC-copy">Fins are thin metal extensions that are added on the casting. They occur from: </li> <li class="JNLC-copy">Incorrect water/powder ratio causing weak investment mold. </li> <li class="JNLC-copy">Investing improperly stored. </li> <li class="JNLC-copy">Investing extended past work time, or flasks disturbed while investment was setting. </li> <li class="JNLC-copy">Flask dropped or otherwise mishandled. </li> <li class="JNLC-copy">Flask placed in furnace with insufficient setting time. </li> <li class="JNLC-copy">Bench set timing should be a one hour minimum. </li> <li class="JNLC-copy">Flask heated too rapidly. </li> <li class="JNLC-copy">Flask allowed to dry and not re-moistened before burnout. </li> <li class="JNLC-copy">Flask burned out and allowed to cool before casting. </li> </ul> Error 11 Darkened or rough casting which can resist deoxidizing in the pickling solution: This mistake occurs when the burnout temperature is too high, exceeding 1450Â° F / 788Â° C. Error 12 Bubbles or nodules on castings: This happens when the wax patterns is not painted with a wetting agent. (Wetting agent should dry a minimum of 20 minutes). Investment slurry and/or invested flasks not sufficiently mixed, vibrated, or vacuumed will also create bubbles on the casting. Error 13 Spauling; when some of the investment moves within the mold: Spauling can be a problem when: <ul> <li class="JNLC-copy">There are sharp corners and bends in the sprue system. </li> <li class="JNLC-copy">The flask is placed in the furnace with insufficient setting. </li> <li class="JNLC-copy">The flask heated too rapidly. </li> <li class="JNLC-copy">The investment is handled past it’s work time. </li> </ul> Error 14 Rough-surfaced castings, other than bubbles or nodules: These can be caused by: <ul> <li class="JNLC-copy">An incorrect water/powder ratio. </li> <li class="JNLC-copy">The flask placed in the furnace with insufficient setting time. </li> <li class="JNLC-copy">The flask is heated too rapidly. </li> <li class="JNLC-copy">The pattern material can be trapped in the mold and boiled against the mold’s surface. </li> <li class="JNLC-copy">Too much "old" metal in cast. Never use more than 50%. </li> </ul> Error 15 Watermarks, or grainy surfaces, on the casting: Investing too rapidly is the cause. Note: The temperature is also important. A colder temperature will extend the work time. A warmer temperature will shorten the work time. Keep within the specified time of 9 to 10 minutes. <a href="/pages/other-techniques"><img src='http://static1.shopify.com/s/files/1/0014/5692/files/Back1.png' alt='' /></a> </div>

