DE3208956C2 - Reinforcement of refractory products by using pin-shaped refractory ceramic embeddings - Google Patents

Abstract

The invention relates to improving the thermomechanical properties of refractory, in particular monolithic, products. The heat resistance and thermal shock resistance are increased by partially or completely replacing the usually granular granules with granules of the same or similar composition in stick form.

Description

Mixtures of granulate and binding agent are used to manufacture refractory products In most cases, granulate is thermally pretreated (e.g. chamotte, muilit and corundum) and has generally high grain strength. The geometrical shape of the granulate is either isometric or splitting. For the grain distribution, a packing that is as dense as possible is often used, based on the grain distribution Fuller for concrete (1) (2) or litzow for firebricks (3) aimed at

The requirements for the binding phase are even higher for unshaped refractory products than for bricks, because processing at the construction site requires good ease of introduction and compaction and, in addition, sufficient green strength and heat-up ability hydraulic, ceramic or chemical binders, combinations are also possible. Hydraulic binders generally give very good green strength, which, however, drops sharply with increasing temperatures (4). Ceramic binders (mostly binding clays) give only moderate green strength, with increasing temperature the strength then increases, only to decrease again at even higher temperatures, mostly above 1100 ^° C. (4). This fact is confirmed by the observation of the fracture mechanism when testing the hot strength.Only in exceptional cases, i.e. hydraulically bound, unshaped products as well as highly burned stones, the limit of the strength of the granulate is reached during cold strength tests.In the other cases, the product fails by exceeding the bonding strength in the binding phase.

One way of improving unshaped products is to reinforce them with heat-resistant ones Steel fibers in order to take advantage of the high tensile strength and ductility of steel (5). It turned out, however, that the There are limits to the possible use of such reinforcements due to the scaling of the alloyed steels. the Oxidation limits the possibility of use in continuous operation and heating on all sides to around 1000 ° C (5). Furthermore, strong tension can occur due to the very different thermal expansion of Refractory material and steel. In addition, it was found that the binding force of the matrix of the product only partial use of the high tensile strength of the reinforcement allows the steel fibers are generally made from Matrix pulled out.

On the other hand, mineral fibers can also be used to reinforce unshaped products and stones with refractory properties are used. However, these fibers are very small at great length Diameter, often 0.002 to 0.005 mm; generally below 0.02 mm (6) (7). Their intermingling in refractories Offsets is not the subject of the invention.

By inserting small, cylindrical, almost isometric bodies in a systematic arrangement in the blank of a refractory brick, an attempt was made (8) to increase the resistance to temperature changes on the assumption that the resulting cracks in the thin-layer, alien embedding substance of these bodies would die out in the event of thermomechanical overstress . However, this measure is not to be regarded as reinforcement.
The object of this invention is to carry out a reinforcement by using the "granules" for refractory

Products partially or completely as a pen-shaped material with a high ratio of length to diameter; |

knife or equivalent diameter is added. According to the definition, this criterion also applies to | j

Fibers for (5), but the diameters named according to the invention are between 0.5 and 10 mm. This j |

The lengths of the pins are each more than 5 times, i.e. at least 2.5 to 50 mm. l |

Attempts to do this have been made with refractory clays and plasticizing additives and mixtures thereof ||

carried out with muilit or corundum flour. Using the plasticity of the mixture, this was transformed into the plastic h

State formed into pins by extrusion. Another way of using these pen-shaped particles is round or Producing a square shape also consists of compression molding or isostatic pressing. The pens made are dried and fired and are then available as »granules« that can be used directly. The advantages of the Use of pen-shaped particles are as follows:

1. The high strength inherent in the granulate can be better applied to the refractory product with the help of the pins be transmitted. The values of the strength, in particular the hot strength, become essential as a result increased, partly multiplied.

2. The refractory product no longer breaks when the maximum strength is exceeded abruptly as otherwise as a brittle book, but occurs after exceeding the maximum breaking strength of the Matrix undergoes a further deformation, which the molding occurs when the individual pins are successively broken open still gives cohesion and residual strength. There is a multiplication of the elongation at break and the work at break before.

