1,7 MB - UAS - United Air Specialists Inc.

United Air Specialists (UAS) push 

developments in the range of oil mist 

and emulsion separation 

Commissioning of ultra-modern test bench 

for electrostatic air filters 

I N D U S T R I A L A I R M O N I T O R I N G 

17

United Air Specialists (UAS) push developments in the range of oil mist 

and emulsion separation 

Commissioning of ultra-modern test bench for electrostatic air filters 

1st issue 05-2009 

Imprint 

Authors: 

Carlo Saling, product manager, UAS United Air Specialists Inc. 

Gerd Munder, head of production department, UAS United Air Specialists Inc. 

Editor: 

UAS United Air Specialists Inc., Branch Office Germany 

Otto-Hahn-Str. 6 | DE-65520 Bad Camberg 

Phone +49 (0) 64 34 / 94 22-0 | Fax -99 

www.uas-inc.de 

Layout: 

IHW Jörn Jacobs & Co. 

Otto-Hahn-Str. 15 | DE-65520 Bad Camberg 

www.ihw-marketing.eu 

Copy, also in extracts, only permitted if consented by the editor. 

2

United Air Specialists (UAS) push developments 

in the range of oil mist and emulsion separation 

Commissioning of ultra-modern test bench for electrostatic 

air filters 

In Germany, coolants are used [1] 

in about 200,000 metal-working 

shops in the scope of chipping 

and chipless production processes. 

They are indispensable in metal 

working and processing. On the 

other hand, coolants bear health 

hazards for the people involved in 

the process when handled carelessly. 

Coolants (KSS) are deemed liquids 

which are used in the production 

processes of chipless processing, 

cutting and machining of materials. 

In the production processes, 

they cool the tool, reduce friction 

between workpiece and tool and 

wear of the tool, and/or remove 

chips among others. 

The variety of applications results 

in many types and different 

compositions of the coolants. 

Coolants can be classified as 

shown in the following figure: The 

coolants in their original state are 

defined as primary substance; the 

secondary substances are developed 

unintentionally during use 

and/or are added. 

[1] VDMA “Cooling lubricants - Fresh air at the 

workplace“, trade association “General ventilation“, 

team ”Aerosols“ 

Coolants 

Non-water-miscible coolants 

(in the past also: cutting oil, grinding oil, 

drilling oil) 

Water-miscible coolants 

e.g. oil-water emulsion 

(in the past also: diluted soluble oil, 

drilling milk) 

Basic materials 

Attendant materials 

Additives 

Reaction products 

Foreign matters 

Microorganisms 

Primary substances 

Secondary substances 

Coolants 

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United Air Specialists (UAS) force development work 

Hazards involved with coolants [2] 

In addition to the general impurities 

at the workplace, vapour, 

smoke, and aerosols are formed in 

the ambient air of liquid coolants. [2] 

This involves the hazard that particles 

may affect the operator while 

the following mechanisms occur: 

Absorption through respiratory 

system: 

Only a small par t of drops 

contained in aerosols with a 

diameter of more than 100 µm is 

normally inhaled. Whereas particles 

with a diameter of less than 

5 µm reach the lower respiratory 

tracts. Drops with a diameter of 

2 to 2.5 µm even penetrate the 

alveoli. 

Absorption via digestive tract: 

Bigger drops deposit in the nose, 

windpipe, and bronchial tubes and 

can thus also be swallowed 

Skin contact: 

The natural protective function of 

the skin is impaired 

As a consequence of the above 

described mechanisms, the following 

effects on the human body 

may occur: 

[2] VDMA “Cooling lubricants - Fresh air at the 

workplace“, trade association “General ventilation“, 

team “Aerosols“ 

Irritant effects: 

Irritation of skin, respiratory tracts, 

and mucous membranes, conjunctivitis, 

vertigo, stimulation, possibly 

euphoria 

Allergenic effects: 

Toxic-degenerative contact eczema, 

allergic contact eczema, rarely 

bronchial asthma 

Toxic effects: 

Alterations of organs, impairment 

of nerves by absorption of 

substances through skin 

Carcinogenic effects: 

Formation of different types of 

cancer as well as tumours of brain 

and respiratory system 

Mutagenic effects: 

Gene mutation by mist of nonwater-miscible 

coolants and nitrosamines 

Further health hazards may be 

involved by microorganisms which 

preferably settle in water-mixed 

coolants. These microorganisms 

are mainly connected to aerosols 

and this is why an efficient separation 

of aerosols is compulsory. 

Germs and funguses may result 

in weakening of the body‘s own 

immune system and cause general 

diseases. 

4

Continuous further development and research for 

improved separation of coolants – why? 

For some years, modern machining 

centres and machine tools have 

been showing a tendency towards 

ever increasing shaft power and 

chipping speeds resulting in higher 

emissions of pollutants and smaller 

particles. 

