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The mold used for the hollow blow molding is composed of two half-side molds, and the main structures of the blow molds of different products are basically the same.
According to the difference of the mold clamping machine, half of them can be used as a fixed mold, and the other half can be used as a dynamic mold, that is, one mold is not moving and the other side is moving.
It is also possible that both half molds are moving molds, and the movements are driven by the respective automatic templates. In actual production, the application of the movable mold is more than two halves, but a few manufacturers can still see the blow mold of half fixed mold and half movable mold.
The structure of the mold
The basic structure of the blow mold mainly includes a mold cavity, a mold main body, a slit portion, a cooling system, an exhaust system, and a guiding portion. In addition, in some structurally complex industrial products, such as auto parts, the mold structure usually needs to be added to the special structure such as insert, core pulling, segmental opening and closing mold, and negative pressure.
The assembly method of the blow mold structure can be divided into the following types.
The two half-side molds of the monolithic structural mold are each machined from a single piece of metal. High-strength stainless steel or die steel can be used to machine cavities, slits, cooling channels, and threads, vents, slots and guides. Columns, sleeves, etc. The mold with integral structure has high precision, small geometric error and durability, and is suitable for some blow molding products with high requirements. In the actual production, there are many small and medium-sized industrial blow molding products and daily chemicals, as well as many packaging bottles such as medicines.
The two half-side molds of the combined structure blow mold are each formed by processing several pieces of metal. The molds with this structure need to be processed separately, and then assembled into one body, usually have certain processing errors, and then need to be manually polished and trimmed. This type of structure is mainly applied to medium and large blow molding product molds, as well as mold processing that does not require high requirements on the products.
The two half-side molds of the inlaid structure blow mold are inlaid by a single piece of metal parts and several hard metal parts. The method of inlaying includes casting inlay, press-in setting and spiral connection inlay. Casting inlay method is mainly to cast the insert into a specified position and then cast it through aluminum alloy, and then carry out subsequent machining. The press-in method is mainly to press the mechanically processed insert into the mold and then machine it. The spiral connection mosaic method is to spirally join all the mold parts after processing into a whole.
4.Steel plate laminated structure mould
The steel plate laminated structure means that the two half-side molds are each formed by laminating a cavity steel plate, a cooling water steel plate, a side blown steel plate, and a back plate or other type of multi-layer steel plate. At present, many manufacturers in China have developed a large-scale full-cooling blow molding die composed of steel plate lamination technology, which greatly improves the cooling speed of the mold. Compared with the original cooling method, the product molding cycle is nearly doubled, which greatly accelerates. The forming speed of large blow molding products. Moreover, the manufacturing cost of such a mold cooling channel is lower than that of a conventional mold.
5.Other types of mold structures
When designing some special blow molding products, it is often necessary to add special structural forms, such as core pulling mold, prefabricated insert mold, split sequential clamping mechanism, high pressure heat sealing mold, partial vacuum mold, local Temperature control negative pressure mold, insert and draw mold. Different combinations of these special structures can also bring about various unused features to achieve the formation of different structural products.
The mold process requirements
1.Exhaust of the mold
When the mold is clamped and the parison is inflated, the gas in the mold is discharged. If the exhaust effect is not good, the gas remaining in the mold cavity will cause streaks, dents, unclear fonts, unevenness, and even appear on the surface of the product. Deformation and other defects. Therefore, this needs to be fully considered in the design and manufacture of the mold, and the following commonly used measures can be taken.
(1)Product surface design
When designing the surface of the product, the necessary text, pattern or groove should be designed in the mold to facilitate the venting of the mold. However, it is also necessary to avoid a large area of smooth surface, or to engrave a lighter pattern on the light surface, which is beneficial to the exhaust of the mold.
(2)Mold cavity processing
Not all mold cavity surfaces are as smooth as possible, and a slightly rough cavity surface not only facilitates mold venting. It also improves the surface finish of the product. Common methods for cavity surface treatment include cavity surface blasting, surface etching pattern, and cavity polishing. However, some products with very high surface requirements, such as high-grade cosmetic containers made of polystyrene, are not suitable.
(3)Vent or exhaust slot
The most effective way to solve the problem of mold exhaust is to open the exhaust groove or exhaust hole in the mold cavity and the parting surface. Several common exhaust methods are as follows.
①Opening a venting groove on the mold parting surface
Opening the venting groove on the parting surface can discharge the air as quickly as possible. Generally, the venting groove is designed on the shoulder and bottom of the parting surface, and can be opened at a special position if it is particularly needed. The width of the venting groove is generally 5 – 25mm; the depth of the venting groove should be selected according to the product production process, container volume and wall thickness, generally 0.01 – 0. Choose between 2mm, the larger the volume, the deeper the groove depth.
②Opening a vent hole in the mold cavity
When it is necessary to open a vent hole in the mold cavity, the diameter of the vent hole near the mold cavity is generally designed to be 0. 1 – 0. 3mm, the diameter is too large, leaving a bump on the surface of the product to affect the surface of the product. If the diameter is too small, pits will appear, and the position of the vent hole in the mold cavity should be considered to not interfere with the arrangement of the cold system. For large volume products, the vent hole diameter can be larger and a specific vent plug is installed for venting. In addition, an venting groove can be provided at the insert in the mold cavity.
When the mold is manufactured, some small holes are drilled in the cavity of the mold, so that they are connected with the vacuum machine, and the air remaining in the mold cavity can be quickly taken away, so that the blown parison is closely adhered to the cavity. In addition, this method is also beneficial to some blow molding products that need to be deepened, the inside of the blow molded product can not be inflated, the surface quality is high, and the interlayer is hollow. The control of the vacuum exhaust system needs to be controlled in conjunction with the electrical control system of the blow molding machine to effectively ensure the accuracy and reliability of the control.
