US2445309A - Copper topped piston - Google Patents

Description

July 20, 1948. BOYD 2,445,309

COPPER TOPPED PISTON Filed Sept. 22, 1944 Inventor landonfiwfio yal wwrazz.

i 'l' I\ 7 I v 7 Patented July 20, 1948 vUNITED STATES PATENT OFFICE 2,445,309 COPPER TOPPED PISTON Landon B. Boyd, La. Porte, Ind.

Application September 22, 1944, Serial No. 555,293

9 Claims.

This invention relates to a copper topped piston and has for one object to provide a ferrous piston having a thin copper top or deck on its upper surface.

Another object is to provide a method of permanently securing the copper deck to the outer surface of the piston head.

Another object is to define a ielationship between the thickness of the copper deck and its diameter.

Other objects will appear from time to time throughout the specification and claims.

The invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:

Figure 1 is a vertical section through one form of the piston;

Figure 2 is a plan view of one form of the piston before the copper deck has been secured in place;

Figure 3 is a side elevation in part section, showing a modified form of piston.

Like parts are indicated by like characters throughout the specification and the drawings.

The invention is not limited to any particular type of piston or piston construction, and those illustrated are merely typical examples of pos-- sible piston constructions.

In general, the invention is embodied in a ferrous piston, to the top or deck of which is applied a thin coating of copper. This copper coating can be applied by various methods.

In the example shown in Figure 1, the invention is embodied on a ferrous piston having a main part I with ring grooves 2 and the other necessary construction for a piston. Permanently secured on the top of the piston is a copper deck 3. I

The upper surface of the ferrous piston may be smooth or roughened. One suitable form of roughening is that shown in Figure 2, in which the piston head portion 4 is provided with a series of concentric grooves or serrations 5, which may be made in any manner by machining or casting or otherwise. Any such roughenings or irregularities provide a more secure anchorage for the copper on the ferrous top.

In the modified form of Figure 3, the main piston body 6 is provided with ring grooves I and a peripheral upstanding flange 8. A copper deck 8 is positioned on the head of the piston and within the space bounded by the upstanding peripheral flange 8.

In forming the piston, the copper is preferably as pure as possible and is free from oxides and all forms of impurities. The copper may be in almost any form when it is secured on the head of the ferrous piston. It might be in the form of a disc. Experience has shown, however, that one of the convenient ways of applying the copper is to put upon the upper surface of the piston a measured quantity of relatively finely divided copper, such as copper shot." If this is done, a dam or peripheral upstanding flange of metal surrounds the copper. This dam or peripheral upstanding flange of metal can be cast or machined on the ferrous piston, and when the copper is in molten form, it will not spill over at the time it is processed in a high temperature furnace. The copper, in whatever form it is used, is placed upon the piston head, and together they are subjected to a heating in a furnace at a sufflcient temperature to cause the copper and the ferrous piston body to become permanently bonded or brazed together.

While the invention is not limited to the use of a flux or in fact to any particular flux, it is convenient for general purposes to use a flux, and one suitable flux includes the following inredients:

Per cent Manganese dioxide 25 Borax '15 and to this amount add Fine copper powder (by weight) 25 The materials above listed are then mixed preferably with any non-petroleum oil as a vehicle to a consistency of thin paint, and they are applied to the surface of the ferrous piston head to which the upper disc is to be brazed or fixed.

One of the reasons for providing a copper deck on a piston is to reduce piston heating. Experience has shown that if t e copper deck is too thick it does not produce this result. Furthermore, if a too thick deck of copper is used it will hold sufliicient heat so that it will conduct this heat rapidly to the body of the piston. If the copper deck is too thin, it cannot absorb the heat of combustion in sufficient quantities, and, on the succeeding cycles, it may not have retained suflicient heat to emit it in the quantities necessary for the correct operation of the piston.

The thickness of the copper deck must bear a specific relationship to the diameter of the piston itself. The effect of a copper deck of the proper thickness is apparently to act as a heat discharging member, so that heat which enters the copper disc does not in the main penetrate to and is not in the main conducted to the body 8 of the piston, but is discharged again into the combustion space. In this sense, the copper may be considered as a heat-reflective agent, or if the heat enters the body of the copper deck, it is reflected outward again from the inner surface of the copper deck or from some point which is between the inner and the outer surface of the deck, and this is given up again into the combustion space and is prevented from entering the body of the piston. Practical tests have shown that pistons equipped with copper decks proportioned according to the formula and explanation given below result in keeping the piston substantially cooler than is the case where the piston is formed of other materials, and particularly where the piston is formed entirely of a ferrous metal or alloy.

