manufacturer Archives

what is bevel gear?

October 22, 2020

The bevel gear is used to transmit the movement and power between the two intersecting shafts. In general

bevel gear

machinery, the angle of intersection between the two shafts of the bevel gear is equal to 90° (but it may not be equal to 90°). Similar to cylindrical gears, bevel gears have indexing cones, addendum cones, tooth root cones and base cones. The cone has a big end and a small end, and the circle corresponding to the big end is called the index circle (its radius is r), the addendum circle, the root circle and the base circle. The movement of a pair of bevel gears is equivalent to a pair of pitch cones for pure rolling.
Application field
Industrial transmission equipment, vehicle differential
Classification
Straight tooth, helical tooth, curved tooth
Features
Noise reduction, shock absorption, light weight, low cost, etc.

Bevel gear actuator is coded 5 in the valve naming system in China, see link: https://www.tanghaivalve.com/valve-model-establishment-and-meaning/

Unit One , valve type (code name):

butterfly valve	safety valve	Diaph-ragm valve	ball valve	gate valve	check valve	plug valve	Pressure reducing valve	globe valve	filter	Disch-arge valve
D	A	G	Q	Z	H	X	Y	J	GL	FL

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

Unit three, valve connection method (code name):

connection	internal thread	external thread	two different connections	flange	welding	wafer	clamp	ferrule
code	1	2	3	4	6	7	8	9

1. Formation of tooth profile
The formation of the tooth profile of bevel gears is similar to that of cylindrical gears, except that the base cone is

The formation of spherical involute

used instead of the base cylinder. As shown on the right, the generating surface S is tangent to the generatrix of the base cone. When the generating surface S is purely rolling along the base cone, any straight line OK on the

generating surface contacting the generatrix ON of the base cone will form an involute curved surface in space. This curved surface is the tooth profile curved surface of the straight bevel gear. The trajectory of each point on the line OK is an involute (the involute at the vertex O is a point). Each point on the involute NK is equidistant from the cone O, so the involute must be on a spherical surface centered on the cone O and the radius is OK, that is, NK is a spherical involute.
2. Back cone and equivalent gear
The following figure shows a pair of special bevel gear drives. Among them, the number of teeth of wheel 1 is, the indexing circle radius is, and the reference cone angle is; the number of teeth of wheel 2 is, the indexing circle radius is, the indexing cone angle=90°, and the indexing cone surface is A plane, this kind of gear is called a crown gear.

Equivalent gear of bevel gear

The large end node P of the wheel 1 is used as the vertical line of the indexing cone generatrix OP, crossing its axis and point O1, and then taking O1 point as the cone tip and O1P as the generatrix, making a cone tangent to the large end of wheel 1 , Call this cone the back cone of wheel 1. In the same way, the back cone of wheel 2 can be made. Since wheel 2 is a crown wheel, its back cone becomes a cylindrical surface. If the back cones of the two wheels are expanded, the back cone of wheel 1 will be expanded into a sector gear, and the back cone of wheel 2 will be expanded into a rack, that is, after the back cone is expanded, the two are equivalent to gears and teeth. Strip meshing transmission. According to the Fan Cheng principle, when the tooth profile of the rack (that is, the back cone of the crown wheel) is a straight line, the tooth profile of the wheel 2 on the back cone is an involute.

Imagine filling up the gap of the unfolded sector gear, and you will get a cylindrical gear. This imaginary cylindrical gear is called the equivalent gear of the bevel gear, and the number of teeth Zv is called the equivalent number of teeth of the bevel gear. The tooth profile of the equivalent gear and the tooth profile of the bevel gear on the back cone (that is, the big end tooth profile) are consistent, so the modulus and pressure angle of the equivalent gear are consistent with the modulus and pressure angle of the large end of the bevel gear. As for the equivalent number of teeth, it can be obtained as follows:

As can be seen from the figure above, the index circle radius of the equivalent gear of wheel 1 is
γv1=γ1/cosδ1=z1m(2cosδ1)

