Are Surfactant-free Neutral Cleaners the Future Technology?

Transcription

1 Cleaning and Pre-treatment I Neutral cleaner concepts In direct comparison Are Surfactant-free Neutral Cleaners the Future Technology? For Industrial component cleaning, a large number of different cleaning concepts are implemented around the globe. Most recently, surfactant-free products have been introduced with great success. It is high time to have a closer look at their application characteristics in comparison to traditional surfactant-containing products and to carry out a detailed evaluation for the potential user. Dr. Florian Treptow, Kai-Philip Wulfestieg, Tom Böhmig tion temperatures below the cloud point of the surfactant package, especially in spray applications. At temperatures above the cloud point they may be considered as low-foaming but they do not work completely free of foam. For true low-temperature applications in the range of 2 to 4 C they often are not considered due to their limitations. Designme Tobais Franke For more than 25 years, salt-free neutral cleaners have been used on a large scale for industrial component cleaning: in first stage, interprocess and final cleaning applications. Product usage takes place most commonly by spray, frequently combined with dip, flood-immersion or ultrasonic applications (Figure 1). Surfactant-based neutral cleaners tend to foam at applica- Figure 1 > Cleaning of gear parts by flood-immersion 36 JOT International Surface Technology 3 I 216 The new surfactant-free neutral cleaners are characterised by extremely low foam generation even at ambient temperatures. This now also makes them relevant in high pressure deburring operations, but also in ultrasonic applications or for bath maintenance by filtration techniques where foam is highly undesirable. In addition to their low foaming characteristics, several other neutral cleaner properties are important, such as: Ability to remove oils and particle/debris contaminations: Metal working fluids normally can be washed off easily, whereas stamping fluids may be more difficult to remove Emulsifying / demulsifying properties: Separation of oils via skimmer and settling tank etc. Multi-metal capability: In addition to steel and cast iron, Al, Mg, stainless steel, copper, brass and titanium are being processed Temporary rust protection: Transport and storage protection without corrosion Stability against microbacterial attack: Resistance against attack from bacteria and funghi Application concentration: Low usage of chemicals, high efficiency, reduced cost

2 Figure 2 > Development of neutral cleaners over past years; Products reviewed in this article marked in blue colour (*CP = Corrosion protection) ath lifetime: Long bath life and extenb ded dump intervals for low cost in use Favourable labelling, no impact onto workers and environment: Products without labelling are being preferred universally. The current article takes up the topic of different neutral cleaner generations (Figure 2) and provides an evaluation of various cleaner concepts. The cleaning products investigated are characterised in Table 1. Experiments and results The test methods applied and the results achieved for the aforementioned neutral cleaners are described in the following sections. Temporary rust protection via chip/filter paper method according to DIN g of iron chips are placed onto a filter paper and soaked with 2g of cleaner solution for 2 hours at ambient temperature. After removal of the iron chips the filter paper is rinsed and dried. The degree of rust is evaluated by comparing the filter with standard pictures for the grades -4 (=no corrosion, 4=strong corrosion). Several cleaner concentrations and water hardness values have been tested. The results are summarised in Table 2. The cleaning products investigated are characterised in Table 1 N-SF N 42 K N 61 Generation 1 Generation 2 Generation 3 Neutral cleaner salt free Neutral cleaner salt free Neutral cleaner salt free Multi-metal capability limited excellent excellent Surfactant containing no* Boron and FAD** free Densitity [g/cm³] 1,6 1,42 1,78 ph of concentrate 9,4 1,2 1,2 ph 3% in demin water 9, 9,8 9,7 Cloud point ( C) 4 <2 none Application temperature [ C] Application concentration [%] ,5 3 Labelling according (EG) No. 1272/28 CLP none sensitising none Type of cleaner Water hazardness class WGK [Index] * free from anionic/nonionic surfactants **FAD=Formaldehyde releasing material 37

