Black spots directly reduce the yield, and is not easy to solve, is a common topic of injection molding industry. This article will take the TPU material mobile phone protection set of injection molding as an example, a brief discussion of TPU injection molding black spots to avoid and solve the method.

Thermoplastic polyurethane elastomer are generally referred to as TPU (thermoplastic polyurethanes), TPU has other plastic materials by the incomparable of many excellent function, because of its superior performance and the concept of environmental protection has attracted more and more welcome. TPU has been widely used in electronic and electrical appliances, health care, industrial and sports and other, used in the production of mobile phone protective sleeve, medical equipment, fitness equipment, shoes, toys, car seat materials and daily necessities. Data forecast, TPU 2013-2017 market size of the average annual growth rate of 11.2%, in 2017 the amount of consumption is expected to reach.

TPU because of its low viscosity, good resistance to flexure, excellent wear resistance, high gloss characteristics in recent years has become the main material of injection molding manufacturers in the production of mobile phone protective sleeve, but in the actual production TPU injection molding products appear the phenomenon of black spots are not uncommon.

The dark spots directly reduce the rate of finished products, and is not easy to solve, is a common topic in injection molding industry. This will be the TPU mobile phone protective sleeve material injection molding as an example, briefly discuss the TPU injection spot avoiding and solving method.

From polymer molding process explain the emergence of black spots in the physical reason is because TPU containing amino and amino activity is strong, in the molten state with viscosity, injection molding process, and screw feed tube contact the TPU raw materials for a long time retention cannot be injection barrel outside, after a period of time between the heat aging, charred decomposition, in the screw, material cylinders of carbon deposition, injection molding process in carbon are occasionally rub off, mixed with molten material, injection molding, resulting in product appears black spots.

In the actual production, to speed up the TPU raw material injection molding production of black spots, there are many reasons, mainly the following:
Workshop production environment is poor

The workshop environment dirty, dust and impurities in the entire manufacturing process links.

 TPU raw material is not pure

In order to reduce the cost, some manufacturers in the raw material infiltrated into many "Shuikou" secondary use, or different brands of raw brand messy mix, low-grade raw materials.
Injection molding machine operation is not standardized

This is divided into many aspects, one is the factors of the mold, the mold itself, such as the shape of the shape, thickness and other design. Now the mobile phone protective sleeve of more and more and more thin, as well as the production of 1 out of 2 or more cavity mold, manufacturers by increasing material temperature filling of the cavity, a long time yellow products and produce black spots, the improper selection of relatively low-end second customer choice of injection molding machine, or a machine, the machine itself capacity can not meet the molding conditions such as setting pressure, speed and other parameters.

Is related to the level of process debugging of the machine user.

Master machine has been the most common way to debug the machine.

User not good operating habits

For example, before the suspension of production, there is no planning to feed the raw material inside the injection of raw materials and put the machine to heat insulation state, raw materials for a long time to heat, resulting in yellow.

Injection molding machine lack of cleaning and maintenance

General continuous production TPU raw material injection molding machine best every turn a class to do a screw and barrel cleaning and maintenance, washing machine cost is not high, than not washing machine caused black spot and waste material costs low, but some manufacturers ignored this.

There are other causes of black spots, which often occur in a number of staggered. Often in the low-end product manufacturers due to cost savings resulting in these cases are more common. High end product manufacturers because of the high profit margins of products appear relatively few of these, they will strictly control the operating specifications, more understanding of the injection molding machine maintenance, and the use of plastic is relatively good.

The use of raw materials is a direct cause of black spots. TPU itself is not good temperature resistance, the nature of the raw material itself, the impact of the difference is more important. Some from Europe (materials such as Bayer (Germany) and Taiwan general than domestic production of the good, some even warmed up to 240 DEG C to 250 DEG C is not "paste", and domestic production of some raw materials, heating more than 230 DEG C, a little longer appear yellow and black spots.

And manufacturers received orders for products of different colors because of, frequent replacement of infiltration in the raw materials of toner, puts a great test of producing good injection molding parts. Used in processing the master summed up the experience: replace the toner follow the order from light to dark, Mr. producing transparent, light colored products, to the dark, black in the end and subsequent cleaning machine over transparent color products. Not in this order in the subsequent replacement of products color production will waste a lot of raw materials. At the same time, but also should pay attention to the temperature resistance of the toner, toner also led to some poor black spots also lead to black culprit.

In the manufacturer's production environment, quality of raw materials, mold and other factors can not change the situation, the design and use process of the injection molding machine itself, there are specialized solutions to solve the problems faced by customers.

According to the needs of the product, adjust the hardware parameters of the injection molding machine. Reducing the time of the raw material in the barrel and the screw rod to control the excessive production temperature, so as to reduce the carbonization of raw materials in the machine. Increase the injection pressure and injection rate, more easy to form. Specific methods are as follows:

1, to machine modified the simplest method is for a feeding tube group, appropriate to reduce the diameter of the screw, the raw materials remain in the barrel of a shorter time, such as the 38cm in the diameter of the standard of the UN120SK product screw screw diameter of 35 cm, also injection pressure enhance the 17%, more conducive to improving the forming of thin-walled products, this particular modification engineering cost difference between the two.

2, another way is to improve the injection speed of injection molding machine (increase the pump motor) and the mold cavity filled, do not raise the temperature of raw materials. However, the agent will be modified to a certain extent, improve the cost of the machine.

There is a small amount of the injection of the machine to change. The production of mobile phone protection sets of injection is generally less, change the amount of injection to reduce the raw material in the barrel, both to reduce the level of a radio station, but also need to modify the cost.

Two, according to the use of parameters design and production of TPU raw material specific screw, the design of the screw is more suitable for the production of TPU materials.
Three, the rational use of machines, the preparation of operational norms.

According to customer's production situation and the injection molding machine's performance, and the preparation of "TPU special machine operating specifications guidance" and "TPU material pipe group cleaning work instructions". "Guide book" does not recommend customers to increase the temperature of production, and recommends that customers on a regular basis to the injection molding machine, washing machines, to avoid prolonged heating of raw materials carbonization decomposition; to clean the machine's operating specifications listed steps.

Iraq's dense through closed-loop manner to solve the problem, customers in the selection of injection machine before buying clear understanding of customer production products, raw materials, and then design department choose the a the parameters meet the conditions of the injection molding machine according to the requirements, to ensure the quality of the injection molding machine parts and components, but also according to customer status, such as production process, die, and method of operation proposed solution to the overall program. Indeed, adaptation of a performance parameter of the screw on the production of will have greatly improved, at the same time, we think that is a very important premise to focus on process and operation standard, to avoid product appears black spots is entirely possible.

At present, the black spot problem of TPU production is not solved once and for all, again good machine also needs reasonable application method. Advise clients before the purchase of injection molding machine and production and processing to consult relevant professionals, to avoid losses caused by artificial selection and operating failures and make the management more standardized, production more smoothly, become more professional TPU production suppliers.