聚氨酯砂改性工艺研究

采用红外光谱技术研究了聚氨酯砂的固化反应机理, 通过向聚氨酯砂中加入呋喃树脂砂进行改性处理, 并采用热失重及扫描电子显微分析技术研究了聚氨酯砂的改性机理。结果表明, 聚氨酯砂中加入呋喃树脂砂以后, 由于在高温下树脂膜分解速度下降, 高温强度得到提高。呋喃树脂砂合适加入量为１０ ％ , 改性聚氨酯砂具有良好的综合性能     

原砂粒度、树脂加入量对呋喃树脂砂强度的影响

树脂砂强度直接影响到铸件品质。树脂砂强度受到多种因素影响,其中,原砂粒度、树脂加入量对呋喃树脂砂的强度有着非常强烈的影响。通过对不同树脂固化剂加入量以及不同原砂粒度的试样强度进行分析,同时利用扫描电镜分析树脂砂粘结、断裂机理,研究了上述因素对呋喃树脂砂强度的影响。结果表明,粘结桥间的气孔将直接影响到树脂砂强度,树脂添加量在1.25%~1.75%时,树脂砂强度较好。原砂粒度较小时,粘结桥容易与原砂发生剥离,降低树脂砂强度。     

Effects of interface adhesive and resin cohesive strength on tensile strength of resin sand based on numerical analysis

A plane-strain unit-cell finite element model was proposed to study the effects of resin/sand interface adhesive and resin cohesive strength on the overall tensile strength of resin sand, as well as the fracture modes. The main micro-scale characteristics of the numerical model were extracted from the micrograph of resin sand specimens by three-dimensional X-ray microscopy(3 D-XRM). The extended finite element method(XFEM) and cohesive behavior method were employed to explicitly describe the resin fracture and sand/resin interface debonding, separately. The corresponding experimental observation of micro-scale failure behavior based on the scanning electron microscopy(SEM) was presented for a comparison. The numerical results show that the initial failure of the model occurs at the sand/resin interface, followed by consequent resin failure. Dependent on the resin cohesive strength, the location of resin failure varies from the central zones to resin neck arc zones. A typical mixed mode fracture is observed, which is consistent with the corresponding micro-scale experimental observation. When the resin cohesive strength ranges between 8 and 12 MPa, the resin cracks occur at the central zone of resin bridges and propagate perpendicularly to the tensile direction until through cracks happen. At a higher range(between 12 and 16 MPa), interface cracks cross with resin cracks, bonding bridges of resin sand are broken. The interface adhesive strength has a more significant effect on the overall tensile strength of resin sand than the resin cohesive strength. The overall tensile strength of resin sand increases first then keeps stable with the increase of the resin cohesive strength. This work attempts to establish a numerical model which accurately describes the complicated mixed mode fracture of resin sand, which is beneficial to understand deeply the fracture mechanism of resin sand.     

Development of a new instrument for measurement of high temperature mechanical properties of resin-bonded sand

The mechanical properties of resin-bonded sand mixtures at high temperatures significantly affect the quality of casting. However, the existing instruments for high-temperature performances testing mainly focus on inorganic binder-bonded sands no matter the test items or the atmospheric protection, while the instrumentss specially designed for resin-bonded sand are not yet available. A new instrument for testing the hightemperature performance of resin sand was designed including the confirmation of the testing parameters, loading, measurement and control systems, and the design of the frame shape and heating furnace. This instrument can test the compressive strength, heat tolerance time and restraining load of phenol-formaldehyde resin coated sand, self-hardened furan resin sand, and trimethylamine(TEA)-based resin bonded sand at high temperatures. The developed instrument has a high accuracy offering smaller than 0.3% deviation at a full scale in the measurement of the high temperature compressive strength and the restraining load over the range of 0-6.8 MPa and 0-2,000 N, respectively. The high temperature heat tolerance time range is 0-300 s and its measurement accuracy is ±1 s.     

