Cylinder dryer – composition and functions of each part
The station-type drum dryer is mainly composed of a station column, a drying drum, bearings and seals, a water trap, steam inlet and drainage pipes, an expander and a transmission device.
The drum dryer uses steam for heating. The steam is passed from the steam main pipe into the hollow column of the dryer (or the steam pipe next to the grooved rectangular column), and is introduced into each drying cylinder respectively. Each steam inlet column (or steam inlet pipe) is equipped with a regulating valve, a safety valve and a pressure gauge. When the steam pressure per unit area exceeds the specified pressure, the safety valve will automatically open to release the overpressure. of steam. The steam entering the drying cylinder transfers heat to the drying cylinder, and then transfers the heat from the surface of the drying cylinder to the water-containing fabric surrounding the surface of the drying cylinder. The steam condenses into water due to the loss of heat, and the condensed water is discharged from the dryer through a drainage hopper or a siphon. tube, enters the stand column (or outlet pipe) at the drainage end, and is discharged out of the machine through the drain. Due to the function of the water trap, water and steam are prevented from being discharged at the same time.
The main parts of the drying drum dryer are the drying drum, the drying drum bearing and the water trap.
1. Drying cylinder
The drying cylinder is one of the main components of the drying cylinder dryer. The diameter is uniformly 570mm, and the working range can be 1100mm, 1200mm, 1600mm, etc. The wrapping angle of the fabric on the drying cylinder is 250°~276°. Large drying cylinders are also used on printing machines, with diameters of 1500mm, 2134mm or 2438mm. According to the material of the cylinder, the drying cylinder can be divided into two categories: copper drying cylinder and stainless steel drying cylinder; according to the different structure of the condensate discharge device, the drying cylinder can be divided into two categories: bucket type and siphon type drying cylinder.
(1) Water bucket type copper drying cylinder is shown in Figure 5-5 : The cylinder body is rolled with 2~3mm red copper plate, and red ferrules are used at both ends to tightly connect the bulkhead and the cylinder body, and then screws are used to fix the flange hollow shaft on the bulkhead mouth. An air safety valve (Figure 5-6) is installed on the bulkhead at the non-drive end of the drying cylinder to prevent the negative pressure in the drying cylinder from being crushed (commonly known as “sucking”) due to negative pressure (such as when the car is turned on or stopped).
The structure of the water bucket is shown in Figure 5-7(a), and its working principle is shown in Figure 5-7(b). The water bucket is made of welded 2~3mm copper plate and is used to discharge the condensed water in the drying cylinder. The wiper blade is welded to the inner wall of the cylinder, and the conical water outlet connected to the bucket body is inserted into the center hole of the flange hollow shaft (Figure 5-5). When the rotation speed of the drying drum is low, the condensed water is concentrated in the lower part of the drying drum due to its own weight.
When the water bucket rotates with the drying cylinder to the lower part and encounters water, the water is scraped into the water bucket by the wiper; when the water bucket continues to rotate with the drying cylinder to the upper part, the water exits through the cone due to its own gravity. The water pipe drains out of the cylinder. Obviously, this bucket-type drainage device is corrosion-resistant, but it is only suitable for drum dryers with low rotation speeds.
There are support hoops installed inside the drying cylinder (Figure 5-5). The support hoop is an elastic ring made of HT15-33 cast iron. There is an open elastic joint on its circumference, and the diameter of the support hoop can be appropriately adjusted with screws. There are 7 notches evenly distributed on the outer ring to facilitate the circulation of condensed water in the drying cylinder. The purpose of adding support hoops is to improve the compressive strength of the cylinder and ensure the roundness of the outer circle of the drying cylinder. Generally, only one support hoop is installed on the drying cylinder. For wide drying cylinders (drying cylinders of 1600mm or above), two or more support hoops can be installed.
(2) Siphon type copper drying cylinder: Its structure is shown in Figure 5-8. The main difference between it and the bucket-type copper drying cylinder is the drainage method. The bucket-type drying drum relies on the gravity of condensed water to drain water, while the siphon-type drying drum uses siphon action to drain water. A siphon is a brass tube that is bent at one end. When driving, the condensed water accumulated in the drying cylinder is forced into the siphon tube by steam. Then, relying on the siphon effect and steam pressure, the condensed water can be continuously discharged out of the drying cylinder. Obviously, the smaller the gap between the curved end of the siphon tube and the inner wall of the drying cylinder, the less condensed water will remain in the cylinder during operation, and the higher the drying efficiency will be. However, since the other end of the siphon tube is fixed at the end of the air inlet cover, it forms a long cantilever with poor rigidity. In order to prevent scratches on the cylinder wall, a certain gap should be maintained between its curved end and the inner wall of the drying cylinder. The distance between the siphon tube and the inner wall of the drying cylinder is normal. It should be controlled at 5~8mm.
