Description of Vulcanizing Equipment for making O-Rings
- Vulcanizing devices were developed over 50 years ago. A patent issued in 1980 describes a kit for making O-Rings, includes a cord measuring and cutting device, a heated mold for clamping the cord stock, and a bucket or pail for water used to quench the heated mold.
- In the early 1990’s, RSF developed a pneumatic operated press "Model P-B" and a mobile bonder “Model M-B”, and in 2010 a smaller Portable bonder “Model E-B”.
- The pneumatic “Model P-B” bench top model consists of a vertical press and an electronic module. With foot control activation, heated dies close against each other, by means of dual air cylinders. The cartridge heaters are operated by a solid state analog temp. controller, heaters are located in both top and bottom dies. Heat is transferred to the rubber cord during the bonding process. The dies are made of a high heat conducting aluminum alloy. It is important to note that rubber has a low heat conducting value. This factor is critical when heating rubber, as time and temperatures must be selected based on the area of the rubber cross section. Simple common sense will apply: Large volume or diameters will require longer time and higher heat settings. Smaller parts; the opposite is true, require shorter times.
- The portable "Model E-B" is a one piece table top unit, hand operated, dies close against each other by a hinge pivot, and a toggle device maintains die closure. The E-B unit has two cartridge heaters, one in the top die and one in the bottom die maintaining constant temperature in the die-set.
- Step One: Prepare the o-ring cord stock, mark where the part will be cut, and cut the o-ring cord to the length required, using the Mini-Cutter supplied. Determine the cut length of the desired o-ring based on these calculations: (I.D. of O-Ring + 1 Cross Section) x 3.1416 = Cut Length. Make sure you have a clean square cut on both ends of the rubber cord.
- Step Two: Apply bonding adhesive to both ends of the cord stock, allow the adhesive to air dry to a dull finish. Pay particular attention to insuring that the edges of the o-ring ends are thoroughly covered with adhesive. In some cases, the adhesive will have a wet/dry condition on the ends. The dry portion will indicate that the adhesive has been absorbed into the rubber. In this situation, apply a second coat of adhesive. Allow the ends to air-dry so that the solvent in the adhesive can evaporate. The ends should have a dull matte finish after the solvent has evaporated.
- Step Three: Wearing the gloves supplied, bring both o-ring cord ends together in the Die-Set and close the top die, this will hold the o-ring cord in place. Depending on the cross-section diameter and material type, the cure time can vary; usually in the range of 3 to 10 minutes. Warm up time should be at least 10 minutes allowing the Die-Set to attain the proper temperature for vulcanization.
- Step Four: After the vulcanizing cycle open the Die-Set, and expose the finished o-ring.
- Step Five: Place the finished o-ring aside to cool, do not flex or stress the bonded joint while still hot.
- Typical Temperature Data:
- The first chart shows o-ring cord temperatures when the Bonder is first switched on. This is known as a Cold Start. For a typical .375 Dia. EPDM o-ring cord, it takes about 10 minutes to reach cure temperature.
- The second chart shows o-ring cord temperatures after the Bonder has warmed up. This is known as a Hot Start. For the same .375 Dia. EPDM o-ring cord it takes about 4 minutes to reach cure temperature.
- Since rubber is not a good heat conductor, the cord temperature will always be lower than the DieSet temperature. Depending on rubber o-ring cord Dia. Smaller sizes will require less cure time. Larger sizes will require more cure time. Time and temperature can be altered to suit the:
- Material and Rubber cord diameter. Test Samples should be made and evaulated for your application
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