Final Report - Effects of Laser Cutting Nuclear Contaminated Material - Daniel Evans

of 21
REDUCTION AND EXTRACTION OF PARTICULATE GENERATED IN THE LASER
CUTTING PROCESS
D. J. Evans, J. R. Tyrer
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University,
Loughborough, Leicestershire, LE11 3TU, United Kingdom
Abstract
A high proportion of decommissioning
operations within the nuclear industry utilise
laser cutting for the size reduction of
contaminated metals. The metal laser cutting
process produces dross and aerosol particles
as secondary emissions.
The aim of this paper is to investigate the
laser cutting process parameters and suggest
optimal conditions for the production of
minimal respirable particulate. This was
achieved by completing standard test cuts on
stainless steel for different laser operational
parameters and measuring the particle
concentration and particle distribution. The
results showed that a high laser power and a
low cutting velocity resulted in a 200%
reduction in the number of particulate
produced compared to a low power and a
high cutting velocity.
Furthermore the effectiveness of a multiple
phase cyclone to extract the particulate from
the airflow is investigated. The effectiveness
was investigated using sizing particulate and
measuring the particle distribution and
particle concentration at different positions in
the cyclone assembly. The results showed
that the cyclone assembly and HEPA filter
removed practically all 0.9µm, 4µm and 60µm
particulate from the airflow. Additionally the
lessons learnt through experimentation were
used to suggest optimisation of the cyclone
design. It was identified that the design
techniques associated with the cyclones of
domestic vacuums are superior to that of
industrial cyclones; therefore adopting these
techniques would lead to an optimised
design.
Contents
Contents ......................................................1
Glossary of Terms........................................2
1 Research Question/Hypothesis.............2
2 Introduction...........................................2
3 Literature Review and Theoretical
Background..................................................3
4 Methodology (Design of the
Experiments)................................................5
4.1 Test Cell ........................................5
4.2 Cyclone..........................................7
4.3 Particle Analysis ............................9
4.4 Cyclone Assembly Effectiveness ...9
4.5 Test Cell Validation Experiment ... 10
4.6 Laser Cutting Experiment Setup .. 10
4.7 Experimentation Procedure.......... 11
5 Results................................................ 11
5.1 0.9µm Zirconium Oxide Particulate ..
.................................................... 11
5.2 4µm Titanium Dioxide Particulate. 13
5.3 60µm Hollow Glass Spheres........ 14
5.4 Test Cell Validation Experiment ... 14
5.5 Laser Cutting ............................... 14
6 Discussion .......................................... 16
6.1.1 0.9µm Zirconium Oxide
Particulate........................................... 16
6.1.2 4µm Titanium Dioxide
Particulate........................................... 16

of 21
6.1.3 60µm Hollow Glass Spheres. 17
6.2 Cyclone Assembly Particulate Tests
.................................................... 17
6.2.1 TSI Particle Sizer Stalling ..... 17
6.2.2 Build up of Particulate and
Suggestion for Cyclone Re-Design ..... 17
6.2.3 Theoretical Cyclone
Calculations ........................................ 18
6.2.4 Test Cell Validation Experiment
18
6.3 Laser Cutting ............................... 18
7 Recommendations for Further Work ... 19
8 Conclusions ........................................ 20
9 References ......................................... 21
10 Conflict of Interest ........................... 21
11 Acknowledgments ........................... 21
Glossary of Terms
CAD Computer Aided Design
HEPA High Efficiency Particulate
Absorption
HSE Health and Safety Executive
LDA Laser Doppler Anemometry
LOE Laser Optical Engineering
PIV Particle Image Velocimetry
1 Research Question/Hypothesis
1) How can the laser cutting parameters be
adjusted to reduce the mass of airborne
particulate generated by the laser cutting
process?
2) How effective are cyclones at removing
airborne particulate and how can cyclone
design be optimised?
2 Introduction
Laser cutting is a non contact cutting
mechanism used throughout
decommissioning operations to cut nuclear
contaminated metal. The majority of metal in
reactive fusion laser cutting is ejected through
the bottom of the cut, however the high power
density at the focal point of the laser causes
some material to vaporise generating a fume.
This causes contaminants on the surface of
the material to become airborne and
respiratory of these could be fatal. In
decommissioning operations it is
advantageous to keep the degree of
contamination to a minimum in order for
reduced de-contamination operations.
A potential solution is to enclose the laser
cutting process and utilise a capture system
to extract the contaminated particulates from
the airborne fume. Cyclones can be used to
capture particulate from the fume. This
investigation will determine the effectiveness
of using a multiple stage cyclone for the
extraction of particulate from the airflow. A
HEPA filter at the extract of the cyclone will
be used to explore the particulate that the
cyclone is unable to capture. The cyclone
experimentation will highlight the limitation of
the cyclone and suggest design optimisation.
However in some situations it may not be
possible to enclose the laser cutting process.
As in the case of laser snake, it would not be
possible to contain the ejected material at the
back of the cut. In reactive fusion cutting the
majority of material is ejected through the
back of the cut because of the gas pressure
forces. Laser snake cuts through objects in
order to gain access to the rear, therefore
containment would not be possible. Utilising a
capture system is only effective if the cut area

