In today's world of engineering and technology, the search for efficient and durable methods of joining materials is crucial to achieving high quality products and structures. INOX stainless steel, with its unique properties, is widely used in various fields, such as industry, construction and medicine. Although welding is the traditional method of joining stainless steel, more and more attention is being paid to bonding technology as an alternative. In this article, we will look at the properties of INOX stainless steel, various welding methods, their advantages and disadvantages, as well as the possibilities of bonding as an innovative approach to joining these types of materials. We invite you to read and discover new perspectives in the field of stainless steel joining technology.

Stainless steel - properties and application

INOX stainless steel (inoxydable - "non-oxidizing") is a group of steels with special physical and chemical properties, resistant to corrosion from e.g. atmospheric agents (gas corrosion), diluted acids and alkaline solutions (corrosion in liquids).

Where and why is stainless steel used?

The main reasons why stainless steel is a widely used material are:

• corrosion resistance
• can be used in aggressive environments
• resistance to high temperatures
• shiny sheen

Stainless steel is most often used in the production of various types of tanks, cisterns, pool basins, industrial installations, turbine blades, industrial fittings, surgical tools, sailing fittings, steel structures, decorations, elevators, cold stores, air conditioners, heat-resistant furnaces, balustrades. In addition, HACCP standards require that items in contact with food be made of stainless steel. This includes, but is not limited to: slaughterhouses, food processing plants and catering establishments.

Traditional methods of joining the popular "stainless steel" include: screwing, which allows easy assembly / disassembly of connections of various materials, but can cause crevice corrosion. An additional downside of this technology is the cost of tools dedicated to stainless steel processing, such as; drills, dies and taps. Other connection methods are soft and hard soldering, mechanical clamping and welding. A modern technology that is rapidly gaining more and more recognition is gluing.

The purpose of this text is to compare the traditional method of welding with the technology of the future - gluing.

Stainless steel welding methods

The table below shows the grades of stainless steel and their weldability. This is very important information for every welder before starting welding. In the case of gluing, we do not use any tables. If we are unable to identify the material to be bonded, we can perform a surface tension test or perform an adhesive test that will show how a given type of steel will stick.

TIG welding of stainless steel

TIG welding is one of the basic processes used to produce structures, especially from high-alloy steels. This method is used to make joints in a wide range of thicknesses of joined elements, from tenths of a millimeter to even several hundred. This method can be used to make manual, semi-automatic and automatic connections, thanks to which it is perfect for workshop and assembly conditions, in all welding positions. TIG welding equipment is cheap and easy to use. One of the shortcomings of this method is a small penetration depth and low efficiency.

Source Klimpel Andrzej: Welding, welding and cutting of metals. Scientific and Technical Publishing House, 1999.

 

Source Klimpel Andrzej: Welding, welding and cutting of metals. Scientific and Technical Publishing House, 1999.

PAW (Plasma Arc Welding)

Another method is arc welding with a non-consumable tungsten electrode in an inert gas shield - PAW (Plasma Arc Welding) To produce plasma, i.e. ionized gas, it is required to heat it to a sufficiently high temperature. Welding can be carried out using a non-consumable electrode (GTA plasma method) and a consumable electrode (GMA plasma method). The plasma of the welding arc is a gas heated to a state in which it is at least partially ionized and thus capable ofconduction of electric current. The temperatures occurring in the TIG arc reach 6000 °C and the arc column is cone-shaped, while in plasma welding the arc is focused thanks to a specially designed water-cooled nozzle. The advantage of such a solution, apart from narrowing the arc, is an increase in its temperature to about 20,000°C. This gas, flowing out of the nozzle as an ionized stream of high temperature, carries enormous energy, which is necessary for welding "with the eyelet". This welding technique allows you to make a weld in a material with a thickness of 3 to 15 mm in one pass, with a very favorable fusion profile and minimal deformation after welding. The achieved welding speeds are 40 - 80% higher than with the TIG method.

GMAW (Gas Metal Arc Welding), also known as MIG / MAG

In the arc welding method using a continuous metal electrode, the arc is shielded with gas supplied from the outside - GMAW (Gas Metal Arc Welding) The method is also known as MIG (welding with a consumable electrode in a gas shield). In this method, the welding heat is generated by an arc struck between a continuously fed metal wire electrode and the workpiece. Unlike the GTAW and PAW welding methods, the electrode here wears out and the arc burns in a shielding gas shield between the consumable welding wire and the workpiece.

FCAW (Flux Cored Arc Welding)

The next method is arc welding using flux cored wire, shielding the arc with flux contained in the wire, additional shielding with gas supplied from the outside - FCAW (Flux Cored Arc Welding). The flux-cored arc welding method is a variant of the GMAW welding method. This is a method in which the welding wire consists of a stainless steel metal coating filled with a solid flux, the role of which is similar to that of the electrode coating in the SMAW manual welding method.

Source Klimpel Andrzej: Welding, welding and cutting of metals. Scientific and Technical Publishing House, 1999.

