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How to reduce shrinkage in plastic mold processing

 

Therefore, various technologies have been developed to minimize shrinkage and improve product quality. Shrinkage is a stubborn disease. Premature cooling at the gate reduces the fill time in the cavity, which increases the chance of shrink marks. In the thicker position of the plastic mold parts of the Huangjiang, such as the ribs or protrusions, the shrinkage is more serious than the adjacent position, because the cooling rate of the thicker area is much slower than the surrounding area.How to reduce shrinkage in plastic mold processing

 

How to reduce shrinkage in plastic mold processing? Shrinkage is the enemy of plastic mold processors, especially for large-scale home appliance precision plastic mold products with high surface quality requirements. There may be one or more reasons for the formation of shrink marks, including processing methods, component geometries, material selection, and mold design. Too short a filling phase will result in increased shrinkage and eventually more or larger shrinkage marks. After the part is filled, the excess material continues to fill the cavity to compensate for the shrinkage of the material. The difference in cooling rate causes a depression at the joint surface, which is a familiar shrinkage mark. This kind of defect severely limits the design and molding of precision plastic mold products for home appliances, especially large-scale thick-walled products such as the bevel case and display case of TV sets. For example, small gates such as tubular gates cool much faster than tapered gates. In addition, the gas-assisted method is also worth a try..

 

A simple solution is to modify the conventional air cooler mould factory core hole, but this method cannot be expected to be suitable for all resins. In fact, for the demanding products such as household electrical appliances, the shrinkage marks must be eliminated, and for products such as toys that have low surface quality requirements, shrinkage marks are allowed. The geometry and material selection are usually determined by the raw material supplier and are not easily changed. Filling pressure and time significantly affect shrinkage. This method may not reduce the shrinkage marks to a satisfactory level by itself, but the molder can adjust the filling conditions to improve the shrinkage marks. Another method is to modify the mold. But moldmakers still have a lot of factors about mold design that can affect shrinkage. For molding workers, adjusting the processing conditions is one way to solve the shrinkage problem. Cooling runner design, gate type, gate size can have multiple effects

 

The high-precision molds in foreign countries, and the same auxiliary mold can be mixed

The needle valve type hot runner saves materials, the surface of the plastic parts is beautiful, and the internal quality is tight and the strength is high. Second, the working principle of the temperature controller: Another component of the hot runner technology is the heating and temperature control system, the advantages and disadvantages of the heating and temperature control system, directly affecting whether the mold can work continuously, it can be said that the heating and temperature control system is

 

The entire hot runner occupies a very important position.. In the heat preservation phase, the working temperature is constant, there is no large fluctuation, and the heating element is always in plastic injection mould a low voltage constant working state, and has no impact on the heating element. The temperature measurement system is updated to make the temperature control system applicable to various thermocouples with an indexing degree, the measurement accuracy is improved to 1%, and the over-temperature alarm is improved. The working principle is as follows: When the system is first turned on, the system automatically enters the soft start state, and the voltage of the heating element gradually rises from zero to the rated voltage. The thyristor zero-trigger device not only ensures the conduction in the zero phase, but also does not damage the power grid, and further improves the service life of the heating element. The soft start function not only can reduce the impact of the heating element when it is heated in the cold state, but also can drive out the moisture generated when the mold is not used for a long time.About hot runner temperature controller

 

The thermostat functions to control the temperature in the hot runner system. The heating and temperature control system of the hot runner basically consists of a heating device, a monitoring point and a control system. The cylinder type * hot runner temperature controller and timing controller control the cylinder to push the needle valve to close, the structure is more complicated, but the design itself is simple. The role. Fluctuations within the scope. The design of the adiabatic runner is complex, but the effect and maintenance costs are very low and do not delay working hours. The ideal control system can not only effectively control the temperature change in the flow channel, but also prolong the service life of the heating device, so as to achieve continuous and long-lasting work of the mold. In the output control mode, the internationally new pulse width adjustment technology and zero-trigger and soft-start mode are adopted. The heating device is generally a heating rod and a heating coil; the monitoring point is a probe disposed near the weak portion or the working surface in the entire hot runner; the control system is used to regulate the temperature of the entire hot runner system to ensure that the temperature is at a certain setting. And falling, when the temperature rises to the set value, the voltage of the heating element is a constant low pressure state, just to supplement the heat loss of the hot runner system. Next, let's briefly introduce the hot runner flow temperature controller. It is necessary to design the voltage of the heating element in the heat preservation stage to be 50% to 60% of the rated voltage, by increasing the broken wire alarm of the heating element. First, the hot runner temperature controller classification: adiabatic flow channel, cold runner, hot runner. When the temperature approaches the set value, the working voltage on the heating element will stabilize with the temperature. The temperature control system selects different heating powers, which has a great influence on the service life of the heating elements. The output control device selects high-power two-way thyristor output, which is stable in operation and reliable in performance. There are two major types of needle valve hot runners in the world (according to the injection principle): cylinder type and spring type. Generally, it is set for 8 to 20 minutes, which also plays a role in protecting the hot runner system of the mold. The open structure is simple, the material has high limitation, the drawing and leakage are easy to occur, the surface quality is poor, and the application is less in the high-precision molds in foreign countries, and the same auxiliary mold can be mixed with the needle valve type of different manufacturers. When designing the control system, it should be considered from the aspects of stability, reliability and durability. The temperature of the nozzle and the heater of the manifold in the system is controlled by the thermocouple to keep the plastic molten; and the temperature control is optimized according to the different characteristics of different plastics

