FAQ, Page 2
We often receive common questions concerning our equipment and products. Peruse the list of typical questions below to see if perhaps your question has been answered before.
Q: How Do I Work With Water Clears?
A: Aliphatic Water Clear (WC) materials are a wonderfully unique material. They have unrivaled clarity and when pigmented they are the most color stable material we manufacture. They offer outstanding UV resistance; some of our WC systems can withstand years of outdoor exposure. Working with them does require a few essential steps to ensure success. First, they are not tolerant of cold casting temperatures. Clarity and physical properties can be severely affected if cast below 70 degrees F. Molds must also be preconditioned to minimum temperature (75-85°F) or heat may be pulled from the curing material. They also require a good vacuum system to pull the trapped air out of mixed material prior to pouring into a mold. BJB Water Clears do not self release entrapped air. Without pulling a vacuum on the mixed material, a cast part may end up looking more like a glass of carbonated soft-drink than a glass of crystal clear water. Casting the part in a pressure tank/vessel can also aid in reducing bubbles in a part by compressing bubbles down to the point they are not visible anymore (see Vacuum and Pressure). Casting in thin sections may also require additional heat to make up for the lack of internal exotherm (less mass equals less self generated heat). Water Clears operate best if preconditioned to a minimum of 75-85°F range and a max of 100-110°F keeping in mind that higher temperatures will shorten work life. Refer to the technical Data Sheet or call BJB for more assistance regarding proper temperature settings.
Q: How do Vacuum and Pressure affect casting materials?
A: When you are hand mixing casting materials, air bubbles are inevitably going to be stirred in. Viscosity, temperature, and surface tension of the material will determine how well the air will or will not self release from the liquid. Other than a few of our low viscosity systems, the mixed material will need to be placed in a vacuum chamber to remove those air bubbles prior to pouring in the mold; also called de-airing or de-gassing. The vacuum expands the trapped air causing the bubbles to grow, rise to the surface of the material and release. After a period of time these bubbles decrease in quantity meaning that air is effectively being removed from the material. This air would otherwise cause voids and potential mechanical issues with your cast part. Cold materials will have higher viscosities and may be more difficult to degass. Raising temperatures lowers the viscosity which will aid in pulling air out of the material but may also reduce working time if taken to extremes. Pressure casting can be an alternative or secondary process to vacuum ‘degassing’ casting material. Pulling air out of the material ensures the material isn’t latent with bubbles as it goes into the mold, but air can be re-introduced into the material as it is poured in from splashing or mold features that trap air (e.g. sharp corners). In some applications, vacuum and pressure must be used in conjunction to produce air free parts. Typical pressure values, when material is degassed, are in the 40-50psi range. Higher pressures may be required if material is not degassed. Pressure does not remove air; it compresses air bubbles down to the point that they are not visible anymore. If pressure is released too soon (before material has had time to set) the bubble could potentially reappear.
Q: Where can I download handling guides for your products?
A: We have a short list of handling guides available for download in Adobe Acrobat PDF format. Please choose one of the following:
[ First Page ] |
