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Valve seal (ring) material usage range comparison table

October 27, 2020

The selection of valve sealing material is determined according to the operating conditions of the valve, such as: pipeline medium, temperature range (high and low temperature), pressure and internal structure of the valve. For

soft sealing marine valve, rubber sealing, valve seat parts

different occasions, the selected seals are also different. Valve seals can generally be divided into two categories: soft seals and hard seals. Users should have a detailed understanding of their codes, operating temperature, pressure, medium and other parameters.

Comparison table of valve sealing material usage range:
Valve sealing material and valve sealing material use range:
Rubber (X) Nominal pressure PN ≤ 1 MPa, operating temperature t ≤ 150℃, applicable valves: globe valves, diaphragm valves, butterfly valves, check valves, etc.
Nylon (N) Nominal pressure PN ≤ 32 MPa, operating temperature t ≤ 90°C, applicable valves: globe valves, ball valves, etc.
PTFE (F) Nominal pressure PN ≤ 6.4 MPa, operating temperature t ≤ 180°C, applicable valves: globe valves, ball valves, gate valves, diaphragm valves, butterfly valves, check valves, etc.
Bus alloy (B) Nominal pressure PN ≤ 2.5 MPa, operating temperature t ≤ 150°C, applicable valves: stop valves for ammonia, etc.
Ceramic (G) Nominal pressure PN ≤ 1.6 MPa, operating temperature t ≤ 150°C, applicable valves: ball valves, plug valves, etc.
Enamel (C) Nominal pressure PN ≤ 1.0 MPa, operating temperature t ≤ 80°C, applicable valves: globe valve, diaphragm valve, check valve, discharge valve, etc.
Copper alloy (T) Nominal pressure PN ≤ 1.6 MPa, operating temperature t ≤ 200℃, applicable valves: gate valve, globe valve, check valve, plug valve, etc.
Stainless steel (H) Nominal pressure PN ≤ 32 MPa, operating temperature t ≤ 450°C, applicable valves: globe valves, ball valves (medium and high pressure valves), etc.
Nitrided steel (D) Nominal pressure PN ≤ 10 MPa, operating temperature t ≤ 540℃, applicable valves: power station gate valves, only for general use
Cemented carbide (Y) Nominal pressure (PN) and operating temperature (t) are determined according to the material of the valve body. Applicable valves: high pressure, ultra high pressure valves, high temperature and low temperature valves

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

What is the positive transmission of gears

October 23, 2020

When the total displacement coefficient of a pair of gears is greater than 0, it is a positive transmission.
Positive transmission refers to the positive displacement design of the gear. If two gears meshing with each other are in positive displacement, their center distance is greater than (the pair of gears) standard center distance. Conversely, if both gears use negative displacement, the center distance is smaller than the standard center distance. To judge whether the position is shifted, it is mainly to compare the measured gear parameters (including center distance) with the standard parameters of the gear to draw a conclusion.
Gear transmission is the most widely used transmission form in mechanical transmission. It has relatively

accurate transmission, high efficiency, compact structure, reliable work and long life. At present, the achievable indexes of gear technology: peripheral speed v=300m/s, rotation speed n=105r/min, transmitted power P=105KW, modulus m=0.004~100mm, diameter d=1mm~152.3mm
Features
1, the instantaneous transmission ratio is constant. The instantaneous transmission ratio of non-circular gear transmission can be designed according to the required change law.
2, the transmission ratio range is large, which can be used to decelerate or increase speed.
3, the range of speed (pitch circle speed) and transmission power is wide, and it can be used for high-speed (v>40m/s), medium-speed and low-speed (v<25m/s) transmission; power is from less than 1W to 105KW.
4, high transmission efficiency. A pair of high-precision involute cylindrical gears has an efficiency of over 99%.
5, compact structure, suitable for short-distance transmission.
6, the manufacturing cost is higher. Certain gears with special tooth shapes or high precision require special or high-precision machine tools, cutting tools and measuring instruments, so the manufacturing process is complicated and the cost is high.
7, low-precision gears, noise, vibration and shock during transmission, pollute the environment.
8, no overload protection
According to the relative position of the two shafts and the direction of the gear teeth, it can be divided into the following types:
<1>Straight tooth cylindrical gear drive;
<2> Helical cylindrical gear drive
<3> herringbone gear transmission;
<4> bevel gear transmission;