 

The following small series tells everyone what kind of conditions

 

The following small series tells everyone what kind of conditions should the injection mold processing factory have? Usually, plastic mold processing enterprises use skilled employees, tend to prefer multiple machines, ensure the operation of the resin box, multiple shifts, injection processing plants Make sure the finished project is in good running. , POM, PBT, PET, polyetheretherketone, polyphenylene sulfide, thermoplastic elastomer, TPV SBS, SEBS, TPE, TPV and most other grades of polymer.What kind of conditions should an injection mold processing factory have?

 

Plastic molds involve the use of thermoplastic materials, including many thermoplastic elastomers to produce first-class finished products. Many companies run 3 x 8 hour shifts for air cooler mould a total of 126 hours a week. Injection molding machines from most injection molding plants can handle a full range of materials and thermoplastic elastomers, including polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene, HIPS, PS, ABS, ASA, PC, PA.

 

Many machines today are automated, using conveyor belts and robotic arms, and placing them on moving belts to send to the storage box. Some materials require specialized production techniques, such as reduced temperature conditions, different release agents, high spray pressures, and custom mold design for plastic mold manufacturers, many of which are considered. The finished product is very suitable for high-volume production because it requires relatively expensive injection molds and requires a high life to ensure a return on investment

 

The mold must not have sharp corners, need chamfering treatment

 

The thimble adopts the hasco or dme standard, which is determined by the mold technical requirements determined by the bom table or other formal notices. The effective locking length of the screw must be SMC moulds factory sufficient, normally 1. If there are two or more inclined guide columns in the same row position, the length, size and inclination of the inclined guide columns must be the same. Drill holes must not be drilled, and sharp angles must be chamfered. A proof of material must be provided, and if it is a hard mold, a heat treatment report must be provided. 7. For the beading and wear-resistant plates, wear-resistant hard materials must be used, and oil grooves are required. The row guide column must be pressed tightly and cannot be rotated or loosened.

 

The inclined top seat is generally hardened with 2510 or cr12 to hrc40-45 degrees. The diameter of the positioning ring must conform to the drawings.15mm. The form and position of the top joint must conform to the drawings. Except where otherwise specified. The inner mold and mold parts must not be welded without consent. 20, the front and back inner molds of all molds, inserts, row position, slant top, straight top (push block), shovel chicken, etc. Because the inclined top seat is subjected to the impact load, it cannot be too hard or it will break and chamfer the c angle at all right angles. . 18. 11. 10, the conventional structure mold must be arranged with the head, the two ends need to be smoothed, the small mold pre-pressure 0. 5.

 

The surface treatment of the internal mold surface must be carried out in accordance with the bom table or other officially notified technical requirements. For all internal mold materials, the mold blank level requirements must be purchased according to the order or the technical requirements officially confirmed during the design review process. The periphery of the mold product must be opened at the appropriate position. This is very important, like friends. The mouth is not nitrided and may have been injured before the mold. 25, the inclined top seat must use wear-resistant hard material. Now it summarizes and summarizes the common problems of mold manufacturing, and establishes standards and implements according to requirements. Can be collected! 1, the hot mouth slot must be rounded to avoid scratching the wire. Do not weld. The tail of the inclined guide column must be processed into a hemispherical or truncated cone shape to help ensure normal movement of the row. 14. According to the bom table or the confirmed pattern, the faucet must be machined and installed according to the die. Before the mold is packaged, the inner mold needs to be sprayed with white/colorless rust inhibitor. The radius of the beak must meet the drawing requirements. Before the mold is transferred, the water pressure should be tested (100pa or more). The processing lines on the non-adhesive surface (line cutting, milling machine, cnc trampoline, spark machine) should also be polished with oil stone. 6. Avoid using a sander to polish the mold as much as possible. The row needs to have a bead and a wear plate. All mold surfaces must be cleaned and then buttered. 23, the position must have a position. After the water is accepted and accepted, the air gun should be used to blow the water clean. 8.1mm, the large mold pre-pressure 0. If it is necessary to use a sander, you must use oil stone to save light (especially the parting surface).Summarize and summarize the common problems in mold manufacturing!

