Study On The Mechanical Properties And The Failure Mechanisms Of High Temperature Resistant Sewing Thread

The high temperature resistant sewing thread is one type of sewing threads which is used tosuture high-temperature filter bag. The high temperature resistant sewing thread’s mechanicalproperties will deteriorate under high-temperature filtration conditions including continuous orintermittent high temperature, highly corrosive gas and dust, which will eventually leads to thebreakage of filter bag’s suture, and then, failure of the filter bag. So, in this paper, hightemperature resistant sewing thread were treated in high temperature, acid and alkalinelisolutions to simulate the high-temperature filter working conditions, and then the acid, alkalineand high temrerature resitance properties were characterized based on the mechanical propertychanges of the sewing thread by scanning electron microscope and fourier transform infraredspectroscopy. Besides, the high temperature resistant sewing thread’s strength will decrease aftersewing, so, we optimized its sewing process to ensure the high temperature resistant sewingthreads have maximum strength during their the initial using stage. The main contents andconclusions are as follows:1. The acid and alkaline corrosion resistance of three high temperature resistant sewingthreads were studied, and the appropriate filtering conditions were suggested. The conclusionsare as follows:（1） The tensile properties of Nomex sewing thread largely declined after acid and alkalitreatment, which was attributed to the amide bond breakage due to hydrolysis under acidic andalkaline conditions. Reagent concentration and treatment temperature increase will accelerate thereaction rate, so as to speed up the strength decline. Nomex sewing thread is suitable for the filtersmoke conditions such as rotary cement kiln and steel blast furnace.（2） The tensile properties of PTFE sewing thread had a hige risistance on acid and alkalicorrosion, because of its special molecular structure. PTFE sewing thread can be used in mostfilter smoke conditions such as incinerator and coal-fired boiler for its perfect acid and alkaliresistance.（3） The tensile properties of alkali-free glass fiber sewing thread declined largely after acid and alkali treatments, but the mechanisms of strength decrease were different in acid and alkalisolutions. After alkali treatments, the skeleton structure [SiO₄] and [AlO₄] of glass networkhave been destroyed. While, after acid treatments, the [BO₃] and=B—O—Si structure of glassnetwork have been destroyed. Alkali-free glass fiber sewing thread is suitable for the filter smokeconditions such as steel blast furnace for its bad acid and alkali resistance.2. The high temperature resistance of three sewing threads were studied, and the appropriatetemperature conditions under which they could be used were analyzed. The conclusions are asfollows:（1） The tensile properties of Nomex sewing thread declined largely after treatment at thetemperature range of230℃-400℃, due to the hydrogen bond breakage and the crystal waterrelease. Above430℃, aromatic nitrile groups appeared, which indicated the macromolecularchain breakage. Nomex sewing threads have a perfect strength resistance below180℃, so it issuitable for the fiter temperature conditions such as steel blast furnace（2）The strength of PTFE sewing thread shows a slight decline and its breaking elongationshows a slow increase when treated at the temperature range of280℃-320℃, which is mainlyresulted from the deorientation in high temperature. Above360℃temperature, PTFE sewingthread melts, above530℃temperature, PTFE begins decomposition. PTFE sewing threads havea perfect strength resistance below230℃, so it is suitable for the fiter temperature conditionssuch as the incinerator and coal-fired boiler.（3） The tensile properties of alkali-free glass fiber sewing thread declined rapidly with theincrease of the processing temperature and time at the temperature range of320℃-400℃.Thealkali-free glass fiber sewing thread has no strength with no cohesion between glass fibers whentreated above560℃temperature due to its surface sizing and PTFE coating decomposition.Alkali-free glass fiber sewing threads have a perfect strength resistance below280℃, so it canbe used in the fiter temperature conditions such as steel blast furnace.3. The effects of different sewing parameters on three high temperature resistant sewingthread`s strength after sewing were studied. Choosing the strength retention after sewing as anassessment index, the optimized sewing parameters were obtained.