Vacuum belt hugger for casting of ribbon

A continuous casting assembly has a pair of contiguously counter-rotating belts for controllably forming a continuous cast metal ribbon. One of the belts is chilled and forms a casting surface for the cast ribbon, while the other belt is intimately positioned to hug the ribbon and improve the quality of the ribbon. The two belts are squeezed together to compress the ribbon by evacuating between the belts and allowing the atmospheric pressure to act on the opposite surfaces of the belts. A sealing box adjacent the lateral edges of the belts includes elongated floating seals and provides the evacuation by connection to a vacuum source. The floating seals are formed of plastic rods and are retained in the sealing box by end wiper seals which also serve to seal against the belts at the ends of the box.

TECHNICAL FIELD 
The invention relates generally to casting continuous metal ribbon by 
depositing molten metal onto a moving chilled substrate. In particular, 
the invention relates to providing a chilled belt and a retention belt 
held together by evacuating between the belts and using the ambient air 
pressure to squeeze the cast molten metal ribbon between the belts for 
improved quality and control and enhanced heat transfer between the ribbon 
and belt members. 
BACKGROUND OF THE INVENTION 
In the process of continuously casting metal strips, such as ribbons, it is 
common practice to dispense molten metal through a nozzle onto a moving 
chilled substrate. The molten metal solidifies soon after contact with the 
chilled surface. If the cooling process is rapid enough, a cast product 
having an amorphous molecular structure is provided. This may be in the 
form of a relatively thin elongated strip or ribbon which has proven to be 
effective for winding into highly efficient cores for electrical 
transformers, and for other uses. Recent developments in the casting of 
amorphous metal strips are reviewed in U.S. Pat. No. 4,142,571. 
It is known in the prior art to cast conventional metal alloys between a 
pair of opposed counter-rotating belts. In U.S. Pat. No. 3,426,836, for 
example, molten metal is deposited in a liquid state between a pair of 
upper and lower moving belts and a pair of lateral belts cooperatively 
forming a moving mold cavity. The molten metal is chilled in the mold 
cavity for solidification as it is moved with the cavity. Pressure is 
applied against the top and bottom belts to urge these belts against 
opposite sides of the interposed cast metal, the pressure being applied by 
either pressure rollers or a pressurized fluid, such as compressed air. 
The applied pressure is designed to compensate for shrinkage of the cast 
metal upon solidification. A further example of cooling molten metal 
between a pair of counter-rotating belts is shown and described in U.S. 
Pat. No. 2,285,740. 
In U.S. Pat. No. 4,202,404, an apparatus for producing continuous metal 
strips on the peripheral surface of a rapidly rotating annular chill roll 
is disclosed. In this last mentioned patent, once the metal strip is 
deposited upon the chill roll, an elastomeric flexible belt frictionally 
engages an arcuate portion of at least 120.degree. about the chill roll 
with the deposited metal strip positioned between the belt and the chill 
roll. The belt is wider than the cast strip so that it overlaps the 
marginal portions of the strip, and direct contact between the casting 
surface and the flexible belt is established immediately adjacent the 
portions of the strip. Flexible belts which engage the casting surface in 
this manner are known in the art as "hugger" belts. 
It is also known in the art to use vacuum conveyor belts. The typical 
vacuum conveyor belt includes a perforated conveyor belt which is moved 
across a manifold. A vacuum is produced in the manifold and communicated 
through the perforations in the belt to secure objects on the surface of 
the belt opposite the manifold. In U.S. Pat. No. 3,642,119, for example, 
an endless vacuum conveyor belt is supported on its ends by circular 
pulleys with an elongated vacuum manifold of generally rectangular 
configuration between the pulleys. A line of perforations is provided in 
the belts and adapted to register with the slot in the vacuum manifold as 
the belt moves over the manifold. A similar type of configuration is shown 
in U.S. Pat. No. 3,889,801. A still further example of a vacuum belt is 
shown in U.S. Pat. No. 3,419,264. 
It has recently been found that amorphous metals can be advantageously cast 
in a partial vacuum. In U.S. Pat. No. 4,154,283, molten amorphous metal is 
deposited in a vacuum chamber onto a rotatable chilled cylinder. The 
pressure in the vacuum chamber is no greater than 5.5 cm. Hg. and quenches 
the molten metal to form an amorphous metal alloy with reduced surface 
irregularities and improved tensile strength. 
