Whip Mix not only manufactures Investment material for the dental industry but also for the jewelry industry.
Jewelry investments, like our Omni-Cast are gypsum based investments which only require water — unlike the mixture of water and colloidal liquid used with phosphate investments. This creates some advantages and disadvantages for the investing process.
The appeal of jewelry investments are; ease of divesting, relatively clean castings out of the mold, and no complex ratios of special liquid and water. Even though gypsum investments are easy to use and for the most part forgiving, to achieve a good result the manufacturer’s directions must be followed.
The most important technique consideration is the water/powder ratio. The second is the temperature of the water, which should be between 70°F – 75°F or (21°C – 24°C). Keep in mind that warmer water will shorten the working time, while colder water will lengthen it (this is Chemistry 101…hot speeds reactions up, cold slows them down).
It is also important to ensure that the weighed powder is added to the correct amount of distilled or deionized water. Tap water, depending on your geographical location, could affect the properties of the investment. When determining working time, remember it is the time elapsed from when the powder is added to the water and the mixture begins to thicken. To determine actual work time, mix each batch, note each step beginning from when the powder is added to the water, until the investment begins to lose its gloss. Subtract 2 minutes from this total time. The time remaining is the actual working time.
For Omni-Cast, it is recommended there be a 30 second hand mix and 2 minute mechanical mix. In addition, the speed of the mixer can effect working time. The published numbers associated with the investment will only be achieved when the technician or jeweler follows all of the instruction parameters.
When investment handling issues do arise, it is important to look not only at the quality of the material, but also at the user’s process and the environment in which the investment is used. All of these factors can affect performance.
The world of dentistry and the world of jewelry are similar in regards to forming a pattern and investing that pattern to create a mold. The mold, developed from the wax or plastic pattern, (do not use gypsum investment for plastic patterns) is filled by burning out the pattern material, then casting.
Dental investment typically is mixed under vacuum, whereas jewelry investment is mixed and then put under vacuum via a bell jar, with air bubbles allowed to rise out of the investment before the actual investing process.
Dental mixing is done at 350-600 RPMs (with 425 RPMs being the industry standard). It would be the slow drive of the Whip Mix Powermixer Plus and the Combination Unit. Care should be taken not to mix faster when using other mechanical technique. Whip Mix investments, including our jewelry investments, are tested for the mechanical mixing portion using these machines. Using a mixer, with varying RPMs above or below the 425 level, will exhibit working times and set times that will fluctuate based on the speed of the mix.
Another aspect, which affects your investment, is the cleanliness and condition of the bowls, storage and spatulas used to mix the investment. Dirty or worn mixing tools can affect even the freshest investment material. Please be sure to clean all of your instruments thoroughly and on a regular basis.
If you have further questions, please feel free to contact us at Whip Mix Technical Support.