DIY Glass kiln - 'singing' contactors

HI All Finally got some power applied to the DIY glass fusing kiln that I was seeking advice on a few months ago.
Gave up waiting for the electrician to call - and laid in the wiring myself (following the installation advice he gave on the one occasion he did turn up!) Had a bit of a battle with the 6mm2 3-core cable - but eventually beat it into submission!
Anyway - 7kw of resistive heating elements are fitted in the top of a 'clamshell'-style kiln, with ceramic fibre insulation & a commercial controller feeding a pair of 40A 'Chint' contactors in series. (The 'safety' circuit that was discussed at length isn't in there yet - but the second contactor will eventually be controlled by it).
All seems good - on switch-on nothing caught fire (!), and only parts inside the kiln got hot.
However - the contactors sometimes 'sing' or 'whistle' to themselves - by the nature of the controller the contactors are turned on & off from time to time. Sometimes they come on silently (apart from the 'thud') - whereas sometimes they whistle.
Looked on the web, and saw some comments from some kiln manufacturers, along the lines of 'they do that - don't worry'
So - is a whistling contactor a cause for concern - or is it just 'one of those things' ?
Thanks Adrian
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
When you say whistling, exactly what is vibrating in the unit to give a singing effect?
Brian
--
From the Bed of Brian Gaff.
The email is valid as snipped-for-privacy@blueyonder.co.uk
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Could this be cheap contactor ironwork with no shading ring?
--
Tim Lamb

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 21/04/2014 21:12, Tim Lamb wrote:

Could be? - I'm a long way from being an expert in such matters.
The part number is Chint IC40/2 - it's rated AC-1/AC-7a 40A, AC-7b 15A - and the load it's switching is about 32A, simple resistance wire wound on a spiral former.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 21/04/2014 21:12, Tim Lamb wrote:

Sorry - duff info - not Chint at all - manufacturer is Lewden, item is IC40/2
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ask Lewden? Usually reliable stuff.
One possibility might be dirt between the faces; preventing the magnet circuit fully closing. Bit of compressed air?

--
Tim Lamb

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 22 Apr 2014 09:34:44 +0100, Tim Lamb wrote:

Wouldn't that make the thing "buzz" rather than "sing"?
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes. On a resistive load, what else could it be.
I think technical support at Lewdens is the place to ask.

--
Tim Lamb

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 22/04/2014 10:18, Tim Lamb wrote:

Good idea! - I've just dropped them an email.... Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.