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This article is reprinted the China packaging container network.Yang Wenfeng sorted out.Please contact us if there is anything wrong.
Introduction
This article is a compilation of definitions,causes,and solutions for stripes in glass manufacturing from various sources,including"Defects in Glass Manufacturing"by Jebsen-Marwedel H.Brückner R.,"Production Techniques of Glass Bottles"by Henry More,and"Analysis and Solution of Glass Stone and Stripes Defects"by Duan Shenghuang.Hope it will be useful for practical operation.
I Definition
Stripes are a common type of glass uniformity defect,and its definition has been unclear due to the various forms.According to the United States Materials Testing Standard,it is"the stripes in glassware are slender glass inclusions,which having optical and other properties different from the main body of glass.“
The stripes can be understood as the transition stage before the melt or solution penetrates through chemical,physical,and structural aspects to achieve complete uniformity.Therefore,the concept of"stripes"can be a general term for glass clamps that can be completely mixed in glass.If conditions permit,they can be completely together with the surrounding material at melting temperature.The difference from the surrounding substances is that the glass inclusion substances have a different chemical composition,thermal state,or(and)structural state.
Due to the presence of stripes,many of the problems are attributed to the appearance of it in terms of the physical nodulation energy changes,which including from minor appearance defects to severely reduced defects of glass defects.
II.Formation of the various stripes
Reasons
Generally speaking,there are some factors following:
improper glass raw material particle size,
incorrect changes in glass composition,
inadequate glass composition design,
improper kiln melting,
unstable output,
erosion of refractory materials,
volatilization of alkaline materials.
III.Methods for resolving stripes:
1,Stripes caused by uneven mixing or incorrect measurement of raw materials.
These can be divided into stripes rich in silica and stripes deficient in silica.If the glass contains alumina,stripes rich in alumina and stripes deficient in alumina may also appear.Stripes rich or deficient in calcium or magnesium are relatively rare.
Stripes caused by differences in raw materials can lead to serious safety issues for bottles.These stripes have a multi-layered appearance with different strengths,are generally spiraled,and extensively spread in cross-sections.They can be either tensile or compressive stress stripes,depending on the severity of the error in the raw materials.
Mixed batch uniformity should be considered from the following aspects:
particle size distribution,which determines the contact area between the reacting substances(raw materials)and the reaction area,should be maximized;
the distribution of each component should be as statistically uniform as possible in space and time,so that the raw material components are fully mixed.Regular monitoring is essential.
In order to accurately measure the amount of added material,the moisture content of the mixed batch should be known at all times.Generally,quartz sand is required to contain 4-5%(by weight)of moisture.Water can be added to the mixed batch during the mixing process when using dry sand.
Density stability can be used as an indicator of potential stripe problems.
If the density fluctuates more than 0.0020 g/cm3 in a day,changes in the composition caused by density may lead to stripes.
The homogenization effect of the clarification process should also be noted.
A large number of bubbles during melting and clarification can cause many displacement reactions,making the composition of the glass close to a statistically average value.The smaller the deviation of each part's composition from this average value,the more uniform the melt.
The"hotspot"is the area with the highest temperature in the clarification zone.It has two main effects.It causes the clarification agent to thermally decompose and drives out the gas in the melt,and it forms two large and several small circulating flows in the glass melting pool.The large circulation flow assists in mixing the bubbles,Causes strong diffusion deformation and makes the melt uniform.Hotspots can be strengthened by two measures:through electrical assisted heating and"bubbling".
After the auxiliary heating of the glass,the refractive index is increased△。=0.0003,the density increased by 4.5%,The degree of inhomogeneity(determined by the Christensen filter method)can be reduced by about 2/3.Bubbing with air in the glass melt reduces the density fluctuation from the original soil 1.1 kg/m3 to 0.45 kg/m3.
Stripes caused by changing mixed batch
It takes a long time of adding the same mixed batch to make the melt in the furnace reach a truly uniform composition.Changes in the chemical composition of mixed batch also take some time to be analyzed in the final product.
There are always glass layers in the furnace that do not flow with the liquid flow,which may be the source of defects.Especially in the vicinity of sudden contractions in the furnace(flow holes),eddies are easily formed,and the substances dissolved in each independent eddy may be different.Although the glass layer formed here is temporary,stripes may form at its boundary.
Due to the mix,striped glass is almost unavoidable(at least temporarily).It also affects the other properties of the glass and causes a failure in the molding operation.
