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 Bureau of Mines Information Circular/1984 
 
 Retrofit Noise Control Modifications 
 for Crushing and Screening Equipment 
 in the Nonmetallic Mining Industry, 
 An Applications Manual 
 
 By R. J. Pokora, T. G. Bobick, and T. L. Muldoon 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
Information Circular 8975 
 
 Retrofit Noise Control Modifications 
 for Crushing and Screening Equipment 
 in the Nonmetallic Mining Industry, 
 An Applications Manual 
 
 By R. J. Polcora, T. G. Bobicic, and T. L. Muldoon 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 William P. Clark, Secretary 
 
 BUREAU OF MINES 
 Robert C. Norton, Director 
 

 \ 
 
 fiH' 
 
 Library of Congress Cataloging in Publication Data: 
 
 Retrofit noise control modifications for crushing and screening equip- 
 ment in the nonmetallic mining industry. 
 
 (Information circular / United States Department of the Interior, 
 Bureau of Mines ; 8975) 
 
 Supt. of Docs, no.: I 28.27:8975. 
 
 1. Sand and gravel plants— Noise control. 2. Crushed stone in- 
 dustry—Noise control. 3. Crushing machinery —Noise. 4. Screens 
 (Mining)— Noise. I. Pokora, R. J. (Robert J.). II, Series: Information 
 circular (United States. Bureau of Mines) ; 8975. 
 
 TN295.U4 [TD893.1V15] 622s [622'. 73] 84-600017 
 
CONTENTS 
 
 Page 
 
 Abstract 1 
 
 Introduction 2 
 
 Federal noise regulations 2 
 
 Background 2 
 
 Noise source Identification 3 
 
 Noise control treatments 4 
 
 Noise control treatment costs 4 
 
 Manual organization and content 4 
 
 Noise control treatment of the screen feed chute 5 
 
 Design and selection of resilient Impact pads 6 
 
 Installation of the chute wall Impact pad 7 
 
 Installation of an Impact pad or dead bed In the chute bottom 8 
 
 Noise control treatment of screens 9 
 
 Design and selection of noise control treatments for screens 9 
 
 Installation of noise control treatments for screens 11 
 
 Noise control treatments for a cone crusher 17 
 
 Design and selection of noise control treatments for cone crushers 17 
 
 Installation of noise control treatments for crushers 18 
 
 Noise control using an operator control booth 21 
 
 General selection guidelines 21 
 
 General construction guidelines 22 
 
 Typical booth Installation 22 
 
 Summary and conclus Ions 24 
 
 ILLUSTRATIONS 
 
 1. Product feed path from the belt conveyor to the screen feedbox 5 
 
 2. Effect of Impact angle of product on resilient pad life 6 
 
 3. Use of a profiled Impact pad to provide a better Impact angle for In- 
 creased wear life 6 
 
 4. Installation of a prof lled-surf ace Impact pad 7 
 
 5. Installation of a resilient Impact pad may cause a change In product 
 rebound 7 
 
 6. Installation of a resilient Impact pad on the bottom of the screen feed 
 chute 8 
 
 7. Impact pad fastened to the bottom of feed chute with countersunk holes for 
 protection of boltheads 8 
 
 8. Installation of a dam to create a dead bed on the chute bottom 9 
 
 9. Combination of a resilient Impact pad and dead bed In the bottom of a 
 
 secondary screen feed chute 9 
 
 *^ 10. Cross section of typical resilient protection for sizing screens 11 
 
 \. 11. Installation of a bolted resilient screen deck and blank Impact panel 12 
 
 ^n 12. Bolted resilient deck with blank panel in the feedbox 12 
 
 13. Resilient feedbox with impact pad where product from the chute strikes the 
 
 f eedbox 12 
 
 "^ 14. Installation of resilient side wing liners 13 
 
 ^, 15. Resilient liners bolted to screen side wings 13 
 
 .sA 16. Installation of a resilient screen deck using side-tension rails 13 
 
 ^^ 17. Resilient screen deck with resiliently lined, side-tension rails 13 
 
 ^ 18. Resilient deck Installed on a horizontal screen using resiliently lined, 
 
 side-tension rails and J-hook clamps 14 
 
ii 
 
 ILLUSTRATIONS— Continued 
 
 Page 
 
 19. Treatment of the screen discharge lip 14 
 
 20. Resilient discharge lip with thicker side liners to funnel the screen 
 
 discharge 14 
 
 21. Installation of resilient liners on a screen discharge chute 15 
 
 22. Resilient liner in a screen discharge chute directly feeding a crusher.... 15 
 
 23. Installation of a drag curtain over the feed chute discharge 16 
 
 24. Drag curtain installed on an inclined screen 16 
 
 25. Resilient liner installed in the crusher feed hopper 18 
 
 26. Installation of a resilient crusher feed cone shell liner 19 
 
 27. Installation of a one-piece resilient crusher feed cone liner 19 
 
 28. Installation of resilient feed cone liner segments 20 
 
 29. Installation of a resilient crusher feed plate 20 
 
 30. Installation of a molded resilient pad for the mantle hold-down cap 20 
 
 31. Installation of a barrier curtain around the crusher main frame 21 
 
 32. Noise barrier curtain installed around the crusher main frame 21 
 
 33 . Basic control booth wall construction 22 
 
 34. View of a primary crushing plant with an operator control booth 23 
 
 35. Operator control booth mounted on separate steel support structure 23 
 
 36. Separate control booth support structure constructed by quarry personnel.. 23 
 
 37. Primary crusher operator at the control station inside the booth 23 
 
 TABLE 
 
 1 . Permissible noise exposures 2 
 
 
 UNIT 
 
 OF MEASURE ABBREVIATIONS USED IN THIS REPORT 
 
 dB 
 
 
 decibel in inch 
 
 dBA 
 
 
 decibel, A-weighted pet percent 
 
 ft 
 
 
 foot ton/h ton per hour 
 
 h 
 
 
 hour 
 
RETROFIT NOISE CONTROL MODIFICATIONS FOR CRUSHING AND SCREENING 
 
 EQUIPMENT IN THE NONMETALLIC MINING INDUSTRY, 
 
 AN APPLICATIONS MANUAL 
 
 By R, J, Pokora, ^ T. G. Bobick, ^ and T, L, Muldoon^ 
 
 ABSTRACT 
 
 This Bureau of Mines report is an applications manual that can be used 
 by the nonmetallic mining industry for guidance in installing noise con- 
 trol materials into crushing and screening plants. These noise control 
 modifications were installed and successfully tested at three operating 
 quarries. This report identifies the major noise sources that can be 
 encountered in crushing and screening plants, and discusses the applica- 
 ble noise control materials and techniques that a plant operator can 
 utilize on a retrofit basis to reduce equipment noise. 
 
 ^Program manager, CARD, Inc., Niles, IL (formerly with Foster-Miller Associates) 
 fining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh PA. 
 ■^Senior engineer, Foster-Miller Associates, Inc., Waltham, MA. 
 
INTRODUCTION 
 
 FEDERAL NOISE REGULATIONS 
 
 Noise levels generated by the crushing 
 and screening of nonmetallic minerals are 
 regulated under 30 CFR, Part 56 — Safety 
 and Health Standards — Sand, Gravel, and 
 Crushed Stone Operations. Section 56.5- 
 50 states: 
 
 Mandatory. (a) No employee shall 
 be permitted an exposure to noise in 
 excess of that specified in table 1. 
 