DISCLOSURE OF THE INVENTION 
The present invention advances the teachings of the prior art by providing 
a casting system which utilizes the ambient atmospheric pressure to force 
a hugger belt into contacting relationship with a casting surface belt and 
a freshly cast metal ribbon interposed between the casting surface and the 
hugger belt. The ambient atmospheric pressure holds the belts together 
with a uniform force and may be used over an extensive length of the 
belts. The invention contemplates depositing a cast ribbon on the exterior 
surface of the casting surface belt and includes means for creating a 
partial vacuum between the contiguously disposed external surfaces of the 
casting surface and hugger belt. The pressure differential on opposite 
sides of the belts results in the application of a compressive force 
against the interior surfaces of the belt from the ambient atmospheric 
pressure. The freshly cast ribbon interposed between the exterior surfaces 
of the belts is squeezably retained by the belts for improved heat 
transfer between the belts and ribbon. Cast ribbon cooled in this manner 
has improved finish and shape. 
One aspect of the invention contemplates that the contiguously 
counter-rotating belts with the interposed ribbon will continuously travel 
through a sealing chamber at the same speed, and that air will be 
withdrawn from the space between the exterior surfaces of the belts and 
the sealing chamber. The sealing chamber sealingly contacts the moving 
belts to pneumatically isolate the internal and external belt surfaces. 
Accordingly, it is a primary object of the invention to use ambient 
atmospheric pressure to squeezably engage a pair of contiguously 
counter-rotating endless belts together for cooling of cast amorphous 
metal ribbons and the like by sandwiching the ribbon between the belts. 
Another object of the invention is to squeezably engage a pair of 
contiguously counter-rotating endless belts togehter over an extensive 
length with uniform force and minimal expense to enhance the quenching of 
a freshly cast metal ribbon interposed between the belts and thereby 
improve the finish and shape, and to accurately control the position of 
the ribbon for delivering it to other systems. 
Still other objects of the invention and advances in the teachings of the 
prior art by the present invention will become readily apparent to thosse 
skilled in the art from the following description. There is shown and 
described a preferred embodiment of the invention, simply by way of 
illustration of one of the best modes contemplated for carrying out the 
invention. As will be realized, the invention is capable of other 
different embodiments, and its several details are capable of modification 
in various, obvious respects all without departing from the invention. 
Accordingly, the drawings and descriptions that follow will be regarded as 
illustrative in nature and not as restrictive.

BEST MODE OF CARRYING OUT THE INVENTION 
Reference is first made to FIG. 1 which schematically depicts a casting 
assembly 10 for casting a relatively thin elongated strip or ribbon of 
molten amorphous metal. The casting assembly 10 includes a pair of 
flexible contiguously disposed counter-rotating endless belts 12 and 14. 
The belt 12 extends between a pair of end rollers 16 and 18 to form a 
moving casting surface for receiving an elongated strip deposited thereon. 
The belt 14 extends between end rollers 20 and 22 and is termed a "hugger" 
belt since, as will be explained more fully below, it includes a portion 
that contacts or "hugs" a cooperating portion of the casting belt 12. In 
the illustrated embodiment of FIG. 1, end roller 16 is positioned 
vertically above end roller 20, and end roller 18 is positioned vertically 
above end roller 22 to position the hugger belt 14 in close parallel 
relationship to the casting belt 12. 
The casting belt 12 includes a working portion 12a proximal to a 
cooperating working portion 14a of the counter-rotating hugger belt 14. 
Each of the belts 12, 14 is completed by a return portion, casting belt 12 
having a return portion 12b and hugger belt 14 having a return portion 
14b. Chilled belt 12 has an interior surface 12c and an exterior surface 
12d while hugger belt 14 has interior and exterior surfaces 14c and 14d 
respectively. End rollers 16 and 18 contact the interior surface 12c of 
chilled belt 12, and end rollers 20 and 22 contact the interior surface 
14c of hugger belt 14. As viewed in FIG. 1, the chilled belt 12 moves in a 
clockwise direction, as indicated by arrow 24, and hugger belt 14 moves in 
a counterclockwise direction, as indicated by arrow 26. 
The chilled and hugger belts 12 and 14 respectively, travel at the same 
linear speed with the respective working portions 12a and 14a traveling in 
closely spaced, substantially parallel paths for at least a predetermined 
distance (illustrated in FIG. 1 as distance d) between the respective end 
rollers 16, 18 and 20, 22. These substantially parallel paths are in close 
proximity so as to permit the belts 12 and 14 to compressingly engage an 
interposed molten strip as they travel in unison through this 
predetermined distance d. 
