Refractory Bricks, Mortar and Castable for Reheating Furnace Lining

17-Jun-2023

Reheating Furnaces serve the purpose of heating various intermediate products of Steel like- ingots, blooms or billets before rolling to give them different shapes of angles, channels, bars, slabs, rods & wires etc 

Read: What are Reheating Furnaces Area wise specifications of Refractory Bricks and Castables or Blocks which can be used for lining of reheating furnaces and the quality of Refractory Mortar which can be used for laying the bricks are given hereunder -

Reheating Furnace Hearth

1. Dense high alumina bricks with low iron content. Alumina (Al₂O₃) 88-90%, Iron (Fe₂O₃) 1.8% (max), Bulk Density (BD) 3-3.2 gm/cc, Apparent Porosity (AP) 16-18%, CCS(kg/cm²) 800 (min), RUL(ta^OC) around 1550-1600, PLC at 1600^OC/2hrs (+/-) 0.2% (max).

2. Basic Magnesia, Mag-chrome bricks. MgO around 55-60%, Chrome (Cr₂O₃) around 12-15%, Silica (SiO₂) 8% (max), AP 18-20%, CCS (kg/cm²) around 450-500, RUL (ta^OC) 1600 (min), PLC at 1600^OC/2hrs (+/-) 0.5% (max).

Furnace Roof

Alumina (Al₂O₃) around 70%, Iron (Fe₂O₃) around 2.5-2.8%, BD 2.6-2.7 gm/cc, AP 21-23%, CCS (kg/cm²) 500 (min), RUL (ta^OC) around 1450-1500, PLC at 1500^OC/2hrs (+/-) 2.5% (max).

Furnace Side-Wall and for General purpose

1. Low porosity dense bricks. Alumina (Al₂O₃) 45%, Iron (Fe₂O₃) 1.6-1.8%, BD around 2.2 gm/cc, AP around 16%, CCS (kg/cm²) around 500, RUL (ta^OC) 1500 (min).
2. Alumina (Al₂O₃) 40%, Iron (Fe₂O₃) 2.0-2.2%, BD 2.1 gm/cc (min), AP 22% (max), CCS (kg/cm²) around 350, RUL (ta^OC) 1400 (min).

Furnace Bottom, Blocks (Burner Block, Well Block, Seating Block, Seating Well Block) and Castables

1. Medium purity Low Cement Castable (LCC). Alumina (Al₂O₃) around 90%, Iron (Fe₂O₃) 1.0-1.5%, BD 2.7-2.9 gm/cc, PCE 37 Orton (min), CCS (kg/cm²) at 110^OC/24hrs 600 (min), at 1500^OC/3hrs 550 (min), PLC at 1500^OC/2hrs (+/-) 1.0% (max).
2. Medium purity Castable conventional type. Alumina (Al₂O₃) around 60%, Iron (Fe₂O₃) 1.8% (max), BD 2.1 gm/cc (min), PCE 36 Orton (min), CCS (kg/cm²) at 110^OC/24hrs 350 (min), at 1500^OC/3hrs 450 (min), PLC at 1500^OC/3hrs (+/-) 1.5% (max).

Furnace Door, Flue Stack, Heaters

Insulating Castables. Iron 1% (max), BD 1.0-1.2 gm/cc, CCS (kg/cm²) at 110^OC/24hrs around 12-15.

Mortars

Have to be compatible with the laying brick quality (chemical spec).

All the data given above are tentative and should not be considered as ‘Typical Specification Data’. 

Methods of installation (Read: Refractory Installation Procedure and Heating Schedule to be followed after starting a Furnace) may be provided by the refractory supplier.

How to Prevent Formation of Iron Spots (Crater) in Refractory Bricks as a measure of Quality Control

21-Jan-2023 (Updated)

What makes a refractory product sell? The factors determining the sales success are many and varied. They include market conditions, the nature of the product, and the image of the manufacturing organization in the market as well as of the product created by advertising, the socio-cultural background of customers, credit facilities, Customer Delight and so on.

But one major factor that appears certainly in all conditions (excluding monopoly or extreme scarcity) is product quality as perceived by the customer. The Production Department must accept its fundamental responsibility for the manufactured quality of its refractory products. The workforce with effective training and adequate equipment must be capable of -
1. consistently producing to specification and 

2. recognizing and reacting when an operation goes out of control.