SMAW (Shielded Metal Arc Welding)

SMAW is otherwise metal arc welding, arc shielding as a result of the decomposition of the electrode coating - (Shielded Metal Arc Welding) Shielded Metal Arc Welding is usually used for repairs of low-responsibility elements made of corrosion-resistant steel. SMAW welding equipment is the least expensive, but the welding process is slower than GMAW or FCAW. With thin elements in the SMAW method, burn-throughs may occur. This method is also known as MMA (Manual Metal Arc).

Other stainless steel welding methods:

We can additionally mention two welding methods, which we will not describe in detail in this article:

• Laser welding using a concentrated and coherent beam of light focused on the joint - LBW (Laser Beam Welding)
• Electron beam welding - EBW

From all the methods mentioned above, the most common welding methods we can come across are: MMA / TIG, MIG / MAG.

Disadvantages of stainless steel welding

The above description shows that we have a wide range of choice among stainless steel welding methods.

Limitations and disadvantages of stainless steel welding:

1. The need to have a qualified welder, there is currently a shortage of this type of specialists.
2. Aesthetic defects arising during welding.
3. The need for specialized equipment.
4. Basic MIG/MAG welding has limited weld pool control, relatively high amperage, potential for spatter.
5. MMA welding may have shortcomings such as spatter, porosity, low productivity
6. The disadvantage of the FCAW method is the high price of the cored wire.
7. The TIG method is limited by a small depth of penetration and low efficiency
8. Welding consumes a lot of electricity.

Stainless steel bonding

In the case of joining stainless steel with each other or with plastics or composites, we can use bonding technology instead of traditional joining methods. Current adhesives available on the market allow us to connect these materials structurally while maintaining high aesthetics of the connection. You can read about how to design such a joint, what to pay attention to and how to prepare for it in this article on our blog.

Of course, like any technology, this one also has some limitations. One of them are health and safety restrictions that you should pay attention to. In the case of one-component adhesives, the downside is the setting time and the associated need to have a holding area for glued elements so that the adhesive can harden. The most important thing is to choose the right adhesive and to have personnel who know how to use this technology. Currently, training an employee in the field of gluing is much cheaper and less troublesome than finding a qualified welder on the market. We usually need the simplest set of tools, which are found in most workshops, they are: a tool for matting the surface (grinder, sandpaper) and, which is the most important element, a chemical preparation for degreasing the glued surface. Here it is best to use agents dedicated by manufacturers. In the case of plastics, I would avoid acetone, which will degrade the degreased surface. A similar situation occurs in the case of extraction naphtha, which is used for degreasing. We strongly advise against degreasing elements with extraction naphtha, as the fractions available on our market leave a greasy film that weakens adhesion and makes it difficult to glue elements. Various types of alcohol are popular degreasing agents. The most popular and very versatile agent is IPA.

The first stage of gluing is the preparation (matting and degreasing) of the surface. Then we can start gluing. The investment we have to make is to equip the employee with a suitable gun for glue application. In the case of advanced two-component technologies and high-capacity pneumatic guns, the one-time cost is about PLN 3,000 net. In the case of using smaller packages or hand guns, you have to spend about PLN 150-900 net for the equipment, depending on the type of device. In our instructional videos you can see how to handle two-component adhesives, which are currently one of the best adhesive solutions for these applications.

The advantage of the gluing technology is relatively quick curing (the element can be moved after 25 minutes). We encourage you to watch our instructional video on bonding stainless steel. It also shows the strength tests of the connections obtained. In most cases, we obtain material strength without interfering with the aesthetics of the glued materials. This is of great importance in the case of elements requiring high aesthetics of the connection.

Summary

1. INOX stainless steel is a material with special properties, such as resistance to corrosion, high temperatures or aggressive environments, which makes it widely used in various industries.
2. Traditional methods of joining stainless steel include welding (e.g. TIG, PAW, GMAW, FCAW, SMAW), which have their drawbacks, such as the need for a skilled welder or the need for specialized equipment.
3. An alternative to welding is stainless steel bonding, which allows for aesthetic and structural joining of materials, but requires a good selection of glue and training of staff in the field of bonding technology.
4. Disadvantages of gluing include health and safety restrictions and setting time in the case of one-component adhesives, which requires a holding area for glued elements.
5. Today, training an employee in bonding is less expensive and less cumbersome than training a skilled welder, and the necessary tools are readily available in most workshops.

It is important that gluing technologies are developing so dynamically that they should be treated very seriously on an equal footing with traditional methods when choosing a bonding method already at the construction stage.

If you have any questions, please write to us or leave them in the comment. We answer all.

Sources:

Klimpel Andrzej: Welding, welding and cutting of metals. Wydawnictwa Naukowo-Techniczne, 1999.
Górka, Jacek, and Sebastian Stano. "Microstructure and properties of hybrid laser arc welded joints (laser beam-mag) in thermo-mechanical control processed S700MC steel." Metals 8.2 (2018)
Yan, Jun, Ming Gao, and Xiaoyan Zeng. "Study on microstructure and mechanical properties of 304 stainless steel joints by TIG, laser and laser-TIG hybrid welding." Optics and Lasers in Engineering 48.4 (2010): 512-517.
Arnold, Ryan W., Edward C. Combe, and John H. Warford Jr. "Bonding of stainless steelbrackets to enamel with a new self-etching primer." American Journal of Orthodontics and Dentofacial Orthopedics 122.3 (2002): 274-276.