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An ongoing drive by machine shops to increase productivity and reduce costs has seen the importance of cutting fluids increase, says Peter Bird of Exxonmobil Lubricants and Specialties.

Cutting fluids have three key functions to perform: lubricating the chip/tool and tool/workpiece contacts to reduce friction, helping to extend tool life and improve the surface finish of the workpiece; cooling the workpiece and tool to dissipate heat in the cutting zone, helping to prevent chip/tool welding and to improve dimensional accuracy; and flushing and removing metal chips (swarf) from the cutting zone.

However, with a multitude of factors including the operating environment, machining application and machined metal type all having an impact on a cutting fluid, no one cutting fluid can provide the lubrication, cooling and protection required in each and every operation.

As such, lubricant and metal working fluid providers, such as Mobil Industrial Lubricants, has developed a range of fluids to meet many of the varied machining operations in machine shops today.

There are two cutting fluid types: neat (straight) and aqueous (soluble/water miscible).

Neat fluids are not mixed with water and are used in machining operations such as tapping and threading of high alloy steels, which are beyond the typical performance profile of aqueous coolants.

Properly formulated products can improve machining in high-speed automated machining centres through high-quality cutting performance, reduced tool wear and enhanced surface finish.

Maintenance professionals should seek products that: are light coloured to allow clear visibility of the workpiece; have low misting characteristics to help workplace safety and product usage; and are chlorine free to support environmental concerns, while balancing with a high degree of lubricity and machining performance.

While neat cutting oils are provided in packs for immediate use, aqueous cutting fluids are provided in a concentrate form and must be diluted with water at the machine shop site before use.

Optimum performance for these aqueous coolants requires an ongoing partnership approach from both the lubricant supplier and machine shop operator to help maximise productivity and reduce unscheduled downtime.

First, operators need to work with their lubricant supplier to identify the most appropriate type of aqueous cutting fluid for the operating conditions.

There are three different types, all with different performance characteristics: milky or conventional cutting fluid – one with a high oil content (60-75 per cent) that forms a milky-looking emulsion on dilution with water; semi-synthetic cutting fluid – one with a low to medium oil content (10-50 per cent) that when mixed with water forms a translucent emulsion that is see through; and synthetic cutting fluid – those that do not contain any oil (chemical solutions) and are generally used for grinding.

Second, different concentrations are required for specific machining operations and metal type so it’s important that the correct concentration level is used.

Using the correct concentration is vital to the performance of the fluid and typically varies between three and 10 per cent.

For example, if a recommended concentration is five per cent, then the fluid has been designed to offer 100 per cent protection and machining performance at that level.

If the concentrate is just one per cent outside of this value there will be 20 per cent more or less additive within the working fluid.

Too high a concentration and there is the potential of issues such as skin irritation, foaming and filtration problems to occur and too low can lead to severe problems such as bacteria growth, corrosion and poor surface finish.

In addition, for machine tool applications, the mixing of different lubricating oils (slideway and hydraulic) and aqueous fluids is unavoidable.

Using lubricants that are fully compatible with the aqueous cutting fluid is important to help remove the build up of ‘tramp oil’.

Tramp oil can compromise the effectiveness of the coolant by shortening its effective life and adversely altering cutting performance.

The use of high-quality, compatible metal working fluids should be used in conjunction with a regular programme of removing (skimming) as much tramp oil as possible to extend the life of the coolant and avoid other potential performance and health and safety issues.

Once the correct type of coolant and operating concentration has been selected it is crucial to monitor the condition of the fluid going forward.

Parameters to monitor are: fluid concentration; pH value; bacterial and fungi count; and dissolved salts concentration and hardness.

Fluid concentration is the most important factor to monitor and should be checked and recorded formally.

During the lifetime of a coolant in service, the fluid concentration can change widely due to water evaporation from heat generation during the cutting process and losses due to highly pressured circulation.

Close monitoring is therefore required on a daily basis and any carefully measured counter actions carried out to remedy the problem.

Simply approximating the amount of water and concentrate to balance the fluid can lead to problems such as lowering the pH value of the fluid and increased bacterial activity, which will result in shorter coolant life, lower quality products and increased costs.

The following actions should be carried out on a daily or weekly basis: check the concentration of coolant with a refractometer at the beginning of every day/shift; check pH value with pH meter or pH paper at the beginning of every day/shift; check diluting water and coolant hardness with water hardness strips every week; remove as much tramp oil as possible every week after the coolant has been static for one hour; always top up with diluted coolant, never with just water; and keep good records of coolant progress using monitoring charts.

Cutting fluids, especially water soluble coolants are sometimes seen as potential problem products due to the amount of variables involved in formulating and monitoring the product in use.

However, by following the suggestions provided above, businesses can help enhance overall efficiency and maximise productivity.

ExxonMobil Lubricants and Specialties

Mobil Industrial Lubricants: A Legacy of Innovation, Advanced Technology and Productivity

For more than a century, the team behind Mobil Industrial Lubricants has been delivering premium products and comprehensive maintenance solutions that help companies boost productivity, enhance the performance and life of their equipment, increase profitability, reduce downtime, and stay ahead of the competition.

Today, Mobil Industrial Lubricants are used extensively in many industrial market sectors – including power generation, general manufacturing, metal working, food and beverage processing, pulp and paper, cement, construction, metals and mining.

Proven Synthetic Technology

For companies that rely on equipment that is often subjected to extreme operating conditions, such as high temperatures, extreme loads and pressures, excessive moisture or high speeds, Mobil SHC lubricants and greases offer an ideal solution.  That’s because they are formulated with application specific performance in mind and are designed to deliver exceptional lubrication, helping to reduce operating temperatures, minimize component wear and extend oil change intervals compared to Exxon Mobil’s conventional mineral oil based products.

In fact, Mobil SHC products are endorsed for use in over 5,800 applications by more than 1,100 major equipment builders around the world for exclusive or preferential use.

To learn more about how Mobil Industrial Lubricants can help unleash your productivity and enhance the performance of your company’s equipment, please visit our website.

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