US2268723A - Method of lapping valve plugs - Google Patents

Description

Jan. 6, 1942,

e. F. SCHERER METHOD 0F -LAPPING VALVE PLUGS Filed NOV. 12, 1938 7 Z7 ZIP *715 g l QQJ INVENTOR- Geoye/Eibererr which a changes.

"ast a. 1942 UNITE STATE! Mnrnon or LAPPING vulva mes George Scherer, San Francisco, assigm" J or to Merco Nordstrom Valve Company, Pittsburgh, Pa., a corporation of Delaware r a Application November 12, weas l-a1 No. 239,995 (Cl; 51-281) 13 Claims.

The present invention relates to plug valves intended for high temperature service. a

It has heretofore been observedthat when plug valves, whether lubricated or not, which have been'carefully lapped and adjustedtobe seater sneue extending missiles tin upright ed against the pressure carriedby the line at ordinary temperatures, are. subjected to services carrying fluid at elevated temperatures, the

valves frequently become stuck or develop leaks,

or both. According to the present invention, 1 fit the valvemember of a valve intoits' seat at a temperature'. above normal or room temperature,

preferably substantially at the temperature for the valve, or for maintaining-the valve atf'ali elevated temperature during theflttingopera- ,tion, and the fitting operation may be carried out in any suitable way. For example, in applying the invention to a plug valve, the valve may be submerged in a bath of high boilin mineral oil, molten metal, or a sand bath or other heat post. 9, suitably supported. A; gas burner It or other suitable source of heat is provided beneath V the tank 6' for heating'the'liquid therein. The

liquid inthe tank maybe any suitable hydrocar bon oil boiling above the temperature at'which .the lapping opera'tionis tobe-performed, or may consist of diphenyl, a metal having allow melting point, or a bath of sand. The plug H, of the i5 carried by the spindle l6 so that the plug may J freely center itself with respectto the valvefseat l'linthecasing; I Spindle lids rotatably supported in, the sleeve is mounted in the outerend of a bracket supported by the upright 9, and the rear, side of sleeveiS is provided with arack 2i meshing with a gear mounted on a shaft 24 journalled in the bracket 20. If desired, one endoff shaft 24 may be square to receive the inner end ota handle 25 carrying a weight 26. The upper end of spindle I'B 'is'joumalled in the'projectingfpart 21 of theiupright 9 and has abevel gear 28 rest- 7 ing on the extension, the Bear .28 being splined transfer medium heated by agas burner or other suitable-source of heat, and, lapped at tempera-- tures of about 400 Fahrenheit to. 1000" Fahrenor. at anyother temperature above room or normal temperature at which thef'valvesare to be operated in service. The lapping compound on the upper end of the spindle l6 so that the spindle may be moved axially therethrough while the gear'is rotating, Gear 28 is driven by bevel gear on one end of-a horizontal shaft 31. journalledin the brackets 32 and 33 and carrying a step pulley 34 which may bedrive'n from any may consist of finely divided *Carborundum or other suitable abrasive suspended in a suitable carrier such as a non-volatile or onlyslightly volatile mineral 011. After lapping the plug, the

valve is removed fromthebath,- cleaned, assembled and tested at the temperature of the lappingoperation, of lapping the valve, the fitting may be accomplished by anyother .method of grinding or by machining at elevated temperatures. n 1 a p v The invention will be described in detail in connection with the aoooncipany-ing drawing, in

Figure 1 shows a preferred apparat for carrying out the method, andv Figures 2 and 3 show diagramm'atically my theory of the distortion due to temperature Referring to Figure 1, a valve ca g 4, shown in longitudinal section, is loosely hel' in a cradle 5 supported on the bottom of a B which may be filled with oil 1 above the levelgot the convenient source of. power. 7

During operation, while the plug rotating,

it is periodically lifted and returnedto its seat.-

This is accomplished by a mechanism compris- 85 ing a cam 36 secured to the shaft 24 co-operating with a cam 31 secured on one end of shaft 39 which is ioumalled in bracket 20. Shaft 39 car- Y ries a gear 4| meshing with a gear 42 secured to.

a shaft 43 journalled in an arm 44 of extension .40 20 and a-boss 46 at the,top .A gear at the top of shaft 43 meshes with a gear 48 carried by a shaft 3|. Preferably, the gearing ratio is such that plug'll does not make a complete revolution in the valve seat when it"is lifted by the engagement of cams 36 and 31, although if desired, the

plug may make slightly more than one revolu-" tion before 'it is lifted. Also, it will be understood that instead of rotating theplug it may be oscillated back and forth and periodically lifted,

50 or the lapping operation may be carried out with any other motion known in the art.

