Rockwell Hardness Test is the most commonly used hardness tests after Brinell Hardness Test, named after the metallurgists Stanley P. Rockwell and Hugh M. Rockwell who developed it in the early 1920s. It is convenient to use and several enhancements over the years have made the test adaptable to a variety of materials.
Rockwell hardness test
In the Rockwell Hardness Test, a cone-shaped indenter or small-diameter ball, with diameter 1.6 or 3.2 mm (1/16 or 1/8 inch) is pressed into the specimen using a minor load of 10 kg, thus seating the indenter in the material. Then, a significant load of 150 kg (or other value) is applied, causing the indenter to penetrate the specimen a certain distance beyond its initial position. This additional penetration distance (d) is converted into a Rockwell hardness reading by the testing machine. The sequence is shown in the above figure. Differences in load and indenter geometry provide various Rockwell scales for different materials.
The most common scales are shown in the below table.
A refrigerant is a substance or mixture. Usually, a fluid, used in a heat pump and refrigeration cycle that can extract heat from another body or substance. Ice, cold water, cold air, etc. can be treated as refrigerants.
Desirable Properties of a Refrigerant:
1. Vapor density:
To enable the use of smaller compressors and other equipment the refrigerant should have smaller vapor density.
2. Enthalpy of vaporization:
To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization.
3. Thermal Conductivity:
Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation.
4. Dielectric strength:
In hermetic arrangements, the motor windings are cooled by refrigerants vapor on its way to the suction valve of the compressor. Therefore, the dielectric strength of refrigerant is an important property in hermetically sealed compressor units.
5. Critical temperature:
In order to have a broad range of isothermal energy transfer, the refrigerant should have a critical temperature above the condensing temperature.
6. Specific heat:
To have the minimum change in entropy during the throttling process, the specific heat should be minimum. For this, the liquid saturation line should be almost vertical.
7. Leak tendency:
The refrigerant may leak out of the system. The problems with a leakage are wearing out of joint or the material used for the fabrication of the system. A denser refrigerant will have fewer tendencies to leak as compared to higher density refrigerant. The detection of leaks should be easy to loss of refrigerant. Leakage can be identified quickly if the refrigerant has a distinct color or odor.
The refrigerant used in air conditioning, food preservation, etc. should not be toxic as they will come into contact with human beings. Refrigerants will affect human health if they are poisonous.
9. Cost of refrigerants:
The quantity of refrigerant used in industries is very less. The price of the refrigerants is generally high when compared to other chemicals in the industry. Shallow industry professional will not take necessary action to control the leaks.
Refrigerants should be available near the usage point. It must be sourced and procured within a short period to enable the user in case of leaks, maintenance schedules, etc.
Properties of Commonly Used Refrigerants:
1. Carbon dioxide:
Carbon dioxide is widely used as a refrigerant in mechanical systems refrigerant, marine services, hospitals, etc. due to its excellent safety properties. It is odorless, non-toxic, non-flammable, non-explosive and non-corrosive.
2. Sulfur dioxide:
Sulfur dioxide was widely used as refrigerant during the early 20th century. However, its use has been restricted nowadays because of its many inherent disadvantages. It is highly toxic, non-flammable, non-explosive, non-corrosive and works at low pressures
Ammonia is one of the earliest types of refrigerants which is still widely used in many applications due to its inheritance excellent thermal properties, It is toxic in nature, flammable explosive under certain conditions, it has low specific volume¸ high refrigerating effect, low piston displacement in case of reciprocating compressors make it an ideal refrigerant for cold storage’s, ice plants, packing plants, skating rinks breweries, etc.
Freon-11 (Trichlorofluoromethane) is used under low operating pressures; it is non-toxic, non-corrosive and non-flammable. Due to low operating pressure and high displacement, it is used in systems employing centrifugal compressors. It is used for air-conditioning applications.
Freon-12 (Dichloro difluoromethane) is non-flammable, non-toxic and non-explosive. It is highly chemically stable. If it is brought into contact with open flame or heater elements, it decomposes into highly toxic constituents. It has not only excellent safe properties but also condenses at moderate pressure under normal atmospheric conditions.
