microdia newsletter no 39 thin wall concentricity
DESCRIPTION
Incidence of the eccentricity on the concentricity factor ( wall min/wall max ).TRANSCRIPT
www.microdia.ch Your expert in extrusion
SWISS MADE
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N EWSLETTER N O 39
Thin wall insulation concentricity.
Fixed center insulation concentricity depends on several important factors:
Cross head lining up. Cross head levelling. Head heating balance. Cross head’s components precision.
THHN stands for Thermoplastic High Heat Resistant Nylon
THWN is a water resistant THHN cable type.
THWN is considered an evolution of THHN
Today's they are one in the same, pretty much all THHN is dual
rated with THWN.
Page 4: Straight from Wire China 2014
Important factors
Insulation concentricity
Insulation concentricity is generally calculated with this formula:
K = 100 means a perfectly concentric insulation.
Wall max
Wall min K = X 100 [%]
Wall min
Wall max Sometimes, ‘’k’’ is simply expressed by:
In that case k=1 means a perfect concentricity
Examples: Core Ø 1 mm; Insulation Ø 2.00 mm; 1.50 mm; 1.25 mm
Insulation Ø 1.5mm
Nominal wall 0.25 mm
eccentricity 0.020 mm
Max wall 0.270 mm
Min wall 0.230 mm
Concentricity 85.2 %
Insulation Ø 2 mm
Nominal wall 0.5mm
eccentricity 0.020 mm
Max wall 0.520 mm
Min wall 0.480 mm
Concentricity 92.3 %
Insulation Ø 1.25 mm
Nominal wall 0.125 mm
eccentricity 0.020 mm
Max wall 0.145 mm
Min wall 0.105 mm
Concentricity 72.4 %
0.5 mm wall thickness 0.125 mm wall thickness 0.25 mm wall thickness
>>>> Concentricity factor decreases dramatically when wall get thinner.
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SWISS MADE
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Newslett er No 3 9 Page 2
Concentricity factor depends only on wall thickness and core/insulation eccentricity
Insulation Ø 4 mm
Nominal wall 0.5 mm
Core Ø 3 mm
eccentricity 0.020 mm
Max wall 0.520 mm
Min wall 0.480 mm
Concentricity 92.3 %
Insulation Ø 2 mm
Nominal wall 0.5 mm
Core Ø 1 mm
eccentricity 0.020 mm
Max wall 0.520 mm
Min wall 0.480 mm
Concentricity 92.3 %
Insulation Ø 6 mm
Nominal wall 0.5 mm
Core Ø 5 mm
eccentricity 0.020 mm
Max wall 0.520 mm
Min wall 0.480 mm
Concentricity 92.3 %
Insulation Ø 2 mm Insulation Ø 6 mm Insulation Ø 4 mm
Examples: wall thickness 0.5 mm; Insulation Ø 2.00 mm; 4.00 mm; 6.00 mm
Very thin insulation requires accurate head lining up and extreme cross head precision
0.700
0.750
0.800
0.850
0.900
0.950
1.000
2 4 6 8 10 12 14 16
wall
min
/ w
all
max
eccentricity [microns]
concentricity factor [ Wall min / Wall max ] against eccentricity
thin wall insulation wall thickness 0.1 mm wall thickness 0.2 mm
Chart shows the relation bet-ween core & insulation eccentri-city and concentricity factor wall min/ wall max. for 2 values of wall thickness, 0.1 mm and 0.2 mm, [ 4 and 8 mils].
For a wall thickness of 0.1 mm a concentricity factor of 0.9 or 90% corresponds to an eccentricity of only 5 microns [ 0.2 mils ].
A cross head is composed of at least 4 elements: 1] head body 2] Distributor 3] Tip or wire-guide 4] Die
Each component has a concentricity tolerance of 5 to 10 microns [ approx 0.2 to 0.4 mils ]. In the assembly, those tolerances might add, subtract or balance depending on their respec-tive orientation. Clearance between conductor and inner bore of the tip is at least 10 microns [ 0.4 mils ].
However, eccentricity of the insulation is generally lower than 10 microns [ 0.4 mils ] because the core is centered by the flow during its transit through the extrusion tooling and not only by the too-ling.
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SWISS MADE
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Newslett er No 3 9 Page 3
Insulation centered by the flow.
Correctly lined up and levelled cross head:
Compound flows evenly around the core.
Friction between conductor and tip is minimal.
Good concentricity of insulation.
Cross head tilted forward:
Compound flows not evenly around the core.
Important friction between conductor and tip, tip quickly worn out, generation of copper flakes, core surface damaged, wire breaks.
Low concentricity factor,
α
Levelling tooling.
Brick layer level
mcrodia square shaped cross heads like this
ecomex are easy to level thanks to their flat
top surface. Spirit level has to be chosen accurate enough for easy head levelling, however,
excessive precision ( frame type spirit lever for instance ) makes the head set up impos-sible.
Prismatic spitit level with an accuracy of 0.3—0.5 mm per division are preferred. Bricklayer’s type level are to be avoided.
Frame type level
Level with prismatic measuring face, Ω shaped
www.microdia.ch Your expert in extrusion
SWISS MADE
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Newslett er No 3 9 Page 4
Straight from Wire China Shanghai 2014
Long die
microdia, unique overseas cross head manufacturer at the show
attracted a large number of wire and cable specialists. On the booth, Mr Patrick Zacchia CEO and Mr Alban Adams In-
ternational sales Director with the efficient support of microdia Asia Pacific team Mrs Yuca Chen and Brian Zu attended the nu-
merous visitors from the five continents.
Six fully operating cross heads on the booth demonstrated mi-crodia expertise and quality allied with simplicity and comfort of mcrodia Asia Pacific sales agent
Brian Zu discussing properties
and advantages of the ecomex Xhead displayed on the booth.
www.microdia.ch Your expert in extrusion
SWISS MADE
°microdia
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Newslett er No 3 9 Page 5
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