All posts by Paul Edwards

Ascott corrosion testing suite at Accelerated Weathering Laboratory.

We are pleased to introduce our extended corrosion testing capability using the Ascott CC, XP and IP series of cyclic corrosion testing chambers allied to an Ascott air conditioning unit which enables fast cooling between segments from ambient to -20C.

Due to increasing demand for test profiles such as Volvo ACT II*, Ford CEPT 00.00-L467*, VW PV1210 and SAE J2334, AWL Ltd have chosen Ascott corrosion testing chambers due to their precise control of temperature and humidity, ease of programming, pleasing aesthetic low level load design and customer service.

For more information regarding our increased capability for cyclic corrosion and salt spray testing please contact us.

*manual method of salt spray application.

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UKAS accreditation for additional UV Weathering and Taber abrasion tests for coatings.

AWL are pleased to announce additional scope for its UV weathering and Taber abrasion testing capability.  ISO 16474-3:2013 specifies methods for exposing coatings to fluorescent UV lamps, heat and water in apparatus designed to reproduce the weathering effects that occur when materials are exposed in actual end-use environments to daylight, or to daylight through window glass. The coatings are exposed to different types of fluorescent UV lamps under controlled environmental conditions (temperature, humidity and/or water). Coatings are exposed to different types of fluorescent UV lamps of specific narrowband wavelengths under controlled environmental conditions (irradiance, temperature, humidity and / or water spray). Different types of fluorescent UV lamp may be used to meet all the requirements for testing different materials. Different types of fluorescent UV lamp may be used to meet all the requirements for testing different materials. Evaluations of results are covered by various parts of the ISO 4628 standard. General guidance is given in ISO 16474-1. NOTE Fluorescent UV lamp exposures for plastics are described in ISO 4892-3. Fluorescent UV lamp exposures for plastics are described in ISO 4892-3 for which AWL are also accredited.

ISO 7784-2:2013 / BS 3900:E14 specifies a method for determining the resistance to abrasion of coatings, for which two loaded, freely rotatable but eccentrically arranged abrasive rubber wheels affect the coating of the rotating test specimen. Rotary Taber abrasion testing at AWL is in high demand due to the ability to provide very accurate relative abrasion performance data. AWL are also accredited by UKAS for testing in accordance with ASTM D4060.

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ISO 9001 audits completed for 2016-2017

Another ISO 9001 audit with zero non-conformances. Well done to all that helped us achieve this. Challenge now is to conform the new version which takes into account risk analysis of the business both technically and financially. ISO 17025 audits (UKAS accreditation) due shortly so none of us are sitting on our hands! Thanks again to all at AWL for your contributions. Paul Edwards, Company Director.

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Local College Asks “What causes corrosion in metals and how do we stop it?”

The Accelerated Weathering Laboratory were pleased to have been approached by a local college to provide an idiots guide to basic corrosion mechanisms, their causes and how to stop it or slow it down to manageable levels when using cheap materials like low carbon steel. The questions were also asked ‘What is Accelerated Weathering?’, and curiously ‘Do we still need Metallurgists?

The audience was to be primarily aimed at BTEC, HTEC students and undergraduates studying Materials Technology as a part of their Mechanical Engineering courses.

The problem for me is that corrosion is such a complex subject. It would be easy for me to send a student to sleep within the first few minutes if I started rattling on about the ‘Galvanic Series’ or ‘ Electrochemical reactions’……………….……so I won’t!

I did an interview back in the day for Granada TV (remember them?) when they were making a programme about the Forth Railway Bridge in Scotland and why it has survived the ravages of the weather for almost 130 years in a very exposed and rainy part of the world despite being made of steel?

Take a peek at my draft script for the interview below. It’s about as basic as it comes and particularly useful at 3am when you can’t sleep. So make yourself a hot milk, turn down the lights and read on……………….…..Night night!

 

Q. Why does metal corrode

A. Moisture and air. The interaction of hydrogen (from the moisture) and oxygen (from the air) starts a reaction at the surface of the steel known as the galvanic cathodic reaction.This produces a by-product called Iron Hydroxide which we all know as Red Rust.

