Glass Gobs Research Articles

A Study on the Correlation between Change in the Geometrical Dimension of a Free-Falling Molten Glass Gob and Its Viscosity.

To produce flawless glass containers, continuous monitoring of the glass gob is required. It is essential to ensure production of molten glass gobs with the right shape, temperature, viscosity and weight. At present, manual monitoring is common practice in the glass container industry, which heavily depends on previous experience, operator knowledge and trial and error. This results in inconsistent measurements and consequently loss of production. In this article, a multi-camera based setup is used as a non-invasive real-time monitoring system. We have shown that under certain conditions, such as keeping the glass composition constant, it is possible to do in-line measurement of viscosity using sensor fusion to correlate the rate of geometrical change in the gob and its temperature. The correlation models presented in this article show that there is a strong correlation, i.e., 0.65, between our measurements and the projected viscosity.

Tribological investigations of the glass‐to‐metal contact during glass forming at an industrial scale

AbstractAn industrial‐scale dynamic friction test set‐up was installed and optimized at the gob‐stage of a prototype container glass forming line. The set‐up was used to generate a fundamental understanding of the tribological interactions during container forming, considering the real‐size glass gob in the viscoelastic range and the respective contact material. The findings are universally applicable for other glass‐forming situations such as spinning, pressing, and blowing, where similar hot contact situations occur. The measured friction loss within that tribological system is correlated to different material properties. In doing so, existing knowledge is further developed, leading to new insights into the matter of glass‐metal interactions. With that a better fundamental understanding of the process at an industry level is obtained.

Multi-Camera Based Setup for Geometrical Measurement of Free-Falling Molten Glass Gob.

High temperatures complicate the direct measurements needed for continuous characterization of the properties of molten materials such as glass. However, the assumption that geometrical changes when the molten material is in free-fall can be correlated with material characteristics such as viscosity opens the door to a highly accurate contactless method characterizing small dynamic changes. This paper proposes multi-camera setup to achieve accuracy close to the segmentation error associated with the resolution of the images. The experimental setup presented shows that the geometrical parameters can be characterized dynamically through the whole free-fall process at a frame rate of 600 frames per second. The results achieved show the proposed multi-camera setup is suitable for estimating the length of free-falling molten objects.

Case Study: Gob Loading in a Glass Moulding Machine

In the industrial production of container glass, it is essential to maintain constant parameters in the forming process. Above all, the delivery of the 1150°C hot glass gob and its loading into the mould is a critical procedure. On machines used today with up to 12 forming sections the current delivery system is reaching its limit. The objective of this work is solving the contradiction – improving gob loading, i.e. temperature constancy, homogeneity, and speed without altering the machine setup – by using the TRIZ method. The result, a modified path of the movement with the trajectory of a clothoid, has been derived theoretically, put into practice, and tested experimentally. Assessment of the new trajectory has been performed by measuring the gob velocity and by recording the gob fall with a high speed camera. By means of the newly designed trajectory, wear of the delivery channel has been reduced. The variation in travelling speed of the gob on its way through the delivery system has also been able to be reduced. Furthermore, the gob loading into the mould has been improved as well. The gob remains standing vertically in the mould and will not tip off to one side. The result of this measure does not only increase the service life, but also improves the quality produced.

