Forming drum for building a tire

A forming drum to be used in tire building for forming a strip-like belt member having a steel cord buried therein into an annular shape. The forming drum includes a plurality of segments divided in the circumferential direction and made of non-magnetic material, which form substantially cylindrical shapes having different outer diameters as moved in the radial direction, and permanent magnet are buried in the circular arc-shaped surfaces of the segments. Between adjacent segments are mounted cover plates made of non-magnetic material, and a cylindrical outer circumferential surface is formed by these cover plates. Each cover plate is fixedly secured to the circular arc-shaped surface of one of the adjacent segments.

BACKGROUND OF THE INVENTION 
The present invention relates to a forming drum for building a tire, and 
more particularly, to a tire belt forming drum for forming a strip-like 
belt member having a steel cord buried therein into an annular shape. 
Generally, a belt forming drum has such structure that a diameter of an 
outer circumferential surface of a cylinder onto which a strip-like belt 
member is to be stuck can be arbitrarily varied so that a formed annular 
belt of various sizes may be obtained. More particularly, as shown in FIG. 
4, a belt forming drum is composed of a plurality of segments 01 severed 
in the circumferential direction, and as a result of movement of these 
segments in the radial direction, the outer diameter of the cylinder 
expands or collapses. In order to cover the gaps between the segments upon 
expansion, heretofore an annular rubber band 02 was provided so as to 
surround the outer circumference of the cylinder. 
However, the rubber band 02 has a limit in elongation, and so, with only 
one kind of rubber band, the size of the annular belt that can be formed 
is extremely limited. Therefore, the scope of the applicable forming size 
was enlarged by preliminarily preparing a several kinds of rubber bands 
having different circumferential lengths and making use of them 
selectively according to necessity. 
But, such type of rubber bands are manufactured to be relatively thin in 
order to increase an expanding/collapsing proportion, hence the work of 
replacing the rubber band is very difficult, and especially the rubber 
band replacement work on a belt forming drum for forming a large-sized 
tire was a laborious time-consuming work. With regard to a sticking 
position of a belt member onto a drum also, since there is no way for 
positively fixing a belt member to segments, there was inconvenience that 
a sticking position of a belt member was displaced in the course of 
sticking or an annular belt was disengaged from a drum due to rotation of 
the drum after sticking. 
Since a rubber band has a tendency of gradually elongating while it is 
used, there was also an inconvenience that when a forming drum is 
collapsed in diameter and a formed annular belt is withdrawn therefrom, a 
rubber band elongated longer than the circumferential length of the 
forming drum when it has the minimum diameter, would be withdrawn together 
with the annular belt. Furthermore, in the event that a rubber band should 
be damaged, there was a fear that the rubber might be suddenly broken 
during expansion of a drum. 
Since the forming drum provided with a rubber band surrounding the outside 
of a plurality of segments is accompanied by the above-mentioned 
shortcomings, a forming drum not making use of a rubber band was proposed 
in U.S. Pat. No. 3,932,256. FIGS. 5a, 5b, 5c, are partial cross-section 
views respectively showing an expanded (the maximum diameter) condition E, 
an intermediate condition I and a collapsed (the minimum diameter) 
condition C of the proposed forming drum, wherein reference numerals 01a 
and 01b indicate two adjacent segments. Between the segments 01a and 01b 
is provided a cover plate 02a slightly bent at its center, and a part of 
the cover plate 02a on the side of the segment 01a is fixedly secured to 
the outer surface of the segment 01a by means of a flat head screw 03. The 
other end of the cover plate 02a is overlapped on the segment 01b. To the 
segment 01b is also fixedly secured a similar cover plate 02b. 
The respective segments are movable in the radial direction, and under the 
collapsed condition illustrated in FIG. 5c, the segments come so close to 
one another that they nearly come into contact with one another to reduce 
the outer diameter of the drum. At this time, the cover plate 02a would 
deeply overlap on the surface of the segment 01b to form a nearly 
cylindrical outer circumferential surface. 
If the segments are moved radially outwards from this collapsed condition, 
then they take an intermediate condition shown in FIG. 5b. Under this 
condition, although the segments 1a and 1b are separated from one another, 
the cover plates 02a cover the gap spaces therebetween and would form an 
almost smooth cylindrical outer circumferential surface. 