The red rust formed is non-protective since its volume is greater than the metal from which it is formed, so it is full of holes and cracks which allow more moisture and more air to reach the fresh metal below so further corrosion takes place.

Stop the water (held in the air, rain and dew) or stop the oxygen (from the air) – and the anodic / cathodic reaction cannot take place and the corrosion will stop. Easier said than done!

 

Q. Why is corrosion a problem for bridges?

A. Primarily due to extreme exposure to the elements, but also due to their cyclic loading. Whether it is a footbridge, and road or railway bridge traffic will produce cyclic loading stresses within the structure. Corrosion will often form pits. These pits can act as initiation points for severe concerns such as fatigue cracking. Combine fatigue cracking and the corrosion, the structure is doomed to failure.

 

Q. What sort of things cause corrosion?

A. We have already mentioned that moisture and air are required. We must remember that moisture is present in air. Air can also carry any number of contaminants, namely salt (if your structure is near to a coastal area) or industrial contaminants like sulphur, nitrates and chlorine.

These air-bourne contaminants speed up that galvanic reaction which will increase the corrosion rate and significantly and reduce the service life of the structure or component.

 

Q. What do engineers do to stop corrosion?

A. In plain carbon steels, they need to do stop the moisture and/or the air from coming into contact with the exposed steel.

In other words, they need to stifle that galvanic reaction. A popular way to do this is to provide a barrier coating over the surface of the steel. These can be simple or complex paint systems, or more robust coatings such as plating or galvanising.

Another way to prevent corrosion would be to play around with the chemical composition of the steel.

For example, if the chromium content is raised typically around 13 to 18% (along with other elemental changes to maintain strength and ductility) a Cr rich oxide layer is naturally formed when exposed to the oxygen in the air.

This provides its own natural barrier coating protecting the steel from tarnishing and further corrosion – hence their term Stainless Steels.

The downside is, these materials are more expensive than plain carbon steels and are sometimes difficult to fabricate.

 

Q. Why is it important to understand metal and what it does over time?

A. Over time structures made from metal experience a wide variety of stresses, some of which are quite complex. They can include tension (pulling), compression (swashing), torsion (twisting), or shear (cutting).

These combined stresses can produce changes in the microstructure which can reduce its service life.

When choosing a material for a given application, the engineer and metallurgist must fully understand what stresses are involved and work within the limits of the material which will include a significant safety factor.

 

Q. What does Galvanising mean?

A. Galvanising means ‘dipping steel into molten Zinc’ to provide a barrier coating over the surface of the steel.

 

Q. What does Galvanizing do to the steel?

A. Galvanising does 2 things to the steel:

    1. Provides that barrier coating protecting the underlying steel from moisture and air.
    2. Provides a ‘sacrificial’ coating to the steel.  At first, this sounds alarming, but the corrosion products of Zinc actually provide extra corrosion protection. This is how it works. Zinc (the primary component of galvanising) has a lower oxidation potential than Iron – i.e. it will corrode quicker than steel, but at a much slower rate protecting the underlying steel as the zinc corrosion cycle continues.

 

Q. What is a sacrificial coating?

A. Being a reactive metal, zinc readily forms a thin protective coating of Zinc Oxide when exposed to air. When exposed to moisture that Zinc oxide layer reacts to form Zinc Hydroxide.

Upon evaporation or drying of the moisture, the Zinc Hydroxide reacts with Carbon Dioxide in the air to form Zinc Carbonate on the surface of the Zinc layer.

These complex layers provide excellent protection to the surface of the Zinc, and in addition will bridge any scratches or damage to the zinc layer that may have exposed the steel.

 

Q. The Forth Bridge isn’t galvanised. How come it has lasted so long?

A. The Forth Railway Bridge has been operational since 1890. The reason it has lasted so long is because it has been continuously repainted so providing a barrier coating to the underlying steel.  Due to the local climate, there are only 90 days available for painting. This high maintenance schedule has not been neglected over the years which explains its conservation up to the present day. I would imagine almost 50% of the total maintenance budget is consumed by the painting costs.

