US1825652A - Metallic bellows and method of producing the same - Google Patents

Description

?atented 6, 1931 WILLIAM H. BUELL, OF NEW HAVEN, CONNECTICUT manure BELLQWS AND METHUD OF PRODUCING THE SAME 3% Brewing.

My invention relates to improvements in metallic bellows and the like and the method of making and producing the same.

These articles have been made for a long time past by various methods, including the spinning as well-as the hydraulic press method shown in United States Patent No. 349,718, September 28, 1886, Herman Hollerith and Samuel G. Metcalf, for Apparatus for corrugating metal tubing.

While the articles produced have been practical and useful, still in their production there has been a large percentage of loss due to breakage, bursting, etc., which has increased the cost of the articles and rendered the production of a perfect article a rather uncertain matter, and those in use frequently break down due to defective construction or weakened material.

It is with a View to avoiding these objections and producing an article which may be manufactured and formed with a minimum amount of breakage or defectiveness, that 1 made this invention.

1 start with the formation of the tube from which the metallic bellows are formed. For example, the material of this tube is preferably of brass and preferably the brass being approximately 80% copper and 20% zinc.

The important feature of this invention is to have the material of the completed tube with the smallest possible uniform grain size and the greatest tensile strength consistent with requisite ductility. This is accomplished in the drawing and annealing operations of the tube previous to the formation of the tube into the bellows, by annealing at a temperature of approximately 500 to 550 degrees centigrade, for relatively long periods, such as thirty minutes or so. This results in the material of the tube having a substantially uniform grain size without mixture of larger grains, which will permit repeated flexing without slippage or other malformation of the material structure which might result in a permanent set and inefiicient operation.

This process and method of drawing and annealing the tube may be carried out in such a way as to predict and predetermine Application filed December 3, 1927. Serial No. 237,976.

the final essential characteristics of the tube and the bellows, so that the above-described advantages will always be obtained, regard. less of the composition of the tube.

To describe the previous processes and objections more fully, it is understood that in the usual methods of producing thin-wall metallic bellows the spinning operation is usually used, and although the tube before the spinning operation might have the desired grain structure, that is, having the grains of uniform size and sufficiently small to secure the above-mentioned advantages, the s inning operation itself, due to the surface iction and local strains from cold work imposed on the material and themesultant necessary intermediate annealing at a relatively high temperature, will result in a structural formation of non-uniform grain size, with some of the grain structure ex- '7 ceeding maximum desirable limits. This is due to the fact that the higher the anneal, the larger the resulting grain structure, and due to areas of unequal cold work, all grains or crystals will not respond equally to low anneals and will produce a variable struc ture. This is an undesirable property due to the greater liability of structural distortion and grain slippage when the completed article is in use.

Heretofore the desirability of starting th forming operation with a material having a small uniform grain size has never been recognized because there was not the need for it in spun bellows. By controlling the drawing operation of the tube or shell and the annealing operation to secure the desirable grain structure and then avoiding any substantial alteration of the grain structure in the bellows forming operation, the resultant bellows is free from local strains due to substantial variations in grain size, which tend to shorten and vary the normal life of the bellows.

I have found that with the use of brass 80% copper and 20% zinc, approximately, and tube thickness of .006, with an anneal of 500 to 550 degrees 0., the resultant grain size will be such as to reduce bursting in form ing to a minimum.

As previously stated, by controllin the drawing and the annealing, the resu tant characteristics, as far as grain structure with the attendant advantages are concerned, may be readily redicted and predetermined, and it is to this road principle that my invention is articularly directed.

n other words, the idea is to keep as close to the transformation oint as possible, consistent with giving su cient ductility to do the work. The transformation point is the point at which crystals which'have been deformed in cold work are rearranged and take a definite shape and where they are in practically a state of rest and not under strain.

Practically all the annealing is done during the drawing and after the tube is formed and before the bellows forming operation. There is no annealing during the forming of the bellows, and while it may be necessary to give a relief anneal, this will be very low, about 250 to 300 F. with 80-20 brass.

All of the above temperatures apply to 80-20 brass. However, brass up to -30 might be used or the zinc content may be reduced below 20%. Brass 80-20 is the most resistant to corrosion and less liable to season crack than with higher zinc content. \Vhen the zinc content is below 20%, there is not the life to the material.

Phosphor bronze may be used, as well as nickel copper alloys, and in these the same type of anneal but at different ranges is used. The thought is to so anneal the tube that the grain structure is small and uniform so that when the bellows is formed therefrom by bydraulic pressure, the structural distortion and grain slippage will be kept at a minimum. Furthermore, such tubes as might be faulty or weak will be eliminated by bursting during the action of the hydraulic pressure in forming, thus insuring a process tested bellows free from pin holes, etc.

In forming the bellows after the tubes are manufactured, I prefer to use the hydraulic method, which will eliminate the possible changes in grain structure due to the spinning operation, though it is to be understood that other methods may be used than the above, as long as there is no introduction of cold work from spinning or surface friction, or intermediate or final anneal other than a low temperature relief anneal. The hydraulic method in itself requires greater strength in the tubes to withstand pressure.

The low temperature anneal referred to hereinbefore is not normally used in drawing as this anneal is so low that the metal is hard :0 drzlrlw and requires more draws for a given If a hydraulic method is used in which the bellows is collapsed by the pressure of the hydraulic ram at the end of the bellows, it has been found essential to allow the ram to dwell at the end of its stroke for an apof the tube would be uniform andthat the metal-would respond more uniformly to the low temperature anneals, because every part of the tube is of necessity worked to the same degree in being forced through the die. Of course, the use of low temperature anneals insures a resultant low percentage of bursts and breakage in forming.

What I claim is As a new article of manufacture, a thin wall metallic bellows of brass composed of approximately per cent copper and 20 per cent zinc, and havlng a uniform grain structure suflicientl small to prevent or minimize slippage and istortion of the structure upon flexing of the bellows within normal working limits.

In testimony that I claim the foregoing, I have hereunto set my hand this 7th day of June, 1927.

WILLIAM H. BUELL.