We created cast Invar components for DESI

Cast Invar components for the Dark Energy Spectroscopic Instrument (DESI)

No strangers to dark energy, we are proud to be involved in machining the cast Invar components for a new spectroscopic instrument designed to measure the spectra of more than 30 million galaxies and quasars covering 14,000 square degrees over a five year period.

The Dark Energy Spectroscopic Instrument (DESI), which is mounted on the Mayall telescope at Kitt Peak National Observatory in Arizona, USA, began its five year operating life last year.

Astronomers use the term ‘dark energy’ to describe the unknown form of energy hypothesised to be responsible for the constant expansion of the universe. Scientists such as DESI hope to be able to learn more about the nature of dark energy in an attempt to help us better understand the universe.

Cast Invar components

We opted to use Invar to cast the components for the instrument due to its unique properties:

Low thermal expansion

The key reason Invar is so popular as a component for the likes of telescopes and microscopes is its low thermal expansion properties. This means that unlike other alloys, it is able to maintain between temperatures of -100°C & 260°C without changing shape. Even small changes can have a huge impact on the accuracy of results, so being able to use a material which isn’t impacted is a huge bonus.


Invar’s low thermal expansion also means it is an incredibly durable material. In fact, it’s a popular choice for transporting liquid natural gases due to the significant insulation it provides.


This combined makes Invar the primary industry choice for machining parts where a high level of accuracy is required. Its stability as an alloy mean it is unrivalled in applications such as clock pendulums (where it was originally used), optical engineering and precision instruments, as well as a variety of scientific instruments.

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Invar parts for the Dark Energy Survey

We are delighted to have been further involved with the Dark Energy Survey (DES), this time making the cast Invar parts.

Having previously worked with developing the Dark Energy Camera for the DES, creating the ring that holds the lens in place, the team knew they could rely on us to deliver the highly accurate work needed.

Invar partsInvar parts

We cast the parts using Invar, due to its high level of durability and stability.

Unlike other materials, this nickel/iron composition is able to maintain its shape between temperatures of -100°C & 260°C, making it ideal for a range of applications where accuracy is key, including clock pendulums, measuring devices, aerospace engineering, microscopes and telescopes.

In fact, one of Invar’s original uses was in clock pendulums. When it was first invented, the pendulum clock was the world’s most precise way of telling the time, however accuracy was limited due to the possible thermal variations in pendulums. In 1839, Clemens Riefler invented the first clock to use an Invar pendulum and its unprecedented accuracy (10 milliseconds per day) meant it served as the primary time standard for national time services until the 1930s!

What is the Dark Energy Survey?

Completed this year, the Dark Energy Survey (DES) was an ambitious international project which scanned approximately one quarter of the Southern skies (a 5,000 square degree area) in depth, mapping hundreds of galaxies in an attempt to understand ‘dark energy’.

A specialist 520-megapixel camera mounted on a four meter telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile recorded data from more than 300 million galaxies over a six year period from 2013 – 2019.

Now scientists are going about the huge task of analysing the vast amounts of data to learn more about never-before-seen distant galaxies.

So far, DES has already released exciting scientific results, including the most precise measurement of dark matter structure in the universe and new discoveries such as dwarf satellite galaxies of the Milky Way and the most distant supernova ever detected.



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Invar parts created for WEAVE

Specialist Castings is delighted to have been involved in an exciting project creating Invar parts for WEAVE (WHT Enhanced Area Velocity Explorer), a new multi-object survey spectrograph being constructed for the William Herschel Telescope (WHT) in the Canary Islands.

We created Invar parts for the WEAVE, a spectrograph that will allow astronomers to understand the Milky Way in greater detailThe spectrograph is an instrument that splits light into wavelengths to make it possible for astronomers to record and analyse and requires a high level of precision to ensure accuracy of results.

The new spectrograph will allow astronomers to take a spectra of up to 1000 stars and galaxies in a single exposure and marks a significant jump forward in the efficiency of the telescope (currently it is only possible to observe 100 objects simultaneously).

