Document np5pwEzdgvwKx3Z3NREbm6k5w

T50R Angler Pipe DATE ATTENTION 07 See below ANSWERDKJ YOURS .`O/iPOHA'rXOii September 16, 1964 PROM Aabler RhD SUBJECT Rubber Rings Por Use With Asbestos-Cement Pipe DICTATED BY C. R. Hutchoroft/sdp C(f Rubber rings ere the seals in our couplings which stake it possible to Join lengths of pipe together into a usable pipe line. Although Certaln~teed Asbestos-Cement Pipe is essentially indestructible when properly laid, a pipe line is no better than its Joints. In order to Insure Joints which will equal the pipe In longevity, the rubber rings used are of the highest quality which can be nade for the purpose. Our suppliers have advised that our specifications are the most exacting in their Industry. Pros tine to tine, custoners and people within our own or* sanitation have asked questions about the rubber rings we use. Dim to this Interest, it was felt that a paper describing these rings, their compounding, manufacture. Inspection, and usage would find an interested reception. Mr. Prank Law, Manager of our Materials Laboratory, pre pared a paper entitled "Rubber Rings for Use With Asbestos-Cement Pipe". It is enclosed herewith. Ms think you will find It both interesting and useful. M. s. R. L. Lanz " C. R. Meek R. A. Sehnelder K. J. Buczkowski J. L. Anderson R. s. Hartman 3. 3. Durkin 3. V. dear A. P. Nagle * R. Relehel R. R. Lassone L. R. Metsger 3. C. Janiceon P. K. Haskins w. R. Seipt M. R. Streepy '--1 H. J. Angstadt P. M. Panelll V. Carl D. P. Maloney H. Seller J. Crawford N. Rhoades K. Bailey R. Shaw R. E. Lander 3. DeLuea L. P. Kass J. S. Harblaon P. J. Law M. C. Shaw Pile CTD001074 RUBIER RDJGS FOR USB WITH ASBESTOS-CagliT PIPS 1 0 Introduction Rubber rings have been used in couplings to Join asbestoscemrnt pipe ever since the first asbestos-oeasnt pipe was cade by X&M in 1938* Rubber rings have been used as the gasketing material because of ease of assembly, reliability* sealing properties* and reasonable cost. The design of the rubber ring has changed from the round and square types used with malleable iron couplings; the 0 type simplex rings; to the present day "Fluld-Tite* ring* which Is considered su perior to any ring used to Join any pipe on the market today. As the asbestos-cement pipe business expanded since 1938 so did the use of rubber rings so that today CPC purchases of rubber rings is in exoess of a million dollars. For this reason and also because the Joint is the most orltleal part of the pipe system, much emphasis has been placed on the quality of the rubber rings; an often heard saying is that the best ring Is not good enough", although reoently a rubber ring manufacturer ms heard to say, "if your pipe la as good as our ring, we can build a pipeline to heaven . Since rubber rings, and "Fluid-Tite" rings in particular, are so Important a pert of our business, it might be well to know a little more about them and rubber in general. 2.0 "Fluid-Tite" Rings A. Pse "Fluid-Tite" rings are used to Join CPC asbestos-eement pipe couplings. They must prevent leakage from both the inside out and the outside In. B. Description One of the big problem in describing "Fluld-Tlte" rings is definitions. A 11 Fluid-Tite" ring is a gasket; it is also a seal and it can be considered an 0 ring. A gas ket is a packing employed in a Joint whose members remain in essentially stationary relationship. A seal is a pack ing which is self tightening; that Is, it requires no manual adjustment--or--a sealing connection, as a water seal. An 0 ring is a packing ring of round cross section used alone In a groove, it la self tightening.. All the above definitions include the word packing and since the ASTM Coeaaittee, which has written the specification for CTD001075 -2 rubber gaskets for use v/ith asbestoa-ceaant pipe -- ASTH D1869-63T, is the packing committee, a definition of packing Is Included. A packing la a device employed to create a gaseous or liquid seal on Joined surfaces suoh as piping or other vessels on containers. "PluldTite" rings meet parts of all the above definitions. It could be described as a gasket (joint which is stationary) used as a packing (a liquid seal used on piping) seal (re quires no manual adjustment) of the 0 ring type (used in a groove of proper dimensions). In addition to the re quirements listed above, it must also be impervious to the material carried In the pipe. In almost all oases water Is carried in asbestos-cement pipe; however, the water is not necessarily potable water. It may contain sewage, or as In the oil fields, light hydrocarbons. The "Fluid-Tite" ring has been especially designed so that It will exert its most effective sealing properties under service conditions. 