Adequate systems must be established to ensure that corrective action is taken. The quality control for Refractory Bricks refers to the following aspects:

=> Manufacturing defects.

=> Dimensional tolerances.
=> Physical & Chemical material properties.
=> Quantities, Marking, Labelling and Packing.

While Sampling for visual and dimensional inspection, iron spot (crater) is always an important criteria of inspection. It is not an uncommon site or if one had a chance of visiting brick yards of a few Refractory manufacturing units then he must have noticed that in many such plants refractory bricks worth crores (millions) or thousands of tons are lying rejected because of developed iron spots (grey fusion spots) in them. 

Before going into the steps as how to control the formation of these iron spots or iron craters in Refractory Bricks let us discuss a few more things in detail.

Iron Craters or similar Black Spots are actually melt phenomena, caused by mainly iron oxide or lime or some other low temperature fusion and melting elements mostly, alkalies. An Iron spot on the surface of a refractory brick can be tested with a hammer (I assume Refractory persons would be acquainted with this tool :-) ) to determine the possible presence of crater which can be dangerous for the brick and so, for the furnace after lining. Some common reasons/sources of these iron spots and preventive actions required to be taken regularly to stop formation of such black spots and maintain the quality of refractory bricks are outlined below:

Refractory Raw Materials
Preventive Measure: Checking the Raw Material & removing free iron from it before grinding / using. Sorting of Slag / Iron patch especially in calcined fire clay and other calcined raw materials at the kiln yard itself.
Responsibility: Mill house, Calcination Kiln, Checking & RM yard.

Own Rejection (Refractory Grog)
Preventive Measure: Iron containing (contaminated) grog to be kept in strict isolation.
Responsibility: Checking & RM yard.

Outside Grog
Preventive Measure: Visual inspection in the Truck itself by breaking up the lumps into pieces before taking into the raw material yard. Briquette test in the Laboratory.
Responsibility: Checking & RM yard. Laboratory (Quality Assurance).

Maintenance Waste
Preventive Measure: Proper cleaning of waste & scraps after Maintenance of any machine in the shop-floor e.g. iron chips, welding tips etc. before handover to the Production Deptt (there should be a proper Handover – Takeover system). Cleaning before & after maintenance of each machine (Mill House, Mixer, Press etc).
Responsibility: Concerned person of the Maintenance Deptt. Shift in charge of the concerned area (Mill House, Press, and Production).

Free iron in Mill House Silo Material
Actions Required: Due to Beater => regular cleaning of Magnetic drum, Plate & Roller Magnets. Due to Rusted plates => Silo cleaning once in a fortnight.
Responsibility: Mill House. Maintenance. Production departments.

Free iron from Press Hoppers / Mill Hoppers
Actions Required: Due to Rusted plates => Hopper cleaning once in a fortnight.
Responsibility: Production.

These are the certain necessary steps which, if taken properly, can arrest the formation of grey craters and iron spots which become visible on the surface of refractory bricks only after the firing is over that means everything is over!

Sampling of the Refractory Specimen for Inspection

21-Jan-2023

The sample selection or what is known as Sampling, is an important function of refractory inspection. The inspection procedure starts by selecting, generally a minimum number of units, called a ‘Sample’, from a lot. A ‘Lot’ is meant for the quantity of refractory materials from which sample specimens are drawn for inspection. The test results of these samples make the basis for acceptance or otherwise of the refractory lot. Since Refractories are characteristically anisotropic in nature so instead of drawing only one sample, a predefined number of sample specimens are collected from the lot while sampling. Although there are provisions for ‘Hundred percent inspection’ and ‘Sampling inspection’ but, hundred percent inspections is not preferred generally since most of the tests are destructive type besides, consideration of factors like time consumption and the costs involved.

Methods of Sampling

Sampling inspection of both refractory bricks and monolithic refractories can be done by two methods - (1) Inspection by Attributes, (2) Inspection by Variables. 

The first method is performed visually by gauging or counting the number of defects and so, is non-destructive and cost effective. The second method is performed by all tests including the destructive ones on Refractories.

Sample size or the number of samples to be drawn from the Refractory lots to be inspected depends on the type of Standard Method being followed for testing. Sampling and their testing are done strictly according to the specified procedures already mentioned in that Method, the results of which should be binding for both the manufacturer and the customer.

What is Standard Method for Testing of Refractories? (To be posted soon)