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2019.09.10 Trends, Maintenance

Maintenance of modern cutting fluids

The four cornerstones to achieving proper cutting fluid economy are chemistry, system design, maintenance, and biological protection. 

These four corner stones are necessary in order to optimize for a sustainable and energy efficient usage – extending the time between changes – as well as a good work environment and health of operators. Provided, of course, that ventilation, extraction and other handling meet, and preferably exceed, the norm.

In a series of blog posts, we will go through each of the four cornerstones. In this post, we are explaining more about cutting fluid maintenance and how the need for maintenance changes as the content of the cutting fluids changes.

The importance of concentration

One of the most important parameters is the fluids' concentration. Traditionally, having the right concentration was important only in terms of having the desired lubricity. In non-sensitive processes the concentration could therefore vary greatly, with it being possible to save the fluids with the addition of biocides.  

Nowadays, biocides as we know them are being phased out. They are not prohibited – but any use requires labelling, air measurements, warning texts, and documentation of management and personnel for many years. That is why many avoid using biocides completely, making the workplace as healthy and attractive as possible.

In order to obtain stable fluids without traditional biocides, the formulas have changed radically in recent years. Instead of biocides, so-called biostatic components are used. This is usually a mix of substances that create an environment unfavorable to bacteria. The components are not registered as biocides, since their primary function is not to kill living organisms but instead to maintain a high pH – however, the purpose is the same and some experts have taken to calling them "unregistered biocides".

Unlike the active biocides used previously, biostatic components aren’t as effective at killing bacteria at a low concentration. Therefore there is now a much higher need for precise measurements, to ensure the concentration is correct and that the liquid can deliver maximal efficiency.

Higher pH

Common to most modern cutting fluids is that the pH value is higher than with older formulas. Between the 80s and the 00s, the lower limit for corrective action was around 8.7. Today, it is usually recommended that pH should be at 9.0-9.2 for most liquids, as a high pH value complements the unregistered biocide package’s bacterial effect.

Worth noting is that when the right concentration is maintained in modern cutting liquids, a correct pH value is also commonly maintained since, in most cases, the pH value and buffer capacity of the concentrate is higher than before. Thus, pH acts as an important parameter in the synergistic function of the new liquids.

So, if you repeatedly suffer from a reduced pH value in your cutting fluid, we recommend using tank-side pH-adjusters, or changing the cutting fluid type. The pH and buffer of the liquid may simply be too low in relation to the actual replenishment of concentrate.

Complementing biological protection with other technologies, such as UV-technology or automatic measurement and control of concentration has become increasingly common, and ensures that the cutting fluid is not spoiled by temporary pH drops or concentration dips. It’s an investment that pays off!

The following tables list the parameters appropriate to measure in single and central systems:

For single systems

Parameter

How it works

Usual frequency

Concentration acc. to refractometer (%)

By measuring the refractive index with a refractometer and using a product-specific conversion factor, one can calculate the actual product concentration (%) in the mixture. The oil in the concentrate affects the refractive index most and that’s why leakage oil can interfere with the analysis. Synthetic liquids generally have higher conversion factor than emulsions and semi-synthetics.

1 time/day

pH value

The pH value is a measure of acidity or alkalinity in the solution. Water-miscible liquids are intended to work within a certain pH range depending on the use. The pH value of the solution may be adversely affected by contamination or bacterial attack. The lower limit before action has previously been around pH 8.7-8.8. Today, the lower limit is usually 9.0-9.2.

1 time/week

Bacteria acc. to dipslide

(CFU / ml)

Bacteria produce acidic substances that can cause corrosion problems, bad odors or, in extreme cases, unstable emulsion . In laboratory analysis, the number of aerobic bacteria per milliliter of fluid is measured. Aerobic bacteria need oxygen to survive and are first to infect water-miscible fluids. Note that many types of bacteria are not detectable by the so-called dipslides used for the analysis.

Previous common limit value: <10 3 CFU / ml.

