US2344630A - Method of tempering glassware - Google Patents

Description

March 21, 1944. MYLCHREEST 2,344,630

METHOD OF TEMPERING GLASSWARE' Filed Nov. 25, 1939 In venio? I Patented Mar. 21, 1944 METHOD OF TEMPERING GLASSWARE George D. Mylehreest, Hartford, Conn., assignor to Hartford-Empire Company, Hartford, Conn., a corporation oi. Delaware Application November 25, 1939, Serial No. 306,113 8 Claims. (CI. 49-89) by a gaseous cooling medium applied externally and internally to the bottle walls. Such early proposal assumed, contrary to the fact, that bottles were of uniform thickness, and the proposer did not present any solution of the difllculties which are inherent because of the usual characteristics of bottles, i. e., (1) the thickness of various parts of the bottle walls vary, this variation normally being in a ratio of more than 2 to 1; (2) the bottles have restricted necks, a large class commonly known as narrow neck bottles having an opening the area of which is of very much less cross section than other portions of the bottle cavity; (3) the shape of the bottles, in that the walls and bottoms usually are of difiering thicknesses and join at an interior angle of about 90; and (4) the sloping shoulders of many bottles provide variation of distance of the walls thereof from the vertical axis of each such bottle, and this, coupled with .the restricted size of the opening, limits the mechanisms which may be employed to efiect the internal cooling. I

It is also known that certain articles, such as plates, lenses, cooking vessels and insulators, involving more or less flat curves or concavities, the entrance into which is of greater cross seetion than the internal portions, may be tempered by chilling the walls internally and externally by jets of cooling gases, the jets being spaced and/or graded to extract heat from the several portions of the articles at rates directly proportionate to the thicknesses of the various parts of the walls.

Thus the prior art, through these and similar proposals, has taught that a glass article having uniform wall thickness may be tempered by uniform cooling of the walls and that when the article has walls of non-uniform thickness, a similar result may be obtained by cooling the several sections of the walls at rates which are directly proportionate to the thickness, because these treatments cause the temperature of the several parts of the article to pass the strain point simultaneously.

Unless one or the other of these things be done, and unless the cooling of the two surfaces is symmetrical, the later cooling parts will, while setting, exert a bending force on the earlier set portions which tends to distort the article, or if the shape does not permit a suilicient change of form, setsup secondary strains which tend to produce tension in a surface layer of the article in certain zones and so weakens the article in these zonesas pro tanto'to defeat the purpose of tempering.

The solution ofthe problems involved in tempering articles of" relatively iiat or open character, such as lenses, etc., are simple compared to those involved in tempering bottles and similar containers, because the shapes of the former articles permit ready application of jets or currents of cooling medium from relatively large nozzles or blowers which may pass through the entrance and be arranged in substantial parallelism to the internal walls. Moreover, the relatively large size of theopenings of such of these articles as are ofcurved shape greatly simplifies the problem of exhaust of the spent medium. In any event, the teaching and proposals of the prior art, such as above referred to, have not heretofore produced a practical method of tempering bottles by internal and external jets of gaseous cooling medium.

Because of the shapes of bottles and similar articles, jets of cooling fluid can not conveniently be applied from nozzles equidistant from all parts of the internal surfaces or the article as is possible with lenses, etc. The thicknesses of different portions of such an article vary considerably. The ratio of thickness of the side walls to the bottom is seldom less than 1' to 2 and may be even considerably higher. The bending force that may be set up by reason of the difierence in time at which the sides and bottom pass through the strain point usually results in tension areas in internal surface layers near the bottom corners and in a belt of the side walls adiacent the bottom of the article. This constitutes a serious defect in the article.

The modern tendency of manufacturers is to reduce the weight of bottles and hence to reduce their wall thickness. Frequently a bottle of intermediate size, as for example a one trip beer bottle, will be produced with portions of the side walls as thin as, or thinner than, 2 mm. The wall thickness of the bottoms may be from two to five or moretimes as thick.

