October 17 2010, 10:13 PM
How to choose plastic injection molding machine
Typically, the important factors when choosing plastic injection molding machine include mold, product, molding requirements and so on. Therefore, you must collect or have the following information before making a choice: mold dimension (width, height, thickness), weight and special design; types and amount of the plastic (single or multiple plastic materials); dimensions and weight of injection molding product (length, width, height, thickness); molding requirements, such as quality condition, production speed and so on.
In obtaining the above information, you can follow these steps to choose a suitable plastic injection molding machine:
- Choose the right type of plastic injection molding machine: make decision by the products and plastic
The plastic injection molding machine has a lot of types, so at the beginning, you should determine that what kind or which series of plastic injection molding machine is fit for the product. For example, for thermoplastic plastic or Bakelite resin or PET, the product is single color, two-color, multi-color, laminated or blending. In addition, some product requires high stability (closed loop), high precision, high injection speed, high injection pressure and rapid production (multi-loop) and so on.
- Able to put it on: the size of mold determine whether the internal spur of large column, the mold thickness, the minimum mold dimension and the mold plate size of plastic injection molding machine are suitable or not, to make sure that it is able to put mold on.
The mold width and height must be less than or at least less than the internal spur of large column; The mold width and height must in the mold plate size range; the mold thickness should be between the thickness of plastic injection molding machine; The mold width and height must be fit with the minimum mold size recommended by the plastic injection molding machine.
- Able to put it out: the mold and product judge whether the “Opening Stroke” and “Ejector Stroke” are enough to remove the finished product.
The opening stroke should at least larger than the product height along the opening direction more than twice, including the length of vertical sprue; ejector stroke should long enough to eject the finished product.
- Able to maintain locked: the product and plastic determine the tonnage of “clamping force”.
When the raw materials inject into the mold cavity in a high pressure, it will create a bulging force, so the clamping unit of the plastic injection molding machine should provide sufficient “clamping force” so that the mold was not subject to distraction. The need of clamping force is calculated as follows:
Clamping force = projected area of product in the direction of opening and closing mould (cm2) ×the number of mold cavity×in-mold pressure (kg/cm2);
Projected area of product in the direction of opening and closing mould is generated by the product appearance size.
In-mold pressure is different with different materials, generally take 350-400 kg/cm2.
The machine clamping force is usually greater than 1.17 times of the bulging force.
- Enough injection quantity: the weight of product and the number of mold cavity determine the “injection quantity” and select the appropriate “screw diameter”.
For stability purpose, the injection volume required for more than 1.35 times of the product, which means the product weight should less than 75% of the injection amount.
- Good injection: plastic determine “screw compression ratio” and “injection pressure” and other conditions.
Some plastic requires a higher injection pressure and appropriate screw compression ratio for a good molding. So when choosing screw, it should considered about the demand of injection pressure and the problems of compression ratio. In general, smaller diameter screw provides higher injection pressure.
- High injection speed: confirm the injection speed.
Some product requires a high injection speed to stabilize the injection molding, such as ultra-thin wall product. In this case, it is necessary to make sure that whether the injection speed and injection rate are enough or not, and whether accumulator and closed-loop control are necessary or not. Generally speaking, in the same condition, a screw in the plastic injection molding machine with high injection pressure has a lower injection speed, on the contrary, a screw with low injection pressure has a higher injection speed. So when choosing the screw diameter, injection volume, injection pressure, and injection rate (injection speed) should be cross considered.
Dakumar is one of the Chinese leading innovators for plastic molding machine's researching and developing. It provides various plastic injection molding machines and plastic molding auxiliary machines, you can get what you want in Dakumar machinery Co.,Ltd.
(edit by DAKUMAR)
Posted in plastic injection molding machine
October 8 2010, 1:31 AM
Problems in the Injection Moulding and the Use of Injection Moulding Machine
- The plastic products burr appear when just getting machine, and lack of plastic after a period of production time. What’s the reason and solution?
The melt plastic in the barrel of injection moulding machine has low viscosity and good fluidity due to the long heating time, so is easy to result burr when just getting machine. After producing for some time, the melting plastic takes away heat continuously, it result in the shortage of meting plastic, large viscosity and poor fluidity, all these make the plastic product lack of plastic.
To resolve these problems, it is necessary to increase the barrel temperature gradually after producing for some time.
- The cause and solution of plastic product ellipse
Ellipse is result from the uneven plastic feeding, which result in uneven pressure around the plastic product.
