Cutting Fluids Part 4 pdf

Most fluid mixers operate based upon the ‘venturi

principle’ 21 and because of this, there will usually be a

degree of fluctuation of the dilution, if the water pres￾sure should change during its operation – particularly

if other equipment within the factory draws water

when required. In view of any potential water pressure

variation, it is normal practice to use a water supply

that is not subject to such fluctuations. Many local

water authorities may well require that a header tank

with an air gap is used, to prevent any possibility of

contamination of the water mains. When mains water

is used, many local authorities will provide the nec￾essary water quality information, but if another water

source is used, it will need to be analysed by the user.

In Fig. 207, the graph illustrates the results of concen￾tration measurements, taken from zero → 6%, obtained

by different techniques, such as:

• Refractometer assessment – more on this apparatus

shortly,

• Measurement of the total alkalinity of a product

containing nitrate,

• Boron determination by Atomic Absorption (AA)

method,

• Measurement of the total alkalinity of a product

not containing nitrate,

• Hypothetical ‘real’ concentration ‘R’, set arbitrarily

at 3%,

• Determination of anionic emulsifier content (b) @

water hardness of 10° GH,

• Determination of anionic emulsifier content (a) @

water hardness of 10° GH,

• Determination of nitride content,

• Determination of anionic emulsifier content (a) @

water hardness of 30° GH.

NB  Water hardness can be easily determined with suf￾ficient accuracy using indicators in tablet form, while

the pH value and bacteria count can be estimated as

21 ‘Venturi principle’, is: ‘A convergent-divergent duct in which

pressure energy is converted to kinetic energy at the throat.’

When utilised with its associated ‘Venturi meter’, this being

a flow meter in which the pressure drop in a Venturi is used

to give an indication of flow. [Source: Carvill, 1997]Where in

the case of emulsion dilution ratios, this fluid mixer arrange￾ment – with the apparatus situated in the top of the drum and

connected to the water supply – can be employed and then

subsequently adjusted in-situ, to give the desired coolant mix￾ture.

described in the following section. For more detailed

analysis, then laboratory facilities are necessary, this

assistance is often provided by the cutting fluid manu￾facturer’s laboratory service department.

8.8.2 Monitoring, Maintenance

and Testing of Cutting Fluid –

in Use

While in use the cutting fluid is subject to various in￾fluences that may affect its properties. Such influen￾tial factors include: leakages from the machine tool’s

lubrication and hydraulic systems (i.e. ‘tramp-oil’);

surface contamination on the work piece: prior to ma￾chining; or by people: spilled drinks; food particles;

environmental influences. It is paramount that the

health monitoring of a cutting fluid is on-going and

undertaken at periodic intervals, whilst spot-checks

may also be necessary in order to detect undesirable

changes in the fluid’s properties, enabling corrective

action to be taken, as appropriate. Hence, the moni￾toring of the cutting fluids are fundamental to their

life, but a relevant question could be raised: ‘What

characteristics do we have to monitor?’ Probably the

most common cutting fluid tests, include the following

measurements:

• Concentration,

• pH (Alkalinity),

• Corrosion protection,

• Fluid stability,

• Bacteria count.

The above tests will shortly be considered in more de￾tail, in the appropriate section. Prior to this, it is im￾portant to ensure that the machine tool is thoroughly

cleaned, before a new ‘charge’ of cutting fluid is poured

into either the machine’s reservoir, or to a central cool￾ant distribution tank – supplying the needs of several

machine tools.

M a c h i n e C l e a n i n g

It is important to any cutting fluid system that it is cor￾rectly cleaned before fresh fluid is introduced, if the

optimum performance from it is to be obtained. Such

machine tool cleaning procedures, should include the

following stages:

Cutting Fluids 411