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Five rubber bands

A rubber band (in some regions known as a binder, elastic band, lackey band, laggy band, lacka band or gumband) is a short length of rubber and latex formed in the shape of a loop. They come in multiple colors, including tan, pink, blue, red, yellow, orange, fuschia, and green. Such bands are typically used to hold multiple objects together. The rubber band was patented in England on March 17, 1845 by Stephen Perry.[1][2]

Contents

Manufacturing

Rubber bands are made by extruding the rubber into a long tube to provide its general shape, putting the tubes on mandrels and curing the rubber with heat, and then slicing it across the width of the tube into little bands.[2][3]

Material

While other rubber products may use synthetic rubber, rubber bands are primarily manufactured using natural rubber because of its superior elasticity[2].

Natural rubber originates from the sap of the rubber tree. Natural rubber is made from latex which is acquired by tapping into the bark layers of the rubber tree. Rubber trees belong to the spurge family (Euphorbiaceae) and live in warm, tropical areas. Once the latex has been “tapped” and is exposed to the air it begins to harden and become elastic, or “rubbery.” Rubber trees only survive in hot, humid climates near the equator and so the majority of latex is produced in the Southeast Asian countries of Malaysia, Thailand and Indonesia.

Today more than three quarters of all rubber products are made from synthetic rubber[2]. Modern synthetic rubber is made by mixing petroleum byproducts in a reactor with soapsuds which produces milky liquid latex. The liquid is then coagulated into rubber chunk and then sold to rubber manufacturers who in turn melt the rubber down and pour it into molds to create various products. The advancement of manufacturing and increased production of synthetic rubber is due partially to the United States being cut off from rubber supplies during World War II.

Rubber Band Sizes

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Measuring

Measuring a rubber band

A rubber band has three basic dimensions: Length, width, and thickness. (See picture.)

A rubber band's length is half its circumference. Its thickness is the distance from the inner circle to the outer circle.

Lay a rubber band down so that it makes a rectangle. The band's width is the height of that band. If one imagines a rubber band in manufacture, that is, a long tube of rubber on a mandrel, before it is sliced into rubber bands, the band's width is how far apart the slices are cut.

Temperature Effects

Temperature affects the elasticity of a rubber band in an unusual way. Heating makes the rubber band contract. And if frozen they expand[4]

Rubber Band Size Numbers

A rubber band is given a [quasi-]standard number based on its dimensions.

Generally, rubber bands are numbered from smallest to largest, width first. Thus, rubber bands numbered 8-19 are all 1/16 inch wide, with length going from 7/8 inch to 3 1/2 inches. Rubber band numbers 30-34 are for width of 1/8 inch, going again from shorter to longer. For even longer bands, the numbering starts over for numbers above 100, again starting at width 1/16 inch.

The origin of these size numbers is not clear and there appears to be some conflict in the "standard" numbers. For example, one distributor[5] has a size 117 being 1/16 inch wide and a size 127 being 1/8 inch wide. However, an OfficeMax size 117[6] is 1/8 inch wide. A manufacturer[7] has a size 117A (1/16 inch wide) and a 117B (1/8 inch wide). Another distributor[8] calls them 7AA (1/16 inch wide) and 7A (1/8 inch wide) (but labels them as specialty bands).

Rubber Band Sizes
Size Length (in) Width (in) Thickness (in)
10 1.25 1/16 1/32
12 1.75 1/16 1/32
14 2 1/16 1/32
31 2.5 1/8 1/32
32 3 1/8 1/32
33 3.5 1/8 1/32
61 2 1/4 1/32
62 2.5 1/4 1/32
63 3 1/4 1/32
64 3.5 1/4 1/32
117 7 1/16 1/32

Thermodynamics

An interesting effect of rubber bands in thermodynamics is that stretching a rubber band will produce heat (press it against your lips), while stretching it and then releasing it will produce an endothermic reaction, causing it to appear "cooler". This phenomenon can be explained with Gibb's Free Energy. Rearranging ΔG=ΔH-TΔS, where G is the free energy, H is the enthalpy, and S is the entropy, we get TΔS=ΔH-ΔG. Since stretching is nonspontaneous, as it requires an external heat, TΔS must be negative. Since T is always positive (it can never reach absolute zero), the ΔS must be negative, inferring that the rubber in its natural state is more entangled (less microstates) than when it is under tension. Thus, when the tension is removed, the reaction is spontaneous, leading ΔG to be negative. Consequently, the cooling effect must result in a positive ΔG, so ΔS will be positive there.[9][10]

Red rubber bands

In 2004 in the UK, following complaints from the public about postmen and women causing litter by discarding the rubber bands which they used to keep their mail together, the Royal Mail introduced red bands for their workers to use: it was hoped that, as the bands were easier to spot than the traditional brown ones and since only the Royal Mail used them, employees would see (and feel compelled to pick up) any red bands which they had inadvertently dropped. Currently, some 342 million red bands are used every year.[11]

Model use

Rubber bands have long been one of the methods of powering small free-flight model aeroplanes, the rubber band being anchored at the rear of the fuselage and connected to the propeller at the front. To 'wind up' the 'engine' the propeller is repeatedly turned, twisting the rubber band. When the propeller has had enough turns, the propeller is released and the model launched, the rubber band then turning the propeller rapidly until it has unwound.

One of the simplest examples of a "Rubber Band Plane" is the Squirrel designed by Darcy Whyte. Squirrel Simple Model Plane

One of the earliest to use this method was pioneer aerodynamicist George Cayley, who used them for powering his small experimental models. These 'rubber motors' have also been used for powering small model boats.

See also

References

  1. ^ March 17 - Today in Science History
  2. ^ a b c d How rubber bands are made. This reference states that the rubber is vulcanized before it is extruded. The rubber is then "cured" on mandrels.
  3. ^ Lee Rubber Products, How rubber bands are made. This reference states that the rubber is vulcanized after it is extruded.
  4. ^ Thermodynamics of a Rubber Band. It can be in cold, cool, and maybe heat. American Journal of Physics -- May 1963 -- Volume 31, Issue 5, pp. 397-397
  5. ^ BigWig Enterprises, BigWig Size Chart
  6. ^ OfficeMax, #OM97352, UPC 011491-973520
  7. ^ Lee Rubber Products, How do rubber bands measure up?
  8. ^ Dykema Rubber Band
  9. ^ http://scifun.chem.wisc.edu/HomeExpts/rubberband.html
  10. ^ CHEMICAL DEMONSTRATIONS: A Handbook for Teachers of Chemistry, Volume 1, by Bassam Z. Shakhashiri, The University of Wisconsin Press, 2537 Daniels Street, Madison, Wisconsin 53704.
  11. ^ The Times: "Posties' red rubber bands stretch public's patience"

Rubber bands and heat - http://scifun.chem.wisc.edu/HOMEEXPTS/rubberband.html

External links


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