Plastic woven bags are made of polyethylene, polypropylene by drawing, weaving, sewing or pasting, loading weight is generally 25-50kg. Because of its good tensile strength, low price and convenient transportation, it is widely used in the packaging of cement, chemical raw materials, chemical fertilizers, minerals, grain, sugar and other powder and granular materials. This kind of packaging has been increasing year by year in recent years. .
Cement is an important building material and its output has increased year by year. This year it will reach more than 850 million tons. Except for the bulk transportation, the rest are all packed in bags, requiring as many as 13.6 billion bags and 70% plastic woven bags. Therefore, the State Bureau of Technical Supervision issued a mandatory "Cement Bag" standard from the 1997 edition to the 2002 edition, and puts the laminated plastic woven bag out of the composite bag as a separate bag type.
In order to ensure the implementation of national standards, local inspection and quarantine departments supervise the production of plastic woven bags, issue quality licenses, and formulate standardized inspection management methods and inspection procedures. Such as the implementation of a plastic woven processing plant license management; the appearance of the factory woven plastic bag batch inspection; physical testing cycle performance; implementation of batch management. This article lists the major issues found in management and practice, with a view to helping the bagging companies achieve a consensus on understanding.
About the aging problem of plastic woven bags In the natural environment under the conditions of direct sunlight, the plastic woven bags will reduce their strength by 25% after one week and reduce by 40% after two weeks, basically no longer available. In other words, the storage and storage of plastic woven bags are very important. In addition, after the plastic woven bag is packaged in cement and exposed to direct sunlight in the open air, the strength will drastically decline; during the storage and transportation process, the temperature will be too high (container transport) or encountering rain, which will lead to a decrease in its strength, thus failing to achieve protection. Quality requirements for interior items. Therefore, the conditions for transportation and storage of plastic-woven bags are very important. Therefore, both GB/T8946 and GB/T8947 have clear regulations for storage and transportation conditions. That is, plastic woven bags should be stored in a cool and clean room, and should avoid sunlight and rain during transportation. They should not be near heat sources and the storage period should not exceed 18 month. In fact, the plastic woven bags may age during 18 months. Therefore, the effective period of plastic woven bags should be shortened. It should be 12 months.
The degree of aging of the woven fabric during the lamination process can be determined by the relative tensile load and the elongation at break of the flat yarn. Before and after coating the film, the tensile load and elongation at break of each sampled flat yarn were tested, and the test results were compared to determine if the technical parameters of the flat yarn did not vary greatly before and after coating, and it could be considered that there was substantially no aging; if before and after coating There are many differences in the technical indicators of the flat yarn, and there may be problems of aging. It is necessary to analyze the reasons and improve the technological process. About Recycled Materials for Plastic Woven Bags
In order to ensure the quality of packaging bags, the aging problem of plastic woven bags should be highly regarded. To this end, the national building materials industry authorities have requested that raw materials in bag making are not allowed to have recycled materials or recycled materials. The amount of filler materials should be strictly limited to no more than 5%. At the same time, the film temperature must be strictly controlled to avoid process problems. Causes accelerated aging problems. Excessive addition of recycled materials is also one of the reasons for the aging of plastic woven bags.
Theoretically speaking, the raw materials of plastic-woven bags are extracted and used after re-drawing, which belongs to the scope of recycled materials. However, as with other products, no scrap or scrap can be produced during the production process. Generally referred to as non-recycled plastic woven bags means that when woven bags are produced, no additional recycled waste is purchased. The flat yarns and waste yarns produced in the production are added in proportion to the new materials, which means “non-recycled woven bags. ". In order to reduce costs, some plastic woven and sack manufacturing companies use recycled materials (side-wire or waste-filament) that exceed the specified ratio, and plastic woven bags will suffer from the problem of unqualified strength, which should attract attention in this regard. In addition, an excessive amount of titanium dioxide is added to the ingredients to increase the dust produced by the plastic woven bags, which also affects the strength of the plastic woven bags. Therefore, the relative tensile breaking force of the woven bag containing the recycled material is significantly reduced. If the secondary return material is added, it is difficult to ensure the relative tensile breaking force of 0.32 N/tex. Elongation at break is not stable, and the fracture rate varies depending on the amount of recycled material added. The brittleness of the regenerated material woven bag is obviously increased, especially the resistance to low-temperature brittleness is worse, the impact resistance is reduced, the electrical insulation is decreased, the aging degree is increased, and the speed is accelerated.
About the suture problem of plastic woven bags
In the years of inspection and management, it was found that some plastic-bonded companies neglected the management of the enterprise, and there was no back-to-back stitching at the end of the suede bag at the bottom of the production, or there was a phenomenon of skipping and it was easy to produce leakage packages. Therefore, under the condition that the braid itself has sufficient strength, the main factors that affect the strength of the stitching should also be noted. The strength of the sewing thread depends on the type of thread (cotton thread, polyester thread), the thickness of the thread (the size of the thread density), the number of strands of the thread (the thread twist and the twist). The sewing stitch length is too large and the stitching strength is reduced; the stitch length is too small, the woven cloth is stabbed and the strength is also reduced. The shape of the suture's chain, whether single or double, the tightness of the sleeve, can be disassembled from one end. Stitching stitching methods, stitching methods are curling, folding, wrapping, overlapping and so on. These include the hemmed width, the hemmed width, the hemming width and method, the amount and method of lap joints, and the distance from the suture to the bottom edge. When stitching, the stitches must be flat and cannot be removed, jumped, removed, or stitched without crimping. The stitch length should be even and the thread breakage should be more than 50mm after stitching to prevent chain stitches from tripping.