There is a saying that ‘You will never finish painting the Forth Bridge’ because as soon as you finish, it is time to start all over again!!

 

Q. Do we really need Metallurgist’s

A. The short answer is a definite yes. Metallurgy was often thought as an old fashioned subject no longer required by the modern engineering sector. Back in the 1980s, many UK companies replaced the Works Metallurgist with new shinny graduate design engineers that were skilful in the design aspect but sadly lacking in the understanding of metals and their dynamics on a molecular level. In my own work experience these so called ‘new wave’ design engineers were so wet behind the ears they couldn’t wear glasses! Sorry about that, I couldn’t resist! This loss of this skill set resulted in many failures in the field. Lessons have been learned and these days design engineers work closely with the Metallurgist at every level to provide greater confidence in quality assurance.

 

Q. Why do we use Accelerated Weathering Tests?

A. We are trying to mimic the effects of real time exposure tests that sometimes take years to complete. We achieve this by subjecting a part or test panel to aggressive environments in order to accelerate the natural corrosion or degradation process over a much shorter length of time for practical purposes. It’s important to understand that no test can guarantee the useful life of coatings, and there is no real-time correlation due to all the variables associated with product placement and natural weathering but Accelerated Weathering Tests can help us predict how long a coating will last in its service environment.

 

Q. What do these tests show you?

A. The tests can show us whether a coating is able to withstand certain environmental conditions or test criteria and still maintain their mechanical properties and performance requirements after the required exposure period.

These conditions can be a combination of extreme humidity, either wet or dry, salt fog and other complex electrolytes at various concentrations and temperatures.

We can also accelerate the effects of sunlight damage using special lamps to simulate either full or part of the sunlight spectrum. Degradation of materials due to sunlight is of major concern on its own, but can also accelerate the corrosivity of any material particularly paint systems and polymers.

End.

                ‘Prefer counting sheep!’………………………………………………………..Zzzzzzzzzzzzzzzzzzzzzzz

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Printed circuit boards showing signs of corrosion? Think Dew Point!

We currently have a number of clients trying to establish why their PCBs and other electrical conductors are showing signs of corrosion. The problem boards we are testing are located within enclosures either by the sea or close to poor air quality regions due to industrial stack emissions in high humidity geographical locations.

One can be forgiven for assuming accelerated corrosion was due to the in-service location by the sea (increased airborne salts) or to sulphate and nitrate air contamination from heavy industrial areas causing an increase in air moisture acidity including acid rain.

Although these factors can indeed increase the rate of corrosion and weathering, consideration to the dew point may be the root cause of these corrosion mechanisms due to the inverse relationship between temperature and humidity (Relative Humidity or RH).

The dew point is the temperature when the surrounding air can no longer hold the amount of moisture. As the air cools during the evening and night it condenses initially as tiny droplets onto surrounding surfaces. This is a particular problem if PCBs are housed within an enclosure (perhaps IP rated) with no form of forced air flow or other mechanism to provide adequate ventilation. Examples are cash point machines, parking meters, petrol pump control panels, electrical sub-stations, rail track point change DUTs, etc..

We have reproduced the dew point effect within poor ventilated enclosures many times in our climatic chambers when a pre-programmed test profile simulating a typical tropical climate of 40oC and 80 – 90% RH for 12 hours followed by 20oC and 50% RH for 12 hours – similar to that of day and night at geographical locations such as Florida USA and the South East Asian tropics.

This test profile in our experiment was repeated for 10 cycles representing 10 days and nights.

Once the climatic chamber had reached the 40 / 85, a simple Tupperware container was opened for 10 seconds then closed allowing the air at 85% RH into the container. This container, once closed had poor ventilation.

All is fine for 12 hours while the temperature remains constant, but as soon it drops by 15 – 20oC (as it does at night) the saturated trapped air begins to condense as visible water droplets form on the inside of the container.

No salts or other air contaminants were introduced during these experiments. The situation within the containers was helped when the lid had was 20% open. (Improved ventilation – less water droplets formed).

Perhaps we should repeat this simple experiment with a new PCB placed inside our Tupperware containers perhaps with a small piece of coiled copper wire or tube and watch them turn white and green!!

