Bookbinding glue, heat-melting color stability, minimal odor, good weather resistance. Suitable for binding with soil-coated paper such as books, catalogs, leaflets, magazines, etc.
Features and application range: (Advanced Hot Melt Adhesive): Very strong viscosity. Hot-melt color stability, minimal odor, good weather resistance. Suitable for binding with soil-coated paper such as books, catalogs, leaflets, magazines, etc.
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The main component of bookbinding glue: ethylene-vinyl acetate copolymer (EVA)
Color: white granular
softening point: softening point
Viscosity: (175ºC) Viscosity (Mpa.s): 74000
Opening hours: 8s
Temperature resistance: 80ºC
Abstract: The outlet pressure of the steam valve frequently fluctuates beyond the limits, and even the loss of regulation function has been a very common problem in the heat supply project. After long-term observation found that one of the major reasons is not the valve itself, but the system due to condensation of water intrusion. Through the research on the structure of decompression and its related effects, due to the characteristics of the valve structure, the stagnation of the valve condensate is inevitable. Analysis of each detail of the working principle of the pressure reducing valve found that condensate has a devastating effect on the regulating function of the valve. The system of condensate separation and removal, that is, to ensure the maximum degree of normal dry steam supply, the decompression device, the key to stable work. Therefore, the basic requirements and related measures of pressure relief device design are proposed. At the same time, but also to recognize that the direct object of the work decompression device z are mostly pressure vessels. "Overpressure" poses a direct threat to the process temperature, product quality and equipment's own safety of the equipment and must be given high priority. When we often hear from the operating personnel where such a reflection: now made of the pressure reducing valve, the quality is not enough, the pressure is often unstoppable after the stage, life is too short, use soon, it does not work. Due to the loss of control valve, resulting in relief valve relief, harsh whistle, scared neighboring four, not only a waste of energy, but also directly affect the safe operation of equipment. The problem is, some units have changed the import valve, use soon, the above problems still appear. Through a large number of uncontrolled devices survey (of course, do not rule out the existence of the valve itself) a common finding: there is a lot of water generally in the valve, many of which are used in the near future the new valve, and the system design did not take Condensate effectively eliminate the measures. Tests show that: After excluding these condensate water, most of the valves can be put into normal operation, which enlightened: Condensate water is the main cause of uncontrolled decompression device? Through thinking, a clear research direction, first, to understand the construction of the valve itself is there any possibility of condensation of water? What part? Second, to solve the condensation of water regulation function is not devastating effect? 1 pressure reducing valve structure and the possibility of stagnant condensate It should be said that the valve is a more complex valve, complex structure, valve sleeve valve (a valve has two distinctly different pilot and Main valve) must understand in detail their structure and related role. At present, the most commonly used domestic Y43H Series Piston Pressure Reducing Valve and imports of pilot-valve-type pressure reducing valve, for example, for comparison. (See Figures 1 and 2). 1.1 The main structure and related differences As can be seen from the figure, regardless of domestic or imported, although the structure is different, but by adjusting spring components, pilot valve components, main valve components and the adjustment of the four major components of the channel. 1.1.1 Adjusting Spring Assembly and Pilot Valve Assembly: Except for the difference in the shape of the pilot valve spool (one is a frustum, one is a sphere). 1.1.2 The main valve components: structurally the exact opposite The main valve spool is arranged below the valve seat, the intake direction is low into the high, was horizontal S-shaped; inlet valve spool arranged on top of the valve seat , Intake direction is high and low, was anti-transverse S-shaped. 1.1.3 Pressure Regulating Channels (α, β, γ in Figure 1, a, b, c in Figure 2) Different domestic valve pressure regulating channels are preset inside the valve body (built-in), inlet valve pressure The adjustment channels are all bolted to the outside of the valve body (external). 1.1.4 β channel and b channel function difference Domestic β channel is from the pilot valve annular steam chamber directly to the piston chamber below the upper chamber, only the connection function. The inlet b-channel is a valve body (a very thin hole) that is shunted from the main supply channel to the downstream outlet and this channel is very special and not only creates a pressure differential with the main diaphragm lower chamber but also helps the main diaphragm Piece of exercise, but also can drain part of the remaining pressure steam and condensate to the downstream outlet pipe section, more conducive to the main valve closing quickly. v domestic valve, as long as the pilot valve is opened, the condensate water will quickly enter from the α channel into the upper part of the pilot valve cavity, β channel and the upper piston chamber, with the piston down, Until the piston stroke reaches the bottom dead center, the cylinder becomes a "water tank" during this process. Domestic valves, due to the structural characteristics of water volume is relatively small, so as long as a small amount of condensate can fill these parts. Inlet valve, when the pilot valve is opened, the condensate water is generally deposited on the cylinder, piston cylinder chamber and the main diaphragm under the main valve movement of the prime mover, and β, a, b channel these pressure transmission system. This shows that due to the characteristics of its own structure of the valve, valve stagnation of stagnant water is inevitable, and are the core parts of the valve work. 2 From the working principle of the pressure reducing valve to analyze the destructiveness of the condensate on the regulator function To investigate the effect of the condensate on the regulator function of the regulator, we must first understand the working principle and relationship of the regulator. 