Patent Description:
In the state of the art, during a mechanical glass tube drawing process such as the Danner process, a fluid flows in a controlled manner through a carrier which carries a refractory tube. The refractory tube in turn provides a surface area onto which molten glass runs which molten glass then is shaped into a glass tube strand in the shaping zone arranged at one end of the refractory tube.

Based on the chosen parameters of the fluid, such as volume flow rate and pressure, the speed of pulling of the glass tube strand from the refractory tube, and the temperature regime in the shaping zone, the geometric parameters of the produced glass tube strand can be influenced.

The fluid, which can be a gaseous medium such as air, flows through the carrier to the shaping zone. The carrier might be in the form of a sleeve shaft, which is for example a hollow shaft made of steel. Often, the refractory tube has temperatures of for example <NUM> degrees C to <NUM> degrees C which in turn heats the carrier since it is arranged within the refractory tube.

Due to high temperatures at the sleeve shaft, the steel material of the sleeve shaft undergoes a cinder-corrosion process in the presence of oxygen. This leads to particles originating from the material of the sleeve shaft in form of cinder particles present in the lumen enclosed by the sleeve shaft. While the fluid flow through the carrier typically is insufficient for whirling the particles within the lumen, the particles are transported along the inner surface of the sleeve shaft to the shaping zone mediated by the fluid flow, gravity (since the refractory tube, hence, the carrier, might be inclined), and the rotational movement of the sleeve shaft.

In the shaping zone, the particles then might be in contact with the inner surface of the glass material of the glass tube strand and contaminate it while it is a viscous fluid. After the glass material had contact with the particles and subsequently has hardened, the particles are permanently confined on the inner surface of the glass tube strand.

Since the particles cannot be removed from the glass tube strand in subsequent process steps, contaminated products are rejected by inspection systems of production process, thus reducing the production yield.

Conventionally, it has been proposed to cover the inner surface of the sleeve shaft with noble metals, ceramics or other corrosion protection coatings of appropriate temperature resistance in order to prevent the occurrence of cinder particles in the lumen enclosed by the sleeve shaft. Other attempts have been directed to using inert gas as fluid, or even using completely metal-free, especially iron-free, sleeve shafts, e.g. made of ceramic or even glass.

However, the results have not been satisfying or the measures are complex, come along with high costs, or are hard to implement.

Also, further processing of the inner surface of the sleeve shaft for the purpose of minimizing the corrosion process, for example by sandblasting of the inner surface, did not yield a significant reduction of the particles.

Furthermore, it was proposed that fluid filters are positioned in the end section of the sleeve shaft and the entire fluid directed through such filters. However, it turned out that the fluid flow dynamics are disturbed by such filters which in turn adversely affect the geometry and quality of the glass tube strand. Furthermore, such filters are subject to clogging which requires regular maintenance of the system and replacement of the filters. This, however, leads to enormous downtimes of the production, hence, to increased costs.

Document <CIT> is related to a sleeve for glass tube molding.

It is, thus, an object of the present invention to overcome the disadvantages described above with respect to the state of the art by providing means which allows a reduction of the contamination of the glass tube strand by particles in an easy and cost-efficient manner or even preventing such contaminations completely. It is further the object of the present invention to provide sleeve shafts and refractory tubes which overcome the known disadvantages.

The invention is defined in the independent claim. Advantageous embodiments of the invention are defined in the dependent claims.

The problem is solved by the invention according to a first aspect in that a refractory tube, into which refractory tube a sleeve shaft with at least one inlay for collecting particles originating from the material of the sleeve shaft at least in part, is inserted,wherein at least one fluid can flow through the sleeve shaft along an axial direction which is parallel to the main extension of the sleeve shaft,wherein the inlay comprises at least one first wall section, wherein the inlay is or can be inserted at least in part into the sleeve shaft such that at least one part of the first wall section has a radial distance from at least one first area of the inner surface of the sleeve shaft, and, hence, that the inlay together with the first area of the inner surface of the sleeve shaft encloses at least one volume domain, which volume domain is limited in the axial direction by a limiting element comprised by the inlay,wherein the inlay comprises at least one zone of cylindrical form, and the first shell of at least one first section of the cylindrical zone comprises the first wall section, wherein the first section comprises at least one first end section of the inlay, is proposed.