Due to the fact of progressing 

development in machining, further 

research is also required in the 

separation of coolants in order 

to ensure work protection under 

changing technical framework 

conditions also in future. 

Seen from this angle, the Company 

United Air Specialists Inc. successfully 

commissioned an ultramodern 

test bench at their site in Bad 

Camberg in Germany in spring 

2009 in order to boost its research 

activities in the range of electrostatic 

and mechanic oil mist and 

emulsion filters for the separation 

of coolants. 

Figure 1: Picture of test bench 

5


Design of test area 

The constructional drawing illustrates the design of the test bench. 

7 

6 

2 

3 

1 

1 Aerosol generator 

2 Isokinetic sampling 

3 Aerosol spectrometer 

5 

4 

4 Filter (here: two-step electrostatic filter) 

5 Fan 

6 Control cabinet with frequency converter 

7 Flow meter 

Figure 2: 3D constructional drawing of test bench 

The aerosol generator (type PLG 

2300 by Palas), which complies 

with the requirements of VDI 

directive 3491, produces finest 

mist of liquids (coolants) which is 

introduced in the air flow of the 

test bench. The generator uses 

the Laskin principle: One nozzle 

atomises a test medium (e.g. coolant 

diethylhexyl Sebacat (DEHS) 

or dioctylphthalate (DOP)) by 

means of compressed air from the 

in-house mains. 

To be able to produce high 

concentrations of aerosol of up to 

100 mg/m³ in the test bench, the 

primary pressure of compressed 

air can be set by means of a needle 

valve (1-8 bar ü) and the temperature 

of the test medium can be set 

in the liquid container inside the 

generator (20-80 °C). 

The nominal temperature of the 

test medium is set to the desired 

temperature using a temperature 

probe. Furthermore, a sensor 

monitors the liquid level in the 

container activating a hose pump 

to fill the container automatically if 

the limit is fallen short of for being 

able to perform long-term measurements 

of the filter in the test 

bench as well. 

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Figure 3 shows a typical emission 

spectrum of the aerosol generator. 

The particle spectrum - measured 

with the lubricant DEHS 

- is subject to the Gaussian normal 

distribution curve; the median of 

the number of particles amounts 

to 0,3 – 0,4 µm. When commissioning 

the plant, it was demonstrated 

that the number as well 

as the distribution of particles 

are constant regarding time and 

are reproducible under equal 

test conditions. This particle spectrum 

corresponds to the results 

obtained with modern machine 

tools (lathes, milling machines, and 

grinding machines) with high shaft 

power and thus reflects actual 

operating conditions [3] . 

[3] “Exhaust and filtration of metal working 

fluids emissions on machine tools“ by German 

Federation of institutions for statutory accident 

insurance and prevention (HVBG), ISBN 3-88383- 

714-8, November 2006 

The samples are taken from the 

piping in an isokinetic way, i.e. a 

part of the air flow is soaked up 

by a nozzle and conveyed to the 

particle sensor at the same speed. 

The nozzles are made of stainless 

steel and comply with the European 

Standard EN 13284-1 [4] . 

In addition, samples are taken 

using electrically conductive plastic 

hoses in order to prevent separation 

by electrostatic charge in the 

hoses. Furthermore, it was seen 

to it that the track where samples 

were taken was vertical and short 

in order to prevent coarser particles 

from depositing or segregating. 

[4] VDI directive 2066: “Particulate matter measurement 

- Dust measurement in flowing gases 

- Gravimetric determination of dust load“, Beuth 

Verlag, November 2006 

Figure 3: Particle spectrum of aerosol generator (DEHS) 

Note: Distribution, absolute number of particles and time constancy 

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Figure 4: Isokinetic nozzles 

The sample gas volume is controlled 

and monitored by the control 

electronics (type welas 3000 by 

Palas). The particles are measured 

by optical white light aerosol 

spectrometers (type welas 3000 

by Palas). The particle diameter 

is defined using the intensity of 

scattered light and the pulses are 

counted over a specified period for 

the purpose of obtaining a statistic 

confidence level of the results. 

We obtain a distribution histogram 

with high resolution (cf. figure 3) 

which illustrates the number of 

particles of the samples as a function 

of the diameter. This histogram 

permits the measurement 

of fractional filtration efficiencies 

when a sensor is used on both the 

crude gas and the clean gas side. 

When measuring the particles, 

typical sources of error such as 

border-zone or coincidence errors 

are eliminated thanks to the white 

light source, 90° scattered light 

detection, and T-stop technology. 

White light aerosol spectrometers 

measure concentrations of up to 

100,000 particles per cm³. As the 

filter elements in the test field 

can also be subjected to extremely 

high pollutant concentrations 

Important for sampling: 

Isokinetics 

Suction from the gas flow in the 

pipe is effected at equal speed 

(isokinetic). Thus, a precise concentration 

can be measured. In case of 

suction at higher speed (hyperkinetic) 

the measured concentration 

would be lower than the actual 

concentration due to inertness of 

particles. On the other hand, the 

measured concentration would 

be higher than the actual concentration 

in case of suction at lower 

speed (hypokinetic). 