When completed, it’s hoped that the telescope will allow us to understand how the Milky Way was assembled by measuring the speeds of several millions of stars being mapped by the European Space Agency’s GAIA satellite.

As accuracy was so critical, we opted to cast parts using Invar, a nickel/iron composition alloy which is used where high dimensional stability is required.

Specialist cutting equipment is essential to complete Invar machining without having a detrimental effect on the material, and our expert team’s experience and equipment means we are perfectly placed to cast Invar parts to the most precise specification.

Why Invar?

Invar is ideal for components that require near constant dimensions as it is able to maintain its shape between temperatures of -100°C & 260°C without experiencing warping or thermal expansion.

Its unique qualities make it a popular choice for a range of applications where accuracy is key, including clock pendulums, measuring devices, aerospace engineering and the transportation of liquid natural gas due to the significant insulation it provides.

It is also a highly durable material, so it is perfect for precision instruments such as microscopes and telescopes.

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st peters church wearmouth

St Peter’s Church has won a Northern Design Award!

The wonderful aluminium slabs that we created in collaboration with local artist Simon Watkinson for St Peter’s Church in Wearmouth, have won a northern design award on Friday night at a presentation in Leeds. The stunning artwork celebrates both the history and importance of the church and also shows its relevancy among the Sunderland community. You can read more about how the slabs were created for St Peter’s Church here.  You can also follow this link to see our project on the Northern Design Awards.

st peter's church

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st peter's church

Stunning cast aluminium floor features installed at Sunderland historic tourist attraction

Sunderland Council recently launched a £1 million redevelopment project to landscape and create a permanent outdoor footprint at St. Peter’s Church in Wearmouth.  The church was built in 674AD and was the home and study place of the Venerable Bede; therefore it was important that the project adequately reflected the cultural and historical significance of the site.


The Council consequently commissioned local artist Simon Watkinson to do justice to this revered site and its new creation, who found inspiration for the project in two key areas:

  • While conducting in-depth research into the history and archaeology of St. Peter’s, Simon discovered that that the founder of St. Peter’s, Benedict Biscop, travelled to Rome six times over the course of his life, which seemed an extraordinary journey for someone living in the late 7th This gave Simon the inspiration to design a timeline that would allow people to “walk the life” of Biscop and his influence on the building.
  • The second major design influence on the project was an installation that Simon had seen while visiting an Emperor’s Garden, Sento Gosho, in Kyoto, Japan. This seemingly unremarkable project was a floor installation that featured a cobbled beach.  What made the project so interesting was that the cobbles had actually been cast with real stones collected from the foot of Mount Fuji.

The idea of a communal art project was born, which would not only commemorate this landmark site, but also involve local communities and Sunderland assets in its creation.

Simon’s idea was to create a “path” of key points in history relating to St. Peter’s and its famous residents.  Visitors would be able to walk around the gardens and read all about how this historic site had been built and used throughout the years.  Each moment in history would be framed by local cobbles from Roker beach, which would be collected by children from local schools.

Key to the success of this project was to ensure that the material from which the path was made was durable, workable and attractive.  Simon needed a reliable supplier, who would be able to provide his paving slabs from such a material.

Specialist Castings were subsequently contacted and asked if they could help.  Immediately they could offer the perfect solution in their production and experience of working with cast aluminium.   Hard-wearing, long-lasting with excellent weathering characteristics, aluminium was the perfect choice.  Specialist Castings 75 years’ experience in casting with aluminium meant that they could offer guidance and expertise to the artist in how best this material could be used.


The local casting company worked alongside the artist to create the full series of slabs to be used within the installation, working in intricate detail to ensure the artistic vision was fully realised.  The text on each panel highlights the significant moments of Biscop’s life and travels and Simon said, “I saw this as a reflection of the simple life of monks on their journeys across Europe, collecting relics for the church.”

The casting process involved creating the required elements for the slab, which in this instance consisted of text/images of key points in the site’s history, along with the cobbles collected by local pupils.  Each design was made up of the different elements, before being transformed into a mould for the aluminium.  The UK-based foundry then used a specified mix of aluminium alloy from which to create the end castings.

