GB2368379A

GB2368379A - Titanium or titanium alloy chains

Info

Publication number: GB2368379A
Application number: GB0026275A
Authority: GB
Inventors: Douglas Berger; Rupert Edward Robert Wilbraham
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-10-27
Filing date: 2000-10-27
Publication date: 2002-05-01
Also published as: GB0026275D0

Abstract

A chain comprising a material selected from titanium and alloys of titanium. The process for making the chain including: optionally annealing the material, forging the material to form a plurality of chain links and welding the links together to form a chain. The chain may be coated and/or hardened after forging. A security device, made from a similar process, is also disclosed.

Description

CHAINS The present invention relates to chains for use in security and marine and freshwater mooring applications and to a security device.

Mooring chains are well known and are used in a wide variety of applications, including anchor chains for vessels, fixtures for offshore installations such as oil rigs and the like.

Security chains and devices are also known, and are used in a wide variety of applications including bicycle and motorcycle chains, locks, shackles and the like.

Mooring chains and security chains and devices are commonly made from iron or steel. These materials have the advantage of being relatively cheap, readily available and strong. However they are subject to certain disadvantages.

In mooring applications, iron or steel chains are subject to corrosion, particularly in salt water, and have a limited life as a result.

In security applications, corrosion may also be a problem with iron or steel chains, locks and shackles, but also the weight of such items can make them undesirable for use, say, in bicycle or motorcycle security chains, locks and shackles. For an iron or steel chain or other security device to be readily transportable there is a limit to the gauge of metal in the chain links or other metal members that can be used before the chain or security device becomes too heavy.

Unfortunately, the need to limit the thickness of the metal is not always compatible with the intended function of the chain as a security device and many current commercial security chains and other devices such as locks and shackles are in fact easily compromised by the action of tools such as bolt cutters and hacksaws.

Other materials have been proposed for use in mooring and security chains and security devices, but all have disadvantages and none has found commercial acceptance to date.

It is an object of the present invention to provide an improved chain for use in mooring and security applications.

It is a further object of the present invention to provide an improved security device for use in security applications.

According to the present invention there is provided a chain comprising a material selected from titanium and alloys of titanium.

Chains according to the invention have a number of advantages over the prior art chains hereinbefore disclosed. Titanium and its alloys have a low specific gravity and yet they exhibit a high tensile strength. Accordingly, chains according to the invention are stronger, weight for weight, than the equivalent chain made from iron or steel. Thus, chains according to the invention can function as security chains for bicycles or motorcycles which are light enough to be readily transportable and yet strong enough to resist attempts to cut through them. Although titanium is an active metal, it forms an oxide layer on its surface which renders the material rather resistant to chemical attack. Thus, chains according to the invention are less corrodible than equivalent chains made from iron or steel.

Preferably, the chain according to the invention comprises at least about 30%, more preferably at least about 40%, even more preferably at least about 50%, still more preferably at least about 60%, yet more preferably at least about 70% and particularly preferably at least about 80% by weight of titanium. In an especially preferred embodiment of the invention the chain comprises at least about 90% by weight of titanium.

Materials that can be alloyed to titanium to provide material suitable for making chains according to the invention include aluminium, manganese, tin, vanadium and iridium. Examples of specific titanium alloys suitable for making chains according to the invention include Ti, Al, Mn 96,2, : 92,4, 4. Ti, Al, Sn 92.5, 5,2. 5: Ti, AI, V 90,4, 6 Ti, Al, Ir 90,5, 5. Another suitable material is titanium alpha class alloy. If a particularly strong chain is required then an alpha-beta class titanium alloy may be used.

According to the present invention there is further provided a process for making a chain comprising the steps of : providing a material selected from titanium and alloys of titanium ; optionally annealing the material; forging the optionally annealed material to form a plurality of chain links, and welding the links together to form a chain.

The optional annealing step is generally only necessary when the selected material comprises alpha-beta class titanium alloy. The annealing step is preferably conducted in a vacuum or otherwise inert atmosphere. Preferably, the annealing step comprises heating the selected material to a temperature in the

range of from about 500 C to about 1000 C, even more preferably from about 600 C to about 900oC, most preferably from about 700oC to about 800oC, and then maintaining the selected material at about that temperature for a period of at least about 15 minutes, preferably at least about 30 minutes, more preferably at least about 45 minutes, before allowing the selected material to cool in the vacuum or otherwise inert atmosphere. One such step according to the invention comprises heating the selected material to about 780oC and then maintaining this temperature for about one hour before allowing the selected material to cool slowly in the vacuum or otherwise inert atmosphere.

The forging step may be a cold forging step. Alternatively, the forging step may be a hot forging step, which involves heating the selected material prior to forging. Preferably the forging step is conducted using a die form. More preferably, the forging step is conducted using a die form automated machine process.

