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Thread: coil building materials question

  1. #1
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    coil building materials question

    Hi all,
    Been reading alot of discussion about the relative merits of different resistance wires, and at the core of it is whether you prefer to risk chrome, aluminium, nickel or titanium oxide being created, vaporised or inhaled. Tough questions cause no one knows for sure if, and if so how much it happens. No one seems to worry about the iron in kanthal, or stainless wicks in gennies. So theres my question. I follow Disley's link to try some titanium (thanks for that and the surrounding discussion) and see medical grade stainless steel resistance wire for coil building, and wonder why this isn't a perfect solution. I know it didn't take off when they used mig welding wire, but hardly anyone knows all the stuff in them. But medical stainless?
    Can anyone tell me why its not popular? What are the pros and cons?
    Thanx
    Last edited by Coxy; 18-06-15 at 11:02 PM.

  2. #2
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    To call a stainless steel medical grade is a very broad term that includes a number of different stainless steels. It all depends on the application that the stainless is required for.
    If you look at the compositions of all of the different stainless steels you will find chromium as one of the components along with nickel in quite a few.
    There are Austenitic,Martensitic and Ferritic stainless steels. If we really want to go further there are many other specialty stainless steel and stainless type alloys like Duplex and Superduplex along with a number specialty alloys like Inconel's

    This is going to explain some differences way better than I am able to.
    A bit of lite reading

    Stainless steel is the term used to describe an extremely versatile family of engineering materials. Selected primarily for their corrosion and heat resistance, these materials offer a wide range of physical and mechanical properties coupled with inert, easily cleaned, surfaces capable of accepting a variety of aesthetically pleasing finishes. Hence, stainless steels find a broad range of applications in industries where hygiene is a major requirement (eg food and beverage processing, pharmaceutical production, drinking water systems, etc).
    What makes the stainless steel family “stainless”?
    Alloys of iron containing 10.5% chromium form a protective, adherent and coherent, oxide film that envelops the entire surface of the material. This oxide film, known as the passive or boundary layer, is very thin (~2 nanometres thick) and forms as chromium in the surface layer reacts with oxygen and moisture in the environment. The passive layer exhibits a truly remarkable property: when damaged (e.g. abraded), it self-repairs as chromium in the steel reacts rapidly with oxygen and moisture in the environment to reform the oxide layer.
    Increasing the chromium content beyond the minimum of 10.5% confers still greater corrosion resistance. Further improvement in corrosion resistance and a wide range of properties may be achieved by the addition of nickel. The addition of other chemical elements may be used to enhance resistance to specific corrosion mechanisms or to develop desired mechanical and physical properties. For example, molybdenum further increases resistance to pitting corrosion, while nitrogen increases mechanical strength as well as enhancing resistance to pitting.
    The Stainless Steel Family
    The stainless steel family may be described in a variety of ways. Perhaps the most accurate way is by reference to the metallurgical phases present in their microscopic structures:
    - Austenitic
    - Ferritic
    - Martensitic (including precipitation hardening steels)
    - Duplex (consisting of a mixture of ferrite and austenite)
    Within each of these groups, there are a number of “grades” of stainless steel defined according to their chemical compositions. These grades are specified in European and International standards, and within its specified range of chemical composition, each grade will exhibit the desired properties (e.g. corrosion resistance, heat resistance, machinability).

    Ferritic stainless steels consist of primarily of chromium (typically 12.5% or 17%) and iron. Generally, ferritic stainless steels contain very little nickel (typically <1%). Their minimal carbon content prevents hardening by heat treatment, but confers superior corrosion resistance to martensitic stainless steels. They possess good resistance to oxidation, are ferromagnetic and, although subject to an impact transition (i.e. become brittle) at low temperatures, possess adequate formability. Their thermal expansion and other thermal properties are similar to conventional steels. Ferritic stainless steels are readily welded in thin sections, but suffer grain growth with consequential loss of properties when welded in thicker sections.

    Martensitic stainless steels consist of carbon (0.2-1.0%), chromium (10.5-18%) and iron. These materials may be heat treated, in a similar manner to conventional steels, to provide a range of mechanical properties. Their corrosion resistance may be described as moderate (ie their corrosion performance is poorer than other stainless steels of the same chromium and alloy content). They are ferromagnetic, subject to an impact transition at low temperatures and possess poor formability. Their thermal expansion and other thermal properties are similar to conventional steels. They may be welded with caution, but cracking can be a feature when matching filler metals are used.

    Austenitic stainless steels consist of primarily of chromium (16-26%), nickel (6-12%) and iron. However, as previously stated, other alloying elements (e.g. molybdenum) may be added in order to develop desired properties. For example, copper is added to improve resistance to acids and/or for the improved deformation needed in the cold heading of fasteners). This subgroup contains more grades, used in greater quantities, than any other category of stainless steel. Austenitic stainless steels exhibit superior corrosion resistance to both ferritic and martensitic stainless steels. Corrosion performance may be varied to suit a wide range of service environments by careful adjustment of their compositions. These materials cannot be hardened by heat treatment and are strengthened by work-hardening. Unlike ferritic and martensitic stainless steels, austenitic grades do not exhibit a yield point. They offer excellent formability and their response to deformation can be controlled by the nickel and copper content. They are not subject to an impact transition at low temperatures and possess high toughness down to cryogenic temperatures. They exhibit greater thermal expansion and heat capacity, with lower thermal conductivity than other stainless or conventional steels. They are generally readily welded, but care is required in both the selection of consumables and the welding practice used for more highly alloyed grades. Austenitic stainless steels are often described as non-magnetic, but may become slightly magnetic when machined or worked
    Duplex stainless steels consist of chromium (18-26%) nickel (4-7%), molybdenum (0-4%), copper and iron. These stainless steels have a microstructure consisting of austenite and ferrite, which provides a combination of the corrosion resistance of austenitic stainless steels with greater strength. Duplex stainless steels are weldable, but care must be exercised to maintain the correct balance of austenite and ferrite. They are ferromagnetic and subject to an impact transition at low temperatures. Their thermal expansion lies between that of austenitic and ferritic stainless steels, while other thermal properties are similar to plain carbon steels. Formability is reasonable, but higher forces than those used for austenitic stainless steels are required. Duplex stainless steels cannot be hardened by heat treatment.
    Surgical steels