6. Cryogenic refrigerants:
Cryogenic refrigerants are those refrigerants which produce minus temperature in between range -157°C to -273°C in the refrigerated space. The cryogenic refrigerants have a shallow boiling point at atmospheric pressure. Some of the widely used cryogenic refrigerants are Helium, Nitrogen, Oxygen, Hydrogen.
Computer Integrated Manufacturing (CIM) describes the integration of Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM). In the early 1960s, Ivan Sutherland developed the SKETCHPAD system, a milestone of research achievement in computer graphics. The evolution of computer graphics has since resulted in the development of CAD. On the other hand, CAM was inspired by numerical control (NC) machines, which were first introduced in the early 1950s. The communication between CAD and CAM systems became possible by reuse of the product model designed in CAD systems and CAM systems.
Computer Integrated Manufacturing Lab of Concordia University
Computer Integrated Manufacturing (CIM) is a general term used to describe the computerized integration of the conventionally isolated functions of manufacturing, such as product design, planning, production, distribution and management. It essentially needs large scale integrated communication system and extensive database. For this, the functions of various elements of a manufacturing system are treated by subsystem serves as the input to another subsystem. Organizationally, the subsystems can be broadly grouped into two sets of functions:
Business Planning: Forecasting, scheduling, material requirement planning, invoicing and accounting.
Business Execution: Production and process control, material handling, testing and inspection.
Improved product quality and increased flexibility in the use of capital are the two board benefits of using CIM. Additionally, CIM offers the following benefits:
Responsiveness to short product life cycles and dynamics of global competition.
Process control results in consistent product quality and uniformity.
Controlling manufacturing operations like production, scheduling and management.
Improved productivity by optimum use of resources.
Revenue of a firm is affected by the policies adopted by the competitors, by the firms pricing policy and changes in market demand for the product and services rendered by the firm. Factors that affect the expenses include the prices paid for inputs, business volume and the efficiency of translating the raw material resources and resources into a product.
The study of the profit-volume relationship of a business helps to identify a point at which a business moves from loss to profit position is termed as a break-even analysis. Break-even analysis is a tool which finds the point, either in monetary terms or in terms of a number of units, at which total costs equal revenues. The point is called the break-even point.
Break-even analysis requires a knowledge of fixed costs, variable costs and revenue.
Steps Involved in Break Even Analysis:
Identify the fixed costs (FC) and sum them.
Estimate the variable cost (VC) associated with the production of each unit.
Fixed costs are drawn on the vertical line representing cost.
Variable costs are then drawn originating from the vertical axis at the point where fixed costs end as shown in the figure below. These are indicated as an incrementally increasing cost with the change in volume as we move to the right on the volume (horizontal) axis.
Revenue line, beginning at the origin and proceeding upward to the right, i.e., increasing by the selling of each unit is plotted.
The point at which the revenue line intersects the total cost line is called the break-even point as shown in the above figure. Areas of the graph enclosed between the two lines, below and above the break-even point, are termed as loss corridor and profit corridor respectively.
Mathematically, it can be calculated as follows:
We can use the below notations to terms for easy understanding.
BEPR = Break-even point in monetary units
BEPx = Break-even point in units of product
P = Price per unit
x = Number of units produced
T.R = Total revenue = P × x
F = Fixed costs
V = Variable costs per unit
T.C = Total costs = F + V × x
At the break-even point,
Total Revenue = Total Cost
P × x = F + V × x
Solving for x, we get
Profit = T.R – T.C
= P × x – (F + V × x)
= P × x – F – V × x
Profit = (Difference in fixed and variable cost) × No. of units produced – Fixed Costs
With these equations, we can directly solve for break-even point and profitability for units to be produced. Break-even analysis helps to identify processes with the lowest total cost for the expected volume. It also identifies the largest profit corridor and thus helps in addressing two major issues with which a process decision be made successful.
The drill does not produce the correct hole size some time with the good surface finish. A hole with precision size can be produced with a good finish off a pre-drilled hole using a reamer tool. The process of the enlarging hole is called reaming.