of 21
can be contained. Furthermore a capture
system does not directly solve the problem of
reducing airborne contaminates, since it
merely removes the particulates from the
fume.
This investigation determines whether it is
possible to reduce the mass of airborne
particulate by adjusting the operational
characteristics of the reactive fusion laser
cutting process. The advantage of reducing
airborne contaminants is that less de-
contamination operations are required after
the cutting process. The further advantages
are reduced cost, reduced time disturbance
and less exposure to radiation.
3 Literature Review and Theoretical
Background
“Standards only become mandatory when
they are given the force of law by citation in
laws, regulations, codes” (Howe, 2008).
Therefore the literature produced by the
Health and Safety (2008) associated with
lasers in the Supply of Machinery (Safety)
Regulations is of most relevance in this
investigation. The regulation identifies two
types of hazard associated with laser
processing; laser radiation and emission of
hazardous materials and substances.
The regulation states “Machinery must be
designed and constructed in such a way that
risks of inhalation, ingestion, contact with the
skin, eyes and mucous membranes and
penetration through the skin of hazardous
materials and substances which it produces
can be avoided. Where a hazard cannot be
eliminated, the machinery must be so
equipped that hazardous materials and
substances can be contained, evacuated,
precipitated by water spraying, filtered or
treated by another equally effective method”
(Health and Safety, 2008). Therefore in order
to comply with the law, all machinery must
adhere to the requirements from the above
regulation.
Laser material processing is not the only
operation that produces a fume. Fume
generation is also associated with welding
and surgery involving lasers and electro-
surgery. Therefore research has been
undertaken into treatment of the fume
generated from welding and surgical
processes.
The Health and Safety laboratory have
identified that welding fume inhalation can be
harmful to human health and have therefore
produced a paper outlining the European and
International Standards on Health and Safety
associated with welding (Howe, 2008). The
purpose of the paper is to increase
international awareness of published
standards and therefore encourage wider
participation in welding standards relating to
health and safety. Tests were undertaken by
the Health and Safety Laboratory in order to
assess welding fume and used “to inform
HSE participation in standardsmaking
activities” (Howe, 2000). Reproducible results
relating to chemical composition were
generated by using a mechanised welder to
weld a test piece inside a fume box. The
analysis involved determining the chemical
composition of the fume generated, not the
size of the particulate produced. The welding
parameters were identified to effect the fume
composition, with voltage having the greatest
effect. Similarly laser cutting has parameters
which effect the composition of particulate
produced. The following report focuses on the
particle size and distribution produced from
laser cutting rather than the chemical
composition.
“Electro-surgery, laser ablation, and
ultrasonic scalpel dissection create a
gaseous by-product commonly referred to as
surgical smoke or plume” (Bigony, 2007). The
surgical smoke contains complex
hydrocarbons and organic material, with
current evidence being inconclusive as to

of 21
whether the smoke contains viral particles or
viable tumour cells (Pillinger, Delbridge and
Lewis, 2003). A review undertaken by the
HSE aimed to analyse research into surgical
smoke and determine whether it posed a risk
to exposed workers (Beswick and Evans,
2012). The HSE identified research
undertaken by Pillinger, Delbridge and Lewis
(2003) to be relevant to the extraction of
surgical smoke. The study by Pillinger,
Delbridge and Lewis (2003) aimed to
determine whether an extraction device
would reduce staff exposure to surgical
smoke in comparison to the same surgical
procedures with no extraction (Beswick and
Evans, 2012). A TSI DustTrak aerosol
monitor can detect particles in the range of
0.1μm to 10μm and was used to sample
particulate at the suprasternal notch on the
surgeon to measure particulate concentration
and distribution around the surgical mask
(Beswick and Evans, 2012). A Lina Grey
Shark smoke extraction system was used
and it was shown to significantly reduce the
smoke reaching the area around the surgical
mask. The Lina Grey Shark extraction system
incorporates ClearFlow filters which were
shown to remove more than 99.9% of
particles down to 0.2μm, therefore ensuring
that minimal particulate was exhausted to the
environment (Beswick and Evans, 2012). The
size of particulate in surgical smoke
measured by Pillinger, Delbridge and Lewis
(2003) was measured to be between 0.05μm
and 25μm. Bigony (2007) concluded that
smoke evacuation would be the only reliable
solution for eliminating the possibility of
inspiring bio hazardous material in the
operating room. The welding study by Howe
(2000) investigated the effect of the welding
parameters on the fume generated. It is
inconclusive from the review by Bigony as to
whether she has discounted or overlooked
the fact that laser parameters could have an
effect on the surgical smoke produced.
This report will now focus on research
relating to the fume produced from laser
cutting.
Laser cutting of metals involves melting the
material and utilising a high pressure gas jet
to eject the molten metal. Lobo (2002)
undertook a study to examine the solid phase
by-products from laser cutting. The author
showed that the laser cutting process
parameters (cutting velocity, laser power and
assist gas pressure) had an effect on quality
parameters (cut surface roughness, kerf
width, striation frequency, striation angle) and
were shown to relate to the size and shape
distribution of the particulate produced. Iso-
kinetic probes in the extraction ducting are
widely utilised (1978) to enable real-time
analysis of the fume. Lobo (2002) sampled
with an iso-kinetic probe which enabled
online analysis of volume mean diameter of
particulates with a laser diffraction instrument.
Based upon the investigations of Hinds
(1998), Lobo (2002) classified the cut zone
emissions from mild steel into two categories;
respirable particulate (<10µm) and non-
respirable particulate (>10µm). Powell, et al.
(1996) recognised the significance of
collecting and extracting respirable and non-
respirable particulate. Lobo (2002)
investigates filtration techniques for
mechanical separation, diffusion devices,
electrostatic separation, magnetic separation
and wet separation. All of these devices
require the fume to be collected and
transported to them. More specifically the
mechanical separation is broken down into
three types; sieves, impactors and cyclones.
Lobo (2002) published that centrifugal
separation was not effective for the capture of
respirable particulate. However, the recent
development of multi stage cyclones in
domestic vacuum appliances has led to
capture of 0.5µm particulate (Dyson, 2015).
HEPA filters are a sieve type of mechanical
separation and are utilised to capture
particulate in the work of Lobo (2002) and
Gunara (2009). This report will identify
whether a cyclone can effectively remove the
respirable particulate.
Lobo (2002) utilised a continuous wave
mode, circularly polarised, 500W coherent

