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Nr. Janta Nagar, Ramol, CTM, Ahmedabad, Gujarat, India-382449.

Bimetallic Screw Barrel

Bimetallic Screw Barrel

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Bimetallic Screw Barrel Manufacturer

Learn Everything About Bimetallic Feed Screw Barrel (Universal Guide)

© 2021 Raj Engineering Works, Helpline +91-8128381431

We offers highest range of bimetallic screw barrel for plastics injection moulding machine, plastics extrusion machine, plastics blow moulding machine, plastics recycling machines, rubber extrusion machine, food processing machine.

Different combination of products as per your budget:

1. Total bimetallic screw barrel set
2. Bimetallic barrel with nitrided screw set
3. Nitrided barrel with bimetallic screw set
4. Cermet coated nitrided screw barrel set
5. Cermet coated screw with bimetallic barrel set
6. Cermet coated screw with nitrided barrel set
7. Cermet coated screw with bimetallic liner barrel
8. Standard stellite coated screw barrel set
9. Standard Colmonoy coated screw barrel set

Following standard size bimetallic screw barrel are available:

Screw diameters range: 22 mm to 250 mm
Barrel outer diameters range: 52 to 355 mm 
Length of bimetallic screw: 800 mm to 9000 mm
Standard L/D ratios for bimetallic screw barrel sets: 6, 8, 10, 12, 20, 21, 22, 25, 26, 28, 30, 31, 32, 33, 34, 35, 36, 38, 40, 45, 50.

What is bimetallic Screw Barrel?

'Bi' means 'Two.
So simply a product which is made up of two metal or alloy. (Two is always better than One)
In bimetallic product two metals are fixed together, and not mixed together. Mixing of two (or more) metal is called alloy. 
Screw Barrel with Bi-metal-lic properties. Bimetallic screw barrel are made of two metals or two alloys of metals and mostly coated with extra layer of carbides and other commercial coating material. 

Bimetallic screw barrel are not different type of screw barrel, like advanced designing etc. A same design screw can be made in Nitrided way and Bimetallic way.

Many customers when having an issue with their screw design (not made by us),  ask us to give them a bimetallic screw just because 'someone' told them to use bimetallic screw. Bimetallic screw are used to increase life of screw and barrel, as bi-metal works better than a mono-metal.

If you are looking for an advanced design screw barrel, like ultra-torque, ultra-speed, and high-output, than please contact our R&D team or read more pages in this website. We make screw barrel as per your need. Advanced designs screw barrel can be made in Nitriding Steel (mono) or Bimetallic (Bi) as per the budget of customers.

fig.1 showing methods of bimetallic screw barrel thermal spray coatings and their difference

Bimetallic screw barrel are made in two alloys (metals): First as base material and second as coating material, so they have more life than single metal steel.

But this is not true in all cases, for example Raj Engineering Works make screw (up to 1250 mm) length in D2 grade tool steel (single metal), so these screw life is same as bimetallic screw (2 to 5 times the Nitriding steel, depending on compound and processing techniques).

Further, these High-Life D2 grade screw of our company can be coated with any Cermet, to enhance wear resistance, and still it is not a Bimetallic screw. Because Carbides (WC) are neither a metal nor a Alloy of metals. For example Tungsten Carbide (WC) is a composite material called Cermet. Tungsten (W) is a metal (hardest) and Carbide is a ceramic, when 
both are mixed in different ratios (4% tungsten to 88% tungsten) the mixture is called Tungsten carbide (Chemical Formula: WC) and this composite mixture is called Cermet.

Important Learnings before we start:
1. Tungsten Carbide is represented by WC and not TC.

