Sound Solutions Case Studies

The noise control case studies listed here were first published in 1995 in 'Sound Solutions' HSG138. This document is out of print but as the case studies contain relevant information they have been republished here.

• Reducing noise in gravel chutes (case study #1)
  A major noise source in quarrying and mineral workings is from materials dropping onto steel chutes or into hoppers.
• A lower noise alternative for compressed air drying (case study #2)
  Compressed air jets, widely used in industry for drying, can emit excessive levels of noise from the high jet discharge.
• Quieter by design - air knives (case study #3)
  Many manufacturing processes use air 'curtains' for drying, film control and product wiping. The use of a long continuous single jet rather than multiple individual jets can reduce noise.
• Flexible acoustic screening material (case study #4)
  Noise reduction can be complicated in situations where noisy machinery has to be quickly relocated as work moves. A practicable alternative is to use a portable acoustic screen.
• Reducing impact noise from aluminium casks (case study #5)
  High noise levels were being generated at a brewery by dropping aluminium casks onto the concrete surface of its distribution yard.
• Removing impactive strike (case study #6)
  Identification marking during the manufacture and refurbishment of beer barrels can result in high noise levels. New machinery combined pneumatics and hydraulics to control the impactive strike, resulting in reduced noise.
• Reducing noise from a sugar beet cleaner loader (case study #7)
  A sugar beet conveyor, comprising a web of metal bars, emitted A-weighted noise levels of 103 dB at the operating position as the web rotated.
• Reducing bottling line noise (case study #8)
  The main bottling hall of a major food manufacturer was a highly reverberant area containing a total conveyor length of 30 m, with A-weighted noise levels above 85 dB.
• Improvements to a bumping machine (case study #9)
  A manufacturer of artificial limbs was concerned with noise levels produced by a small bumping machine used for hand-forming sheet metal components of complex shapes.
• Enclosing a can filler (case study #10)
  A soft drinks can filling line, operated by a large food manufacturer, contained three closely-spaced machines, a can filler, an aeration unit and a lid seamer for closing the filled can. The machines were all situated in a reverberant room where A-weighted noise levels of 99 dB were measured.
• Acoustic refuges (case study #11)
  A firm that manufactured cardboard containers installed a noise refuge to provide an effective working area close to the main production lines where A-weighted noise levels approaching 97 dB had been measured.
• Active noise control - pneumatic transport system (case study #12)
  In one drinks canning plant, a six-bladed radial fan in the filler room supplied air to move cans along lines. The fan produced a tone at about 300 Hz with an A-weighted noise level of over 90 dB.
• Reducing noise from a glass tempering line (case study #13)
  A company was producing 4 mm thick glass. In this plant, the fans had to be mounted internally. With fan A-weighted sound power levels in excess of 126 dB, the effective acoustic enclosure of the fans was essential
• Enclosing cold heading machines (case study #14)
  The factory floor of one shoe manufacturer contained a considerable number of similar cold heading machines, with A-weighted noise levels measured at around 104 dB.
• Removing jet noise (case study #15)
  A health care company immersed the pharmaceutical containers it produced in a rinsing bath. To dry off excess moisture, employees blew them dry using a hand-held compressed air hose.
• Reducing noise from a plastic mould cleaning gun (case study #16)
  A company engaged in hydraulically moulding thermosetting plastic components used a compressed air gun to clear flash and powder deposits from the die moulds. The interaction of the high-velocity jet and the surface of the moulds produced A-weighted noise levels reaching 105 dB.
• Reducing noise from screw compressors (case study #17)
  Screw compressors providing an air supply for the aeration tanks of a sewage treatment works were exposing maintenance engineers to A-weighted noise levels of about 100 dB.
• Treating low-frequency compressor noise (case study #18)
  Large reciprocating air compressors in a manufacturing plant drew air from the roof where items of equipment needed regular attention. The A-weighted noise level near the air intakes was found to be 88 dB, the noise being dominated by low frequencies.
• Enclosing ammonia compressors in seafood freezing (case study #19)
  Refrigerant compressors are a common source of noise in the food processing industry. Sometimes they have to be located close to the production facility served, occasionally in occupied areas.
• Acoustic lagging for a pneumatic conveying system (case study #20)
  Conveying solid particle products through rigid pipe systems is an inherently noisy process as the particles hit the undamped metal pipe walls.
• Modifying an edge trimming machine (case study #21)
  In shoe manufacture, sole forming leaves excess material at the edges which must be removed by holding each shoe against a high-speed rotating blade. The open front of the machine gives little acoustic protection for the operators and A-weighted noise levels can exceed 90 dB.
• Active control of low-frequency, pure-tone noise (case study #22)
  Sound pressure can be reduced in some cases by active noise control, sometimes known as 'anti-noise'. Attention has turned to the possibility of active noise control in larger spaces subjected to low-frequency, pure-tone noise. One example was the suppression of engine-induced 'boom' inside cars.
