Nadolny K., Kapłonek W., Ungureanu N. | Journal of Mechanical and Energy Engineering, Vol. 1, No. 1, 2017, pp. 1-8 3

Tab. 1. General characteristics of grinding conditions

parallel to the mean line runs through, which is the top roughness limit; T/W (line 2) – the contractual border of vertexes - roughness zones T (Top Zone) and working zone W (Working Zone). The criterion used in estimating this border for the cooperating surfaces roughness is such an area of contact where there no mounting galling takes place (the border value of the contact length equaling 2% was adopted); ML+Ra (line 3) – the line running on the height - that is the sum of values of the profile mean line (ML – Mean Line) and the average Ra arithmetic roughness profile deviation; ML (line 4) – the mean line of the roughness - profile; ML-Ra (line 5) – the line running on the height of - ML-Ra; W/Q (line 6) – contractual border of the roughness - zones: working W and quasi-nominal zone Q, which runs on the height of contact that equals 98% of the measurement section; D-D (on line 7) – the depth of SCGC pits, i.e. the - lowest point of the roughness profile, which the line parallel to the mean line runs through, which is the bottom border of the roughness profile. The area between lines 1 and 2 is the vertexes zone T with height of t, the one between lines 2 and 6 is the working area W with height of w, while the area between lines 6 and 7 determined the quasi-nominal zone Q with height q. The SCGC curve is the border between the material (located under the curve) and the free spaces (above the curve). For this reason the print-out contains values of roughness zones surfaces (Area of Top Zone, Area of Working Zone). The surface of the quasi-nominal zone is the difference between the complete surface and the sum of surfaces of the working and top zones.

Process	Peripheral internal cylindrical traverse grinding
Grinding machine	Universal grinding machine RUP 28P equipped with spindle type EV-70/70- 2WB produced by Fisher AG, min-1, Switzerland (max. rpm 60 000 power of machine cutting 5.2 kW)
Dressing parameters	Dresser: single grain diamond dresser Qd = 1.25 kt, nsd = 12 000 rpm, vfd = 10 m/s, aed = 0.0125 mm id =10, = 0.38-1.15°, b = 15-5 mm c
Grinding parameters	vs = 60 m/s, vw = 0.6 m/s, vfa = 1.0 mm/s, ae = 0.10 mm, QC = 5.0 l/min
Coolant	5% water solution of Castrol Syntilo RHS oil
Workpiece	Internal cylindrical surface of rings, made of 100Cr6 steel, internal diameter: dw = 40 mm, width: bw = 18 mm

Analysis of the material ratio RTp of the profile of the grinded surfaces was carried out using Symmetrical Curve of Geometrical Contact (SCGC) [15]. The SCGC method may be considered alternative and informative in relation to the material ratio of the RTp profile using the Abbott-Firestone Curve (AFC) and RTp , RTp parameters. SCGC (Fig. 3) is the 20 50 conversion of the curve in such a way that each of its abscissas illustrating the geometric contact is moved parallel so that the center of its length is found on the normal perpendicular to the measurement section midway through its length.

##### 3.2. Grinding wheels

Five types of grinding wheels with zone- diversified structure made using ceramic bond with glass-crystalline structure were applied. These tools were made from grains of polycrystalline white fused alumina 99A and microcrystalline sintered corundum SG®. type Table 2 presents the characteristics of grinding wheels selected for the tests. Designation of the grinding wheels given in Table 2 is the abbreviated technical characteristic adopted to simplify the presentation and description of the investigation results. Both the hardness and the structure of particular grinding wheel zones remained unchanged for all types of grinding wheels used during the tests. Level K of hardness was applied to the rough grinding zone, and level I for the finish grinding zone. In both zones structure No. 7 was adopted.

Fig. 3. Sample shape of the SCGC for a surface roughness profile obtained by the traverse grinding using zone- diversified structure grinding wheels What can be determined using SCGC are height parameters (including Ra), contact parameters (horizontal), which characterize the expected geometrical contact and the developed surface taking into consideration the surface roughness and the material volume, as well as the so-called hollows, i.e. free spaces in the roughness zone. Thanks to that, more data for forecasting the behavior of surfaces when it is used in different conditions are obtained. Figure 3 presents the following SCGC parameters: point P (on line 1) – is the SCGC peak, i.e. the highest point of the roughness profile, which the line