Trying to describe the relative tactility and hardness of an elastomer is difficult without a sample reference. The table below offers a level of guidance and comparison between scales.
Rubber hardness is measured by comparing the difference of depth of indentation between the small initial force and the much larger final force applied by a standard size and shape impacting gauge. ISO International Rubber Hardness Degrees or IRHD uses a dead load to indent a rigid ball into rubber specimens, expressing the results in the range ‘0’ (corresponding to zero elastic or Youngs’s modulus) to ‘100’ (effectively infinite elastic modulus). Shore measures the materials resistance to a spring loaded blunt point impressed on the surface. The primary difference between the two main Shore scales is that Shore A uses a truncated 35degree conical probe and Shore D uses a 30degree conical needle point probe.
SO HOW CAN WE HELP YOU…
Well, how long is a piece of string? Let’s just keep to what we’re good at, injection moulding and all its disciplines, a well-practised method of mass producing all sorts of product that touches nearly every aspect of modern life. But have you noticed some of the more recent multi shot trends, here’s just a few: -
• Control knob with integral pointer or graphics, quite often the pointer material is opaque or clear to act as a light pipe so that it can be illuminated. Just take a look inside your car. The climate or heater control knobs, the hazard button and the auxiliary control buttons are almost certainly made using the multi shot injection-moulding process. Some multi shot control knobs are simply two colours of the same material such as you may find on audio, studio and other electronic equipment and others have tactile surfaces also produced using this process.
• Cases with integral seals. Not so easy to find, as to do so would require some disassembly which we do not recommend, but be assured they are out there. Examples include cordless appliances where the base connector may require protection against water ingress or perhaps an electronics package that may require protection against humidity, spray or even complete immersion. Some manufacturers of electronic key fobs insist that the product must be able to survive an automatic washing machine cycle should the worst happen. Consider also a limit switch housing where the integral seal and actuator diaphragm is formed in one or as in the key fob where the seal and tactile keypads are formed in one.
• Handles with soft tactile areas such as you may find on your toothbrush, screw driver or power tool. Soft touch areas that give enhanced grip and tactility, attributes that are also very welcome in medical equipment and ancillaries, and especially useful for those of us with an impaired ability to grip things.
• Shock protection in the form of elastomer pads moulded onto the corners of cases used to house sensitive equipment or complete surfaces such as you may find for instance on the lens rings and base caps of industrial torches, there specifically to make the product rugged and tactile.
• Windows. Yes, mould the window first and then mould your case around it. All in one simple process. Most of the amorphous materials used in these applications bond together well.
• Articulated Assemblies. By the careful selection of moulding materials that do not bond, fully articulated assemblies can be produced from one multi shot process. The classic example of this is the louvered air vent in a particular automobile.