Pyrex glass in Chemical Industry, insulators mentioned

INCREASING USE OF GLASS IN CHEMICAL INDUSTRY

Papers Read at Meeting of American Chemcial Society Give Interesting Comment

on Development of Low-Expansion Glass For Use in Various

Chemical Processes.

At the spring meeting of the American Chemical Society held in New Haven during the week of April 2, J. F. Greene, of the Kimble Glass Co., of Vineland, N. J., discussed "Glass in the Chemical Industry," and A. E. Marshall, consulting engineer of Baltimore, talked on "Industrial Pyrex." During the meeting, the new chemical laboratory at Yale University, the gift of John W. Sterling, was dedicated.

The following summaries of the papers by Messers Greene and Marshall are from Chemical and Metallurgical Engineering:

GLASS IN CHEMICAL INDUSTRY

"Glass as a material for industrial construction has been known and used for some time. Recently, however, it has seen new application in the use of low-expansion glass for the fabrication of pieces much larger and heavier than any previously attempted. The properties of glass which make it a desirable element in industrial chemical engineering practice are: (1) Its transparency, (2) its possible perfection of finish making a 'glassy finish' a byword for supreme smoothness, (3) resistance to chemical attack, (4) the facility with which it can be blown, drawn, pressed or cast. All these properties are not inherent to the highest degree in all glasses, and usually a glass which rates high in one desirable quality will be less suitable in another respect.

"The disadvantages of glass are likewise more apparent in some types than in others. They are: (1) brittleness and (2) low tensile strength in the piece, due to the enormous influence of scratches and cracks. Two other properties that come in question are resistance to heat shock and easy of annealing. Glasses vary widely in the possession of these qualifications.

"Having in mind the necessary properties of the material which is to compose any industrial piece, the chemical engineer will arrive at a reasonable decision by considering how well any commercial glass meets his specification and how its total cost (first cost and maintenance) will compare with that of any other material from which the piece might be fabricated. It will sometimes be found that a very expensive material will be cheapest in the end due to low maintenance costs and fewer interruptions to production. In other words the cheapest possible material will be the only one really economical.

In application where transparency is the determining factor, glass is almost without a rival. Such applications are sight feed glasses, high-pressure gage glasses, glass plates for peep holes, etc. Sigh feed glasses, gage glasses, etc., are usually connected to a metal fitting. In selecting a glass for this service, accuracy of sizing should be considered, since a good fit is essential. The glass should be selected to meet the temperature, pressure and heat shock requirements of the particular use. The more trying these are the more expensive glass must be used.

"For resistance to chemical attack, glass is excelled in some instances by tin and platinum. It is superior to them in its resistance to phosphides, sulphides and the halogens. Earthenware has the disadvantage of porosity, and chemical stoneware improves in resistance as it approaches a glass in composition. No glass, offers complete resistance to strong alkalis. However, much glass is used as small parts of electrolytic caustic plant, because the attack that takes place does not harmfully contaminate the caustic and the pieces can easily be replaced. Thus are used brine wells, a molded tube 3x9 in. with a 3/4 in hole drilled in the bottom and caustic tubes, eccentrically shaped tubes about 12 mm. in diameter. The manufacture of these small parts in any other material than glass would be more expensive and not so satisfactory in use.

"At a recent application of glass as a resistant material was described by F. C. Zeisberg in a late number of Chemical and Metallurgical Engineering. Small glass rings were used as a tower packing. It is possible to make glass rings very much smaller than earthenware or stoneware rings and as a result obtain a packing material with an enormously increased surface in a given volume. The use of glass pipes, known as 'powder tubes,' for pipe lines in the powder industry is an application of long standing. The well-known Hart condenser, with tube 3 inches in diameter and 6 feet long; is still another application.

"Its ease of fabrication makes glass a desirable material for many applications where transparency and resistance are not especially necessary. Jets and nozzles of various types and sizes are readily made of glass. The fire-polished finish gives a nozzle which offers the minimum resistance to flow, and allows a perfectly untroubled stream to issue. Such jets are usually made from glass tubing by reworking at the lamps, although larger sizes could be blown in a mold.

"There are numerous small parts and fittings in use in the chemical industries which could be made of molded or pressed glass, doing away with expensive alloy metals and machine work. The glass piece would besides be of good resistance to chemical attack and could be fabricated from a glass having the necessary strength and resistance to heat shock.

"Before settling on the final design of parts which could be made of glass, it is well to inform the manufacturer of the service under which the material is expected to stand up. He may be able to suggest minor changes in design which will greatly increase ease of manufacture. A serious consideration of industrial glass shapes and products will well repay the designing engineer."

INDUSTRIAL PYREX

Mr. Marshall discussed Industrial Pyrex from the stand point of desirable basic characteristics and the methods of fabrication, saying:

"The interest displayed by chemical engineers and manufacturers in the adaptation of Pyrex glass to plant uses has resulted in a continuous progression of development work and has also provided an indication of the demands of the chemical industry for materials with acid-and heat-resisting, properties.

"In a previous article published in Chemical and Metallurgical Engineering an outline was given of the initial stages of applying a material, familiar in laboratory shapes and sizes, to actual plant-scale operations. The present article is a summary of more recent developments and the reasons which lend interest to the future possibilities of Pyrex in the industrial field.

"A general consideration of the essential requirements for plant construction materials indicates the following as desirable qualities:

"1. Resistance to chemical corrosion over a wide range of temperatures.

