We recommend that at least one vent be attached to each QuickCast pattern in the assembly. Although it is possible to successfully cast QuickCast patterns that are not vented, vents reduce the risk of failure in two important ways.
Vents allow steam to enter the pattern during the autoclave cycle. The steam softens the internal support structure of the Quickcast pattern, turning to the consistency of gummy bears. As a result, the pattern can collapse inwardly as it was intended to avoid cracking the shell. Much more detail is given in the autoclave section in part 4.
Vents significantly increase airflow to the pattern during the burnout process, increasing the amount of oxygen available for combustion.
Vents can be created by adding wax plugs to the pattern, which will be opened after the shelling operation. Pieces of ¼” spaghetti wax, about 2” long is often used for these vents.
Vents can be designed into the CAD model so they are built in place on the QuickCast pattern. Building QuickCast vents will eliminate some of the manual labor needed during processing, but it does require careful consideration of where the vent will be after the pattern is assembled. After assembly, the vent should be on the outside of the assembly where it can be easily reached and opened, rather than on the interior of the assembly.
One of the easiest ways to vent patterns is to use the vent kits available from your on 3D Systems on Demand sales representative. The vent kits have unique features which simplify and speed not only the assembly process, but several other steps in the casting process. The following charts illustrate the vent and their use.
|The vent kit consists of two parts; a molded wax vent and a ceramic plug that will plug the vent hole.|
The vent has some unique features:
|The first step is to drill a 3/16”-1/4” hole into the pattern. This can be done with a drill, with a hand grinder with an appropriately sized bit, or even with a hot iron.|
|The vent is then attached over top of the hole, locating the vent so that the blind hole is directly over the drilled hole. The vent can be attached with sticky wax.|
|The pattern is then shelled normally with some care taken to avoid knocking off the vent.|
|After the shell is built, the end of the vent is cut off to ex- pose the air passage. The cutoff is most easily done with hand held electric cutter, but can also be ground off. The pattern is now ready for autoclaving. The air passage will allow steam to enter the pattern quickly and soften the internal structure, enabling the pattern to collapse internally as intended.|
|After autoclaving, the vent will have melted out, leaving a larger air passage. This passage will serve as a chimney during burnout and will allow air to flow through the mold, bringing in fresh oxygen for combustion.|
|After burnout, the pattern will be reduced to a small amount of ash. The vent now will make rinsing the shell easier to remove any ash remaining in the shell.|
|After rinsing, the plug can be inserted into the vent pas- sage. Because the angle of the plug is the same as was on the vent, it will seal tightly.|
|The last step is to lock the plug in place. This can be done easily with a little foundry mud. As the mud cures, that portion of the mud extending into the locking ring area will lock the mud into the shell, preventing the plug from backing out during the pour.|