Patent Application
20220112115
The present invention pertains to laminated glass tubes, and their manufacture, and more specifically to colored low-thermal-expansion borosilicate glass tubes and their manufacture.
In the glass art industry, particularly within the torch working (also known as lampworking) field of glass blowing, glass which is in the form of a tube (hollow cylinder) is a common starting geometry for the creative process. Much like the paints, paint brush and canvas of a painter, glass artists use colored and clear glass tubes and colored and clear glass rods, and a high-temperature flame from a torch (utilizing fuel-air or fuel-oxygen) to accomplish their creative process. The glass tubes and rods used by a glass artist are available in different colors, translucent hues and clear.
Colored low-thermal-expansion borosilicate glass in rod form is abundantly available and can be purchased easily in a wide variety of colors by anyone. Colored low-thermal-expansion borosilicate glass in tube form is not abundantly available, with supply and production of this material being limited in volume and technological development.
The supply of glass in rod form (solid cylinder) to the glass art industry is well matured, and glass rods (industry standard diameter is approximately 7 mm for color rods) of many colors and clear can be purchased easily. The ample supply of glass rods to the glass art industry is a result of the manufacturing process being mechanized and perfected by suppliers, resulting in efficiency and ease in repeatability. A mechanism to draw glass or extrude glass in rod form from a reservoir (such as a crucible) of molten glass is not technically complex, and can be designed and manufactured with minimal technical and monetary investment. Manufacturing glass in rod form is achievable by any company or entity with minimal investment of resources.
Glass in tubing form falls into several categories with varying degrees of commercial availability, methods of manufacture, and intended application of use.
The first category of glass tubing is clear glass tubing that is manufactured in industrial settings in very large commercial volumes (1,000s-1,000,000s of tons per year). This clear tubing is made to precise dimensions (outer diameter, wall weight and circularity are precisely controlled). Manufacturing of clear tubing is executed by roughly a dozen companies globally and occurs in China, Czech Republic, United States, Germany, and Russia as a few examples. The most common industrial methods of manufacture of clear tubing include the Danner Process, Vello Process, and Updraw Process. Clear tubing is produced out of numerous glass types including medium-thermal-expansion borosilicate glasses for pharmaceutical applications, high-thermal-expansion glasses such as soda lime glass for art and technical applications (neon and glass-to-metal sealing), aluminosilicate tubing which is used for halogen lamps and other applications where gas permeability by the glass is not acceptable, and low-thermal-expansion borosilicate glass (Pyrex, Duran, Simax, 33 expansion glass), which is the primary type used by glass artists and scientific glassblowers. Glass in this first category is produced in highly refined manufacturing environments (factories), which require significant capital investment ($100s K-$billions USD) to build. Typically, the processes used in these commercial scale tubing factories are the result of many decades of progressive research and developmental effort. The hardware and equipment used in these factories is state-of-the-art and is highly technically developed. Glass in this category is available in a wide range of sizes from less than 1 mm in diameter to over 300 mm in diameter. Glass in this category is available for purchases easily by anyone and in large volumes.
A second category of tubing is that of “Asian” colored low-thermal-expansion borosilicate glass tubing. This glass is manufactured for use by glass artists and comes in several dozen colors. It is typically low cost allowing a glass artist to acquire a large quantity of glass tubing at affordable prices. This glass is considered 2nd quality and is inferior in many aspects to the first category of glass described. It is typically referred to in conversation between artists as “China Glass” or “Asian Glass.” The dimensional control of “Asian Glass” tubing is of moderate precision and tubes are often bowed (curved significantly) or may be oval in cross-sectional geometry while circular is what is intended by the manufacturer. The thickness of the tubing walls can be inconsistent. The refined quality of the glass is often fair to poor with refractory stone inclusions, air lines, and bubbles occurring frequently enough that it can be problematic for the user of the material. Critical properties of “Asian Glass” for use in glass art, such as thermal expansion coefficient, annealing temperature, and softening temperature are not uniform from one color to the next, often rendering the glass to be incompatible or unusable where a first quality colored low-thermal-expansion borosilicate glass would typically be used with no problems (deep encasement of the colored glass in clear glass such as in manufacturing of marbles, or sealing with other colors). This category of glass, “Asian Glass,” is used quite a bit by glass artists where they need colored tubing that is just good enough to get the job done, but quality is not a first priority. This category of tubing exists in limited colors. The colors that are available are mostly traditional glass colors such as cobalt or copper blues, copper/bismuth reds, copper or chrome/iron greens, and other simple glass color chemistries that have been established decades or even centuries ago and that are easily transferrable to the base chemical composition of low-thermal-expansion borosilicate glass. However, more exotic and/or chemically complicated colors are beginning to emerge from the Asian suppliers as they have begun to reverse engineer glass color chemistries of United States manufacturers' low-thermal-expansion borosilicate glass.
