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What Makes a Chain High Security

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Chains are an integral part of the world around us. We use and see chains every day, from lavatory chains to key chains, chain link fences, anchor chains and door chains - we are all very familiar with what chains are. But how has chain-technology developed to enable the production of the remarkably heavy duty, high security chains available tod

History of Chains and Chain-making

The word ‘chain’ is derived from the Indo-European language family. The earliest recorded use of a metal chain is from 225 BCE when a metal bucket chain, made from interconnected metal rings, was used to raise water from a well. 

It was Leonardo da Vinci who, in the 16th century, sketched what are thought to be the earliest steel chains. The development of chain technology was very much based upon the advances made in reliable steel production. So it wasn’t until the 19th century, when steel production techniques had matured and stabilised, that steel chains really took off.

Leonardo DaVinci Chains

The first development in chain technology was the cast-detachable chain which is made up of identical, cast chain links. And cast-link chains are still in use today. Then came the pintle chain, which uses a separate pin - another historic chain design that’s still commonly used today. Further developments in the late 1800s resulted in steel chains with greater resistance to wear. These new improvements in chain technology were used on bicycles and in the rear wheel drive of early automobiles and in 1903 a steel bushing chain was used as the propeller drive system in the Wright brothers’ early aircraft.

Development of Steel

The evolution of chain-technology is very much tied into the development of steel, which has a long history. Around 4000 years ago the most widely used metal had been bronze but this was progressively replaced by iron for weapon and tool production.

Knowledge of the properties of iron and smelting processes progressively advanced as the demand for iron increased. But it wasn’t until the 19th century that metallurgists focused on finding solutions to iron’s key failings of brittleness and inefficient production. It was in 1856 that Henry Bessemer developed a way to use oxygen to reduce the carbon content of iron - and the modern steel industry was started.

Cast iron is strong, but brittle, due to the carbon content of around 2.5% to 4.5%. This brittleness makes it difficult to work. It was the development of puddling furnaces by Henry Cort in 1784 that enabled the production of low-carbon content wrought iron. By 1860 there were as many as 3000 puddling furnaces in Britain but the puddling process required a huge amount of fuel to achieve the required high temperatures and demanded a lot of human labour in the process.

It was in 1856 that the Bessemer Process was introduced. This technique passed oxygen through the molten metal causing it to react with the carbon which was then released as carbon-dioxide, resulting in higher purity iron. Although the process was faster than puddling, it initially removed too much of the carbon and left unwanted oxygen in the metal. At around this time another metallurgist called Robert Mushet was experimenting with a compound of iron known as spiegeleisen which included manganese, known to remove oxygen from molten iron. So Bessemer began using it in his process, which was highly successful.

However, the remaining presence of phosphorous in the metal made it brittle. This meant that only phosphorous-free iron ore could be successfully used in steel production. But luckily a Welshman named Sidney Gilchrist Thomas determined that by adding limestone to the Bessemer process the unwanted phosphorous could be removed.

This new innovation mean that steel production could use iron ore derived from any location in the world. New steel production techniques resulted in the price of steel dropping more than 80% between 1867 and 1884 and the worldwide steel industry really kicked off.

Further developments including the open hearth process, electric air furnace steelmaking and oxygen steel-making have resulted in the cost-efficient steel manufacturing processes used today.

High Security Chain Attributes

The required attributes of chains for security applications differ from those required for chains used in other applications such as boat mooring chains, ships anchor chains and towing chains. Chains for these applications will have high tensile strength, which means they are resistant to breaking under tension. They will also be ductile, offering some elasticity which makes them less brittle and able to withstand considerable tensile load.

High security chain

Attack Resistance

High security chains must withstand typical forms of human attack. These include attempts to cut the chain using bolt-croppers or by sawing and by making the chain metal more brittle by freezing allowing it to be shattered with a hammer blow. High security chains should withstand all of these without failing.

