JPH03285836A - Manufacture of heat-resistant glass container - Google Patents

Abstract

PURPOSE:To obtain a heat-resistant glass container free from a scattering phenomenon at the time of breaking with good productive efficiency at low cost by molding a prescribed glass container by soda-lime glass having a specified compsn., controlling its temp. and thereafter tempering the glass by cooling in a specified manner. CONSTITUTION:At first, soda-lime glass essentially consisting of by weight, 60 to 80% SiO2, 5 to 20% CaO and 5 to 20% Na2O is prepd. Next, by using this soda-lime glass, a glass container with <=15cm depth in which the opening angle at the mouth part against the bottom face is regulated to >=5 degrees, the radius of the curved part in the bottom part is regulated to >=25mm and its central angle is regulated to >=45 degrees is molded. Then, this glass container is subjected to temp. controlling, is thereafter mildly exposed to a cooling wind in such a manner that the heat transfer coefficient (h) in the surface is approximately regulated to 0.001 (Cal/sec.m<2>. deg.C) and is tempered by the cooling. In the above-mentioned manner, a layer subjected to compressive stress in which the compressive stress value on the surface of the glass container lies in the range of 250 to 650kg/cm<2> is formed, by which the objective glass container can be obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for manufacturing a heat-resistant glass container, and more particularly to a container made of soda lime glass, the inner and outer surfaces of which are formed by rapid cooling strengthening. The present invention relates to a method for manufacturing a heat-resistant glass container with improved heat resistance by forming a compressive stress layer.

(Prior Art) Glass containers such as glass containers such as cups and plates, and glass packaging bottles such as juice bottles and food bottles have traditionally been made of the most common glass composition called soda-lime glass. It consists of However, the heat resistance strength (temperature difference) of this soda lime glass container is at most 50 ~
It is 60℃.

Immediately after placing high-temperature contents in this glass container, if it comes into contact with water or the like and is rapidly cooled down, the temperature difference will exceed the heat resistance strength, and there is a risk of damage due to thermal shock (see Figure 6 below) .

Therefore, conventional efforts have been made to improve the heat resistance of glass containers by forming compressive stress layers on the inner and outer surfaces of such glass containers using chemical strengthening methods using ion exchange or rapid cooling strengthening methods using cooling air. In the former case, the disadvantages are that the manufacturing cost is high and that the material deteriorates significantly due to damage and cannot withstand repeated use.
In the latter case, there was a risk of glass fragments scattering when broken, posing a safety problem.

Furthermore, so-called heat-resistant glass is also known, in which boron oxide (B203) is added to the glass composition to reduce the coefficient of thermal expansion and increase heat-resistant strength, but this heat-resistant glass has a special composition and has poor meltability. There was a problem that it was not suitable for mass production and the molding cost was extremely high.

(Problems to be Solved by the Invention) In view of the above-mentioned conventional problems, the present invention has sufficient heat resistance, no scattering phenomenon when broken,
It was also proposed for the purpose of providing a method for manufacturing heat-resistant glass containers made of soda lime glass that has good production efficiency, high mass productivity, and low manufacturing costs.

(Means for solving the problem) That is, the present invention solves the problem
0 (wt%), Cab: 5-20 (wt%), N
A2O: Made of soda lime glass whose main component is 5 to 20 (wt%), the depth is 15 cm or less, the opening angle of the mouth to the bottom is 5 degrees or more, and the radius of the curved part of the bottom is 25 cm.
A glass container with a diameter of 45 degrees or more and a central angle of 45 degrees or more is molded, and after temperature control, the heat transfer coefficient (h) on the surface of this glass container is approximately 0.001 (cal/
The cooling is strengthened by gently blowing cooling air so that the temperature is about secem'*"o), and a compressive stress layer with a compressive stress value in the range of 250 to 650 kg/cm2 is formed on the surface of the glass container. The present invention relates to a method for manufacturing a heat-resistant glass container.

(Function) The glass container of this invention has Si02: 60-8
0 (wt%), CaO: 5-20 (wt%), Na
20: It is made of soda lime glass whose main component is 5 to 20 (wt%), and is widely used for glass tableware, glass packaging bottles, etc. In addition to the above main components, it goes without saying that it may contain trace amounts of Al2O3, K2O, MgO, etc., and necessary amounts of compounds such as Fe, Cu, Cr, Ni, etc. may be added for the purpose of coloring. Sometimes.

As is well known, the rapid cooling strengthening method using cooling air is
This method strengthens the glass by rapidly cooling the glass surface in the temperature range of 00° C. with cooling air to form a compressive stress layer on the glass surface.