If the segments are further moved radially outwards from this intermediate 
condition, then the expanded condition shown in FIG. 5a is realized, where 
an also smooth cylindrical outer circumferential surface having the 
maximum outer diameter can be formed. In this way, the outer diameter of 
the drum can be arbitrarily varied from the condition where the segments 
are placed close to one another, up to the external condition where the 
free end portions of the cover plates can overlap on the outer surfaces of 
the adjacent segments, and in the course of the variation a nearly smooth 
cylindrical outer circumferential surface can be formed. 
A strip-like belt is wound around the thus formed cylindrical outer 
circumferential surface, stuck there and brought into tight contact with 
the drum, and thereby an annular belt having a desired size can be formed. 
However, there is no means for positively bringing the strip-like belt 
into tight contact with the drum, but only the stickiness of rubber 
forming the strip-like belt is relied upon. Accordingly, when the 
strip-like belt is wound around the forming drum, an inconvenience that a 
small gap space may be produced between the cylindrical outer 
circumferential surface of the drum and the belt member and hence the 
opposite ends of the belt member upon finishing of the winding may not 
coincide with each other, resulting in a gap space therebetween, is liable 
to occur. 
SUMMARY OF THE INVENTION 
It is therefore one object of the present invention to provide a forming 
drum which makes it possible to easily form a desired annular belt by 
bringing a strip-like belt member having a steel cord buried therein into 
tight contact with the drum. 
To that end, according to the present invention, in a forming drum for 
building a tire which forms a strip-like belt member consisting of a 
rubber-coated steel cord into an annular belt, and which comprises a 
plurality of segments divided in the circumferential direction and adapted 
to form substantially cylindrical shapes having different outer diameters 
as moved in the radial direction, the aforementioned plurality of segments 
are formed of non-magnetic material, permanent magnets are buried in the 
circular arc-shaped surfaces of these segments, cover plates made of 
non-magnetic material are respectively mounted between adjacent ones of 
the segments to form a cylindrical outer circumferential surface by these 
cover plates and each of the cover plates is fixedly secured to the 
circular arc-shaped surface of corresponding one of the segments. 
Since every cover plate having one end fixedly secured to the circular 
arc-shaped surface of the corresponding segment has the other end extended 
up to the adjacent segment to form a continuous cylindrical outer 
circumferential surface, the outer diameter of the forming drum can be 
enlarged or reduced within the range where the cover plate can bridge the 
adjacent segments. In addition, since permanent magnets are buried in the 
circular arc-shaped surface of the segment made of non-magnetic material, 
the strip-like belt member having a steel cord buried therein is brought 
into tight contact with the drum via the above-mentioned cover plates due 
to magnetic forces of the above-described permanent magnets. Accordingly, 
it would never occur that a gap space is produced between the outer 
surface of the drum and the belt member or a displacement is produced in 
sticking of the belt member onto the outer surface of the drum. Hence a 
desired size of annular belts can be easily and accurately formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a side view showing a part of a forming drum according to the 
present invention. Slide members 2 are supported in a radially slidable 
manner in radial slots formed in a cylindrical support member 1 at equal 
intervals in the circumferential direction. At the tip end of the slide 
member 2 a circular arc-shaped segment 3 made of non-magnetic material 
such as aluminum or the like, is fixed. On the support member 1 are 
provided, for example, forty slide members 2. As a result of these slide 
members sliding uniformly in the radial direction, the outer 
circumferential surfaces of the above-mentioned segments 3 form various 
cylindrical surfaces having different outer diameters. In FIG. 1, 
reference character C designates the condition of adjacent two segments 3 
where the outer diameter of the above-mentioned cylindrical surface has 
become minimum. At this moment, the respective segments 3 come close to 
each other, and one-twentieth of the circumferential surface of the 
collapsed cylinder is formed by these two segments. 
Outer ends of links 5 are pivotably mounted respectively to the vicinities 
of the tip ends of the respective slide members 2, and the inner ends of 
these links 5 are pivotably supported in sequence along one concentric 
circle on a base 4 having a smaller diameter than the above-mentioned 
cylindrical support member 1. Accordingly, as a result of relative 
rotation of the base 4 with respect to the cylindrical support member 1, 
the slide member 2 is made to slide in the radial direction by the 
intermediary of the links 5. Under the collapsed condition C, the links 5 
take a fallen state, but under the intermediate condition I, the links 5 
take a somewhat rising state, and under the expanded condition E, the 
links 5 are almost perfectly rising and the slide members 2 would be 
positioned nearly along the radii passing through the pivotal support 
portions at the base ends of the links 5. 