Effect of Al2O3 coated glass preform on glass-mold sticking behavior

Molding of low Tg glasses with high refractive index (nd) is very difficult due to the existence of a high concentration of active elements in the glasses. This research tried depositing a very thin layer of aluminum oxide (~20nm) on various low Tg glass-preforms (with nd>1.80) using a water based sol–gel process to reduce sticking between the glass and the mold material. High temperature glass wetting and molding tests were carried out to investigate the high temperature interfacial reaction between the coated glass gobs and the mold materials.When the uncoated glass-preforms were brought into contact with WC/Co (3%), the contact angle decreased with increasing heating duration at the softening point (Sp). Owing to the severe interfacial chemical reaction, all transparent glasses gradually turned translucent or opaque and severe sticking with the mold materials was observed. In the case of Al2O3 coated glass-preforms, the variation of the contact angles was very limited, and most of them showed no sticking and no wetting behavior. It was found that the acceptable molding temperature range is very narrow for molding uncoated low Tg glasses even with a Pt–Ir film on the mold surface. The molding conditions become more flexible when using glass preforms with an Al2O3 film on the surface, and the surface qualities of molded glass lenses were improved at the same time. The optical transmission of those lenses molded from the coated glass-preforms exhibited very little or no change after the molding process at a moderate molding temperature.

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Glass with a low transition temperature (Tg) has the advantage of extending the service life of molding dies. However, low Tg glasses normally demonstrate poor chemical durability and scratch resistance. The molding of low Tg chalcogenide glasses is very challenging due to their fragile and unstable characteristics. This research tried to deposit a very thin layer of aluminum oxide on chalcogenide glass-preforms using a water-based sol-gel process. High temperature glass molding experiments were carried out to investigate the high temperature interfacial reaction between the coated glass gobs and the WC/Co substrate. It was found that surface defects appearing on the molded glass lenses were mainly due to the interfacial chemical reaction between the chalcogenide glass and molds, which leads to a low yield of molded glass lenses than expected. In the case of Al2O3 coated glass-preforms, no reaction products were detected on the surfaces of the molded lenses after the molding test. The surface qualities and yield were significantly improved.

The Effect of TaN Interlayer on the Performance of Pt-Ir Protective Coatings in Glass Molding Process

The glass molding process provides great potential for mass production of precise glass optical components at low cost. The key issue for achieving a low production cost is to extend the service life of the expensive mold inserts. The precious metal based alloy is one of the coating materials for the molds which provides excellent glass anti-sticking results. However, the inter-diffusion between the WC/Co mold materials and precious metal coatings will deteriorate the coatings which needs to be resolved. It is essentially to deposit an interlayer as the diffusion barrier to improve the inter-diffusion problem. A thin layer of TaN was deposited on the WC/Co substrate as the diffusion barrier using a magnetron sputtering system, and followed by the deposition of Pt-Ir layer as the protective layer. Low Tg Glass gobs (L-BAL 42) were placed on the coated substrate to investigate inter-diffusion between the substrate and coating at high temperature. The surface interaction between the glass gobs and protective coatings was also examined. The obtained TaN and Pt-Ir multilayer had a dense nano-crystalline structure. High temperature wetting tests showed that the TaN film could effectively resist the cobalt and tungsten diffusion into the precious metal protective layer and, as a result, minimized the possibility of oxidation and interaction between glass and protective coating. The coated substrates retained a good surface finish and the glass gobs stayed fully transparent after 6 hours reaction test at 700°C.

Thermal Stability of Al<sub>2</sub>O<sub>3</sub> Coated Low Transition Temperature Glass

There are growing varieties of glasses available on the market for the manufacture of molded optical lenses. A glass with a low transition temperature (Tg) has the advantage of extending the service life of molding dies. However, most of the low Tg glasses have a high content of alkali metal oxides and tend to induce severe glass sticking problems. This has made the molding process of these kinds of glasses very difficult indeed. The low Tg glasses normally demonstrate poor chemical durability and scratch resistance. As a result, the yields of fabricating the glass-preforms are frequently rather low. This research tried depositing a very thin layer of aluminum oxide on various glass-preforms by a water based sol-gel process. A high temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coated glass gobs and stainless steel substrate. It was found that when the uncoated glass-preforms were brought into contact with stainless steel, the contact angle decreased with increasing heating temperature and duration. Owing to the severe interfacial chemical reaction, the originally transparent glass gradually turned translucent. In the case of Al2O3 coated glass-preforms, the variation of the contact angles was very limited, which presented no sticking and no wetting behavior. No reaction products could be detected on the contact area after the wetting test. The optical transmission of those lenses molded from the coated glass-preforms exhibited no or very little changes after the molding process.