3.0 Rubber The problem of finding a material that Is plentiful, of good quality, reasonable cost, long life. Impervious to water and water contaminants, will act as a seal In a confined groove and Is self tightening, is formidable. Fortunately there Is a material that meets all of the above requirements when pro perly prepared. Ala material Is rubber. Rubber In this sense Is used as a generic term and Includes both natural rubber and synthetlo rubber. A. Description The first question that comes to mind Is "What is rubber?" Because of the many types present on the market today, a definition must be all Inclusive. The one property that Is common to all rubbers is its tremendous elasticity. This property also sets rubber apart from other substances. From the elastic property the word elastomer is derived, therefore rubber is an elastomer. Elasticity is the pro perty that allows a material to be deformed without per manent deformation when the stress is withdrawn; a good exaaple Is a rubber band and & pleoe of tin. Stretch a rubber band and It will return to its original slse when the stretoh is released; put a dent in a piece of tin, the dent will remain when the object used to make the dent is withdrawn. CTD001076 *3" The elastic property of rubber is not enough to define It, so more common ground must be found. All rubber oontains carbon and hydrogen. This Is another elite. Zt Is not enough to have Just carbon and hydrogen, they must also be in a certain arrangement. Carbon of Itself ean be a diamond, graphite, charcoal, coke, or lampblack. Hydrogen la a gas, the lightest substance known. Carbon la the basis for organic chemistry which oonslsta of hundreds of thousands of compounds. A property which carbon has Is its ability to combine with Itself In either a straight line called a chain; l.e. C-C-C or a olrole called cyclic, l.e. -- O. (C is the ohealcal symbol /i for Carbon. H is for Hy- cm ci drogen). The straight chain series Is sailed aliphatic compounds and the cyclic, aromatic compounds. Rubber Is concerned with the straight chain or aliphatic compounds. One of the simplest compounds of straight chain carbon is hydrocarbons, the affinity or carbon for other carbon Atoms and hydrogen. The length of the oarbon chain and the number of hydrogen atoms tied to the chain determine what properties the com br)pound will have; l.e.C/^ s * \ la methane, a very light explosive gas, while Cio ***** 1> 10 carbons in a straight chain with 22 hydrogen atoms attached to the chain, is kerosene. As the chain Increases In length, the com pounds become more dense. Carbon also has the ability to form double or triple bonds with another oarbon; for instance, acetylene H-C*C-H. The double and triple bonds make the carbon atom much more remotive. Aa Is well known, acetylene Is highly explosive and bums with tremendous heat. The double and triple bonds are mentioned here for they are l^ortant In rubber as will be seen later on. Rubber contains carbon and hydrogen. The combination of the carbon and hydrogen in the molecule is always the same, the rubber molecule is CeHg h -c - " The ehemlcal name for this molecule is lsoprene. ^ -c.'" H - C 9" ' ** This molecule taken by itself is) a g*a*s but when the mole cule Is repeated many many times. It becomes rubber. The combination of two or more identical molecules la called a polymer. The formula for rubber la usually written (Cj-Hq J 20,000 - this means there are twenty thousand of the xsoprene molecules oomblned to form one molecule of rubber. By varying the length of the chain different pro perties may be given to the rubber. CTD001077 -4- The lsoprene molecule represents natural rubber. The synthetic rubbers are combinations of polymers with other polymers and/or the replaolng of one of the hydrogen atoms with other compounds. For Instance, neoprene replaces one hydrogen atom with a ohlorlne atom in each molecule {neo prene is often called chloroprene). Therefore rubber is a polymer with elastomeric properties. The elastoasrle pro perties are given to the polymer not only by the length of the moleoular chain but also by the arrangement of the molecules. The molecules in rubber are In a haphazard ar rangement. When they are stretched, they straighten out. When the stretch is released, they return to their original condition. They can be likened to a oolled chain; when it Is suspended, each link forms a pattern with the other link In a straight line pattern. When the chain is dropped, the links fall haphazardly. The above explanation on elasto mers, polymers, and rubber is over simplified but for the purposes of this dissuasion Is believed to be adequate. / B. History A brief history of how this all started might be of interest. When the Europeans first explored Central and South America, they noticed that the natives used the exudation of certain trees to make balls which bounced well and also to make a crude water proofing type boot. The natives