of 21
CO2 laser with a raw beam diameter of 15mm
and a Gaussian distribution. Steen and
Mazumder (2010) show that the reflectivity of
steel is dependent upon the wavelength of
the laser. Subsequently the reflectivities for
fibre and CO2 lasers are 60% and 90%
respectively. A fibre laser is being used in this
investigation since it is better suited to
decommissioning projects due to reduced
reflectivity and it has the ability to be
transmitted through optical fibre. Although
not documented in Lobo’s work, the low
absorption of the CO2 laser into the steel may
have required Lobo to apply impurities or
roughen the surface to reduce reflectivity,
which could have had significant effects on
the particulate produced.
Lobo (2002) and Howe (2000) discuss the
use of a test cell to encapsulate processing
on a test piece and therefore enable
reproducible results to be generated. The test
cell utilised by Lobo (2002) had an extract for
airborne particulate and an aluminium tank to
collect large particulates and dross. It is
recognised by Lobo (2002) that the majority
of the fume produced from laser cutting is
below the work piece. This was therefore be
taken into account in the design of the test
cell.
Lobo (2002) investigated the effects of
power/cutting velocity ratios on the cut quality
and was able to identify parameters which
produced optimum cut quality. Cut quality is
important in the manufacture of products,
however in the decommissioning of nuclear
contaminated material the health and safety
aspect with respect to particle size
distribution is of greater significance.
“There are three regimes of melt ejection and
particle formation during laser cutting –
droplet formation by pressure flow, droplet
formation by melt shear and fine particles
produced by the Kelvin-Helmholtz
instability”(Lobo, 2002). In the cutting of
nuclear contaminated material it may be
advantageous to run the laser process at high
power and low cutting velocity since these
parameters favour pressure flow and melt
shear to occur which results in larger
particulate sizes and favours dross. From a
quality perspective this causes an increased
striation angle which causes the melt
viscosity to increase, therefore the melt is not
easily ejected. Conversely a low power and a
high cutting velocity favour Kelvin-Helmholtz
instability and create greater concentrations
of airborne particulates. This produces a cut
of better quality since the cut front is almost
vertical and the gas jet is tangential to it.
To conclude Lobo (2002) was taking an
approach to achieve the highest quality of the
cut, whereas this report focuses on achieving
minimal respirable products. Therefore as
discussed above a high power and low
cutting velocity was utilised since this favours
melt ejection by pressure flow and melt
shear.
4 Methodology (Design of the
Experiments)
A 300W fibre laser with oxygen reactive
assist gas was used throughout testing. A
stainless steel work piece was cut within a
test cell to encapsulate the process. Relative
movement between the work piece and laser
was achieved through movement of the
machine bed. The main constituent
equipment for the experimentation is
discussed below.
4.1 Test Cell
A test cell was designed using CAD and
manufactured to encapsulate the fumes
produced from the laser cutting experiments.
This design is loosely based on the fume
capture system for offline analysis used by
Lobo (2002). Figure 1 shows the CAD model
of the test cell assembly. Figure 2 shows a
CAD model of the test cell assembly with the
shutters suppressed.

