A RUBBER STAMP A Chemisfry Project for Students at the Secondary Level
HOWARD R. WILLIAMS Western Reserve Academy, Hudson, Ohio
The manufacture of the apparatus and the compounding of the materials necessary lo the making of a rubber stamp are described. The stamp is made from crude rubber erukanized with lithar~eand sulfur in entirely home-made apparatus.
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HARLES GOODYEAR'S discovery of the process of vulcanizing rubber has almost re-made our civilization in the last three-quarters of a century. Today, vulcanized rubber products form one of the most important items of commerce. The amount of rubber used in a country is one of the indexes of its prosperity. Why, then, should not a chemistry student become interested in vulcanizing rubber? If it were possible to have the chemistry student make some useful rubber article, beginning with the crude rubber, it is altogether probable that the process of vulcanizing, in its simplest aspects, and its implications in industry would become a permanent part of the mental equipment of the student. It might also very easily lead to an interest in rubber chemistry which would help the student find his niche in the world. Such a project is one of fairly easy accomplishment. A rubber stamp has been chosen as the article to be made because its manufacture involves all the important steps in the making of most rubber articles, because it is easy to make a successful stamp, and because the stamp when completed is a useful article that may be kept and used for years. In preparation for the work, the student should first of all learn all he can about the process of vulcanization. The school library and the public library should be good sources of information. In addition, a very fine and practical way to learn about the process and its technic is to visit a rubber works where the process may be watched and possibly a conference with the head chemist may be had. The materials necessary for the successfulprosecution of this project are easily obtained common things. The following list of materials should be gathered together before the actual work is begun so that delays may be avoided when the work starts. Three pieces of flat iron plate about ' / 8 * to 3/16" thick, 2" wide and 3" long, three stove bolts, a half-dozen soft iron rivets, two 6" sections of 3 / r Y pipe, about 30" of 3/8" iron rod, two pieces of 3" angle iron about 21/a" long, about 2' of old lead pipe to be melted, a flat-type one-pound coffeecan, a thermometer registering to about 200°C., a ring-stand, a burner,
some iron wire (baling wire), precipitated calcium carbonate, plaster of Paris, crude rubber, lead oxide (litharge), flowers of sulfur, piece of muslin, hacksaw, drills, hammer, file, emery wheel, emery cloth, etc. Before starting the actual work of stamp making, it will be necessary to build three pieces of apparatus-a frame in which to vulcanize the stamp under pressure, a calender in which to mix the crude rubber and other ingredients, and a vulcanizing oven. I t is probably best to start by fabricating the vulcanizing frame. This frame is made from the three iron plates. I t may be made in almost any practical size and shape; however, if a signature stamp is to be made a frame two by three inches will be found adequate for names of average len@h. If iron plates of suitable size and shape are not a t hand it is fairly easy to make them from sections of 11/2"iron pipe. Hacksaw off a section of pipe 2" long. Place it in a vise and split it lengthwise along one side with the hacksaw. Place this piece in the school furnace or fire box under the boiler till it is red hot, then with hammer and tongs flatten it out. Cut one of the necessary plates from this piece. The other two may be made similarly. All three plates should be made of the same material so there will be no warping of the frame, when heated, due to unequal expansion.
Next, an oblong hole '/rU by 2lI4"should be cut in the center of the plate to be used as the middle plate of the frame as shown in Figure 1. This bole may be cut out by drilling - and hacksawing- and then smoothed with a fiie. The bottom plate should next be prepared for riveting to the middle plate. It is necessary that this plate should have a flat, smooth upper surface as the face of the stamp type is to be made against it. This plate can be made quite smooth and flat by working it down with emery cloth folded over a flat block of wood just as sandpapering is done on a flat wooden surface. If the plate is very far from flat in the beginning, it can be hammered first, then worked with a coarse emery cloth and finally finished with a cloth of fine emery. When the bottom plate is ready it should be clamped to the middle plate and the holes for the rivets drilled
through both at once. Before the rivets are inserted, the holes in the middle plate should be reamed out to half the thickness of the plate with a countersink, so that the hammered heads of the rivets may not protrude above the upper surface of the middle plate. The two plates may now be riveted together. A fair-sized finishing nail may be used as a rivet. The head of the nail makes an excellent rivet head. The nail should be cut off so as to protrude only about '/a" above the surface of the middle plate. The iron of a nail is just about the right softness for riveting. The two bottom plates riveted together are shown in Figure 2. The top plate needs no particular preparation except to be made as flat as can be conveniently done by hammering. This plate will lie against the back of the rubber stamp and be the means of applying pressure to the rubber while vulcanizing. Now the three plates should be clamped together and three holes to receive the stove bolts drilled through all three plates. Strong stove bolts may then be used to fasten the top plate to the bottom assembly as shown in Figure 3.