called this material "cachue". The English scientist Priestly found out It could be used to rub out pencil marks and called it "rubber" which name has been used ever since. The development of rubber was not advanced for nearly a hundred years after it was first found. The Spanish, who first found it, never did develop It. In the early l800's Hancock In England and Goodyear in the United States began working with rubber as they felt any material having such unusual properties should be put to practical use. Zt was flexible, tough, waterproof and Impermeable to air. In the beginning many products made with rubber appeared to be excellent when first made; however they did not last long as there were two major troubles. The articles got brittle and stiff in cold weather and soft and sticky in hot wea ther. In 1839 Goodyear discovered that when rubber is heated with sulfur. It becomes drastically changed. The strength and elasticity are greatly increased and hot and cold temper atures no longer affect It. There is one story that Good year accidentally dropped some sulfur into boiling rubber and discarded the mixture. The following spring he noticed CTD001078 *5- that the rubber atill maintained Its original properties even though being exposed to the winter weather. Whether the ator? is true or not. It has developed Into over a billion dollar a year industry. With the advent of the automobile, the prlee of rubber sky rocketed and was ruthlessly exploited. At about this time seedlings taken from Brasil to Kew Gardens In London were transplanted in Ceylon and Malaya. The story of the Mutiny On The Bounty is connected with this trip and is true. The great demand for rubber caused a coomerclal interest in growing the rubber trees. The growth in Ceylon, Malaya, Indonesia and 2ndo*China was phenomenal and by 1920 pro duced 90 of the world supply. At the time Goodyear and Hancock were working on robber, great strides were made in organic ohemlstry, Including trying to make synthetic rubber. While this was not suc cessful till later, the non hydrocarbon products produced in these efforts found outlets as accelerators, anti-oxldants, plasticisers, etc. until an industry within an in dustry was developed. Natural rubber reigned supreme with very little serious attempts to make synthetio rubber. The cost of H&D for synthetic rubbers waa high as waa the processing. At the saw time natural rubber waa plentiful and the cost reason able. The synthetic rubbers gained prominence for two main reasons: 1. Natural rubber is easily attacked by other aliphatic hydrocarbons, kerosene, gasoline and the like. In 1930 Neoprene, Buna N, and Thlokols were produced. These products showed excellent resistance to petro leum oils and solvents and improved resistance to light, heat, and ozone. These products cost more, but the dif ference in price was mads up by their much longer life. 2. The second reason, and the most important one, was Vorld War II. Very early in the war Japan out off 950 of the world supply of natural rubber. Militarily they had a tremendous advantage as was shown by the Allied Blockade of Germany in World War I. When the nations were preparing for World War II, the necessity of replacing natural rubber was known. A orash program was started under the sponsorship of the U.S. Govern ment . The problem was solved and synthetic rubber was CTD001079 6- * produced. While in the beginning it was not as good as natural robber, it was sufficient to do the Job. Once the carrier had been cracked, improvements were rnde rapidly and new polymer's were developed. Today the synthetic polymers amount to 70Jo of the total robber usage. The advantages of synthetic robbers are: More uniform quality, low cost because of large volume, can be compounded for specific properties; l.e. low com pression set or ozone resistance. It must be remembered that up to the present time, there has not been a synthetic robber developed that has all the properties of natural rubber. In the manufacture of 'Pluid-Tite" rings there are three main robbers that are used: Natural Rubber - NR, ButadieneStyrene Rubber - SBR, and Butadiene-Acrylonitrile Rubber NBR (Buna N or Oil Resistant). Each will be discussed sep arately. 