of 21
Figure 1 : CAD Model of Test Cell Assembly
Figure 2 : CAD Model of Test Cell Assembly with Shutters Suppressed
The principle features of the test cell are the
following:
o Honeycomb at the inlet duct of the test
cell to ensure a laminar airflow over the
work piece.
o Square to round transition ducting at the
extract of the test cell to avoid stagnant
airflow and therefore build up of
particulate.
o Smooth bore anti static extraction tubing
to prevent loss of particulate in
transportation and prevent static
discharges which could be an ignition
source.
o Shutters on the top surface of the test
cell to allow laser entry to the test cell
and minimise particulate loss through the
top of the test cell. The shutters are
traversed with respect to the test cell to
enable the laser to cut different areas of
the work piece.
o Removable aluminium tray below the
work piece to collect dross. Aluminium
has been selected since it has a higher
thermal conductivity than steel,

of 21
therefore preventing dross welding to the
tray.
Figure 3 shows the fabricated test cell
assembly. A further fixture was manufactured
to clamp the test cell to the machine bed.
Figure 3 : Fabricated Test Cell Assembly
4.2 Cyclone
Lobo (2002) discusses the use of cyclones
and HEPA filters to capture the particulate.
Principally a single cyclone is utilised with a
second stage HEPA filter. This report will
focus on the investigation of a three phase
cyclone with a fourth stage HEPA filter to
capture any particulate that pass through the
cyclones.
Figure 4 shows the cyclone assembly used in
the experiments. The first stage LOE cyclone
is connected in series to a dual phase
cyclone and HEPA filter from a Dyson DC19
domestic vacuum.

of 21
Figure 4 : Annotated Image of Cyclone Experiment Setup
This is not promoting the use of a domestic
appliance for capturing particulate, more so
that it is a cost effective sub system capable
of removing particulate down to 0.5µm
(Dyson, 2015). Lobo measured the size
distribution of particles when cutting 2mm
mild steel with a 175W laser and noted that
there were zero particulate with a diameter
less than 0.9µm. Therefore validating the use
of the Dyson dual phase cyclone. The volume
flow rate of air in a cyclone is critical in order
for the centripetal force to separate the
particulate from the airflow. Therefore the
suction system from the vacuum was used to
generate the airflow in the cyclone. Reverse
engineering of the dual phase cyclone has
been undertaken to understand the working
principles.
Figure 5 shows an annotated cross section of
a Dyson DC14 dual phase cyclone. This is
very similar to the cyclone of the DC19 used
in the experimentation. The first Dyson
cyclone drops heavier particulate and the
second cyclone drops lighter particulate. A
shroud is incorporated into the design to
prevent large foreign objects such as hairs
passing to the second phase cyclones. The
waste streams for the two cyclone phases are
separated which is necessary to prevent
contamination of the two cyclone phases. The
advantage of a cyclone over a HEPA filter is
that the pores of the filter clog up with debris
and the filter loses its effectiveness.

of 21
Figure 5 : Dyson DC14 Cyclone (Amazon, 2015)
4.3 Particle Analysis
A TSI Optical Particle Sizer 3330 was utilised
for online analysis of the particle
concentration and particle size distribution for
distributions between 0.3µm and 9.784µm.
The sizer samples the particulate through iso-
kinetic sampling. In experimentation the
sampler was moved to different locations in
the cyclone and HEPA filter to analyse
particle size and concentration with respect to
position. The TSI equipment was used to
record a background reading which was later
subtracted from the measured samples to
provide true sample readings.
4.4 Cyclone Assembly Effectiveness
The effectiveness of the cyclone assembly
was investigated using sizing particulate of
different diameters. This procedure generates
a repeatable experiment to validate the
cyclone assembly prior to collecting laser
cutting particulate.
The following sizing particulates were used:
1. 0.9µm Zirconium Oxide
2. 4µm Titanium Dioxide
3. 60µm Hollow Glass Spheres
Previous tests with the LOE cyclone have
shown high efficiency for particulate above
10µm. Therefore for this investigation it was
not deemed beneficial to test particulate
within the 4µm to 60µm distribution.
A petri dish containing a measured quantity of
particulate was held at the inlet of the first
stage cyclone to introduce the particulate to
the airflow.
The iso-kinetic sampler for the TSI optical
sizing equipment was positioned at the
following locations:
1. Inlet of first stage LOE cyclone
2. Outlet of first stage LOE cyclone
3. Outlet of Dyson before HEPA filter
4. Outlet of Dyson after HEPA filter
The mass of particulate collected by the first
stage cyclone and the Dyson cyclones was
measured for offline analysis.
The mass collected by the Dyson cyclones
was measured by calculating the difference in
the mass before and after testing, since
reverse engineering identified the potential
particulate collection areas in the cyclone.

of 21
The cyclone assembly was dismantled and
cleaned between tests to prevent cross
contamination of particulates.
4.5 Test Cell Validation Experiment
4µm titanium dioxide particulate was used to
test the effectiveness of particulate removal
from the test cell. The test cell was connected
to the inlet of the cyclone assembly as shown
in Figure 6.
Figure 6: Test Cell Connected to Inlet of Cyclone
Assembly
The following methods as shown in Figure 7
were used to introduce particulate to the test
cell:
1. Pushing particulate from top slide
2. Particulate on sheet
3. Particulate on sheet with restriction to
test cell inlet
Figure 7 : Methods of Introducing Particulate to
Test Cell
Off line analysis involved measuring the mass
remaining in the test cell.
4.6 Laser Cutting Experiment Setup
Figure 8 shows the laser cutting experiment
setup. The cyclone assembly sat external to
the fibre laser cutting cell. The smooth bore
extraction pipe connecting the test cell to the
cyclone passes through the brush seals at
the back of the fibre laser cutting cell.
Figure 8 : Annotated Image of Laser Cutting Experiment Setup