 TABLE 1. - Permissible noise exposures 
 
 Duration per day, 
 hours of exposure 
 
 Sound level, dBA, 
 slow response 
 
 8 90 
 
 6 92 
 
 4 95 
 
 3 97 
 
 2 100 
 
 1-1/2 102 
 
 1 105 
 
 1/2 110 
 
 1/4 or less 115 
 
 NOTE. — No exposure shall exceed 115 
 dBA. Impact or impulsive noises shall 
 not exceed 140 dB, peak sound pressure 
 level. 
 
 NOTE: When the daily noise expo- 
 sure is composed of two or more peri- 
 ods of noise exposure at different 
 levels, their combined effect shall 
 be considered rather than the indi- 
 vidual effect of each. 
 
 If the sum 
 
 (Ci/T,) + (C2/T2) + . 
 
 (Cn/Tn) 
 
 exceeds unity, then the mixed expo- 
 sure shall be considered to exceed 
 the permissible exposure, Cn indi- 
 cates the total time of exposure at 
 a specified noise level, and Tp in- 
 dicates the total time of exposure 
 
 permitted at that level. Interpola- 
 tion between tabulated values may be 
 determined by the following formula: 
 
 Log T = 6.322 - 0.0602 SL, 
 
 where T is the time in hours and SL 
 is the sound level in dBA. 
 
 (b) When employees' exposure ex- 
 ceeds that listed in table 1, feasi- 
 ble administrative or engineering 
 controls shall be utilized. If such 
 controls fail to reduce exposure to 
 within permissible levels, personal 
 protection equipment shall be provid- 
 ed and used to reduce sound levels to 
 within the levels of the table. 
 
 Enforcement of the standards has shown 
 that an acute noise exposure problem ex- 
 ists in the sand and gravel and crushed 
 stone industries. 
 
 BACKGROUND 
 
 In 1981, a Bureau of Mines study'* of 
 the noise exposures of workers in crush- 
 ing and screening plants concluded that 
 plant operators and plant cleanup person- 
 nel can have full-shift noise exposures 
 that range from three to four times that 
 allowed by the standard. The study also 
 included an analysis of the major noise 
 sources that contribute to the overexpo- 
 sure problem. 
 
 As part of this same research program, 
 retrofit noise control treatments for 
 the major sources were designed, in- 
 stalled, and evaluated in three crushing 
 and screening plants. The three plants, 
 
 4pokora, R. J., and T. L. Muldoon. 
 Demonstration of Noise Control Techniques 
 for the Crushing and Screening of Non- 
 metallic Minerals (contract J01 00038, 
 Foster-Miller, Inc.). BuMines OFR 50-83, 
 1981, 187 pp.; NTIS PB 83-173039. 
 
which were selected from a series of 
 eight surveyed, included — 
 
 • A primary crushing plant that re- 
 ceived run-of-mine product from the quar- 
 ry. The plant used a 16-ft by 42-in vi- 
 brating feeder grizzly and a 32- by 42-in 
 jaw crusher. 
 
 • A secondary plant that used a 5- by 
 14-ft inclined double-deck screen, and a 
 4-1/4-ft cone crusher. 
 
 • A secondary plant that used a 5- by 
 14-ft horizontal double-deck screen, and 
 a 5-ft cone crusher. 
 
 All three plants had a capacity of 200 to 
 300 ton/h. 
 
 The noise control treatments described 
 in this manual were developed for this 
 program and are, therefore, somewhat spe- 
 cific to these sizes and types of plants. 
 The basic treatments, however, with some 
 modifications, are applicable to all 
 crushing and screening plants, 
 
 NOISE SOURCE IDENTIFICATION 
 
 The first step in any noise control 
 effort is to determine what noise sources 
 are contributing most significantly to 
 the overexposure problem. Noise level 
 measurements, coupled with on-site obser- 
 vations, identified the following major 
 noise sources as those that could be 
 treated in the field: 
 
 Screen feed ehute, — Typically, mate- 
 rial enters the screen through a steel 
 chute from a belt conveyor. The product 
 discharged from the conveyor impacts the 
 sides, wall, and bottom of the steel 
 chute. 
 
 Screen feedhox. — Additionally, the 
 product discharging from the screen feed 
 chute impacts a steel screen feedbox that 
 is an integral part of the screen. 
 
 Screen » — The normal screening medium is 
 either punched steel plate or woven wire 
 cloth. Some screens are furnished with 
 
 steel side wings. High noise levels are 
 generated by the impact of the product on 
 both the deck and wing liners. 
 
 Screen discharge, — Typically, the over- 
 size product from the top screen deck 
 drops onto a steel discharge lip or di- 
 rectly from the screen onto a steel plate 
 in the crusher. The undersize product 
 passes through the screening media and 
 impacts a discharge chute, transfer con- 
 veyor, or another screen deck. 
 
 Crusher feed hopper or chute, — The feed 
 to the crusher impacts a cylindrical- 
 conical collection hopper that directs 
 the feed into the crushing cavity. Often 
 the feed to the crusher is sparse and the 
 impacting product strikes the hopper in- 
 dividually. A heavily fed (choke-fed) 
 crusher has the opportunity for a bed of 
 material to build up and, therefore, 
 attenuate the noise. 
 
 Crusher feed plate, — Most cone crushers 
 are supplied with an abrasion-resistant 
 metal feed plate. Product dropping into 
 the crusher strikes the feed plate — par- 
 ticularly if the crusher is not choke 
 fed. 
 
 Crusher feed cone, — Typically, the feed 
 cone is lined with manganese steel plate 
 for wear. The product fed to the crusher 
 strikes the feed cone. 
 
 Crusher main frame, — The shell sur- 
 rounding the crushing cavity typically is 
 impacted by product discharging from in- 
 side the crusher. The shell acts as a 
 radiator for all of the noise generated 
 in the product reduction process from 
 within the crusher itself. 
 
 Crusher discharge, — The product dis- 
 charged from the crusher is typically 
 transferred via another steel chute to a 
 belt conveyor that transports it to the 
 next comminution stage or to a stockpile. 
 
 These sources are common to all crush- 
 ing and screening plants and are acces- 
 sible without major disassembly of the 
 plant . 
 
NOISE CONTROL TREATMENTS 
 
 The noise associated with each of the 
 sources is usually generated by the im- 
 pact of the product on the steel compo- 
 nents. The impact forces cause the com- 
 ponents to resonate, creating airborne 
 noise. 
 
 Noise control treatments can be applied 
 to — 
 
 • Minimize the impact forces. 
 
 • Damp a vibrating steel component. 
 
 • Enclose the source to block the air- 
 borne noise. 
 
 the main frame. Noise measurements at 
 plant operating positions and cleanup 
 areas showed noise reductions of 4 to 7 
 dBA. These reductions, which approxi- 
 mately double the allowable exposure 
 times in these work areas, should reduce 
 the full-shift noise exposures of cleanup 
 and maintenance personnel to within those 
 specified by Federal regulations. 
 
 At the primary crushing plant, an op- 
 erating booth was manufactured and in- 
 stalled to enclose the crusher operator. 
 Noise measurements showed a reduction of 
 approximately 20 dBA resulting in noise 
 levels in the booth of less than 80 dBA. 
 
 NOISE CONTROL TREATMENT COSTS 
 
 • Enclose the worker to block the air- 
 borne noise. 
 
 At the two secondary plants addressed 
 during the Bureau program, resilient ma- 
 terials were applied at certain locations 
 to minimize the noise produced by product 
 impact on the structure. Specific treat- 
 ments included — 
 
 The costs, in 1981 dollars, for the 
 treatments described for the two second- 
 ary plants averaged $15,500 ($14,003 and 
 $17,085) for materials. Quarry labor re- 
 quired for installation of the treatments 
 averaged 67.5 work-hours (66 and 69 h). 
 The booth, purchased commercially, cost 
 $4,919 (1981) and required 40 work-hours 
 for installation. 
 
