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Functions of break system in flour milling process وظائف سلندرات الدشات (نظام الكسرات ، نظام الدشات) في عملية طحن الدقيق

يختص بما يتعلق بقسم الطحن وتقنياته وفنياته
صورة العضو الرمزية
Osama Badr
مؤسس المنتدى
مؤسس المنتدى
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اشترك في: الخميس مايو 03, 2018 2:46 pm
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Functions of break system in flour milling process وظائف سلندرات الدشات (نظام الكسرات ، نظام الدشات) في عملية طحن الدقيق


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Functions of break system in flour milling process
وظائف نظام الكسرات او نظام الدشات في عملية طحن الدقيق


كود: تحديد الكل

Functions of break system in flour milling process
By Sanjeewa Dharmarathna - Understanding mill operation
وظائف نظام الكسرات او نظام الدشات في عملية طحن الدقيق

Prior to milling, cleaning and conditioning of the grain is the most important aspect of milling. Because flour is a human consumption food product. Quality and purity of the final product is very vital. Flour quality and purity define as the percentage of ash content of the flour. Objective of milling is to separate endosperm from the bran and germ without contamination and grinding endosperm in to flour. Miller’s responsibility is to produce less contamination of flour with higher extraction rates. Maximum permissible level of ash content to the flour is 0.5%.

Considering botanical component of wheat endosperm is around 81-84%. Total Ash content of endosperm is around 1.8%. With in that, Aleurone layer having 60% of ash due to presence of high mineral content. Alurone layer content is 6-7% from total wheat. Therefore, although botanically alurone layer is a part of endosperm, present high minerals and enzyme content, millers remove it with the bran to achieve desired purity level of endosperm. Means part of the endosperm separate with bran and results maximum extraction rate around 72-74%. This is the challenge facing by millers all over the world. According to final product types, flour quality parameters are vary. By analyzing of flour quality, stream blending can be done according to requirement. To overcome this challenge functions and differentiation of break system is very important. 

According to type of wheat is using, the design of the mill is vary. The number of break passages, Type of cleaning machines, tempering conditions are among them. If, for example the mill is using hard wheat, required break passages are less than soft wheat mill. Break passages can be designed with five passages for maximum extraction. 

Break System

The break system is the beginning of the actual milling process. The objectives of the break system are,

1.0 On the head breaks (B1, B2, and B3), to cut open the wheat kernel and scrape the  endosperm away from the bran skin and germ in as course sizes as possible and at the same time leaving the bran in as large flat flakes as possible without damaging.

2.0 Separation of maximum yield of endosperm

3.0 On the lower breaks (B4 and B5), to scrape off any adhering endosperm from the bran skins as cleanly as possible, with as little bran powder being generated as possible.

Throughout the breaking process, the bran should be kept as whole as possible and any excessive grinding, which produces bran powder, is to be avoided. Bran powder cannot be separated from flour and it result deterioration of quality of the flour.

On the other hand germ contamination also should be avoided. Germ contamination cause to reduce the shelf life of the flour and hydrolytic rancidity. Similarly focusing on economically, maximum endosperm should scrape from bran without contamination. Because bran and germs are by products.

Some of the countries separate germ from the bran and endosperm at the end of the process. Quality of the germ is define as free from starch. Increase the purity level, duster machine can be used with very low rpm level. General production of germ percentage is lie around 0.5%.

Normally in the flour mill, there are around 4 -5 break passages (B1, B2, B3, B4, and B5). Function of different break passages are vary according to given objectives. Most common differences among break passages are Flute angles, land of the flutes, spiral, and disposition and roll gap. Depending on those differences, functions of break rolls also vary. Apart from roll differences, type of wheat and conditioning moisture content influence the functions of rolls.

This breaking open of the wheat and releasing of the endosperm from the bran gradually is a mechanical process achieved by passing the wheat between fluted rolls, these flutes being cut in a spiral, and the two rolls running at different speeds to produce a cutting or shearing action. The amount of grinding decide by the degree to which the rolls are adjusted, and is measured by the amount of endosperm released from the bran in this operation. The flutes also have a sharp edge and a dull edge, the arrangement of these is known as the disposition of the flutes.

B1 roll passage

Individually 1st break passage has given separate objectives to fulfill overall objectives of break passages.

