Resurrection of a CFEI 100 KVA Induction Furnace

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awemawson:
Matthew I think that you are entirely correct - diesel HAS to have some lubricity otherwise the injector pump would sieze up, and this is why 'certain travelling folk' add oil to stolen central heating oils as it's "slipperyness" is much less.

Pekka, the oil 'should' remain at ambient temperatures when in use (barring disasters :bugeye:) so it's viscosity isn't going to decrease sadly. All my farming equipment uses ISO32 as it's rare that we get very hot here.

This morning I drained down the oil / red diesel mixture and re-filled with neat red diesel. Timing the rise (pour time) it is now at 18 seconds which is about acceptable but I'd still prefer to be able to set it a bit faster.

Obviously this is as fast as I'm going to get without either:

a/ Raising system pressure (a pain as it uses my air distribution system common to many machines)

b/ Increasing hose bore

c/ Finding an incompressable medium more fluid than Red Diesel (unlikely)

PekkaNF:
OK. Because that system has no pumps, tanks, filters etc. there is no real reason to use hydraulic oil. Unless there is no special seal/hose/componenet reason you could go down to 5W straight/mineral transmission oil. Multigrade engine oils has allready many (unnecessay on this one) additives, and the car 5W-something oils actually have higher viscosity than VG32 hydraulic oil at room temperature.

https://www.engineeringtoolbox.com/iso-vg-grade-d_1206.html

There noteworthy thing is viscosity at +40C, different grades are defined very different ways. They don't compare in simple relationship.

There are very low viscosity oils, but they are a bit special and have their own issues. Hard to get lower than that mineral base oils...needs to check too many variables....hydraulic system might work with PAO-base oils too. But where to get them in cosumer market? And they suck at fire resistance :doh:

https://www.machinerylubrication.com/Read/31106/polyalphaolefin-pao-lubricants

Interesting problem.

awemawson:
Yes it has all sorts of ramifications Pekka. For instance the exhaust port silencer now puts out quite a bit of diesel vapour as the cylinders are discharged, so much so that I've put a plastic cup under it to catch the drips.

Obviously is not viable when actually pouring molten metals instead of testing. I am tempted to go back to 'straight air' and drain the reservoir again. I originally went to 'air over oil' as I was getting rather too much bounce with just air, but maybe if I throttle it back it'll be OK? -

. . . I'll experiment if time permits tomorrow.

John Rudd:
Dnot wishing to teach grany etc. etc.
If operating speed is an issue whether pneumatic or hydraulic, cant you use speed restrictors to increase the operating time?

PekkaNF:
Air tends to be bouncier than incompressive liquid...I understand the merit of the air-over-liquid, liquid throttless nicer.

I wonder if a simple viscous damper would work in addition of the orginal air system? But it involves additional mounting poins, a little calculation and experiment. Also it probably does not not work equally well with min/max loads.

I never used waterbased hydraulics...apparently algae growth is a problen there, glycol coolat based might work, but that one too needs special seals. I would use the original system with air and add separate damper cylinder with liquid throttling or viscous damper.

We used once a system that had two hydraulic cylinders to perform same "swing" because the weight sifted "over the centre" of the gravity. Simplest form was to laod one cylinder (one side) with a constat pressure to prevent load from sifting direction at the middle of the stroke (that would produce a major jolt). There are load lowering valves etc...but each solution has it's own set of problems.

I have seen very well dampened pneumatic systems, but they had servos....

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