Injection Moulds Usually Encounter Problems And PVD Coating Plays A Role

- Jan 10, 2019-

Injection moulds usually encounter problems and PVD coating plays a role


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With the wide adoption of glass and metal fiber reinforced engineering plastics and non-flammable resins, as well as the increase in batch production of plastics, the working conditions of plastic molds become increasingly severe, and severe wear and corrosion often occur on the surface of the mold cavity, which affects the appearance of products and causes the difficulty of mold release, and greatly shortens the service life of the mold cavity.


The practice has proved that the application of surface strengthening technology to improve the surface hardness, wear resistance, friction reduction, corrosion resistance and fatigue resistance of molds and relative moving parts is an effective way to avoid early failure of molds and improve the service life.


A set of injection moulds is usually assembled from several different parts.Such as plastic injection mold should have the following characteristics: first, withstand the pressure caused by the force.Secondly, several metal moving parts without lubrication will be subject to: 1. Bite abrasion; 2.2, corrosion and wear, plastic powder heat brings corrosion and products broken grain attractive wear.In addition, some mold areas should bear: 1.2, because some products will add glass fiber caused by abrasive wear;3. Corrosion caused by the decomposition of chlorine-containing polymer and abrasion caused by product particles;4. The "internal combustion effect" (diesel effect) of combustible exhaust gas will be generated due to the dual effects of heat and pressure in some parts of the sealing and mating areas, sometimes causing flash fire or burning, etc.


In the mold, some parts that have undergone harsh working conditions are injection nozzle, moving tappet, drawing rod, guide rod or guide rail, etc.Suffered fatigue, wear and corrosion conditions can produce defects on the mould, these defects will reduce the die life, may cause the deterioration of mould: 1, plastic and mold filling speed operating speed and general sliding friction coefficient is inversely proportional to mold parts, mold defects certainly influence on the speed of operation, thus directly impact the cost of the mould operation;2, mold surface and injection mold material between the physical and chemical interaction will cause plastic, rubber or aluminum alloy "knot" disease, or can be called malignant "adhesion".For example, in an injection molding factory, the original steel used for the plastic mold is 35NCD16(35Ni4CrMo steel), which is cooled by water inside.Due to slime and "internal combustion effect", the mold needs to be cleaned and polished after processing one million pieces. The average operation time for each piece is 17s, which seriously reduces the production efficiency.The molds were then coated with a PVD coating, 3um after a single mask, with high wear resistance, and the mold material was converted to cu-be alloy (beryllium bronze) with good thermal conductivity, which can Be cooled without water.The molds after this treatment do not have "internal combustion effect", and the myxoma phenomenon is greatly reduced, so that the cleaning can be carried out after every 6 million injection molding.In addition, due to the small chemical affinity between the mold coating and the plastic, the average operation time decreased from 17s to 10s.The second example is a polystyrene plastic spoon mould made of high alloy steel Z38CDV5(1.2343, equivalent to us H2 steel).The existing problems are the poor filling properties of plastic injection cavity and the phenomenon of mold slime.In order to increase the filling speed, some PVD coating was applied to the mold, with amazing results and a 30% reduction in operating time.Because the friction between the plastic and steel is reduced, demoulding force is reduced, mold pattern carving need not be too much trouble.The third example is a synthetic rubber o-ring mould, which was originally plated with hard chromium, but is now coated with chrome-based PVD.When hard chromium plating is used, the die is cleaned (brushed and removed in the cleaning solution) after every 20,000 jobs due to severe "nodules".In order to reduce maintenance costs and production stoppage costs, the hard chromium layer was changed to a single 4um thick chrome-based PVD coating.The result of this replacement is clear: the cleanup can be carried out after every 100,000 units, with a five-fold reduction in idle hours.