Achieving Quality Output From Your Asphalt Batch Mix Plant

FABHIND brings this blog series with the purpose of sharing its long-standing expertise by providing guidance for its readers on the salient objectives that should be kept in mind while operating a typical Asphalt Batch Mix plant. In this two-part series we will be discussing eight major objectives that should be kept in mind while operating a typical Asphalt Batch Mix Plant.

Quality – one goal accomplishing multiple objectives

We all know how important producing quality work means to us. We chase it because we know that in pursuing one goal, we achieve numerous objectives including quality output, client satisfaction, sustained reliability and brand value, and of course consequentially, profits. FABHIND stresses on relying on quality machinery for quality outcomes; however, with our extensive experience in this sector, we cannot stress enough on the need for following certain standard operating procedures while operating any plant machinery. One may have the best plant machinery at his disposal, but if one does not operate it properly, either it the machinery will malfunction or it will not produce the output of a desirable and standard quality. Therefore we believe, diligently following the standard operating procedures and checks of your plant machinery are critical to your firm’s performance.

i. Physical Space for plant installation

It is really worthwhile to have a clear idea of the physical layout where your batch mix plant will be erected with the view on whether you will be able to ensure sufficient and appropriate space for stockpiling the raw materials and their smooth delivery into the plant at its various entry points or not. We would advise you to avoid the erection and arrangement of your batch mix plant in congested locations where quick and smooth handling of the material might be restricted. Experiences tell us that a uniform mix is produced when the batch mix plant is facilitated by adequate space for the maintenance of large stock-piles of the raw-materials.

ii. Feeding of the cold aggregates

The aggregates of different sizes are entered into your Asphalt Batch Mix plant through their own separate feeder bins. The aggregates are also referred to as cold aggregates in this stage and the process is also known as ‘cold feeding’. It is very important that the plant functioning in this section ensures uniform input of each aggregate size and at the pre-determined speeds. For a uniform output, one has to give a uniform input. Some points to keep in mind to ensure this are:

• Ensure there is no mixing or segregation of the aggregates in their respective stockpiles.
• Feeder gates should be properly calibrated so that they remain free flowing.
• Due to their size, the fines have the propensity to coalesce into larger sizes. To avoid this, the fines’ feeder bin is attached to a vibrator that runs as long as the fines are entering the plant. It is important to note that vibration of the bin beyond its running time will lead to excessive packing of the fines in the bin.

To ensure the above, the batch mix plants are furnished with calibrators at the feeder gates. Your plant operator or the engineer should calibrate the batch mix plant before operating it on the site for work using real aggregates. The calibration process will involve setting the plant to produce the output at the desired rate, of desired consistency, and for pre-determined volume.

iii. Appropriate aggregate moisture content

Gradation of the aggregates and their moisture content are regarded by the industry-experts as one of the three most critical aspects to keep in mind when one desires a perfect and workable asphalt mix at the construction site. In fact, moisture content of the aggregates lying in the stock-pile and the feeder bins can vary with the surrounding environment including temperature.

Moisture content variation in aggregates affects the working in the Drying Drum in the following manner:

• Energy consumption incurred in the Drying drums will also increase with the increase in moisture content of the aggregates. It may also work inefficiently - sometimes over-drying an already dry aggregate or giving out an insufficiently dry aggregate.
• Aggregates leaving the drying drum will have varying temperatures due to which the temperature recorded at the Pug-Mill section will be incorrect.

iv. Drying drums

For efficient operation in the drying drum section of your batch mix plant, it is important that the air that is combined with the fuel for combustion is provided in appropriate amount. Lack of insufficient air will cause incomplete combustion, leaving an oily coating on the aggregates which will in turn affect the quality of the finished mixture. The flow of air in a drying drum is provided by a blower and maintained by also having an exhaust fan on the other end.

To check for oil coating on the aggregates, operators of the batch mix plant often take some of the aggregates coming out of the drying drums by a shovel and put them into a bucket of water. If there is a film of oil floating in the water, it indicates a lack of balance in the draft or the flow of air between the blower and the exhaust. This imbalance of air draft causes ‘hack pressure’ in the drying drum and puffing back at the burner end. The solution to this issue is to increase the draft of the air or reduce the pressure of the blower air.

It can be noted that while heavy film on the water during the performance of the check is of immediate concern, presence of a slight film is not bothered about by most operators.

Drying drums not only achieve the desired moisture content in the aggregates but also heat them to the desired temperature. Under-heated aggregates are difficult to be coated by the asphalt, thereby producing a non-workable mix as output. Therefore batch mix plants have pyrometers for the operators to measure the temperature of the aggregates coming out of the drying drums. Since these are very sensitive instruments, it is highly recommended that they are shielded by the heat and vibrations of the plant. It is usually placed with its head several feet away from the dryer and connected to its sensing elements by wires of accurate length, size, splice and coupling. It is also highly recommended to calibrate the pyrometer before the plant is put to use on the field. To avoid time lag in temperature measurement, the pyrometer is cleaned to remove the dust accumulating on it regularly.

To be continued in Part 2..

There are four more critical aspects that will require your attention while you operate your asphalt batch mix plant. Watch out for them in Part 2 coming up soon on our website. Meanwhile, we would like to remind our readers that you can always rely on FABHIND for any plant manufacturing machinery. For more information, visit our website or contact us directly.