First, in order to uniformly form a compressive stress layer on the surface of a glass container using cooling air, it is necessary to reliably supply cooling air. For this purpose, a range of preferred shapes for glass containers is defined. That is, as shown in FIG. 1, in a glass container lO having an opening shape, the inner depth (D,) is 15 cm or less, the opening angle (di) of the mouth with respect to the bottom is 5 degrees or more, and the bottom Radius (r) is 25m
m or more and whose central angle (d2) is 45 degrees or more, it is possible to supply cooling air more uniformly and reliably, and it is possible to perform rapid cooling strengthening treatment with a more stable process. For containers outside this shape range, ordinary air supply methods cannot reliably supply air to the surface of the glass container, making it difficult to form a uniform compressive stress layer.

Next, the strength of the glass itself improves in proportion to the stress value of the compressive stress layer; however, when attempting to form a stress layer of, for example, 700 kg/cm2 or more, variations in the stress value occur. This is unavoidable, and as a result, there are areas with extremely high stress values locally, resulting in large plane distortions, and there is a risk of glass fragments flying off when broken. In addition, if the stress value is less than 250 kg/cm2, the desired heat resistance strength (temperature difference of 120°C or more) cannot be obtained.For this reason, the compressive stress layer formed on the inner and outer surfaces of the glass container is less than 250 kg/cm2. ~650kg/crrr
It is desirable that the stress value be in the range of .

Furthermore, as for the rapid cooling strengthening method that has the above stress value, the heat transfer coefficient (h) at the surface of the glass container is generally O,0O1cal/s e c a
It is desirable to strengthen cooling by applying cooling air gently so that rn'e ''C is achieved.

As is generally known, residual stress is proportional to the coefficient of thermal expansion, glass wall thickness, and heat transfer coefficient. The heat transfer coefficient (h) is 0°0002 to 0.00 in normal natural convection.
03 (cal/5ecenfe℃), but in the current general rapid cooling strengthening method, it is approximately 0.
．． It is 005. However, such rapid cooling increases the compressive stress value, and there is a risk of glass scattering when the glass breaks as described above. Therefore, in the present invention, by cooling slowly so that the heat transfer coefficient (h) becomes approximately o, ooi, it is possible to prevent glass from scattering and to have sufficient heat resistance strength.

In the glass container obtained in this way, a compressive stress layer is formed on the inner and outer surfaces by the rapid cooling strengthening method, and the compressive stress layer significantly improves the breaking stress due to tensile stress, and the compressive stress layer Since thermal fatigue is completely prevented by the presence of , the strength against thermal shock due to the temperature difference during rapid cooling increases, resulting in an improvement in heat resistance strength. Moreover, the compressive stress value mentioned above is 250 to 650 kg/cr.
Since it is within the range of n', it is safe because glass fragments will not scatter when broken.

(Example) Next, to explain an example, FIG. 1 of the attached drawings is a central vertical sectional view showing an example of a glass container showing an example of the present invention, and FIG. 2 is a relationship between glass thickness and compressive stress value. FIG. 3 is a schematic process diagram showing an example of the method of this invention, and FIG.
FIG. 5 is a graph showing the temperature change in the heat treatment process, FIG. 5 is a graph showing the heat fatigue resistance of the glass container according to the present invention, and FIG. 6 is a graph showing the heat fatigue resistance of unstrengthened glass.

As shown in FIG. 3, first, a known glass forming machine 2
0, a small bowl 10 made of soda lime glass as shown in FIG. 1 is formed.

The composition (weight %) of this small glass bowl 10 is as follows.

S i O: 72, 5 CaO: 11.5 N a 20: 13.0 A1203: 1.5 KO: l, Q MgO: 0.5 The shape of this small bowl is that the inner diameter of the mouth is 140 mm and the inner diameter of the body is 12 mm.
0mm, depth (D) 50mm, maximum wall thickness 5.5mm, minimum wall thickness 3.5mm, mouth opening angle (d) with respect to the bottom surface.
l) is about 15 degrees, the radius of the bottom (r) is 36 degrees, and its center angle (d2) is 75 degrees.

After forming the small bowl 10, as shown in FIG. 3, the small bowl 10 is transferred to a baking process 30 via a conveyor 21.The mouth of the small bowl 10 is heated and formed in a baking process 3o, and then a preheating process is carried out. After passing through step 35, the variation in the overall temperature of the product is further reduced, and the product is sent to the next temperature control step 40. In this temperature control step 40, as shown in the temperature graph of FIG. 4, the temperature of the glass product is controlled to generally be within 650° C. plus or minus 3 CI.

