In the manufacturing industry, idle machines are a sore sight. Idle period of machining is not only a threat to business in general, but also to the metal working fluid.
Water miscible coolants are designed and optimised for continuous mass flow and aeration. Therefore, longer system downtimes are not conducive for coolant health and longevity. Since coolants are used to constant top up – circulation and energy intake, microbiology (bacteria/fungus) and phase separation are possible threats during long idling periods (running into multiple days). Performance problems, therefore, are a consequence upon reactivation after a long downtime or idling period.
In order to avoid/milden the performance problems and enable water miscible coolants to endure long idle periods, the following methods should be considered depending on the type of water miscible metal working fluid and the fluid system.
It is important to note that a lot depends on the formulation of the coolant. It is finally an engineered product that involves technology and careful selection for robust ingredients. A well-formulated coolant will have a higher capacity to withstand idle times.
Anyhow, the following are generally applicable advice and can be considered as standard procedure during idle times:
Increasing concentration of the coolant
Before stopping a system, the concentration of the coolant should be increased a couple of percentage points, above the minimum prescribed by the supplier. For example, if the minimum concentration prescribed by the supplier is 5%, then it should be increased to 7-8% before the start of the idle period. In case of the HYCUT two component metal working fluid, only the concentration of additive must be increased maximum up to 3.5%.
Circulate the coolant
As coolants are designed for continuous mass flow and aeration, it is highly advisable to circulate the coolant as much as possible during the lockdown, as bacterial growth is inhibited at higher oxygen levels.
Treating the emulsion with a broad-based biocide
The emulsion could as well be treated with a broad-based biocide; for example, ADDI PROX MB/R for preservation before stoppage. If the system has already been stopped and then the biocide is added, one should make sure to circulate the coolant.
Keep checking the pH & concentration
One should keep checking the pH and concentration as frequently as possible. They should remain within the range prescribed by the supplier. Should these two remain stable, it is quite likely that the coolant will sustain the idle period. Formulation of the product is quite crucial here.
Get rid of the tramp oil
The idle period is a good time to get rid of the tramp oil. Wherever possible, one should let the oil skimmers run. Tramp oil could inhibit aeration, leading to biostability issues and might also affect the dispersion (droplet size) of an emulsion leading to physical stability issues.
Getting rid of chips and swarf deposits
It is also advisable to let chip conveyors run during idle period to remove chips form coolant tank beds. Chips and swarf deposits could become ideal breeding grounds for bacteria and fungus. Getting rid of them helps in maintaining the emulsion health.
As worrying as the times are, they provide a good opportunity to investigate one’s process thoroughly. Because of the COVID-19 lockdown and various restrictions imposed, we all have limited resources which could be deployed for such maintenance activity. Therefore, a process evaluation helps in identifying machines/systems where it’s worth deploying such resources for organisational benefit.
Taking the opportunity
Various parameters, such as (but not limited to) coolant service life (sump life), achieved level of filtration/chip extraction from the machine, the tank capacity of the machine, coolant tank type (stand-alone or central), etc must be considered while deploying preservation steps for coolant during such extended lockdowns. For example, in case of stand-alone machines, it is much wiser to try to preserve the coolant in 1000 plus litre or larger tank (machine coolant sump) than a 200L tank, where the coolant has already delivered, let’s say, a 12-month service life.
Likewise, for a central system, not all parts of the system may be continuously flushed and circulated. For example, individual high-pressure tanks on some machine connected to the central tank. The opportunity must be taken to clean such subsystems.
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