May 24, 2016 Volume 12 Issue 20

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Flex Locators for quick fixture changeover

Flex Locators from Fixtureworks are designed for quick changeover of small and large fixtures, automation components, and more. They are ideal for applications that require frequent disassembly, providing excellent repeatability for locating and clamping in a single operation. Manual and pneumatic versions are available. Just turn the handle, knob, or screw!
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Copper foam -- so many advantages

Copper foam from Goodfellow combines the outstanding thermal conductivity of copper with the structural benefits of a metal foam. These features are of particular interest to design engineers working in the fields of medical products and devices, defense systems and manned flight, power generation, and the manufacture of semiconductor devices. This product has a true skeletal structure with no voids, inclusions, or entrapments. A perennial favorite of Designfax readers.
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New torque inserts provide design flexibility

Reell's TI-330 torque insert completes the gap in torque range between the TI-320 and TI-340 models in the TI-300 series, providing enhanced design flexibility for a wider range of applications. With torque options ranging from 1.0 to 2.5 Nm, the TI-330 features a powdered metal package configuration designed to be press-fit into round holes for quick and easy installation. Mounting profile options include exposed knurled shaft end and a knurled zinc adapter for installation into plastics.
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Superior fastening solution for securing rotating components to a shaft

SDP/SI Shaftloc® fasteners offer distinct advantages over other fastening methods when securing rotating components to a shaft. The key to this compact, efficient design is its asymmetric thread geometry that produces a greater clamping force -- outperforming other fastening methods. Shaftloc is a patented fastening system manufactured by SDP/SI.
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Great design: Handle with integrated lighting/signaling

Signaling and indicator lights, switches, and buttons -- elements that hardly any machine can do without. The new JW Winco cabinet U-handle EN 6284 integrates all these functions into a single, compact element. The new U-handle is designed to enhance the operation of systems and machines. It features an integrated button and a large, colored, backlit area on the back of the handle. These elements can be used individually or in combination, providing a versatile tool for system control and process monitoring that can be seen from across the room.
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SOLIDWORKS: FeatureManager tips for assemblies

Discover tools to make your SOLIDWORKS assembly Feature-Manager design tree display easier to view and use. Learn options to limit the amount of information in each component listing, combine multiple instances of a component into a single listing, and separate fasteners mates into a new folder. Lots more tips on the SOLIDWORKS YouTube channel.
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Top die casting design tips: Xometry

Optimize your die casting project's manufac-turability with these 23 top design tips from Xometry. Ensure your work is cost effective too, so you can hit the ground running and have the highest chance of success. Tips include: fillets and radii, wall thicknesses, ribs and metal savers, holes and windows, parting lines, finishes, and more.
Read the Xometry article.


8 top ways to wreck your coupling-driven system

Engineers at Ruland Manufacturing Co. have compiled the eight best ways to consistently sabotage or damage your coupling-driven system -- and how to avoid these pitfalls in the future. Misunderstanding performance criteria such as misalignment, torque, or rpm can be all it takes to cause a critical and costly failure.
Read the full article.


New washer tech for leak-free automotive sealing

Trelleborg Sealing Solutions has just launched the Rubore® Washer, a unique solution offering virtually leak-free sealing beneath screwheads to safeguard critical systems in vehicles, especially electric ones.
Read the full article.


How Reell electric wrap spring clutches work

Electric wrap spring clutches are ideally suited for critical timing applications requiring consistent, repeatable engagement and disengagement performance. Wrap spring technology used in Reell clutches provides the capability to transmit a large amount of torque in a small size -- package sizes smaller than other clutch technologies such as friction disk, tooth, or magnetic particle. Reell's technology has very positive engagement characteristics and also limits the effects of wear.
Read this informative Reell article.


New 'breathable' rupture disk tech provides overpressure and vacuum relief

To increase equipment safety and reliability, a new rupture disk technology activates at a set burst pressure, but it can also "breathe" to relieve minor pressure fluctuations. The patent-pending, dual-function device from BS&B Safety Systems is ideal for use on low-pressure vessels that are susceptible to ambient temperature changes.
Read the full article.


Engineer's Toolbox: 9 considerations for specifying a slewing ring bearing

In applications that require a bearing to support a structure while it rotates (e.g., cranes, radar, tank turrets), premature bearing failure can put people and equipment at risk. While slewing ring bearings have proven themselves countless times in such applications, designers must consider many factors when specifying them. According to engineers at Kaydon, the bearing's support structure, mounting (including bolt strength, tensioning, and hole patterns), installation, and even storage are all factors in a bearing's success or failure.
Read the full article.


ClampDisk micro fastener is new alternative for automotive and consumer electronics

Designed as a unique alternative in assemblies for the automotive and consumer electronics markets, the ClampDisk Press-on Fastener is a new offering from PennEngineering that delivers a fast, simple way to achieve sheet-to-sheet clamped fastening while replacing the use of standard screws, nuts, and adhesives. The most common challenges that can be eliminated or reduced by using ClampDisk include over installation, cross threading, stripped screw heads, broken screws, and damaged product. This fastener can be removed easily with a sharp-edged tool.
Learn more and see how ClampDisk works.


