Natural rubber is usually vulcanized, process by which it is heated and added sulfur or selenium, whereby the binding chain elastomers is achieved, in order to improve its resistance to temperature variations and elasticity. Cold vulcanization, developed in 1846 by Alexander Parkes, consists of immersing the rubber in a solution of sulfur chloride (Cl2S2). This process is used to produce soft rubber items, such as gloves and lingerie articles.
Since 1823, rubber is used as clothing material, on the basis that this kind of clothing is a "second skin". The hypoallergenic rubber can be produced from guayule. While more than half of the rubber produced today is synthetic, several million tons of natural rubber are annually manufactured.
In injection molding, the raw material is placed in a spindle, which carries it to a heated tank and subsequently into the closed mold, with a lower temperature than the injected material. After a few seconds/minutes the finished part is removed. The injection pressure is high, depending on which material is being processed. Injection molding is a fast and recommended process to produce large numbers of identical products. From components of high-precision engineering to consumer goods of common use.
This is a technique where the raw material – in preformed rubber pieces - is introduced into a heated mold (between 140°C and 160°C), and subjected to high pressure. The heat and pressure are maintained until the reaction is complete. After a few minutes – depending on the piece’s thickness – the material is plasticized and cured (inside the same mold), and the final product can be removed. This molding method is used to produce small series or special rubbers that cannot be produced with injection molds.
In the transfer molding, the process is similar to the above, excepting that in this one, the raw material is preheated before being introduced into the mold and transferred hydraulically. This system is used generally in molds with movements and with holes, tool inserts, etc.