Heaters for a Gear Lubrication System

Need to know the approx. volume of oil you have to heat.

Could some of the waste heat from the kiln be ducted around the black oil container instead?

Could the oil tank and pipework be raised so that the natural convection of the waste heat from the kiln keeps it warm?

if you use electical heating pay attention to the ratio watt/cm² if it is too big you can crack the oil and compromise its lubricant effect.

Electrical heating is the easiest to control but it could be better for safety to use hot damp or water since the temperature locally cannot go too high.

Look at the suggestion to use some of the heat in the process if possible it is a good one.

Another way other than inserting a Flanged Heater into the oil is to apply Trace heating cable/Heater cord to the outside of the Container or Hopper. be carefull not to exceed the permisable/recommended watt density of the oil or you will cause the oil to carbonise/burn the oil.

In order to calculate the wattage required we would need to know,

1) size of container/hopper,

2) temp that the oil is required to work at

3) minimum temp in winter (is unit indoors or outdoors)

4) Ex or non-hazordous area

With the above info its a basic calc.

Basic rule of thumb for oil of that viscosity is about 2.4kW per 600 Lt's. We use low density heater (with thermostatic control) that is 3Ph (has three elements each to a phase). This is left on all the time. If you require a rapid heat up you can use a larger heating element but it must be placed into a pocket so that the element does not come into direct contact with the oil (see post 3 above).

To fit the low density heater, you will need to slightly more than half empty reservoir and then weld a 2" BSP socket into the side. Do not weld near bottom of reservoir. Heater screws into socket with a BSPT thread. Can be bought in virtually any length to suit width of reservoir.

PW Slack has got the best idea and it's environmentally friendly.

Good advises are included into previous replies - especially pw-slack proposals for using waste heat. However the physical nature of the problem is still missing. First forget about the oil volume, that has nothing to do with the required heating power. The heating power is dependent from loss of heat by convection (and radiation) from oil tank and oil pipes. Therefore the surface area to ambient air of tank and pipes need to be known (Aconv (in m²)). Next the max. Temperature difference ambient air to required minimum oil temp. needs to be determined (dT (in K)). The heat transfer from oil tank than can be calculated to:

Pconv = ALPHA x Aconv x dT (in W)

ALPHA (in W/(m² K)) is the specific heat transfer from a surface. For a tank made from sheet metal (steel or alu) but without cooling fins you may try a value of about 18 to 24 (for not moving air ==> no forced air/wind streams assumed).

The heating power Pheat needs to be equal or bigger than Pconv ! The relations showing clearly that measures for thermal insulation of the tank would save you a lot of heating power!

It already was mentioned by other participients that the heat from immersed heaters must be selcted carefully not to crack the oil. This really is important - and for gear oil it is more important because often those oils containing additives of low thermal stability. The max. ratio W/cm² of the heater must not exceed 1.2 W/m². With this figure you now can calculate the required Wattage and geometrical size of the oil heaters.

It is highly recommended (for this thick oil especially) to place the heaters in a region where the the oil has a good movement ==> keep the oil streaming through the heater, otherwise the heat is concentrated to the heaters location but not heating the full volume (you may use a pump to get a good oil circulation and heat distribution if there is insufficient streaming of oil).
Heating shall be controlled by a thermostatic switch, limiting the max. temperature.

Hope this will help to get a well heating designed.

Albert

On re-reading your original question, there may be another solution. If you have significant pipe runs from the reservoir to the bearings, it may be feasible to utilise the original lube pump off line and while not operating to lube to pass the gear oil along the pipes and divert through a pressure relief valve (thus generating heat) and bleed back to the reservoir. This will also keep the gear oil moving, the heat fairly evenly distributed and keep oil in the extremities of the system fluid.

I'm not quite sure how to predict the heat generation with this system (given the provided info') although I have seen it used in Penguin country way down south of my location!

If your original lube' system is a fairly low pressure setup, you may need to consider a dedicated pump as the described system requires high pressure to generate worthwhile heat at the PRV.

I think that your ideas are ok, but there is a much better idea that will not require any modifications to your system.

Schaeffer Oil has a product that will flow down to -40 F.

The answer is to change your lubricant. The rep can be located at lubricants@rgreenwald.com (216-401-1845).