1. UltraScreen TM
Core Defect and Screen Extrusion Disruption
B Scan Display Exemplars
May 2015
Author: Dr Gareth Humphreys-Jones
2. Introduction to UltraScreen Operation and B Scan Display Format
Each of the following exemplar single channel B Scan displays – which have been rotated
through 90o
to provide perhaps a more natural viewing layout – represents about 15s of
production run with typical line speeds in the range 1–2m/min, So each display presents a
cable length of typically 25-50cm. Radially the system measures to an accuracy of ~10 micron
and on one of the displays radial cursor measurements are included to provide a sense of
scale. In the rotated view provided, the cable is running through the machine from left to right
across the displays.
3. Ex1
Ex 2
Repeated core defects and
associated inner screen
protrusions / fall-ins, not large
enough to affect the outer
screen.
Core fall-in and associated inner
screen disruption, large enough
to affect the outer screen.
4. Ex 3
Ex 4
Shorter core fall-in and
associated inner screen
disruption, just large enough to
affect the outer screen.
Combination of core fall-in and
tape ruckle with associated inner
screen disruption, large enough
to affect the outer screen.
5. Observations
Ex 1 is more typical of the scale of the core defects and inner screen perturbations that are
generally auto-detected on-line during a production run.
In general the structure of the inner screen perturbations exhibits a thickening of the screen
width at the ‘head’ of the core defect, and a thinning of the screen width at the ‘tail’ of the
core defect. This structure can be seen very clearly in Ex 1 where protrusions can be seen
at the heads of both of the raised core sections, whereas fall-ins can be seen at the tails of
both. It is as if the core defect creates a ‘bow wave’ at its head forcing the inner screen
outwards, and then creates ‘suction’ at its tail sucking the inner screen inwards.
Because of this generic structure, the severest thinning of the inner screen generally occurs
at the tail of a core defect – with cases where the inner screen has essentially disappeared
being detected.
Ex 2 presents an exemplar where the inner screen width increases more than fourfold,
1.22mm : 5.74mm. However, whilst this can be seen in the ultrasonic imagery to create a
distortion at the outer screen, from this exemplar and from Ex 3 & 4, it can be seen that
even in these cases of very significant inner screen disruption, the effects at the outer
screen are quite smooth and not that pronounced and are therefore easily missed by visual
inspection, etc. Also, from Ex 1, it can be seen that the core defect / inner screen
disruptions more typically detected do not produce a visually detectable effect at the outer
screen. This leads to the conclusion that visual cable inspection cannot be relied upon to
detect the presence of such significant core defect / inner screen disruptions that are, of
course, occurring deep within the structure of the cable.
From all the exemplars it may be seen that the core defect / inner screen disruptions
typically only persist for a few cms - and sometimes as little as a few mms - thus any
system that doesn’t carry out rapid scanning measurements and/or averages its
measurements along the cable length probably does not have the capability to detect such
significant defects
To put the significance of the scale of these core defect / inner screen disruptions into
perspective, Ex 5 presents a much smaller protrusion / fall-in inner screen disturbance –
again associated with a much smaller core fall-in - auto-detected on-line by the UltraScreen
system. The importance of this image lies in the fact that this inner screen disturbance
caused this cable to fail in subsequent over-voltage testing. So to be of practical use in an
extrusion quality monitoring role, this is the scale of core defect / inner screen disruptions
that needs to be detected – not just the much larger scale exemplars presented in Ex 1–4!
6. .
Ex 5
Core fall-in and associated inner
screen disruption, large enough
to cause a cable breakdown.