With regard to non-laminated plastic woven bags or combination liner bags, after investigation, there are still cement packaging bags that are not produced according to national standards. The most dangerous ones are non-laminated plastic woven bags and non-laminated plastic woven bags. Lined paper combination bag. When the bag is filled in the cement plant, a large number of broken bags are generated. After transport, handling, and circulation, the bags are broken, and some of them are loaded with cement pallets or stored in the open air. They can be broken in a few days. It is not easy to handle. This poor quality non-laminated plastic woven bag can not withstand ultraviolet light and wind blowing, ash leakage is serious, but not moisture, so that a large number of leaks inside the cement, drop, agglomeration, deterioration and even the entire bag of cement scrap.
About the problem of punching and laminating bags
No matter how the plastic film is coated on the plastic woven fabric, it will cause airtightness. At present, in the use of this kind of film-plastic woven bags, it is necessary to ensure that the cement is filled in time under the action of a certain pressure, and that the purpose of moisture prevention is achieved during transportation, handling, and storage. At present, micropores can only be punctured on the face of a plastic film bag, and no other technical method is available. In addition to meeting the basic functions of cement packaging, laminated plastic woven bags, like other structural packaging bags, must also address the issues of exhaust, temperature resistance, and moisture protection during cement filling. The problem of punching holes in laminated plastic bags is the key to solving these technical problems.
Most cement companies use gas-conveying cement filling methods during cement filling. When filling cement, the exhaust problem is not solved. First, the efficiency of filling is affected. Second, the qualified rate of bag weight cannot meet the requirements. For the laminated plastic woven bags, the running, running, and ash leakage during filling must be taken into consideration and the moisture-proof problem during transportation must be taken into consideration. Large exhaust hole, large number of holes, good exhaust performance, high filling efficiency, but the cement runs badly during filling, poor moisture resistance; small exhaust hole, small number of holes, poor exhaust performance, filling The efficiency is low, but the cement runs less when filling, and the moisture resistance is also good. Therefore, the size and density of the pinholes are the key factors that affect the ash emission during cement filling and the moisture resistance of cement. The needle diameter of 2mm or 1.5mm can meet both requirements. The general operation is: in the longitudinal direction of the laminating fabric, one eyelet every 6mm, one eyelet every other side in the transverse direction, the conical needle is used as the punching needle, and the vent hole is punched out from the inside to the outside. Through this process, the laminated film and plastic woven bag can be easily discharged from the inside to the outside during filling, thereby satisfying the exhaust requirement during cement filling, and also ensuring the qualified rate of the bag weight, and at the same time, filling the bag. The grey phenomenon has also been resolved. The cement-packed bag is automatically closed after the vent hole contacts the belt in the process of contacting the belt, which better solves the moisture-proof performance of the cement package during transportation and storage.
Because cement production process and equipment level are different, the temperature of cement exit is not the same, generally between 50°C and 100°C. If the quality of the base fabric of the laminated film and plastic woven bags can meet the requirements of the GB8974 national standard, it can completely solve the problem of temperature resistance of the cement package. When the temperature of the cement exit is high, the thickness of the plastic film woven bag can be appropriately increased. If one-sided pursuit of cost reduction, the use of inferior plastic raw materials, adding excessive amounts of additives, the process conditions are not stable, the equipment level can not meet the product quality requirements, even if the plastic woven bag is thick, it can not fundamentally solve the problem of packaging temperature.
About other aspects of quality issues
For those who only engage in double-film bag making and do not engage in drawing, circular knitting and other production processes, companies that purchase plastic-braided cloth as the base material must strictly control and must not purchase large amounts of recycled materials, powder materials and more than 5 % Filler base material.
Plastic woven fabrics are caused to curl during weaving. Due to improper tension adjustment, creases are left in different degrees on the fabric surface, so that the bags of the rewound film are impacted by wind pressure when filling the cement, and are easily broken at the creases. In order to reduce this drawback, a crease-stretching device shall be installed on the top of the mold without cast filming to ensure the formation of the cloth.
Folding bag folding is a major process. Because the width of the woven cloth is not uniform, it is easy to tear when it is too narrow. Therefore, the structure of the hemming device should be changed to be elastic to solve the problem of tearing in the hemming process.
It is necessary to strictly control and test the ingredient ingredients, drawing strength, and breaking strength of monofilaments, the width and density of the fabrics that are produced or purchased in-house. These are important issues in ensuring the number of times, peeling strength, ageing resistance, breaking strength of the bag surface, and cost reduction of plastic film and plastic woven bags.
The width and defect of the base fabric of the laminated plastic woven bag must be strictly controlled, otherwise tearing will occur when passing through the pleated tire, resulting in a large amount of waste products. Similarly, it is necessary to strictly control the hole at the edge of the folded base fabric, otherwise, a large amount of waste products will also be generated when passing through the folding device. There must be no grease on the surface of the bubu cloth, otherwise it will affect the composite fastness.
In the process of film lamination, the design of extruder, die head, heating coil configuration and process temperature shall be organic with the accuracy of the base fabric, heating coil area, lamination properties, main engine speed, cutting speed and temperature instrumentation. In combination, designing a reasonable process temperature can guarantee the production of a qualified laminated film cement bag and ensure the improvement of efficiency.
Laminated resin material is a key material for laminated plastic woven bags, which plays a crucial role in the peel strength and cost of the product. Therefore, it is necessary to purchase a composite resin material produced by a regular petrochemical enterprise.
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