of 21
4.7 Experimentation Procedure
The laser cutting test pattern shown in Figure
9 was used to investigate two laser
characteristics for the cutting of 0.92mm thick
stainless steel. The shutters of the test cell
were positioned with a gap of 30mm to allow
the laser head to access the work piece.
Figure 9 : Laser Cutting Test Pattern
For both laser characteristics the assist gas
was oxygen and the pressure was 2.5bar.
The two laser characteristics investigated
were:
1. Low power, high velocity cut: Power =
225W. Cutting Speed = 2.5mm/s
2. High power, low velocity cut: Power =
300W. Cutting Speed = 1mm/s
The sampler of the TSI optical particle sizer
was positioned at the inlet of the first stage
cyclone for online analysis. Off line analysis
involved visual inspection and measurements
of the cut.
5 Results
5.1 0.9µm Zirconium Oxide Particulate
Table 1 shows a summary of the collection
efficiency based on the particulate mass
collected for the first stage and Dyson
cyclones. Collection efficiency is the
percentage of the particulate collected
compared to the total particulate introduced
to the system.
Table 1 : Cyclone Assembly Collection Efficiency
Figure 10 shows the particulate collection
points in the cyclone assembly.
Figure 10 : Collection Points in Cyclone Assembly
Figure 11 shows the spirals on the internal
surface of the Dyson cyclones. The spirals
represent the path taken by the particulate
through the cyclone.
Figure 11 : Particulate Spirals in Cyclone

of 21
Figure 12 shows the particulate count as a
function of particulate size for the different
positions of the iso-kinetic sampler discussed
earlier.
Figure 13 shows the particulate count as a
function of particulate size before and after
the HEPA filter.
Figure 12 : Particulate Count as a Function of Particulate Size for Different Locations in Cyclone Assembly
Figure 13 : Particulate Count as a Function of Particulate Size Before and After HEPA Filter.

of 21
5.2 4µm Titanium Dioxide Particulate
Figure 14 shows the particle count as a
function of particle size for different locations
in the cyclone assembly. Since the particulate
diameter was 4µm, the results from the
sample bins below 3.46µm have not been
included.
Figure 14 : Particulate Count as a Function of Particulate Size for Different Locations in Cyclone Assembly
Table 2 shows a summary of the cyclone
efficiency based on the particulate mass
collected.
Table 2 : Collection Efficiency
Figure 15 shows some of the collection points
for the 4µm particulate tests.
Figure 15 : Collection Points

of 21
5.3 60µm Hollow Glass Spheres
As discussed earlier the TSI equipment can
measure particulate between 0.3µm and
9.784µm.
Testing showed that the collection efficiency
was 102.8% based on mass. The first stage
cyclone removed all of the particulate and the
Dyson removed no particulate.
5.4 Test Cell Validation Experiment
The results for the test cell validation
experiment are shown in Table 3.
Table 3 : Particulate Application
5.5 Laser Cutting
The TSI equipment showed that the laser
cutting process produced particulate in the
0.3µm-2µm range only. Figure 16 shows the
particulate count for the 0.3µm-2µm bin as a
function of time for the duration which
includes the laser switching off.
Figure 17 shows the particulate count for the
0.3µm-2µm bin as a function of time for the
high power laser cutting test.
Figure 18 shows the particulate count for the
0.3µm - 2µm bin as a function of time for the
low and high power laser cutting tests.
Figure 19 is a bar chart showing particulate
produced in the 0.3µm - 2µm bin for a
standard laser cutting test. The total
particulate produced for a low power and high
power cut are 81568 and 39786 respectively.
Figure 20 shows a comparison of the low and
high power cut. The figure shows that the kerf
width is approximately the same for both cuts.
Figure 21 shows a comparison of the dross
for low and high power cuts. The average
dross height for the low and high power cuts
is 0.39mm and 0.94mm respectively.
Figure 16 : Particle Count when Laser is Switched off

of 21
Figure 17 : Graph Showing Particle Count as a Function of Time
Figure 18 : Graph to Show Particulate Count for 0.3µm - 2µm bin as a Function of Time for Low and High Power
Laser Cutting Test
Figure 19 : Bar Chart to Show Particulate Produced in 0.3µm - 2µm Bin for Standard Laser Cutting Test

