| Are there different manufacturing processes for composite insulators? |
Today, the following manufacturing technology are state of the art:
· Single shot moulding
· Multi shot moulding (for larger units)
· Single mounting and vulcanization of sheds (pre-manufactured sheds): For more information, please visit our Download Center and read our Technical Paper entitled: “Design Criteria for Composite Insulators for use in HV Outdoor Applications”.
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| What are the advantages and disadvantages of specific manufacturing/ production methods? |
a) Single and multi shot moulding:
Advantages:
· Cost effective for larger quantities of relatively small (short) insulators of the same design
Disadvantages:
· Low flexibility concerning design changes and housing profile variations
· Expensive moulds required
· 2 piece moulds lead to “moulding” lines along the insulator housing
· material flow problems (inhomogeneous in material properties) in larger moulds
b) Single mounted and vulcanized sheds (pre-manufactured sheds):
Advantages:
· Cost effective for all sizes of insulators
· Chemical bonding between all insulating parts due to hot temperature vulcanization
· Highest design flexibility concerning insulator housing profile
· No moulding lines along the insulator housing
Disadvantages:
· None
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| Why are composite insulators equipped with pre-manufactured sheds preferable to those composite insulators manufactured by injection moulding? |
No moulding lines along the insulator housing. Moulding lines in parallel to the electrical field are critical concerning T&E phenomena. Premature failure due to T&E always starts at such weak points. Furthermore, the material composition of housing material in the vicinity of the moulding lines differ from that of the bulk material, even if the lines are properly removed. Often internal mechanical stresses caused by material inhomogenities lead to premature cracking of the rubber within the moulding line area.
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| How can single mounted pre-manufactured sheds be completely chemical bonded to housing material of shank? |
This can be reached with special vulcanization agents and pastes that are applied to the interface between shank and shed before shed mounting. An hot temperature vulcanization process at 180°C/3h assures that the HTV silicone materials of shed and shank (extruded HTV silicone layer) are vulcanizing together to 100%. After vulcanization, the HTV silicones of shed and shank are completely chemical bonded.
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| Why should moulding lines be avoided? |
Moulding lines in parallel to the electrical field are critical concerning T&E phenomena. Premature failure due to T&E always starts at such weak points. Furthermore, the material composition of housing material in the vicinity of the moulding lines differ from that of the bulk material, even if the lines are properly removed. Often internal mechanical stresses caused by material inhomogenities lead to premature cracking of the rubber within the moulding line area. For more information, please visit our Download Center and read our Technical Paper entitled: “Design Criteria for Composite Insulators for use in HV Outdoor Applications”.
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