Powder granularity: It stresses that tungsten powder granularity has an effect on tungsten copper electrode and other properties. Generally, the higher sintering temperature, the larger average granularity and the better strength of tungsten skeleton. However, if the granularity of tungsten powder exceeds a certain degree, the contact area among tungsten powder will be reduced and the tungsten powder can not be necking, which decreases the strength and hardness of tungsten skeleton and material.

Some scientists do some researches about tungsten powder granularity and volume fraction effects on density of tungsten copper electrode, they thought it depends on original grain size of tungsten powder and this effect will decrease by the increasing temperature of sintering temperature.

More infomation about tungsten copper electrode infiltration, click here:

http://news.chinatungsten.com/en/tungsten-information/79730-ti-10171

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In part 13 we know that the two major materials for reamers are high-speed steel and tungsten carbide, and tungsten carbide reamers are less affected by heat in machining process, but with so brittle and blunt cutting edges that they are not for light machinery. And here we list the different applications of the reamers made of the two categories of materials.

 (To be continued. This article is divided into several parts and this is part 14, for part 13 please refer to http://news.chinatungsten.com/en/tungsten-information/79733-ti-10198)

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In part 12 we know that the life of a tungsten carbide reamer can be up to 30,000 holes keeping size quality consistent if used properly and reamers are usually used with a drill press, lathes, machining centers or the similar. And here we explain two categories of materials used to build reamers.

Two materials for reamers

Like other cutting tools, there are two categories of materials used to build reamers: heat treated and hard. Heat treated materials are composed by different steels, most notably plain carbon (unalloyed, considered obsolete today) and high-speed steels. The most common hard material is tungsten carbide (solid or tipped), but reamers with edges of cubic boron nitride (CBN) or diamond also exist.

The main difference between both categories is that hard materials are usually unaffected by the heat produced by the machining process and may actually benefit from it. The down side is that they are usually very brittle, requiring slightly blunt cutting edges to avoid fracture. This increases the forces involved in machining and for this reason hard materials are usually not recommended for light machinery. Heat treated materials, on the other side, are usually much tougher and have no problem holding a sharp edge without chipping under less favorable conditions (like under vibration). This makes them adequate for hand tools and light machines.

 (To be continued. This article is divided into several parts and this is part 13, for part 12 please refer to http://news.chinatungsten.com/en/tungsten-information/79704-ti-10192; for part 14 please refer to http://news.chinatungsten.com/en/tungsten-information/79734-ti-10199)

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Infiltration is kind of process that uses the metal or alloy which has lower melting point than the product to fill in the pores of products in molten state. For tungsten copper electrode, copper solution has lower melting point and it fill in the porous tungsten skeleton, which has excellent density and strength so that tungsten copper material has better properties, such as thermal conductivity, electric conductivity and high hardness.

The process is: Tungsten powder (W) + shaping agent (or adds Cu-induced powder) → tungsten skeleton (suppressing + degreasing + sintering) → copper infiltration (Cu) → after treatment. And the most research focus on:

1. Powder granularity

2. Tungsten skeleton

3. Infiltration process

4. After treatment.

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In order to reach the theoretical density, researchers add some trace activated elements to improve liquid sintering. Compared with high-temperature sintering, liquid activated sintering decreases the sintering temperature, reduces the sintering time and improves the properties of tungsten copper electrode.

The research proved that Co and Fe is beneficial for improving the density of tungsten copper electrode, Ni and Pd neither. As a result of Co and Fe comes onto being W₆Co₇ or other metal compounds, it can promote rearrangement and spreading effect in the process of tungsten copper electrode activated sintering. However, Ni and Pd easily becomes unlimited solid solution with Cu, which is useless to sintering. The more specific data shows that when the content of Co is 0.35% and the temperature is 1300℃, tungsten copper products have better properties. The relative density of W-10Cu-0.35Co reaches 98-99% and the hardness is 300HV.

