Showing posts with label Press. Show all posts
Showing posts with label Press. Show all posts

June 12, 2009

Quality Assurance during Green Production of Refractory Bricks

Quality is defined as what the customer wants in a product (here ‘Refractory’), not just meeting specifications. Quality ensures customer delight. Consistently achieving the specifications without failure is one of the most important requisites for Quality. Then, a question automatically arises that how can one be effectively consistent in any regular operation. The answer is: one has to plan and follow some Standard Operating Procedures or SOPs, a term more popular among Quality Circles. Standards promote good work habits among all levels of the organization. To standardize is to choose the best method and promote consistency which is essential for quality.


Operator running a Friction Screw Press (FSP) image

Fig.- Operator Running a Friction Screw Press (FSP)


There has to be SOPs for each and every operation starting from raw material testing, acceptance to brick dispatch in a refractory plant. But merely having SOPs will not help in any respect except for showing them to any customer, if such a situation arises! However, following these SOPs religiously will not only benefit in getting the quality in various refractory products but also, help in increasing the productivity and reducing the rejection percentage at every level thus, ultimately bringing down the cost of production.


An array of Friction Screw Presses in a Refractory Plant image

Fig.- An Array of Friction Screw Presses in a Refractory Plant

Nevertheless this article is not to discuss the advantages of SOPs or Standardization which will be discussed in a separate post. Here our point of discussion is how to ensure quality in a refractory brick during its green production. For this each and every brick must pass through a process of checking as a part of standard procedure in the process of production. Below is a list of such things (parameters) that have to be checked during green production of refractory bricks as a criterion for their acceptance or before sending them to drier.


GREEN BRICKS CHECKING LIST


1. Size and critical Dimensions as per actual & shrinkage given in the Production Programme (Refer Drawing if required).

2. Quality / Plate mark / Special instructions.

3. Right angle, Centre slope.

4. Warpage, Bulging.

5. Die Plate jam, cleaning.

6. Spongy, Texture.

7. Rags, Corner loose.

8. Lamination, Crack (Hammering).

9. De-airing & Pressing stroke (Set-up approval).

10. Green B.D, Refractory Composition.

11. Sieve analysis report of Powder (Mixture).

12. Free iron in the Powder/Mixrure.


Related Posts:


Indian Refractory Entrepreneurs: Are They Delivering Customer Delight?


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


Glimpses of the Growth of Refractory Industry in India.

June 4, 2009

Effects of Compacting (Forming) Pressure on Sintering and other Properties of Refractory Bricks

We assume that the reader is already aware with the concept of ‘Sintering’, types of sintering and also the effects of sintering on refractories. In this article we will discuss on the effects of compacting pressure or applied pressure on sintering and various other properties of refractory bricks.

It has been established much before by Budnikov and Blyumen that sintering processes and reactions in the solid-state are interrelated and proceed with on the phase boundaries, as in a heterogeneous system. The basis of sintering, according to their broad definition, is the capacity of the solid phase to recrystallize, which, in turn, is related to the physiochemical nature of the crystal. Pressure is said to be an important factor in accelerating reactions in solid state and in facilitating sintering at relatively low temperatures in a refractory brick.

Precautions must be taken to eliminate any pressure variation during compaction of the refractory shape. The main deleterious effect of pressure variation is the corresponding differences in green bulk density resulting into non-uniform shrinkage after firing and some sort of distortion of warping is inevitable. The frictional force between the die wall and the powder is directly proportional to the radial stress at the wall. During a uniaxial pressing, the applied stress is in the axial direction and is parallel to the die (mould) wall. For a given axial stress the resultant radial stress depends on the fluidity of the powder under compaction. For example both the radial and axial stresses are equal when a liquid is compacted. However, when a non-elastic and incompressible solid is under axial compaction, there should not be any radial stress. Thus, it is desirable to decrease the powder fluidity in order to minimize the radial and frictional stresses or the density and stress gradients in the refractory brick.

There is no doubt that the forming pressure affects the firing behavior of the refractory materials. Theses effects may be due to:

>> Decrease in pore size and better particle contact,

>> Strain energy added due to plastic flow,

>> Strain energy added due to particle interlocking, or

>> Fracture of particles at contact points.

In general increasing pressure enhances the Green Density, decreases Shrinkage, and often increases the Fired Density of refractory bricks. Higher compacting (forming) pressures may cause plastic flow, increased strain energy, or particle fracture, which causes further increase in bulk density in refractory bricks. The effect of these variations on firing properties of a refractory brick depend on the firing time and temperature, and the nature of the refractory aggregates or refractory raw materials used, but in general decreased pore size due to compaction or particle fracture leads to increased density at lower firing temperature in a refractory brick.

What is ‘Sintering’ in Refractory Bricks ? [Read]



October 14, 2008

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

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 -

· consistently producing to specification and

· 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 in this country then he must have noticed that bricks worth crores (millions) of rupees or thousands of tons lying rejected for not satisfying the customer specified criteria of iron spots (craters). Before going into the steps as how to control the formation of these iron spots in Refractory Bricks let us discuss some more about Craters.


Craters are defined as melt phenomena, caused by mainly iron oxide or lime or some other low temperature melting elements like, 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 while in operation. The various reasons/sources of these iron spots and actions required to be taken to prevent their formation in a refractory brick are outlined below:


Refractory Raw Material

1. 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.

2. Responsibility: Mill house, Calcination Kiln, Checking & RM yard.


Own Rejection (Refractory Grog)

1. Preventive Measure: Iron containing (contaminated) grog to be kept separately.

2. Responsibility: Checking & RM yard.


Outside Grog

1. Preventive Measure: Visual inspection in the Truck by breaking up the lumps into pieces before unloading. Briquette test in the Laboratory.

2. Responsibility: Checking & RM yard. Laboratory (Quality Assurance).


Maintenance Waste

1. Preventive Measure: Cleaning of waste & scraps after Maintenance e.g. iron chips, welding tips etc. Handover to Production Deptt after maintenance of any Machine (Handover – Takeover system). Cleaning before & after maintenance of each machine (Mill House, Mixer, Press etc).

2. 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

1. Actions Required: Due to Beater => regular cleaning of Magnetic drum, Plate & Roller Magnets. Due to Rusted plates => Silo cleaning once in a fortnight.

2. Responsibility: Mill House. Maintenance. Production departments.


Free iron from Press Hoppers

1. Actions Required: Due to Rusted plates => Hopper cleaning once in a fortnight.

2. Responsibility: Production.


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