Extrusion molding of plastic profiles
DATE：2022/10/18 8:55:11 / READ： / SOURCE：This station
Extrusion molding of plastic profiles
Plastic profile refers to the thin-walled or solid structure of plastic products whose sectional shape is different from that of circular tubes, rods and plates. It is a plastic product with irregular sectional shape. As shown in Figure 8-1, it is a typical profile with hollow or open section.Figure 8-1 Section Shape of Several Shapes
The profile can be extruded with PVC, polyethylene, polypropylene, ABS polycarbonate, polymethyl methacrylate, polyphenyl ether and other materials. But PVC resin is the most widely used at present. Extrusion equipment can be single screw extruder or twin screw extruder.
There are many kinds of profiled materials. There are profiled materials made of plastic for all products, and profiled materials made of plastic and non plastic. There are also non foaming and low foaming products in plastic profiles. According to the section shape of profile, it can also be divided into hollow profile, open profile and solid profile.
Plastic profiles are widely used, and have partially replaced wood or steel in construction, furniture, transportation, machinery and electronics and other engineering structural materials. For example, plastic door frames, door panels, window frames, wall panels, floor strips, handrails, integrated circuit boards, various furniture accessories, and mechanical molding equipment at zero price are shown as production machines, molding molds, molding cooling devices, traction machines, and cutting equipment for plastic profile extrusion molding
Figure 8-2 Plastic Profile Extruder Production Line
Forming mould; 3 Certain type of cooling device; 4 - Cooling water tank; 5 - Tractor; 6 - Cutting machine; Product inspection and stacking platform (there is no cooling water tank device in the auxiliary machine for hollow profiled materials)
The production process sequence of the screw extruder is as follows.
The department measures according to the formula requirements → raw material mixing → extruding, plasticizing and mixing raw materials and granulating → extruding parison → cooling and shaping → traction → cutting → quality inspection → packaging and warehousing of twin-screw extruder. The production process sequence is as follows:.
The materials shall be measured according to the formula requirements → raw material mixing → extruding machine plasticizing powder to form the product parison → traction → cutting → quality inspection → packaging and warehousing. The extrusion of plastic profiled materials from the machine can be done by single screw extruder or double screw extruder. At present, for the extrusion of plastic doors and windows, the intermeshing counter rotating parallel twin screw extruder and conical twin extruder in the multi-purpose twin screw extruder can be applied. Single screw extruders are generally only used for extruding and molding sections. If it is powder, it needs to be mixed, plasticized, extruded and granulated before extruding. The screw of single screw extruder shall be of equal spacing and unequal depth gradual type, with the length diameter ratio of 25): 1 and compression ratio of 3:1. The profile extruded by twin-screw extruder can be put into production with evenly mixed powder. This not only saves granulation process, man hours and energy, but also increases production. Therefore, twin-screw extruder is often used for extrusion of profile. The relationship between the maximum width of profile and the type of conical twin screw extruder
Table 8-1. Table 8-1 Relationship between the maximum width of profile and the model of conical twin-screw extruder
Extruder model SJSZ-55
Maximum width of profile/mm
② After the raw material of the molding die is molded into a molten state in the barrel of the extruder, the rotating screw is pushed into the molding die body. At this time, the cylindrical molten material moves forward in the cavity of the die, and gradually deforms with the change of the cavity section shape in the die body, becoming a section close to the product shape, and extruding the molded product blank from the lip of the die. This is the role of the forming die.
As shown in Figure 8-3, it is a mold structure formed by combining several steel plates after processing. It is easy to process each part and assemble it into a mold. However, when processing and assembling each part, it is necessary to ensure that the center line of each part is on the same axis line after processing and assembling, the transition surface at the indirect contact of two parts is smooth, there is no stagnant material dead angle sleeve and it is shaped into a small number of profiled materials
Figure 8-3 Structure of Plate Combined Molding Mold
Stereotype sleeve
1. Specific board of the first mock examination; 2 - Shrink mouth plate; 3 One mouth formwork; 4 Positioning pin; 5-Connecting screw
As shown in Figure 8-4, the streamlined profile in the cavity of the molten material runner in the profile forming mold is processed on a part body. The surface of the molten material runner is smooth without stagnation. There is no contact transition surface for cooling the assembly of fixed parts. However, the processing of this streamlined curve is difficult
③ Auxiliary machine Extruder for profile forming The auxiliary machine on the production line extrudes large amount of hard pipe, increasing the manufacturing cost of the mold. The components of the auxiliary machines are basically the same. The special part of the profiled auxiliary machine is the shaping cold part
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Fig. 8-4 The inner cavity is streamlined mold structure
1. The first mock examination is specific; 2 - Split cone; 3 - Mandrel; 4 - Middle sleeve; 5 - Mouth mold; 6 - Adjusting screw
The length of the sleeve and the setting table is relatively long, usually about 5-6m or more. This is because the structural shape of the profile is complex, and the parison needs to be fully cooled, solidified and shaped to reduce the deformation of the products after molding. The shaping cooling jacket is divided into several sections. The dimension of the shaping jacket cavity close to the end of the shaping die is slightly larger than that of the cavity in the shaping die (this is because the profile blank expands slightly after extruding from the shaping die mouth). The cavity size of the shaping jacket in the following sections gradually reduces until it is the same as the shape and size of the product.
