QUALITY

REQUIRES

CONSTANT

ATTENTION

GLASS EDGE QUALITY AND STRENGTH LDC 691.615:666.1.053:666.1.037.4

L. A. Shitova, N. V: Lalykin, and T. A0 Kuznetsova

The edge formed by cutting sheet glass has defects governed by the cutting conditions. Edge quality is particularly important if there is no additional processing that will remove the defects, which are centers where failure can start, e.g., during quenching. Information is available on edge quality in cutting cold glass, but quantitative evaluation data are few. There are no data on cutting sheet glass in the viscoelastic state (at 600-650~ and the resulting edge quality. We have examined the strength in bending as a criterion for glass edge quality. Cutting involves two operations: forming a notch with a hard-alloy roller and breakage along the notch line. A high-grade edge is formed on breaking glass containing a crack with an adequate depth-(0o3-0.5 mm). The basic notching parameters are~ roller taper, roller pressure, and cutting speed. The wear on the cutting edge, the roller material, and the use of a liquid additive have marked effects on the notch quality. However, even a good notch may not produce a good (strong) edge because defects may arise during the breakage~ The strength has been determined in three-point bending with an R-0.5 tester. The specimen resting freely on the supporting prisms was loaded by a central force, with the relevant edge under tension. The glass specimens 160 • 20 mm were notched, withthe test edge on the long side. The specimen were cut in a set order.with marking out on the sheet because the strength varies across the sheet. The other edges should be free from defects in order that the strength should not be affected. The strongest edges (defect-free) are smooth ones on the side opposite to the notch. If it is impossible to make such an edge (e.g., if the glass is patterned), the opposite edge should be treated mechanically or chemically. We checked how the treatment affected the edge strength with polished glass notched under identical conditions and divided into five batches of 6 0 i t e m s each. The specimens in the first two batches were not treated. The edges in the other batches were processed mechanically: the third batch had the edges rounded with a diamond wheel, while those in the fourth batch were ground and polished with chamfer, and the fifth the same but without chamfer. We tested smooth edges in the first batch (defect-free edges opposite the notches were under tension), while in the second, the edges were as cut. The mean strength was determined for each batch (Fig. i). Mechanical treatment on the cutting side raises the strength by about 30%, although the strength of specimens with smooth edges is not attained. The mean strength with worked edges is almost the same for all forms of mechanical working, but the spread in the strength with grinding plus polishing was least, so if necessary, it is best to use that treatment. The defect types were examined with an MBS-I microscope before the strength testing. The following types were identified: indents, chips, and teeth on the end faces, and on the notch surfaces, indents, chips, and grooves (Fig. 2). Defects on the faces had very little effect on the strength, apart from coarse indents with depth more than 1 mm, which were rare and usually arose not during the cutting but as a result of mechanical impact. Defects on the notch surface had appreciable effects on the strength. Hard-alloy roller cutting at 600-650~ produced the same characteristic defects as cold cutting (Fig. 3). We compared polished and rolled sheets. The latter had corrugated or smooth surfaces. -The cutting was done manually at room temperature or mechanically at 600-650~ with a hard-

Tekhstroisteklo Cooperative.

Translated from Steklo i Keramika, No. 8, pp. 2-3, August,

1991. 0361-7610/91/0708-0327512.50

9 1992 Plenum Publishing Corporation

327

~, MPa

\

250

\ \

zoo

~f %

150

\

\

100

~.2", 5G ll

C

Edge type

Fig. 1

Fig. 2

Fig. i. Strength in relation to edge treatment: a) smooth; b) rounded with a diamond wheel; c) processed by grinding and polishing with chamfer; d) the same, without chamfer; e) from the cutting side; i-3) maximal, average, and minimal strengths. Fig. 2. Characteristic defects in glass edges: b) indents; c) chipping; d) grooves.

a) teeth;