bevel gear

<5> cross-axis helical gear transmission.
According to the working conditions of the gear, it can be divided into:
<1>; Open gear transmission type gear transmission, the gears are exposed, and good lubrication cannot be guaranteed.
<2>; half-open gear transmission, the gear is immersed in the oil pool, with a protective cover, but not closed.
<3>; closed gear transmission, gears, shafts and bearings are all installed in a closed box, with good lubrication conditions, difficult for dust and sand to enter, accurate installation,
Gear transmission has good working conditions and is the most widely used gear transmission.
Gear transmission can be classified according to the relative position of its axis.
Gear drive can be divided into cylindrical gear drive, bevel gear drive, non-circular gear drive, rack drive and worm drive according to the shape of the gear.
According to the tooth profile curve, it can be divided into involute gear transmission, cycloid gear transmission and arc gear transmission. A transmission composed of more than two gears is called a gear train. The gear transmission can be divided into ordinary gear transmission and planetary gear transmission according to whether there are gears with axis movement in the gear train. The gears with axis movement in the gear train are called planetary gears. Gear transmission can be divided into closed type according to its working conditions
Gear transmission calculation
Open and semi-open transmission. Sealing the transmission in a rigid case and ensuring good lubrication is called closed transmission, which is more commonly used, especially for higher-speed gear transmissions, which must be closed transmission. Open transmission is exposed and cannot guarantee good lubrication. It is only used for low speed or unimportant transmission. Half-open transmission is somewhere in between.
The law of meshing: 　The smoothness of gear transmission requires the instantaneous transmission ratio in the process of gear tooth meshing i=angular speed of driving wheel/angular speed of driven wheel=ω1/ω2=constant, this requirement is guaranteed by tooth profile. Figure 2 shows that the two meshing tooth profiles E1 and E2 are in contact at any point K, and the common normal line N1N2 of the two tooth profiles is made through the point K, which intersects the connecting center line O1O2 at point C. The condition for maintaining contact during the meshing process of the two tooth profiles is that the velocity of the K point on the tooth profile E1, vK1, and the K point velocity on the tooth profile E2, vK2, are equal in the direction of the common normal line N1N2, that is, vKn1=vKn2=vKn. Make perpendicular lines from O1 and O2 to the N1N2 line and intersect at points N1 and N2. The above formula shows that the two-wheel tooth profile must meet the following conditions: “No matter where the two-wheel tooth profile is in contact at any position, the common normal line passing through the contact point must pass the fixed point C ─ ─ node on the connecting center line.” This is a circular gear. The basic law of tooth profile meshing. There are many curves that can meet this law. In fact, the requirements of manufacturing, installation and load-bearing capacity should be considered. Generally, only involute, cycloid and arc are used as the working tooth profile of the gear. Part of the tooth profile is involute.
For involute gears, the base radius rb1 and rb2 of wheel 1 and wheel 2 are respectively. The N1N2 line is the internal common tangent of the two base circles, that is, the common normal of any contact point of the two tooth profiles coincides with it. Because the two base circles have only one internal common tangent in one direction, the common normal of any contact point passes through the fixed point C, which shows that using an involute as the tooth profile conforms to the basic law of tooth profile meshing.
The two circles drawn through node C with O1 and O2 as the centers are called pitch circles. The pitch radius of wheel 1 and the pitch radius of wheel 2 Involute gears have the following characteristics: ①N1N2 is the trajectory of the contact points of the two tooth profiles, called the meshing line, which is a straight line. ②The common tangent line tt of the two pitch circles of gear transmission through node C is called the meshing angle α’between it and the meshing line N1N2, which is a constant. ③The pressure between the tooth surfaces is always along the direction of the common normal line N1N2 of the contact point, so the pressure direction between the tooth surfaces does not change when the involute gear transmits power. ④The transmission ratio is inversely proportional to the radius of the base circle of the two wheels. After the gear is made, the base circle is determined. Therefore, even if the center distance is slightly deviated from the design during operation, the transmission ratio will not be affected. This feature is called the separability of the transmission. It affects the processing, assembly and Maintenance is very beneficial. ⑤The two tooth profiles only have no sliding between the tooth surfaces when the node C is in contact, and there is sliding between the tooth surfaces when they are in contact at other points, and the farther away from the node, the greater the sliding. ⑥Since the involute gear can mesh with a rack with a linear tooth profile, it can be processed by a tool with a linear tooth profile. The tool is easy to manufacture and the machining accuracy can be high.
Coincidence degree: Coincidence degree is an important parameter that affects the continuous transmission of gears. As shown in Figure 2, gear tooth meshing starts from the contact between the tooth root of the driving wheel and the tooth tip of the driven wheel, that is, the intersection A of the tooth tip circle of the driven wheel and the meshing line is the starting point of meshing. As the wheel 1 rotates, the wheel 2 is pushed to rotate, and the contact point moves along the meshing line. When the contact point moves to the intersection E of the addendum circle of the wheel 1 and the meshing line (the dotted line in the figure), the tooth profile When the meshing ends, the two tooth profiles begin to separate. Point E is the meshing end point, which is the actual meshing line length. If the front pair of teeth are still in contact at point D before point E, and the latter pair of teeth are in contact at point A, then the transmission is continuous; if the front pair of teeth has left at point E, and the latter pair has not yet entered meshing , Then the transmission is interrupted. Considering the influence of gear manufacturing, installation errors and deformation, ε≥1.1～1.4 is often required in practice. The greater the coincidence degree, the more stable the transmission. The above refers to the coincidence degree of the end face of the cylindrical gear, and there is a longitudinal coincidence degree for the helical cylindrical gear.
The condition for a pair of gears to be able to mesh correctly is that they must have equal modulus and equal pressure angle.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Accuracy requirements of Equipment installation