 • Resilient impact pads installed on 
 the wall and bottom of the screen feed 
 chute. 
 
 • Resilient liner for the screen feed- 
 box. 
 
 • Resilient screen decking. 
 
 • Resilient liners for the screen side 
 wings , 
 
 • Resilient screen discharge lip. « 
 
 • Resilient liner for the crusher feed 
 hopper. 
 
 • Resilient liner for the crusher feed 
 cone. 
 
 • Resilient crusher feed plate(s). 
 
 In addition, an acoustical curtain was 
 used to enclose the crusher shell to 
 block the airborne noise radiating from 
 
 These costs are for purchasing and in- 
 stalling materials manufactured specif- 
 ically for the three plants treated in 
 this program. They are a good estimate 
 for the costs of treating similar-sized 
 plants using commercially available mate- 
 rial and plant labor for installation. 
 Costs will probably be higher for larger- 
 sized plants, or for treatments Installed 
 by an outside firm. 
 
 MANUAL ORGANIZATION AND CONTENT 
 
 This manual is primarily intended as a 
 general guide for the design, selection, 
 and installation of noise control treat- 
 ments for crushing and screening plants. 
 Most of the treatments discussed have 
 been installed in two secondary crushing 
 and screening plants, and the drawings 
 and photos are oriented toward that type 
 of plant. The treatments, however, are 
 applicable to other plant sizes and 
 types. 
 
The main portion of this manual divides 
 the plant into major components for dis- 
 cussion. The discussion for each compo- 
 nent covers — 
 
 • How the noise is produced. 
 
 • Typical noise levels generated. 
 
 • The design and selection of noise 
 control treatments. 
 
 • How the noise control treatments are 
 installed. 
 
 • Any potential problems created by 
 the treatments. 
 
 The manual also includes a section on 
 the design, fabrication, and installation 
 of control booths for protecting the 
 plant operators. 
 
 The manual is not plant specific. It 
 does not specify materials by type, and 
 does not specify dimensions. There are 
 a number of well-known manufacturers of 
 the types of materials recommended in 
 this manual. It is not the Bureau's 
 intent to make specific recommendations; 
 the appropriate noise control treatment 
 will depend on the actual operating 
 conditions encountered and the noise 
 levels measured at a plant. Thus, it is 
 not possible to state exact dimensions or 
 specific material requirements. The 
 manual, however, does provide general 
 design considerations, and does discuss 
 what information must be provided by the 
 plant operator to a noise-control 
 material manufacturer to ensure proper 
 material design. 
 
 NOISE CONTROL TREATMENT OF THE SCREEN FEED CHUTE 
 
 Typically, screens receive product to 
 be processed via a steel chute that is 
 fed by a belt conveyor. Product dis- 
 charged from the conveyor strikes the 
 sides and wall of the chute, rebounds, 
 and falls to the chute bottom where it 
 discharges to the screen through the 
 feedbox (fig. 1). Noise levels measured 
 adjacent to these chutes normally exceed 
 110 dBA with a coarse product feed. 
 Noise levels at normal operating posi- 
 tions near these chutes approach 100 dBA. 
 
 The recommended 
 ments include — 
 
 noise control treat- 
 
 • Installing a resilient impact pad on 
 the chute wall and/or sides. 
 
 • Using a resilient impact pad or a 
 product dead bed in the chute bottom. 
 
 The purpose of these treatments is to ab- 
 sorb the force of the product impact, 
 thus reducing the amount of energy trans- 
 ferred to the steel chute. If properly 
 
 designed and installed, they will not on- 
 ly reduce noise, but also significantly 
 increase chute life. 
 
 Belt conveyor 
 
 Screen 
 feed - 
 chute 
 wall 
 
 Dribble chute 
 
 Screen 
 feedbox 
 
 FIGURE 1, - Product feed path from the belt con- 
 veyor to the screen feed box. 
 
DESIGN AND SELECTION OF 
 RESILIENT IMPACT PADS 
 
 Proper design of impact pads for maxi- 
 mum noise reduction and minimum wear re- 
 quires designing for — 
 
 • Product type. 
 
 • Product size. 
 
 • Product impact angle. 
 
 • Product velocity. 
 
 The angle that the product strikes an 
 impact pad will determine the life of the 
 pad (see figure 2). Impact angles of 
 less than 50° will result in rapid wear 
 and less life than steel. Impact angles 
 between 50° and 70° will yield a wear 
 life comparable to steel. Angles greater 
 than 70° and less than 90° are considered 
 optimum. If the impact angle is 70° or 
 above, the impact pad can be a flat 
 sheet. If the angle is less than 70°, a 
 profiled surface that provides a greater 
 impact angle is recommended (fig. 3). 
 
 Product Impact angle 
 path N^ ^^ 
 
 Impact angle 
 
 Resilient pad 
 
 FIGURE 2, - Effect of impact angle of product on 
 resi lient pad life. 
 
 u 
 
 7, 
 
 Product^ Impact angle 
 path 
 
 Poor design with o shotlow 
 impact angle 
 
 Good design using a profiled 
 surface to increase the impact 
 angle to greater than 70° 
 
 FIGURE 3» • Use of a profiled impact pad to pro- 
 vide a better impact angle for increased wear life. 
 
 The thickness of the pad must be suffi- 
 cient to minimize crushing damage to the 
 liner. The required thickness depends 
 upon both the size of the product strik- 
 ing the pad and the velocity of the prod- 
 uct at impact. Generally, the larger the 
 product and the higher the velocity, the 
 greater the thickness of material that 
 is required for optimum wear. This in- 
 creased thickness, however, must be bal- 
 anced against available space within the 
 chute. In small chutes, the rubber 
 thickness could interfere with the head 
 pulley or belt scraper and could retard 
 product flow out of the chute. 
 
 The type and the mechanical properties 
 of resilient materials (selected for the 
 impact pads) are site specific, and de- 
 pend primarily upon the size, shape, and 
 type of product being processed. 
 
 Selection of the material, in terms of 
 its hardness, thickness, and proper sur- 
 face profile, should be the responsibil- 
 ity of the material manufacturer. The 
 user, however, must provide the follow- 
 ing information for proper impact pad 
 selection: 
 
 Type of product being processed. 
 
 Size of product being processed. 
 
 Velocity of the product — for the chute 
 side wall, the belt speed should be ade- 
 quate; for the chute bottom, the height 
 of the drop is required. 
 
 Dimensions of the chute. 
 
 Angle of product impact . 
 
 Relative position of the head pulley, 
 belt cleaner, and dribble chute. 
 
Representatives of companies of any 
 potentially applicable resilient materi- 
 als will definitely have to visit the 
 quarry operations before specifying any 
 products. This may be the only oppor- 
 tunity for the material manufacturer 
 and the quarry operator to actively dis- 
 cuss the implied and explicit warranties 
 of the resilient materials, the extent 
 of the required labor needed for materi- 
 al installation, and whose responsibil- 
 ity it will be to make field modifica- 
 tions to any improperly fitting resilient 
 products. 
 
 INSTALLATION OF THE CHUTE 
 WALL IMPACT PAD 
 
 The impact pad for the chute wall can 
 be either bolted to the wall or suspended 
 in the chute. Figure 4 shows a profiled 
 surface pad installation. Holes are 
 drilled or burned through the chute wall. 
 Corresponding holes are drilled through 
 the impact pad. Drilled steel bars 
 should be placed between the resilient 
 pad and boltheads for better support. 
 The pad should be the full width of the 
 chute wall and should extend both above 
 and below the impact area. 
 
