Linear actuators . . .Airflow design software . . .Contracting material . . .
Dear Search Engineer: I am looking for a linear actuator with an adjustable stroke of up to 10 inches. It has to be smooth operating from -60 to +200F and repeatable to 0.032 inch. We use it to cycle test parts in an environmental chamber. We have tried pneumatic actuators without any luck. Any suggestions? —C.M., Frankfort, IL
Dear. C.M.: Try pneumatic and hydraulic actuators with internal position sensors (advertised accuracy to 0.002 inch). Check out Parker's actuators (http://rbi.ims.ca/4388-535).
Dear Search Engineer: Stainless steel has gone out of sight in price. We manufacture seals for pumps and wheel bearings, and we use stainless steel because of its corrosion resistance. Are there any substitutes we could look at?—P.S., DN reader
Dear P.S.: Zirconium in nuclear applications and titanium in the aircraft industry would provide the corrosive resistance. However, the cost may be a problem.
Dear Search Engineer: Is there a software/CAD system that can help with the design of fans and airflow? One that works with a knowledge of engineering and CAD, but without requiring a course on computational fluid dynamics? Any suggestions?—E.E., DN reader
Dear E.E.: Any CAD product can do this. Use a light in the location of where the exhaust is. The deflection of light will show the direction of airflow. Wind and air are two very difficult attributes to replicate on a predictable basis. A simple program such as DesignCAD Max 3D Plus could do this with ease. It is expensive, but you can download a free trial of it (http://rbi.ims.ca/4388-536). The program will also allow you to draw spirals and helix designs using a circular array, or sweeping in a third dimension. CFDesign's fluid flow analysis also works with different CAD systems.
Dear Search Engineer: Is there a material that contracts when a small current is applied to it, similar to how human muscle tissue works? —R.M., Pittsburgh
Dear R.M.: Several readers weighed in on this discussion. One suggested all piezoelectric materials, while another reader replied that a material called Terfenol may be suitable (http://rbi.ims.ca/4388-537). Shape Memory Alloy wires or coil springs could also work. At their "lower temperature" state, you can plastically deform it (stretch it), and when you supply electricity through them, resistive heating occurs in the material, thereby increasing its temperature. At this "higher temperature," it will contract and come back to its original shape. Another reader suggested Muscle Wires (http://rbi.ims.ca/4388-538), which are thin strands of a special nickel-titanium alloy that actually shorten in length when electrically powered. They are easy to use, and they can lift thousands of times their own weight. The direct linear motion of Muscle Wires offers experimenters a source of motion that is very similar to that of a human muscle, providing possibilities not available with motors or solenoids.