So
zv1=z1/cosδ1

For any bevel gear there is
zv=z/cosδ

With the help of the concept of bevel gear equivalent gear, the correct meshing condition of a pair of bevel gears should be that the modulus and pressure angle of the large ends of the two wheels are equal respectively; the coincidence degree of a pair of bevel gear transmission can be calculated approximately according to the coincidence degree of the equivalent gear transmission ; In order to avoid undercutting of gear teeth, the minimum number of teeth for bevel gears without undercutting zmin=zvmincosδ
3. Analysis of gear tooth force
Similar to the cylindrical gear, the nominal normal load Fn is decomposed into the circumferential force Ft1, the radial force Fr1 and the axial force Fa1 at the average index circle of the pinion gear. The direction of each force is shown in the figure on the right, and then according to the force balance The geometric relationship between the conditions and the forces is calculated, namely

bevel gear force analysis

Force Analysis of Straight Bevel Gear

The force analysis on the big gear is similar to that on the small gear.
4. Geometric parameters and calculations
Bevel gears use the big end parameter as the standard value, so when calculating their geometric dimensions, the big end should also prevail. As shown in the figure below, the index circle diameters of the two bevel gears are respectively
d1=2Rsinδ1, d2=2Rsinδ2

In the formula, R is the distance from the tip of the indexing cone to the large end, which becomes the cone distance; δ1 and δ2 are the indexing cone angles of the two bevel gears (referred to as the cone angle for short).
The transmission ratio of the two wheels is

i12=w1/w2=z2/z1=d2/d1=sinδ2/sinδ1

When the shaft angle Σ=90° between the two bevel gears, the above formula becomes due to δ1+δ2=90°

i12=w1/w2=z2/z1=d2/d1=cotδ1=tanδ2

Geometry of bevel gear transmission

When designing bevel gear transmission, the value of the cone angle of the two wheels can be determined according to the above formula according to the given transmission ratio.

As for the size of the bevel gear tip cone angle and the tooth root cone angle, they are related to the head clearance requirements of the two bevel gears when they are meshed and driven. According to national standards (GB/T 12369-1990, GB/T12370-1990), equal head-clearance bevel gears are now used for transmission. The head clearance of the two wheels is equal from the big end to the small end of the gear. The cones of the degree cone and the root cone coincide at one point. However, because the generatrix of the tooth tip cone of the two wheels is parallel to the generatrix of the tooth root cone of the other bevel gear meshing with it, the cone tip no longer coincides with the indexing cone cone tip. This kind of bevel gear is equivalent to reducing the tooth tip height of the small end of the tooth, thereby reducing the possibility of the tooth tip being too sharp; and the tooth root fillet radius is larger, which is beneficial to improve the load capacity of the tooth, tool life and storage Oil lubrication.

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 Spur gear?

October 21, 2020

Spur gear is a classification of gears. According to the relative position and tooth direction of a pair of gear axes (whether the two circles are parallel), it can be divided into plane gear rotation and space gear rotation; according to

Spur gear

the working conditions of the gears, it can be divided into open transmission and closed transmission; according to gear teeth or tooth profile. The gear is divided into straight teeth, helical teeth, herringbone teeth, or straight teeth, curved teeth, as per the shapes.

The code name is 4 for valve drive mode. see details at: https://www.tanghaivalve.com/valve-model-establishment-and-meaning/

Unit One , valve type (code name):

butterfly valve	safety valve	Diaph-ragm valve	ball valve	gate valve	check valve	plug valve	Pressure reducing valve	globe valve	filter	Disch-arge valve
D	A	G	Q	Z	H	X	Y	J	GL	FL

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

Unit three, valve connection method (code name):

connection	internal thread	external thread	two different connections	flange	welding	wafer	clamp	ferrule
code	1	2	3	4	6	7	8	9

Classification
Straight cylinder/spur gear
Meshing mode: external meshing, internal meshing, gear and rack
Basic characteristics: The tooth profile contact line is a straight line parallel to the axis. A pair of tooth profiles enter or exit the mesh at the same time along the tooth width, which is likely to cause shock and noise, and the transmission stability is poor.

Straight bevel gear:
Pitch cone, index cone, tooth tip cone, tooth root cone, base cone; used for transmission between intersecting two shafts, the gear teeth are distributed along the cone surface, and the size of the starting gear teeth gradually decreases toward the cone tip.
In order to enable the gear to rotate in both directions, the tooth profile on both sides of the gear tooth is composed of involute surfaces with the same shape and opposite directions. The names and symbols of each part are: addendum circle, tooth root circle, tooth Slot, tooth thickness, tooth pitch, modulus m, index circle d, tooth top and tooth root, top clearance

Gears are divided into spur gears, helical gears, herringbone gears, and curved gears according to the shape of the tooth line. The spur gears are gears whose teeth are parallel to the axis.

