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Making a Burner
by Mike Firth Rev. 3/20/95 8/19/95 6/20/96 2006-11-30
If you are just beginning to consider making a burner, please check out Burner Choices before getting too involved with this page.
One well-known way to build a burner with a blower is with a pipe T. I have built 6 or 8 burners with various sized pipe, from 1/4" to 1-1/2" for various purposes. (See below.) I almost always build mine so the gas is injected on one side of the top of the T and the air is blown or sucked in the bottom. I try to build my blown burners so that if the power fails the jet is located so as to suck in enough air - using high pressure propane - to keep a reasonable heat up. This involves moving the intake pipe to the right position during construction. On an unblown burner, the same step must be taken just to make it work. [I was asked where the air comes from, since it seems closed, but when power fails, the valve is open (as shown at right) and thus air enters the intake of the blower, passes through the slots of the squirrel cage and up the pipe. Some kinds of blowers - expensive - would not pass air like this when stopped.]
Here are some specific directions for a full sized burner (like for a glory hole or furnace) using 1-1/2" NPT fittings for the T. The burner is shown on the right side of the glory hole shown below and in an image cut from the photo further down.
The burner is built as a T of the 1-1/2" fittings onto which are added the brass fittings for the gas, the blower adaptors and the feed to the furnace/glory hole. Not all details are shown in the drawing.
Valves Gate valve for 1 1/2" pipe with 3" nipple or wooden substitute (see below) or Valve for 2" PVC
|Dayton blower Model: 4C440 A shaded pole blower 1/125
horsepower, 2-1/8" outlet opening, 60 CFM Free air, 23 CFM
at 0.5" Static Pressure.
Start with the iron T. Drill #19 bit the top of the T to be tapped with a 1/4" bolt thread unless you have another plan for mounting. In the base of the T put a short pipe nipple using ordinary pipe dope or Teflon tape. On one arm of the T place a short nipple (4-6" as space requires) using high temp anti-seize compound which should also be used to connect a 1-1/2" black iron connector or 1-1/2" to 2" adaptor on the burner end of a nipple (if not using a ceramic burner head.) The connector/adaptor acts as a swirl chamber and absorbs some of the heat of the furnace, the joint breaking some of the heat flow, and allowing replacement when damaged.
To start assembly of the gas feed side, screw the 3/4" x
1 1/2" iron adaptor in the other side of the top of the T.
The hole of the 3/4"x3/8"* brass adaptor is sized so
the 1/4" brass pipe slides through perhaps a bit loosely.
The nipple will be soldered or epoxied later. The purpose of the
adaptor is to allow removal of the set with the cap in place.* Drill a #60 hole in the center of the cap from
the inside (per Dudley Giberson). Slide the 1/4" IPS nipple
thru the adaptor and screw the cap and the flare fitting on the
ends. Use pipe dope on the threads; do not use the white Teflon
tape used with water as it isn't rated for gas.
Adjusting the nipple -
Finishing the blower attachment
* I previously recommended using a 1/4" IPT x 3/4" IPT brass adaptor. After attempting to work one of these after losing a useful tool and after pricing large drill bits and taper reamers and after having worked with the burner, I now feel that a slip fit with the larger hole and epoxy rather than braising is a much more economical choice.
** I am experimenting with metal flex tubing used with driers vents, 3" size. More later. [Later: Bad idea. Tubing is fragile - bends, kinks, comes apart.]
ADAPTING A BLOWER
Making a blower fit the pipe can be a challenge. The recommended blower has a flat flange. Similar blowers have a tubular outlet, the wrong size. A scrounged blower may have a square opening, flanged or unflanged. I recommend using a six inch piece of soft pine 2x6 as an adaptor. Check the next section on adding a gate valve. Drill or saw a hole through the wood matching the size of the PVC or the blower outlet ID, which ever is smaller. Then cut part way in the other side to match the larger diameter. If the blower is flanged, screw the blower in place. If it is not flanged, fit it into the opening, Taper the opening with a rasp for best air flow if needed. Use screws inside the outlet, through the sheet metal into the wood to hold the blower, with caulk if needed. Press fit the PVC and use silicone tub caulk (or epoxy) to hold it on the other side of the board.
