Apparatus for stretching dough

An apparatus for stretching dough comprising two pairs of rollers and means for imparting vibrations to the dough positioned between the pairs of rollers is provided. In this apparatus, vibrations are imparted to dough, which causes the thixotropic effect in the dough. Such dough can be readily stretched by being subjected to a tensile stress caused by the difference in the peripheral speed of the pairs of rollers. Therefore, dough can be stretched without subjecting it to high pressure during the stretching process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus and method for stretching dough, and 
in particular to an apparatus and method for stretching dough in which the 
elasticity of the gel structure in the dough is prevented from being 
changed during the method. 
2. Prior Art 
U.S. Pat. No. 3,593,676 discloses a dough sheeting apparatus. This 
apparatus is a typical conventional dough stretching apparatus. It 
comprises a plurality of pairs of compression rollers. In this apparatus 
dough is supplied to the space between the respective pairs of rollers and 
is compressed by the upper and lower rollers to have a predetermined 
thickness. To stretch dough by compression, the dough should be subjected 
to a pressure higher than the point at which the dough loses its 
elasticity. In other words, in the conventional process, the dough is 
stretched by causing an elastic fatigue in the dough. However, such a high 
pressure destroys the gel structure of the gluten in the dough. As has 
been known to those skilled in the art, dough whose gel structure has been 
damaged tends to expand insufficiently when it is baked, resulting in 
bread of poor quality. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide an apparatus and method for 
stretching dough in which the dough is not subjected to pressure higher 
than the point at which it loses its elasticity, and thus prevent the gel 
structure of the dough from being damaged. In one aspect of this invention 
an apparatus for stretching dough is provided, comprising 
(a) an upstream pair and a downstream pair of rollers, each pair of said 
rollers positioned and spaced apart from each other to provide a path for 
said dough and rotating in the same direction where they face each other 
and at the same peripheral speed. 
(b) means for imparting vibrations to said dough positioned between said 
upstream pair and said downstream pair of rollers. 
(c) means for adjusting said space between the rollers in each pair so that 
the space between said upstream pair of rollers is wider than that between 
said downstream pair of rollers, 
(d) means for driving said upstream pair and said downstream pair of 
rollers so that the peripheral speed of said upstream pair of rollers is 
slower than that of said downstream pair of rollers. 
Further, in another aspect of this invention, a method for stretching dough 
is provided, comprising 
(a) supplying said dough into a first space between a first pair of rollers 
rotating in the same direction where they face each other and at the same 
peripheral speed, and then into a second space, narrower than said first 
space, between a second pair of rollers positioned downstream of said 
first pair of rollers and rotating in the same direction where they face 
each other and at the same peripheral speed, which is faster than said 
peripheral speed of said first pair of rollers, said first and second 
spaces being adjustable, 
(b) stretching said dough under tensile stress while vibrations are 
imparted to said dough by a vibration means positioned between said first 
and second pairs of rollers. 
In this invention, dough is not stretched by compressing it between a pair 
of rollers, but is stretched by imparting vibrations to it while it is 
under a tensile stress. Please note that when vibrations are imparted to 
dough, the thixotropic effect occurs in the dough. 
Because of the thixotropic effect, dough in the area to which vibrations 
are imparted becomes fluid and starts to flow. Therefore, the dough in 
such a condition can be easily stretched by subjecting it to just a low 
tensile stress. In this invention vibrations are imparted to the area of 
the dough located between the upstream pair and the downstream pair of 
rollers by the means for imparting vibrations while this same area of the 
dough is subjected to a tensile stress caused by the difference in the 
peripheral speed of the upstream pair and downstream pair of rollers. 
Accordingly, the dough can be stretched without being subjected to a high 
pressure that exceeds the point at which the dough loses its elasticity. 
Thus, the gel structure of the dough is prevented from being damaged.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 the apparatus for stretching dough of a preferred embodiment of 
this invention is shown. The apparatus comprises a first pair of 
vertically juxtaposed rollers (2, 2'), a second pair of vertically 
juxtaposed rollers (3, 3') located downstream of and spaced apart from the 
first pair of rollers, and a vibration imparting mechanism that includes a 
transfer roller (4) and a vibration imparting body (5). 
