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17.Proposal No.1 to achieve 'factor 4' in molding factories

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17.Proposal No.1 to achieve 'factor 4' in molding factories

The President's Green Column

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17.Proposal No.1 to achieve 'factor 4' in molding factories

In my previous entry, I have explained the goals of Matsui regarding 'factor 4' and also how we intend to achieve them.
I would elaborate on examples of proposals in these few upcoming entries of mine.

Proposals to achieve 'factor 4' in molding factories

  • 1.Eliminate Energy Wastage
  • 2.Eliminate Resin Wastage
  • 3.Eliminate Water Wastage
  • 4.Enhancement of Productivity

With these proposals, we aim to 'Halve Energy, Resin, Water Consumption' while 'Doubling Productivity' of plastic molding. I will elaborate on the 'Elimination of Energy Wastage' in this entry.

Eliminate Energy Wastage

Main consumptions of energy in the molding process are as follows.

  • 1.Energy consumed to melt resin and inject them
  • 2.Energy consumed to dry resins with dryers
  • 3.Energy consumed to cool melted resin to appropriate temperature
  • 4.Energy consumed to automatically convey resin

Although there is wastage of energy in all processes, I would like to focus on proposals to eliminate energy wastage in dryers.

Energy wasted from drying of resins

In the plastic molding process, before resins are melted for injection, very often moisture level in resin has to be reduced to a certain level. For that, a dryer is necessary.
An example of choosing the appropriate dryer would be like that below.

In a particular molding line, under the best possible molding condition, it uses a maximum of 9kg of resins in an hour.
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Leaving some leeway, a dryer that can dry 10kg/hr will be sought for.
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Equipment makers of dryers like Matsui, would advise that a dryer that can at least dry 12kg/hr should used.
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In the case that a dryer of capacity, 12kg/hr is not available, a dryer that can dry 15kg/hr would be suggested to the user.

As a result, the following occurs.

  • ・A line that requires drying capacity of 9kg/h is being fixed with a dryer that dries 15kg/hr.
  • ・Furthermore, the requirement of 9kg/hr has been derived from under best possible conditions that are usually not the case.
  • ・In addition, molding is not carried out at full force all the time. It may be halted for exchanging of mold or maintenance.
  • ・A dryer that dries 15kg/hr is running at full force under such circumstances.

It is being said that under normal conditions, about half of the energy consumed is been wasted. Moreover, most of the energy wasted contributes to the exhaust heat in the air of molding factories which then consume energy for them to be cooled.

How to prevent such wastage?

The reason behind this wastage of energy is the designing of dryers to be used at full force under all circumstances.

In order to eliminate wastage, it is essential for drying power to be adjusted according to varying resin volume. So, how can we adjust drying power without affecting drying quality?
For examples,

  • 1. Measure the moisture content in the dryer and adjust drying power to just sufficient for the desired drying quality.
  • 2. Measure the mass of resin in the hopper regularly and adjust drying power to that adequate for the mass.

Either ways, a large amount of time is consumed to carry out measurements. Cost incurred will also be increased and not recommended.

The 'Drying Adjustment System' that prevents excessive drying of resins

Matsui suggest the following

3. Controlling of drying flow rate to maintain returning air from the drying hopper at a particular temperature.

Generally, when materials are being conveyed from the dryer, new batch of materials will be fed into the dryer from the top. The new batch of materials is usually of a temperature near the ambient temperature. At such, when materials are being replenished frequently, the temperature of returning air from the drying hopper average to a lower temperature. On the other hand, when materials replenishment occurs less often, the temperature of returning air from drying hopper increase continuously.

The temperature of returning air from the drying hopper is deeply influenced by the consumption rate of materials from the dryer.

Making use of this characteristic, a thermometer can be used to measure the temperature of returning air from the drying hopper and using its result, control drying flow rate and prevent excessive drying.
For dehumidifying dryers, the above method can be modified to achieve energy saving in the regenerating process of moisture absorbent.
The above energy-saving function can also be added to current dryers as an 'Option'.;

Upon modification with this 'Drying Adjustment System', most dryers are being tested to have saved energy by 30~40%. Furthermore, this method requires only the simple adjustment of motor rotation and valve opening to control the flow rate according to the thermometer, making the modification affordable.

The cost incurred from modifying can be recouped within 3 years with the savings from the electrical bills of the dryer in most cases. Putting into consideration the reduction of burden on air-conditioning, cost can be recouped within a shorter time period.

Other proposals to eliminate energy wastage

Other proposals include use of insulating material on the cylinder of injection molding machine, drying hopper and hose that connects mold temperature controllers with the molds. On top of these, we also propose 'Free Cooling' of molds to eliminate energy wastage from cooling.

For details, please kindly refer to Matsui's 'Create More with Less' Handbook.

Click here to access the 'Create More with Less' Handbook.

In my next entry, I would give explain an example to 'Eliminate Water Wastage'

08 Oct 2009 Hironobu Matsui

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