A sealing box 28 is disposed about the respective working portions 12a and 
14a of the belts 12, 14, within the predetermined distance d. The working 
portions 12a and 14a of these belts are advanced to enter the sealing box 
28 through a first longitudinal end 28a and exit through the opposite 
longitudinal end 28b. The chilled belt 12 also has a cooling box 30 
disposed about the return portion 12b to continuously chill the casting 
belt 12. As illustrated, the cooling box 30 includes a plurality of water 
jets 32 directing chilled water onto the interior surface 12c of the 
return belt portion 12b. As will be apparent hereinafter, the cooling of 
the chilled belt 12 expedites solidification of molten metal deposited 
thereon during the casting process. 
A crucible 34 is disposed above the end roller 18. The crucible 34 contains 
an amorphous molten metal 36 which is discharged through a nozzle 38 
intimately positioned above the chilled belt 12. As the molten metal 36 is 
discharged from the crucible 34, it is deposited onto the chilled belt's 
exterior surface 12d. After the molten metal 36 is deposited on the 
chilled belt 12, it quickly solidifies to form a continuous elongated 
strip or ribbon 40. 
As chilled belt 12 continues to move in the clockwise direction of arrow 24 
in FIG. 1, the elongated ribbon 40 formed from the molten metal 36 is 
carried into a nip formed between end rollers 18 and 22. The hugger belt 
14 begins to "hug" or forcibly contact the interposed ribbon 40 at this 
location, squeezably confining the ribbon 40 between the belts 12, 14. The 
endless belts 12 and 14, as noted above, travel at the same linear speed 
and continue in contacting relationship for the predetermined distance d 
along their substantially parallel paths. During their travel along the 
distance d, the belts 12, 14 pass through the sealing box 28. In a manner 
which will be explained in greater detail below, the air between the 
exterior surfaces of belts 12 and 14 is evacuated in the sealing box 28 to 
allow the atmospheric air pressure to apply a compressive engagement force 
against the interior surfaces 12c and 14c of belts 12 and 14 respectively 
to hold these belts in firm engagement with the interposed ribbon 40. 
Forcing the belts 12, 14 against the interposed ribbon 40 leads to better 
confinement and control of the ribbon 40. The ribbon 40 cast with the 
compressive force of the hugger belt 14 has a higher quality finish and is 
more uniform in thickness. Forcing the hugger belt 14 against the ribbon 
40 a1so enhances the heat transfer between the ribbon 40 and the belts 12, 
14 for more efficient cooling and solidification of the metal. 
The relationship between the belt working portions 12a and 14a and the 
sealing chamber 28 is best illustrated in FIG. 2 which depicts one side of 
the sealing box 28. The edges of working portions 12a, 14a are shown in 
close parallel relationship with the interposed ribbon 40 sandwiched 
therebetween. The sealing box 28 has a pair of floating elongated linear 
seals 44 and 46 depicted in the preferred illustrated embodiment as rod 
configurations. However, as will be apparent to those skilled in the art, 
any number of geometrical configurations for the sliding seals 44 and 46 
could be used within the spirit and scope of the present invention. The 
sliding seals 44 and 46 are ideally formed of plastic rods having a low 
coefficient of friction and having high wear resistance. In the preferred 
embodiment, tetrafluoroethylene has been selected as the sliding seal 
material. Sliding seal 44 is in contacting relationship with the top (as 
shown in FIG. 2) or interior surface 12c of the chilled belt's working 
portion 12a, and linear seal 46 is in contacting relationship with the 
interior or bottom (as shown in FIG. 2) surface 14c of the hugger belt's 
working portion 14a. The seals 44, 46 are contained within elongated open 
box-like recesses 50 and 52 defined by upper and lower legs 54 and 56 of 
the sealing box 28. These upper and lower sealing chamber legs are 
integrally joined by a connecting section. 
An interior vacuum chamber 60 is formed in the sealing box 28 by the upper 
and the opposed, lower legs 54, 56. An air conduit 62 extends through an 
aperture 64 in connecting section to put the vacuum chamber 60 into fluid 
communication with a vacuum source V (as shown in FIG. 3). The vacuum 
source V of the system may take the form of a vacuum pump or any of 
several other conventional apparatus for evacuating air. As noted above, 
FIG. 2 depicts only one side of the sealing Chamber 28. The opposite side 
is a virtual mirror image of the illustrated side. 