Figure 5-9 is the structural diagram of the siphon stainless steel drying cylinder. It is characterized by lightness, low transmission power, corrosion resistance, ability to withstand large pressure, and easy cleaning. However, since the thermal conductivity of stainless steel is smaller than that of copper, the drying efficiency is lower. Under the same drying conditions, the speed of the stainless steel drying cylinder should be about 10% lower than that of the copper drying cylinder to ensure the drying effect.
2. Drying cylinder bearings and sealing components
In addition to supporting the drying cylinder, the drying cylinder bearing must also seal the steam introduced into the drying cylinder or the condensed water discharged from the drying cylinder. Currently, three types of seals are widely adopted: packing seal type, plane seal type and spherical seal type.
(1) Packing sealed drying cylinder bearing: as shown in Figure 5-10. The steam passes through the steam inlet hole of the bearing seat and directly enters the inner hole of the drying cylinder shaft head. Adjust the compression screw to compress the spiral asbestos rubber filler through the gland, causing radial contraction and forming a rotating cylindrical seal with the shaft head. This kind of seal has a large rotational resistance to the drying cylinder shaft head, is easy to wear, and increases the consumption of transmission power. However, due to its simple structure, easy arrangement, maintenance and repair, and low installation requirements, although it is relatively old, it is still used today.Use.
(2) Plane sealed drying cylinder bearing: shown in Figure 5-11 In order to adopt the end face seal of solid lubricating materials, its main feature is to change the support of the drying cylinder shaft head from the sliding bearing on the front to a rolling bearing, which reduces friction and improves transmission efficiency. The rotary seal adopts the end face seal form of plastic graphite die casting. Use a siphon to drain the condensed water.
The steam enters the inner hole of the drying cylinder shaft head from the steam cover through the spring gland. The rotary seal is mainly formed between the plastic graphite die-casting part and the two end faces of the sealing ring, and a spring is used to press and seal them. The circular rubber sealing ring seals the casting and the steam inlet head housing and prevents it from rotating with the shaft head; the other cylindrical sealing ring seals the sealing ring with the shaft head and prevents it from rotating with the shaft head. Rotating sealing rings are used to prevent grease leakage in rolling bearings.
Figure 5-12 shows another structure of flat sealed drying cylinder bearing. Its sealing mainly relies on springs and pressure rings to compress the flat sealing ring so that it is close to the end face of the shaft head to form a seal. The function of the annular sealing ring is to prevent steam from leaking from the outer circle of the steam pipe. This flat sealing structure has good sealing performance, long service life, low rotational power consumption, and the drying cylinder neck is not easily worn. At present, water bucket drying cylinders generally adopt this sealing form.
(3) Spherical sealed drying cylinder bearing: As shown in Figure 5-13, it is installed on the outside of the drying cylinder rolling bearing. The sealing tube and the drying cylinder shaft head are tightly connected by threads. The steam enters the inner hole of the shaft head of the drying cylinder from the steam inlet cover through the sealing tube and then enters the drying cylinder. The rotation seal is achieved by the spherical friction between the fixed spherical sealing ring, the sealing ring and the sealing tube. The spring compresses the two friction spherical surfaces to prevent steam leakage. The condensed water is discharged from the siphon pipe through the water outlet elbow.
3. Drain trap
Drain trap is commonly known as steam return trap, also called steam blocking drain valve. Its purpose is to prevent steam leakage, reduce heat loss, and improve heat transfer efficiency while discharging condensed water. There are many types of water traps. There are three commonly used types of float traps, bell-shaped float traps and eccentric thermodynamic traps.
(1) Working principle:
① Working principle of float type water trap :The structure of the pontoon type water trap is shown in Figure 5-14. Figure 5-15 is a diagram of its working principle. When the condensed water and part of the steam enter the steam trap, the buoyancy of the water causes the float to rise, and the stop valve closes to block the leakage of water vapor, see Figure 5-15(a). As the condensed water continues to flow in, the water level gradually rises. When the liquid level rises to a certain height, it overflows into the float, see Figure 5-15(b). When the weight of the condensed water in the float exceeds the buoyancy force on the float, make the float sink and open the stop valve. The condensed water in the float will be discharged through the casing, stop valve and regulating valve under steam pressure, see Figure 5-15 ( c). After a certain amount of condensed water is discharged, the buoyancy force causes the float to rise again and close the stop valve. The condensed water continues to flow in, and the second cycle is performed.
Because there are often There must be a certain amount of condensed water, and the water level is higher than the lower end of the casing, forming a water seal and preventing steam from leaking out. The regulating valve is used to adjust the water flow speed during drainage so that the float rises slowly to avoid strong impact.
Some traps are equipped with a straight-through valve near the regulating valve to release air and discharge accumulated condensed water when driving. A viewing valve is installed at B to check the working condition of the steam trap. When the valve is unscrewed, condensation water can be sprayed out intermittently, then the operation is normal; if a large amount of steam is continuously sprayed out, the working condition is not good, and it should be adjusted or repaired in time.
This type of steam trap has a reliable structure, almost no steam leakage, and does not require a double filter. But it is large and heavy, and is an intermittent type of drainage.