Very thin glass must be chilled with great rapidity to impart to it even a moderate temper, and if this high rate of cooling be proportionately increased tor the thicker sections, such sections may 'the interior layer.

become so highly tempered that they will "dlce c-r fly in small fragments when broken. Such dicing of a part of a container is dangerous to the user, so that in spite of the greatly increased strength resulting from high temper, it is desirable to keep the temper of bottles below the dicing point.

My invention provides novel methods of overcoming the difficulties indicated above.

The method of the invention in its broader aspect comprises the cooling of the entire internal and external surfaces of the wall of the article from a suitable temperature above to one below the strain point of the glass, at rates which will produce the desired degree of temper, the rates of cooling of the several portions of the walls of unequal thickness, being neither the same nor proportionate to the thicknesses of the portions, so that the differences in the times at which adjacent portions of the walls become set tend to create secondary or bending stresses which, if unopposed, would place surface layers in local sections of the bottle walls in tension, and opposing these secondary stresses by creating other and opposing stresses of such character that the surface layers in such sections are in compression when the tempering is completed.

The opposing stresses may be primary in character and created by an increased local chilling of the surfaces of the sections in question, or they may be of secondary character and created by asymmetrical chilling of portions of the walls removed from the sections. In the latter case, the changes in shape which result create secondary or bending stresses in the sections in question.

The method of my invention may be carried out by the use of any desired coolant and by any suitable apparatus.

In the accompanying drawing I have illustrated my method through illustration ofthe effects of the steps thereof on lower portions of a narrow neck bottle, such as a one-trip beer bottle, the effects being somewhat exaggerated for the sake of clearness.

Figure 1 shows in vertical section a bottle before the tempering operation is begun. As there shown and as is usual in such bottles, the side wall I is substantially thinner than the bottom 2. These two portions form an interior angle roughly approximating 90 which I have indicated as angle A.

Fig. 2 'mdicates the change in shape which results from chilling the hot bottle walls so that the thinner side walls become set earlier-than the thicker bottom wall. In the case illustrated, the rate of chilling of the thicker bottom is proportionately slower than that of chilling the side walls. The angle between the side walls and bottom is now greater than that of Fig. 1 and is indicated as A plus B, this increase in the interior angle having been caused by the bending in of the side walls by the shrinkage of the bottom after the side walls had set.

The dotted line 3 indicates the position of the line of zero stress which in the side walls separates the inside surface layer which is in compression from the interior layer which is in ten- .sion. Dotted line 3 similarly indicates the zero tension linebetween the outside surface layer and It is noted that the line 3 approaches and runs out of the inner surface of the bottle at the point 4 and appears again in the bottom at the point 5, indicating the fact that the surface layers of the area between the points 4 and 5 are in tension. This undesirable condition, which is obviated by methods of the present invention, has been caused by the increase of the angle A to A plus B and the uncompensated attendant bending stress in the surface layer 4-5 as the thicker bottom becomes set after the thinner side walls have been cooled to a set condition.

Fig. 3 shows a condition similar to that of Fig. 2 except that an additional primary compression stress on the area 4-5 has been produced in accordance with a method of the present invention by increased local cooling applied to the surface area 4-5, as by jets 6. Such primary stress is shown as having opposed and overcome the secondary tension stress in that particular area to such an extent that the resultant of the two stresses in that area places the surfacelayer 4-5 in compression.

Fig. 4 illustrates the effect of practicing my method by asymmetrical cooling of a portion of the glass removed from the section affected by the secondary stress, resulting from the later chilling of the bottom. In this case, the increase of the angle A is opposed by an increased cooling on the inner surface of the bottom of the bottle as indicated by the arrows 1. This causes the upward doming of the bottom and tends to a reduction of the angle between the bottom and the sides. In this case the line 3 of zero tension is maintained within the surface.

