A machine model identifies the envelope. Your PVC recipe identifies much of the duty inside it. This guide shows how to convert formulation, product and wear records into a conical twin screw barrel specification that a manufacturer can actually review.
Why the PVC recipe is part of the hardware specification
PVC reaches the extruder as a formulation, not as resin alone. A current KraussMaffei PVC processing white paper separates the additives into processing aids, such as lubricants and stabilizers, and mineral fillers. It also explains that flight count, pitch and mixing grooves affect residence time, friction and homogeneity. That is why two plants with the same nominal extruder size can need different screw details.
The EJS conical twin screw barrel page makes the same practical point in a different way. It offers several screw designs for different CaCO3 levels and stresses the importance of the clearance between the two screws and between the screws and barrel. The useful conclusion is simple: size, formulation and clearance belong in one technical review.
A replacement copied only from an old purchase order can reproduce a diameter and length while missing the current duty. This happens when the plant has increased filler, introduced regrind, moved from pipe to profile, changed the die, or raised the output target since the original set was supplied.
Translate the recipe into hardware load
The safest RFQ does not hide a proprietary recipe behind the words "standard PVC." It can protect the exact percentages while still identifying the variables that affect screw design. If confidentiality is required, use a nondisclosure agreement and provide the formulation directly to the engineering contact.
| Input to report | Why the screw manufacturer needs it | Useful evidence |
|---|---|---|
| PVC type and resin grade | Defines the material family that must be conveyed and plasticized. Do not combine rigid PVC, flexible PVC and CPVC under one label. | Supplier grade, K-value if used by your plant, and current technical data sheet. |
| Complete CaCO3 amount | Mineral filler changes the abrasive duty and is an explicit EJS design input. | Actual amount plus the calculation basis, such as parts by weight or mass percentage. Never send a number without its basis. |
| Other fillers and pigments | The total mineral package matters. CaCO3 alone may not describe the wear load. | Material name, amount, supplier grade and any change from the last proven recipe. |
| Stabilizer, lubricant and processing-aid package | These ingredients affect fusion behavior, friction and the process window. They help explain a change in torque or melt quality. | Package type, supplier grade, dosage basis and mixer record. |
| Regrind or recycled content | Variation, contamination and embedded hard particles can change wear and process stability. | Percentage range, source, screening method and contamination controls. |
| Product and die | Pipe, profile and panel production impose different output, pressure and dimensional targets. | Finished product drawing, die or head identification, and normal pressure if measured. |
| Operating window | Actual speed, torque, temperature and output show the duty that the existing set experiences. | Stable production log plus a problem-run log, not only the machine nameplate. |
This record prevents a common diagnosis error. If output falls after a recipe change, the old screw may be worn, the new formulation may be processing differently, or both may be true. A bore measurement and recipe revision history help separate those causes.
How to read the EJS CaCO3 design bands
EJS currently publishes four "classical designs" for different CaCO3 amounts on its conical product page. The values are useful because they show that EJS does not treat all filled PVC recipes as one geometry. They are incomplete as a purchasing specification because the visible page does not identify the unit or formulation basis.
| EJS design label | Published CaCO3 band | What the buyer should do |
|---|---|---|
| Design A | Less than 100 | Send the exact CaCO3 amount and state how it was calculated. |
| Design B | 100 to 150 | Confirm that EJS uses the same unit and recipe basis as your plant. |
| Design C | 150 to 200 | Add current torque, output and wear evidence to the formulation. |
| Design D | Over 200 | Request geometry and alloy review. Do not assume the label alone defines the finished screw. |
What belongs next to the CaCO3 number
Record the resin amount used as the recipe base, the CaCO3 supplier and grade, whether the filler has changed, and the total mineral package. Also state the regrind range. A single number cannot show whether a plant has changed filler source, introduced a second mineral, or allowed contaminated scrap into the feed.
The selection question is therefore not "Which design handles my number?" It is "Which geometry and wear protection fit this verified formulation, product, process window and machine interface?"
Screen the construction against the wear mechanism
EJS lists full-body nitriding, a bimetallic extrusion section followed by whole-body nitriding, and selected tool-steel lining among its conical barrel options. Its current bimetallic versus nitrided guide publishes the working-layer depths and alloy families below. These values describe EJS options. They do not predict a fixed service life.
Separate the base steel from the working surface
The EJS conical product page lists 38CrMoAlA (1.8509), 34CrAlNi7 (1.8550), 31CrMoV9 (1.8519), 40Cr, 42CrMo, D2 (1.2379), SKD61 and SKD11 among its material choices. The dedicated pipe and profile pages list the first five, while the panel page also lists D2, SKD61 and SKD11. These names should not be mixed with Ni60, Colmonoy 56, Colmonoy 83 or EJS01 to EJS04 as if they were one hardness ranking.
| Material decision | EJS examples | Question it answers |
|---|---|---|
| Base or body material | 38CrMoAlA, 34CrAlNi7, 31CrMoV9, 40Cr, 42CrMo | Which steel supports the part, heat treatment and machine interface? |
| Tool-steel or lining route | D2, SKD61, SKD11 as listed for selected conical constructions | Does the barrel design call for a different local or lining construction? |
| Screw working alloy | Ni60, Colmonoy 56, Colmonoy 83 | Which deposited surface fits the abrasion and corrosion balance? |
| Barrel working alloy | EJS01, EJS02, EJS03, EJS04 | Which bore lining fits the abrasion, corrosion and temperature duty? |
A useful material specification names both levels. For example, it should state the approved base steel and heat treatment, then identify the working surface, deposited or lined zone, required layer and hardness range. The drawing should show where the protected zone starts and stops.
| Construction | EJS published working layer | When it enters the review | Limit of the shortcut |
|---|---|---|---|
| Nitrided screw or barrel | 0.4 to 0.7 mm nitrided case | Controlled PVC duty where abrasion and corrosion are modest and the existing nitrided set has a satisfactory wear record. | A thin hard case can be consumed locally. Hardness alone does not show remaining usable geometry. |
| Bimetallic screw | 1.0 to 1.5 mm PTA-welded alloy layer | Review when mineral loading, measured wear or corrosion calls for a thicker working layer. | The alloy must match the actual mechanism. A wear-focused grade is not automatically the best corrosion choice. |
| Bimetallic barrel | 2.0 to 3.0 mm centrifugal-cast lining | Review for a thicker replaceable wear surface in the barrel bore under demanding duty. | The screw and barrel still need compatible hardness, geometry and matching clearance. |
Use alloy data as a screen, not a ranking
For the screw, the EJS guide lists Ni60 at HRC 56 to 62, Colmonoy 56 at HRC 53 to 58, and tungsten-carbide-bearing Colmonoy 83 at HRC 50 to 55. For the barrel, it lists EJS01 at HRC 58 to 62, EJS02 at HRC 50 to 58, EJS03 at HRC 55 to 60, and tungsten-carbide-bearing EJS04 at HRC 55 to 60.
The same guide positions EJS02 and EJS03 toward corrosion-led service, and EJS04 toward high abrasion. It also identifies Ni60 and Colmonoy 56 as corrosion-resistant screw options, while Colmonoy 83 provides stronger abrasion resistance. This is a first screening step. The finished selection should still consider the recipe, temperature, known attack pattern, base steel and compatibility of the screw and barrel surfaces.
A high CaCO3 number does not automatically command the hardest listed combination. If the old set shows chemical attack, plating damage, localized contact or feed contamination, an abrasion-only answer can miss the cause.
Pipe, profile and panel labels are starting points
EJS has dedicated pages for PVC pipe, plastic profile, and plastic panel and board conical twin screw barrels. Those categories help route the inquiry, but the category name is not enough to reproduce the screw.
| Application | Send with the machine data | Why it changes the review |
|---|---|---|
| PVC pipe | Pipe type, diameter and wall range, number of layers, die or head, normal output, pressure if available, and formulation. | The product range and head resistance help define the stable conveying and metering duty. |
| PVC profile | Profile cross-section, weight per meter, die, calibration setup, output, surface defect photos, and formulation. | Surface quality or dimensional complaints can come from process, die, formulation or worn hardware. The record narrows the cause. |
| PVC panel or board | Board width and thickness, solid or foamed construction, filler and regrind package, die, output, and current wear map. | EJS lists panel, board and WPC panel duty, but these products can expose the screw to different mineral and recycled feed conditions. |
| PVC granulation | Dry-blend recipe, pelletizing head, throughput, venting arrangement, temperature and torque trend. | The downstream resistance and residence-time target differ from direct profile or pipe production. |
If the drawing is missing, the EJS conical page states that on-site measurement can be arranged after the old set is removed and cleaned. A measurement route still needs machine identity and part history. A visually similar barrel can differ at the flange, feed opening, port locations, center distance, bore taper or screw-end connection.