②The working principle of the bell-shaped float type trap: Figure 5-16 shows the bell-shaped float type trap, which consists of a shell It is composed of body, upper cover, valve, metal double spring piece, bucket (i.e. bell-shaped float) and connecting rod. This kind of drain trap uses the characteristics of the metal spring leaf to bend when heated to block steam and drainage.
When part of the steam and condensate enter the drain through the filter at the bottom of the drain At this time, the steam pressure makes the bucket float, and through the connecting rod, the valve disc is driven to close the valve seat to prevent steam leakage. At the same time, as the temperature inside the bucket rises, the spring leaf is heated and elongated. The cover at the end of the spring leaf closes the drainage hole on the bucket, which increases the pressure inside the bucket and causes a water level difference between the inside and outside, as shown in Figure 5-17(a). As the condensate water continues to flow in, part of the steam condenses, the steam pressure in the barrel drops, and the water level rises, see Figure 5-17(b). When the water level reaches a certain position, the metal spring leaf shrinks due to cooling, the drain hole valve cover opens, and a large amount of condensed water enters the bucket. The bucket sinks due to its own weight. Through the connecting rod, the valve disc is opened to discharge the condensed water. See Figure 5-17(c). When the condensate water is discharged to a certain amount, steam enters the bucket, the temperature rises, the spring plate is heated and stretches to close the valve cover, and the bucket floats to close the valve disc, thus starting a second cycle.
This kind of water trap starts reliably, can continuously discharge saturated water and unsaturated water, has good operating performance, simple structure and small volume. However, maintenance must be strengthened.
③The working principle of the eccentric thermodynamic steam trap: Figure 5-18 shows the eccentric thermodynamic steam trap. It is mainly composed of a shell, an upper cover, a valve plate, a valve seat filter, etc. It uses the principle of thermodynamics to block steam and drain water.
When the condensed water flows from the inlet through the filter into hole A and reaches the bottom of the valve plate, the steam in the pressure transformer chamber D, annular groove B and outlet pipe C condenses due to the temperature drop and reduces the pressure. Under the action of steam pressure, the condensed water opens the valve plate, passes through the annular groove B, and is discharged from the C hole, see Figure 5-19(a).
When the steam enters the steam trap, because the outlet hole C is smaller than the inlet hole A, the steam encounters resistance, that is, along the edge of the valve plate Enter the transformer room D, as shown in Figure 5-19(b). As the steam continues to flow into the pressure transformer chamber D, the indoor pressure increases. At the same time, when the steam flows to hole C at high speed along the annular groove, according to the principle of thermodynamics, an area with negative pressure will appear around it, causing the pressure below the valve plate to be less than the pressure above it. Coupled with the weight of the valve plate itself, the valve plate will fall rapidly, closing the channel and blocking the continued leakage of steam, as shown in Figure 5-19(c). Due to the heat dissipation of the water trap, the steam in the pressure transformer chamber condenses, which reduces the pressure in the pressure transformer chamber.
When the condensed water flows into the trap again, the above cycle will be carried out again.
This type of water trap has relatively good performance, large hydrophobic capacity, simple structure, small size, long service life, and convenient maintenance.
(2) Selection of water trap: The selection of water trap is mainly considered from the aspects of working temperature, working pressure and drainage volume. Generally, the maximum medium temperature allowed by a steam trap is 250°C and the maximum working pressure is 980kPa, which are both much higher than the steam temperature and pressure of the drying drum heating system. Therefore, the main consideration is the drainage volume. Generally, a drum dryer consumes 1.5kg of steam to dry 1kg of moisture, and accordingly produces 1.5kg of condensed water. Therefore, based on the high vehicle speed and the moisture content of the wet and thick fabric being dried, the condensed water discharged from the drying cylinder per hour can be calculated, and then this value is multiplied by the correction coefficient k (≈3), which is the selected drainage volume. basis.
(3) Installation of the steam trap: As shown in Figure 5-20, the function of the direct discharge valve (also called the bypass pipe) is to speed up the process when there is a lot of condensed water before starting the vehicle or there is a lot of water accumulated in the steam trap. Drain the condensate. Sometimes there is debris in the trap that affects drainage, and a direct valve can be used to drain water directly. The function of the inspection pipe is to open the stop valve at any time to check the drainage condition of the trap.
(4) Precautions when installing the water trap:
① Keep it close to and below the drying cylinder that discharges condensate water. The drainage pipe should have a certain slope to facilitate the discharge of condensed water.
②A bypass pipe and a straight-through valve should be installed next to the steam trap to discharge a large amount of condensed water and dirt when necessary or when driving. The bypass pipe cannot be installed under the steam trap.
③Traps cannot be installed in series, but can be installed in parallel if necessary.
(5) Maintenance of steam trap:
① Regularly check the sealing between the valve seat, thimble, valve disc and valve disc. If there is steam leakage, repair or replace it immediately.
②Replace the water trap regularly, disassemble it for comprehensive inspection and verification.
③Regularly clear the debris in the drain trap (including the filter).
④ If the vehicle is parked for a long time in winter, antifreeze work should be done.
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