Choose screw and barrel materials by matching the structural steel, working surface and manufacturing process to the actual formulation and failure mechanism. A higher hardness number alone cannot tell you whether a replacement will resist filler abrasion, chemical attack or metal contact; specify the screw and barrel separately, then verify their fit as a pair.
A useful material quotation explains which steel carries the load, which surfaces receive protection, and how those surfaces will be inspected. It should also identify the conditions behind the recommendation. The same resin name can describe an unfilled product, a mineral-filled compound or a recycled blend with very different demands on the machine.
By EJS Industry Technical Team
Before comparing quotations:
- Identify whether the old parts show abrasion, corrosion, contact damage or a mixture.
- Separate the base steel from the surface treatment and working alloy.
- State the complete compound, including filler type and loading.
- Check the screw and barrel at corresponding axial positions.
- Agree on material identification, protected areas and acceptance measurements before production.
1. Start with the failure mechanism
Abrasion from fillers and contamination
A worn flight tip and an enlarged bore are reasons to investigate abrasive duty, but the material name on the purchase order is only part of the investigation. Record the filler type, its concentration, the feedstock source and where material loss is greatest. Compare these details with the formulation used when the original parts were specified.
An increased filler loading is a reason to reopen the material review. So is a change from a controlled virgin feed to a recycled stream with uncertain contamination. Keep representative compound samples and photographs of the old parts alongside the measurements. Those records give the supplier something more useful than a request for a harder screw.
Corrosion and metal contact need different investigations
Davis-Standard's feedscrew and barrel guidance distinguishes abrasive wear, corrosive attack and adhesive wear caused by metal contact. It identifies some PVC compounds, corrosive flame retardants and fluorocarbons as corrosion concerns, while alignment, straightness, heating uniformity and mismatched working surfaces can contribute to contact damage.
Use that distinction to choose the investigation, rather than diagnosing the complete problem from one photograph. Pitting directs attention toward the chemical environment and surface condition. Local scoring calls for a machine and alignment review. Gradual dimensional loss across working zones calls for a wear map and formulation review. Several mechanisms can occur on the same component.
| Observed damage | Evidence to collect | Direction for the material review |
|---|---|---|
| Flight-tip loss and bore enlargement | Matched axial measurements, formulation history and operating records | Review abrasive duty and the protected surfaces on both parts |
| Pitting or localized chemical attack | Compound chemistry, temperatures, deposits and surface photographs | Review corrosion resistance and protection coverage |
| Local scoring or contact marks | Straightness, supports, alignment and heating checks | Investigate the machine before specifying an alloy upgrade |
The table is an inspection guide, not a replacement threshold. The acceptance limits should come from the machine's approved drawing and engineering assessment. A damage description helps narrow the questions; it does not establish a universal material answer.
Engineering schematic of damage patterns. Not to scale; surface appearance alone does not establish the cause.
2. Separate base steel, surface treatment and working alloy
The steel and the working surface do different jobs
Treat a screw and barrel specification as a description of construction. The screw's core must carry the drive load. The barrel body provides the structure around the bore and its interfaces. Their working surfaces must also suit the compound. Combining those requirements into the phrase "wear-resistant steel" hides the information a buyer needs.
Three terms frequently appear in quotations, but they describe different things. A designation such as 38CrMoAlA identifies a base steel. Nitriding identifies a surface treatment. Colmonoy 83 identifies a hardfacing alloy. A screw can therefore have a 38CrMoAlA base and Colmonoy 83 on specified flight surfaces without those descriptions contradicting each other.
EJS's bimetallic product specification lists structural steels separately from screw and barrel alloys. This is the useful way to read a quotation: identify the component, base material, process and protected area before comparing its price.
Protection coverage matters as much as the alloy name
The screw flight land, flight flank, root and mixing features are different surfaces. A hardfaced flight does not automatically mean the complete melt-contacting surface has the same protection. Likewise, the barrel bore lining does not describe the material of the flange, feed opening or other features outside that lining.
