Plastics Construction Materials
Textile Fibers Plants Plastics have contributed in an important way to the solution of many operating problems in textile fibers manufacturing plants. Most early applications were concerned primarily with corrosion of the materials of construction or problems of maintaining dimensional stability. More recently, the problem of reducing metallic contamination of the process materials has given fresh impetus to consideration of the use of plastics wherever their use can possibly be justified. Much experimental work has been necessary. One Du Pont plant has set up a small but well equipped molding and fabricating shop for small lot production of experimental plastic pieces. They felt justified in going to this length to get the answers they needed quickly.
W. A. HALDEMAN AND E. F. WESP E. I . du Pont de Nemours h Co., h e . , Wilmington, Del.
I
T WOULD be strange indeed if plastics were not receiving careful attention today in textile fibers plants, since many of the man-made fibers are themselves a special form of plastics having, relatively speaking, infinite length and infinitesimal diameter. Plastics have been in continuous use in D u Pont viscose rayon plants since the first of these plants started operating in the early 1920's. The earliest applications were for small molded parts of spinning machines, such as spinning funnels and bucket covers; and, of great importance, the spinning buckets themselves. Practically all these early plastic parts were made successfully of the phenolic compounds. I n recent years many possible new applications for plastics have been investigated The increased interest in these materials can be attributed largely to the development of thermoplastic compounds having a relatively good combination of chemical resistance and toughness. Some of the thermoplastic resins available today which are of interest t o us are the poly(viny1 chlorides), both plasticized and unplasticixed (in addition t o providing good resistance to most chemicals, these are thermosealing), the modified styrene poly-
COMPARTMENT CO
Figure 1. Cross-sectional diagram of rayon buckettype spinning machine July 1955
mers, polyethylene, poly( methyl methacrylate), and the fluorocarbon polymers. RAYON SPINNING MACHINE COMPONENTS
Since most early applications of molded plastics were for viscose rayon spinning machines, these applications make a n appropriate starting place for a review of current plastic usage. Figure 1 shows a cross section of a basic type 8"D/AM. of bucket spinning I machine in present operation. Portions of the machine are exposed to the coagulating "spin" bath, either by direct immersion, e n t r a i nment, carry-over on the thread being spun, or drip, and to fumes c o n t a i n in g bath and products of reaction. T h e Figure 2. Cross section of phenolic, rayon spinning bucket containing 10% sulfuric acid plus appreciable percentages of sodium sulfate and zinc sulfate has a temperature of 45" to 50" C.; the products of reaction add carbon disulfide and hydrogen sulfide to the corrosive atmosphere in which these components operate. Figure 2 is a cross section of a small spinning bucket used in current production. This bucket is a molded phenolic reinforced with cloth and with stainless steel wire. It can operate at speeds well over 5000 r.p.m., and must safely withstand the centrifugal force not only of the bucket material itself but also of the load of wet yarn inside of the bucket weighing as much as 4 pounds. It is in continuous contact with the acid spin bath which is carried into the bucket with the yarn. Early spinning buckets for this service were made of molded hard rubber, aluminum, and Bakelite-lined aluminum, but these were unsatisfactory after a time for one or more of the following reasons:
I
1. 2. 3. 4.
Insufficient dimensional stability Poor resistance to chemical attack Lack of sufficient strength Linings did not stay tight
INDUSTRIAL AND ENGINEERING CHEMISTRY
1359
Figure 3. Plastic components for rayon spinning machines 1. Molded polystyrene washrack distribution 2. Spinning bucket 3. Molded hard rubber spinning funnel 4. Molded phenolic bucket cover 5. Molded hard rubbcr bucket compartment cover 6 . Pump housing of phenolic and methyl methacrylatr 7. Hard rubber-covered aluminum cake rod 8. Molded phenolic take-off ring 9. Molded phenolic bath rollers of various sizes and shapes 10. Hard rubber candle filter housing 11. Doffing tool with molded phenolic contacting shoes 12. Laminated phenolic cake insert
These shortcomings aggravated difficulties of maintaining dynamic balance and yarn uniformity and contributed to yarn abrasion. The present satisfactory bucket material maintains smooth internal surfaces and resists chipping, nicking, and scratching in handling. Most recent Du Pont bucket purchases have been made of Micarta. Records of useful life run as high as 12 years, with an average of 6 to 8 years. The fact that this material has been in use for such a long time and is still being used today to a large extent is evidence that plastics have served 28'
Ui
.SUCT/OrJ
Figure 4.
