A charcoal-fired lance to burn in a roll up stove pipe

This post is about using a charcoal-fired lance to change the shape memory or burn-in or heat treat roll up stove pipes. It is an improvement on my previous alcohol and gas flame lances that have been described in other posts. It has the power to rapidly treat large-diameter stove pipes.

Note: This is just part of a 12 part series on improved stove pipe rolling. You may wish to start at Part 1 to taste from the banquet.

Introduction

Alcohol and gas lance

I have previous posts on a rather feeble alcohol flame lance and then in a subsequent post on a more powerful gas flame lance. These methods were suitable for pipes with small diameters in the range 35-40mm and became rather pathetic for a 50mm pipe. So a stronger source of heat was required for the task with a 60+ mm diameter pipe, particularly when it was 3,000mm long.

Stove pipe Draft

The draft in a flue pipe is essential to supply oxygen to the alcohol and gas flame techniques. However, it becomes counterproductive as the stove pipe becomes hotter and or longer. It pulls the flame and heat away from the zone or band of pipe that should be being heat treated. This means that a better heat source would be one that did not depend on either the stove pipe draft or flame.

Charcoal

In the title of this post, I have slipped in the word ‘fired’ in place of ‘flame’. This because of the unique property of charcoal combustion with a forced-air input. There is a minimal flame, and instead, there is the intense heat that is directly radiated from the 1,000C charcoal surface.

I found out that such heat, if continued for a long time, could be very destructive to stove metal, as shown below. I figured that, sooner or later, my bowerbird brain would find a practical use for such a powerful localised source of heat (Apart from firing my ceramics).

In this post, I demonstrate that with appropriate management the radiant heat from forced-air charcoal combustion could rapidly heat treat successive small bands of the flue pipe as it was steadily passed through the pipe.

Why heat treat?

I describe the reasons for using heat memory forming, various method of doing it and their limitations elswhere. In short, it makes the metal in a virgin roll of stove pipe foil ‘remember’ its new stove pipe shape. This in turn makes it easier to deploy while camping.

In this post, I describe a larger charcoal-fired lance that uses air pumped in from a USB fire blower to achieve high temperatures.

My green credentials have been battered by admitting that I cleanly burn tiny slivers of plastic as fire starters, so using charcoal (from fallen sticks) instead of alcohol or gas should lift them a little.

Here is another obligatory ode to fuel selection for this special heat treatment task;

Fuel for the whole length of a flue pipe to heat treat,
A tiny round mobile intense source of heat, 
A fuel that is clean, cheap, natural and green,
Charcoal and forced air will be hard to beat.

Method

A simple source of intense heat

In my stove posts, I extol the wonders of blower stoves and my USB fire blower. They make a simple and potent source of heat from almost any organic material.

Destructive heat put to good use

In the above posts, I also caution about the extremely high and destructive temperatures that can occur when mainly charcoal is burnt with a fire blower. “The burn is delightfully hot, but in the long term it would be destructive to the stove metal.”

Charcoal provides localised heat

The intense heat from charcoal combustion with forced air is concentrated in a narrow band where the air first impacts the charcoal. With very little actual flame, there is little heat transported away as with an alcohol, gas or wood flame. From the colour of the wall of the charcoal-burner, when related to the chart below, the temperature would be exceeding 1000C. This should be more than sufficient to heat treat a flue pipe.

The charcoal burner

I decided that a cylindrical charcoal burner with a localised band of intense heating could be excellent for heat-treating a stove pipe. The burner could fit closely within the flue pipe. It could be passed slowly up through the pipe, just like the gas flame lance. However, air would be pumped up through the supporting pipework instead of gas. This lance would no longer require a natural convected source of air from below. Also, the heat intensity would be largely unaffected by the stove pipe draft.

[Add a nighttime photo of the charcoal lance burning brightly— use this as the featured image when ready]

Note: It is interesting to think that if a charge of wood sticks were used as fuel in the same burner, the whole load would start to combust with a big flame and eventually with a lot of unburnt smoke. By contrast, with only charcoal as the fuel, the combustion is intense but limited to a small band. It does not advance up through the waiting charcoal reserve. This is because the combustion in the lowest layer used up all the available oxygen in the air stream. Instead, the lowest layer of charcoal must burn away before more charcoal can move down into the combustion zone. “It makes an ideal steady-state source of intense heat. There is no significant smoke and the rate of combustion is limited by the air pumping rate.”

I made another lance for my KISS Stove stove pipe that is only 37mm in diameter. The slender lance is shown in the photo below.

Results and discussion

Two-step heat treatment

The pipe was treated in two steps. In step1, it was treated from one end to the midpoint. In step 2 the process was repeated from the other end.

Step 1. In the first step, the prototype lance was made of stainless steel. It had a diameter that was just a little too large. This meant that when it got very hot and expanded (As stainless steel does), it was difficult to move steadily through the pipe. This resulted in more heat treatment than was necessary (darker colouration at the far end of the photo).

Step 2. For the second step, I made a new burner with a slightly smaller diameter. I used ‘bean can’ tin-plate that has a much smaller thermal expansion coefficient than the stainless steel of the prior burner. This meant that it could be easily passed up through the pipe without getting stuck. This provided for easy movement and more moderate and calibrated heat treatment.

A 6.15mm diameter*3,000mm long flue pipe was the first one to be heat treated with the charcoal-fire lance (photo below).

The section treated in step 2 has a pale copper/gold colouration (On the half of the stove pipe closest to the camera). As this colour developed on the surface of the pipe, it indicated that the lance could be advanced to treat the next section of the pipe.

Conclusion

The loose-fitting charcoal-fired lance can provide a powerful heat source that can conveniently, uniformly and quickly heat treat long stove pipes with diameters in the range 37- 60mm.

The charcoal-lance has the unique advantage of being unaffected by the strong draft that would otherwise develop while using alcohol or gas lances to do the same task. This becomes increasingly important as stove pipe length is increased.

It is a significant improvement on the alcohol and gas flame lances and I expect that customized charcoal lances probably could be used to more effectively heat treat stove pipes of any diameter or length.

Lastly, my green credentials can be recovered a little more because the successful lance was made from a discarded tent poles (from curb-side rubbish, a baked-bean can and was fuelled with charcoal from waste sticks.

Tim

Addendum 1- An improved charcoal lance holder

Initially, found that handling a hot stove pipe with thick leather gloves provided inadequate protection for my hands. This was particularly the case while withdrawing the lance when the bottom half of the pipe was very hot.

Consequently, I made an insulated pipe holder for the bottom of the pipe and a second ring holder to control the tilt of the pipe. This little refinement made it easy to safely manipulate the very hot pipe to provide nice even heat treatment. I could carefully observe the gentle change of colour of the pipe to determine when to advance the lance. A feint release of smoke from the surface of the hot pipe also coincided with the development of the feint copper/gold colour.

Given that the insulated holding tools made the task much more relaxed and easy, I used the opportunity to give the pipe a second heat treatment while steadily withdrawing the lance.

“There was no smoke from the surface while withdrawing the lance. I think the smoke was coming from the organic component of my fingerprints that I had left on the pipe. The prints became visible to me only when the pipe surface got up to the combustion temperature of organic matter. I presume that it was the trace of residual sweat ash that revealed my prints. There was nothing combustible left on the pipe to make smoke during the withdrawal of the lance”

Tim