The basic material composition of ordinary refractory ramming materials is basically similar to that of refractory castables and plastics, and it is also composed of refractory aggregates, powders, binders, and additives in proportion. The amount of binder is small, soft clay is usually added to increase the viscoplasticity and sinterability of the material, and it is constructed by ramming method, so it is called refractory ramming material.
According to the different types of refractory aggregates, it can be divided into clay, high alumina, mullite corundum, siliceous, magnesia and silicon carbide, etc. According to the type of binder, it can be divided into phosphoric acid and phosphate, Aluminum sulfate, water glass, cement, binding clay and organic binders, etc.
The composition of refractory ramming material is generally 60~65% of refractory aggregate and 35~40% of refractory powder, so that a larger bulk density can be obtained, and the density of the lining body after ramming is also larger. The critical particle size of refractory aggregate is 10mm, and 5mm is also useful, and the mass ratio of coarse and fine aggregate is 3:7~4:6. More fine aggregates are easier to ram and compact.
When the refractory ramming material is constructed on site, it can be rammed by mechanical methods such as air picks. The inner lining of the refractory ramming material has a low moisture content, and its performance is better than that of the refractory castable of the same material if the ramming material is compact. The construction speed of refractory ramming material is slow and labor-intensive.
The high-alumina ramming material is made of bauxite clinker containing 82% aluminum oxide as aggregate and powder, and more fused corundum powder is added to improve the performance of the matrix, and clay is added as a plasticizer.
Magnesium-aluminum-chromium ramming material is prepared with fused magnesia-chromium composite material and aluminum-magnesium spinel.
The aluminum-zirconium ramming material is made of bauxite clinker containing 85% of aluminum oxide as refractory aggregate and powder, and zircon powder containing 64% of zirconium dioxide and Jiaozuo mud are added.
The mixing ratio of magnesia-chromium refractory ramming material: 55% and 15% respectively for brick-making magnesia aggregate and powder containing 91% magnesia, 15% for chromite aggregate and powder containing 47% Cr2O3, respectively. The water glass solution is 4~5%.
High-strength magnesia refractory ramming material is made of fused magnesia containing 97% magnesia as bone powder. The critical particle size is 5mm, four-level ingredients, and the ratio of bone powder to powder is between 7:3~6:4; phosphate is used as a binder, and the dosage is 2~4%, plus composite metal powder.
Basic characteristics of refractory ramming mix
Refractory ramming material has the following basic characteristics:
(1) It has hot hardness, peeling resistance, wear resistance and erosion resistance; adding tar to dolomite ramming material can enhance hydration resistance; adding tar to graphite ramming material as a binder has good workability.
(2) It has a high operating temperature, generally between 1450 and 1700 °C.
(3) The bulk density of silicon carbide ramming materials should not be less than 2.2t per cubic meter, and the bulk density of dolomite and magnesia ramming materials with tar should not be less than 2.9t per cubic meter; high alumina, The bulk density of magnesia ramming material should not be less than 2.95t per cubic.
(4) The construction ramming material should be the finished material produced by the specialized manufacturer, and the finished ramming material should have the factory certificate and instruction manual.
(5) The particle size of the ramming material should be evenly matched, the ratio of coarse, medium and fine particles is roughly 4:2:4, and the maximum particle size is between 5~7mm.
Quality requirements for constituent materials
(1) The variety and grade of the finished refractory ramming material shall meet the design requirements;
(2) The quality of the refractory ramming materials prepared on site shall meet the following requirements:
①Strictly inspect the quality of each constituent material, and prepare according to the design mix ratio;
②The high-alumina ramming material is made up of high-alumina aggregate, powder, water glass and sodium fluorosilicate in proportion, and the materials should meet the requirements;
③ The magnesia ramming material is composed of metallurgical magnesia, clay refractory mud, bauxite, iron oxide powder, brine or coal tar, and the constituent materials should meet the quality standards of relevant materials.
④ Dolomite ramming material is composed of dolomite and anhydrous tar;
⑤Graphite ramming material is composed of metallurgical coke powder, dehydrated coal tar and coal tar, and the constituent materials should meet the quality standards of relevant materials.
The scope of application of ramming material
The scope of application of commonly used refractory ramming materials is as follows:
(1) The high-alumina ramming material is suitable for the furnace entry of the electric furnace and the discharge port of the rotary kiln;
(2) Magnesium ramming material is suitable for the bottom of electric furnace, open hearth and converter;
(3) Dolomite ramming material is suitable for the bottom of converter and ferroalloy electric furnace;
(4) Graphite and silicon carbide ramming materials are suitable for blast furnaces and molten iron ditch.
Spreading and ramming
Before ramming the ramming material, the spread should be uniform. For example, when tamping with a pneumatic hammer, it should be pressed with one hammer and half a hammer, and rammed continuously and evenly layer by layer. The second laying should be carried out after the surface of the knotted ramming material is messed up, and the working wind pressure of the pneumatic hammer should not be less than 0.5MPa.
Carbon ramming material
Carbon ramming material can be constructed by cold ramming method or hot ramming method. Before ramming the bottom of the furnace, the furnace base should be dried and cleaned.
The temperature of the cold ramming carbon material during ramming should be about 10°C higher than the softening temperature of its binder.
 
For hot ramming carbon material, the finished material should be used. Before ramming, the carbon material must be crushed and heated evenly. The heating temperature should be determined according to the mixing temperature of the finished material. There should be no lumps in the heated carbon material. A hot hammer should be used when ramming, and the material temperature should not be lower than 70°C.
When ramming with a pneumatic hammer, the thickness of each layer should not exceed 100mm. The tamping density of each layer of carbon ramming material should be checked according to the specified bulk density or compression ratio. The compression ratio is: reduction/loose thickness × 100%, and the value should be 40~45%.
When the ramming of the carbon ramming material is interrupted and then ramming is continued, the surface of the ramming solid should be cleaned, shaved and painted with coal tar.
Use coal tar and coal tar as binder ramming material
The magnesia or dolomite ramming material with coal tar and coal tar as binder should be rammed with a hot hammer. Coal tar, coal tar and aggregate should be mixed after dehydration and heating respectively, and stir well.
Main points of magnesia ramming material with tar pitch as binder
The construction of magnesia ramming material with tar pitch as binder is as follows:
①The magnesia used should be dried and heated, and the material temperature during ramming should be 80~130℃.
②The temperature of the masonry surface should be heated to 50~60℃.
③ Before ramming, the surface of masonry should be cleaned and painted with a layer of tar pitch;
④ When ramming, layer materials should be layered, and the thickness of each layer should be 20~30mm, until the surface is smooth and the wind hammer can feel the rebounding force and the metal sound can be emitted.