Dryer clothes

Posted on December 6, 2012 by admin

The dryer clothes or dryer screen or felt has a significant function in the dryer part. Synthetic dryer cloth or fabric is also recognized as conveyor belts.
When paper web exceed press section of a paper machine, it contains more than half of its weight is water. Most of this water of the paper web should be removed in the dryer section of the paper machine to ensure 4%-6% of final water content. The drying section is one of the most energy consuming parts (about 60%) of the paper machine. Consequently the role of dryer clothes or screen is absolutely enormous.

Function of dryer screen:
The dryer cloth presses the paper web against the surface of steam-heated drying cylinders. Therefore the temperature of the paper web increases and water is evaporated into and through a porous dryer screen. Moreover dryer clothes assist to support the paper web to shift from one cylinder to another cylinder. Dryer screen controlled paper web shrinkage.

Selection of dryer screen or felt:
The selection of dryer screen or felt is depending on the various paper machine parameters such as paper grades, Dryers configuration, Dryers temperatures, air balance in the hood etc. Dryer screen design and materials are also very important.
For a particular paper machine; the permeability, design and materials of the dryer clothes should be adapted to make sure optimum drying from a drying section. The air permeability of the dryer screen or felt has a great impact on the rate of evaporation of water. If the permeability is decreased, then it is reduction in drying capacity of the dryer screen. The dryer screen, whose air permeability range between 700-1000cfm is used on paper machine for producing higher gsm Kraft and board varieties. On the other hand 200-400cfm dryer screen widely used in medium and high speed paper machine and below these rage used in lower speed paper machine. High numbers of contact areas with the drying surface ensure uniform drying. Proper chosen of dryer clothing improve paper machine runnability, increased drying rate, improved paper quality and savings energy.
Moreover the dryer clothes or felt should have the following parameters or characteristics:- Aerodynamic Properties, Heat Transfer, Fabric Tension, Sheet Support, caliper, heat resistant, wet-resistant, should be less elongation at heat, durability, silent drive, easy to operation etc.

Classification of dryer screen or clothes:

Dryer screen or clothes can be classified depending on weaving, category and combination mode. According to the category, synthetic polyester dryer fabric can be divided into one layer, one and a half layer, double layer etc. In accordance with weaving, synthetic polyester dryer screen or fabric can be divided into 3-shed, 4-shed etc. And in relation to the combination mode, dryer clothes can be divided into insert, pin, pin ring and spiral ring join.

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Specification of dryer clothes or screen

Posted on November 22, 2012 by admin

The dryer clothes or dryer screen or felt plays an important role in the dryer section. The drying section is one of the most energy consuming parts of the paper machine. About 60% of energies are consumed in this section. Hence the function of dryer clothes or screen absolutely vast.
The dryer clothes or felt have to some particular parameters such as air permeability, Aerodynamic Properties, Heat Transfer, Fabric Tension, Sheet Support, caliper etc. All dryer cloth are not suitable for all paper grades, such as 3-shed one layer and a half polyester dryer fabric are suitable for drying papers below 70g. On the other hand, 4-shed double layer polyester dryer fabric is suitable for drying papers above 70g. Whatever the characters of dryer clothes or screen are acid-proof, alkali-proof or high temperature resistance? Hence a specification of dryer clothes or screen is needed.
I include here the specification of dryer screen of a Paper mill industry.

Specification:
All Synthetic dryer screen (except SLDF type), Batt-on-mesh (BOM), Needled type to get smooth surface against the paper provided with suitable seam for easy installation.

  • Basis Weight: 1400 gsm
  • Air Permeation (CFM): 150 with special spiral seam 070
  • Thickness (mm):
  • Dryer Screen Size: 42.00×3.45 M

NB: Dryer clothes Sample and seam is to be submitted with the offer.

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Retention Aid

Posted on November 14, 2012 by admin

Retention Aid is the key to cost savings in paper mill. Retention aids are used wet end of the paper mill to improve retention of fine particles, fillers, additives & sizing agent during the formation of paper. Particularly retention aid is need to be added in alkaline paper making process, but not in acidic paper making process because in this process alum act as a retention aid. The modern paper making technology is alkaline paper making process. Moreover modern paper mill operate high speed paper machine and they increased the usage of recycled fibers. In this case the task of retaining is more challenging and paper machine runnability will be decreased. As a result the papermaking process becomes less economical. Hence the demand of retention aid is increased to saving cost.
The chemical most used as retention aids are polyacrylamide, polyethyleneimine.