October 23, 2020

1. For static equipment
The vertical deviation of vertical equipment should not be greater than L/1000 and not greater than 10mm. Unless the drawings have special requirements.

lug type butterfly valve, ductile iron, center lined,

The horizontal deviation of horizontal equipment should not be greater than L/1000 in the axial direction and 2D/1000 in the radial direction.

2. For moving equipment
When the pump is aligned, the selection of the installation datum and the allowable deviation of the level must meet the requirements of the “special specification” or the pump technical file. Generally, the allowable deviation of horizontal horizontality is 0.10mm/m, and the allowable deviation of vertical horizontality of the installation datum part is 0.05mm/m. The leveling and alignment values must not be adjusted by loosening the anchor bolts.
1. The pump that is disassembled and installed is based on the processing surface of the pump body, and the allowable deviation of the horizontality of the pump in the vertical and horizontal directions is 0.05mm/m.
2. The integrally installed pump should be leveled based on the inlet and outlet flange surface or other horizontal processing datum plane. The allowable deviation of horizontality is 0.05mm/m in the longitudinal direction and 0.10mm/m in the transverse direction.
3. When the driving shaft and the driven shaft are connected by a coupling, the centering deviation of the two shafts and the gap between the end faces of the two shafts should be:
Centering deviation: the radial displacement is not more than 0.03mm.
The axial tilt should not be greater than 0.05/1000.
The end face gap is 1.00~3.5mm.

What is assembly error and how to control it?

October 23, 2020

Assembly error refers to the difference between the installation position of the parts and the ideal position required by the assembly specifications and design regulations and processes.