The rollers of each pair are positioned spaced apart from each other so 
that a conveying path for dough (1) is provided between them. In FIG. 1, 
the distance between the rollers of the first pair where they are closest 
is a, which is equal to or less than the thickness c of the dough to be 
stretched (1), and the distance between the rollers of the second pair 
where they are closest is b, which is equal to or less than the thickness 
e of the dough after stretching (6). These rollers (2, 2', 3, and 3') are 
driven through a belt or chain by a driven motor (not shown). These 
rollers (2, 2', 3, and 3') rotate in the same direction where they face 
each other as indicated by the arrows in FIG. 1. Rollers of a given pair 
rotate at the same peripheral speed. The rollers are driven so that the 
peripheral speed of the first pair of rollers V.sub.1 is slower than that 
of the second pair of rollers V.sub.2. 
In this embodiment, the positions of the upper rollers (3, 2) of the first 
and second pairs can be raised or lowered so that the distances a and b 
are adjusted to the thickness c of the dough to be stretched (1) and the 
thickness e of the dough after being stretched (6), respectively. In 
contrast, the lower rollers (2', 3') and the transfer roller (4) are 
fixedly positioned so that their uppermost parts align on a straight line 
as shown in FIG. 1. 
The transfer roller (4) is a roller freely rotatable about its axis. 
Therefore, as the dough is conveyed by the first and second pairs of 
rollers (2, 2', 3, and 3'), the transfer roller (4) on which the dough is 
supplied rotates in the same direction as that of the lower rollers (2', 
3') of the first and second pairs of rollers. 
The vibration imparting body (5) consists of an elongated member positioned 
transversely of the dough and has a bullet-like cross-sectional shape. As 
indicated by arrows m, the body (5) is repeatedly raised and lowered so 
that its round lower end can touch and press the upper surface of the 
dough (1). 
FIG. 2 shows a mechanism to vertically move the vibration-imparting body 
(5). The mechanism comprises a cam (10), a housing (23), and a cam tracing 
roller (20) connected to the body (5) via an arm (21) extending from the 
bottom wall of the housing (23). A plate (22) is fixed on the arm (21). By 
connecting the plate (22) and the top wall of the housing (23) with a pair 
of springs (11), the cam tracing roller (20) is forcibly contacted by the 
periphery of the cam (10). As shown in FIG. 2, the cam (10) has an 
eccentric shape and the distance from its axis to its periphery varies. 
The axis of the cam is connected to a motor (not shown) so that the cam 
(10) rotates as shown by an arrow r in FIG. 2. As the cam (10) rotates, 
the body (5) is vertically moved as shown by arrows m, while the cam 
tracing roller (20) traces the periphery of the cam (10). 
Returning to FIG. 1, the vibration-imparting body (5) is positioned above 
and spaced apart from the transfer roller (4). As shown in FIG. 1, the 
distance between the lowermost part of the body (5) and the uppermost part 
of the transfer roller (4) when the body is in its lowermost position (5') 
as indicated by a dotted line in FIG. 1 is shown as d. The position of the 
vertical movement mechanism of FIG. 2 holding the body (5) can be raised 
or lowered so that the distance d can be adjusted to be less than the 
thickness c of the dough (1) and thus to be less than the distance a of 
the space between the first pair of rollers when the body (5) is at it 
lowest position, and the distance d can be adjusted to be sufficiently 
greater than the thickness c of the dough (1) when the body (5) is at its 
highest position. 