 The pad can also be suspended in the 
 chute using cables or steel straps that 
 secure it to the chute side walls. If 
 
 space permits , the pad can be suspended 
 away from the chute wall, allowing it to 
 swing freely. This will help reduce 
 crushing forces on the pad and should in- 
 crease its life. Care must be taken, 
 however, to insure that the pad does not 
 swing into the conveyor belt head pulley 
 when the feed is shut down and the prod- 
 uct flow into the pad stops. 
 
 Once the pad is installed, the clear- 
 ance between it and the head pulley 
 should be checked regularly to ensure 
 that the pad does not interfere with the 
 pulley or belt scrapers. Additionally, 
 the flow of the product in the chute 
 should be observed. Using a resilient 
 impact pad can change the angle at which 
 the material rebounds from the chute wall 
 (shown in figure 5). Depending on the 
 chute depth, a change in angle might cre- 
 ate another impact point before the prod- 
 uct reaches the chute bottom; this may 
 then require an impact pad for the drib- 
 ble chute. An important caution is that 
 the installation of impact pads may cre- 
 ate material handling and/or equipment 
 problems if the conveyor speeds are too 
 high, if incorrect idlers are used, or if 
 insufficient clearances exist around the 
 conveyor. Specifications from the Con- 
 veyor Equipment Manufacturer's Associa- 
 tion for the design and installation of 
 conveyors must be followed. Questions 
 concerning proper design and fine tuning 
 a conveyor system are best answered by 
 the manufacturer. If dust control sprays 
 are used in the chute, then adequate 
 clearance has to be provided before in- 
 stalling the impact pad. The water 
 
 STEEL CHUTE 
 
 Feed chute 
 
 IMPACT PAD INSTALLED 
 
 v,^^ Conveyor 
 
 -^Dribble chute Feed chute 
 
 Feedbox 
 
 -^ Dribble chute 
 
 Feedbox 
 
 FIGURE 4» • Installation of a profiled-surface 
 impact padt 
 
 FIGURE 5. - installation of a resilient impact pad 
 may cause a change in product rebound* 
 
sprays will have to be readjusted after 
 restarting the circuit to accommodate any 
 change in the rebound of the product. 
 
 INSTALLATION OF AN IMPACT PAD 
 OR DEAD BED IN THE CHUTE BOTTOM 
 
 An impact pad should also be bolted to 
 the bottom of the feed chute, as shown in 
 figure 6. Holes can be drilled or burned 
 through the chute after marking it to 
 correspond to those that are drilled 
 through the pad(s). The holes in the pad 
 should be countersunk by the material 
 manufacturer so the boltheads will be be- 
 low the pad surface, as shown in fig- 
 ure 7. The pad should cover the entire 
 chute bottom. 
 
 Most resilient materials have a higher 
 coefficient of sliding friction than 
 steel. Installation of the pad, there- 
 fore, may tend to retard the product flow 
 out of the chute. If product flow is un- 
 satisfactory, the angle of the chute bot- 
 tom may have to be increased to overcome 
 the increased friction of the pad. 
 
 The chute bottom can also be modified 
 by creating a dead bed. A dead bed is 
 nothing more than a buildup of product 
 at the area of impact, A dead bed is 
 created by installing a dam at the dis- 
 charge end of the chute bottom (as shown 
 in figure 8) to retard the product flow. 
 The dam can be made from resilient mate- 
 rial or channel iron, should be bolted to 
 the chute bottom, and should extend the 
 entire width of the chute. The height of 
 the dam will depend on the angle of re- 
 pose of the product flowing through the 
 chute and the angle of the chute bottom.. 
 It must be high enough to create a layer 
 of product that covers the entire chute 
 bottom. A dead bed is also recommended 
 
 in combination with a resilient impact 
 pad to improve the life of the pad. A 
 combination of an impact pad and dead bed 
 installed in a chute bottom is shown in 
 figure 9; the impact pad is covered by 
 the dead bed, however, and is not visible 
 in the figure. 
 
 FIGURE 6. - Installation of a resilient impact pad 
 on the bottom of the screen feed chute. 
 
 mpact pad 
 
 7777 Chute bottom 
 
 FIGURE 7, - Impact pad fastened to the bottom of 
 feed chute with countersunk holes for protection of 
 boltheads. 
 
Dam 
 
 FIGURE 8. - Installation of a dam to create a dead 
 bed on the chute bottom. 
 
 FIGURE 9, - Combination of a resilient impact pad 
 and dead bed in the bottom of a secondary screen feed 
 chute. 
 
 NOISE CONTROL TREATMENT OF SCREENS 
 
 Typically, the product discharged from 
 the screen feed chute impacts a steel 
 feedbox that is an integral part of the 
 screen. The product then passes over the 
 screening medium, which is either punched 
 steel plate or woven wire cloth. Depend- 
 ing on the discharge trajectory, the 
 oversize product either passes over or 
 falls onto a steel discharge lip. Most 
 screens are furnished with either steel 
 side wings or with steel side-tension 
 rails that are also impacted as the prod- 
 uct passes along the deck. 
 
 High noise levels are generated by the 
 product impacting on the steel feedbox, 
 on the deck, against the side wings or 
 tension rails, and on the steel dis- 
 charge lip. Noise levels measured beside 
 screens handling coarse material often 
 exceed 105 dBA. 
 
 The recommended noise control treat- 
 ments include — 
 
 • Resilient linings for the screen 
 feedbox. 
 
 • Resilient screen decking. 
 
 • Resilient side wing liners, or re- 
 silient material liners on the side- 
 tension rails, 
 
 • Resilient screen discharge lip, 
 
 DESIGN AND SELECTION OF NOISE CONTROL 
 TREATMENTS FOR SCREENS 
 
 Most screen manufacturers do not recom- 
 mend discharging product directly onto 
 the perforated part of the screen deck. 
 This is especially true for screens hand- 
 ling coarse product with a large drop 
 height from the feed chute. These 
 screens are provided with a blank metal 
 panel at the feed end preceded by a feed- 
 box that is often protected by metal wear 
 plates where the product impacts the 
 screen. The blank panel should be re- 
 placed by a thicker, blank resilient pan- 
 el. A resilient impact pad should be in- 
 stalled in the screen feedbox to increase 
 the thickness of the area that is im- 
 pacted by the product from the feed 
 chute. The back and sides of the screen 
 feedbox should also be treated with a re- 
 silient liner. 
 
10 
 
 The screening medium (punched plate or 
 woven wire) should be replaced with a re- 
 silient deck. ;^n selecting the resilient 
 deck, it must be remembered that the use 
 of a resilient cloth may reduce screening 
 efficiency and throughput. This reduc- 
 tion can be caused by — 
 
 • Less percent open area for the same 
 deck area. 
 
 • The resilient cloth (being thicker 
 to maintain strength) may cause blinding 
 of the screening medium, thus further re- 
 ducing the percent open area in the deck, 
 
 • Screening is normally accomplished 
 in the initial one-third of the deck; if 
 a screen is marginally sized for a spe- 
 cific capacity, then arbitrarily replac- 
 ing a perforated panel with a blank 
 one will also reduce the screening 
 efficiency. 
 
 The actual thickness of the cloth de- 
 pends upon the maximum feed size and the 
 thickness of the bed depth. The cloth, 
 however, should not be thicker than the 
 size of the openings in the deck. 
 
 When ordering resilient decking, it is 
 important to specify the following infor- 
 mation to the deck manufacturer: 
 
 Use of the screen in the circuit (siz- 
 ing, scalping, transferring, etc.). 
 
 The efficiency of the screen (i.e., the 
 percent near size and undersize material 
 contained in the oversize product). 
 
 Type and size of product being 
 screened. * 
 
 Dimensions of the existing deck. 
 
