CN108439983B - 一种石墨陶瓷复合管成型方法 - Google Patents
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Abstract
本发明公开了一种石墨陶瓷复合管成型方法,主要包括以下几个工艺环节:将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照一定比例机械混合均匀;将混合粉末分批次地添加到预热、带有环形空腔的金属模具中,每填料一次,预压一次,重复多次,获得石墨陶瓷复合管坯体;在真空气氛保护下对石墨陶瓷复合管坯体高温处理,获得石墨陶瓷复合管预制体;最后真空压力浸渍硅溶胶,待干燥后即获得高强度石墨陶瓷复合管。所制备的石墨陶瓷复合管具有良好的抗压强度和较低的电阻率,在聚晶金刚石复合片生产中可作为加热元件替代传统的石墨管或金属管,有助于反应腔建立合理稳定的温度场,从而改善产品质量,降低生产成本。
Description
技术领域
本发明提供了一种石墨陶瓷复合管成型方法,属于无机非材料成形及工程应用技术领域。
背景技术
聚晶金刚石复合片(Polycrystalline Diamond Compact,简称PDC)是在超高压高温条件下(一般1300℃~1600℃,5~6Gpa)将金刚石微粉复合在硬质合金基底上的一种新型功能材料,因其既具有金刚石的高硬度、高耐磨性与导热性,又具有硬质合金的强度与抗冲击韧性,已成为制造高性能切削刀具、钻井钻头及其它耐磨工具的理想材料。
聚晶金刚石复合片通常是在六面顶压机的超高压高温反应腔中合成的,超高压高温反应腔中同时存在着压力场和温度场,其中,温度场的稳定性和合理性直接影响着聚晶金刚石复合片的显微组织结构、性能与质量,因此,对反应腔内温度场的调控尤为重要。若合成温度过高,会导致己烧结的金刚石石墨化,金刚石层中将残留过多的石墨,使得PDC性能大幅下降;若合成温度过低时,不能产生足够的液相,烧结过程无法持续,只能在界面产生烧结,其它部分仍保持原有形态,烧结后呈现松散的结构。总之,合成高品质PDC产品的关键是建立合理而稳定的反应腔温度场。PDC反应腔的温度场是由上下顶锤给加热元件施加大电流,通过电阻发热而产生的,目前常见加热元件一般为石墨管或金属管,加热元件自身电阻率及其稳定性直接影响反应腔内部的温度场。此外,PDC反应腔组合方式(图1为一种常见的PDC反应腔组装示意图)也会对温度场和PDC耐磨性、硬度性能产生明显的影响。
石墨管一般由人工合成石墨圆棒料切削加工而成,选择石墨管作为反应腔加热元件时,有几个方面问题:首先,由于本身抗压强度较低,在上下顶锤压力作用下,石墨管极易破裂,导致电阻值产生变化,从而影响实际发热效果以及PDC反应腔温度场的稳定性,严重的出现冒气现象,导致事故发生;其次,受现有人工合成石墨生产工艺水平的制约,石墨管内部组织成分以及孔隙分布的随机性也会影响电阻率的稳定性,需要对高温合成PDC工艺参数做出动态调整,这增加了PDC高温合成操作难度;石墨管作为一种薄壁结构件(其壁厚一般小于2mm),除了材料利用率低、成品率较低、成本偏高之外,机械切削加工难度大,需控制粉尘污染;因石墨管属于易损件,也给运输、反应腔组装带来了一定的困难。
选择金属管作为PDC反应腔加热元件时,由于金属管不易破损,生产组装以及运输比较方便;然而,金属管电阻率非常小,仅为石墨管的百分之一,根据热量计算公式Q热=0.24I2r内,为了产生相等的热量,获得相同的加热效果,需要将六面顶压机的电流值调高十倍以上,而由此带来不利影响是:增加了能源消耗,此外,在大电流冲击下,上下电极压头易烧损,增加了生产维修成本。总之,为了保证PDC反应腔的温度场的合理性及稳定性,低成本地合成高品质PDC产品,亟需发明一种具有较高的抗压强度和适宜的电阻率石墨陶瓷复合管成型方法。
发明内容