The volatility of materials and dust are the source of stripes
Volatility and dust of materials are the sources of stripes Both phenomena may cause defects in two adverse effects:
This special situation mainly occurs in low-alkaline borosilicate glass,which requires a certain amount of boron oxide(which is easy to volatilize)and high temperature to melt the glass,making the glass rich in silicates.If this glass is introduced into the glass flow system,stripes may occur.
Although the change in the composition of the glass is local,it may appear on a large surface of the melt and cause obvious stripes.
Slag is formed on the refractory materials above the glass liquid level.It not only causes stripes in the glass,but also corrodes the refractory materials themselves.
Usually,this type of stripe can be subdivided by type and only exists in part of the cross-sections.It appears as vertical stripes on bottles and has a shape like"nodules"in cross-sections.
In the forehearth,the temperature is low,and the erosion of glass and refractory materials is slow.However,the glass liquid still has erosion and corrosion on the refractory materials.After being eroded,it is difficult to diffuse due to the low temperature.However,when the temperature of the material channel changes,it flows along the bottom of the material channel into the glass product.Such stripes on the same group of products are mainly the same in shape and form"cat claw"stripes.
The solution to this type of stripe is to add a stirring device to the forehearth.
In addition,the angle radius of the intersection of the forehearth wall and the bottom should be increased,the dead corners should be reduced to avoid the formation of slow-moving"dead materials,"and the insulation of the bottom of the material channel should be strengthened to increase the temperature of the bottom glass liquid,reduce its viscosity,and increase its flow and diffusion.
The advanced structure abroad is a discharge device on the forehearth.
4.The Stripes Caused by Improper Melting
1)Stripes Caused by Unstable Furnace Temperature.When the furnace temperature is unstable and fluctuates,a stationary layer(or slow-moving layer)at the bottom of the original pool may shift.
Differences in composition and viscosity may also cause stripes,which appear as block-like shapes.
The temperature changes can cause different residual materials with different compositions in the furnace to mix and melt with the majority of the glass in the pool,resulting in stripes.
Changes in furnace operation,such as excessive changes in discharge amount,uneven combustion on one side of the furnace,significant changes in melting electrodes or foaming,and uneven glass flow in the pool,can also cause stripes.
2)Stripes Caused by Inappropriate Furnace Atmosphere
The furnace atmosphere refers not only to the composition of gases and pressure of various gases in the space above the melt but also to the temperature of the gases.The furnace atmosphere has a significant impact on the glass melt.According to Novak,"the effect of the furnace atmosphere is almost equivalent to one component in the mixed batch,and it must be precisely controlled like the mixed batch itself."The furnace atmosphere is particularly sensitive to fluctuations in the degree of flame reduction,affecting color glass and sulfate glass.Maintaining a constant temperature is also essential,as each temperature corresponds to an equilibrium state that must remain undisturbed.Temperature fluctuations create transitional states that inevitably lead to uneven results.
Some glass contains multivalent cations or sulfides and selenides that can change color through redox reactions.The furnace atmosphere can cause color stripes in such cases.
The causes of brown stripes are varied.In addition to the reduction of glass and selenium,there are also the iron mixed in the broken glass or the iron parts in the kiln structure into the glass.When changing the glass color varieties,the old glass liquid is not cleared,the small furnace position is not appropriate,plus the reduction of clear sulfate,carbon chips in the broken glass may increase the sulfur content of sulfide in the glass and make the glass color.Amber stripes and color bands appear in the glass similarly.
Stripes Caused by Adding Crushed Glass
In general,adding crushed glass to the mixed batch makes melting smoother than without.However,crushed glass lacks some alkali,which evaporates during the melting of the original batch,and this difference does not need to exceed 0.2%Na2O to cause unevenness in the melt.Therefore,crushed glass differs in composition from the glass material introduced from the batch.The surface of crushed glass tends to absorb components in the air,especially moisture.In terms of composition,the surface of crushed glass is different from its interior.After melting,a layer(stripe)appears,separating it from the surrounding melt.Care should be taken to prevent differences in the glass composition of crushed glass and the furnace's glass composition.The composition of externally purchased crushed glass should be analyzed regularly,and the glass formula should be adjusted based on the results.
People have gradually mastered the technology of the"circulation"of broken glass in the melting of glass.In the past,some sodium carbonate can be added to the mixture with 30-35%broken glass without causing harm.Today,it has been successfully produced by melting 66%to l00%broken glass in large production tests,and it does not affect many important properties of glass such as folding strength.Impact resistance strength and uniformity.E-modulus,thermal expansion,resistance,etc.
Stripes Caused by Unstable Discharge Amount
The most common occurrence of stripes during production is when products are replaced.When a product changes,and the glass liquid flow rate changes,the rate of change must be strictly controlled.