Causes of assembly errors:

Double flange butterfly valve (1)

①Part error: the additional error caused by the manufacturing error of the part and the deformation and wear after operation and use.
② Errors in tools and measuring tools: tools and quantities have manufacturing errors, and system errors will occur if they are used for measurement and positioning.
③Operation error: due to hand feeling (such as tightness, flatness, sharpness, smoothness, beating, shaking, vibration, spacing, pulling force, hand tapping, hand-hand gap, hand feeling loose, etc.), visual inspection (size, level, straight , Vertical, parallel, aligned, tangent, etc.), ear hearing (various abnormal noises), nose smell (leakage, etc.), the error generated by the human sensory identification.
④Environmental errors: errors caused by temperature, relative humidity, light direction, air flow direction, movement of the foundation, etc.
⑤ Consciousness error: error caused by lack of concentration or lack of responsibility.
How to control assembly error:
1. Choose a reasonable assembly benchmark
In order to make the assembly position of the part accurate, select a certain part (point, line, surface) of the already positioned part as the positioning basis for the part to be installed. This part is called the assembly datum. The correct choice of assembly benchmark is an important factor in improving assembly accuracy and reducing assembly errors, and must be taken seriously. The following factors should generally be considered for the correct selection of the assembly datum.
(1) Try to choose parts with higher machining accuracy, that is, parts with small dimensional tolerance, high shape accuracy, small position deviation, and low roughness as the reference. For example, the diameter tolerance and radial runout of the groove part during the manufacturing of the roller are lower than those of the smooth surface. Therefore, when checking the roller bending and correcting the roller gauge, the groove part is the reference.
(2) The reference position should be as close as possible to the assembly adjustment point. For example, when the car surface is flat, the height of the car surface should be adjusted by the frame lifting screw, so the flat ruler should be placed as close to the frame as possible. For example, if the flat-foot iron rest is placed far away from the frame, and the reference point is far away from the frame, when the height of the adjacent frame is adjusted, the iron rest will be driven to rise and fall to make the reference drift. As shown in Figure 1, suppose the center distance ab of the two frames is 1008mm, point a is the point where the top surface of the car has been leveled, and point b is the point where the top surface of the car is to be leveled. The flat ruler should be placed at point a. If it is not placed at point a, it should be placed at point d, 100mm (ad) away from point a. When correcting the length of the car to be horizontal, the car surface at the adjustment point is from point b Adjusted to point c, increased by 0.10mm (bc), this flat ruler bar was also driven to rise from point d to point e, rising by 0.01mm (de), that is, the benchmark is raised by 0.01mm.
This shows that the farther the flat-foot rail is from the frame, the greater the change in the height of the reference plane, which affects the assembly accuracy.
(3) Try to reuse the same datum as much as possible to eliminate the deviation of the part surface shape. For example, because the top surface has a certain degree of lengthwise bending and widthwise distortion, it is necessary to look at the length of the car surface to the level of the flat ruler, the level to look at the width of the car surface and the level of the front roller to support the height line. Line round rollers are placed in the same position to avoid additional errors caused by uneven top surface of the car.
(4) When selecting the benchmark, the convenience of flat mounting operation should also be considered. For example, there are generally two methods for positioning the helical gear of the spindle shaft: one is to insert the spindle, and use the spindle as the reference, and use the card board to locate; the other is to not insert the spindle, and the lower dragon-jin oil cup is the reference. Although the tolerance of the spindle diameter is smaller than the tolerance of the oil cup hole, it is more difficult to locate after inserting the spindle. Taking the oil cup hole as the reference, it can meet the left and right positioning requirements of the spindle gear, and the spindle can not be inserted, which makes the operation convenient.