The abrasive compound used for the lapping operation preferably consists of 'a mixture of a high boiling mineral oil and a line grade of valve. The tank 8 may be supported ma ame fCarborundum abrasive powder, and if desired,

valve having a port I2 is held loosely by a chuck the lapping compound maybe thickened by the addition of asphalt or other suitable thickening agents. The actual proportions and type of material used for the lapping operation may be varied in known manner in accordance with the nature of the metal of which the valve is made, and the temperature at which. the lapping operation is carried out.

A mineral oil bath may be used for carrying out the lapping operation up to about 600 Fahrenheit, and for higher temperatures the sand bath methodmay be employed, as most oils are volatile abovethis temperature. It will also valve port and passage are ground 01!, thus producing a plug having a circular form at the elevated temperature at which lapping occurs, which has aperfect lit with the seat. It is, of course, apparent'that when a valve is so lapped and fitted at a high temperature it will assume a slightly oval shape in cross section at lower tembe understood that, if desired, the bath may be made up of molten lead or, other solid material having a suitable high boiling point so that it will not be volatilized at the temperature at which the lapping operation is carried out. The lapping operation may be carried out at any de-.-

sired temperature up to about 1000 Fahrenheit.

or higher. 7

I believe that the difficulties heretofore experienced in attempting to operate cold lapped valves at elevated temperatures is due to the unequal expansion of the metal, which results from the fact that the various sections of metal in the valve are not of equal thickness. Thus, referring to Figure 2, if a plug ll having a port I! therethrough is heated, the chord 5| forming the walls of the port-will expand greater than the wall"along the transverse diameter, indicated by thedot and dash line-I2, and the edges ofthe port will form projecting lips. These lips may-project about ten thousandths of an inch or more, depending on the temperature, properties of the metal, and relative sizes oi: the various sections. In other words, the plug will assume a generallyelliptical shape between the ends of the port, as indicated bythe dot and dash line 53. At the same time the seat II will expand unequally,'the lips 54 adjacent the: passageway expanding less than the rest of the seat and as a .iWhile I have illustrated peratures. However, in lubricated valves, the

slight oval shape appears to have no disadvantage, as the lubricant has sufllclent viscosity at low temperatures to provide an adequate seal for the valve. In such a valve, although the viscosity of the lubricant'is reduced at higher temperatures, the closer fit of the plug and seat compensates for the decrease in efliciency of the lubricant film and provides a satisfactory seal.

The temperature at which difliculties in operation will be experienced with cold lapped valves will depend on the nature of the metals in the valve, and on other factors. In general, ordinary carbon steel or alloy steels intended for operation at temperatures at or above 400 Fahrenheit should be hotilapped according to the present invention.

At high temperatures a close fit of the plug to its seat isquite essential because at such temperatures the lubricants-employed losetheir viscosity and sealing properties, whereas in a valve which has a loose fit at low temperatures it is not ditlicult to provide lubricant at such temperatures having the proper viscosity to seal the valve and'prevent leakage.

to a plug'valve, it will be understood that the inresult the 1ips53 of the plug port wi1l-abut vention may be applied to. any other type of valve. without departing from the spirit. or scope thereof;

What I claim as my invention and desire to secure by Letters Patent is:

1. The method of fitting a valve plug into its seat whichc'omprises lapping the plug in its seat in the presence of an abrasive lapping compound at a temperature above normal tionof extraneous heat.

' 2. The method of fitting a valveplug into its seat which comprises lapping the plug in' its seat in the presence of an abrasive lapping compound by the. applicaat a temperature of about 400 Fahrenheit or higher. V

3.'In the manufacture of a plug valve, the method which comprises cutting the plugmemher and its seat, to a' substantially circular cross section form at a temperature above normal obtained by the application ofextraneous heat.

. GEORGE my method applied

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