固化剂自动控制仪在自硬砂造型线上的应用

在酸硬化呋喃树脂砂造型线上配置固化剂自控仪，再生砂的树脂加入量为砂质量的0．65％-0．85％，A＋B固化剂加入量为树脂质量的30％～40％，解决了自硬砂造型中再生砂砂温对固化速度影响的问题，保证了铸型和砂芯的品质。     

Effect of gel time of 3D sand printing binder system on quality of sand mold/core

Two important factors affecting the performance of sand mold/core generated by 3D printing (3DP) are strength and dimensional accuracy,which are not only closely related to the reactivity of furan resin and the phase transition of silica sand,but also the curing agent system of furan resin.This paper studies the influence of gel time on the strength and dimensional accuracy of a 3DP sand mold/core,taking the furan resin system as an example and using a sand specimen generated by a 3DP inkjet molding machine.The experiment demonstrates that the gel time of 3 to 6 min for the sand mixture suits 3DP core-making most under the experimental condition.However,it should be noted that under the same resin condition,the strength of a no-bake sand mold/core is higher than that of a 3DP sand mold/core.The dimensional accuracy of the sand mold/core does not change significantly when the gel time is less than 15 min.Improving the activity of binder and developing ultra-strong acid with low corrosion shall be an effective way to improve the quality of the mold/core by 3D printing.     

固化剂自控仪在自硬砂造型线上的运用

简述了呋喃树脂A+B固化剂自动控制仪的工作原理和结构特点,介绍了该固化自控仪在酸硬化呋喃树脂砂造型线上成功运用的工艺要素和注意事项,并发现砂温与A,B泵的频率以及固化剂的平均总酸度的关系.在酸硬化呋喃树脂砂造型线上配置圣泉公司的固化剂自控仪,再生砂的树脂加入量为O.65%～O.85%(BOS),A+B固化剂加入量为30%～40%(BOR),解决了自硬砂生产中的再生砂的砂温对固化速度的影响,保证了铸型和砂芯的质量,降低了生产成本.     

A new low-cost method of reclaiming mixed foundry waste sand based on wet-thermal composite reclamation

A lot of mixed clay-resin waste sand from large-scale iron foundries is discharged every day; so mixed waste sand reclamation in low cost and high quality has a great realistic significance. In the study to investigate the possibility of reusing two types of waste foundry sands, resin bonded sand and clay bonded sand which came from a Chinese casting factory, a new low-cost reclamation method of the mixed foundry waste sand based on the wet-thermal composite reclamation was proposed. The waste resin bonded sand was first reclaimed by a thermal method and the waste clay bonded sand was reclaimed by a wet method. Then, hot thermal reclaimed sand and the dehydrated wet reclaimed sand were mixed in certain proportions so that the hot thermal reclaimed sand dried the wet reclaimed sand leaving some water. The thermal reclamation efficiency of the waste resin bonded sand was researched at different heat levels. The optimized wet reclamation process of the waste clay bonded sand was achieved by investigating the effects of wet reclamation times, sand-water ratio and pH value on the reclaimed sand characteristics. The composite reclamation cost also was calculated. The research results showed that the properties of the mixed reclaimed sand can satisfy the application requirements of foundries; in which the temperature of the thermal reclamation waste resin bonded sand needs to be about 800 oC, the number of cycles of wet reclamation waste clay bonded sand should reach four to five, the optimal sand-water ratio of wet reclamation is around 1：1.5, and the pH value should be adjusted by adding acid. The mass ratio of hot thermal reclaimed sand to dehydrated wet reclaimed sand is about 1：2.5, and the composite reclaimed sand cost is around 100 yuan RMB per ton.     

