During the process of bottle blowing, we often change different preforms and bottle shapes, so to make everyone switch bottle shapes faster, the following are some adjustment methods of fully automatic bottle blowing machines compiled by LNFRO TECH.
The two-step bottle-blowing process of the bottle-blowing machine is stretching-pre-blowing-high-pressure blowing-exhaust. LF series bottle-blowing machines will have three blows after the high-pressure blowing.
The time of these actions is very short, but these times must be coordinated well. In particular, the first and second items determine the overall distribution of the material and the quality of the bottle blowing, so we must adjust: the starting time of stretching, the speed of stretching, the starting point of pre-blowing, and the end time of pre-blowing, the pressure of pre-blowing and the flow rate of pre-blowing.
There is also the overall temperature distribution of the bottle preform and the temperature difference between the inner and outer walls of the bottle preform. The two factors that have the greatest impact on the stability of the bottle-blowing quality in the entire bottle-blowing process are heating and pre-blowing. Today we will mainly talk about one of these two links – the setting and adjustment method of heating.
- Heating
The preform heating of the two-step blow molding machine is completed by the heating light box, and the heating temperature is set manually. Some blow molding machines also have automatic adjustment and automatic heat preservation functions. The far-infrared lamp in the lightbox emits far-infrared rays to radiate and heat the preform. The preform rotates while moving forward in the light box, so that the preform is heated more evenly.
The heat of the lightbox is determined by the number of lamps turned on, the power of the lamp set, and the power of the overall output of the lamps. The number of lamps turned on should be adjusted according to the length of the preform and the effect of pre-blowing.
If you want the lightbox to play a better role, the setting of the lightbox’s balancing fan and the blowing fan is also very important. There is also the adjustment of the water channels inside and outside the lightbox. If these adjustments are not done well, problems such as an enlarged bottle mouth and a hard neck ring (neck material cannot be pulled open) will appear during the bottle-blowing process.
Method to adjust the internal and external water channels: first remove the light box, then put a few preforms in the heating furnace in manual mode, and adjust the position of the water channel so that the water channel is 2~3mm away from the front and back and high and low positions of the support ring, to protect the bottle mouth more effectively.
Before starting the machine, check whether all the lamps are normal and whether the reflector is deformed or aged. If the lamp is not bright or the reflector is deformed and aged, it will affect the heating effect.
Before turning on the heating, check whether all the fans in the lightbox are working normally. (Including the exhaust fan)
Before blowing the bottle, it is necessary to ensure that the temperature of the preform used is above 20℃. Too low preform temperature will affect the heating effect, and after heating, there may be a large temperature difference between the inner and outer walls. At the same time, do not pour preforms with large temperature differences into the preform storage bucket at the same time, which will also affect the heating effect of the preform.
The temperature of the preform during the heating process is as high as 100℃ or more. Depending on the different models, the heating time is also different. During the heating process, the internal stress and moisture of the preform will be eliminated.
Before the preform is heated and put into the mold for trial blowing, we must check the heating effect of the preform. We can turn on the “unload preform” button, and the heated preform will fall automatically. We pick up the heated preform and pinch it with our hands. If the inner wall of the preform sticks together after deformation, it will bounce back immediately after release. In this case, you can try blowing. If the preform cannot be pinched by hand, then increase the heating temperature. If the preform turns white after heating, or cannot bounce back when pinched by hand, it means that the heating temperature is too high, and it is necessary to lower the heating temperature before adjusting.
Before adjusting the process, be sure to check whether the lower limit on the bottle-blowing machine has been replaced. The height of the lower limit is adjusted according to different bottle types. Generally, we will match the corresponding lower limit according to the customized mold height. The function of the lower limit is the distance from the stretch rod to the bottom of the bottle. If this is not replaced, it may cause damage to the bottom mold and bending of the stretch rod.
- Pre-blowing
Pre-blowing guides the distribution of bottle raw materials to obtain the required bottle performance. Because the pressure and speed of high-pressure blowing are very fast, if there is no pre-blowing, the raw materials of the bottle will be difficult to distribute and difficult to form.
The role of pre-blowing is to move the raw materials outward during the stretching process to obtain the correct wall thickness distribution. Stretching and pre-blowing are a two-way extension process, which determines the distribution of the wall thickness of a bottle and the molding effect.
During the pre-blowing process, the start and end time of pre-blowing, the pressure of pre-blowing, and the flow rate of pre-blowing are very important adjustment parameters. The distribution of bottle raw materials and the molding effect are directly related to these parameters.
Therefore, when adjusting the pre-blowing, we must ensure that the pre-blowing is controlled, the pre-blowing pressure is stable, and the pre-blowing flow valve works normally. The pre-blowing flow valve of each mold cavity is the same.
General pre-blowing pressure: 6bar~12bar
Pre-blowing flow: generally 2~5 turns. (Adjusted according to the pre-blowing effect)
Inappropriate pre-blowing pressure and pre-blowing start position will directly lead to unreasonable distribution of bottle raw materials, or the bottom of the bottle will be wrapped around the stretch rod and other phenomena.
Too much pre-blowing pressure will generally cause bottle explosion, bottleneck hard ring, bottle bottom eccentricity, uneven distribution of bottle materials, white bottle bottom, etc.
Pre-blowing pressure that is too low will generally cause material accumulation at the bottom of the bottle, thick center point, bottom wrapping stretch rod, thin neck, uneven wall thickness distribution, and in severe cases, bottle breakage.
Pre-blowing flow rate that is too large will generally cause the bottle top heavy and the bottom to be light, bottle bottom eccentricity, thin center point, white bottom, neck hard ring, uneven wall thickness, etc.
Pre-blowing flow rate that is small will generally cause: button-shaped material accumulation at the center of the bottom of the bottle, less material at the neck, heavy bottom and light top, uneven wall thickness, and in severe cases, bottle explosion.
Pre-blowing position that is advanced will generally cause: bottom center point bias, bottle top thick and bottom thin, uneven wall thickness, white bottom, neck hard ring, and even bottom rupture.
Pre-blowing position that is too late will generally cause the bottle top to thin and bottom to thick, material accumulation at the bottom, easy to-wrap stretch rod at the bottom, and in severe cases, stretch rupture of the preform.
