Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
THIN SEAT BELT WEBBING AND METHOD
BACKGROUND OF THE INVENTION
This invention relates to woven belting for
safety belts, preferable with a 2 binding, and to a method
for its manufacture.
In the automotive industry, belt systems with
belt winders, especially automatic ones, are used to
secure the occupants, in regular belt systems such as
three-point belts, and also in passive belt systems.
The automotive industry is demanding from the
belt system manufacturers the development of smaller and
lighter belt winders, especially automatic ones. If the
volume and weight of automatic belt winders can be
reduced, it will be a contribution towards increased com-
fort and improved efficiency of the motor vehicle.
To the producer of safety belt systems, smaller
belt winders in conjunction with less weight means pri-
marily the development of thinner belting because a belt
winder of a volume smaller than that o-f conventional win-
ders will allow only the winding up of a shorter length ofbelting of conventional thickness and weight.
Accordingly, it would be desirable to provide
woven belting of less thickness while retaining the other
belt properties, such as elongation, strength, abrasion
properties, etc.
SUMMARY OF THE INVENTION
According to the invention, this problem is
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solved in that the weft denier is less than 2/300 dtex or
1/600 dtex; that the number of wefts per 10 cm is at least
70; and that the warp is at least 2~ shorter than that in
comparable woven products of greater weft denier and less
wefts with the same elongation, scrength and abrasion pro-
perties.
In addition, in accordance with this invention
there is provided a method for the manufacture of seat
belt webbing having warp and weft yarns, characterized
by the steps of:
a. employing weft yarns of a denier less than
2/300 dtex or 1/600 dtex, and
b. weaving the weft yarns through the warp yarns
in such a manner to provide at least 70 weft yarns per 10
cm, the length of the warp yarns in the webbing being at
least 2% shorter than in comparable woven webbing of
greater weft denier and fewer wefts with the same elonga-
tion, strength and abrasion properties.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Given the above problem of creating a practical,
thinner belt, it was found that one possible influential
factor was a change of the material density per unit of
area, i.e. per cm2. One possiblity of reducing the
material density per cm2 was reducing the weight of the
wefts. The teaching of the invention, namely to make the
wefts of the new belting thinner than in conventional
belting, was contradicted, first of all, by the disadvan-
tage that it causes the seam strength to become too weak.
Another possiblity would have been the reduction of the
number of wefts per unit of length. But then, too poor
abrasive properties of the finished belt would have had to
be expected. Also, the cohesive strength of the belt in
transverse direction or, in other words, its transverse
strength, would then have become worse.
However, in conjunction with the other features
of the teaching of this invention it has been discovered
that the wefts can he made thinner than in conventional
belts or, in other words, that the weft denier can be
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reduced. This makes it possible, due to the smaller
amount of material per unit of area in the belt, to obtain
thinner woven belting. ~he unit dtex is expressed in
weight per 10,000 m, and it is the known unit of the yarn
thickness, here of the weft. The expression 2/300 dtex
refers to a needle system in which a yarn of 300 deni~r is
inserted twice into one opening in an in and out fashion,
whereas the expression 1/600 dtex refers to a shuttle
system in which a yarn of 600 denier is inserted once into
one opening.
The other measure according to the teaching of
the invention and connected with reducing the weft
thickness is the increase in the number of wefts per unit
of length. This step can be taken without thereby
reaching overall a comparable amount of material per
cm2 in the belting as in conventional woven products. But
the salient advantage resulting therefrom is the improve-
ment of the abrasion properties due to the increased
number of wefts.
Another measure to solve the problem is the
shortening of the warps by 2% compared to the warps of
comparable woven products. Comparable woven products are
those of conventional type having a weft denier greater
than, say, 2/300 dtex and a smaller number of wefts than,
say, 70 per 10 cm; while elongation, strength and abra-
sion properties of the heavy, thick belting of conven-
tional type should be the same as those of the thinner
belting according to the invention. A reduction of the
warp length compared to warps in known belts is obtainable
even when the number of wefts per unit of length is
increased over that in conventional belts to improve the
seam strength and the abrasion properties of the belt.
Another result of using thinner wefts has been that the
crimp of the warps, i.e. their reorientation around the
wefts, becomes less, whereby better utilization of the
strength of the warps can be obtained to advantage.
For example, assuming a linear load of a warp
yarn without crimp to be 100% this strength is reduced to,
72~3
--4--
say, 80~ due to the reorientation of the warps around the
wefts, as is known. Conse~uently, the better utilization
of the linear strength of the warp plays quite a substan-
tial role.