2.1 Domestic pressure reducing valve works Pilot valve are open using the top of the adjustment bolt clockwise to move the spring shrinkage of the elastic force, so that the pilot valve diaphragm depression down, the role of the pilot valve rod on the force , Make it down to open the pilot valve. After the pilot valve is opened, the steam in the chamber A upstream into the steam pipe section passes through the alpha channel (for the steam regulating passage) and enters the pilot valve annular steam chamber through the pilot valve and is directly sent to the upper piston chamber by the beta channel. Under the constant supply of steam in chamber A, the pressure continues to rise, pushing the piston to open the main valve downwards, at which point steam flows continuously from chamber A to chamber B. When the downstream outlet pipe B chamber load to meet the circumstances, the more steam in turn B chamber pressure continues to rise. Rising pressure is fed back to the lower diaphragm of the pilot diaphragm via the y-channel (pressure sensing channel), causing the diaphragm of the pilot diaphragm to protrude upward, overcoming the pressure of the upper regulating spring, causing the pilot valve to be closed or closed. Thus, the steam source from the upstream alpha channel is turned off or off. When the piston cylinder pressure on the cavity down, the role of the following reset spring, the main valve is closed down or closed, then the pressure began to fall within the B cavity, so that the cycle to achieve the purpose of regulating. 2.2 The working principle of the inlet valve When the pilot valve is opened, as can be seen from Figure 2, the steam upstream of the A cavity quickly into the internal filter cover, through the pilot valve to a channel (for the steam adjustment channel), when a channel Filled with steam directly to the main valve diaphragm chamber, while a portion of the steam through the b channel (pressure control channel) is diverted into the B cavity. The lower diaphragm of the main valve is continuously supplied with steam from channel a. The main diaphragm is pressed upward and then pushed upward. The thrust generated urges the main valve rod to move upward to open the main valve. The same steam flows continuously from chamber A to chamber B . When the downstream outlet pipe section load is satisfied, more steam also makes the pressure in chamber B continuously increase, and the increasing pressure is transmitted to the lower cavity of pilot diaphragm through c channel (pressure sensing channel) When the pilot diaphragm projects upward, overcoming the pressure of the upper adjustment spring, the pilot valve is closed or closed, reducing and shutting off steam from chamber A. When the pressure in the lower part of the main valve diaphragm is gradually reduced, the upper main valve spring acts to move the main valve spool back to the seat and the main valve is closed or closed (excess steam is simultaneously released through the b-channel into the B-chamber. The main valve Quickly closed), making the B cavity pressure continues to decline, so to achieve regulation. (Pilot valve open principle, import valve and domestic valve the same, abbreviated) 2.3 Condenser water damage regulator Regulatory mechanism analysis When the downstream pressure (B cavity) when the need for pressure reduction. Under normal circumstances, the high pressure in chamber B is transmitted to the pilot valve through the pressure sensing channel (γ) so that the pilot valve is closed or closed to close and shut off the vapor source from chamber A. When condensate enters the cylinder or annular chamber, the main valve's return spring completely loses its function as the water is incompressible. At this moment, the piston can not go up and the main valve can not close and the steam in the inlet (chamber A) , Through the main valve normally open state into the B cavity. Make the pressure high and out of control. The same example, see the import valve (see Figure 2) when the system is filled with condensate a, b channel and the main diaphragm when the lower chamber. From the A cavity steam thrust, the main valve diaphragm in a state of upward bulge. Similarly, the water is incompressible, so that the upper return spring can not go back to the seat, the main valve is also normally open, and the stability adjustment function is damaged. Here it is important to emphasize that while the pressure relief valve is part of a proportional control valve, the nature of the proportional control changes completely when the condensate water fills these core workings in the valve. The key issue is the friction of the moving parts The role of resistance and sequence of actions has time difference, determines the main valve movement has a lag. (Pilot Operate First, Main Valve Trailing) After accepting the overpressure information from the γ and c channels, first, close or close the pilot valve. In this way, cut off the valve back to the condensation of water, it is clear that the piston and the main valve diaphragm can not move. Based on the above analysis and discussion, it is clear that system condensate has no beneficial effect on the heat supply project. From this conclusion, the system condensate is the most basic reason to destroy the regulation function of the steam relief valve. 