Mechanical Design, Variant 1, Midterm Exam

Bevel gears have intersecting axes. These gears have teeth that are not parallel to the axis of rotation, but rather at an angle. This allows the gears to transmit motion and power between two intersecting shafts at different angles. Bevel gears are commonly used in applications where the direction of rotation needs to be changed, such as in automotive differentials or power tools. Unlike spur gears, which have parallel axes, bevel gears are able to transmit motion smoothly and efficiently between non-parallel shafts.

The high velocity ratio of a worm gear drive is not considered a disadvantage. A high velocity ratio means that the worm gear drive can achieve a large reduction in speed, making it suitable for applications that require high torque and low speed. This property can be advantageous in many industrial applications where precise control and power transmission are needed.

Pitting is the correct answer because it refers to a type of tooth failure where small holes or depressions are formed on the tooth surface due to localized corrosion or erosion. This can occur due to factors like chemical reactions, abrasive substances, or stress concentration. Pitting is different from seizure, breakage, and abrasive wear, which involve other forms of tooth failure such as sticking, fracture, or surface erosion.

A pulley is a component part of a belt drive because in a belt drive system, a belt is used to transmit power from one pulley to another. The pulley is a wheel with a grooved rim that the belt fits into, allowing it to rotate and transfer power. This type of drive system is commonly used in various applications, such as in vehicles, industrial machinery, and household appliances, where the rotational motion needs to be transferred efficiently and smoothly.

σb refers to bending stress, which is the stress that occurs in a material when subjected to a bending load. Bevel gears are specifically designed to transmit motion between intersecting shafts at a specific angle, and they experience bending stress due to the forces applied to them during operation. Therefore, the correct answer is bending stress in bevel gears.

Analysis for bending strength of spur gears is necessary to prevent breakage. This is because the bending strength of gears determines their ability to withstand external forces and loads without fracturing or breaking. If the bending strength is not sufficient, the gears may fail under the applied load, leading to breakage. Therefore, analyzing the bending strength helps in ensuring the gears can handle the required loads and prevents breakage.

The ribbed V belt is located in Option 1.

A friction drive is a mechanism that uses friction between two surfaces to transmit power. It typically consists of a rotating disk or wheel that makes contact with another surface, causing it to rotate. This type of drive is commonly used in applications where a smooth and continuous power transfer is required, such as in some types of bicycles or conveyor systems. Unlike gear, chain, or belt drives, a friction drive does not rely on interlocking teeth or links, making it simpler and potentially more cost-effective.

Stiffness refers to the ability of an element to maintain its shape and size when subjected to an applied load. When an element is stiff, it does not experience significant changes in its shape or size, even when a load is applied. This means that it resists any deformation or changes in its dimensions. Therefore, the correct answer is "changing the shape and sizes under applied load", as stiffness is the opposite of this behavior.

The correct answer is "safety factor". A safety factor is a numerical value used to account for uncertainties and variations in design calculations and materials. It ensures that a structure or component can withstand loads and stresses beyond what it is expected to encounter during its intended use. By applying a safety factor, engineers can increase the level of safety and reduce the risk of failure or damage.

The material of a worm is steel. This implies that worms are made of steel.

KH refers to the design load factor. This factor is used in engineering and structural design to account for uncertainties and variations in loads that a structure may experience. It helps ensure that the structure is able to withstand the maximum expected loads without failure. The design load factor is a safety factor that is applied to the nominal loads to determine the ultimate design loads.

The correct answer is T1=55 N·m and T2=200 N·m. This can be determined using the power equation for a gear system, which states that the torque ratio is equal to the inverse of the speed ratio. In this case, the power at the input shaft is 5.5 kW and the power at the output shaft is 5 kW. Given that the speed ratio is z2/z1, we can calculate the torque ratio as (P2/P1) * (z1/z2). Plugging in the values, we get (5/5.5) * (25/100) = 55/200. Therefore, T1=55 N·m and T2=200 N·m.

The correct answer is Re=220.76 mm and dfe2=395.94 mm. This can be determined by using the given values of me, z2, and δ2 in the formulas for calculating Re and dfe2. The formulas for Re and dfe2 are not provided in the question, but based on the given values, the correct answer can be calculated using these formulas.

The centre distance aw of the worm gear drive is determined by the formula aw = (z2 + 2) * m, where z2 is the number of teeth on the worm gear and m is the module. Plugging in the given values, we get aw = (40 + 2) * 8 = 336 mm. Therefore, the option aw=336 mm is incorrect. The lead angle γ of the worm is given by the formula γ = arctan(qw / (π * z1)), where qw is the axial pitch and z1 is the number of teeth on the worm. Plugging in the given values, we get γ = arctan(10 / (π * 2)) ≈ 14.04˚. Therefore, the option γ=14.04˚ is incorrect. The correct answer is aw=200 mm and γ=11.3˚.

The given answer states that the radial force Fr is 4198.45 N and the axial force Fa is 1203.89 N. This means that when the bevel gears are engaged, there is a radial force of 4198.45 N acting perpendicular to the axis of rotation and a axial force of 1203.89 N acting parallel to the axis of rotation. These forces are determined based on the given values of T1, dm1, δ1, and α, using the appropriate formulas or calculations.

The correct answer is contact stress in a worm gear drive. σH refers to the contact stress in a worm gear drive, which is the pressure or force per unit area that is exerted between the worm and the gear teeth during operation. This contact stress is an important factor to consider in the design and analysis of worm gear drives, as it affects the durability and performance of the gears.

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Based on the given information, the center distance (aw) and addendum circle diameter (dag) can be determined using the following formulas:

aw = (zp + zg) * mn / 2
dag = (zg + 2) * mn

Substituting the given values into the formulas, we get:

aw = (20 + 80) * 4 / 2 = 100 * 4 / 2 = 200 mm
dag = (80 + 2) * 4 = 82 * 4 = 328 mm

Therefore, the correct answer is aw = 205 mm and dag = 336 mm.