The invention is, thus, based on the surprising finding that due to the nature of the particles and the given general conditions, the particles are typically moving closely along the inner surface of the sleeve shaft rather than being distributed across the entire lumen enclosed by the sleeve shaft. Thus, it is possible to prevent the contact of these particles with the glass material, preventing a contamination of the glass material. By providing a volume domain within the sleeve shaft where respective moving particles, such as cinder particles originating from the material of the sleeve shaft, can be collected, the particles are prevented from moving to the shaping zone.

By using the proposed refractory tube, the volume domain can be provided in a very straight forward and cost-efficient manner. The inlay itself can be designed to be inserted into the sleeve shaft of a refractory tube quickly and easily. This makes it easy to retrofit nearly any existing refractory tubes with an inlay according to the invention in an efficient and inexpensive manner. Particularly, neither the entire sleeve shaft has to be replaced nor any covers have to be applied at places within the sleeve shaft which are usually difficult to access. Both would be highly complex and would require to remove the sleeve shaft from the refractory tube with subsequent external processing. Hence, with the present invention downtime of the production process can be reduced to a minimum.

Since the inlay is much smaller than the sleeve shaft, it is possible to use materials for the inlay or corrosion-preventing coatings for the inlay's inner surfaces, which previously have been excluded from use with the sleeve shaft due to their high costs.

For example the inlay might comprise <NUM>-<NUM> % by weight, preferably <NUM>-<NUM> % by weight, of Fe.

In preferred embodiments the inlay has an axial length of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, more preferably of between <NUM> and <NUM>, and most preferably of <NUM>.

The inlay has the further advantage that it can be designed such that it provides a sufficiently large volume for trapping particles so that the inlay can remain within the sleeve shaft during a production process for several years without the need to remove the collected particles from the volume domain.

In various tests conducted by the inventors and as confirmed by monitoring the glass tube strand in production it has been proven that the inlay neither affects the fluid flow within the sleeve shaft or in the shaping zone nor does it affect the quality or geometric properties of the glass tube line.

The volume domain is limited in radial direction by the first wall section and the first area of the inner surface of the sleeve shaft and in axial direction by the limiting element.

The invention, thus, provides a cheap and powerful solution for preventing the contamination of the glass tube strand with particles such as cinder particles originating from the material of the sleeve shaft.

In one embodiment it might alternatively or in addition be preferred that the particles, which are moving at least in part mediated by the fluid flow and/or gravity along the inner surface of the sleeve shaft along the first axial direction, reach the volume domain and get trapped, hence, are prevented from moving further along the axial direction.

In one embodiment it might alternatively or in addition be preferred that the inlay comprises at least one zone of cylindrical form, and the first shell of at least one first section of the cylindrical zone comprises the first wall section, wherein preferably the first section comprises at least one first end section of the inlay.

If the inlay comprises a zone of cylindrical form it can be particularly easily inserted within the sleeve shaft, which typically provides an enclosed volume, i.e. lumen, of cylindrical form. For example, the inlay can then be arranged concentrically within the sleeve shaft in an easy manner. At the same time the first shell (of a first section) of that zone can provide the first wall section which leads to a compact design.

If the first section is an end section of the inlay, it is possible to provide the volume domain far inside the sleeve shaft, hence, a large volume domain is possible.

In one embodiment it might alternatively or in addition be preferred that the second shell of at least one second section of the cylindrical zone, which is different to the first section of the cylindrical zone, comprises at least one second wall section, wherein the first outer diameter of the first wall section is smaller than the second outer diameter of the second wall section, wherein preferably the second section comprises at least one second end section of the inlay and/or wherein the second section follows after the first section along the axial direction, especially the second end section of the inlay being at the opposite end of the inlay than the first end section of the inlay.

If the second shell of a second section of the cylindrical zone provides the second wall section, the inlay can be fitted to the inner geometries of the sleeve shaft.

In one embodiment it might alternatively or in addition be preferred that the limiting element is formed and/or arranged in at least one end section of the first wall section, preferably the limiting element is in one piece with the first wall section and/or the end section of the first wall section is facing away from the first end section of the inlay.

Arranging the limiting element at the end section of the first wall section allows defining a definite volume domain.

In one embodiment it might alternatively or in addition be preferred that the limiting element is formed by at least one transition from the first wall section to the second wall section, wherein preferably the transition is designed in at least one cross sectional plane in form of at least one step and/or in form of at least one arc segment.

If the transition between the first and second wall sections is used as limiting element, a compact design and an inherent, hence, efficient realization of the limiting element is possible.

