September 11, 2012
Presented by RTP Company
Think specific gravity is your enemy? Then it’s time to think again! Density modified thermoplastics can increase productivity, add perceived value, replace metal materials, or be eco-friendly. Jason Westby, product development engineer with custom compounder RTP Company, will review the advantages and implementation strategies for density modified compounds.
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Questions and Answers
Q: Are you producing the glass bubbles or are mostly involved in compounding these in your products
A: We specialize in the compounding process and not producing raw materials so we do not make the glass bubble additive.
Q: What Filler would you use for conductive material? Can they be another color than black?
A: Since we can also use reinforcing fibers in combination with High Gravity Compounds, we would be most likely to utilize carbon fiber to heighten conductivity. Colorability will vary depending on the conductivity required and how high of a specific gravity you need to target.
Q: Can VLF material be used to replace some of the Stainless Steel or Alu Enclosure. Explosion Proof Enclosure -Temp Range -40 to +60 degrees.
A: In some cases it can. Suggest you refer to a previous RTP Company webinar on VLF technology. There are a number of recorded RTP Company webinars for your reference.
Q: What is the most frequent application for long glass fibers? What is the input to the specific gravity compared to typical glass fibers?
A: The specific gravity of a 30% long glass fiber composite will be the same as a 30% short glass fiber composite because they are the same percent by weights. The main difference is the VLF material has a higher strength, stiffness, & impact resistance because the fibers have a higher aspect ratio over traditional short glass fibers. The higher aspect ratio fiber is better able to distribute forces throughout the material. The most common application for VLF materials if for metal replacement but can be used in many other areas were increased mechanical properties are needed.
Q: Did glass bubbles degenerate the Strength of the material?
A: The glass bubbles act like a low aspect ratio filler. To understand the role that aspect ratio plays in changing mechanical properties, you can watch the RTP Company / UL IDES webinar entitled “Increasing Mechanical Performance of Plastics” (and more RTP webinars can be found here). Low aspect ratio fillers will generally increase stiffness (modulus), but will reduce strength, elongation, and impact resistance.
Q: Does the addition of metallic additives increase molding complexity / mold wear exponentially, similar to the way it affects cost??
A: Mold wear and complexity will not necessarily increase at an exponential rate but will increase wear just as a highly filled glass fiber loaded material will increase wear.
Q: What is the nominal tensile strength impairment of a 94% tungsten filled 6 nylon
A: The average tensile strength for a 94% tungsten filled Nylon 6 is between 7000-7500 psi, ASTM D 638. A common value for an unfilled Nylon 6 is approximately 11000 psi per the same standard.
Q: The obvious question regarding the Glass Bubbles is, how do you process without breaking the bubbles?
A: There will always be some breakage of the glass bubbles during compounding and molding but there are various techniques to limit the percentage of glass bubbles that are broken. Factors that affect glass bubble breakage in compounding include: screw RPM’s, screw profile design, and techniques of feeding. Ideal molding conditions for glass bubble composites include low RPM speeds, low back pressure and slow injection speeds.
Q: What is the size of the glass bubbles?
A: This will be dependent of the required grade of glass bubbles used but they generally range between 10-80 microns.
Q: Are density-modified materials available in shapes (sheet or rod, for instance)?
A: All of the density modified materials we produce here at RTP Company will be in pellet form for injection molding and compression molding purpose but can be considered for profile extrusion if the required melt flow and melt strength is met.
Q: What is the maximum specific gravity RTP Company can obtain with a non-metallic filler?
A: Using what would generally be considered cost-effective raw materials, the highest specific gravity you can expect without using metal fillers is around 2.5 to 3.0. However, there are some minerals that we have experimented with that can achieve a specific gravity of up to about 4.0 without using metal additives. These are also much, much more expensive than the less than 3.0 products using more standard fillers.
Q: What specific gravity of glass bubbles is the minimum that you recommend for injection molding applications to prevent them from being crushed?
A: No answer
Q: Can we overmold high gravity compound without compromising adhesion?
A: You can work with RTP Company to design a system that works to optimize adhesion between specially designed TPE Compounds and High Gravity Compounds. RTP Company has the ability to tweak both the TPE and the rigid substrate.
Q: Are there other additives besides glass bubbles that can be used for decreasing specific gravity?
A: Foaming agents can be used to decrease specific gravity by incorporating voids in the final part. Since that is more a process-related technology than a material-related technology, it lies beyond the scope of this particular presentation.
Q: Can ABS be made in to a heavy weight platable polymer?
A: Yes it can, but adhesion of the plating may not be as good as it is with the unfilled polymer.
Q: Is there a specific consideration about geometries or change of section to use?
A: Standard plastic design practices still apply with these types of materials.
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