Clinkers - Two Questions

[slowpoke]

Question #1 - Why is it that clinkers impair the process of forge welding? Air blockage? Heat sink? Other?

Question #2 - What are the better methods of fire management to reduce clinkers (besides coal quality).

Thanks.
Slowpoke

[Mr Smith]

My understanding is they are both a heat sink and a source of impurities.

[Randy]

Question #1 - Why is it that clinkers impair the process of forge welding? Air blockage? Heat sink? Other?

Answer: Yes, air blockage. No air, no heat. Think of it this way, oxygen, air, is part of your fuel. Not so much heat sink. Other: dirt. Dirty fires are harder to weld in.

Question #2 - What are the better methods of fire management to reduce clinkers (besides coal quality).

Answer: When you get ready to weld stop your blower for a couple of minutes to let the fire die down. Then go in for your clinker. The clinker will drop to the bottom of the fire box and solidifies with surounding clinker so is easier to remove. It also darkens faster and darker than the fire so it's easier to see it to get it out of there. Once the clinker is out open up your trap door on the tuyere to let ash and clinker fines out so you don't blow it back into the fire. Then close the trap door, start your blower again and do your weld.

Experiment with your coal. Some coals clinker worse when wet. If that's the case use less water to control the fire.

[Mr Smith]

Randy - would you say the same applies to charcoal?

[Frank Turley]

Clinker is formed of earthy matter that is entrained in the coal. It exudes and can be somewhat gooey. In a bottom blast forge, it coagulates and being heavier than coke, it wants to settle by gravity toward the bottom of the fire pot. The clinker is glowing hot, but being non combustible, it doesn't contribute as a fuel. It can chill the blast a little, since the blast contacts clinker before it contacts coke. It can obstruct the tuyere. Bits of clinker may be blown up through the fire and stick to your workpieces.

With very dirty coal, it is best to take the entire fire apart. Shovel the fire onto the hearth and begin sorting and flushing. Sometimes you can begin a new fire with the still glowing coke. It the coal is fairly clean, you can use your clinker breaker, but it helps to lift your fire away from the tuyere with a straight poker and shake the fire a little. as you do this. Sometimes, you can shovel about one half of the fire pot contents (coke) onto the hearth and withdraw clinker with a small hook-ended poker or a long "wienie fork."

If you're going to do serious fire welding, it is best to remove the fire from the pot completely and rebuild after cleaning.

Post Script. Two other terrible coal fires are fly ash fires and hollow fires. Fly ash should be got rid of before building a fire. A hollow fire is one that looks good on top but the center has burned away. This creates an oxidizing fire causing much scale. It is not just clinker that interferes with forge welding.

[FieryFurnace]

Question #1 - Why is it that clinkers impair the process of forge welding? Air blockage? Heat sink? Other?

Clinkers don't burn!
When you are forge welding you want what is referred to as a "reducing" fire. At the bottom of the firepot, there is a large amount of air being forced into the forge. Air produces oxidation and oxidation reduces the likelyhood of successfull welding. The bottom of the firepot is an oxidizing fire. You don't want your metal stuck down in the bottom of the firepot.
At the top of the firepot, air is being pulled in by burning coal. This is again an oxidizing fire. You don't want your metal laying on top of the fire because there is too much air.
Typically, the metal is put in the center of the fire. Here is the reducing fire where the oxygen has been burned up and is no longer oxidizing the metal.
How does this tie into clinkers? I began with "clinkers do not burn." A huge chunk of clinker in the bottom of the firepot is not using any of the oxygen being supplied by the blower. That oxygen makes it up into the center of the pot, creating an oxidizing fire where it is supposed to be a reducing fire. That's why you can weld with small clinkers in the fire. Typically a large chunky clinker in the bottom of the fire will make welding more difficult though.

Question #2 - What are the better methods of fire management to reduce clinkers (besides coal quality).

When you tear down your fire after work, simply rake the good coke off the top and let it cool from there. Don't dig down in your firepot and scatter everything on the hearth. You'll end up mixing ALL your clinker and ash with the good fuel. If you rake the good stuff off and leave the bad stuff alone in the bottom of the firepot, then the next morning you can sift out the ash by hand, and pick all of the clinkers out in chunks not pieces. For the most part, ash and clinkers are the only thing left. A good clean, ashless fire, made from the previous fire's coke, is your best bet.
Do your forge welding in the morning. If I am forging all day long, my best welds are before lunch. The fire still has a low ash content, and no large clinker chunks. If I need to do some afternoon welding, I dig through the fire very thoroughly to remove as much clinker and ash as possible.

[yesteryearforge]

coagulates
I love it when y'all use big words

[ThomasPowers]

Trying to save too much of the lower contents of the firepot is bad economy; often there is a lot of small bits of clinker mixed in that will speed up problems when restarting.

I tend to dump the bottom stuff and let it cool and pick out major chunks of coke and let the rest gravel my drive.

[John B]

Clinkers has been well covered, With regards to fire management, as an observation from watching many smiths using many different types of fuel, and as a generalisation, the ones who have most problems with producing clinkers, ( and having to wire brush their workpieces when removing them from the fire,) are the ones who have what I would regard as having

An excessive air blast,

Load new fuel directly into the working fire, a particular problem with the inexperienced.

Excessively disturbing the fire when replacing and reheating the workpiece in the fire.

This applies to most commonly used fuels, whether used in side blown or bottom blown forges

[SReynolds]

There is a youtube video demonstarating the use of clinkers to START a forge fire.

There is a ferrier supply website w/demmos that clearly demonstrate wire brushing the workpiece (horse shoe) each time it is removed from the fire. I have never done that because I never really understood why you'd have to.

[clinton]

Use clinker to start a fire? I would like to see that, just because it is on youtube does not mean its right

[slowpoke]

Thanks so much to everyone for the info. Frank, thanks for the tip on the fly ash & the hollow fires. And Dave - good point on the clinkers changing the location of the reducing/neutral work area for good forge welding. Loving learning every day...