Brittle rubber cabling - UK Vintage Radio Repair and Restoration Discussion Forum

jbraes · 31st Mar 2008, 10:01 pm

In the radio I am working on, a Murpy U102, virtually all the rubber cabing is hard and brittle, except for black.
By far the wost is red, followed by blue, green and yellow. Black is still soft and supple.
Why are the pigments, used to colour the the rubber, affected by heat in different ways?
I know from experience, that green angling waders are susceptable to uv, which is possibly why commercial waders are black. In radios, uv, I wouldn't have thought, would be an issue, or is it a different type of uv?
Cheers John.

Nickthedentist · 31st Mar 2008, 10:05 pm

It may just be something mundane, e.g. that the black came from one manufacturer and red from another etc.

Oldtimer74 · 16th Apr 2008, 11:03 pm

No it won`t be UV unless the cable has been outside . Depending on the age of the rubber different formulations were used. In some cases one suspects that it was more of an art than a science! Prewar stuff was probably almost all made from natural rubber but since then many different types have been produced. The manufacturing process will almost certainly have involved vulcanisation using sulphur or a compound and the final mixture is not always very stable. In those days simulated long term testing was rarely done. You never can tell what will last and what won`t! I cannot say that I have noticed any particular colour to be bad but certainly 3 core cable can have one core OK and the others a sticky mess or cracked hard. Increase in temperature is probably the worst offender for cracking. Similar things happen to early plastic cable with the plasticiser forming a sticky mess after a time. Modern rubbers are a well controlled polmer but early ones often had some natural rubber present and the chemical composition of that is variable with reactive components possibly still being present. I do not know what dyes are or were used but they may well have reacted slowly with the base rubber.
Rubber chemistry is a complex subject!!
Pat

ChristianFletcher · 18th Apr 2008, 8:09 pm

Thats funny in my CR100 all the wiring is good but but the black and that falls apart as soon as look at it. I also have a 62 Set and the rubber cable is turning to sticky goo. I have read that the decomposition of rubber can be quite toxic

Chris

31st Mar 2008, 10:01 pm	#1
jbraes Triode Join Date: Jan 2006 Location: Ullapool, Scotland Posts: 18	Brittle rubber cabling In the radio I am working on, a Murpy U102, virtually all the rubber cabing is hard and brittle, except for black. By far the wost is red, followed by blue, green and yellow. Black is still soft and supple. Why are the pigments, used to colour the the rubber, affected by heat in different ways? I know from experience, that green angling waders are susceptable to uv, which is possibly why commercial waders are black. In radios, uv, I wouldn't have thought, would be an issue, or is it a different type of uv? Cheers John.

31st Mar 2008, 10:05 pm	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,874	Re: Brittle rubber cabling It may just be something mundane, e.g. that the black came from one manufacturer and red from another etc.

16th Apr 2008, 11:03 pm	#3
Oldtimer74 Rest in Peace Join Date: Apr 2008 Location: Worcester, Worcestershire, UK. Posts: 330	Re: Brittle rubber cabling No it won`t be UV unless the cable has been outside . Depending on the age of the rubber different formulations were used. In some cases one suspects that it was more of an art than a science! Prewar stuff was probably almost all made from natural rubber but since then many different types have been produced. The manufacturing process will almost certainly have involved vulcanisation using sulphur or a compound and the final mixture is not always very stable. In those days simulated long term testing was rarely done. You never can tell what will last and what won`t! I cannot say that I have noticed any particular colour to be bad but certainly 3 core cable can have one core OK and the others a sticky mess or cracked hard. Increase in temperature is probably the worst offender for cracking. Similar things happen to early plastic cable with the plasticiser forming a sticky mess after a time. Modern rubbers are a well controlled polmer but early ones often had some natural rubber present and the chemical composition of that is variable with reactive components possibly still being present. I do not know what dyes are or were used but they may well have reacted slowly with the base rubber. Rubber chemistry is a complex subject!! Pat

18th Apr 2008, 8:09 pm	#4
ChristianFletcher Heptode Join Date: Dec 2003 Location: South Yorkshire, UK. Posts: 900	Re: Brittle rubber cabling Thats funny in my CR100 all the wiring is good but but the black and that falls apart as soon as look at it. I also have a 62 Set and the rubber cable is turning to sticky goo. I have read that the decomposition of rubber can be quite toxic Chris __________________ Every Silver Lining Has Its Cloud https://youtube.com/channel/UCvBpiuUUnErJlNBm6DWb3Ww