FIGURE3.-THE VULCANIZING FUME COMPLETELY ASSEMBLED
I t will be necessary to make an instrument for leveling the matrix when it is placed in the vulcanizing frame as shown in Figure 4. This may be hacksawed or cut with snips from any convenient sheet metal of heavy gage. The use of the leveler will be explained when directions are given for the preparation of the matrix. Next, it will be necessary to construct a calender for mixing the crude rubber and the ingredients with which it is to be vulcanized. From a mechanical viewpoint, a rubber calender is little more than a clothes wringer with iron rolls. If you can devise some way to substitute iron rolls in an old clothes wringer you will have an excellent calender for your purpose. Failing this you may make a calender as follows. Saw two 6" sections from some 3/r" black iron pipe. . These will be your rolls. Next, cut a section of 3/ " iron rod long enough to extend about I/%" beyond each end of one of these pipes. This rod is to serve as the axle for the upper roll. The axle for the other roll will protrude '/%" from the roll on one end but about 15" from the other end. This long piece will later be bent into a crank. Before placing the axles in the rolls, notches should be ground into them with an emery wheel so that the molten lead, with which they are held in the rolls, will have something to grip. This is shown in Figure 5. The next problem is to hold the rod in the center of the pipe while pouring the molten lead. This is an important step. If the axles are not centered in the rolls the rolls will wabble and it will be very difficult to calender the rubber in such a machine. However, it is not a difficult problem to center the axles. Take a
Heavy tin o r
sheet won -)
Matrix ' m i x t u r e FIGURE 4.-THE
CONSTRUCTION A N D USE
OF THE
LEVELER
brace and a bit large enough to bore a hole in a piece of 7/8'' board so as to just admit the end of the pipe roll. Do not bore this hole all the way through the board but just about deep. Then after withdrawing the larger bit complete the boring of the hole with a smaller one which will bore a hole just large enough to admit the rod used as an axle. This second hole will then be exactly centered in the h t . Two such pieces of board should be prepared, one for each end of the roll. The board to be used on the top of the roll should then have a notch sawed out so as to leave a pouring hole for the molten Wood lead. This assembly is shown in Figure 6. Molten lead is next poured in to fill completely the space between the roll and the axle. To make doubly sure that the axle and the roll will always remain integrally connected, it is advised that a hole be drilled completely through the roll and the axle about '/," from each end and a r i v e t swaged into each hole. The ends of these holes should he reamed out with a countersink before insertion of the rivets so that upon completion therivet heads will be flush with the surfaces of the rolls. Two pieces of 3" angle iron, each I blwk Small hole f o r axle about 2 l / % "long, are used in mounting the rolls. Two TEDD IN THE ROLL h i l e s should be
drilled, one exactly above the other, in each upright section of the angle iron. These holes should be just the right size to receive the protruding ends of the axles of the rolls and far enough apart so that the rolls will have a clearance of about Two holes should be d r i e d in the horizontal parts of the angle iron to receive lag screws for fastening the calender to the base. In assembling the parts of the calender, be sure to face both angle irons in the same direction as shown in Figure 7. Otherwise the horizontal flange will interfere with the bending and operation of the crank. The bending of the crank is the last steD in ma kin^ the calender. This may furnish a little &allenge, b; with care and patience it may be accomplished with hammer, vise, and a pair of pliers. A simple vulcanizing oven is the next and last piece of apparatus necessary. A very simple and quite workable oven may be made from an ordinary low-type one-pound coffee can. The only thing necessary to have a complete oven is to punch a hole in the center of the lid large enough to admit the stem of the thermometer to be used. It would be well to make a wire support for the thermometer so that there will be no danger of its toppling out of position. This may be made from a round piece of tin plate and three short lengths of baling wire for legs. A hole for the thermometer is made in the disc of tin plate and three wire legs attached to it either by twisting or soldering. The thermometer is then slipped through the hole in the support and through the hole in the lid, and the legs of the support are set on the lid of the coffee can as shown in Figure 8. The oven should be heated by an adjustable burner of some sort. A Fisher burner makes an excellent
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wL~
..- - - - .--. . FIGURK 7.-THE CALENDER ASSEMBLED
MAY, 1933 Thermometer
FIGURK 8.-A
DETAILOF
THE CANIZING
APPARATUSDURING TEE
PROCESS
VUL-