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of up to 100 mg/m³ which may 

be produced by modern machine 

tools with high shaft power, the 

sample gas on the crude gas side 

is to be diluted correspondingly 

using a dilution system (type DC 

10000 iP by Palas) and a side channel 

blower (type SE3 by Elektror). 

The dilution factor is considered 

automatically in the calculation of 

the crude gas concentration. The 

error of measurement caused by 

the dilution system is < 5 %. 

The test bench serves the testing 

of filters with electrostatic and 

mechanic filter elements. They can 

be tested optionally either with or 

without pre-filter. 

The directly driven fan controls 

the volume flow by means of a 

frequency converter (type Varispeed 

E7 by Omron) and maintains 

the desired nominal value 

(frequency). The latter is matched 

with the actual value through a 

Vortex flow meter (type VA40 by 

Höntzsch) which is factory-calibrated. 

This calibration was checked 

using a Prandtl flow pipe (type 

ManoAir by Schiltknecht). The 

square coefficient of correlation 

of the characteristic curve amounts 

to R² = 0.999. To provide reliability, 

calibration is verified at regular 

intervals. 

The pressure loss of the filter 

elements – in particular essential 

for mechanic filter systems – 

can be recorded and monitored 

by a differential pressure sensor. 

A digital meteorological station 

(temperature, relative humidity of 

air) records the climatic conditions 

in the laboratory. 

In a next step, the test bench will 

be provided with a digital oscilloscope 

to effect high-frequency 

measurements (current and voltage) 

of the ioniser and collector 

in the electrostatic separator. 

Valuable conclusions can then be 

drawn regarding long-term tests of 

prototypes. Furthermore, emulsion 

measurements are planned. This 

requires an insulation/temperature 

setting of the test bench. 

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Collecting efficiency (%) 


Summary 

100 

The test bench allows testing and 

further development of electrostatic 

and mechanic filter cells 

according to pertinent directives. 

Original cells can be tested 

whilst excluding errors of measurement 

as a consequence of 

down-scaling of test filters.[5] 

When designing the test bench it 

was taken into consideration that 

even extreme pollution loads of 

up to 100 mg/m³ can be measured 

and fractional filtration efficiencies 

in the lower sub-micrometer range 

(0.3 to 10 µm) can be determined. 

By indicating the total gravimetric 

filtration efficiency – as usual in 

Figure: Alveolar fraction (A fraction) 

Mass fraction of inhaled particles which penetrates the respiratory tracts (alveoli) 

practice – the quality of a filter 

cannot be evaluated sufficiently 

and misinterpretations may result 

therefrom. 

Thus the test bench also satisfies 

the requirements of modern 

machine tools regarding pollutant 

concentrations and particle spectrums 

with which work pieces are 

machined at high shaft power [6] . 

In particular, aerosols which are 

smaller than 1-2 µm and cannot be 

seen with the naked eye present 

the highest hazards for employees 

for these particles penetrate 

the alveoli and thus get into the 

DIN EN 481 

not respirable 

50 

Tracheo 

bronchial 

dust 

Nose, throat, 

larynx dust 

alveolar 

penetrating the thorax 

respirable 

10 

1 

2 5 10 20 50 100 

Aerodynamic particle diameter (µm) 

Figure 5: 

Total efficiency (hazard) as a function of particle diameter [6] 

[5] “DIN EN 481 – Directive: Workplaces atmospheres; 

size fraction definitions for measurement 

of airborne particles“, Beuth Verlag, 1993 

[6] “Exhaust and filtration of metal working fluids 

emissions on machine tools“ by German Federation 

of institutions for statutory accident insurance 

and prevention (HVBG), ISBN 3-88383-714-8, 

November 2006 

10

loodstream. A precise size cannot 

be indicated for these particles but 

only a size distribution. 

This range is described in DIN 

EN 481 (cf. figure 5). The shown 

curve for the A fraction thus illustrates 

the probability of a particle 

of a certain aerodynamic diameter 

depositing in the alveoli [7] . Thanks 

to the test bench we are able to 

focus on the separation of these 

fine and hazardous particles which 

cannot be measured with conventional 

portable meters. 

Last but not least, the test bench 

permits the in-house development 

of tailored solutions for machine 

tool manufacturers in order to 

present effective and efficient 

filter systems. 

[7] “Was ist Staub“, informative page under 

http://www.bgglaskeramik.de/d/staub-info/ 

definition/index.html by BG Glas und Keramik 

(German trade association for glass and ceramics) 

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Notes 

12

Notes 

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Tel. +49 (0) 64 34 / 94 22-0 | Telefax -99 | info@uas-inc.de | www.uas-inc.de 

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