EP0769126B1 - Reinforced ceramic rollers for ovens - Google Patents

Description

The invention relates to ceramic rollers for ovens roller.

A roller oven is a pass-through oven with the bottom is composed of ceramic rollers arranged in parallel to each other and rotated around their axis central by means of a drive system. All rollers rotate in the same direction and substantially at the same speed. This movement causes the load to cook at through the oven.

These ovens are mainly used for cooking ceramic tiles used for flooring and walls. The cooking tiles are placed directly on the rollers at the entrance of the oven. However, rollers are also used to bake pieces of complex shape: tableware, sanitary, electronic substrates. In this case, the products to be cooked are loaded onto slabs forming supports, these then being placed on the rollers.

Current rollers have a length of 1200 to 4000 mm and their outside diameter is between 25 and 55 mm for a wall thickness of 5 to 6 mm.

• Contraintes mécaniques :
  • poids propre et charges provenant des produits à cuire ;
  • fatigue dynamique (rotation).
  □ Agressions chimiques :
  • par les vapeurs alcalines dégagées par les produits à cuire ;
  • par oxydation (dans le cas des rouleaux en SiC).
• Gradients thermiques : entre la partie située à l'intérieur du four et les extrémités traversant les parois du four.
• Chocs thermiques :
  • lors de l'introduction d'un rouleau neuf froid dans un four en fonctionnement pour remplacer un rouleau défaillant ;
  • lors des mises en veilleuse ou arrêts pour entretien.

They are subject to various types of constraints:

• Mechanical constraints :
  • dead weight and loads from the products to be cooked;
  • dynamic fatigue (rotation).
  □ Chemical attacks :
  • by the alkaline vapors given off by the products to be cooked;
  • by oxidation (in the case of SiC rollers).
• Thermal gradients : between the part inside the oven and the ends passing through the walls of the oven.
• Thermal shocks :
  • during the introduction of a new cold roller into an operating oven to replace a faulty roller;
  • during standby or maintenance shutdowns.

• les rouleaux formés de matériaux réfractaires à base d'oxydes cuits à température modérée (< 1500°C), tels que les matériaux alumine-mullite-cordiérite (comme le matériau Siroll LP commercialisé par la Société Nuova Sirma, Italie);
• les rouleaux à base d'alumine, d'alumine-mullite ou de mullite cuits à très haute température (>1500°C) ;
• les rouleaux formés de matériaux réfractaires à base de carbure de silicium et/ou de nitrure de silicium et/ou d'oxynitrure de silicium et/ou de sialon (appelés ci-après matériaux à base d'au moins un composé du silicium), tels que les matériaux formés de grains de SiC liés par un liant nitrure de silicium (tel que le matériau Advancer commercialisé par la Société Norton), le carbure de silicium recristallisé (tel que le produit Crystar de Norton), ou les matériaux à base de carbure de silicium imprégnés de silicium.

There are three types of rollers on the market:

• rolls formed of refractory materials based on oxides baked at moderate temperature (<1500 ° C), such as alumina-mullite-cordierite materials (such as the Siroll LP material sold by the company Nuova Sirma, Italy);
• rolls based on alumina, alumina-mullite or mullite baked at very high temperature (> 1500 ° C);
• rolls formed of refractory materials based on silicon carbide and / or silicon nitride and / or silicon oxynitride and / or sialon (hereinafter called materials based on at least one silicon compound), such as materials formed from SiC grains bonded by a silicon nitride binder (such as the Advancer material sold by the company Norton), recrystallized silicon carbide (such as the Norton Crystar product), or materials based on silicon carbide impregnated with silicon.

Rollers based on oxide baked at moderate temperature have the disadvantage of only supporting modest loads: thus, the best rolls based on alumina-mullite-cordierite are limited to maximum loads such as the total bending stress (load + self-weight), i.e. less than 50 kg / cm ² for a maximum working temperature less than or equal to 1250 ° C. This greatly limits their usefulness for certain applications.

Rolls based on alumina, alumina-mullite or mullite baked at very high temperature withstand bending stresses of up to 80 kg / cm ² for maximum working temperatures of 1300-1350 ° C or less, but their cost is much higher than that of rolls baked at low temperature.

On the other hand, rollers formed from a material based on at least one silicon compound withstand bending stresses of 200 to 500 kg / cm ² , for a limit temperature of use which can reach 1600 ° C., but their cost is 7 to 20 times that of the oxide-based rollers.