of 21
Figure 20 : Comparison of Low and High Power Cut
Figure 21 : Dross Comparison for Low and High Power Laser Cuts
6 Discussion
6.1.1 0.9µm Zirconium Oxide Particulate
The collection efficiency of the cyclone
assembly is relatively high.
Figure 12 shows that the particulate count for
particulate in the 0.3µm-2µm bin is greater at
the outlet of the first stage cyclone compared
to the inlet of the first stage cyclone. This is
not true since the mass of particulate must be
greater at the inlet of the first stage cyclone
compared to the outlet. There are two
possibilities for this discrepancy. Firstly, the
cyclone assembly was not cleaned between
tests, therefore stagnant particulate in the
cyclone assembly may have been made
airborne by the airflow. Additionally the iso-
kinetic sampler at the inlet of the first stage
cyclone may have been incorrectly
positioned. The sampler was located through
a hole in the top of the inlet pipe
approximately 20mm from the entrance. It is
thought that the sampler was too close to the
entrance and at the incorrect orientation since
the inputted particulate was observed to pass
below the sampler due to the effect of gravity.
Figure 13 shows that the particulate count is
less after the HEPA filter than before for all
particulate sizes. Interestingly the particulate
count for the 0.3µm-2µm bin is negative
which suggests that the HEPA filter has
removed particulate from the background
environment.
6.1.2 4µm Titanium Dioxide Particulate
Figure 14 shows that the first stage cyclone
removes a fraction of all particulate between
0.3µm and 9.784µm. As expected the outlet
of the HEPA filter contains the least
particulate and the inlet of the first stage
cyclone contains the most.

of 21
6.1.3 60µm Hollow Glass Spheres
The results show that the Dyson cyclone was
redundant since the first stage cyclone
removed all 60µm particulate. The collection
efficiency was 102.8%, which cannot be true
since the cyclone assembly is a closed
system. This is discussed further in the
following section.
6.2 Cyclone Assembly Particulate Tests
6.2.1 TSI Particle Sizer Stalling
When the iso-kinetic sampler was positioned
at the outlet of the Dyson before the HEPA
filter it was identified that the TSI particle
sizer was generating errors. Upon diagnosing
the problem it was observed that there was
approximately zero flow rate going into the
TSI equipment. This is because the pump in
the TSI equipment was over powered by the
suction generated by the Dyson. The problem
was rectified by changing the position of the
iso-kinetic sampler.
6.2.2 Build up of Particulate and
Suggestion for Cyclone Re-Design
The collection efficiencies for the cyclone
assembly based on mass for 0.9µm, 4µm and
60µm particulate is 96.73%, 73.73% and
102.8% respectively.
Upon cleaning the cyclone assembly of
contaminants a number of particulate
collection points were identified. The 102.8%
collection efficiency is a result of stagnant
particulate in the cyclone assembly being
made airborne by the airflow. The following
collection points were identified:
 First stage cyclone
 Reducer coupling
 90o
elbow joint
The collection bucket of the first stage
cyclone utilises a lead screw to provide
sufficient force to enable a seal to be made
between the bucket and the gasket at the
base of the cyclone. Upon removal of the
collection bucket an accidental collision
between the bucket and the base of the
cyclone caused a large amount of particulate
to become dislodged and fall into the bucket.
Furthermore the cyclone allowed for the
collection bucket to be incorrectly fitted to the
base of the cyclone. This led to incomplete
sealing between the collection bucket and the
gasket at the base of the cyclone and
significantly decreased the air velocity at the
inlet of the cyclone.
There was a significant build up of particulate
around the inlet, outlet and base of the
cyclone. Initial tests were repeated since
metal particulate in the cyclone from previous
tests were skewing the data. The error
associated particulate build up are a result of
sharp changes in geometries. The particulate
has a greater momentum than air, therefore
when the geometry changes this causes the
fluid flow to change direction and therefore
the heavier particulate is collected at the
internal surface of these geometry changes.
The square edge reducer coupling was
identified as an area of particulate build up.
The reducer coupling could be changed for a
tapered fitting which would remove the sharp
geometry created by a square edge and
reduce the build up of particulate.
Upon cleaning the cyclone of contaminants it
was identified that specific areas were difficult
to clean due to the internal geometry of the
steel fabrication.
The experimentation could have been
improved by weighing the cyclone before and
after each test to account for the build up of
particulate.
Alternatively the first stage cyclone could be
re-designed to remove a large quantity of the
error. The cyclone should be coated internally
with a low friction material such as Teflon to
prevent the build up of particulate on internal
surfaces. Furthermore the collection bucket
should include a location fixture to prevent
incorrect fitment of the collection bucket to
the cyclone. The cyclone should also be
designed to allow access for adequate
cleaning. The cleaning procedure could
involve a wash down and a cleaning cycle in

of 21
an ultrasonic bath to remove particulate. The
cyclone could be cast, 3D printed or injection
moulded to prevent sharp geometry changes
which would be generated by a steel welded
fabrication or a machined part. Domestic
vacuum appliances have caused a large
development in recent cyclone design. These
developments include easy cleaning and the
absence of areas whereby particulate build
up. Injection moulding polycarbonate-ABS
has enabled this to be achieved relatively
simply on a large scale production.
Furthermore injection moulding allows for
smooth internal surfaces with no sharp edges
which could generate stagnant areas and
cause the build up of particulate. Industry
should utilise these developments to
manufacture cyclones of ceramic or metal.
Advances in 3D printing metal could enable
these complex structures to be additive
manufactured.
6.2.3 Theoretical Cyclone Calculations
The airflow inlet velocity of the first stage
cyclone was measured to be 6.5m/s using an
anemometer.
Figure 22 shows the theoretical model for the
cyclone efficiency for the first stage cyclone
with 60µm particulate. The theoretical model
shows that the cyclone efficiency is 8.5%
which is significantly less than that
determined experimentally.
Figure 22 : Cyclone Efficiency for First Stage Cyclone
The geometry of the Dyson cyclone was
compared with the LOE theoretical model and
it was shown that the proportions and ratios
were different.
6.2.4 Test Cell Validation Experiment
The results show that placing the particulate
on a sheet with the inlet of the test cell
restricted was the most efficient method of
particulate extraction from the test cell. In
practice the laser cutting mechanism will
generate airborne particulate therefore the
experiments undertaken are not true
representations. However the experiments
show that generating a restriction to the inlet
of the test cell causes a greater velocity of
airflow in the test cell and therefore results in
a greater particulate removal efficiency.
6.3 Laser Cutting
The radius of curvature of the anti static pipe
created interference issues with the housing
of the fibre laser. Therefore a flexible wire
reinforced hose was used. The problem with
utilising a hose which is not a smooth bore is
that the particulate may build up in the