Ask for a drawing that marks the protected areas. If the old screw has root damage while the replacement proposal only changes the flight-tip alloy, the proposal needs another discussion. The selected protection must reach the surface that is failing.
Nitriding also needs precise language. It changes the steel's near-surface condition; it is not a separate cast liner. The base material may remain part of the melt-contacting construction. Avoid assuming that a component described as treated has an independent alloy layer covering every working surface.
For each part, request a construction statement in this order: base steel, heat-treatment condition, surface process, working alloy where applicable, protected area and final inspection requirement. That sequence makes differences between quotations visible before an order is placed.
3. Common base steels and their selection limits
Read the grade in the context of the finished component
The current EJS material portfolio includes 38CrMoAlA, 40Cr, 42CrMo, 34CrAlNi7, 31CrMoV9, SKD11, SKD61, D2 tool steel and Hastelloy. The availability of a grade does not make it the default for every screw or barrel. The finished construction and the application still determine its role.
For a treated screw, ask how the chosen steel and heat-treatment condition support the required surface process. For a lined barrel, distinguish the body material from the bore alloy. For a tool-steel component, ask about the actual condition of supply and the working surface rather than assuming that the grade name proves a particular hardness.
| Material named by EJS | Question to resolve before ordering |
|---|---|
| 38CrMoAlA, 34CrAlNi7 or 31CrMoV9 | What core condition and surface treatment are specified for this screw? |
| 40Cr or 42CrMo | Is this the structural body material, and what protects the working bore? |
| SKD11 or D2 tool steel | What exact grade, treatment condition and component construction are proposed? |
| SKD61 | How does the selected condition fit the actual temperature and load? |
| Hastelloy | Which specific alloy designation is required for the chemical environment? |
Avoid loose international grade substitutions
A cross-reference table is useful for communication, but an approximate counterpart is not permission to substitute material. Specify the governing grade or standard and have the supplier identify the material actually supplied. If another grade is proposed, review it as a substitution with its own chemical and mechanical requirements.
This matters especially when a quotation uses a broad family name. "Tool steel" and "nickel alloy" each describe many possible materials. Even a familiar commercial family name may need a specific grade suffix. A material certificate should resolve that identification, not repeat the same broad wording as the quotation.
The construction decision also involves competing properties. In its metallurgy discussion, ENTEK explains why a load-carrying core and a wear-resistant exterior may be designed differently. That supports evaluating the structural and working-surface requirements separately. It does not establish that another manufacturer's proprietary construction is an EJS product.
4. What nitriding, chrome and bimetallic construction change
Compare the process and the area it protects
A process comparison is useful only when the quotation says where the process applies. Nitriding changes a near-surface region of the steel. Chrome plating adds a deposit. Weld hardfacing adds a working alloy to selected surfaces. A bimetallic barrel combines its body with a working bore alloy. These are different constructions, not interchangeable names for a coating.
EJS identifies gas nitriding on its nitrided screw barrel page. Its materials guide describes PTA hardfacing for screws, centrifugal casting for barrel linings and chrome plating as a separate treatment. Read those descriptions together with the drawing for the actual order.
| Construction | What changes | What the specification must identify |
|---|---|---|
| Nitriding | The near-surface condition of the steel | Treatment area, hardness method and agreed case-depth definition |
| Chrome plating | A deposited surface layer | Location, finished thickness, finish and inspection criteria |
| Screw hardfacing | Added alloy on specified screw surfaces | Alloy grade, coverage, finished deposit and geometry |
| Bimetallic barrel lining | Working alloy inside the structural barrel body | Bore alloy, manufacturing route and finished lining requirements |
Finished dimensions and layer definitions must agree
EJS's bimetallic product page lists a screw-alloy thickness of 1.0 to 1.5 mm for its Ni60, Colmonoy 56 and Colmonoy 83 options. That published range is a useful starting point, but the order should state the finished requirement for the actual component. A deposited layer before machining is not automatically the remaining layer on the finished part. Source: EJS bimetallic screw table.