2.Cooling of the mold
The cooling of the blow mold is one of the important molding process conditions, which directly affects and determines the production efficiency and product quality of the product. The design of the mold cooling system must take into account factors such as cooling location, cooling area, heat transfer efficiency, product cooling uniformity, cooling water temperature, flow rate, pressure, temperature and heat capacity of the molten resin. Therefore, necessary consideration should be given to the design of the cooling system of the mold. Commonly used mold cooling channels include box cooling channels, drilled cooling channels, casting buried cooling channels, and laminating mold cooling channels. Either way, the arrangement of the cooling channels should be imported below the mold and the outlet above the mold so that the cooling water flows in the direction of natural warming.
3.Mold cuts and tail grooves
In order to clamp and close the parison, cutting the parison tailings requires arranging the cuts in the neck, bottom, handle and handle of the parting surface of the mold.
The width of the slit depends on the type of material, the thickness of the parison, and the volume of the product. Generally, 1 – 4. Between 5mm. The depth of the slit is affected by the volume of the product and the thickness of the parison.
The depth of the slit is too shallow, the mold cannot be completely closed, and the parison is less likely to be cut. If the depth of the slit is too large, the parison tailings cannot be completely in contact with the mold and cannot be cooled quickly.
Generally, the depth of the cutting edge is 80% – 90% of the wall thickness of the parison. A tail groove is formed at the outer edge of the mold slit, so that the cut portion can be stored in the trough and the joint portion of the product can be locally thickened.
The depth of the tailing trough also has a great influence on the product. See the recommended table for the groove depth interval used by different materials. The general groove depth is 80% -90% of the parison wall thickness, which can increase the joint of the product. Thick effect.
The material of the mold
The material of the blow mold can be comprehensively considered according to the thermal conductivity, tensile strength, wear resistance, castability, polishing property, service life, and the variety of plastics used, the quality requirements of the products, the production batch value, and the cost. Since the mold clamping pressure and the blow molding pressure are relatively low during the blow molding process, the blow mold does not need to be made of a material having a high tensile strength. Commonly used mold materials are steel, aluminum and aluminum alloy, beryllium copper alloy, cast iron, zinc alloy, polymer materials and so on. In practical applications, polymer materials are generally used for testing blow molds. Cast iron molds are generally only used for manual hinged molds and small batches. They are usually not used in mass production. The performance characteristics of main mold materials are as follows. table.
It is generally believed that when the blow molding products are large in batch size and the production time is long, and the mold incision requires high strength, hardness and wear resistance, the effect of selecting carbon steel for the mold material is ideal. The mold made of carbon steel can reach more than 10 million times of service life. The mold can be manufactured by various mechanical processing methods such as casting, turning, die milling, welding, engraving, and the like. Although its heat transfer performance is not as good as that of aluminum alloy, zinc alloy and beryllium copper alloy, it can effectively improve the heat transfer condition if a better cooling water channel structure is adopted. Steel can also be used to form wearable parts of the mold, such as the neck insert, the insert insert, the guide post and the guide sleeve. The steel has good welding performance and is advantageous for welding processing. Using low carbon steel in carbon steel as the mold material, the surface of the mold can be treated by carburizing (nitriding) technology, and the carburizing (nitriding) treatment can be performed on the low carbon steel mold that has been used for a period of time. .
2.Aluminum and aluminum alloy
The mold made of aluminum material has good quality, good thermal conductivity, good mechanical processing and extensibility, but low hardness, easy wear and tear, poor weldability and high material cost. Large blow molds are generally made of cast aluminum. The mold cooling channels can also be made of seamless steel tubes or stainless steel into coils directly placed inside the mold. The cast aluminum material is then melted and cast into a mold blank together with the cooling water pipes. The mold can be machined. Aluminum alloy is generally used to improve wear resistance, and the service life of aluminum alloy molds is also 2 million times.
3.Beryllium copper alloy
Beryllium copper alloy is one of the more commonly used materials. It has good thermal conductivity, hardness, wear resistance, corrosion resistance and mechanical properties. It is mainly suitable for the production of large and medium-sized blow molding products and blow molds. The main disadvantages are high cost, high relative density and long machining time. Beryllium copper alloy is more commonly used in molds such as polystyrene when the hardness of plastic raw materials is large. It can also be processed into wearable parts of other material molds, such as cut blank inserts in aluminum alloy blow molds. The general composition of beryllium copper alloy is w( Be) 2. 75%, w(Co)0. 5%, the rest is copper. Changing the content of niobium in the alloy allows it to have different strength, hardness, thermal conductivity, corrosion resistance and wear resistance. Beryllium copper alloy can be fabricated by mechanical processing, hot extrusion, casting, etc., w( Be) 1. 7% of the niobium alloy is suitable for casting, and the insert can be selected as w(Be) 2. 0% beryllium copper alloy. Beryllium copper alloy prevents scaling in the mold cooling water channel. The beryllium copper alloy can achieve a hardness of 38 to 40 after heat treatment, which can be worn for a long time.
Zinc alloy has good thermal conductivity, low cost, easy casting and machining, and is mostly used for the manufacture of blow molding molds with irregular shapes, but the abrasion resistance is slightly worse. The cut portion of the mold is generally embedded in the casting by steel. Molds made of polymer materials are generally used for blow molding products or experimental materials such as epoxy resins and acrylic resins. The thermal conductivity of zinc-nickel alloy is between copper-aluminum alloy and aluminum alloy, but the hardness is lower than that of beryllium copper alloy.
Above is about blow molding machine mold related knowledge.
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