Spinning bath eductor of asbestos-filled phenolic
wcll i n this applictitioii. UntlouLtcdlv. this is one oi the outstandiiigly ~i~ccessiul :ipplications of plastic nlaterinls. Figure 3 shon.s several rayon ni:ic.hiiie parts which, lor y c n r ~ ,have been macln of pldstic ni:ttcriala. .ill the spinning mnchine parts illustrated (except 8 and 1l)nrc.exposrdto direct contact with the spin bath and with the products of the chrniical reaction between the bnth and the spinning solutiori. 'L'hcy mrwt ) X J $ S('PS dimensional stability, strength. ant1 wear msis t r tic D . Th(.In st cl i:i VR ('1 rri?t ic : i ~ ~ ~ ~ l i e s e ~ ~ etoc the i i i lb:tth l y rullct L whivh serve as pulleys to guide the yarn under the bath. They must rotate on glass
1360
Figure 3A.
Plastic bobbin, creel tension device, and balloon baffle
or Hastelloy pins without sticking a i d with almost no wear; with only occasional polishing, their peripheral surface must remain smooth and free of surface imperfections in order not to damage the hundreds of miles of fine rayon filaments which contact their surfaces. The average life of these rollers is 6 to 10 years. Figure 3A shows a molded phenolic tension device and a modified styrene polymer "balloon" baffle which are used on a bobbin creel. I n addition to the two items labeled, the bobbin itself, one end of which is clearly shown on the right hand side of the photograph, is a molded phenolic. Figure 4 is a crosssectional diagram of a spinning bath eductor made of asbestosfilled phenolic resin. This component operates in continuous contact with the acid spinning bath and maintains reasonably good strength and dimensional stahility. VENTILATING DUCTS AND HOODS
Many ventilating installations of various plastic materials of construction are in use. Approximately 2 years ago, in one of our viscose rayon plants, 36,000 square feet of aluminum fresh air supply duct was replaced with a modified styrene polymer. Figures 5 and 6 are views of the completed project. Duct sections are either square or rectangular with some sections as large as 9 feet 6 inches square. Fabrication consists of cementing flat sheets, usually of '/*-inch thickness, to extruded joining strips, sketches of which are shown in Figures 7 and 8. The cement used was made by dissolving shavings of the material in methyl ethyl ketone. The whole assembly is reinforced at intervals with aluminum angles and suspended from the room ceilings with an aluminum structure.
Figure 5 and Figure 6.
Air-supply ducts of modified styrene polymer, high impact fire-retardant grade
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 47,No. 7
Plastics Construction Materials
id‘x l
d‘CHANNEL
$SLOT
CORhFg ANGL€ SEC77ON
Figure 7. Modified styrene polymer used for assembling ducts 1. 2.
