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ISSN 1350-4789/10 © 2011 Elsevier Ltd. All rights reserved.
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Contents
sealing
ISSN 1350-4789
July-April 2016 www.sealingtechnology.info
TECHNOLOGY
Hydratight’s latest SCT makes critical tasks in
the nuclear industry safer
ISSN 1350-4789/16 © 2016 Elsevier Ltd. All rights reserved.
This journal and the individual contributions contained in it are protected under copyright by Elsevier Ltd, and the following terms and conditions apply to their use:
Photocopying
Single photocopies of single articles may be made for personal use as allowed by national copyright laws. Permission of the publisher and payment of a fee is required for all other photocopying, including multiple or sys-
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News
Hydratight’s latest SCT makes
critical tasks in the nuclear
industry safer 1
Oil collector ring prevents oil
leakage into ship’s engine room 2
Intelligent gasket tagging reveals
flange content 2
Change gasket gains
TA Luft accreditation 2
Seal supply system complies with
API 682 Fourth Edition 3
Dow launches Molykote
brand grease with
double-duty technology 4
Company News
Federal-Mogul receives merger
proposal from Icahn Enterprises 4
Greene, Tweed opens elastomer
centre for semiconductor market 4
SKF secures major contract in the
marine segment 5
Donation aims to encourage more
women into engineering 5
ChemChina acquires KraussMaffei 6
Flexitallic supports growth of
family-owned business 1, 16
Conferences and Meetings News
71st STLE Annual Meeting and
Exhibition takes place in May 6
Publications of Interest
Medium molecular-weight
polyisobutylene market analysed 6
Feature
Oil bearing seals and aircraft
cabin air contamination 7
Recently Published Papers 10
Regulars
In Brief 3 & 5
Patents 12
Events Calendar 16
Contents
sealing
ISSN 1350-4789
April 2016 www.sealingtechnology.info
TECHNOLOGY
Joint integrity company Hydratight
Ltd has designed a piece of technol-
ogy which brings greater safety and
efficiency to nuclear power plants.
The company says that it has already secured
four orders for its newly-launched lightweight
Self-Contained Tensioner (SCT) across the
USA and Asia.
‘The SCT has been in development for two
years and in live tests has reduced typical ten-
sioning time from up to four hours to under
an hour, with 25% less manpower, resulting
in lower potential RAD exposure time and
greatly-reduced reactor downtime,’ explained
Gavin Coopey, Global Nuclear Market Leader,
Hydratight.
This product is described as an advanced, reac-
tor pressure vessel (RPV) stud tensioner. It needs
only a power source – no hydraulic connections
or remote pump-control unit, says the firm.
Coopey continued: ‘In other systems, ten-
sioners must be connected to a central control
unit. Both the new lightweight SCT and our
original Hydratight SCT streamline the whole
process. They eliminate the separate control
unit as each of these tensioners has its own
built-in pumping control system.’
‘Crucially, each lightweight SCT networks to
the other units, and each one displays the read-
ings of the others in use. This means in a typi-
cal set-up, one operator can control all devices.’
According to Hydratight, the lightweight
SCT system is the next step in its already suc-
cessful RPV tensioning and operator safety pro-
grammes. It says that it is 20% lighter than the
previous comparable system, which means that
it is more easily manoeuvred around the RPV.
‘The success of this product to date is testa-
ment to the sophistication of the new technol-
ogy and the business benefits it can bring,’
concluded Coopey.
Contacts:
Hydratight Ltd, Bentley Road South, Darlaston,
West Midlands WS10 8LQ, UK. Tel: +44 121 5050600,
Fax: +44 121 5050800, Web: www.hydratight.com/en/
products/tension/speciality-tensioners
Hydratight Pte Ltd, 83 Joo Koon Circle, Unit 01–03,
629109 Singapore. Tel: +65 6515 4971,
Fax: +65 6515 4972, Email: singapore@hydratight.com
Hydratight Inc, 1102 Hall Court, Deer Park, TX 77536,
USA. Tel: +1 713 860 4200, Fax: +1 713 860 4201,
Email: houston@hydratight.com
Visit us today at:
www.sealingtechnology.info
8
Hydratight Ltd’s latest Self-Contained
Tensioner is 20% lighter than the previous
comparable system.
Flexitallic supports growth of family-owned business
International sealing products man-
ufacturer Flexitallic Ltd is support-
ing the development of a family-run
business based in Warwickshire, UK,
after it reached a distribution agree-
ment that will enable the company
to significantly expand the range
of products that it offers industry.
