Extrusion blow molding of plastic hollow products - polyethylene barrel (2)
DATE：2022/12/3 8:51:51 / READ： / SOURCE：This station
Extrusion blow molding of plastic hollow products - polyethylene barrel (2)
The following points should also be paid attention to in the mold structure and application of hollow products formed by blowing.① The junction of the die cavity surface should be an arc transition, and there should be no right angle transition line.
② The end of the forming die shall be provided with a clamping blank pipe orifice, from which the excess material of the product and the blank pipe before clamping and inflating shall be cut. The shape and size of the clamping opening are shown in Figure 11-5. The determination of several dimensions should take into account its influence on the forming and strength of products. The empirical data generally take h=1~2.5mm, H=3~5mm, β= 15°~45°。
③ In order to make the expanded parison close to the inner cavity wall of the mold and get a better product surface, an exhaust hole shall be reserved between the parison and the mold, and an exhaust hole of 0.2~0.5mm shall be drilled at an appropriate position or an exhaust groove of 0.1~0.2mm shall be reserved on the junction surface of the mold cavity.
④ The mold shall be made of materials with good thermal conductivity and capable of withstanding mold closing strength and blowing pressure. Common materials include aluminum, aluminum alloy, steel and stainless steel.
⑤ In order to speed up the cooling of products after blowing, if necessary, circulating cooling water shall be used to cool the molding mold of products. The mold temperature for polyethylene blowing products shall not be greater than 40 ℃ during operation.
⑥ The surface roughness of the inner cavity of the mold is not required to be high. If necessary, the inner surface needs to be sandblasted (40 meshes) to facilitate the escape of air between the mold and the surface of the product when inflating the product.
(3) The barrel temperature for plasticizing raw materials of the molding process extruder: 140~180 ℃ for LDPE and 150~210 ℃ for HDPE (the temperature increases gradually from the feeding section of the barrel to the homogenizing section).
The mold temperature of hollow products formed by blowing is 20~40 ℃. The inflation air pressure is 0.3~0.5MPa.The blowing ratio is 1.5~3. Blow up ratio refers to the ratio of the transverse maximum diameter of the product after blow up to the diameter of the barrel blank tube (generally, a larger blow up ratio is used for small hollow products, while a smaller blow up ratio is used for large hollow products).
(4) Quality requirements The quality requirements of polyethylene plastic barrel shall comply with the provisions of GB 13508-92. The main contents are summarized as follows.
① The classification standard of barrels by use is: S represents barrels for food and medicine packaging, H represents barrels for chemical product packaging not listed as dangerous goods, and T represents special barrels for dangerous goods packaging.② When threaded structure is used for opening and cover, it must be rotated for more than 1 turn from tightening to tripping.
③ The actual capacity of the barrel shall be greater than 5% of the nominal capacity.
④ The allowable deviation between the actual quality of the barrel and the approved quality is ± 8% (referring to the specification of the barrel 1~30L).
⑤ The allowable deviation between the actual overall dimension of the barrel and the design overall dimension is ± 5mm (referring to the outer diameter and height of the barrel when the barrel size is 1~30L).
⑥ Appearance quality of barrel: 1~5L barrel shall be free of bubbles, and when it is larger than 5L, no more than 2 bubbles with a diameter less than 2mm are allowed; Black spot impurities, with a length less than 1.5mm, shall not exceed 3 in 1~2.5L and 5 in 3~5L. Black spot impurities with a length less than 0.5mm shall not be counted, but penetrating impurities are not allowed; There shall be no cracks and holes, no boils with poor plasticization, no oil stains, no surface scratches, and the wall thickness and color shall be uniform.
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