-
Y~-inchplastic sheet to be continuously cemented to appropriate extrusion Angles, channels, or tees to he fastened to duct with YE-inch-diameter plastic rivets or bolts
When the decision was made to proceed with a project to replace the existing worn-out duct system, it was generally assumed that the replacement would be in kind-Le., aluminum-and a preliminary estimate of cost was developed on this assumption However, about the t8imethis estimate was completed, attention was focused on the use of a modified styrene polymer as an alternat,e to aluminum. Published data available on the modified styrene polymer indicated that this material could be substituted for aluminum at a slight increase in cost and in view of the advantages of having a nonmetallic and noncorroding duct over the spinning machines, a project was authorized based on the use of this material. When detailed design work got under way, it became apparent that the physical property data available were not sufficiently dependable to be used for the large duct sections involved, and i t became necessary to undertake a test program to determine the long time allowable tensile strength of this material under the stress and temperature conditions to be encountered in operation. These tests were followed by a program of preliminary design, building of a large test section, redesign to secure greater rigidity, improvement in design of slotted joining strips, improvement in cementing technique, and finally, the generous use of styrene copolymer rivets and bolts during final field assembly to obtain satisfactorily tight joints. 4 s a result of the experience gained on this installation, si~fficient know-how was developed to fabricate modified styrene polymer duct work satisfactorily in the field. Subsequent installations have been satisfactorily fabricated by both the construction division and plant maintenance forces. This project was fairly typical of the problems of pioneering new plastic materials of construction on a sizable scale. Where severe corrosion is a problem and especially where metallic contamination must be avoided, ducts of modified styrene polymer are justified and should be considered seriously for fresh air supply ducts and possibly for exhaust ducts in some applications, although i t has not proved very successful f o r exhausting fumes from viscose spinning rooms in our plants. Much difficulty has been experienced with condensate leakage and resultant sodium sulfate crystal build-up a t cemented joints in a duct system for exhausting fumes from coagulating bath purification equipment at one plant. This installation is shown in Figure 9 with the original aluminum duct on the left and the new plastic duct on the right, immediately after installation. Unfortunately, the appearance of the plastic duct after several months of operation is now, because of joint leakage, much like that of the aluminum which i t replaced. Leakage occurs not only a t the flange faces but also through the cemented joints in the extruded joining strips. Consequently, this installation is not considered fully satisfactory. Of course, this is entirely a joint design problem and does not reflect on the suitability of this material for the corrosive conditions involved. On the other July 1955
Figure
8.
Typical duct construction modified styrene polymer
with
hand, large test sections of modified styrene polymer are in good condition after 8 months in an exhaust hood system handling acid vapors substantially free of entrained salts. It was previously mentioned that poly(viny1 chloride) has exceptionally good chemical resistance which makes it adaptable to many chemical plant operations. Although many experimental installations are being made in Du Pont plants, its use for large duct installations, has been very limited. This is primarily true because of high cost of fabrication, attributable in large measure to the limited speed t\-ith which thermosealing or “welding” can be accomplished. The use of this material is considered to be economically justified for some exhaust duct applications involving unusually severe corrosion or fabrication problems, but up to the present time it has not been competitive in cost with modified styrene polymer where this material can be used. The fact that unplasticized PVC can be thermosealed makes this material adaptable where leakproof joints are a must or where much intricate fabrication is involved. Figures 10 and 11 show poly(viny1 chloride) ventilating ducts which illustrate how the thermosealing ability of this material permits fabrication into intricately shaped hoods and ducts which must be tailor-made for specific machine locations. Both the installations shown are applications where fume concentrations and corrosive conditions are severe. The chemical resistance of PVC together with its ability to be fabricated into intricate shapes makes it competitive to rubber-
Figure 9.
Exhaust ducts
Aluminum on left; modified styrene polymer on right
INDUSTRIAL AND ENGINEERING CHEMISTRY
1361
Figure 11. Figure 10. Nonplasticized PVC ventilating ducts for rayon spinning machines
covered steel for many applications. An exhaust hood installation of an unplasticized PVC located over the bath system on a spinning machine has been in service 3 l / 2 years with no noticeable deterioration. This is considered to be a generally satisfactory material for handling these hot sulfuric acid fumes containing entrained sodium sulfate. However, a t the time it was installed, its cost was estimated to be considerably more than conventional materials. We believe that the PVC will outlast previous hoods by a sufficient margin to justify its use. I n the manufacture of viscose spinning solution, caustictreated cellulose is reacted with carbon disulfide to form cellulose xanthate. This operation is carried out in large revolving drums known as barattes (a French word meaning churn). Flexible exhaust ducts made of polyethylene are inserted into these barattes immediately on opening them after each charge t o remove residual carbon disulfide fumes before dumping their charge.