The result was a perfect collaboration between designer and manufacturer, with the installation now fully installed and enjoyed by the countless visitors who come to St. Peter’s every year.

Siobhan Carton, deputy head teacher from St. Mary’s RC Primary School said “The children really enjoyed collecting and decorating the pebbles.”. Simon said, “This gave them both a strong sense of ownership of the works and a history lesson to boot!”


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A direct comparison of Centrifugally Cast Tubular Anodes and Die Cast Tubular Anodes

The best way to verify the integrity of the sub-surface structure of a casting is by x-ray. By taking x-ray shots along the length of the casting to ASTM E94 it is possible to view images of the structure. Therefore, generally defining the overall integrity of the casting. X-ray acceptance standards ASTM E186 and ASTM E446 list defects from severity level 1 (the best level) down to level 5 (the worst level).

Many companies are now specifying that anodes should be supplied that pass an x-ray test to level 1, level 2 or level 3 ASTM E186. Although it is not economically viable to carry out an x-ray test on every anode, it is possible to demand that anodes supplied should pass an x-ray criteria level such as level 2 or better and that a percentage of anodes should be tested. An x-ray test might cost approximately $100 per test so it is common for specifications to require 1 in 50 anodes to undergo testing, hence adding $2 to the cost of each anode.

What is the significance of defect levels?

By examining the quality of levels 1 to 5 that are displayed by anodes you are able to understand how the theoretical life design of the anode system will be affected.

The table below represents the most up to date summary for assessing the design life against the x-ray level acceptance criteria. Some companies, such as the ENI Group simply state their refusal to accept any anodes that are below level 3 and other companies have based their design life on their own experience and installations.

X-Ray Level Design Life
Level 1 100%
Level 2 80-100%
Level 3 60-80%
Level 4 20-60%
Level 5 <20%

Level 1

If the x-ray testing determines the casting flaws are level 1 then it is highly unlikely that the life of the anode will be cut short.

Level 2

At level 2 for the acceptance criteria, there are some specific flaws that will influence the overall life of the anode. However, the size and frequency of these flaws are sufficiently small so their existence does not immediately require the need for the casting to be scrapped. The x-ray acceptance criteria should (and does) take in to account both the size, frequency and type of defect present.

Level 3

At acceptance criteria level 3 the casting may not perform correctly. Even though the silicon iron material retains gas porosity, if the anodes are produced to level 3 then there are additional flaws in the manufacturing procedure which are quantifiable and ideally should not be accepted.

Level 4 and 5

This is the same for level 4 and 5 as these flaws are increasing and the design life will be dramatically shortened.


We set out to evaluate the silicon iron castings and the quality and properties for die-cast versus centrifugally-cast anodes through controlled accelerated corrosion tests.  These are our key findings.

Comparison Results

image 1

This x-ray shows a die-cast anode.

centrifugally cast anode

This x-ray shows our centrifugally-cast anode.

In the top x-ray (of the die-cast anode) dark circular shadows depicting sub-surface shrinkage can be seen around the area of the pouring cup, i.e. where the metal has been poured into the anode. These shadows are depicting an area of shrinkage and it is clear from the image that the area around the pouring cup also contains additional fragmented pockets of shrinkage seen as ‘dark patches’ scattered away and around the pouring cup position. In the image, this area has been de ned as a level 3 defect. If an accelerated corrosion test was carried out on the whole anode, then this area would be consumed at a faster rate than the remainder of the anode. Furthermore, these areas around the pouring cup and riser have historically been the source of fissuring and cracking of the anode causing premature failure.

Likewise, if a mechanical test bar was machined out of this section of the casting, the results would fall far short of those exhibited by any section of the centrifugally-cast anode. We have retained these pieces for further testing by any interested party, if so desired.

die cast anode

This x-ray shows a die-cast anode

This change in section is an inherent weakness in the design of a die-cast anode because the change in wall thickness means the thicker part of the casting cools more slowly than the narrow section. This slower cooling rate not only causes an inferior grain structure that is almost as poor as sand-cast anodes, but also necessitates an additional riser to help feed the shrinkage that is catalysed from the change in section. The x-ray image of the die-cast anode above shows a serious casting aw visible as a dark shadow in the connection area and is a real-life sample con rming the di culties encountered with this design.