Surveying method:
The spur gear is one of the most common gears in actual production and use. Damage is inevitable during use. Therefore, it is necessary to make a new gear that is the same as the original one. For various reasons, the customer cannot provide the required spur gear. In order to ensure the normal use of the processed products, the gear drawings need to be accurately surveyed and mapped. The surveying and mapping work is a complicated task. Since there are few data on the surveying and mapping of spur gears, it is naturally inconvenient to consult. The work experience and methods of surveying and mapping spur gears in several actual production are summarized by the operation. The introduction is as follows:

First of all, although there are many parameters and dimensions of spur gears, the standard system of various gears stipulates the modulus or diameter pitch as the calculation basis for other parameters and the dimensions of each part. Therefore, the surveying and mapping work should make every effort to accurately determine the size of the modulus or the diametral pitch. At the same time, the pressure angle is the basic parameter to determine the tooth profile, and accurate determination is equally important.

Secondly, we need to understand the usage and production country of the gear being surveyed, so that we can estimate the standard system adopted by this gear. Generally speaking, China, Japan, Germany, France, Czech Republic, and the former Soviet Union all adopt the modular system. You can also observe the tooth profile of the gear. If the tooth profile is curved and the bottom of the tooth groove is narrow and arc-shaped, it can be preliminarily judged as a modular system. The standard pressure angle is mostly 20 degrees; the United States and the United Kingdom adopt diameter control, and the standard pressure angles are 14.5 degrees and 20 degrees. Observing that the tooth profile is relatively straight and the bottom of the tooth groove is wider and the arc is small, it can be preliminarily judged as the diameter control. The pressure angle is 14.5 degrees. You can also use gear hobs or standard rack samples to determine which pressure angle is. If you know the above conditions, you can actually survey and map:

(1) Method of measuring the diameter of the addendum circle Dm

First count the number of teeth Z of the gear, and then use a vernier caliper to measure the diameter Dm of the addendum circle. If it is determined that the gear is a modular standard tooth profile, its modulus:

m = Dm/Z+2

If it is determined that the gear is a standard tooth profile with diameter control, its diameter pitch is

Dp=25.4*(Z+2)/ Dm

However, it should be noted that if the number of teeth of the gear is even, it can be directly measured; if the number of teeth is odd, the measured size is not the addendum diameter Dm, but two teeth from the tip of a tooth to the opposite tooth space. The distance D between the intersection of the face and the addendum circle is smaller than the diameter of the addendum circle. Usually, Dm is multiplied by the correction coefficient k to get the addendum circle diameter D, namely:

Dm=k*D

In practice, the diameter of the addendum circle calculated by the odd-numbered gear addendum circle diameter correction coefficient k (Table 1) is generally small. The diameter of the addendum circle calculated using the corrected correction coefficient k (Table 2) according to the above formula is more Close to the real value, Table 2 is more accurate than Table 1, and the number of teeth is finer, for reference.

fig.1-Odd tooth gear Addendum circle diameter Correction coefficient K

fig.2-Correction coefficient after correction k

If the odd-numbered gear is not a gear shaft but has a hole, you can also measure the inner hole diameter d and the distance H from the hole wall to the tooth tip, and get the tooth tip circle diameter by the following formula:

Dm=2*H+d

(2) Method of measuring the height of the tooth

When the gear is inconvenient to measure the diameter of the addendum circle due to large modulus, tooth punching, etc., the full height h of the tooth can be measured to determine the modulus or diametral pitch. The total tooth height h can be measured with the depth tail needle of a vernier caliper, and other depth measuring tools are also available, depending on the site conditions; if the gear has a hole, the tooth total height h can be obtained indirectly by measuring the inner hole wall to the tooth tip and tooth root The subtraction of the distance is the total tooth height h, and the modulus or diametral pitch is calculated as follows:

m=h/2f+c Dp=25.4*(2f+c)/h

f:: Addendum height coefficient c: Radial clearance coefficient

f, c can be found by checking the gear standard system parameter table[3]

(3) Method of measuring center distance A

When the gear teeth are sharp, worn, or rolled, the above two methods cannot be measured. At this time, we can ask the customer to provide the center distance A of the two paired gears and the number of teeth of the two gears. These are easy to do. Calculate the modulus or diametral pitch as follows:

m=2*A/Z1+Z2 Dp=25.4*(Z1+Z2)/2*A

Z1, Z2: Number of teeth of matched gear

The modulus or diametral pitch calculated by any one of the three methods is compared with the standard modulus or diametral pitch series, and the closest one is fine.

