Basic knowledge

Degreasing of sheet metal and metal parts - advantages and possibilities

| Editor: Theresa Knell

"Like dissolves like" - this chemical principle provides orientation when selecting the optimum cleaning medium. Watery media should be suitable for the process technology used, spray or ultrasonic cleaning.
"Like dissolves like" - this chemical principle provides orientation when selecting the optimum cleaning medium. Watery media should be suitable for the process technology used, spray or ultrasonic cleaning. (Source: Mafac Ernst Schwarz Machine Factory)

Contaminated component surfaces, such as those caused by residues of forming oils, impair the quality during production. Degreasing as a cleaning process therefore makes a significant contribution to the economic efficiency of the production process.

When processing sheet metal parts and metal, the use of lubricants and oils is sometimes necessary. For example, cooling lubricants are used before turning and milling or forming oils. Since the residues of grease and oils can have a disturbing effect in further processing steps, degreasing is part of the preparatory surface treatment. Special solvents, so-called degreasing agents, are used to this end. The dissolve greases and oils from the surface of the workpiece, thus degreasing and de-oiling them. Degreasing can be carried out with liquid solutions or in the form of dry degreasing.

When processing sheet metal parts and metal, the use of lubricants and oils is sometimes necessary. For example, cooling lubricants are used before turning and milling or forming oils. Since the residues of grease and oils can have a disturbing effect in further processing steps, degreasing is part of the preparatory surface treatment. Special solvents, so-called degreasing agents, are used to this end. The dissolve greases and oils from the surface of the workpiece, thus degreasing and de-oiling them. Degreasing can be carried out with liquid solutions or in the form of dry degreasing.

For the subsequent process to succeed, formed parts must be clean and free of grease.
For the subsequent process to succeed, formed parts must be clean and free of grease. (Source: Pero)

Why should metal sheets be degreased?

While lubricants and oils are necessary in certain processing steps and facilitate the above-mentioned forming, turning and milling processes, they have an aggravating effect in other processes. Among other things, they hinder the application of an even and durable coating. Before painting and applying a powder coating, it is therefore necessary to degrease the workpiece and prepare it for coating.

The same applies to other processes, such as anodizing aluminum or joining processes. Last but not least, degreasing can also be a demanded by the customer. The removal of greases, lubricants and corrosion protection oils can therefore also be useful or necessary if no further processing (in the company itself) takes place.

Degreasing of Sheet Metal and Metal

There are five basic types of degreasing processes:

  • Spray cleaning or rinsing of the workpieces
  • Immersion baths
  • Steam degreasing
  • Vibration cleaning
  • Dry degreasing

Thanks to the spacious meshed container measuring 1,250 x 840 x 970 mm, this parts degreasing system handles batches of up to 1,000 kg.
Thanks to the spacious meshed container measuring 1,250 x 840 x 970 mm, this parts degreasing system handles batches of up to 1,000 kg. (Source: Dürr Ecoclean)

Degreasing by rinsing

In this variant, the degreasing agents are applied to the workpiece under pressure through nozzles. The surface of the metal is thus rinsed. This does not only result in degreasing. Other residues and dirt, such as chips, are also removed from the workpiece. This type of degreasing involves chemical and mechanical cleaning. However, it is unsuitable for sheet metal parts or metal pieces with complicated shapes and some sections are more difficult to access.

Degreasing by immersion baths

In this form of degreasing, the workpieces are immersed in solvents. The degreasing agents remove the residues and remove them. However, this does not involve mechanical cleaning. In order to avoid this problem, additional ultrasound offers one solution. This technology ensures that grease and oil in grooves, cracks and drill holes can also be removed. This is due to the ability of ultrasound to generate micro- and macro-vibrations in the liquid. In order to make better use of the chemicals for degreasing, a cascade circuit is also used in some cases for the immersion baths. It also reduces water consumption. Depending on the shape of the workpieces and the available technology, the two processes of spray cleaning and immersion with ultrasound can also be combined.

Surtec has developed the Surtec 609 A Zetaclin for simultaneous surface degreasing and conversion in single chamber spray system.
Surtec has developed the Surtec 609 A Zetaclin for simultaneous surface degreasing and conversion in single chamber spray system. (Source: Surtec)

Steam degreasing is suitable for workpieces which are only slightly contaminated by grease and oil. The degreasing process is carried out in a chamber. The solvent is heated to boiling point and the steam is then directed onto the cold workpiece. In this case, the steam condenses and the solvent condensate is used to rinses the surfaces.

Degreasing with vibratory cleaning

In vibratory cleaning, no chemicals or aqueous solutions are required. Instead, the workpieces are vibrated, the frequency of which overcomes the adhesive force of grease, oils, chips and other residues on the metal. Dirt and lubricants are "shaken off" and then sucked off. No solvents are required, which has a positive effect on costs and the environment.

In this video Wacker shows part of the component cleaning process using modified alcohol for degreasing.

Dry degreasing

Dry degreasing requires neither water nor chemicals. This process was developed by BIP-Industrietechnik and is based on the effect of physisorption. Oil and grease bind to zeolites and can therefore be removed from the surfaces of the workpieces. Since there is no need for solvents or water, the subsequent drying of sheet metal and metal and the disposal of chemicals in the dry degreasing process are no longer necessary.

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Which substances are required for degreasing?

