The general concept and layout of a combination: belt driven torque increasing system and torque increasing gearbox has progressed to the stage wher

The general concept and layout of a combination: belt driven torque increasing system and torque increasing gearbox has progressed to the stage where the detailed design can now be undertaken. The general system layout is as follows:

The detail design will be undertaken in three phases, firstly the belt drive system, secondly shaft drive system, and thirdly the gearbox system.

QUESTION 1 Motor (1 point)

The electric motor is a 3-phase, 4-pole (per phase) induction motor supplied with 415V and 50 Hz AC.

Data for this motor is available in the following WEG Motor Catalogue SUMMARY below:

Fill in the blanks:

Last number of student number X = [3], the required power is [15] kW, and the SMALLEST motor that can meet the required transmitted power requirement has a rated speed of [] RPM.

QUESTION 2 Machine class (0.75 points)

Using the examples of driven machine type from Table A1 of AS2784, select which Class is appropriate for a mixer.

QUESTION 3 Service factor (0.75 points)

If the last digit of your student (X) number is even, the motor uses an electronic controller such that the starts are 'soft' according to TABLE A1 of AS2784.

If the last digit of your student number (X) is odd, the motor starts direct-online, meaning that the starts are 'heavy' according to TABLE A1 of AS2784.

The motor system runs for 20 hours per day.

Complete the following sentence:

For my type of starts, the service factor is [], meaning my design power is [] kW.

QUESTION 4 Wedge belt selection (0.5 points)

Using Figure A1 from AS2784, select an appropriate Wedge Belt size for your design power and shaft speed.

NOTE FOR QUESTIONS 5 THROUGH 11:

When designing a system such as this, there is not simply one answer to how the system can be designed. In fact, there are many different combinations of components that when put together will solve the design problem at hand. It is up to us as designers to look at all the potential options available to us, evaluate them, and decide on which combination we think solves the design problem the best; this is the job of an engineering designer.

For this reason, in the following questions we will work through investigating all of the potential solutions to the design problem, and in Question 11 you will decide what your final selection of components is for the design, and detail why you made this selection. Complete questions 5 to 11 first, exploring all options, then once a final selection is made, come back and provide the answers to each of the questions.

QUESTION 5 Pulley selection (0.75 points)

The pulley selection should allow the output shaft to run as close as possible to 460 rpm when the motor is running at its rated speed.

Noting that the larger pulley OD must be less than 800 mm, select appropriate pitch diameters for the small and large pulleys from Table 9 of AS2784.

Determine all potential pulley combinations which provide an output rpm with 5% error.

After completing question 11, fill in the following details for your final pulley selection:

The small pulley pitch diameter is [small_d] mm, the large pulley pitch diameter is [large_d] mm, meaning the error in shaft speed (measured in rpm), is [error_rpm] RPM.

QUESTION 6 Belt power rating (1 point)

Using AS2784 power rating tables (Table A2 for SPZ belts, Table A3 for SPA belts and Table A4 for SPB belts) define the Power Rating of a single belt for each of the potential pulley combinations found in question 5.

After completing question 11, fill in the following details for your final pulley selection:

For my belt system the small pulley diameter is [small_d] mm, the small pulley shaft speed is [shaft_rpm] RPM and the Power Rating (in kW) from AS2784 is [power_rating] kW.

QUESTION 7 Power increment per belt (0.75 points)

Using AS2784 power rating tables (Table A2 for SPZ belts, Table A3 for SPA belts and Table A4 for SPB belts) define the Power Increment Per Belt.

After completing question 11, fill in the blanks for your chosen belt system:

The small pulley diameter is [small_d] mm, the small pulley shaft speed is [shaft_rpm] RPM and the speed ratio is [speed_ratio], therefore the Power Increment per belt is [power_increment] kW.

QUESTION 8 Belt selection (1 point)

AS2784 Table A13 describes available belt lengths within the standard, and sections A3 and A4 provide formulae for the calculation of belt length and centre distance, respectively.

Given that the centre distance may not exceed 1000 mm. What is the smallest and largest possible belt sizes that can be used, considering all possible pulley combinations found in question 5.

Fill in the blanks:

The smallest possible belt length that I can use in the system is [small_belt_length] mm, with pulley sizes of [small_d_1] mm and [large_d_1] mm in diameter. The largest possible belt length I can use in the system is [large_belt_length] mm, with pulley sizes of [small_d_2] mm and [large_d_2] mm in diameter.

