Development of the New Material MZ01 with Excellent
Wear Resistance and Corrosion Resistance for TwinScrew Extruder Parts
耐摩耗性と耐腐食性に優れた二軸押出機部材用新材料『MZ01』の開発

Fumiya KUROGI

Katsuya MASHIMA

Yasunori MINAGAWA

Shuji UENO

黒木 史哉

真島 克弥

皆川 泰範

上野 修司

Keywords； wear resistance, corrosion resistance, MZ01, twin-screw extruder parts,impact resistance, lightness
キーワード; 耐摩耗性，耐腐食性，MZ01，二軸押出機部材，耐衝撃性，軽量Abstract
In twin-screw extruders used for producing high-functionality plastic compounds, the consumptionof these parts is becoming serious owing to the increase in a number of hard filler and flame retardants
added. We developed a new material, MZ01, using powder metallurgy technology that achieves thelong-life of twin-screw extruder parts. The wear resistance and corrosion resistance of MZ01 are muchbetter than those of the conventionally used alloy tool steel SKD11 and powder high-speed steel
SKH40. In user evaluation of actual equipment, MZ01 achieved a life span of more than 15 times
longer than that of SKD11.
高機能プラスチックコンパウンドの生産に使用される二軸押出機において，硬質フィラ
ー添加量の増加や難燃剤の添加により部材の消耗が深刻化している．我々は粉末冶金技術を用いて二軸押出機用部材の長寿命化を実現する新材料『MZ01』を開発した．
『MZ01』の耐摩耗性および耐腐食性は従来使用されてきた合金工具鋼『SKD11』や粉末ハイス『SKH40』と比較してはるかに優れていることが確認された．ユーザーでの実機評価において，『MZ01』
は『SKD11』の 15 倍以上の長寿命化を達成することができた.

- 1 -Nippon Tungsten Review Vol.42 (2024)

1. Introduction
1.1 Current state of the high-functionality plastics industry
In recent years, the weight reduction of automobiles has been accelerating, conventional metalmaterials are being replaced with functional resin materials such as fiber-reinforced plastics and multimaterialization are progressing. Functional resin materials are also widely used in electroniccomponents such as automobile parts and semiconductor encapsulants for 5G technology. Reducing
the weight of automobiles and developing IoT technology are trends that will have a major impact onbuilding a sustainable society in the future, accordingly technological innovation is increasinglyrequired.
1.2 Problems in the high-functionality plastics industry
In general, twin-screw extruders are used to produce functional plastics compounds. The parts of thistwin-screw extruder wear out due to attack by the hard filler added to the resin and contact between
parts. Wear of the parts causes a decrease in production efficiency, contamination of foreign matter
into the resin being kneaded and deterioration of kneading quality. Special hard steels are usuallyapplied to the parts. However, there are needs for materials with lower metal contamination and higher
wear resistance owing to the increase in the filler loading in recent years. In addition, materials withhigh corrosion resistance together with wear resistance are required. This is because some additives
induce corrosion of screw element parts when adding additives such as phosphoric acid flame
retardants to hard filler.
1.3 Adoption of cemented carbide and new problems
Cemented carbide is a sintered alloy mainly consisting of hard tungsten carbide and cobalt as a binder.
It is mainly used as a cutting tool for metal processing because it is very hard and has moderate
toughness. Furthermore, cemented carbide can control the mechanical properties by the tungsten
carbide particle size, proportion of the metal components and trace additives, and it is widely used inwear-resistant applications, such as cutting blades, molds, and rollers.
In many cases, special steels are used as twin-screw extruder parts due to their high wear resistance.
However, with the increasing use of hard filler in plastics and interest in reducing metal contamination,materials with higher wear resistance are demanded. Thus, we have had a lineup of screw elements
and barrel liners made of cemented carbide, and we have been increasing our track record of adoptionof these parts. Photographs of the appearance of alloy tool steel SKD11 and cemented carbide after
use in the actual machine to produce a glass-fiber high-filling compound are shown in Fig. 1. The lifeof alloy tool steel that in commonly used with excellent wear resistance is 3 months. On the other hand,
the life of cemented carbide is 33 months, more than 10 times longer than that of alloy tool steel.
Although it has been confirmed that cemented carbide has excellent wear resistance through fieldtests using actual machines, the high specific gravity of cemented carbide is a major issue in its use as
screw elements. Cemented carbide parts are about twice as heavy as steel, and twin-screw extruders
are designed to mount multiple elements on a cantilevered shaft, which causes the shaft to sag. For
this reason, the number of cemented carbide screw elements that can be loaded is limited. Those who

Nippon Tungsten Review Vol.42 (2024)-2-have used cemented carbide have requested that light materials be developed to load more screw
elements.

