Airbag construction. Influence of the weaving defects on proper functioning of the airbag.

Stefanuta, Ioan ; Vrinceanu, Narcisa ; Roman, Marius 等

Abstract: The present paper is focused onto influence of the weaving defects on proper functioning of the airbag. The approaching is oriented to basic tests for fabric characteristics, as well. Considering the reduced quantity of operations in the production processes, high degree of automation of the machines and efficient control systems mounted on them, it was determined that the number and the variety of defects that can appear on the fabric is relatively reduced compared with production quantity.

Because the required safety standards for the functioning of the airbag are very constricted, it is necessary an analysis of impact of every defect on proper functioning of the products

Key words: airbag, technology, weaving, yarn, automotive, weaving defects

1. INTRODUCTION

Identification of possible weaving defects has to be performed according with the production process taking into consideration the following:

--type of machinery used : degree of automation, safety and control systems available;

--control procedures utilized in the process;

Considering the reduced quantity of operations in the production processes, high degree of automation of the machines and efficient control systems mounted on them, it was determined that the number and the variety of defects that can appear on the fabric is relatively reduced compared with production quantity.

Because the required safety standards for the functioning of the airbag are very constricted, it is necessary an analysis of impact of every defect on proper functioning of the products.

2. WEAVING DEFECTS. LOCALIZATION, TYPES, CAUSES AND EFFECTS (Takata, 2007)

--Warping: fluffs, oversized knots, very high frictions on the guiding systems, weavers knots executed incorrectly, portions with very low resistance that can fail at weaving, supplementary forces between yarns at weaving (Fig. 1);

--Weaving: group of broken ends in the warp, accidental contact with a foreign object, portions with lower resistance in the fabric, forming of zones like "efforts concentrators" where the adherence degree between ends decreases (Fig. 2);

--Weaving: folded yarn in the fabric, failure of the edge cutting system, modifications of the density and bigger floats in the warp (Fig. 3);

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--Warping: loose ends, disorder of tensioning systems, very high frictions between ends at weaving;

--Weaving: density in warp and weft incorrect on a narrow portion, deficiency in start-up of the weaving machine at a normal working regime, lower burst resistance of the fabric.

--Weaving: missing yarn in the weft, lower functioning pressure of the insertion system, barriers formed by the warp ends, finishing of the weft yarn, zones of the fabric with lower burst resistance and high permeability;

--Weaving: tension too low of the warp ends, incorrect warping procedure, producing of entangled yarns and obstruction of the weft insertion, portions of fabric with missing yarns or structure modifications;

--Weaving: conglomerations of yarns with broken filaments, intense frictions between yarns and/or with guiding systems (Fig. 4);

--Weaving: air splice knots, incorrect functioning of the airsplicer, incorrect knots that produce additional friction between ends, negative modifications of the fabric structure (Fig. 5).

3. BASIC TESTS FOR FABRIC CHARACTERISTICS (ULBS, 2007)

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For relevance of the tests results and observation of the impact on the functioning of the airbag was taken into consideration the most frequent defect: conglomeration of yarns with broken filaments or bulge. The fabric type: 70 ends /inch in the warp and weft.

Performed tests:

--tensile strength and elongation

--tear force

--high pressure air permeability

The results are listed in the graphs Fig. 6 to Fig. 9.

4. PROCEDURES, METHODS AND CONTROL POINTS

According with the operations of the production process one example of the quality control system on the production line is:

4.1. Warping:

--visual check at every start and end of the shift of the machine by the operator (all the devices that came in contact with the yarn are checked).

--tensioning devices on the creel of the wrapper are fitted with sensors that stop the machine in case of yarn brakeage.

--2 cameras count all the time the number of ends to be according with the article type that is produced. Contrary the machine will be stopped.

--one scanner checks all the time the diameter of the yarns in order to detect possible broken filaments and stops the machine automatically for each yarn that has broken filaments.

--verification of the machine at each beginning/end of the shift with "dummy" samples for proper functioning.

--the tensions of the yarns on the creel and the unwinding from the bobbins are permanently controlled by the machines computer according with the settings.

--verification of the run out of the braking pads on the beamer

--reed dents are checked and also the width reed for wear off.

--the beam flanges are checked for wear off.

4.2. Weaving:

--at each beginning and end of the shift the machine status is checked

--at each warp beam that is changed preventive maintenance is performed for the weaving machine (washing, greasing, etc.)

--at each beginning of new fabric roll it is verified in the laboratory the fabric density and the flammability

--on the right side of the machine there is a sensor "IR feeler" that detects if the insertion was complete. Contrary the machine will stop.

--with ten meters before warp is finished from the beam there is a adhesive band that reaches a sensor who stops the machine.

--automatic system for proper length that is needed for one weft insertion.

4.3. Coating:

--the machine is provided with control devices that measure all the time the density of the fabric before and after coating.

--the add-on for the coating amount is measured permanently by an NDC gauge.

5. CONCLUSIONS

--even if the automation degree of the operations is very high, some defects may appear mostly at weaving, their number being in the control limits;

--the most frequent defects are broken filaments and broken ends;

--the influence of this defects on the basic properties of the fabric is controllable, the results being within the specified ranges from the standards;

--for safety on the proper functioning of the airbag portions of the fabric that have defects are rejected, or if the product was produced they are scrapped at the final control check.

--the policy of the airbag production firms is "zero defects".

6. REFERENCES

AKLV (Arbeitskreis Lieferantenvorschriften)

ASTM (American Society for Testing Methods) Documentation, 2007

FMUSS (Federal Motor Vehicle Safety Standard) Documentation, 2007

EASC (European Airbag Standardization Committee) Documentation, 2007

Tehnical Documentation Takata-Petri Sibiu, 2007

ULBS--Testing results from laboratory, 2007