Three point feeding will make plastic product has an even feeding.
- The requirements of precision mould
Good rigidity for mould material, small elastic deformation, small thermal expansibility coefficient.
- The purpose of plastic product acid-resisting test
Plastic product acid-resisting test is to test product internal stress and the focus position in order to remove the product internal stress.
- The metal insert in plastic product is easy to crack by force, what’s the reason and solution?
Putting insert in plastic product, the internal stress will form when the hot melting plastic met the cold insert, which will decrease the plastic product intensity and make it easy to crack.
Do preheating for insert in the production.
- The mould exhaust pointreasonability and selection method.
The unreasonable mould exhaust point not only would not achieve the exhaust effect, but also result in plastic product deformation or dimensional change, so the mould exhaust point should be reasonable.
To select the mould exhaust point, we should set exhaust in the place where last full fill the plastic and the product areas where burn the trapped gas.
- The cause and solution of plastic product embrittlement
Plastic product is easy for embrittlement is due to the too much of gate materials and regrind usage or the long residence time in the barrel which result in the plastic aging.
Increase the proportion of new materials and reduce the recycling number of gate material, generally not more than three times, to avoid the plastic stopping in the barrel for a long time.
- The effect of feed port temperature to plastic product
Too high or too low feed port temperature will cause unstable machine feeding back, so that feed amount is unstable and plastic product size and appearance will be affected.
- Reasons and solutions of white point in transparent plastic product
White point in transparent plastic product is result from the entrance of cold slag in the plastic product or the dust within the material.
Improve the nozzle temperature and add cold slag well, attention to materials preservation to prevent dust from entering.
- What’s the injecting capacity of injection moulding machine
injecting capacity= injection pressure(kg/cm2) ×injection volume(cm3)/1000
- Analysis of toggle abrasion
Poor lubrication result in the toggle abrasion.
- The cause and preventive measures of Gelin column fracture
Gelin column fracture is due to the inequality of clamping.
Adjust clamping parallelism to prevent Gelin column fracture.
- How to test clamping parallelism and what’s the adjustment method?
Test: measure the stretched length of Gelin column when clamping by four dial indications to see whether it is in the tolerance.
Adjust: adjust the Gelin column nut to adjust clamping parallelism.
- Cause and treatment of scream when melting the plastic
The scream when melting is due to friction between the screw and the material or the screw and the barrel.
Polish or electroplate the screw, so that a smooth surface will reduce friction; adjust the screw centrad to avoid the friction with the barrel.
Posted in Injection Moulding
September 20 2010, 9:40 PM
PVC Plastic and Pipe Fitting Mould
PCV (Vinyl Chloride), especially rigid PVC, is the most widely used plastic materials. It is mostly used in pipe fittings. Accordingly, there are many pipe fitting and pipe fitting mould suppliers. But producing pipe fittings or pipe fitting mould is not easy, content below will tell you the reasons.
PVC has an amorphous structure with polar chlorine atoms in the molecular structure. Having chlorine atoms and the amorphous molecular structure are inseparably related. Although plastics seem very similar in the context of daily use, PVC has completely different features in terms of performance and functions compared with olefin plastics which have only carbon and hydrogen atoms in their molecular structures. And PVC materials are often added stabilizers, lubricants, auxiliary processing agents, pigments, anti-impact agents and other additives.
PVC materials have Chemical stability because of its chlorine atoms. Furthermore, it own fire retarding properties, high strength, resistance to climate variability and excellent geometric stability.PVC has superior fire retarding properties due to its chlorine content, even in the absence of fire retardants. And the heat released in burning is much lower than PE, and PP. Therefore, in the terms of safety, PVC is very suitable for people’s daily lives.PVC have a nice resistance to climate variability .Under normal conditions of use, resistance to oxidation by atmospheric oxygen is the primary factor to judge whether it’s durable or not. PVC is highly resistance to oxidative reactions because of the chlorine atom. In addition, PVC have a strong resistance on the reductant and acid.
- PVC process
The melting temperature of PVC is a very important process parameter in the processing time. Incorrect parameter set will result in material decomposition. PVC have very poor flow characteristics and a very narrow scope of its technology. In particular, high molecular weight PVC material more difficult to process (this material is usually added to improve the flow characteristics of lubricants), so commonly used are small molecular weight PVC material. PVC’s shrinkage rate is very low, generally 0.2 to 0.6%.