By comparison, any impurities in a centrifugal casting are thrown to the bore of the casting by application of Stoke’s law and are thus not detrimental to the life of the anode. This is a unique feature of the Centrifugal Casting method and is highly advantageous to the integrity of the casting.

It should be noted that the type of defect seen on the x-ray and its position in the casting will further influence the design life. For instance; a linear shrinkage defect in the wall of the casting may well cause a more dramatic reduction in life if it causes the part of the anode to ssure or tear along its axial length when in use.

Additionally, the centrifugally cast anode utilises a straight-walled anode design that has no change in cross section or thickness at the centre of the anode and no complex arrangement of sand cores (die cast anodes require up to 10 sand cores per anode) which are susceptible to individual discrepancies between every casting.

Specialist Castings have a manufacturing plant in the UK and a state of the art $2m manufacturing facility at Ningbo in China, where both tubular anodes and solid anodes are made. We have anodes stocked in 2 locations in the USA, utilising purpose-made connectors that have been used in over 1 million anodes over the last 35 years (see g 4 for TA2 and TA5A connectors). We have previously been the only manufacturer exclusively supplying tubular anodes to the Durichlor 51 Anode company. The only tooling that is required to make these connections are 2 torque wrenches (1.2 metres long) that tighten the bolt heads at the end of the connectors, to a pressure of 40lbs (ft/lbs) or 54Nm. These connections can be made in the factory or in the eld.

We have 3 XRF chemical analysis machines (in both the UK and China) and our pricing re ects the signi cant disparity between production costs when comparing foundry production costs in China to those in North America. This chart shows a comparison in sizes between Specialist Castings Anodes and other common anode sizes.

You can download the full report of this testing here.

To contact us about this report or any other area we can help with please use our contact page


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Partnership with Yuxi moves forward with Joint Venture

We are proud to announce the launch of a joint venture in America with our anodes partner Yuxi.

We  have formed a JV company with manufacturing facilities both in China and a U.S. company in Texas that promotes, stores and distributes these joint-venture products.

The factories in China produce Magnesium, aluminum, zinc and MMO anodes, in addition to cathodic protection accessories.  Following over 7 years of investment and technical development with Yuxi Ningbo, our JV operations own all of these foundries outright, with considerable input in developing these foundries to become the highest quality foundries producing C.P. anodes.  Yuxi Ningbo is now the largest CP company in China and the first to be listed on the Beijing Investors Exchange.”


2014- Formed agreement with Ningbo Yuxi to share technical information on the production of anodes

2016-Set up formal joint venture with Ningbo Yuxi with USA office.

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Lens Ring created for the Dark Energy Survey

We are proud to have been the manufacturer and supplier of the lens ring for the Dark Energy Survey.  lens ring for the dark energy survey

“The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

Over five years (2013-2018), the DES collaboration is using 525 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey is imaging 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.”

Text taken from www.thedarkenergysurvey.org

We were approached by the team involved to cast the ring to hold the lens due to our experience in precision and quality casting of large objects.  The accuracy level of this project was highly demanding, as the impact of fractions of mms movement of the lens would impact hugely on the rDARK ENERGYesults of galaxies viewed at such distances.

We worked closely with the team to understand the requirements for the material composition, which was a specially blended alloy free from residual elements to give a cleaner alloy
.  Our manufacturing processes took into account an oxygen-free annealing environment  since the heat treatment is critical to ensuring the correct TEC and we consulted with the team throughout our full proof-machining, pattern and casting process.  We then carried out rigorous MPI and x-ray tests on the ring, along with analysis of heat-treatment charts and chemical composition reports, to ensure the absolute certainty of quality for the lens ring for the dark energy survey.


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