Scraped-surface heat exchangers and similar apparatus employing scraper blades hinged to a shaft so as to scrape a fluid being processed from an elongated cylindrical wall are improved so as to obviate any need either for separate bearings at opposite ends of the shaft or for special skids to be used in disassembly and reassembly and so as to allow the blades to be biased against the wall without separate springs. Each blade bears on the wall not only at its leading or scraping edge but also at a trailing or bearing surface, so as to center the shaft and facilitate its rotation, so as to hold the edge in uniform relation to the wall, and so as to bias the edge of the blade against the wall.

BACKGROUND OF THE INVENTION 
Scraped-surface heat exchangers and similar apparatus employing hinged 
blades to scrape a fluid being processed from an elongated cylindrical 
wall or exemplified in U.S. Pat. Nos. 2,281,944, 2,235,002, 3,385,354, 
3,568,463, and 3,848,289; cf. U.S. Pat. No. 2,776,765, which shows fixed 
blades. Various uses of such apparatus are described in A. E. Bailey, 
INDUSTRIAL OIL AND FAT PRODUCTS (3rd edition, Interscience Publishers, 
Division of John Wiley & Sons) at pages 1066 et seq. and in Bulletin V300 
entitled "VOTATOR.RTM. Scraped Surface Heat Exchangers" and published by 
Chemetron Corporation, P.O. Box 35600, Louisville, Kentucky 40232. 
Such apparatus generally comprises a chamber having an elongated 
cylindrical wall, within which a shaft is rotatable concentrically, and 
scraper blades are hinged to the shaft, as by radial pins. In some 
apparatus, the blades are biased by separate springs into edge contact 
with the wall. 
As manufactured and sold by Chemetron Corporation, such apparatus often are 
several feet or more long with a ratio between eight and twenty-four of 
overall length to inner diameter of the wall. In prior apparatus, 
particularly horizontal apparatus as commonly used as scraped-surface heat 
exchangers, the ratio has been limited so as to avoid excessive flexure 
and consequent misalignment of the shaft. Furthermore, it has been 
conventional to employ roller bearings at opposite ends of the shaft. 
Intermediate bearings within the chamber have been tried to some extent to 
minimize the flexure of the shaft. 
Serious problems can occur in disassembly and reassembly, as for purposes 
of sanitation, wherein tube scoring and blade damage can easily result as 
the shaft and blade assembly is moved through one end of the tube. 
Although elongated spacers known as "shaft skids" are available to 
separate the shaft and the tube so as to prevent destructive contact 
between the pins hinging the blades and the tube, such "skids" are not 
always employed and tube scoring and blade damage thus have not been 
effectively eliminated before this invention. 
SUMMARY OF THE INVENTION 
This invention not only eliminates any need for conventional bearings at 
opposite ends of the shaft but also effectively addresses such problems in 
disassembly and reassembly and also enables the blades advantageously to 
be biased against the wall without separate springs. Good sanitation is 
enhanced by this invention. 
As in conventional apparatus, a tube has an elongated cylindrical wall, and 
a shaft is concentric with the wall and rotatable about their common 
central axis. Each blade is hinged to the shaft, as by conventional pins, 
for pivotal movement about an axis parallel with such axis and scrapes the 
fluid from the wall as the shaft rotates. 
According to this invention, each blade contacts and bears on the wall not 
only at its leading or scraping edge but also at a trailing or bearing 
surface, which is formed on the blade. By suitable arrangement of plural 
blades, the respective bearing surfaces can serve effectively as the only 
rotational bearings required to center the shaft and facilitate its 
rotation. Furthermore, the edge of the blade can be biased against the 
wall without separate springs, by frictional engagement between these 
surfaces and the wall. 
In disassembly and reassembly, each blade serves as a skid, so as to 
prevent destructive contact between the pins hinging the blades and the 
wall as the shaft and the blades are drawn through one end of the tube. 
Frictional contact between the blades and the tube is characteristic of 
normal operation of such apparatus and thus causes no difficulties in 
disassembly and reassembly. 
Commercially available pre-polished stainless steel tubes may be 
economically and effectively used without further boring or honing 
operations. Good sanitation is enhanced as separate springs are not 
employed and long lightweight shafts may be employed. 
The foregoing and other objects, features, and advantages of this invention 
will be evident from the following detailed description of a presently 
preferred embodiment of this invention with particular reference to the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1 shows one portion of an exemplary scraped-surface heat exchanger 10, 
generally of a type sold for many years by Chemetron Corporation under its 
trademark VOTATOR.RTM. and particularly as improved by this invention. In 
its conventional aspects, the heat exchanger 10 generally comprises a tube 
12, which is surrounded by a layer of suitable insulation 14, and a sleeve 
16, which surrounds the insulation 14. Another tube 18 is disposed 
concentrically within the tube 12 so as to form an annulus 20. A heating 
or cooling medium is passed through the annulus 20 between the tube 12 and 
the tube 18 via respective inlet and outlet conduits (not shown) which 
communicate with the annulus 20. 