1. Cut open the grain

2. Produce courser midlings- roll gap 0.5mm

3. Produce bran flakes without bran cutting

The degree of achievement of objectives depend on type of wheat to produce flour. Hard wheat is easy to cut open in B 1 than soft wheat. Because the bran layer is hard in nature in hard wheat. Flake formation can be easily get from hard wheat than soft wheat. Powder formation ability is high in soft wheat.

Conditioned moisture content and conditioned time also affect for the function of break release in first break. High moisture wheat results less break release and less bran cutting. Low moist wheat result more bran powder formation. There for optimum conditioned moisture and conditioned time is vital.

The intention of B1 passage is to cut open the grain and not to produce flour. The appropriate roll disposition for B1 roll is D/D thus Sharp flutes results more bran cutting and less scraping action.

If flutes angles are less, create sharp cutting edges of flutes. It will results more bran powder formation and less scraping action. There for comparatively higher flute angles are used in B1 roller passages. E.g. - 40/70, 

Spiral action is more crucial for bran powder formation. Little increment of spiral results vast variation of break release. For B1 4% of spiral is ideal. Land of the flute control the grinding. To scrape large bran flakes and large midlings higher land size required. Normally B1 rolls land size is 0.2mm/ up to 8 flutes per cm.

Among all of requirements roller gap plays crucial role on achieving objectives from each and every roller passages. The standard and appropriate roller gap is 0.5mm for B1 to produce courser midlings, while avoiding bran cutting. 

Broken stocks are fed to the second and lower breaks are separated into coarse, medium and fine segments which are respectively fed to coarse, medium and fine fluted rolls for each stage.

B2 roll passage

Objectives

1. Scrape the endosperm from bran

2. Higher production of purifiable semolina- roll gap 0.3mm

3. Preventing bran cutting

Maximum scraping yield- 55%, take place from B2 rolls. Especially courser middling/semolina extraction is the objective. Higher scratch stock is produced. 

Disposition of the rolls D/D or D/S can be positioned. Because more courser middling production is the objective and flute angles 35/65 or 40/70 are appropriate. Spiral is little higher than B1 rollers. Normally it is 6%. Standard roller gap is 0.3mm.

B3 roll passage

Objectives

1. Scrape endosperm further deeply

2. Produce fine, clean semolina- roll gap is 0.1mm

3. Preventing bran cutting

Major objective is to produce clean and fine semolina. Same as B2 passage, Disposition can be kept as D/D or D/S. flute angles, 35/65 are appropriate. Spiral is set up to 8%. Standard roller gap is 0.1mm.

Specially from B1, B2 and B3 passages, objective is not to produce flour, therefor any excess crushing of the released endosperm particles must be avoided, as the larger particle size, the easier to purifier and make separations necessary for correct quality flour. Front Break roll passages (B1, B2 and B3) are called first quality passages. Adjustment of B3 rolls are critical. Because B3 passage supply product to second quality passage (B4 and B5). If B3 passages could not scrape total endosperm, most of it pass to the B4 passage, this leads for degrading of 1st quality flour, reduce the extraction rate and increase the bran percentage. As well as higher maintenance requirement for B3 rolls, Because of less roll gap, less land, less roll size results more ware and tare to the flutes. B3 and B4 rolls worn out immediately.  

 Although it would be ideal to make nothing but large semolina particles, in practice however, some of the endosperm is reduced to medium sized particles (middlings) very fine particles (dunst) and some as flour which at this stage is called break flour.

B4 and B5 roll passage

Objectives

1. Deeply scrape left over endosperm from the bran

2. Produce very fine endosperm- rolls are just touching

B4 passage received bran particles which are very less adhered endosperm to it. To separate those endosperm, very deep scraping is required. Roller gap set in these passages as just touching. Very fine middling release from B4 passage and dull in color. Because produced middling are coming out from nearer to the Alurone layer. This stock is called second quality stock. These passages are called end break passages. 

Break roll release percentage

As already remarked, the main objective of the break system is to cut open the wheat kernels and release the endosperm. This process is best done gradually so as to obtain optimum efficiency of the separation, and also to keep the different qualities of the released materials suitably distinct for further treatment. For this reason the amount of material released at each stage is limited and is normally adjusted to a predetermined percentage of the feed to the break rolls. This is checked by ascertaining the percentage amount passed through a test sieve having mesh size 1000 micron (20WM) similar to those of the actual sifter scalping or over tailing covers following the break stage, from 250g of sample within 03 minutes of time.

Standard releases are 

• B1- 28-32%

• B2- 50-55%

• B3- 55-60%

• B4 and B5- totally release, clean out the bran.