2. Bimetallic screw barrel are used to increase life of screw barrel and not output and quality of your final products.

Let's start from Basics:

Plastics/rubber/food/chemical processing feed screw barrel are basically round, threaded metal shafts with tight tolerance. They are always at the risk of abrasion wear or corrosion because of harsh and high pressure environment. That is why screw barrel are made in selected grades of steel, and case hardened, nitrided to stand against these problems. But generally this does not work with abrasive material processing, and high pressure environment like glass fiber filled material, calcium carbonate filler, harsh additives, fluoropolymers, recycling of plastics, elastomer compounds, high speed and in large size barrels. Once the screw wear out it causes many problems in processing, like degrade in final product quality, low throughput, high energy consumption etc. At this time we replace our old screw barrel with new one. But this cause downtime. Now where there downtime matters most, we have to arrange some other innovative solutions to stop frequent screw barrel replacement. Sometimes a cheap nitrided screw (which was not nitrided properly) can wear out even before 6 months. 

So a single steel (nitriding) wear outs easily, industry has developed many grades of performing steel alloy for specific functions and requirements, But they are very costly.  To make complete screw barrel in that one particular performing grades or in superalloy, may cause 6 to 8 times cost than nitrided screw. Why ? because superalloy and other performing alloys needs special machining, they take more time for milling than 4140 or En41b or 38CrmoAlA type nitriding steel.

That's is where Bimetallic screw barrels comes in play. Bimetallic screw barrel cost only 1.5 to 2 times the nitriding one but there life increases 2 to 5 times the nitriding one.

The base material in all bimetallic feed screw barrels is Nitrided steel.

In plastics/rubber/petrochemical industry we use Nitriding Steel to manufacture feed screw and barrels. While to process food we use stainless steel grades. Stainless steel is harder and costly than Nitriding steel, it does not requires any post milling hardening. While Nitriding steel goes in to nitriding furnace to gain further hardening.

In this further hardening, nitrogen atoms deposit in the external layer of steel where they bond with Fe atoms to make surface harder, this is why it is called Case Hardening or Surface Hardening process. The value of hardening measured in Rockwell scale (RC or HRC) as you see in quotation letters and specification description.

At Raj Engineering Works we maintain a minimum 65-70 HRC hardness either by Gas, Liquid or Plasma medium.

Grades of Nitriding Steels:

With a high surface hardness (compare to other normal steel) nitriding steel grades offer increased wear resistance.
There are several steel alloys those can be Nitrided. Many of them can be used for feed screw barrel manufaturing:


AISI E71400
DIN 1.8509

4140 HT
DIN 41CrAlMo7

DIN 41CrAlMo7-10
EN 41CrAlMo7-10

BS 905M39
EN 1.8509

Table 1: showing different nitriding grade steel materials 

Naming a steel grade - 
Steel numbering systems in world:

There are multiple numbering systems and they also use multiple standards for naming steel grades. 

Unified numbering system(UNS) of ASTM International.
the Society of Automotive Engineers (SAE).
American Iron and Steel Institute: AISI 
British Standards: BS
European/Indian - EN 10027
Japanese: Japanese Industrial Standards (JIS) standard and NK standard
Germany: DIN standard
China: GB standard
Czech: CSN standard
Russia: GOST standard
Spain: UNE standard
France: AFNOR standard
Italy: UNI standard
Sweden: SIS standard
Norway DNV standard

and sometimes only a chemical composition/formula can also be written to represent a steel grade. For example 38crMoAlA.
This half information may confuse us so 
let's make it more simple to understand which steel grade is better for making screw and barrels.

India's famous En41b nitriding steel can also be written as -

British: BS 905M39

German: DIN 1.8509, DIN 41CrAlMo7, DIN 41CrAlMo7-10
Swedish: SS 2940
Japanese/SACM grade: SACM645
AISI (American): E71400 or Nitralloy or N135M
Russian: GOST 38Ch2MJuA
Chinese GB system: 38CrMoAlA
European/Indian: EN41B

Other: 41CrMoAl7

So as you can see a same steel has different name and numbers, so this is not sufficient to know the grade number, because it just tells manufacturing location name but the important thing to know is 'company name' which is actually manufacturing this steel, because as like 'everything' steel quality also depends on the manufacturing company brand.

At REW we use nitriding steel grade En41B because this is most successful grade for base material. We also use 38CrMoAlA Imported Chinese grade or German DIN 1.8509 grade when customers specially mention this.