In one embodiment it might alternatively or in addition be preferred that the inlay comprises at least one fastening means for arranging the inlay at the sleeve shaft, at least one distant element and/or at least one stop element, preferably the stop element is designed in form of at least one collar, is designed at least in part in one piece with the limiting element, is designed at least in part in one piece with the second wall section, and/or is provided in at least one end section of the inlay, especially at the end section of the inlay opposite the first wall section.

Providing one or more fastening means allows securing the inlay safely at the sleeve shaft. This improves security. A stop element allows for a comfortable and safe installation of the inlay within the sleeve shaft because the stop element efficiently prevents inserting the inlay too deep into the sleeve shaft.

A distant element allows that the inlay is held in a safe and/or concentric manner within the sleeve shaft.

In one embodiment it might alternatively or in addition be preferred that the inlay is or can be connected with the sleeve shaft by welding, in a positive locking manner and/or frictional locking manner, and/or that the volume domain is at least in part in form of at least one ring volume.

If the inlay is suitable for being connected (or even if it is connected) to the sleeve shaft by welding, in a positive locking manner and/or in a frictional locking manner, a safe connection can be provided between the inlay and the sleeve shaft.

The inlay, in one preferred embodiment, might comprise fastening means. Fastening means allow arranging the inlay at a sleeve shaft securely. Especially some fastening elements allow reversible release of the inlay. This allows removing particles from the volume domain very easily.

A positive locking here means connections that are created by the interlocking of at least two connecting members. As a result, the connecting members cannot loosen even if the force transmission is interrupted or not present at all. In other words, in a positive locking connection, one connecting members is in the way of the other. Under operational load, compressive forces act in a normal direction, i.e. perpendicular to the surfaces of the connecting members. Such "blocking" occurs in at least one direction. If a second homogeneous pair of surfaces is arranged opposite, the opposite direction is also blocked. If the pair consists of two coaxial cylindrical surfaces, positive locking exists in all directions of the plane perpendicular to the cylinder axis.

A frictional locking here means connections that require a normal force on the surfaces to be connected. Their mutual displacement is prevented as long as the normal force caused by the static friction is not exceeded by a tangential force. The normal force or frictional connection is eliminated and the surfaces slip with respect to each other, if the tangential load force is greater than the static friction force.

A ring volume is particularly preferred because it provides rotational symmetry of the system, hence, a stable operation of the system is possible.

In one embodiment it might alternatively or in addition be preferred that the particles comprise oxidation products of the sleeve shaft material, cinder particles and/or corrosion particles, which particles preferably are created by the reaction of steel, especially chromium-nickel steel, together with oxygen at temperatures of between <NUM> to <NUM> degrees C.

Here, preferably the particles might alternatively or in addition also comprise particles contained in the fluid.

In one embodiment it might alternatively or in addition be preferred that the inlay does not substantially affect the fluid flow within the sleeve shaft negatively and/or does not substantially affect the shape, the quality or the geometric properties of the produced glass tube strand.

If the inlay does not affect the fluid flow, the production process of the glass tube strand is not adversely affected. Hence, the inlay does not affect the quality of the glass tube strand in a negative manner.

The problem is solved by the invention according to a second aspect in that a sleeve shaft with at least one inlay according to the first aspect of the invention for collecting particles originating from the material of the sleeve shaft at least in part, wherein at least one fluid can flow through the sleeve shaft along an axial direction which is parallel to the main extension of the sleeve shaft,.

If a sleeve shaft is provided with a respective inlay, the advantages of the inlay as described above with respect to the first aspect of the invention can be applied without any further efforts.

In one embodiment it might alternatively or in addition be preferred that the sleeve shaft comprises at least one steel, especially chromium-nickel steel and/or <NUM> steel, as material.

The proposed materials have been proven to provide a preferred sleeve shaft of good quality and stability even under rough environment conditions such as heat.

Preferably in one embodiment the sleeve shaft comprises a material comprising: <NUM>-<NUM> % by weight of Cr, <NUM>-<NUM>% by weight of Fe, <NUM>% by weight of Al and <NUM>-<NUM>% by weight of Ni.

Preferably in one embodiment the sleeve shaft comprises a material comprising: <NUM>-<NUM>% by weight of Ni, <NUM>-<NUM>% by weight of Cr and <NUM>-<NUM>% by weight of Fe.

In one embodiment it might alternatively or in addition be preferred that the inlay is arranged at the sleeve shaft by means of at least one fastening means, especially comprised by the inlay, and/or wherein the inlay is connected with the sleeve shaft in a welded manner, in a positive locking manner and/or frictional locking manner.