of 21
stagnant flow areas around the reinforced
wire in the hose.
Figure 16 shows a significant reduction in the
particle count for particles between 0.3µm
and 2µm at 38 seconds when the laser is
switched off.
Figure 17 shows oscillations in the particle
count with time. There are 6 peaks and 5
troughs shown in the graph which represent
the 6 negative X-direction cuts and the 5
positive X-direction cuts respectively. The
particle count should have been the same for
both cuts therefore the assist gas jet focus
must not be concentric with the laser focal
point.
Figure 18 shows that the duration of the lower
power test is significantly less than that of the
high power. Although the particulate count is
significantly higher for the lower power, the
oscillation in particle count observed with the
high power is not observed with the low
power cut.
Inspection of the laser cuts showed that the
dross height was 2.4 times greater for the
high power cut compared to the low power
cut. In terms of cut quality dross is a factor
which is typically driven to a minimum,
however for nuclear applications it is
advantageous for dross to be a maximum in
this case as this reduces the airborne
particulate produced.
7 Recommendations for Further Work
There are a number of areas which require
further development. Listed below are the
recommendations for further work.
1) The measurement of the air flow velocity
at the inlet of the cyclone needs to be
more accurate. This could be achieved
through the use of LDA or PIV.
2) The positioning of the iso-kinetic sampler
at the inlet of the HEPA filter is not
consistent with the other measurements.
Therefore methods to prevent the pump
stalling in the TSI equipment need to be
investigated in order for the sampling
position with respect to the airflow to
remain consistent.
3) The tests on the 0.9µm, 4µm and 60µm
particulate should be repeated using only
the Dyson cyclone.
4) The tests on the 0.9µm, 4µm and 60µm
particulate should be repeated using a
newer Dyson vacuum. This is because the
cyclone technology has improved to
utilise a further stage of parallel cyclones
which will enable smaller particulate to
be extracted from the airflow.
5) Place the Dyson directly at the exit of the
test cell and identify whether the hot
particulate from laser cutting affects the
surface of the polycarbonate-ABS. If the
surface of the polycarbonate-ABS is
affected then consider manufacturing a
cyclone from aluminium using additive
manufacture.
6) Repeat the laser cutting experiment using
smooth bore pipe rather than a flexible
wire reinforced hose to connect the test
cell to the cyclone.
7) Produce detailed designs for an
optimised industrial cyclone. This would
incorporate a low friction surface finish
on internal surfaces, a location fixture to
prevent incorrect fitment of the
collection bucket and be manufactured
using injection moulding to prevent sharp
geometries associated with welding and
machining.
8) Write a method statement for the
cleaning procedure of the industrial
cyclone.
9) Complete laser cutting tests on different
thicknesses of stainless steel test pieces.
10) Investigate the effects of other laser
cutting parameters (assist gas pressure,
assist gas type, focal length).
11) Investigate the effects of surface material
preparation on the particulate produced.