In operation, the dough (1) is supplied into the space between the first 
pair of rollers (2, 2'). The dough fed out of the first pair of rollers 
(2, 2') passes through the space between the transfer roller (4) and the 
vibration-imparting body (5) and then is supplied into the space between 
the second pair of rollers (3, 3'). Since the peripheral speeds (V.sub.1, 
V.sub.2) of the first and second pairs of rollers are selected so that a 
tensile stress is imparted to the area of the dough (1) which is between 
the points where the upper rollers (2, 3) of the respective pairs of 
rollers (2, 2', 3 and 3') are closest to the lower rollers (2', 3'), the 
dough is stretched. Because of the rhythmic vibrations imparted to the 
area of the dough with the body (5), the thixotropic effect occurs, which 
causes the flow of the dough in the area. Therefore, the dough can be 
easily stretched by being subjected to a low tensile stress without being 
subjected to high pressure exceeding the point at which it loses its 
elasticity. In this area of the dough, tensile stress is averaged, and the 
dough is uniformly stretched without being torn. 
Assuming that the width of the dough is unchanged throughout the 
stretching, and the dough resillience is zero, the result of the following 
equation approximately holds: 
EQU bV.sub.2 =aV.sub.1 
where a and b are representative values of the distances between the upper 
and lower rollers of the first and second pairs respectively, and V.sub.1 
and V.sub.2 are representative values of the peripheral speeds of the 
first and second pairs of rollers, respectively. 
It has been discovered by conducting experiments that dough can effectively 
be stretched when the position of the vertical movement mechanism is 
adjusted so that the distance d of the body (5) equals about 1/3 of the 
thickness c of the dough to be stretched (1). However, when the thickness 
reduction ratio e/c (the ratio between the thickness e of dough after 
stretching (6) to the thickness c of dough to be stretched (1)) is small, 
the position of the vertical movement mechanism is adjusted so that the 
distance d of the body (5) equals about 1/4 of the thickness c. In 
contrast, when the thickness reduction ratio e/c is large the position of 
the vertical movement mechanism is adjusted so that the distance d of the 
body (5) equals 1/2 of the thickness e. 
Please note that in this invention the thickness reduction ratio e/c also 
varies based on the number of vibrations imparted by the body (5). That 
is, if the thickness reduction ratio e/c decreases, the number of 
vibrations imparted should increase. 
In an experiment, dough (1) having a thickness c of 30 mm was supplied at a 
speed of 3 m/min (v=3000 mm/min), and the vibration imparting body (5) had 
a width f of 50 mm. When the body (5) was adjusted so that the distance d 
was 1/3 of the dough thickness c, and the number of vibrations imparted by 
the vibration imparting body (5) was set at 20 to 50 per second, the 
thickness reduction rate e/c was 1/5. That is, the dough (1) was able to 
be stretched to a final thickness e of 6 mm. 
The above result is very remarkable as compared to the thickness reduction 
ratio e/c obtained by the above-mentioned prior art apparatus that 
includes a plurality of pairs of compressing rollers. 
In this apparatus, dough can also be stretched to have a desired thickness 
by adjusting the distances a and b, and the peripheral speeds V.sub.1 and 
V.sub.2. For example, under the conditions of the above-described 
experiment, a dough of 30 mm can be stretched to have any thickness 
greater than 6 mm by changing the parameters a, b, V.sub.1 and V.sub.2 in 
the above equation: bV.sub.2 =aV.sub.1. 
In FIG. 3 the apparatus for stretching dough of the second embodiment of 
this invention is shown. In this apparatus, the construction of the 
apparatus is the same as that of the apparatus in FIG. 1, except that the 
body (5) is replaced with a roller mechanism (10). 
The roller mechanism (10) comprises an axis (7) extending transversely to 
the dough (1) and positioned above the transfer roller (4) and a roller 
(9) connected to the axis (7) via arms (11) mounted to both ends of the 
axis. The roller (9) is freely rotatable about its axis (8). The axis (7) 
is connected to a driven shaft of a motor (not shown) so that the arms 
(11) rotate about the axis (7) as indicated by the arrow f in FIG. 3. 
Therefore, the roller (9) moves along a locus (9') as shown by dotted 
lines in FIG. 3. The position of the axis (7) can be raised or lowered so 
that the distance d between the lowest part of the roller (7) and the 
highest part of the transfer roller (4) when they are closest to each 
other can be adjusted. 
In operation, the roller (9) contacts and is pressed against the dough and 
then is repeatedly released from it as the arms (11) rotate about the axis 
(7). Therefore, the roller mechanism (10) imparts vibrations similar to 
those imparted by the body (5) in FIG. 1. 
