Surface-grinding operations

Surface grinding is used to produce flat accurate surfaces. This can be illustrated by considering the grinding of all surfaces of the component shown in Fig. 10.14. 

It is important to first establish the datum faces A and B from which all faces are then ground. 

For soft ductile materials e.g. Soft steel, aluminium For rapid stock removal e.g. Rough grinding Wheie suiface finish is not important For large areas of contact 

For hard materials For rapid stock removal For large areas of contact 

For hard brittle materials e.g. Hardened tool steels For small amounts of stock removal Where a fine suiface finish is required Where small corner radii are lequired For small areas of contact 

Clamp face B against an angle plate supported on a parallel and grind face A to clean up. Fig. 10.18 

Use large grain size Use small grain size 

For soft ductile materials, e.g. soft steel, aluminium For hard brittle materials, e.g. hardened tool steels 

---

A constant temperature is required for close-tolerance measuring, gauging, machining, or grinding operations, to prevent expansion and contraction of machine parts, machined products, and measuring devices. In this instance a constant temperature is normally more important than the temperature level. Relative humidity is secondary in importance but should not go above 45% to minimise formation of a surface moisture film. 

The theoretical energy efficiency of grinding operations is 0.06 to 1 percent, based on values of the surface energy of quartz [Martin, Trans. Inst. Chem. Eng. (London), 4, 42 (1926) Gaudin, Trans. Am. Inst. Min. Metall. Pet. Eng., 73, 253 (1926)]. Uncertainty in these results is due to uncertainty in the theoretical surface energy. 

RAT grinding operations. This surface layer was removed except for a remnant in a second grind. Spectra - both 14.4 keV and 6.4 keV - were obtained on the undisturbed surface, on the bmshed surface and after grinding. The sequence of spectra shows that nanophase Oxide (npOx) is eiu-iched in the surface layer, while olivine is depleted. This is also apparent from a comparison of 14.4 keV spectra and 6.4 keV spectra [332, 346, 347]. The thickness of this surface layer was determined by Monte-Carlo (MC)-Simulation to about 10 pm. Our Monte Carlo simulation program [346, 347] takes into account all kinds of absorption processes in the sample as well as secondary effects of radiation scattering. For the MC-simulation, a simple model of the mineralogical sample composition was used, based on normative calculations by McSween [355]. 

One estimate of the efficacy of a crushing or grinding operation is the crushing efficiency, E, described as the ratio of the surface energy created by crushing or grinding to the energy absorbed by the solid (45). 

Materials mined from a mineral deposit usually consist of a heterogeneous mixture of solid phases that are generally crystalline and contain various minerals. Crushing and grinding operations are used to liberate the mineral species from one another and to reduce the size of the solids to a range suitable for subsequent processing. Of the various separation techniques, those of froth flotation and agglomeration exploit the chemical and physical properties of the surfaces of minerals, which can be controlled by various chemical interactions with species in an aqueous phase. 

Natural sources of ATH (Gibbsite extracted from Bauxite) and magnesium hydroxide (Brucite) are available but generally have large particle size as a result of grinding operations and contain significant amounts of impurities. In wire and cable applications, finer particles sizes are utilized for higher FOI values, improved mechanical properties, lower brittleness temperatures, and smoother surface characteristics despite the drawback of increased mixture viscosity.75... 

The discrepancy in values for the small particle sample (quartz A) as opposed to the large particle sample (quartz B) has been reported (14, 16). This behavior has been explained in terms of the semi-amorphous character of the smallest quartz particles obtained in crushing and grinding operations. While larger particles are believed to be representative of increasing ideality in surface crystalline order, there is, at present, no confirmation for the supposition that the larger (20- to 40-micron) quartz B particles approach the ideal crystal structure. Thermal analysis shows that, relative to the large particles, as much as 48% of the less than 5-micron material may be noncrystalline with respect to the a — j quartz transition (16). 

Related Calculations. This procedure can be used to calculate average sizes, moments, surface area, and mass of solids per volume of slurry for any known particle size distribution. The method can also be used for dry-solids distributions, say, from grinding operations. See Example 10.7 for an example of a situation in which the size distribution is based on an experimental sample rather than on a known size-distribution function. 

The hypothesis indicates that energy consumption per unit area of new surface produced increases faster than the linear ratio of feed and product dimensions, a phenomenon already noted and explained. The proportionality of net energy input and new surface produced has been confirmed in some grinding operations. 

In many milling applications, mill manufacturers offer a choice of steels for product-contact surfaces (such as mill liner), usually at least one low-alloy carbon steel, and higher-alloy stainless steels. The exact alloys vary significantly with mill type. Stainless steels are used in applications where corrosion may occur (many wet grinding operations, but also high-alkali or high-acid minerals), but are more expensive and have lower wear resistance. 

Sample preparation requires extreme care to avoid the introduction of contamination in the cutting and grinding operations. This is an area where operator experience is of prime importance. Extensive cleaning and etching may be required to provide an analysis representative of the sample composition. A further cleaning step is provided In the instrument itself by sparking the sample surface energetically to clean away the first few atomic layers. This prespark can be recorded on the photoplate to provide qualitative information about the chemistry of the surface. 

---