Introduction to Refractories...

Introduction to Refractories Refractories are defined in ASTM C71 as non metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems that are exposed to environments above 538 deg C. Refractories are inorganic, nonmetallic, porous and heterogeneous materials composed of thermally stable mineral aggregates, a binder phase and additives. These materials have ability to retain its physical shape and chemical identity when subjected to high temperatures. Refractories perform four basic functions namely (i) act as a thermal barrier between a hot medium and the wall of the containing vessel, (ii) represent a chemical protective barrier against corrosion, (iii) ensure a physical protection, preventing the erosion of walls by the circulating hot medium and (iv) act as thermal insulation for heat retention. Refractories are classified in the different following ways. Classification based on chemical composition –  Refractories are classified on the basis of their chemical behaviour into following three classes. Acid refractories – These are those refractories which are attacked by alkalis or basic slags. These are used in acidic atmosphere or where slags are acidic. Example of these refractories are silica and zirconia. Basic refractories – These refractories are attacked by acid slags but stable to alkaline slag, dust and fumes at the elevated temperatures. These refractories are used in alkaline atmospheres. Example of these refractories are magnesia, dolomite and chromite. Neutral refractories – These refractories are chemically stable to both acids and bases and used in the areas where slag and environment are either acidic or basic. Examples are carbon graphite, chromites and alumina. Grphite is the least reactive and is extensively used in the furnaces where the process of oxidation can be controlled. Classification based on physical form – Refractories are classified according...

Project Evaluation Review Technique (PERT) and Critical Path Method (CPM)...

Project Evaluation Review Technique (PERT) and Critical Path Method (CPM) Pert evaluation review technique (PERT) and critical path method (CPM) are two management techniques which are used to plan, schedule, budget and control different activities normally associated with a project. These techniques were developed in 1950s. PERT was developed by US Navy for the planning and control of Polaris missile programme while CPM was developed by DuPont and the emphasis was on the trade-off between the cost of the project and its overall completion time. PERT was originally designed to examine projects from the stand points of uncertainty while the CPM was designed to examine projects from the standpoint of costs. These techniques have been combined over time. Both the techniques rely heavily on the use of networks to help plan and display the coordination of all the activities of a project. In PERT activities are shown as a network of precedence relationships using activity on arrow network construction and using probabilistic activity time estimates. In CPM, activities are shown as network of precedence relationships using activity on node network construction and using time estimates which can be predicted with considerable certainty due to the existence of past experience. Comparison of PERT and CPM is given in Table 1. Tab 1 Comparison of PERT and CPM PERT CPM 1. PERT uses event oriented network 1. CPM uses activity oriented network 2. Estimates of time for activities are  not so accurate and definite 2.Duration of activity can be estimated with a fair degree of accuracy 3. It is used mostly in projects of non repititive nature 3.It is used extensively in construction projects 4. Probabilistic model concept is used 4. Deterministic concept is used. 5. PERT is basically a tool for planning 5. CPM can...

Tundish and its role in Continuous Casting Sep28

Tundish and its role in Continuous Casting...

Tundish and its role in Continuous Casting Continuous casting of steel is a widely used process and an important step in the production of steel. The share of continuously cast steel around the world has increased significantly in the last 35 years or so. Presently this share is above 95 percent. However, concurrent with this increase in production levels, there are stringent quality requirements that have become crucial in the face of progressively increasing throughputs of continuous casting machines and larger dimensions of the cast products. In the process of continuous casting, to transfer liquid steel from a steel teeming ladle to the mould, an intermediate vessel, called a tundish, is used. A tundish is a rectangular big end up refractory lined open container which may have a refractory lined cover on the top. The tundish bottom has one or more holes with slide gate(s) or stopper rod(s) for controlling the metal flow. It is used to feed liquid steel into the copper moulds of a continuous casting machine, so as to avoid splashing and give a smoother flow. The tundish being a reservoir of the liquid steel ensures the feed of the liquid steel to the continuous casting machine during the change of steel ladles, thus acting as a buffer of liquid steel. It smoothens out flow, regulates steel feed to the mould and cleans the metal. Metallic remains left inside a tundish are known as tundish skulls and need to be removed, typically by mechanical means (scraping, cutting). Scrap recovered in this way is ordinarily recycled in the steelmaking process. The tundish is required to deliver the liquid steel to the moulds evenly and at a designed throughput rate and temperature without causing contamination by inclusions. The number of moulds is normally 1 to 2...

United Nations Framework Classification of Mineral Reserves/Resources...

United Nations Framework Classification of Mineral Reserves/Resources United Nations Framework Classification (UNFC) of Mineral Reserves/Resources consists of a three dimensional system with the following three axes: Geological assessment, Feasibility assessment and Economic viability. The process of geological assessment is generally conducted in stages of increasing details (Fig 1) Fig 1 Classification of minerals The typical successive stages of geological investigation i.e. reconnaissance, prospecting, general exploration and detailed exploration, generate resource data with a clearly defined degrees of geological assurance. These four stages are therefore used as geological assessment categories in the classification. Feasibility assessment studies form an essential part of the process of assessing a mining prospect. The typical successive stages of feasibility assessment i.e. geological study as initial stage followed by prefeasibility study and feasibility study/mining report as well defined. The degree of economic viability (economic or sub economic) is assessed in the course of prefeasibility and feasibility studies. A prefeasibility study provides a preliminary assessment with a lower level of accuracy than that of a feasibility study, by which economic viability is assessed in detail. The various terms used in this classification and their definitions are as follows: Total Mineral Resource It is a concentration(or occurrence) of material of intrinsic economic interest. It has resonable prospects for eventual economic extraction. Its location, grade, quantity, geological chracteristic is known, estimated or interpreted from specific geological evidence and knowledge. Total mineral resource are of three types. Measured Mineral Resouce – Itm is that part of mineral resource for which tonnage, density, shape, physical characteristics, grade and mineral content can be estimatedwith a high level of confidence i.e. based on detailed exploration. Inducated Mineral Resource – In this category tonnage, densities, shape, physical characteristic, grade and mineal content can be estimated with reasonable level of...

Statistical Quality Control...

Statistical Quality Control Statistical quality control (SQC) is the term used to describe the set of statistical tools deployed for evaluating the organizational quality by the quality professionals. Statistical quality control can be divided into following three broad categories. Descriptive statistics – These are the statistics used to describe certain quality characteristics such as the central tendency and variability of the observed data. It also describes the relationship. Descriptive statistics include statistics such as the mean, standard deviation, the range, and a measure of the distribution of data. Statistical process control (SPC) – It consists of statistical tools that involve inspecting a random sample of the output from a process and deciding whether the process is producing products with characteristics that fall within a predetermined range. SPC answers the question whether the process is functioning properly or not. These tools are very important for a process since they help in identifying and catching a quality problem during the production process. Acceptance sampling – It helps in evaluating whether there is problem with quality and whether desirable quality is being achieved for a batch of product. Accepting sampling consists of the process of randomly inspecting a sample of goods and deciding whether to accept the entire lot based on the results. This sampling decides whether a batch of goods is to be accepted or rejected. There are seven basic tools employed for SQC. The seven basic tools of quality is a designation given to a fixed set of graphical techniques identified as being most helpful in trouble shooting issues related to quality. They are called basic because they are suitable for people with little formal training in statistics and because they can be used to solve the vast majority of quality related issues. These seven basic tools are described below. Check...