 Type of mounting — whether the deck is 
 bolted to the screen frame or if it is 
 held by side-tension rails. 
 
 Type, location, and dimensions of 
 screen support members. 
 
 Type and dimensions of holddown 
 clamping. 
 
 Resilient materiale are extremely dif- 
 ficult to "modify-to-fit" in the field; 
 thus, exact equipment dimensions must 
 be provided to the resilient material 
 supplier . 
 
 If the deck is bolted to the screen 
 frame, nonperf orated areas should be spe- 
 cified over the deck support members. 
 The nonperforated areas will protect the 
 support members and prevent accumulation 
 of product between the deck and supports , 
 which can cause excessive wear of the 
 frame. If the screen has steel side 
 wings, resilient liners that are at least 
 1 in thick and high enough to protect the 
 side wings from product impact should be 
 specified. 
 
 If the screen cloth is attached using 
 side-tension rails, the type and size of 
 rail have to be specified. Most manufac- 
 turers of resilient decks supply side- 
 tension rails equipped with a resilient 
 impact liner that is bonded or bolted to 
 the rails. Trowel- or paint -on resil- 
 ient coatings have had limited durabil- 
 ity, and their use is not recommended. 
 
 As mentioned, the type and size of sup- 
 port members have to be specified. Sup- 
 port members require a resilient protec- 
 tive molding (shown in figure 10^4), 
 called a bumper strip, to minimize deck 
 wear and properly crown the deck. The 
 type of deck clamping also has to be spe- 
 cified. If the screen uses a center 
 clamping bar, a resilient molding for the 
 bar (fig, lOB) is available from the man- 
 ufacturers. Screen clamping with J-hooks 
 should use a resilient block or ring 
 (fig, IOC) to protect the nut and threads 
 on each hook. These blocks or rings are 
 also available from the deck manufactur- 
 er. The Bureau recommends ordering extra 
 clamping hardware at the outset because 
 any discontinuity on the screen deck sur- 
 face appears to accelerate the wear on 
 the clamping device. 
 
 The discharge lip and sides should also 
 be lined with resilient material. For a 
 straight lip discharge, the thickness of 
 the bottom pad should be the same as the 
 thickness of the deck. The resilient 
 
11 
 
 B 
 
 FIGURE 10. - Cross section of typical 
 resilient protection for sizing screens. 
 A, Molding (bumper strip) for support mem- 
 bers; B, molding for a center bar clamp; 
 C, block or ring for a J-hook clamp. 
 
 liners for the sides of the lip should be 
 thicker than those on the side wings. 
 Increasing the thickness of the side lip 
 liner will funnel the screen discharge 
 and help prevent product from being 
 jammed between the screen and the screen 
 discharge hopper, A horizontal screen 
 discharge, which feeds a crusher directly 
 by choking the feed down to the opening 
 size of the crusher feed hopper, requires 
 a resilient liner on both the sides and 
 bottom of the discharge chute. To mini- 
 mize installation problems, the exact 
 size and shape of the chute bottom and 
 sides should be specified. Most resil- 
 ient liners that are used in coarse 
 screening are reinforced with steel plate 
 or woven wire; thus, modifying them in 
 the field during installation is extreme- 
 ly difficult and time consuming. 
 
 INSTALLATION OF NOISE CONTROL 
 TREATMENTS FOR SCREENS 
 
 Treating the screen feedbox with a re- 
 silient liner, installing an impact pad 
 or plate, and replacing the perforated 
 metal (or woven wire) deck with resilient 
 decking is fairly straightforward, pro- 
 vided the measurements were obtained 
 carefully. Installation of a resilient 
 deck that is to be bolted in place (fig. 
 11) requires — 
 
 • Removing the steel screen deck and 
 blank feedbox panel. 
 
 • Carefully measuring and locating 
 bolthole locations on the resilient deck 
 and blank feedbox panel (if not furnished 
 predrilled) . 
 
 • Drilling and countersinking holes in 
 the resilient deck and feedbox panel (if 
 not furnished predrilled). 
 
 • Installing new 
 required) . 
 
 bumper bars (where 
 
 • Bolting the panels in place. 
 
 Figure 12 shows an inclined sizing 
 screen equipped with a blank, resilient 
 feedbox panel and a resilient screen 
 deck. As mentioned earlier, a feedbox 
 handling coarse material with a large 
 drop height from the feed chute should 
 have a thicker resilient pad at the point 
 of impact. This pad can be bolted to the 
 metal (screen) feedbox, as shown at the 
 right of figure 13. 
 
 Installation of the side wing liners, 
 shown in figure 13, requires the follow- 
 ing modifications to the previously in- 
 stalled side wings: 
 
 Drilling or burning boltholes through 
 the top and bottom of the side wings. 
 (CAUTION. — Do not drill through the side 
 plates of the screen unless the manufac- 
 turer has provided approval for the 
 holes , since this can affect the struc- 
 tural integrity of the screen.) 
 
12 
 
 ! 
 
 ® 
 
 f 
 
 ® 
 
 f 
 
 rs> 
 
 Up o o 
 
 © 
 
 o 
 
 tk ♦ 
 
 
 o o o o 
 
 do o^ 
 
 4 • 
 
 10 o » 
 
 o « 
 
 a 
 
 JMM^ 
 
 SBtttt 
 
 
 I 
 
 r 
 
 —J^ 
 
 o| e o o o J© 
 
 o I e e e e le 
 
 FIGURE lit" Installation of a bolted resilient 
 screen deck and blank impact panel* 
 
 FIGURE 12, • Bolted resilient deck with blank 
 panel in the feedbox. 
 
 FIGURE 13, - Resilient feedbox with impact pad 
 where product from the chute strikes the feedbox. 
 
 Locating, drilling, and countersinking 
 bolt holes through the resilient 
 liner. 
 
 Bolting the liner in place. 
 
 Thicker liner sections (fig. 14) can also 
 be bolted along the length of the side 
 wings and/or at the discharge lip to fun- 
 nel the product flow towards the center 
 of the screen deck. An installed side 
 wing liner is shown in figure 15. 
 
 Installation of a resilient deck using 
 side-tension rails is shown in figure 16. 
 Installation requires — 
 
 • Removing the steel deck and side- 
 tension rails. 
 
 • Locating, drilling, and countersink- 
 ing boltholes through the resiliently 
 lined, side-tension rails. 
 
13 
 
 Side liners 
 
 Thicker liner 
 
 
 Discharge end 
 FIGURE 14. - Installation of resilient side wing 
 
 iners. 
 
 Side wing 
 
 ,**■; 
 
 / * 
 
 n^ 
 
 Resilient liner 
 
 \. 
 
 '. ? 
 
 ^ ¥.-.- if .^ 
 
 ^.^1iC. 
 
 i 
 
 FIGURE 15. - Resilient liners bolted to screen 
 side wings. 
 
 • Installing resilient protective 
 moldings (bumper strips) on screen sup- 
 port members. 
 
 • Installing the deck and side-tension 
 rails on the screen frame. 
 
 • Clamping the screen deck using 
 either J-hooks with resilient protective 
 blocks or rings, or using a center bar 
 clamp with resilient protective molding. 
 
 Figure 17 shows a resilient screen deck 
 equipped with resiliently lined, side- 
 tension rails that had been installed 
 on a horizontal screen. The completed 
 
 Resilient rings 
 
 Side-tension rail 
 
 iDDfjninQodu gaa quo \ 
 
 /ooocoaaoaSaaaaa ^ 
 
 /ccooaQaoomaaaaa < 
 
 /coooooauuinau QQQ ' 
 
 ' DDUDoa DUD aaa aaa ' 
 
 ' DDDDDDDaUUUU aOQ ' 
 
 Bumper strip 
 
 'L J 
 
 FIGURE 16. " Installation of a resilient screen 
 deck using side-tension rails (longitudinal screen 
 deck support). 
 