QUESTION 9 Power correction for belt pitch length (0.75 points)

Using AS2784 Table A13 determine the Power Correction Factor for Belt Pitch Length for all possible belt sizes (i.e., between the smallest and largest length, inclusive).

After completing question 11, then fill in the blanks for your chosen belt system:

The SP belt type is [belt_type], the belt length is [belt_length] mm, and therefore the Power Correction for Belt Pitch Length is [belt_correction].

QUESTION 10 Power correction for angle of wrap (0.75 points)

Now that you have a list of all possible pulley combinations, and all possible belts that can be used for each pulley combination, using AS2784 Table A12 define the Power Correction for Angle of Wrap for each combination of pulley and belt.

After completing question 11, then fill in the blanks for your chosen belt system:

The small pulley diameter is [small_d] mm, the large pulley diameter is [large_d] mm, my selected centre distance is [centre_distance] mm, and therefore the Power Correction for Arc of Contact is [arc_correction].

QUESTION 11 Number of belts (1 point)

From all possible combinations of pulley and belt length, select one particular combination that you think solves the design problem the best.

Please summarise this particular selection of belts, as well as their performance characteristics below, and calculate the number of belts required for your system:

The Power Rating from AS2784 is [power_rating] kW.

The Power Increment per belt is [power_increment] kW.

Power Correction for Belt Pitch Length is [belt_correction].

The Power Correction for Arc of Contact is [arc_correction].

Therefore the total Power per Belt is [total_power] kW.

The design power for my system is [design_power] kW.

Therefore the total number of belts required is [total_num] belts.

QUESTION 12 Belt Length Selection (1 points)]

In the box below state your selected belt length and briefly describe two factors that you have considered when selecting this belt length.

QUESTION 13 Excess belt power (1 points)

In the following box describe what percentage fraction of a total belt power is in excess of the power required to satisfy the design power.

For example, if your system requires 7.8 belts, you must use 8 belts, but 20% of a belt is provided in excess of the requirement.

Describe briefly how you could modify the belt system design so that this fraction of wasted power was reduced.

QUESTION 14 Design worksheet (2 points)

In preparing your answers for the previous section you have developed a spreadsheet that clearly articulates the process by which design variables were selected, including different permutations of pulley sizes, belt lengths and centre distances.

It is important that this document be clearly presented and readily understood such that the process by which design decisions were made is clear, and that the spreadsheet enables efficient alterations of design variables, and aids in error checking by another engineer.

Please upload a screenshot (not the actual spreadsheet) of this spreadsheet.

QUESTION 15 Pulley Catalogue Selection (1 points)

Using the SKF pulley catalogue provided within the reference material select an appropriate small and large pulley. Ensure the pulley can accommodate the number of belts required for the system.

Provide a screenshot of the catalogue data used, with the selected pulleys highlighted. An example is provided below.

Question 16 Belt tension (2 points)

The following image shows the first paragraph of Appendix 1 of AS2784.

With reference to Appendix B of AS2784 (you will need to download a full copy, see announcements for instructions) complete the following questions relating to the belt tension.

The belt system I have designed satisfies Condition [condition]. (Please enter either 1 or 2 here).

The largest value of "Required deflection force", P from table B1 of Appendix 1 AS2784 is [def_force] N.

The "Correction for centrifugal tension", K (calculated by the equation give in Appendix 1 of AS2784 is [K_factor].

For the belt system I have designed:

The "Static hub load", Ws, is defined as the magnitude of the force that is exerted on the pulley by the belt system when the pulleys are NOT rotating. For the system I have designed, Ws is equal to [stat_hub] Newtons.

The "Dynamic hub load", Wr, is defined as the magnitude of the force that is exerted on the pulley by the belt system when the pulleys ARE rotating. For the system I have designed, Wr is equal to [run_hub] Newtons.

QUESTION 17 PART 1 Bearing specification (1.5 points)

In the previous question you calculated a belt load for running and static cases. Given that the shaft length is 1 meter, calculate the reaction forces on the bearing near the pulley (bearing 1) and the bearing at the far end of the shaft (bearing 2).

For this question you will upload a hand-drawn solution, including free-body diagrams and calculations, for the reaction forces for bearings 1 & 2 for the static and running cases.

Some hints:

This solution will require you to draw known forces and find unknown reactions in 2 perpendicular planes and then add the horizontal and vertical reaction forces as vectors to find the reaction force (hypotenuse).

Bearings are usually mounted as near as possible to the ends of the shaft without fouling the other machine elements. The bearing at the far shaft end can be mounted at the 1 meter point. The bearing at the pulley end should allow at least 25 mm clearance after the pulley on the shaft.