Percentage release figures differ considerably for different mills, depending on the length and design of the system, and in particular on the number of break passages and the allocation of roll surface for each stage. At some stage, releases have to be adjusted to suit the changes in the wheat blend or the wheat characteristics, usually being increased for soft wheat and correspondingly reduced on the succeeding breaks. Release figures may also be adjusted to suit the type of flour being produced. An example in this case is that higher early releases may be required when a higher percentage of patent flour is required or for higher flour extraction. 

The extent that the endosperm must be scraped off the bran skin depends on the flour extraction required. Also the extent to which the endosperm can be scraped off the bran skins depends on many items such as the condition of the wheat used, the design of the fluting on the rolls and the roll adjustment itself. It depends on the number of roller mills used in the “roll surface” at each stage which is expressed as mm per 100 kgs per 24 hours.

Length of the break system

The number of breaks needed to release the stock with the minimum production of break flour depends on the percentage of flour extraction required overall e.g. 70%, 72%, 74%, 76%, or even higher according to the quality required. The normal number of breaks is four with an extraction of 72% to 74% as the target.

Apart from the extraction however, the type of wheat also has an influence on the number of passages, the increased addition of soft wheat in miller’s grits has resulted in the break passages increasing to five. This is due to the difficulty in cleaning the bran of endosperm in the soft wheat.

Another factor that has influenced this change is the characteristics of wheat being produced currently where the virtuousness has drastically reduced due to demand by millers from producers, the hard wheat have more medium hard wheat mixed in consignments.

Also with the price of wheat rising more sharply over recent years as compared the selling price of flour, the value of extraction has increased and so millers have also wished to raise the rate of extraction above 72 to74%. This has also called for the number of passages being increased from to four to five.

Although reference is only made to break roller mills, it is a fact that Detachers and bran finishers or brushers can supplement the work of the lower breaks.

The following is a general idea of the number of break passages according to the extraction required.

1. for 72-74% extraction 4 breaks

2. for 74-76% extraction 4 breaks and bran finishers and detachers

3. for 76-78% extraction 5 breaks and bran finishers and detachers.

Roll Surfaces

The number of break passages can vary according to the size of the mill. If, for example the mill is designed with five passages for maximum extraction and the number of roller mills in each passage is below that, this will not assist in the milling operation to obtain the best extraction with the minimum production of bran powder and fine break flour. In each of the various break systems therefore, there is a certain amount of break roll surface for each kg of flour produced present as mm per 100 kilograms per 24 hours of wheat ground.

First break 5.4 to 7.2 mm

Second break 6.6 to 8.4 mm

Third break 4.8 to 6.6 mm

Forth break 4.2 to 5.4 mm

It must be understood that these all are only approximate indications mentioned above, actual allocations will depend on whether the mill is to operate mainly on strong or weak wheat or an average blend. Roll speeds and feeds have drastically increased over the years. While four or five break systems are still the rule, surface allowance is as low as 2.1mm and are being successfully used, and are far more usual in practice.

Prior to the reduction passages, the different granulation of semolina’s are treated on purifiers where the miller attempts to remove as much of the smaller particles of bran as possible.

Plan sifter function on break rolls

Sifter surface allocation is important and the miller has to ensure that the sieves are properly replaced after maintenance and when repairs are carried out. Sifter separation inspections on a shift basis has to be done by every shift to be able to detect any anomalies that can occur during the normal operation of the mill. For this to be maintained throughout the run of a mill, flour stream inspection must also be done on a per shift basis or when the QA department informs millers of out of spec production. Engineering staff have to ensure that planned lubrication and belt drive inspection if carried out.

Purifier function

These machines do what their name indicate, in that the stock to the reduction and recovery passages are, cleaned of any light branny particles and the clean wholesome endosperm, then directed to the head reduction roller mills while the composite particles of endosperm and branny stock is directed to the lower reduction or recovery roller mills. Purifiers are to be set in such a manner to ensure that the stocks are thoroughly separated and that there is not contamination in the separations. The miller must exercise his skill and knowledge when adjusting purifiers. Sieve choice and cleaning brush movement is important in order to achieve the desired separations and produce high quality flour or semolina.

Reduction system

In this section of the mill, the miller must have knowledge of the degree of roll grind for each stage of reduction passages, to ensure that flour produced is free from bran contamination and that the extraction value required is achieved, one must not sacrifice quality for extraction. Balancing the feed to like rolls is extremely important for this to be attained.

