microdia newsletter no 41 wires concentricity measuring issues
DESCRIPTION
Substantial saving is achieved with a perfectly concentric wire as outer diameter can be kept at the minimum of its tolerances.TRANSCRIPT
www.microdia.ch Your expert in extrusion
SWISS MADE
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N EWSLETTER N O 41
Wires concentricity measuring issues
November 2014
E
e x 100
Is the formula widely used to define the concentricity of an
insulated conductor.
e = minumum wall thickness.
E = maximum twall thickness
Every wire parameter:
Core roundness.
Insulation roundness.
Foam cells homogeneity
Can affect the measured concentricity factor value
Bad cut
Broken cells
Low magnification
Burrs on edge
Wall thickness measuring precision depends highly on operator
skill , type and condition of the extrusion line, etc.
Slice thickness, quality of cut have a incidence on the wall thickness measured values, particularly with small wall
thicknesses below 0.2 mm.
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Pa ge 2
Flattened insulation
Oval core; oval insulation
Along the cooling trough, on multipass cooling capstan’s sheaves, on take-up dancer reversing wheels, numerous are the spots where
insulation can be damaged.
Example on the right shows a minor flat on the
insulation top ; wall thickness is smaller there.
If this minor wall thickness is not ignored, microscope concentricity check will give a factor of 97.6 % although core and insulation
are 100% concentric !
In a similar way, if the core or the insulation is not perfectly round, although both are perfectly concentric, microscope view will show wall thickness difference and therefore an
apparent lower concentricity factor.
Newsletter No 41
In those two examples of 0.6 mm x 1.0 mm insulated wire, a core or insulation ovality of 0.006 mm [ 0.0236 mils] will result in wall thicknesses of .200 mm (wall min) and .203
mm, (wall max).
Although core and insulation are 100% concentric ,
microscope check will give a concentricity factor of 98.5 %
round insulation , oval core round core , oval insulation
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During extrusion, no matter how precise cross head , tip and die are , the core will move slightly around the center within 0 to 2 microns if extruder delivers a homogenous melt, as it appears on
the on-line concentricity meter’s screen.
The reason is that the core is mainly centered by the flow of
compound and not by the tip (wire guide).
It is interesting to notice that in spite of a clearance of 20 to 30 microns between tip inner diameter and core diameter it is possible to maintain the average eccentricity stable around 2 microns if the extrusion conditions are optimum, but of course, every viscosity variation, wire tension variation, wire vibration will
shift the core aside and affect the final product concentricity.
Newsletter No 41 Pa ge 3
Average values
During the steps following the extrusion: wires pairing, pairs assembling, etc. of a Lan cable for example, the single wire insulation shape will probably be deformed when passing through multiple reversing wheels, assembling dies etc. and loose its original
shape.
In fact the most important point is to maintain a good average concentricity without focusing on the irregularities of only a single
slice of insulation.
Therefore it is necessary to take several sample on a certain length and calculate the
average values.
Extrusion
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Newsletter No 41 Pa ge 4
m ic r od ia S. A. off ice in Germany
Phi l ippe Chasse loup Sales Manager Deutschland & Austr ia Tel.: +49 171 8654289 Fax: +41 24 445 12 28 [email protected]
Skype: microdia deutschland
Contact in Switzerland:
Stephanie Chasseloup
Sales assistant
Microdia Head Office
+ 41 24 447 3510
To be closer to its numerous German and Austrian customers
microdia S.A. Has opened an office in Germany. This office will be
managed by Mr. Philippe Chasseloup, sales manager.
Mr. Chasseloup assistant will be Mrs Stephanie Chasseloup who is
based in microdia head office in Switzerland.
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SWISS MADE
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Newsletter No 41 Pa ge 5
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www.microdia.ch
Phi l ippe Chasse loup Sales Manager Deutschland & Austr ia Tel.: +49 171 8654289 Fax: +41 24 445 12 28 E-mail: [email protected]
Skype: microdia deutschland
For USA & Germany
Contact in Switzerland:
Stephanie Chasseloup
Sales assistant
Microdia Head Office
+ 41 24 447 3510
m ic rod ia S. A .