The above are the commonly used methods for surveying and mapping spur gears in actual work. It is best to use two methods to check each other, so that the determined modulus or diameter section is more accurate, and the surveying and mapping work is basically completed. Special attention: The above surveying and mapping methods are carried out under the condition that we can pre-determine or investigate the standard system adopted by the gear. If the gear’s “all conditions are unknown”, the above methods can only be referred to, and then comprehensively judged by other means. It is believed that the above several surveying methods will be helpful to colleagues who have just joined the work soon or for the first time to survey and map spur gears. It is worth referring to.

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

Check valve model designation method

October 21, 2020

Check valve model representation method Check model preparation instructions
Check valve (one-way valve) model compilation instructions:
Check valve (one-way valve) is also called check valve or reverse flow valve. It is an automatic valve that opens or

tilting disc swing check valve (3)

closes the disc through the flow of the medium itself, and can only flow in one direction and cannot be reversed. It is mainly used for In the piping system, prevent the medium from flowing back or flowing backward. Check valves have a wide range of uses and types. Different types of check valves are also different in different pipelines, operating conditions and connection methods. In order to avoid selecting the wrong model when purchasing a valve, and causing unnecessary working conditions during the application process due to improper model selection, users should have more understanding and awareness of the following check valve model preparation instructions. Check valve (check valve) model compilation instructions are mainly to make a detailed analysis of the additional conditions, connection methods, structural forms, sealing materials, pressure ratings and shell materials of the check valve. Hope it helps you when you buy check valves.

Check valve (check valve) model representation method:
Additional code of check valve: HH: micro-resistance slow-closing check valve, BH: heat preservation check valve, HQ: rolling ball check valve;
Check valve code: H stands for check valve;
Connection code: 4 flanges, 6 welding, 7 wafer;
Code of structural form: 1: lift type, 2: vertical type, 4: swing type, 6: double flap type, 8: butterfly type;
Sealing material code: B: babbitt alloy, F: fluorine plastic, H: stainless steel, M: Monel alloy, X: rubber, Y: cemented carbide, W: direct processing;
Pressure grade code: 16=16 kg pressure, PN1.6-25mpa, pound grade 150LB-2500LB, Japanese grade 5K-63K;
Shell material code: Q: ductile iron, C: carbon steel, P:304, R:316, A: titanium alloy, I: chromium molybdenum steel;

Example of model preparation of check valve (check valve):
H44H-16C swing flange check valve
H: indicates the check valve;
4: Flange link;
4: Swing type;
H: The sealing material is stainless steel;
16: The pressure is 16 kg (1.6mpa)
C: The valve body is carbon steel.

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

Description of lining material for rubber lining valve

October 12, 2020

Overview of rubber-lined valves:
Rubber-lined valve (lined valve) is a valve suitable for pipelines containing corrosive media and high sealing requirements. Generally, the applicable temperature should not be too high, and it is not suitable for use in media

double-wing-check-valve-3

containing particles to avoid scratches. Scratches or scratches the sealing surface, causing the valve to leak. Rubber-lined valve is a kind of plastic product produced by the chemical reaction of many chemical substances. The main materials are: soft rubber, hard rubber, butyl rubber, natural rubber, EPDM rubber, fluorine rubber, Lining silicone rubber, etc., its main working purposes are: diversion, adjustment, throttling, cut-off, check, diversion, overflow, etc., which means that as long as it is a general fluid valve, it can be controlled.

The main lining materials of rubber-lined valves:
【Neoprene, Code CR】
Applicable temperature: -10℃~105℃ Animal oil, vegetable oil, inorganic lubricating oil and corrosive slurries with a wide range of pH value, good wear resistance.
【Soft Rubber Code BR】
Applicable temperature: -10℃~85℃
Applicable medium: good wear resistance. Mainly used for sulfuric acid below 50%, sodium hydroxide, potassium hydroxide, neutral salt bath solution and ammonia solution, cement, clay, cinder ash, granular fertilizer and solid fluids with strong abrasiveness, and thick viscous liquids of various concentrations Wait. _
【Butyl Rubber Code IIR】 Applicable temperature: -10℃~120℃
Applicable medium: corrosion resistance and wear resistance. Can withstand most organic acids, alkalis and hydroxide compounds, inorganic salts and inorganic acid element gases, alcohols, aldehydes, ethers, ketones, esters, etc., ≤30% sulfuric acid, phosphoric acid, hydrofluoric acid, animal oil , Vegetable oil, caustic alkali and a variety of lipids. _
【Hard Rubber Code NR】 Applicable temperature: -10℃~85℃
Applicable medium: hydrochloric acid, fluorosilicic acid, formic acid and phenolic acid, hydrochloric acid, 30% sulfuric acid, 50% hydrofluoric acid, except strong oxidants (such as organic solvents such as acid, chromic acid, concentrated sulfuric acid and hydrogen peroxide) Acid, 80% phosphoric acid, alkali, salt, metal plating solution, sodium hydroxide, potassium hydroxide, neutral salt solution, 10% sodium hypochlorite, wet chlorine, ammonia, most alcohols, organic acids and aldehydes, etc.

Conversion of valve nominal diameter and inch | comparison table

October 12, 2020

Valve nominal diameter|valve nominal diameter
Definition of valve nominal diameter:

ductile iron, DI, butterfly valve, manufacturer, center line, TH valve

Nominal diameter (or nominal diameter), also known as average outer diameter, refers to the size of all piping accessories in the piping system. The nominal diameter is a convenient round integer for reference. The nominal diameter of the valve is marked with a number followed by the letter DN. DN represents the internal diameter of the pipe in millimeters. For example, DN50 is 50 millimeters. The American standard valve is usually expressed in inches (“), and the fractional valve is to express the internal diameter of the pipe in inches. The conversion formula is 1”=25.4mm, such as 8” is equivalent to the domestic DN200mm.

Valve nominal diameter comparison table:
The nominal diameter of the valve (NPS-NOMINAL PIPE SIZE) is not necessarily the same as the diameter of the flow channel. For the selection of its size, the required Cv value is calculated from the conditions of the conveying fluid, and then the Cv value (refer to the manufacturer’s catalog) is used to select a suitable valve The nominal diameter (NPS) is the nominal inner diameter that characterizes the valve diameter. The national standard is expressed by DN and the unit is mm. The American standard is expressed in inches. The conversion relationship between inch NPS and metric DN is as follows:

No.	inch	DN/mm	No.	inch	DN/mm	No.	inch	DN/mm
1	1/8	4	17	10	250	33	42	1050
2	1/4	8	18	12	300	34	48	1200
3	3/8	10	19	14	350	35	54	1350
4	1/2	15	20	16	400	36	60	1500
5	3/4	20	21	18	450	37	64	1600
6	1	25	22	20	500	38	72	1800
7	11/4	32	23	22	550	39	80	2000
8	11/2	40	24	24	600	40	84	2100
9	2	50	25	26	650	41	88	2200
10	21/2	65	26	28	700	42	96	2400
11	3	80	27	30	750
12	31/2	90	28	32	800
13	4	100	29	34	850
14	5	125	30	36	900
15	6	150	31	38	950
16	8	200	32	40	1000

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

Comparison table of valve diameter (DN) and pipe diameter

October 10, 2020

The size of the valve caliber has an inevitable relationship with the size of the pipeline. It is usually said that the pipe diameter (outer diameter) is matched with the valve. The valve diameter needs to be calculated according to the actual parameters. Generally speaking, the pipeline will be larger, and the valve actually needs to be smaller. It mainly depends on the flow rate to be controlled by the valve position, and the pipeline size only needs the flow capacity.
(1) Comparison table of pipe fitting size and valve diameter and inches:

Diameter/inch	DN (Norminal diameter) mm	pipe OD (mm)
1/4＂	8	13.7
3/8＂	10	17.14
1/2＂	15	21.3
3/4＂	20	26.7
1＂	25	33.4
1.2＂	32	42.2
1.5＂	40	48.3
2＂	50	60.3
2.5＂	65	73
3＂	80	88.9
4＂	100	114.3
5＂	125	141.3
6＂	150	168.3
8＂	200	219.1
10＂	250	273
12＂	300	323.8
14＂	350	355.6
16＂	400	406.4

(2) Valve diameter DN (nominal diameter) corresponds to the outer diameter of the pipe Ф (mm):

Norminal diameter/DN	pipe OD small	pipe OD big	Norminal diameter/DN	pipe OD small	pipe OD big
15	18	22	350	360	377
20	25	27	400	406	426
25	32	34	450	457	480
32	38	42	500	508	530
40	45	48	600	610	630
50	57	60	700	720
65	73	76	800	820
80	89	89	900	920
100	108	114	1000	1020
125	133	140	1200	1220
150	159	168	1400	1420
200	219	219	1600	1620
250	273	273	1800	1820
300	324	325	2000	2020

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

Working principle diagram of lift check valve

October 9, 2020

Lifting check valve structure:

Lifting check valve is a kind of valve that prevents pipeline media from flowing back, mainly composed of valve body, valve seat, valve flap, valve cover and other related parts. The lift check valve is equipped with a spring to ensure that the disc is always in a dynamic equilibrium state under the action of the spring. Regardless of the medium pressure at the inlet of the valve, the valve can maintain a balanced operation.

lift check valve Working principle diagram

The working principle of the lift check valve:

The lift check valve has a guide rod on the disc, which can move up and down freely in the guide hole of the valve cover. When the pipeline medium flows in in the specified direction (from left to right), and the pressure below the valve flap exceeds the pressure above it, push the valve flap to rise along the center line of the guide hole of the valve cover, and the valve will automatically open to allow the medium to flow; if the fluid flows from the right to the right Left flow, that is, when it flows backward, the pressure above the valve flap is greater than the pressure below it. The pressure difference between the upper and lower pressures and the weight of the valve flap press the valve flap on the valve seat, so that the medium cannot pass through, that is, the fluid cannot flow back; and pipeline fluid The greater the pressure, the tighter the sealing surface is, and the better the sealing effect.

The seat sealing surface of the lift check valve can be welded, or it can be made into a seat sealing ring and then expanded or threaded on the valve body; when the valve body is made of stainless steel, the sealing surface can also be on the valve body It is directly processed from above. The sealing surface of the disc can be directly processed on the disc, or can be processed after surfacing or welded on the disc with the inner and outer periphery of the sealing ring. The straight-through lift check valve can only be installed on the pipeline in a balanced way, and the center line of the valve flap is vertical to the horizontal plane, while the vertical lift check valve is not subject to this restriction.

What is butt welding? (9)- New technology of flash butt welding

September 29, 2020

New technology of flash butt welding
1) Program-controlled reduced-voltage flash butt welding is characterized by the use of higher secondary no-load voltage at the beginning of the flash to facilitate the initiation of the flash. When the end surface temperature rises, the low-voltage flash is used and maintained The flash speed remains unchanged to improve thermal efficiency.

flash butt welding-schematic diagram

When approaching the upsetting, increase the secondary voltage to make the flash stronger to increase the self-protection effect.
Program-controlled reduced-voltage flash butt welding is compared with preheated flash butt welding. It has the advantages of short welding time, low power required, and uniform heating.

2) Pulse flash butt welding. The characteristic of this welding method is that in the stroke of the moving clamp, a reciprocating vibration stroke is superimposed through the hydraulic vibration device, the amplitude is 0.25-1.2mm, and the frequency is 3-35Hz. Tune. Due to the vibration, the end face of the weldment is alternately short-circuited and pulled apart, resulting in a pulse flash.

Compared with ordinary flash butt welding, pulse flash butt welding has no spontaneous blasting of the lintel, the splashed particles are small and the flame is shallow, so the thermal efficiency can be more than doubled, and the upsetting allowance can be reduced to 2/3-1/ 2.

The above two methods are mainly to meet the needs of flash butt welding of large section workpieces.

3) Rectangular wave flash butt welding Compared with power frequency AC sine wave flash butt welding, this welding method can significantly improve the stability of the flash. Because the sine wave power supply will instantly interrupt the flash when the voltage is close to zero, and the rectangular wave can evenly produce the flash in the full cycle. It has nothing to do with the voltage phase.

The number of flashes per unit time of the rectangular wave power supply is 30% higher than that of power frequency AC, the sprayed metal particles are fine, the flame is shallow and the thermal efficiency is high. The rectangular wave frequency can be adjusted within the range of 30-180Hz. This method is mostly used for continuous flash butt welding of thin plates and aluminum alloy wheels.

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 butt welding? (7)- Flash butt welding of common metals

September 29, 2020

The following describes the characteristics of flash butt welding of several commonly used metal materials:

1. Flash butt welding of carbon steel

This kind of material has the advantages of high resistivity, the oxidation of carbon element during heating provides a protective atmosphere for the interface CO and CO2, and does not contain elements that generate high melting point oxides. Therefore, they are all materials with better weldability.

flash butt welding-schematic diagram

As the carbon content in steel increases, the resistivity increases, the crystallization interval, the high temperature strength and the hardening tendency increase. Therefore, it is necessary to increase the upsetting pressure and the upsetting allowance accordingly. In order to reduce the effect of quenching. Preheating flash butt welding can be used, and post-weld heat treatment can be performed.

