US2182712A - Rotary scraper for tubular heat exchanger - Google Patents

Description

Dec. 5, 1939 w G V L 2,182,712

'ROTARY SCRAPER FOR TUBULAR HEAT EXCHANGER Filed Oct. 26, 1938 2 Sheets-Sheet l Dec. 5, 1939. w. G. VOGEL ROTARY SCRAPER FOR TUBULAR HEAT EXCHANGER Filed Oct. 26, 1938 2 Sheets-Sheet 2 Patented Dec. 5, 1939 pmrso srrss ROTARY scaArEn FOR TUBULAR HEAT EXCHANGER Werner G. Vogel, Louisville, Ky. Application October 26, 1938, Serial No. 237,135 Claims. (01. 259-109 This invention relates to rotary scrapers for tubular heat exchangers and particularly those of the double pipe chiller type. Such generally comprises a sinuous conduit consisting of a plu- 5; rality of straight substantially horizontal jacketedpipe sections serially connected at the ends by return bends. pumped through the conduit while a refrigerant circulates through the jackets surrounding the For this purpose, it is customaryto mount driven scrapers in the straight pipe-sections of the chiller with spring blades which revolve against the inner surface of the conduit dislodging the adherent matter and keeping the surface of the conduit polished Perhaps the scrapers find their greatest work to do when starting up after long rest periods of the chiller withinwhich periods the adherent matter has had time to become firmly and thickly attached to the walls of .the

' conduit.

The scraper blades may in general be of two types, straight blades which extend in the longitudinal direction of. the conduit, andv helical blades.

the conveying function is quite subordinate to the scraping function inasmuch as. the liquidbe ing treated is pumpedthrough the chiller,-the spiral disposition of the bladesbeing rather for the purpose of meeting the adherent matter at an angle thus performing an inclined shearing cut.

Scraper blades are generally of the narrow or ribbon type and may be either rigidly or resil- ,1ently supported from a driven shaft arranged.

coaxially within the chiller pipe.

The advantage lies with the spring supported blades, for not only can they accommodate them:

selves to variations in the diameter of the pipe making 100 percent linear contact with the inner surface thereof, and automatically adjusting themselves to compensate for wear, but they can be so constructed and arranged as to yield upon making contact with persistently adherent matter, dislodging it with gradually built up pressure The liquid to be chilled is Where the latter type of blades is used,

ratherthan by a rigid impact blow which is apt to be detrimental to the scraper blades as well as to the surface of the chiller pipe.

Scraper blades that are supported by leaf springs are subjected to vibrations which cause chattel by which is meant a "succession of vibratory impulses immediately following the release of the spring upon dislodgment of a difl'lxcultly removable particle of adherent matter,

which succession of vibrations tends to flatten or 1H score or groove the inner cylindrical wall of the chiller pipe, 2. condition which promotesrapid wear of the scraper blade and chiller pipe, encourages the adhesion of sedimentary matter, and in general lowers the heat exchanging efficiency of the apparatus.

One of the objects of the-invention is'the provision of a rotary scraper with spring mounted blade construction which will not produce score marks, grooves or flattening of theinner .cylindri- 20 cal surface of the pipe against which the scraper operates through spurious vibrations generally known as chattering.

Another object of the invention is to provide a rotary, scraper for tubular chillers, with leaf 25 spring supported blades, incorporating means for quickly dampening or,,quenching the vibratory impulses of'the character above referred'to.

Another object of the invention is to provide a scraper blade construction as described in which' the vibration quenching means has the additional function of progressively stiffening the spring as the resistance to dislodgment,;by the adherent matter, persists.

Other objects of the invention will appear as 35 the following description of a preferred and practical embodiment thereof proceeds.

In the drawings which accompany'and form a part of the following specification and'throu'gh. out the several figures of which the same characters of reference have been employed to desiga hate identical parts: j 1 v Figure 1 is a longitudinal viewof a scraper for tubular chillers, embodyingthe principles of the present invention;- I

Figure 2 is a cross section taken along the; line 2-2ofFigure1; "A

Figure 3 is a longitudinal view of. a slightly modified form of scraper, still embodying the principles of the invention; j

Figure 4 is a cross section taken along the line 4- 5 of Figure 3;

Figure 5 is a section through the rebound snubbing or quenching washer. including broken lines illustrating the. progressive shortening of the radius of swing which occurs as the scraper blade bends about the convex face of the washer;

Figure 6 is a longitudinal view of the scraper embodying a coil spring blade support; and

Figure 7 is a cross section taken along the line 1--1 of Figure 6.

