Janusz Konstanty

Theoretical analysis of stone sawing with diamonds

Abstract A theoretical model of natural stone sawing by means of diamond impregnated tools is presented. It is well known from the field practice that stone processing is a multidimensional problem. Therefore, the relevant system characteristics have been identified and discussed. The chip creation and removal process has been quantified with the intention of assisting both the toolmaker and the stonemason in optimising the tool (diamond impregnated segment) composition and sawing process parameters, respectively.

Sintered diamond tools: trends, challenges and prospects

Abstract Recent trends in the technology, production and applications of diamond tooling are reviewed. The continuing fall in the price of synthetic diamond as production volumes increase provides a strong incentive for tooling companies to reduce the cost of matrix materials and of their manufacturing processes, with an accompanying need for research in these areas. Diamond wires for the cutting of granite and other rock continues to grow in application and provides another focus for materials and technology advances.

Production of Diamond Sawblades for Stone Sawing Applications

The objective in writing this article is to acquaint the reader with the processes involved in the production of diamond sawblades, used extensively in stone cutting oper ations, but also in diverse construction jobs, road repair, sawing ceramics, etc. For reasons of space, its technical contents relate mainly to the design and fabricate]on of diamond im pregnated segments. Great emphasis is placed on providing guidelines for the selection of metall ic matrix and diamond abrasives. The sawblade assembling and finishing steps are also r eviewed, but, as they have only been given condensed accounts, the reader is encouraged to consult the rel evant source literature included in the comprehensive list of references. Historical Background The modern application of diamond tools is roughly a century old although the early use of diamond as an engraving tool goes back to 350 BC [1]. The first diamond circular sawblades for cutting stone were developed by Felix Fromholt in France in 1885. Fourte en years later, a large diameter blade was first used in practice in the Euville stone quarries. The early blades used carbonados set around their periphery and were utilised to cut limestone s and marbles during the construction of large buildings in Paris. Progress in the tool production r outes, by making good use of powder metallurgy techniques, resulted in developing diamond grit impre gnated sawblades to be finally put into operation around 1940 [1]. Further developments in the tool manufacturing technology may chiefly be attributed to the invention of synthetic diamond. Natural diamond has been used for centuries a nd efforts to manufacture synthetic crystals also date back at least sever al hundred years. They had remained fruitless until 1953, when positive and fully reproducible results were obtained by a team of researchers at ASEA [2]. Quite independently, and entirely without knowledge of what ASEA had been doing, General Electric announced its capability to manufacture synthetic diamonds on an industrial scale in 1955 [3]. While ASEA kept the diamond experiments secret, GE was first to apply for a patent and described the process in the scientific lite ratur . Therefore the invention has officially been attributed to GE. Permanent progress in the manufacturing technologies fostered the commercial importance of synthetic grits, which in the early 1990’s constituted around 90% of al l industrial diamonds consumed [2]. Over the past four decades, modern production techniques based on dia mond tooling have widely been employed in the stone and construction industries, road r epair, machining of glass and ceramics, grinding of metals, woodworking, finishing of plastic and rubber components, etc. enabling to do the job faster, more accurately and at less cost. N owadays the market for diamond tools continues to grow rapidly. Figures revealed currently indic ate that the demand for diamond abrasives reached a volume of 700 million carat in 1997, with Europe being th largest market [4]. Interestingly, the production of sawblades for stone cutting and const ruction applications has been identified as the biggest segment accounting for 50% of the overall consumption of industrial diamonds in Europe [4]. The current trend is to diversify into applicati ons still dominated by traditional abrasives with particular interest in developing linear blades for sawing granite as well as in applying diamond grits on a broader scale in the surface finishing operations [5] . Diamond Tool Design and Fabrication A typical fabrication process, commonly used in the manufacture of diamond impregnated Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 1-12 doi:10.4028/www.scie tific.net/KEM.250.1

Diamond tool design and composition

This chapter focuses on tool design and the composition of its cutting layer, which plays a key role in the economic machining of materials. Great demands are made on the tool life, its free-cutting ability, the precision of the job, edge quality, and the surface finish. The proper choice of slot geometry and the arrangement of segments give improved tool performance in terms of quality of the cut, noise, abrasive wear, fatigue life of the steel centre, flow of coolant to the cutting zone, and reduced segment wear by abrasion. The fatigue life of the steel centre often becomes a critical consideration in saw blades used under heavy-duty conditions as well as in large diameter blades for stone sawing. The two basic functions of the metallic matrix are to hold the diamond tight and to wear at a rate compatible with the diamond loss. The Diamond Grit Selection focuses on diamond type, grit size, and concentration. The proportion of each diamond particle that performs work is small when compared to the portion which is lost because the matrix is unable to retain it.

New Fe-Ni and Fe-Mn Powders Used in Manufacturing Diamond Tools

The work attempts substitution of very expensive, wear resistant Co-WC powders, that are commonly used in the production of sintered diamond tools, with cheap iron-base counterparts manufactured by ball milling. It has been shown that ball milled Fe-Ni and Fe-Mn powders can be consolidated to a virtually pore-free condition by hot pressing at 900°C. The as-consolidated materials are characterised by high hardness and resistance to 3-body abrasion.

