Question: What modules range can be achieved in medical-grade silicones?
Answer: The modulus for medical silicone is low compared to traditional materials with a modulus ranging between 150 to 1500 psi for silicone. Many of the properties are temperature dependent and nonlinear but the supplier may provide you with properties and guidance in selecting liquid silicone materials.
If you have any other questions, please comment or ask me directly at mbont@albright1.com.
Question: Does silicone lose its’ elasticity over time?
Answer: Although other properties such as resistance to compression set and hardness improve over a period of time, elasticity decreases. As shown below, silicone material which is heat-aged at different temperature, begins to drop its elongation as the time increases.
Question: What are the catalysts in medical silicones and what is the definition of medical grade silicones?
Answer: In medical silicones, only a platinum cure system is used due to the fact that this cure system does not produce any extractable. Peroxide silicone cure systems produce acid residue and out gassing of the peroxide as by-products and therefore, are not suitable for medical applications because they do not pass biocompatibility testing.
The term “medical grade silicone” simply implies to a silicone which is rigorously tested to certify into a Class VI material. There are three types of medical silicone: non-implantable grade, restricted grade, and unrestricted grade.
If you have any questions please feel free to post a comment or email me directly at veasna@albright1.com.
Question: I have noticed that silicone oven mitts are becoming more widely used. I have to assume that they can withstand great temperatures. Can they be considered a direct replacement due to their thermal insulation properties?
Answer: The thermal conductivity of some silicones is reported to be approximately 0.22 W/m*K compared to cotton fabrics at 0.029W/m*K suggesting the cotton is a significantly better insulator. Silicone may provide benefits in protection against steam and fluid, stain resistance, and spilling over traditional cotton and the wall thicknesses are easily controlled to address the difference in thermal conductivity.
If you have any questions please feel free to post a comment or email me directly at mbont@albright1.com.
Question: We have noted that some materials inhibit the cure reaction of our liquid silicone rubbers, among these are masking tape and certain latex gloves. Can you give me a list of “bad” materials to have around LSR?
Answer: Latex gloves (and other latex items) will absolutely inhibit the cure of Liquid Silicone Rubber (LSR). I would advise using Nitrile gloves for any liquid silicone handling. Other items that may come into contact with liquid silicone and can have terribly negative effects on the liquid silicone rubber cure include: Isopropyl (or rubbing) alcohol, Mineral Spirits, cutting (machining) oil, anything contain sulfur or having a sulfur byproduct, any epoxies, and also prevent the liquid silicone material from coming into contact with any strong industrial cleaners/solvents (Naphtha, Methyl Ethyl Ketone, etc.).
If you have any other questions, please comment or ask me directly at kevin@albright1.com
Question: Is liquid silicone self leveling?
Answer: It depends upon the viscosity of the material. Lower durometer materials usually have a viscosity closer to water, and are seen to self-level when permitted to stand at lower temperatures (than processing temperatures).
If you have any other questions, please comment or ask me directly at kevin@albright1.com
Question: Can a silicone part be created that has a varying hardness? For example, hardness ranges from 60 A at one end to 70 D at the other end of the part?
Answer: Silicones do not get much harder than 90 Shore A. Shore D better reflects the hardness of many plastics. Molding silicone over plastic can be done but common issues include failure to achieve a high strength bond, balancing silicone high cure temperature versus plastic low operating temperature and incompatibility with plastic additives. Multishot molding of silicone can be done but the cost and time to mold often reflects the increased complexity. Similar silicones often bond easily but controlling the transition line varies in difficulty depending on the geometry and rigidity of the part. Molding a low viscosity material onto a higher durometer silicone base is more controllable than molding high onto low. Often two molds are utilized; one for the base part and one that locates the base part and over molds the second material.
If you have any questions please feel free to post a comment or email me directly at mbont@albright1.com
Question: What is the best way to prototype and evaluate parts in different silicone durometers to determine which is best for your application?
Answer: The best way to determine durometer is to start with coupon samples and get a handle on the difference between the durometers and materials. If the samples provide enough feedback to choose a durometer than you are all set. If you need to just test your part, using a vendor specializing in silicone prototyping can provide fast samples of different durometers often on the same tool. Lower durometer materials tend to have low resistance to bending and stretching and higher friction coefficients compared to higher durometers. Verifying that your prototype is made of the right material durometer requires comparing your objectives with the functionality of the prototype.
Question: Why is silicone the preferred material to make molds from to cast resins?
Answer: Silicone if fully cured does not bond well to other materials and it has a relatively high elongation and low modulus which all aid part release. It has resistance to temperatures up to 500 degrees F compared to many other resins which may degrade at temperatures over 200 F. Silicone has properties that facilitates removal of cast parts from the silicone mold. Silicone molds are also often easily reproduced from the original mold.
If you have any questions please feel free to post a comment or email me directly at mbont@albright1.com
If you have any other questions you can comment or ask me directly at veasna@albright1.com