Wooden Gate Valve
installation will be different. Burners should be fairly firmly mounted,
especially those which have white ceramic heads which are fairly fragile and
should be mounted with a half inch space between the head and the burner port.
My choice of mounts, used on both my furnace and glory hole, is to hang the
burner below a support bar that can be shifted for correct lineup but which is
unlikely to shift in normal use.
Sources: High pressure regulators, high pressure gas hoses,
larger tanks - Most places selling a variety of propane cooking
equipment will have the regulators for the high pressure burners
used with large outdoor cookers. In Dallas, specific places are
Elliott's Hardware (Motor & Maple off I-35) and NW Butane (11551
Harry Hines) the latter carrying the larger tanks as does U-Haul
at I-30 and Furguson.. Note that some high pressure regulators
are not adjustable - fixed at 10 or 12 psi. For future use,
adjustable is nice.
PRESSURE - Three different pressures are involved with propane:
Tank pressure, high pressure regulated and low pressure regulated.
ASME propane tanks are built to 250# working pressure. Under
normal circumstances, the vapor pressure at 100 F is 172 psi."
"Tank Pressure-Unregulated pressure in any size propane tank
or cylinder can range on average from 80 to 250 psi; High
Pressure-Regulates pressure received from tank or cylinder
pressure. Maintains a constant outlet pressure between 8 to
12 psi.; Low Pressure-Regulates pressure received from the high
pressure regulator. Maintains a constant outlet pressure
between 11 to 14 inches of water column. (28 inches=1 psi) "
A standard 20# BBQ tank will freeze up when delivering enough gas to fire a full sized glory hole - either a bigger tank is needed - 100# (pound) is my choice - or a manifold with several tanks on it (at right in an early setup.) Freezing means literally that: when gas expands, it must absorb heat or it cools the remaining gas and tank. In humid conditions, the outside of the tank will be covered with 1/4" or more of ice. In cool conditions this happens faster. The propane does not convert from liquid to gas as quickly with the cooling and pressure drops. With small torch tanks, one will hear of putting the tank in a can of warm water. I have not tried anything to keep the tanks warm.
Propane is sold by the gallon for larger tanks, by the refill for smaller. Look under Propane (and/or Butane) in the Yellow Pages. For serious glassblowers (only in a non-urban environment?) the rate is negotiated with a company that delivers propane and a 250-500 pound tank is installed in the backyard away from the shop and plumbing run. A propane tank truck with a long hose comes somewhere between once a week and once a month (depending on usage) and refills the tank. In this case, the rate for tank rental, placement fee, and cost per gallon are all subject to negotiation. Once usage is proven, a lower rate can be negotiated - one rural glassblower is the highest summer user of propane for the delivery company and is well up the list in the winter.
Q#1: What are examples of high pressure
and low pressure propane. Which is a 20lb bottle on the BBQ
considered to be?
Q#2: What is the size of the gas bottle
you use on the Hole and how long does it last? What is
the cost to refill?
|The larger burner at right must be blower driven because of the location of the gas input [since rebuilt.] It is used with my aluminum melter and was built this way to fit inside the limits of the brick BBQ pit. The blower - attached to the white PVC pipe - and the gas - using the quick connect at a right angle to the T - are located outside and in front of the pit. The elbow in the larger pipe is propped up so the flame enters the side of the melter downward at a 45º angle. By using high temp anti-seize compound, I am able to keep the last nipple and flared piece removable so a nipple only can be installed for heating in the Fire Hole. The smaller burner uses a tiny copper tube and pipe cap with a drilled hole to make a small pre-heater burner, mostly for drying and preheating the glory hole sitting outside. A burner in between these two in size has also been used for preheating and for maintaining heat for cooking in the BBQ pit, where it is set on low flame and put through a hole in the bricks in the bottom of the back wall.|
--- In glassblowing_topics@y..., fsankar10@h... wrote:
> Mike how did you know how far to slide in the brass
nipple and why
Drill Bits- Drill bits come in two sets of sizes in the United States measure - fractional sizes and number/letter sizes also called wire sizes. Fractional drill bits are available in various materials in steps as small as 1/64" (0.015625") Number/letter size drills are based on holes in a plate matching dies for wire - gauges - originally. Today, the letter size are much less used than the number size because they overlap the fractional bits, while the number bits get much smaller than fractional drill bits. Click for a complete table The smallest bit I have seen in a good store is a #80 (0.0135 inch) while the table shows down to a #97 (0.0059") and a metric 0.010mm (0.0040). The #80 is so fine it will think about breaking if you look at it.:-) 1/64" is 0.015625" and is slightly smaller than a #78 bit (0.0160"). Lightweight aluminum foil is about 0.011mm or 0.0043". Most of the smaller bits will not fit in a standard chuck and require a pin vise or similar add-on chuck. Please note that wire size drills are NOT regularly spaced in their diameter - there is 0.0015" difference from an #80 to a #79 while only 0.0010" from a #79 to a #78 so even the difference varies.
