Document Vje7Vk005RYLgmz2D9M9NkKZZ

682 JEROME R. COX, JR. neath the cans. The irregularities in the wire rope running under the cans duce considerable noise. Replacing the wire rope with a flat belt will iesu||T a quieter operation, but an adjustable idler wheel must be installed becauE^91 belting is more likely to stretch than the wire rope. In addition, splicing,^ loading problems limit the system to fairly short runs. In spite of these diffioullf the flat-belt line may be a worth-while substitution where the can conveyor^ the prime source of noise. i. Conveyors for Small Parts. Small parts that are handled in bull1 metal chutes, conveyors,' and elevators are often noisy as a result of the imf" of the parts against each other. A single part traveling alone will move .quieSls if the conveyor or chute has been treated to minimize noise (page 679). rl||u the conveyor system should avoid the accumulation of parts at any pomtP* the storage of parts is necessary, a rubber-lined reservoir that is completely closed should be used. .-jf In general, worm-feeding mechanisms are quieter than gate-feeding becau parts can be taken continuously from a reservoir rather than in a noisy, rhytbiFl|f fashion. j. Chipping Hammers. Noise from the impact of the chisel of a clnpfii hammer striking a metal casting or a steel tank can be extremely intens^Sp though it is unlikely that satisfactory engineering control for this problerhV be found in the near future, steps can be taken that will be of some iielff conserving hearing. Ify ... -Bhipping-opera-tions-ahould-n&ver.he-carried_Qut on metal surfaces. Wo benches or wooden-block or dirt floors are better. -s A jig that will clamp the work and minimize vibration may be p'r.Au<| for operations where production is high. It is necessary that large areas jiT vibrating surface be damped and the forces involved are quite large. Dang materials, such as rubber, are usually ineffective, but lead sandwiched; bet?' the clamping jig and the work may be satisfactory. Submerging the w,orkj|| cleaned by chipping in a liquid bath is another method of noise control thap have some merit. The work must be supported by a frame that is isolaterlir the tank to prevent the transmission of vibration to the outside. '^ k. Rotary Cutters. Cutting strands or sheets of plastic into small.cp5Jt -is-iisually-accomplished-by-feeding-the-material to a set of rotating;knlj^sr11 entiro.-cutting,..assembly should be- isolated from the rest of the,idpy,i<!.pj mizethe transmission of vibration to the housing where it may be radi'ap sound. .^.-The-.kniys^and. the plate that they cut against should be rigid and"h The knives should not strike tKF^r5rlT'ffl'l"alr-ontre--butrrather-begih-TO-';;" one side and progress smoothly toward the other in a shearing fashion.^,, one knife has completely passed through the material, the next knife should^ position to start at the opposite side. Reducing the rotational speed of thej|; reduces the noise somewhat because the knife strikes the work wi.t.h.....a\,L. NOISE AND THE CONSERVATION OP HEARING 683 fjfciti"iTnereasing the number of knives on the cutter will restore the original luciiivKcapacity of the machine.27 5/l^Voise from Piping. The hammering of liquid in pipes can produce an ecessSty noise at great distances from the pumping equipment. For quiet ^ipnfflexible sections of piping and air cushions should be installed in the fm?fv?oj&the offending valves and pumps. Commercial products and materials llradPile to aid in the solution of these problems.28 Pfi'eumatic Hammers Used in the Manufacture of Paper Boxes. In the gr^boxldndustry the scrap is separated from the box by means of a vibrating -'"'aciPited by a chipping hammer. The reciprocating piston in the hammer "pi? end of the chisel and produces a ringing at. high frequencies.. The teeam of air escaping from the exhaust port of the hammer produces ||i||p!ncy sound. In contrast to chipping castings and steel tanks, the noise ifi by the tool itself. Noise reduction is obtained by using a collector ^ifpMng the exhaust port, to channel the exhaust air to a single opening llBahaa long hose (Figure 28). The;muffling action of the long hose and MEPSww't i **.$* ................... . 1y 1 > -- :'i iV.f-'V ..................... ,. , o.i.fcan ...... ...................... ..... . ........... . ii imiiim m-- collector in place on a pneumatic KamtffeE.T)ie'of tne'exh'aiist j|LjffdclffcJhe noise from this tool during certain operations in'ihe^manufactuie^of`'paper .. *ar'v, tju>'.::: Sen'ore4pcation of the. noisy, open end of the hose-roesj&ultfHc-ri.man opei|tipn4*ha t ""swUwfflsgtoy- quieter.26 ^ vipg t;uui>T(ji i ut a btraila cuucerjir __________ . piiBng.components, J. Acoust. Soc. Am., 24, 725 (1952). Noiae reduction, of pneumatic hammers, Noise Control, l,s78 (January,-i S85jiK5S,,' C''Chaifee. Reduction of noise in industrial pneumatic tools, Noise Control, 1, 10' BInK.yj i065g'