A fastening element allows securely arranging the inlay at the sleeve shaft. Especially some fastening elements allow reversible release of the inlay. This allows removing particles from the volume domain very easily.

If a welded connection is chosen a very reliable connection is provided.

Further, reference is made to the definition provided above for the terms "positive locking" and "frictional locking", which apply here, too.

In one embodiment it might alternatively or in addition be preferred that the inlay comprises at least one zone of cylindrical form and the shell of at least one section of the cylindrically zone, especially the second section according to the first aspect of the invention, comprises at least one second wall section, wherein the second wall section contacts at least one area of the inner surface of the sleeve.

This arrangement allows provision of the volume domain in an efficient and easy manner. Furthermore, the contact area allows for a more reliable connection between the inlay and the sleeve shaft which increases safety.

In one embodiment it might alternatively or in addition be preferred that the first area of the inner surface of the sleeve shaft is an inner surface of a first section of the sleeve shaft, said first section having an inner diameter which is larger than the inner diameter of a further section of the sleeve shaft, which further section of the sleeve shaft follows said first section of the sleeve shaft in a direction antiparallel to the axial direction.

It has been found that if the fluid flows through the sleeve shaft from a section of smaller inner diameter into a section of larger inner diameter, it is possible that the fluid flow near the inner surface of the sleeve shaft is deflected so to say into the shadow area of the volume enclosed by the sleeve shaft in the section with larger inner diameter. This is because a radial velocity seems being created by means of the transition from smaller to larger inner diameter.

This way, particles which are close to the inner surface of the sleeve shaft are directed closer towards the trapping volume enclosed between inlay and sleeve shaft. Furthermore, it has been noted that the absolute fluid velocity in that shadow area is significantly reduced so that the time the particles have in order to get trapped is increased. This in turn increases the possibility that the particles actually get trapped.

In one embodiment it might alternatively or in addition be preferred that the ratio of the inner diameter of the further section and the inner diameter of said first section is (a) <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, preferably <NUM> or larger, (b) <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, preferably <NUM> or smaller, and/or (c) between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>;
and/or
that the transition from the further section to said first section is designed in the form of a step-like transition and/or in form of a tapered transition section, especially having a conical shape and/or being arranged between the further section and said first section, and wherein preferably the tapered transition section has in axial direction a length of (a) <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, preferably <NUM> or more, (b) <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, preferably <NUM> or less, and/or (c) between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

A transition, such as a tapered transition, has been proven to provide an improved radial velocity so as to improve trapping of the particles.

The problem is solved by the invention according to a third aspect in that a refractory tube, especially for use in a glass tube drawing process, into which refractory tube a sleeve shaft according to the second aspect of the invention is inserted, especially in a coaxial manner, wherein preferably the refractory tube has at least one outer surface which outer surface comprises platinum and/or at least one platinum alloy is proposed.

If a refractory tube is provided with a respective sleeve shaft, the advantages of the sleeve shaft as described above with respect to the second aspect of the invention can be applied without any further efforts.

An outer surface of the refractory tube which comprises platinum and/or at least one platinum alloy provides a heat resistant surface. This is particularly preferred for the contact surface where the molten glass runs onto the refractory tube.

In one embodiment it might alternatively or in addition be preferred that a total axial length L of the inlay, a heat resistance parameter γ of at least parts of the material of the inlay and an axial distance d between the position where molten glass runs onto the refractory tube and the end of the refractory tube, from which end the glass tube is drawn, meet the condition: <MAT> wherein the heat resistance parameter γ is defined as <MAT> with E(T) being the Young's modulus of a metal material comprised by the inlay at temperature T, and wherein the position where molten glass runs onto the refractory tube is defined as the center of the axial extension of the shell of the refractory tube.

More preferably, the total axial length L of the inlay meet the condition: L ≤ <NUM>γd. More preferably, the total axial length L of the inlay meet the condition: L ≤ <NUM>γd. More preferably, the total axial length L of the inlay meet the condition: L ≤ <NUM>γd. More preferably, the total axial length L of the inlay meet the condition L ≤ <NUM>γd. Even more preferably, the total axial length L of the inlay meet the condition L ≤ <NUM>γd. Even more preferably, the total axial length L of the inlay meet the condition L ≤ <NUM>γd. Even more preferably, the total axial length L of the inlay meet the condition L ≤ <NUM>γd. Even more preferably, the total axial length L of the inlay meet the condition L ≤ <NUM>γd. Even more preferably, the total axial length L of the inlay meet the condition L ≤ γd.