A shaft 24, which is tubular as shown in FIG. 2, may be called a mutator in 
common parlance. The shaft or mutator 24, which carries a plurality of 
scraper blades 26 of particular construction according to this invention, 
is concentric with the tube 18 and rotatable, as described hereinbelow, 
about a common central axis of the tube 18 and the shaft 24, and so as to 
form an annulus 30 between the shaft 24 and the tube 18. Conventional 
means (not shown) are used to close and seal opposite ends of the annulus 
20 and the annulus 30 and to allow the shaft 24 to be rotated by a 
conventional prime mover (not shown). In conventional manner, a product to 
be heated, sterlized, cooled, crystallized, or processed otherwise is 
passed through the annulus 30 via respective inlet and outlet conduits 
(not shown) which communicate with the annulus 30. The blades 26 are 
similar to conventional blades in two purposes, which are to plow, scrape, 
or remove accumulated product from the inner cylindrical wall 32 of the 
tube 18 and to mix the product within the annulus 30. 
Various media including water, steam, brine, and ammonia, as well as fluids 
suitable for high temperatures and refrigerants suitable for direct 
expansion, may be passed through the annulus 20 either to heat or to cool 
the product as may be appropriate. The product to be processed may be a 
liquid, a slurry, or other product pumpable through the annulus 30. 
As shown in FIG. 2, the blades 26 are hinged to the shaft 24, for pivotal 
movement about an axis parallel to the axis about which the shaft 24 
rotates, by a pair of conventional pins 38 extending radially from the 
shaft 24 and cooperating with elongated slots 40 to enable the blades 26 
to be mounted to the shaft 24 and dismounted. Analogous uses of similar 
pins to mount scraper blades of other constructions are shown in FIGS. 4 
through 6 of U.S. Pat. No. 3,848,289. 
As also shown in FIG. 2, one edge 42 of each blade 26 leads a plane defined 
by the axis about which such blade 26 pivots and the axis about which the 
shaft 24 rotates--vertical plane in FIG. 2--to scrape the product being 
processed from the inner cylindrical wall 32 of the tube 18 as the shaft 
24 rotates in a given rotational sense, which is counter-clockwise as 
shown in FIG. 2. Each leading and scraping edge 42 is sharpened to an 
angle of approximately 45.degree.. 
One material useful for the blades 26 is polysulfone, which is available 
commercially from Union Carbide Corporation as 
UDEL#P-1700-Natural-11-Polysulfone, but other materials known for scraper 
blades are expected to be suitable. As described below, the blades 26 have 
a novel and advantageous construction, which not only provides the only 
bearing surfaces required to center the shaft 24 and facilitate its 
rotation but also effectively addresses aforementioned problems in 
disassembly and reassembly and also allows the blades 26 advantageously to 
be biased against the wall 42 without separate springs. 
According to this invention, each blade 26 bears on the wall 32 at 
respective outer bearing surfaces 46, which are formed as described 
hereinbelow, and which trail the plane mentioned above--vertical plane in 
FIG. 2--as the shaft 24 is rotated, as to hold its edge 42 in scraping 
relation to the wall 32 as the shaft 24 is rotated. Each blade 26 is thin 
and flat and may be molded in one piece, as conventional blades are made, 
except for respective roll-like portions 48 protruding from the blade 26 
and comprising respective portions of the surface 46, whereby the blade 26 
contacts the wall 32 only at the edge 42 and respective surfaces 46. 
As shown in full lines in FIG. 2, two blades 26 of like construction are 
mounted in like manner to the shaft 24, in diametric opposition to each 
other. As suggested in phantom lines in FIG. 2, two blades 26 of like 
construction may be mounted in like manner to the shaft 24, in diametric 
opposition to each other with approximately 90.degree. of angular 
separation between the blades 26 in full lines and the blades 26 in 
phantom lines. Preferably, the blades 26 are arranged in an overlapping 
and staggering relationship, as shown and described for different blades 
in U.S. Pat. No. 3,235,002. 
Each blade 26 also has respective inner bearing surfaces 54, which also are 
formed on the roll-like portions 48, and which are adapted to bear on the 
shaft 24. Thus, radial movement of the shaft 24 toward the wall 32 is 
limited by the roll-like portions of the blades 26, and slight clearances 
at the pins 38 allow the shaft 24 to float within the wall 32. As shown, 
four blades 26 having approximately 90.degree. of angular separation 
respectively therebetween provide the only bearing surfaces needed to 
center the shaft 24 therewithin and to facilitate the rotation of the 
shaft 24. 
The blades 26 eliminate any need for "shaft skids" in disassembly and 
reassembly, as each blade 26 serves as a "skid" between the surfaces 46 
and the surfaces 54. Frictional contact between the blades 26 and the wall 
32 is characteristic of normal operation of the heat exchanger 10 and thus 
causes no difficulties in disassembly and reassembly. 
Commercially available pre-polished stainless steel tubes may be used, 
particularly for the tube 18 and the shaft 24, which do not require 
further boring or honing operations because of this invention. Slight 
cambers, as commonly encountered with such commercially available tubes, 
may be accommodated easily. An elongated tube, as accordingly may be used 
for the shaft 24, may be sufficiently limber to accommodate a camber in 
the tube 18. Large ratios of overall length to inner diameter thus may be 
achieved at low costs as compared with the costs of conventional 
scraped-surface apparatus. 
Frictional contact between the surfaces 46 of the blades 26 and the wall 32 
advantageously tends to rotate the blades 26, counterclockwise as shown in 
FIG. 2, and thus to bias the leading or scraping edges 42 of the blades 26 
against the wall 32. Separate springs and similar expedients are 
unnecessary.