There are many structures of cooling jacket device for profile blank shaping. When it is used for the cooling and shaping of hollow profile, there are vacuum shaping (the structure is like the vacuum shaping sleeve used for the cooling and shaping of pipes) and internal pressure shaping. The degree of vacuum pumping is 0.08~0.09MPa during vacuum shaping
The structure of vacuum setting sleeve is shown in Fig. 8-5.
Fig. 8-5 Structure of vacuum setting sleeve
1; 11, 13, 15, 18, 24 hexagon socket head cap screws; 2 - End plate; 3 - Cover plate; 4 - Pumping air; 5~7 One type plate 8, 19 press plate; 9 - Lifting ring; 10,14-side profile plate; 12 - Gasket; 16 - Locking mechanism; 17 - Pull rod;
20 - Hinge; 21 Downshift; 22 slider; 23 - Base plate
If the profile is an open bending profile, the extrusion molding can be used to form a plate parison die structure. After extruding and forming the blank, it enters the sliding type setting die to bend the profile section shape required for forming, and becomes silver after cooling and setting. This method of forming profiled materials can use a molding die with simple structure. The production method and process of this molded product are shown in Figure 8-6.
Figure 8-6 The length of the shaping device for the shaped cooling sleeve used for the blank of the open bending profile profile is determined by the schematic diagram, which has a great impact on the molding quality of the products
1 - Molten material inlet; 2 - Mold for forming plate; Table 8-2 lists some parameters when designing
3 - Bending setting die; 4 Cooling and shaping once entering
Chapter 8 Plastic Profile Extrusion Molding
The working mode and equipment structure of the traction machine and cutting machine in the auxiliary machine are identical with those of the auxiliary machine for hard pipe production. Crawler tractor for production of general hollow profiled materials; Open type
Roller tractor for profile production.
See Table 8-3 (2) for the technical parameters and manufacturer of auxiliary machines for profile extrusion molding. The raw materials for PVC profile extrusion molding are mainly SG4, SG5 or SG6 in suspension PVC resin. Then, according to the requirements of extrusion process and profile use conditions, a certain proportion of stabilizer, modifier, filler and other auxiliary materials are added to the main raw materials to form the material formula. See Table 4-7 for the formula of materials for profile extrusion.
(3) Forming process
① See Chapter 4 for the mixing and granulation process conditions and parameters of raw materials. ② Process temperature of extruded products
a. The temperature of each section of the barrel is 110~140 ℃ in the feeding section, 150~170 ℃ in the plasticizing section, and 170~190 ℃ in the homogenizing section.
b. The temperature of forming die is 175~185 ℃.
The process temperature of screw extrusion is slightly lower than that of single screw extrusion, about 10~15 ℃ lower. However, it should be noted that the temperature of the feeding section is much higher.
(4) Quality requirements The quality requirements for products produced from profiled materials are specified in GB/T8814-1998 as follows.
The profiled materials can be divided into A and B according to the application environment. Type A refers to external doors and window frames, and type B refers to internal doors and window frames.
Requirements for appearance and color of profile: the surface of profile shall be smooth and free from cracks, impurities affecting the use and uneven defects of convex and concave. Generally, most profiles are white. The color shall be uniform.
See Table 8-4 for the specification of profile dimension deviation. Physical and mechanical properties of profile
See Table 8-5 for regulations.
(5) Key points of process operation
① After the raw materials for profiled products are measured according to the formula, they are mixed and stirred in a high-speed mixer. During operation, resin, plasticizer and stabilizer shall be added first. The mixing and stirring temperature is 80~90 ℃ and the time is about 5~8min; Then add colorant and filler - 471 - allowable deviation items, allowable deviation items and lubricant, discharge materials to cool down when the material temperature reaches 90~100 ℃, and when the material country reaches 0, use 80 mesh screen to sieve and then put them into bags or tanks.
② When the profile is extruded by a single screw, the raw materials that are mixed and stirred evenly shall be extruded for granulation first, and then extruded for molding.
③ When the profile is molded by a twin-screw extruder, it can be directly extruded by a uniformly mixed body. Pay attention to the barrel temperature control of the extruder. The temperature of the feeding section should be higher than that of the extrusion section. This is conducive to the discharge of volatile gas from the material. The cost section temperature of conical twin screw extruder is as follows: feeding section 170~180 ℃, middle section 170 ℃, homogenizing section 165-
170 ℃, connecting section 170~175 ℃.
The temperature of the forming die from the inlet to the outlet is 170~175115
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