A third category of glass tubing is that of hand-pulled colored low-thermal-expansion borosilicate glass tubing (low-thermal-expansion, 33 expansion glass). This glass is very labor intensive to produce and is manufactured with the intended purpose being for use by glass artists. It is very expensive to purchase by the end user. The glass tubes are literally pulled by hand through the careful choreography of two or more individuals that stretch a large bubble of hot molten glass into a long tube.
At this time in the world, the primary glass type used by glass artists (lampworkers, also known as torch workers) are colored low-thermal-expansion borosilicate glasses and clear low-thermal-expansion borosilicate glass (common trade names for the clear glass are Pyrex, SCHOTT Duran, Simax or generally 33 expansion glass). The glass art industry is intimately entangled with the swiftly developing cannabis industry as legalization of marijuana is happening rapidly across the United States. A primary or common product of glass artists efforts are glass pipes that are used by members of the cannabis industry. There is very significant money in the cannabis industry which is directed to the glass industry via purchase of handmade glass pipes. The handmade glass pipes often sell for hundreds or many thousands of dollars. The demand for glass art (including pipes and other wares) is significant and the demand for raw materials and supplies to make glass art is proportionally significant and also increasing.
The majority of colored low-thermal-expansion borosilicate glasses used by glass artists are manufactured by one of several small companies in the United States which use primitive processes (by industrial glass manufacturing standards). The process of coloring low-thermal-expansion borosilicate glass is a relatively new field of glass chemistry which began gaining significant interest in the late 1990's. It is not always possible to apply glass color chemistries of more developed glass types such as soda lime glass directly to low-thermal-expansion borosilicate glass. In some situations, the color chemistry can be directly transferred such as with a cobalt blue; however, for many colors, what works in soda lime glass does not work in low-thermal-expansion borosilicate glass.
Domestic manufacturers of colored low-thermal-expansion borosilicate glass are in a state of constant research and development as they are discovering new colors and refining already existing colors. Many of the colored low-thermal-expansion borosilicate glasses and color effects (sparkles in glass by carefully grown metallic crystals) that have been discovered and/or refined over the past three decades are stunning in their visual effect. The compositions and color chemistries of these new glasses, which are highly innovative and created through exhaustive efforts by the manufacturers, are carefully guarded and treated as proprietary. The “Asian Glass” company(s) have been slowly reverse engineering these compositions and making attempts to produce them at lower cost.
United States production of colored low-thermal-expansion borosilicate glasses typically happens in small volumes of less than 500 lbs. for each color. Each melt of glass is done in a crucible that is less than 80 liters in volume. The crucible sits in an electrically heated oven and is heated to a temperature high enough to melt the glass. The crucible is filled with clear low-thermal-expansion borosilicate glass and different metals and metal oxide are added to the clear glass to color it (the clear glass is doped to make color). When the glass has been melted for long enough and is in a refined sate, it is extracted from the crucible either by pulling a rod continuously using a simple tractor mechanism, or by dipping an already formed tube in the glass to make a thicker tube (large, elongated bubble with a handle), and then stretching it to make a long piece of tubing. The manufacturing process is low technology.
