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6.1 Explain the operating principles of a punch and shear machine - NSC Mechanical Technology Welding and Metalwork - Question 6 - 2019 - Paper 1
Question 6
6.1 Explain the operating principles of a punch and shear machine . 6.2 Describe the operating principles of the plasma cutter. 6.3 Describe the process of cutting... show full transcript
Worked Solution & Example Answer:6.1 Explain the operating principles of a punch and shear machine - NSC Mechanical Technology Welding and Metalwork - Question 6 - 2019 - Paper 1
Step 1
Explain the operating principles of a punch and shear machine.
Answer
A punch and shear machine, often referred to as a cropper, is activated either by hand or foot. This machine performs heavy-duty cutting by shearing metal sheets to create specific profiles and punching holes.
The operating principles involve:
- Activation: Cropper machines can be operated via hand controls or foot pedals.
- Cutting Action: They utilize electrically or hydraulically driven blades to shear and punch materials. These blades are designed to cut through various metal profiles.
- Setting Process: It is essential to set the punches and corresponding dies according to the desired size prior to operation.
- Cooling Requirements: Notably, these machines do not necessitate cooling fluids, as the shearing process generates minimal heat.
Step 2
Describe the operating principles of the plasma cutter.
Answer
The plasma cutter operates by creating an intense electrical channel of ionized gas, known as plasma. The process involves the following steps:
- Electrical Channel Creation: The plasma cutter initiates a flow of ionized gas through the workpiece, which then forms a complete electric circuit returning to the plasma cut through a grounding clamp.
- Focused Cutting: Compressed air is used to blow the arc toward the material, directing it through a focused nozzle at high speed.
- High-Frequency Arc: This action generates a high-frequency arc that forms in the gap between the electrode and the nozzle, facilitating the cutting through the workpiece efficiently.
Step 3
Describe the process of cutting an internal thread on a work piece using taps.
Answer
To cut an internal thread in a workpiece using taps, follow these steps:
- Drilling: First, drill a pilot hole of appropriate size related to the desired thread diameter.
- Taps Arrangement: Use three taps in succession for better threading, ensuring to follow the correct order when using tapping tools.
- Final Check: Once the threading is completed, check the thread with a gauge or bolt to ensure that it meets the required specifications.
Step 4
Describe the Brinell hardness test process.
Answer
The Brinell hardness test involves the following procedures:
- Indenter Use: A steel ball is used as an indenter to press into the surface of the material being tested.
- Load Application: A specific load is applied to the indenter for a prescribed amount of time.
- Microscope Measurement: After removing the load, the indentation left by the ball is measured under a microscope to determine the diameter of the indentation.
- Hardness Calculation: Finally, the Brinell hardness number (BHN) is calculated using the formula, which gives an indication of the material's hardness.
Step 5
What is the advantage of using Rockwell hardness testing over the Brinell hardness testing?
Answer
The Rockwell hardness test offers several advantages compared to the Brinell test, including:
- Direct Readout: The results from the Rockwell hardness test can be read directly on the scale, making it quicker and more efficient.
- Rapid Testing Time: The Rockwell method allows for faster testing, considerably reducing the time needed for hardness measurements. This speed is especially beneficial in scenarios requiring routine hardness checks.