The sliding seals 44 and 46 are movable upwardly and downwardly 
(perpendicular to the direction of belt movement) within the recesses 50 
and 52 into and out of the vacuum chamber 60. The sides of belt working 
portions 12a and 14a also extend into the chamber 60 between the sliding 
seals 44 and 46. When air is evacuated through air conduit 62, the 
resulting partial vacuum within vacuum chamber 60 urges the seals 44 and 
46 into the chamber 60 toward the external vacuum source. This movement of 
the seals 44 and 46 into the chamber 60 is limited by the interior belt 
surfaces 12c and 14c. As a result, the seals 44 and 46 are sealingly urged 
against the belts 12 and 14 along sealing contact lines 49 and 51 
respectively. The partial vacuum within chamber 60 also urges the seals 44 
and 46 against the interior walls of recesses 50 and 52 along sealing 
contact lines 48 and 53 respectively. The sealing engagement of seals 44 
and 46 against the interior surfaces 12c and 14c also places upper limits 
on the application of vacuum to the area between the exterior belt 
surfaces 12d, 14d of the belts. The movability of the seals 44 and 46 
within the recesses 50 and 52 allows them to maintain their sealing 
relationship as they wear and further enables them to accommodate relative 
movement between the belts 12, 14 and the legs 54, 56. 
The creation of a partial vacuum between the belts 12 and 14 results in a 
disparity in the pressure acting against the interior 12c, 14c and 
exterior 12d, 14d surfaces of the belts with the result that the ambient 
atmospheric pressure compressively urges the belts 12, 14 together. The 
differential pressure acting against the belts 12, 14 is schematically 
illustrated in FIG. 2 by a plurality of arrows P. As mentioned above, the 
ribbon 40 is interposed between the belts 12 and 14. Thus, the ambient 
atmospheric pressure P forces the belts 12 and 14 together with the ribbon 
40 sandwiched therebetween. Forcing the traveling belts 12 and 14 together 
in this manner through the generation of a vacuum in a sealing chamber 
permits forced contact between the belts over an extensive length with 
substantial cost savings over other means of forcibly holding the moving 
belts together. 
Since the sliding seals 44, 46 are urged into forcible sealing contact with 
the traveling belts 12, 14, the belts 12, 14 tend to move the seals 44, 46 
in the direction of belt travel. As depicted most clearly in FIG. 1, end 
wiper seals 68, 68a, and 70, 70a are transversely mounted adjacent the 
recesses 52 and 50 to seal the ends and limit movement of the seals 44, 
46. The downstream end seals 68, 68a are compressed since the belts 12, 14 
are always moved in the directions illustrated. However, both sets of the 
end seals 68, 68a and 70, 70a serve to pneumatically isolate the chamber 
60 from the ambient atmosphere. 
Preferably, the end seals 68, 68a and 70, 70a are attached to the ends of 
the respective sliding seals to float therewith and wipe the belts 12, 14 
during operation. Alternatively, the end seals may float separately with 
springs in the recesses 50,52 urging the seals toward the belts 12,14. All 
of the seals 44, 46, 68,68a,70,70a are preferably fabricated of material 
having substantially the same wear properties. 
The sectional and longitudinal dimensions of the seals 44, 46 inherently 
limit the pneumatic forces which can be exerted by the pressure 
differential between the ambient atmosphere and vacuum chamber 60. Thus, 
greater or lesser sealing force at the sealing contact lines 49 and 51 may 
be controlled by judicious determination of the seal dimensions. 
In summary, numerous benefits have been described from employing the 
concepts of the invention. The invention permits two contiguously 
traveling belts 12, 14 to be forced together over an extensive length by 
the anbient atmospheric pressure to controllably sandwich a freshly cast 
metal ribbon 40 therebetween. Forcibly sandwiching the ribbon between the 
belts in this manner enhances the quenching of the ribbon through improved 
heat transfer between the belts and the interposed ribbon. The invention 
also results in improved finish or shaping of the interposed ribbon 40 and 
improved control over its position relative to the belts for improved 
delivery of the ribbon from the belts to winding and measurement systems. 
The use of the ambient air pressure to force contact of the two contiguous 
belts permits the interposed ribbon to be squeezed over an extensive 
length with substantial cost savings over equivalent equipment. 
The foregoing description of the preferred embodiment of the invention has 
been presented for purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. Obvious modifications or variations are possible in light of 
the above teachings. The embodiment was chosen and described in order to 
illustrate the principles of the invention and its practical application 
to enable one of ordinary skill in the art to utilize the invention and 
the various embodiments and with various modifications as they are best 
suited to the particular use contemplated. It is intended that the scope 
of the invention be defined by the claims as appended hereto.