More infomation about tungsten copper electrodeliquid activated sintering, click here:

http://news.chinatungsten.com/en/tungsten-information/79706-ti-10164

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Liquid sintering is a kind of processing that it includes two component of powder at least or sinter in liquid. And it can be specifically divided into two types, one is keeping the liquid state during the whole process, another is liquid disappears in later stage, which tungsten copper electrode belongs to. Activated sintering can be divided into physical activated sintering and chemical activated sintering.

Physical activated sintering improves the sintering process through adjusting sintering temperature, exerting mechanical vibration, ultrasonic and the circle of external stress. Chemical activated sintering includes that pre-oxidation sintering, change the component in sintering atmosphere, add some trace elements and use superfine powder or high-energy ball milling for sintering. This paper mainly introduces that add some trace elements to improve tungsten copper electrode liquid sintering.

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Tungsten Copper Electrode and Other Material Comparison Table

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In part 11 we read that the accuracy and consistency of hole sizes made by a tungsten carbide reamer is affected by many variables in reaming process, such as reamer design and materials involved, and coolant fluid is recommended since it helps repeatedly maintain the hole size to be as close as possible to reamer diameter.And here we learn about the longevity of a tungsten carbide reamer and the equipments used for it .

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In part 10 we know that the tungsten carbide reamer called tapered reamer non precision is used for enlarging a hole or riding of burs on softer metals non-precisely with a cross handle and tapered to tip body and it is commonly applied to MRO work. Here below with several parts we with explain how the process variables affect the reaming effect.

To achieve highly accurate and consistent diameters with a tungsten carbide reamer, one must consider process variables that can influence the overall quality of the hole being reamed. Variables such as reamer material, reamer design, material being reamed, temperature at the reamed surface, reamer speed, machine or operator movement, etc. must be addressed. By controlling these variables to the best extent possible, the reaming process can easily produce highly accurate and consistently sized holes. Reamers should not be reversed in use as this will tend to dull the cutting edges.

Size – accuracy and repeatability

The final hole size that is achieved by a tungsten carbide reamer subsequently depends on the reaming process being used in conjunction with the reamer design and materials involved. Studies have been conducted which demonstrate the effect of coolant use during reaming. The continuous use of a coolant stream during the reaming process has been shown to consistently (75% of the time) result in hole sizes that are 0.0001 in. (0.0025 mm) larger than the reamer itself, with a process spread of +/- 0.0002 in. the remainder of the time. Similarly, using a semi-wet reaming process often results in hole sizes that are 0.0004 in. larger than the reamer itself, approximately 60% of the time, with a process spread of 0.0006 in. favoring an increase in size. Dry reaming should be discouraged due to its low level of repeatability (20%) in size and wide process spread of sizes up to 0.0012 in. (0.030 mm) larger than the reamer size.

(To be continued. This article is divided into several parts and this is part 11, for part 10 please refer to http://news.chinatungsten.com/en/tungsten-information/79659-ti-10186;for part 12 please refer to http://news.chinatungsten.com/en/tungsten-information/79704-ti-10192)

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In part 9 we read that a tungsten carbide combination reamer, in a pattern resembling the work piece’s multiple internal diameters, is economically used for long run, tight tolerance electronic parts, and mostly used in screw machines or second-operation lathes instead of CNC machines.And here we learn about another common tungsten carbide reamer: tapered reamer  non-precision.

Tapered reamer non-precision

A tapered reamer may be used for cleaning burrs from a drilled hole, or to enlarge a hole. The body of the tool tapers to a point. This type of reamer consists of a body which, typically, is up to 1/2 inch in diameter, with a rod cross piece at the large end acting to form a handle. It is especially useful for working softer metals such as aluminum, copper, and mild steel. Another name for it is "maintenance reamer", referring to its use in the miscellaneous deburring and enlarging tasks often found in MRO work. A similar tool can be seen on select Swiss Army Knives such as the electrician model, to be used on conduit.

(To be continued. This article is divided into several parts and this is part 10 for part 9, please refer to http://news.chinatungsten.com/en/tungsten-information/79658-ti-10185)

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