Analysis of manual operation:
furnace can be operated purely on by hands with a handle. The diameter of
the handle is not more than 500 mm. After investigation it can conclude
that manual operation has the following pros and cons:
User can feel the condition of pouring by hands.
The production cost is the lowest.
It is easier for maintenance since it has the least equipment.
It is easier for configuration since it has the least equipment.
It is easier to install a locking system since only a brake is needed
to be installed in the handle.
It is easy to operate.
It consumes very little space so it is space saving.
Its efficiency is high.
Its response rate is very fast.
Much greater force is needed to pull the handle backwards since the
distance between rotary center and center gravity decreases, then the displacement
of the moment decreases, so the moment required should be increased.
User should stand close to the furnace. It is very dangerous because
the temperature is high (see appendix 1). Whilst user can stand more far
away from the furnace by using other method
3. Since the handle is placed on one side of the furnace, user may not see the pouring condition clearly.
Analysis on motor operation:
According to the product specification, we hope to find a motor that would fulfill the requirements like economic, stable, durable, easy to operate, install and maintain, having high efficiency and providing a minimum torque not less than 109.789 Nm. As a result, a research on motors was carried out. The result is shown as below:
I) DC motor:
1. permanent magnets DC motor
2. electromagnets: shunt-field winding motor ; series-field winding motor ; compound motor
(i) Shunt Motor:
From the speed equation, ω = [V – IaRa] / kωΦ
From the torque equation, T = kωΦIa
For a shunt motor, Φ≒ constant
∴ω proportional to [V – IaRa] ; T proportional to Ia
(ii) Series Motor:
According its speed / armature current, torque / armature current and speed /torque characteristics curves, we found that:
ω α 1/Ia ; ωα (V–Ia(Ra + Rse)) ; Tα Ia ; Tα Ia2 ; ωα 1/T
That is when torque is low, rotational speed is high. So the d.c. series is essentially a variable speed motor with large excess torque
capability, hence it is suitable for traction application.
The disadvantage is that a series motor should never be turn on no load.
The disadvantage is that a series motor should never be turn on no load. When Ia is small the speed of the motor is very high and the
centrifugal force developed may damage the armature winding. A series motor should always be solidly coupled to the load.
II) A.C. Motor:
(i) Single-Phase induction motor (typically moderate starting torque with low starting current, ranging from 30W to 0.4kW)
In order to mostly fulfill the requirement we set before (mostly importantly: slow motion, starting torque >110 Nm, speed control
available), from the above analysis, it seems that wound-rotor type three phase motor is most suitable one but very high cost (it require
frequent maintenance and a frequency speed control to vary the speed).
Second priority is DC shunt motor. As the installation of it is very simple, its size is small, it is relatively cheaper, speed control can
done by simply connecting a regulating resistance and also it just requires a simple and cheap starter to start running.