Silent Glass Recycling Bin

Standard glass containers are a known source of noise. Typically, they consist of large metal or plastic boxes with one or several round holes at the top - these holes are used to insert glass bottles and jars into the box. Upon insertion, the glass containers fall to bottom of the box, where they create noise by colliding with other glass objects, the hollow recycling bin typically boosting the effect.

The purpose of the Silent Glass Recycling Bin is to significantly reduce the noise emission of glass recycling bins.

Prior Art
This page went online on May 30, 2008.

The idea Silent Glass Containers was posted on the Creativity Pool website on July 2, 2002.

The noisy glass collection process seems to be a problem not only for neighborhoods, but also for glass collectors. The Powerpoint presentation Noise and kerbside glass collection posted on the UK's Environmental Services Association website gives a brief outline of the topic from a waste management perspective. The presentation mentions a modified collection vehicle with trows lined with Astroturf underlay and a hinged flap over the aperture - these modifications reduced noise emission by 4-5 dB.

There are no known patents that solve this issue.

Further Development
There are no known new developments since this page originally went online on May 30, 2008.

Problem Analysis
In the glass recycling bin, the noise is caused by glass bottles and jars making hard contact with other objects, particularly other glass bottles.

Approaches to reduce the noise involve one or several of the following steps:
 * Avoiding the hard contact
 * Reducing velocity and impact of the hard contact
 * Containing the noise of the hard contact inside the bin

Further Requirements
Apart from the technicalities, it is also important to keep in mind that recycling bins need to be robust, safe to operate even by uneducated users and relatively cheap.

Reducing the falling height
Since the velocity of the bottles is due to gravity, reducing the falling height will lessen the impact and make it less noisy. Glass bins are fairly deep, so making the bins shallow instead would also make them less noisy. The downside is that a shallow bin would have to be emptied more frequently. To solve that issue, regular sized bins could be equipped with some sort of lifting platform. The weight of the glass pushes the platform further down as the bin is filling up, thus keeping the falling height constant. The platform could be sitting on a spring or be controlled by a hydraulic mechanism. Alternatively it would also be possible to use a deflatable object similar to a ballon.

Reducing the falling speed
The velocity of the falling bottles can be reduced by replacing the air inside the bin with another substance, e.g. water. Bottles fall slower in water than in air, so the impact won't be that hard. Plus, sound doesn't travel that well in water, so the impact will be even less noisy. Downside: Having bins of mucky water standing around can cause problems in summer (smells, insects) but also in winter (freezing).

Alternative: The falling bottles could also be slowed down by a set of strings or wires inside the box. Downside: The strings/wires might get in the way when the bin needs to be emptied. They could also tear, making the bin a constant object of maintainance.

Padding the bin
Padding the bin with a substance similar to Styrofoamwould also help reducing the noise. The downside of this method is that the styrofaom would only prevent the hard contact of the bottles against the bottom and the side walls of the bin, but not the contact between the bottles themselves. However, the styrofoam would also insulate the sides of the bin, thus reducing the noise emissions. Broken glass might however damage the padding, thus making it ineffective and/or contaminating the glass with other materials that could jeopardize the recycling process.

Crushing the bottles
If the bottles were crushed immediately, they would create a bed of small broken glass bits that would be realtively noiseless (at least compared to bottles and jars). This would introduce extra machinery to the recycling bin though which might be costly and also be a possible point of failure. Generally a powerful public crushing machine (no matter if it's automatic or operated by hand) would also be dangerous. Last but not least, this might also be detrimental to the recycling process, which includes manual inspection and removal of objects that are not made of glass.

Preventing the hard contact
In the bin, a noise absorbing material could be applied between the bottles, e.g. cardboard. The material could be automatically wrapped around bottles when they are inserted, or sheets of the material could be lowered into the bin as it gets fuller. It would be beneficial if the substance could be put in the melting pot with the glass without reducing its quality, which is why paper/cardboard comes to mind. Downside: This wastes extra resources, whereas the purpose of recycling is to preserve resources.

Solution
A solution for this problem hasn't been posted yet.