This page contains relevant Scientific principles and how I applied them to my work.

This document discusses the problems/challenges in this project that relate to science, mathematics, and analysis, where I then identify the theory, key areas of knowledge and laws and formulae to apply.

Problems Analysis

One of the main issues I have with my remanufactured skateboard wheels project is choosing a suitable polyurethane to pour in a mould over an old wheel core.

This is because the polyurethane must have the suitable qualities needed for the wheels to pass the relevant British Standard tests.

To ensure I have all the knowledge necessary to make this decision I have conducted relevant research which you can find here.

Another problem that arises in this project is how to ensure the manufacturing processes produce quality wheels. There are many factors that play a part in this, such as the methods chosen to manufacture, the materials used such as the form the polyurethane comes in, the amount of hardener mixed with the polyurethane to achieve a hardness of 99A.

Manufacturing methods

The manufacturing methods used to remanufacture skateboard wheels include milling, using a lathe, injection moulding and the use of an industrial oven to cure the wheels. The main principle with injection moulding is “the “all-phase” control strategy, which is defined to include variables that are continuously controlled throughout the moulding cycle and are equally important in all phases.” (1)

“Melt temperature, which is a fundamental variable in the injection-molding process, needs to be continuously controlled and held to a specific level. A change in melt temperature affects a number of variables including the melt flow rate, the nozzle pressure, and the cavity pressure (28). It is therefore desirable to have accurate melt temperature control in all phases. During the plastication phase, the barrel temperature can be used, while during the filling phase, the nozzle temperature might be used as an indirect measure of melt temperature. During the holding phase, the melt temperature is a critical parameter in the PVT relationship. A number of models for melt temperature have been proposed.

Ma (29) proposed the following simplified relationship

where Tb, = melt temperature in the barrel, N = screw rotational speed, P, = melt pressure, Tb = barrel temperature, and 61 = disturbance caused by material property variation and/or screw geometry variation due to wear.

Kinematics/Kinetics

Performance is affected by size, shape and the forces acting on it. understand this in relation to project to help optimize wheels for speed, acceleration, braking.

Friction Test – calculate the coefficient of friction of the wheels ​(1)​

μs = F /(40+M)gn​​

F= force applied in Newtons​​

M= mass of skateboard in kg​​

Gn= 9.81m/s^2

Dynamics

Behaviour of wheels such as motion and stability can be analysed, principle dynamics involved.

References

(1) Agrawal, A.R., Pandelidis, I.O. and Pecht, M. (1987). Injection-molding process control?A review. Polymer Engineering and Science, 27(18), pp.1345–1357. doi:https://doi.org/10.1002/pen.760271802.

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