US2337903A - Pump rotor manufacture - Google Patents

Description

Dec. 28, 1943. J. A. LAucK PUMP RoToR MANUFACTURE Filed March 2, 1942 PatentedDec. 1943 UNITED STATES PATENT oFFicE 2,331,9o3 I PUMP noron MANUFACTUBE John A. Lauck, South Euclidfohio, assignor z.

Pesco Products Clo.; a corporationof Ohio Application March z; 1942, serial No. 433,041

4 claims.

by employing a non-metallic composition maa terial having the requisite critical properties when treated in accordance withV the method herein disclosed. The material used must have substantially the same coefficient of 'expansion as the lightweight metal housing in which the rotor is to operate. In the present instance this ment of rotors, the manufacture of which forms the principal subject matter ofthis invention;

Fig. 2 is a perspective-like view of a bar of phenolic compound stock in the preferred shape for use in practicing the first s tep of the present method of manufacture. l

Fig. 3 is a perspective-like view of apump rotor which has been rough-machined from the bar stock of Fig. 1 in accordancewith the first-step of the present method of manufacture.

Fig. 4 is a view indicating schematically an electric furnace for carrying out the second method step.

coeiiicient of thermal expansion must be substantially the 'same as that of either aluminum or magnesium, since it is contemplated that the housing is to be formed of one of these metals.

.This relationship is important because of the extremely high temperatures present in the'operation of this-type of dry air pump. The material employed must have the additional property of not picking up or galling when the tip of the rotor contacts the aluminum or magnesium alloy hous- Referrlng in greater detail first to Fig. 1 of the drawing, a dry air pump III ofthe present type is made up essentially of a main enclosing housing II preferably of aluminum or magnesium and formed internally with a pair of overlapping cylindrical chambers I2 and I3, each chamber adapted to receive therein an identical toothed rotor referred to generally at I6. Each of these rotors I8 has a generally overall triangular transing as is sometimes unavoidable in this type of installation, and which accounts largely for the fact that metallic rotors have been found unsatisfactory. Itis important to notethat this is clearly distinguishable from a bearing relationship, and while a particular compound may have acceptable properties from the point of view of .a bearing, the same may be completely unsuitable.

Other and more particular objects.A advantages -and uses of my invention will become apparent from a reading of the following specification taken in connection with the appended drawing forming a part thereof and wherein: A Fig. 1 shows a vertical cross-sectional view through a dry air pump bringing out to advantage the particular construction and arrange-Y verse cross-section, each apexA I 6a being given a small arcuate extremity corresponding to the contour of the enclosing cylindrical chamber walls. The joining side wall dening portions of .the rotor forming impeller surfaces each having an intermediate axially extending recess I 6b therein for embracingly receiving a complementary apex of the adjacent rotor to thus accomplish pumping upon the rotation of the rotors. It is of particular importance to note that each rotor I8 is supported on an independent supporting shaft I1, keyed to the respective rotors in torque-transmitting relation .bypins I8. 'I'hese independent supporting shafts are iournalled in the'opposed ends of housing II and each driven by a suitable gear and motor driving arrangement (not shown). The extremities lSa ofrotors I 8 are formed to have normally a. very small clearance with the inner periphery of chambers I2 and I3. This is important as these rotors must be operatedat-a very high speed, and hence the rotors and their surrounding walls, then any slight differential expansion due to uneven heating results in metallic contact between the rotors andthe surrounding walls which results in freezing the rotor to the housing. I have solved the above and related proble by fabricating rotors i6 o f a selected non-metallic compound, which when treated according to the herein disclosed method, results in a rotor having all of the essential characteristics of a metallic rotor without the accompanying disadvantages. be readily made from a numberAk of phenolic condensation products, particularly those impregnated with bers such as asbestos. `While a number of such nonmetallic composition products or materials may be used with satisfactory results, I have found that the product known as Formica Grade AA and complying with the following essential specifications, gives particularly satisfactory and improved results:

Formica Grade AA here referred to is a composition available on the open market and manufactured and supplied by the Formica Insulation Co. of Cincinnati, Ohio, under a formula in existence on March 2, 1942. It comprises a laminated asbestos cloth or, alternatively. a macerated asbestos cloth, impregnated with a phenolic resin and cured under heat and pressure.

The method of forming and treating will now be described. The phenolic compound is preferably obtained from the'supplier in the form of cylindrical bars of stock such as indicated at 30 in Fig. 2. In the rststep of my method a bar 30 of phenolic stockis subjected to a machining operation to produce a rough-machined rotor. This may be a breaching or bobbing operation involving removing or cutting away a portion of stock 30 to produce a gear-like shape such as illustrated in Figs. 1 and 3, having roughly the desired overall dimensions. Next, a plurality of theserough-machined rotors are mounted on'a rack 40 and introduced into a baking furnace indicated schematically at 4| in Fig. 4 and including a housing 42 to which access is had through a door 43 closing, but not completely sealing the housing 'in order that moisture may be driven out. An electric furnace heating. element 4d is supplied with current from a source (not shown).

I have found that such a rotor may I'he temperature in the furnace 4i -is raised to a desired degree and maintained for a predeterf mined length of time. Temperatures referred to herein are Fahrenheit.