4.0 Natural Rubber - NR Natural Rubber occurs in the latex cf the Hevea Brasiliersi3 tree. It is contained in tubes which are located directly in the bark of the tree. These tubes spiral left to right as ;hey ascend the tree. The exact function of the latex to the tree is not known. These trees, although originally coming from Brazil, are cultivated almost exclusively in the tropical rain forest regions of all continents. The trees are cultivated In plantations. By cross breeding from the original trees, the yield has been increased from 250 lbs. per year per acre to 1500 lbs. per year per asre with some being as high as 3000 lbs. All seedlings taken from one tree are called clones. The latex is obtained from the tree by tapping. This is done by making a spiral cut downward in the bark of the tree through the ducts. The latex then is collected in a cup. The latex is collected and sent to a central factory or collecting sta tion. As the latex is being collected, a preservative is added to prevent coagulation. At the factory the latex is strained to zemove dirt ami bark particles, then coagulated, formed Into sheets, washed and hot air dried (with wood smoke in some cases) and packed into bales. The robber is classified into various types and grades. The type refers to the preparation given to the robber and the grade to the quality. Only the highest type and grade of natural robber is used in "Pluid-Tite" ring. Natural robber contains small amounts of materials other than the robber hydrocarbon molecule after it has been processed. CTD001080 These Materials are from the L.v;ex and have a pronounced ef fect on the rubber. These jcater-ials include fatty acids, im portant for vulcanization; natural sterols and esters neces sary for protection of the rubber from the air and sunlight; ;nd proteins. The protoins ere troublesome. if they are not extracted they are subject to bacterial attack and will even tually destroy the rubber. The rubber in the uncurad state is sticky, has poor strength, fantastic elongation properties, poor resistance to cglng, or in other v.orcs, the same as Goodyear first found It. The con tinuity j'cory of natural rubber shall be picked up Tatar, after S3R and KER rubbers, a3 the processing in the manufacture of the finished product 13 the sense for all of then, 5.0 Butadiene-Styrene Rubber - SBR The Butadiene-Styrene Rubber received its first impetus during World War I in Germany when the supply of natural Rubber was cut off -7 the Allied Blockade. The first attempts were rather poor and after the war, when natural fibber was plentiful, the development v-as carried out c-n a small scale. When World War II loomed on the horizon, the U.S. Goverrssant became interested in Bathetic rubtar and took over plants to produce It. Prc-a this came the old term "R-S vGovenunent Rubber - Styrene). The development of this material was so successful that today it compi-icea aopi:oai.::ataiy '60-% of all synthetic rubbers. l*a principal -id vantages arc uniformity, low cost, plentiful, and in many oasa 3 cart air. properties can bo processed into it. In an earlier uircusaiors on ::hat is a poiyiaer, it was pointed out that it Is the addition of two or more identical molecules. In SBR, the aid.ilion Is ci* t.;o polymers to produce co-polymers. The thief rjw materials are butadiene C4iig and styrene'CgH-<Cl{=CH-, The butadiene is a by-product from petroleum while a tyrene''Is obtained from the reaction of benzene and ethyiene. Beth the butadiene ar.d styrene ere polymerised in the same reaction chamber to form a complex molecular co-polymer. The process ing and chemistry .involved are very complex and beyond the scops of this discussion. An interesting note on 3HR 13 that for years butadiene rras polymerised Into a rubber as ras styrene. Neither v?.3 clc3e to giving the properties of natural rubber, however mien they- are co-polymerized, the co-polymer exhibits many properties superior to natural rubber. SBR rubbers do not have the ivcd:ir?us that natural rubber has end therefore are harder vo pr-o:eoc. Since they have less double bonds than CTD001081 -o- r.atural rubter, they are net as reactive and have less ten dency to overcuro. The resilience, tensile and elongation of SBR rubbers are not as good as natural rubber, while the cob* pression set and abrasion resistance can be superior. The amount of butadiene to styrene Is Important, J0% butadiene to 30 styrene la rubber; reverse the percentages and the material la a dense plastic. The processing will be picked up later. 6.0 Butadiene-Acrylonitrile Rubbers - HER These rubbers are ccmonly called Buna N or Oil Resistant Rubbers. Like SBR, it Is a product of co-polymerlsation, in this case between butadiene Ci.IL; and acrylonitrile (CHg CH C = *0, 'he processing is similar to 5BH although it is manufactured under 150 pel pressure. Qur primary function of NBR is its excellent resistance to petroleun oils and solvents. The amount of resistance to petroleum oils and solvents is determined by the amount of acrylonitrile to the amount of butadiene in the co-polyner, the more the acrylonitrile, the greater the oil re sistance. In general, the NBR compounds are more resistant to chemical attack than natural rubber or other synthetlo rubber. In any case where the chemical resistance of the rubber to a substance la not known, the safest (and most practical) approach is to test it in the laboratory first. Buna