Production of glass tubing made out of these domestically produced colored low-thermal-expansion borosilicate glasses is typically accomplished by hand pulling tubing. A clear glass tube (readily commercially available) or a color glass tube is closed on one end by conventional glassblowing process to render what is effectively a large test tube. The closed end of the tube is dipped (by hand) into a crucible of molten colored low-thermal-expansion borosilicate glass rendering a tube with a thick coating of molten colored glass on the outside. The heat of the molten glass which is coating the tube softens and melts the tube within. The very tip of the closed end is secured in some type of handheld clamp such as a glassblower's diamond sheers and a person pulls that end in one direction while a second person pulls in an opposing direction, stretching the glass to several times its length at the beginning of the stretch. (It is common for the person on the open end of the tube to blow during stretching to prevent the diameter of the formed tube from reducing too much.) This stretching process is done vertically, as attempting this process horizontally would result in the glass drooping and it is not practical for the humans that are doing the stretching to rotate the glass effectively to prevent it from drooping uncontrollably towards earth, per the effect of gravity. A ladder, staircase. or hydraulic lift may be employed so that the person on the top end of the stretching process is able to travel far enough from the other participant in the process. The product of this stretching is a long thick tube with colored glass on the outside and thin layer of clear (or color if a color tube was used at the beginning) on the inside. The typical length of a tube pull of this sort is around 2-3 meters with an approximate diameter of approximately 18-40 mm. The hand-pulled tubing is inconsistent in diameter and wall weight and it is impossible to have perfect repeatability. The dimensional repeatability of glass made by this process is low. The glass can be grouped in a similar size range (diameter and wall thickness), but none of it will be identical. The hand pulling process is labor intensive and lacks precision and repeatability, which render various commercial challenges. It can be difficult to cut and section a hand-pulled tube and inventory it for sale when each piece is a different size and weight. Also, the end user (the glass artist) would typically greatly prefer to have a tube that is consistent and predictable in its wall thickness as when the wall of a tube is too thick it makes working with the glass more difficult and takes more time.
Manufactures of colored low-thermal-expansion borosilicate glass would benefit greatly from a method to make tubing out of their colored glasses, which would be more repeatable and less labor intensive than the hand pulling process currently used. The reason no tube drawing machine or automated process (such as what is used in the first mentioned category of glass tubing) is implemented could be because such an investment is beyond the technical and monetary resources of the domestic manufacturers of colored low-thermal-expansion borosilicate glass.
Small manufacturers of technical glasses (optical glasses, acid soluble glasses, glasses with special electrical properties, etc.) also wish to produce tubing of the glasses they manufacture, but they face a similar challenge as the colored low-thermal-expansion borosilicate glass manufacturers. The challenges can include the required investment both of technical resource and money being beyond what is feasible or justifiable (return on investment for such equipment may not be possible or have a large enough profit margin) for them. The manufacturers of technical glasses have figured out a way to extrude tubes of short lengths which gives them what they need, but the extrusion process is difficult to adapt to the colored low-thermal-expansion borosilicate glasses because the colored low-thermal-expansion borosilicate glasses require much higher temperatures to process and the extrusion equipment must be adapted accordingly. It quickly becomes an expensive and challenging engineering project to extrude color low-thermal-expansion borosilicate glass.
Kishinev ski et al., U.S. Patent Publication 2018/0244558, describes use of a draw tower in the manufacture of glass canes, but not glass tubing. A glass cane is manufactured by filling a glass tube with a combination of glass structures forming a cross-sectional pattern within the glass tube, to form a preform. The preform is attached to a draw tower. The draw tower is operated to draw the preform to a reduced-diameter glass cane by passing the preform through a furnace of the draw tower while pulling the preform and rotating the preform.
It is an object of the invention to provide a mechanized process for producing glass tubing for the glass art community or for special technical or optical applications.
According to the invention, a colored glass tube, waveguide or optical component is manufactured by nesting a smaller glass tube within a larger glass tube leaving a space between the two, intentionally. A layer or ring of colored, patterned or clear glass rods or bars is created by inserting the rods or bars into the space in between the outer tube and inner tube. Upon initial insertion of the colored, patterned, or clear glass rods or bars into the interstitial volume between the inner and outer tube, they are not sealed together, but are just constrained next to each other.