Continued on page 16...
April 2016 Sealing Technology 7
fEATurE
Oil bearing seals and aircraft
cabin air contamination
The use of compressed “bleed” air for aircraft
ventilation and pressurisation systems com-
menced in military jet aircraft in the late
1940s and was seen as “fortuitous”. However,
early commercial jet aircraft, such as the
Boeing707andDouglasDC8,initiallydid
not take air from the compressor to supply
the breathing/ventilation air, but instead they
relied on drawing air from outside the aircraft
using separate blowers or compressors.
The introduction of synthetic jet engine oils
– replacing mineral oils – was required for the
new higher performing and higher tempera-
ture turbine engines, however, the toxicity was
deemed speculative.
The use of air bled off the compressor (bleed
air) to supply the pressurised and breathing air
supply was utilised on military jet aircraft in the
early 1950s, such as the Boeing B-52 and North
American Aviation F100 Super Sabre using the
Pratt & Whitney J57 engine. This was soon
followed by the French manufactured SudSE
210 Caravelle in 1955 – the first commercial air-
craft to use the bleed air system – and then the
Boeing 727, 737 and DC9 in the early 1960s.
Unacceptable
contamination
It was soon recognised that engine bleed air
used for the air conditioning ventilation
supply was increasingly subject to unacceptable
contamination.
The compressor bearing seals, which were
leaking oil, were identified as the main source
of contamination. Both the military and
civil aviation industry were receiving reports
of adverse effects related to the presence of
smoke and fumes associated with the thermal
decomposition of the engine oils that had
leaked into the gas turbine compressors and
then into the bleed air supply. US military
studies were, therefore, undertaken into the
inhalation toxicity of the heated oils. These
found that the ester-base stocks of the syn-
thetic oils and their pyrolysis products when
exposed to temperatures above 260°C (600°F)
rapidly became very toxic.
The system of utilising the compressor
bleed air to supply aircraft breathing air is
used in almost all commercial transport air-
craft except for the new Boeing Dreamliner
(B787).TheB787usesanelectriccompressor
system, drawing in fresh air directly from out-
side, rather through the engines.
Bleed air (used on most aircraft) is not filtered
before it enters the air supply. Air is diverted
from the mainstream gas path for a variety of
purposes, including cooling, sealing and cabin
pressurisation. A variety of air and oil seals are
required in order to minimise the amount of
engine air used so as to reduce the adverse effects
on power and efficiency of the engine.
Oil leakage seen
in three ways
Oil is supplied under high pressure to all main
shaft bearings, with oil seals required to prevent
too much air leaking into the bearing chamber
and loss of oil out of the chamber. Oil leakage
out of the bearing chamber may cause aircraft
oil pollution, cabin odour or visible smoke with
the use of bleed air.
There is a “general acceptance” that cabin air
can be contaminated by compounds released
from pyrolysed oil from engines and occurs
“with some regularity”.[1, 2] This is increasingly
supported by a wide variety of sources.[3]
Oil leakage is essentially seen in three ways:
• sealbearingfailureorminorsystemsfailures,
includingwornseals;
• sealbearingfailure,maintenance
irregularitiesordesigndeficiency;and
• design.
Both seal failure and maintenance irregulari-
ties are regarded as rare. However, the seal-
ing design requirement to seal the oil in the
bearing chamber across the whole engine
operating range, including transients, is rarely
referenced, but a normal function of engine
operation. Therefore, this background third
category – the design factors involved in the
use of pressurised oil bearing seals – warrants
closer review.
Bearing chamber oil seals are required to
seal across the whole engine operating range,
including transients – momentary changes in
engine operating conditions. However, it is
increasingly recognised that all bearing seals
leak as a design feature of using a pressurised
sealing system, and that the seals are less
efficient during transients.
Improvements in seal design continue and
are recommended. Leakage of oil into the air
supply is seen as a design feature with the use
of compressor-generated bleed air, along with
low-level leakage at various phases of flight
and residual oil contamination.
A few examples that recognise normal
aircraft/engine operation low-level oil leakage
include:
• oilsealleakageisreportedtooccurduring
certain events, such as engine switching,
top of descent, older aircraft with chronic
vapours “continuously leak through seals in
tinyamounts”;[4]
• oilleakingfrombearingscanbeeither
“slowly varying and somewhat continuous
orsporadicandquiteintermittent”;[5] and
• background,lowlevelsofoiladditivesand
other substances are expected in normal
flight.[6]
It is apparent that there are differing views
on how oil leakage from the bearing chamber
may contaminate the aircraft bleed air sup-
ply – that is, as a rare failure or maintenance
problem or low-level chronic leakage as part of
the normal operation using the pressurised oil
bearing chamber and bleed air supply systems.