Troubles of low retention:
Papermaking is in essence a filtration process. The paper machine wire cloth can be considered as a continuous filter; where a proportion of the solids in the stock is retained and some fine particles are drain through the wire cloth mesh with water and formed white water. The greater part of the white water is returned to the stock, with the result that the concentration of fines and fillers gradually increases. It should be retention otherwise face to following troubles:

  • Fine fiber particles and filler drainage
  • Higher additives and sizing cost
  • Increased deposits
  • Decreased runnability
  • More downtime for cleaning
  • Filling of wet-press felts
  • Bad paper sheet formation
  • Higher sewer losses

Function of retention aids
The best retention of fine particles and colloids in the papermaking process normally occurs when the zeta potential is near to zero and retention aid doing that. The main functions of retention aid are following:-

  • Accelerate drainage, hence increased machine speed
  • Improved retention of fines and fillers
  • Reduced wet-end additives and sizing usage
  • Reduced steam usage due to better surface contact
  • Reduce deposits
  • Reduce sheet breaks
  • Improves paper machine runnability
  • Improved paper sheet formation
  • Increased brightness
  • Cleaner white water system
  • Reduce downtime for cleaning

    • Overall, Increase the productivity

Disadvantages of retention aid
If retention aid is used as overdoses than a highly flocked sheet is formed. Moreover increase paper web break, two sideness and decrease paper machine runnability. Hence to optimize runnability it is need to be adding only the proper amount of retention aid.

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Specification of Retention Aid

Posted on November 12, 2012 by admin

Retention Aids is the key to cost savings in paper mill. The task of retaining chemical and fibers are more challenging in each and every paper mill. Retention aids are available as powders and in liquid emulsion form. Every paper mill used retention aid depends on some criteria. Here I mention a specification of a paper mill.

Specification

  1. Appearance: Colorless liquid.
  2. ingredient: Organic Bromine compound.
  3. pH (neat): 4-4.5
  4. Specific gravity: 1.o4±0.05 g/cm3
  5. Viscosity (at 25°C): 25000 cps max
  6. Shelf life: 5 month.
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Dry strength additives

Posted on November 3, 2012 by admin

We meant by dry strength additives, a number of natural and synthetic polymers that are mixed in paper mill industry with the stock at the wet end to improve some properties of the dry paper. Normally dry strength additives are water soluble.

Dry strength additives are used in paper mill to increase the strength of paper. It increases the strength of paper by increasing internal bond formation. Moreover dry strength additives improve bust strength, tear strength, wax pick values, folding endurance, stiffness, machine runability, increase levels of paper filler uses etc. Dry strength additives also reduced linting and dusting.

The polyelectrolyte’s dry strength additives become part of the existing complex colloid suspension of wet end side of paper mill industry and can be act as a retention aid. But this beneficiary is depends on a certain levels of uses. High addition rate can be brings negative effect, resulting poor retention and poor water removal.

Dry strength additives are used for greatly in printing and converting grades paper than in packaging grades. Dry strength additives are the highest uses in coating base papers, paper grades from recycled fiber and mechanical pulp.

Different gums, vegetable extractives and synthetic polymers are used in paper mill as dry strength additives. Such as cationic and amphoteric starches, natural gums (guar, locust bean or tamarind), cationic polyacrylamides, cationic glyoxylated resins, modified polyamines, carboxymethyl cellulose etc. The dry strength additives can be used individually or in combination.

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Defoamer

Posted on October 28, 2012 by admin

Defoamer is used in a pulp mill and a paper mill to reduce foam problems. It tackles both problems with surface foam and entrained or entrapped air. Defoamer also hinders the formation of foam. Defoamers are surface active agents such as esters or amides of fatty acids and polyethylene glycols. It is also called antifoaming agent.

Properties of defoamer
Defoamer (antifoaming agent) has surfactant properties. Defoamer is highly insoluble in the foaming water medium. The viscosity of defoamer (antifoaming agent) is very low therefore it is spread very rapidly on foamy surfaces as tiny droplets. Defoamer has affinity to spread air-liquid interface and this is the causes for collapse of surface foam. Some other important parameter of defoamer (antifoaming agent) are pH value, solid content, active material content, specific gravity, emulsifier type (ionic/non-ionic), diluent and shelf life.