本发明提出了一种石墨陶瓷复合管成型方法,石墨陶瓷复合管可以作为PDC生产中的加热元件,替代传统的石墨管或金属管。发明思想如下:分批填料,在多次挤压力作用下,天然鳞片石墨粉末有序地叠加在一起,石墨层间接触更加充分紧密,提高了抗压能力的同时保证了导电性;经高温处理后,酚醛树脂热解生成玻璃碳,并分别与二氧化硅和硅原位反应生成碳化硅纤维和碳化硅颗粒,从而提高了石墨陶瓷复合管耐高温能力;将纳米二氧化硅浸渍到石墨陶瓷复合管预制体中,提高了致密性及抗压能力。
具体工艺过程如下:
(1)将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照一定比例混合均匀。其中,天然鳞片石墨质量分数为50~65wt%,热固性酚醛树脂粉末质量分数为15~25wt%,二氧化硅粉末质量分数为3~5wt%,余为硅粉;天然鳞片石墨含碳量不低于99.5%,粒度为150~270目;所述热固性酚醛树脂粉末粒度为500-900目,二氧化硅粉末纯度不低于99.5%,粒度为500~800目,所述硅粉纯度不低于99%,粒度为200~500目;分批将上述粉末分批加入干法高效滚筒式球磨机中,机械混合4-8h,转速控制在300rpm以下。
(2)将上述混合粉末分批次地添加到事先预热、带有环形空腔的金属模具中,每填料一次,预压一次,重复多次,获得石墨陶瓷复合管坯体。建议每次混合粉末填充高度不超过3mm,以保证石墨陶瓷复合管坯体密度,石墨陶瓷复合管坯体密度应不小于1.80g/cm3。优先地金属模具温度为160-180℃,每次成型压力不低于15MPa,每次保压时间不少于5min。
(3)在真空气氛保护下对石墨陶瓷复合管坯体高温处理,获得石墨陶瓷复合管预制体。将石墨陶瓷复合管放入真空气氛烧结炉中,用含碳量不低于99%的石墨粉末包埋,抽真空至10Pa以下,同时以120~360℃/h升温至360℃;随后通入99.99%的高纯氩气或高纯氮气保护,继续升温至800℃,并在800℃保温0.5~1h;以240~600℃/h升温至1450℃~1550℃并保温保温0.5~1h,随炉冷却至室温后取出,获得石墨陶瓷复合管。
(4)真空压力浸渍硅溶胶溶液,烘干处理,获得石墨陶瓷复合管。将石墨陶瓷复合管预制体放入真空压力浸渍机中,抽真空至1pa以下,注入浓度为25~30%的硅溶胶溶液,将预制体完全浸没,通入2-4MPa 99.9%的氮气对硅溶胶溶液施压3~5min。随后,取出,在50℃~60℃烘箱中烘干,即得所述石墨陶瓷复合管。
本发明所述的一种石墨陶瓷复合管成型方法,其优点在于:
(1)本发明所提供石墨陶瓷复合管由天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末等混合料直接热压成型、再经高温处理、浸渍硅溶胶而获得的,与传统的石墨管切削加工成型方法相比,极大地提高了材料利用率,降低了生产成本。
(2)鳞片石墨粉末在压力作用下自主取向,层叠在一起,同时有碳化硅增强相生成增加了鳞片石墨粉末间连接强度,二氧化硅纳米粒子填充制品孔隙中,提高了致密度,因此,所制备的石墨陶瓷复合管具有较高的抗压能力,不易破损,也降低了PDC反应腔组装难度,减轻了运输保管压力。
(3)通过改变混合粉末各物料比例,可以控制石墨陶瓷复合管中各相组成,对电阻率进行主动调控,获得合适的电阻值,从而避免了PDC高温合成中过烧或欠烧等现象产生。
附图说明
图1 为所述的PDC反应腔组装示意图,1.导电钢圈,2.Ti片,3.硬质合金基体,4.金属片5.金属箔,6.叶腊石,7.石墨管/金属管,8.金刚石,9.石墨片。
图2为所述的石墨陶瓷复合管内部层叠的天然鳞片石墨201、碳化硅增强相202和纳米二氧化硅203示意图。
图3为所述的石墨陶瓷复合管。
图4为所述带有环形空腔的金属模具,其中包括环状外模401,环状内模402,环形空腔403。
具体实施方式
一种石墨陶瓷复合管成型方法,首先,将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照一定比例机械混合均匀;其次,将混合粉末分批次地添加到预热、带有环形空腔的金属模具中,所述金属模具包括环状外模401,环状内模402,环形空腔403,每填料一次,预压一次,重复多次,获得石墨陶瓷复合管坯体;再次,在真空气氛保护下对石墨陶瓷复合管坯体高温处理,获得石墨陶瓷复合管预制体;最后真空压力浸渍硅溶胶,待干燥后即获得高强度石墨陶瓷复合管。下面结合具体实施方式对本发明做进一步说明。
实施例1
(1)将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照下述要求准备(其中,天然鳞片石墨质量分数为60wt%(其含碳量99.6%,粒度为150目),热固性酚醛树脂粉末质量分数为15wt%(粒度为500目),二氧化硅粉末质量分数为5wt%(纯度99.5%,粒度为500目),余为硅粉(纯度为99.5%,粒度为200目)。将上述粉末分批加入干法高效滚筒式球磨机中,机械混合6h,转速为150rpm。
(2)将所制备的混合粉末分批填充到预热温度为160℃的带有环形空腔的金属模具中,所述金属模具包括环状外模401,环状内模402,环形空腔403,每填料一次,预压一次,多次重复直至粉末充满整个环形空腔403,获得石墨陶瓷复合管坯体。对于内直径27mm、厚度为2mm、高为30mm石墨陶瓷复合管,每次混合粉末填充高度3mm,每次预压成型压力为30MPa,保压时间15min,确保石墨陶瓷复合管坯体密度达到2.0g/cm3。
(3)将石墨陶瓷复合管坯体取出,放入真空烧结炉内,并将石墨陶瓷复合管坯体用含碳量为99.5%的石墨粉末完全包埋,进行高温处理。首先抽真空至5Pa,同时以360℃/h升温至360℃;随后通入99.99%的高纯氩气,继续升温至800℃,并在800℃保温30min;以300℃/h升温至1450℃并保温30min,随炉冷却至室温后取出,获得石墨陶瓷复合管。
(4)将石墨陶瓷复合管预制体放入真空压力浸渍机中,抽真空至0.1pa,注入浓度为30%的硅溶胶溶液,将预制体完全浸没,通入2MPa、99.9%的氮气对硅溶胶溶液施压3min。随后,取出,在60℃烘箱中烘干。
测得石墨陶瓷复合管的电阻率为12.5μΩ·m,密度为1.95g/cm3,抗压强度为50MPa。
实施例2
(1)将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照下述要求准备(天然鳞片石墨质量分数为60wt%(其含碳量99.5%,粒度为200目),热固性酚醛树脂粉末质量分数为20wt%(粒度为800目),二氧化硅粉末质量分数为3wt%(纯度99.5%,粒度为600目),余为硅粉(纯度为99.5%,粒度为300目)。将上述粉末分批加入干法高效滚筒式球磨机中,机械混合5h,转速为240rpm。
(2)将所制备的混合粉末分批填充到预热温度为170℃的带有环形空腔的金属模具中,所述金属模具包括环状外模401,环状内模402,环形空腔403,每填料一次,预压一次,多次重复直至粉末充满整个环形空腔403,获得石墨陶瓷复合管坯体。对于内直径27mm、厚度为1.5mm、高为30mm石墨陶瓷复合管,每次混合粉末填充高度2.5mm,每次预压成型压力为25MPa,保压时间10min,确保石墨陶瓷复合管坯体密度达到1.95g/cm3。
(3)将石墨陶瓷复合管坯体取出,放入真空烧结炉内,并将石墨陶瓷复合管坯体用含碳量为99.5%的石墨粉末完全包埋,进行高温处理。首先抽真空至1Pa,同时以240℃/h升温至360℃;随后通入99.99%的高纯氮气,继续升温至800℃,并在800℃保温45min;以240℃/h升温至1500℃并保温45min,随炉冷却至室温后取出,获得石墨陶瓷复合管。
(4)将石墨陶瓷复合管预制体放入真空压力浸渍机中,抽真空至0.01pa,注入浓度为30%的硅溶胶溶液,将预制体完全浸没,通入3MPa 、99.9%的氮气对硅溶胶溶液施压5min。随后,取出,在50℃烘箱中烘干。
测得石墨陶瓷复合管的电阻率为15.3μΩ·m,密度为1.90g/cm3,抗压强度为45MPa。
实施例3
(1)将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末按照下述要求准备(天然鳞片石墨质量分数为55wt%(其含碳量99.5%,粒度为270目),热固性酚醛树脂粉末质量分数为25wt%(粒度为800目),二氧化硅粉末质量分数为5wt%(纯度99.5%,粒度为800目),余为硅粉(纯度为99%,粒度为500目))。将上述粉末分批加入干法高效滚筒式球磨机中,机械混合3h,转速为290rpm。