In India many company produce En41B steel but we buy it from Mahindra-Sanyo-Special-Steel-Ltd (Previous name - Mahindra-Ugine Steel Co. or MUSCO).
Sanyo is a Japanese firm who has collaboration with Mahindra to produce steel at Mumbai.

If Ahmedabad based any company says they buy steel from Japan then don't forget that Japanese company is situated at Mumbai. (Bingo!) 


Many screw barrel manufacturer who don't understand steel grades and have no idea about what they are buying, mistakenly pronounce it MOSCOW-Steel. This is really ridiculous. However we tried hard to aware other manufacturers at Ahmedabad about this 'musco' word (correct but old name of MSSSPL).
The advantage of buying from MSSSPL (MUSCO) is trust with industry experience and consistent quality.

During 2017 we published a blog regarding this issue, which became very popular and many popular screw barrel manufacturer at Ahmedabad removed 'Moscow' word from their websites. 

Nitrided screw barrel are still most preferred in India, due to their economical replacement.

After the 'base' screw made, a second metal used as lining or cladding or as spin-cast by metallurgical bonding on the nitrided screw to fight against corrosive and abrasive wear. This increase the life of screw 3-5 times by virtue of coated strong metal (Bimetallic) or metal composites (Cermet).

Bimetallic cladding, lining and casting:

So, as it is now clear that bimetallic is a coating solution for extending the life of normal nitriding screw barrel. Bimetallic screw barrel are manufactured in different material and coated with protective layer.
This protective layer can be made up by more than 20 types of metals, mostly
Performance Alloys or Superalloys, below is given the list and information regarding these materials. 

The bimetallic layer can vary from 0.025 mm to 4 mm in screw and 0.025 mm to 25 mm in barrel.
This layer is either can be coated or cladded by different techniques, and these
techniques of coatings are also important to play a vital role in the performance of bimetallic screw barrel.
While in barrels the bimetallic solution is of two kinds:
1. Sleeve (Internal Lining)
2. Coating by centrifugal casting,
which we will learn here in this page later.

Surface Treatments & Coating Techniques:

In Terms of Bimetallic Screw Barrel:

Cold Isostatic Pressing:

Hot Isostatic Pressing: 
Oil/Water quenching:
Vacuum Quenching:
Physical Vapor Deposition (PVD): 

Gas Nitriding:


Bimetallic Hardfacing and Full Encapsulation:

Hardfacing describes anything from thermal spray to laser cladding to weld overlaying.
All of these use various heat sources to apply metalized coatings.

In bimetallic treatment of base metal by layer deposition of another harder metal, Cobalt, Chromium, Molybdenum, Tungsten, Titanium and Nickel based alloys are used and Cermet-Carbides of Tungsten and Chromium are used to enhance performance.


(methods of making bimetallic is important to ensure quality and life)

PTA welding
PTA Atomized Product Feeding (REW Exclusive)
Laser cladding
Powder Coating

Laser Cladding:

Advantages: Metallurgical Bond

The biggest advantage to laser cladding is the metallurgical bond achieved at relatively low temperatures. Since laser cladding uses metallurgical bonding, there is little to no porosity in the coatings, resulting in fantastic long-term corrosion resistance.

But note, this is a very costly method and also when thin coating required it doesn't work because laser cladding produces very thick coatings.

So what is the economical solution?

1. Integrated PTA Powder cladding + Laser cladding approach
developed by in-house R&D department of Raj Engineering Works.

2. Cold spraying

In cold spraying, powders are sprayed with a supersonic compressed gas jet at temperatures below their melting point in very high velocity. The impact binds the particles into the surface and thick layers of deposited material can be built up rapidly. The deposition efficiency is very high, above 90% in some case.

Cold gas-sprayed tantalum or niobium coatings, for instance, provide excellent corrosion resistance in non-oxidizing environments. They provide outstanding protection against hot sulfuric acid.