of 21
12) Apply the conservation of mass
calculations to the laser cut and compare
the calculated and collected masses of
airborne particulate.
13) Generate a computational fluid dynamics
simulation of the cyclone prior to
manufacture to assess velocities and
identification of potential particulate
hold points.
14) Position the iso-kinetic sampler at
different locations within the Dyson
cyclone to determine particulate
concentration for different areas.
15) It is believed that the shroud of the
Dyson cyclone is redundant in these
experiments, as the shroud is there for
domestic purposes in order to remove
hair and other large objects. It would be
interesting to remove or modify the
shroud to determine whether it is
possible to improve the cyclone
efficiency.
16) Replace the square edge reducer
coupling with a tapered reducer coupling
in order to reduce the build up of
particulate.
17) Identify the particulate hold points in the
test cell and use this information to
optimise the design.
18) Increase the depth of the honey comb in
order to ensure laminar flow over the
test piece.
19) Identify the optimal position for the iso-
kinetic sampler at the inlet to the first
stage cyclone. This is because sample
results produced from this position were
inconclusive as the particle concentration
was shown to be higher at the exit of the
first stage cyclone compared to the inlet.
20) Identify the most appropriate way of
seeding the particulate into the airflow.
The rate of seeding needs to be
controlled in order to introduce
repeatability and prevent error
generation on the TSI equipment.
21) Identify whether the assist gas jet focus is
concentric with the laser focal point.
8 Conclusions
Offline analysis of mass and online analysis
of particle concentration and particle size
distribution was utilised to investigate the
effectiveness of the cyclone assembly. The
collection efficiencies for the cyclone
assembly based on mass for 0.9µm, 4µm and
60µm particulate is 96.73%, 73.73% and
102.8% respectively. The TSI particle sizer
showed that the cyclone assembly and HEPA
filter removed practically all 0.9µm, 4µm and
60µm particulate from the airflow.
The test cell validation experiment showed
that the highest particulate extraction
efficiency from the test cell was achieved
when a restriction was applied to the inlet
honeycomb.
The cyclone assembly testing with the sizing
particulate highlighted the errors associated
with the build up of particulate. More
specifically the first stage cyclone was
identified as the main source of error in
experiments and therefore classified as a
necessary area for improvement for future
testing. The re-design would incorporate a
low friction surface finish on internal surfaces,
a location fixture to prevent incorrect fitment
of the collection bucket and be manufactured
using injection moulding to prevent sharp
geometries associated with welding and
machining. The development in cyclone
design associated with domestic vacuum
appliances mean that the improvement
criteria outlined above is currently utilised.
Online analysis of the particulate produced
from two laser cutting characteristics showed
that a low power and high cutting velocity
produced over twice the amount of 0.3µm-
2µm particulate compared with a high power
and low cutting velocity. Furthermore it was
shown that the dross height of the high power
cut was 2.4 times greater than that of the low
power cut. Therefore it was concluded that a
high power and low cutting velocity is most
appropriate for laser cutting in nuclear
applications since minimal particulate is
desirable and cut quality is unimportant.

of 21
9 References
Howe, A., 2008. Eurpean and International
Standards on health and safety in welding,
Health and Safety Laboratory, Derbyshire.
Health and Safety. 2008. The Supply of
Machinery (Safety) Regulations. No. 1597..
London, The Stationery Office Limited
Howe, A., 2000. Assessment of Exposure to
Chemical Agents in Welding Fume: Final
Report, Health and Safety Laboratory,
Derbyshire.
Bigony, L., 2007. Risks Associated with
Exposure to Surgical Smoke Plume: A
Review of the Literature, AORN, Colorado.
Pillinger, S.H., Delbridge, L. & Lewis, D.R.
2003. Randomized clinical trial of suction
versus standard clearance of the diathermy
plume. British Journal of Surgery 90: 1068-
1071.
Beswick, A, Evans, G., 2012. Evidence for
exposure and harmful effects of diathermy
plumes (surgical smoke), Health and Safety
Laboratory, Derbyshire.
Steen, W.M, Mazumder, J, 2010. Laser
Material Processing, Fourth edition, London,
Springer
Hinds, W.C, 1998. Aerosol Technology –
Properties, behaviour, and measurement of
airborne particles, 2nd
edition, John Wiley &
Sons
Powell, J, Hafercamp, H, Bach, F, Seebaum,
D, Hampe, A. 1996. Filtration of the fumes
generated by industrial CO2 laser cutting,
Journal of laser applications 8, 241-246
(1996).
BS893:1978, Method for the measurement of
the concentration of particulate material in
ducts carrying gases. 1978
Amazon, 2015. Dyson DC14 AllFloors
Cyclone Upright Vacuum Cleaner, . [online]
Available at
<http://www.amazon.co.uk/Dyson-AllFloors-
Cyclone-Upright-Cleaner/dp/B0007LJO2C>
[Accessed 15 January 2015].
Dyson, 2015. Dyson Allergy, . [online]
Available at
<http://www.dyson.co.uk/allergy.aspx>
[Accessed 15 January 2015].
Gunura, K., 2009. Investigating into the
effects of varying cutting tool parameters on
aerosol particulate generation for remote size
reduction. BEng. Lancaster University.
Lobo, L.M., 2002. Solid Phase By-Products of
Laser Material Processing. PhD.
Loughborough University.
10 Conflict of Interest
There is no conflict of interest.
11 Acknowledgments
The author acknowledges the invaluable
support and information provided by the
following people.
o Daniel Lloyd for providing assistance on
cyclone theory and operation of the TSI
equipment.
o Dave Britton, Mark Capers and Lewis for
their invaluable advice and support using
the fibre laser.
o John Tyrer for providing knowledge and
helping identify relevant research.
o Malcolm Joyce for providing relevant
dissertations from Lancaster University.
o Steve Tarlton for providing assistance on
sampling and filtration techniques.

Final Report - Effects of Laser Cutting Nuclear Contaminated Material - Daniel Evans

Recommended

Recommended

More Related Content

What's hot

What's hot (7)

Similar to Final Report - Effects of Laser Cutting Nuclear Contaminated Material - Daniel Evans

Similar to Final Report - Effects of Laser Cutting Nuclear Contaminated Material - Daniel Evans (20)

Final Report - Effects of Laser Cutting Nuclear Contaminated Material - Daniel Evans