×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Shrinkage and Carbon Black

Shrinkage and Carbon Black

Shrinkage and Carbon Black

(OP)
Hello Again!

Just a quick question today....can changes in carbon black (supply rather than grade) change the shrinkage of the material?
I have been led to believe that the polymer used has more impact on the shrinkage.

Basically I am trying to find out what affects changing different components of a compound would have on the shrinkage (polymer, carbon lack, oil and cure system).

Thanks

Elastomatt

RE: Shrinkage and Carbon Black

The more carbon black is in compound the lower shrinage is.

RE: Shrinkage and Carbon Black

Changes in the supply of carbon black should have very little effect on shrinkage so long as the grade is the same and the suppliers are reputable! By far the more important factors are a) the viscosity of the gum polymer and b) the level of filler. High viscosity polymers can handle a higher degree of fillers, a highly extended compound should be less susceptible to shrinkage. The make-up of the fillers and especially the particle size (surface interaction) can have a bearing but are of less significance.
 

www.white-cross-rubber-products.co.uk

RE: Shrinkage and Carbon Black

Are we talking about shrinkage after cure or after extrusion or calendering?

Please bear with me on what I write next, as it talks about nerve rather than shrinkage (but they are very similar):

Nerve is the elastic recovery that compounds exhibit after deformation.  While a pronounced elastic response is necessary in the application, if it excessive in the rubber's uncured state it can cause processing problems.  Therefore, it must be reduced during mixing to improve processing, dimensional stability, die swell and calender shrinkage.

Methods of controlling nerve:

1.    Mastication reduces nerve.
2.    Increasing filler loadings will reduce nerve.
3.    Using high structure in place of normal structure carbon blacks will reduce nerve.
4.    The addition of factice, mineral rubber, or reclaim can be useful but one can expect some loss of physical properties.  For example, use WB grades of CR although T-types are available that do not show nerve in later processing stages.
5.    Calendering at higher temperatures will also reduce nerve but can cause the compound to stick to the rolls.

Control of shrinkage during extrusion or calendering is down to several things including take off belt speed.  If the take off speed is greater than the speed the rubber is leaving the extruder die or calender bowl then you can expect varying levels of shrinkage before curing.  If you match the speeds more closely (ideally take off speed is 1-2% faster) then stretch is minimised; thus making shrinkage much less of a problem.

RE: Shrinkage and Carbon Black

(OP)
Thanks to all, I am mainly concerned with moulding and extrusion shrinkages.

Given me lots to think about (and look up!) winky smile

 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources