外文翻譯--玻璃纖維增強(qiáng)復(fù)合材料水輔注塑成型的實(shí)驗(yàn)研究

1、<p><b>　　附錄</b></p><p><b>　　附錄1</b></p><p>　　An experimental study of the water-assisted injection molding ofglass fiber filled poly-butylene-terephthalate (PBT) com

2、posites</p><p>　　Abstract：The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate(PBT) composites. Experiments were carried out on a

3、n 80-ton injection-molding machine equipped with a lab scale water injection system,which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator,and a con

4、trol circuit. The materials included virgin PBT and a 15% glass fiber filled PBT composite</p><p>　　Keywords: Water assisted injection molding; Glass fiber reinforced poly-butylene-terephthalate (PBT) compos

5、ites; Processing parameters; B. Mechanical properties; Crystallinity; A. Polymer matrix composites;</p><p>　　1. Introduction</p><p>　　Water-assisted injection molding technology [1] has proved i

6、tself a breakthrough in the manufacture of plastic parts due to its light weight, faster cycle time, and relatively lower resin cost per part. In the water-assisted injection molding process, the mold cavity is partially

7、 filled with the polymer melt followed by the injection of water into the core of the polymer melt. A schematic diagram of the water-assisted injection molding process is illustrated in Fig. 1.Water-assisted injection mo

8、</p><p>　　Fig. 1. Schematic diagram of water-assisted injection molding process.</p><p>　　Water assisted injection molding has advantages over its better known competitor process, gas assisted i

9、njection molding [5], because it incorporates a shorter cycle time to successfully mold a part due to the higher cooling capacity of water during the molding process. The incompressibility,</p><p>　　low cost

10、, and ease of recycling the water makes it an ideal medium for the process. Since water does not dissolve and diffuse into the polymer melts during the molding process, the internal foaming phenomenon [6] that usually oc

11、curs in gas-assisted injection molded parts can be eliminated.In addition, water assisted injection molding provides a better capability of molding larger parts with a small residual wall thickness. Table 2 lists a compa

12、rison of water and gas assisted injection molding.Wi</p><p><b>　　Table 1</b></p><p>　　Advantages and disadvantages of water-assisted injection molding</p><p>　　2. Experi

13、mental procedure</p><p>　　2.1. Materials</p><p>　　The materials used included a virgin PBT (Grade 1111FB, Nan-Ya Plastic, Taiwan) and a 15% glass fiber filled PBT composite (Grade 1210G3, Nan-Ya

14、 Plastic, Taiwan).Table 3 lists the characteristics of the composite materials.</p><p>　　2.2. Water injection unit</p><p>　　A lab scale water injection unit, which included a water pump, a press

15、ure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit, was used for all experiments [3]. An orifice-type water injection pin with two orifices (0.3 mm in diamet

16、er) on the sides was used to mold the parts. During the experiments, the control circuit of the water injection unit received a signal from the molding machine and controlled the time and pressure of the inject</p>

17、<p>　　2.3. Molding machine and molds</p><p>　　Water-assisted injection molding experiments were conducted on an 80-ton conventional injection-molding machine with a highest injection rate of 109 cm3/s

18、. A plate cavity with a trapezoidal water channel across the center was used in this study. Fig. 2 shows the dimensions of</p><p>　　the cavity. The temperature of the mold was regulated by a water-circulatin

19、g mold temperature control unit. Various processing variables were examined in terms of their influence on the length of water penetration in water channels of molded parts: melt temperature, mold temperature, melt</p

20、><p>　　fill pressure, water temperature and pressure, water injection delay time and hold time, and short shot size of the polymer melt. Table 4 lists these processing variables as well as the values used in th

21、e experiments.</p><p>　　2.4. Gas injection unit</p><p>　　In order to make a comparison of water and gas-assisted injection molded parts, a commercially available gas injection unit (Gas Injectio

22、n PPC-1000) was used for the gas assisted injection molding experiments. Details of the gas injection unit setup can be found in the Refs. [11–15].The processing conditions used for gas-assisted injection molding were th

23、e same as that of water-assisted injection molding (terms in bold in Table 4), with the exception of gas temperature which was set at 25 C.</p><p><b>　　2.5. XRD</b></p><p>　　In orde

24、r to analyze the crystal structure within the water-assisted injection-molded parts, wide-angle X-ray diffraction (XRD) with 2D detector analyses in transmission mode were performed with Cu Ka radiation at 40 kV and 40 m

25、A. More specifically, the measurements were performed on the mold-side and water-side layers of the water-assisted injection-molded parts, with the 2h angle ranging from 7 to 40. The samples required for these analyses

26、 were taken from the center portion of these molded p</p><p><b>　　Table 3</b></p><p>　　Characteristics of the glass–fiber reinforced PBT composite</p><p>　　samples on a

27、rotating wheel on a rotating wheel, first with wet silicon carbide papers, then with 300-grade silicon carbide paper, followed by 600- and 1200-grade paper for a better surface smoothness.</p><p>　　2.6. Mech

28、anical properties</p><p>　　Tensile strength and bending strength were measured on a tensile tester. Tensile tests were performed on specimens obtained from the water-assisted injection molded parts (see Fig.

29、 3) to evaluate the effect of water temperature on the tensile properties. The dimensions of specimens for</p><p>　　the experiments were 30 mm · 10 mm · 1 mm. Tensile tests were performed in a LLOY

30、D tensiometer according to the ASTM D638M test. A 2.5 kN load cell was used and the crosshead speed was 50 mm/min.</p><p>　　Bending tests were also performed at room temperature on water-assisted injection m

31、olded parts. The bending specimens were obtained with a die cutter from parts (Fig. 3) subjected to various water temperatures.The dimensions of the specimens were 20 mm · 10 mm · 1 mm. Bending tests were perfo

32、rmed in a micro tensile tester according to the ASTM D256 test. A 200 N load cell was used and the crosshead speed was 50 mm/min.</p><p>　　2.7. Microscopic observation</p><p>　　The fiber orienta

33、tion in molded specimens was observed under a scanning electron microscope (Jeol Model 5410).Specimens for observation were cut from parts molded by water-assisted injection molding across the thickness (Fig. 3). They we

34、re observed on the cross-section perpendicular to the flow direction. All specimen surfaces were gold sputtered before observation.</p><p>　　3. Results and discussion</p><p>　　All experiments we

35、re conducted on an 80-ton conventional injection-molding machine, with a highest injection rate of 109 cm3/s. A plate cavity with a trapezoidal water channel across the center was used for all experiments</p><

36、p><b>　　Table 4</b></p><p>　　The processing variables as well as the values used in the experiments</p><p>　　Fig. 3. Schematically, the positioning of the samples cut from the mold

37、ed parts for tensile and bending tests and microscopic observations.</p><p>　　3.1. Fingerings in molded parts</p><p>　　All molded parts exhibited the water fingering phenomenon at the channel to

38、 plate transition areas. In addition,molded glass fiber filled composites showed more severe water fingerings than those of non-filled materials, as shown photographically in Fig. 4. Fingerings usually form when a less d

39、ense, less viscous fluid penetrates a denser,more viscous fluid immiscible with it. Consider a sharp two phase interface or zone where density and viscosity change rapidly. The pressure force (P2P1) on the</p><

40、;p>　　and part fingerings. For the displacement of a dense, viscous fluid (the polymer melt) by a lighter, less viscous one (water), we can have Dl = l1l2 > 0, and U > 0 [16].In this case, instability and the rel

41、evant fingering result when a more viscous fluid is displaced by a less viscous one, since the less viscous fluid has the greater mobility.The results in this study suggest that glass fiber filled composites exhibit a hi

42、gher tendency for part fingerings. This might be due to the fact that the </p><p>　　Fig. 4. Photograph of water-assisted injection molded PBT composite part.</p><p>　　3.2. Effects of processing

43、parameters on water penetration</p><p>　　Various processing variables were studied in terms of their influence on the water penetration behavior. Table 4 lists these processing variables as well as the value

44、s used in the experiments. To mold the parts, one central processing condition was chosen as a reference (bold term in Table</p><p>　　By changing one of the parameters in each test, we were able to better un