N rubbers have considerably lower tensile strengths and elongations, but better aging properties and compression set characteristics than natural rubber and SBR. Prom this point on the processing and eoopoundlng of the rubbers Is the same, keeping in mind that the processing times and the amounts of the various ingredients nay vary. 7-0 Processing A. Compounding The rev rubbers cannot be used for useful products. To oaks then into a useful product Is the function of the corapounder. The compounder wist find out what the end use of the product will be and to what conditions It will be ex posed. For instance. If high resistance to petroleian oils is necessary, he would select a stock that has a high acrylonitrile content; or as in the case of Fluid-Tite rings, he would select plasticizers that are not soluble in water. CTD001082 ) Co^Dpour.ding Ingredients In the compounding of rubber there are many Ingred ients used. They will be defined In general terms with few specific references made. The most important function of "Fluid-Tite" rings is to form a seal so that no water may leak out or in. In addition this seal must be maintained for as long as the pipe lasts {perhaps 100 years or more). Iherefore compression set is the mobt important property in CPC rubber rings, with resistance to compression a close second and aging properties third. The rubbers in their uncured state have extremely poor compression set and no strength in addition to poor aging character istics. The cured rubbers with no additions have com pression sets of approximately 50$, poor aging and very, high coats hense the heed of additives to the rubber stock. These additives are: a. Accelerators - These are organic compounds used to speed up the vulcanization or curing process. They are used in addition to sulfur. Using sulfur alone, the curing process would take hours. With the ac celerators, the curing process is cut to minutes. Many accelerators are natural fungicides end bacteriacides. - necessary for vulcanization in most com pounds'. However some compounds use peroxide cure-, v.hile sees ethers will use litharge or metallic ~ % v c. Plasticisers - Two types. Chemical Plasticizers - which effect the crude rubber and make them more workable by cutting the chain length. This type of plasticizer has little effect on the vulcanized product. Physical Plasticizers - which effect both the raw and vulcanized rubber. This type of plasticity lubricates the rubbers sc the chains slide past each other. They do not chemically Join with the rubber and as*e not driven out during vulcanization. In the cured rubber they give softer {less hard) and more elastic rubber with reduced strength. With this type of plasticizer, it le most important that the solubility be determined against whatever media the final product is to be used. Another point to CTD001083 -10- bo ^phaslzed with physical plastioizers is that they rt_3t be non-toxic. The physioal plasticisers are commonly kne\7n as softeners, SBR and MBil stocks will use sere plasticizers than will natural rubber. E::ter4ars - Are aotually physical plasticizers but the eta in function Is to cut the' coat of the stock. (Dilute the rubber). These are hot used in this sense in "Fluld-Tite" rings. e. Ant i-Oxidanta and Antl-Oalnants - In the previous discussion It was pointed out that the double bonds in the molecular chain were important. These double bonds are the weakest part of the chain as they are most active chemically. A chain that contains many double bonds readily reacts with the oxygen and ozone .leading to the degradation of rubber. Oxygen deter ioration is the more oomaoa of the two typse of at tack and will be described briefly* reatabering the ozone attack is similar except the rubber must be stretched for ozone to attack. Depending on the compound* oxygen attack will work in two waye. In natural rubber* the oxygen attack will decrease the tensile, elongation, flexibility and hardness. If the -ittcok Is severe, the end reeult may be rubber soup. In SBR the tensile, elongation, flexibility are decreased as hardness Increases giving a brittle product. In NBR the tensile and hardness increase while elongation and flex decreases. This also gives a brittle product. The promoters of oxygen are heat (almost always associated with oxygen attack), and light. Seat Increases the oxygen attack by ereatlng more double bonds in the rubber. Oxygen attacks the double bonds and creates free radicals. The free radicals, in turn, react with the rubber molecules to give more double bonds and the proeess repeats. Oxygen attack accelerates once It starts. Anti oxidants react with the free radicals to form a harm less by-product, thus stopping the cycle. In some cases they offer the oxygen a more active material than the double bond of the rubber molecule. This ties