Parts of the inlay which are located closer to the position where molten glass runs onto the refractory tube (or its shell) are exposed to increased heat than parts of the inlay which are farer away from that particular position. With increasing heat, also the number of particles originating from the inlay material itself may be increased. Hence, making the inlay longer comes with the positive effect of e.g. providing more space for collecting particles. But it may come with the negative effect of increased production of particles once the inlay is inserted in the sleeve shaft of the refractory tube. Because the additional particles may lead to further contamination of the fluid flowing through the sleeve shaft.

It has been found that a preferred maximal total axial length of the inlay can be determined if a heat resistance of the inlay's material is taken into account. Surprisingly, a heat resistance can be expressed as a simple parameter basically based on the Young's modulus of the metal material of the inlay.

The solution is based on the finding that the Young's modulus typically decreases with increasing temperatures and, thus, provides a good basis for assessing the quality of the metal material in the context of heat exposure.

It has been further found in that respect that a robust overall estimation can be made if the Young's modulus at the temperatures of <NUM> and <NUM> are considered. This is because the respective temperature range can be regarded as roughly covering the temperatures of the molten glass during its presence on the refractory tube.

If the total axial length of the inlay is chosen so as to meet the provided condition, a preferred compromise between the increased trapping volume on the one hand and the increased particle production rate on the other hand can be achieved.

Below, preferred features of refractory tube of the invention are disclosed. The features may be employed alone or in any combination.

Preferably, the inlay has a total axial length of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>.

Preferably, the inlay has a total axial length of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more.

Preferably, the inlay has a total axial length of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less.

For example, the inlay may have a total axial length of <NUM>, <NUM> or <NUM>.

Preferably, the inner diameter of the inlay is constant.

Preferably, at least one inner diameter of the inlay has a value of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>.

Preferably, the or at least one inner diameter of the inlay has a value of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more.

Preferably, the or at least one inner diameter of the inlay has a value of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less.

For example, at least one inner diameter of the inlay may have a value of <NUM> or <NUM>.

The inner surface of the inlay may be the surface of the zone of cylindrical form of the inlay.

Preferably, the inner surface of the inlay has a value of between <NUM><NUM> and <NUM><NUM>, preferably of between <NUM><NUM> and <NUM><NUM> or <NUM><NUM> and <NUM><NUM>, especially of between <NUM><NUM> and <NUM><NUM>.

Preferably, the inner surface of the inlay has a value of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more.

Preferably, the inner surface of the inlay has a value of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less.

For example, the inner surface of the inlay may have a value of <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, or <NUM><NUM>.

For example, it might be preferred to define a ratio of the value of the inner surface of the sleeve shaft and the value of the inner surface of the inlay.

Preferably, the ratio has a value of between <NUM> and <NUM>, especially of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM>, of between <NUM> and <NUM> or of between <NUM> and <NUM>.

Preferably, the ratio has a value of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more.

Preferably, the ratio has a value of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less.

For example, the ratio may have a value of <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

Preferably, the sleeve shaft has a total axial length of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>.

Preferably, the sleeve shaft has a total axial length of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more.

Preferably, the sleeve shaft has a total axial length of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less.

For example, the sleeve shaft may have a total axial length of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

For example, the first area of the inner surface of the sleeve shaft is a surface of a section of the sleeve shaft of constant inner diameter. This may be the respective diameter of the bore within the sleeve shaft where the inlay is or can be inserted.

The respective section of the sleeve shaft of constant inner diameter may have an axial length of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, especially <NUM>.

Preferably, the constant inner diameter has a value of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>, preferably of between <NUM> and <NUM>.

Preferably, the constant inner diameter has a value of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more, preferably of <NUM> or more.

Preferably, the constant inner diameter has a value of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less, preferably of <NUM> or less.

For example, the constant inner diameter may have a value of <NUM>, <NUM> or <NUM>.

The inner surface of the sleeve shaft may be the inner surface of the bore of the sleeve shaft.

Preferably, the inner surface of the sleeve shaft has a value of between <NUM><NUM> and <NUM><NUM>, preferably of between <NUM><NUM> and <NUM><NUM>, preferably of between <NUM><NUM> and <NUM><NUM>, preferably of between <NUM><NUM> and <NUM><NUM>.

