Factors Affecting the Production of Bottles by a Blow Molding Machine

　　Preforms, heating, pre-blowing (position, pressure, and flow rate), stretching rod, high-pressure blowing (pressure, position), and molds, etc., these are factors affecting the process blow molding machine manufacturing The factors affecting the bottle.

　　1. Preforms

　　Preforms, also known as parisons, are injection-molded from PET pellets. They require that the recycled material ratio does not exceed 10%, and the number of recycles does not exceed two. Preforms after injection molding or those reheated must be cooled for more than 48 hours, and the storage time of the preforms used cannot exceed 6 months. Preforms of different production dates, especially those with long intervals, cannot be mixed. The main reason is the difference in the raw material Model, the proportion of secondary materials mixed in, and the residual stress in the preforms, and these factors have a significant impact on the blow molding process and should be treated specifically according to the actual situation.

　　2. Heating

　　The preforms are heated by a heating furnace, which is set manually and adjusted automatically. The height of the heating furnace should be around 25mm, and the distance from the conveyor wheel should be around 19.6mm. The preforms continuously rotate on the conveyor wheel through the entire oven, so the preforms are heated more evenly, allowing for better molding and overcoming the shortcomings of uneven heating due to the previous static heating and manual rotation of the preforms. However, if the heating furnace is not adjusted properly, it will cause uneven distribution of the wall thickness of the blown bottles (e.g., lighter on top and heavier on the bottom), oversized bottle mouths, hard necks, and other product defects, and may even cause mechanical parts torque failure. The temperature of each area can be adjusted specifically according to the product molding situation, while considering the opening status of the oven lamp tube. In addition, the setting of the oven output power also has a great impact on the heating of the preforms, controlling the output of the entire oven heat. When the machine is not turned on for a long time, when it is turned on again, the initial output power should be set higher accordingly, and then gradually reduced to the normal state during normal production. The output power should generally be around 80%, especially when the ambient temperature is below 5℃, the effect is more significant.

　　The blow molding production process is also related to the ambient temperature. The ambient temperature is generally suitable for room temperature (around 22℃). If the temperature is too high, the product is prone to coagulation; if the temperature is too low, the product performance is unstable when the machine starts, and the specific operation should be adjusted according to the actual situation and experience.

　　3. Pre-blowing

　　Pre-blowing in blow molding machine The role of the blow molding process is to give the preform a preliminary shape and to increase its longitudinal strength by longitudinal stretching with the stretching rod. The entire process is completed by the pre-blowing cam pushing the three-way valve to the pre-blowing position during the blow molding process, with the cooperation of the one-way valve. The pre-blowing position, pressure, and flow rate can all affect the quality of the bottle.

　　Position: If the pre-blowing position is advanced, the bottle bottom center point will be skewed and thinned, the foot wall thickness will be uneven and whitish, it will be heavy on top and light on bottom, with a hard neck, and even defects such as bottom penetration; if the pre-blowing position is delayed, it will result in defects such as being light on top and heavy on the bottom, thickening of the center point, and indentation.

　　Airflow: The pre-blowing airflow is controlled by a one-way valve, generally 3-4 turns are recommended. If the airflow is large, the bottom is heavy, the center point is thin and skewed, the foot is white, and the wall thickness is uneven; if the airflow is small, the center point thickens, and the weight of the segmented part exceeds the standard.

　　Pressure: The pre-blowing pressure should be 0.8-1MPa. When the pressure is high, it may cause the top to be heavy and the bottom to be light, the center point to be skewed, the foot wall thickness to be uneven, and whiteness; when the pressure is low, it cannot be fully stretched, resulting in a heavy bottom and a thick center point.

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

　　4. Stretching rod

　　The stretching rod is a device that stretches the heated preform with the cooperation of the pre-blowing air at the same time as pre-blowing, and it is reset after high-pressure blowing and venting. The stretching rod must be able to move up and down vertically and smoothly during the blow molding process, with a driving pressure of 0.55-0.8MPa, and a gap of 2.3-2.5mm with the bottom mold, which is 1/3-1/2 the thickness of the preform. If the gap is too large, the center point of the bottom will shift; if the gap is too small, the center point will thin.

　　5. High-pressure blowing

　　The role of high-pressure blowing is to allow the molten material to fully stretch and adhere to the mold wall, so that the bottle is fully formed, and to carry out lateral stretching to improve its lateral strength. The main influencing factors are position and pressure.

　　The high-pressure blowing pressure is generally 3.7-4MPa, which is determined by its molding characteristics and the properties of the beverage (carbon dioxide) being filled. It has two positions: the position of high-pressure gas and the position of venting, and the time between the two is the pressure holding time during molding. The length of this time has a great impact on the stability of the bottle capacity. Insufficient high-pressure gas can easily cause improper bottle molding and insufficient blowing of the foot.

　　6. Mold

　　The mold is one of the important factors affecting the blow molding of bottles. The bottle body is a half mold, and the bottle bottom is independent, which is a typical blow molding mold. During production, the mold must be kept at a constant temperature, clean, and with unobstructed vents.

　　When the mold heating and cooling system malfunctions, defects such as crooked bottle necks, tilted bottles, changes in volume and height, and heavier bottoms will occur; maintaining the mold temperature can also prevent condensation on the mold surface. PET has a large shrinkage rate after molding, generally 1.8%, which is slightly reduced after adding glass fiber reinforcement, but still reaches 0.2%-1.0%. Generally, the shrinkage rate is large at high mold temperatures and small at low mold temperatures. In order to maintain the stability of the PET bottle volume, the mold temperature must be strictly controlled. Generally, the bottle body temperature is slightly higher, at 20-45℃, and the bottom temperature is required to be lower, at 6-15℃. A high bottom temperature will make the bottom heavier and the center point thicker.

　　In actual production, nozzles and other factors will also affect the molding of PET bottles.