Nonplasticized PVC ventilating ducts on rayon spinning machines
siderable damage occurs to the steel tank. The wide differences in thermal expansion coefficients between the plastics and suitable structural reinforcing materials such as steel also presents problems which tend to limit the usefulness of the plastics. Tanks made of asbestos-filled phenolic have been used for service involving sulfuric acid. This has been satisfactory where they are not subjected to physical abuse or where special care is taken to eliminate deflection stresses on the material. A nutsche tank made of an asbestos-filled phenolic lasted approximately 5 years. This tank is used t o filter sodium sulfate crystals out of a crystalizer discharge batch having a sulfuric acid concentration of 10% and saturated with sodium sulfate at 20" C. In this case, it is our opinion that failure was due primarily to inadequate design for this material. One of the plants currently has under test a wash tank fabricated of glass-reinforced polyester. At the time it was installed, we had rather high hopes for this material, but it began to show signs of failure in approximately 15 months. Another plant, which is now evaluating glass-reinforced polyester tanks, is having a similar experience. The service is hot water having
TANKS AND PROCESS VESSELS
For many services where plastics are potentially applicable, it is often difficult to obtain a satisfactory combination of structural strength and chemical resistance at the operating temperatures involved. Where attempts have been made to solve this problem by lining steel tanks with unplasticized PVC, using welded joints, the results have generally been disappointing because leaks in the lining cannot be detected readily until con-
Figure 12.
1362
Slasher cans, Teflon coated to prevent sticking
Figure 13. Waste-catcher tubing of plasticized PVC
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
Plastics Construction Materials has occurred in threads principally because a suitable pipe dope was not used. Thermal expansion of the pipe must be taken into consideration and proper provisions made for it. An important factor in delaying a more widespread use of plastic piping has been the temperature limitation of most of the available materials. Many applications, even a t very low pressures, will be ruled out because the plastic pipe will be too weak t o support itself a t the operating temperatures involved. This objectionable characteristic tends to keep it from replacing lead in many places in our plants, even though lead also has its support problems. Although rubber-lined steel pipe is still hard to beat on a cost basis for many applications, plastic pipes have the advantage of being resistant to external corrosion too. This is of particular importance in corrosive atmospheres where lines must be installed over open bath troughs or other process equipment where corrosion products may drop o f f and cause contamination of the process materials. In fact, appreciable amounts of maintenance labor in rayon plants are expended in coating overhead steel piping and structural steel wjth protective coatings or wrappings to prevent such contamination. For many years lead has been the standard material of construction for coagulating bath supply and return lines from rayon spinning machines, because nothing else was economically suitable for the corrosive conditions. Lead is far from ideal for the following reasons:
Figure 14.
Waste-catcher tubing of plasticized PVC
a trace of sulfuric acid. These have been in service about 18 months and are showing very noticeable signs of attack on the surface. Information available to date indicates that glass-reinforced polyester is not satisfactory for any of the strengths of sulfuric acid encountered in rayon spinning baths or wash tanks. PIPING
Plastic pipe is receiving much attention for many types of service in Du Pont plants. In the rayon plants, it is being used to an increasing extent for carrying coagulating bath, and in all textile fibers plants it is being used for carrying soft and demineralized water. Its chemical resistance and cleanliness are important factors. Most of the piping used to date has been either the modified styrene polymer or the unplasticized PVC. The troubles that have occurred were usually confined to joints. Flanged connections have not been sufficiently rigid, and leakage x
1. It requires an additional supporting structure 2. It is expensive to fabricate 3. It contributes metallic contamination 4. It is especially subject to sludge build-up
-i
6 d b / AM.
