MQA UNIT-3

UNIT 3. MQA  PYQ QUESTIONS 

Q.1) Write short notes on Talysurf for surface roughness measurement with systematic diagram.

Talysurf is a highly accurate and versatile instrument used for surface roughness measurement. It employs a non-contact method to assess the texture, finish, and roughness of a surface. The system consists of various components that work together to provide precise measurements. Here are some short notes on Talysurf, along with a systematic diagram:

1. Probe: The Talysurf system features a sensitive probe that scans the surface of the object being measured. The probe contains a stylus or a diamond-tipped stylus that makes physical contact with the surface.

2. Vertical Drive: The vertical drive mechanism controls the movement of the probe in the vertical direction. It ensures that the probe maintains a consistent force against the surface during measurement.

3. Transducer: The transducer converts the mechanical motion of the probe into electrical signals, which can be further processed for analysis and measurement.

4. Position Sensor: A position sensor is used to precisely track the movement of the probe along the surface. It provides accurate positional data for generating a detailed profile of the surface.

5. Controller Unit: The controller unit acts as the brain of the Talysurf system. It receives signals from the transducer and position sensor, processes the data, and controls the overall operation of the instrument.

6. Display and Analysis Software: The Talysurf system is typically equipped with a display screen that shows the measured surface profile. The software accompanying the system allows users to analyze the data, calculate roughness parameters, and generate reports.

7. Computer Interface: The system can be connected to a computer for data transfer and advanced analysis. The computer interface enables seamless integration with other software and data management systems.

8. Calibration Standards: Talysurf systems are calibrated using known surface standards to ensure accuracy and traceability of measurements. Calibration standards are used to verify and adjust the system's performance periodically.

Systematic Diagram:

Q.2) Explain Tomlinson surface tester with neat sketch.

The Tomlinson surface tester is a mechanical instrument used to measure the surface roughness and texture of a material. It operates based on the principle of stylus profilometry. Here is an explanation of the Tomlinson surface tester:

1. Stylus: The Tomlinson surface tester consists of a stylus that is attached to a sensitive measuring arm. The stylus is a fine-tipped probe that makes physical contact with the surface being measured.

2. Vertical Drive: The instrument is equipped with a vertical drive mechanism that controls the movement of the stylus in the vertical direction. It allows the stylus to move up and down while maintaining a constant force against the surface.

3. Horizontal Drive: The Tomlinson surface tester also features a horizontal drive mechanism that moves the stylus laterally across the surface. This movement is typically controlled by a motor and a positioning system.

4. Transducer: A transducer is integrated into the instrument to convert the mechanical motion of the stylus into electrical signals. These signals are then further processed for analysis and measurement.

5. Controller Unit: The controller unit serves as the central processing unit of the Tomlinson surface tester. It receives the electrical signals from the transducer, performs calculations, and controls the overall operation of the instrument.

6. Display and Analysis: The instrument is typically equipped with a display screen that shows the measured surface profile in real-time. Specialized software allows users to analyze the data, calculate roughness parameters, and generate reports.

Working Principle:

1. Calibration: Before measuring a surface, the Tomlinson surface tester is calibrated using a standard reference sample with a known surface roughness. This calibration ensures accurate measurements.

2. Measurement: Once calibrated, the stylus is placed in contact with the surface to be measured. The vertical drive applies a constant force, allowing the stylus to traverse the surface while recording the vertical displacement.

3. Scanning: The horizontal drive moves the stylus laterally across the surface, scanning a predetermined path. The stylus follows the contours of the surface, recording the vertical displacement at each point.

4. Data Processing: The electrical signals from the transducer are sent to the controller unit, where they are processed and analyzed. The data is typically converted into a profile graph or other visual representations.

5. Roughness Calculation: Using the measured profile data, the Tomlinson surface tester calculates various roughness parameters such as Ra (average roughness), Rz (mean peak-to-valley roughness), and Rt (total roughness).

6. Result Presentation: The calculated roughness parameters and surface profile are displayed on the instrument's screen. Users can interpret the results and compare them to desired specifications or standards.

Q.3)  Explain concept of RMS and CLA value for surface roughness measurement.

RMS (Root Mean Square) and CLA (Center Line Average) are two commonly used parameters for surface roughness measurement. They provide quantitative values that characterize the texture and irregularities of a surface. Here's an explanation of each parameter:

1. RMS (Root Mean Square):

RMS is a measure of the average height deviation of the surface from its mean line or centerline. It quantifies the roughness by calculating the square root of the average of the squared height deviations of the surface profile points.

Mathematically, RMS can be calculated as follows:

RMS = √[(1/N) * ∑(hᵢ²)]

Where:

- N is the total number of profile points.

- hᵢ represents the height deviation of each profile point from the mean line.

RMS is useful for evaluating the overall roughness of a surface. It considers both the positive and negative deviations from the mean line, providing a comprehensive measurement of the surface texture.

2. CLA (Center Line Average):

CLA is a measure of the average roughness height of a surface. It represents the average distance between the surface profile and a reference line called the centerline. The centerline is calculated by drawing a line that passes through the highest and lowest points of the surface profile.

Mathematically, CLA can be calculated as follows:

CLA = (1/L) * ∫(|h(x)|)dx

Where:

- L is the evaluation length of the surface.

- |h(x)| represents the absolute value of the height deviation at each point along the surface.

CLA provides an indication of the typical surface roughness height and is particularly useful in applications where the mean line is of interest, such as in sealing or gasketing applications.

Both RMS and CLA are widely used in industry to quantify surface roughness and ensure consistency in manufacturing processes. However, it's important to note that these parameters are just two examples among several other roughness parameters that can be used depending on the specific requirements of a given application.