Preferably, the inner surface of the sleeve shaft has a value of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more, preferably of <NUM><NUM> or more.

Preferably, the inner surface of the sleeve shaft has a value of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less, preferably of <NUM><NUM> or less.

For example, the inner surface of the sleeve shaft may have a value of <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, or <NUM><NUM>.

Preferably, the ratio of the total axial length of the sleeve shaft and the total axial length of the inlay is between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM> or between <NUM> and <NUM>. Preferably, the ratio of the constant inner diameter of the sleeve shaft and the or at least one inner diameter of the inlay is between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

The main part of the particles may be created in the hottest area of the refractory tube at the level of the glass run-up (glass temp. <NUM>-<NUM>). However, an inlay which would protrude into the sleeve shaft bore into this area would be exposed to extreme production of particles from its inner surface (at these temperatures, this can hardly be influenced by the choice of steel grade for the scale stop).

The temperature of the sleeve shaft in the head area (glass temperature approx. <NUM>), on the other hand, is much lower. It is even the location with the lowest possible temperature inside the sleeve shaft and thus also with the lowest possible rate of particle production of the inner surface of the scale stop.

Therefore, it might be preferred to choose the total axial length of the inlay comparatively small. For example the inlay may not reach the area (within the sleeve shaft) where the hot glass runs onto the outer surface of the refractory tube. For example the inlay may be arranged in the head portion of the refractory tube.

Due to the temperature profile inside the sleeve shaft along its axis, an inlay projecting further into the sleeve shaft bore might be subject to bending (deterioration of the air flow conditions) or at least be under tension (which is undesirable) due to the different thermal expansion of different components.

The inlay may be designed such as to be not conical.

Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of preferred embodiments, when read in light of the accompanying schematic drawings, wherein.

<FIG> shows a cross-sectional view of a first refractory tube with a sleeve shaft <NUM> with a first inlay <NUM> according to the invention for collecting particles originating from the material of the sleeve shaft <NUM> at least in part.

At least one fluid can flow through the sleeve shaft <NUM> along an axial direction R which is parallel to the main extension of the sleeve shaft <NUM>.

The inlay <NUM> comprises a first wall section <NUM>.

The inlay <NUM> is inserted in part into the sleeve shaft <NUM> such, that at least one part of the first wall section <NUM> has a radial distance D from at least one first area <NUM> of the inner surface <NUM> of the sleeve shaft <NUM>. Hence, the inlay <NUM> together with the first area <NUM> of the inner surface <NUM> of the sleeve shaft <NUM> encloses a volume domain <NUM>. The volume domain <NUM> is limited in the axial direction R by a limiting element <NUM> comprised by the inlay <NUM>. The volume domain <NUM> is at least in part in form of a ring volume. The limiting element <NUM> is arranged at an end section of the first wall section <NUM>.

The inlay <NUM> further comprises a stop element <NUM>. The stop element <NUM> allows easy arrangement of the inlay <NUM> within the sleeve shaft <NUM>. The stop element <NUM> is designed in one piece with the limiting element <NUM>.

It is apparent from <FIG> that the inlay <NUM> comprises a zone <NUM> of cylindrical form and the first shell <NUM> of a first section <NUM> of the cylindrical zone <NUM> comprises the first wall section <NUM>. In <FIG> the first section <NUM> is identical to the first wall section <NUM>, which, however, is not required in general. The first section <NUM> comprises a first end section <NUM> of the inlay <NUM>.

The sleeve shaft <NUM> and the inlay <NUM> are arranged in a coaxial manner. The inlay <NUM> preferably is connected with the sleeve shaft <NUM> in a welded manner, although other types of connections are possible as well.

<FIG> shows a cross-sectional view of the first inlay <NUM> alone. The inlay <NUM> can be inserted into the sleeve shaft <NUM> as described above with respect to <FIG>.

<FIG> shows a cross-sectional view of a second refractory tube with a sleeve shaft <NUM>' with a second inlay <NUM> according to the invention for collecting particles originating from the material of the sleeve shaft <NUM>' at least in part.

Indeed, sleeve shaft <NUM>' and inlay <NUM>' are both similar to, respectively, sleeve shaft <NUM> and inlay <NUM> described above with respect to <FIG>. Hence, for the same structural features the same reference numerals are used, however, single apostrophed. It is, therefore, also sufficient to describe only the differences between sleeve shaft <NUM>' / inlay <NUM>' and sleeve shaft <NUM> / inlay <NUM> while for the remainder reference can be made to the description provided above with respect to sleeve shaft <NUM> / inlay <NUM> in combination with <FIG>.