The reamer is commonly used to remove the minimum amount of metal (100 to 150 micron for rough reaming and 5 to 20 micron for fine reaming) from the hole. During reaming operations, the job should be properly supported and rigidly held. A stock wrench of appropriate size for holding the reamer is used. The reamer must be kept in its correct position about the job. It must be rotated slowly, and excessive feed must not be given. It should always be-be turned in the cutting direction. Sufficient amount of cutting fluid should also be used. When removing the reamer, it must be turned in the cutting direction. Reamers with blunt or chipped edges must not be used.
Various kinds of reamers are classified and described as under:
Spirally fluted reamer
Straight fluted reamer
Some common types of the reamer used in fitting workshops are discussed as under.
1. Hand Reamer:
It is operated by hand to finish the holes and remove its ovality. Its cutting edges are backed off in the same manner as those of twist drills to give suitable clearance. It is made up of carbon or high-speed steel material. It is used for excellent internal turning in the hole by placing a tap wrench on the square end of the reamer.
2. Machine Reamer:
It is designed for slow speeds for use on drill presses, lathes, vertical milling machines, etc. It is chamfered on the front side of cutting edge. It possesses straight or tapered shanks and comprises of either straight or spiral flutes.
3. Taper reamer:
It is widely used for finishing taper holes smoothly with precision. It is also used to provide a taper to a drilled hole when a taper pin is to be used. It is performed with either straight or spiral flutes. It has spaces ground into the cutting edges or teeth to prevent overloading the entire length of each tooth of the reamer. These spaces are staggered on the many teeth to help in stock removal.
4. Spirally fluted reamer:
It performs greater shearing action than one with straight flute.
Saint-Venant’s principle states that if the forces acting on a small portion of an elastic body are replaced by a statically equivalent system of forces on the same portion of the surface, the effect upon the stresses in the body is negligible except in the immediate area affected by the applied forces. The stress field remains unchanged in areas of the body which are relatively distant from the surfaces upon which the forces are changed. ‘Statically equivalent systems‘ implies that the two distributions of forces have the same resultant force and moment.
Saint-Venant’s principle allows simplification of boundary condition application to many problems as long as the system of applied forces is statically equivalent.
Stress concentration at Point Load, Hole, abrupt changes in cross-section:
We have already known through Hooke’s law, the relationship between strain and stress. Strain to be proportional to stress, we can get a good idea about the magnitude of normal stress by examining the normal strain in a material as it is being subjected to some loads. To allow this, we can draw lines parallel to the normal plane and see if they remain plane during load application. In each of the following cases, witness how near the discontinuity there is a non-uniform distribution in the strain (and therefore stress) field, while farther away the distribution is linear (ie. the lines remain straight).
Shielding gas is commonly used in factories to prevent the molten metal from the harmful effect of the air. Even small amounts of oxygen in the air will oxidize the alloying elements and create slag inclusions. Nitrogen is solved in the hot melted material but when it solidifies the solubility decreases and the evaporating gas will form pores. Nitrogen can also be a cause of brittleness. The shielding gas also influences the welding properties and has great importance for the penetration and weld bead geometry.
Argon (Ar) is one of the most popular shielding gases. As an inert gas, it has no chemical interaction with other materials. Therefore it is ideal for sensitive materials such as aluminum and stainless steel. At metal inert gas welding of mild steel, an addition of C02 or a small amount of oxygen will increase the welding properties, especially for short arc welding. Contents of up to 20% C02 improves the penetration (limits the risk of lack of fusion) while 5-8 % will give reduced spatter.
Helium-like argon is an inert gas. It gives more heat input to the joint. Mixed with argon, it increases welding speed and is advantageous for the penetration of thick-walled aluminum or copper where it compensates for the high heat conduction.
Drawbacks with helium is a high cost and the low density. At Tungsten inert gas welding, high contents of helium will reduce the ignition properties.
Carbon dioxide (C02):
Pure carbon dioxide (C02) can be used for short arc welding. It is commonly available gas and cost of gas is cheap, it has good properties for welding of galvanized steel and gives better safety against the lack of fusion than argon-based gases. Drawbacks are a higher amount of spatter and the fact that the gas cannot be used for spray arc.
Small additions of hydrogen (H2) can be used to increase heat input and welding speed in the same manner as helium, but it is much cheaper. Because of the risk of cracks, hydrogen can only be used for welding of austenitic stainless steel. It actively reduces the oxides and is therefore also used in root gases.