I consider as being a particularly important part of the herein `disclosed invention, the selected temperature maintained'in furnace 4i during the baking operation, which has been found to be critical within certain definite limits. I have determined that very satisfactory results are secured by maintaining a temperature of approximately 350 Fahrenheit during the baking 'operation If the temperature is lowered as y ture should be approximately 350 Fahre`nh eit.

-With reference to the proper time of exposure or baking, generally speaking, this is not as criti- -cal and controlling as is the above described temperature factor. However, a certain relationship must be observed within limits in order to obtain the best results. I have determined that very satisfactory results are obtained in the treatment of a three-inch overall diameter rotor by baking the same under the above described temperature conditions for a period of three hundred hours. Similarly, effectiv results have been obtained by exposing or baking a six-inch overall diameter rotor of the same phenolic material for a period of five hundred hours. These two examples are believed to present fairly satisfactorily the relationship between size of rotor and the number of hours baking required, from which it will be seen that the time required goes up rapidly with any increase inoverall diameter. The preferred baking time may be arrived at approximately by multiplying the rotor diameter raised to the 0.75 power by the factor 131. It has been observed that any substantial departure from the above outlined general relationship between time and size results in an inferior rotor. For examl` ple, it has been found that where a six-inch over; all diameter rotor was exposed to 350 Fahrenheit within furnace 5I for only four hundred fifty hours, there resulted a slight shrinkage after the rotor had been installed in a pump and operated at an elevated temperature. However, by increasing this time to fivehundred hours, it was found that only negligible shrinkage occurred after installation and operation in a pump under equivalent conditions.

Following the completion of this baking step, rack fill is withdrawn from furnace Iii and the rotors allowed to cool to room temperature.

vThe final operation prior to installation in a pump, is the finish machining operation to provide the proper tolerances.

The results of the above machining operation` and heat treating is a finished rotor having the equivalent operating characteristics of an aluminum or magnesiumrotor including particularly the same coefhcient of expansion when subject to the heat present in normal operation While not having the undesirable properties of an aluminum or magnesium rotor such for example particularly as the objectionable property of picking up. or galling when incidental contact occurs with the housing wall which renders metallic rotors unsatisfactory.

While I have disclosed my invention by reference to certain specific apparatus and steps. it will be understood that equivalent variations are contemplated as coming within the broad scope A thereof.

I claim:

1. The method of manufacturing a dry air pump rotor adapted to operate in a lightweight metal housing, which method comprises first rough-machining a body composed of a phenolic resin to form teeth thereon adapted to interiit between successive teeth in aA corresponding adjacent rotor, next baking said rotor in an oven at from 330 Fahrenheit to 370 Fahrenheit, this baking being, carried out over a period cf-from one hundred to five 'hundred hours, depending upon the size of the rotor and then performing a finish machining operation to bring the radial extremities of said rotor to the proper close clear ance with the cooperating wall of said housing, said heating step being effective to remove any appreciable tendency of the phenolic resin to shrink -when subsequently operating at elevated temperatures in an associated pump.

2.'Thel method of manufacturing a dry air pump rotor adapted to operate in a lightweight metal housing, which method comprises first associated pump and wherein any incidental con- Itact between the extremities of said rotor and a finish machining operation to bring the radial extremities of said rotor to the proper close clearance with the cooperating wall of said housing. said heating step being eiective to remove any appreciable tendency of the phenolic resin to shrink when subsequently operating at elevated temperatures in an associated pump.

3. The method of manufacturing a rotor for an aircraftdry air pump of the type having a lightweight metal surrounding housing and requiring a correspondingly lightweight rotor which mu'st have substantially the same heat coeicient of expansion as that of said housing, said method comprising rough-machining a cylindrical bar of phenolic resin stock to form thereon coaxially extending teeth adapted to be receivedin the groove or valley between successive teeth of an adjacent complementarily formed rotor wheninstalled in a housing and rotated, next baking said rotor in an oven at from 330 Fahrenheit to370 Fahrenheit, said baking operation being extended for a period of from one hundred to ive hunl dred hours, the particular heating time selected between these two limits being determined in accordance with the size of said rotor, said heating operation being effective to produce a rotor which has no appreciable tendency to shrink when operated at elevated temperatures in an the enclosing housing wall produces no adverse effect upon the operation thereof.

4. The method of manufacturing a rotor for an aircraft dry air pump of the type having a lightweight aluminum alloy housing formed with a rotor chamber therein and requiring a correspondingly lightweight rotor having the 4same coelcient of expansion as that of the housing,

said method comprising rst rough-machiningV one hundred to ve hundred hours, the particular heating period selected between these two limits 'being determined in accordance with the overall diameter of the rotor, a three-inch overall diameter rotor being baked at the above temperature for one hundred hours while a six-inch rotor is baked for a period of five hundred hours, said baking operation being eiective to so condition said phenolic material forming the same as to'eliminate any appreciable tendency of said rotor to shrink when operating at elevated temperatures in an associated pump and wherein any incidental contact that may subsequently occur between said phenolic rotor and said associated metal housing does not adversely atleet the operation thereof.

` JOHN A. LAUCK.

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