Top 10 Noise Control Technologies

01

  DAMPING  

Typical applications

Chutes, feeders, machine guards, sheets, conveyor belts, tanks, ......

Technique

There are two basic techniques:

1. Unconstrained layer damping, gluing a layer of asphalt sand glue (or similar) high damping material on the surface layer;

2. Constrain layer damping to build a stack.

Constraint layer damping is coarser and generally more effective. Whether recycled steel (or aluminum) protectors, sheets, or other components from sound-dampening steel or self-purchased viscous steel sheets, the restraint layer damping can be easily glued to existing elements (inside and out), covering approximately 80% of the flat surface area, reducing the radiated noise by 5-25 dB (treated with sheets with a thickness of 40% to 100%).

Limitations: For thicker flakes, effectiveness decreases. With flake thicknesses of more than 3 mm, it becomes increasingly difficult to achieve significant noise reduction.

02

  FAN INSTALLATIONS  

Typical applications

Axial or centrifugal fans

Technique

Maximum fan efficiency corresponds to minimum noise. As a result, any fan mounting feature that tends to reduce fan efficiency can increase noise. Two of the most common examples are elbows near fans (especially on the side of air inlets) and airflow regulators (near fan inlets or exhaust outlets).

Ideally, to achieve maximum fan efficiency and minimal noise, ensure that there are at least 2-3 duct diameters (straight ducts) between any feature that may interfere with airflow and the fan itself, typically reducing noise by 3-12dB.

03

  DUCTWORK  

Typical applications

Extraction, ventilation, cooling, window openings in walls and enclosures.

Technique

Airborne noise from ducts or window openings can often be reduced by 10-20dB by lining the final bend of the duct with an acoustic absorbent material (foam or asbestos/fiberglass) without the need for a muffler. Or build a simple absorbent-lined right-angled bend mounted on the window hole. Ideally, both sides of the curve should be lined at twice the length of the duct diameter. Where the airflow velocity is high (>3m/s), consider using cloth absorbents. Duct vibrations can usually be dampened (see above).

04

  FAN SPEED  

Typical applications

Axial or centrifugal fans

Technique

Fan noise is roughly proportional to the fifth level of power at the fan speed. Therefore, in many cases, the noise can be greatly reduced by changing the size of the control system or pulleys and resetting the airflow regulator to slightly reduce the fan speed.

05

  PNEUMATIC EXHAUSTS  

Note: A well-designed muffler does not increase system backpressure. By being equipped with an effective muffler, it is almost always possible to permanently reduce the pneumatic exhaust noise by 10-30dB. Here are the practical takeaways from success or failure:

Backpressure: Equipped with large connectors and mufflers.

Clogging: Equipped with a pass-through muffler that does not clog (and has no back pressure).

Multiple exhaust outlets: Concentrate them into a larger-diameter monotube that fits the tail muffler of virtually any type of car, typically with a reduction of 25dB.

06

  PNEUMATIC NOZZLES  

Typical applications

Cooling, drying, blowing......

Technique

In most cases, an existing nozzle (usually a simple copper tubular outlet) can be replaced with a quiet, efficient component. These components not only reduce noise levels by up to 10dB, but also use less compressed air. The type of nozzle to look for is entrainment elements of various sizes from various manufacturers (simplified below).

07

  VIBRATION ISOLATION PADS  

Typical applications

Machine tool footing, pump, mezzanine installation......

Technique

Mounting motors, pumps, gearboxes, and other items of equipment on cork (or similar) gaskets cemented with rubber can be a very effective way to reduce vibration transmission and thus the noise radiated from the rest of the mechanism. This is especially true if the vibrating element is bolted to a metal bracket or to the ground. However, a common failure with these gaskets is that the bolts are "short-circuited" to the gaskets, resulting in no vibration isolation on the left side of the diagram below. It must be equipped with an additional spacer under the bolt head as shown on the right in the figure below.

There are a variety of ready-to-use anti-vibration mounts, such as rubber/neoprene or springs. The most suitable type of isolator depends on the quality of the equipment and the frequency of vibrations to be isolated.

08

  EXISTING MACHINE GUARDS  

Technique

Existing protective devices on many machines can often be improved to significantly reduce noise. The two elements involved, which must be combined, are:

Minimise Gaps: Reducing the "gap" open area in a range of protections by half reduces noise by 3dB. If the gaps (flexible seals, additional tight sheets, etc.) can be reduced by 90%, the noise can be reduced by 10 dB.

Acoustic Acoustic Absorbing Materials: Lining the protective device with a significant proportion of acoustic acoustic absorbing material (foam, asbestos/fiberglass) reduces the noise "trapped" by the protective device. As a result, less noise can escape through arbitrary gaps. Failure to line the protective device can result in an increase in noise at the operator (if the settings are as above, the gap is minimized).

In most cases, both sets of corrections can be tested in the form of a mock-up of the acoustic foam protection area and the temporary fit area extended by cardboard (wide type). Not only does this process help with the practical aspects (getting started, visibility, etc.), it also often provides a very good indication of the amount of noise reduction expected. It's very "flag-starting", but it's also very effective. Protective device vibrations that radiate in the form of noise can also be treated by damping (see above).

09

  CHAIN AND TIMING BELT DRIVES  

Technique

Noisy chain drives can often be replaced directly by quieter synchrotronized belts. Within the range of synchronized toothed belts available, there are also quiet designs with different tooth profiles to minimize noise. There is also a very new strap design for severe noise situations, which is herringbone to provide very quiet operation. With this approach, noise reductions are typically in the range of 6-20dB.

10

  ELECTRIC MOTORS  

Technique

Many companies use most motors directly, from fans to pumps to machine tools. However, instead of choosing a normal usable working motor (which costs very little) as is generally believed, it is necessary to choose a suitable motor that is as quiet as 10dB(A) or more. The best way to do this is to define the scenarios and conditions under which the motors will be used, so that all the defined motors can become quiet motors.