Material Properties

Since steel is a stronger material and has a modulus of elasticity which is considerably more than 2.1 times higher than cast iron, while designing  the pressure vessel safety codes allow for better design parameters on steel. The much higher allowable stresses for steel mean that the shell wall can be thinner, which gives the positive benefit of higher heat transfer rates.

Lower shell root thickness for steel means the resulting heat flow is higher through the cylinder. This gives a higher evaporation rate which can flexibly either be used: to increase the production rate at constant energy input or, when the machine speed is kept constant, to reduce the drying energy.

Furthermore, during casting, pinholes are often developed in body, which need to be filled or repaired; otherwise, these create different quality issues on paper. Such an issue is never seen in steel dryers.

It is interesting to note that CI has a better compressive strength compared to steel, and that makes it more suitable for compressive loads like machine framings, sole plates, base plates etc. Probably, this is the reason that many old papermakers still consider CI a better option than steel. However, the ultimate tensile strength of steel is much higher (even 4 times) than that of CI. To add further to it, one must also keep in mind that specially developed high strength steels now have even more strength than the conventional ones.

Higher heat transfer and lower energy costs

Cast iron and steel have essentially comparable thermal conductivity, so as the shell is thinner, better heat transfer can be assured.

Another benefit of the reduced shell thickness and higher heat transfer is that lower steam pressure can be used for drying. In such a case, the same production rate can be reached using lower steam pressure with higher Latent Heat of Vaporization.

With the grooving inside the shell, overall heating area is considerably increased resulting in better conductivity. The result is lower total energy consumption. Depending on the cost ratio between the different energy sources, significant energy cost savings are possible in tissue machine with fabricated dryers, in fact the energy cost shall be lower in steel Drying Cylinders compared to a C.I. one. The investment cost for steel cylinders are also favorable while compare to the cast iron variety, and the physical weight is also less as well helps less engine power consumption.

Automation, today, is considered the most significant part of any process. Having a dryer of lesser thickness means having lesser heat capacity of the dryer, which leads to faster and efficient control. Hence, you can see better and quicker response to your actions (change in set point of dryer steam pressure, resulting in change in paper moisture). This results in better quality and quality consistency of paper being produced. Not only this, this also results in quicker start-up of the machine after a long stoppage, like a wire/felt change.

Metalizing benefits on carbon steel yankee

It should be mentioned that steel Yankee & dryers can be metalized prior to increase the surface hardness, life and water resistance.  Metallization eliminates the need for re-grinding of the shell wall base metal, which on cast iron can eventually result in de-rating. Metallization is also a key reason that steel Yankees are far less prone to developing chatter problems.

Safety

Safety is of course a very prime factor for consideration for all organizations of the industry. Failure with Explosions on cast iron drying cylinders unfortunately have sometimes happened due to the poor material properties & brittleness of cast iron. Thus the cylinder can explode due to excess pressure, loaded with excessive load, or in case of an accident for other reasons. Steel, on the other hand, will have a better performance in the event that internal stresses exceed than allowable limits.

In the event that internal stresses on the steel shell exceed the yield strength, the steel shell may deform but stay intact.

If the stresses inside a cast iron dryer exceed the yield strength, the dryer may explode.

Top former is a part of the PM wire part. It is installed between the under-pressure and suction boxes, approximately in the second third of the wire table. Its most important part is a three-chamber suction box with different under-pressure values in particular chambers. Through separators this suction box is connected to the vacuum system. On the bearing structure, type cantilever, there are driving roll, guide roll with positioning, wire run regulator, wire stretching device, spraying showers and wire cleaning system installed. All the rolls are provided with doctors. Under the bottom wire, on the bearing structure, there are white water trays with discharge branches installed and used for splashing. The top former itself is completed also with service bridges. It is used particularly in new and reconstructed PM wire sections with operating speeds up to 1.500 resp. 1.600 m/min. Dryness on the bottom wire is 10-12%.

Design

The most important part of the top former is its suction box with diverse vacuum capacity and gradually increasing under- pressure values.

Under the suction box of top former and under the bottom wire there is a forming box installed with height-adjustable and pneu-matically controlled bars in order to improve formation of the paper on the wire. Behind the forming chamber there is a suction box keeping the paper web on the bottom wire in the place of division of the top and bottom wire.

Main parts

• Supporting structure – cantilever design (1)
• Guide rolls (2)
• Wire stretching units (3)
• Wire run regulator (4)
• Suction box – top former (5)
• Forming box – bottom wire (6)
• Oscillating system (7)
• Suction box for wire cleaning (8)
• Doctors
• Suction box – bottom wire (9)
• Sensing of wire stroke
• Collecting tanks (10)
• Covering and walkways

Accessories

• Under-pressure system
• Drive
• Control system with control panel
• Dewatering wire
• System for vapours suction
• Fixtures for rolls and wire replacement

Construction design and machine safety are in compliance with EU and EAC standards.