45、derstand the effect of each parameter on the water penetration behavior of water assisted injection molded composites. After molding, the length of water penetration was measured. Figs. 5–10 show the effects of these pro

46、cessing parameters on the length of water penetration in molded parts, including melt fill pressure, melt temperature, mold temperature, short shot size, water temperature, and water pressure.The experimenta</p>&

47、lt;p>　　the water channel and increase its void area, instead of penetrating further into the parts [4]. The hollow core ratio at the beginning of the water channel increases and the length of water penetration may thu

48、s decrease.Increasing the mold temperature decreases somewhat the length of water penetration in molded parts (Fig. 7).This is due to the fact that increasing the mold temperature decreases the cooling rate as well as th

49、e viscosity of the materials. The water then packs the channel and inc</p><p>　　further into the core of the parts [3]. Increasing the water pressure also helps the water penetrate into the materials.The len

50、gth of water penetration thus increases.Finally, the deflection of molded parts, subjected to various processing parameters, was also measured by a profilemeter.The maximum measured deflection is considered as the part w

51、arpage. The result in Fig. 11 suggests that the part warpage decreases with the length of water penetration.This is due to the fact that the longer the w</p><p>　　Fig. 5. Effects of melt fill pressure on the

52、 length of water penetration in molded parts.</p><p>　　Fig. 6. Effects of melt temperature on the length of water penetration in molded parts.</p><p>　　Fig. 9. Effects of water temperature on th

53、e length of water penetration in molded parts.</p><p>　　Fig. 7. Effects of mold temperature on the length of water penetration in molded parts.</p><p>　　Fig. 8. Effects of short shot size on the

54、 length of water penetration inmolded parts.</p><p>　　Fig. 10. Effects of water pressure on the length of water penetration inmolded parts.</p><p>　　3.3. Crystallinity of molded parts</p>

55、<p>　　PBT is a semi-crystalline thermoplastic polyester with a high crystallization rate. In the water-assisted injection molding process, crystallization occurs under non-isothermal conditions in which the cooling

56、 rate varies with cooling time. Here the effects of various processing parameters</p><p>　　(including melt temperature, mold temperature, and water temperature) on the level of crystallinity in molded parts

57、were studied. Measurements were conducted on a wideangle X-ray diffraction (XRD) with 2D detector analyses(as described in Section 2). The measured results in Fig. 12 showed that all materials at the mold-side lay erexhi

58、bited a higher degree of crystallinity than those at the water-side layer. The result indicates that the water has a better cooling capacity than the mold during th</p><p>　　Fig. 11. Measured warpage of mold

59、ed parts decreases with the length of water penetration.</p><p>　　3.4. Mechanical properties</p><p>　　Tensile tests were performed on specimens obtained from the water-assisted injection molded

60、parts to examine the effect of water temperature on the tensile properties.Fig. 14 showed the measured decrease subjected to various water temperatures. As can be observed, both yield strength and the elongational strain

61、 at break of water assisted molded PBT materials decrease with the water temperature. On the other hand, bending tests were also performed at room temperature on water-assisted injection m</p><p>　　3.5. Fibe

62、r orientation in molded parts</p><p>　　Small specimens were cut out from the middle of molded parts in order to observe their fiber orientation. The position of the specimen for the fiber orientation observa

63、tion is as shown in Fig. 3. All specimen surfaces were polished and gold sputtered before observation. Fig. 16 shows the microstructure of the water-assisted injection molded composite parts. The measured result suggests

64、 that the fiber orientation distribution in water-assisted injection molded parts is quite different from that o</p><p>　　three zones. In the zone near the mold-side surface where the shear is more severe du

65、ring the mold filling, fibers are principally parallel. For the zone near the water-side surface,the shear is smaller and the velocity vector greater.In this case, the fiber tends to be positioned more transversely in th

66、e direction of injection. At the core, the fibers tend to be oriented more randomly. Generally speaking,the glass fibers near the mold-side surface of molded parts were found to be oriented mostl</p><p>　　wi