    There is a popular misconception that special “surgical” steels are used for all medical devices. However, as medical devices represent approximately 1% of the total production tonnage of stainless steel, there is little justification for the development of special surgical steels. Furthermore, stainless steel medical devices are produced in low volume, batch processes or in high volume processes utilising small quantities of material. Most non-implant medical devices (eg dental and surgical instruments, kidney dishes, theatre tables, etc) are, therefore, manufactured from commercial grade stainless steels. These stainless steels adequately meet clinical requirements where contact with human tissue is transient.

    However, implant applications are an exception to this generalisation. Stainless steels used for implants must be suitable for close and prolonged contact with human tissue (ie in warm, saline conditions). These clinical requirements were the driver for the development of special “implant” steels. These materials, now produced with enhanced chemical compositions, were originally developed from commercial grade 1.4401 (AISI 316) stainless steel. Specific requirements for resistance to pitting corrosion, and the quantity and size of non-metallic inclusions apply to implant grade stainless steels, which do not apply to commercial stainless steels. Hence, special production routes (ie vacuum melting or electroslag refining) are required to produce implant steels.
    Non-Implant Medical Devices

    ISO 7153-1 specifies stainless steel for surgical and dental instruments, and also provides an indication of medical device applications for each grade. It should be stressed that, although the grades listed in ISO 7153-1 are generic, they can be related to European and National steel standards for readily available, steels intended for commercial applications. These steel grades are used, throughout the world, in non-implant medical devices.
    Austenitic stainless steels find applications in medical devices where good corrosion resistance and moderate strength are required. For example, canulae, dental impression trays, guide pins, hollowware, hypodermic needles, steam sterilisers, storage cabinets and work surfaces, thoracic retractors, etc. These applications often require a material that is easily formed into complex shapes.

  3. #3
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    Thanks again Midlife. Nothing to gain with stainless then. Kanthal it is.
    Midlife likes this.

  4. #4
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    Good read, thanks
    Midlife likes this.

  5. #5
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    I've seen stainless steel wire for sale, and it's being used for vaping.
    I'll try it eventually, but at the moment it's not easily available to us.

    Seriously, unless there's something specific which is known to be harmful, being produced by heating SS coils, I'm not going to worry about it.
    Take whatever precautions you feel are necessary, but use your common sense, not your imagination.

    We have more reason to be scared of the radio-active pollution that's leaked into the Pacific ocean, from the meltdowns at the Fukushima power stations.
    The cancer council should be concerned about that, it's a real threat to the health of millions.
    Bobthebuilder and Coxy like this.

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  7. #7
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    That means absolutely nothing to me.
    Hi lite where it says it will kill me please.

  8. #8
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    This is all I can find, understandable to average vapers.
    Metals emitted from e-cigarettes are NOT a reason for health concern
    The results of our risk assessment analysis clearly show that exposure to metals from e-cigarettes is not expected to be of significant health concern for smokers who switch to e-cigarette use. However, there is the need to improve the quality of the products, to further reduce unnecessary exposure. Finally, there is no reason for a non-smoker to be exposed to any levels of metals, thus, we do not recommend use of e-cigarettes by never smokers.
    By Dr Farsalinos

  9. #9
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    There's mention of SS being used at ECF and they're working out its uses with TC vaping.
    Stainless Steel

    Stainless Steel has a coefficient of 0.00094, less than one-sixth of Nickel's.

    This means that SS can not be properly used for TC without adjusting the coefficient - its resistance increases with temperature too little for normal mods, that are expecting Ni200, to use effectively.

    Some people have vaped SS on normal TC mods, and it does somewhat reduce dry hits, but it will still burn cotton. To use it effectively, a coefficient adjustment is necessary.

    Once the coefficient is adjusted, Stainless Steel works well - no burnt cotton. However my testing thus far has still required a temperature offset, albeit not as much as people have had to do with Titanium. When using the Infinite Nickel Purity feature, I have set an offset of around 50°F when using SS.

    The advantages of Stainless Steel versus Ni200 are the same as for Titanium - micro/contact coils, higher resistance ranges, stronger. The advantages of SS versus Titanium is that it's much easier to work with - malleable, easy to coil. It is also readily available, and cheap. Crazy Wire/The Mesh Company in the UK sell SS 317L under the brand TMC.

    The safety aspects of it are unknown at this point in time, though theoretically it should be safe at TC type temperatures (and perhaps safer than Ni200, though don't quote me on that!)​

    https://www.e-cigarette-forum.com/fo...stance.676506/

  10. #10
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    I posted the charts above to show the chemical composition of the different materials (alloys)

    What I don't understand with all of this talk of concerns about certain materials when you will find them in most of the wires that are being discussed. That is why I posted the charts.

    I am not posting this info because of safety concerns but more so to show the materials that are common in so many of these alloys.
    Fatman likes this.

 

 
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