Today’s limit value: > 10 ^ 4 -10 ^ 5 CFU / ml

1 time/week

Mold/yeast

(Y/N)

Mold and yeast development can be limited to "inaccessible" places in a circulating fluid system and the source can be difficult to trace. Therefore, the results are not quantitatively stated. Mold and yeast should always be physically removed where possible, as they can form a sponge-like surface, so-called biofilm, that can block filters, pipes, and nozzles if not addressed.

1 time/week

In central systems used commonly in larger production plants, errors and disturbances in the cutting fluid can lead to large costs and production losses. Therefore, best practice is usually to perform a series of tests on these systems to see trends and conjunctions. These usually take place more frequently. See the table below for examples of common tests and recommended frequency for central systems:

For central systems

Parameter

How it works

Usual frequency

Concentration acc. to refractometer (%)

See table above

1-2 times/day

pH value

See table above

1 time/day – 1 time/week

Bacteria acc. to dipslide (CFU / ml)

See table above

1 time/day – 1 time/week

Mold/yeast

(Y/N)

See table above

1 time/day – 1 time/week

Concentration acc. to TA (%)

All water-miscible liquids must first be mixed with water to the correct concentration. By measuring the alkalinity (= buffer capacity) and using a product-specific conversion factor, the actual product concentration (%) in the mixture can be calculated.

1 time/week

Leak oil (%)

By comparing the concentrations according to IR and cleavage, one can calculate how much leak oil there is in the system. The principle is that leak oil does not contain lubricating ester or fatty acids – which is why the difference between the cleavage concentration and the IR concentration results in leak oil. Too much leak oil can affect the droplet size of the emulsion.

1 time/week

Concentration acc. to cleavage (%)

All water-miscible liquids must first be mixed with water to the correct concentration. Here, the system’s total oil content is analyzed, i.e., oil from both the cutting fluid and the leak oil. Based on this, the product's concentration is calculated using a product-specific conversion factor. This way, the actual product concentration (%) in the mixture can be calculated.

1 time/week

Chloride

The chloride content is measured on recirculating synthetic cutting fluids and sometimes in emulsions, as too much chloride can impair the anticorrosive capacity of the cutting fluid. A common limit value for synthetic liquids is 100 ppm, for emulsions usually a little higher.

1 time/week

Corrosion (iron filings on filters)

This method measures the rust protection in a product. If the product does not contain enough protection, the goods being processed or the machinery may rust. The reason a product contains too little rust protection may be that it has been consumed in the system.

1 time/week

Suspended solids (mg/l)

This analysis measures the amount of solid particles in a water-miscible liquid and shows the purity of the liquid. High particle levels can be a sign of filter system problems and lead to disruptions in the process.

1 time/week

General notes

Not every test described above need to be used for all systems. There are also additional tests applicable in specific systems for better control. It is not possible to set recommended limit values for each analysis, as these vary with the specific product and operation.

Read more

We have developed a checklist where you can clearly see what works well in your workplace - and where there are gaps that must be addressed.

(JÖ)

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Hans Ahlgren
Hans Ahlgren

Hans introducerade processvätskerening inom Wallenius Water 2011 efter ett flertal lyckade fältinstallationer. Processvätskerening är idag ett av Wallenius Waters fokusområden. I dag arbetar Hans med strategisk partnerutveckling inom affärsområdet.

+46 8 120 138 37
moc.retawsuinellaw@nerglha.snah
Hans introduced process fluid purification within Wallenius Water in 2011 after several successful field installations. Today purification of process fluid is one of Wallenius Water's focus areas.

+46 8 120 138 37
moc.retawsuinellaw@nerglha.snah
Hans führte die Reinigung von Prozessflüssigkeit innerhalb Wallenius Water im Jahr 2011, nach mehreren erfolgreichen Feldinstallationen, ein. Heute ist die Reinigung von Prozessflüssigkeit eine der Schwerunkte von Wallenius Water.

+46 8 120 138 37
moc.retawsuinellaw@nerglha.snah

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