During flash butt welding of carbon steel, because carbon diffuses to the heated end surface and is strongly oxidized, and during upsetting, the molten metal with high carbon content in the semi-melting zone is squeezed out, so a low carbon content is formed at the joint. Carbon layer (white, also called bright band). The width of the carbon-depleted layer increases as the steel content increases and the preheating time increases; as the carbon content increases and the gas medium oxidation tendency decreases, it becomes narrower. Long-term heat treatment can eliminate the carbon-poor layer.

The most frequently used is carbon steel flash butt welding. As long as the welding conditions are selected appropriately, there will generally be no difficulties. The same is true even for cast iron, which is difficult to weld for melting.

Cast iron usually uses preheated flash butt welding, and continuous flash butt welding is easy to form a white hole. Due to the high carbon content, a large amount of CO and CO2 protective atmosphere is generated during flashing, and the self-protection effect is strong. Even when the process parameters fluctuate greatly, there are only a small amount of oxidized inclusions in the interface.

2, flash butt welding of alloy steel

The influence of alloying element content on steel properties and the process measures to be taken are as follows:

1) Aluminum, chromium, silicon, molybdenum and other elements in steel are prone to produce high melting point oxides. The flash and upsetting speed should be increased to reduce their oxidation.

2) As the content of alloying elements increases, the high temperature strength increases, and the upsetting pressure should be increased.

3) For pearlitic steel, the increase in alloying elements increases the tendency to quench, and measures should be taken to prevent quenching embrittlement.

The welding characteristics of low alloy steel are similar to that of medium carbon steel, and have a tendency to harden, so the corresponding heat treatment method should be adopted. This type of steel has high high-temperature strength and is easy to generate oxide inclusions. It requires higher upsetting pressure, higher flashing and upsetting speed.

In addition to the characteristics of high-carbon steel, high-carbon alloy steel also contains a certain amount of alloying elements. Due to the high carbon content and wide crystallization temperature range, the semi-melting zone at the interface is wider. If the upsetting pressure is insufficient and the plastic deformation is insufficient, the liquid metal remaining in the semi-melting zone will form a loose structure. It also contains high melting point oxide inclusions due to alloying elements. Therefore, higher flashing and upsetting speed, larger upsetting pressure and upsetting allowance are required.

The main alloying elements of austenitic steel are Cr and Ni. This kind of steel has high high-temperature strength, poor electrical and thermal conductivity, low melting point (compared to low carbon steel), and a large number of alloying elements that easily form high melting point oxides ( Such as Cr). Therefore, a large upsetting pressure, high flashing and upsetting speed are required. The high flashing speed can reduce the heating zone, which can effectively prevent the rapid growth of grains in the heat-affected zone and the reduction of corrosion resistance.

3, flash butt welding of aluminum and its alloys

This type of material has the characteristics of good electrical and thermal conductivity, low melting point, easy oxidation, high oxide melting point, and narrow plastic temperature zone, which bring difficulties to welding.

Aluminum alloy butt welding has poor weldability, and improper selection of process parameters can easily produce defects such as oxide inclusions and looseness, which will sharply reduce the strength and plasticity of the joint. In flash butt welding, high flash and upsetting speed, large upsetting allowance and forced upsetting mode must be used. The specific power required is much larger than that of steel parts.

4. Flash butt welding of copper and its alloys

Copper has better thermal conductivity than aluminum and has a higher melting point, so it is more difficult to solder than aluminum. In pure copper flash butt welding, it is difficult to form a liquid metal layer on the end surface and maintain a stable flash process, and it is also difficult to obtain a good plastic temperature zone. For this reason, high final flash speed, upsetting speed and upsetting pressure are required during welding.

Copper alloys (such as brass, bronze) are easier to butt welding than pure copper. During brass butt welding, the performance of the joint is reduced due to the evaporation of zinc. In order to reduce the evaporation of zinc, a high final flash speed, upsetting speed and upsetting pressure should also be used.

Aluminum and copper flash butt welding transition joints are widely used in the motor industry. Because their melting points are very different, aluminum melts 4-5 times faster than copper, so the extension length of aluminum should be increased accordingly. The process parameters of aluminum and copper flash butt welding can refer to the following table. When aluminum and copper are butt welded, the intermetallic compound CuAL2 may be formed, which increases the brittleness of the joint. Therefore, it is necessary to squeeze out CuAL2 from the interface as much as possible during upsetting.