Regulating the feed to the nip of the rolls across the entire roller milling process will help extend the life of the fluted rolls and avoid inconsistent flour quality due to roller mills engaging and disengaging too often, as this in turn results in sifter rich, then bare dressing because of the feed being on and off. Smooth roll scrapers have also to be inspected regularly and adjustments or replacement made as required.

Impact detaches and bran finishers play an important part in achieving flour quality and recovery. These pieces of equipment must be inspected on regular intervals to ensure proper functioning during normal operation.

Flour collection and transfer to storage is equally important and equipment and flour streams must be part of a millers’ checklist per shift.
Functions of break system in flour milling process
وظائف سلندرات الدشات (نظام الكسرات او نظام الدشات) في عملية طحن الدقيق
By Sanjeewa Dharmarathna - Understanding mill operation


قبل عملية الطحن ، يعتبر عملية تنظيف وتكييف الحبوب (مرحلة الترطيب والتكييف) أهم جانب من جوانب عملية الطحن. لأن الدقيق هو منتج غذائي مخصص للاستهلاك البشري.

جودة ونقاء المنتج النهائي (المقصود الدقيق) أمر حيوي للغاية. تحدد جودة الدقيق ونقاوته بأنها النسبة المئوية لمحتوى الرماد في الدقيق.

الهدف من عملية الطحن هو فصل الاندوسبرم عن النخالة (القشرة ، الاغلفة ، الردة) والجنين (الجيرما) دون تلوث وطحن الاندوسبرم وتحويله الى الدقيق. تتمثل مسؤولية الطحان Miller في تقليل تلوث الدقيق (اى بالقشرة والجنين) مع معدلات استخراج عالية . الحد الأقصى المسموح به لمحتوى الرماد للدقيق هو 0.5٪.

النظر في المكون النباتية للقمح يمثل الاندوسبرم حوالي 81-84٪. يبلغ إجمالي محتوى الرماد في الاندوسبرم حوالي 1.8٪. وبذلك تكون طبقة الأليرون تحتوي على 60٪ من الرماد لوجود نسبة عالية من المعادن. تمثل طبقة الأليرون من اجمالى حبة القمح 6-7٪.

لذلك ، على الرغم من أن طبقة الأليرون النباتية هي جزء من الاندوسبرم ، وتحتوي على نسبة عالية من المعادن والمحنوى الإنزيمى ، إلا أن المطاحن يزيلونها بالنخالة لتحقيق مستوى النقاء المطلوب من الاندوسبرم. يعني أن جزءًا من الاندوسبرم ينفصل مع النخالة وينتج عنه أقصى معدل استخلاص حوالي 72-74٪.

هذا هو التحدي الذي تواجهه المطاحن في جميع أنحاء العالم. وفقًا لأنواع المنتجات النهائية ، تختلف معايير جودة الدقيق. من خلال تحليل جودة الدقيق ، يمكن إجراء المزج (عملية التخليط) بسن استريمات الدقيق وفقًا للمتطلبات. للتغلب على هذا التحدي تظهر وظائف وأهمية اختلافات نظام الكسر أى الدش (نظام الدشات ، البيهات ، الكسرات) بأنها مهمة جدا.

يختلف تصميم المطحن وفقًا لنوع القمح المستخدم. من بينها عدد مراحل الدشات ونوع آلات التنظيف وظروف الترطيب والتكييف.
على سبيل المثال ، إذا كان المطحن يستخدم القمح الصلب ، فإن مراحل الدشات المطلوبة تكون أقل من مطحن القمح اللين (السوفت). يمكن تصميم مراحل الدشات بخمسة مراحل للحصول على أقصى استخلاص.

نظام الدشات
نظام الدشات هو بداية عملية الطحن الفعلية. أهداف نظام الدش هي :-


1- على الدشات الأولية (B1، B2، و B3)، قطع و فتح حبة القمح وكشط الإندوسبرم بعيدا عن النخالة والجنين فى رقائق كبيرة قدر الإمكان وفي نفس الوقت تترك النخالة في رقائق مسطحة كبيرة قدر الإمكان دون سحقها .

2- فصل أقصى ناتج/مردود من الاندوسبرم .

3- على الدشات الأخيرة (B4 و B5)، كشط أي اندوسبرم ملتصق بالنخالة (ورق الردة) بحيث يكون الاندزسبرم الناتج نظيف قدر الإمكان، مع وجود مسحوق من النخالة بنسبة قليلة قدر الإمكان (ناتج عملية الكشط الميكانيكية).
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