On one end of the assemblage of the tubes and colored, patterned, or clear glass rods or bars contained within, the inner clear tube (or a color tube may be used instead of clear) is sealed closed (typically to a round or semispherical shape) by means of a traditional glassblowing technique. On the opposing end of the assembly, the inner tube is sealed to the outer tube, creating a seal that is restrictive to the flow of gas or completely hermetically sealed. When such a seal is executed between a smaller and larger tube by means of glass blowing technique (using a high-temperature focused flame) and the smaller inner tube remains approximately concentric to the outer tube, it is classically referred to as a Dewar seal. Such a seal is employed in glass thermoses and cryostats. A thermos is a classic example of a Dewar seal.
The assembly as just described, composed of a smaller and larger glass tube with a ring or layer of glass rods or bars placed in between, the inner tube being sealed closed on one end and the inner and outer glass tubes being sealed together on the opposing end creating a Dewar seal, will be referred to as a “preform” from here forward.
The preform is attached to a machine, such as a draw tower, which can raise or lower the preform vertically at a controlled rate. The draw tower is operated to pass the preform through a high-temperature furnace of the draw tower while pulling vacuum on the preform, evacuating the volume in between the outer tube and inner tube, in which the glass rods or bars are contained within. As the preform is passed into the high-temperature furnace, per the nature of glass when it is heated above the glass transition temperature, the inner and outer tubes, and the rods and bars contained within, achieve a state of plasticity and collapse towards each other, sealing the rods or bars of glass in between to each other and the inner and outer tubes, rendering a laminated glass tube.
The effect of the inner and outer glass tubes collapsing towards each other while heated under vacuum is that the glass rods or bars, which were installed in between the inner and outer glass tubes at the time the preform was assembled, are constrained and fused together and are permanently laminated by the inner and outer tubes, yielding a single piece of glass in tube form. The glass tube produced by the method has dimensional uniformity as perceived visually throughout the glass tube.
While the preform is lowered into the high-temperature furnace at a controlled rate, there is a stage or pedestal that is supporting the bottom of the preform, preventing the glass from free falling by the effect of the force of gravity, as it is heated to a plastic state in the high-temperature furnace. The stage or pedestal is mounted on a long rod or pole and is lowered at a controlled rate, supporting and allowing the glass which is heated in the high-temperature furnace to exit the high-temperature furnace at a controlled rate, instead of free falling. The stage or pedestal that controls the descent of the glass out of the high-temperature furnace may have a finger protruding from it which extends into the bottom of the preform and formed tube. The pedestal or stage may also be raised or lowered by any other means which achieves the precise control necessary to lower the glass at a controlled rate. The stage or pedestal may be flat or cup shaped. In the configuration in which the stage or pedestal is mounted to a long rod or pole, the rod or pole may be hollow, allowing for the introduction or exhaust of air or gasses which may be utilized for expanding or constricting the laminated tube as it is formed. The stage may also be pneumatic such that the bottom of the tube exiting the furnace feeds into a cylinder which is pressurized in a controlled manner allowing a controlled descent of the glass tube into the cylinder.
The pedestal which receives and supports the glass as it exits the high-temperature furnace may move at a rate equal to or greater than the rate that the preform is fed into the high-temperature furnace. If the pedestal, which is supporting the glass as it is heated in the furnace, is lowered at a rate greater than the rate that the glass is being fed into the furnace, there will be an attenuation of the diameter of the formed tube. The pedestal may be lowered at a rate greater than the rate the preform is fed into the high-temperature furnace with the intended result being that of making a smaller diameter final tube.
In certain embodiments, the preform may be raised upward through the furnace and the pedestal or platform supporting the bottom of the preform also moves upward, essentially executing the aforementioned process in a reverse direction. In such an embodiment, the supporting pedestal or platform at the bottom of the preform would move at a rate equal to or less than the rate that the preform is raised through the furnace. In this configuration the top of the preform would be consolidated and fused into a tube first and the laminating process would progress downward, the length of the preform.