Contrary to inlay <NUM>, here, for inlay <NUM>' the stop element <NUM>' is not designed in one piece with the limiting element <NUM>'. Moreover, the stop element <NUM>' is separate from the limiting element <NUM>' and provided at an end section of the inlay <NUM>' which is opposite the first wall section <NUM>'.

It is apparent from <FIG> that for the inlay <NUM>' (in contrast to inlay <NUM> described above) there is also a second shell <NUM>' of at least one second section <NUM>' of the cylindrical zone <NUM>', which is different to the first section <NUM>' of the cylindrical zone <NUM>'. The second shell <NUM>' comprises a second wall section <NUM>', wherein the first outer diameter OD1' of the first wall section <NUM>' is smaller than the second outer diameter OD2' of the second wall section <NUM>'. In <FIG> the second section <NUM>' is identical to the second wall section <NUM>'.

The second wall section <NUM>' contacts at least one area of the inner surface <NUM>' of the sleeve <NUM>'.

<FIG> shows a cross-sectional view of a third refractory tube with a sleeve shaft <NUM>" with a third inlay <NUM>" according to the invention for collecting particles originating from the material of the sleeve shaft <NUM>" at least in part.

Indeed, sleeve shaft <NUM>" and inlay <NUM>" are both similar to, respectively, sleeve shaft <NUM>' and inlay <NUM>' described above with respect to <FIG>. Hence, for the same structural features the same reference numerals are used, however, doubled apostrophed. It is, therefore, also sufficient to describe only the differences between sleeve shaft <NUM>" / inlay <NUM>" and sleeve shaft <NUM>' / inlay <NUM>' while for the remainder reference can be made to the description provided above with respect to sleeve shaft <NUM>' / inlay <NUM>' in combination with <FIG>.

Contrary to inlay <NUM>', here, for inlay <NUM>" there is no stop element comprised by the inlay <NUM>". The second section <NUM>" comprises a second end section of the inlay <NUM>", wherein the second section <NUM>" follows after the first section <NUM>" along the axial direction. Indeed, the second end section of the inlay <NUM>" is at the opposite end of the inlay <NUM>" than the first end section <NUM>" of the inlay <NUM>". The inlay <NUM>" is entirely within the sleeve shaft <NUM>". Of course, this is not mandatory in general.

In <FIG> particles <NUM>" which move along the inner surface <NUM>" of the sleeve shaft <NUM>" or which are already trapped in the volume domain <NUM>" are indicated for illustration purposes.

<FIG> shows a cross-sectional view of a fourth refractory tube with a sleeve shaft <NUM>‴ with a fourth inlay <NUM>" according to the invention for collecting particles originating from the material of the sleeve shaft <NUM>‴ at least in part.

Indeed, sleeve shaft <NUM>‴ and inlay <NUM>‴ are both similar to, respectively, sleeve shaft <NUM>' and inlay <NUM>' described above with respect to <FIG>. Hence, for the same structural features the same reference numerals are used, however, three times apostrophed. It is, therefore, also sufficient to describe only the differences between sleeve shaft <NUM>‴ / inlay <NUM>‴ and sleeve shaft <NUM>' / inlays <NUM>' while for the remainder reference can be made to the description provided above with respect to sleeve shaft <NUM>' / inlay <NUM>' in combination with <FIG>.

Contrary to inlay <NUM>', here, for inlay <NUM>‴ the stop element <NUM>‴ is designed in one piece with the second wall section <NUM>‴.

Inlay <NUM>‴ further comprises a distant element <NUM>‴ for securely arranging the inlay at the sleeve shaft <NUM>‴.

<FIG> shows the simulated pressure distribution and streamlines of the fluid flow, respectively, of a fluid flowing within a refractory tube with a sleeve shaft <NUM> with an inserted inlay <NUM> according to a preferred embodiment of the invention. The pressure distribution is indicated by respective shapes (hatches) and the streamlines of the fluid flow are indicated by respective lines within the sleeve shaft of <FIG>.

For the sleeve shaft with inserted inlay in <FIG> there is apparent the advantageous distribution of the pressure. Especially at position <NUM>, i.e. close to the inner surface of the inlay <NUM> at its end, there is a positive pressure. This leads to a smooth fluid flow from the larger volume enclosed by the sleeve shaft <NUM> to the smaller volume enclosed by the inlay <NUM>. The smooth fluid flow is also indicated by respective smooth streamlines. Especially the streamlines have no interruption in this transition area from larger to smaller volume. Consequently, avoiding a negative pressure at position <NUM> improves fluid flow.