Why foam is generated
There are many causes to create foam in a paper mill and pulp mill. Many mechanical factors are involved to create foam. Every paper mill must have several pumps. If the pump is leaky seals it may be caused to create foam. A high pressure pump can also be created foam. Moreover agitation also builds up foam. Especially air bubble or foam raise during coating color circulation.
There are many chemical used in paper mill for paper making process. Some of them build up foam. Foam creation also depends on sizing agent. When acid sizing agent or rosin sizing agent is used then foam produce more than the use of alkaline or neutral sizing agent.

Various trouble that caused by foam in paper mill
Various kinds of troubles occur due to build up foam, dissolved and entrained air in a paper mill. Such as-
1. Formation problem in a paper mill.
2. Lessening of pump effectiveness
3. Development of bacteria.
4. Formation of deposit
5. Drainage problems
6. Coating color may be contain by air bubbles until drying
7. Downtime to cleaning system, ultimate increasing cost due to chemical drainage.

Benefits of defoamer or antifoaming agent
Defoamer (antifoaming agent) improves drainage in the paper mill. It is also improves drainage in the Kraft pulp stock, sulfite stock, bleaching plant screen room area in the pulp mill. A defoamer (antifoaming agent) reduces paper breaking and hence improves paper machine runnability. Therefore increases paper mill production. Defoamer (antifoaming agent) also lessen steam consumption in the dryers and resultant energy savings as well as cost savings. Defoamer avoids paper formation of holes by removing fine bubbles in fibers.

Dosage of defoamer or antifoaming agent
For batter effectiveness of defoamer (antifoaming agent) should be used proper dosages. If insufficient defoamer is used, the paper mill does not attain its goal. On the other hand, if too much defoamer is used, it negatively affects the performance of sizing agents and dry strength additives, moreover deposit dilemma. Hence to use of proper dosage of defoamer, it should be test the air content of headbox furnish.

Types of defoamer or deaerator
A wide variety of defoamer are available for paper mill such water based defoamers, oil based defoamers, powder defoamers, silicone based defoamers, polymer defoamers (EO/PO based defoamers) and alkyl polyacrylates defoamers.

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Specification of wire cloth

Posted on October 24, 2012 by admin

Wire cloth (forming fabric) is a very important part for a paper machine. We can say, it is the heart of the paper machine. Basis on the paper machine category, paper machine speed, and types of paper grade needs specific type of wire cloth for a paper mill. Here I refer to a single layer wire cloth’s specification for a paper machine whose speed 200 to 220 m/m.

Specification
Single layer synthetic forming fabrics mesh 29/27 per cm, 5-shaft broken diagonal strands, 0.20/0.25 mm dia, polyester monofilament, endless with spliced. Non-marking seam.
Size: 25.80 × 3.48m
Elongation: at 50N/cm, 0.5% max.

N.B: Sample must be submitted along with offer.

1.For new party whose material has been proved earlier may be allotted given only one piece on trial.
2.Management reserved the rights to give order on or more party to divide the total order quantity among different parties.
3.Actual carrying cost will be given not exceeding the offered estimated carrying cost.
4.Delivery to be made within 4 to 6 weeks form date of opening.

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Wire cloth

Posted on October 23, 2012 by admin

Wire cloth or forming fabric is a very important for a paper machine in a paper mill. In general formation of paper depends on wire cloth and refining of paper pulp. Paper machine wire cloth (forming fabric) made from polyester or polyamide monofilaments. To shape an uninterrupted belt, it is made by endless of a seam. During woven of wire cloth, filaments are composed of paper machine direction and paper machine cross direction. The filaments of paper machine direction or lengthwise are called warp. One the other hand the filaments of paper machine cross direction are called weft or Shute or filling. The construction of wire cloth depends on some weaving variables such as pattern, mesh, yarn, diameter, degree of crimping etc. Mesh is very important for a wire cloth (forming fabric). Water drainage and retain of fibers are depends on it.

According to the category, wire cloth (synthetic forming fabric) can be divided into single layer wire cloth, 1.5 layer wire cloth, double layer wire cloth, two and a half layer wire cloth, triple layer wire cloth and 3.5 layer wire cloth. In accordance with weaving, wire cloth (forming fabric) can be divided into 2-shed, 4-shed, 5-shed, 7-shed, 8-shed, 16-shed, 24-shed etc. A paper machine wire cloth has two surfaces. One is the forming surface or top surface and another is the wearing surface or underside surface.