• Low-cost noise control of an engine test cell (case study #23)
  In one company, an engine test cell had been generating high noise levels in maintenance areas near the exhaust discharge. The engine exhaust stack ran from ground level to the test cell roof where it ended in a pair of reactive and absorptive silencers.
• Reducing noise in a dump truck (case study #24)
  The cabs of large dump trucks operating on mineral working and construction sites were found to have A-weighted noise levels of about 95 dB.
• Reducing noise in a drag-line cab (case study #25)
  A company using tracked drag-lines in quarrying found that drivers were being exposed to A-weighted noise levels of 96 to 100 dB. The particular problem was that the main drive engine was located in the same all steel 'box', separated from the driver's cab only by a sheet steel bulkhead containing a door.
• Reducing noise in crew cab road vehicles (case study #26)
  Noise levels in crew-carrying road vehicles can be high enough to cause concern. In some untrimmed vehicles such as refuse collectors, A-weighted levels have been measured as high as 103 to 105 dB.
• Isolating a hydraulic guillotine (case study #27)
  The hydraulic power pack of a 250 tonne billet hydraulic guillotine was found to be generating A-weighted noise levels of between 90 and 95 dB. Noise was generated through vibration transmission from the motor pump unit to the machine frame and impacts from the valve bank.
• Pneumatic impact press noise reduction (case study #28)
  A bench-mounted pneumatic impact press used for riveting small switch components was found to be generating excessive noise levels. The main peak noise emissions were from the release of compressed air at the actuator exhaust and from the impact of the metal actuator ram as it struck the metal tool ram.
• Using a pneumatic squeeze press (case study #29)
  One drawback of using bench-top, pneumatic impact presses is the high noise resulting from the metal actuator striking the tool rams. One way to avoid this is to use a squeeze press.
• Machining alternator castings (case study #30)
  Machining an alternator end casting was producing A-weighted noise levels of 104 dB, principally in a high pitched 'squeal' radiating from the casting. The solution was to apply a simple damping treatment to reduce the casting's vibration.
• Reducing noise when loading dump trucks (case study #31)
  During quarrying, A-weighted noise levels of 96 dB can be produced when the shovel or conveyor drops its first loads of material onto the bare metal of the body of dump trucks.
• Material change - block making machine (case study #32)
  In a firm manufacturing paving blocks, the blocks were moved along the line on wooden pallets. The pallets were propelled by a series of metal catches. A-weighted noise levels of over 100 dB were generated when the catches snapped back to the horizontal and fell onto the metal bar.
• Reducing impact noise from cocoa beans (case study #33)
  On a machine used in processing cocoa beans, the beans were transported along a vibrating tray beneath an array of gas burners. Impacts between the hard bean cases and the steel conveying tray produced A-weighted noise levels of between 88 and 90 dB.
• Very high performance drywalling (case study #34)
  Many production areas create high noise levels. To reduce risks to workers' hearing, it is often desirable to have acoustic separation between the areas.
• Enclosing a nail sorting machine (case study #35)
  An engineering firm, manufacturing components for conveying systems, has developed a batch collation system. The nails are first shaken up a spiral to the top of the machine and then aligned into collation boxes along a vibrating chute. Although very effective, the machinery generated A-weighted noise levels of over 100 dB.
• Reducing combustion noise by flow control (case study #36)
  Typical A-weighted noise levels generated by a dryer oven, used in malting grain, reached up to 95 dB. A low-frequency 'boom' at a tone of 82 Hz dominated.
• Quieter by design - paring machine (case study #37)
  A major shoe manufacturer has designed a new paring machine; an early prototype provided a reduction of up to 5 dB.
• Reducing foundry pipe spinning noise (case study #38)
  An automatic pipe spinning machine in a foundry was generating A-weighted noise levels in excess of 90 dB.
• Quieter by design - strand pelletisers (case study #39)
  Strand pelletisers are used in the plastics industry to convert continuous strands of plastic into small pellets for use in subsequent manufacturing processes. A company manufacturing strand pelletisers has developed a series of new machines which incorporate a number of important noise reducing features.
• Acoustic enclosure of small plant (case study #40)
  A major chemical manufacturing company anticipated A-weighted noise levels above 95 dB from a pneumatic conveying fan to be installed in the centre of an occupied production floor. It opted to control the noise by installing an acoustic enclosure.
• Reducing noise from pneumatic screwdrivers (case study #41)
  Pneumatically-driven screwdrivers can produce high A-weighted noise levels of over 80 dB, particularly when used in large numbers and in confined spaces, eg on production lines.
• Reducing air exhaust noise in vertical grinders (case study #42)
  Pneumatic tools can emit high noise levels, much of it from the exhaust of the compressed air that drives the motor. One manufacturer of such tools has achieved good attenuation without causing excessive back pressure by using a spring-loaded valve in the exhaust.
• Dynamic absorption of power press vibration (case study #43)
  A strip-fed, 115 tonne power press, installed to stamp oil filter base plates, generated A-weighted noise levels of 99 dB, principally in 'bell-like' tones radiated by the flywheel.