up the oxygen and prevents further attack. The main difference between oxygen (OgJ and osene (O3) attack la that ozone attack will only affect CTD001084 -11- rubber under teiisicn. The ozcr.e attach la al;;ayr. characterised by severe cracking. Anti-czants pre vent ozone attack by migrating to the surface and reacting with the ozone to fora a harmless by product. In boss cues, waxes are used which form, a barrier to the rubber. If the wax becomes craoked, the ozone attacks rapidly. f. Reinforcing Agents - Reinforcing agents are used In the rubber compound to give strength to the canpound and in many cases desired compression set characteristics. They are alao extremely important for abrasion resistance, 'the primary reinforcing agent is Carbon Black. The story and chemistry of carbon black is as fascinating and oomplex as is rubber Itself. There are many types of carbon black and methods of manufacture much too long and In volved to go Into here. The more common carbon blacks are Furnace Blacks, Channel Black, and Thermal Blacks, each type black having individual characterlatlaa to impart to the rubber. The particle size, the pH and the structure (single partleles cr chain) are the most Important properties of oarbon black. The carbon black gives strength to the rubber, regu lates compression set, increases hardness, reduces elongation, Increases abrasion resistance axel tear strength. g. Fillers - Fillers are used in rubber to (l) semetinea as a coloring agent, (2) primarily to reduce cost. Fillers have some effect on oertaln proper ties of the finished compound; l.e. hardness, but In general do not have a pronounced effect. Fillers used with rubber are clay, silicas, whitlogs, mica, cork, asbestos, zinc oxide, and many more too numerous to mention. All the Ingredients necessary to make rubber rings are now present. The raw stock (natural rubber, SBR or NBR, plastlolzers, sulfur, reinforcing agent filler, accelerators, anti-ozonants and anti-oxidants. These materials ars all cocabined (in their proper amounts In a ^ixer - Banbury), thoroughly mixed (very important), sheeted, extruded into a round cross section, color ooded9 placed Into a compres sion mold and vulcanized. CTD001085 12- B. Vulcanization The vulcanization is the most Important step In the manu facture of any rubber article, for no matter how well the formula precipe) has been made and mixed, how good the raw rubber is^ it is all for nought If the vulcanization is not right. Vulcanization is named after the Reman God Vulcan, the god cf fire, who was also supposed to be familiar with sulfur. Today definition of vulcanization ia any treat* sent that decreases the plasticity of the rubber at the same time maintaining Its elasticity. What is believed to happen In vulcanization is that cross links occur at points in the rubber molecule (at some of the double bonds). In the previous analogy of the rubber polymer being like a linked chain, each chain was separate to itself. After vulcanization these chains are eroee linked to each other at regular Intervals. Another analogy Is the uncured rubber is like two lengths of rope. After vulcanization the ropes are joined so that a rope ladder results. This prevents movement in all directions but does not limit stretch In the original direction more than pre viously. The more sulfur present the more cross linking and the harder the rubber. Vulcanization is accomplished by time and temperature. The proper, or optimum, cure for a given compound la deter* mined In the laboratory. This is usually accomplished by curing the compound at different lengths of time and at different temperatures. Specimens are taken from these different cured compounds and testa run on them. From these t&sts the optimum oure Is determined. The most com mon test used for this purpose is the best tensile strength plotted against the modulus at 300J6 elongation (Modulus is pounds required to stretch the compound to the desired elongation). In many cases, however, the Laboratory will use the test that is most critical for the end vise function of the produet to determine optimum cure; in the case of "Fluid-Tite" rln^s, the compression set test. In other words the proper temperature and length of time at that t^xrature to give the lowest compression set Is deter mined. It ia in vulcanization that accelerators are neces sary. 