67、th increasing distance from the mold-side surface.Finally, it should be noted that a quantitative comparison of morphology and fiber orientation [21] in waterassisted molded and conventional injection molded parts will b

68、e made by our lab in future works.</p><p>　　Fig. 16. Fiber orientation across the thickness of water-assisted injection molded PBT composites.</p><p>　　4. Conclusions</p><p>　　This

69、report was made to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate(PBT) composites. The following conclusions can be drawn based on the current study.</p><p>

70、　　1. Water-assisted injection molded PBT parts exhibit the fingering phenomenon at the channel to plate transition areas. In addition, glass fiber filled composites exhibit more severe water fingerings than those of non-

71、filled materials.</p><p>　　2. The experimental results in this study suggest that the length of water penetration in PBT composite materials increases with water pressure and temperature, and decreases with

72、melt fill pressure, melt temperature, and short shot size.</p><p>　　3. Part warpage of molded materials decreases with the length of water penetration.</p><p>　　4. The level of crystallinity of

73、molded parts increases with the water temperature. Parts molded by water show a lower level of crystallinity than those molded by gas.</p><p>　　5. The glass fibers near the surface of molded PBT composite pa

74、rts were found to be oriented mostly in the flow direction, and oriented substantially perpendicular to the flow direction with increasing distance from the skin surface. </p><p>　　玻璃纖維增強(qiáng)復(fù)合材料水輔注塑成型的實(shí)驗(yàn)研究</

75、p><p>　　摘要：本報(bào)告的目的是通過實(shí)驗(yàn)研究聚對(duì)苯二甲酸丁二醇復(fù)合材料水輔注塑的成型工藝。實(shí)驗(yàn)在一個(gè)配備了水輔注塑統(tǒng)的80噸注塑機(jī)上進(jìn)行，包括一個(gè)水泵，一個(gè)壓力檢測(cè)器，一個(gè)注水裝置。實(shí)驗(yàn)材料包括PBT和15%玻璃纖維填充PBT的混合物以及一個(gè)中間有一個(gè)肋板的空心盤。實(shí)驗(yàn)根據(jù)水注入制品的長(zhǎng)度的影響測(cè)得了各種工藝參數(shù)以及它們的機(jī)械性能。XRD也被用來(lái)分別材料和結(jié)構(gòu)參數(shù)。最后,作了水輔助和氣體輔助注塑件的比較。實(shí)驗(yàn)發(fā)現(xiàn)

76、熔體壓力,熔融溫度，及短射類型是影響水注塑行為的決定性參數(shù)。材料在模具一面比在水一面展示了較高的結(jié)晶度。氣輔成型制品也要比水輔成型制品結(jié)晶度高。另外，制品表面的玻璃纖維大部分取向與流動(dòng)方向一致，而隨著離制品表面距離的增加，越來(lái)越多的垂直與流動(dòng)方向。</p><p>　　關(guān)鍵詞：水輔注塑成型，玻璃纖維增強(qiáng)PBT，工藝參數(shù)，機(jī)械性能，結(jié)晶，</p><p><b>　　1．前言<

77、;/b></p><p>　　依靠重量輕，成型周期短，消耗低，水輔注塑成型技術(shù)在塑料制品制造方面已經(jīng)取得了突破。在水輔注塑成型中，模具行腔被部分注入聚合物熔體，而后向這些聚合物中心注入水。水輔注塑成型的原理如圖1</p><p>　　圖1 水輔注塑成型的原理如圖</p><p>　　水輔注塑成型能夠在更短的循環(huán)時(shí)間內(nèi)生產(chǎn)出收縮小，翹曲小，表面質(zhì)量好的各種薄厚的

78、制品。水輔注塑成型工藝也可根據(jù)工具及設(shè)備的承受壓力在設(shè)計(jì)，節(jié)省材料，減輕重量，減少成本方面取得更大的自由。典型的應(yīng)用有棒，管材，水路管網(wǎng)建設(shè)用的大型復(fù)合結(jié)構(gòu)管。另一方面，盡管有很多優(yōu)勢(shì)，由于加入了額外的工藝參數(shù)，模具和工藝控制變的更加嚴(yán)峻和困難。水也可能腐蝕模具鋼，同時(shí)一些材料包括熱塑性塑料難以成型。成型后水的清除也是對(duì)這個(gè)新技術(shù)的一個(gè)挑戰(zhàn)。表1列出了水輔注塑成型技術(shù)的優(yōu)勢(shì)和局限性。</p><p><b&

79、gt;　　表1</b></p><p><b>　　表1</b></p><p><b>　　2．實(shí)驗(yàn)步驟</b></p><p><b>　　2.1 材料</b></p><p>　　實(shí)驗(yàn)材料包括PBT（牌號(hào)1111FB，南亞塑料，臺(tái)灣）和15%玻璃纖維填充PBT

80、的混合物（牌號(hào)1210G3，南亞塑料，臺(tái)灣）。表3列出了此混合材料的特征。</p><p>　　表3 纖維增強(qiáng)PBT復(fù)合材料特征</p><p>　　2.2 水輔注塑元件</p><p>　　一個(gè)實(shí)驗(yàn)室注水元件，包括一個(gè)水泵，一個(gè)壓力檢測(cè)器，一個(gè)注水閥，一個(gè)配備了溫度調(diào)節(jié)裝置的水箱，以及一個(gè)控制電路。這個(gè)孔板型注水閥每邊有兩個(gè)孔，用來(lái)成型制件。實(shí)驗(yàn)過程中，注水閥的控

81、制電路收到由注塑機(jī)產(chǎn)生的信號(hào)實(shí)現(xiàn)對(duì)時(shí)間和注水壓力的控制。在注入模具行腔之前，水在有溫控裝置的水箱里加熱30分鐘。</p><p><b>　　2.3注塑機(jī)和模具</b></p><p>　　水輔注塑成型實(shí)驗(yàn)在一個(gè)最高注塑速率109cm3/s的80噸注塑機(jī)上進(jìn)行。研究使用了一個(gè)中間有一個(gè)肋板的空心盤。圖2顯示了這個(gè)行腔的尺寸。模具溫度由一個(gè)水循環(huán)模溫控制元件調(diào)節(jié)。實(shí)驗(yàn)根

82、據(jù)水注入制品的長(zhǎng)度的影響測(cè)得了各種工藝參數(shù)，包括熔體溫度，模具溫度，熔體充模壓力，水溫和水壓，注水延遲時(shí)間和保持時(shí)間，以及熔體短射類型。表4列出這些工藝參數(shù)及在實(shí)驗(yàn)中的數(shù)值。</p><p>　　為了對(duì)水輔和氣輔注塑成型制件進(jìn)行比較，氣輔注塑成型實(shí)驗(yàn)使用了一個(gè)商用氣輔注塑成型元件，其具體配置可參考RCFS。氣輔注塑成型工藝控制和水輔注塑成型一樣，除了氣體溫度設(shè)置為25外。</p><p>

83、<b>　　2.5 XRD</b></p><p>　　為了分析水輔注塑成型制品的晶體結(jié)構(gòu)，實(shí)驗(yàn)使用了具有二維探測(cè)分析傳輸模式的廣角X射線衍射儀。更特別的是實(shí)驗(yàn)對(duì)水輔注塑成型制品模具一邊和水一邊的樣品在7到40的范圍內(nèi)進(jìn)行測(cè)量。分析所用的樣品來(lái)自制品中心。為了獲得XRD樣品要求的厚度，多余的部分在一個(gè)旋轉(zhuǎn)輪上打磨掉。首先用濕的碳硅紗布，而后用粒度300的，再用粒度600和1200的，以獲得更

84、好的表面質(zhì)量。</p><p><b>　　2.6機(jī)械性能</b></p><p>　　拉伸強(qiáng)度和彎曲強(qiáng)度測(cè)試在一個(gè)拉力測(cè)試機(jī)上進(jìn)行。實(shí)驗(yàn)對(duì)水輔注塑成型制件樣本進(jìn)行拉力測(cè)試以評(píng)估水溫對(duì)拉伸性能的影響。樣本的尺寸為30mm*10mm*1mm.</p><p>　　水輔注塑成型制件的彎曲實(shí)驗(yàn)也在室溫下進(jìn)行。彎曲樣本的尺寸為20mm*10mm*1mm