"2. Resistance to heat and to changes of temperature.

"3. A reasonable degree of mechanical strength.

"4. Possibility of production in a variety of shapes.

"5. A cost which makes the complete plant unit a commercial possibility.

"No single manufactured product completely meets all of these requirements, although nature has provided certain precious metals which possess ideal characteristics. In the case of precious metals, however, the quantities available and high cost largely remove them from consideration as industrial possibilities. Plant materials have therefore to be selected with due regard to a balancing of useful properties against known limitations.

"A survey of the chemical physical characteristics of Pyrex indicates many desirable factors coupled with certain present limitations in size which somewhat restrict its field of application or call for the development of new types of construction based on available shapes. Some of the basic engineering data for Pyrex glassware follow:

Specific gravity.........................................................................   2.25

Specific heat ............................................................................   0.20

Elasticity coefficient..............................................6230 kg. per sq. mm.

Linear expansion coefficient 19°-350°C. .............. 0.0000032 per deg. C.

Thermal conductivity ..............................................................   0.0027

Electrical resistivity. (surface)............. 10^14 ohms at 34 per cent humidity

"Mineral acids, with the exception of hydrofluoric and phosphoric, have no appreciable action up to their respective boiling points.

"The limitations of size which have been referred to are of importance to the engineer, as lack of this information may call, for substantial changes in design. An appreciation of the present limits can best be secured through a consideration of the various processes employed in fabricating industrial Pyrex. The principal methods of production are: Pressing, blowing and working by lamp.

"The maximum size of a pressed article is a factor of weight of glass and nature of shape. Simple shapes such as hemispherical dishes can be made 24 inches in diameter, 30 liters capacity. More complex shapes have smaller limits, centrifugal pump liners, for instance, being a possibility up to 15 inches maximum diameter. Pressed shapes are desirable whenever fairly, accurate external dimensions are desired, although it should be realized that the precision of a machined metal product cannot be obtained in Pyrex except with an extremely high rejection factor.

"The second process, blowing, is restricted, in the case of industrial Pyrex, to blowing into molds. This gives a useful degree of external surface accuracy and also permits manufacture with wall thicknesses adapted to the intended use. Condenser parts made in molds can be held to one-sixteenth to one-tenth of an inch walls and high cooling efficiencies secured in the complete condensing apparatus. Conversely, socket pipes can be made with heavy walls to withstand the abuse of careless handling and mechanical shocks. Present sizes of mold-blown ware range from 72 liters capacity for flask or retort shapes to 12-inch diameter for socket pipes and cylinders.

"The third process, working in the lamp, is an extension of glass-blowing practice to the manufacture of complex shapes incapable of production by pressing or blowing. T's, L's and other fittings are made by lamp working and have a present limit of three-inch bore. Lamp work is also resorted to in the attachment of side connection, spigots, etc., to articles produced by the mold-blown process.

"All three processes are being gradually developed toward the production of larger sizes, and an evidence of this progress is best supplied by a comparison of material available six months ago and at the present time. The final limits of size, will, of course, be set by structural consideration, but these limits are a long way beyond any of the available methods of manufacture.

USES OF INDUSTRIAL PYREX

"Industrial uses of Pyrex can be grouped under specific applications of properties as this method affords a useful guide to the consideration of new apparatus not included in the list. Four classifications have been followed in preparing the summary, although it will be recognized that in some cases several factors are concerned in the one piece of equipment.

"1. Uses where acid resistance is important: Acid distillation sets. Hart nitric acid condenser tubes, 'S' bend nitric acid condenser, hydrochloric acid coolers, pipe lines for acid gases and liquids, small tanks and pots.

"2. Uses where resistance to heat shock is desirable: Condensers for organic liquids, parts for tubular evaporators, receivers for hot condensates, etc., pans and trays for driers.

"3. Uses where purity of product is essential: Evaporating and crystallizing dishes, pipe lines for liquid food products, drying trays for biologicals, alkaloids, etc., tanks for precious metals solutions, reels for silk dyeing machines.

"4. Uses involving transparency: Sight glasses for stills, etc., gage tubes for boilers, tanks, etc., tail boxes for distilling columns, sight pipe sections for chamber plants, apparatus for photochemical synthesis.

"The majority of the applications given above relate to complete pieces of equipment, so in these cases special features of construction are not involved. The user of industrial Pyrex should remember, however, that while the material has a remarkably low coefficient of expansion, it should not be heated by a direct flame. Suitable provision in the design of the heating arrangement to obviate direct flame contact does not imply any appreciable loss utilization of heat units.

"Pyrex pipe lines, whether of the flanged or socket type, call for modification of usual methods of construction. Flanged pipes are not bolted together direct, but use is made of an extra pair of loose flanges (aluminum, cast iron or pressed steel) and external rubber gaskets between the metal flanges and the pipe. The surfaces of the Pyrex pipe flanges are ground true and suitable gaskets inserted.

"Socket pipes should not be cemented with hard setting socket fillers, but a cement employed which will give the desired resistance to the acid gas or liquid with retention of plasticity. An asbestos rope forced into the bottom of the socket space has been found often to be a desirable feature of this form of construction.

"Development work on a number of new industrial applications of Pyrex is being actively carried on, and it is confidently expected that Pyrex will soon pass from the 'new material' stage and become one of the accepted standard materials for chemical "plant construction."