A conical twin screw barrel combines two tapered, intermeshing screws with matching tapered bores. Geometry identifies the system; resin, filler, alloy and wear-layer depth decide how long it holds that geometry.
That definition sounds simple until a buyer has to replace an installed set. A photograph may show a taper but hide the spline. A nameplate may give a model but not the drawing revision. An old screw may preserve the drive connection while its working diameter has already worn away. A replacement review must decide which evidence still describes the original part.
What does conical describe?
Conical describes the geometry of the processing pair. Each screw becomes larger toward the drive end, and the two matching barrel bores do the same. This differs from a parallel twin screw set, where the nominal diameter and shaft spacing remain constant through the working section.
The taper changes more than the outside silhouette. The flight diameters, root diameters, bore envelope and screw-to-screw relationship all vary along the axis. A replacement drawing therefore needs axial locations. A diameter written without its distance from a defined reference face is incomplete.
Conical does not identify one universal process. Milacron's current conical range targets PVC and CPVC pipe and profile work. KraussMaffei lists conical machines within its counter-rotating PVC range. EJS also publishes conical hardware pages for PVC pipe, plastic profile and panel or board equipment. That application label helps start the review, but it does not establish the actual screw profile or material specification in your machine.
How to identify conical hardware without guessing
Start with observations that a photograph or existing record can support. Keep each observation separate from the conclusion. This prevents a sales label, model code or old purchase description from becoming stronger evidence than it is.
| Evidence you have | What it can support | What it cannot settle |
|---|---|---|
| Full side view of both screws | Visible taper, overall arrangement, obvious left and right differences | Original unworn diameters, internal barrel dimensions, spline fit |
| Photos of both screw ends | Tip form, drive-end form, relative orientation | Tooth form, engagement length, concentricity or tolerances |
| Machine nameplate | Manufacturer, model, serial number and sometimes size family | Whether the process unit or gearbox was modified later |
| Old purchase order | Previous supplier terminology and ordered description | Whether the delivered part matched the current installed part |
| Approved machine or part drawing | Reference geometry, dimensions, interfaces and revision | Current wear condition or undocumented field changes |
| Removed, cleaned parts | Physical interfaces, visible wear pattern and measurable surviving features | Dimensions that wear, repair or deformation has erased |
Photograph the pair before separating the record
Assign simple IDs such as Screw A and Screw B before creating close-ups. Mark the drive end and discharge end in the photo set. State the viewing direction whenever you record "left," "right," "clockwise" or "counterclockwise." Those words are ambiguous without a viewpoint.
A useful photo set includes the complete pair together, each drive connection, each discharge tip, the feed opening, barrel ports, heater or cooling connections, the discharge flange and the gearbox mounting end. Place an identification card in the frame with the machine model and photo orientation. A ruler in one photo provides scale, but it does not replace calibrated dimensional inspection.
Why the screws and barrel form one matched system
The two screws do not work as isolated shafts. Their flights occupy a shared, changing envelope inside the tapered bores. At every axial station, four relationships matter: each screw's geometry, the relationship between the screws, the relationship between each screw and its bore, and the relationship between the complete process unit and the gearbox.
This is why a supplier should review the screws, barrel and drive interfaces together even when the buyer plans to replace only one component. The review does not automatically mean every component must be replaced. It means the scope decision should account for the parts that control fit and interaction.
Record the pair as a pair. Keep A and B identities through measurement, drawing review, packing and installation. If an existing drawing labels the screws differently, preserve the drawing's labels and add your field labels as cross-references instead of silently renaming them.
Which materials and treatments does EJS list?
The current EJS twin conical screw barrel page lists eight material families for this product: 38CrMoAlA, 34CrAlNi7, 31CrMoV9, 40Cr, 42CrMo, D2, SKD61 and SKD11. It also lists three construction routes: full-body nitriding; bimetallic alloy on the extrusion section followed by whole-body nitriding; and SKD61 or SKD11 lining.