Fig. 1 Photographs of the appearance alloy tool steel SKD11 and cemented carbide after use as thescrew element to produce a glass-fiber high- filling compound

2. Development concept of the new material MZ01
Generally, the ceramics and cermet have both wear resistance and light weight. Although bothmaterials have high hardness and excellent wear resistance, they are difficult to apply to screw
elements because of their low impact resistance.
The largest difference between cemented carbide and these lightweight materials is that cemented
carbide contains high specific gravity tungsten carbide as a hard phase.
We focused on the hard phase and started developing new materials that are light weight and havewear resistance and impact resistance equivalent to cemented carbide by adding various lightweight
metal carbides as hard phases. The characteristics of each material are given in Table 1, and theconcept for developing the new material is shown in Fig. 2.
Using technology of controlling structure, additive technology and an alloying process, we developed
the new material MZ01.
Table 1 Properties of various materials used for twin-screw extruder parts- 3 -Nippon Tungsten Review Vol.42 (2024)

Fig. 2 Development concept of the new material

3. Characteristics of MZ01
3.1 Material properties of MZ01
A comparison of various properties of MZ01 and other materials are shown in Table 2. In general,
there is a trade-off relationship between the hardness and toughness of materials, therefore it is difficult
to achieve both wear resistance, which is correlated with the hardness, and impact resistance, whichis affected by the toughness. MZ01 maintains high hardness and high toughness due to its uniquestructure. In addition, the magnetic properties and volume resistivity necessary to remove chips whenthe extruder parts are chipped have been controlled to a practical level.

Table 2 Characteristics of the new material and other materials

3.2 Wear resistance of MZ01
The wear resistance evaluation of rubber wheel tests for each material are shown in Fig. 3. The wear
resistance of each material was compared with that of alloy tool steel based on the wear volume before
and after the test. Wear resistance of MZ01 showed 4.7 times higher than that of alloy tool steel and1.3 times higher than that of cemented carbide (equivalent to VM50). This cemented carbide wasconfirmed to have more than 10 times longer life than that of alloy tool steel in the aforementioned
actual machine.

Nippon Tungsten Review Vol.42 (2024)-4-Fig. 3 Wear test results of each material

3.3 Corrosion resistance of MZ01
Fig. 4 shows the corrosion test results of each material in 10% aqueous solution of various acids andphotographs of the appearance of the test pieces after the corrosion tests. This figure shows thevolumetric residual rate of each material after 24 h of immersion in the acid solution. MZ01 showed
excellent corrosion resistance to any acid solution. It was confirmed that MZ01 has a clear advantage
over alloy tool steel and powder high-speed steel, which are widely used as twin-screw extruder parts,
and it is also applicable to kneading highly corrosive materials.
During the promotion of MZ01 products, we received many inquiries about the corrosion resistanceof MZ01 compared with that of nickel-based alloys with excellent corrosion resistance. As shown inFig. 4, MZ01 has slightly lower corrosion resistance than Inconel 600, a nickel-based alloy. However,Ni-based alloys are materials with low wear resistance, so it cannot be expected to extend the life oftwin-screw extruder parts. In order to extend the life of the parts, it is important that the material has
both wear resistance and corrosion resistance. Based on results of the twin screw extruder parts life,
we visualized the performance positioning of each material in terms of the wear resistance andcorrosion resistance. As an example, the corrosion resistance and wear resistance performance
positioning against phosphoric acid is shown in Fig. 5. Generally, the importance of wear resistanceor corrosion resistance will vary depending on the user's usage conditions, so this positioning should
be used as a reference when selecting materials against phosphoric acid corrosion and wear. We also
have accumulated data on the wear and corrosion tests for each material We will provide the data uponrequest.

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Fig. 4 Corrosion test results of each material

Fig. 5 Performance positioning of each material against phosphoric acid
3.4 Actual performance of MZ01
Photographs of the alloy tool steel and MZ01 screw elements after use in the production of a glassfiber high-filling compound are shown in Fig. 6. Comparing the degree of wear of the parts based on
their shape and weight, it was confirmed that the wear resistance of MZ01 was 15 times higher thanthat of alloy tool steel. The MZ01 screw element is still in continuous use. These results confirmedthat MZ01 has wear resistance equal to or higher than that of cemented carbide and its specific gravity
is half that of cemented carbide. The MZ01 material has been adopted for the production of hard-filler
high-filling compounds, there are many demands from our customers.

Nippon Tungsten Review Vol.42 (2024)-6-Fig. 6 Photographs of the appearance of alloy tool steel and MZ01 as the screw element after use toprepare a glass-fiber high-filling compound

4. Conclusions
Some radar charts comparing the characteristics of MZ01 with those of other materials in four aspects,wear resistance, corrosion resistance, impact resistance, and light weight are shown in Fig. 7. The highspecific gravity of cemented carbide is a disadvantage, and it is unsuitable for this application. Nickelbased alloys have high corrosion resistance, but their wear resistance is low, making it difficult toextend the lifespan of twin-screw extruder parts. We succeeded in developing MZ01, which has highwear resistance and corrosion resistance while compensating for the shortcomings of these existingmaterials. As mentioned above, MZ01 has a sufficient level of magnetic and electrical properties forremoving from the compound, and it is a new material that combines the elements necessary for theparts of twin-screw extruders with good balance.

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Fig. 7 Comparison of the characteristics of the four materials

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