Autumn on the blow line: what changes when the plant gets cooler

Why autumn throws off summer settings

In October, Shymkent and Turkestan Region still get warm days, but nights and mornings are noticeably cooler. An unheated plant cools down overnight, and so do the preform boxes in the store. The first preforms in the morning enter the oven colder than those after lunch, and settings dialled in during a hot July start giving different bottles at the start and end of a shift.

The preform itself does not change in autumn. What changes is its temperature at the oven inlet, the air around the oven and the humidity. So a seasonal re-tune is not a repair but planned work, best done once in early October rather than fighting rejects every morning.

Preform temperature at the oven inlet

The blow moulder oven has to bring the preform body into the blowing window of roughly 95-110 °C. The colder the preform at the inlet, the more heat it needs in the same time. If lamp power is still on summer settings, the body heats less, especially the inner layer of the wall, and the material stretches poorly.

Wall thickness makes the effect stronger. Heavy preforms with a thick wall, such as 39.4 g and 40 g for a 1.5 L bottle, take longer to heat through, and the gap between the outer and inner layer is larger. Light 0.5 L items respond to heating changes faster, so adjust them in small steps.

Humidity, condensation and compressed air

Humidity rises in autumn and the temperature gap between store and shop widens. Open a cold box in a warm, humid shop and condensation forms on the preforms. Droplets evaporate unevenly in the oven and upset heating. A second, less obvious source of moisture is the compressed air line, where condensate builds up faster in cold weather.

Storage and feeding preforms to the line

Half of autumn problems are solved not in the oven but in in-plant logistics. If the boxes for the morning shift spend the night in a cold store or by the doors, no setting will make the first bottles match the afternoon ones. Simply change how boxes reach the shop:

• bring the boxes for the morning shift into the shop the evening before;
• keep them closed until the preforms reach room temperature;
• keep boxes away from doors, heaters and the wet rinsing area;
• use batches in order of arrival and log the batch number in the shift record.

In autumn the task is the opposite: stop the batch from cooling down before blowing.

An autumn re-tune, step by step

In the south of Kazakhstan, early October, after the season, is a good time for the re-tune. The golden rule: change one parameter at a time and check the result on the bottles.

1. 01
   Stabilise the inlet

   Bring boxes into the shop in advance and keep them closed until the preforms reach room temperature. Then morning and afternoon preforms enter the oven alike.

2. 02
   Stop draughts

   Close doors near the oven or put up a screen. A cold air stream cools one side of the preform.

3. 03
   Check the compressed air

   Drain receivers and filters and check the dryer. Moisture in the air upsets the pre-blow.

4. 04
   Add heat zone by zone

   Start with overall power, then adjust the zones showing whitening or a heavy base. Small steps, with test bottles after each one.

5. 05
   Re-check the pre-blow

   If material stays at the bottom, move the pre-blow timing.

6. 06
   Save an autumn recipe

   Record the settings for each preform item separately. Next spring and next autumn you start from a ready recipe.

Keep a separate heating recipe for each itemFull catalogue

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Checking the first bottles

In autumn the first bottles of each shift and the first ones after a new batch tell you the most. Checking takes a few minutes and saves hours of rejects. You will need scales and calipers.

The preform is the same in autumn as in summer. What changes is its temperature at the oven inlet, and that is what to stabilise first.

Questions and answers