The sleeve shaft <NUM> and the inlay <NUM> are designed in line with the proposed geometric properties in order to achieve the advantageous pressure distribution and fluid flow.

<FIG> shows the simulated magnitude velocity of the fluid flow within a refractory tube with a sleeve shaft <NUM> with an inserted inlay <NUM> according a further preferred embodiment according to the invention.

The velocity magnitude is indicated by respective shapes (hatches). Furthermore, also the streamlines of the fluid flow are indicated by respective lines within the sleeve shaft <NUM>.

Since the sleeve shaft and inlay are similar in <FIG> and <FIG>, the same reference signs have been used.

Also for the sleeve shaft <NUM> and inlay <NUM> in <FIG> the advantageous positive pressure at position <NUM> and the smooth streamlines are present. In addition, close to the inner surface <NUM> of the sleeve shaft <NUM> the absolute velocity of the fluid is quite small. Hence, there is the improved chance that the particles which are already close to the inner surface <NUM> get actually trapped within the volume enclosed between the sleeve shaft <NUM> and the inlay <NUM>.

<FIG> shows a detail view of the area indicated with a rectangle in <FIG>. In <FIG> the radial velocity of the fluid flowing within the sleeve shaft is indicated by respective shapes (hatches). At the corner <NUM>, a high radial velocity is present which supports that particles reach the volume enclosed between sleeve shaft <NUM> and the inlay <NUM>, where they get trapped.

It is, therefore, preferred that the inner diameter of the sleeve shaft <NUM> has an increasing inner diameter from left to right in <FIG>.

Hence, the simulations shown in <FIG>, <FIG> illustrate that the proposed sleeve shaft with inlay may provide positive pressure at the end of the inlay and/or increase the time the particles have in order to get trapped.

Claim 1:
Refractory tube, into which refractory tube a sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴) with at least one inlay (<NUM>, <NUM>', <NUM>", <NUM>‴) for collecting particles (<NUM>") originating from the material of the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴) at least in part, is inserted,
wherein at least one fluid can flow through the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴) along an axial direction (R, R', R", R"') which is parallel to the main extension of the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴),
wherein the inlay (<NUM>, <NUM>', <NUM>", <NUM>"') comprises at least one first wall section (<NUM>, <NUM>', <NUM>", <NUM>"'),
wherein the inlay (<NUM>, <NUM>', <NUM>", <NUM>"') is or can be inserted at least in part into the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴) such that at least one part of the first wall section (<NUM>, <NUM>', <NUM>", <NUM>‴) has a radial distance from at least one first area (<NUM>, <NUM>', <NUM>", <NUM>‴) of the inner surface (<NUM>, <NUM>', <NUM>", <NUM>‴) of the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴), and, hence, that the inlay (<NUM>, <NUM>', <NUM>", <NUM>‴) together with the first area (<NUM>, <NUM>', <NUM>", <NUM>‴) of the inner surface (<NUM>, <NUM>', <NUM>", <NUM>‴) of the sleeve shaft (<NUM>, <NUM>', <NUM>", <NUM>‴) encloses at least one volume domain (<NUM>, <NUM>', <NUM>", <NUM>‴), which volume domain (<NUM>, <NUM>', <NUM>", <NUM>‴) is limited in the axial direction (R, R', R", R‴) by a limiting element (<NUM>, <NUM>', <NUM>", <NUM>"') comprised by the inlay (<NUM>, <NUM>', <NUM>", <NUM>‴),
wherein the inlay (<NUM>, <NUM>', <NUM>", <NUM>‴) comprises at least one zone (<NUM>, <NUM>', <NUM>", <NUM>‴) of cylindrical form, and the first shell (<NUM>, <NUM>', <NUM>", <NUM>‴) of at least one first section (<NUM>, <NUM>', <NUM>", <NUM>‴) of the cylindrical zone (<NUM>, <NUM>', <NUM>", <NUM>‴) comprises the first wall section (<NUM>, <NUM>', <NUM>", <NUM>‴), wherein the first section (<NUM>, <NUM>', <NUM>", <NUM>"') comprises at least one first end section (<NUM>, <NUM>', <NUM>", <NUM>‴) of the inlay (<NUM>, <NUM>', <NUM>", <NUM>"').