(5) Try to be consistent with the reference parts of the machine manufacturer’s parts processing and pre-assembly.
2. Avoid multiple transmissions of assembly standards (reduce cumulative errors)
There are two ways to divide a 1m long straight line into ten equal parts: one is to use a 150mm steel ruler, and the steel ruler is moved every 1oomm for ten times; the other is to use 1m steel The ruler does not move, but takes ten points in sequence according to the corresponding scale line. It is obvious that the error of the second method is relatively small. Because of the former method, due to multiple movements of the measurement reference, two or more assembly errors (tools, operating errors) are superimposed together, and cumulative errors are generated. By the same token, when measuring the gap with a feeler gauge of specified degree, a single-page feeler gauge should be used as much as possible to measure more accurately, and avoid using two or more thin feeler gauges to measure.
3, master the law of change of error (eliminate system error)
If the variation law of the error is found and the value is ascertained, it is like trying to eliminate the error value during assembly. This kind of regular error is called systematic error. For example, when the inner diameter measuring claw of a vernier caliper wears out 0.02mm, making the reading of each measurement imaginaryly larger by 0.02mm, you can automatically subtract 0.02mm from the reading to get the actual reading you need. Another example is when the level of the bubble is inaccurate, after the positioning and U-turn inspection, it is found that the bubble is inaccurate. After positioning to a certain end, it is horizontal. Therefore, when looking at the level, you should deliberately make the main bubble to a certain end. , So that the parts reach a level state.
4. Reasonable allocation or adjustment error value (reduce assembly error)
1). Mutual loan
When large castings such as the drawing locomotive face, bottom plate, roving frame head and tail wall panels, frame, and face are twisted and deformed, due to the inconvenience of orthopedics, only the verticality or levelness of multiple points can be checked to make the readings positive and negative after flat mounting The maximum value of the direction is equal, or the difference after subtracting the maximum value of the positive and negative directions is not greater than the allowable error. This method is called the mutual loan method.
2). Adjustment method
When the cumulative error in assembly exceeds the allowable error, the size, shape or shape of one of the links can be changed, or an unimportant size can be discarded without control, so that the total size is within the allowable range. This changeable link is called the “adjustment ring”. For example, when adjusting the draw frame roller seat to open the gear, first determine the left and right positions of the upper wall panel from the outer line of the front of the car, and then set the first roller seat position based on the upper wall panel of the front of the car. Set the position of the second, third, and fourth roller seat in turn, and the size between the fourth roller seat and the upper wall panel of the car can only be abandoned, and it is impossible to correct it. In actual work, the size, shape or position of the adjustment ring Changes are often achieved by filing, padding, welding, or adjusting with adjustable parts, such as adjusting screws, adjusting washers, and foot pads. Using these parts to adjust can improve assembly accuracy and save manual work. File repair and other work.
3). Select right assembly method
In order to reduce assembly errors and improve the accuracy of parts assembly, parts with certain errors can also be matched or grouped through selection, so that the upper and lower errors between the parts can be matched to appropriately improve the accuracy, which is called selective assembly. For example, group the rubber roller core and the iron shell to make the gap consistent; divide the diameter of the rubber roller into several gears to make the diameter of the rubber roller of the same machine or the same zone be the same.