Bearing reaction forces are typically simplified as a single point load through the bearing centre.

QUESTION 17 PART 2 Bearing specification (0.5)

Fill in the blanks for the position of mounted components along the shaft:

My large pulley has a width of [large_pulley_width] mm. Bearing 1 is mounted [position_bearing_1] mm from the start of my shaft. Bearing 2 is mounted [position_bearing_2] mm from the start of my shaft.

QUESTION 18 Bearing selection (1 points)

We will simplify our design by using the same bearing for both bearings at either end of the main shaft.

This approach is quite common as it is much easier to implement and costs less to buy two bearings of the same type, rather than two specific bearings. It also helps the engineer to sleep well at night as they dont have to worry about whether the bearings are assembled the right way around.

But using the same bearing type for both ends of the main shaft means that we must design for the bearing that sees the greatest load (we will call this the worst case loaded bearing).

State the Static Load [stat_load] and Dynamic [dyn_load] that you have calculated for the worst case loaded bearing.

If we require an L10 design life or 7,000,000 cycles using a rolling element bearing (k = 3.0), state the Static Load Rating [static_load_rating] and Dynamic Load Rating [dyn_load_rating] required for the worst case loaded bearing.

QUESTION 19 Shaft design equation (1 point)

The shaft runs in one direction only (power applied) and is started once per day and used for a total of 20 hours per day. Which equation (1, 2, 3 or 4) from Table 2 of AS1403 (Design of Rotating Steel Shafts) is appropriate for this application.

QUESTION 20 Bending moment diagram (2 points)

In the previous section for bearing design you identified reaction forces at the bearings. From these known loads draw the bending moment diagram for this shaft and upload this as an image. Indicate the value of the input forces and the value of the maximum bending moment, Mq.

Note: this bending moment diagram can be calculated in two perpendicular planes through the shaft (as we did for the bearings loads) or can be a single plane based on the resultant of these forces.

QUESTION 21 Peak shaft torque (2 points)

To calculate the shaft diameter, we require the maximum shaft torque, Tq. Upload a screenshot of a section of your design notes that clearly shows the value of Tq as a function of all the relevant design variables (input motor speed, motor power, service factor, speed ratio, design power). For this calculation we can assume that power is transmitted with 100% efficiency.

This question is intended to assess whether you can clearly present your design logic to another engineer. The screenshot that you upload can be from a handwritten design diary, or a word document or from a spreadsheet that you use for design. The important thing is that you show how you have calculated Tq.

QUESTION 22 Trial shaft diameter (1 points)

Using Appendix A from AS1403 (Design of Rotating Steel Shafts, excerpt available in the Week 5 tutorial materials) (shown below) complete the following statement.

For my design scenario, the maximum bending moment, Mq is [bm_max] and the maximum shaft torque, Tq is [T_max]. Therefore from Appendix A of AS1403, the estimated shaft diameter using high strength steel is [trial_shaft_d] millimetres.

QUSTION 23 Stress Raising Factors (1 Points)

Determine the following stress raising factors for your trial diameter using high strength steel. Use the endurance limit of the material for the tensile strength when reading off graphs:

Size Factor

Fitted Rolling Element Bearing with interference fit

Fitted Component Without Key or Spline with interference fit

Fill in the blanks:

The size factor for my trial diameter is [size_factor]. The stress raising factor for a fitted rolling element bearing is [K_bearing]. The stress raising factor for fitted component without key or spline is [K_fitted].

QUESTION 24 Minimum shaft diameter (1 points)

Using the equation found in question 19, and the loads applied to the shaft, as well as an initial trial diameter, determine the minimum possible diameter for the shaft.

Note: The equation found in question 18 must be iteratively solved until a convergent diameter is found. This means to take the diameter calculated in your first iteration and use it as the new trial diameter to find stress raising factors and solve the equation again. Repeat this process until the diameter you get out is approximate to the diameter you put in. Below is an example of the process from page 22 of AS 1403:

Fill in the blank:

The minimum possible shaft diameter is [min_shaft_d] mm.

QUESTION 25 PART 1 Bearing Catalogue Selection (1 point)

Using the Timken deep groove ball bearing catalogue provided in the reference material, select a bearing which can service the worst case static and dynamic load rating calculated within question 17.

Ensure that the internal diameter of the bearing is greater than the minimum required shaft diameter calculated in question 22 and specify the final shaft diameter to the internal diameter of the bearing.

Provide a screenshot of the catalogue data used, with the selected pulleys highlighted. An example is provided below.

