Study On Fabrication And Mechanical Properties Of Flat Knitted Fully-fashioned Multi-way Pipe Preform

Multi-way pipes are tubular joint connectors in the pipeline used to transport liquid and gas,including T-shaped pipes,Y-shaped pipes,and so on.The main function of the multi-way pipe is to change the direction of the fluid.In the automotive field,multi-way pipes made of rubber are often used as joint connectors of various hoses to complete power transmission and transportation of water,gas,and fuel.Due to the environmental conditions for use of automobile hoses are harsh,the high temperature resistance,corrosion resistance,high pressure resistance,fatigue resistance and other properties of the hose are required.The fabric-reinforced rubber composite material can be flexibly designed according to performance requirements.Therefore,most of the current automotive hoses are fabric-reinforced rubber products.However,for multi-way pipes of various shapes,the reinforcing fabric is required to be a three-dimensional structure,and the shape of the fabric can be easily changed according to the shape of the multi-way pipe,and it is better to be integrally formed without stitching.Among all the fabric knitting methods,the knitting process design of flat knitting is flexible,and the structure and shape of fabric can be changed simply and quickly according to product requirements.And with the development of the flat knitting fully-fashioned technology,it has become possible to knit three-dimensional fully-fashioned fabrics with complex shapes on flat knitting machines.Based on the research of the flat knitting fully-fashioned process,this subject designs the forming process of the multi-way pipe preform.The preparation of the multi-way pipe preform was completed on a flat knitting machine and its mechanical properties were studied,in order to provide a reference for the development of the multi-way pipe preform.Firstly,this subject researches the mechanism composition and working principle of the double-bed fully-fashioned computerized flat knitting machine,and explores its fully-fashioned knitting process which is different from the ordinary double-bed computerized flat knitting machine.Through research,it is found that the double-bed fully-fashioned computerized flat knitting machine uses fully-fashioned knitting needles,while the loop is held in the needle hook,the sliding piece is used to transfer the needle.Fully-fashioned full-needle-knitting multi-way pipe preforms can be realized,and the fabric structure is more compact.When knitting,the basic structure of the multi-way pipe preform is knitted by the fully-fashioned cylindrical knitting process,and the shape is changed by the fully-fashioned process of narrowing and widening and the partial knitting process.Secondly,using the fully-fashioned knitting process,this subject designs the forming process of the multi-way pipe preform,including T-shaped pipe and Y-shaped pipe.When designing,it is first necessary to transform the three-dimensional structure of the multi-way pipe into a two-dimensional shape.According to the size parameters and fabric density of the multi-way pipe,the knitting process parameters are calculated according to the process model,and the dimensional forming process of the multi-way pipe preform is designed by using the fully-fashioned cylindrical knitting process.Then,according to the different angles between the multi-way pipes,different knitting and narrowing ratios are adopted,and the angle forming process of the multi-way pipe preform is designed by using the partial knitting process and the narrowing process.Finally,according to the designed forming process,the preparation of the multi-way pipe preform is completed by using a double-bed fully-fashioned computerized flat knitting machine.Through using different angle forming processes,different pipe diameters and fabric density,the correctness of the knitting process model and the feasibility of the design method are verified.In the end,the multi-way pipe preform that basically meets the size and angle requirements is obtained.Finally,in order to explore the effects of partial knitting,narrowing and different narrowing processes on the mechanical properties of multi-way pipe preforms,a tensile fracture experiment was carried out on all fabrics in the multi-way pipe preform.Through the use of consistent knitting process parameters and tensile test parameters,a single variable experiment for fabrics with different structures is designed.Through experiments,it is found that the narrowing process will reduce the strength of the fabric,while the partial knitting process will increase the strength of the fabric.In addition,through the comparison of experimental results,the narrowing process that has the least impact on the mechanical properties of the T-shaped pipe and Y-shaped pipe preforms is obtained respectively.