In certain embodiments the preform may be rotated at a controlled rate while it is lowered or raised into the high-temperature furnace. The stage or pedestal only moves vertically and is not rotated and resists rotating, holding the end of the preform stationary, and the result is a glass tube that has intentional twisting around its perimeter, like the twists on a candy cane or the twists of a barber shop pole. Such twisting may serve only aesthetic purposes, but may also have an optical function such as achieving certain wave guiding properties and behavior in the final formed tube. Alternatively, the receiving pedestal may rotate while the preform does not rotate, to induce a twisting effect similar to or the same as if the preform is twisted while it is lowered into the high-temperature electric furnace.
The glass rods or bars inserted within the interstitial volume between the inner and outer glass tube may include a combination of glasses of differing colors, glasses with patterns or twists, glasses with specific optical properties, chemical properties such as acid being acid or water soluble, and may further include clear glass. Patterned glass rods may mean twisted glass canes (Zanfirico glass, latticino, filigree, filigrana, etc.) or glass rods or bars that have been colored or patterned (painted, silk screened, etc.) with enamel or though alternative techniques.
In certain embodiments the preform is attached to the draw tower vertically and the preform is drawn in a vertical direction. The step of attaching the preform to the draw assembly may include connecting an open end of the preform with a vacuum source, and the step of operating the draw tower may include operating the vacuum pump while performing the step of passing the preform through the high-temperature furnace while a receiving pedestal controls the output rate of the glass from the furnace and prevents it from free falling per the force of gravity. The step of connecting the open end of the preform with a vacuum source may include attaching the open end to a reduction fitting having a connector for connecting with the vacuum source. A coupling may be secured around the preform and the reduction fitting so that at least a partial hermetic seal is formed between the preform and the reduction fitting.
In certain embodiments, the glass tube yielded from this process may contain or be made of acid or water-soluble glasses or generally glasses with poor chemical durability which can be later removed by a wet chemical etching process.
In certain embodiments, the glass tube yielded from this process may contain or be made of high or low-index optical glasses yielding a component or final product that may be used for guiding light (fiber optics) or for manufacturing optical fibers or waveguides by means of a subsequent drawing process, such as incorporating a high or low-index-of-refraction core bar and redrawing.
In certain embodiments the preform may be passed through a high-temperature furnace and the fusing process of the outer and inner tubes with the glass rods or bars in between happens in a progressive manner, gradually from one end of the preform to the other.
In certain embodiments the pedestal receiving and supporting the preform as it is exiting or entering the high-temperature furnace may have a cup geometry or tapered cone and contain the end of the preform instead of the preform simply resting on top of the pedestal or stage.
In certain embodiments the pedestal or cup, receiving and supporting the preform as it is exiting or entering the high-temperature furnace, may be mounted to a pole or rod which is hollow, allowing for gas to be fed into the internal volume of the preform during heating, resulting in a controlled expansion of the preform.
In certain embodiments the pedestal or cup, receiving and supporting the preform as it is exiting or entering the high-temperature furnace, may be mounted to a pole or rod which is hollow, allowing for gas to be removed from the internal volume of the preform during heating, resulting in a controlled contraction or collapse of the preform.
In certain embodiments the preform may be placed entirely into a high-temperature furnace or oven and the fusing process of the outer and inner tubes, with the glass rods or bars in between, happens to the whole length of the preform at one time.
In certain embodiments, a ring of colored, patterned or clear glass rods or bars is created by inserting the rods or bars into the space in between the outer tube and inner tube and the ring may be composed of two or more layers of patterned or clear glass rods or bars.
The details of various embodiments of the invention are set forth in the accompanying drawings and the description below. Numerous other features and advantages of the invention will be apparent from the description, the drawings, and the claims.
Identical parts are indicated by the same reference numerals.
