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Quieter by design - air knives

The problem

Many manufacturing processes use air 'curtains' for drying, film control and product wiping. The air knife, for example, consists of a tubular plenum chamber stretching across the width of the product line, with a slot along its length. Air is supplied to the plenum at high pressure and leaves the slot as a high velocity 'blade' of air directed to strike the product line passing below.

A-weighted noise levels of between 90 and 95 dB can be generated by a conventional multi-jet system supplied with air from belt-driven, single-stage blowers.

The solution

The use of a long continuous single jet rather than multiple individual jets can decrease velocity, thus reducing noise output from the jet itself. Jet noise can be further reduced if the air supply plenum is designed to have an aerodynamically smooth approach to the blade nozzle entry.

One manufacturer of this type of dryer used two direct-drive, multi-stage, centrifugal blowers for the air source to produce a flow of some 112 litres per second and a static pressure of up to 16 kilopascals (KPa).

Cross-section of an air knife

Air knive diagram

Use of single jet

Usage of a single jet diagram

The cost

About £2000. (1995)

The result

A noise reduction of about 15 dB at 3 m.

Source

Equipment supplied by Air Control Installations (Chard) Limited.

Link URLs in this page

  1. Noise at workhttps://www.hse.gov.uk/noise/index.htm
  2. Regulationshttps://www.hse.gov.uk/noise/regulations.htm
  3. Worried about your hearing?https://www.hse.gov.uk/noise/worried.htm
  4. Overview - Worried about your hearing?https://www.hse.gov.uk/noise/worried.htm
  5. Audio demonstrationhttps://www.hse.gov.uk/noise/assets/video/index.htm
  6. Overview - Advice for employershttps://www.hse.gov.uk/noise/advice.htm
  7. Employers' responsibilitieshttps://www.hse.gov.uk/noise/employers.htm
  8. How do I assess the risks?https://www.hse.gov.uk/noise/risks.htm
  9. Managing noise risks checklisthttps://www.hse.gov.uk/noise/checklist.htm
  10. Overview - How do I protect my workers?https://www.hse.gov.uk/noise/protect.htm
  11. How do I control the risks from noise?https://www.hse.gov.uk/noise/controlrisks.htm
  12. Use the information from my risk assessment?https://www.hse.gov.uk/noise/useinfo.htm
  13. Reduce noise?https://www.hse.gov.uk/noise/reducenoise.htm
  14. Choose quieter equipment and machinery?https://www.hse.gov.uk/noise/choosequieter.htm
  15. Hearing protectionhttps://www.hse.gov.uk/noise/hearingprotection.htm
  16. What do I need to tell my employees?https://www.hse.gov.uk/noise/assets/video/tell-index.htm
  17. Employee and safety representativeshttps://www.hse.gov.uk/noise/safetyrep.htm
  18. Health surveillancehttps://www.hse.gov.uk/noise/healthsurveillance.htm
  19. Advice for manufacturershttps://www.hse.gov.uk/noise/advice-for-manufacturers.htm
  20. Noise calculatorshttps://www.hse.gov.uk/noise/calculator.htm
  21. Key messageshttps://www.hse.gov.uk/noise/keyfacts.htm
  22. Overview - Industry good practicehttps://www.hse.gov.uk/noise/goodpractice/index.htm
  23. Overview - Managing noise riskshttps://www.hse.gov.uk/noise/goodpractice/managingrisks.htm
  24. Over-protectionhttps://www.hse.gov.uk/noise/goodpractice/hearingoverprotect.htm
  25. Accounting for 'real-world' factorshttps://www.hse.gov.uk/noise/goodpractice/hearingrealworld.htm
  26. Advice on issuing hearing protectionhttps://www.hse.gov.uk/noise/goodpractice/hearingadvice.htm
  27. Workplace designhttps://www.hse.gov.uk/noise/goodpractice/workplacedesign.htm
  28. Plastic productshttps://www.hse.gov.uk/noise/goodpractice/plastics.htm
  29. Overview - Wood workinghttps://www.hse.gov.uk/noise/goodpractice/woodworking.htm
  30. Saw millinghttps://www.hse.gov.uk/noise/goodpractice/sawmilling.htm
  31. Air turbulencehttps://www.hse.gov.uk/noise/goodpractice/airturbulence.htm
  32. Planing and mouldinghttps://www.hse.gov.uk/noise/goodpractice/planingmoulding.htm
  33. Overview - Concrete and cementhttps://www.hse.gov.uk/noise/goodpractice/concrete.htm
  34. General informationhttps://www.hse.gov.uk/noise/goodpractice/concretegeninfo.htm
  35. Avoiding impactshttps://www.hse.gov.uk/noise/goodpractice/avoidingimpacts.htm
  36. Music and entertainmenthttps://www.hse.gov.uk/noise/goodpractice/music-and-entertainment.htm
  37. Overview - Case studieshttps://www.hse.gov.uk/noise/casestudies/index.htm
  38. Full indexhttps://www.hse.gov.uk/noise/casestudies/fullindex.htm
  39. Sound solutionshttps://www.hse.gov.uk/noise/casestudies/soundsolutions/index.htm
  40. Overview - Resourceshttps://www.hse.gov.uk/noise/furtherinfo.htm
  41. Publicationshttps://www.hse.gov.uk/noise/publications.htm
  42. Researchhttps://www.hse.gov.uk/noise/research.htm
  43. Statisticshttps://www.hse.gov.uk/noise/statistics.htm
  44. Overview - Policy statementshttps://www.hse.gov.uk/noise/policy.htm
  45. Acoustic shockhttps://www.hse.gov.uk/noise/acoustic.htm
  46. Noise calculatorshttps://www.hse.gov.uk/noise/calculator.htm
  47. Noise: Don't lose your hearing https://www.hse.gov.uk/pubns/indg363.htm
  48. Noise at work: A brief guide to controlling the riskshttps://www.hse.gov.uk/pubns/indg362.htm
  49. Hearing loss - what's it like?https://www.hse.gov.uk/noise/assets/video/index.htm

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Updated 2010-04-02