'Siey act as a catalyst to the sulfur linkage and greatly reduce the time cycle. The average temperature for vulcanization Is 260 ?. for 20 minutes in the ease of rubber rings. Of oourse these times will vary between NR, SBR and NBR, with NBR beleg the longest (25 minutes) and SSI the shortest (15 minutes). In some cases the time will be reduced by increasing the temperature. CTD001086 -13- The two main dangers of vulcanization are overcure and undarcure. Overcure may be shown in two ways for SBR and HBR. The hardness increases, the modulus Increases, the tensile and elongation drop off. In HR the rubber reverts to it3 original properties, lower hardness, mod ulus and tensile and higher elongation. For this reason it is desirable to obtain cures that have a long plateau; that Is, when the compound reaches its maximum cure It will maintain these properties even though the tenperature may be held for additional lengths of time. When the compound is undercured, it leaves the finished pro duct with properties somewhere between the raw state and the desired level. The aging characteristics are par ticularly poor In undercured compounds. 8.0 Specifications After the "Fluid-Tite" rings era cured and trimmed (getting rid of excess flashing), there must be assurances that they will perform satisfactorily the purpose intended. These assurances are obtained by means of specifications. Specifi cations are designed so that the properties believed to be necessary for a ring to satisfactorily perform the service Intended are put forth and the methods of testing to sake sure these requirements are met. There are tv;o main specifications governing "Fluid-Tito" rings: (1) ASTM Specification D 1869-63$ -- "Rubber Rings for Asbestos Cement Pipe" (2) CPC Purchase Specification No. 503 -- "Fluld-Tlte" Rings. Since all the requirements of ASTM C 1869-63$ are included in CFG No. 5C3, only the latter will be discussed. The more important tests and the reasons for having them are given. It should be pointed out that wherever possible ASTM Test Methods are used as this gives the producer and consumer common grounds on which to compare results. Also these test methods are time tested and under the vigilance of sos of the best rubber men in the country. The tests are: A. Testa (l) Tensile Strength - The tensile strength is determined on specimens taken from the finished rings. This test is conducted on the specimens "as received" end after oven aging. The tensile strength on the "as received" speoisens is to detemins if the rings were CTD001087 -14- oada froa a high quality raw rubber. The test on the aged specimens Is an indication of how the rings will hold up in usage. (It should be eophaslzed that the service conditions of coolness* darkness* and aoistneee are ideal conditions for rubber rings). The test after aging is also an indication that the rlngB were properly cured. {2} Elongation - This test detemines the elasticity of the rubber compound. How far it will stretch before breaking. This test is conducted at the sane tine on the sane specimens as the tensile strength test* on both the "aa received1' and aged state. When the results of this tsst are used in conjunction with the results of the tensile strength test* it is an excel lent indication of sure. For instance* a low tensile said high elongation of a natural rubber compound would' indicate either over or undercure (1^3roper cure). On the other hand a high tensile and low elongation on an NBR compound would indicate an overcure. A low tensile and low elongation on an SHR compound would in dicate overcure while a low tensile and high elongation would lndloate underoure. These tests are also valuable in Indicating the uniformity of the rings from shipment to shipment. (3) Modulus at 30096 Elongation - This gives an indication of the "nerve" of the stock. In practical application a high modulus fibs . to stretch the rubber 3000 of its original length; would indicate very hard assembly ef fort. A low modulus would indicate a weak compound and danger of blow-out. (4) Hardness - Perforated on the rings and specimens In the "as received" and after aging condition. Wien per formed on the rings "as received"* it is a control test that detemines the uniformity of the rings from ship ment to shipment and also that the rings are within hardness limits of what is known to perform satisfac torily in service. When performed on rings and speci mens after aging (exposure to both heat and water)* it is an Indication of how the ring will "stand up" upon exposure and In service. Excessive changes in hard ness mi aged rings or specimens would cause Investiga tion of the compound. The excessive change in hardness would not necessarily point out the cause* but show that something is wrong. CTD001088 -15- The hardness test Is fey use of a durcmeter and Is the measure of the resistance to the indentor point pene tration by the rubber. (5) Compression Set - This Is the most Important test run on the "Pluid-Tite" ring. This test deteralnes that when the ring is confined In the pipe and coupling. It vill continue to exert pressure against both the pipe and ooupllng groove. Compression set Measures the amount of permanent set the ring will take. Knee ing the dimensions of the pipe, coupling* and ring and the