When the liquid flow rate needs to increase,it is best to gradually increase the machine speed.
As the discharge amount increases,and especially when the glass liquid surface fluctuates significantly,the high viscosity melt corroded from both sides of the pool flows into the production stream,forming stripes.When the discharge amount increases,the flow rate of the stationary layer at the bottom of the original pool becomes faster or changes,forming stripes due to the influence of the glass's own viscosity.
The best solution is to gradually increase the machine speed and strengthen control measures to stabilize the furnace melting conditions.
Another situation is when the glass liquid flow rate decreases after a product change.This situation is generally due to a decrease in product weight,an increase in forming temperature requirements,and a need for increased working parts and feed channel temperature.As the temperature rises,the residual materials in the working parts and feed channel are carried by the glass liquid flow and mixed into the forming glass flow,forming stripes.
The best solution is to gradually increase the working parts and feed channel temperature before changing products and strengthening control measures to stabilize the furnace melting conditions.
Compared to stripes caused by differences in the mixed batch,this type of stripe tends to be at lower stress levels during annealing and is not widespread during cutting.
Stripes formed by crystal precipitation and"stones"interacting with the surrounding melt
Both cases are related to the offset of the solubility equilibrium.
Stripes caused by refractory materials
Refractory materials are non-glass materials that come into contact with the glass melt,aside from the furnace atmosphere.Their resistance is limited,and they slowly dissolve into the melt,becoming the source of stripes.
The source of stripes formed by slagging of the upper structure of the furnace
Slag produced by the invasion of alkali in the dust of the batch can also cause stripes on the upper components of the furnace.If the slagging situation is normal,it will not be too harmful.However,when it develops beyond the eutectic point and partially softens to form slag flowing into the glass melt,it may produce a large number of stripes.
The furnace bricks of the glass melting furnace may also have stalactite-like and other slag shapes due to the loose joints.Loose joints may be caused by inaccurate brick size(brick protrusion,bending,deformation due to uneven forging,inconsistent wedge angles,etc.),careless construction during bricklaying,inappropriate or insufficient use of mortar,and some types of bricks that are particularly vulnerable to slag corrosion.
Improper heating of the furnace bricks can also cause the originally tight joints to open and allow gas to pass through.
Selecting the appropriate brick size and calculating the heating curve(the expansion effect caused by the temperature gradient in the brick thickness direction)can also make the opened joints tightly sealed.It is recommended to carefully inspect the furnace bricks of the melting furnace every 4 to 5 months and repair the heavily eroded parts.
The key area for stripe formation is the liquid surface scouring location.Every fluctuation of the glass liquid surface will drive the glass liquid containing corrosion products to rise or fall at the scouring location.This liquid surface change may be caused by furnace malfunctions that reduce the melting amount or may be deliberately reducing the glass liquid level on rest days.However,the harm caused will not be slight,so it is necessary to avoid a large number of stripes entering the glass liquid flowing through there when the glass liquid surface fluctuates up and down.Therefore,it is necessary to use suitable optical control devices to strictly maintain a stable glass liquid surface.
Thermal stripes
When a certain part of a uniform liquid or glass melt is heated,a part with a higher density and a part with a lower density appear,which refracts the transmitted light and moves under stress to produce a shadow image,which can undoubtedly be called stripes.This non-uniform phenomenon(so-called"thermal stripes")can also be displayed by stripe optical and stress optical methods,just like stripes formed by chemical reasons.These"thermal stripes"can only be eliminated after heating the structural units in the glass to a certain flowability(annealing range),and they can also be called"physical stripes."
IV Methods to examine the types and compositions of stripes:
Professionals often infer the source of defects from the appearance or color of stripes.
Check stripes from"total reflection."
Measure permanent stress.Glass bottles are usually observed with a polarizing microscope to measure the level of circumferential uniformity.
The difference in refractive index between stripes and the main glass can be used to infer the type of stripes,and sometimes their source.The entire range and structure of all stripes can be displayed by stripe method,interference method,shadow method,and refractive index gradient measurement.
When possible(such as some"nodules"),the stripe material can be separated from the main glass for analysis by grinding or grinding slices.
The type of stripes can be inferred by corrosion with hydrofluoric acid,boron fluoride acid and hydrochloric acid,sodium hydroxide,etc.
Crushed glass with stripes can be separated from the main glass in solutions with different densities for further analysis.
Crushed glass with stripes can cause light scattering in immersion solution,and the degree of unevenness can be measured by the Krescenthson filter method.