Referring now in detail to the several figures and first adverting to that form of the invention illustrated in Figures 1 and 2, the numeral represents a shaft which as shown is hollow and which supports in spaced relation the ribbon-type blades 2 which are here shown as extending rectilinearly in the longitudinal direction of the scraper. The blades 2 are suitably fixed at the outer ends of the leaf springs 3, the outer edges 4 of said blades sweeping the inner cylindrical surface of the chiller pipe, which surface is diagrammatically indicated at 5 in Figure 2. Each blade may be supported by several springs as is indicated in Figure 1. By virtue of the blades being of ribbon form and being resiliently supported, they are capable of sufficient deformation to enable them to accommodate themselves to slight unevenness in the diameter of the chiller tube and to compensate for wear so that they make percent linear contact with the inner surface of the chiller pipe. As has been stated in the prefatory paragraphs of the specification, the action of the blades is to scrape away adherent matter as well as to polish the inner surfaces of the chiller pipes which are customarily made of a metal characterized by good thermal conductivity, such as copper.

In that form of the invention shown in Figures 1 and 2, the supporting leaf springs lie tangential ly with respect to the shaft I at diametrically opposite points and in opposite phase. Their inner ends are preferably bent to conform to the cylindrical surface of the shaft I so as to hold the springs perpendicularly to the axis of the shaft and they are secured in place by a common bolt 6 passing through aligned apertures in the inner ends of said springs and in said shaft.

Figure 2 shows that between the securing means and the springs 3, the washers l are interposed. Said washers each have a portion which is bent to conform to the curvature of the inner end of the spring with which it is associated and is perforated to secure the common securing bolt 6. Said washer is formed with an extension 8, adjacent the base of the spring 3 and convex on the side which faces said spring. The spring is free to flex within the angle between the surface of the shaft and the extension 8.

Referring now to Figure 2, the arrow therein depicted indicates a direction of normal rotation of the scraper and 1: represents a particle of adherent matter. It will be readily understood that upon contact of the blade 4 with the adherent particle, the spring 3 will be deflected back against the curved surface of the shaft, progressively shortening the effective length of the spring, thereby stiffening it and at the same time building up a pressure which will finally result in the particle a: being dislodged, or in unusual instances cause the blade 4 to ride over the particle and spring out on the opposite side of the particle.

In either instance the result is the same, the whip of the release springs sets it in oscillatory vibration. Inasmuch as it will contact the inner surface of the surrounding chiller pipe immediately upon being released, this vibratory impulse will take the form of waves passing through the spring 3 and causing the blade to thrust endwise against the inner surface of the chiller pipe in a succession of impulses. This vibratory action of the spring causes uneven wear of the inner surface of the chiller pipe through a phenomenon known as chattering, resulting in the inner surface of the chiller pipe being grooved or scored or fiattened; in other words, destroying the smoothness of its cylindrical contour. The extension 8 of the washer 1 is within the range of the oscillatory vibration of the spring 3 so that when the latter swings back against said washer it is bent back against the convex face of the extension 8, thus shifting the fulcrum of swing of the blade progressively outwardly, in effect shortening the portion of the blade which has freedom to vibrate. According to the law of the pendulum which is also the law governing the vibration of springs each length of pendulum has a definite period of amplitude which period is different for each length of pendulum. When the effective length of the spring 3 is progressively shortened the progressive change in its period of oscillation creates interference so that the vibratory impulses of the spring are dampened and quenched.

In the modified form in which the invention is embodied in Figures 3 and i, the springs 9 are U- shaped with the closed bight l0 of the spring facing in the direction of rotation of the scraper. Aside from this differentiation the forms of the invention shown in Figures 1 and 2 and in Figures 3 and 4 are the same. In Figures 3 and 4 however the direction of normal rotation is the reverse of what it is in Figures 1 and 2 so that when an adherent particle :1: is contacted by the blade I I the effect will be to bend the spring 9 against the convex extension 8 of the washer 1. increasing the resistance of the spring through shortening it just as was done in connection with Figures 1 and 2. When the particle finally dis lodged or when the blade ll finally rides over the particle, the spring becomes released and immediately snaps back away from the extension 8. On the first rebound however it is deflected against the convex face of the extension 8 which quenches its further vibration in the manner described in connection with Figures 1 and 2.

Referring now to the modified form of scraper illustrated in Figures 6 and 7 the shaft l is provided at spaced longitudinal intervals with spring mountings I3, each comprising a sleeve l4 surrounding the shaft I and fixed thereto in any suitable manner. At opposite sides the sleeve I4 is provided with housings l5 and I6 for receiving the coil springs I1 and I8. The housings are parallel and tangential. The opposite end of each housing is bifurcated forming the slots is and 20 which straddle the backs of the rebound blades 2|. Said blades are pressed upon by means such as the thrust plates 22 which are pressed by the springs l1 and I8. The blades are thus continuously resiliently pressed into contact with the inner cylindrical wall of the pipe 5. The blades are preferably freely retained in the slots l9 and 20 by means of a pin and slot connection, the pin being designated by the reference character 23 and the slot by the reference character 24. The blades are guided by the slots l9 and 20 and are free to move inwardly, but are prevented from any lateral displacement-such as characterizes the invention disclosed in Figures 1 to 5. inclusive.