85、</p><p><b>　　2.7顯微鏡觀察</b></p><p>　　用電子掃描顯微鏡（型號(hào)5410）觀察制品中纖維的分子取向。樣品為取自注塑成型制件厚度方向上（圖3）。在垂直于流動(dòng)方向了對(duì)截面進(jìn)行觀察。觀察前，所有樣品表面鍍金。</p><p>　　圖3拉伸和彎曲測(cè)試切取樣品的位置圖示</p><p><b

86、>　　3結(jié)果和討論</b></p><p>　　所有實(shí)驗(yàn)在一個(gè)最高注塑速率109cm3/s的80噸注塑機(jī)上進(jìn)行。所有研究中使用了一個(gè)中間有一個(gè)肋板水道的空心盤。</p><p>　　3.1制品的指形效應(yīng)</p><p>　　所有制品都在水道的過度區(qū)域出現(xiàn)了指形效應(yīng)。并且，玻璃纖維增強(qiáng)的復(fù)合材料指形效應(yīng)比不增強(qiáng)的更嚴(yán)重，如圖4所示。指形效應(yīng)一般在一種

87、密度小，粘性低的液體穿過另一種密度大，粘性高的不相溶液體時(shí)產(chǎn)生?？紤]一個(gè)密度和黏度變化都很快的兩相界面或區(qū)域。流體移動(dòng)的壓力P2-P1導(dǎo)致有效的置換量用下式描述</p><p>　　這里U是特性速率，K是穿透性。當(dāng)壓力為正時(shí)，任何很小的置換量都會(huì)被放大，導(dǎo)致不穩(wěn)定并出現(xiàn)指形效應(yīng)。當(dāng)一種液體被比它密度低，黏度小的液體置換時(shí)，我們知道ｕ=ｕ1-ｕ2》0，而且U》O。這時(shí)，當(dāng)一個(gè)黏度較高的液體被一種黏度較低的液體置換時(shí)

88、，這種液體流動(dòng)性較高，會(huì)出現(xiàn)不穩(wěn)定和指形效應(yīng)。這次研究的結(jié)果顯示玻璃纖維增強(qiáng)的復(fù)合材料更傾向于指形效應(yīng)。這也許是因?yàn)椴ＡЮw維增強(qiáng)的復(fù)合材料和水的黏度差比較大。因此水輔注塑成型復(fù)合材料顯示了更嚴(yán)重的指形效應(yīng)。</p><p>　　圖4 PBT復(fù)合材料水輔注塑成型照片</p><p>　　3.2工藝參數(shù)對(duì)水穿透的影響</p><p>　　實(shí)驗(yàn)根據(jù)水穿透行為的影響測(cè)得了各

89、種工藝參數(shù)。表4列出這些工藝參數(shù)以及實(shí)驗(yàn)中使用的數(shù)值。為了成型制件，引用了一個(gè)重要工藝條件。通過在每一個(gè)實(shí)驗(yàn)中改變一個(gè)參數(shù)，我們可以更好的理解在復(fù)合材料水輔注塑成型中每個(gè)參數(shù)對(duì)水穿透行為的影響。成型后，實(shí)驗(yàn)測(cè)量了水注塑的長(zhǎng)度。圖5-10顯示了工藝參數(shù)對(duì)水注塑長(zhǎng)度的影響，包括熔體充模壓力，熔體溫度，模具溫度，短射類型，水溫以及水壓。</p><p>　　實(shí)驗(yàn)結(jié)果顯示，水在純凈PBT中比在玻璃纖維增強(qiáng)PBT復(fù)合材料中

90、穿透更深。這是由于玻璃纖維增強(qiáng)復(fù)合材料冷卻過程中體積收縮更小，因此，制品被水穿過的長(zhǎng)度要短些。</p><p><b>　　熔體充模壓力</b></p><p>　　圖5，熔體充模壓力對(duì)水穿過長(zhǎng)度的影響</p><p><b>　　熔體溫度</b></p><p>　　圖6 熔體溫度對(duì)水穿過長(zhǎng)度的影

