Analysis of Influencing Factors in Blowing Process of Blow Molding Machine

Blow molding machine preforms and their heating, pre-blowing (position, pressure and flow), stretch rods, high pressure blowing (pressure, position) and molds, etc. This is a key factor affecting the bottle making process of the blow molding machine.

Preforms, also known as parisons, are injection molded from polyester pellets. It requires no more than 10% of recycled materials and no more than two recycling times. The preforms that are re-used after injection molding or heating must be cooled for more than 48 hours, and the storage time of the used preforms shall not exceed 6 months. Different consumption dates, especially preforms that are too far apart, cannot be mixed. The main reasons are the different types of raw materials used by the blowing equipment, the proportion of mixed secondary materials and the residual stress in the preform. These factors have a serious impact on the molding process of the blowing machine, and should be dealt with in detail according to the actual situation.

The heating of the preform is completed by the heating furnace, which is manually set and automatically adjusted. A suitable height for the furnace is about 25mm and about 19.6mm from the conveyor wheel. The preform runs through the entire oven continuously on the conveying wheel, so that the preform is heated evenly and can be formed better, which overcomes the defects of uneven static heating and manual rotation heating of the preform in the previous bottle blowing machine. However, if the heating furnace is not properly adjusted, the defects of the product, such as uneven distribution of the wall thickness of the blown bottle (such as light and heavy), excessive expansion of the bottle mouth, and hard neck, etc. Will form, and even cause torsion problems in mechanical parts. The temperature of each zone can be adjusted in detail according to the molding of the product, taking into account the opening of the oven light. In addition, the setting of the oven output power has a great influence on the heating of the preform and controls the heat output of the entire oven. When you don't start it for a long time, when you start it again, the initial output power should be set higher accordingly, and then gradually decrease to the normal state during the normal consumption process. The output power is generally around 80%, especially when the ambient temperature is below 5, the effect is more significant.

The consumption process of bottle blowing is also related to the consumption environment temperature, which is generally room temperature (about 22). If the temperature is too high, the product is prone to agglomeration at the freezing point; if the temperature is too low, the product performance is unstable when the machine is started, and the specific operation should be adjusted according to the actual situation and experience.

Blow Molding Machine

The function of pre-blowing in the blowing process is to shape the preform, and at the same time increase the longitudinal strength of the preform through the longitudinal stretching of the stretching rod. During the whole blowing process, the pre-blowing cam pushes the three-way valve to the pre-blowing position, which is done by the cooperation of the one-way valve. Pre-blow position, pressure and flow can affect the quality of the bottle.

When the pre-blow position is early, there will be defects such as the offset and thinning of the center point of the bottom of the bottle, the uneven and whitening of the foot wall thickness, the light weight of the top, the hard neck, the penetration of the bottom, etc.; Defects such as lower weight, center point thickening, and depression.

The pre-blowing flow of the air flow is controlled by the one-way valve, and it is generally advisable to open 3-4 turns. The air volume is large, the bottom is heavy, the center is thin and biased, the feet are white, and the wall thickness is uneven; the air flow is small, the center point becomes thicker, and the weight of the segmented parts exceeds the standard. The pre-blowing pressure is 0.8-1MPa. When the pressure is high, the top may be heavy and the bottom may be light, the center point is skewed, and the foot wall thickness is uneven and white; when the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center point is thick.

The shape of the bottle foot and center point has the greatest impact on the quality of the bottle. Improper adjustment will often cause fatal defects such as bottle burst (under normal experimental conditions) and leakage.

During pre-blowing, a stretching rod is installed to stretch the heated preform, and the blowing machine is reset before exhausting after high-pressure blowing. During the blowing process, the stretch rod must be able to move vertically and smoothly up and down. The driving pressure is 0.55-0.8 MPa, and the gap with the bottom mold is 2.3-2.5 mm, which is 1/3-1/2 of the thickness of the preform. If the gap is too large, the center point of the bottom of the bottle will be offset; if the gap is too small, the center point will become thinner.

The function of high pressure blow molding is to fully stretch the melt, close to the mold wall, so that the bottle is fully formed, and at the same time stop the transverse stretching to improve its transverse strength. The main influencing factors are location and pressure.

Generally, the pressure of high-pressure blowing is 3.7-4MPa, which is determined by its molding characteristics and the properties of the filled beverage (carbon dioxide). There are two positions, namely the position of high-pressure gas and the position of exhaust gas, and the time between them is the holding time during molding, which has a great influence on the stability of bottle capacity. Lack of high-pressure air can easily lead to improperly formed bottles without foot blowing.

Blow Molding Machine

Mold is one of the important factors affecting bottle blow molding. The bottle body of the bottle blowing machine equipment is a Huff mold, and the bottom of the bottle is independent, which is a typical blow molding mold. In the process of consumption, the mold should be kept at a constant temperature and clean, and the ventilation holes should be unblocked.

When there is a problem with the heating and cooling system of the mold, defects such as neck tilt, bottle tilt, volume and height changes, bottom weight, etc. can occur; maintaining a constant temperature of the mold can also avoid condensation on the mold surface.

The shrinkage rate of PET after molding is relatively large, generally 1.8%, and it decreases slightly after glass fiber reinforcement, but still reaches 0.2%-1.0%. Under normal circumstances, the mold temperature is high, the shrinkage rate is large, and the mold temperature is low, the shrinkage rate is small. In order to keep the volume of the PET bottle stable, the mold temperature must be strictly controlled. The temperature of the bottle body is generally required to be slightly higher at 20-45, and the bottom requirement is slightly lower at 6-15. A high bottom temperature will make the bottom heavier and the center point thicker.

In actual consumption, the nozzle will affect the molding of PET bottles.