Hermes Bonded Abrasives, Basics
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Bonded Abrasives Hermes Bonded Abrasives

Grinding processes are subject to continuous change with the objective of constant improvement of workpiece quality and process productivity. this can be achieved by using new and optimized grinding systems and parameters. the core of the process is the bonded abrasive. it’s composition is a key determining factor in the quality and performance values of the process.

Hermes – a competent “grinding” partner all over trAdition hAs A Future At herMes Hermes Schleifmittel is a company with roots going back as far as 1927. Hermes does not only hold a key market position in producing precision bonded abrasives, but it is one of the world‘s leading manufacturers of coated abrasives. Hermes owes this market position to its insistence on absolute top quality. We feel obligated to this tradition and it is our primary guiding principle for the future. This is an obligation that is the greatest possible motivation and to which we devote all our energies and...

the world sustAininG nAture And environMent Compliance with national and international laws and regulations is one of the key principles of Hermes corporate policy and protection of the environment is a core constituent of our corporate responsibility. As a consequence, as long ago as 1996, Hermes was the fi rst European abrasives factory to be successfully audited on a voluntary basis in line with the EMAS (Eco-Management and Audit Scheme). The management system, currently being implemented, covers all areas of the company. All processes relevant to the environment and also to quality are...

Grinding applications Grinding is one of the most important production processes for generating the required workpiece geometry and its surface quality. Surface grinding • using peripheral grinding process • using creep-feed grinding process • using profiled wheels in a profile/surface grinding process • using continuous-dressing grinding process • using segments • using cups • using rings • using cemented or screw mounted abrasive wheels Production engineering defines grinding as “machining with geometrically undefined cutting edges”. Via the surface to be generated and its characteristics...

Basic Hermes research is involved among other things with the effects on the out- come of work of varying grinding system and parameters. This work provides information which shows, for example, the effect of variations in input parameters on the grinding result and indicates options for increasing the performance of the abrasive tool. The diagrams below are an excerpt of results which can be used as a guide in practical applications. EFFECT OF SPECIFIC STOCK REMOVAL RATE Q'w

An abrasive has to have the following properties: • high hardness • sharp cutting edges • high thermal resistance • chemical stability • tendency to splinter • high degree of consistency of Charge properties These requirements are satisfied only by the synthetically produced hard materials: • fused aluminium oxide (Al2O3), • microcrystalline aluminium oxide (Al2O3), • silicon carbide (SiC), • cubic boron nitride (CBN), • diamond (D). They are therefore used intensively in modern grinding technology. Friable aluminium oxides with mixtures EKW EKR EKD EKT EWR EWD ERD EWT ERT EDT FP TKR EKE...

Cubic boron nitride (CBN) is the second-hardest material after diamond, but has greater thermal resistance and is not subject to chemical wear when cutting steel. With cubic boron nitride, up to one hundred times longer wheel lives can be achieved compared to aluminium oxide abrasive wheels. Cubic boron nitride (CBN) CBN is especially suitable for processing steels which are hard to cut and for the high-performance grinding of high production volume components. Diamond is the hardest material known, but when processing steel, tends to be subject to chemical wear. Its high degree of hardness...

Grit size Aluminium oxide, sintered ceramic and silicon carbide The grit size indicates the size of the individual particles of abrasive grit. The sizes are described by means of the grit particle distributions (F 8 - F 1200) standardized in DIN ISO 8486-1. The designation (e. g. F 60) describes the mesh width of a screen given in number of mesh squares per inch. Grit size F 60, for example, is defined by the 60 mesh squares of the nominal screen for one inch of screen length. A large number therefore describes a fine grit and a small one a coarse grit. The grit sizes of these abrasives are...

Grit selection Together with hardness, the selection of grit size has a key influence on the grinding result. Grit size is selected to achieve specified roughnesses and radii. Grit sizes F 46, F 60 and F 80 are most frequently used for precision grinding. Summary of grit sizes Coarse Very fine It is possible and often also advantageous to combine grit sizes. This is stated in the specification of the bonded abrasive. Examples Example 1: When grinding the outside diameter of a shaft, a roughness of R z ≤ 2 µm is required. Three grit sizes come into question: F 60, F 80 or F 100. If the...

Degree of hardness Extremely soft A, B, C, D Very soft Very hard Extremely hard The nominal hardness quoted in the specification is indicated by the letters “A” (extremely soft) to “Z” (extremely hard). This hardness is a measure of the force required to break a particle of grit out of the bonded abrasive structure. It is controlled by the strength of the links in the bond and by the inherent strength of the bond. Rising nominal hardness in a specification and process management which otherwise remain constant yields a higher G ratio (less wear) but also higher grinding forces and thus...

Classes of structure Dense 0, 1, 2, 3 The structure of the bonded abra­ is indicated in the sive specification by the figures “1” (very dense) to “22” (very open). This structure number is a measure of the concentration of abrasive in the bonded abrasive. It drops continuously from structure number 1 to 22, with the distance between the cutting edges increasing in the process. Effect on tangential force of different structures for the same nominal hardness. The structure has to be adapted to the grinding process and to the material to be cut. Typical for the cylindrical grinding of steel is...