Rubber is by no means a new substance, dating back to 1500 B.C., although it is one that has evolved significantly in the last 140 years. This evolution has come from chemical alterations being applied to natural rubber in its molten state, creating specialized versions known as synthetic rubbers. How rubber is formed and manufactured is a parallel evolution, as more efficient and detail oriented techniques, such as rubber molding, are now equally as popular as the rubber extrusion techniques that have been around longer. Technological advancements are changing the face of our world in wonderful ways, including the natural progression occurring with materials such as synthetic rubber and the processes that turn it into useful products, such as rubber molding. However, this evolution does not mean that the older die casting methods and the original substances like natural rubber are forgotten. In this case progression does not wipe out the competition; it only dominates it.
“Tapped” Natural Rubber Image by Mohd Hufiz Noor Shams
Beginning with the basics, natural rubber is a substance developed from latex, which is a milky substance extracted from a few flowering plants. The most notable source is the Pará rubber tree, although other latex producers include the rubber fig and the Panama rubber tree. Much like the process for collecting maple sugar, a rubber source has a hole drilled into it and a container attached to the tree to collect the latex as it leaks out, which is known as “tapping”. Before natural rubber can be used to create the abundance of rubber products on the market today, it must be treated so that when it is shaped it will hold that shape.
This is partly why the production of synthetic rubber was so obvious in the progression of the material, because it already required additional substances to be useable. The inherent characteristics of rubber include strength, excellent elasticity and a water-proof surface. When synthetic rubbers were produced, such as neoprene, EPDM and silicone rubber, additional characteristics such as heat resistance, chemical inertness, corrosion resistance and adjustable rigidity and flexibility were added to the list. This evolution of rubber has benefited the industrial world as well as everyday consumers without wiping out the natural rubber sources, which are still utilized although not to the same degree.
Rubber molding therefore deals with synthetic rubber substances more than it does with natural rubber, just as most industrial manufacturing companies that use rubber utilize molding methods a bit more often then rubber extrusion. The technique rubber extrusion uses involves a screw extruding machine, which presses molten rubber through a specially cast die. The rubber comes out the other end in an identical shape to that of the die it passed through. This is a quick and effective process, although it cannot be used to create the same complex, multidimensional geometries that molding can. However, rubber extrusion is still a viable process utilized often to make items such as weather-stripping, trim, grommets, bumpers and seals, all of which are used for climate and moisture control in specific environments. It is also the platform from which rubber molding launched their more precision focused methods.
The variety of rubber molding techniques have rejuvenated the way industrial manufacturing is able to produce rubber products, and it has increased the possibilities when trying to create exactly what is necessary for a specific application. For example, the rubber seals used in high-pressure environments such as the construction of a space shuttle need to be developed and designed to fit perfectly where they are needed. Processes like injection molding, compression molding and transfer molding, which all involve closed dies where molten rubber is injected so that every nook and cranny of the mold is filled with the rubber substance for an exact replica, meet that need for perfection. The evolution of one process into another has enabled us to create items that make products safer and more perfect, which in some cases is just aesthetically pleasing and in other cases is the difference between life and death. Progression is what we as a human race have embraced since we began living on this earth, and something we should never stop doing, regardless of the arena in which we are doing it. Rubber molding and synthetic rubber are just two of many examples in the evolution of human technology and human experience.