(2)将所制备的混合粉末分批填充到预热温度为180℃的带有环形空腔的金属模具中,所述金属模具包括环状外模401,环状内模402,环形空腔403,每填料一次,预压一次,多次重复直至粉末充满整个环形空腔403,获得石墨陶瓷复合管坯体。对于内直径27mm、厚度为1.5mm、高为20mm石墨陶瓷复合管,每次混合粉末填充高度2.0mm,每次预压成型压力为20MPa,保压时间8min,确保石墨陶瓷复合管坯体密度达到1.90g/cm3。
(3)将石墨陶瓷复合管坯体取出,放入真空烧结炉内,并将石墨陶瓷复合管坯体用含碳量为99.5%的石墨粉末完全包埋,进行高温处理。首先抽真空至0.1Pa,同时以120℃/h升温至360℃;随后通入99.99%的高纯氮气,继续升温至800℃,并在800℃保温60min;以480℃/h升温至1550℃并保温35min,随炉冷却至室温后取出,获得石墨陶瓷复合管。
(4)将石墨陶瓷复合管预制体放入真空压力浸渍机中,抽真空至0.01pa,注入浓度为30%的硅溶胶溶液,将预制体完全浸没,通入4MPa 、99.9%的氮气对硅溶胶溶液施压3min。随后,取出,在55℃烘箱中烘干。
测得石墨陶瓷复合管的电阻率为20.5μΩ·m,密度为1.85g/cm3,抗压强度为47.6MPa。
Claims (5)
1.一种石墨陶瓷复合管成型方法,包括以下几个工艺环节:
(1)将天然鳞片石墨粉末、热固性酚醛树脂粉末、硅粉和二氧化硅粉末混合均匀;天然鳞片石墨质量分数为50~65wt%,热固性酚醛树脂粉末质量分数为15~25wt%,二氧化硅粉末质量分数为3~5wt%,余为硅粉;
(2)步骤(1)的混合粉末分批次地添加到事先预热、带环形空腔的金属模具中,每填料一次,预压一次,重复多次,获得石墨陶瓷复合管坯体;
(3)将石墨陶瓷复合管坯体放入真空气氛烧结炉中,抽真空至10Pa以下,同时以120~360℃/h升温至300-380℃;随后通入大于99.99%的高纯氩气或高纯氮气保护,继续升温至750-850℃,并在750-850℃保温0.5~1h;以240~600℃/h升温至1450℃~1550℃并保温0.5~1h,随炉冷却至室温后取出,获得石墨陶瓷复合管预制体;
(4)将石墨陶瓷复合管预制体放入真空压力浸渍机中,抽真空至1Pa以下,注入浓度为25~30%的硅溶胶溶液,将预制体完全浸没,通入2-4MPa纯度大于99.9%的氮气对硅溶胶溶液施压3~5min后,取出,在50℃~60℃烘箱中烘干,即得所述的石墨陶瓷复合管。
2.根据权利要求1中所述的石墨陶瓷复合管成型方法,其特征在于:所述的天然鳞片石墨含碳量不低于99.5%,粒度为150~270目;所述的热固性酚醛树脂粉末粒度为500-900目;所述的二氧化硅粉末纯度不低于99.5%,粒度为500~800目;所述的硅粉纯度不低于99%,粒度为200~500目。
3.根据权利要求1中所述的石墨陶瓷复合管成型方法,其特征在于:将混合粉末分批加入球磨机中,机械混合4-8h,转速控制在300rpm以下。
4.根据权利要求1中所述的石墨陶瓷复合管成型方法,其特征在于:步骤(2)中每次混合粉末填充高度不超过3mm,带有环形空腔的金属模具内温预热至160-180℃,每次成型压力不低于15MPa,每次保压时间不少于5min,石墨陶瓷复合管坯体密度不小于1.80g/cm3。
5.根据权利要求1中所述的石墨陶瓷复合管成型方法,其特征在于:步骤(3)中高温处理时,将石墨陶瓷复合管坯体放入真空气氛烧结炉中,抽真空至10Pa以下,同时以240℃/h升温至360℃;随后通入大于99.99%的高纯氩气或高纯氮气保护,继续升温至800℃,并在800℃保温0.5~1h;以240~600℃/h升温至1450℃~1550℃并保温0.5~1h,随炉冷却至室温后取出。
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