source of heat. However, one of the newer-type Bunsen burners with the gas adjustment should prove perfectly satisfactory. Having completed the necessary pieces of apparatus, the actual work of stamp making may now be nndertaken. The next step is the preparation of the matrix or mold in which the rubber of the stamp is to be vulcanized. A mixture of equal parts of precipitated calcium carbonate and plaster of Paris make a satisfactory material for the matrix. The two ingredients should be mixed dry and then water enough added so that the plaster may be poured into the vulcanizing frame. Of course only a small amount will be required. After the plaster has been poured into the frame to a trifle over half its depth, the surface should be smoothed with the leveler as shown in Figure 4. A proper and nniform thickness for the matrix is obtained by passing the leveler several times over the wet plaster and removing the surplus plaster. The plaster should be allowed to set for about twenty minutes before attempting to write or draw designs in it. Whatever is to be the writing or design for the stamp should next be lightly traced on the surface of the plaster. It is well to begin with a fairly simple design. Then by means of a sharp-pointed stylus the design should be very slowly and carefully worked through the plaster to the iron plate beneath. Here is a place where care and artistry can play a big part in the success of the project. Block letters are more easily made than script, but patience and practice will make either successf"lly, as shown in the photographs in Figure 9. After completing the matrix it should be allowed to dry thoroughly (several hours) be-
fore being used. If used while still moist, steam bubbles are pretty sure to deface the stamp. While the finished matrix is drying is a good time to calender or mix the crude rubber and other ingredients for vulcanizing. Enough rubber may be calendered a t one time to make several stamps as it keeps indefinitely after calendering. Crude rubber may be bought in sheets very cheaply from chemical supply houses. Take whatever amount of rubber you will need and weigh it. Then force it through the rolls of your calender until it is homogeneous and quite tacky or sticky. This will probably take from one-half to threequarters of an hour of calendering. Then make up a mixture of yellow oxide of lead (litharge) and flowers of sulfur as follows: for each 100 g. of rubber take 7 g. of litharge and 6 g. of sulfur. Of course if you have taken more or less than 100 g. of rubber you may calculate the weights of litharge and sulfur necessary by means of a simple proportion. This mixture of litharge and sulfur should be added to the rubber a little a t a time by sprinkling, folding, and constant calendering until the whole is a homogeneous mass. This will probably take an hour or more. It will be readily seen that the power-driven automatic machinery of the modern rubber plant is a great aid in making rubber goods cheaper and better, for the quality of the finished article depends greatly upon the thoroughness of the calendering. However, patience and perseverance should be rewarded with more than a fair degree of success in such a hand process as this. The next job is to put the calendered rubber into the matrix for vulcanizing. First roll out the rubber until it is about i/g" thick. Then, with a pair of shears, cut a piece just large enough to fit into the slot of the vulcanizing frame over the thoroughly dry matrix. Next cut a piece of muslin the size and shape of the rubber and place i t on top of the rubber. Then lightly grease the edges of the vulcanizing frame and under surface of the top plate with vaseline to keep the rubber from sticking to the metal during vulcanizing. Now place the top plate on the muslin, insert the stove bolts and screw them down as tightly as possible. Use plenty
hXJRE
9.-THREE
HOE-MADE RUBBER STAMPS AND
THE
IM-
harm, but the more evenly the temperature is kept a t 160' the better will be the results. At the end of thirty-five minutes, remove the flame, take the lid from the oven, and allow i t to cool. The vulcanizing frame may then be opened and the rubber stamp stripped out. It may stick some around the edges, but it can be cut away with a knife while pulling the stamp away from the metal. The stamp should next be trimmed with a pair of shears leaving only about margin outside the letters. The stamp is now ready to he cemented onto a piece of wood for a handle. Ordinary glue may be used. Any amount of ingenuity may be used in making the handle. The stamp maker may suit his own fancy in this matter. Some good suggestions may be got by FIGURE 10.-THE APPARATUSUSEDIN PRODUCING THE HOME-MADE RUBBER STAMPS SHOWNIN FIGURE 9 examining stamps of commercial manufacture. (A) The stamp inking pad, ( B ) the vulcanizing frame, (C) the vulcanizing oven, (D) the stamps made with the apparatus, ( E ) the rubber calender. It now only remains to get an ink pad and trv the stamo. If a oad is not available. a of pressure. Yon cannot get too much. Then place very good one may be quickly and easily made by laying the frame in the vulcanizing oven setting it on the long a couple of thicknesses of felt on a wooden block of apends of the stove bolts, as a tripod, so as to keep i t a propriate size and shape and covering felt and block with little above the bottom of the oven as shown in Figure muslin. I n case a finished job is desired, it is very easy 8. Insert the thermometer and you are ready to vul- to frame the ink pad block with either wood or metal. If the directions have been carefully followed, the canize. During the vulcanizing the temperature should he worker has now, not only a serviceable rubber stamp controlled as carefully as possible. This will require and the apparatus for making more and better stamps, constant attention. Vulcanize for thirty-five minutes but what is more to the point, a fair working knowledge a t lGO°C. Allowing the temperature to vary five de- of what goes on in the manufacture of rubber goods in grees either way for a few minutes will do no serious general.
