Background
Rubber bands are used by numerous individuals and industries for a wide variety of purposes. The largest consumer of rubber bands in the world is the U.S. Post Office, which orders millions of pounds a year to use in sorting and delivering piles of mail. The newspaper industry also uses massive quantities of rubber bands to keep individual newspapers rolled or folded together before home delivery. Yet another large consumer is the agricultural products industry. The flower industry buys rubber bands to hold together bouquets or uses delicate bands around the petals of flowers (especially tulips) to keep them from opening in transit. Vegetables such as celery are frequently bunched together with rubber bands, and the plastic coverings over berries, broccoli, and cauliflower are often secured with rubber bands.
Raw Materials
Rubber bands are made from organic rubber because it offers superior elasticity. Natural rubber comes from latex, a milky fluid composed primarily of water with a smaller amount of rubber and trace amounts of resin, protein, sugar, and mineral matter. Most non-synthetic industrial latex derives from the rubber tree (Hevea brasiliensis). 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. To “tap” the substance from a Rubber Tree, rubber harvesters cut a “V”-shaped wedge in the bark to reach the latex without cutting into the sap vessels.
The Manufacturing Process
Step 1 – Processing natural latex – Impurities such as tree sap and debris are filtered out and combined with acetic or formic acid to form slabs. The slabs are squeezed between rollers to remove water and pressed into bales or blocks usually 2 or 3 square feet.
Step 2 – Mixing and milling – Slabs are machine cut into small pieces. Using a banbury mixer the rubber is mixed with other ingredients: sulfur to vulcanize, pigments to color, and chemicals to adjust the required elasticity of the rubber bands. Milling entails heating the rubber and squeezing it flat in a milling machine.
Step 3 – Extrusion – Rubber sheets are cut into strips. Still hot from the milling, the strips are fed into an extruding machine which forces the rubber out in long, hollow tubes to form into a tube shape.
Step 4 – Curing – The tubes of rubber are then forced over aluminum poles called mandrels which have been covered with talcum powder to keep the rubber from sticking. Although the rubber has already been vulcanized, it’s rather brittle at this point, and needs to be “cured” before it is elastic and usable. To accomplish this, the poles are loaded onto racks that are steamed and heated in large machines.
Step 5 – Cutting – Removed from the poles and washed to remove the talcum powder, the tubes of rubber are fed into another machine that slices them into “rings” that are finished rubber bands.
Step 6 – Quality Control – Sample rubber bands from each batch are subjected to a variety of quality tests. One such test measures modulus, or how hard a band snaps back: a tight band should snap back forcefully when pulled, while a band made to secure fragile objects should snap back more gently. Another test, for elongation, determines how far a band will stretch, which depends upon the percentage of rubber in a band: the more rubber, the further it should stretch. A third trait commonly tested is break strength, or whether a rubber band is strong enough to withstand normal strain. If 90 percent of the sample bands in a batch pass a particular test, the batch moves on to the next test; if 90 percent pass all of the tests, the batch is considered market-ready.
Temperature affects the elasticity of a rubber band in an unusual way. Heating causes the rubber band to contract, and cooling causes expansion.
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, and its width is the distance from one edge to the other.
Rubber band size numbers
A rubber band is given a 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 31⁄2 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.
| SIZE # |
LENGTH |
CUT WIDTH |
WALL |
||||
|
(LAY FLAT ) |
(APPROX.) |
THICKNESS |
|||||
|
MM |
INCH |
MM |
INCH |
MM |
INCH |
||
| 9 |
25 |
1 |
1.7 |
1/15 |
1.1 |
1/25 |
|
| 10 |
35 |
1 |
3/8 |
1.7 |
1/15 |
1.1 |
1/25 |
| 12 |
40 |
1 |
5/8 |
1.7 |
1/15 |
1.1 |
1/25 |
| 14 |
50 |
2 |
1.7 |
1/15 |
1.1 |
1/25 |
|
| 16 |
60 |
2 |
1/2 |
1.7 |
1/15 |
1.1 |
1/25 |
| 18 |
76 |
3 |
1.7 |
1/15 |
1.1 |
1/25 |
|
| 19 |
87 |
3 |
1/2 |
1.7 |
1/15 |
1.1 |
1/25 |
| 20 |
94 |
4 |
1/4 |
1.7 |
1/15 |
1.1 |
1/25 |
| 30 |
50 |
2 |
3.0 |
1/8 |
1.1 |
1/25 |
|
| 31 |
60 |
2 |
1/2 |
3.0 |
1/8 |
1.1 |
1/25 |
| 32 |
76 |
3 |
3.0 |
1/8 |
1.1 |
1/25 |
|
| 33 |
87 |
3 |
1/2 |
3.0 |
1/8 |
1.1 |
1/25 |
| 36 |
165 |
6 |
1/4 |
3.0 |
1/8 |
1.7 |
1/15 |
| 39 |
228 |
9 |
3.0 |
1/8 |
1.7 |
1/15 |
|
| 61 |
50 |
2 |
6 |
1/4 |
1.1 |
1/25 |
|
| 62 |
60 |
2 |
1/2 |
6 |
1/4 |
1.1 |
1/25 |
| 63 |
76 |
3 |
6 |
1/4 |
1.1 |
1/25 |
|
| 64 |
87 |
3 |
1/2 |
6 |
1/4 |
1.1 |
1/25 |
| 65 |
100 |
4 |
6 |
1/4 |
1.1 |
1/25 |
|
| 72 |
62 |
2 |
1/2 |
6 |
3/8 |
1.1 |
1/25 |
| 73 |
76 |
3 |
9 |
3/8 |
1.1 |
1/25 |
|
| 78 |
140 |
5 |
1/2 |
9 |
3/8 |
1.1 |
1/25 |
| 82 |
62 |
2 |
1/2 |
12 |
1/2 |
1.1 |
1/25 |
| 84 |
87 |
3 |
1/2 |
12 |
1/2 |
1.1 |
1/25 |
| 105 |
120 |
4 |
3/4 |
15 |
5/8 |
1.5 |
1/16 |
| 106 |
160 |
6 |
1/4 |
15 |
5/8 |
1.5 |
1/16 |
| 107 |
178 |
7 |
15 |
5/8 |
1.5 |
1/16 |
|
| 291 |
41 |
1 |
5/8 |
3 |
1/8 |
1.5 |
1/32 |
| 5″TH |
122 |
5 |
1.7 |
1/15 |
1.1 |
1/25 |
|
| 6″TH |
165 |
6 |
1/4 |
1.7 |
1/15 |
1.5 |
1/16 |
| 7″TH |
178 |
7 |
1.7 |
1/15 |
1.5 |
1/16 |
|