That list is not a pick-any-metal menu. The base steel carries the load and provides the machinable body. The working surface deals with the polymer, filler and corrosive by-products. A material request should therefore identify both parts of the build: base steel plus nitriding, hardfacing or bore lining.
| EJS-listed route | What is on the working surface | Information needed before selection |
|---|---|---|
| Full-body nitrided | A diffused nitride case in the selected steel | Resin, filler, regrind, stabilizer package, process temperature and existing wear history |
| Bimetallic screw plus nitriding | PTA-welded alloy on the screw's working area, with nitriding on the remaining body | Whether abrasion, corrosion or both are driving the failure |
| Bimetallic barrel | Centrifugally cast alloy lining on the bore surface | Compound chemistry, filler loading, bore geometry and available wall section |
| SKD61 or SKD11 lining | A tool-steel liner in the barrel | Drawing, barrel wall, fit method, process duty and repair history |
Wear-layer depth is part of the specification
EJS publishes different working depths for nitrided and bimetallic construction. The figures below are construction data, not a service-life guarantee. They show how much hardened or alloy material is available before the softer supporting steel becomes exposed.
| Construction | Screw working layer | Barrel working layer | Practical reading |
|---|---|---|---|
| Nitrided | 0.4-0.7 mm diffused case | 0.4-0.7 mm diffused case | Suitable for cleaner, less abrasive duty when the nitride case is not being cut away by filler |
| Bimetallic | 1.0-1.5 mm PTA hardfacing | 2.0-3.0 mm centrifugally cast lining | More wear material is available for abrasive, corrosive, filled or recycled feed |
EJS screw hardfacing alloys
The EJS material guide states that the screw alloys below apply to single, parallel twin and conical twin screws. The hardness figure does not rank abrasion resistance by itself. Colmonoy 83 contains tungsten carbide and carries EJS's highest anti-wear rating even though its matrix hardness is lower than Ni60.
| Screw alloy | Published composition | Anti-wear | Anti-corrosion | Hardness |
|---|---|---|---|---|
| Ni60 | Ni + Cr + Fe + Si | Very good | Excellent | HRC 56-62 |
| Colmonoy 56 | Ni + Cr + Si + Fe | Very good | Excellent | HRC 53-58 |
| Colmonoy 83 | Ni + WC + Cr + C | Excellent | Excellent | HRC 50-55 |
EJS barrel casting alloys
EJS uses a separate alloy family for the barrel bore. This matters in an RFQ: asking for "Colmonoy" without saying screw or barrel mixes two different construction systems. The current EJS material guide publishes a 2.0-3.0 mm barrel alloy layer and the following grade data.
| Barrel alloy | Published composition | Anti-wear | Anti-corrosion | Hardness | Max. temperature |
|---|---|---|---|---|---|
| EJS01 | Fe + Ni + Cr + B | Very good | Good | HRC 58-62 | 400 degrees C or below |
| EJS02 | Ni + Cr + Co + B | Good | Very good | HRC 50-58 | 450 degrees C or below |
| EJS03 | Ni + Cr + Co + V + B | Very good | Very good | HRC 55-60 | 450 degrees C or below |
| EJS04 | Ni + WC + Cr + B | Excellent | Very good | HRC 55-60 | 600 degrees C or below |
For PVC, do not choose from hardness alone. Calcium carbonate increases abrasive load, while PVC degradation chemistry can add corrosion. EJS02 and EJS03 carry stronger corrosion ratings; EJS04 carries the highest wear rating. The screw and barrel grades should be selected together from the actual formulation, filler loading and process temperature.
How long does a conical twin screw barrel last?
EJS does publish a life comparison. Its Bimetallic Barrel Screw page states that bimetallic construction costs about 1.5 to 2 times as much as nitriding and increases life by about 2 to 3 times. That is useful purchasing data, but it is not a universal result for every conical extruder.
The newer EJS service-life guide explains the boundary. On clean, unfilled resin, neither surface is under severe attack, so the life gap can be small. On mineral-filled PVC, contaminated regrind or another abrasive or corrosive compound, the thicker and correctly matched bimetallic layer has more material to lose before the supporting steel is exposed. In that duty, the published 2 to 3 times comparison has a physical reason behind it.