3. The resistance to temperature changes is ensured by the stick-shaped granulate despite increasing bulk density and decreasing porosity multiplied

On refractory products with stick-shaped »granules«, significant improvements in resistance to temperature changes have been made, the hot tensile, hot flex and hot torsional strengths were also determined the pressure-softening behavior is improved

example 1

Pins 33 mm in diameter and 10 times longer were drawn from a refractory binding clay in an extrudable state by extrusion. The cold bending strength of the individual pins after drying and firing was between 100 and 200 N / mm ² . These values are approximately ten times higher than for test specimens made from unshaped products (4). These pins were sprinkled up to the edge in molds for test specimens to test the hot flexural strength - format 150 mm × 25 mm × 25 mm - and poured a mixture of jüchamot flour, high-alumina cement and water over them. The following offsets were used:

1. 800 g fireclay flour 0-1 mm

200 g high alumina cement A with high alumina content
240 g mixing water

2. 800 g fireclay flour 0-1 mm

200 g high-alumina cement B, medium alumina content
270 g mixing water

Testing the heat flexural strength was carried out at 900 to 1200 ⁰ C; the following values were measured:

Test temperature hot bending strength with

Alumina cement A Alumina cement B

900 ⁰ C 31.6 N / mm ² 12.1 N / mm ² 100O ⁰ C 233 N / mm ² 113 N / mm ² 1100 ° C 12.2 N / mm ² 9.1 N / mm ² 1200 ° C 6.2 N / mm ² 6.2 N / mm ²

The absolute values of these hot strength measurements are more than twice as high as for analog refractory concretes with grained granules (4). The path of the deformation until the complete separation of the broken halves during the test at 1200 ⁰ C was for test specimens with grain isometric about 0.2 mm and mm for test piece having pin-shaped chamotte in about 2, so the tenfold.

Example 2

In another series of tests, the isometric was used in a fireclay concrete with 20% cement Granulate replaced by 20% or 40% clay sticks with a diameter of 2.5 mm and lengths of up to 30 mm. Of the Concrete was mixed in a mixer as usual and, according to the 26th PRE recommendation (9), turned into normal bricks shaped The determination of the thermal shock resistance of 'A normal bricks according to DIN 51 068 (10) showed no differentiation after 30 air quenching. The subsequent water deterrents resulted in a multiplication of the thermal shock resistance of the pin-reinforced concretes, although their The bulk density increases and the open porosity decreases.

Bond: Alumina cement A

granules

Bulk density

porosity

Number of deterrents

Without pens
20% pens
40% pens

2.07 g / cm ³ 2.12 g / cm ³ 2.19 g / cm ³

13.1%
12.7%
10.5%

literature

30 χ air and 6 χ water
30 χ air and 26 χ water
30 χ air and 60 χ water

(1) Fuller, W.B., Thompson, S.E .: Proc. Amer. Soc. Civil engr. 33 (1907), p. 222

(2) DIN 1045 concrete and steel construction, January 1972

(3) Litzow, K .: Glastechn. Ben 8 (1930), p. 149

(4) Braun, M., Majdic, A .: Keramische Zeitschrift (1980), H 9, p. 484

(5) M & jdic, A, Braun, M .: Reinforcing Castables with Stainless Steel Fibers, Interceram 29 (1980), p.

(6) Neville, Α .: RILEM Symposium 1975, Fiber Reinforced Cement and Concrete, Lancaster 1975

(7) Swamy, R. N-: RILEM Symposium 1978, Testing and Test Methods of Fiber Cement Composites

(8) US-PS 21 84 601. Manufacture of Ceramic Ware, Inventor: Kamillo Konopicky

5 (9) Federation Europeenne des Fabricants de Produits Refractaires 1978 (Zurich, Switzerland): 26th PRE recommendation: Manufacture of test specimens from unshaped products

Part 1: Dense refractory concretes (10) DIN 51 068 Testing of ceramic raw materials: Determination of the resistance to rough

Temperature change (May 1976) ι ο Part 1: Water quenching method for refractory bricks

Part 2: Air quenching method for refractory bricks.

Claims (4)

Patent claims: 1. Process for the manufacture of refractory ceramic products in which at least partially instead of the usual granular granules, those in stick form with refractory properties and similar or different composition is used, this with the other ingredients is mixed and shaped, characterized in that ceramic stick-shaped granules with the dimensions: diameter or equivalent diameter of 0.5 to 10 mm and in lengths of at least 2 ^ 5 to 50 mm (diameter: length less than 1: 5) is used. 2. Production of unshaped refractory products according to claim 1, characterized in that ίο processing and introduction by mixing and pouring, as well as compaction by vibration, Poking or pounding occurs 3. Manufacture of unshaped refractory products according to claim 1, characterized in that processing and introduction by mixing and spraying or centrifuging in the dry or wet process he follows 4. Manufacture of shaped refractory products according to claim 1, characterized in that the The stones are produced by compression molding or isostatic pressing