What is machining accuracy, machining error, tolerance?

October 23, 2020

1. Machining accuracy: the degree to which the actual geometric parameters (size, shape and position) of the part after processing are in line with the ideal geometric parameters. The higher the degree of conformity, the higher the processing accuracy.
2. Machining error: the degree of deviation of the actual geometric parameters of the part from the ideal geometric

U-type-flange-butterfly-valve-2

parameters after processing is called the machining error. The magnitude of machining error indicates the level of machining accuracy, and machining error is a measure of machining accuracy.
3. Tolerance refers to the allowable error of the part processing clock.
What is the difference between them? “processing accuracy” and “processing error” are two different concepts for evaluating the accuracy of geometric parameters of parts. In the actual production, the method of controlling the processing error or the modern active adaptation processing method is used to ensure the processing accuracy.
Machining accuracy and machining error are described from different angles, but the size of the machining error is measured by the deviation of the actual measurement of the part, and the level of machining accuracy is measured by the tolerance level or tolerance value, and by the machining error To control the size. Generally speaking, the machining accuracy can only be guaranteed when the machining error is less than the tolerance.

What is the transmission ratio

October 23, 2020

In a mechanical transmission system, the ratio of the angular velocity or rotational speed of the driving wheel at the beginning and the driven wheel at the end.
Transmission ratio (i) = ratio of driving wheel speed (n1) to driven wheel speed (n2) = inverse ratio of gear index circle diameter = ratio of driven gear teeth (Z2) to driving gear teeth (Z1).
That is: i=n1/n2=D2/D1 i=n1/n2=z2/z1
For multi-stage gear transmission
1: The transmission ratio between every two shafts is calculated according to the above formula
2: The total transmission ratio from the first axis to the nth axis is calculated according to the following formula: Total transmission ratio ι=(Z2/Z1)×(Z4/Z3)×(Z6/Z5)……=(n1/n2)× (N3/n4)×(n5/n6)……

For multi-stage gear transmission

Extended information

The ratio of the angular velocities of the two rotating components in the mechanism is also called the speed ratio. The transmission ratio of component a and component b is Ⅰ=ωa/ωb=na/nb, where ωa and ωb are the angular velocities (radians/sec) of components a and b, respectively; na and nb are the rotational speeds of components a and b respectively ( Rpm) (Note: a and b after ω and n are subscripts).
When the angular velocity in the formula is an instantaneous value, the obtained transmission ratio is the instantaneous transmission ratio. When the angular velocity in the formula is an average value, the obtained transmission ratio is the average transmission ratio. For most gear transmissions and friction wheel transmissions with the correct tooth profile, the instantaneous transmission ratio is unchanged; for chain transmission and non-circular gear transmission, the instantaneous transmission ratio is variable.
For meshing transmission, the transmission ratio can be expressed by the number of teeth Za and Zb of wheel a and wheel b, i=Zb/Za; for friction transmission, the transmission ratio can be expressed by the radius Ra and Rb of wheel a and wheel b, i=Rb/Ra, At this time, the transmission ratio generally means the average transmission ratio.
In hydraulic transmission, the transmission ratio of the hydraulic transmission element generally refers to the ratio of the turbine speed S and the pump wheel speed B, that is, =S/B. Hydraulic transmission elements can also be combined with mechanical transmission elements (generally with various gear trains) to obtain various transmission ratios of different values (see gear trains for gear train transmission ratios).

Types of mechanical transmission

October 23, 2020

There are many forms of mechanical transmission, which can be divided mainly into two categories:
1. Friction transmission that transmits power and motion by friction between parts, including belt transmission, rope transmission and friction wheel transmission. Friction transmission is easy to achieve stepless speed change, and it can mostly adapt to transmission occasions with large shaft spacing. Overload and slip can also play a role in buffering and protecting the transmission device. However, this type of transmission is generally not used in high-power applications and cannot guarantee accuracy. The transmission ratio.
2. The meshing transmission of power or movement by the meshing of the driving part and the driven part or the meshing of intermediate parts, including gear transmission, chain transmission, spiral transmission and harmonic transmission. The meshing transmission can be used in high-power applications with accurate transmission ratio, but generally requires higher manufacturing accuracy and installation accuracy.

According to the forms of force transmission, mechanical transmission can be divided into:

1 Friction drive.
2 Chain drive.
3 Gear drive.
4 Belt drive.
5 Turbo worm drive.
6 Ratchet drive.
7 Crankshaft connecting rod drive
8 Pneumatic transmission.
9 Hydraulic drive (hydraulic planer)
10 Universal joint drive
11 Wire rope drive (most widely used in elevators)
12 coupling drive
13 Spline transmission.
1. Features of belt drive
Including driving wheel, driven wheel and endless belt.
1) It is used in the situation where the two axes are parallel and the rotation direction is the same, which is called the concept of opening motion, center distance and wrap angle.
2) The belt type can be divided into three categories: flat belt, V belt and special belt according to the cross-sectional shape.
3) The focus of application is: calculation of transmission ratio, stress analysis and calculation of belt, and allowable power of a single V belt.
Advantages-suitable for transmission with a large center distance between two axles; the belt has good flexibility, can alleviate impact and absorb vibration; slip when overloaded to prevent damage to other parts; simple structure and low cost.
Because the belt is elastic and is driven by friction, it has a simple structure, stable transmission, low noise, and can buffer and absorb vibration. When overloaded, the belt will slip on the pulley and protect other parts from overload. It is suitable for center distance Advantages such as larger transmission.
But belt transmission also has many shortcomings. The main ones are: accurate transmission ratio cannot be guaranteed, transmission efficiency is low (approximately 0.90～0.94), belt service life is short, and it is not suitable for use in high temperature, flammable, oil and water situations.
2. Gear transmission
Classification: plane gear transmission, space gear transmission.
Features
Advantages-Wide range of applicable peripheral speed and power; accurate, stable, and high-efficiency transmission ratio; high reliability and long life; transmission between parallel shafts, intersecting shafts at any angle and intersecting shafts at any angle can be realized.
Disadvantages-requires higher manufacturing and installation accuracy, higher cost; not suitable for long-distance transmission between two shafts.
The names of the basic dimensions of involute standard gears include addendum circle, tooth root circle, index circle, touch number, pressure angle, etc.
1. The range of power and speed transmitted by the gear is very large, the power can be as small as hundreds of thousands of kilowatts, and the peripheral speed can be as small as more than one hundred meters per second. The gear size can range from less than 1mm to more than 10m.
2. Gear transmission belongs to meshing transmission, the gear tooth profile is a specific curve, the instantaneous transmission ratio is constant, and the transmission is stable and reliable.
3. High gear transmission efficiency and long service life.
4. There are many kinds of gears, which can meet the needs of various transmission forms.
5. The manufacturing and installation of gears require high precision.
4. Features of chain drive
1) To ensure a more accurate transmission ratio (compared with belt transmission)
2) Power can be transmitted when the center distance between the two shafts is far (compared to gear transmission)
3) Can only be used for transmission between parallel shafts
4) After the chain wears out, the chain links become longer, which is easy to cause chain disconnection.
5. Worm gear drive
It is suitable for movement and dynamics between two axes that are vertical and not intersecting in space.
Features
Advantages-large transmission ratio. ; Compact structure size.
Disadvantages-large axial force, easy to heat, low efficiency; only one-way transmission.
The main parameters of the worm gear drive are: modulus, pressure angle, worm gear index circle, worm index circle, lead, number of worm gear teeth, number of worm heads, transmission ratio, etc.
Single-stage transmission can obtain a large transmission ratio, compact structure, smooth transmission, no noise, but low transmission efficiency. Two-stage transmission solves the shortcomings of single-stage transmission.
6. The characteristics of spiral transmission: high transmission accuracy, stable operation, no noise, easy to self-lock, and can transmit greater power.

In the valve industry, there are many ways to open and close the valve plate. we call it valve drive method. as below:

Unit two, valve drive mode (code name):

drive mode	Electro-magne-tism	Electro-magnetic hydraulic	Electro-hydraulic	tur-bine	Spur gear	Bevel gear	pneu-matic	Hydr-aulic	Gas-hydr-aulic	elec-tric	han-dle	Hand-wheel
code	0	1	2	3	4	5	6	7	8	9

See the link for more details: https://www.tanghaivalve.com/valve-model-establishment-and-meaning/

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Form and types of Gear transmission

October 23, 2020

Gear transmission types:

As per the mutual position of the two wheel axes, gear transmission can be divided into plane gear transmission and space gear transmission.
According to the type of gear transmission:

BS5163-BB-NRS-soft seated-wedge gate valve-DN700-PN16-bevel gear (8)

1. According to the relative position of the two shafts and the direction of the gear teeth, it can be divided into the following types:
<1>Cylinder gear drive;
<2>Bevel gear transmission;
<3> Cross-axis helical gear transmission.
2. According to the working conditions of the gear, it can be divided into:
<1> Open gear transmission, the gears are exposed, and good lubrication cannot be guaranteed;
<2>Half-open gear transmission, the gear is immersed in the oil pool, with a protective cover, but not closed;
<3> Closed gear transmission, gears, shafts and bearings are all installed in a closed box, with good lubrication conditions, difficult to enter dust, accurate installation, gear transmission with good working conditions, and it is the most widely used gear transmission.
3. According to the hardness of the tooth surface:
<1>Soft tooth surface gear The hardness of the tooth working surface is less than or equal to 350HBS or 38HRC;
<2>Hard tooth surface gear The hardness of the tooth working surface is greater than 350HBS or 38HRC. When a pair of gears are driven.

