Ask The Search Engineer

Vacuum booster… Electrical specs… Steel deflection… Weighing pineapples…

Dear Search Engineer: I need to change the material of the body valve of a car vacuum booster made from bakelite with a thermoplastic material which has a good long-term dimensional stability and can withstand -40 to +120C working environment and good wear resistance. —B.M., Iran

Greetings B.M.: My suggestion would be to look into Delrin material (for background information, go to http://rbi.ims.ca/3853-511). Another possibility is Ryton BR-111 (polyphenylene sulfide) or BR-111BL. These materials were specifically formulated to have high strength and low creep in automotive "under-the-hood" environment. Data can be found at http://rbi.ims.ca/3853-512.

G'day Search Engineer: I'm writing a specification for electrical installations on railway rollingstock and have come across references to UL94 V-0 rated plastics. UL94 is an Underwriter's Laboratories standard. Is there an equivalent Australian or International standard? —E.D., Queensland

Hello to the Land of Oz: We've found a similar flammability rating standard for Europe—EIC 707. The classification FV0 is similar to UL94-VO. Fair dinkum!

Dear Search Engineer: Is there a documented method that can be used to determine the deflection of a rectangular steel frame? Often diagonal members are required to reduce load deflection, but I have never seen a documented method to determine the loads transferred to and from the diagonal members. I know that if frame deflection exceeds 1/8 inch in 10 feet of length, broken weld joints will result. Structural engineers must have a method that is not taught to mechanical engineers. —P.L. in PA

Dear P.L.: To answer your question, yes there is a method used by mechanical engineers to determine deflection of any type of geometry. This would definitely fall into the realm of a structural engineer, but mechanical engineers should know how to solve for deflection in a beam. The main drivers in beam deflection are: type of material, geometry, wall thickness, how the beam is loaded, and how the beam is affixed. Once you have that data, it is as simple as "plugging" the numbers in an equation to solve for deflection. Or you can look in the Manual of Steel Construction by the American Institute of Steel Construction, Inc. (AISC) for general guidelines for steel design/construction, including details of how to calculate allowable stresses for different shapes based on its unsupported length.

Dear Search Engineer: I'm currently in charge of machine improvements and process and am looking for a mechanism/weigher that can measure a product's weight on conveyor belts running at a certain speed. Estimated rate is 20 tons of pineapple fruits per hour. —C. D., HI

Aloha C.D.: Thermo Ramsey makes belt scale equipment that will calculate based on speed if fitted with the optional encoder. Check out their Weighting and Inspection solutions at http://rbi.ims.ca/3853-513.