There is set out below an algebraic formula by means of which the thickness of a copper deck for a given diameter of piston may be readily determined. In the explanation the expresison "mean thickness appears. In some cases the upper surface of the head of the ferrous piston is smooth. In that case the thickness of the deck may be uniform. In cases, however, where the upper surface of the ferrous piston is roughened, serrated or grooved, the expression "mean thickness means the thickness half way between the serrations, grooves or irregularities and the deck. The formula and its explanation are as follows:

X=mean thickness of copper deck Y=a constant used in the equation and shown in table set out below D=diameter of piston B=coefllcient multiple (The expression coeificient multiple" means the number of times the coefficient of iron will divide into the coefficient of copper. For the sake of simplicity this is taken at a ratio of 4 to 1 rather than carrying it out to the fifth and sixth decimal places in a complete calculation.)

Inches in Diameter Constant For pistons of approximately 8 inches of diameter and up, a copper deck thickness of approximately a, inch is satisfactory. The thickness of the copper deck for a piston of a diameter between any two diameters above given is calculated by interpolation between the constants for the said diameters. Thus for a piston 01 3% inches diameter, the constant Ywill be between 4360 and 5270.

The formula above is accurate as indicated for general commercial diameters of pistons. In practical and laboratory tests, it has been proved accurate as applied to pure copper. Obviously if other non-ferrous metals were used instead of copper, because of their different coefficients of heat conductivity, a different constant would be used.

The details of the brazing cycle form no part of the present invention and are not disclosed in detail herewith. Any heating cycle which will cause the copper to be permanently bonded to the ferrous piston is suitable. Many methods of brazing copper on ferrous metals are now known and in practice. Hydrogen brazing that is to say, brazing in a furnace with any reducing atmosphere-may be used for the brazing heating. In general, all that is required of the heating cycle of this invention is that the copper be adequately bonded to the ferrous metal of the piston and that the physical properties of the ferrous metal be not rendered unsatisfactory.

I have set out above a method of producing and a method of calculating a piston which includes a ferrous main structure and a copper deck. Such pistons have been highly successful both from a point of view of a long engine life, long piston life and improved engine eificiency. Pistons made as described above have operated for long periods of time in practical commercial use with outstanding success. Pistons for engines of various sizes and types can be made if the instructions above given are followed. The theoretical explanation of the successful operation of such pistons set out above is believed to be valid and accurate. However, the successful results are proved and can be repeated by following the teachings above set out, irrespective of any theoretical considerations of operation.

I claim:

1. A copper topped piston comprising a main ferrous piston body and a thin desk of pure copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to the following formula:

X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coefllcient multiple of the copper, and Y a factor varying with the piston diameter.

2. A copper topped piston comprising a main ferrous piston body and a thin deck of copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to the following formula:

X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coefllcient multiple of the copper, and Y a factor whose value is determined by the piston diameter.

3. A copper topped piston comprising a main ferrous piston body and a thin deck of copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to th following formula:

X equalling the mean thickness of the copper deck, D th diameter of the piston, B the heat transmission coefficient multiple of the copper, and Y equalling a factor of the order of 4360 for a piston having a diameter between 2 inches and 3% inches, and a factor of the order of 5270 for a piston having a diameter between 3 inches and 3% inches, and a factor of the order of 6400 for a piston having a diameter between 4 inches and 4 inches, and a factor of the order of 8540 for a piston having a diameter between 4% inches and 5% inches, and a factor of the order of 10,800 for a piston having a diameter between 5 inches and 6 inches, and a factor of the order of 13,000 for a piston having a diameter between 6 inches and 7 inches.

4. Av copper topped piston comprising a main ferrous piston body and a thin deck of copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to the following formula:

X X equalling the means thickness of the copper deck, D the diameter of the piston, B the heat transmission coefficient multiple of the copper,

and Y equalling a factor of the order of 4360 for a piston having a diameter between 2 inches and 3% inches.

5. A copper topped piston comprising a main ferrous piston body and a .thin deck of copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to the following formula:

X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coefficient multiple of the copper, and Y equalling a factor of the order of 5270 for a piston having a diameter between 3% inches and 3% inches.

6. A copper topped piston comprising a main ferrous piston body and a thin deck of copper bonded to the upper surface of said piston, the thickness of said copper deck being calculated according to the following formula:

X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coemcient multiple of the copper, and Y equalling a factor of the order of 6400 for a piston having a diameter between 1' inches and 4% inches.

'7. A copper topped piston comprising a main ferrous piston body and a thin deck of copper bonded to the upper surface of said piston, the

thickness of said copper deck being calculated according to thefollowing formula:

Bur "T X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coefficient multiple of the copper, and Y equalling a factor of the order of 10,800

'for a piston having a diameter between 5% inches and 6 inches.

9. A copper topped piston comprising a main ferrous piston body and a thin deckof copper bonded to the upper surface of said piston, the thickness of said copper deck being calculatedaccording to the following formula:

X equalling the mean thickness of the copper deck, D the diameter of the piston, B the heat transmission coefficient multiple of the copper, and Y equalling a factor of the order of 13,000" for a piston having a diameter between 6% inches. and 7% inches.

LANDON B. BOYD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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