Therefore, a closer look at the key types of
bearing seals used in aircraft turbine engines is
necessary.
Dr Susan Michaelis PhD, ATPL, Michaelis Aviation Consulting, Horsham, West
Sussex, UK
On board aircraft, the common use of engine compressor, pressurised air to seal the
oil bearing chamber and as a source for the cabin bleed air supply provides a mech-
anism for low-level oil leakage in routine engine operations. Although this problem
was identified in the 1950s with the advent of synthetic jet engine oils, the problem
remains ongoing today with over-reliance on seal failure conditions only.
Sealing Technology April 2016
8
Engine bearing
compartment sealing
The philosophy behind engine bearing com-
partment sealing (Figure 1) involves using pres-
surised air to maintain the bearing compart-
ment at a lower pressure than its surroundings,
therefore inducing an inward flow to prevent
an outward oil leak.
The pressurised oil bearing seals used in
most aircraft today are generally clearance lab-
yrinth seals or mechanical contact face seals –
both of which rely on compressor pressurised
air as part of the sealing function. Both types
of seals are responsive to variations in engine
operating conditions.
Labyrinth (clearance) non-contact seals
(Figure 2) rely on tight clearances and a con-
trolled leakage of air to reduce pressure over
the seal, so as to keep the oil in the sump.
Higher air-pressure on the outside of the seal,
compared with the lower pressure air and oil
pressure in the sump, should keep the oil from
migrating out of the sump over the seal.
Labyrinth seals are often used to seal bear-
ing compartments and are seen as low cost,
reliable, simple and subject to reduced wear.
However, these seals are subject to high air-
leakage rates over the seals and, given the
clearance, oil may therefore leak out with a
reversal of pressure, which means they are not
seen in isolation to provide a complete barrier
to leakage. In addition, labyrinth seals do not
respond well to dynamics with increases in
seal clearances during shaft movements and
transients.
Mechanical positive contact seals, carbon
face seals (Figure 3) rely on precision flat
faces, held in sealing contact by a combination
of the force of a spring and positive system
pressure, to ensure adequate loading of the
carbon elements to minimise leakage and
wear. These seals are also often used to seal
bearing sumps. However, they are regarded as
more expensive, more complex, maintenance
intensive, with a shorter service life and more
subject to wear, particularly during transients.
Carbon seals use a thin film of oil between
the faces. This is typically 1-µm thick, which
is thick enough to provide lubrication of the
contact faces and long life, but thin enough to
minimise oil leakage into the compressor.[7]
This type of seal will leak a very small
amount of oil vapour, estimated between a few
ppm to 10 cc/min.[8] Increased speed and small
increases in clearance between the faces can
cause higher oil leakage over the seal.
Whilst carbon seals are more tolerant of
pressure differentials at varying stages of flight
than labyrinth seals, they are more tempera-
ture critical, with oil coking occurring on the
flat faces, causing distortion with thermal and
pressure effects.
Oil leaks more
than realised
A common aspect of using labyrinth and carbon
contact seals includes relying on compressor-
pressurised air over the seal and, therefore, this
is responsive to variations in engine operating
conditions. In addition, sealing of the bearing
compartments is recognised as being difficult.
Common assumptions associated with the
use of both types of seals are that oil will not
leak out of the sump if the pressure is always
positive – with higher pressure outside and
lower pressure inside the chamber. This positive
gradient is assumed to ensure leakage is always
into the chamber.
It is also often stated that absence of seal/
bearing failure and the avoidance of reverse
pressures will ensure that oil leakage out of the
chamber does not occur. However, the litera-
ture suggests this is not always the case and oil
does leak more than generally realised for sev-
eral reasons, which are summarised below.
• Apositivegradientisdifficulttomaintain
under all operating conditions.
• Oilmayflowoppositetothepositive
pressure gradient with both types of seals.
Pressures generated in the oil film between
the mechanical (carbon) face seals can cause
liquid in the film to overcome the pressure
gradient and leak both with and against the
pressure gradient. [9] Dalton’s law of partial
pressures, in which a gas tries to create a
constant partial pressure, indicates that
high-pressure air will not actually prevent
oil vapour from permeating through the
fEATurE
Figure 1. Bearing sump (ExxonMobil 2009).