The same discipline applies to a nitrided case: state how depth is defined and measured. A surface hardness reading cannot describe the complete hardness profile beneath it. For a barrel lining, specify the grade and finished condition instead of assigning one thickness to every alloy and barrel geometry.
Buyers comparing both constructions can use the EJS bimetallic versus nitrided guide for the broader trade-off. Here, the selection question is narrower: which process protects the surfaces exposed to this formulation, and how will the finished protection be verified?
5. Compare alloy grades beyond hardness
Keep screw and barrel alloys in separate tables
EJS names Ni60, Colmonoy 56 and Colmonoy 83 for screws, and EJS01 through EJS04 for barrel alloys. Keep those groups separate when reviewing a quotation. A screw hardfacing grade and a barrel lining grade describe different components and manufacturing conditions. Source: EJS alloy tables.
| Screw alloy | Item to compare in the proposal |
|---|---|
| Ni60 | Exact supplied alloy, protected area and suitability for the stated compound |
| Colmonoy 56 | Supplier designation, deposited condition and working-surface requirements |
| Colmonoy 83 | Carbide-containing construction, deposit condition and suitability for abrasive duty |
| Barrel alloy | EJS's published relative wear/corrosion ratings |
|---|---|
| EJS01 | Very good / good |
| EJS02 | Good / very good |
| EJS03 | Very good / very good |
| EJS04 | Excellent / very good |
These ratings reproduce EJS's qualitative comparison, not standardized test results. They help start a discussion; they do not establish a measured wear rate, a chemical-resistance limit or a service-life multiplier. Source: EJS barrel table and rating legend.
A useful example from the alloy manufacturer
Wall Colmonoy's September 2025 Colmonoy 83 technical data sheet describes tungsten carbide within a nickel-chromium-tungsten matrix. It gives overlay hardness ranges of HRC 45 to 55 for the -150+53 µm powder grade, and HRC 43 to 57 for the -180+63 µm powder grade. These are alloy-manufacturer deposit ranges for the stated powder grades, not acceptance measurements from an EJS finished screw. Source: Colmonoy 83 technical data sheet.
The carbide-containing structure explains why bulk hardness alone is an incomplete comparison. Ask about the constituents that resist wear, the matrix, the deposit condition and the application. Two alloys with similar bulk hardness can still require different engineering assessments.
Specify a test, not just a number
ASTM E18 covers Rockwell hardness testing and cautions that a reading at one location may not represent the entire part. ASTM E384 covers microindentation hardness and the assessment of hardness variations over small distances. Those are distinct measurement questions: a bulk reading and a profile across a treated region provide different information.
For abrasive comparisons, ASTM G65 reports dry sand/rubber wheel test results as volume loss in cubic millimeters under a specified procedure. Lower loss indicates greater resistance in that test. The standard also warns against treating its result as an exact prediction for a specific operating environment.
If a supplier supplies test data, compare the same method, procedure and specimen condition. None of these standards turns an alloy name into a guaranteed operating life, and naming the standard does not establish that a particular shipment was tested to it.
6. Match the material system to the actual formulation
Give the supplier the compound, not only the resin family
The purchasing description "PP screw barrel" is incomplete when the machine processes filled PP. State the resin grade, filler identity and loading, additives, recycled fraction and the expected changes between products. Explain whether the replacement must cover one stable formulation or several duties on the same line.
Separate formulation information from operating information. The material review also needs actual process temperatures, the running speed range, pressure information where available, and the damage history. A nominal resin family does not tell the supplier which surfaces have been failing or whether the machine has experienced contact damage.
| Actual duty | Questions that change the selection |
|---|---|
| Clean, unfilled resin | Is the existing construction performing acceptably, and is the replacement preserving the approved specification? |
| Mineral-filled or glass-filled compound | What filler and loading are present, and where is dimensional loss concentrated? |
| PVC or a formulation with potentially corrosive additives | What chemistry, temperature and deposits accompany the observed damage? |
| Recycled feed | How stable are the composition, contamination controls and batch-to-batch conditions? |
| High-temperature or chemically demanding service | Which exact alloy and surface construction suit the actual environment? |
The matrix organizes the information needed for a recommendation. It deliberately avoids assigning one alloy to every resin family. Davis-Standard's wear guidance supports considering both abrasive and corrosive duty, along with the machine condition.