The size and shape of the forged links may be selected as desired. Where the resulted chain is intended for use in mooring applications, these parameters may be selected with reference to the Lloyds Register of Shipping as detailed in their certification requirements on"Equipment for Mooring and Anchoring".

Usually, the chain links will be elliptical in shape.

Preferably the links are welded together by a process selected from electron beam welding and fusion welding (otherwise known as DC Argon Arc Welding).

Preferably, the process of the invention comprises the further step of stress relief annealing and tempering the chain.

The stress relief annealing and tempering step is preferably carried out by

heating the chain in a vacuum or otherwise inert atmosphere to a temperature in the range of from about 550oC to about 1050oC, even more preferably from about 650oC to about 950oC, most preferably from about 750oC to about 850oC, and then maintaining the chain at about that temperature for a period of at least about 15 minutes, preferably at least about 30 minutes, more preferably at least about 45 minutes, before allowing the chain to cool in the vacuum or otherwise inert atmosphere to a temperature of from about 310 C to about 810 C, even more preferably from about 410 C to about 710oC, most preferably from about 510 C to about 610 C, maintaining the chain at this temperature in the vacuum or otherwise inert atmosphere for a period of at least about 3 hours, more preferably at least about 4 hours and most preferably at least about 5 hours before allowing the chain to cool in the vacuum or otherwise inert atmosphere. One such step according to the invention comprises heating the chain in a vacuum or otherwise inert atmosphere to about 800oC and then maintaining this temperature for about one hour before allowing the chain to cool in the vacuum or otherwise inert

atmosphere to a temperature of ab. out 560oC, maintaining the chain at about this temperature in the vacuum or otherwise inert atmosphere for a period of from about 6 to about 8 hours before allowing the chain to cool slowly in the vacuum or otherwise inert atmosphere.

Where an inert atmosphere other than a vacuum is used, this may be provided by means, for example, of an inert gas such as argon.

For certain applications for chains according to the invention, it may be desirable further to treat the chains to increase their hardness. Security applications are one such instance.

Accordingly, the process of the invention may comprise the further step of hardening the chain.

The hardening step may comprise a nitrogen diffusion hardening step.

Preferably, the nitrogen diffusion hardening step comprises heating the chain in an

atmosphere of nitrogen to a temperature of at least about 600oC, more preferably at least about 700oC, most preferably at least about 800oC at a pressure (of nitrogen) of at least about 6 atmospheres, more preferably at least about 7 atmospheres, most preferably at least about 8 atmospheres, for a period of at least 6 hours, more preferably at least about 7 hours, most preferably at least about 8 hours. One preferred process according to the invention involves heating the chain for about 9 hours at about 9 atmospheres (of nitrogen) at about 900oC.

The heating may be carried out, for example, in a vacuum oven by a gas or plasma process.

The hardening step may comprise a nitriding step. In one such process, the chain is placed in a vacuum oven, heated to a temperature of at least about 200oC, preferably at least about 300oC, for example about 400OC and bombarded with titanium nitride (produced in situ by reacting a stream of titanium ions with nitrogen) for a period of at least about one hour, preferably at least about 2 hours, for example about 3 hours. This process forms a layer of titanium nitride on the surface of the chain to a depth of about 250um. As well as being extremely hard, the resulting surface may have a light brown or golden appearance which may have aesthetic appeal in certain applications.

Further hardening of chains according to the invention may be effected by coating the hardened chain. Suitable coatings are nickel with composite particles of silicon carbide, aluminium or diamond or tungsten carbide or chromium carbide. Such coatings can be electroplated or autocatalytically deposited onto the surface of the chain. Other suitable coatings include cermets (ceramic like materials containing metals).

In other applications of chains according to the invention, particularly in mooring applications, it may be desirable to provide the chain with a coating, whether or not the chain has been hardened. Although the oxide layer which forms on the surface of titanium protects the material to some extent from corrosion, in a linked chain there still may exist the problem of fretting erosion, caused by the links rubbing together. In applications where chains according to the invention contact other metals, for example steel bollards, cleats or anchors, an electrochemical potential is established which can lead to accelerated corrosion of the steel.

Accordingly, in one process of the invention there is provided the further step of coating the chain (which may or may not be hardened).

The coating step may comprise the step of providing an anodised coating on the chain.

The coating step may include the step of providing a metallic coating on the chain. Metallic coatings may be electroplated on to the chain. However, preferably, the metallic coating is autocatalytically plated on to the chain.