5. Flash butt welding of titanium and its alloys

The main problem of flash butt welding of titanium and its alloys is the reduction of joint plasticity due to quenching and gas absorption (hydrogen, oxygen, helium, etc.). The quenching tendency of titanium alloys is related to the added alloying elements. If the stable β-phase element is added, the quenching tendency will increase and the plasticity will be further reduced. If continuous flash butt welding with strong flash is used, a satisfactory joint can be obtained without adding shielding gas. When using flash and preheated flash welding with a low upsetting speed, the welding should be performed in an Ar or He protective atmosphere. The preheating temperature is 1000-1200 degrees, and the process parameters are basically the same as when welding steel, but the amount of flash reserved is slightly increased. At this time, a higher plastic joint can be obtained.

What is butt welding? (4)- flash butt welding

September 29, 2020

2. Resistance and heating of flash butt welding

The contact resistance Rc during flash butt welding is the total resistance of the liquid metal lintel between the end faces of the two workpieces, and its size depends on the number of lintels and their cross-sectional area at the same time. The latter two are related to the cross-sectional area of the workpiece, the current density and the

flash butt welding-schematic diagram

approach speed of the two workpieces. With the increase of these three, the number of lintels and their cross-sectional area simultaneously existing increases, and Rc will decrease.

The Rc of flash butt welding is much larger than that of resistance butt welding, and it exists throughout the flashing stage. Although its resistance value gradually decreases, it is always greater than the internal resistance of the workpiece. Rc does not disappear completely until the upsetting starts. Figure 14-5 shows the general law of Rc, 2Rω and R changes during flash butt welding. The gradual decrease in Rc is due to the increase in the approach speed of the workpiece as the end surface temperature increases during the flashing process, and the number and size of the lintels increase accordingly.

Because Rc is large and there is the entire flashing stage, the heating of the joint during flash butt welding mainly depends on Rc.

Three, flash butt welding welding cycle, process parameters and workpiece preparation

1, welding cycle

The welding cycle of flash butt welding is shown in 14-7, and the reset time in the figure refers to the time from loosening the workpiece to returning to the original position. There are two preheating methods: resistance preheating and flashing preheating. The figure (b) uses resistance preheating.

2, process parameters

The main parameters of flash butt welding are: extension length, flash current, flash flow, flash speed, upsetting flow, upsetting speed, upsetting pressure, upsetting current, clamping force, etc. Figure 14-8 is a schematic diagram of each flow rate and extension length of continuous flash butt welding. The following describes the influence of various process parameters on welding quality and the principles of selection:

(1) Elongation length l0 is the same as resistance butt welding, l0 affects the temperature distribution along the axial direction of the workpiece and the plastic deformation of the joint. In addition, with the increase of l0, the impedance of the welding circuit increases, and the required power also increases. Under normal circumstances, bar and thick arm tube l0=(0.7-1.0)d, d is the diameter of the round bar or the side length of the square bar.

For thin plates (δ=1-4mm), in order not to lose stability during upsetting, generally l0=(4-5)δ.

When different metals are butt welded, in order to make the temperature distribution on the two workpieces consistent, usually the metal with poor electrical and thermal conductivity should be smaller. Table 1 is the l0 reference value for flash butt welding of different metals.

(2) The flash current If and the upsetting current Iu If depend on the cross-sectional area of the workpiece and the current density jf required for the flash. The size of jf is related to the physical properties of the welded metal, flashing speed, the area and shape of the workpiece section, and the heating state of the end surface. In the flashing process, as vf gradually increases and contact resistance Rc gradually decreases, jf will increase. During the upsetting, Rc disappears quickly, and the current will increase sharply to the upsetting current Iu. When welding large-section steel parts, in order to increase the heating depth of the workpiece, a smaller flash speed should be used, and the average jf used generally does not exceed 5A/mm2. Table 2 shows the reference values of jf and ju for flash butt welding of workpieces with a cross-sectional area of 200-1000mm2.

The magnitude of the current depends on the no-load voltage U20 of the welding transformer. Therefore, in actual production, the secondary no-load voltage is generally given. When selecting U20, in addition to considering the impedance of the welder circuit, when the impedance is large, U20 should be increased accordingly. When welding large-section workpieces, the method of adjusting the secondary voltage in stages is sometimes used. At the beginning, a higher U20 is used to excite the flash, and then it is reduced to an adaptive value.

(3) Flash flow rate δf The flash flow rate should be selected so that there is a molten metal layer on the end of the workpiece at the end of the flash, and the plastic deformation temperature is reached at a certain depth. If δf is too small, the above requirements cannot be met, which will affect the welding quality. If δf is too large, it will waste metal materials and reduce productivity. When choosing δf, you should also consider whether there is preheating, because the δf of preheating flash butt welding can be 30-50% smaller than continuous flash butt welding.

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