We also know from EP-A-19077 a roller composite which has a hollow outer metal cylinder and a ceramic inner core which can be a little more short than the outer cylinder to facilitate coupling with mechanical drive systems. The ceramic inner core is the supporting element and the outer metal cylinder has the function of protecting the core against thermal shock and against contact with products to be cooked. Neither the properties (module in particular), neither the composition of the material constituting the core are indicated.

It would therefore be very useful for the industry to have rollers with improved properties compared to rollers based on conventional oxides, while being less expensive than rolls based on alumina, alumina-mullite or very high temperature or base sintered mullite of at least one silicon compound currently marketed.

The invention aims to satisfy this need.

More specifically, the invention relates to a roller composite for roller ovens comprising a roller hollow exterior made of a refractory ceramic material based of oxides and a reinforcing element of a material refractory with a modulus of elasticity at 1200 ° C more higher than that of the material of the outer roller, disposed at the inside of the outside roller, the largest dimension of the cross section of the reinforcing element being slightly less than the inside diameter of the roller outside.

Advantageously, the modulus of elasticity at 1200 ° C. of the reinforcing element material is at least 2 times that of the outer roller and, preferably, at at minus 3 times. The module of the reinforcing element can be up to 20 times, and even more, than that of material of the external element.

The outer roller will usually be made in one inexpensive oxide material suitable for manufacture of oven rolls, for example of a material based on oxides cooked at moderate temperature, such as alumina-mullite cordierite material cited above. Such a material typically has a modulus of elasticity at 1200 ° C from 10 to 25 GPa. The wall thickness of the outer roller is typically of the order of 5-6 mm, without these values having critically important.

The interior reinforcing element may have various shapes, for example that of a hollow cylinder or that of a hollow bar with a hexagonal, square section, triangular or an X-shaped profile.

Preferably, for reasons of saving material, mechanical strength and ease of manufacture, will use a hollow cylindrical reinforcement element, i.e. tube-shaped, having a wall thickness on the order of 1.5 to 4 mm.

The reinforcing element can be produced, for example example, a material based on oxides cooked at high temperature, such as an alumina, alumina-mullite material or mullite or a material based on at least one composed of silicon such as those mentioned above, between other. Materials based on alumina, alumina-mullite or of mullite cooked at high temperature typically have a modulus of elasticity at 1200 ° C from 50 to 200 GPa, while the materials based on at least one silicon compound have typically a modulus of elasticity at 1200 ° C from 150 to 400 GPa.

The inner reinforcing element has advantageously a length less than or equal to 0.9 times that of the outer roller to be reinforced. For reasons saving material, we prefer to use an element of reinforcement of length substantially less than that of the outer roller, for example of a length representing 0.15 to 0.65 times that of the outer roller. For example, for an outside roller 3 m long, the reinforcing element preferably has a length of 0.5 to 2 m approximately.

The maximum dimension of the cross section of the reinforcing element should be slightly less than that of the inside diameter of the outside roller for allow the reinforcing element to be put in place and to exert its action as soon as the outer roller bends a little under a load. For example, a clearance of 0.1 to 0.5 mm is usually satisfactory without these values being critics.

The reinforcing element will advantageously be centered relative to the roller bearings on the bearings of the oven supporting the roller, or in relation to the loads supported by the roller in service, so that the exterior oxide roller is reinforced mechanically in the area where, in service, the maximum bending stress.

Experience has shown that it is not necessary to interpose ceramic felt or a layer of glue or cement between the reinforcing element and the roller outside. During assembly, the element of reinforcement can be held in place with a little glue organic. During commissioning, it burns and the reinforcing element will be held in place in the position chosen by the arrow effect.

In the drawing, the single figure is a sectional view longitudinal, of a composite roller conforming to the invention.

In the figure, the reference 1 designates the roller exterior based on oxides, reference 2 an element of tube-shaped reinforcement less than that of the outer roller, reference 3 designates the zones where the roller will be, in service, supported on bearings, and the reference 4 designates the part of the roller which will project from the oven and will receive means for driving the roller, by example a toothed wheel (not shown).

The following nonlimiting example is given for the purpose to illustrate the invention.