- Injection Moulding process conditions:
Drying: Drying is usually not required.
Melting temperature: 185 ~ 205C
Die temperature: 20 ~ 50C
Injection pressure: can be as large as 1500bar
Holding pressure: can be as large as 1000bar
Injection speed: in order to avoid material degradation, the general use of the injection speed must be considerable
Runner and the gate: all of the conventional gate can be used. When processing of smaller components, it’s better to use pin-point gate or submarine gate; for thicker parts, it is best to use fan-shaped gate. The minimum diameter of the pin-point gate or submarine gate should be 1 mm; fan-shaped gate thickness can’t less than 1mm.
- Typical uses
water supply pipes, home pipes, housing wall panels, business machine housing, electronics packaging, medical devices, food packaging.
Sino Mould Co., Ltd, a professional pipe fitting mould manufacture, is good at producing PVC pipe fitting mould. And SINO MOULD keened on moulds structures developing and innovating. They produce pipe fitting mould with collapsible cores, pipe fitting mould with curve sliding cores, pipe fitting mould with unscrewing cores, pipe fitting mould with normal mechanical or hydraulic direct sliding cores and so on.
(edit by firstname.lastname@example.org)
September 12 2010, 10:54 PM
Thin wall Injection Molding
Thin wall Injection Moulding has requirements on injection moulding machine, mould, and plastic. This article discusses the thin wall's characteristics, economic benefit, and device's design.
What's the thin wall?
In a simple view, when the wall's thickness is less than 1mm, it is called thin wall. More comprehensively,the definition of thin wall is related to the procedure /thickness ratio, the plastic viscosity and the heat transfer coefficient.
Mahishi and mabney make a definition on the thin wall like that the injection whose L/t=100 or more than 150 is called thin wall injection moulding. L procedure from the mould's sprue to the farthest point of the product, and t stand for the product's thickness t. L/t is called the procedure /thickness ratio.
Why we need thin wall injection moulding?
The cost of plastic is always in the majority of product's cost, such as 50-80%. Thin wall injection moulding will reduce the cost. Due to consumptive electronic equipments such as cell phone,MP3,digital camera, palmtop computer, are smaller and more convenient, the related plastic parts are thinner.
Thin wall injection moulding machine.
Conventional injection moulding machine is difficult to be useful in the thin wall injection moulding. For example, the injection time of thin wall injection moulding is very short, it is unable to follow the speed curve in such a short period time. Therefore, an injection moulding machine with high-resolution MCU is necessary. In the whole thin wall injection moulding process, the pressure and the speed should be controlled independently. While conventional injection moulding machine is controlled by speed in the injection period and pressure in the holding period.
The barrel of thin wall injection moulding machine is smaller than it in conventional injection moulding machine. Because the thin wall products need less plastic materials, so if the barrel is as big as the usual one, it will result in the material's dissociation due to the long residence time. And each inject 35%-75% of the maximum injection volume is the best. It should be cautious to choose a thin wall injection moulding machinery company. DAKUMAR is a good choice.
The mould in thin wall injection moulding
The mould for thin wall injection moulding should be designed specially. The mould's structure, feed system, cooling system, venting system, and ejection system are all may change a lot.
- Mould structure
In order to withstanding high pressure when moulding, thin wall injection moulding mould must have a large rigidity and a high intensity. So the bottom clamp plate , the top clamping plate and the support plate should be thicker than conventional mould. There are more locking and positioning mechanism in the mould to ensure the accurate positioning and good collateral support, and avoid bending and offset.
- Feed system
When forming thin wall plastic product, especially the thickness of thin wall plastic product is very small, edge gate is necessary, and the gate should bigger than the wall thickness. If the gate is direct gate, it should set slag well to reduce gate stress and help filling, and ease the damage when wiping off the gate in the same time. In order to ensure the enough pressure to filling the cavity, it should be to minimum the pressure drop in the runner system as far as possible, and the runner pressure drop should not upper than 15% of the pressure offered by injection machine. Therefore, the runner sectional area should be designed bigger than the usual one, and limiting the residence time of melting materials to avoid plastic dissociation.
Some feed system in thin wall injection moulding mould imports hot runner technology and sequence valve gate (SVG) technology. The hot runner technology enable the melting plastic provide high pressure at the gate after through a long path. However, the hot runner is easy to result in plastic degradation and degradation in a high temperature for a long residence time, so the residence time must be limited. SVG technology is a new class type hot runner control technology developed by U.S.,GE in the process of thin wall injection moulding. SVG can reduce moulding pressure efficiently. It plays an important role in producing large thin wall injection moulding plastic.
