What are the common defects in thermoplastic products?

A. Appearance quality: including integrity, color and gloss;

B. Dimensions and relative position: in line with product drawings and assembly requirements;

C. Mechanical properties related to use, chemical properties: such as tensile test, impact test, environmental resistance test, etc.

2. Reasons for product defects:

A. Plastic problems: including plastic quality ingredients and baking materials;

B. Tuning problems: including injection pressure, temperature and cycle;

C. Mold problems: including mold design, manufacturing and wear. The mold problem is the most common and difficult problem to solve.

III. Analysis and solutions of common defects of products

1. Insufficient filling (short shot): The beer parts are incomplete, or the individual cavity beer is not full when there is a multi-cavity.

(1) Improper adjustment of feed, lack of material or more materials;

(2) Insufficient injection pressure, temperature and time;

(3) The material temperature is not enough;

(4) The mold design is unreasonable: the flow path is too long, the turning is too much; the exhaust system is bad; the flow path cold well is not enough; the multi-cavity mold cavity is too many, the ranking is wrong, the gate position, form is wrong or the quantity insufficient. The water transport design is unreasonable.

2. Flash (film, flash): excess thin wings appear on the edges of the plastic products, the joints of the inserts and the thimbles.

(1) The mold manufacturing precision is poor;

(2) The mold design is unreasonable:

-- Unreasonable ranking and unbalanced pressure;

- improper position of the gate, causing one side to lack material, while the side is out of the front;

-- The locking force of the line is not enough.
- The mold is poorly exhausted, and the parting surface is opened under high pressure.

(3) The locking force of the beer machine is not enough;

(4) Improper adjustment: the pressure is too high, the temperature is too high and the feeding amount is too large.

3. Silver streak (commonly known as water splash, silver streak): the surface of the bubble is broken. When the plastic is filled with too much water vapor, decomposition gas, solvent gas and air, the surface of the product forms a series of silver-like needle-like or mica flakes along the flow direction.

(1) Water vapor.

(2) Decomposition gas: high material temperature, poor plastic quality and excessive shearing force.

(3) Plastic is not pure.

4, shrinking depression (sink mark): the surface of the plastic part due to internal shrinkage caused by pits. The main reasons are poor pressure retention, uneven cooling, excessive wall thickness or bone width, and no preheating of the insert.

Solution:

(1) The wall thickness should be as uniform as possible.

(2) Strengthening cooling in thick-walled parts.

(3) The design of the gating system should be reasonable:

A. The size of the gating system should be compatible with the size, wall thickness and complexity of the rubber parts;

B. The gate responds to the wall thickness and easy to shrink.

(4) Adjustment aspects

A. Increase injection pressure, holding time and injection time;

B. Increase the injection speed

5. Weld line (weld line): When the melt glue is merged, the temperature of the material is lowered, resulting in poor joint welding, trace or strength reduction. The method of reducing or eliminating weld lines is basically the same as shrinking dents.

When the weld mark cannot be eliminated

a. The position of the gate and the wall thickness of the part can be changed to guide the weld mark to a position that does not affect the appearance.

b. An overflow well is opened near the weld line.

6. Transparent parts defects:

(1) Bright spots, silver streaks and cracks:

1) Eliminate pollution <including moisture>,

2) Reduce the material temperature, adjust the section,

3) increase the injection pressure;

4) Improve the flow path and cavity exhaust;

5) shorten the molding cycle;

6) If it has been produced, it can be eliminated by annealing.

(2) Poor surface gloss:

A. The cavity core is not polished well;

B. The melt is prematurely cooled and hardened, and the excellent finish of the die face cannot be completely reproduced;

(3) Shock pattern <ripple>:

A. Increase the barrel temperature, especially the nozzle temperature, and increase the injection pressure and speed;

B. Increase the mold temperature;

C. Improve the exhaust to increase the flow rate.

(4) Whitening, halo: Eliminate water vapor; increase material temperature and mold temperature; increase injection pressure and back pressure.

7. Warpage:

1> Product design problems: uneven wall thickness and unreasonable structure.

2> When designing the mold:

a, the size and form of the gate should be reasonable;

b. The cooling of each part of the mold should be uniform.

3> Plastic varieties: Crystalline plastics (PE, PP, PA, POM, etc.) shrinkage rate is much larger than amorphous plastics, solidification is fast, and the parts are easy to warp and deform;

4> Tuning:

(1) The material temperature should not be too low or too high;

(2) increase the injection pressure, time, speed;

(3) Guaranteed pressure holding time;

(4) After demolding, use a clamp to shape or temper.