One action in a shutdown is often carried out on the way past: cutting the power to the heating circuit. The action itself is not wrong, but between cutting the power and the oil in the tank going cold there is still a considerable stretch of time. The tank wall, the heating element and the oil are all hot, and after the power is cut they keep exchanging heat with each other: the residual heat continues to move into the oil and continues to dissipate into the surroundings.
The oil does not cool at once
Once the heating circuit stops, the temperature in the tank does not stay at the set value. It falls away from it, and how fast it falls depends on several conditions: how much oil is in the tank, whether the tank is insulated, how much heat the heating element itself holds, and the ambient temperature. The TYA series is given a temperature control range of 45~80 °C, with the upper limit pulled down to 70 °C when the water content is high, and a shutdown inside that range leaves a substantial amount of residual heat.
The heating method on this machine is far-infrared carbon fibre heating, and the tank wall takes part in the heat transfer, so after shutdown the heat released by the wall returns to the oil as well. This matters most during oil draining: draining hot and draining after cooling are different working conditions.
Where the residual heat can be used
If another batch of oil has to be processed within the next few hours, that residual heat is worth something. The oil in the tank is still close to the temperature control range, so the next batch does not have to be heated up from ambient temperature again and part of the warm-up time is saved outright. For a site that processes batch after batch, that is a return that needs no extra investment.
The conditions for using it are specific: the next batch goes into the tank shortly, the gap between the two batches is short, and there is enough oil in the tank to hold the temperature up. If elements have to be changed, the machine stripped down or the tank emptied in between, the residual heat is of no use, and hot working conditions bring problems of their own.
The residual heat is also being consumed
Looked at from the other side, in a short stop where production is not about to resume, keeping the heater on is a cost rather than a return. The total power of the ZYD-100 is 72 + 5 kW, and the energy drawn with the machine under full load is clearly higher than the energy used for keeping it warm. During the warm period the temperature no longer rises, but the heating circuit still makes up the heat loss under temperature control, and that heat keeps flowing out to the surroundings for as long as it goes on.
| Shutdown situation | How to handle the heating | The reason |
|---|---|---|
| The gap between two batches is short and the next batch goes in at once | Keep temperature control, or hold a lower setting | The residual heat goes straight into preheating the next batch |
| A long shutdown with no certainty about when work resumes | Cut the power | The electricity used while keeping warm is pure cost |
| Elements have to be changed, the machine stripped down or the tank emptied | Cut the power first and wait for the temperature to fall | Hot working conditions are hard on seals and on the people doing the work |
| Nobody on site overnight, but work starts early the next day | Cut the power and start the machine earlier to warm up | The cost of the unattended hours is saved and the warm-up happens when someone is there |
Write the shutdown rule as three sentences
Rather than deciding afresh every time, it is better to fix the rule: at shutdown, first establish how long it will be before the next batch arrives and then decide whether the heating is kept or cut; before any dismantling work, cut the power and wait for the temperature to fall; and do not keep a machine warm for no reason during unattended hours. The working ambient temperature range of the machine is -20~45 °C, and the difference in heat dissipation between winter and summer is clear, so the time parameters behind one rule are not the same in every season.
Cutting the power is not the same as cooling: the residual heat can save the next batch its warm-up time, and it can also keep your meter running while nobody is there.