FIG. 2 is an enlarged cross-section view showing the segment portions under 
the collapsed, intermediate and expanded conditions, respectively, and 
FIG. 3 is a developed view of a drum circumferential surface under the 
expanded condition. On the circular arc-shaped surface of the segment 3 
are formed a plurality of grooves directed in the axial direction, and in 
these grooves are fitted permanent magnets 11 with iron plates 10 laid 
thereunder. The circular arc-shaped surfaces of the thus formed segments 3 
are covered by cover plates 12 consisting of thin plates made of 
non-magnetic material such as stainless steel or the like. 
The cover plate 12 is subjected to press working so as to maintain a 
circular arc-shape, and a front half portion thereof covers the segment 3 
and also is fixedly secured to the circular arc-shaped surface of the 
segment 3 by means of flat head screws 13. The rear half portion of the 
cover plate 12 forms a free end portion and bridges the next adjacent 
segment 3. It is overlapped on the front half portion of the cover plate 
12 fixedly secured to this adjacent segment 3. 
The cover plate 12 is press-worked in such manner that the circular 
arc-shape of the pressed cover plate may coincide with the configuration 
of the drum circumferential surface under the collapsed condition C. In 
the collapsed condition C, the free end portion of the cover plate 12 
covers more than one-half of the circular arc-shaped surface of the 
adjacent segment 3, and is held in tight contact with the cover plate 12 
fixedly secured onto the adjacent segment 3. 
If the segments 3 slide in the radially outward direction starting from 
this collapsed condition, then the diameter of the drum becomes larger, 
and the intermediate condition I is attained. At this time, while the gap 
space between the adjacent segments 3 is broadend, the cover plate 12 can 
cover the broadened gap space to form a continuous cylindrical outer 
circumferential surface. If the segments 3 slide further in the radially 
outward direction, then the expanded condition E is attained. In this 
expanded condition, the free end portion of the cover plate 12 overlaps on 
the surface of the adjacent segment 3 to a certain extent to cover the gap 
space between the adjacent two segments 3. 
Since the cover plate 12 is preliminarily given permanent warp by 
press-working so that the radius of curvature thereof may coincide with 
the radius of curvature under the collapsed condition C, under the 
intermediate condition I and the expanded condition E, the cover plate 12 
would be subjected to elastic deformation, resulting in increase of the 
radius of curvature, accordingly the free end portion of the cover plate 
12 is pressed on the cover plate 12 fixedly secured to the next adjacent 
segment 3 due to elasticity thereof, and thereby a tight contact condition 
can be always maintained between the adjacent cover plates 12. 
As the illustrated embodiment is constructed as described above, the outer 
diameter of the forming drum can be arbitrarily varied over a wide range 
from the collapsed condition C up to the expanded condition E, and under 
any condition, always a continuous cylindrical outer circumferential 
surface can be formed easily. 
In addition, the permanent 11 buried in the surface of the segment 3 has 
its magnetic force increased by the iron plate 10, and attracts the 
strip-like belt member having a steel cord buried therein and placed on 
the cover plate 12. Accordingly, when the strip-like belt member is wound 
around the forming drum, the strip-like belt member is brought into tight 
contact with the cover plate 12 without forming a hollow space 
therebetween, and so, at the time point when the belt member has finished 
to be wound, the front edge and the rear edge of the strip-like belt 
member preliminarily cut into a predetermined size can precisely coincide 
with each other. Also, displacement of the strip-like belt member with 
respect to the drum would not arise, and an annular belt can be easily 
formed at a high precision. 
The annular belt after formation also can be held stuck to the drum 
strongly by the magnetic forces of the permanent magnets 11. Thus, this 
annular belt would not be displaced with respect to the drum. As the cover 
plate 12 itself is made of non-magnetic material, it would not be directly 
attracted to the strip-like belt, and hence, when the formed annular belt 
is taken out, the magnetic force would not obstruct the take-out 
operation.