Improving the quality of glass containers production with plunger process control

The production of glass containers is a very complex and demanding procedure which has to be very well equipped and optimally adjusted in order to produce glass containers that satisfy even the most demanding customers, at the same time being competitive on the market. Glass containers have to be maximally light, as well as less expensive, and at the same time they have to withstand maximal mechanical loads, greater internal pressure, thermal shocks (pasteurization), etc. For the glass containers to be able to meet these requirements, apart from a well designed container it is necessary to achieve also excellent glass distribution (uniform thickness of glass container wall), which can be achieved by the production procedure of NNPB (narrow neck press and blow process). The paper shows how the control system of the pressing procedure on glass machines achieves greater stability of glass gob masses, contributing also to improved quality of glass containers and increased production lines productivity. A comparison has been made, namely, of the production lines that are equipped with the system for controlling the pressing procedure WISEPPC (wireless sensor plunger position control) and those that are not.

High Temperature Interfacial Reaction between Glass Gobs and Sol-Gel Coated Al<sub>2</sub>O<sub>3</sub> Films

. Glass molding process is considered to have a great potential for the mass production of optical components with lower cost. Up to now, the service life of molding dies is still not satisfied. This study mainly focuses on the development of sol-gel derived Al2O3 coatings in order to extend the service life of glass molding dies. High temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coatings and glass gobs. The 304 stainless steel were used as the substrate materials. The sol-gel coated Al2O3 was selected as the protective coating. OHARA L-BAL42 glass gobs were chosen as the test materials. It can be observed that very severe interfacial reaction occurs between stainless steel and glass at high temperature. The contact angle dramatically decreases from initial and then gradually approaches 25° at 825°C after 2 minutes holding time. The severe interface chemical reaction also results in the loss of transparency in glass appearance. The reaction products such as Zn and Ba are mainly from glass material. For the case of Al2O3 coated substrate, the variation of the contact angles varied from 152 to 138°, presents anti-sticking or non wetting behavior. There are no reaction products can be found on the glass contacted area after wetting test.

In-situ determination of the heat flux density at the glass/mould interface during a glass pressing production cycle

The glass pressing process involves heat transfer between the glass gob and the forming tool which are among the most important parameters influencing the thermo-mechanical stresses in the moulds. The present paper presents the development of the instrumentation of a mould for the measurement of temperatures during the production cycle. These measurements are exploited with an inverse method to evaluate the heat flux densities at the working surface of the mould. The influence of each process stage and of the location at the surface of the mould on the thermal loadings are described. The evaluated heat flux densities are used as boundary conditions in a finite element calculation. The validity of these results are discussed taking into account the differences between experiment and calculation, the hypothesis of the inverse method and the time response of the thermocouples.

Investigations on glass-to-mold sticking in the hot forming process

Abstract The sticking behavior of various mold materials and coatings for hot glass melt forming processes, like, e.g. glass container manufacturing, was investigated using a new testing procedure. The mold material specimens under test were subjected to frequent contact with hot viscous glass gobs in a pressing process with presetting well defined non-isothermal pressing parameters to simulate industrial working conditions. Three different glass compositions were used in this investigation, soda-lime silicate glass, lead crystal glass, and borosilicate glass. The sticking characteristics of the tested mold materials and coatings were described by two quantities, a ‘lower’ and an ‘upper’ sticking temperature, which are specific for each mold material and type of glass in the non-isothermal pressing process. The ‘lower’ sticking temperatures of uncoated mold materials were found to depend monotonically on the thermal effusivity (heat penetration coefficient) of the bulk mold materials. All of the coating materials applied to various substrate mold materials were found to reduce the ‘lower’ sticking temperature as compared to the uncoated materials. Most of the coating materials were found to reduce also the ‘upper’ sticking temperature.