In some cases it is desirable while cooling the interior of the bottom to apply a local increased cooling influence externally to the bottom corners of the article as indicated by the arrows 8 in Fig. 4. This is desirable if the interior angle is made substantially less than prior to the tem- Bering.

It will be apparent that my method may be carried out with the conjoint use of both primary and secondary stresses created as explained above, and opposing the secondary stress caused by the unequal chilling of the relatively thick and thin portions of the walls. The principles illustrated herein with respect to the lower portion of the bottles may tions thereof.

By the employment of the method herein de scribed, bottles of very light weight have been successfully tempered, these oottles having wall thicknesses varying from below 2 mm. in the thin parts to 4 mm. or more in the thickest parts. Such bottles are substantially stronger than similar bottles when annealed.

Such bottles have all the surface layers of their walls in compression and the interior in tension of more than 300 grams per square mm., which is several times the value of the tension in annealed bottles. Such bottles have been produced in which the maximum tension was below that at which the bottles would dice upon breaking; that is, when broken, the pieces will be so many and so small that the original shape of the part is not discernible.

Certain of these bottles, when viewed through a. polariscope, clearly show the tendency of the zero tension line to approach, the internal wall surface of the bottle adjacent the lower corners, and the existence of the primary compression stress opposing this tendency. The distortion of the lower portions and the increase of the interior angle at the corners, though slight, may be demonstrated to have taken place. Also it may be shown that in bottles in which the doming" step has been employed, the shape of the bottom and lower comers has been altered.

be applied to other por- These characteristics readily distinguish the bottles from bottles made in the same or similar molds, prior to tempering or after they have been annealed.

Bottles tempered accordingto the present invention constitute improved articles of commerce which may be produced in practical operations in glass factories. Such bottles have improved resistance to blows, scratches, thermal shock and pressure, and may be produced in quantity and at reasonable cost.

Having described my invention, what I claim i. The method of tempering glassware having a single opening and having side walls and a bottom wall, the latter being thicker than the side walls and forming therewith an interior angle approximating 90, which comprises rapidly cooling the surfaces of the side walls and said bottom from a temperature above to one below the strain point of the glass by extracting heat from the side walls and bottom wall at different rates which are disproportionate to their thicknesses in that the rate of extraction of heat from said bottom is less than proportionate to its thickness, thereby increasing the interior angle between the bottom wall and side opposing stress suflicient to overcome said tendtency and to place the said internal surface layer in' compression.

2. The method of tempering hollow glassware having a single restricted opening and having walls of non-uniform thickness, which comprises rapidly chilling all parts of said walls from a temperature above to a temperature below the strain point of the glass by extracting heat from the severalportions of differing thickness at difierent rates which are disproportionate to the thicknesses of such portions in that the rate of extraction of heat from a thick portion is less than that proportionate to its thickness, and opposing stresses of secondary character resulting in a surface layer of the glass at the juncture of adjacent relatively thick and thin portions of the containerwalls from the difference in the time at which the mean temperatures of different portions of the walls of the article pass below the strain point of the glass thereof by chilling the portions of the walls in which such stresses of secondary character occur at a rate sufliciently high to create therein primary compressive stresses substantially in excess of the secondary stresses, the chilling of all surfaces of the walls being at such rates and so distributed that the surface layers of relatively low, and, during such chilling of said walls, more intensely chilling at a surface thereof the glass located between and connecting adjacent relatively thick and thinner portions of the walls to produce locally in the surface glass at that place compressive strains adequate to obviate tensional strains therein which the disproportionate chilling of said adjacent relatively thick and thinner portions would otherwise create.