91、響</p><p><b>　　模具溫度</b></p><p>　　圖7模具溫度對(duì)水穿過長(zhǎng)度的影響</p><p><b>　　短射類型</b></p><p>　　圖8短射類型對(duì)水穿過長(zhǎng)度的影響</p><p><b>　　水溫</b></p&

92、gt;<p>　　圖9水溫對(duì)水穿過長(zhǎng)度的影響</p><p><b>　　水壓</b></p><p>　　圖10水壓對(duì)水穿過長(zhǎng)度的影響</p><p>　　由圖5可以看出，水穿過長(zhǎng)度隨著熔體充模壓力的增大而減小。這可以解釋為由于熔體充模壓力增大，模具行腔對(duì)流動(dòng)的阻力增加，因此水更難以進(jìn)入材料的內(nèi)部。水穿過長(zhǎng)度因而變短。</

93、p><p>　　圖6可以看出成型PBT復(fù)合材料制品時(shí)，隨著熔體溫度是增加水穿過長(zhǎng)度也會(huì)變短。這也許是因?yàn)殡S著溫度增加聚合物熔體的黏度降低。較低的熔體黏度有利于水包裹住水道，減少空閑區(qū)域，而不是更深的穿透。水道開頭孔的變小導(dǎo)致了水穿過長(zhǎng)度的變短。</p><p>　　如圖7，增加模具溫度稍微降低了水在成型制品中的穿過長(zhǎng)度。這也許是因?yàn)樵黾幽＞邷囟冉档土死鋮s速率以及材料的黏度。于是水就包裹了水道，

94、減少了水道口附近的空閑空間，而不是更深的穿透制品。</p><p>　　如圖8，增加短射率降低了水穿過長(zhǎng)度。在水輔注塑成型中，模具行腔被部分注入聚合物熔體，而后向這些聚合物中心注入水。聚合物熔體短射率的增加降低了水在成型制品中的穿過長(zhǎng)度。</p><p>　　作為實(shí)驗(yàn)中的工藝參數(shù)，增加水溫或者水壓都增加了水在成型制品中的穿過長(zhǎng)度。增加水溫降低了冷卻速率，是聚合物熔體更長(zhǎng)時(shí)間內(nèi)保溫，它的黏度

95、也因此降低。這有利于水更深的進(jìn)入進(jìn)品中心。增加水壓也有利于水穿過物體，因此而獲得更深的穿透長(zhǎng)度。</p><p>　　最后，制品的偏差，各種工藝參數(shù)測(cè)量的主觀性，</p><p>　　最大的制品偏差是翹曲。表11的結(jié)果顯示制品翹曲隨著水在成型制品中的穿過長(zhǎng)度的降低而減少。這是因?yàn)樗┻^制品的長(zhǎng)度越長(zhǎng)，包裹聚合物材料的水就越多。制品的翹曲和收縮也因而降低。</p><p&

96、gt;<b>　　水穿過制品的長(zhǎng)度</b></p><p>　　3.3成型制品的結(jié)晶</p><p>　　PBT是一個(gè)結(jié)晶速率很高的半結(jié)晶熱塑性聚脂。在水輔注塑成型過程中，結(jié)晶在非等溫條件下發(fā)生，冷卻速率隨著冷卻時(shí)間而變化。這里研究了各種工藝參數(shù)包括充熔體溫度，模具溫度，以及水溫對(duì)成型制品結(jié)晶的影響。測(cè)量使用了2維廣角X射線衍射儀。表12的結(jié)果顯示所有材料在模具層的結(jié)