Depending on paper machine and various paper grades wire cloth also difference. The uses of double layer wire cloth (forming fabric) is increasing day by day.

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Types of Paper filler

Posted on October 8, 2012 by admin

The filler materials that are used in paper mill can be classified into two groups. These are Inorganic fillers and organic fillers. The most common inorganic paper fillers used in paper mill are precipitated calcium carbonate (PCC), ground calcium carbonate (GCC), Kaolin clay, Talc and titanium dioxide ( TiO2). Other noticeable inorganic paper filler are Alumina trihydrate, precipitated silica and silicates (PSS) etc. Organic paper fillers are polymers (plastic pigments). They are hollow micro-spheres or porous filler.

In paper mill mostly used inorganic filler materials. But organic filler materials are used rarely; because of their high price. Organic paper filler used for special paper.

All paper filler are not suitable for all paper mills. It should be use basis on kind of pulp furnish, paper grade, process and paper machine configuration. Calcium carbonate (GCC or PCC) is not suitable for acid paper or wood-containing paper. It is suitable for wood-free or neutral-to-alkaline paper-making medium. Titanium dioxide is appropriate for special paper like offset but not talc. 

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Paper Filler

Posted on October 5, 2012 by admin

Filler is the most important material of paper mill. It is usually used in paper mill to reduce cost. Depending upon the performance characteristics of the particular filler as well as the percentage added these materials can enhance the physical, optical, price-performance & esthetic properties of the finished paper. Fillers is used in the wet end operation of paper making.

A good paper filler should be exhibit good distribution within the sheet, no dusting, maximize strength, maximize bulk etc.

One of the survey shows that the filler used in North America PCC 70%, GCC 13%, Kaolin 15%, TiO2 2%, Silica/Silicates 0.3%, talc 0.1% and Aluminium Trihydrate 0.1%. In Europe used of PCC increased day by day.

Advantages of paper filler

Fillers that are dominantly applied in the paper mill are mostly minerals. There are quite a lot of reasons why fillers are used in papermaking. The main reasons are their low cost compared to fiber; since the cost of paper filler is one third or one fourth of fiber. The application of fillers also increased brightness, opacity, productivity, improve printability (smoothness, ink absorption, show through), gloss of paper, sheet formation (fill in void), dimensional stability, paper’s appearance etc. In addition they increased water drainage and drying rate of the formed sheets. 

Problems of using paper filler

There are some negative effects on paper with the use of filler such as reduced paper strength, increasing the demand for sizing agents, retention, abrasion, dusting, sheet two-sidedness and reduced bulk. Moreover Calcium Carbonate filler is unsuitable in acid papermaking and wood-containing paper. A final product of higher density is also a drawback.

The choice of filler material and the loading level are determined according to kind of pulp furnish, paper grade, process and paper machine configuration.

Important characteristics of paper filler

Particle size, particle shape, specific surface area, light absorption properties, particle charge, refractive index and abrasion are more important characteristics of filler materials.
Particle size: It is plays an important role on the optical properties of any paper filler. If particle size of filler is fine, then it scattered good light. Particle size also affect on drain-ability and resultant reduction in steam consumption.
Particle shape: Particle shape is a significant factor for optical properties. It is also affects abrasion values. Minor the abrasion value longer the wire-life.
Specific surface area: The specific surface area of paper filler depends on the particle size, shape & degree of agglomeration. It is helps in light scattering & also influences the strength & printing characteristics of the paper.
Effect on paper strength: filler material has negative effects on paper strength. If more filler uses, then it is interfering with fiber to filler bonding within the sheet. Hence the bond formation is weak, so reduced the paper strength. Moreover weak bond will be increasing the dusting tendency. 
 Abrasion: The abrasive characteristics of paper fillers increase wear to wire on the paper machine and to the printing plates in the printing press. The crystalline nature, hardness, impurities and large particle of the filler tend to be more abrasive.

Refraction Index: Refraction index is one of the important characteristics of paper filler. Light scattering is influenced by this property. If refracted index of a filler is higher, then it will be scattered more light. As a result opacity improves.

Retention: Higher fine material content in the circulating water system reduced retention. Hence some retention aids have to be used, as a result increased paper production cost.

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