- cooling system
Thin wall injection moulding plastic, unlike the conventional thin wall plastic, can't withstand the large residual stress which is created due to nonuniform heat transfer. In order to ensure the plastic dimension stability, and control the shrinkage and warpage in an acceptable range, we must strengthen the mould cooling to ensure the cooling balance.
- venting system
thin wall injection moulding mould generally requires a good venting, it's best to operate in a vacuum. The mould's abundant venting, especially the venting in the flow front gathering area, is very important to prevent trapped gas ignition because of the short injection time and high injection speed.
- ejection system
Thin wall injection moulding plastic's wall and tendons are thin, they are very easy to damage, the contraction along the thickness direction is small, and the high holding pressure make it to shrink smaller, these make the tendons and other small structure easy to glue. Thin wall injection moulding requires more and larger ejection pins when compared with conventional injection moulding.
Posted in thin wall injection
September 3 2010, 5:08 AM
Plastic Cap Or Aluminum Cap, which one is better
Plastic anti-thef caps is light and easy to open. Using it in the beverage packaging, is not only convenient for consumers, but also speed up the development of the beverage industry. Many enterprises has imported foreign equipment, plastic cap began mass production and application. However, aluminum cap is still widely used. Even some wine enterprises invested in 35% of the cost in aluminum caps.
Previously, the main material of anti-thef caps is aluminum. But since the mid-90s Coca-Cola used the Plastic cap instead of aluminum cap, Plastic Cap has been pushed to the front of beverage packaging. Plastic cap or aluminum cap, which one is better?
At present, the liquor, the wine and the medicinal liquor’s bottle cover are mostly made with aluminum. This is because grass bottles are used in these fields. By using hot forming process, there are large errors in the aperture size. But using can achieve the relatively high seal. In the terms of the raw material, the cost of aluminum is lower than the plastic (an aluminum cap cost the half of an plastic cap), and anti-thef cap’s structure is very complicated, the current production lines in wine industry are designed for installing aluminum caps, if replaced by plastic caps, it will not only the cost of raw materials, but also has a series of problems about change production lines, bottle, cap re-design and so on. Therefore, companies are not willing to cost energy and financial resources. What’s more, the aluminum anti-thef cap is finished with high-quality aluminum alloy. It has superior performance, and can be mechanized, mass production, and no pollution, and can achieve 100% recycling, and also can meet special requirements such as high-temperature steam sterilization. In addition, aluminum cap tend to replace the cork because of the unnecessary of special open tool, and it has got many wine companies favor.
Plastic cap can’t be close to the thermal forming grass bottle, so it’s difficult to achieve a higher seal. As the plastic cap is easy to absorb the dust in air, and the debris created when welding is difficult to eliminate, there is no complete solutions to avoid the plastic debris and dust to pollute the wine. Meanwhile, some plastic cap producers doped material which is not environmental to reduce the cost. It can’t protect the health and the safety of consumers. But the plastic cap is not nothing. The structure has the capacity of anti-intrusion, surface treatment is varied, it has a strong three-dimensional sense, unique modeling and is easy to open.
Whether aluminum cap or plastic cap, each one has its own advantages and disadvantages. Expert said that in a long period of time, aluminum is still the preferred one in the anti-thef cap industry.
Since the mid 90s, Coca-Cola has produced PET bottled drink. They use plastic cap replaced aluminum cap. Since then, plastic caps have been used in drink industry more and more widely. The industry believes that technological innovation has become a driving force for the rapid development of Plastic Cap. And sometimes, the role of plastic in the bottle can not be replaced. Because of a survey, people prefer the plastic cap with its strong security and easy open process. Many businesses find that a small plastic cover is huge market.
The expert said that the replacement of the bottle’s materials will bring more choices of caps. Recently there have been two companies to develop a suitable high-capacity high-density polyethylene plastic bottles of high sealing screw cap. This cap can pull ring with plastic sealing film, consumers do not rotate when the lid open, you can remove the cover, then pull the ring in the bottleneck of the film, you can open the bottle. According to reports, this new lid sealing, have anti-theft feature, and cost less than aluminum closures, and no need to purchase special sealing equipment, will be able to adapt to the existing bottle plant. Survey, 80% of consumers choose such a cap.
|Last update||Oct 17, 2010|