| Life driver | Why it changes wear | What the buyer should record |
|---|---|---|
| Compound | Glass fiber, calcium carbonate, talc and contaminated regrind abrade the working surface; degraded PVC can add chemical attack | Resin, filler type, loading, stabilizer package and regrind percentage |
| Material passed | Wear follows throughput and running hours, not the calendar | Machine hours, output rate and total material processed |
| Layer depth and alloy match | A thicker layer helps only when its alloy addresses the actual abrasion or corrosion | Grade, layer depth, hardness and material certificate |
| Alignment and clearance | Side contact from misalignment or incorrect paired clearance can destroy a good alloy early | Baseline clearance, gearbox condition and wear location |
| Process discipline | Chronic surging, overheating, poor filtration and damaging cleaning methods accelerate loss | Temperature, pressure, drive load, screen-change practice and fault history |
Turn service life into a wear rate
Measure a new set before installation, then repeat the same measurements at fixed axial stations during a planned shutdown. At each station, calculate radial clearance as (barrel bore inside diameter minus screw flight outside diameter) divided by two. Subtract the baseline clearance from the current clearance, divide by elapsed running hours, then multiply by 1,000. The result is wear in millimeters per 1,000 running hours for that compound on that machine.
For conical screws, record every measurement with its axial station. The diameter changes along the taper, so a reading without a location cannot be compared reliably at the next shutdown. Track output, drive current, melt temperature and head pressure at the same reference condition. A set may show a production penalty before one convenient clearance reading looks alarming.
What a conical size code tells you
A code such as 65/132 commonly denotes the smaller front diameter and larger rear diameter in millimeters. Current Milacron documentation, for example, labels its conical screw data as front and rear diameters. EJS publishes a broader list of common pairs on its conical twin screw barrel category page.
The code is useful for locating a size family. It is not an interchange standard. It does not fully define the screw length, taper rate, axial profile, drive spline, tip, rotation, barrel ports, flange pattern, temperature-control connections or gearbox interface. Even the same nominal pair can belong to different machine platforms or revisions.
If your main question is how 55/110, 65/132, 80/156 and related codes are read, handle that as a separate size-code check. On this page, the important point is that the code cannot reconstruct missing geometry.
Build a conical reference record from one datum
Choose one stable reference face and use it for axial locations. The gearbox-side barrel mounting face is often easy to identify, but the approved drawing should control the final datum scheme. Avoid a chain of short measurements taken from feature to feature. Each link adds another opportunity for accumulated error.
| Record group | What to capture | Why it changes the replacement |
|---|---|---|
| Machine identity | Make, model, serial number, line output, gearbox plate and modification history | Separates similar size families and reveals possible field changes |
| Reference scheme | Named datum face, axial direction, viewing direction, Screw A and Screw B labels | Keeps every dimension and photograph in the same coordinate system |
| Drive connections | Spline or coupling form, tooth count, major and minor diameters, engagement length, shoulders and retaining features | Controls whether the screws connect to the existing drive |
| Screw bodies | Overall length, working length, diameters at defined stations, flight details, tip form and handedness | Defines the tapered working envelope and paired interaction |
| Barrel body | Overall length, bore geometry, mounting faces, feed opening, vent and sensor ports | Controls fit with the screws and the rest of the process unit |
| Utility connections | Heater arrangement, cooling channels or fittings, sensor locations and thread standards | Prevents a mechanically fitting barrel from missing line connections |
| Discharge interface | Flange diameter, pilot, bolt pattern, sealing face and adapter details | Controls connection to the head or downstream tooling |
| Service conditions | Resin or dry blend, filler and additives, product, operating symptoms and wear locations | Provides context for geometry review and material selection |
Create an axial station map
Give major features station names on a marked photograph or sketch. A simple record might call the drive mounting face Station 0, then identify the feed opening, vent, barrel support, discharge face and screw tip as later stations. At each station, record the distance from Station 0 and the feature being measured. Do not assume the reader will infer which face of a flange or port you used.
For a conical screw, a diameter without an axial station is especially weak evidence. Two technicians can measure the same part accurately at different positions and report different values. Both readings may be correct, but neither is useful until its location is known.