It is obvious that if the blades 2| were in the diametrical longitudinal plane of the shaft and if they were to meet an adherent obstruction on the inner surface of the pipe 5 they would either forcibly dislodge the obstruction or if the obstruction had a sloping side, the blade would rise upon the said obstruction and immediately move inward and upon passing said obstruction delivering a hammer blow against the surface of the pipe. Since a series of wavelike forces traverse a coil spring after such an impact blow the inner surface of the pipe would be subjected to a plurality of pressure impulses gradually diminishing to zero. Such an action of the blades has the effect eventually of scoring the wall of the pipe with more or less parallel grooves which as has been stated encourage the adhesion of deposits and increases the rateof wear upon the surface of the pipe as well as the edges of the blades. By placing the blades in a tangential position with respect to the shaft l, the blades continually press against an inclined surface. This gives them a chisel action so that they cut into the deposits removing them with much less pressure than is required in the hypothetical location of the blades above described and if by chance the blades ride over an obstruction and come down on the other side they are engaging an inclined plane. Therefore the force of impact will be cushioned and the vibratory pressure of the blade brought to zero much more quickly than if the blade should strike in a direction normal to the surface of the pipe.

Thus generically the same effect is produced by the coil pressed reciprocable blade acting against the inclined surface of the pipe as in the case of the leaf spring blade supports with the vibration dampening washers 8.

While I have in the above description disclosed What I believe to be a preferred and practical embodiment of the invention, it will be understood to those skilled in the art that the details of construction as illustrated and described are by way of example and not to be construed as limiting the scope of the invention as defined in the appended claims.

What I claim is:

1. Rotary scraper for heat exchanging pipes comprising a shaft, a blade extending longitudinally of said shaft and spaced therefrom adapted to scrape the inner cylindrical surface of a pipe in which said shaft is axially inserted, a leaf spring fixed to said shaft and said blade supporting the latter at a distance from said shaft, and means on said shaft adjacent the point of fixation of said spring comprising a rigid stop having a convex face adjacent the base of said spring positioned at a point within the path of oscillation of said spring, against which face said spring is adapted to bend, progressively shortening the radius of oscillation, thereby setting up interference in the period of oscillation of said spring and quenching the vibrations thereof.

2. Scraper for heat exchanging pipes comprising a shaft, a blade extending longitudinally of said shaft and spaced therefrom adapted to scrape the inner cylindrical surface of a pipe in which said shaft is axially inserted, a leaf spring fixed to said shaft at one end, and extending tangentially therefrom, said blade being fixed'to the opposite end of said spring and supported thereby, and means on said shaft adjacent the point. of fixation of said spring comprising a rigid stop having a convex face adjacent the base of said spring, positioned at a point within the path of oscillation of face said spring, against which said spring is adapted to bend, progressively shortening the radius of oscillation, thereby setting up interference in the period. of oscillation of said spring, and inhibiting its vibration.

3. Rotary scraper for heat exchanging pipes comprising a shaft, a blade extending longitudinally of said shaft and spaced therefrom adapted to scrape the inner cylindrical surface of a pipe in which said shaft is axially inserted, a U-shaped leaf spring fixed to said shaft at one end and extending tangentially therefrom, said blade being fixed to the other end of said spring and supported thereby, the bight of said spring extending in the direction of rotation of said scraper, and means on said shaft adjacent the point of fixation of said spring comprising a rigid stop having a convex face adjacent the base of said spring, against which said spring is bendable "responsive to resistance of the adherent matter on the surface of said pipe for progressively stiffening said spring, said stop being positioned at a point within the path of oscillation of said spring, whereby vibratory oscillations of said spring which bring it into contact with said stop are quenched through interference in the period of oscillation set up by the progressive shortening of the radius of swing of said spring.

4. Rotary scraper for heat exchanging pipes comprising a shaft, a blade extending longitudinally of said shaft and spaced therefrom adapted to scrape the inner cylindrical surface of a pipe in which said shaft is axially inserted, a leaf spring fixed to said shaft and blade, supporting the latter, a washer, common means for securing said washer and spring to said shaft, said washer having an extension forming a stop having a convex face adjacent the base of said spring positioned at a point within the range of oscillation of said spring against which said spring is adapted to bend, progressively shortening the radius of oscillation, thereby setting up interference in the period of oscillation and quenching the vibrations of said spring.

5. Scraper for heat exchanging pipe comprising a shaft, a blade extending longitudinally of said shaft and spaced thereby adapted to scrape the inner cylindrical surface of a pipe in which said shaft is axially inserted, a leaf spring fixed to said shaft and blade, supporting the latter, said spring extending tangentially from said shaft, a washer, common means for securing said washer and spring to saidshaft, said washer having an extension forming a stop having a convex face adjacent the base of said spring positioned at a point within the range of oscillation of said spring against which said spring is adapted to bend, progressively shortening the radius of oscillation, thereby setting up interference in the period-of oscillation of said spring and quenching the vibrations thereof.

WERNER G. VOGEL.

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