3. Thermal Spray


The process is easily automated and very little subsequent machining is required, But the bonding in this method is mechanical and for screw barrel we need metallurgical bonding. As an screw barrel manufacturer we can do machining (because that is what we do) but we will not compromise the costly coatings thus we uses the methods which provide metallurgical bonding, so at Raj Engineering works we generally not recommend HVOF coatings. 

In HVOF Fatigue failures and coating failures is a problem. Do not fall in trap of any HVOF marketing.

Advanced than HVOF only available at Raj Engineering Works in India. Typically used when only Tungsten carbide coating is required.

Thermal sprays can also build up thicker coatings by doing multiple, robotically controlled passes.

Spray and Fuse:
This two-step process (spraying followed by fusing) results in a dense coating and a metallurgical bond.

Atmospheric plasma spraying:
Spraying molten powdered materials onto the surface on another material using plasma arcs.

Note 1:

Tungsten Carbide coatings where tungsten presence is more than 80%, is very costly solution when doing by HVOF technology and the resulting bond is also weak mechanical bond. That is why we at Raj Engineering works developed an Integrated PTA, Spray & Fuse cladding in technology collaboration with world's best companies in this field. Also, there are more than 50 other solution than tungsten carbide, those can be used according to a specific or multiple requirements.
Some coating companies only know about HVOF Tungsten-Carbide coatings so they recommend to go for only this.

While at Raj Engineering Works we have several techniques and alloys for customer-specific technique and product and this make everyone's budget. 


Note 2:

At Raj Engineering Works in our Integrated Approach PTA plays an important role because of its Automation feasibility (Robotic) and metallurgical bonding.
There is a difference between PTA and Plasma Arc Welding (PAW) and this is important in terms of Screw-Barrel coatings.
Some company uses Plasma Welding (PAW) and they call it PTA.
Our Integrated PTA Cladding approach can produce coatings similar to laser cladding.


Note 3:
At Raj Engineering we uses HVAF, Spray & Fuse, PTA Cladding, Plasma Spraying technology-integration with an R&D and continuous learning from world's top companies of the sector like Wall-Colmonoy®, Kennametal Inc, Hoganas group etc. We can not disclose everything on website because our competitors follow our website to get new and advance information.

Fig.2: showing durability and economy of different bimetallic cladding processes.

Which coating technique is best for producing bimetallic screw barrel at lower price?
Any process which involves metallurgical bonding between substrate (base) and coating alloy. PTA, Laser cladding, spray and Fuse are best choice while HVOF and Plasma Spray will not be good option as they are highly priced and results in mechanical bonding.

Learn more in our 15 point screw barrel purchase guide

Bimetallic products used at Raj Engineering Works Ahmedabad

ULTIMET® alloy
Colmonoy® 4
Fe-based alloys
Colmonoy® 7403-60
with Tungsten Carbide
Stellite 12
Colmonoy® 45
Colmonoy® 84
with Chromium and Tungsten
Colmonoy® 83
with Tungsten Carbide
Stellite 6
WC-CO-Cr 86-10-4
Colmonoy® 5
Colmonoy® 57
with Chromium and Tungsten
Stellite 20
Ni-based alloys
Colmonoy ® 56
Colmonoy ® 88
with Chromium and Tungsten
Stellite 21
Co-based alloys
Colmonoy® 6
Colmonoy® 7303-60
with Tungsten Carbide
Stellite 1,

& More ..

Note 4:

In Rubber extrusion feed screws some customer complains about Tungsten carbide failure done by HVOF methods because of high pressure and absence of metallurgical bonding between substrate and coating and Stellite welding failure due to filling in the grooves of screw flights.
So, Raj Engineering Works has developed advance technologies to avoid these failures. Please call us to discuss rubber, Plastics, food grade, and petrochemical feed screw barrel coatings. We provide economical solutions.
Call +91-8128381431 for more understanding and discussion.
Raj Engineering is India's most advanced and best choice for Bimetallic Screw Barrels. Share this information so that many indian buyers can contribute to Atm-Nirbhar-Bharat and Make-In-India initiatives. 