The form of gear transmission:
1. Parallel shaft gear (cylindrical gear)
(1) Spur gear: A straight cylindrical gear with tooth ribs parallel to the axis.
(2) Rack (Rack): A linear gear that meshes with a spur gear. It can be said to be a special situation when the pitch of the gear becomes infinite.
(3) Internal gear: The inner gear of a straight cylinder that meshes with the spur gear.
(4) Helical gear: Cylindrical gears with helicoid teeth.
(5) Helical rack: a linear gear that meshes with a helical gear.
(6) Double helical gear: a helical gear formed by left and right spiral tooth ribs.

2. Right-angle shaft gear (bevel gear)
(1) Straight bevel gear: A bevel gear whose tooth ribs are consistent with the generatrix (straight line) of the pitch cone.
(2) Spiral bevel gear: A bevel gear with a bevel line with a spiral angle.
(3) Zero helical bevel gear (Zerol bevel gear): a bevel gear with zero helix angle.

3. Gears with staggered shafts (worm gear and worm)
(1) Cylindrical worm gear: Cylindrical worm gear is the general name of worm (Worm) and gear (Wheel).
(2) Staggered helical gear (screw gear): This is a cylindrical helical gear, which is called when it is used for transmission between staggered shafts (also known as skew shafts).
(3) Other special gears: Face gear: a disc-shaped face gear that can mesh with a spur gear or a helical gear. Concave worm gear: Concave worm gear and its meshing gear. Hypoid gear: Conical gear that conveys the wrong axis. The shape is similar to a curved bevel gear.

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How to Find Gear Modification Coefficient

October 23, 2020

How to calculate gear modification coefficient:
1. Total displacement coefficient:

Total displacement coefficient

2. Coefficient of variation of center distance:

Coefficient of variation of center distance

3. Coefficient of change of addendum height:

Coefficient of change of addendum height

4. The modification coefficient table of the number of teeth z=8～20 cylindrical gear:

The modification coefficient table of the number of teeth z=8～20 cylindrical gear

Gear Modification Coefficient

What is the gear modification coefficient

October 23, 2020

The standard gear transmission has some limitations:
(1) Limited by undercutting, the number of teeth should not be less than Zmin, making the transmission structure not compact enough;
(2) Not suitable for occasions where the installation center distance a’is not equal to the standard center distance a. When a'<a, it cannot be installed, when a’>a, although it can be installed, it will produce excessive backlash and cause shock and vibration, which will affect the stability of the transmission;
(3) When a pair of standard gears are driven, the pinion has a small tooth root thickness and more meshing times, so the strength of the pinion is low, and the wear of the tooth root is also serious. Therefore, the pinion is easy to be damaged, and it also limits The carrying capacity of the big gear.
In order to improve the performance of gear transmission, a shifted gear appeared. As shown in the figure, when the tooth top line of the rack slotting tool exceeds the limit meshing point N1, the cut gear will undercut. If the rack is inserted away from the wheel center O1 for a certain distance (xm) and the tooth top line no longer exceeds the limit point N1, the cut gear will not undergo undercutting, but at this time the index line of the rack and the division of the gear The degree circle is no longer tangent. The gear cut after changing the relative position of the tool and the tooth blank is called the displacement gear, the distance xm the tool moves is called the displacement, and x is the displacement coefficient. The displacement of the tool away from the wheel center is called positive displacement, at this time x>0; the displacement of the tool moving closer to the wheel center is called negative displacement, at this time x<0. The standard gear is the gear with the modification coefficient x=0.

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