FIG. 4 shows the apparatus for stretching dough of the third embodiment of 
this invention. In this embodiment, around the lower rollers (2', 3') of 
the first and second pairs of rollers endless belts (30, 30') are wound 
and three transfer rollers (4.sub.1, 4.sub.2, 4.sub.3), roller (4), and 
three vibration-imparting bodies (5.sub.1, 5.sub.2, 5.sub.3), are arranged 
in series between the lower roller (2' and 3'). The three rollers 
(4.sub.1, 4.sub.2, 4.sub.3) are driven at different speeds so that the 
peripheral speed of any one of the rollers is faster than that of its 
upstream roller. The lower roller (2') of the first pair is driven so that 
its endless belt (30) moves slower than the peripheral speed of the most 
upstream roller (4.sub.1) of the three rollers. The lower roller (3') of 
the second pair is driven so that its endless belt (30') moves faster than 
the peripheral speed of the most downstream roller (4.sub.3). These 
endless belts are wound around the lower rollers (2', 3') and rollers (not 
shown) to construct conventional endless belt conveyors. The structure of 
the bodies and transfer rollers are the same as those in FIG. 1. 
The bodies (5.sub.1, 5.sub.2, 5.sub.3) are arranged so that the lowermost 
parts of the bodies are positioned on a straight line. The uppermost parts 
of the transfer rollers (4.sub.1, 4.sub.2, 4.sub.3) are also positioned on 
a straight line. The gap formed between the straight lines defined by the 
uppermost parts of the transfer rollers (4.sub.1, 4.sub.2, 4.sub.3) and 
the lowermost parts of the bodies (5.sub.1, 5.sub.2, 5.sub.3) becomes 
progressively narrower in the downstream direction. The positions of the 
vertical movement mechanisms (not shown) holding the bodies (5.sub.1, 
5.sub.2, 5.sub.3) are lowered or raised so that the distances between the 
bodies (5) and the transfer rollers (4) are smaller than those between the 
first pair of rollers (2, 2') when they are at their lowest positions and 
are greater than the thickness of the dough to be stretched when the 
bodies (5) are raised to their highest positions. By repeatedly raising 
and lowering the bodies (5), vibrations are imparted to the dough while it 
is subjected to a tensile stress caused by the difference in the 
peripheral speeds of the rollers (2', 3', 4.sub.1, 4.sub.2, 4.sub.3). 
Alternatively, these transfer rollers (4.sub.1, 4.sub.2, 4.sub.3) can be 
replaced with an endless belt device that is driven at a speed faster than 
the peripheral speed of the first pair of rollers (2) and slower than that 
of the second pair of rollers (3). 
Further, the transfer roller (4) in FIG. 1 can be replaced with a roller 
driven at a peripheral speed faster than that of the first pair of rollers 
(2, 2') and slower than that of the second pair of rollers (3, 3'). The 
transfer roller (4) in FIG. 1 can also be replaced by an endless belt 
device driven at a speed slower than the peripheral speed of the first 
pair of rollers (2, 2') and faster than that of the second pair of rollers 
(3, 3'). 
In the apparatus of this invention no high pressure damaging the gel 
structure of gluten in dough can be imparted to the dough during the 
stretching step. For example, we measured, by a strain gauge, the 
instantaneous pressure imparted to dough where dough 30 mm thick was 
supplied into the space between the vibration-imparting body (5) and the 
transfer roller (4) of the first embodiment, where the distance d was set 
at 10 mm. This measurement disclosed that an instantaneous pressure equal 
to or less than 500 g/cm.sup.2 was able to be imparted to dough during the 
stretching process. We found that such a pressure does not damage the gel 
structure of gluten in dough. 
Since the gel structure of gluten, which provides an elasticity to dough, 
can be maintained without being damaged, dough of an excellent quality can 
be provided when it is stretched by the apparatus of this invention. Such 
dough expands sufficiently when it is baked and can provide puffy and 
tasty bread.