酮醛改性呋喃树脂砂制备工艺研究

介绍了一种新型酮醛改性呋喃树脂制备工艺,通过对呋喃树脂砂抗拉强度的测定、呋喃树脂游离甲醛含量的测定以及多元醇B剂替代试验,分析了丙酮与甲醛摩尔比、碱性反应时间以及酸性反应时间对改性呋喃树脂砂强度的影响.结果 显示:(1)当丙酮与甲醛摩尔比为1∶1.25,碱性反应温度为80℃,碱性反应时间为2h,碱性反应pH值为9.5,...     

再生砂对呋喃树脂自硬砂工艺性能的影响及其控制

分析了呋喃树脂再生砂的灼减量、微粉含量、含氮量、砂温、酸耗值对型砂工艺性能的影响。通过对砂铁比、浇注温度、粘结剂和固化剂用量加以控制,优化型砂性能,减少铸件不良品的产生。     

Influence of furfuryl moulding sand on flake graphite formation in surface layer of ductile iron castings

The influence of the use of moulding sand with furan resin, prepared both with fresh sand and reclaimed matrix, on the formation of a flake graphite formation at the surface layer of ductile iron castings has been investigated. A series of experimental heats of ductile iron cast in moulds made of moulding sand characterised by different levels of surface active elements (sulphur, oxygen) were performed. The effect of the wall thickness and the initial temperature of the metal in the mould cavity on the formation of flake graphite in the surface layer of the casting is shown in the paper. Investigations carried out by means of scanning electron microscopy (energy dispersive X-ray spectroscopy and wavelength dispersive X-ray spectroscopy) showed concentration of gradient profiles of surface active elements in the castings surface layer, which are responsible for their quality. Finally, it has been shown that there exists a significant effect of the quality of the sand on the formation of the flake graphite layer and the surface characteristics of ductile iron castings.     

树脂砂自动控制仪的研制与应用

为彻底解决呋喃树脂砂生产中砂温波动对固化速度的影响,研发了树脂砂自动控制仪.为满足仪器的要求,对自控仪专用液料进行了开发与研制.结果表明,新型吠喃树脂及其配套的快慢固化剂能很好地适用于该自控仪,且适用生产的砂温和起模时间的范围较大,固化剂与树脂保持最佳配比,较低加入量就能得到较高砂型强度,经济效益显著.     

呋喃树脂砂球铁件表层球化不良的防止措施

介绍呋喃树脂砂球铁件表层球化不良的原因和防止方法。由于呋喃树脂砂采用磺酸做固化剂,其所含的S在高温下渗进铸件表层并与Mg化合,使起球化作用的w(Mg)量降低,因而引起球化不良。通过降低再生砂的酌减量(由5.0%降至3.5%),采用型号为G-51-Ⅱ和G-18-Ⅱ的低S固化剂、FQ10防渗S涂料,降低了型砂中的w(S)量,成功解决了铸件表层球化不良的问题。     

型砂级配对树脂砂抗拉强度的影响

采用呋喃树脂为型砂粘结剂,研究了型砂的不同级配对砂型抗拉强度的影响.研究结果表明:当采用单筛砂时,抗拉强度值较低.当采用40/70的三筛砂、40#的配比在10％～20％时,σ1为0.50～0.82 MPa,σ2～σ２４为1.05～1.90 MPa；采用50/100的三筛砂、100#的配比小于10％时,σ1为0.35～0.58 MPa,σ2～σ24为0.62～1.42 MPa.当采用40/100的四筛砂、40#的配比为5％～10％且100#的配比为5％～15％时,σ1为0.32～0.46 MPa,σ2～σ24为0.50～1.35 MPa;当采用50/140的四筛砂、140#的配比为5％～10％时,σ1为0.20～0.35 MPa,σ2～σ24为0.35～1.05 MPa.只要适当提高级砂的粒度,抗拉强度将会提高.     

