Monday, February 14, 2011

How to improve rubber process : Reducing Backrinding in compression moulding

In Compression moulding process , when the expansion of the cure rubber is concentrated in a limited area and is greater than the ultimate cure elongation of the compound the mould is opened after cure , the phenomenon is called Backrinding The resulting in a rupture at the part line (o-ring ,rubber seals, solid tire,rubber mounts ,rubber gaskets etc.) . There are some ideas which may help prevent or eliminate backrinding but these general ideas may not work in all specific situation.

  1. Mould Temperature : Curing a compound at a lower temperature for a longer period of time will allow more rubber to exit the mould from thermal expansion before scorch and cure are reached. The rubber compound will most likely have better tear resistance at lower temperature.
  2. Mould Design : Backrinding can be severe in the moulding of lage, bulky articles with a lage amount of mass .In design the rubber mould, if the ration of surface area to volume can be increased then backrinding may be less of a problem. In design the mould place the part line in a noncritical area the does not affect product performance .
  3. Cooling the mould to lower the pressure that will be released on demoulding is another option to consider to reduce or eliminate backrinding.
  4. Preheat the preform before placing it in the mould
  5. Extending scorch time through compound modifications should favor reduced backrinding becouse it provides more time for rubber to exit mould cavity before curing occur.
  6. Improving tear resistance of rubber compound (hot tear resistance)

Warning : Change to reduce backrinding will certainly effect other properties.

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