Dear customer, thank you for using our brand material - Jialixin PP material. All our modified materials are based on new materials, and the production process and quality monitoring of the materials from sample delivery to mass production are all managed using the ERP system. If you have any unpleasant experience using our materials, please contact us in a timely manner, and our technical team will fully cooperate.

一、 Forming process

1. Barrel temperature: When the injection pressure and injection speed are low, a lower barrel temperature can be selected. Generally, the temperature of the material barrel is controlled at 190~210 ℃, and the temperature of the nozzle is 10~30 ℃ lower than the temperature of the material barrel. When forming thin-walled and complex plastic parts, the higher the temperature of the material barrel; When the plastic part is thicker, the lower the temperature of the material barrel.

2. Mold temperature: PP has a strong crystallization ability. Increasing the mold temperature helps to increase crystallinity and also helps to relax macromolecules, reduce molecular orientation, thereby reducing internal stress of the plastic part and reducing defects such as material shortage and bubbles. In production, the mold temperature is often adjusted to 20-60 ℃.

3. Injection pressure: During injection molding, increasing the injection pressure is beneficial for increasing the fluidity of the melt. The injection pressure of the plunger type injection molding machine is higher than that of the screw type. The general control is between 70-100MPa, and the specific value is determined by the trial mold, based on the absence of material shortage, overflow, dents, and bubbles in the plastic part.

二、 Barrel temperature

Feeding area: 30-50 ℃ (50 ℃)

Zone 1: 160~190 ℃ (200 ℃)

Zone 2: 190~200 ℃ (220 ℃)

Zone 3: 190~200 ℃ (220 ℃)

Zone 4: 190~200 ℃ (220 ℃)

Zone 5: 190~200 ℃ (220 ℃)

Nozzle: 190~200 ℃ (220 ℃)

Melt temperature: 190~220 ℃

Material barrel constant temperature: 220 ℃

Mold temperature: 20-70 ℃

Injection pressure: With good flow performance, avoid using excessively high injection pressure of 80-140MPa (800-1400bar), except for some thin-walled packaging containers, which can reach 180MPa (1800bar)

Maintaining pressure: To avoid wall shrinkage of the product, it takes a long time to maintain pressure on the product (approximately 30% of the cycle time); Approximately 30% to 60% of injection pressure

Back pressure: 5-20MPa (50-200bar)

Injection speed: High injection speed (with accumulator) is required for thin-walled packaging containers, and moderate injection speed is often more suitable for other types of plastic products

Screw speed: High screw speed (linear speed of 1.3m/s) is allowed, as long as the plasticization process is completed before the end of the cooling time is met

Metering stroke: 0.5-4D (minimum to maximum); It is important to provide sufficient dwell time for the molten material with a 4D metering stroke

Pre drying: Dry at a temperature of 80 ℃ -90 for 4 hours to 2 hours

Shrinkage rate: High degree of shrinkage (1.2-1.8%), no further shrinkage after 24 hours (shrinkage after molding)

Machine downtime: We need to use materials recommended by our company for specialized cleaning work;

三、 Reasons and troubleshooting steps for defects in injection molded products

Dents

Dents mostly appear in areas where materials accumulate, and are plastic shrinkage marks caused by the failure to compensate for pressure loss in injection molded parts.

1. The principle of dent formation:

During the cooling process of plastic, thermal effects cause natural shrinkage of the plastic. If these contractions are not compensated in a timely manner, shrinkage marks (dents) may appear in some parts of the plastic product. Due to insufficient cooling, the internal stress generated when the surface of plastic parts is cooled before it stabilizes is pulled inward.

2. Possible causes of dents formation:

The three main reasons for defects are: 1) slow solidification rate. 2) The effective pressure holding time is too short. 3) Due to the high resistance of the molten material flowing in the mold cavity, or the narrow position of the injection molding components and gate system, there is not enough pressure to transmit to certain parts of the mold cavity.

3. Steps for checking dents:

Check whether the remaining amount of molten material padding is too small or the molten material amount is unstable. Measures: Increase the storage stroke, check the check ring or barrel, and check the transportation process of raw materials.

Check whether shrinkage marks (dents) appear near the gate or in the thick position of the injection molded part. Measures: Increase holding time, increase holding pressure, improve sol temperature, improve injection speed, and improve mold wall temperature.

Check whether shrinkage marks (dents) appear far from the gate or in a thin position on the injection molded part. Measures: Optimize the holding time, increase the holding pressure, increase the sol temperature, accelerate the injection speed, and increase the mold wall temperature.

Inspection: Whether there are shrinkage marks (dents) immediately after the injection molded part leaves the mold cavity. Measures: Check the exhaust, check the size of the main flow channel and gate, use a flow acceleration groove, check the state of the material particles, remove the accumulated rubber material, and use materials with low shrinkage rate.

If the inspection does not meet items a, b, c, and d, extending the cooling time can solve the problem.

Speckled mark

Spots can be divided into burnt marks, air marks, color difference marks, glass fiber marks, etc. They look very similar, but it is difficult to distinguish them with the naked eye. If similar marks appear, our company needs to obtain relevant information of injection molded parts to evaluate the types of spots. The following are the judgments, causes, and troubleshooting steps for some traces proposed by our technical department.

1. Air trace characteristics

Most air marks are prone to extinction, with silver and white marks appearing in recesses, reinforced ribs, and areas with significant thickness changes. Layered marks will appear at the starting point of the glue inlet, and air marks will also appear at the lettering or depression.

