Radial clearance is the fitting clearance between the screw and charging barrel. If the clearance is too large, the plastication capacity of the machine shall be reduced and the refluence of refused materials during injection shall increase, should the clearance be too small, the difficulty for the mechanical processing of screw and charging barrel as well as the power consumption of screw shall both be increased. Usually the radial clearance =(0.002-0.005)D o Length-Diameter Ratio and Segmentation The ld radio of screw refers to the ratio between thread length of the screw and the diameter screw, generally taking 16-20. The larger the ratio, the better the quality of plastication is, the temperature shall be more uniform and the effect of mixing and fusing shall be better; meanwhile the rotation speed of screw shall be improved on the premises that the quality of plastication be ensured. If the LD radio is too large, however, it shall be difficult for the mechanical processing of screw and charging barrel. Hence, when the quality is ensured, the ratio should be taken as small as possible, since short screws are not only easy to be manufactured but also can shorten the body of njection molding machine. Furthermore, it is also easy for cleaning The segmentation of screw refers to the proportion in the threaded part of the screw as taken by the feeding section, plastication section and measurement section of the screw for injection, where the feeding section generally takes 50%, and the compression and measurement section each takes 25% Depth of Spiral Flute and Compression Ratio The charging barrel is a container for heating and pressurizing plastics. The feeding of injection molding machine mostly depends on the deadweight of granular materials which freely fall into the charging barrel through the hopper. Therefore, shape of the inlet of the barrel should be suitable for the deadweight falling of granular materials, so that the transmission capacity during automatic feeding can be ensured During injection, the fused materials in the charging barrel, subjecting to the movement of screw, flow rapidly through the nozzle and into the mold cavity, thereby being molded. The nozzle thus plays such part as connecting the charging barrel and the mold as well as endowing the materials with high injection speed. The materials, when flowing through the nozzle, shall undergo large-scale cutting and be further plasticated due to the reduction of the nozzle's inner diameter On the other hand, the moisture in the raw materials of plastics shall directly influence the quality of injected products, especially engineering plastics. It is therefore quite necessary to pre-dry he moisture absorptive plastics, which can not only improve the(products')surface glossiness improve the bending strength and tensile strength and avoid occurrence of silver lines, crackles, air bubbles and spots inside the parts, but also can improve the plastication capacity and shorten molding cycle. The moisture in the raw materials of plastics exists into two types. One is that the materials absorb moisture and enter the inside of the matrix, such as ABS and Perspex etc. The other is that the materials is wet on the surface, the moisture only wraps around the surface of the basal body and seldom infiltrates to the inside, such as polyethylene and 6-3 list the admissible injection molding temperature range for partial plastics and their drying condition. During the drying, different method should be adopted according to the different materials and different forms of moisture absorption. Attention should be made that whichever nethod is used. the dried materials must be sealed for storage or heated and insulated cannot be exposed in the air for too long time(including in the hopper with a lid thereon), wherein
Radial clearance is the fitting clearance between the screw and charging barrel. If the clearance is too large, the plastication capacity of the machine shall be reduced and the refluence of refused materials during injection shall increase; should the clearance be too small, the difficulty for the mechanical processing of screw and charging barrel as well as the power consumption of screw shall both be increased. Usually the radial clearance e = (0.002 ~ 0.005)D . z Length-Diameter Ratio and Segmentation The LD radio of screw refers to the ratio between thread length of the screw and the diameter of screw, generally taking 16~20. The larger the ratio, the better the quality of plastication is, the temperature shall be more uniform and the effect of mixing and fusing shall be better; meanwhile, the rotation speed of screw shall be improved on the premises that the quality of plastication be ensured. If the LD radio is too large, however, it shall be difficult for the mechanical processing of screw and charging barrel. Hence, when the quality is ensured, the ratio should be taken as small as possible, since short screws are not only easy to be manufactured but also can shorten the body of injection molding machine. Furthermore, it is also easy for cleaning. The segmentation of screw refers to the proportion in the threaded part of the screw as taken by the feeding section, plastication section and measurement section of the screw for injection, wherein the feeding section generally takes 50%, and the compression and measurement section each takes 25%. z Depth of Spiral Flute and Compression Ratio The charging barrel is a container for heating and pressurizing plastics. The feeding of injection molding machine mostly depends on the deadweight of granular materials which freely fall into the charging barrel through the hopper. Therefore, shape of the inlet of the barrel should be suitable for the deadweight falling of granular materials, so that the transmission capacity during automatic feeding can be ensured. During injection, the fused materials in the charging barrel, subjecting to the movement of screw, flow rapidly through the nozzle and into the mold cavity, thereby being molded. The nozzle thus plays such part as connecting the charging barrel and the mold as well as endowing the materials with high injection speed. The materials, when flowing through the nozzle, shall undergo large-scale cutting and be further plasticated due to the reduction of the nozzle’s inner diameter. On the other hand, the moisture in the raw materials of plastics shall directly influence the quality of injected products, especially engineering plastics. It is therefore quite necessary to pre-dry the moisture absorptive plastics, which can not only improve the (products’) surface glossiness, improve the bending strength and tensile strength and avoid occurrence of silver lines, crackles, air bubbles and spots inside the parts, but also can improve the plastication capacity and shorten molding cycle. The moisture in the raw materials of plastics exists into two types. One is that the materials absorb moisture and enter the inside of the matrix, such as ABS and Perspex etc. The other is that the materials is wet on the surface, the moisture only wraps around the surface of the basal body and seldom infiltrates to the inside, such as polyethylene and polypropylene etc. Table 6-2 and 6-3 list the admissible injection molding temperature range for partial plastics and their drying condition. During the drying, different method should be adopted according to the different materials and different forms of moisture absorption. Attention should be made that whichever method is used, the dried materials must be sealed for storage or heated and insulated, since they cannot be exposed in the air for too long time (including in the hopper with a lid thereon), wherein
for sunny days not exceeding 3h and rainy days Ih. Table 6-2: injection molding temperature range of partial plastics Plastic Types Temperature of Barrel℃ of mold℃ PS Types HIPS 220-270 190~260 150~160 ABS 220~270 190-260 SAN 220~270 200-250 150~160 LDPE 20-60 230~310 HDPE 230~310 220~300 130~200 220~325 140~180 PVC Types Hard PVc 170~200 140~150 Soft pⅤC 170~200 70~115 230~270 PMMA PA Type PA6 50-80 210-230 210-230 200-210 PA66 250-280 250-280 190~250 175~210 160-180 CA Types CAB 30~75 140~150 140~150 120~130 30-75 l80~200 150~18 180~210 190~22 160~180 Table 6-3: drying temperature and time range of partial plastics Plastic type Drying temperature and time range PS Types(PS-ABS PMMA 68h 80~100℃10~14h CAB-VP Ty 2. Mold Clamping System The mold clamping device should meet the following requirements To have sufficient clamping force and to ensure that no overflow of the mold shall occur under the pressure from fused materials To have sufficient mold plate area, stroke and space to suit for the molding of plastic parts with different shapes and dimensions The running speed of mold plate should be first fast then slow during mold clamping and first slow then fast during mold opening to avoid collision of molds during mold clamping and to have the plastic parts ejected steadily Sufficient intensity of the mold plate should be ensured to avoid distortion or damage to the molds during molding as incurred by the frequent pressure applied thereto, which may influence the steadiness of the products' dimension and service life of the injection molding The mold clamping device mainly consists of the mold clamping unit, mold adjusting unit, ejector front and rear retainer plate, moving plate and rod as well as the oil tank etc According to the different method for achieving clamping force, the common structural forms of the
for sunny days not exceeding 3h and rainy days 1h. Table 6-2: injection molding temperature range of partial plastics Temperature of Barrel℃ Plastic Types Temperature of Mold℃ Inject#1 Inject#2 Inject#3 PS Types PS HIPS ABS SAN 10~75 10~75 10~80 10~80 200~280 220~270 220~270 220~270 200~260 190~260 190~260 200~250 150~160 150~160 150~160 150~160 LDPE Types LDPE HDPE PP 20~60 20~60 10~80 230~310 230~310 220~325 220~300 220~300 220~290 130~200 130~200 140~180 PVC Types Hard PVC Soft PVC 20~60 20~60 170~200 170~200 170~200 140~200 140~150 130~140 PC 70~115 300~350 280~340 230~270 PMMA 30~70 190~240 190~220 140~170 PA Types PA6 PA66 50~80 50~80 210~230 250~280 210~230 250~280 200~210 190~250 POM 60~90 190~210 175~210 160~180 CA Types CAB CA CP 30~75 30~75 30~80 140~150 180~200 180~210 140~150 150~180 190~220 120~130 130~150 160~180 Table 6-3: drying temperature and time range of partial plastics Plastic types Drying temperature and time range PS Types（PS-ABS） 60~80℃ 1~4 h PC 100~120℃ 7~8 h PMMA 70~80℃ 6~8 h PA Types 80~100℃ 10~14 h CA-CAB-VP Types 70~80℃ 2~4 h 2. Mold Clamping System The mold clamping device should meet the following requirements: z To have sufficient clamping force and to ensure that no overflow of the mold shall occur under the pressure from fused materials. z To have sufficient mold plate area, stroke and space to suit for the molding of plastic parts with different shapes and dimensions. z The running speed of mold plate should be first fast then slow during mold clamping and first slow then fast during mold opening to avoid collision of molds during mold clamping and to have the plastic parts ejected steadily. z Sufficient intensity of the mold plate should be ensured to avoid distortion or damage to the molds during molding as incurred by the frequent pressure applied thereto, which may influence the steadiness of the products’ dimension and service life of the injection molding machine. The mold clamping device mainly consists of the mold clamping unit, mold adjusting unit, ejector unit, front and rear retainer plate, moving plate and rod as well as the oil tank etc. 1) Mold Clamping Unit According to the different method for achieving clamping force, the common structural forms of the
mold clamping unit fall into the hydraulic type and hydraulic-mechanical type a) Hydraulic Mold Clamping Device The hydraulic mold clamping device achieves the opening and clamping as well as locking of As indicated in Fig 6-6 is the basic sti a simplest sin direct-acting hydraulic mold clamping device, which is mainly applied to mini-injection molding machine. The mold clamping oil tank is also referred to as mold locking oil tank, whose principa function is to push and lock the mold plate through the oil pressure in the oil tank. The front and rear mold plates are supported by the rod and secured by the nut, ensuring that the moving plate can move forward and backward on the rod 1. mold clamping oil tank; 2. rear fixed mold plate; 3. moving plate: 4. guide bar 5. mold: 6. front fixed mold plate: 7. nut of guide bar Fig 6-6: single-tank direct-acting hydraulic molding clamping device The hydraulic mold clamping device comprises the following features Space between the molds and the range of thickness of the molds are both large The adjustment of clamping force can be achieved through adjusting oil pressure; the clamping force can be directly numerated, which is quite convenient a The moving plate can stop at any place within the range of stroke, which is very convenient for adjusting mold space The par be self-lubricated and is low in abrasion Injection molding machine with strong clamping force requires large mold clamping oil tank and high oil hich is disadv for the sealing and manufacturing of hydraulic therefore the poor steadiness of clamping force shall influence the quality of products b)Hydraulic-Mechanical Type As indicated in Fig. 6-7, a large clamping force can be gained through small oil tank pushing force and the enlargement of bar linkage mechanism. Such mold clamping unit combined by hydraulic and mechanical function improves the speed of mold clamping and saves power consumption, which is very vantageous for improving equipment structure and reducing product cost. Current commonly-used types are the single-toggle and double-toggle hydraulic-mechanical mold clamping devices The hydraulic-mechanical mold clamping device embodies the following features Having power enrichment function, which can reduce power consumption. a Having self-locking function. Even if the oil pressure is removed, clamping force shall not disappear. The molds can be securely and steadily locked a The moving speed of the mold plate is variable, wherein during mold clamping it is from fast to low and during mold opening from slow to fast then to slow again, which ensures the
mold clamping unit fall into the hydraulic type and hydraulic-mechanical type. a) Hydraulic Mold Clamping Device The hydraulic mold clamping device achieves the opening and clamping as well as locking of molds through hydraulic pressure. As indicated in Fig.6-6 is the basic structure of a simplest single-tank direct-acting hydraulic mold clamping device, which is mainly applied to mini-injection molding machine. The mold clamping oil tank is also referred to as mold locking oil tank, whose principal function is to push and lock the mold plate through the oil pressure in the oil tank. The front and rear mold plates are supported by the rod and secured by the nut, ensuring that the moving plate can move forward and backward on the rod. 1. mold clamping oil tank; 2.rear fixed mold plate；3. moving plate；4. guide bar； 5.mold；6. front fixed mold plate；7. nut of guide bar Fig.6-6: single-tank direct-acting hydraulic molding clamping device The hydraulic mold clamping device comprises the following features: Space between the molds and the range of thickness of the molds are both large. The adjustment of clamping force can be achieved through adjusting oil pressure; the clamping force can be directly numerated, which is quite convenient. The moving plate can stop at any place within the range of stroke, which is very convenient for adjusting mold space. The parts can be self-lubricated and is low in abrasion. Injection molding machine with strong clamping force requires large mold clamping oil tank and high oil pressure, which is disadvantageous for the sealing and manufacturing of hydraulic system. The plenty of pipeline for hydraulic system tends to be difficult for ensuring no leakage, and therefore the poor steadiness of clamping force shall influence the quality of products. b) Hydraulic-Mechanical Type As indicated in Fig.6-7, a large clamping force can be gained through small oil tank pushing force and the enlargement of bar linkage mechanism. Such mold clamping unit combined by hydraulic and mechanical function improves the speed of mold clamping and saves power consumption, which is very advantageous for improving equipment structure and reducing product cost. Current commonly-used types are the single-toggle and double-toggle hydraulic-mechanical mold clamping devices. The hydraulic-mechanical mold clamping device embodies the following features: Having power enrichment function, which can reduce power consumption. Having self-locking function. Even if the oil pressure is removed, clamping force shall not disappear. The molds can be securely and steadily locked. The moving speed of the mold plate is variable, wherein during mold clamping it is from fast to slow and during mold opening from slow to fast then to slow again, which ensures the
steadiness of mold during opening and clamping and avoids the impact and collision of molds when contacting each other The toggle link unit is easily worn and requires high rigidity and abrasion resistance When the thickness of molds varies, the space between moving plate and fixed should be a The clamping force must be measured by special instrument and is hard to be adjusted ④3 1. tie-bar lock unit: 2. fixed plate: 3. mechanical safety bar stopper 4. mechanical Safety Stop Bar: 5. movable Plate: 6. movable plate link 7.cross head link; 8. long link: 9. main link: 10.end plate link: 11. end plate: 12 clamping cylinder 13. clamping cylinder rod: 14.cross head: 15.ejector cylinder: 16 ejector pin: 17. movable plate slider: 18tie-bar Fig 6-7: hydraulic-mechanical clamping unit structure 2)Mold Adjusting Unit The mold adjusting unit is set for the variation of mold thickness, especially for draulic-mechanical mold clamping device. Since the stroke of moving plate cannot be adjusted,a mold adjusting unit must be set to meet the requirements of molds with different thicknesses Space adjustment for thread toggle link. Space adjustment for movable mold clamping oil tank Space adjustment for rod nut Space adjustment for the connecting nut between movable mold plates 3) Ejector Unit The ejector unit is set for ejecting the plastic parts in the mold cavity and therefore should be provided with sufficient ejection force and stroke. The unit usually falls into three forms: mechanical ejection, hydraulic ejection and pneumatic ejection ■ Mechanical Ejection The ejector pin, which is unmovable in itself, is fixed on the frame of the machine During mold opening, the moving plate moves backward and the pin spreads through the center port in the plate, acts on the ejector plate of the mold and pushes the ejector plate to eject the plastic parts from the mold
steadiness of mold during opening and clamping and avoids the impact and collision of molds when contacting each other. The toggle link unit is easily worn and requires high rigidity and abrasion resistance. When the thickness of molds varies, the space between moving plate and fixed should be adjusted, which tends to be troublesome.。 The clamping force must be measured by special instrument and is hard to be adjusted. 1.tie-bar lock unit；2.fixed plate；3.mechanical safety bar stopper； 4.mechanical Safety Stop Bar；5.movable Plate；6. movable plate link； 7.cross head link；8.long link；9.main link；10.end plate link；11.end plate；12.clamping cylinder； 13. clamping cylinder rod；14.cross head；15.ejector cylinder；16.ejector pin；17.movable plate slider；18.tie-bar Fig.6-7: hydraulic-mechanical clamping unit structure 2) Mold Adjusting Unit The mold adjusting unit is set for the variation of mold thickness, especially for hydraulic-mechanical mold clamping device. Since the stroke of moving plate cannot be adjusted, a mold adjusting unit must be set to meet the requirements of molds with different thicknesses. Space adjustment for thread toggle link.。 Space adjustment for movable mold clamping oil tank.。 Space adjustment for rod nut.。 Space adjustment for the connecting nut between movable mold plates.。 3) Ejector Unit The ejector unit is set for ejecting the plastic parts in the mold cavity and therefore should be provided with sufficient ejection force and stroke. The unit usually falls into three forms: mechanical ejection, hydraulic ejection and pneumatic ejection. Mechanical Ejection The ejector pin, which is unmovable in itself, is fixed on the frame of the machine. During mold opening, the moving plate moves backward and the pin spreads through the center port in the plate, acts on the ejector plate of the mold and pushes the ejector plate to eject the plastic parts from the mold
Length of the ejector pin is determined by the thickness of the molds and adjusted by the thread ■ Hydraulic Ejection As indicated in Fig. 6-7, an ejection oil tank is assembled at the back of the moving plate and is used to drive the plunger, i. e the ejector pin, to work. The bolt on the plunger can be used to adjust the length of the ejector pin; during mold opening the mold plate moves backward and ejection oil tank drives the ejector pin which spreads out and begins working. The force, speed, time and stroke of ejection can be adjusted through hydraulic system and can automatically restore. The plastic parts can thereby be ejected during or after mold opening, which is beneficial for shortening the cycle of injection and molding Large injection molding machines usually comprise both mechanical and hydraulic ejection, wherein the ejection oil tank is usually located between the moving plate and the mechanical ejector device is set on the two sides of the mold plate Pneumatic ejection is achieved through compressed air which directly blows out the plastic parts through the many mini holes on the mold. This method can avoid ejection mark on the surface of the plastic parts, yet a pneumatic auxiliary device shall be needed 2. Hydraulic Control System As indicated in Fig. 6-8, the hydraulic control system of injection molding machine consists of the power system, execution system, control system, auxiliary system as well as the driving medium oil. The power system mainly provides hydraulic oil (including such parts as the motor and pump unit etc. )for he system. The execution system mainly refers to the various oil tank on the injection molding machine, including mold clamping oil tank, ejection oil tank, integral movable oil tank, injection oil tank as well as the motor for driving oil, which altogether transfer the pressure energy of liquid into mechanical energy and drive the execution unit to apply force onto other parts. The control system mainly controls the pressure, quantity and direction of flow of the hydraulic oil to achieve scheduled working procedur and power parameters. It mostly comprises pressure control valve, quantity of flow control valve as well as direction control valve. The auxiliary system mainly refers to such parts as the oil tank, oil filter, energy accumulator, pipeline, joint and pressure meter etc, which mainly act as auxiliary to help other systems complete their functions. The hydraulic oil is the"blood"of hydraulic system, through which the conversion, transfer and control of energy can be carried out During the injection and molding, the fused materials are injected into the mold cavity through high ressure,and therefore, the mold clamping oil tank must be provided with sufficient cla avoid flash of the plastic parts due to expansion of the molds. In addition, the hydraulic system must meet the requirement for speed during