3 system condensate is the only source In the process of writing this article, my colleagues suggested that the valve in its own work process of heat will produce condensate? The issue put forward so that we have to consider whether the internal pressure relief valve will also precipitate the problem of condensate? So it is necessary to understand the working process of the valve thermal state. In order to more vividly illustrate the problem, to borrow LgP-I diagram to analyze to see if the pressure is reduced, the state of their changes in the relevant parameters, there will be an answer. Assuming that the upstream inlet pressure is P1 and the downstream outlet pressure is P2, P1 intersects the dry saturated steam line at O1 along the isentropic line. The downstream outlet pressure P2 intersects the isentropic line at O2. When the pressure drops from P1 to P2, other relevant parameters also change correspondingly. As can be seen in Figure 3, the pressure decreases from P1 to P2 along the isentropic line, so the enthalpy does not change, but the entropy increases from S1 to S2, and the specific volume increases from V1 to V2 as well, but the temperature drops from t1 to t2. Seen in this light, the flow of steam through the valve, it should be considered the process of adiabatic throttling. This adiabatic throttling process is irreversible adiabatic expansion and other enthalpy flow process. After the steam throttling enthalpy unchanged, specific volume and entropy have increased, the temperature decreased slightly. Steam through the valve, not only does not produce condensed water, and steam dryness has also been improved, it can be said that the production of condensed water from the system, and is unique. In this way, measures to prevent and reduce the flow of condensate into the pressure relief valve have also been simplified. 4 measures and methods 4.1 pipe condensate excluded A good practice Steam heat source to the steam terminal, along the way as few as tens of meters, as many as a few hundred meters or longer, with some equipment intermittent gas , Steam pipe and the environment continue to heat exchange, this part of the condensate removal of water is usually used to solve the segmented hydrophobic. So what is the effect? From Figure 4, we can see that, because of our selection of hydrophobic pipe diameter are relatively small, it is conceivable that when the tube steam flow rate of dozens to tens of m / s, the actual situation is not condensate in the discharge of how much It has been run through the drain tube. This traditional method of drainage efficiency is low, the effect is not satisfactory. Between the steam main and the drainage pipe, a section of condensate pooling pipe is installed between the main pipe and the drainage pipe. The pipe diameter is coarse and the water collection ability is strong. The drainage pipe leads from the waist of the condensate short pipe to form a water seal steam and is not easy to escape. Condensate short pipe diameter and steam pipe than the recommended 1/2 ~ 2/3. Such as Dn100 caliber for the steam pipe, condensate collection short tube diameter can choose 50 ~ 80 caliber. This method of large displacement, good effect, the current methods commonly used abroad, it is worth learning. 4.2 Pressure Reducing Device The setting of the water separator is crucial. Adding a water separator can ensure the supply of dry steam to the maximum extent. It is an important guarantee for the stable working and service life of the pressure reducing device. According to the principle of gravity separation and combination of suspense the author designed a water separator, the actual use of the effect is not bad, for reference purposes only. Looking at foreign separator products, divided from the principle of gravity, condensate, centrifugal. From the formal point of view there is horizontal, vertical, variety and diverse, complete specifications. However, there is no product available in the domestic market. Now mostly used foreign products. (Expensive, discouraged.) Detention of condensate is detrimental to a steam heating system. Therefore, the research and development of water separator there are many things to do, hope counterparts are concerned about. 4.3 decompression device design of several issues: (1) in the water separator condensate discharge port must be provided at the bottom of a separate discharge port for drainage equipment starts. (2) Bypass settings, preferably over the relief valve, or parallel. (3) Steam filter installed close to the pressure relief valve. (4) The choice of pressure reducing valve flow to be appropriate, the device's steam consumption to be accurate calculation. The author's experience, the pressure relief valve flow should be larger than the equipment consumption of steam 10 ~ 20% is appropriate, do not appear, "Malaysia's car situation", otherwise, the stability of the decompression conditions also have an impact. 5 Concluding Remarks 5.1 Improvement of Steam Decompression Heating Specifications The pressure reducing valve has the characteristics of "fear of water". The design and installation of the decompression device must pay attention to the separation and elimination of the condensate water in the system. At the same time, it is hoped that these safeguards will be fully considered in the revision of the standard Supplementary measures. 5.2 domestic steam steam water separator research and development as soon as possible to make the product diversified, series specifications for the stability of the decompression device to create a basic condition 5.3 from a fundamental understanding of the stable operation of the decompression device, its safety and economic significance In fact, the objects requiring decompression heating, such as material reaction pots and heat exchangers, are often pressure vessels. There are many explosion accidents every year. There are many reasons for the out-of-control safety fittings such as safety valves and rupture disks. A fact tells us: security attachments for various reasons can not be 100% reliable. The general idea is that the decompression device overpressure does not matter, anyway, the back of the safety accessories will automatically relief, decompression device depends on the sensitivity of the safety attachment, whereas the safety accessories out of control, "overpressure" will directly lead to accidents The occurrence of the accident, and the culprit. It should be said that as long as the decompression device is stable and reliable, in order to ensure the safe operation of the system and economic operation. It is clear that the safe operation of the decompression device is the first (concept of prevention) The role of safety attachments is second (concept of governance), only "prevention first, prevention combined with prevention" in order to eliminate from the source Accident happened. The scientific design of pressure relief devices is of great importance both in terms of safety and economy.