1
Thus, several years ago, our plants gradually began turning to the replacement
cases both rubber-lined and rubber-covered steel pipe. While this construction has been fairly satisfactory in h chemical resistance, sludge build-up is still a problem and since noway is known t o clean hard sludge from rubber-lined steel pipe, the plants are now wondering if Figure 15. Cross section of rubber-lined steel pipe is phenolic bobbin the best answer for lead rep l a c e m e n t. W e believe that plastic pipe will eventually be the answer. However, the use of plastic in the past has been complicated partly by the sizes of the lines involved. Many of these limes are in excess of 4 in-
*I I
I
Figure 16. Braider bobbin Figure 17. Tex- Figure 18. Creel spindle parts of Figure 19. Magnetic yarn tension of molded nylon and tile spindle bolsmolded nylon brake with molded nylon pulley aluminum ter of molded nylon
July 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
1363
Figure 20. Twister take-up roll bearing of molded nylon
ches in diameter, which was until fairly recently, beyond the range of sizes available in “all-plastic” piping for most of the suitable materials. When plastic pipe and fittings and good joint m a t e rials and techniques become readily available in sizes up to 10 or 12 inches, i t is likely that they will be used in preference to much of the lead and rubber-lined steel now in use. LININGS
From a chemical resistance standpoint, rubber-lined steel for a long time was considered the only available economic alternative to lead for viscose rayon operating conditions. Several plastic materials in sheet form are now available and are being used. One, of these is saran. The 6-inch finish return line from a rayon slasher is lined with saran. It was installed at the time because i t was quicker to procure than the stainless steel which had been used previously, and its installed cost was about the same as stainless steel. It has now been in use 2‘/2 years with no maintenance expense. Saran-lined valves are being used with good results on rayon spinning bath lines. An application of a lining of Teflon (tetrafluoroethylene resin) which has been very successful and which has reduced operating and maintenance expense, is its use as a lining for plug cocks handling liquid carbon disalfide. These plug cocks require no lubrication and thus avoid the contamination resulting from the lubricants formerly required. Teflon and Kel-F are both being used for diaphragms in Saunders-type valves in rayon spinning bath service. COATINGS
Plastic coatings of various kinds are commanding increasing attention for many applications. Teflon is advantageous in several specific applications. One of these is the coating of rayon slasher “cans” where the yarn is dried after the application of finish solutions. These cans are shown in Figure 12. The nonstioking surface properties of Teflon have completely eliminated former troubles experienced because of finish adhering 1364
to the drums and thereby have contributed very appreciably to higher machine efficiency in spite of a lower over-all heat transfer rate. An interesting application of a coating of Teflon is in a wet polymer chute in one of our newer synthetic fiber plants. An aluminum chute is used to deliver wet polymer from a filter on the third floor of a building to the floor below. Much difficulty was originally experienced because of polymer sticking in this chute; constant operator attention was required to keep the chute open. We had just about decided to revise the installation, locating the chute vertically and using B screw conveyor to take care of the horizontal run required. However, as a last resort before starting the redesign, we took down the chute, brushed a coating of Teflon on the inside with a long-handled brush, and baked it as best we could with makeshift equipment, since only a limited amount of down time was available. The chute was reinstalled the next day, and there was no more trouble with polymer sticking in the chute. Thus, a comparatively negligible expense for Teflon coating undoubtedly saved $5000 to $10,000 in redesign and fabricating costs for this system. A similar application of Teflon coating is found in viscose manufacturing operations where xanthating barattes are coated inside with Teflon. When dumping uncoated barattes, operators spent much time scraping the insides to free portions of the charge which adhere t o the vessel, especially in the corners. Teflon has almost completely eliminated this lost time. A coating, somewhat of an old standby, that has been used for years in many applications and is still considered valuable is Heresite, a baked phenolic coating. This coating is used to a considerable extent in textile fibers plants on equipment used for handling or exposed t o various textile finish oils. Finish oils present a variety of problems. Some may be quite corrosive, others may be very efficient paint removers as well. The baked phenolic coating has proved to be one of the best means of protecting equipment exposed to these finishes, as well as of eliminating possible contamination of the finishes. I n addition, it is easy to keep clean-a very important requirement. Other newer coatings such as poly(viny1 chloride) plastisols are being tried out in various applications and promise to fill a real need. This material, applied by dipping, permits the coating of intricate parts which would be virtually impossible by any other method. We are a t present trying it for applications on rayon monorail carriers exposed to weak sulfuric acid liquid and fumes. FILTER SCREENS