3 Aluminium Copper Brass Zinc Cleaning and Pre-treatment I Neutral cleaner concepts In direct comparison It is obvious that the generation 2 und 3 products provide excellent temporary corrosion protection even at low product concentration of 2% and in city water of 2 dgh. The generation 1 product is inferior in that respect and cannot compete. ity for components made of light and yellow metals. For cast zinc parts the generation 1 product is completely incompatible. The generation 2 and 3 products are equally compatible with all tested substrates. Slight discolouration, if at all, may be observed on zinc surfaces (Figure 3). Multi-Metal capability with strip test Metal strips made of aluminium, copper, brass and zinc are cleaned and polished and subsequently partly immersed in a 3% neutral cleaner solution in demineralised water for 1 min at 5 C. After rinsing and drying, the metal strips are evaluated visually. A weak attack onto the metal surface is shown by a discolouration at the three-phase boundary, a significant attack by a discolouration on the entire surface. As a result, the generation 1 product proves a limited multi-metal capabil- Foaming behaviour in shaking test 1 ml of a 3% cleaner solution in demineralised water of 2 C are transferred into a measuring cylinder and mixed thorougly. The foaming behaviour is evaluated immediately after shaking the measuring cylinder. The results of the shaking tests for the neutral cleaners investigated are shown in Figure 4. Both surfactant-based products show a distinct tendency towards foaming whereas the surfactant-free product does not foam at all. Figure 3 > Results from metal strip tests. Metal strips from left to right: N-SF; N 42 K; N 61 N-SF N 42 K N 61 Generation 1 Generation 2 Generation 3 2% concentration / 3.5 dgh [Index] -1 3% concentration / 1 dgh [Index] 3 4% concentration / 2 dgh [Index] 3 38 JOT International Surface Technology 3 I 216 Table 2: Results of chip/filter paper method according to DIN Figure 4 > Results of shaking test and detailed view. Left N-SF, middle N 42 K, right N 61 Remark: N 42 K has a low cloud point of 2 C and appears milky-white at ambient temperature

4 COLOSSAL CLEANING Figure 5 > Foaming behaviour determined with Foam Analyzer DFA 1 Conditions: 3% cleaner in DIW, 5 C, 2 ml bath volume, 6s air injection Table 3: Results of minimum cleaning time measurements N-SF N 42K N 61 Generation 1 Generation 2 Generation 3 Mineral oils 9, 2, 5 mm²/s Mineral oil 5 mm²/s, 12 h 7 C aged Stamping oil, chlor-free Stamping oil, chlor-containing Temporary protection, oily Temporary protection, wax PERO R5 CLEANING PLANT Efficient cleaning of large volumes and heavy loads The standard cleaning plant PERO R5 provides technical cleanliness, degreasing and preservation especially The qualitative results obtained in the shaking test has been further quantified by means of foam measurement with the Foam Analyzer DFA 1 from Krüss. Foaming behaviour analysed with Foam Analyser DFA 1 from Krüss 2 ml of a 3% cleaner solution in demineralised water are filled into the Foam Analyzer DFA 1, heated to the preset temperature of 5 C and then purged with air for 6 seconds. The build-up and breakdown of foam is tracked by means of an LED light and light sensor. It has shown that the surfactant-based neutral cleaners produce 9-1 mm of foam height, which is about five times more compared to the surfactant-free product. Also, the foam breaks down much slower than in the latter product. For the surfactant-based products it takes about 15 seconds for the foam to reduce to 3% of the peak value, whereas it takes only 3 seconds in case of the surfactantfree product (Figure 5). Consequently the qualitative results from the shaking tests are fully confirmed by the measurements with the Foam Analyzer. Emulsifying / demulsifying properties 1 ml of a 3% cleaner solution in demineralised water of 2 C are transferred into a measuring cylinder. After the addition of 2% hardening oil: Isorapid 277 HM, the phases are mixed thoroughly. The demulsifying property of the neutral cleaner so- energy-efficient cost-effective fast and reliable Test clean your own parts in our competence center. Call +49 () PERO ADVANCED PARTS CLEANING SYSTEMS 39