The present invention provides an alternative method of producing glass tubing which involves inserting a smaller glass tube within a larger glass tube and filling the space which is formed between the smaller and larger tube with colored, patterned or clear glass rods or bars. On one end of this assembly, the end of the inner tube and end of the outer tube are sealed together using traditional glassblowing technique to form a seal known traditionally as a Dewar seal. The opposing end of the inner tube is sealed closed prior to assembly, hence upon creation of the Dewar seal, a hermetic chamber is created between the inner tube and outer tube in which the colored, patterned or clear glass rods or bars are nested. The assembly consisting of the inner tube and outer tube with the colored, patterned or clear glass rods or bars nested in between is fed into a high-temperature furnace which maintains a temperature above the glass transition temperature (Tg) of all of the glasses incorporated in the assembly. While the assembly is fed into or placed within a high-temperature furnace, vacuum is being pulled on the chamber (volume) in between the inner tube and outer tube in which the colored, patterned or clear glass rods or bars are nested and held captive. As the glass softens the outer tube collapses inward and makes contact with the colored, patterned or clear glass rods or bars, collapsing and squishing them against each other, and as the heat propagates inward, softens the inner glass tube which also expands outward towards the colored, patterned or clear glass rods or bars also making contact with them, as the outer tube did. As the two layers of tubing and colored, patterned or clear glass rods or bars trapped in between are passed through the high-temperature furnace and all gasses and air are continuously evacuated from this space, the glass consolidates into one piece with the colored, patterned or clear glass rods or bars fusing to each other and the inner and outer tubes fusing to them.
The product of this process is a laminated tube consisting of an inner layer and outer layer of glass and a central layer which is composed of whatever the colored, patterned or clear glass rods or bars were that were placed in between the inner and outer tube at the start of the process.
The feeding of the assembly into the high-temperature furnace to accomplish the laminating process is done vertically as it eliminates the need to rotate the hot glass to keep it on a central axis (as glassblowers have to do when heating a piece of glass on a lathe). The laminating process is typically done by lowering the assembly towards the force of gravity into and through the high-temperature furnace; however, it is alternatively possible to pull the assembly upward to accomplish the same result. The bottom of the assembly is supported by a platform or pedestal that is raised or lowered at a controlled rate which may be equal to or some fraction or factor of the rate that the assembly is fed into the furnace. The platform or pedestal prevents the bottom of the glass assembly from free falling under the force of gravity when it is heated above the glass transition temperature. In an instance when the assembly is lowered or raised at a rate equal to the rate that the supporting platform or pedestal is raised or lowered, there will be only a minor reduction in outside diameter of the assembly upon consolidation and fusing of the glass layers and as the lamination process completes. The minor reduction in diameter is the result of the outer tube collapsing inward onto the colored, patterned or clear glass rods or bars contained within. If a rate differential is purposely implemented between the supporting platform or pedestal and the assembly as it is passed through the furnace, an effect of stretching the glass can be produced, further reducing the outside diameter of the final laminated glass tube. It is also possible that during the process, air or gas can be fed into the central volume of the glass assembly to expand the laminated tube during formation and to increase its diameter in a controlled manner.
By using colored or patterned glass rods or bars, a tube which is uniform in color or highly ornate with a structured pattern or intentional aesthetic properties can be created.
The space between the inner and outer tube is carefully optimized by selecting inner and outer tubes of a specific size. A possible outer diameter glass tube size would be a tube with a 41 mm diameter and a 2 mm wall thickness. The inner tube would have a 22 mm diameter. This leaves 15 mm of free space between the inner diameter of the large tube and the outer diameter of the inner tube. For an application where the laminated tube is going to be used for glass art, the colored, patterned or clear glass rods or bars which will be used will be colored low-thermal-expansion borosilicate glass rods that are typically 7 mm in diameter. A total of thirteen of these colored glass rods will fit in between the inner and outer tubes of the sizes mentioned in this paragraph. There will be a little bit of looseness which is important because there is some dimensional variation of all of the glass used, and if there is not a little extra room, the colored rods may not fit.
| Number | Date | Country | |
|---|---|---|---|
| 63091320 | Oct 2020 | US |