EXAMPLE

• rayon extérieur    : 20 mm
• rayon intérieur    : 15 mm
• longueur    : 3 m
• module d'Young à 1200°C    : 22000 Mpa
• coefficient de dilatation    : 5,2 x 10^-6K^-1
• masse volumique    : 2360 kg/m³

Composite rollers of the type shown in the figure were produced, the roller 1 of which was produced from SIROLL LP (material of the Alumina-Mullite-Cordierite type sold by the company Nuova Sirma) and had the following characteristics:

• outer radius: 20 mm
• internal radius: 15 mm
• length: 3 m
• Young's modulus at 1200 ° C: 22000 Mpa
• expansion coefficient: 5.2 x 10 ^-6 K ^-1
• density: 2360 kg / m ³

• rayon extérieur    : 14,5 mm
• rayon intérieur    : 12,5 mm
• longueur    : 0,5 m
• module d'Young à 1200°C    : 225000 Mpa
• coefficient de dilatation    : 4,8 x 10^-6K^-1
• masse volumique    : 2820 kg/m³

The reinforcing element 2 was made of ADVANCER (SiC grains linked by a silicon nitride binder sold by the company Norton) and had the following characteristics:

• outer radius: 14.5 mm
• internal radius: 12.5 mm
• length: 0.5m
• Young's modulus at 1200 ° C: 225,000 Mpa
• coefficient of expansion: 4.8 x 10 ^-6 K ^-1
• density: 2820 kg / m ³

The rolls thus produced were mounted in an oven roller for firing ceramic tiles at one temperature of the order of 1200 ° C.

The distance between the supports of each roller on the oven bearings was 2.91 m and the loaded length was of 1.83 m.

First experience

We compared the arrow taken by these rollers composite to that of identical rollers in SIROLL LP not and reinforced Advance rollers identical with a wall thickness of 5-6 mm.

It can be seen that the weight of the reinforcing elements in Advancer leads to an increase in the deflection composite rolls of about 1 mm, compared to that Unreinforced Siroll LP rollers. However, in circulating a charge in the oven, corresponding to a load of 1.25 kg per roll distributed over the portion central roller, length 1.83 m, we note that the composite rollers of the invention have an arrow about 3 times lower than that of non-rollers reinforced: 3.4 mm instead of 11.1 mm, while the boom rolls in Advancer is 2 mm.

Second experience

We loaded the rolls in Siroll LP with a load 3 kg per roll distributed over a length of 1.83 m. The measured deflection is 12 mm and the break occurs very quickly, after a few hours of operation.

However, the deflection measured is 6.0 mm for composite rollers of the invention supporting the same charge.

The present invention therefore makes it possible to obtain service performance far superior to that of rollers based on standard oxides for a cost less than that of rolls made of material baked at high temperature and much lower than that of rollers based on at least one composed of silicon. Indeed, the reinforcing element used in the invention has a much lower volume to that of a roller made entirely of high-density material performance, because its diameter, thickness wall and its length can be much less.

The invention also makes it possible to exploit the good hot stiffness of alumina, alumina-mullite materials or mullite cooked at high temperature (overcooked), without risking rupture by thermal shock, during their introduction into a working oven. Indeed, the roller exterior, very resistant to thermal shock constitutes a protective cover for the reinforcing element interior, sensitive to thermal shock.

It goes without saying that the embodiment described is not than an example and we could modify it, in particular by substitution of technical equivalents.

Claims (10)

1. Composite roller for roller kilns including a hollow external roller (1) made of an refractory material and a reinforcing component (2) made of a refractory material, arranged inside the external roller, the maximum dimension of the cross-section of the reinforcing component being slightly smaller than the internal diameter of the external roller characterized in that the external roller (1) is made of an oxide-based ceramic material and in that the reinforcing component (2) has a modulus of elasticity at 1200°C which is higher than that of the material of the external roller.
2. Roller according to Claim 1, wherein the internal reinforcing component (2) is in the form of a tube.
3. Roller according to Claim 2, wherein the reinforcing component (2) has a wall thickness of 1.5 to 4 mm.
4. Roller according to Claim 1, wherein the reinforcing component (2) is shorter than the external roller.
5. Roller according to Claim 4, wherein the length of the reinforcing component (2) represents 0.15 to 0.65 times that of the external roller.
6. Roller according to Claim 1, wherein the reinforcing component (2) is centred in relation to the seats of the roller on the bearings (3) of the kiln supporting the roller.
7. Roller according to Claim 1, wherein the reinforcing component (2) is centred in relation to the loads supported by the roller in use.
8. Roller according to Claim 2, wherein the modulus of elasticity at 1200°C of the material constituting the reinforcing component (2) is at least 2 times higher than that of the external part.
9. Roller according to Claim 8, wherein the modulus of elasticity at 1200°C of the material constituting the reinforcing component (2) is at least 3 times higher than that of the external roller (1).
10. Roller according to Claim 1, wherein the external roller (1) is made of alumina-mullite-cordierite and the reinforcing component (2) is made of a material selected from the group consisting of materials based on alumina, alumina-mullite or mullite, materials based on at least one silicon compound, chosen from the group consisting of silicon carbide, silicon nitride, silicon oxynitride and sialons.

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