Introduction
Gears are essential for transmitting mechanical power from one rotating shaft to the other. Typically, gears are tooth cylindrical wheels essential for the change of speed, and increase the torque. Efficient benefits of gear drive include reversibility, configuration between input and output.
Gears are categorised as follows:
Parallel axis gears: This is categorised into spur gear, helical gears, and internal gears.
There are also Non-parallel, co-planar gears that consist of bevel gears, face gears, and conical involute gearing. The other type of gear is Non-parallel, non-coplanar gears, which consist of crossed axis helicals, cylindrical worm gearing, single enveloping worm gearing, double enveloping worm gearing, and hypoid gears.
For designing a gear, this paper chooses spur gear because it is the most economical out of all the gears listed.
Spur gear
The paper chooses designing a spur gear because it is the cheapest of all gears. Spur gear has straight teeth that allow it to run using sliding and clutch mechanism. (See fig 1). There are some applications that involve in spur gear, this includes manual, automatic machine tool drives, automatic motor vehicle gearboxes, electric motor gearboxes, conveyor systems, timing mechanisms, and power tool drives. Typically, spur gear is manufactured with the use of hardened steel, iron, brass and bronze, and polymers.
Most of the materials of spur gear are listed in Table 1:
Table 1: Material used for spur gear.
Other materials include for manufacturing of spur gear include iron, brass and bronze, and polymers.
There are mechanisms that should be taken into consideration when designing spur gear. For example, the number of wheel selected in the gear must be equal to the product of an integer where the same gear wheel should touch the same teeth on the pinion. However, there should be avoidance of an integer ratio between the number of teeth and pinion, and this can be achieved by adding extra tooth to the gear wheel. It should be noted that there is need for continuous lubrication in the gear mechanisms, and gear train to ensure counteract centrifugal effects on the oil.
Designing a spur gear requires various geometry, and specifications to achieve, and there is need for laying out the geometry for a pair meshing spur gear and the procedure for designing spur gear is set below: (See fig 2).
Construction of spur gear requires full dept involutes, which are the class of curves known as conjugate curves. The involutes gear teeth make the gear to be in constant proportion to the speed of the pinion. Construction of gear geometry is illustrated in Fig 2
Typically, gears can undergo two type of stress. The stress can occur during transmission of load, which may lead to bending stress at the root of the teeth. Contact stress can also occur if there is repeated impact of one tooth surface against another.
The calculation of determining the stress can be based on Lewis formula as calculated as follows:
σ = W1 / FmY
Where: Wt = transmitted load (N),
F = face width (m or mm),
m = module (m or mm)
Y = the Lewis form factor.
In addition, the increase in torque power generally can be done by increasing with the means of gearing.
It should be noted that bevel gear could be used for motor transmission differential drive and mechanical instrument.
Transmission
Power transmission involves transmission of electric energy in the machine from one rotational drive to another. Transmission of power can be achieved through variety of means. Chain, gear drives, and belt have been noted to transmit power, however, their use depend on the suitability and optimisation. Operation of transmission depends on the constant speed ratio, and angular position of driving, and these are very critical to operation.
Typically, belt and chain drives can transmit power from one rotational drive to another, and the speed ratio depends on sprocket diameters, which is given when rotational speeds are of the order of 10 m/s to 60 m/s. Typically, chain drives are used for lower speed, and have higher torque than belts; however, belt drives have numerous advantages over gear, which include easy installation, low maintenance, high reliability, adaptability to non-parallel drive and high transmission speeds.
However, chains are more compact than belt drive, and this enhance the speed ratio, and its power capacity. It should be noted that chain has an advantage of being economically than gear drive, and competitive to belt drives.
In designing transmission, this paper will design belt drives for transmission.
Although, there various type of belt drives, which include flat, round, V, wedge, and synchronous belt drives, however, V belt drives are widely used for transmission. Fig 3 reveals different types of belts
There can be frequent application of belts drive to reduce the speed of output from electric motors. Typically, belts have high strength, can be used for large speed ratios (>8:1), and has low pulley cost, which gives low noise levels and is very good at absorbing torsional vibration.
Fig 4 illustrates Pulley configurations of belts drive.
However to manufacture of the specified quantity of products for Sussex products company, there are criteria that needs to be consider.
Cost of manufacture of Sussex Products Company
To calculate the cost of manufacturing 600, 000 spur gears, some criteria must be taken into consideration.
First, there should be calculation of all overhead cost for the production from start to finish.
Typically, the overhead costs are the cost of running a business, and this type of cost cannot be directly allocated to a specific product, this cost may be spread on all products produced by an organisation. The overhead may be categorised into two:
First, overhead is categorised as the costs associated with design and manufacture.
Second overhead is the cost for running a business, which is known as commercial overheads.
The items categorised under the costs associated with design and manufacture is as follows:
- The cost of administration of the design organisation,
- the cost of administration on the organisation manufacturing.
- production planning;
- The cost of services and utilities used by these departments.
Overheads may also entail new tools or machinery not directly applicable to the project, and will be of general use in the organisation. Thus, the cost of such item will be distributed on all the business.
Commercial overhead also include the following:
The cost of running a business sometimes known as commercial overheads includes:
- Rent
- rates;
- Water, gas, telephone, electricity.
- Stationery
- salaries of plant engineers;
- management salaries;
- Security
- general maintenance activities;
- computer systems;
- salaries of office staff;
- salaries of accounts & accounts staff;
- quality management;
- salaries of purchasing staff;
- transport;
- salaries of marketing staff;
- general sales and marketing activities.
Having discussed the items to be considered for the overheads, it is essential to develop the cost of overhead for the manufacturing of 600, 000 gears of Sussex Products Company.
Estimate the overhead costs for the Sussex products company.
From the calculation of overhead for Sussex Products Company, it is revealed that total overheads are £ 500, 565.
Based the figure above, this paper calculates profit and loss from the cost of manufacturing of 600, 000 quantities.
Profit and loss for the Sussex products company.
Overhead to remove in case of salary increase
Sometimes in an organisation, there are occasion when there is increase in salary as the case of Sussex Products Company. Thus, with the case of Sussex Products Company, there is arbitrary increase in salaries and wages of employees and management wish to maintain the present profits. To maintain the present profits, there is need to remove some overheads that serve as cost of production. Some of the overhead that need to be removed are commercial functions, stationery, and agents.
References
University of Sussex (2009), Engineering Design section 2: Bearings and shafts.
University of Sussex (2009), Engineering Design Section 3: Gears.
University of Sussex (2009), Engineering Design Section 5: Design management
University of Sussex (2009), Engineering Design Section 4: Belt and chain drives.
Notes from Excel on profit and lost account.