Rope threading system is used for rewinding and longitudinal slitting of the paper web from the paper machine reel spool into paper rolls of required sizes.

Design

The winding part of the machine consists of two rolls, each of these carrying rolls has its separate drive. A hydraulically controlled ejector of the reeled up rolls and hydraulically controlled cross cutter, which separates the paper web from the wound up roll, are installed in the first carrying roll bedding in the paper web run direction. The carrying roll guard bedding is done in the same way on the second roll, it is controlled pneumatically and serves for a safer roll manipulation in the area between the tilting table and the smooth carrier roll.

Both rolls are dynamically balanced according to the required winding speed. Surfaces of both rolls are plasma-sprayed. Both carrying rolls are driven by AC variable-speed motors. The paper roll is laterally guided by mandrels that are pneumatically lifted or dropped down. They are retractable hydraulically or pneumatically. Every paper roll, while being reeled up, is pressed down from the top by a rider roll, its loading is controlled according to diameters of the paper roll while being reeled up. Pressure roll guiding is equiped by the system
against the roll crash.

The slitting section of the machine is arranged according to required width of strips to be cut, max. operating speed and type and width of the paper web. It is controlled pneumatically or electro-pneumatically on principles of so-called shears slitting with a tangential slit or a slit with embracement on the slitting roll. The machine is equipped in front of and also behind the slitting section with spreader rolls used for correct paper web guiding and cross stretching in the input part just before cutting and when coming to carrying rolls.

These spreader rolls are installed on feeders for an optimal adjustment of the paper web run. The slitting section comprises also a device for direct measuring of the paper web tension located on the guide roll with its constant embracement by means of which the required tension of the reel can be controlled. In the slitting section, there is also an equipment for a dust exhaustion which significantly reduces the amount of impurities on the paper surface.

The paper web threading system serves for a transfer of the paper web from an unwinding stand through transfer, spreader and guide rolls, the slitting section and its spreader roll up to the space between carrying rolls of the rewinder. It comprises V-belt conveyers, chutes, air nozzles, clamping roll device and underpressure system with a sucking of the paper web onto the first carrying roll of the rewinder.

The unwinding stand is arranged as a twin frame with two stands on which reel spool beddings with locking levers and an ejector of empty reels spool, combined with hydraulic dampers on ends of unloading arms, are installed. The brake for unwinding is manufactured either with an AC generator motor, a pneumatic disc brake with air or water cooling, or a drum brake. A clutch installed between the brake and the reel spool is equipped with a grooved shaft on which the coupling part is pneumatically displaced in dependence on the reel spool carrier. The entire unwinding stand is equipped with a cross and longitudinal feed for correct adjustment of the paper web run when entering the machine.

The machine can be also delivered with a complete electric installation, including the control system, automatic paper web threading system, equipment for dust exhaustion from the paper web surface, equipment for suction of trimmings in the slitting section, and reel spools. Besides production of new machines, the company offers also complete overhauls and reconstructions of rewinders and their parts. Machine design and work safety are in compliance with EU and EAC standards.

Main parts

• Bearing structure – individual stands made of profile steel, attached to each other by fixing bolts and locks (1)
• Supporting rolls (2), pressure roll (3)
• Core clamping mandrels
• Paper rolls ejector (5), tilting table (6)
• Spreader rolls (7)
• Slitting section (8), paper web threading (9)
• Unwinding stand (10)
• Machine hydrostatic drive
• Machine pneumatic circuit
• Machine electric part (switchboard boxes, cabling, control board)
• Control system incl. software
• Machine guards, machine drive (11)

Accessories

• Equipment for suction of trimmings
• Automatics for paper web threading
• Equipment for dust exhaustion
• Reel spools with rubber or polyurethane cover
• Automatic roll core threading
• Cross knife
• Vacuum on a grooved carrying roll
• Barrier increasing safety of reel spools handling on unwinding stand
• Central lubrication system

Scope of delivery

• Machine according to main parts description
• Accessories optionally

Material

• Bearing structure – common steel
• Roll coats – common steel with a surface treatment

• Open Head Box for Machine speed up to 350 meters/ minute.
• Slice width up to 3 800 mm are regularly manufactured.
• Profile variation across the deckle in maximum ±3 GSM
• Cylindrical Tapered and Rectangular Tapered with Polypick diffuser, Stainless Steel diffuser, Manifold are provided depending upon the quality and production capacity.
• Two numbers Properly designed Evener rolls for evening effect and better deflocculation.
• Machined and Ground Top and Bottom Lip for smooth flow of stock.

Hydraulic headbox operates without air cushion and is fully filled with paper stock. It has some elements as classical high pressurized closed headbox. Main difference lays in built-in block with stage diffuser and an installation of pulsation damper in front of the headbox. This headbox is proper for paper machines operating with lower consistency and speed above 300 m/min.