 FIGURE 17. - Resilient screen deck with re- 
 siliently lined, side-tension rails. 
 
 installation with protected J-hook clamp- 
 ing is shown in figure 18. 
 
14 
 
 Side lip iiners 
 
 FIGURE 18. • Resilient deck installed on a hori- 
 zontal screen using resiliently lined, side«tension 
 rails and J-hook clamps. 
 
 Resilient liner for 
 discharge lip 
 
 
 ^ 
 
 
 ¥ 
 
 «-- JI/ o o\ o o ° ° 
 
 w\ 
 
 Discharge 
 hopper 
 
 FIGURE 19t • Treatment of the screen discharge lip. 
 
 The screen discharge lip and discharge 
 chute liners are also bolted in place. 
 For the screen discharge lip (fig. 19), 
 any existing steel wear plates are re- 
 moved and the resilient liner is bolted 
 in place. Side lip liners can also be 
 bolted to the screen side wings. As men- 
 tioned, the side liners installed at the 
 discharge should be thicker than the side 
 wing liners along the deck to funnel the 
 material flow and prevent product from 
 jamming between the screen and the adja- 
 cent screen discharge hopper. Figure 20 
 shows a resilient discharge lip and 
 thicker side liners installed on an in- 
 clined sizing screen. 
 
 Installation of resilient liners for a 
 screen discharge chute, which feeds a 
 crusher by choking the product flow down 
 to the size of the opening of the crush- 
 er, is illustrated in figure 21. These 
 liners are also bolted to the bottom and 
 sides of the steel chute. Figure 22 
 shows the treatment of a screen discharge 
 chute at a secondary sizing plant. Note 
 that the boltheads are countersunk in the 
 resilient material to protect against ex- 
 cessive wear caused by product slid- 
 ing over them, and also to eliminate a 
 
 FIGURE 20. - Resilient discharge lip with thicker 
 side liners to funnel the screen discharge. 
 
 potential secondary noise source that is 
 caused by the product striking the metal 
 bolthead. 
 
 The use of a resilient screen deck can 
 cause potential operating problems, 
 primarily decreased screening efficiency 
 because of plugging of screen openings. 
 These problems have already been 
 
15 
 
 discussed earlier in this report, 
 potential problems include — 
 
 Other 
 
 m 
 
 ^;m§^mm 
 
 FIGURE 2], - Installation of resilfent liners on a 
 screen discharge chute. 
 
 FIGURE 22» = Resilient liner in a screen discharge 
 chute directly feeding a crusher. 
 
 • The product tends to bounce more on 
 a resilient deck, especially on an in- 
 clined screen receiving coarse product, 
 
 • Resilient decks may require changes 
 in the screen's throw amplitude, speed, 
 and direction to maintain the usual 
 productivity and screening efficiency. 
 Most screens have this flexibility; if 
 changes are required, the manufacturer or 
 the screen operating manual should be 
 consulted. 
 
 When product strikes a resilient sur- 
 face, it tends to bounce more than when 
 it strikes steel. This higher bounce 
 combined with the increased thickness of 
 a resilient screen deck can result in 
 clearance problems between the deck and 
 either overhead or between-deck vibra- 
 tors. If product does strike the vibra- 
 tor, a resilient pad should be added to 
 the vibrator housing to prevent potential 
 damage. Another alternative for an over- 
 head vibrator would be to install a 
 spreader curtain at the screen feed end. 
 This spreader curtain, made of used con- 
 veyor belting, can be attached to the 
 feed chute to help distribute the screen 
 bed depth uniformly and minimize product 
 bounce. The belting should be attached 
 to the chute and extended to the under- 
 side of the vibrator. Do not attach the 
 belting to the vibrator; rather let it 
 hang free to raise as product passes un- 
 der it. 
 
 The higher bounce can also create safe- 
 ty and feed distribution problems , par- 
 ticularly on an inclined screen process- 
 ing coarse feed. The product striking 
 the resilient impact pad in the screen 
 feedbox may tend to bounce further down 
 the screen, thus negatively affecting the 
 distribution of the product along the 
 screening surface; given the right set of 
 circumstances, the product may bounce 
 over the screen side wings. To eliminate 
 both the feed distribution and safety 
 problems , a drag curtain should be in- 
 stalled over the feed chute discharge 
 (fig. 23). 
 
16 
 
 
 D O lO O 
 
 1 
 
 O O O I., 
 © O © Q\ 
 
 Q O O d' 
 
 >Z!C> lO O O Q O <t) 1 
 
 'm 
 
 FIGURE 23, - Installation of a drag curtain 
 over the feed chute discharge. 
 
 The drag curtain should be made of a 
 heavy, abrasion-resistant, resilient ma- 
 terial. (Conveyor belting is not recom- 
 mended because it wears rapidly and does 
 not have enough mass to retard the prod- 
 uct flow.) The drag curtain should be 
 the full width of the screen and should 
 extend from the top of the feed chute 
 discharge opening to the end of the blank 
 panel. The curtain can be bolted to the 
 feed chute; installation of a drilled 
 steel bar, inserted between the curtain 
 and the boltheads , is recommended for 
 added support. A drag curtain that has 
 been installed on an inclined sizing 
 screen is shown in figure 24. 
 
 The use of a resilient deck may also 
 require changes in the screen's throw am- 
 plitude, speed, and direction to maintain 
 productivity and screening efficiency. 
 For example, if the screening efficiency 
 decreases (too much near-size product is 
 being discharged off the screen deck) , 
 the throw direction can be changed from 
 with-flow to counterflow rotation. If 
 the bed depth becomes too shallow, the 
 speed can be reduced along with the throw 
 direction. This will result in a thicker 
 bed depth. The amplitude of the throw 
 can also be varied to obtain a more de- 
 sirable operating condition. In fact, 
 all three of these parameters may have to 
 be changed to optimize the screening 
 capacity and efficiency. 
 
 FIGURE 24, • Drag curtain installed on an inclined 
 screen. 
 
17 
 
 Although these changes were not made at 
 any of the three cooperating quarries, 
 the researchers had discussed these pos- 
 sibilities with them. An important point 
 
 to remember is that manufacturer's recom- 
 mendations should always be requested 
 before any operating parameters are 
 changed . 
 
 NOISE CONTROL TREATMENTS FOR A CONE CRUSHER 
 
 A typical secondary crushing and 
 screening plant uses a cone crusher to 
 reduce the oversized product from the 
 screen. This oversized product is trans- 
 ferred into a steel hopper that feeds the 
 crusher and then into the crusher feed 
 cone, which is typically equipped with 
 steel wear liners. The screen discharge 
 also strikes the crusher feed plate 
 and/or the mantle hold-down cap. 
 
 High noise levels are generated when 
 the product impacts these steel compo- 
 nents , and by the actual crushing pro- 
 cess , which produces noise from the 
 crusher main frame. Noise levels mea- 
 sured beside cone crushers typically ex- 
 ceed 110 dBA. 
 
 The recommended noise control treat- 
 ments for a cone crusher include — 
 
 • Resilient liners for a surge-type 
 feed hopper, feed cone hopper shell, and 
 the feed cone. 
 
 • A resilient feed plate or pad for 
 the mantle hold-down cap. 
 
