FAQ
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: What is Double Mixing?
A: Double mixing involves mixing the A&B components thoroughly in one container and then transferring the mixture into a new, clean container. This process leaves much of the unmixed material that hides in the corners and sides of the cup behind, ensuring a more thorough mixture. Unmixed material can show up in the part as soft spots or unsightly swirls/streaks. This process is extremely important when casting silicones and water clear materials.
Q: What is Cure Inhibition in Silicones?
A: Some materials can have chemical incompatibilities when poured into or up against other materials causing an uncured, sticky mess. For example, platinum silicones may show inhibition characteristics against natural rubbers, cyanoacrylates, tape residue, sulfur based clays, and some urethanes. Whenever in doubt, a small side test is always recommended.
Q: What is Cured Inhibition in Urethanes?
A: Certain urethane systems may be affected by the type of silicone mold you cast into. Tin based silicones (condensation cured) are known to cause issues with many Shore A Elastomer urethane systems and also Aliphatic urethanes (e.g. our Water Clear materials). Silicone mold material must be carefully selected depending on the urethane system you plan to cast. Casting a urethane into an incompatible silicone can be an expensive disaster; both money and time.
Q: Why do I need to Mix Individual Components/Containers?
A: With many urethane systems, the individual components in a container may need to be mixed and/or stirred prior to weighing out on a scale. With storage time and ambient temperature changes, ingredients in the material may separate out and need to be remixed. It is of critical importance with fire retardant materials to pre-mix before every use or the heavier fillers may settle at the bottom. Filled or pigmented materials may also need stirring prior to weighing out on the scale for the same reasons. Water Clear materials are very sensitive to cold storage temperatures and may need to be both heated and stirred to ensure a clear end product.
Q: What happens if I want to Demold early?
A: Casting materials need time to chemically crosslink and to gain physical properties. Removing a part from a mold early or casting in cold temperatures increases the risk of breaking a part due to brittleness or low tear strength. With most materials, adding heat can speed up demold time but the mold material must be able to withstand elevated temperatures without deforming. Some of the Shore A Aliphatic systems (e.g. Shore A Water Clears) will have adverse affects if you heat them too much before they have time to gel. See How Do I Work with Water Clears.
Q: What is Work Time?
A: The time you have from the moment you begin mixing to the point you can still easily pour material into a mold. Once the material starts to gel (or get higher in viscosity) the material does not have good flow characteristics and may not produce a good part. Always be aware of the working time rated on the data sheet and listed mass it is calculated at. Adding more mass (e.g. 400g vs. 100g) will shorten the working time. Mixing an appropriate batch size can assure you have time to vacuum and pour your material. Always choose an appropriate working time based on how difficult your cast is and how much material will be mixed prior to casting.
Q: How does Temperature affect Casting Materials?
A: Ambient temperature and storage temperature can have a drastic affect on materials. Working time, demold time, viscosity, and physical properties of the material are all affected by temperature. In cold winter months working with thermal set systems (urethanes, epoxies, etc.) can present challenges not seen in more moderate seasons. Materials can be much higher in viscosity making mixing, degassing, and pouring more difficult. You can also experience brittleness on demold. This is not the fault of the material; it is the nature of chemistry for these materials. Extra care should be taken to pre-warm materials prior to mixing and the same goes for molds. Warm material poured into a cold mold can have undesired results, especially if the material has a long working time. Also, heat can work to your advantage if you need to process faster but it can also work against you. Pre-heating materials can lower viscosity making it easier to mix and pour but it will shorten your work time. Sometimes going with a longer work life and heating the material can give you the benefit of lower viscosity without sacrificing valuable work time. Elevated temperatures can also greatly increase strength of materials. See Post Curing for more details.
Q: What is Post Curing?
A: Pre-warming a mold and material will help the cure on the front end of a job, but what about after it has initially set up? Doing a post cure at elevated temperatures with most materials can increase the physical properties of a material; tear strength, flexural strength, heat distortion can benefit from a proper post cure. Some rigid materials may appear brittle upon demold after the initial cure. A post cure will finish up the last bit of chemical cross linking to maximize the material’s physical properties above and beyond what can be achieved at ambient temperature over several days. Post curing is best done in a controlled parts oven (never a household oven). Always refer to the data sheet for proper post cure conditions. Some materials can have undesired results at elevated temperatures (swelling, bubbles, deformation) so always check the recommended procedure on the Data Sheets.
Q: What is the difference between Aromatic and Aliphatic urethanes?
A: Aromatics are one of the more common chemistries in the world of casting urethanes. They tend to be more economical to produce, have good physical properties, and range from low durometer elastomers to rigid plastics. Their downsides tend to be poor UV resistance and lower chemical resistance. The Aliphatic urethanes have outstanding UV stability, color stability, and chemical resistance. Their down side tends to be longer gel and demold times, low heat distortion, low tolerance to colder casting temperatures, and higher material costs. Blends of Aliphatic and Aromatic urethanes can exhibit excellent UV resistance, good heat distortion, and good physical properties.
[ Next Page ] |