While the basic assumption had to be that the
weft thickness can possibly be reduced to reduce the
thickness of a conventional belt, the general conviction
was that the number of warps must not be reduced because
an intolerable loss of ultimate strength would otherwise
have to be expected. Due to the advantageous effect of
the reduced crimp and the better utilization of the linear
strength it is possible, according to another expedient
feature of the invention, to reduce the number of warps
also, in comparison to their number in conventional belts.
It has turned out that while there is a certain increase
in the crimp due to the greater number of wefts per unit
of length, the crimp still stays low enough to obtain the
said better utilization of the strength of the warps.
Thus, it is possible to reduce the number of warps by 5 to
7%, for example, without reducing the strength.
The above measures are by no means a matter of
course in woven belting, especially since the high safety
factors attained by the conventional belts are prohibited
by stringent laws from being jeopardized, and these values
are in no way sacrificed by the teaching of the invention,
although a thinner belt has been created.
In advantageous further development of the inven-
tion, the number of wefts per 10 cm in the new belting
ranges between 70 and 85, pre~erably between 73 and 80.
The most expedient values can be adjusted here in adap-
tation to the specifications respectively demanded,
because numerous parameters play a role; one only has to
think of the choice of material for the warps of and
wefts, for instance. Basically, the weft denier could be
set as small as possible; however, the lower li~it is
determined bv the specified seam strength and the abrasion
properties.
The above measures also have their effect in
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belting types having bindings other than the 2 binding
preferentially considered here, for beltings with a 3, 4
3 4
or 5 binding may be provided also. Preferably, the yarns
are polyester or nylon yarns.
A conventional seat belt has an elongation of
e.g. 8 to 10% at a belt thickness (not calendered) of
about 1.2 mm. Such a belt weighs 60 g per m at a
strength of 2900 daN, and the weft density, i.e. the
number of wefts per unit of length, specifically per 10
cm, being 68. The weft denier here of the polyester yarns
is 2/550 dtex.
The thinner belt according to the invention has
the same elongation, strength and abrasion properties (as
the above described conventional belt). However, the
thickness of the new belt is (in one embodiment) 1.0 mm,
it weighs 52 g per m, its weft density is 79 per lO cm,
and its weft denier of the polyester yarns is 2/280 dtex.
The above example clearly demonstrates the impro-
vement of the new belting over the conventional belting in
regard to thickness and weight, with safety charac-
teristics remaining unchanged.
Both belts described above have a 2 binding.
In order to prevent a thinner belt according to
the teaching of the invention from being produced and
becoming floppy, i.e. too flexible, it may be expedient,
in further development of the invention, to have infrared
rays act upon the belting to fix it thermally. It is
already known that certain technical properties such as
elongation, abrasion properties, and flexibility can be
imparted to the belting by heat setting. However, this
thermal fixation is generally in the form of contact heat
or hot air (e.g. 230C). This shrinks, fixes, or
stretches the belting by heat setting. But the disadvan-
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tage of this known thermal fixation is that the tem-
perature can be applied mainly to the outer surfaces only
of the woven products to be fixed.
Due to the action of infrared rays on the woven
belting, complete fixation through and through is obtained
to advantage. The infrared rays heat the belt through
completely. This makes it possible also for a thin belt,
produced by using thinner wefts, for instance, to attain
good stiffness or the desired correct flexibility.
A total weight saving of 32 g can be achieved in
a specific automatic winder through the measures according
to the invention. This figure demonstrates the advantages
of a belt winder with the new woven belt.
Other advantages, features and possible applica-
tions of the present invention follow from the descriptionbelow in connection with the drawings in which Fig. 1
shows, in transverse section and greatly enlarged, a por-
tion of a woven seat belt according to a conventional
system, and Fig. 2 shows a view similar to that of Fig. 1,
but with thinner wefts and, hence, a thinner belt overall.
The known type of weaving according to Fig. 1 as
well as the new one according to Fig. 2 has a 2 binding.
According to this binding, the warp 1 is severely crimped
around the wefts 2. The use of these relatively thick
yarns results in an uncalendered thickness of the known
belt of D = 1.25 mm approx.
The wefts 3 of the new belt according to Fig. 2
are thinner so that the warps 4 and the weEts 3 are inter-
woven with less crimp so that the resultant total uncalen-
dered belt thickness is d = 1.00 approx.