Q.4) Explain terms in gear with neat diagram, 

i) Module 

ii) Diametral pitch

iii) Circular pitch

iv) Pressure angle

1. Module:

The ratio of the pitch diameter to the number of teeth in the gear. 

Module is denoted by the symbol 'M' 

Module (M) = Pitch Diameter (D) / Number of Teeth (N)

2. Diametral Pitch:

Diametral pitch is the number of teeth per inch of the pitch diameter. 

Diametral pitch is denoted by the symbol 'P' and is measured in teeth per inch (TPI).

Diametral Pitch (P) = Number of Teeth (N) / Pitch Diameter (D)

3. Circular Pitch:

Circular pitch is the distance between  adjacent gear teeth to pitch circle. 

It represents the arc length along the pitch circle corresponding to one tooth. 

Circular pitch is denoted by the symbol 'CP' 

Circular Pitch (CP) = π x Pitch Diameter (D) / Number of Teeth (N)

4. Pressure Angle:

Pressure angle is the angle between the line of action and a line perpendicular to the teeth. 

The angle at which the gear teeth exert force on each other.

Commonly used pressure angles in gears are 14.5°, 20°, and 25°.

Q.5) Explain in detail primary & secondary texture

In the context of surface texture analysis, primary and secondary texture refer to different types of surface characteristics that contribute to the overall texture of a material. Let's explore each of these in detail:

1. Primary Texture:

Primary texture refers to the inherent or natural texture that is formed during the manufacturing or processing of a material. It is typically a result of the production method, such as machining, casting, or grinding. Primary texture is usually intentional and can be controlled to some extent.

Primary texture can include the following:-

a) Machining Marks: When a material is machined, such as through turning, milling, or grinding, the cutting tool leaves characteristic marks on the surface. These marks can be in the form of grooves, ridges, or patterns that correspond to the tool's motion.

b) Casting Texture: In casting processes, the surface of the material may exhibit features like grain boundaries, dendritic structures, or flow lines. These textures are formed due to the solidification of the molten material during casting.

c) Forming Texture: Materials that undergo forming processes like rolling, extrusion, or forging can develop primary textures caused by the deformation and flow of the material. These textures can include elongated grains, directional flow lines, or undulations.

2. Secondary Texture:

Secondary texture refers to the surface features or modifications that are intentionally added or altered after the primary texture is formed. It involves surface treatments or finishing processes applied to enhance or modify the primary texture.

Secondary texture can include the following:-

a) Polishing or Grinding: Polishing and grinding processes are used to smoothen the surface and remove or minimize the primary texture. This results in a finer, more uniform surface finish with reduced roughness and irregularities.

b) Coatings: Applying coatings, such as paints, varnishes, or protective layers, can alter the surface texture. Coatings can provide a smoother or rougher appearance, change the color or glossiness, or add texture through textured paints or coatings.

c) Surface Treatment: Various surface treatments like shot peening, sandblasting, or etching can modify the surface texture. These treatments can introduce controlled roughness, micro-indentations, or surface patterns for functional or aesthetic purposes.

d) Additive Manufacturing Texture: In additive manufacturing processes like 3D printing, the layered deposition of material creates a distinct surface texture. This texture can be further modified through post-processing techniques like sanding or polishing.

Both primary and secondary texture contribute to the overall surface roughness, appearance, functionality, and performance of a material. Understanding and controlling these textures is essential in various industries, including manufacturing, engineering, design, and aesthetics.

Q.6)  Explain effective diameter measurement by three wire method.

The three-wire method is a widely used technique for measuring the effective diameter of a threaded object, such as a screw or a bolt. The effective diameter is a critical dimension that determines the fit and functionality of threaded components. The three-wire method allows for accurate and reliable measurement of the effective diameter using three wires of known diameter. Here's how the three-wire method works:

1. Wire Selection: Three wires of the same diameter are selected for the measurement. The diameter of the wires should be chosen based on the thread size and pitch of the threaded object being measured. The wires are typically made of hardened steel and have precise diameters.

2. Wire Placement: The three wires are placed in the thread grooves of the threaded object. The wires are positioned equidistant from each other in the same plane, forming an equilateral triangle with the threaded object at its center. The wires should be in contact with the flanks of the thread.

3. Measurement: The threaded object with the wires is placed on a flat surface, such as a surface plate or a granite block. The object is rotated carefully to settle the wires in the thread grooves and achieve good contact.

4. Micrometer Measurement: A micrometer is used to measure the total thickness of the threaded object and the three wires together. The micrometer is adjusted to lightly touch the wires and record the measurement.

5. Wire Correction Factor: The wire correction factor is a constant that corrects for the effect of wire diameter on the effective diameter measurement. It depends on the wire diameter and the thread form being measured. Standard wire correction factors can be found in reference tables.

6. Effective Diameter Calculation: The effective diameter is calculated using the following formula:

Effective Diameter = Measured Diameter - (2 x Wire Correction Factor)

The measured diameter is the total thickness of the threaded object and the three wires as obtained from the micrometer measurement.

7. Repeat Measurement: To ensure accuracy, the measurement process is repeated multiple times by repositioning the wires and taking new measurements. The average of these measurements is used to obtain the final effective diameter value.

The three-wire method provides an indirect measurement of the effective diameter by utilizing the relationship between the measured diameter and the known wire diameter. It compensates for the width of the wire and accurately determines the effective diameter of the threaded object. This method is commonly employed in industries where precise thread measurements are crucial for ensuring proper fits, functionality, and quality of threaded components.