An important application of saran which has come to our a b tention is its use for filter screens. Saran woven fabric has been very satisfactory for a rotary vacuum filter screen filtering sodium sulfate crystals out of a sulfuric acid bath. Coarse saran filter screens are standard equipment on the discharge side of coagulating bath filter beds (sulfuric acid) to prevent dislodged particles of filter bed material from entering return lines t o spinning ma,chines. TUBING
I n corrosive atmospheres both saran and Plasticized PVC tubing have been used as substitutes for copper tubing in air supply lines for pneumatic control systems. The cost is 20 to 40% greater than for copper lines in this service. Saran, plasticized PVC, and polyethylene have been used in small tubing sizes for production, laboratory, and experimental setups where small liquid flows are used and where i t is convenient to use pinch cocks as valves. I n some specific applications, the process flows being handled involved sulfuric acid in various concentrations ranging from 1 to 10%. However, our experience has been that saran tubing tends to become brittle after about 6 months service in hot dilute sulfuric acid solutions. In one D u Pont textile plant, 11/2-inch-diameterplasticized PVC
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 47, No. 7
Plastics Construetion Materials tubing is used as a flexible conduit to convey waste yarn in an air stream from an operator’s pick-up nozzle to a stationary waste-catcher box. The advantages of this tubing are its flexibility and its internal smoothness which avoids snagging the yarn with consequent plugging of the tubing. Figures 13 and 14 show this installation. Plast,icized PVC tubing is also extensively used for handling textile finish solutions. TEXTILE MACHINE COMPONENTS AND ACCESSORIES
r
The growth of the application of plastics t o the entire field of textile machinery components and accessories has been phenomenal. When it is realized that the textile industry leads all other industries in the number of people it employs and that there are 24,000,000 spinning spindles alone in the 3000 textile mills in the United States. one can gain some idea of how textiles are contributing to the growth of the plastics industry. Of course, it is impossible, in the space limitations of a general survey paper such as this, to cover adequately even a small part of the machine component applications of plastics. Therefore, only a few representative items have been included. Additional specific information can be .obtained from the polychemicals department of D u Pont and from other plastics manufacturers. Figure 15 shows the dimensions of a bobbin used in some of the D u Pont textile fibers plants; these are made of a paper-base phenolic. They successfully withstand high centrifugal stresses when empty of yarn and high crushing stresses when full. Over 200,000 of these are now in use. They represent the results of many months of experimental testing to find a satisfactory replacement for the materials previously used which included chrome plated steel, brass, and aluminum. The plastic bobbin is economical, very resilient, and easy to handle. Operators’ hands are not subject to cuts from nicks or burrs as is the casc with metal bobbins, and they do not mar the metal driving surfaces on which they are mounted. Furthermore, the cost of these bobbins has not increased over the years to the extent that other materials have-for instance, these bobbins today, of much better quality, are only about 50y0 more than they were in 1938. Another more recent development in the textile bobbin line (Figure 16) is a new braider bobbin made of nylon resin and aluminum. The nylon is molded around and through the aluminum hub to give extreme toughness, and the ratchet teeth, which are molded into the nylon, successfully resist wear and chipping. Nylon’s outstanding impact resistance, toughness, low coefficient of friction, and dimensional stability under all atmospheric conditions combine to make this development eminently successful. Figure 17 shows a molded nylon bolster of a type which has been in use for several years on textile spinning and twister spindles. This material, because of its low coefficient of friction, exhibits almost negligible wear, reduces power consumption. and lubrication problems, compared to metal bolsters,
