Question: What shrinkage value should be used when designing a silicone mold?
Answer: Shrinkage is defined as “the amount or proportion by which something shrinks” (http://www.thefreedictionary.com/shrinkage). A material’s shrinkage must be accounted for when designing a mold to produce a silicone part that meets all required dimensions. Silicone normally can shrink from 1% to 4%. The shrinkage analysis is sometimes not provided when we buy silicone from manufacturers. Based on my personal opinion, 2% can usually be used for a standard shrinkage value when designing a silicone mold. Nevertheless, variation between material lots can significantly affect the shrinkage percentage as well as the part’s geometry. For example, a long hollow cylinder part that has a thin wall is going to shrink differently on different axes. Specifically, the long section of the part is going to shrink more than other axes. In this case, the part must be scaled differently on different axes.
The suggested shrinkage value will work most of the time. However, in a case where the material’s shrinkage doesn’t meet the standard shrinkage allowance or a part has a similar geometry to the one described above, educated estimation on shrinkage value should be made when designing a silicone mold.
Read our April Newsletter to find out!
Read our latest newsletter for exciting news about Albright Technologies.
While it is difficult to provide one general answer to your question, if I had to limit my response to one word, “yes”, because the cost of parts is typically very dependent upon the cost of the raw materials, and the cost of raw silicone is usually more expensive than the cost of plastic resins. Even the least expensive silicones may cost $5 – $10 per pound, while plastic resins run closer to a couple dollars.
However, in the medical device market, lots of parts are very small or microscopic. Micro molding is much less dependent upon the cost of the materials since there is so little physical volume. The cost of a micro part is driven more by the processing that goes into demolding, quality control inspection, and packaging, as all of these activities will require the use of microscopes that would not be required for larger parts.
But in general, molded or extruded silicone medical parts will cost more than plastics, thermoplastic elastomers, and petroleum based rubbers. The tradeoff is the biocompatibility and implantability that you get with silicone products, as well as other contributing factors like the physical, chemical and mechanical properties required of the device. Silicone may not always be the best material for the job, but when it comes to soft, flexible parts for medical applications it is a very good place to start.
Don’t forget to visit us at booth 1091 at MD&M West this week from February 12-14. Stop by to find out how to get a free silicone sample and ask us questions about your silicone molding projects.
Click here to read the rest!
In a few weeks Albright Technologies will be exhibiting at MD&M West from February 12-14 in Anaheim, CA. Stop by booth 1091 to find out how to get a free silicone sample and ask us questions about your silicone molding projects.
Silicone, especially liquid silicone will conform well to just about any mold shape that can be dreamed up, the difficulty is typically in the mold making process. In the prototyping sector, we see a lot of cutting edge design concepts that push the envelope with features that are very small and precise. Every molder has their own specialty and also their own limitations. At Albright we specialize in quick-turn micro medical device parts molded in liquid silicone rubber. One design limitation that we frequently contend with is the size and geometry of micro features, we like to use “The 3X Rule”, which basically means that if you have a microscopic opening in your part design (which would be reflective of a raised boss in the mold) the overall height of that feature shouldn’t exceed three times the diameter (or side length) of the feature. That would mean that if you wanted to form a 0.005″ diameter hole in your molded part, you wouldn’t want to go much more than 0.015″ deep into the part, from a tool making standpoint.
Click here to read the rest of this answer and our latest newsletter!
Albright Technologies has released an entirely new version of their popular Silicone Molding Design Manual
, a valuable resource used by design engineers in medical and other industry applications. The Silicone Molding Design Manual 6th Edition, now over 200 pages, is searchable and offers users the most extensive compilation of silicone data in the industry. The manual was downloaded over 2,000 times in 2011 alone by a wide variety of industry professionals. The new manual is now available to download for free
The revised manual now features white papers from Nusil Silicone Technology, Applied Silicone and Bluestar Silicones. These white papers include information on factors to consider when selecting medical grade silicones, adhering to difficult substrates with silicone adhesives and treatment systems, silicone molded tubing assembly, as well as a review of the benefits obtained by providing the molder control of the LSR cure kinetics. Also included in the manual is valuable information from Wacker Silicones and Dow Corning on topics including: short and long term implantable components, silicone gaskets, o-rings and diaphragms, as well as high temperature silicones and vibration dampening silicones.
For more technical information contact Bob Waitt, 978-466-5870 or email@example.com.
Question: When you buy a certain durometer of silicone from the manufacturers, what is the actual durometer are you getting?
Answer: Silicone is a very useful material that has been widely used in both non-medical and medical application for decades. For example, silicone has a wide range of operational temperatures (between -150 °F and -600 °F). Moreover, silicone has another interesting property that enables it to be widely used. It has a wide hardness range without additional additives. Shore A scale is typically used to identify the silicone’s hardness and liquid silicone rubber (LSR) is typically available from 01 to 80 durometers (typically in increments of 10 durometers). Nevertheless, there is a variation in hardness when you buy silicone from the manufacturers. The industry standard tolerance for silicone is ±5 durometers. This is due to the variation in the vinyl gums and treated filler used to make them plus the ±2 potential test error in determining the durometer. As a result, you normally don’t get the exact durometer of silicone as listed from the manufacturers; you only get a range of durometers that is close to the desired durometer.
How is the “softness” (durometer) of medical grade silicone measured?
This is a question that comes up almost every day when discussing new project ideas with perspective clients. The softness or durometer of all polymers/elastomers/rubbers is measured essentially the same way and the term while commonly used to describe the material hardness, actually originated from the device used to take the measurement a duro-meter. There are lots of different designs for this device, click here to compare pricing and options and get a general feel for what they look like and how they work.
Click here to read the rest of our October Newsletter!