Figure 4. The propensity of partial pressures
to cause vapour leakage against the pressure
gradient (Journal of Biological Physics and
Chemistry, Vol 14, 2014).
Figure 2. Fluid and abradable lined labyrinth
seal (‘The Jet Engine’, Rolls-Royce, 2005).
Figure 3. Typical carbon seal (‘The Jet Engine’,
Rolls-Royce, 2005).
April 2016 Sealing Technology 9
fEATurE
labyrinth against the pressure gradient[9]
(see Figure 4).
• Reversepressure(higherpressureonthe
chamber side of the seal than outside) and
changes in pressure gradients do occur at
various transient phases of flight, allowing
leakage in the opposite direction.
Industry recognition of seal leakage as a
function of design includes: ‘Increased oil
leakage may occur when the engine or APU
is started and the seals are not at operational
pressure and temperature or during transient
operations such as acceleration or deceleration.
Some systems rely upon internal pressure to
maintain the sealing interface, which may open
up on shut-down allowing some oil to exit the
oil wetted side of the seal. Upon start-up, the
oil will be entrained into the air entering the
compressor, with the seal interface again estab-
lished once the engine internal pressure returns
to operating norms.’ [10]
The volume of leakage for both seal types
depends on the seal design, clearance and
pressure differential across the seal – with a
face seal allowing considerable leakage should
the face open with the reverse pressure,
unless this is taken into account at the
design stage.[9]
Just about all known seals will leak – with
seals designed to limit leakage and no such
thing as a seal that does not leak – even if a
very small amount, perhaps an emission occurs
rather than leakage.[9]
Zero leakage is said to be an oxymoron.[11]
Only very small amounts of oil need to leak
to generate a noticeable cabin odour[12] and
it will be possible to smell oil before high oil
consumption is noticed.[13] Light oil contami-
nation – well below permissible leakage levels
– is often difficult to confirm during inspec-
tion procedures.
The aviation industry is seen as unique
in that environmental aspects drive sealing
requirements as opposed to regulatory emission
limits, as occurs in other critical industries, and
the general environment.[14]
Customer satisfaction – a cabin free of smells
– and performance parameters drive aerospace
sealing technology.[11, 14] Where emission lim-
its apply, single, double or tandem seals may
be used. However, few limits apply to the aero-
space industry where leakage may be defined as
10 000 ppm or as a visible mist.[14]
Low-level leakage
The question of low-level leakage, well below
the permissible engine oil consumption level,
is at the heart of the issue, with some suggest-
ing that oil leakage refers to amounts above
the manufacturer stated permissible leakage
rate, identified purely to prevent in-flight
shutdown.
Lower-level leakage, or what some may call
emissions, is suggested by some to be not seen
in the same light and importance.
The major part of oil consumption is per-
missible leakage past seals, oil leaks and escape
of mist or aerosol through the oil system
breather.[15, 16] Over the years there has been
awareness within the oil sealing community
that the oil seals were subject to leakage. Some
examples include statements such as: “carbon
sealswillalwaysleakasmallamount”;“shaft
seals must function as seals not flow restric-
tors”;“air/oilsealsmustbeimprovednow”;
“future research needs to include transient
behaviourofseals”;and“shaftsealtechnol-
ogy has not kept pace with advances in major
engine components”.
Conflicting views
There are conflicting views on which of the
commonly used seal types are more effective,
with some suggesting conversion from laby-
rinth seals to mechanical carbon seals, given the
higher labyrinth air leakage rates. OEMs are
said to be satisfied with labyrinth seals to seal
many bearing sumps for many years to come.
Improvements in seal design are available,
including brush seals and other advanced seal
types.[11] Axial lift mechanical seals are sug-
gested to have a number of benefits, including
no oil loss in reverse pressures – eliminating oil
pollution in the cabin.[17] Whilst some aspects
of seals are suggested to have come a long way
in recent years, [8] the concerns about oil fumes
in the aircraft cabin remain ongoing.[3,18&19]
Other factors
There are various factors related to exposure
to oil fumes and other aircraft fluids that can
enter the air supply via the bleed air system.
These are summarised in the sections below.
Hazardous substances
The substances in the oils and fluids are classi-
fied as hazardous under the EU Classification
(CLP) and REACH regulations, with one
substance listed as a Substance of Very High
Concern (SVHC) under REACH article 57.
Hazardsincludeirritant;sensitiserandneu-
rotoxiceffects;geneticdefects,harmtothe
unborn,andinfertility;verytoxicbyinhala-
tion;drowsiness;dizziness;asthma;breathing
difficulties;andsuspectedcancer.