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Accelerated weathering correlation statements – A risky marketing strategy.

An initial enquiry for UV testing goes something like this:

Dear Accelerated Weathering Laboratory Ltd.

Our marketing department has requested our literature should state that our product is capable of withstanding 2 years outside exposure without significant fade. We believe our products are photo-stable over this period so we require an accelerated weathering test programme to prove this.

As 500 hours exposure is equivalent to 1 year outside, please would you quote us for 1000 hours exposure in accordance with BS EN ISO 4892 part 2. Your test report should state that our mouldings are photo-stable over a min period of 2 years if they have a dE shift less than 2.

Regards,”

Fudgit and Bodge Mouldings UK Ltd.

 

Now………. There are no short answers to this one without going into ‘geek mode’ so please accept my apologises and find the actual reply from AWL by return email below:

 

FAO Mr Fudge and Mr Bodge.

Thank you for your enquiry concerning accelerated weathering testing.

I am concerned you have made a definitive correlation statement regarding accelerated weathering tests and real time correlation.

At the set point irradiance level, BP temperatures and humidity levels of ISO 4892-2 I do not agree with the 500 hours = 1 year statement. Our experience with many different materials suggests correlation to be in the region of 1000 – 1500 hours depending on geographical location and local climatic conditions.

Please be aware that correlation statements in marketing literature should be used with extreme caution and that AWL Ltd would NEVER underwrite such a statement. If you do decide to take this route, please ensure you include a robust disclaimer!!

 It is our view that colourfast / photo-stability performance statements should be based on the test cycle, the exposure period and acceptance criteria usually based on dE shift and / or ISO 105 grey scale assessments.

 For example, Product X – Weathering performance standard is: BS EN ISO 4892-2 : 2012 – Cycle 1 – Method A – 1000 hours – dE shift <2 / ISO 105 A02 = 4 max. These are preferred ‘Performance Standard Statements’ recommended by AWL Ltd and similar is required from the BBA.

 AWL can provide a full explanation / interpretation of the above statement if required.

We can quote you for a 1000 hour test, but we cannot make any statements within the test report regarding +2 years of guaranteed photo-stability.

Sorry to be so negative, but I would not be doing my job properly if I do not make you aware of the complexities of accelerated weathering and the dangers of litigation using real time weathering correlation statements for products going into the marketplace during this contract review discussion.

 

Kind regards,

Paul Edwards.

Technical Director

Accelerated Weathering Laboratory Ltd

www.awlltd.co.uk

 

Phew!

My response was a bit ‘War & Peace’ but hopefully it will educate those new to accelerated weathering in terms of its limitations and how best data can be used.

It is our view that any test house making correlation statements should only be doing so as a guide for costing advice and NEVER FOR warrantees or marketing literature statements.

 

Disclaimer: Although our email response was real, the recipient company name and personnel are fictitious to protect the innocent (just to show that although I can turn into a geek I still have a sense of humour which is important in this business). Any similarity to a company called Fudgit and Bodge Mouldings UK Ltd is by unfortunate coincidence only. No plastic mouldings or marketing people were harmed during the publication of this newsletter. Smile PJE.

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Taber abrasion data from AWL Ltd verifies improved wear resistance of new flooring lacquer.

You know what it’s like. A lacquer manufacturer provides marketing literature or statements over the phone suggesting their product is harder wearing than the competition.

The question that should be asked is ‘On what data do you base that statement?’ Upton Wood Flooring based in Oxfordshire showed due diligence by asking AWL Ltd to provide independent testing to establish the relative wear resistance of 3 lacquers from different manufacturers on their wood flooring samples and they were in a desperate hurry for results!

Upton contacted AWL Ltd on a Monday for initial contract review discussions and it was clear test protocols were not available and a starting point needed to be established by AWL Ltd.

Despite this lack of information, they needed to be going into production with the best lacquer by the end of that week!!

To that aim it was agreed that prepared samples were to be delivered by hand to AWL on the Tuesday.

Testing was carried out on the Wednesday using our experience to provide the correct choice of abrasive wheel, load and number to cycles to prevent wearing through the lacquer during the test.