Read the old set before choosing the new one
The old screw and barrel are physical process records. Photograph them before repair or disposal. Measure them at repeatable axial stations and mark every point on a sketch. EJS explains in its service-life guide that abrasive fillers, corrosive chemistry, contamination, poor alignment and process conditions can all shorten usable life.
| Observed pattern | Questions to ask | Evidence to send |
|---|---|---|
| Broad polishing and gradual flight loss | Did filler, regrind or output increase? Is wear concentrated in the plasticizing or metering zone? | Axial wear map, formulation revisions, output and torque trend. |
| Pits, rough attack or discolored local areas | Is the duty corrosion-led? Were material, stabilizer package, shutdown or cleaning practices changed? | Close photos before polishing, material safety data where relevant, temperature and shutdown records. |
| One-sided scoring or metal contact | Are the screws synchronized and centered? Is the gearbox, thrust system or barrel alignment within the machine owner's limits? | Contact side marked on a drawing, gearbox findings, runout and alignment report. |
| Damage near the feed opening | Could metal or hard contamination enter with regrind? Is feeding stable? | Screening and magnet controls, contaminant sample, feed-rate history and inlet photos. |
| Output loss without major measured wear | Did the formulation, die, temperature profile or operating target change? | Before-and-after production logs and a complete recipe change record. |
Do not diagnose from color or a single photograph alone. Cleaning, measurement and process history are needed. Also avoid turning a material table into a life multiplier. Service life depends on how quickly usable geometry and clearance are lost in the real process.
Control formulation changes like hardware changes
A screw set can appear to "fail early" when the process duty changed without being recorded. Give each approved recipe a revision number and keep it in the same production history as the screw serial number or installation date.
- Freeze the baseline. Record the recipe revision, raw-material grades, normal output, screw speed, torque, barrel temperatures, head pressure if available, and product quality when the line is stable.
- Log the change. Mark any increase in CaCO3, new filler grade, regrind increase, stabilizer or lubricant change, new PVC grade, die change or higher output target.
- Check the process response. Compare torque, temperature, pressure, venting, output and defects against the baseline. Keep the same units and sampling method.
- Inspect on a fixed interval. Use the same measurement stations on the screw and barrel. Trend clearance instead of waiting for output to collapse.
- Trigger an engineering review. Review geometry and construction when a recipe crosses an EJS design band, the wear mechanism changes, or the process no longer operates inside the proven window.
This record creates a useful feedback loop for the next replacement. It shows whether the selected construction improved the observed wear pattern without pretending that one plant's operating hours can be promised to another.
Build an engineering-ready RFQ
Use this as a preparation form. Send the drawing, formulation sheet, product information and wear evidence through the approved EJS inquiry channel. Do not submit confidential details through an unapproved form connection.
Frequently asked questions
What CaCO3 level can an EJS conical twin screw design handle?
EJS publishes Design A for less than 100, Design B for 100 to 150, Design C for 150 to 200, and Design D for over 200. The current product page does not state the unit or formulation basis. Send the complete recipe and state how the CaCO3 amount was calculated before using a design label.
Does higher CaCO3 automatically require a bimetallic screw and barrel?
No. Higher mineral loading makes abrasion an important review item, but the selection should also use the old set's wear pattern, corrosion evidence, process window, contamination controls, geometry and matching clearance. EJS lists nitrided and bimetallic routes, and engineering should select between them for the verified duty.
Which EJS alloys are screened for corrosion-led PVC duty?
The current EJS material guide positions EJS02 and EJS03 barrel alloys toward corrosion resistance and lists Ni60 and Colmonoy 56 as corrosion-resistant screw options. The final choice still needs the actual formulation, temperatures, observed attack and compatibility with the mating surface.
Can the same conical screw design run PVC pipe, profile and panel products?
Do not assume it can. EJS supplies hardware for all three applications, but product geometry, die or head, output, formulation and operating duty must be reviewed. Send the existing drawing and stable production data for the exact product.
Is a nitrided conical twin screw barrel enough for PVC?
It can be a candidate where the verified abrasion and corrosion duty is modest and the existing nitrided set has a satisfactory wear record. EJS publishes a nitrided case depth of 0.4 to 0.7 mm. The measured wear pattern and formulation should decide whether a thicker bimetallic working layer needs review.
Which formulation changes should trigger a new screw review?
Review the hardware when CaCO3 or another mineral changes materially, regrind rises, resin grade changes, the stabilizer or lubricant package changes, the product or die changes, or output is increased beyond the proven operating window. Also review after a new wear mechanism appears.
What should I send for a replacement conical twin screw barrel quotation?
Send the extruder maker and model, current size code, complete dimensional drawing, full formulation with units and calculation basis, product and die data, target output, actual speed and torque, temperature and pressure records, regrind range, current material, installation history, measured wear map and clear photos.