Cutting fluid

Find the cutting speed of a 50mm diameter bar being turned with a spindle speed of 178rev/min. 

The manufacturers of cutting-tool materials give recommendations for the cutting speeds at which their tool materials will cut various work materials such as brass, aluminium, steel and so on. A selection of these values is given for guidance in Table 7.2. 

At what spindle speed would a 200 mm diameter high-speed-steel milling cutter be run to machine a steel workpiece, if the cutting speed is 28 m/ min  

What spindle speed would be required to turn a 150 mm diameter cast iron component using cemented-tungsten-carbide tooling at a cutting speed of 160 m/min  

The basic role of a cutting fluid is to control heat, and it may do this by direct cooling of the work, chip and tool or by reducing friction by lubricating between the work, chip and tool. To cool effectively, a cutting fluid should have a high specific heat capacity and a high thermal conductivity. 

The fluids most readily associated with cooling and lubricating are water and oil. Water has a higher specific heat capacity and thermal conductivity than oil, but unfortunately will promote rust and has no lubricating properties. Oil does not promote rust, has good lubricating 

In general, the use of cutting fluids can result in less wear on cutting tools, the use of higher cutting speeds and feeds, improved surface finish, reduced power consumption, improved control of dimensional accuracy. 

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Antimicrobials. In slightly alkaline aqueous solutions, nitro alcohols are useful for the control of microorganisms, eg, in cutting fluids, cooling towers, oil-field flooding, drilling muds, etc (8—15) (see INDUSTRIAL ANTIMICROBIAL AGENTS Petroleum). However, only... 

Some cutting fluids, eg, oils, may present a fire ha2ard. Some work materials, eg, magnesium, aluminum, titanium (under certain conditions), and uranium, in finely divided form, also present fire ha2ards. Very small metal chips or dust may ignite. 

Consider short-sleeved overalls for workers using metal cutting fluids (avoids skin friction from cuffs saturated with oil and holding particles of swarf)... 

Tramp oil is caused when heat slideway, gear, hydraulic and spindle lubricants leak into water-based cutting fluids and can cause problems such as ... 

Reduced bacterial resistance of cutting fluids and subsequent reduction in the fluid life... 

All these problems directly affect production efficiency. Recent developments have led to the introduction of synthetic lubricants that are fully compatible with all types of water-based cutting fluids, so helping the user to achieve maximum machine output. 

New machining techniques are constantly being introduced. Conventional workpiece materials have improved progressively through close control of manufacturer and heat treatment, and new materials have been fostered by the aeronautic and space industries. The results have been ever improving output, dimensional control and surface finish. The continuous development of cutting fluids has enabled these increasingly severe conditions to be accommodated. 

These combined effects raise the temperature of the tool, workpiece and chip to a level that would be unacceptable in most operations if it were not for the presence of cutting fluid. Since the cooling effect is the greatest benefit, cutting fluids are widely known as coolants . In... 

Figure 52.12 Heat is generated both by deformation of workpiece material and by the friction of the chip across the tool tip. A cutting fluid acts as a lubricant to reduce frictional heat and simultaneously cools the whole cutting zone...

Cutting fluids provide benefits such as extended tool life, dimensional accuracy and good surface finish, all of which contribute to high rates of production. Almost invariably, the coolant that adheres to workpieces is relied on to protect ferrous components against corrosion while they are waiting further machining or assembly operations. 

However, its cooling properties can be utilized when other materials are added to improve machining performance. One of the most common water-based cutting fluids is the so-called soluble oil, which, in fact, is not a true solution but an oiTin-water emulsion in which very fine droplets of oil are suspended in water. Such a fluid has very effective cooling power and the petroleum oil and its additives provide its lubricating and protective properties. 

Machine operators working with emulsions can become susceptible to skin infections because of the combination of the de-fatting effect of soluble-oil emulsifiers and the abrasive action of metallic scarf, but bacteria in cutting fluids are seldom the source of such infections. High standards of personal hygiene and the use of barrier creams should prevent such problems. A more difficult situation arises when a soluble-oil emulsion becomes infected with bacteria capable of utilizing the emulsifier and mineral-oil components in the system. Even in clean conditions, untreated soluble-oil emulsions and solutions cannot remain completely sterile for any length of time. 

Neat oil is the name given to an orthodox petroleum cutting fluid, whether or not it contains additives, to enhance cutting properties. Oils of this sort are available in a very wide variety, and many combinations of work piece material, machining characteristics and tooling requirement justify special formulations. The neat oils have lower specific heat than water, so they have to be fed to the cutting zone in copious amounts to provide the optimum cutting effect. 

The increasing diversity of operations, new materials and processes and the constant demand for improved production efficiency can only be met by various additives and compounding agents being blended into the oil to enhance its performance. Additives tend to be expensive and the selection of enhanced cutting fluid is only justified by overall production economies. 

The cutting fluid has to cool and lubricate without allowing grinding debris to clog (or load) the surface of the wheel. This could produce a burnished surface rather than a ground one - which might appear satisfactory but would be metallurgically unsound. 

Water from towns main supplies is usually suitable for the preparation of water-based cutting fluids. That from factory bore holes is also generally suitable, although occasionally it contains excessive amounts of corrosive salts. Water from rivers, canals and ponds usually contains undesirable contaminants, and should be tested before use. A good first test is to mix a small quantity of emulsion and allow it to stand for 24 hours in this time, no more than a trace of the oil should separate. If serious separation occurs, the water should be analyzed to indicate the sort of remedial treatment required. 

Although some neat cutting fluids can be used almost indefinitely if well maintained, most fluids eventually reach the end of their useful life, so the system has to be drained and refilled with new fluid. On such occasions, the system should be thoroughly cleaned out before the new charge is poured in. The nature of cleaning depends on the type of cutting fluid. 

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