Aqueous parts cleaning after TEM deburring

The absence of burrs and cleanliness play an increasingly important role in all sectors of industry. Many manufacturing companies rely on thermal deburring (TEM) to effectively remove production-related burrs. The process produces components that are covered with an oxide layer. In this area, aqueous parts cleaning systems ensure safe, high-quality and at the same time economical cleaning of stubborn residues.

During thermal deburring, ridges, fraying and splinters of a workpiece are loosened with the aid of combustion processes. To this end, a precisely dosed gas mixture is ignited in a hydraulically sealed chamber. During a combustion period of about 20 ms, temperatures between 2000 and 3000 °C arise, whereby the excess burrs oxidise with the oxygen in the chamber and burn. The advantage of this method is that burrs and particles can be easily removed even in areas that are difficult to access, such as drilled holes or undercuts. However, during deburring, oxides are formed on the part surfaces, which impair the subsequent production steps such as coating, painting, welding or soldering as well as the optical appearance. Careful cleaning is therefore indispensable.

Cleaning - a key process

With a view to the subsequent processes, but also for the deburring process itself, cleaning plays an important role, because the parts should already be freed from superfluous oil, grease and coolant residues prior to deburring. The different oxide layers that form on the part surfaces during TEM deburring dependent on the material are altogether challenging to remove. On workpieces made of steel and grey cast iron reddish brown to black-brown rust is generated, which is partly firmly adhering, partly rests loosely on the surface as sooty dust. Especially on the rough surfaces of cast parts, oxide and graphite settle deep into the pores, which is particularly persistent and difficult to clean. On aluminium parts however, oxide arises in the form of firmly adhering white, partly yellowish spots and streaks. The task of parts cleaning is now to gently but effectively clean the various oxide layers and then protect the surfaces from corrosion.

Aqueous cleaning - an effective process for oxide removal

Especially aqueous cleaning systems using the kinematic process principle achieve excellent results when cleaning firmly adhering oxide layers. During the wet phase of this process, turbulences are created in a targeted manner by means of the co- or counter-rotation of the basket receptacle and spraying systems, which, in combination with temperature, cleaning additives and time, achieve a safe and effective cleaning effect.

With the aid of this cleaning principle, a three-stage cleaning process, during which spraying and flooding processes alternate, is recommended after TEM deburring. Tank 1 contains a neutral deruster, tank 2 a cleaning agent for post-cleaning and in tank 3 the final rinsing process with corrosion protection takes place. When choosing the neutral deruster, a distinction must be made between steel and aluminium. In the case of steel, for example, a neutral deruster with a weakly acidic pH value is needed. The advantages: a neutral deruster is gentle on the material, user-friendly and can be combined with suitable surfactants to improve wetting of the part surface. In addition, this deruster does not result in hydrogen embrittlement, which could lead to component defects at a later stage. The pH value can be additionally corrected by the addition of additives.

When using aluminium as a material, a cleaning agent with a more acidic pH value (pH 2-4, organic acid) is mostly used as a deruster.

The advantages of a three-stage cleaning process become particularly evident on the example of grey cast iron. During the first phase, the actual removal of the oxides takes place, mostly by combined spraying / flooding processes and the additional use of ultrasound. By adding an alkaline cleaner to tank 2, the highly active part surface is immediately neutralised and a further post-cleaning effect is achieved with the aid of ultrasound. The actual, temporary corrosion protection is then applied in tank 3. In order to maintain the efficiency of the deruster in tank 1 and not to neutralise it, it is important to eliminate cascading from tank 2 to tank 1 and to prevent the overflow. Tank 1 therefore requires its own fresh water supply.

Economical and resource-friendly

Combining kinematic process technology with a three-bath system reduces the need for cleaning chemicals by up to 15 % compared to other processes. This not only simplifies the bath change, but also saves costs for energy and cleaning chemicals. In addition, there is significantly less carryover between tank 3 and tank 2, which leads to a prolonged bath service life. Thanks to the wide variety of cleaning agents that have become available in the meantime, aqueous cleaning systems can be set up very flexibly and adapted to the high demands before and during TEM deburring. The plant and machine technology currently available permits gentle and high-quality cleaning, which reduces the use of highly concentrated, caustic cleaning chemicals to a more user-friendly level or even completely dispenses with them. In addition, efficient part drying technologies such as rotary hot blowing or vacuum drying significantly reduce CO₂ emissions.