Pipe Sizes Link
This page talks about home building burners. There are several ways of making burners which are more complicated and therefore are only for buying or for dedicated machinists.
VENTURI - A venturi burner uses a wasp waist shape to suck in air with high pressure gas providing the power - in other words it is a quality version of what is shown above. Of the greatest importance is that the air flow is much more proportional to the gas flow than the simple T pipe burner - increasing the gas flow increases the air flow while coming reasonably close to maintaining a constant proportion. The disadvantages of a venturi is that there are limits to its range - too little gas and no air is sucked in and too much gas means not enough air can fit through the throat. The biggest advantage is that it requires no electric power - as long as the gas flows, the flame will exist.
RIBBON - This is a term that is used for two different
burners, unfortunately. The older use of the term is for a shape
not unlike a pipe with a lot of holes drilled in one side. A
mixer sends a gas/air mix down the pipe and out the holes. In
tamer form these are used for heating BBQ's, ovens, etc. It
hotshot forms, it is used for softening a length of tubing for
bending in neon work.
RECUPERATIVE - Here the fuel is injected into the preheated air at the last instant, so the total design must reflect that fact. In a recuperative design, the exhaust gases of the furnace heat the incoming air either directly by having the outgoing passages and the incoming passages closely aligned and the air separated from the exhaust by pipe walls or panels that will withstand the heat or indirectly by having two piles of refractory heat storage (fire bricks) one of which is heated by the exhaust while incoming air passed over the previously heated other one - periodically the flows are exchanged. The former is more commonly used on small studio furnaces, the latter on very large industrial glass melters. The fuel is added to the heated air, which may be 500F degrees or more, just at the last moment in an all refractory nozzle, the air being driven by blowers located on the cool input side of the recuperative unit. 2005-12-16
BURNER TUNING Notes
What happens if the pressure is too low for the size of the
burner is that the flame works it way back down the list, trying
to burn inside the pipe, etc. That is the pop pop. When you
turned up the pressure and the flame moved out of the pipe, it
was far enough out that it did not overheat the tip - no redness, lower noise.
BURNER BOOK REVIEW
I have been sent a book on burners [Gas Burners for Forges, Furnaces, & Kilns, Michael Porter, Skipjack Press, Ocean Pines MD 2004, ISBN 1-879535203] to review. My overall reaction was positive at first, but I am rather more neutral on further reading. It took me a while to figure what was going on. At first I thought it gets a bit too focused on the particular design promoted in the book, which is built around using predrilled MIG and torch welding tips to produce a long narrow nozzle point.
After rereading, I found that the structure hides confusion. There is a good drawing of parts and the whole and a complete numbered parts list with matching numbers on the drawing. But as construction develops, it turns out that two parts have the same number and most parts have three names - the piece name (MIG tip), the group name within the burner (adjustable tip) and the major subpart within the burner (accelerator). Because a part number is assigned to the first name - we can have a sentence like this on page 42 "Screw the second contact tip into the other inverted female nut." Because the female nuts are assigned part 13, there is no good way of telling them apart, although they end up looking different after grinding.
Part of being too focused is failing to describe burners to begin with. My father used to teach experienced workers how to be teachers of their skill to new workers and one exercise he did was to take the teacher through the process of getting up, going to the door, and turning the handle - but doing it step-by-step without telling in advance what the overall goal was to be. Most adults want to fit their learning into their previous experience, so they want a framework or outline of the subject. This book launches with a description of some complicated parts without sketching the system they fit in.
