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What are the factors affecting the process quality of the Blow Molding Machine?

Views: 1     Author: Site Editor     Publish Time: 2022-08-23      Origin: Site

The factors affecting the quality of the blow molding process are bottle blanks and their heating, pre-blowing (position, pressure, and flow), stretching bar, high-pressure blowing (pressure, position) and molds, etc.

Blow Molding Machine

1. Bottle blank


Bottle blanks, also known as type blanks, are generally formed by Injection of PET pellets, which requires that the proportion of recycled material should not exceed 10% and the number of recycling should not exceed twice. The bottle blanks after injection molding or reuse after heating must be cold, the period can not exceed 6 months, different production dates, especially the interval is too long to mix the bottle blanks, the main reason is the type of raw materials used in the bottle blanks, mixed with the proportion of secondary materials and residual stress in the bottle blanks caused by different, and these should be treated according to the actual situation.


2. Heating


The preform heating is usually done by the heating furnace, which is set manually and adjusted automatically. The height of the heating furnace is about 25mm, about 19.6mm from the conveyor wheel. The bottle billet is continuously running on the conveying wheel through the whole baking well into shape, overcoming the shortcomings of the previous static heating of the bottle billet and uneven heating by manual rotation. However, improper adjustment of the heating furnace will cause uneven distribution of the wall thickness of the blown bottle up and down (such as the top light and bottom heavy), and the bottle mouth becomes more significant than the torsional failure of mechanical parts.


The bottle blank heating temperature is generally set at 85-120 ℃, with colorless bottle blanks being higher with color bottle blanks being lower. Temperature setting too high or too low can cause product defects, such as pulling through, white mist, etc. At the same time, the temperature of each area should consider the oven lamp opening situation. In addition, the setting of the output power of the oven has a significant influence on the heating of the bottle blank, which controls the output of the whole oven heat.


When the machine is not turned on for a long time, when it is turned on again, the initial production process is then gradually reduced to the normal state. The appropriate output power is generally about 80%, especially when the ambient temperature is below 5 ℃, the effect is more significant.


The blowing production process and production environment temperature also have a special relationship. The ambient temperature is generally room temperature (about 22 ℃) appropriate. The products are prone to condensation point caking if the temperature is too high. The temperature is too low. The machine starts when the product needs to be adjusted to the nature and experience.


3. Pre-blowing

The role of pre-blowing in the blowing process is to make the initial shape of the bottle, while the longitudinal stretching by the stretching bar increases its longitudinal strength. The whole process is a pre-blowing cam in the blowing process to push the three-way valve to the pre-blowing position, and by and flow can affect the quality of the bottle.


Pre-blow position in advance, there will be defects such as skewed and thinning of the bottom center point of the bottle, uneven and whitish wall thickness at the foot, top-heavy and bottom-light, rigid neck, and even bottom penetration.


Pre-blowing position after the wrong, it will appear on the light under the airflow pre-blowing gas flow is controlled by a one-way valve, generally open 3-4 turns is appropriate. Gas flow is large, the bottom-heavy, the center point is thin, partial, the foot is white, wall thickness is not uniform; gas flow is small, the center point becomes thick, segmented pieces of heavy overpressure pre-blowing gas pressure in 0.8-1MPa is appropriate. When the pressure is high, it may cause the top-heavy under the light. The center point is skewed, an uneven wall thickness of the foot, whitening, etc.; low pressure, can not be fully stretched, the bottom-heavy, thick center point The bottle foot, the center point of the molding situation on the bottle quality has the most significant impact, improper adjustment often causes burst bottles, leakage, and other fatal defects.


4. Stretching rod

The stretch rod is in the pre-blowing at the same time as the pre-blowing gas with the heated bottle blank stretching device, which is reset after high pressure blowing before exhaust. The stretching rod must be able to blow the bottle in the process of vertical and smooth movement, drive gap of 2.3-2.5mm, that is, the thickness of the billet 1/3-1/2. The gap is too large. It will cause the bottom of the bottle's center point to shift; the gap is too small, and the center point thinning.


5. High-pressure blowing

The role of high-pressure blowing is to make the melt fully extended, close to the mold wall, so that the bottle is fully formed, while the transverse stretching improves its transverse strength, the main factors affecting the location and pressure.


High-pressure blowing pressure is generally 3.7-4MPa, which is determined by its molding characteristics and the nature of the filled beverage (carbon dioxide). There are two locations, namely the location of the high-pressure gas and the location of the exhaust. The length between the two significantly impacts the stability of the bottle capacity. Insufficient high-pressure gas, easy to make the bottle improperly formed, the foot blowing insufficient, etc.


6. Mold

Mold is one of the critical factors affecting bottle blow molding. The bottle body for the Haff mold, the bottom of the bottle is independent, is a typical blow molding mold. Keep the constant mold temperature clean during the production process and vent holes open.


The bottleneck will be crooked when the mold heating and cooling system fails. The bottle will be tilted, the volume and height will change, and the bottom will become heavy and other defects; maintaining the mold constant temperature also prevents the mold surface from condensation.


PET shrinkage rate after molding is extensive, generally 1.8%, slightly reduced after adding glass fiber reinforcement, but up to 0.2%-1.0%. In general, a high mold temperature shrinkage rate is significant. To maintain the PET bottle capacity system, the low mold temperature shrinkage rate is minor. Generally require a slightly higher bottle temperature of 20-45 ℃. The bottom requirements are lower, 6-15 ℃. The high bottom temperature will make the bottom heavier and the center point thicker. Automatic Blow Molding Machine experts conclude a sentence, the actual production or the actual prevail.


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