Wear-resistant iron-based Mn–Cu–Sn matrix for sintered diamond tools

ABSTRACT The objective of the present work was to determine the suitability of a new iron-based Mn–Cu–Sn matrix alloy for the manufacture of diamond-impregnated tool components. A number of specimens were consolidated by the hot press route from ball-milled powders. Density, microstructural features, phase composition, bending properties and hardness were evaluated. The results revealed excellent mechanical properties, including σ0.2 > 850 MPa in 3-point bending and HK0.5 > 300. A commercial Co-WC reference matrix alloy was also produced for comparison purposes. Diamond-impregnated specimens with different matrices were tested for wear rate on abrasive sandstone using a test rig specially designed to simulate tool application conditions. The tests that involved 3- and 2-body abrasion ranked the alloys in different orders. Statistical analysis showed that the wear rate of diamond-impregnated composites was mainly affected by diamond concentration, but statistically significant contribution of the matrix resistance to 3-body abrasion was also found.

Wear properties of the matrix

This chapter discusses the complexity of the matrix wear, which seems to be equally a system property and material characteristic. During sawing or grinding with diamond tools, the interactions between the work piece debris and matrix occur in a variety of forms depending on the size of the abrasive swarf, its shape, cleavage properties, hardness, loading conditions, particle movement, speed and pattern, etc. Identification of minerals in the work piece, that cause abrasion, is also an important consideration. Minerals that are too soft to abrade may still wear the material but the mechanisms involved are different; for example, thermal fatigue, oxidation, and removal of oxide layers by abrasion, etc. The two-body abrasive wear is the most rapid and severe means of removing material; therefore, it is of utmost importance that the diamond protrusion ensures sufficient clearance to keep the matrix remote from the work piece surface asperities. The three-body abrasive wear arises when hard abrasive particles are introduced between a pair of sliding surfaces. Diamond crystals protruding above the matrix aid its overall wear resistance by preventing the matrix from direct rubbing against the processed material and direct blockage of abrasion grooves.

Microstructure of the matrix

This chapter describes the relationship among the properties of raw powders, processing conditions, and microstructure of the consolidated product. Diamonds embedded in Cobalite CNF retain their original color and shape, whereas Cobalite 601 powder, which requires very high sintering temperature of 1100°C to be properly consolidated, causes massive degradation of diamond crystals through their dissolution in austenite thus disqualifying the product for application. The compacting pressure applied to the powder confined in a die or mould has to be above the yield strength at the temperature applied. This leads to the strengthening of the material by increasing the density of lattice defects—such as dislocations, vacancies, interstitial atoms, etc. In contrast to hot pressing, the consolidation of matrix powders by means of the cold pressing/sintering process generally favors grain growth due to the longer processing at higher temperature in a reducing gas. Pores are an inherent part of virtually all sintered materials. A thermodynamically justified affinity between the pores and grain boundaries enhances the probability that a pore will remain attached to a grain boundary thus contributing to deceleration of grain growth.

Mechanical properties of the matrix

The existing theoretical knowledge of diamond retention has evolved from simplistic models and can hardly give a satisfactory explanation of the complexity of individual diamond pullout events observed in industrial practice. Certain material characteristics—such as hardness, yield strength, and impact strength—are generally believed to control the matrix capacity for diamond retention. At lower consolidation temperatures, hardness increases in direct proportion to the amount of plastic deformation and the density of the material. When full density is approached, then other processes like recrystallization and grain growth can be activated to soften the material. The yield strength is usually determined in the tensile test and, as with hardness, the results may prove irrelevant to high strain rate conditions, which are typical for certain applications; for example, circular sawing. The impact strength of powder metallurgy (PM) materials is influenced in a complex manner by their density, chemical and phase composition, grain size, contents of impurities, etc. It is essential that the material is fully densified, otherwise its toughness declines dramatically with increasing porosity.

Diamond tool fabrication

The diamond impregnated tool components are initially produced by the powder metallurgy (PM) route and then, in the final stage, they are attached to the tool support, which may require further processing. The matrix powder preparation consists of mixing the selected component powders so as to achieve the pre-determined chemical composition, particle shape, and size distribution considering the final product application. The mixing process has a great effect on the quality of the final product. The non-uniform distribution of both matrix powder particles and diamond crystals causes premature wear of the segment. Therefore, when each diamond crystal is separately coated with the matrix powder, the formation of diamond clusters in the segment is practically eliminated. Cold pressing is always applied as a pre-sintering operation and prior to hot pressing in the manufacture of saw segments having a layered structure. The end product of the PM processing cannot be directly applied as a tool and must be subjected to further finishing operations. These involve attaching the diamond-impregnated segments, or beads, onto a suitable steel carrier, which is also equipped to cope with the forces applied during use.