4. The method of tempering hollow articles of glassware having walls which vary substantially in thickness and are formed to provide a surface of angular configuration at the juncture of' two adjacent relatively thick andthinner portions of such walls, comprising rapidly chilling all walls of such an article from a temperature above to a temperature below the strain point of the glass thereof at rates which are disproportionate to the thicknesses of said walls in that the chilling of the thicker portion is at a reduced rate, and, during such chilling of said walls, more intensely chilling at its said angular surface the glass at the juncture of said two adjacent relatively thick and thinner portions to produce locally in the surface .glass at that place compressive stresses adequate to obviate tensional strains which the disproportionate chilling of said adjacent relatively thick and thinner portions tends to set up therein.

5. The method of tempering an article of hollow glassware, such as a bottle, which has an opening of restricted area at one end and a bottom at the opposite end of greater thickness than thus tending to enlarge the interior angle bethe walls, both inside and outside of the article,

tionate to the thicknesses of said walls in that the rate of chilling of the thicker portion is tween the side walls and the bottom and to set up tensional strains in the internal surface glass .at said angle, increasing the chilling medium applied to the inner surface of the bottom at the center thereof in relation to the chilling medium applied to the opposite outer surface of the bottom during said chilling of the article of glassware to cause upward doming of the bottom to obviate the aforesaid enlargement of said interior angle and the production of said tensional strains in the internal surfaceglass' at said angle and tending to cause tensional strains in the outer surface layer of glass at the exterior of said angle, and applying a chilling medium locally to the outer surface layer-of glass at said angle to create therein compressive stresses to oppose and obviate tensional stresses in said outer surface layer of glass. p

6. The method of tempering a bottle, jar, or other container having an opening at one end and a bottom at the opposite end of greater thickness than the side .walls of the container, which comprises bringing the glass of the container to a temperature above its strain point, then applying a chilling medium to the inner and outer surfaces of the glass of the side walls and bottom of' the container and at their juncture with each other in amounts which are different for diiferent portions of the container to cool the glass of such container to a temperature below its strain point at cooling rates which are disproportionate in that the average cooling rate of the glass of the relatively thick bottom is relatively low in relation to the average cooling rate of the glass of the thinner side walls and the cooling rate of the glass at the juncture of the side walls and the bottom is relatively higher at its inner surface than at its outer surface.

7. The method of tempering a bottle, jar,. or other container having an opening at one end and a bottom at the opposite end of greater thickness than the side walls of the container,

the bottom and said side walls forming an internal angle of approximately 90 at their juncture, which comprises bringing the glass of the container to a temperature above its strain point,

then applying chilling medium to the inner and outer surfaces of the glass of the container side walls and bottom and at their juncture to cool the glass of the container to a temperature below its strain point at cooling rates which are disproportionate for different parts of the container in that the average cooling rate of the glass of the relatively thick bottom is disproportionately low in relationto the average cooling rate of the glass of the thinner side walls, and the glass of the central portion of the relatively thick bottom is cooled at its internal surface at a higher rate than at its opposite outer surface to cause inward doming thereof as the bottom is cooled to a set condition to oppose entom and side walls is at a largement of the internal angle at the juncture of the relatively thick bottom with the thinner side walls of the container, caused by the cooling of such bottom to a set condition after the side walls.

8. The method of tempering a bottle, a jar,

or other container having an opening at one end and a bottom at the opposite end of greater thickness than the side walls of the container, the bottom and said side walls forming an internal angle of approximately at their juncture, which comprises bringing the glass of the container to a temperature above its strain point. then applying chilling medium to the inner'and outer surfaces of the glass of the container side walls and bottom and at their juncture to cool the glass of the container to a temperature below its strain point at cooling rates which are disprpportionate for different parts of the container in that the average cooling rate of the glass of the relatively thick bottom is disproportionately low in relation to the average cooling rate of the glass of the thinner side walls, the glass of the central portion of the relatively thick bottom is cooled at its internal surface at a higher rate than at its opposite outer sur face to cause inward doming thereof as the bottom is cooled to a set condition, and the cooling of the glass at the angular juncture of the botelatively high rate at its outer surface as compared" with the cooling rate at its opposite inner surface.

GEORGE D. MYLCHREEST.

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