~, MPa 140

d, MPa ,Q

80 ,20

i00 ~ 80

60 ~, le

Go 4~

2~

a

.!. c d ~ I g ~ Edge type Fig. 3

/

4G

z9 / JO 40

~O

FO

70 P, N

Fig. 4

Fig. 3, Strength in relation to edge defects in hot cutting: a) edge free from defects; 5) with chipping of depths up to 0.75 mm; c) the same, over 0.75mm; d) with chipping passing into cracks; 3) with grooves of depth up to 0.75 ram; f) the same, over 0.75 mm; g) grooves in places of width up to 0.5 ~ml; h) continuous grooves of width up to 0.5 mm. Fig. 4. Glass strength as a function of load on roller with taper angle 130 ~ . alloy roller with taper angle 130 ~ . T h e load on the roller was 50-70 No The bending strength of the polished glass was higher. In cold cutting, the edge strength was reduced by about 60% in both forms of glass. With hot cutting on the corrugated surface~ the strength was also reduced by 60%, as against cutting on a smooth surface, where it was reduced only by 30-35%. Cutting smooth rolled glass at 600-650~

328

results in a less-defective edge~

TABLE I Edge under tension in three~ point bending _ _ Smooth edge (no notches): polished glass rolled glasa; corrugated surface smooth surface Edge from cold cutting: rolled glass with smooth surface Edge from hot cutting, rolled glass L_

Strength, MPa -~ ~ M P a

Standard 5oefficient deviation, %of variation 58,4

31,6

69 90

32,7 30,4

2S,5 24,3

284

[ ,~6 I

g5

200 216

I i4 125

[

106 98

70 59 ] I

44 37

14,0 i~.4

20.0 25,4

87 117

46 I

15

17.9 19,0

39.1 22,5

i

This method can be used in choosing the optimum cutting parameters. Edge defects that reduce the bending strength occur if the roller load is greater than or less than the optimal value (Fig. 4)9 and the same occurs if there are deviations in the cutting temperature, lack of auxiliary liquid,,etco The bending strength can thus be used to characterize edge quality and optimize cutting~

PRODUCING CAST STONE SHEETS TO CLOSE SIZE TOLERANCES Go G, Rastegaeva and B~ Kho Khan

UDC 666o19-41

Shaped cast stone sheets with single curvilinear surfaces are produced on a large scale by petrurgical organizations and are used in lining equipment to protect the metal from corrosion and abrasive wear. The working reliability and life will be dependent on the installation quality, which is governed by the geometrical accuracy of the cast stone components. The conditions used in making cast stone are dependent on the raw materials the crystallization behavior in the liquidj the shaping parameters, and the heat treatment. Cast sheets are traditionally made in disposable sand molds~ which are previously fired~ They are also used in the heat treatment. That technology does not provide the required size accuracy~ An advanced technique was devised in the mid-1970s~ which employs permanent metal molds and heat treatment in a single-layer presentation in a tunnel furnace [l]o Structure control in the crustal layer during the initial solidification in the massive mold is one of the main factors in this technoiogy [2]~ Those molds complicate shaping and heat treatment because of supercooling~ the formation of a vitreous zone at the contact, the need to crystallize it~ the considerable temperature differences in the cross section~ and cooling control to eliminate internal stresses~ Cast stone has been made from melted basalt, diahase, and pyrozene porphytite with various additives to provide the necessary crystallization b~havioro Th~ additives contain magnesium, calcium~ and iron, which compensate for the deficiency in modifier cations involved in producing the pyroxene~ and also chromite, which provides crystallization centers and improves the general crystallization. Table I gives average compositions for the liquids used in testing and implementing the advanced technology with casting in metal molds. The liquids in the main were of pyroxene composition (pyroxene modulus 2.74-2.81), but they differed in contents of the constituent oxides and thus in crystallization [3]~ The glasses formed on chilling the liquids "also showed differences in crystallization~ Casting Institute, Academy of Sciences of the Ukrainian SSR, Materials Science Institute, Academy of Sciences of the Ukrainian SSR. Translated from Steklo i Keramika, No. S, pp. 3-5, August, 1991. ~ 0 @ 0361-,610/91/0,0o-0329~I~.S0

9 1992 Plenum Publishing Corporation

329