  In order to improve the quality of the mold, the plastic mold company minimizes the complaints about the quality of the mold and handed it to the customer's satisfactory mold. All relevant proofs. Positioning methods include slingshot, wave bead, hasco (dme) standard position clip, etc. 17, all screws and mold parts need to be the preferred standard parts, the screw head can not be sawn off. 22, the outer surface of the mold embryo in the manufacturing process, need to pay attention to maintenance, to prevent rust, scratches. Important wearable parts such as row position, push block, shovel chicken, and pout must be nitrided and hardened. If the thimble position is not horizontal on the product, you need to make the ejector pin 'd' type or use the anti-rotation key to position. 12, mold transfer acceptance: need to cooperate with the mold engineer according to the 'mold check table' acceptance before passing the package to mold. 15. 24.., which need to be in accordance with the requirements of each project. A sloping top guide (bronze) is required. 4. All the words on the mold must be neat, correct, and not to be twisted. If the side lock cannot be installed, you need to install a taper lock or a cone lock. 9, the mouth should be nitrided, you need to do a resale. 21, thimble, cylinder, thimble, slant top and thimble board should be engraved with the corresponding identification code for easy installation. 13.1mm-0. 19. For the specifications of the exhaust groove, please refer to the mold design manual. 3, the mold must not have sharp corners, need chamfering treatment. 16, the mold needs to be installed on the four sides of the side lock (straight body lock)

 

The plastic mold is poorly ventilated, and the gas in the cavity is compressed

 

What is the role of the plastic mold in setting up the exhaust system?

In the injection molding process of plastic mold products, problems such as whitening, black spots, shrinkage, bubbles, silver filaments, flashing, and the like of plastic parts are often encountered. If the plastic injection molding process parameters are adjusted, the plastic products still have insufficient filling, high internal stress, bubbles, etc., which is likely to be the exhaust problem of the plastic mold.

 

The plastic mold is poorly ventilated, and the gas in the cavity is compressed, which generates a large back pressure. It is this back pressure that prevents the normal rapid filling of the molten plastic, making injection molding difficult. In the case of difficulties in injection molding, injection molding personnel often adopt a method of increasing the injection pressure, which leads to prolonged holding time, delayed molding cycle, reduced production efficiency, increased energy consumption of the injection molding machine, and the like.

 

Even sometimes corrosive gases build up in the cavity, contaminating the plastic mold, reducing the life of the mold and increasing the cost of the plastic mold. The source of gas in the injection molding mold: the air present in the cavity and the casting system; the water vapor generated by the evaporation of the moisture contained in the plastic material pipe fitting mould factory at high temperature; the gas generated by the decomposition of the plastic at high temperature; the volatilization or chemical occurrence of certain additives in the plastic Gases generated by the reaction, such as thermosetting plastics, often produce gases due to chemical reactions.

 

There is also a mold that is a mold for mass production

 

What is the classification of plastic molds and what should be paid attention to when selecting plastic molds? Nowadays, plastic mold injection production is mainly divided into two types. One is a conventional plastic mold. This kind of mold has a life expectancy of 10-20 million molds under normal conditions. Mainly used for small batch injection molding, usually refers to 100-2000 per processing.

 

There is also a mold that is a mold for mass production. This type of mold has a long service life and basically does not come down to the injection molding machine. It is produced all the time and has high requirements on the life of the mold. The mold materials are cable tie mould manufacturer more than double the cost of processing technology, materials and processing after heat treatment, with a capacity of more than one million times. The good wear resistance of the plastic surface gloss and accuracy is directly related to the wear resistance of the injection mold cavity surface, especially some plastics add glass fiber, inorganic fillers and pigments, they and the plastic melt flow, at high speed flow Cavity.

 

The surface of the cavity is rubbed. If the material is not worn, it will wear quickly and the quality of the plastic will be lost. Mold materials must have good dimensional stability for injection molding. It is best to choose the appropriate tool steel for heat treatment. The mold is sprayed with a rust inhibitor after the end of production. Reduce the possibility of rusting of the cavity and core. Therefore, the mold material must be corrosion resistant.