Changes in feedstock can invalidate an old recommendation
Keep the original approved formulation with the material specification. If the filler loading rises or the recycled stream changes, the old recommendation should be reviewed against the new conditions. The component may be correctly manufactured to the old specification and still be unsuitable for the revised duty.
For chemically demanding materials, provide the exact polymer and relevant additives. ENTEK's metallurgy guidance discusses the separate demands of severe corrosion and abrasion. Do not interpret that as a blanket recommendation for every fluoropolymer or as proof that any nickel alloy is interchangeable with another.
Where the application involves food contact or pharmaceutical requirements, identify those requirements in the inquiry and specify the documents needed. A steel name, surface treatment or general product description does not establish certification or compliance for the finished assembly.
7. Check the pair and the machine before upgrading the alloy
Factory perspective: turning a hardness request into a measurable specification
On our nominal 90 mm single-screw replacement project, the buyer's first request was for higher hardness. I began with the complete PP formulation, which contained 30% calcium carbonate by weight, then reviewed the original drawing and the worn screw and barrel dimensions. That order of work kept the material discussion tied to the actual machine.
I mapped the screw and barrel measurements to corresponding axial positions. Measuring a screw flight at one position and comparing it with a bore measurement elsewhere would not describe the local fit. The metering-section readings showed that the replacement needed to restore the drawing's clearance as well as provide the selected working materials.
We specified the screw and barrel separately. The screw used a 38CrMoAlA base with Colmonoy 83 flight hardfacing; the barrel used a 42CrMo body with an EJS04 lining. I included the protected areas and inspection requirements with the material descriptions. That made the proposal more precise than a general promise of higher hardness.
For acceptance, I treated the dimensions and the material identification as separate checks. A correct alloy name would not make an incorrect diameter acceptable. Equally, a component could meet its dimensions without proving that the specified working alloy had been supplied. Both requirements belonged on the order.
This project also reinforced a limit on single-point measurements. The result at the metering-section station established the clearance there. I required the other axial positions and machine interfaces to be checked separately. Buyers should use the same distinction when reading an inspection report: identify what was measured, where it was measured and which drawing requirement it addresses.
Project measurements: restoring the specified cold clearance
At the worn metering-section station, the screw flight outside diameter was 89.65 mm and the barrel bore was 90.25 mm. The calculated cold radial clearance was:
(90.25 − 89.65) ÷ 2 = 0.30 mm
The approved drawing specified 0.10 mm at that station. During dimensional acceptance, the new screw flight measured 89.95 mm, and the corresponding new bore measured 90.15 mm:
(90.15 − 89.95) ÷ 2 = 0.10 mm
| Measurement at the same axial station | Worn pair | New pair |
|---|---|---|
| Screw flight outside diameter | 89.65 mm | 89.95 mm |
| Barrel bore diameter | 90.25 mm | 90.15 mm |
| Calculated cold radial clearance | 0.30 mm | 0.10 mm |
Source: EJS Industry's filled-PP replacement project measurements and approved drawing requirement.
The replacement restored the specified cold clearance at that station, reducing it by 0.20 mm. That dimensional result is distinct from an operating-performance result. Throughput, screw speed, melt temperature and subsequent wear measurements provide the operating record needed to evaluate the replacement in service.
Keep cold clearance and running behavior separate
The calculation above divides the diameter difference by two. It describes the nominal radial clearance for the corresponding circular sections; it is not a measurement of the gap at every point around an eccentric or damaged assembly. The 0.10 mm figure belongs to this project's drawing, not a universal setting for all 90 mm machines.