Additionally, a number of substances are
listed as endocrine disruptors. These sub-
stances attract a wide variety of adverse effects
under the various official databases, including
International Chemical Safety Cards (ICSC)
and Hazardous Substances Data Bank (HSDB).
Many of these are the effects that are com-
monly being reported.
Flight safety
There is a wide range of organisations recog-
nising that exposure to these substances in
flight can compromise flight safety: A 2015
International Civil Aviation Organization
(ICAO) guidance circular reports that ‘par-
ticular concerns have been raised regarding
the negative impact on flight safety when crew
members are exposed to oil or hydraulic fluid
fumes or smoke, and experience acute symp-
toms in flight.’
Impairment associated with exposure is
documented at levels around 32%, despite
wide recognition that crews are frequently
not reporting fume events and crews are not
always acting appropriately subsequent to
exposures.[3]
Adverse health effects
The published literature supports that a wide
variety of adverse health effects, associated
with fume events, is being reported. Effects are
broadlycategorisedasrespiratory;neurologi-
cal;neuropsychological;cardiovascular;general
effects,includingfatigue;chemicalsensitivity;
gastrointestinal;andtheemergenceofselected
cancers.
Of 274 UK pilots who participated in a
health survey, focusing on a particular aircraft
type acknowledged for higher than average oil
seal leakage, 13% were retired with ill health
or deceased. The findings were consistent with
exposure to jet oils, and fluids including organ-
ophosphates (OPs) and supported the emerging
discrete occupational and public health issue,
termed “Aerotoxic syndrome”.[3]
Exposures
A number of studies undertaken into OPs in
the engine oils have identified tricresyl phos-
phate (TCP) in air, swab and high-efficiency
particulate air (HEPA) filter samples in normal
flights, without fume events, ranging from
17–95% of samples/flights undertaken.
Frequency
Fume events are often said to be very rare.
However, a UK Government sponsored com-
mittee suggested that such events were being
reported by pilots in 1% of flights.[20]
Sealing Technology April 2016
10
fEATurE/rECENTLY PubLISHED PAPErS
A review of US Government databases
reports 2.1 events per 10 000 departures, along
with recognition of under-reporting[21] widely
noticed elsewhere. However, there is increasing
recognition that background or low levels of
the fluids substances are being found routinely,
supporting the suggestion that low-level leakage
occurs as a function of design and operation
using the bleed air system.[3]
Science
The literature supports an increasing number
of studies that have been done, or are currently
on-going, indicating concern with exposure to
the substances in the lubricants.
In one example, a University of Washington
study on biomarkers associated with triaryl
phosphates (TAPs), including TCP, identified
that one of the commercial formulations of TCP,
DURAD 125, is inhibiting a number of enzymes.
A German environmental research centre
study has identified that functional neurotoxicity
is observed with very low TOCP (isomer of TCP
or tri-o-cresyl phosphate isomer) concentrations,
and in the absence of structural damage.
Industry initiatives
Whilst studies into the effects of exposure to
the synthetic lubricants commenced in the early
1950s, they have continued to increase in
number over the last one to two decades.
A few on-going examples include:
• twoEASA-sponsoredstudiesintothecabin
airqualityandoilpyrolysis;
• REACHreviewofTCP;
• ICAOfumeeventsguidancecircular;
• IATAmedicalresponseguidancetofumeevents;
• CENcabinairqualitystandarddevelopment;
• EUCleanskydevelopmentofelectric
compressor for the environmental control
system(ECS);and
• twocasesbeforetheUKCoroner’sCourt.
The way forward
Some continue to suggest that there is no
evidence of a link between exposure to the
fumes and adverse effects and that the term
Aerotoxic syndrome has not been medically rec-
ognised as yet. However, the evidence available
is extensive and a toxic mechanism cannot be
ruled out and acute effects have been officially
recognised with long-term effects reported.[18]
Therefore, it would make complete sense
to enact a variety of solutions that do exist, or
could be implemented. These include bleed-
freeaircraft;betteroilseals;filterorcleanthe
engine/APUbleedair;providedetectionsys-
tems;bettermaintenance;andlesstoxicoils.
Importantly, seal providers should be brought
in at the start of the design process.
It is clearly recognised that the oil seals do
leak or emit low levels of fluids. These low
levels, clearly below the permissible oil con-
sumption level, have been regarded as negligible
and safe. The focus has been on secondary air
leakage and its effect on engine performance,
rather than lower levels of oil leakage – yet
awareness of the lubricant leakage does exist.
