Used-en­gine-oil burner

The Shed - - Make a forge - Of

After see­ing the Ja­panese forge run­ning on used en­gine oil I was very keen to try my ver­sion of it on this lit­tle forge. The prin­ci­ple was very sim­ple. If you spray oil into a hot forge it will burn very well with­out any smoke or smell. I found that a litre of diesel in four litres of used en­gine oil made it run much bet­ter than just straight en­gine oil (Im­age A).

The oil spray is made us­ing two 0.9 mm MIG-weld­ing tips (B). The fixed bot­tom one is the oil sup­ply, which goes into a four-litre con­tainer of used en­gine oil. The top tip blows com­pressed air across the oil tip cre­at­ing a vac­uum that sucks the oil up from the con­tainer. It is ad­justed by the screw so that the dis­tance from the bot­tom tip can be var­ied. By rais­ing or low­er­ing the tip, more or less oil is put into the fur­nace and this con­trols the heat. I ran it on about 20psi of air pres­sure but it will take more if re­quired.

The se­cret to get­ting a clean burn from the start is to en­sure that the fur­nace is hot be­fore in­tro­duc­ing the oil spray, so I mounted a small home-made LPG burner on the side of the oil burner. I used the same jet assem­bly as I used in the forge in a much smaller burner tube. The burner tube is 12mm ID with a sheet­metal flare on the end (C–E). Easyflo was used to fix it in place. Four 6mm holes were drilled in the pipe for air to mix with the gas.

When the fur­nace is hot the air to the oil burner is turned on and the gas burner can be turned off.

It is a lit­tle bit tricky to get the air and oil noz­zles in the cor­rect po­si­tion for good suc­tion but once ev­ery­thing is ad­justed it works well. You can watch a video of it op­er­at­ing on The Shed web­site. A friend in Australia has the forge now. He is us­ing it to heat up rail­road spikes to make into knives. Prior to get­ting the oil-burn­ing forge he was us­ing LPG but was find­ing it just too ex­pen­sive.

flare ta­per in the brick. The gap around the burner should be packed with some Kaowool to pre­vent air en­ter­ing (40).

Open up the front and rear forge doors. Im­por­tant: Al­ways do this be­fore light­ing!

Close up the choke till it is just level with the top of the in­take re­ducer, turn on the gas slightly, and light the fur­nace us­ing a bar­be­cue spark ig­niter.

The burner should now be run­ning with a very soft yel­low/blue flame. Care­fully ad­just the choke to ad­mit more air un­til the flame is a strong blue colour. To min­i­mize scale for­ma­tion on steel it is im­por­tant to have a neu­tral flame run­ning in the forge (41). We have mea­sured the in­ter­nal tem­per­a­ture of the forge after run­ning for 10 min­utes at 1300°C (42). I mounted the forge on a mo­bile stand made out of some old Dex­ion an­gle fram­ing that I had ly­ing about.

Cylin­dri­cal forge run­ning on used en­gine oil

The cylin­dri­cal forge that I made uses the in­te­rior steel cas­ing from an old mains pres­sure wa­ter cylin­der. The steel cas­ing is 3mm steel plate with a glazed lin­ing. The first job is to re­move the outer sheet-metal skin off the cylin­der to ex­pose the in­su­la­tion (43).

If you are lucky you may strike one that has loose glass-fi­bre in­su­la­tion, which is easy to re­move. If not you may get one that has ex­panded polyuretha­ne foam in­su­la­tion, which will take a lot more work to get off. In any case a dust mask should be worn while re­mov­ing it. The cylin­der I had had a 300mm di­am­e­ter in­ter­nal steel cas­ing. Us­ing a cut­ting disc in an an­gle grinder, I re­moved the top and bot­tom to give me a 400mm long cylin­der (44).

I cut and welded four 50x50x6mm an­gle-iron feet to the cylin­der and also welded four lengths of ½-inch wa­ter pipe in­ter­nally. These func­tion as guides for the ex­tend­able 12mm re­bar work rest (45).

In the side of the cylin­der, about 100mm down from the cen­tre line, I cut an 80x80mm square hole. This is where the gas or used-en­gine-oil burner will en­ter.

In­su­la­tion

The cylin­der is now ready for in­stalling the in­su­la­tion. I used 25mm thick Kaowool and 25mm thick high­tem­per­a­ture light­weight in­su­lat­ing board. ‘Kaowool’ is a ce­ramic fi­bre in­su­la­tion ca­pa­ble of with­stand­ing more than 1200°C. Kaowool is not con­sid­ered to be haz­ardous but a dust mask should be used when han­dling it.

