| Polydicyclopentadiene(PDCPD)is a kind of environment-friendly material with excellent mechanics and low molding requirements,it is polymerized by the olefin complex decomposition reaction of dicyclopentadiene(DCPD)purified by C5 fractions,and with the support of national policy in recent years,PDCPD's domestic research and development,production and application have grown rapidly.PDCPD has made great progress in the use of reactive injection molding of single pieces,large single pieces and thin-walled parts,but the continuous production of plates and tubes with high demand and special performance requirements has not been able to make a breakthrough.This has become one of the bottlenecks to restrict PDCPD's research and development and application expansion.PDCPD's excellent weather resistance,corrosion resistance and low density have natural advantages over conventional plastic pipes,and the future development and application prospects are huge.Therefore,the DCPD continuous reaction extrusion scheme is proposed,and the continuous extrusion process is studied based on the scheme design extrusion head and computer simulation technology.The main research contents and results are as follows:(1)The DCPD continuous reaction extrusion structure and molding process scheme are proposed.In the structural scheme,since DCPD aggregation is a heat-induced reaction,the oral mold is set up three-stage temperature control,the role is to isolate the reaction heat to avoid early curing,heating trigger reaction and cooling to release temperature.Because DCPD is liquid,an active tube plug is set to maintain its shape and form a negative pressure.On the process scheme,the temperature control is carried out by the fluid medium,and it brings the advantages of good stability and good thermal uniformity.In addition to the use of three temperature control methods,the temperature difference between the mouth mold and the core bar can be achieved to achieve the high temperature zone first reaction and ensure its surface quality,and the direction of shrink stress is single.It is proposed to use numerical simulation to determine the size of traction.(2)The thermal balance of the extruder head is analyzed.The convection heat exchange model of the doughnut water flow on the mouth mold is equivalent to the flat-wall convection heat exchange model,the core rod water flow is the circular tube convection heat exchange model,the heat exchange equation of convection heat exchange is established by similar criteria,the energy equation system of the extruder head is established,and the energy equation system is solved to obtain the flow rate of ambient cooling water,fast heating water,low temperature cooling water and core cooling water under the designed size conditions.(3)Models of DCPD material fluency,curing dynamics and extrusion process are constructed to establish a basis for simulation.The DCPD viscosity model is simplified by analysis.This paper summarizes the experimental and modeling methods of DCPD reaction curing dynamic equations,introduces convection terms to modify static reaction curing dynamic equations,and establishes its boundary conditions to adapt to the dynamic continuous extrusion process.The expression of reactive heat is deduced,the energy equation of the extrusion process is established,and the coupling with the reaction curing dynamic equation is realized by the thermal source terms related to the reaction curing gradient.COMSOL simulation results show that DCPD's temperature curve change law is consistent with the temperature change law caused by its reaction dynamics behavior,which proves the correctness of the modified reaction curing dynamics and heat source terms.(4)Based on modeling,the DCPD reaction extrusion process simulation is carried out,and the influence of structure and process parameters on the extrusion process is analyzed.Through the mathematical model of COMSOL software coupling reaction curing dynamics and extrusion process,the pressure field,flow field,temperature field and curing field of DCPD reaction extrusion process are solved,and the results show that the three-segment temperature control method can effectively control the length of each reaction segment of DCCD and realize DCCD efficient continuous extrusion.Reaction heat release causes DCPD temperatures to reach up to 90 ? or more,so low temperature cooling must be set to cool down.The influence law of geometric structure parameters and process parameters on extrusion process is studied,and the optimal parameters are obtained,the main conclusions are as follows.1)Geometric parameters have little effect on the pressure field,pressure drop is only 0.5% on different compression angles,buffer length and thickness;However,the effect on flow rate stability is great,and the results show that the geometric parameters with the best stability are 34 degrees compression angle,80 mm buffer length and 14 mm thickness.2)Too low extrusion speed will cause a sharp increase in the cumulative temperature of the head and too long PDCPD curing section in the head,and there is a tendency to cure ahead of time to clog the head;With the increase of extrusion speed,the length of the curing transition zone of 0-1increases.When the extrusion speed of this device is 0.019m/s,the extrusion efficiency is highest,the temperature distribution is uniform and moderate,and the traction difficulty is low.3)The longer the length of the heating area,the slower the curing,but the length increased to a certain degree of curing has not much impact on the curing degree,in the actual design should minimize the length of the heating area,and the device's optimal length of heating area is 70mm;The length of the cooling area has little effect on the curing distribution,but the optimal length obtained by this device is 100 mm due to the release temperature and pipe strength.4)When the temperature difference is too small,reaction heat release will make the temperature of the core rod boundary in the back section of the head anti-super-mouth mode boundary temperature,indicating that the core rod boundary cooling is not good;When the temperature difference is too large,the reaction rate difference between the mouth mold boundary and the core rod boundary will be too large,which will eventually cause the stress concentration inside the pipe;The optimal parameters obtained by this device are: the die temperature is 70 degrees C,the core bar temperature is 50 degrees C or 40 degrees C.(5)The traction calculation method is proposed,and the traction control equation is calculated with the optimal geometry and process parameters as an example.The friction of PDCPD in different lengths was calculated by ANSYS,and the f-L curve relationship was obtained by linear regression fitting of the calculated data.The PDCPD curing length in different extrusion speeds was calculated by COMSOL,and the L-U curve relationship was obtained by linear regression fitting of the calculated data.Finally,the DCPD reaction extrusion process is analyzed and the traction control equation is integrated.(6)The flow field simulation under the three auxiliary buffer structures is completed,and the flow field is analyzed and optimized.The results show that the large inclination of slope and the increase of injection port can effectively improve the flow rate of DCPD and prevent the curing blockage of DCPD.The spiral buffer structure,on the other hand,causes a severe slow flow rate at the bottom of the spiral groove.The analysis obtained the optimal geometric parameters and buffer structure is 130 degrees bevel inclination symmetrical injection port. |
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