Beginning with safety is a good idea and starting with a hand torch that can be used to build the other burners and, with a temporary mount, can be used to build itself is a terrific sequence. I see nothing wrong with the burner design although the fact that the orifices must each be built from scratch and can not easily be drilled out means the design must be taken on faith. While the use of a long thin tapering orifice clearly would increase the pickup of air, I do question the importance the designer places on gas flow inside the nozzles.
Chapter 1 is Safety, Chapter 2 is The Burner System and Its Fuel and Chapter 3 is Building the 1/2-inch Burner. (In total, there are 12 chapters, footnotes, glossary, resources and index.) Logically, one would expect Chapter 2 to draw the image of a burner system, mention the variations, and then go into the details. It just goes into the details and is very good at them. But I am sure someone with less experience with burners is going to be bewildered. It is not even clear what the shape of the burners in this book is going to be, much less how they fit in the design patterns of other burners a novice or intermediate equipment builder might have seen.
Throughout the book, the author pays good attention to safety, making it clear why propane tanks - which are used as shells for several of the projects - must be treated with considerable care while opening them up.
All of the burners in the book are high pressure propane, induced air flow, burners. Chapters 2, 3, 4, 7 & 8 are each devoted to the detailed steps of building gradually increasing burners based on the nominal pipe size - 1/2 to 1-1/4 inch. They cover every single piece needed and how it is drilled and assembled with good drawings and alternative choices in some cases. Some of the parts are specialized and it will certainly help to use the resources given, have a terrific junk bin, or know people who have cutoff pieces.
Chapters 5, 6, 9, 10, and 11 are devoted to equipment that can use the burners, starting with a forge (burner aimed down at a kiln shelf), then a forge cart (burner aimed up), a foundry furnace (aimed horizontally), a farrier's forge (smaller) and a glass furnace (a small unit that I have problems with.) Chapter 12 covers braising. Among the differences between the units is how various combinations of ceramic fiber, castable refractory, and Perlite enhanced refractory are used, with good and given reasons for doing so. Depending on the intensity of the flame and heat, the fiber is, in various units, rigidized, and coated. The author really likes ITC #100, but as far as I could find, never explains what it is, although on page 121, in a parts list it is finally described as "infrared reflective coating". It is, in fact, a fairly new product that has been discussed on glass forums with some question as to how well it works. The book does mention that it is expensive.
Considering the detail the author goes into (for example, reminding us to dry off a retractable measuring tape after using it as a dip stick to measure water depth in a tank), I am particularly bothered by the design of the foundry furnace. The lid hinge is built with one long arm that extends beyond the pivot bolt. In a caption for a picture of the shape of the parts, it is stated "It is not safe to use this extended hinge tab for a handle." Considering how much the lid is going to weigh, I would agree with that. But for the entire life of the unit, the long tab is going to be sticking out the back - what is its use? I expected it would be part of stop to keep the lid from falling back or a point to hang a counterweight. In fact, its only purpose is to hold a short length of chain with a pin on the end, keeping the pin far enough from the furnace to keep it cool. The pin is used to hold the lid open angled over the lower pot. So every time the furnace is to be accessed, someone is going to have to lift the lid, reach around under the hot lid, get the pin and put it in the holes in the hinge and later reach under the lid again to pull the lid out. I would have been much happier with a design that built a stop into the hinge design so that it could be opened from the front, not go too far and rest open. The author likes that the pin allows the lid to be tilted over the hot chamber.
The glass furnace design begins with the disclaimer that using a home made burner for a glass furnace is folly because it would not pass inspection so this is really a small foundry and glory hole. In fact, the burner design has little to do with inspection - the gas train, which is covered back in chapter 2, being more important. The other furnaces seem to be more based on experience, being mostly simple straight forward designs, while this one is complicated - pivoting in its frame with an expectation that for some uses, the frame will be filled with Perlite that will be removed for other uses. Sorry, but I think a design like my Fire Hole, with a rectangular frame around it so it can be set upright or horizontal is much easier than the pivot axle arrangement.
As I look at the burner designs in review, the burners seem pretty fragile across the air intake slots - there is a fair amount of weight hanging off the intake on thin metal supports. There are, in fact, warnings about torqueing the area when making connections. Since my blower based burners are working reasonably well, I don't know if working through one of the designs is something I want to do just to possibly disprove my doubts. 2004-03-29
Contact Mike Firth