 • A barrier curtain around the exte- 
 rior of the crusher main frame, 
 
 DESIGN AND SELECTION OF NOISE CONTROL 
 TREATMENTS FOR CONE CRUSHERS 
 
 Noise treatments for the crusher surge 
 hopper, feed shell, and cone should be 
 designed after the resilient deck has 
 been installed and any adjustments to the 
 screen have been completed. This se- 
 quence of treatment is recommended be- 
 cause the product flow from the screen 
 may change, thus changing the impact 
 points in the feed hopper. The crusher 
 feed cone and the feed cone hopper can be 
 treated completely because they rotate 
 during liner wear and/or setting. Re- 
 silient linings are required for all hop- 
 per surfaces impacted by the product. 
 
 not only during full-load operation, but 
 also during screen startup and shut- 
 down. Proper design of the liner for 
 the crusher surge hopper requires sup- 
 plying the manufacturer the following 
 information: 
 
 Size and type of product. 
 
 Drop height or velocity of the product 
 at Impact. 
 
 Dimensions of the hopper. 
 
 Sketch of the hopper showing impact 
 areas. 
 
 Location of 
 bars, if used. 
 
 dust suppression spray 
 
 the lining may 
 in sections to 
 handling pr ob- 
 is recommended 
 be interchange- 
 
 If the hopper is large, 
 have to be manufactured 
 minimize installation and 
 lems. Additionally, it 
 that the lining sections 
 able, if possible. This flexibility will 
 allow the panels to be rotated to accom- 
 modate uneven wear rates. It is also 
 recommended that the lining be designed 
 so that it can be suspended away from the 
 hopper wall. This type of installation 
 will reduce the localized crushing forces 
 on the liner, and thus reduce the re- 
 quired liner thickness. 
 
 Resilient linings are also recommended 
 for the crusher feed shell and cone. 
 Care has to be taken in sizing the liner 
 thickness so the thickest liner possible 
 can be used, and yet not interfere with 
 the material flow through the crusher. 
 Ideally the shell and cone liners should 
 be a one-piece assembly. This one-piece 
 assembly can be simply inserted over the 
 existing shell and cone or replace the 
 fabricated steel liner assembly. The 
 lining can also be manufactured as seg- 
 ments for easier handling and attaching 
 to the existing steel liners. This is 
 
18 
 
 not recommended, however, because of the 
 possibility of a segment coming loose and 
 passing through the crusher, which can 
 cause significant damage. Another bene- 
 fit of the full assembly, particularly on 
 crushers without a rotating bowl, is that 
 the liner can be rotated for more even 
 wear. 
 
 along the top edge of the curtain to pro- 
 vide easy installation on bolts that can 
 be welded to the adjustment ring. The 
 curtain should be long enough to go com- 
 pletely around the crusher, plus one 
 extra foot for an overlap that will 
 ensure the acoustical Integrity of the 
 treatment. 
 
 For cone crushers with a steel feed 
 plate, the plate should be replaced by 
 one manufactured with resilient material. 
 The new feed plate should be cast by the 
 material manufacturer using a mold that 
 matches the steel one. It is, however, 
 recommended that the resilient plate be 
 manufactured thicker and larger in diam- 
 eter than the steel one to prevent pre- 
 mature failure of the material located 
 between the hold-down bolts and the out- 
 side diameter of the plate. Additional- 
 ly, the resilient feed plate should be 
 manufactured with an integral steel cen- 
 tering plate to match the machined female 
 fit of the feed distributor or the main 
 shaft nut. Replacing the steel plate 
 with a resilient one will not affect the 
 unbalanced forces of the crusher. 
 
 For crushers without a feed plate, a 
 resilient pad for the mantle hold-down 
 cap is recommended. The pad would also 
 have to be custom cast by the material 
 manufacturer to match the existing hold- 
 down cap. This treatment is not neces- 
 sary if the crusher is consistently choke 
 fed. A crusher that is choke fed has 
 sufficient product in the crushing cavity 
 to protect the mantle hold-down cap from 
 impact. This is the same noise control 
 technique as the dead bed for a product- 
 transfer chute. 
 
 To control the noise radiating from the 
 crushing zone and from product impacting 
 the main frame liner, an acoustical bar- 
 rier curtain should be installed around 
 the crusher exterior. The curtain should 
 be fabricated from loaded vinyl that has 
 a layer of absorptive material on one 
 side. The material should be purchased 
 wide enough to extend from the adjustment 
 ring to the base of the main frame 
 flange. Grommets should be specified 
 
 INSTALLATION OF NOISE CONTROL 
 TREATMENTS FOR CRUSHERS 
 
 The resilient liner for the crusher 
 feed hopper can be either bolted directly 
 to the hopper wall or can be suspended 
 away from the wall to improve wear. A 
 suspended liner is shown in figure 25. 
 In this suspended installation, the liner 
 was bolted to the hopper wall along the 
 top edge and allowed to hang freely. The 
 bolts, which are above the impact area, 
 did not have be be countersunk in the 
 material. 
 
 The crusher feed cone shell and feed 
 cone liners, if fabricated as a one-piece 
 assembly, can be simply forced into place 
 (fig. 26). This is done after removal of 
 the steel wear plates or bars that might 
 have been installed. The shell liner can 
 also be bolted in place with a steel ring 
 for added support. An installed one- 
 piece resilient crusher feed cone is 
 shown in figure 27. 
 
 FIGURE 25. • Resilient liner installed in the 
 crusher feed hopper. 
 
19 
 
 FIGURE 26. - Installation of a resilient crusher 
 feed cone shell liner* 
 
 The installation of a segmented resil- 
 ient feed cone liner requires — 
 
 • Removing any steel wear liners. 
 
 FIGURE 27* - Installation of a one-piece resilient 
 crusher feed cone liner. 
 
 • Locating, drilling, and countersink- 
 ing boltholes in the resilient liner seg- 
 ments (if not ordered that way from the 
 material vendor), 
 
 • Bolting the segments in place. 
 
 The installation of resilient liner 
 segments in a feed cone is shown in 
 figure 28. 
 
 The installation of the resilient feed 
 plate (fig. 29) is straightforward. The 
 old feed plate is removed and the new 
 feed plate is bolted in place. 
 
 Installation of a resilient pad on the 
 mantle hold-down cap (fig. 30) would 
 require — 
 
 • Cleaning product from the recess for 
 the main shaft bolt. 
 
 • Welding a mounting bolt for the pad 
 on the head of the main shaft bolt. 
 
 • Installing the pad, making sure that 
 the bolt and nut are below the pad 
 surface. 
 
 • Burning or drilling boltholes 
 through the feed cone. 
 
20 
 
 FIGURE 28. - Installation of resilient feed cone 
 liner segmentst 
 
 FIGURE 29» - Installation of a resilient crusher 
 feed plate* 
 
 The noise barrier curtain (fig. 31) is 
 attached to the adjustment ring and hangs 
 freely to the base of the main frame 
 flange. This free hanging will allow 
 vertical movement when the crusher passes 
 
 Fillet weld to 
 feed cone 
 
 FIGURE 30, - Installation of a molded resilient pad 
 for the mantle hold-down cap. 
 
 tramp iron and will not interfere with 
 normal crusher servicing. Installation 
 of the curtain requires the following: 
 
 • Use the curtain grommets as a tem- 
 plate to mark locations on the crusher 
 adjustment ring. 
 
 • Weld studs or cap screws to the ad- 
 justment ring at the marked locations, 
 
 • Mount the curtain on the studs or 
 screws. 
 
 • Make cutouts in the curtain for hy- 
 draulic lines and around the crusher 
 countershaft box. 
 
 An Installed curtain is 
 figure 32. 
 
 shown in 
 
21 
 
 Fillet weld bolt to 
 ajustment ring 
 
 (Srl 
 
 ^ Cut out for countershaft, 
 as needed 
 
 ^^Cut out for hydraulic 
 lines, OS needed 
 
 FIGURE 31. - Installation of a barrier curtain around 
 the crusher main frame. 
 