2. Formation of air marks

When the molten material is filling the mold cavity, due to the failure of the gas to be discharged in a timely manner, it is instead supported and pressed on the surface of the injection molded part along the flow direction, especially in the lettering, reinforcing ribs, semicircular spheres, and concave areas. The gas will be trapped by the molten material passing over the front, forming gas marks.

3. Investigation of Air Traces

Check if there are any air ducts. Measures: Cooperate with the injection speed, modify the sharp edges at the transition position, and change the depth of the engraved characters.

Check whether the air mark is close to the gate. Measures: When releasing pressure, the rotation speed of the screw should be reduced, the release pressure should be reduced, and a stop valve should be used.

Check if there are bubbles in the plastic sol material. Measures: Increase the driving pressure, check the material usage and transportation situation, and increase the amount of plasticization.

If not a, b, c, or above, the following measures need to be taken:

① Matching injection speed

② Provide sufficient scheduling

③ Modify sharp edges at transition positions

④ Changing the Gate Position

⑤ Check the sealing performance of the nozzle

Chromatic aberration mark

1. Color difference mark features

Color difference marks are caused by uneven distribution of component coloring or differences in the arrangement of colorants and the direction of sol flow

2. Formation of color difference marks

During the coloring process, uneven mixing occurs due to the rapid formation or aggregation of color masterbatches or pigments, resulting in poor color distribution and the formation of color difference marks.

If color mixing is carried out on site, color difference marks often occur due to the inability of the dyed material to fully blend with the granular material.

Similar to thermoplastic plastics, both color masterbatches and pigments are highly sensitive to high processing temperatures and prolonged residence times. If thermal damage is the cause of color difference marks, it is necessary to first deal with burnt marks.

D Excessive stress in injection molded parts, such as stress caused by excessive demoulding force or distortion, will also cause color difference. Because in the deformed area, the light condition will be different from other places, resulting in visual differences.

3. Investigation of color difference marks

Check whether the processing range of plastic can withstand high shear forces. Measures: Improve the mechanical solubility of plastics. Increase pushing pressure and speed. Increase injection pressure. Use fine gates and sprues.

Glass fiber mark

1. Characteristics of Glass Fiber

When using glass fiber reinforced materials, there may be dull surface marks and rough surfaces, such as spots formed by metallic reflective glass fibers on the surface of injection molded parts.

2. The reasons for the formation of glass fibers

Due to the slender shape of glass fibers, their arrangement direction during the injection molding process is affected by the injection flow direction, which is consistent with the flow direction of the adhesive material. If the adhesive suddenly solidifies when it comes into contact with the mold wall, some of the glass fibers will not be able to be sealed. In addition, the surface of injection molded parts may become rough due to the significant contrast in shrinkage between glass fiber and plastic. Due to the glass fiber hindering the shrinkage rate of plastic during cooling, the surface of injection molded parts is uneven.

3. Inspection of glass fiber marks

Check: Can the injection molding process be optimized. Measure: Provide injection molding speed. Increase the mold wall temperature. Increase the temperature of the molten material. Optimize the holding time. Increase the holding time.

Check whether glass fiber marks appear near the fusion line. Measure: Change the gate position (guide the fusion line to an inconspicuous position)

Fusion line

1. Fusion Line Features

In most cases, the fusion line is the location where the optical performance and mechanical strength of injection molded parts are relatively weak. There may be gaps or discoloration on the fusion line. The gap is particularly noticeable on dark or smooth transparent injection molded parts or injection molded parts with high polishing brightness.

2. Formation of fusion lines

When two or more molten streams meet, a fusion line is formed. When encountering other molten flows, the curved flow ripple summit is flattened and bonded with other molten flows. During this process, the high viscosity flow peak will be stretched. If the temperature and pressure at the fusion joint are insufficient, it will be difficult to fill the corners of the front section of the fusion. On a smooth surface, the gaps along the fusion line can be clearly seen, while on a structural surface, there will be differences in gloss at the edges of the fusion line. In addition, the position of the fusion line interface is not single-phase fusion, which can lead to the formation of fragile points.

3. Troubleshooting of fusion lines

Check whether there are any gaps or differences in gloss at the fusion line position. Measure: Increase the mold wall temperature. Change the injection molding speed. Increase the melting temperature. Optimize the holding time. Increase the holding pressure. Change the gate position.

Check whether there is color difference at the fusion line position. Measure: Use smaller color masterbatches. Change the gate position.

Inspection: The strength of the fusion line is not sufficient. Measures: Increase the melt temperature and holding time. Increase the mold wall temperature. Add a flow channel at the fusion line position. Change the gate position.

Bubble

Process adjustment:

1. Increase the holding pressure.

2. Extend the pressure holding time.

3. Increase the mold wall temperature.

4. Reduce the melt temperature.

Design improvements:

1. Increase the cross-sectional area of the gate and shorten the rubber channel.

2. Increase the nozzle hole.

3. Open the glue inlet in the thick wall area.

Product adhesive mold

1. The gate size is too large, the material temperature is too high, or the injection pressure is too high.

2. The injection time parameter is set too long.

3. The cooling time parameter is set too short.

4. The surface of the in-mold product has not cooled and hardened or the mold temperature is too high

We are still working hard to integrate and certify more defects, and constantly update them. The successful injection molding of plastic products is achieved through a series of system engineering. The production of a qualified product seems simple, it only takes more than ten seconds to produce a the first mock examination, but it needs efforts from all aspects to adjust and produce qualified products. The basic indicators of raw materials, injection molding machines, process parameters, plastic molds, and auxiliary equipment need to be coordinated in order to make plastic raw materials into qualified products that meet the requirements