MODEL BOILERS - John-Tom

1 MODEL BOILERS . A booklet devoted to the construction of Get stampings rather than castings, as the MODEL BOILERS may well open with a few first are more homogeneous, and therefore cautionary words, as the dangers connected can be somewhat lighter. with steam-raisers are very real; and though Flanging boiler Ends MODEL - boiler explosions are fortunately rare, if they do occur they may be extremely To make a good job, a plate for an end should disastrous. be screwed to a circular block of hard wood (oak or boxwood), having an outside diameter Therefore the following warnings: less than the inside diameter of the boiler (1.) Do not use tins or thin sheet iron barrel by twice the thickness of the metal of for BOILERS . One cannot tell how far the end, and a rounded-off edge. The plate internal corrosion has gone. The scaling must be annealed by being heated to a dull of 1/100 inch of metal off a "tin" is red and dipped in cold water.

2 The process obviously vastly more serious than the must be repeated should the hammering same diminution in the thickness of, make the copper stubborn. say, a 1/4-inch plate. Brass and copper are the metals to employ, as they do not deteriorate at all provided a proper .. should be used liberally, and be screwed water supply be maintained. and nutted at the ends. As the cutting of the screw thread reduces the effective diameter, (2.) If in doubt, make the boiler much the strength of a stay is only that of the more solid than is needed, rather than section at the bottom of the threads. run any risks. (3.) Fit a steam gage, so that you may Riveting know what is happening. Though stays will prevent the ends of the (4.) Test your boiler under steam, and boiler blowing off, it is very advisable to rivet don't work it at more than half the them through the flanges to the ends of the pressure to which it has been tested.

3 Barrel, as this gives mutual support (See p. 220.) independently of soldering or brazing. Proper boiler rivets should be procured, and annealed In the present chapter we will assume that before use. Make the rivet holes a good fit, the barrels of all the BOILERS described are and drill the two parts to be held together in made out of solid-drawn seamless copper one operation, to ensure the holes being in tubing, which can be bought in all diameters line. Rivets will not close properly if too long. up to 6 inches, and of any one of several Dies for closing the rivet heads may be bought thicknesses. Brass tubing is more easily for a few pence. soldered, but not so good to braze, and generally not so strong as copper, other Soldering, etc. things being equal. Solid-drawn tubing is Joints not exposed directly to the furnace more expensive than welded tubing or an flames may be soldered with a solder melting equivalent amount of sheet metal, but is not below 350 degrees Fahrenheit.

4 Surfaces to considerably stronger than the best riveted be riveted together should be "tinned" before tube. riveting, to ensure the solder getting a good boiler hold afterwards. The solder should be sweated right through the joint with a blow-lamp to .. may be purchased ready turned to size. make a satisfactory job. Page 1. MODEL BOILERS . All joints exposed to the flames should be Some Points in Design silver-soldered, and other joints as well if the working pressure is to exceed 50 lbs. to the The efficiency of a boiler is governed chiefly square inch. Silver-soldering requires the use (1) by the amount of heating surface exposed of a powerful blow-lamp or gas-jet; ordinary to the flames; (2) by the distribution of the soft soldering bits and temperatures are heating surface; (3) by the amount of fuel ineffective. Brazing is better still, but should which can be burnt in the furnace in a given be done by an expert, who may be relied on time; (4) by avoiding wastage of heat.

5 Not to burn the metal. It is somewhat risky to The simplest form of boiler , depicted in Figure braze brass, which melts at a temperature not 78, is extremely inefficient because of its far above that required to fuse the spelter small heating surface. A great deal of the heat (brass solder). Getting the prepared parts of a escapes round the sides and the ends of the boiler silver-soldered or brazed together is boiler . Moreover, a good deal of the heat inexpensive, and is worth the money asked. which passes into the water is radiated out again, as the boiler is exposed directly to the air. Page 2. MODEL BOILERS . Page 3. MODEL BOILERS . Page 4. MODEL BOILERS . Figure 79 shows a great improvement in A Vertical boiler design. The boiler is entirely enclosed, except at one end, so that the hot gases get right The vertical boiler illustrated by Figure 80 is round the barrel, and the effective heating easily made.