5 Cleaning and Pre-treatment I Neutral cleaner concepts In direct comparison Figure 6 > Demulsifying properties for 2% hardening oil Isorapid 277 HM at 2 C; left N-SF, middle N 42 K, right N 61; left picture 3s separation time, middle picture 5 min separation time; right pictures are detailed pictures after 3s (above), 5 min (below) Table 4: Examples of industrial applications for the cleaners investigated N-SF Generation 1 N 42K Generation 2 N 61 Generation 3 Industry segment Diesel engines Metal hardening OEM Supplier Type of parts Crank case Splined shafts Support straps Type of metal Alloyed steel Alloyed steel Steel Plant function Final cleaning Entrance cleaning Final cleaning Plant type Dip plant Dip plant Tunnel spray plant Sequence Clean-Rinse-Rinse Clean-Rinse-Dry Clean-Rinse-Dry Application Dip + Spray Dip Spray (<8 bar) Bath volume [m³] ,4 Temperature [ C] Concentration [%] 1,5 2,-2,5 1,5 Bath lifetime [weeks] n.b. >5 1 Requirement #1 Cleanliness of component Cleanliness of component Cleanliness of component Requirement #2 Surface w/o stains No impact on diffusion biostable, no foam Requirement #3 - No impact on protective paste Rust protection Downstream process VCI packaging for transport/storage Case hardening, plasma nitriding Assembly lution is evaluated visually after 3 seconds and 5 min. As a result, the generation 2 and 3 products exhibit significantly better demulsifying properties for lubricants and oils compared to the generation 1 product (Figure 6). In practical applications, excellent demulsifying properties are important for avoiding re-contamination of the cleaned components. In addition, the emulsifying/ demulsifying properties play an important role with respect to the sepa4 ration of oils via skimmer and settling tanks, hence affecting the lifetime of the cleaner bath. Minimum cleaning time for oil based, cutting, stamping and rust preven tion fluids based on VDA For minimum cleaning time measurements, a 3% cleaner solution in demineralised water is transferred into a 9L GS spray washer.then 7.5x15 cm cold-rolled steel panels supplied from Q-Lab contaminated with oil of approximately 5 g/m² are sprayed for in- JOT International Surface Technology 3 I 216 creased periods of time in measured steps. After each spray cleaning cycle the panels are rinsed with water and the wetting properties are evaluated after draining for 3s. The minimum cleaning time is reached when >95% of the steel panel area exhibits a water break-free surface and the water film pulls back only slightly from the cut edges. The minimum cleaning time for spray application at 6 C for various mineral oil based industrial products are summarised in Table 3. A minimum clean-

6 ing time of <1s has been observed in all cases. Therefore a distinction between the neutral cleaners investigated is not possible. The results show that the removal of oily contaminations takes place fairly rapidly and hence is not an issue in practical applications where typical treatment times are in the range of several minutes. Comparison with line experience Typical applications of the three neutral cleaner types investigated are summarised in Table 4. The quality profiles of the products determined under laboratoy conditions with respect to cleaning performance, multi-metal capability, foaming behaviour, demulsifying properties and temporary corrosion protection are fully in line with the practical experience made in industrial applications. Conclusions and Future Outlook The comparative tests show that neutral cleaners of earlier generations may still be used for standard applications, i.e. applications where multi-metal capability, low-foam properties and high temporary corrosion protection do not play a major role. The generation 2 product takes an intermediate position, but gets very close to the surfactant-free product in various respects. It cannot compete, however, with the low-foam properties of the latter. Where excellent temporary corrosion protection, full multi-metal capability, reduced bath temperature and zero-foam properties are required, the surfactantfree neutral cleaner of the latest generation will be the product of choice. Further product advantages exist with respect to ultrafiltration (no drag-out of surfactants), the suitability for high pressure applica- tions such as high pressure deburring (currently tested up to 2 bar), the extremely low consumption and the markedly increased bath life. Through the use of this product type all current tasks in industrial component cleaning can be covered as well as the exploration of new applications.// The Authors Dr. Florian Treptow, Kai-Philip Wulfestieg Tom Böhmig Petrofer Chemie, Hildesheim info@petrofer.com, Innovative Measurement Technology in premium FISCHER quality Knowledge, Competence, Experience the FISCHER hallmark. Since 1953, FISCHER has developed and produced increasingly innovative, powerful and versatile technologies for a variety of industries and applications. Today, FISCHER instruments are in use all around the globe wherever trueness, precision and reliability are essential. Whether for flexible and precise coating thickness measurements, exact material analysis and testing or micro hardness determination in nanometre range, FISCHER always offers the matching technology for optimal results with highest precision. Worldwide, FISCHER customers in industry, research and science depend on the reliability and accuracy of these fine instruments. FISCHER rises to this challenge with its rigorous quality standards and relentless development strategy to produce the most technically advanced, yet practical and easy-to-use measuring systems and software on the market. Coating Thickness Material Analysis Microhardness Material Testing 41