A cold deck (cold runner) system is an assembly of insulated feeding units that prevents liquid silicone from curing while conveying silicone into the cavities of the mold. The following are a few reasons that using a cold deck system can be very cost effective in high volume molding applications.
1. The cold deck eliminates waste (sprue and runners) that is generated in a conventional silicone injection molding.
2. The cold deck also reduces cycle time because it eliminates the need for a secondary process to remove the sprue and runner from the molded part.
3. A cold deck can also provide you with greater flexibility with both gate style (open vs. valve gated) and location.
Read the rest of Albright’s November newsletter.
Earlier this month Albright Technologies‘ Project Engineer, Matt Bont, gave a presentation at the Shin-Etsu Silicones Open House on Alternative Methods of Prototyping Liquid Silicone Parts.
Click here to view the presentation as well as other presentations from industry suppliers.
Click here to read the rest of the October newsletter.
Click here to read more or to register for the Open House on October 7, 2013.
The Massachusetts Life Sciences Center (MLSC) and the Massachusetts Neuroscience Consortium announced the first round of awards to fund research on neurological diseases since the consortium launched in 2012.
Click here to read article or visit Mass Life Sciences website for more information.
After recently being named President of Albright Technologies, Bob
Waitt will be receiving an EMERGE Award this week. This award is given to 10 young professionals who work in North Central Massachusetts for their outstanding work professionally and in the community. Each nominee was scored by a small selection committee on his or her career history and trajectory, community involvement, community dedication and recognition by others.
Read the rest here.
Question: What criteria should people consider in selecting the hardness of a silicone compound?
Answer: Criteria for hardness may be best answered by considering what it means. Durometer is a measure of the resistance to indentation by a probe tip. Most silicones fall into shore A range although there are exceptions. Lower durometers feel softer like pressing a rubber band versus harder like an eraser. Neither of which are silicone but make the point.
The durometer does not necessarily indicate a materials elongation, modulus, tear strength, chemical resistance, or opacity but in the same product lines higher durometer does often but not always come with greater strength and modulus but lower elongation and viscosity. From one supplier to another and from one product line to another doesn’t always apply.
The criteria to use depends on your need, you may need to look at other properties for highly engineered products with strict performance requirements such as diaphragms, valves, gaskets, etc. On the other hand, products such as handles, covers, and skin contact components may lend themselves to the feel by durometer. Samples of different durometers can be helpful for both types of products to give you a sense of the differences between materials
Question: What is the risk of a piece of medical silicone breaking off and becoming a choking hazard? How much force to tear?
Unfortunately like many problems, the answer to your question depends on the application, loads, and part size and geometry.
The risk of choking is difficult to quantify but a quick search suggests that thin sheets or hard round shapes like coins are significant choking hazards as we all know. The question becomes how to quantify risk of a deformable body with very low wet friction being released into the windpipe. It may be worthwhile to consult a physician specializing in respiratory to better understand the physiology and failure modes associated with choking.
To answer the second part of the question, factors affecting the tear strength may include temperature, degree of cross linking (how complete the curing reaction is), and sterilization but let’s assume a perfect material. If we choose a 70 durometer implantable material such as Nusil’s MED-4870 and we look up the tear strength of 1350psi on their website. The referenced standard uses the original cross sectional area. So using simple rod geometry in tension at 1mm (0.0394in) tearing occurs at 1.6lb while a 1/8” rod would tear at 16.5lb. As the complexity increases so does the challenge of estimating failure loads such as in balloons or composite products. This is where prototyping and early testing offers the ability to drive a product to failure without risk to life.
The primary difference between silicone and plastic properties drives the differences in mold design. The largest difference is the temperature profile between silicone and plastic. The mold design and construction will also be dependent on the product geometry, size, materials, equipment, quantities, cycle times, undercuts, flash limitations, and parting line and gate restrictions.
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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.