Design of Protective Coatings for Glass Lens Molding

The glass molding process is considered to have a great potential for the mass production of aspherical glass lenses with high precision and low cost. However, glass molding has a serious problem of mold sticking with glass which needs to be resolved. This research investigates the interface reaction between glass and mold by high temperature wetting experiment, which provides the reference for the designing anti-stick coatings. The SUMITA K-PSK200 optical glass gobs with low Tg were used in this study. The influence of operation temperature, ambient gas, substrate materials, and thin film composition on wettability of glass at high temperature were studied. The results show that the higher the temperature, the smaller the wetting angle between glass gob and substrate could be observed. This indicates that severe interface chemical reaction occured and resulted in the loss of transparency in glass appearance. The wetting experiment in nitrogen ambient improved the sticking situation. The combination of chemically stable substrates and coatings, such as Sapphire (substrate) / GaN (film) and Glass (substrate) / Al2O3 (film) can achieve the best antistick propose. The precious metal films, such as Pt, Ir, coated on the ceramic substrates can effectively reduce the interface reaction between the glass and substrates.

Computer vision system for estimating and controlling the weight of glass gobs during their industrial formation process

We present a computer vision system for measuring the weight of gobs during a glass-forming process, and a control strategy to automatically correct any weight deviation from a given set point. The system is based on a reliable gob area estimation using image-processing algorithms. A monochrome CCD high-resolution camera and a photodetector for synchronizing acquisition are used for registering gob images. Assuming that the gob has symmetry of revolution about the vertical axis, the proposed system estimates the weight of gobs with accuracy better than ±0.75%. A learning weight control strategy is proposed based on a proportional-integral (PI)-repetitive control scheme. The weight deviation from a set point is used as a control signal to adjust the glass flow into the feeder. This regulation scheme enables effective weight control, canceling mid- and long-term effects. The tracking error of ±1.5% means a reduction of 40% when compared with a traditional PI controller.

Transient cooling of a cylindrical glass gob

Transient cooling of a hot glass gob by internal combined conduction and radiation is analyzed. The spectral dependence of the absorption coefficient on wavelength and temperature is appropriately accounted for by solving the radiative transfer equation for the axisymmetric cylindrical geometry. Specularly reflecting boundaries are considered and Fresnel's equations are used to predict the spectral directional reflection and transmission characteristics of the interfaces. The finite volume method is used to solve numerically the thermal energy equation, and discrete ordinates method (DOM, S–N method) is employed to solve the radiative transfer equation. Dynamic cooling calculations have been performed and transient temperature distributions, temperature gradients, convective and combined convective plus radiation results are presented and discussed. The results show that for the initial and thermal conditions of interest, the interior of the glass cools primarily by radiation and only in the surface layers (0.8< r/ R<1.0) is conduction of the same order of magnitude as radiation.

Digital Control Application on a Class Gob Feeder

The adjustments in a glass gob feeder, to maintain a constant gob weight are made at present manually. This paper deals with the application of a digital system to control said weight, taking as a base the gob temperature. Several tests were performed in a “green” glass container production line. Correlation methods were used to determine the behavior of the variables that influence the gob weight. It was found that these variables are linearly related with a -0.9 correlation factor. Taking into consideration these results, a digital system will be used to control the process.

Some aspects of glass control in container production

Efficient production of glass containers depends initially on feeding the machine with glass of controlled composition, weight of deviations from desired glass composition, temperature and level and indicates that the most critical variable is glass temperature. Control of glass gob temperature should start with accurate control of working end temperature to within ±4°C or better for white flint glass; control of the working end temperature can be effected by controlled heating or cooling. The desirable entrance temperature can be inferred from mathematical studies of forehearth behaviour using the 2DL model developed by Carling at the University of Sheffield. The design and operation of forehearths can also be assisted by the use of the 2DL model and the design and operation of working ends by a 3D model also developed by Carling. The paper is based on numerous measurements of temperature in working ends and forehearths in a number of factories in United Glass Limited.