The substances required for degreasing depend on the type of degreasing process and the metal or sheet to be degreased.

View into the Rotainer pickling line from Siedentop: In this closed container system, the components are sprayed with immersion pickling.
View into the Rotainer pickling line from Siedentop: In this closed container system, the components are sprayed with immersion pickling. (Source: Oliver Farys)

In the past, halogenated hydrocarbons were used for degreasing. This substance has a very high cleaning performance and can therefore be used effectively. However, substances, such as trichloroethylene and perchloroethylene, have negative effects on the environment. Their use is no longer desirable due to modern environmental standards. Non-halogenated agents are a widely used alternative. A solution consisting of three components is also frequently used:

  • Electrolyte solutions with a pH value adapted to the material, ranging between mild and strongly alkaline
  • Salt mixture
  • Surfactants, i.e. cleansing substances

Electrolyte solution has a high water content, which is usually around 90 percent. The degree of alkalinity depends on the sheet metal or metal to be degreased. Mild alkaline solvents are used for aluminum, non-ferrous metals and zinc die casting, for instance. Strong alkaline solutions are used for degreasing steel and stainless steel. The salt mixture serves as a so-called builder substance. They therefore form the basis or grid of the solution. They are inorganic dirt carriers and saponify the grease.

Most people know surfactants from detergents and dishwashing liquids in their households. There, they fulfill the same purpose, but rather degrease sheet metal and metal and not dirty dishes: They wet, dissolve and emulsify or demulsify the grease and oil. When emulsifying, the grease is retained in the solution. When demulsifying, the greasy dirt floats on the surface of the solution - similar to the grease drops on a soup.

Visitors to Parts2Clean in Stuttgart.can learn everything about industrial parts and surface cleaning.

Which substance is used in dry degreasing?

Zeolites are used for the dry degreasing process described here. Zeolites are aluminosilicates in crystalline form. They occur in nature but can also be produced synthetically. In dry degreasing, grease-binding zeolites are applied directly or with the aid of a pad to surface of the workpiece. The grease binds to the inner surfaces of the zeolites and can then be removed from the sheet metal or metal together with the granules.

Which substance can be used on what metal?

Rising demands on cleanliness and increasing cost pressure make component cleaning and degreasing of formed parts a manufacturing step critical for quality assurance.
Rising demands on cleanliness and increasing cost pressure make component cleaning and degreasing of formed parts a manufacturing step critical for quality assurance. (Source: Höckh)

As mentioned above, mild alkaline solvents are used for aluminum and non-ferrous metals. For steel and stainless steel, on the other hand, stronger alkaline solutions are required. However, the selection of substances does not only depend on the material on which they are used. The degree of contamination and the type of grease or oil used also play a role. In the case of the above-mentioned solvent consisting of three components, the concentration and type of the individual substances can be matched and adapted to each other.

A blanket statement cannot therefore be made. It is important that the substances are selected to suit the material, the degreasing process and the type of grease. In practice, this adaptation may require tests and laboratory examinations, provided that the substances are not yet available in a prepared and efficient form.

Problems during degreasing

Degreasing is an essential step prior to coating, printing, varnishing and other processes, but is sometimes associated with challenges and problems. These include:

  • Selection of the appropriate procedure
  • Efficiency
  • Recycling costs
  • Disposal of chemicals

Selection of the appropriate degreasing process

As mentioned above, the choice of the degreasing process for sheet metal (parts) and metal is determined by the following factors:

  • Type of metal or sheet metal
  • Type of grease or oil to be removed
  • Degree of contamination, for example, if chips or other residues are still present on the workpiece

Additionally, the technology and capacities available for degreasing are also decisive factors. If a separate degreasing system is not to be installed, dry degreasing can be a suitable alternative. In the same way, outsourcing of the degreasing process to a specialized company is also a way of keeping your own costs as low as possible.

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Efficiency

Halogenated hydrocarbons achieve a very high cleaning efficiency. At the same time, however, these substances are also very harmful to the environment and are therefore rarely used any more. Today, the following media are more common for degreasing, which, depending on the design and process, also achieve high cleaning effects while at the same time reducing the impact on the environment:

  • Chlorinated hydrocarbons
  • non halogenated hydrocarbons
  • polar solvents
  • aqueous media

These substances are used in the following procedures:

  • Steam degreasing
  • Injection flood washing
  • Spray cleaning or rinsing of the workpieces
  • Immersion cleaning
  • Dry cleaning
  • Ultrasound

The various degreasing processes can be combined depending on their efficiency and the desired result. For instance, injection flood washing is suitable for coarse pre-cleaning, in which chips and some of the grease and oil are removed. Subsequently, the workpiece, which is only slightly soiled at this point, can be finely cleaned, for example by steam degreasing or spray cleaning.

Recycling costs and disposal of chemicals

If chemicals have been used for degreasing, they do not always have to be disposed immediately after use. It is also possible to recycle them. However, the procedures involved in this entail additional costs. This includes expenditures for:

  • Secure packaging
  • Transport
  • Reprocessing

Again, it is not possible to provide a specific number for the costs. This is because they depend on the type and quantity of chemicals used for degreasing. The same applies to the disposal of chemicals if they cannot be reprocessed. In the long term, processes such as dry degreasing or the use of ultrasound and vibration are therefore more cost-effective, since no chemicals are used during degreasing.

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This article was first published by belchnet.

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