• Shielding a printing press (case study #44)
  The dominant noise source from a printing press came from the second print head air drum. Secondary noise sources included drying fans and suction systems. Together these generated A-weighted noise levels of up to 95 dB. Given the size of the press and the access requirements, an acoustic enclosure was ruled out.
• Reducing pump noise by good maintenance (case study #45)
  A major soft drinks manufacturer was advised that a pump used for transferring fruit juice concentrate was producing A-weighted noise levels of 103 dB. A preliminary inspection showed mechanical deterioration of the pump which required a complete overhaul.
• Use of absorption in a noise control programme (case study #46)
  A-weighted noise levels from high-speed presses operating in the production area of a health care company manufacturing metered dose aerosols were generally over 85 dB. Most of the operators' exposure was due to direct radiation from the nearest presses, but reflected noise also built up as reverberant sound energy.
• Flexible PVC enclosure of automatic punch presses (case study #47)
  A company producing air-conditioning systems had two high-speed automatic presses generating A-weighted noise levels of up to 93 dB. The company wished to reduce the noise radiated to adjacent areas but needed to maintain all-round access. The solution was to install a PVC strip enclosure around each machine.
• High speed press noise - modifying safety guarding (case study #48)
  A health care company manufacturing medical containers used a process of multi-stage forming on high-speed, automatic, coil-feed transfer presses. A sound intensity survey identified those presses that were the major contributors to overall shop noise and how that output was distributed over the various panels of the machine
• Anti-vibration treatment of high-speed presses (case study #49)
  A high-speed, strip-fed punch press used for stamping electrical trip-catch components caused A-weighted levels of 101 dB. A noise reduction of about 9 dB was achieved through isolation and damping.
• Controlling noise in a press shop (case study #50)
  Five overhead reciprocating presses were located within a small batch production press shop. The presses were used to produce small batch runs and so had an unusually high down time. As a result, an operator's overall noise exposure was strongly influenced by the noise from neighbouring presses.
• Active/absorptive silencer for a rotary blower (case study #51)
  The introduction of a hybrid active silencer reduced discharge noise by 42 dB from a rotary blower.
• Reducing stone cutting noise (case study #52)
  When using conventional steel saws in stonemasonry, A-weighted noise levels of over 102 dB can be generated from the impact of each blade segment on the stone and by the mechanical vibrations exciting the blade as it rotates at high speed.
• Reducing noise from extrusion line cut-off saws (case study #53)
  One company had up to 20 cut-off saws operating in an open production area with employees being regularly exposed to A-weighted levels of 100 dB. The saws were adequately protected by safety guards. However, as these were all in open steel mesh, they offered no attenuation of sound radiation from the saw blades.
• Fitting silencers to steam trap discharges (case study #54)
  High-pressure steam is essential during the manufacture of Styrene. Unwanted condensation has to be discharged to the outside air through specially-designed steam traps. This steam discharge can produce A-weighted noise levels up to 100 dB near the traps.
• Silencing pressure vessel discharges (case study #55)
  A firm producing fibre mouldings for the automotive industry made use of a number of fibre pulp header tanks, pressurised to ensure a constant flow to the pulp presses. On reaching a set limit the pressurised air was released to the atmosphere through a 50 mm port. The tanks were located in working areas of the factory, exposing employees every 10 minutes to A-weighted noise levels of about 101 dB for about 3 to 4 seconds.
• Modifying acoustically-treated control booths (case study #56)
  The manufacture of steel rod involves a continuous production line to heat billets in a furnace before passing them through a series of forming stands. They are then coiled and secured as finished wire ready for despatch. In one company, the production line was 200 m long and A-weighted noise levels averaged about 90 dB. The size and nature of the plant rendered acoustic treatment impracticable.
• Removing woodworking machine noise by adjustment (case study #57)
  Timber planer-thicknessing machines usually produce high noise levels, characterised by strong tonal content. The tone was being produced by air turbulence between the cutting head and the table.
• Reducing noise in a high-speed transfer press (case study #58)
  In one design of multi-stage transfer press, the clearance between cam profiles and the up and down ram lifting arms was as much as 100 mm, resulting in a number of metal-on-metal impacts during each rotation of the cam shaft. This produced high noise levels and limited machine efficiency. The machine manufacturers replaced the two separate cams with a single cam.
• Rubber damping landing chutes (case study #59)
  In the automated finishing of castings, a mechanical arm lifted the casting out of the machine and dropped it from a height of about 1 m onto a metal chute. The impact of the components onto the chute created peak A-weighted levels of 100 dB.
• Damping compounds on heavy plates (case study #60)
  A common source of noise in the warehousing and distribution industries is caused by hard-wheeled pallet trucks passing over decks of dock levelling plates and scissor lifts. These decks are usually manufactured in a heavy gauge undamped material such as steel or aluminium, with chequered or similar top surfaces for slip resistance. Peak A-weighted noise levels of up to 108 dB have been measured.