amount of permanent set* It can easily be de termined whether the ring will continue to exert pres sure or not. (6) Water Immersion - This test la conducted at elevated temperatures and Is an aging teat. This teat deter mines If the compound will break down In water. There are dangers In this test as some material could be taken from the compound and replaced with water. The change would be hard to detect. {7) Shrinkage--mot ASTM - This test Is also a water Immer sion test with a drying process added. The whole ring Is used and the Change In dimensions recorded. This la a very severe but very necessary test to avoid the possibility of ring shrinkage In ssrvlos. (8) Oxone Resistance - This tsat datemines ths resistance of the rubber to ozone attack. In effect it Is to de termine If sufficient anti-oxlnant la present In ths compound. (9) Low Temperature Flexibility - This la to determine that ths rings may be used in cold weather without breaking or cracking. (10$ Oil Immersion - HER Only. This test Is to determine whether allphatlo oils or solvents fprimarily petro leum) will rav.se the !EP. ccapound to swell or loss Its physical properties to the point where it would be use less. ?11) Assembly Effort--not ASTM - ls test is condustsd on finished rlxie* at room temperature and at 10"P. me teat determined the amount of foroe necessary to aasemble a pipe and coupling. The test la performed CTD001089 -16- using standard pipe and coupling and measuring the foroe necessary to assemble them. A very high as sembly effort would indicate an unsuitable compound as it might lead to forcing the ring out of the coup ling groove rather than compress it. The low temper ature (10*?) la important for the same faot. The standard aging temperatures and time for MR end SBR compounds for the tensile strength and elongation teats are 158? for 168 hre. The compression set teat is con ducted on specimens from finished rings ooogtressed 50% and exposed to 158? temperature for 22 hrs. The standard aging temperature and time for HER compounds for the tensile strength and elongation testa are 212*F for 70 hours. The compression set test la conducted an specimens from finished rings compressed 50 end exposed to 212 P for 22 hre. The.rater Immersion test on all compounds Is conducted at 210*? for 21 days. The shrinkage teat on all compounds is submerged in tap water at room temperature for 168 hre. followed by drying in an oven at 158P for 168 hours. The test requirements of nFluid-Tlte" rings are severe in order to maintain high quality rings, however it is known that no specification is perfect and that a great deal of che success of "Fluld-Tite" rings depend on the Integrity of the supplier and the knowledge of the compounder. CPC is fortunate in having suppliers that have both theme much needed attributes. Presently CPC uses two types of compounds for "Pluld-Tite" rings: NR, natural rubber, and KBR - Buna N or oil resis tant. The natural rubber la used in most rings aa the KBR is not in as mush demand. Matural rubber is used because it has the beet properties necessary for successful usage of "Fluid-Tito" rings. The drawbacks of natural rubber are low temperature range (it should not be used In pipelines subjected to over 120?. over an extended time), end the anti-csonant and anti-ooeidsnt properties must be added to the compound. CTD001090 17 The HBR 'Suna H} compound is core expensive and is, there fore, only used in lines where oils might be present. This compound has excellent ^properties, its main drawback being that it is very difficult to add anti-ozonants to it be cause cf a compatibility problem.' SER has not ceen used mainly because the natural rubber has been plentiful and has done an excellent job. As can be seen, the enemies of rubber are light and heat. The rings are packed in cartons and stored in a cool place. In service the conditions are ideal -- cool and moist, both conducive to long life for the rubber confound. In the future, aa more and more net* polymers are being de veloped, it is hoped that a single ring oan be developed that will be oil resistant, have reasonable cost, will be able to withstand 300*7. temperature, have natural anti oxidant and anti-osonant properties and have compression set properties even better than the present. EPILOGUE Rubber gaskets installed over 100 years ago are still perform ing satisfactorily in Europe and England. With the many im provements in manufacturing methods, reflnementste machinery, and the rapidly advancing new polymers since that time, there is every reasen to believe and expect an even longer life from the present day "Fluld-Tlte" gaskets. It is hoped this paper leads to a better understanding of the use, properties and problems associated with rubber rings and a promise of even better rings in the days to coma. CTD001091