6 The absence of a water jacket to surface has been more than doubled by fitting the furnace is partly compensated by fitting a number of water-tubes, aaa, bbbb, which lie six water-tubes in the bottom. As shown, the right in the flames, and absorb much heat barrel is 8 inches long and 6 inches in outside which would otherwise escape. The tubes diameter, and the central flue 1-1/2 inches slope upwards from the chimney end, where across outside solid-drawn 1/16-inch tubing, the heat is less, to the fire-door end, where flanged ends, and four 1/4-inch stays-- the heat is fiercer, and a good circulation is disposed as indicated in Figure 80 (a) and thus assured. The Babcock and Wilcox boiler (b)--are used. The 5/16 or 3/8 inch water- is the highest development of this system, tubes must be annealed and filled with lead or which has proved very successful, and may be resin before being bent round wooden recommended for MODEL BOILERS of all sizes.

7 Templates. After bending, run the resin or lead The heating surface may be increased out by heating. The outflow end of each pipe indefinitely by multiplying the number of should project half an inch or so further tubes. If a solid fuel-coal, coke, charcoal, through the boiler bottom than the inflow end. fire is used, Mark out and drill the tube holes in the the walls of the casing should be lined with bottom, and then the flue hole, for which a asbestos or fire-clay to prevent the metal series of small holes must be made close being burnt away. together inside the circumference and united with a fret saw. Work the hole out carefully till The horizontal boiler has an advantage over the flue, which should be slightly tapered at the vertical in that, for an equal diameter of the end, can be driven through an eighth of barrel, it affords a larger water surface, and an inch or so.

8 The flue hole in the top should is, therefore, less subject to "priming," which be made a good fit, full size. means the passing off of minute globules of water with the steam. This trouble, very likely Rivet a collar, x (Figure 80, a), of strip brass to occur if the boiler has to run an engine too 1/4 inch above the bottom of the flue to form large for it, means a great loss of efficiency, a shoulder. Another collar, y (Figure 80, c), is but it may be partly cured by making the needed for the flue above the top plate. Put steam pass through coils exposed to the the ends and flue temporarily in place, mark furnace gases on its way to the engine. This off the position of y, and drill half a dozen "superheating" evaporates the globules and 5/32-inch screw holes through y and the flue. dries the steam, besides raising its Also drill screw holes to hold the collar to the temperature.

9 The small water-tube is boiler top. preferable to the small fire-tube connecting The steam-pipe is a circle of 5/16-inch copper furnace and chimney, as its surface is exposed tube, having one end closed, and a number of more directly to the flames; also it increases, small holes bored in the upper side to collect instead of decreasing, the total volume of the steam from many points at once. The water in the boiler . other end is carried through the side of the boiler . Page 5. MODEL BOILERS . Assembling silver-solder both ends of the flue, the bottom ends of the stays, and the joint between The order of assembling is: -- Rivet in the bottom and barrel. The water-tubes are then bottom; put the steam-pipe in place; rivet in inserted and silver-soldered, and one finishes the top; insert the flue, and screw collar y to by soft-soldering the boiler top to the barrel the top; expand the bottom of the flue by and fixing in the seatings for the water and hammering so that it cannot be withdrawn; steam gages, safety-valve, mud-hole, filler, insert the stays and screw them up tight; and pump-if the last is fitted.

10 Page 6. MODEL BOILERS . The furnace is lined with a strip of stout sheet and doubled (see Figure 84), or even trebled, iron, 7 inches wide and 19-1/4 inches long, the heating surface may be increased to 180- bent round the barrel, which it overlaps for an 200 square inches. With a powerful blow-lamp inch and a half. Several screws hold lining and this boiler raises a lot of steam. barrel together. To promote efficiency, the furnace and boiler is jacketed with asbestos -- Tubing the Furnace Flue or fire-clay round the furnace -- secured by a Before any of the holes are made, the lines on thin outer cover. The enclosing is a somewhat which the centres lie must be scored from end troublesome business, but results in much to end of the flue on the outside. The positions better steaming power, especially in cold of these lines are quickly found as follows: -- weather.