What a worn sample can and cannot preserve
A removed sample is valuable because it preserves interfaces that may be absent from a catalogue. It also carries the history of the machine. Wear, previous hardfacing, polishing, corrosion, bent tips or repaired splines can move the sample away from the original design.
| Sample condition | Risk if copied directly | Evidence to add |
|---|---|---|
| Flight crest is visibly worn | The copied diameter may reproduce wear as new geometry | Original drawing, unworn reference zones, matching barrel inspection and wear map |
| Only one screw is available | The missing hand, pair relationship and orientation remain uncertain | Photos of the installed pair, gearbox data, the other screw's drawing or previous records |
| Barrel has been repaired | The current bore or mounting face may not match the original revision | Repair record, current inspection report and machine-side interface measurements |
| Drive end has fretting or spline damage | A reverse-engineered connection may repeat a damaged fit | Gearbox shaft or coupling inspection and an approved mating-part specification |
| Tip is chipped or deformed | Tip length and form cannot be recovered reliably from that area | Earlier drawing, the companion screw, undamaged reference features or machine-maker data |
The EJS twin conical screw barrel page states that EJS can work from connecting dimensions and can arrange on-site measurement after removed parts have been cleaned when no drawing is available. Treat measurement as a reconstruction project, not a promise to copy every worn surface. The resulting manufacturing drawing still needs review and approval before production.
Separate three kinds of evidence
- Original design evidence: approved drawings, machine documentation and revision-controlled part records.
- Current interface evidence: the gearbox, mounting faces, ports, adapters and other parts the replacement must meet now.
- Condition evidence: wear maps, photographs, operating symptoms, repairs and measurements of the removed set.
Do not merge these into one unlabeled spreadsheet. A measured worn diameter is not an original nominal diameter. A catalogue dimension is not proof that a modified machine still has the catalogue interface.
Prepare a conical replacement inquiry
Send enough information to identify the platform, understand the existing interfaces and separate original geometry from current wear. EJS can then confirm what can be quoted from the available evidence and which details still need measurement.
Minimum attachment checklist
- Machine and gearbox nameplates
- Approved drawing with revision
- Full screw pair photo
- Both drive-end photos
- Both discharge-tip photos
- Barrel feed and vent locations
- Mounting and discharge faces
- Marked axial station sketch
- Dimension report with datums
- Wear map and repair history
- Material and additive description
- Target part scope and destination
Frequently asked questions
How can I tell whether my twin screws are conical?
View the complete working length. A conical pair has smaller diameters toward the discharge end and larger diameters toward the drive end, with matching tapered barrel bores. Confirm the identification with the machine model, drawing and end views because a partial photo can hide the taper.
Are all conical twin screw extruders counter-rotating?
Do not assume rotation from the conical label alone. KraussMaffei currently lists conical machines within its counter-rotating PVC range, while Milacron's conical range also targets PVC and CPVC processing. Check the machine manual, gearbox data and recorded viewing direction before specifying rotation.
Is a 65/132 code enough to order a replacement?
No. The code commonly identifies the smaller and larger nominal screw diameters, but it does not define length, taper, drive connection, flight profile, rotation, barrel ports or machine interfaces. Use it to identify the size family, then confirm the approved geometry.
What materials does EJS list for conical twin screw barrels?
EJS lists 38CrMoAlA, 34CrAlNi7, 31CrMoV9, 40Cr, 42CrMo, D2, SKD61 and SKD11 for conical hardware. Published surface routes include full-body nitriding, bimetallic alloy on the screw working section followed by nitriding, centrifugally cast barrel alloys, and SKD61 or SKD11 lining.
How much longer does an EJS bimetallic screw barrel last than a nitrided one?
The EJS Bimetallic Barrel Screw page publishes a general comparison of about 2 to 3 times the service life at about 1.5 to 2 times the cost of nitriding. Actual life on a conical extruder still depends on the compound, filler loading, throughput, alignment, process control and whether the selected alloy matches the wear mechanism.
Can one conical screw be replaced by itself?
That decision requires inspection of the companion screw, barrel and drive interfaces. A single component may be the requested scope, but its drawing and condition must still be reviewed against the parts it will run with.
Can EJS make a conical twin screw barrel without an original drawing?
EJS states that it can work from connecting dimensions and can arrange measurement support for removed, cleaned parts when drawings are unavailable. The sample condition, location and available machine records determine what can be reconstructed. A manufacturing drawing still needs approval.
Why should a diameter measurement include an axial location?
The screw diameter changes along a conical working section. Two correct measurements taken at different positions can produce different values. Tie each diameter to one defined datum and axial station so the supplier knows exactly where it applies.