A somewhat similar application of molded nylon is its use for the creel spindle parts (Figure 18). Five parts of this assembly are molded nylon which take care of both radial and thrust loads. The result is low friction and negligible lubrication problems. The unique properties of molded nylon were put to good use in the development of the GE magnetic yarn tension brake (Figure 19). The tension pulley is a complex nylon molding which is suited to its design better than any other material because it possesses the necessary resiliency, strength in thin sections, durability, and resistance to permanent deformation I n all textile machinery, lubrication of high speed components presents problems, not the least of which is that of staining yarns by oil throw from shafts or wicking along surfaces of guides and pulleys. Elimination or reduction of the need for lubrication is one of the important reasons for the rapid growth of molded nylon bearings such as the bearing used on the twister take-up roll shown in Figure 20. Lubricated metal finish roll bearings used to give much trouble because of finish oils getting into the bearings, washing out or diluting the lubricant, and causing sticking of the rolls. Zytel molded nylon bearings need no lubrication, and no particular trouble occurs if finish gets into these bearings. Wherever dust and lint can accumulate on textile machinery, there is always the possibility of yarn contamhation. One winding machine manufacturer has reduced this possibility on the finish emulsion rolls of his winding machines by closing the open ends of his finish rolls with end caps of molded Lucite, acrylic resin (Figure 21). The rolls so equipped are much easier to clean and keep clean. The end caps are attractive in appearance, re& breakage and discoloration, and can be molded rconomically in a 70-second molding cycle. An important development which has capitalized on the resiliency, toughness, light weight, and low coefficient of friction of molded nylon is its use for twister ring travelers (Figure 22). These properties in combination with the ability to operate a t high rubbing speeds with little or no lubrication have resulted in superior performance and less machine down time for changing travelers. Teflon has also demonstrated particular usefulness as a bearing material in textile machine applications. For instance Figure 23 shows a bobbin holder in which potential trouble from oil and grease leakage from metal bearings has been completely eliminated by substituting a self-lubricating bearing of filled Teflon. This resin makes an excellent hearing material for such applications. It has zero water absorption and will not swell or distort even in extremely humid ronditions--en important consideration where humidity must be held a t a high level for processing control. Product designers and production engineers in general are familiar with the advantages of molded plastics in the manufacture of assemblies involving small lightly loaded gears, bearings, and cams in such items as movie cameras, projectors, business
Figure 21. Winding machine Figure 22. Twister ring trav- Fieure 23. Bobbin Fieure 24. Textile machine drive emulsion roll end cap of molded - eler of molded nylon holder bearing of gears of molded nylon acrylic resin braided Teflon
-
July 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
1365
machines, and calculators. Here again the textile machine designer is not to be outdone. Figure 24 shows how one manufacturer has used molded nylon gears. His customers employ thousands of spindles so equipped which have given exceptional service over periods as long as 4 years, to date, without replacement. The advantages are: 1. Elimination of lubrication avoids adherence of yarn particles and abrasion, which ground and pitted steel gears rapidly 2. Cost is one third less than steel gears 3. They are quiet and neither moisture nor cleaning solvents corrode them 4. They will not chip or break MISCELLANEOUS APPLICATIONS
An interesting use of plastics, which is undergoing experimental evaluation in our plants, is not confined to textile fibers plants, but has application wherever air-conditioning air washers are used. It is the use of plastic instead of metal for eliminator blades on air-conditioning air washers. The purpose of these blades is t o catch and remove entrained water from the stream of air leaving the air washers. These blades usually are made of aluminum or galvanized iron. They are subject to some corrosion and require frequent cleaning. Test installations of extruded polystyrene blades have been made and have proved very successful. The advantages of the plastic blades are that they do not corrode, do not collect dirt readily, and the slight accumulations of dirt on the surface which occur after long operating intervals can be wiped clean. However, these blades have one serious disadvantage which has prevented a more widespread application-