I first cut some of the in­su­la­tion board to fit be­tween the wa­ter pipe. The pur­pose of that was to give sup­port to the in­su­lat­ing board that was go­ing to serve as the floor of the forge. The spa­ces be­tween the sup­ports were filled with Kaowool (46).

When that was done a larger piece of in­su­lat­ing board for the floor was cut and fitted. I se­cured it by weld­ing four tabs on to the forge wall (47).

With the base in place the Kaowool could then be in­stalled. By care­fully cut­ting it to length it was self­sup­port­ing when pushed into place against the floor. I put in two lay­ers to give 50mm of in­su­la­tion, which left

me with ap­prox­i­mately 200mm in­ter­nal di­am­e­ter (48).

A 60mm di­am­e­ter hole was cut in the Kaowool for the gas/oil burner port.

If Kaowool is ex­posed to the di­rect flame of a burner it will erode away, re­leas­ing fi­bres into the at­mos­phere, so it must be coated with a re­frac­tory to pre­vent that hap­pen­ing. I got what is known as a ‘rigidizer’ from the sup­plier of the Kaowool. This is a col­loidal sil­ica com­pound that you paint onto the Kaowool. When it dries and is hard­ened with the heat of the fur­nace, it puts a thin, eggshell-like coat­ing on the sur­face.

A 12mm re­bar han­dle was made and welded to the body of the forge. The end walls were made from the light­weight in­su­lat­ing board fixed to 12mm re­bar. These were made adjustable so that the right gap could be de­ter­mined to pre­vent the burn­ers from be­ing re­stricted (49).

The work rest was bent up from 12mm re­bar. I did not in­stall a lock­ing screw be­cause fric­tion be­tween the bar and pipe was suf­fi­cient to hold it in place.

A 100mm long x 12mm re­bar rod was welded to the side of the forge for mount­ing the burn­ers.

At the Hal­swell Men­zshed we have a num­ber of en­thu­si­as­tic knife mak­ers. Ian has made a forge that uses two LPG gas burn­ers, and we have also ex­per­i­mented with us­ing diesel to fire a forge. It ran very hot but the noise level was over 100dBA (50).

An­other mem­ber, Ross, has pro­duced a num­ber of knives and his fur­nace is a very sim­ple pile of bricks that he quickly as­sem­bles and dis­man­tles as re­quired. He uses an LPG weed burner for heat. He has pro­duced knives from old files beaten into shape and care­fully ground while oth­ers are made from old hand shears (51).

With the new brick forge up and run­ning, I sus­pect that we will see a lot more cre­ative knife-mak­ing in the shed.

‘Kaowool’ is a ce­ramic fi­bre in­su­la­tion ca­pa­ble of with­stand­ing more than 1200°C

A I found that a litre of diesel in 4 litres of used en­gine oil made it run much bet­ter than just straight en­gine oil

C–E: The se­cret to get­ting a clean burn from the start is to en­sure that the fur­nace is hot be­fore in­tro­duc­ing the oil spray, so I mount a small home­made LPG burner on the side of the oil burner E

B The oil spray is made us­ing two 0.9 mm MIG-weld­ing tips

C

D

42 We mea­sure the in­ter­nal tem­per­a­ture of the forge at 1300°C after run­ning it for 10 min­utes

40 The gap around the burner should be packed with some Kaowool to pre­vent air en­ter­ing

41 To min­i­mize scale for­ma­tion on steel it is im­por­tant to have a neu­tral flame run­ning in the forge

43 The first job is to re­move the outer sheet-metal skin of the cylin­der to ex­pose the in­su­la­tion

44 I re­moved the top and bot­tom to give me a 400mm long cylin­der

45 These func­tion as guides for the ex­tend­able 12mm re­bar work rest

49 The end walls are made from the light­weight in­su­lat­ing board fixed to 12mm re­bar

46 The spa­ces be­tween the sup­ports are filled with Kaowool

47 I se­cure it by weld­ing four tabs onto the forge wall

48 Two lay­ers in place to give 50mm of in­su­la­tion

50 This diesel-fired forge runs very hot with its noise level over 100dBA! Ear muffs will be re­quired

Knives made from old hand shears and files 51

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