Crucibles,Great prices/lighting a gas furnace

[tool_man]

Need a crucible?Go to Mifco.They have the best prices I have seen.I ordered 2/#16 silicon carbide crucibles for $78 each.Be prepared to wait at least 3 weeks for delivery.Salesman told me they go out as fast as they receive them.With those prices I can understand why.Also they are having problems with the web site.Better to look up what you need and give them a call.
I bought a Johnson model 900 crucible furnace recently.It is ready to go.Problem is that I don't have an insruction manual.The guy that owned it before me said that he singed his eyebrows when he tried to light it.Didn't ask any questions as to the proceedure he used.The following is the proceedure I plan to use.Any suggestions are welcome.
1.Place 2 layers of cardboard on the bottom of the furnace even though I will be using a steel crucible.My reasoning is that the burning cardboard should sustain a flame until the furnace is hot enough to sustain the flame.
2.place crucible in the center of the furnace and close the lid.
3.turn on the blower at minimum speed.
4.hold the ignition switch in while slowly opening the gas valve.
5.when it lights...release ignition switch.If it doesn't stay lit,shut off the gas and wait a few minutes for the blower to purge the furnace.Start over again.
This furnace has a momentary contact,pushbutton switch for the ignitor.Should I replace it with a toggle switch?I am not afraid of this furnace.Just want to be safe and make sure I touch all the bases.

[Kipper]

From what I understand of your post (written words never really convey our exact meaning) you are using gas and need to ignite it and sustain a flame without toasting yourself..imo gas is very easy to ignite and sustain a flame with from my playing with gas my procedure was as follows.
1: turn on fan
2: turn on gas (then immediately if not simulataneus No3 )
3: press ignition...and all with the lid off!
A few questions..Is this an electonic ignition furnace ie does it have piezo type ignitor? or do you have to drop an oily rag or some such in to enable it to heat the walls sufficient to maintain combustion?

[tool_man]

The ignitor is a high voltage transformer with a spark plug.When the main power switch is turned on,the blower starts.There is a potentiometer to control the blower speed.The high voltage transformer is energized by depressing a pushbutton switch connected to the primary of the transformer.The ignitor will stay on as long as the button is held in.From the sound of it,the ignitor plug is really putting out a hot arc.Sounds like a swarm of angry bees.I have no doubt it will instantly light the gas.My concern is keeping the flame going until the furnace reaches a temperature that sustains the flame without having to hold the switch in for a long period of time.You would recommend leaving the lid open while lighting the furnace?You may be right on that point.Not sure.I am going to e-mail Johnson Gas Appliance and see if they will send me an owners manual for the model 900 crucible furnace.I think I will pick up a face shield also.Thank you for your input.

[Kipper]

See if you can find some foundry gloves (heat resistant) I touched the molten Aluminium today accidentally and they saved my bacon...Take care as Al just loves to stick to you good boots pants and a leather apron are all nice things to have.... Stay safe and enjoy matey imho it's a great addition to any shop.

[tool_man]

Good advice.Before I sart casting,I will have all the necessary safety gear.Including a respirator,which I believe everyone should consider.Especially when melting brass.I understand that safety equiptment is expensive but,when you consider what could happen to you if something goes wrong,the cost is insignificant.

[jphagen]

Normaly, a commercial unit will have a flame safeguard control.
It first proves that the blower is running, next starts the ignitor and then
opens the gas valve. It then detects the flame and keeps the gas valve open,
if no flame is detected within 3 sec. it will shut down the gas valve and purge the unit. Some on flame failure after the purge it will try again, others lock out and need a manual reset.
Allmost all of the commercial units keep the ignitor (spark type) going during
the burn cycle.

[tool_man]

Johnson Gas Appliance offers flame control units with a U.V. flame detector for their units but,they are very expensive.Better to keep things simple on a small furnace.When I am ready to cast my parts,everything should be ready.I should have nothing to do but to watch the furnace.If I were to add anything more,I think I would rather have the built in pyrometer.