Main parts

Pulsation damper (1) is installed before headbox itself, including inlet section, perforated plate with stage openings and top part with side outlet to the distributor. Air cushion occurs above the stock level in the damper. Stock inlet is either vertical or horizontal. Optimal stream through the headbox is done by inlet geometry, perforated plate and keeping the proper stock level. Major task of this system is dampening of pulsation in main stock stream caused by cleaners in approach flow system. The equipment could be designed as round distributor as well because all benefits of the system remain but stock inlet to the headbox is done through distribution hoses having identical diameter and length. Last case utilizes favorably consistency control with diluting water.

Inlet body(2). Its role is guide the stock to paper machine run direction and distribute it homogenously across whole paper web width. Inlet bodies are suited with recirculation. Recirculation setting is very important due to certain paper properties. When the round distributor and headbox is connected through the distribution hoses an inlet body with constant cross profile without recirculation is used.

Stage diffuser block (3) distributes the stock regularly across whole width of the headbox and produces controlled turbulences to de-flocculate the fibres and let to each stock stream from diffuser outlet even flow profile. The block is produced from plastic or stainless steel with plastic inserts. The third alternative enables optimizing in case when real throughput doesn’t correspond with dimensioned throughput or when the intensity of turbulence should be changed.

The same could be done in case of throughput break for instance headbox lip damage. Identical inserts don’t have to be installed across the whole diffuser but inserts with smaller or bigger profile can be used in the edge parts. Concerning this aspect the stage diffuser has big potential for operation optimizing.

Inlet chamber with outlet nozzle (4) brings the paper stock to the wire and rectifies its outlet. It is of stainless steel and parts of headbox coming in touch with the stock are of stainless steel to and electric chemically polished. Use of quality material provides headbox with great stability and long life.

Adjusting equipment (5) serves for adjusting of headbox slice slip and stock outlet onto the wire.

Possibilities of cross profile control

• Manual control of top lip shifting mechanisms, eventually valves of dilution water (without automatics)
• Fully automatic control of cross profile through QCS of PM control system – step motors of shifting mechanisms, eventually electronic controlled valves for diluting water

Material

• Headbox is made of stainless steel
• Stands are from common steel, zinc coated outside, respectively of stainless steel
• Base rails are from cast iron
• Part coming in touch with stock are made from stainless steel and polished

Accessories

• Headbox stands
• Front foot bridge or front and back foot bridge incl. ladders
• Source of pressurized air
• Inlet pipes
• Base rails
• Slide valve of the knotter
• Format guides
• Source of dilution water-pump + distribution

Scope of delivery

• Complete machine according to main parts description
• Accessories according to customer’s inquiry

Use of hydraulic headboxes

• For closer flow scope which is important namely in cases when narrow assortment of paper is required
• With round distributor is suitable for speeds above 700 m/min

The multi-nip press part – TRI-NIP is one of the possible configurations of press rolls in the press part. The TRI-NIP is a compact set of four press rolls forming three nips. It is used particularly for the conception of the press part with a shoe-press module in the position of the third nip. As a central roll of the 1st and the 2nd nips, a three-chamber suction roll is used, containing two chambers with a high-vacuum, ensuring the suction of water out of the felt in the point of the nip, and one chamber with a low-vacuum, ensuring the transfer of the paper from the 1st nip to the 2nd nip. A smooth press roll without a felt is placed in the position of the central press roll of the 2nd nip and the 3rd nip. The roll is dimensioned for two nips with a linear load up to 1200 kN/m. The smooth roll surface ensures the transfer of the paper from the 2nd nip to the 3rd nip.

A combination of a shoe-press module and a stationary press roll is used in the position of the 3rd nip, permitting to press with a higher linear load in the wider nip and to achieve a better dewatering of the paper.

The main advantage of the multi-nip press part TRI-NIP is the shortening of the paper track in the press part and the elimination of free draw forces. During its passage through the press, the paper remains in a permanent contact with one of the rolls and it is not necessary to equip the press part with additional guide rolls.

The compact configuration of press rolls considerably shortens the press part. The use of the shoe-press module in the position of the 3rd nip permits to reach the dryness volume after the press higher than 50 %.

The multi-nip press part TRI/NIP with the shoe-press module is useful particularly in high-speed machines, enabling to reach compact dimensions of the press part, a high volume of dryness after the press and the stability of the paper during its passage through the press part.

Main parts

• Pick-up – one-chamber or two-chamber suction roll for the transfer of the paper from the wire part into the press part
• Bottom press roll with felt (Ø 980 mm with coating)
• Three-chamber suction press roll with felt (Ø 1.120 mm with coating)
• Central press roll (Ø 1.250 mm with coating)
• Bearing structure
• Shoe-press module
• Nosná konstrukce
• Equipment for the felt guiding, cleaning and dewatering.

Material

• The bearing structure and guide rolls are made of common steel
• the press rolls embedding is made of cast iron

Accessories

• Roll removal equipment
• “Jumbo” press drive (mechanical and § electric part, control included)

Scope of delivery

• Complete machine in accordance with the main parts description
• Accessories optionally