The new process of calcine for ammonium paratungstate to tungsten trioxide by microwave was investigated. The results of experiment show that the maximum decomposing rate of ammonium paratungstate is 96 .67 % after 4 min bymicrowave heating. In the new calcining process, the primary influnce factor is ammonium paratungstate' s weight, the secondary factors are time and microwave power. In this experiment range, the optimum conditions are that the microwave power is 650 W, the calcining time is 4 min, and the ammonium paratungstate′s weight is 10g .

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Matches usually start from 501 in competition darts but other common starts are 301, 401, 701, and even 1001. Sometimes darts matches are played where a “double” is required to start each “Leg” of the match. However, the most common form of play is “straight start” which means that players/teams can begin to score points immediately with the first darts game thrown. Both teams start on the agreed starting number and the object is to score down to zero as quickly as possible. The value of the different sectors of the dartboard can be seen in Fig 1. above. Each section or “leg” of the match must be finished with a “double”, this means the outer scoring ring. For example as one approaches the end of a “leg” a player or team may have 40 points left to score. This means Double 20 is required and to end the “Leg” a dart must be thrown into the “double” section of the “20” sector. Should the thrower miss “double” 20 and hit (for example) a single 1, the the thrower would require 39 to win the “leg” where a single 7 then “double” 16 could be an option. Another example could be the player or team require 51 points. Then there would be several alternatives to end the “leg”. The usual route would be either a single 11 and then “double” 20, or perhaps a single 19 and then “double” 16. The first player or team to hit the required “double” wins the “leg”. A new leg is then started and the procedure repeated until one of the players or teams has won the required number of “legs” to win darts game.

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A game of darts always starts, and ends, with a handshake.

A game of darts can be played in played in several forms. The most common forms are:- One player against another which is known as “Singles” or teams of two players per team which is known as “Doubles” or “Pairs”. A game of darts is played over an agreed number of sections which are known as “legs”. The number of “legs” in a game is always an odd number usually 1, 3, 5, or 7 “legs”. Matches are played as (for example) “Best of 5 “legs”. This means that the first player or team to win 3 “legs” win the match.

Players throw alternately in “Singles” matches. In “Doubles” or “Pairs” matches each “Pair” throws alternately with each player in the respective “Pair” also throwing alternately. A “Throw” consists of “3” darts. If a player completes the “Leg” or the match in less than three darts the remaining dart or darts gameare not thrown.

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It should not rush into buying a set of darts. The weight and shape of darts varies enormously, as do the shapes of the flights.

We recommend that you try as many different types of darts and flights as possible before making a purchase. After a while you will soon become aware that each different type of dart behaves differently when YOU throw it. Take your time, find a set that you feel comfortable with before you buy.

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Dart caring need to keep the needle tip dart degrees.

First, dart beneath the blanket has a certain area of the pad or other cushioning material, so when racing game, dart needle or damage the floor.

Second, the target ring long metal darts in use carom, may loosen, just to nail nailed to move one position.

Third, the paper target darts have various reasons such as climate, there will be some cracks are normal and do not affect the results.

Fourth, sisal darts, in the humid climate, use hair dryer to dry the target surface, to maintain a certain dry to prevent mildew. If mildew occurs. Hair brush can be useful to the stain, wipe clean with alcohol, then blow dry, do not affect the results.

Fifth, keep the needle tip dart degrees, pull the dart, the barb, which will damage the target surface, the impact dartboard life otherwise.

Six, dart bar, dart feathers, dart needle is wearing parts, consumables, dart caring for use when replacing the need to press models, specifications with purchase.

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the life of tungsten carbide cutting tools. Cutting edge surface usually produces the following defects: flash, micro-gap edge region, the residual stress and the blade surface area cobalt leaching.

3. Residual Stress
tungsten carbide cutting tools due to its texture, structure and manufacturing process and other factors, in the manufacturing and sharpening process, the remaining energy will be unevenly accumulate on the surface or inside of the tool, the performance of the residual stress and stress concentration. Residual stress and stress concentration exists, the tool in the cutting process is more sensitive to stress and thermal stress, prone to fatigue cracking and chipping, leading to decreased tool life or damage.