New nylon constant torque hinge

Southco has expanded its line of E6 Constant Torque Hinges with a compact, nylon version designed for small applications. The newest addition to the company's E6 50 Constant Torque Position Control Hinge series measures 45 mm with a torque range of 4 to 16 in./lb and is 65% lighter compared to the standard E6 50 Hinge. It provides constant resistance throughout the entire range of motion, enabling users to easily position doors, display screens, and other mounted components and hold them securely at any desired angle.
Learn more.


What injection molding material do I use?

How do you decide what type of plastic to use for your next injection molding project? Xometry can help you narrow your choices. Discover the different strengths and applications for materials that could be ideal for your application by learning about the most common plastic injection molding materials in detail.
Read this detailed Xometry article.


Can your rooftop handle solar panels? Sandia tests say 'probably so'

An analysis of rooftop structural strength by Sandia National Laboratories provides a new tool in evaluating homes for solar installations. [Photo courtesy: Sandia National Laboratories]

 

 

Most U.S. rooftops in good repair can take the weight of solar photovoltaic (PV) systems. That's the conclusion of a three-year study by a research team led by Sandia National Laboratories.

"There is a misperception in the building industry that existing residential rooftops lack the strength to carry the weight load of rooftop solar photovoltaic installations," said Sandia structural engineer Steve Dwyer. "Most existing well-built wooden rooftops can support PV system loads."

Sandia took on the job of analyzing rooftop structural strength to address concerns raised in the U.S. Department of Energy's (DOE) Solar America Cities program. The agency named 25 cities to promote adoption of solar technology at a comprehensive, local level through photovoltaics.

At least one city reported the primary barrier to solar was the difficulty and cost of obtaining construction permits for rooftop solar installations because of structural issues. "I couldn't believe it was a problem," said Dwyer, who led the Sandia test team. "Solar PV systems represent little additional weight, and roofs are very strong."

He said many code officials aren't familiar with solar technology and lack the training to evaluate how a solar PV system might affect roof structure. So they bring structural engineers into the permitting process, adding time and money for the system owner and the solar contractor. Often, they then deny engineering certification for solar PV installations on wood roofs, declaring the structures too weak.

Load-bearing capacity is several times higher
In two, first-of-their-kind studies funded by DOE's SunShot Initiative -- which seeks to make solar energy cost competitive with other energy sources by the end of the decade -- and conducted in partnership with the University of New Mexico (UNM), Sandia stressed wood rooftop structures to the point of failure and compared the data with allowable loads identified in the International Residential Code and the National Design Standard.

They concluded the actual load-bearing capacity for residential rooftop structural systems is several times higher than the calculated values.

In a University of New Mexico lab, roofs were built and stressed to the breaking point to show the solar permitting community how strong they are. The tests were done by Sandia National Laboratories in partnership with UNM. [Photo courtesy: Sandia National Laboratories]

 

 

 

 

Sandia hopes engineers and permitting officials will use the results when they make decisions about rooftop strength and solar PV applications, increasing the number of safe, cost-effective rooftop solar PV installations.

"Safety is a crucial factor in building codes and must be considered when there is any change to a structure," Dwyer said. "Understanding how weight loads affect the structural integrity of a roof is important to homeowners, code officials, solar installers, and builders. These results provide a new tool and set of data for consideration in evaluating rooftops for solar PV installations."

The roof acts as a whole
Dwyer said engineers doing rooftop structural analysis often calculate stresses on the basis of an individual beam, rafter, or truss. That approach assumes each component of the structure acts alone. "It fails to consider the rooftop system as a whole or consider the load-sharing or load redistribution effects of a roof system," he said. "The result is a conservative analysis that does not accurately represent the roof's ability to support a PV installation. It's not a fair assessment."

And he said engineering evaluations are not universally applied across cities and states. "Some do them, and some don't," he said. "Local governments pick and choose what they accept. Not everybody uses the same method, so it can be difficult for solar installers and residents to know what to expect. All these issues have posed serious challenges to the solar industry."

Dwyer said the Sandia team realized building codes won't change, so they tackled the problem by building some roofs, breaking them, and showing the permitting community just how strong a roof is. Starting about three years ago, the team built different roof sizes in a UNM lab.

"We did a lot of testing," Dwyer said. "First, we wanted to be sure we were on the right track. We thought, 'OK, the engineers are not giving credit for load sharing,' so we tested a two-by-four, broke it in half, then nailed a piece of sheeting to it to see if it added strength. It did, 35 percent with nailing and 74 with gluing. We were on the right track."

They built scaled versions of roofs in different lengths with five rafters or trusses 8 to 20 feet long and applied a uniform load over the whole thing. "We used air as the load," Dwyer said. "We built bladders of different sizes and used them to put pressure on top of the roof by filling them with air at up to 144 pounds per square foot. We broke every size rafter and the more commonly used trusses, five sets of each."

On average, the rafter-based tests demonstrated a 330 percent excess load-bearing capacity compared to values computed in the National Design Standard. "This suggests that current rooftop structural evaluations are overly conservative in evaluating the ability of roofs to support additional loading from solar PV installations," Dwyer said. "A well-built home that meets local building standards and has not been adversely modified or damaged should have enough load-bearing capacity to support a roof-mounted PV system."

You can learn more about Sandia's energy programs here.

Source: Sandia

Published May 2016

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