Full Encapsulation:

Full encapsulation in screw means 100 % covering of base (substrate) metal by coating material (bimetallic product). Full encapsulation is not needed in barrels, however full internal diameter (ID) coating is a general thing. Bimetallic sleeve (also called Internal Lining) and centrifugal spin casting by alloy powder or cermet powder are two major way of bimetallic barrel manufacturing. Typically bimetallic screw are only hardfaced. That means their flights (outer diameter or OD) only are hardfaced with a bimetallic coating. But for some application, where polymer, additives and fillers cause screw breakage or corrosion wear, root diameter (RD or sometimes called ID od screw) also coated with the same coating material along with OD. So when OD and ID are coated in screw, it is called full encapsulation.
Full encapsulation can also be provided on nitrided screws without going for bimetallic screw, by the use of tungsten carbide powders like WC-Co matrix (88-12), WC-Ni (88-12) or 
WC-CO-Cr matrix (86-10-4). 

Partial Treatment:

Another good choice for protecting screw barrel from damage is partial coatings, which works in screw and as well as in barrel.
Partial coatings are more economical as they are done only at most wear prone areas in screw and barrels. In feed screws we can skip the bimetallic cost and can do thin carbide coatings directly on the flights (OD) of base screw (nitrided screw). 
Suppose you have a screw of 1500 mm length, with 20 flights of 6 mm each, so in partial coating the effective length for coating will be 120 mm only, so you have to pay only for 120 mm coating length and not for 1500 mm. If you use a less abrasive and corrosive compound and every time your screw wear out in a particular zone only, let's say in feed zone or metering zone, and this zone has only 4 flights, then you can choose 'only 4 flight coatings', so you will have to pay only for 24 mm length coating. If you choose this option (
this 2 or 4 or 6 flight only coatings) with any HVOF coatings providers then they will charge you more than of your actual cost, because 'this' is not economical for 'them'. But at Raj Engineering works, we provide a single flight coatings with our in-house Integrated Coating Method.
barrels partial coatings is not possible with centrifugal spin casting, but only applicable with lining or sleeves. sleeves if fitted with an expertness are best choice for bimetallic barrels because they are thick so works better than centrifugally spin casted bimetallic barrels. For partial treatment way, we can choose a limited length of barrel for lining/sleeve, same as in screw, this length will be the most wear prone zone. For example when you look inside Grooved feed sleeve barrel, the grooved feed section is always fitted with bimetallic sleeves. They are generally HSS or Tool Steel made sleeves. We can choose 1 to 2 zone in barrel for bimetallic sleeve fitting, and can leave rest of the barrel nitrided to save a lot of cost. 

Centrifugal Spin Casting Vs Bimetallic Sleeve (Lining)

In the manufacturing sector, in Europe and America, the dependency on Man-Power based work is a problem. Without discussing the cause and effect let's directly comes to the point, so they continues to develop manpower-less solutions, like advance automation, robotic works etc.
The job of sleeve-fitting (Lining) in barrel is a mostly manpower based and attributes like quality and accuracy depends on the the expertness of the expert man, who is doing this job. Problem arises when 'that expert man' quit that job or leaves the company or by any reason company 
accidently lost that expert! In cases where there is no one available to fill this gap of expert fitter, the manufacturing company has to abandon that work in the absence of expert, because you can not do precision engineering jobworks with average experienced team. 

