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Quality failure analysis of plastic bottle cap during processing
Feb 11, 2018

Quality failure analysis of plastic bottle cap during processing.

Plastic bottle cap is a commonly used package in bottle packaging, especially in the field of beverage.Generally, polyolefin is the main raw material, through injection molding, hot pressing and other processing molding.However, in the process of processing, there are many kinds of quality problems, such as the lack of materials and the overflows etc., due to various reasons such as process, mold, equipment and materials.In this article, we will solve the problem of two aspects, namely, the overflows and the lack of materials.

Overflows 1

This is the quality term used in the plastics industry. It refers to the useless part of the product at the edge of the product.The plastics industry is sometimes referred to as burrs, frills, and overflows.

1.1 process factors

(1) the filling pressure is too high and the speed is too fast, which can cause the expansion mold, which leads to the situation of overflow. The filling pressure and speed should be reduced properly, or the melting temperature should be reduced to increase the viscosity. 

(2) the pressure protection pressure is too large, the plastic is forced condensation, there will be a large residual stress, so that the strength decreases, and there is a possibility of the overflow situation, the pressure should be reduced properly. 

(3) the temperature of the material tube or the hot runner is too high, the viscosity of the melt is reduced, the fluidity is too good, the temperature can be reduced properly, or the injection pressure can be reduced appropriately. 

(4) the mold temperature is too high, not only will there be a cover, but also the defects such as product deformation, which can be adopted to lower the temperature of the chiller or increase the water channel, and reduce the mold temperature. 

(5) improper injection switch position, large switch position or small dosage.

1.2 equipment factors

(1) internal leakage of the machine lock cylinder should be overhauled and replaced with oil seal.

(2) the columbine is not parallel, and the fixed plate and movable plate are not perpendicular to the movable plate and the copper sleeve is worn, and the parallel degree of the machine and the connecting rod copper sleeve should be adjusted.

(3) there is not enough clamping force in the machine, so that there is a gap in the parting surface, and the mould should be adjusted to increase the clamping force.

1.3 mold factors

(1) the vent is too thick and should be reprocessed.

(2) the sliding block is not in place and should be repaired or replaced with the bolt and slider to improve the accuracy. 

(3) improper installation of the die insert, reinstall the inserts and adjust the matching accuracy between the inserts.

(4) the flow path is not balanced, and the hot runner and impurities should be removed from the mold to balance the flow path and use clean raw materials.

(5) the mold inserts are damaged, and the inserts should be repaired and replaced.

(6) the inserts are filled with glue, and the mold is repaired to reduce the clearance between the mold inserts, or the filling switch position increases the dosage to reduce and reduce the pressure and speed of pressure protection.

(7) the mold core and cavity and each insert shall be in poor cooperation with each other. Repair the mold to reduce the gap between the mold core and the cavity and the inserts.

Material lack 2

The lack of material is the partial incomplete phenomenon at the end of the material flow or incomplete filling of a part of a cavity, which usually occurs in a place far away or thin section.

2.1 technological factors

(1) the filling pressure is too small and the speed is too slow. During the injection molding process, the cavity pressure is insufficient due to the pressure loss, and the melting material is difficult to fill the entire cavity.

(2) the injection time is too short, the melt is not filled with the cavity, the injection process is finished, and the injection time can be extended appropriately or the infusion speed can be increased.

(3) the mold temperature is too low, the flow resistance of the molten material increases, the flow rate slows down, and even in the flow path, the gate or the mold filling, it is not easy to fill the cavity.The temperature of the chiller can be adjusted to increase the mold temperature.

(4) the temperature of the feeding tube or the heat flow channel is too low, which will affect the fluidity of the molten material, which can easily lead to insufficient mold filling, which may increase the temperature appropriately or increase the injection pressure.

2.2 equipment factors

(1) the nozzle is blocked, which affects the material, should clean the nozzle and use clean raw materials.

(2) the injection oil cylinder is discharged, and the injection oil cylinder is repaired and the oil seal is replaced.

(3) the nozzle leakage should be adjusted to the center of the machine and the center of the mold or to replace the nozzle.

2.3 mold factors

(1) the mold exhaust is poor, and the air in the cavity can not be discharged in time, resulting in insufficient filling, which can reduce the filling speed properly, or reduce the mold release and clamping force, or increase the vent hole. 

(2) the mold design is not reasonable, modify the position of the injection gate of the mold, and increase the injection gate or mold reducing meat.

(3) the inserts are loose and tighten the insert screws.

(4) the hot runner is not balanced or the hot runner is blocked, resulting in the flow of molten material, which can be used to adjust the heat flow temperature and adjust the flow path or the cleaning rubber of the product, and use clean raw materials. 

(5) the thimble is not returned, the effective filling space is reduced, and the top pinhole should be polished and the thimble should be replaced.

(6) the silk tube is not returned, and should be polished or replaced.

Guangzhou Jeepine Intelligent Compression Molding Machine Co.,Ltd have the powerful cap compression molding machine manufacturing team,While guaranteeing the production and quality of the bottle cap making machine, we will devote a lot of energy to research and development, and continue to share the technological achievements with the main bottle cap making factories.

Jeepine plastic cap compression moulding machine’s Advantages:

Main machine Feature: 

A.Rotary muti compression molding process and advanced hydraulic system bring the highly stable and accurate production

B.Muti-cavity continuous high speed rotation, short cycle time, and high production efficiency

C.Low energy consumption in heating and cooling process.No hot runner, save energy effectively

D.No raw material wasted in spilling and hot runner circuit, Every single granule of raw material is fully used

E.Safe machine door interlock,emergency stop switch,rigid machine housing, U/L certified

D.Fully automatic in line production, no hand touching, avoid contamination

Compared with injection moulding machine and other plastic closure making machine manufacturers,Jeepine’s plastic closure compression molding machine have the following advantages:

Plastic closure Compression molding technology as a well known technology around the world in plastic closure production.

Energy saving

Less Energy Consumption,Overall energy savings per cap can be as high as 45%.

Because plastic closure compression moulding machine need lower heating temperature,which means less energy consumption in both heating and cooling.

High specific density and less shrinkage

Equal molding pressure, lower molding temperature allows the result of a higher density. Furthermore, less heating and cooling temperature gap accomplish less shrinkage of caps.

Quick color changeover without hot runners,only with the extruder.

Shorter cycle time (2 seconds) and therefore higher productivity

Due to lower extrusion temperature, caps are more quickly to be cooled down 

in mould.It makes shorter cycle time, thus capacity rises.

Easy and flexible maintenance 

Independent molds make it easier to change molds, only with hand tools but not crane.

Less material waste    

Advantages of compression cap mold:

1.High Quality 

The major cap mold material has excellent wear resistance, high

corrosion resistance and high machinability, high coating hardness

2. High Precision 

All the molds can precisely meet the dimension tolerance of cap


Jeepine has professional manufacture equipment, dedicated to

mold design and development, absolutely cope with your needs

Guangzhou Jeepine Intelligent Compression Molding Machine Co.,Ltd 

Address:C4 Building of Scientific&Technogical Enterprise Accelerator,11# Kaiyuan Avenue,Science Town of Luogang Development Zone,Guangzhou,China