快速加热型石膏包埋料对铸造精度影响的研究

Evaluation of cast accuracy for rapid burnout type gypsum-bonded investment

目的研究快速加热型石膏包埋料包埋后放置时间对其膨胀及铸件铸造精度的影响。方法选用传统型石膏包埋料CRISTOBALITE P(CBP)、快速加热型石膏包埋料CRISTOBALITE PF(CBPF)和CRISTQUICK20(CQ)。根据包埋料类型及包埋后放置时间不同分组为CBP、CBPF-30、CBPF-60、CQ-20、CQ-40、CQ-60。分别测定各组包埋料的硬化膨胀率和热膨胀率。以六棱柱形状蜡型为铸件原型,应用各组包埋料包埋铸造,测量各组所得铸件的尺寸变化率。结果CBPF-30组、CQ-20组的硬化膨胀率和热膨胀率均小于CBP组。随着包埋后放置时间的延长,CBPF和CQ各组的硬化膨胀率明显增大,热膨胀率逐渐减小。CBPF-30组和CQ-20组包埋料所得铸件的收缩率均大于CBP组。CBPF两组所得铸件的尺寸变化率无差别,CQ3组所得铸件的尺寸变化率无差别。结论在一定限度内适当延长快速加热型石膏包埋料包埋后放置时间对铸件的铸造精度无明显影响。

Objective To investigate the effects on expansion and cast accuracy of the time from setting to heating for rapid burnout gypsumbonded dental investment. Methods Conventional gypsum-bonded investment （CRISTOBALITE P （CBP））and two kinds of rapid burnout gypsum-bonded investments（CRISTOBALITE PF （CBPF） and CRISTQUICK 20 （CQ）） were employed. According to the differences of type and time from setting to heating, investments were designed for such 6 groups as CBP, CBPF-30, CBPF-60, CQ-20, CQ-40 and CQ-60. The set- ting expansion and thermal expansion of each group were measured. The hexagonal wax pattern was made as original model. After the cast had been carried out, the percentage of size change for each casting was calculated, compared with the corresponding original model. Results The setting expansion and the thermal expansion of CBPF-30 and CQ-20 were smaller than those of CBP. With the time from setting to heating extending,the setting expansion of CBPF and CQ increased, while the thermal expansion decreased. The cast shrinkage of the castings for CBPF-30 and CQ-20 was bigger than that of CBP. There was no difference in the percentage of size change for each group of CBPF and CQ respectively. Conclusions The cast accuracy for the rapid burnout gypsum-bonded dental investment is not affected by the extending of the time from setting to heating certain extent.