There has been reluctance by the OEMs to
change seal types, address low-level leakage and
implement more advanced sealing technology.
However, given that most current commercial
aircraft use the compressor pressurised air for both
sealing the oil bearing chamber and the cabin air
supply, this common path cannot preclude low-
level leakage of oil in normal engine operations.
It is no longer possible to suggest oil leak-
age may only contaminate the air supply when
bearing/seals fail or are not working as intended.
Given the six-decade-old history of oil leakage
into the air supply, low-level leakage in normal
operations and the evidence rapidly growing, the
above solutions need to be implemented.
References
1. AAIB(2013)AAIBBulletin:5/2013;
D-AIRX;EW/G2012/10/12.
2. AAIB (2004) 1/2004 (EW/C2000/11/4)
BAe 146 G-JEAK.
3. Michaelis S., PhD Thesis, ‘Health And
Flight Safety Implications from Exposure
to Contaminated Air in Aircraft’ UNSW,
Australia (2010).
4. de Boer et al. Chemosphere, 9 June 2014.
5. Overfelt ACER – Airliner Cabin
Environment Research. Proposed Test
Plans for a Study of Bleed Air Quality in
Commercial Airliners, June 2013.
6. Spengler. J.D. et al. In-flight/onboard
monitoring: Report no: RITE-ACER-
CoE-2012-6 (2012).
7. Flitney, R., ‘Seals and Sealing Handbook’,
5th edition (2007).
8. Boyce,M.,‘GasTurbineEngineering
Handbook, 4th Edition (2011).
9. Flitney, R., Journal of Biological Physics
andChemistry14,85–89(2014).
10. SAE Society of Automotive Engineers,
Aerospace Information Report
AIR4766/2 (2005).
11. Chupp, R. et al., Sealing in Turbomachinery,
NASA/TM-2006-214341 (2006).
12. Airbus, ‘A Clean APU Means Clean Cabin
Air‘ FAST #52 (2013).
13. SHK Statens Haverikommission,
Report RL 2001:41e on 12 November
1999(2001).
14. Hendricks, C. Environmental and
customer-driven seal requirements. Seals
Flow Code Development-93 NASA
CP 10134 p 67 (1993).
15. Edge, R. and Squires, A., ‘Lubricant
Evaluation and Systems Design for Aircraft
Gas Turbine Engines’ Rolls-Royce, SAE
690424, 1969.
16. ExxonMobil, Jet Engine Oil Consumption.
Tech Topic. 2014.
17. Tran, H. et al. High-performance Lift
Augmentation Dynamic Seals for Turbine
Bearing Compartments, Sealing Technology
2004 (January 2004) pp 5–10.
18.UKCommitteeofToxicity(COT),Position
Paper on Cabin Air. England (2013).
19. German Federal Bureau of Aircraft
AccidentInvestigation,BFU803,1–14
(2014).
20. UK Committee on the Toxicity (COT),
Review of Cabin air. Final Report. (2007).
21. Shehadi, M., et al. (2015). Indoor Air,
pp. 1–11.
Contact:
Dr Susan Michaelis PhD, ATPL, Michaelis Aviation
Consulting, Office 2, The Courtyard, 30 Worthing Road,
Horsham, West Sussex RH12 1SL, UK.
Tel: +44 7880 554 551,
Email: susan@susanmichaelis.com,
Web: www.susanmichaelis.com
(This article is based on a presentation by
the author at BHR Group’s 23rd International
Conference on Fluid Sealing that was held in
Manchester, UK, on 2-3 March 2016.)
Recently
Published Papers
• J.StarcevicandV.L.Popov,BerlinUniversity
of Technology, Berlin, Germany, and Tomsk
StateUniversity,Tomsk,Russia;andR.Pohrt,
Berlin University of Technology, Berlin,
Germany: ‘Plastic properties of polytetrafluor-
oethylene (PTFE) under conditions of high
pressure and shear’, Wear, Volumes 326–327,
15 March 2015, pages 84–87. The authors
of this study investigated, experimentally, the
behaviour of a thin sheet of polytetrafluoro-
ethylene (PTFE) between a steel plate and
a cylindrical steel indenter under combined
action of a high normal force and torsion.
Under these actions the PTFE layer is par-
tially squeezed out of the contact area. The
thickness of the remaining layer is studied
as function of the applied normal force, the
torsion angle and the radius of the indenter.