So, to counter this man-dependent issue in bimetallic barrel manufacturing business, industry has developed a man-less solution which is called centrifugal spin-casting. However the solution was not invented by barrel manufacturers. This technique was already present in steel casting industry long before the need of barrel manufacturers. So barrel manufacturers started adopting this centrifugal casting technique and moved on marketing this technique and bimetallic barrels made by these techniques.
Benefits was: 1) In long term, the Labor work is costlier than machine work so priced decreased. 2) Consistency, 3) less error chances, 4) data based optimization
centrifugal spin casting is not an automated job, it also require expert manpower like machine operator and high experience and understanding of substrate-coating metallurgy.
Before we talk about Raj engineering works bimetallic barrels, first comes India and Ahmedabad. First of all in India, the availability of cheap man power is easy, and automation is costlier in comparison to Europe and America, secondly the Ahmedabad (city where our company is located) is world's second largest hub (after China) for plastic processing equipment and machinery. So it is very easy to get experienced mechanical technicians and engineers at Ahmedabad. Also in the last 30 years plastic processing equipment and machine manufactures has developed a big ecosystem around themselves, so establishing new business within this ecosystem became easy due to mutual benefits and interdependence of businesses. 
Forget the "expert man" Ahmedabad has many small businesses who does only sleeve fitting/lining job works for many large OEM companies. We have expert companies not only expert man or woman. Hurray!!

So in India the all screw barrel manufacturers prefers the manual ways of bimetallic barrel manufacturing, because not only this is economical but as we said, 

sleeves if fitted with an expertness, are best choice for bimetallic barrels because they can be made in any size without increasing the cost, a 20 mm bimetallic lining is a common thing, liners or sleeve are thick (5 to 25 mm) so works better than centrifugally spin casted bimetallic barrels, because more the thickness more the resistance power against abrasive/corrosive wear. 

In centrifugal spin casting of barrels, nitrided barrel is filled with coating alloy powder or carbide powder and the barrel is heated at very high temperature and also the powder filled inside is heated, so the powder start melting. At that time the barrel is rotated (centrifugal spin) so melted coating powder spreads evenly on internal face of barrel. Than barren is cooled and checked.
In this process when heated (just below the melting temperature of barrel but enough to forge) barrel rotate, its internal and external dimension face serious deformations. So special care is needed and special arrangements are made for the straightening of deformed barrels. Barrel, in comparison to its screw is a heavy object to put under hydraulic press for straightening process. rejection probability is higher in centrifugally spin-casted barrel than in manually sleeve fitted bimetallic barrel. That is why the cost of manufacturing is also high, and the coating thickness we get is very nominal in comparison to lining option.

Problem with centrifugal spin casted barrels:

The main and biggest problem with centrifugal spin casted bimetallic barrel is repairing. Yes this is a serious problem, you can not do anything except buying a new barrel. (again the european and american policy of no-repairing, only replacement with new products). If (any) repairing is possible that will cost same as the cost of new barrel and sometime even more than that.
So at this point we can say, sleeve fitting is not only easy and economical thing but also a
Greener Approach for our environment.

You will not face any problem in spin-casted bimetallic barrel until it completes it life (3 to 5 years with reprocessing). As we all know everyone is looking for greener alternatives, so Reprocessing and Recycling is the future of industry. So today or later everyone has to face the issue of repairing of barrel.
In sleeve fitting bimetallic barrels the repairing is as easy as nitrided barrels. Because removing and refitting of liner sleeve is very easy in comparison to casting.

At Raj Engineering Works, our job of making bimetallic barrel is not completely manpower based, contrary to this we have a team of 10 members who are highly experienced at this. The team leader of this liner sleeve fitting Mr. Rajesh Kushwaha is Ahmedabad's most experienced and number 1 expert in Ahmedabad city.
Even other screw barrel manufacturers when having problem with their barrels consult and take help of our team.

Since 2000, Raj Engineering Works has made and supplied more than 2000 of bimetallic barrels and they are all running successfully, and if we count the Grooved feed fitted barrels (partial bimetallic barrels) than this number will increase two times.

Inconel® is a registered trademark of Special Metals Corporation USA.

ULTIMET, HASTELLOY®, ULTIMET®, MULTIMET® are the registered trademark of Haynes International USA.

AMPERWELD®, AMPERIT®, and AMPERSINT® etc are the registered trademarks of the Hoganas group Germany.

Colmonoy® and WALLEX are registered trademarks of Wall-Colmonoy USA.

Stellite and Tribaloy are registered trademarks of Kennametal Inc USA.

REW is the India's first screw barrel manufacturer with in-depth R&D.

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