再生砂微粉含量对树脂砂强度的影响

研究了再生砂微粉含量对树脂砂强度的影响。结果表明:为保证型(芯)砂终强度稳定在0.8~1.6 MPa,必须严格控制再生砂微粉含量在2.0%以下;要保持抗拉强度不变,微粉含量越高,所需要的树脂加入量越多;大量微粉的存在不但降低树脂砂透气性,而且大量消耗树脂,导致树脂砂的发气量增大,发气时间延长。     

Study on binder system of CO2-cured phenol-formaldehyde resin used in foundry

A new aqueous alkaline resol phenol-formaldehyde resin has been prepared from phenol and formaldehyde using NaOH as catalyst; the optimum synthetic process has been determined. With addition of some cross-linking agents, after passing carbon dioxide gas through the resin bonded sand, high as-gassed strength and 24 h strength are achieved. The bonding bridge of the resin bonded sand fracture has been analyzed by using SEM.     

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology.The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand,and zircon sand moulds) under different freezing temperatures and water contents was studied.Results show that with the decrease of freezing temperature and the increase of water contents,the tensile strength and air permeability of the sand moulds are gradually improved.Meanwhile,computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water.The results show that in silica sand moulds,the form of water film is lumpy,and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds,while in zircon sand moulds,the form of water film is membranous.At the same freezing temperature and water content,the tensile strength of zircon sand mould is the highest,and 100-mesh silica sand mould is the lowest.A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould.The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting,but the primary α-Al phase grows in the form of dendrites,and the eutectic silicon phase is coarse needle-like in the resin sand mould casting.The difference of microstructure is caused by the different cooling rate.The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.     

黏土旧砂完全再生技术

分析了旧砂中黏土膜的分离机制,采用不同的再生工艺评估了黏土旧砂再生技术的可行性,确定了700℃焙烧＋机械再生＋微粉分离的黏土旧砂完全再生工艺,研究了黏土完全再生砂的工艺适应性,并介绍了黏土砂完全再生系统的组成。结果表明,视不同的型砂工艺,黏土完全再生砂可分别用于混制水玻璃砂、覆膜砂、冷芯盒砂或热芯盒砂,但不能用于自硬呋喃树脂砂的制备。     

Q345R板材表面冷喷涂Al-Zn涂层的组织及性能研究

目的 研究添加元素Zn含量的变化对涂层的显微组织、孔隙率、硬度及涂层-基体间界面结合强度等的影响规律.方法 采用冷喷涂技术在Q345R板材表面制备性能优良的纯Al和Al-Zn复合涂层,通过扫描电子显微镜对涂层的形貌进行分析,通过维氏显微硬度计对涂层的力学性能进行表征,并揭示涂层与基体间的界面结合机理.结果 冷喷涂纯Al和Al-Zn复合涂层与Q345R钢基体的结合良好,界面处无明显的孔洞及裂纹.随着Zn含量的增加,复合涂层的致密度、硬度逐渐提高;纯Al和Al-20wt.％Zn复合涂层的界面结合强度相当,且失效断裂形式为典型的界面粘结断裂.随着添加元素Zn含量的增加,涂层与基体间的界面结合强度逐渐增大,Al-40wt.％Zn涂层的结合强度为35 MPa,且断裂方式由界面粘着断裂转变为以界面粘着断裂为主、涂层内部粘聚断裂为辅的复合失效模式.结论 以低温固态沉积为特点的冷喷涂技术可有效避免氧化、相变、热裂等高温导致的不利影响,在沉积过程中,随着添加元素Zn含量的增加,对涂层的夯实作用不断加强,提高了涂层的致密性,从而使涂层的力学性能得到改善.     

酯硬化碱性酚醛树脂砂模拟再生试验

通过对酯硬化碱性酚醛树脂旧砂的模拟再生试验,分析了再生前后砂样的灼烧减量、发气量等性能的变化,以及对型砂强度的影响因素。结果表明：采用模拟再生工艺可使再生砂回收率达到95％左右;在再生砂中加入质量分数10％～20％的新砂,可明显提高再生砂的黏结强度,为更好运用酯硬化碱性酚醛树脂砂生产高强度钢种的铸件提供旧砂再生工艺方案。