 FIGURE 32» - Noise barrier curtain installed around 
 the crusher main frame. 
 
 NOISE CONTROL USING AN OPERATOR CONTROL BOOTH 
 
 The noise control treatments described 
 in the previous sections were aimed at 
 reducing noise at the source or enclosing 
 the noise source. Another treatment, 
 which is extremely cost effective for 
 stationary plant employees, is the con- 
 struction of a control booth, A control 
 booth is not expensive to construct or 
 purchase, can provide noise reductions of 
 15 to 25 dBA, requires very little main- 
 tenance after installation, and also 
 helps protect the operator from the 
 weather and other environmental hazards, 
 such as dust. 
 
 GENERAL SELECTION GUIDELINES 
 
 The construction or purchase of a booth 
 is straightforward and quite a number 
 have been installed in the industry. 
 Many, however, are not as effective as 
 they could be for the following reasons: 
 
 The booth is not large enough. 
 
 The booth does not have adequate air- 
 conditioning. 
 
 The booth does not provide the operator 
 an adequate field of view. 
 
 The booth is not acoustically tight. 
 
 The booth is mounted directly on the 
 plant structure. 
 
 For a control booth to be effective, it 
 not only has to reduce the noise, but al- 
 so has to provide enough comfort so the 
 operator will stay inside the booth dur- 
 ing normal plant operation. An operator 
 will not stay in a booth if it is too 
 cramped, too hot, or does not provide 
 adequate visiblity. 
 
 If a booth is going to provide maximum 
 noise reduction it must be tightly con- 
 structed. Any holes or openings in the 
 booth will let outside noise pass inside. 
 Many plants have installed booths that 
 look nice, but do not provide adequate 
 noise reduction because they fail to seal 
 leaks (after construction) around doors, 
 windows , or where control cables have to 
 pass through the booth. These types of 
 leaks can easily reduce the effectiveness 
 of a booth by 10 to 15 dBA. 
 
 The effectiveness of a booth can also 
 be compromised by where and/or how it is 
 mounted. A booth mounted directly on the 
 
22 
 
 plant structure will have vibrations from 
 this structure pass directly into the 
 booth's structure. This vibration, which 
 is usually severe, causes the booth's 
 surfaces to radiate noise. If the booth 
 has to be mounted on the plant structure, 
 correctly designed vibration isolators 
 will have to be used. An alternative 
 would be to mount the booth on a separate 
 structure that is not in contact with the 
 plant; the plant controls would have to 
 be relocated to the booth. 
 
 GENERAL CONSTRUCTION GUIDELINES 
 
 A control booth can either be purchased 
 or can be constructed by plant labor. 
 The construction of an effective booth, 
 however, requires some modification of 
 standard building practices. 
 
 The walls of an effective booth can use 
 a standard 2- by 4-in stud construction, 
 with a 5/8-in plywood exterior. The in- 
 terior, however, should have a double 
 layer of gypsum wallboard with staggered 
 joints. The wall should be insulated 
 with a fiberglass that is attached to the 
 exterior wall; this is primarily for tem- 
 perature control. The thickness of the 
 fiberglass should be less than the thick- 
 ness of the stud. The basic construction 
 is shown in figure 33. 
 
 staggered joints) is recommended, 
 tightly sealing the wall joints. 
 
 as is 
 
 The windows should be double pane with 
 a 3/ 4-in air gap between them. The win- 
 dows should be mounted in the frame using 
 rubber gaskets to provide a tight seal. 
 The windows should be large enough to 
 provide the operator with an adequate 
 field of view, but no larger. Windows, 
 even double pane, are less effective 
 noise barriers than the surrounding 
 walls. Making the windows larger than 
 necessary will reduce the effectiveness 
 of the booth. 
 
 The doors for the booth should be solid 
 core. They can be either solid wood or a 
 metal skin with an insulating foam core. 
 The doorframe should also be gasketed to 
 provide a tight seal. 
 
 After the booth is constructed, check 
 for and plug all leaks. As mentioned be- 
 fore, this step is critically important 
 and can increase the effectiveness of the 
 booth by 10 to 15 dBA. Areas to check 
 include — 
 
 • Doorframes and window frames, 
 
 • Wall-to-wall, wall-to-roof, and 
 wall-to-floor joints. 
 
 The roof of the booth can be a standard 
 construction, but must be sealed at the 
 wall joints. A drop ceiling using acous- 
 tical tile is recommended inside. The 
 booth floor can also be standard 
 construction. A double floor layer (with 
 
 X 4-in X 8-ft stud 
 
 INSIDE 
 
 OUTSIDE 
 
 /s-in gypsum panel 
 
 /e-ln plywood 
 2-/4-10 fiberglass 
 
 /2-in gypsum panel insulation (R II) 
 
 FIGURE 33, - Basic control booth waif construction. 
 
 • Holes cut for control and power 
 lines. 
 
 • Holes cut 
 heater. 
 
 for air-conditioner and 
 
 It is also important to include the 
 booth on a regular maintenance schedule. 
 Gaskets and seals around doors and win- 
 dows, for example, should be routinely 
 checked and repaired. 
 
 TYPICAL BOOTH INSTALLATION 
 
 The control booth installed, during 
 this research program, for a primary 
 crusher operator is shown in figures 34 
 through 37. The 8- by 10-ft booth was 
 purchased for $4,919. 
 mounted on a separate 
 that was constructed by 
 using 6-in I-beams. It reduced the noise 
 levels at the operator's location from 97 
 to 78 dBA. 
 
 The booth was 
 
 support structure 
 
 quarry personnel 
 
23 
 
 FIGURE 34. - View of a primary crushing plant with 
 an operator control booth. 
 
 FIGURE 35. • Operator control booth mounted on 
 separate steel support structure. 
 
 FIGURE 36. - Separate control booth support struc- 
 ture constructed by quarry personnel. 
 
 FIGURE 37. • Primary crusher operator at the con- 
 trol station inside the booth. 
 
24 
 
 SUMMARY AND CONCLUSIONS 
 
 Treatment techniques employed the 
 use of commercially available, wear- 
 resistant, resilient materials. These 
 products can be utilized for noise abate- 
 ment by all sizes of crushing and screen- 
 ing operations. Treatment costs for the 
 portable plants were about 5 to 7 pet 
 of the purchase price of a new 200- to 
 300-ton/h plant. Reasonably maintained 
 plants invest this amount annually to 
 repair material handling equipment or 
 product transfer points. The wear per- 
 formance, the noise reduction, and the 
 reasonable cost of the resilient products 
 have led to the conclusion that retrofit 
 noise treatments can be economically 
 applied to all sizes of crushing and 
 screening plants. Additionally, manufac- 
 turers of crushing and screening plants 
 can easily incorporate noise control 
 technology as the plants are built, thus 
 
 addressing additional noise sources. A 
 retrofit program can only modify field- 
 accessible areas; new plants, however, 
 can be designed and fabricated to incor- 
 porate resilient materials for improved 
 wear and noise control from the beginning 
 of the project. For example, the sizing 
 screen feedbox seems to be a high mainte- 
 nance area; the feedbox could be routine- 
 ly fabricated with a resilient impact pad 
 incorporated for the requirements of a 
 specific plant. Cost tradeoffs for new 
 plants are possible when wear-resistant, 
 resilient materials are substituted for 
 abrasion-resistant metals. Thus, the 
 program results have indicated that the 
 modifications that were tested could be 
 expected to result in lower noise levels 
 and reduced maintenance when applied to 
 the design of a new plant. 
 
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