Check machine alignment, straightness, barrel support and heating condition before treating an alloy upgrade as the complete remedy. These checks follow the contact-wear concerns described by Davis-Standard. A more wear-resistant surface cannot correct an installation that forces the screw against the bore.
For continuing measurement and spare-parts planning, the EJS service-life guide explains how to use a baseline and repeat measurements. Keep that wear history with the formulation record so the next material decision has evidence behind it.
8. Put a verifiable material specification on the order
Build the order from requirements the receiving team can check
Write the screw and barrel requirements on separate lines. Each component should have an identifiable base material, working-surface construction and acceptance basis. Avoid an order that names one alloy and leaves the other component described only as "matching barrel."
Use this sequence when preparing the technical inquiry:
- Identify the machine and attach the approved screw and barrel drawings, including the revision used for the order.
- State the complete formulation and operating duty, with the old-part damage and measurement map where available.
- Specify the base steel and condition for each component, or request a clearly identified proposal for approval.
- Identify the screw hardfacing and barrel lining separately, with the manufacturing process and protected surfaces.
- Agree on finished layer requirements or the defined nitrided case requirement, plus the hardness method and measurement locations.
- List the final dimensions, interfaces and inspection records needed to accept the parts.
- Retain the accepted dimensions as the installation baseline for later wear checks.
That sequence also makes quotations easier to compare. If one proposal changes the base steel, another changes only the flight hardfacing, and a third replaces both working surfaces, they are different technical offers. Resolve those differences before comparing total prices.
Material records and contact information
EJS states that its supplied screw barrels include an inspection report and material certificate. Use those documents to connect the agreed specification with the delivered component: the material identification and dimensional report answer different acceptance questions. Source: EJS quality-inspection description.
For broader interface and purchasing checks, use the extruder screw barrel buyer's guide. For a material review with EJS, send the machine drawings, formulation and old-part evidence to sales@ejsscrewbarrel.com, or call +86-574-83065911. E.J.S Industry Co., Ltd.'s office address is 55 Dongdu Road, Haishu District, Ningbo, China. Source: EJS contact page.
Include the application and documents you require with the first inquiry. A quotation can then identify the proposed construction and the evidence needed for acceptance, rather than asking you to choose between unexplained hardness numbers.
9. Frequently asked questions
What are extruder screws and barrels made of?
The construction can combine a structural steel with a treated surface, screw hardfacing or barrel lining. Identify each component's base material and working surface separately. EJS lists steels including 38CrMoAlA and 42CrMo, plus named screw and barrel alloys in its bimetallic specification.
Is 38CrMoAlA better than a bimetallic screw barrel?
They describe different things. 38CrMoAlA is a base steel, while bimetallic describes a construction with a working alloy. A screw can use a 38CrMoAlA base and an added alloy on its flights. Compare complete constructions for the actual duty, not those two terms in isolation.
Does higher hardness always mean better wear resistance?
No. Consider the alloy structure, protected area, deposit condition and wear mechanism. ASTM G65 evaluates abrasion through volume loss under defined test conditions, while ASTM E18 addresses Rockwell hardness. Neither measurement alone predicts the operating life of a complete assembly.
Must the screw and barrel use the same alloy?
No. They must form a suitable working pair, but the screw hardfacing and barrel lining can be different materials. Our filled-PP project used Colmonoy 83 flight hardfacing with an EJS04 barrel lining. Review material compatibility, surface condition and the specified fit together.
Should a filler or recycled-feed change trigger a material review?
Yes. Provide the revised formulation, filler loading, feedstock controls and operating conditions. Compare those changes with the duty used for the original selection. Keep the old-part measurements and damage record so the review can address the affected surfaces rather than defaulting to a harder alloy.
What documents should accompany a material specification?
Request material identification and the agreed inspection records for each part. The order should also define protected areas, surface-process requirements and measurement locations. EJS's product page states that inspection reports and material certificates accompany its supplied screw barrels; define the project-specific scope before production.