After this temperature adjustment step 40, a cooling step 5o is entered. In the example, the surface temperature of the product was approximately 640'C! At that time, cooling air at a temperature of 15°C was jetted from a nozzle at a wind speed of 10 m/sec for about 20 seconds to strengthen the glass surface by rapidly cooling it, and the glass surface temperature was lowered to about 30°C.

(In addition, in conventional rapid cooling strengthening, it usually takes about 20 seconds or less to
It is common for the temperature to drop rapidly to ℃. (See the broken line in the graph of FIG. 4) After the cooling step 50, the small glass bowl is gradually cooled down to room temperature via conveyors 51, 52, etc.

The thickness of the compressive stress layer on the surface of the small glass bowl obtained by the above manufacturing method is approximately 750 mm. The average compressive stress value is 450
kg/cm2.

Now, regarding the relationship between glass thickness and compressive stress value, FIG. 2 is a graph showing the relationship between the two.

As can be understood from the figure, there is a nearly constant proportional relationship between the glass thickness (1) and the compressive stress value, and the compressive stress value 250
The thickness of glass products within the range of ~650 kg/crn' (
1) is approximately within the range of 2.5 to 6.5 mm.

(Experimental Example) Next, a comparative experimental example of glass products produced by the method of this invention will be explained. First, we will discuss the experimental results of the invented product and a comparative product regarding the shape of the product, particularly the shape of the curved bottom portion.

Both are made of the same soda lime glass and have a depth of 50 mm.
It is a round pot with an inner diameter of 120 mm and a wall thickness of 3.8 to 4.6 mm. Product A is the product of the present invention, and B is the comparative amount. Both reinforcing conditions were as follows: After uniformly heating the product to 640°C, the product was rapidly cooled at 15°C with cooling air at a speed of 10 m and 7 seconds, resulting in a compressive stress value on the product surface. 350~450kg/ct
A compressive stress layer of n' is formed.

The test method is to gradually deepen the scratches by hitting the center of the bottom of the glass pot and the oil level part of the bottom with a hammer with a sharp tip, and then observe the state of damage.

Next, a thermal fatigue test will be explained according to FIGS. 5 and 6.

In this experiment, the compressive stress value after rapid cooling strengthening was approximately 280 kg.
/cm' glass product (soda lime glass with a softening point of 720°C, round bar with a diameter of 6 to 6.5 mm) was subjected to a thermal shock test, and the white circle at the top of Figure 5 indicates a thermal shock temperature difference of 150°C. In the case of , the black circle at the bottom is the case where the damage was done intentionally and the thermal shock temperature difference was 150°C. In either case, no change in bending strength occurred after 30 impacts, and almost no thermal fatigue occurred.

On the other hand, Figure 6 shows an experiment conducted on the same unstrengthened glass product as in Figure 5, but with this unstrengthened amount, the bending strength decreased continuously up to 15 thermal shocks. , 30 times, 2 out of 35 were damaged, indicating that large thermal fatigue had occurred.

(Effects) As illustrated and explained above, according to the present invention, soda lime has sufficient heat resistance, no scattering phenomenon at the time of breakage, good production efficiency, high mass productivity, and low manufacturing cost. It has been possible to provide a method for manufacturing a heat-resistant glass container made of glass.

[Brief explanation of drawings]

Fig. 1 is a central vertical sectional view showing an example of a glass container showing an embodiment of the present invention, Fig. 2 is a graph showing the relationship between glass thickness and compressive stress value, and Fig. 3 is an example of the method of this invention. A schematic process diagram, FIG. 4 is a graph showing the temperature change in the heat treatment process, FIG. 5 is a graph showing the heat fatigue resistance of the glass container according to the present invention, and FIG. 6 is a graph showing the heat fatigue resistance of unstrengthened glass. . Figure 1 Figure 1 Figure 1

Claims (1)

[Claims] SiO_2: 60-80 (weight%), CaO: 5-2
0 (wt%), Na_2O: 5 to 20 (wt%) as the main component, the depth is 15 cm or less, the opening angle of the mouth to the bottom is 5 degrees or more, and the radius of the curved surface of the bottom is 25 mm or more. A glass container with a large center angle of 45 degrees or more is molded, and after temperature control, the heat transfer coefficient (h) on the surface of this glass container is approximately 0.00.
The compressive stress on the surface of the glass container is within the range of 250 to 650 kg/cm^2. A method for producing a heat-resistant glass container, characterized by forming a layer.