QUESTION 25 PART 2 Bearing Catalogue Selection (1 point)

Complete the following statement. For my design scenario, the selected bearing has a dynamic load rating of [dyn_load_rating] and a static load rating of [static_load_rating]. The final shaft diameter has been specified to [internal_bearing_diameter], the internal diameter of the bearings selected.

QUESTION 26 Gear design torque increase (1 point)

Sometime after the gearbox has been commissioned the end-user decides to re-purpose the mixing machine for another application that requires the output torque to be increased by (50+5*X)% (where X is the last digit of your student number, so if your number is s234567, the torque must be increased by 50+(5*7)=85%).

Then complete the following statement: Given that the last digit of my student number is [s_number], the torque must be increased by [percentage_increase] %.

QUESTION 27 Spur gear module (1 points)

Your design team proposes that a single-stage spur gear reduction could be used to achieve this torque increase, the gearset would schematically look something like the following (shown without the gearbox housing).

You are advised to begin your design with 21 teeth on the pinion, but with a pinion pitch diameter of no less than 2.5 times your shaft diameter. With reference to AS2938 (Spur and helical gears) identify what is the smallest 1st choice module that satisfies this requirement.

Then complete the following statement: Given that my shaft diameter is [shaft_d], according to AS2938, the smallest 1st choice normal module that can accommodate 21 teeth on the pinion with a pinion pitch diameter of no less than 2.5 times the shaft diameter is [smallest_module] mm.

QUESTION 28 Gear specification (1 points)

Please complete the following sentences:

For my student number a torque increase of [t_increase]% is required and I have selected a module of [design_module] mm for my design.

For 21 teeth on the pinion, the number of teeth on the mating gear that most closely achieves this required torque increase is [gear_teeth] teeth.

For this number of teeth on the mating gear, and the module I have selected, the gear pitch dimeter will be [gear_pitch_d] mm and according to the standard tooth profile of AS2938, the addendum diameter of the mating gear will be [add_d] mm and the dedendum diameter of the mating gear will be [ded_d] mm.

QUESTION 29 Gear design (2 points)

The following section requires you to estimate the tooth face width for your gear set. The following assumptions are relevant (read these carefully as you cant answer without these):

Geometry factor J is calculated from the following chart assuming a 20 degree pressure angle and load applied at tip of tooth, (no sharing).

The velocity factor (Kv) is calculated from the following chart assuming that our design is based on line C for precision shaved and ground teeth.

Complete the following sentences for your design:

Based on the number of teeth on my pinion [n_teeth_pinion], the Geometry Factor (found from the table below, based on the above assumptions) is [J_factor].

For a pinion shaft speed of [pinion_shaft_speed] RPM, and pinion pitch circle diameter [pinion_pitch_diameter] mm, the pitch line velocity is [pitch_line_velocity] meters per second, and the Velocity factor, Kv, (found from the table below based on the above assumptions) is [velocity_factor].

QUESTION 30 Gear face width (2 points)

Please summarise the gear selection that you have made in the previous questions:

The Geometry factor, J, found in the previous question is [J_factor].

The Velocity factor, Kv, found in the previous question is [velocity_factor].

The module for my pinion is [module_value] mm.

For the following assumptions:

The mounting factor (Km) is assumed to be 1.4 (this a common assumption for initial design purposes)

The overload factor (Ko) is assumed to be 1.5 (again this is a common assumption)

The gears are made of 4340 normalised steel with bending strength (St) of 474 MPa

Using the AGMA method (shown in equation below) and the assumptions above, the minimum required face width, b, for the pinion is: [face_witdth] mm.

QUESTION 31 Gear design worksheet (2 points)

In preparing your answers for the gear design sections you have developed a spreadsheet that clearly articulates the process by which the chosen gears were selected, including different permutations of gear tooth module and gear pitch diameters.

It is important that this document be clearly presented and readily understood such that the process by which design decisions were made is clear, and that the spreadsheet enables efficient alterations of design variables, and aids in error checking by another engineer.

Please upload a screenshot (not the actual spreadsheet) of this spreadsheet.

QUESTION 32 Gear CAD (1 points)

You are required to make third projection detailed drawing for the large gear. This drawing should include the fundamental technical details that are relevant to correct function.

Other geometric details also need to be included so that the gear can be manufactured. These should be sized according to your intuition but should allow the gear to be manufactured without uncertainty.

In addition to detailed drawings for the gear, please also provide a screenshot of the drawing used to create the involute tooth profile.

The uploaded image should be in PDF format.

Note, CAD is not required for the pinion.