One preferred process according to the invention includes the step of providing a coating comprising electroless nickel. Preferably, the coating further comprises phosphorous in an amount of up to about 12%, for example up to about 7%, for example up to about 2% of phosphorous. The coating may comprise further hard particulate materials selected from silicon carbide, chromium carbide, tungsten carbide, diamond, alumina, or mixtures thereof. These materials, or mixtures thereof, may be incorporated in the coating in an amount in the range of from about 2% to about 50% by volume, preferably from about 3% to about 45% by volume, more preferably from about 5% to about 40% by volume and most preferably from about 10% to about 35% by volume of the coating. The particle size of these materials is typically in the range of from about 1 to about 100 urn,

even more typically from about 2 to about 60um and most typically in the range of from about 3 to about 3 5 urn.

Such coatings can provide wear resistance and corrosion protection of the chain. Self lubricating deposits can be formed when the composite material is PTFE, Cfx or Boron Nitride. Preferably, prior to coating the surface of the chain is prepared by blasting it with non-ferrous abrasive media.

Where it is desirable for the chain to have non-magnetic properties (e. g. in securing mines) the electroless nickel deposit should be one that has a high phosphorous content of from about 11 to about 12.5% by weight of the coating.

It is also possible to use non-metallic coatings such as PTFE, fluorocarbon polymers, boron nitride and organic coatings such as paint and powder coating, for example epoxy type paint.

Suitable coatings and processes for hardening chains according to the invention may be selected from process/coating liquid lubricants and greases, acid anodising, alkaline anodising, heat treatment and work hardening, shot peening, lube impregnated anodised films, salt bath hardening, nitride films, electroplated metals, electroless plated metals, co-deposited metals and polymers, thermal spray coatings, weld overlay with titanium alloy, and diamond-like carbon.

Shot peening of the chain may help prevent fretting and loss of fatigue strength.

Treatment of titanium in various proprietary molten salts at temperatures around 800oC can produce surface hardness up to 800HV on surface layers composed of interstitial oxides. Carbides and nitrides up to. 04mm effective thickness. Thermal spraying covers a range of processes including plasma spray, high velocity oxy-fuel (HVOF), vacuum plasma, and detonation gun. A very wide range of ceramics, carbides, metals and alloys can be applied to titanium by HVOF and plasma, these covering requirements for enhancement of abrasion and galling resistance, heat resistance, electrical insulation, erosion etc. Semi porous or porous coatings may enhance wear resistance further by providing a reservoir of absorbed lubricant. Hydroxyapatite flame sprayed coatings are applied to titanium body implants to improve fixation by simulating bone ingrowth. Soft metals such as copper, or copper alloys with nickel and indium or aluminium bronze can be effective to improve sliding wear and fretting resistance.

Diamond like carbon coatings can be applied at low temperature (150 200 DC) by plasma assisted chemical vapour deposition (CVD), or by laser arc.

The films are thin, extremely hard and have very high resistance to wear and are biocompatible.

Also provided in accordance with the invention is a security device, such as a padlock and shackle, comprising material selected from titanium and alloys of titanium.

The invention further provides a process for making a security device comprising the steps of : providing a material selected from titanium and alloys of titanium; annealing the material; machining and/or forging the annealed material to form a security device.

The steps in the process for making a security device according to the invention are similar to those described above in respect of chains according to the invention.

In one preferred process according to the invention, a padlock body is made from an alpha-beta class titanium alloy billet by annealing the billet and then machining holes for a shackle and space for a lock body into the annealed billet. An alpha-beta class titanium alloy bar is used to make the shackle, the bar being annealed and then cut to length and machined to provide retaining holes and/or notches. The bar is then forged, for example, into a U-shape using a die form automated machine process and then welding to the lock body.

Claims

CLAIMS 1. A chain comprising a material selected from titanium and alloys of titanium.
2. A chain according to claim 1 comprising a material which has been hardened after forging.
3. A chain according to claim 1 or claim 2 wherein the chain comprises a coating.
4. A chain according to claim 3 wherein the coating prevents contact between neighbouring links of the chain.
5. A chain according to claim 3 or claim 4 wherein the coating is selected from anodised coatings, metallic coatings, organic coatings and cermet coatings.
6. A chain according to claim 5, wherein the coating further comprises a hard particulate material.
7. A chain according to claim 6, wherein the hard particulate material is selected from silicon carbide, chromium carbide, tungsten carbide, diamond, alumina, or mixtures thereof.
8. A process for making a chain comprising the steps of : providing a material selected from titanium and alloys of titanium; optionally annealing the material; forging the optionally annealed material to form a plurality of chain links; and welding the links together to form a chain.
9. A process according to claim 8 comprising the further step of stress relief annealing and tempering the chain.
10. A process according to claim 8 or claim 9 comprising the further step of hardening the chain.
11. A process according to any one of claims 8 to 10 comprising the further step of coating the chain.
12. A security device comprising a material selected from titanium and alloys of titanium.
13. A process for making a security device comprising the steps of : selecting a material selected from titanium and alloys of titanium; annealing the material; machining and/or forging the annealed material to form a security device.