August 15, 2022
How to deal with the hazards of injection molding machines
(1) According to different load requirements, check and adjust the pressure of the relief valve frequently to make it just right.
(2) Reasonable selection of hydraulic oil, especially oil viscosity, when conditions permit, try to use a lower viscosity to reduce viscosity friction loss.
(3) Improve the lubrication conditions of moving parts to reduce friction loss, which is conducive to reducing workload and heat generation.
(4) Improve the assembly quality and precision of hydraulic components and hydraulic systems, strictly control the matching clearance of matching parts and improve lubrication conditions. The sealing material with small friction coefficient and the improved sealing structure are used to reduce the starting force of the hydraulic cylinder as much as possible to reduce the heat generated by the mechanical friction loss.
(5) Add cooling device if necessary.
Generally speaking, most customers who have been in the injection molding industry for many years have the ability to judge and choose the appropriate injection molding machine for production. However, in some cases, the customer may need the assistance of the manufacturer to decide which specification of injection molding machine to use, or even the customer may only have a sample or idea of the product, and then ask the manufacturer whether the machine can be produced, or which model to compare Suitable for.
In addition, some special products may require special devices such as accumulators, closed circuits, injection compression, etc., in order to be produced more efficiently. It can be seen that how to determine the appropriate injection molding machine for production is an extremely important issue. The following information is provided for the reader's reference.
The important factors that usually affect the selection of injection machines include molds, products, plastics, molding requirements, etc. Therefore, the following information must be collected or available before making a selection:
Mold size (width, height, thickness), weight, special design, etc.;
Type and quantity of plastic used (single raw material or multiple plastics);
Appearance dimensions (length, width, height, thickness), weight, etc. of injection molded products; molding requirements, such as quality conditions, production speed, etc.
After obtaining the above information, you can follow the steps below to choose a suitable injection machine:
1. Select the right type: The model and series are determined by the product and plastic.
Since there are many types of injection molding machines, it is necessary to correctly determine which injection molding machine or series the product should be produced by at the beginning, such as general thermoplastics or bakelite raw materials or PET raw materials, etc. Color, two-color, multi-color, interlayer or mixed color, etc. In addition, some products require conditions such as high stability (closed loop), high precision, ultra-high injection rate, high injection pressure or rapid production (multi-loop), and the appropriate series must also be selected for production.
2. Put down: Determine whether the "large column inner distance", "mold thickness", "mold minimum size" and "mold size" of the machine are appropriate according to the size of the mold, so as to confirm whether the mold can be put down.
The width and height of the mold must be smaller than or at least one side is smaller than the inner distance of the large column;
The width and height of the mold are preferably within the size of the mold plate;
The thickness of the mold needs to be between the mold thickness of the injection molding machine;
The width and height of the mold must meet the minimum mold size recommended by the injection molding machine, and it will not work if it is too small;
3. Take it out: It is judged by the mold and the finished product whether the "opening stroke" and "supporting stroke" are enough for the finished product to be taken out.
The mold opening stroke must be at least twice the height of the finished product in the direction of opening and closing the mold, and the length of the sprue must be included;
The pallet stroke should be enough to eject the finished product;
4. Can be locked: The tonnage of "clamping force" is determined by the product and plastic.
When the raw material is injected into the mold cavity under high pressure, a mold-pulling force will be generated, so the clamping unit of the injection molding machine must provide enough "clamping force" so that the mold will not be opened. The clamping force requirement is calculated as follows:
Calculate the projected area of the finished product in the direction of the opening and closing die from the appearance size of the finished product;
Supporting mold force = projected area of the finished product in the direction of opening and closing the mold (cm2) × number of mold cavities × pressure in the mold (kg/cm2);
The pressure in the mold varies with the raw material, and the general raw material is 350~400kg/cm2;
The clamping force of the machine needs to be greater than the force of the supporting die, and for the sake of safety, the clamping force of the machine usually needs to be more than 1.17 times the force of the supporting die;
So far, the specifications of the clamping unit have been preliminarily determined, and the tonnage of the model has been roughly determined. Next, the following steps must be performed to confirm which injection unit has a more suitable screw diameter.
5. Full shot: Determine the required "shot volume" by the weight of the finished product and the number of mold cavities, and select the appropriate "screw diameter".
When calculating the weight of the finished product, the number of mold cavities (several cavities in one mold) must be considered;
For the sake of stability, the injection volume should be more than 1.35 times the weight of the finished product, that is, the weight of the finished product should be within 75% of the injection volume;
6. Good shot: The "screw compression ratio" and "injection pressure" are determined by the plastic. Some engineering plastics require a higher injection pressure and a suitable screw compression ratio design to have a better molding effect. Therefore, in order to make the finished product shoot better, it is also necessary to consider the injection pressure requirements and compression ratio issues when selecting a screw. .
In general, smaller diameter screws provide higher injection pressures.
7. Shooting fast: and confirmation of "shooting speed".
Some finished products require high injection rate and rapid injection in order to be stably formed, such as ultra-thin products. In this case, it may be necessary to confirm whether the injection rate and injection rate of the machine are sufficient, and whether it needs to be equipped with accumulator, closed-loop control and other devices. Generally speaking, under the same conditions, a screw that can provide higher injection pressure usually has a lower injection rate, and conversely, a screw that can provide a lower injection pressure usually has a higher injection rate. Therefore, when selecting the screw diameter, the injection volume, injection pressure and injection rate (injection speed) need to be cross-considered and chosen.
In addition, a multi-loop design can also be used to shorten the molding time by synchronizing compound actions.
After the above steps, in principle, it is possible to determine the injection molding machine that meets the needs, but there are some special issues that may also have to be considered, including:
Size matching problem:
In some special cases, the customer's mold or product may have a small mold but a large shot volume, or a large mold but a small shot volume. In this case, the standard specifications set by the manufacturer may not be able to In order to meet customer needs, the so-called "size matching" must be carried out, that is, "big wall and small shot" or "small wall and big shot". The so-called "large wall and small shot" means that the original standard clamping unit is matched with a smaller injection screw. On the contrary, "small wall and large injection" means the original standard clamping unit is matched with a larger injection screw. Of course, there may be several levels of difference between clamping and injection.
The idea of a fast machine or a high-speed machine:
In practical application, more and more customers will ask to buy the so-called "high-speed machine" or "fast machine". Generally speaking, in addition to the needs of the product itself, the purpose is to shorten the molding cycle and increase the output per unit time, thereby reducing production costs and improving competitiveness. Generally, to achieve the above goals, there are several approaches:
Increase the injection speed: increase the motor and pump, or add a pressure accumulator (preferably with closed-loop control);
Increase the feeding speed: increase the motor motor and pump, or reduce the feeding hydraulic motor to speed up the screw speed;
Multi-loop system: double-loop or triple-loop design is adopted to perform compound actions synchronously and shorten the molding time;
Increase the mold waterway to improve the cooling efficiency of the mold;
However, "there is no free lunch in the world". Although the improvement and transformation of machine performance can increase production efficiency, it often increases investment costs and operating costs. Therefore, the benefit evaluation before investment needs to be carefully evaluated before the most suitable machine can be selected. type to produce the highest benefit.
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