mold opening and clamping: first fast then slow during mold clamping and first slow then fast and again slow during opening. The ratio of fast and slow speed is generally very large. Usually such methods as double-pump in parallel connection, multi-pump in hierarchical control and throttle governing are employed to adjust the speed of mold opening and cla The integral movable oil tank for the injection seat should possess sufficient pushing force to drive e seat to move rapidly forward and backward, and meanwhile should ensure the close sealing and secure jointing between the nozzle and the mold gate The injection oil tank should be able to flexibly adjust the injection pressure and speed in accordance with the variety of plastics and the shape of plastic parts. For plastics of high viscosity or plastic parts with thin walls, large area and complicated shapes, the injection pressure should be higher
Length of the ejector pin is determined by the thickness of the molds and adjusted by the thread. Hydraulic Ejection As indicated in Fig.6-7, an ejection oil tank is assembled at the back of the moving plate and is used to drive the plunger, i.e. the ejector pin, to work. The bolt on the plunger can be used to adjust the length of the ejector pin; during mold opening the mold plate moves backward and ejection oil tank drives the ejector pin which spreads out and begins working. The force, speed, time and stroke of ejection can be adjusted through hydraulic system and can automatically restore. The plastic parts can thereby be ejected during or after mold opening, which is beneficial for shortening the cycle of injection and molding. Large injection molding machines usually comprise both mechanical and hydraulic ejection, wherein the ejection oil tank is usually located between the moving plate and the mechanical ejector device is set on the two sides of the mold plate. Pneumatic Ejection Pneumatic ejection is achieved through compressed air which directly blows out the plastic parts through the many mini holes on the mold. This method can avoid ejection mark on the surface of the plastic parts, yet a pneumatic auxiliary device shall be needed. 2. Hydraulic Control System As indicated in Fig. 6-8, the hydraulic control system of injection molding machine consists of the power system, execution system, control system, auxiliary system as well as the driving medium oil. The power system mainly provides hydraulic oil (including such parts as the motor and pump unit etc.) for the system. The execution system mainly refers to the various oil tank on the injection molding machine, including mold clamping oil tank, ejection oil tank, integral movable oil tank, injection oil tank as well as the motor for driving oil, which altogether transfer the pressure energy of liquid into mechanical energy and drive the execution unit to apply force onto other parts. The control system mainly controls the pressure, quantity and direction of flow of the hydraulic oil to achieve scheduled working procedures and power parameters. It mostly comprises pressure control valve, quantity of flow control valve as well as direction control valve. The auxiliary system mainly refers to such parts as the oil tank, oil filter, energy accumulator, pipeline, joint and pressure meter etc, which mainly act as auxiliary to help other systems complete their functions. The hydraulic oil is the “blood” of hydraulic system, through which the conversion, transfer and control of energy can be carried out. During the injection and molding, the fused materials are injected into the mold cavity through high pressure, and therefore, the mold clamping oil tank must be provided with sufficient clamping force to avoid flash of the plastic parts due to expansion of the molds. In addition, the hydraulic system must meet the requirement for speed during mold opening and clamping: first fast then slow during mold clamping and first slow then fast and again slow during opening. The ratio of fast and slow speed is generally very large. Usually such methods as double-pump in parallel connection, multi-pump in hierarchical control and throttle governing are employed to adjust the speed of mold opening and clamping. The integral movable oil tank for the injection seat should possess sufficient pushing force to drive the seat to move rapidly forward and backward, and meanwhile should ensure the close sealing and secure jointing between the nozzle and the mold gate. The injection oil tank should be able to flexibly adjust the injection pressure and speed in accordance with the variety of plastics and the shape of plastic parts. For plastics of high viscosity or plastic parts with thin walls, large area and complicated shapes, the injection pressure should be higher