Results were completed, reviewed and reported in accordance with ASTM D4060 on the Thursday and the data was conclusive.

Production of flooring protected by the best lacquer took place on the Friday as scheduled with added confidence the correct choice had been made.

Upton Flooring were happy to say the least, and AWL Ltd were pleased to have helped.

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Accelerated Weathering Laboratory Ltd celebrates its 10th year of Materials Testing

As AWL Ltd celebrates its 10th year in business with year on year steady growth in terms of turnover and profits, I would like to take this opportunity to thank all of our clients, both UK and overseas for their continuous business and support.

I would also like to thank our small team of dedicated staff who have provided the efforts required to maintain this growth by response to demand in a timely and efficient manor in accordance with our ISO 17025 / ISO 9001 quality systems and policies.

I would also like to thank our key suppliers for their support over the past 10 years.

Paul Edwards, Technical Director, Accelerated Weathering Laboratory (AWL) Ltd.

 

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Help! What’s the difference between LRV, LAB and ΔE values ???

We are often asked to provide LRVs and / or CIE colour-space values with Delta E (ΔE or dE) after accelerated weathering tests to quantify photo stability performance. However, these three sets of numbers are often misunderstood or not understood at all!

We would like to shine some light on the matter (pun intended) and provide a very basic understanding of their differences and how best they can be used.

LAB CIE colour-space readings and Delta E (ΔE)

The CIE LAB colour-space model is a complex mapping system that uses tristimulus (a combination of 3 colour values close to red, green and blue) which are plotted as a 3D space. When these values are combined they can reproduce by providing coordinates for, any colour the human eye can perceive.

Deltas E is defined as the difference or change between two colours within LAB colour space and are used in our laboratory for quantifying photo stability performance after accelerated weathering testing. LABs are best used as raw data for calculating Delta E values to provide a measure of colour shift in any direction after UV exposures and are particularly useful for pigment manufactures when a primary colour may degrade from a secondary colour changing it completely.

For example, if a secondary colour like green is manufactured from a mix of primary colour pigments blue and yellow, the LAB coordinates will show whether it is the blue or yellow pigment (or a combination of both) ‘burning out’. This will identify ‘weak pigments’ should there be even a subtle colour shift.

Please also be aware that although Delta E values provide us with a number to quantify colour shift, the perception of colour change for the same dE value will be strong in a grey scale, but weaker in some colours.

Light Reflectance Values or LRVs

Light Reflectance Values (LRVs) describe the quantity of visible light reflected by a surface in all directions when illuminated by a light source. The LRV is similar to (not the same as) the CIE colour space direction ‘L’ from black to white.

LRV measurements are used to establish how much light a particular colour reflects, and conversely how much light is absorbed. LRVs are reported as percentage values from 0% to 100%. Zero assumed to be absolute black and 100% assumed perfectly reflective white. The instrument is calibrated at 0 and 100% using black and white calibration tiles.

LRVs are best used to measure fade after accelerated weathering tests but are more commonly used to provide interior designers and architects a perception of how much colour will be reflected back into a room when the lights are turned on. You will often see LRVs stated on colour swatches in your local DIY store which is an establishment I avoid like the plaque!

Hope this helps.

Still confused?

Yes I agree, we should both get out more!

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Paddy Hopkirk visits AWL Ltd to discuss number plate testing

It was a pleasure to receive a visit from the icon Paddy Hopkirk (1964 Monte Carlo rally winner) last week to discuss number plate testing, legislation and his involvement with the charity SKIDZ.

SKIDZ provide industry-recognised training and education in motor vehicle maintenance to young people of all abilities. They have also launched a business to provide motor manufacturers, dealerships and fleet firms with everything they need to create their own number plates on demand.

The project is being championed by SKIDZ Patron Paddy Hopkirk, the legendary rally driver, is in its infancy but SKIDZ believes it has massive potential with profits from the enterprise going to support SKIDZ students. Check out their website at skidz.org.uk

AWL Ltd were pleased to be approached by Paddy with the prospect of providing consultation and validation for their suppliers in terms of performance against the current British Standard for number plates BS AU 145d.

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