The important chain attributes which affect the level of security provided and attack resistance are:

  • The dimensions (diameter) of the steel used in the chain links.
  • Welding of chain links.
  • Case hardening of chain links.
  • Through hardening of chain links.

Thick steel chain links are far more difficult to attack and break than thinner steel links which is why high security chains are usually specified based on this dimension. High security chains will typically use chain links with metal diameters of from 10mm to a super-robust 22mm. High quality 22mm security chains may be guaranteed to be impossible to cut by hand using bolt croppers.

Welded chain links means that the two ends of the chain link metal have been welded together. Unwelded links could potentially be pried apart so it makes sense that high security chain links should be welded.

Case hardening is also known as surface hardening. It’s a process used to harden the surface of metal chain links while allowing the metal at the centre to retain some malleability. Surface hardening chain links makes the chain more resistant to abrasion and the cumulative impact of wear and tear. It’s a desirable attribute in high security chains as the hardened surface prevents saw blades from biting into the metal thereby enhancing protection against saw attacks.

Through hardening is a process which increases the hardness and tensile strength of steel. It’s used on high security chain links to make them resistant to bolt cropper attack. 

The very best high security chains use a combination of high quality steel, thick steel chain links, welded chain links along with case and through hardening to ensure that they are highly resistant to all common forms of attack.

Security Chain Standards

While it’s great to understand the primary attributes of high security chains it’s more useful to recognise relevant security chain standards and whether chains comply with these. The standards to look out for in the UK are Sold Secure.

Sold Secure is an independent security product testing organisation established in 1992 by Northumbria and Essex Police but now owned and administered by the Master Locksmiths Association. 

Security products are classified as:

  • Bronze - for medium to high security products.
  • Silver - for high security products.
  • Gold - for extra high security products
  • Diamond - for selected super high security products.

All high security chains, in the UK, should meet either the Sold Secure Gold or Diamond standards.

Which Security Chain Do You Need?

When considering the purchase of a security chain you need to think about exactly what the chain is required for. Do you want a security chain for a bicycle, to be used while on the move? Or are you looking for a motorbike security chain that you can carry with you? Or maybe you want to secure a boat, a trailer or maybe a caravan?

An important point to keep in mind when investing in security measures is not to skrimp. A good rule of thumb when considering your security budget is to allocate around 10% of the value of the item to your security measures. So if, for example, you are looking for locks and chains to keep your new £1000 mountain bike safe then be prepared to spend around £100 on chains and locks. Similarly, if you want to secure a caravan that’s worth around £10,000 then you need to be prepared to spend around £1000 on your security measures.

Item(s) Security Standard High Security Chain Specification
Bicycles, wheelie bins, trailers, lawn mowers etc. Sold Secure Gold
  • At least 10mm diameter steel.
  • Welded links.
  • Case hardened.
  • Through hardened.
  • Protective sleeve to prevent chafing.
Motorbikes, Motor Scooters Sold Secure Gold (Motorcycle)
  • At least 13mm diameter steel.
  • Welded links.
  • Case hardened.
  • Through hardened.
  • Protective sleeve to prevent chafing.
Boats, Caravans, High-end Motorcycles

Sold Secure Gold 

Sold Secure Diamond

  • At least 19mm diameter steel.
  • Welded links.
  • Case hardened.
  • Through hardened.
  • Protective sleeve to prevent chafing.

As noted, it’s worth ensuring that your selected security chain comes fitted with a strong protective sleeve to protect the paintwork on the secured item from chafing. You also need to ensure that the locks you choose to use with your new high security chain meet the same level of security. Similarly, when locking valuable items to wall or ground anchors you need to ensure that these meet the same rigorous safety standards and importantly, that the ground or wall anchors are immovable. You also need to be aware that higher security chains with thicker chain links are heavy. For example a 22mm diameter protector chain can weigh 10kg per metre.

If you need help or advice regarding high security chain selection or any other aspect of your security requirements we are here to help. Just give us a call on 01273 475500 for free, impartial advice.

This message was added on Monday 24th June 2019

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