flammability. Air supply systems are not an ideal place to use flammable materials for eliminator blades or duct work, and, therefore, in the interest of safety and fire protection further extension of this use for plastics is suspended pending a complete study of the hazards involved and the possibility of substituting less flammable varieties of plastic in this application. SUMMARY
In appraising plastics for use in textile fibers plants, today we believe that corrosion alone is the easiest problem to solve with the materials now available. Were this the only problem, it would be relatively easy to find a plastic that would meet successfully most of the corrosion problems encountered in textile fibers plants. The big minus value which is encountered, particularly in piping, is the temperature limitation. If permissible operating temperatures could be raised another 50' to 60' C., or even half of that, without loss of chemical resistance or ~ O E E of physical strength, there would be a considerable immediate increase in application possibilities. Judging from what has already been done and the rate of growth in machine component applications for molded plastics, there seems to be no limit t o what can be done and justified. ACKNOWLEDGMENT
The authors wish to thank those men of the D u Pont Co. Textile Fibers, Polychemicals, and Engineering Departments who supplied material and assisted in the preparation of this paper. RRCEIVED for review September 17, 1954.
AC~EPTED May 10, 1954.
Food Processing Plants LAWRENCE J. TURNEY T h e H . W . Madison Co., Medina, Ohio
B
ECAUSE of the possible consequences of toxicity and contamination, food processors must give these factors more careful consideration than manufacturers of most other products. The food industry is generally reluctant to accept new or different materials of construction without complete toxicological and chemical resistance data. Since foods are never pure chemical compounds, the possibility of plastic deterioration as a result of reaction between the plasticizer and the ingredients of the food product is a strongly limiting factor Copper and iron as contaminants may accelerate the development of rancidity in vegetable oils and will discolor vinegar and vegetables. Rubber and metals, when attacked, will impair the taste and aroma of food products. We have learned that certain materials of construction are apparently not attacked by either of two food ingredients individually but may be by a combination of them. For example, Type 316 stainless steel is quite resistant t o sodium chloride solutions and acetic acid but is more readily attacked by a solution containing both. The food industry has learned these and many other facts about currently used materials of constructmion. However, relatively little is known about the results which may be obtained through the use of plastics. Through honest, intelligent recommendations, the plastics industry can do much to hasten the widespread use of their materials in food processing plants. The Food and Drug Administration through its divisions of Pharmacology and Food has already done L good deal of work
1366
that should prove helpful in evaluating resins, plasticizers, stabilizers, release agents, antioxidants, accelerators, colorants, and emulsifiers. Many of the materials are considered not acceptable because of inadequate toxicological data. A list of the materials considered as well as the criteria and procedures used for the evaluations may be obtained from the agencies. The plastics industry would do well not only to cooperate with the Food and Drug Administration in this work but t o conduct separate studies to determine which of their materials may be acceptable and to find substitutes for those which are not. This is a procedure that must be followed by all suppliers interested in introducing a new substance into food products. The food industry i s much in need of materials superior to those presently used. Many types of stainless steel are commonly used, but for some applications they are not entirely satisfactory and are quite expensive. Plastics may alleviate some of these conditions that are accepted as necessary. It is difficult for those not familiar with food processing plants to realize the corrosiveness of sodium chloride, acetic, lactic, and other food acids as well as the aromatic hydrocarbons and spices. However, I believe that manufacturers of stainless steel will readily admit that the food industry presents serious corrosion and erosion problems to which their products have merely come closest to a distant solution. Many food manufacturers and processors have been conducting experiments with various types of plastics as possible replace-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
