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Discussion for hardness and abrasion principle of Omega301 Alloy

Jul 13,2016

As we all know, when some kinds of plastic are running inside an extruder and an injection machine, there is a friction between barrel and screw, and a cut force between plastic and machine parts. Also there is a case that these machine parts are eroded by a corrosion gas which comes into being when the plastic is heated. The best way to solve these problems is to use bimetallic barrel and bimetallic screw, for on a working surface of these bimetallic machine parts, there is a special wear and corrosion alloy layer, for example the alloy named as Alpha 301 made by Shanghai Alpha Machine Company.


To find out this case, firstly we have to study the abrasion principle of Omega301 alloy ( 301 alloy is equal to X-800 alloy from XALOY in USA.)


1. Before discussing the issues about 301 Alloy, we should know what the 301 alloy material is, please check its component as below: 

C

Mn

Si

B

Cr

Fe

Ni

 Co

W

1.3

~3.5

1.0

~Max

0.5

~3.3

1.0

~3.0

5.0

~Max

5.0

~25.0

Balance

3.0

~7.0

25

~35


The structure feature of 301 Alloy is WC grains with weak intermiscibility and high wear-resistance are dispersed in the Ni-based alloy, it accounts for about 30% in 301 alloy. Ni acts on corrosion-resisting. On various occasions, the corrosion resistance function of Ni is the same as 201 alloy. it performs better especially in dilute hydrochloric acid, dilute sulphuric acid, oil of vitriol, dilute fluoric acid and other usual chemical solvent. Meanwhile, due to the mixture of great amount of WC grains, Ni-carbide, carborundum, chrome carbide and other carbide molecule, which are generated inside the alloy under high temperature perform better wear-resistance.


2. There is a factor largely decides the wear-resistance performance of 301 alloy layer, that is at present the molding method of bimetallic barrel alloy is mostly centrifugal casting at home and abroad, and this factor is ignored usually! Because the proportion of WC inside 301 alloy is far more than Ni-base material (up to 30% of the alloy), under the centrifugal force, these WC grains is closer to the joining plane with base material during its centrifuge process, not the inner wall of the barrel. That’s to say, the WC grains which perform high wear-resistant function is not equably dispersed in the alloy sleeve. Then the original function of 301 alloy is concealed during its centrifuge process.


3. The main ingredient of 301 alloy above are WC grains and other carbide grains, its average Knoop microhardness is KHN2000, this is the important reason that 301 alloy performs excellent wear-resistance. After analyzing the structure of 301 alloy, we learn that WC grains are dispersed in Ni-based material, so it is impossible that probe of HRC hardometer and Vickers hardometer detect so small WC grains, then the result show two features: (1) the hardness value is a wide range when detecting at random, such as HRC55~64; And the WC grains which inside Ni-base material is uneven, so the hardness of somewhere in alloy layer even lower than above. (2) The hardness value of 301 alloy we detected is macrohardness , only display random hardness value of 301 alloy, can not display the real average hardness of the alloy. Such as carborundum grains disperse in the clay and you step on the clay, do you feel it hard?


4. When plastic material being run by an extruder, if this material could mainly make the barrel to be eroded, such as CPVC, CPE, PTFE, PAA with filling in some glass fiber, carbon dioxide, limestone, and all these filler are not so more, it is the best choice to use 301 alloy bimetallic barrel. As there is almost no any Fe inside 301 alloy, it is one kind of inert metal alloy and is able to resist the corrosion from various acid.


5. When plastic material being run by an extruder, if this material could mainly make the barrel to be wore by high physical press and friction, such as in extrusion of PVC with metal powder filled, though PVC could decompounds out Cl ion when heated, which would corrode metal, in running process, the metal powder in this material strongly press on the internal wall of barrel and result in that barrel to be wear-off quickly. If 301 alloy bimetallic barrel to be used in this case by error, when metal powder presses on the internal wall of barrel, it takes base material Ni away during its contact friction, also takes WC grains away together. It is a pity that these WC grains do not play its function until they were taken away. If you doubt wear-resistance function of 301 alloy accordingly, it is inequitable!


Chief Engineer Office
Shanghai Omega Machinery Co., Ltd

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