Oxygen (O2) is also used as a small addition to stabilizing the arc at metal inert gas welding.
Nitrogen (N2) can be used as an alloying element in ferritic-austenitic stainless steels. A small additive of nitrogen in the shielding gas compensates for the losses when welding.
Several techniques (slip casting, extrusion, dry pressing, wet pressing, hot pressing, isostatic pressing, jiggering and inspection molding) are available for processing ceramics into useful products (shown in below table 1), depending on the type of ceramics involved and their shapes. Production of some ceramic parts (such as pottery, floor tiles) generally doesn’t involve the same level of control of materials and processes as do high-tech components (made of such structural ceramics as silicon nitride (Si3N4) and silicon carbide (SiC) and cutting tools.
Generally, however, the procedure involves the following steps
Crushing or grinding raw materials into very fine particles.
Mixing them with additives to impact certain desirable characteristics.
Shaping, drying and firing the material.
Processing steps involved in making ceramics parts.
Table 1: General Characteristics of Ceramic Processing
Large parts, complex shapes, low equipment cost.
Low production rate, limited dimensional accuracy.
Hollow shapes and small diameters, high production rate.
Parts have constant cross section, limited thickness.
Close tolerances, high production rates with automation.
Density variation in parts with high length to diameter ratios, dies require abrasive wear resistance, equipment can be costly.
Complex shapes, high production rate.
Limited parts size and dimensional accuracy, tooling cost can be high.
Strong, high density parts.
Protective atmospheres required, die life can be short.
Uniform density distribution.
Equipment can be costly.
Low tooling cost, high production rate with automation.
Limited to axisymmetric parts, limited dimensional accuracy.
Complex shapes, high production rate.
Tooling can be costly.
Ceramics may be subjected to additional processing, such as machining and grinding, for better control of dimensions and surface finish.
The first step in processing ceramics is the crushing of the raw materials. Generally crushing is done in a ball mill, either dry or wet. Wet crushing is more effective because it keeps the particles together and also prevents the suspension of fine particles in the air. The particles then may be sized filtered and washed.
The ground particles are then mixed with additives the functions of which are one or more of the following:
Binder: Binder is used for holding ceramic particles together.
Lubricant: Lubricants are used to reduce internal friction between particles during molding and to help remove the part from the mold.
Wetting agent: the wetting agent is used to improve mixing.
Plasticizer: Plasticizer is used to make the mix more plastic and formable.
Agents: Agents are used to controlling foaming and sintering.
Deflocculant: deflocculant are used to make the ceramic-water suspension more uniform by changing the electrical charges on the particles of clay (so that the particles repel rather than attract each other). Water is added to make the mixture some pourable and less viscous. Commonly used deflocculants are Sodium carbonate (Na2CO3) and Sodium silicate (Na2SiO3) in amounts of less than 1%.
The three basic shaping processes for ceramics shaping are casting, plastic forming and pressing.
High-Speed Steels (HSS) are the cutting tool materials used for machining of materials. The HSS will be used for machining of materials. The General use of HSS is 18-4-1.
18% of Tungsten or Molybdenum, used for increasing hot hardness temperature of tool material.
4% of Chromium, used for increasing the strength of resistance to deformation of the cutting tool material.
1% of Vanadium, used for improving the wear resistance of the cutting tool material or for maintaining the keenness of cutting edge.
In addition to these 2.5 to 10 %, cobalt is used to increase the red-hot hardness of tool.
Drill bits made of High-Speed Steels
If 18% tungsten is used in the HSS is called tungsten based HSS and if 18% molybdenum is used in HSS is called molybdenum based HSS. Out of the two the most commonly used HSS is the tungsten-based HSS even though the molybdenum is cheaper than tungsten because the tungsten-based HSS will have higher wear resistance than the molybdenum-based HSS.
HSS is the most commonly used cutting tool material for machining of materials with a cutting velocity of 40 to 50 m/min. HSS cutting tool is preferable to use for machining of large carbon workpieces because the presence of nearly 76% of iron in the HSS cutting tool will attract the carbon atoms from the high carbon workpiece and produce Built Up Edge (BUE) on the HSS tool. Hence for machining of large carbon workpieces in place of HSS the satellite cutting tools are used.