97、晶比在水層的結(jié)晶度要高。這個(gè)結(jié)果標(biāo)志著在冷卻過程中水有著更好的冷卻能力。這與我們?cè)缦韧ㄟ^測(cè)量模內(nèi)溫度分布得到的結(jié)果一致。另外，表12C的實(shí)驗(yàn)結(jié)果顯示成型材料的結(jié)晶隨著水溫的增加而增加。這是因?yàn)樵黾铀疁亟档土死鋮s過程中的材料冷卻速率。成型制品因而有更高的結(jié)晶度。</p><p>　　另一方面，為了對(duì)水輔和氣輔注塑成型制品的結(jié)晶作一個(gè)比較，我們?cè)谕慌_(tái)注塑機(jī)上做了實(shí)驗(yàn)，不同的是注塑機(jī)裝備了一個(gè)高壓氮?dú)庾⑺苎b置。結(jié)果顯

98、示氣輔注塑成型制品比水輔注塑成型制品有著更高的結(jié)晶度。這是因?yàn)樗瓤諝獾睦鋮s能力高，冷卻快。因而水輔注塑成型制品比氣輔注塑成型制品的結(jié)晶度要低些。</p><p><b>　　3.4機(jī)械性能</b></p><p>　　對(duì)水輔注塑成型制品樣本進(jìn)行拉伸測(cè)試以觀察水溫對(duì)拉伸性能的影響，表14的測(cè)量結(jié)果顯示其隨水溫增高而降低。正如我們看到的，PBT材料的屈服應(yīng)力和拉伸應(yīng)力都

99、隨著溫度增高而降低。另一方面，PBT水輔注塑成型制品彎曲強(qiáng)度測(cè)試也在室溫下進(jìn)行。圖15的測(cè)試結(jié)果顯示，制品的彎曲強(qiáng)度也隨溫度升高而降低。</p><p>　　一般來(lái)說，增高水溫降低了冷卻速率，使制品的結(jié)晶度增高。正如我們所知，對(duì)于半結(jié)晶熱塑性塑料，較高的結(jié)晶度意味著較低的自由體積因而增加了制品的剛度。但是，實(shí)驗(yàn)結(jié)果顯示，結(jié)晶度對(duì)PBT力學(xué)性能的影響是微不足道的，有更重要的增加了PBT材料的拉伸和彎曲應(yīng)力。成型材料

100、的機(jī)械性能取決于成型過程中結(jié)晶的數(shù)量和晶體類型。PBT的延展性隨著結(jié)晶降低的事實(shí)說明PBT在冷卻速率較低的成型過程中結(jié)晶度和剛性增加，因?yàn)槿狈ρ诱剐裕尚椭破吩诶鞙y(cè)試中的數(shù)值較高，而剛度沒有預(yù)期的高。無(wú)論如何，需要更詳細(xì) 的實(shí)驗(yàn)研究水輔注塑成型制品的形態(tài)參數(shù)以及相關(guān)的機(jī)械性能。</p><p>　　3.5成型制品中纖維取向</p><p>　　從制品的中間切取小的樣品用來(lái)觀察纖維的取向。

101、觀察的位置如圖3所示。觀察前，所有樣品的表面被磨光并鍍金。圖16顯示了水輔注塑成型制品的微型結(jié)構(gòu)。</p><p>　　圖16 PBT復(fù)合材料水輔注塑成型制品的纖維取向</p><p>　　測(cè)量結(jié)果顯示水輔注塑成型制品中的纖維取向與常規(guī)注塑制品有明顯區(qū)別。</p><p>　　在常規(guī)注塑制品中一般觀察兩個(gè)區(qū)域：薄壁處與中心。在薄壁區(qū)域，所有纖維取向與流動(dòng)方向平行，而

102、在中心，纖維在流動(dòng)平面內(nèi)取向隨意。與常規(guī)注塑成型相比，水輔注塑成型技術(shù)的充模方式不同。對(duì)于常規(guī)注塑機(jī)，一個(gè)循環(huán)周期被定義為充模，保壓，冷卻3個(gè)階段。而在水輔注塑成型過程中，模具行腔被部分注入聚合物熔體，而后向這些聚合物中心注入水。這個(gè)新穎的充模方式明顯影響了纖維的取向。</p><p>　　由圖16可以看出，水輔注塑成型制品的纖維取向大致可分為3個(gè)區(qū)域，在模具一邊的表面，這里充模時(shí)剪切很嚴(yán)重，纖維很規(guī)則的平行。在