2008-10-10T20:08:07-04:00

15-common-molds-casting-errors 498132

2008-10-10T20:08:07-04:00

145692

15 Common Molds & Casting Errors 2008-11-04T11:54:06-05:00 <notextile> <div class="jnlc-container" id="jnlc-container"> 15 common mold & casting errors Error 1 Cut mold is warped and doesn't seal evenly: The usual causes for warping are when the rubber used in packing has begun to vulcanize. Under-packing the mold or over-packing the mold also causes this problem. Error 2 Voids in the mold due to air entrapment: There can be a number of reasons for this problem including: <ul> <li class="JNLC-copy">The model is not filled in with rubber. </li> <li class="JNLC-copy">The platens are not at the proper curing temperature. </li> <li class="JNLC-copy">The platens close down too quickly. </li> <li class="JNLC-copy">The mold is not cured for the recommended time. </li> </ul> Error 3 The mold delaminates after curing: This occurs when the surfaces of the strips are not clean. Use new strips when necessary and do not contaminate the surfaces with your hands or any extraneous dirt and dust. Error 4 The mold is soft and sticky in the center: This happens when the mold is underheated or when the cure cycle is too short. Be sure to cure 15 minutes for each ¼"/6 mm. Error 5 Overheating the mold: Overheating can cause a number of problems that will make the mold unusable. <ul><li class="JNLC-copy">The mold having a pebbly surface </li> <li class="JNLC-copy">The mold being sticky -Excessive shrinkage </li> <li class="JNLC-copy">Lack of flexibility in the mold These items can be avoided by checking the calibration of the vulcanizer. </li> </ul> Error 6 Shiny castings before pickling (without the use of deoxidizing investment): This is caused from incomplete elimination of wax. Carbon residue deoxidizes cast metal. Error 7 Porous castings, which will show a dispersion of fine cavities in the metal: This can happen when: <ul> <li class="JNLC-copy">The pattern is improperly sprued. </li> <li class="JNLC-copy">Incomplete wax burnout. -Metal overheated. </li> <li class="JNLC-copy">Mold too hot. </li> <li class="JNLC-copy">Too much "old" metal in cast. Never use more than 50% old. </li> <li class="JNLC-copy">Metal insufficiently fluxed. </li> <li class="JNLC-copy">Too much flux added to metal. </li> </ul> Error 8 "Non-fills" for incomplete castings: The pattern improperly sprued because they are either too thin, too long, or too few. There can also be incomplete wax burnout, the mold can be too cool when casting, the metal can be too cool when casting, or there may be insufficient ammounts of metal by weight. Error 9 Foreign particle inclusions in castings: There can be a number of reasons foreign particles are mistakenly introduced in casting. Such as... <ul> <li class="JNLC-copy">Sharp corners and bends in sprue system. </li> <li class="JNLC-copy">Flask placed in furnace with insufficient setting time. </li> <li class="JNLC-copy">Flask heated too rapidly. </li> <li class="JNLC-copy">Sprue hold not checked for particles after sprue base is removed. </li> <li class="JNLC-copy">Molten metal contained foreign particles. </li> <li class="JNLC-copy">Flask contained rust or is unclean from prior cast. </li> <li class="JNLC-copy">Crucible old and disintegrating or insufficiently fluxed. </li> </ul> Note: Graphite has a tendency to absorb moisture and break down if not properly dried. Error 10 Fins or Flash on castings: <ul> <li class="JNLC-copy">Fins are thin metal extensions that are added on the casting. They occur from: </li> <li class="JNLC-copy">Incorrect water/powder ratio causing weak investment mold. </li> <li class="JNLC-copy">Investing improperly stored. </li> <li class="JNLC-copy">Investing extended past work time, or flasks disturbed while investment was setting. </li> <li class="JNLC-copy">Flask dropped or otherwise mishandled. </li> <li class="JNLC-copy">Flask placed in furnace with insufficient setting time. </li> <li class="JNLC-copy">Bench set timing should be a one hour minimum. </li> <li class="JNLC-copy">Flask heated too rapidly. </li> <li class="JNLC-copy">Flask allowed to dry and not re-moistened before burnout. </li> <li class="JNLC-copy">Flask burned out and allowed to cool before casting. </li> </ul> Error 11 Darkened or rough casting which can resist deoxidizing in the pickling solution: This mistake occurs when the burnout temperature is too high, exceeding 1450Â° F / 788Â° C. Error 12 Bubbles or nodules on castings: This happens when the wax patterns is not painted with a wetting agent. (Wetting agent should dry a minimum of 20 minutes). Investment slurry and/or invested flasks not sufficiently mixed, vibrated, or vacuumed will also create bubbles on the casting. Error 13 Spauling; when some of the investment moves within the mold: Spauling can be a problem when: <ul> <li class="JNLC-copy">There are sharp corners and bends in the sprue system. </li> <li class="JNLC-copy">The flask is placed in the furnace with insufficient setting. </li> <li class="JNLC-copy">The flask heated too rapidly. </li> <li class="JNLC-copy">The investment is handled past it’s work time. </li> </ul> Error 14 Rough-surfaced castings, other than bubbles or nodules: These can be caused by: <ul> <li class="JNLC-copy">An incorrect water/powder ratio. </li> <li class="JNLC-copy">The flask placed in the furnace with insufficient setting time. </li> <li class="JNLC-copy">The flask is heated too rapidly. </li> <li class="JNLC-copy">The pattern material can be trapped in the mold and boiled against the mold’s surface. </li> <li class="JNLC-copy">Too much "old" metal in cast. Never use more than 50%. </li> </ul> Error 15 Watermarks, or grainy surfaces, on the casting: Investing too rapidly is the cause. Note: The temperature is also important. A colder temperature will extend the work time. A warmer temperature will shorten the work time. Keep within the specified time of 9 to 10 minutes. <a href="/pages/other-techniques"><img src='http://static1.shopify.com/s/files/1/0014/5692/files/Back1.png' alt='' /></a> </div> </notextile>