Blow Mould Machinability And Ductility Are Good And Low Density
Regular maintenance of the blow mold (machinery should be cleaned regularly, especially the extruder screw and nose) and to keep the machinery, raw materials and workshop clean and clean, help to ensure the normal blow molding. So how to carry out maintenance and maintenance?
Parison head cleaning. Keeping the parison head clean is an important prerequisite for extruding blown high performance products. Some polymers are degraded during processing, especially if the melt is to be retained in the storage chamber for a period of time when the processing temperature is high or intermittent blow molding. In addition, blow molding grade polymers contain a variety of additives, the melting process will form by-products. These degradation products or by-products will accumulate in the nose of the machine, so that the surface of the parison appears stripe, affecting the appearance of the product. The flow path of the nose is chunk or chrome can reduce the appearance of parison fringes. So that the inflated parison in the contact blow mold cavity when a higher temperature, may be appropriate to offset the effect of parison stripes on the appearance of the product. The production process with copper, etc. to remove the nose in the mouth of the aggregates, and sometimes can eliminate the stripes on the stripes. If not, we must shut down to conduct a comprehensive clean-up. Here are some ways to clean up the head.
Blow molds require less material and a wide range of options. Blow mold material selection should take into account the thermal conductivity, strength, wear resistance, corrosion resistance, polishing, cost and the use of plastic and production volume and other factors. For example, for plastics that produce corrosive volatiles (such as PVC, polyacrylonitrile, polyoxymethylene, etc.), use corrosion-resistant materials to make molds or to coat corrosion-resistant metals on the mold cavity. Manufacturing blow mold material mainly in the following several.
(1) aluminum. Aluminum is the use of extrusion blow mold earlier is also commonly used materials. Aluminum has good thermal conductivity, machinability and ductility, low density, but low hardness, easy to wear. Aluminum alloy wear resistance will be higher. The toughness of cast aluminum is low, so the blanks are made of steel or copper beryllium. Aluminum mold life of about 100,000 to 200,000 times. Aluminum has a porous nature, and sometimes infiltrates a trace of plastic melt, affecting the appearance of blow molded products. This can be solved by coating the sealant on the mold cavity, but this will reduce the heat transfer performance between the product and the mold wall.
(2) copper-based alloy. Copper beryllium alloy is a kind of material which is often used in blow mold. It has good thermal conductivity, hardness, abrasion resistance, corrosion resistance and mechanical toughness. The main drawback is the high cost, mechanical processing performance than aluminum (mechanical processing time than aluminum about 1/3), the density of aluminum alloy is about 3 times, which further improve the cost (unit volume of copper beryllium alloy copper beryllium alloy Can be machined, cast and hot extrusion to produce mold. Beryllium containing higher (such as 1.8% ~ 2.0%) of copper beryllium alloy hardness is higher, to use mechanical processing methods; to create by casting to the shape of irregular (Such as 1.65%) of the copper beryllium alloy. Most of the copper beryllium used in the manufacture of blanks embedded with aluminum mold with the use of sometimes (especially for corrosive plastic) full set of blow mold Are made of copper beryllium alloy, for example, copper beryllium alloy will not be PVC processing hydrogen chloride corrosion, but also to prevent the cooling channel of water scaling, to avoid heat transfer efficiency. Copper beryllium alloy mold easy to weld or mosaic To repair.
Beryllium is harmful to human health, inhalation of beryllium dust damage to the lungs, it is also suspected to be a carcinogenic substance, so in the mechanical processing and casting should be noted. In addition to copper beryllium alloys, there are M / Si / Cu, Cr / (u and aluminum / bronze alloys, which are used to make blow molds, where the thermal properties of the first two alloys are about 2 times that of copper beryllium and 3 times.
(3) steel. Steel is mainly used in the manufacture of PVC and engineering plastic blow mold, this is because the steel hardness, wear resistance and toughness is extremely high, through the etching cavity can make the product made a good surface pattern. The main drawback of steel is poor thermal conductivity, through the cooling system design and cooling fluid temperature and flow status to compensate. Corrosive plastics (such as PVC) molds should be made of stainless steel. Steel molds can be manufactured using machining, cold extrusion, casting or welding (for large molds). Steel mold life of up to 10 million times, so the production of blow molding products is large, steel is a preferred material. Steel (such as general tool steel) is also used to make blow mold parts to wear, such as blanks, rods, guide posts, guide sleeves and stencils, which require hardening of steel. But in general, steel in the manufacture of blow molds used less.
(4) other materials.
① zinc alloy. Its thermal conductivity is good, low cost, can be used for casting large molds or irregular shape of the mold, but also through the mechanical processing to create mold. Zinc alloy hardness than aluminum alloy is low, it is necessary to use steel or copper beryllium alloy to create a blank block. Zinc can also be made of aluminum or copper alloy, which has good dimensional stability, but poor corrosion resistance.
② zinc-nickel-copper alloy. Can also be used as a blow mold material, the thermal conductivity between the copper beryllium alloy and aluminum alloy, however, in similar thermal conductivity, the hardness of copper beryllium lower than some.
③ synthetic resin (such as polyacrylate, epoxy resin). Can be used for casting low-cost test mold, the production of a small number of mold or sample mold. They can be filled with metal powder or glass fiber to improve dimensional stability and thermal conductivity.