4. Cobalt leaching
In the process of grinding of tungsten carbide cutting tools, grinding fluid not only can reduce the grinding temperature, but also serve to improve the quality of grinding and grinding efficiency effects, and therefore widely used in the processing. China Tianjin University graduate student Zhang good strong analyze the mechanism of cemented tungsten carbide cobalt leaching, and the use of oleic acid, triethanolamine and borax as a cutting fluid additives. Experimental results show that this method can suppress the leaching of cobalt tungsten carbide elements, thereby increasing tool life and reduce the cutting fluid on the human body. Grinding tungsten carbide grinding fluid when it is possible to make use of tungsten carbide cobalt leaching. Cobalt cemented tungsten carbide as binder, it will greatly reduce the leaching tungsten carbide cutting resistance to mechanical impact and service life.


 

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After grinding of tungsten carbide cutting tools, will be on the cutting edge defects, these defects can cause instability in the cutting process, the impact of the machined surface quality and reduce the life of tungsten carbide cutting tools. Cutting edge surface usually produces the following defects: flash, micro-gap edge region, the residual stress and the blade surface area cobalt leaching.

1. Burr
Tungsten carbide cutting tools on the cutting edge, there are many prominent thorn-like or burrs, called flash. Burr is small, the naked eye can not be observed, edges seem weak, but in reality is quite stubborn, using only grinding general, it is difficult to completely wear off. Cutting process, the burrs on the machined surface have swipe action, affecting the quality of the machined surface; moreover Burr easily collapse out or curl, curled edge will cause the cutting edge or chipping, thereby affecting the cutting tools.

2. Micro-gap
Tungsten carbide cutting tools after ordinary wheel or diamond grinding wheel, there are different degrees of micro-gap, these microscopic gaps are naked eye can not be observed, the microscopic gap width is generally 0.01 ~ 0.05mm, the width of the larger of 0.1mm or more. During cutting tool edge micro-gap easily extended, as the extension of the tool gap, increased wear, chipping and other phenomena will follow, accelerating tool wear and damage. If after grinding tool edge passivation, the tool becomes smooth edge, eliminating the exclusion of teeth, etc. jagged and crack defects.




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Heavy alloy (tungsten) is a kind of material as the substrate of tungsten (W content of 85-99%), and added Ni, Cu, Co, Mo, Cr and other elements of the alloy. Press alloy composition characteristics and uses into W-Ni-Fe, W-Ni-Cu, W-Co, W-WC-Cu, W-Ag and other major series, having a density of up to 16 .5-19.0g / cm3, and is the world known heavy alloy, it has a range of excellent features, heavy: General accounting for high 16.5-18.75g / cm3 ,, strength: tensile strength 700-1000Mpa, strong ability to absorb radiation: its capacity than lead 30-40%, thermal conductivity coefficient: 5 times mold steel; thermal expansion coefficient is small: only iron or 1 / 2-1 / 3, good conductive properties of steel; has good weldability and formability . Given the high proportion of these alloys have excellent features, it is widely used in the aerospace, aviation, military, oil drilling, electrical instrumentation, medical and other industries.




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There are many different types of darts on the market from brass though to tungsten by far the most popular are tungsten nickel darts. Dart barrels is a dense heavy weight metal ideal for darts.

Tungsten has been used for the production of darts since the early 1970's because it is twice as dense (heavy) as brass and a dart made from tungsten will be half the size of a brass equivalent. This means it is easier for a player to achieve close grouping and score the maximum 180!

High percentage tungsten darts cost more than lower content dart barrels, the main reason for this is down to the machining of the billet. High percentage tungsten darts take longer to make and wear the cutting tools faster. The speed of the cutters has to be turned down to a slower speed so to prolong the life of the cutting tool therefore this increases the production cost of making the finished dart barrels.

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In the recent years , many users at home and abroad have strict quality requirement not only in chemical composition but also in physical properties . Including particle-size and distribution (or apparent density ), crystal shape and so on .therefore, it is important to investigate the preparation of APT with coarse grain has been investigated systematically. A new technology for the crystallization of ammonium paratungstate with coarse grain has been studied. The factors influencing the physic-chemical properties of ammonium paratungstate crystal, such as temperature ,concentration in the process, and the addition of seed crystal and agitation with air is also in favor of the system. Ammonium paratungstate crystal with particle size of 36-42um and apparent density of 2.0-2.2g/cn-3 were obtained by controlling suitable technological parameters.

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