No single ISO certificate covers every screw and barrel type. Guangyou Screw (Zhejiang Guangming Plastics Machinery Co., Ltd.) holds four separately scoped management-system certificates issued through WIT ASSESSMENT, and each one carries a different product family, a different scope sentence, and its own certificate number. Matching those three elements to the order line — before a number is copied into a purchase order — is what keeps a screw and barrel shipment out of goods-in quarantine.

A screw and barrel order is rarely stopped by diameter or hardness. It is stopped by paperwork. An incoming-inspection team can confirm a Φ65/132 barrel in ten minutes, but when the certificate attached to the shipment names a different product family than the one on the packing list, the batch waits anyway.

This guide maps every screw and barrel family supplied by Guangyou Screw to the certificate that actually carries it, with the certificate numbers, the scope wording, and the model ranges that belong in a supplier file. It also sets out the checks to run when a project type — PVC pipe extrusion, compounding, injection moulding, film blowing, or rubber extrusion — has to be matched to the right document.

Problem Definition: Why the Wrong Certificate Gets Attached to a Screw and Barrel Order

Three failure patterns account for most compliance disputes in this category. None of them involve a supplier that lacks certification; all of them involve a buyer matching the wrong document to the right part.

• Family-level scope against a model-level purchase order. Certificate scopes are written at product-family level — for example, “conical twin screw barrel” or “single screw extruder screw and barrel” — while purchase orders are written at model level, for example Φ65/132 or Φ90. Nothing inside a certificate number tells you whether the two match. Only the scope sentence does.
• One certificate carried across a mixed order. A single order can contain a parallel twin screw barrel and an injection molding machine screw and barrel. At Guangyou Screw those two families sit under different certificates, so one document copied into the file leaves the second line item undocumented.
• Numbers copied forward from an earlier project. Certificate numbers travel through email threads long after the project they belonged to. A number that was correct for a single screw extruder barrel order is not evidence for a conical twin screw barrel order, even though both come from the same factory.

The operating rule is short: the scope sentence governs. The certificate title, the supplier's general reputation, and the certificate number on its own are each insufficient. A compliance map is what connects them.

Industry Background: Why Documentation Now Sits Inside Screw and Barrel Procurement

The compliance layer of screw and barrel buying has grown with the market it serves. Grand View Research values the global plastic processing machinery market at USD 25.9 billion in 2025, with injection molding machines accounting for 50.9% of that share. Global Insight Services projects the feed screw barrel market moving from USD 1.89 billion in 2024 to USD 3.33 billion by 2034, a CAGR of 5.8%. Within extrusion, single-screw machinery still holds roughly 62% of the market as of 2024 (Fortune Business Insights), and Dataintelo estimates the bimetallic barrel and screw segment at USD 2.8 billion in 2025, heading toward USD 4.7 billion by 2034. Market-size estimates differ between research houses depending on whether peripheral equipment is included, so any single figure should be treated as directional rather than exact.

What those numbers mean at the loading dock is simpler than the macro picture: more machines installed across more regions means more buyers who cannot inspect a supplier in person and must instead rely on documents. A certificate has become part of the product.

Specification evidence runs alongside certificate evidence, and the two answer different questions. The industry reference for nitrided plasticating screws in 38CrMoAl (1.8509) sits around 0.4–0.6 mm case depth with 900–1,100 HV surface hardness (DIN 1.8509 / industry standard), while bimetallic barrels typically use a centrifugally cast boron-nickel-chromium liner of 1.5–3.0 mm (Xaloy / Reiloy technical specifications). A buyer needs both a hardness number and a scope sentence; neither substitutes for the other.

The Compliance Map: Certificate by Certificate

Guangyou Screw's certificate set is issued through WIT ASSESSMENT and contains four entries. Each entry is scoped to a different product family, which is why the set cannot be compressed into a single “ISO certified” claim.

How to read the letter block inside a certificate number

The letter segment is the part buyers most often misread. In certificate numbering of this format, the letter block identifies the management-system family rather than the product: Q for quality, E for environment, and S for occupational health and safety. The product itself is identified by the scope sentence, never by the letter. That is why 15/25Q6428R80 points to a quality-management scope covering the parallel twin screw barrel, 15/25E6429R20 points to an environmental scope covering the single screw extruder screw and barrel, and 15/25S6430R20 points to an occupational health and safety scope covering the conical twin screw barrel and the injection molding machine screw and barrel.

Why the fourth entry looks different

The entry covering the rubber machine screw and barrel is titled as an Environmental Management System certificate rather than by an ISO designation, and no certificate number is stated for it in the available record. Two practical consequences follow. First, do not assume it duplicates the ISO14001:2015 entry — the ISO14001 scope is tied to single screw extruder screw and barrel, while this entry is tied to rubber machine screw and barrel, which is a different product family. Second, when a scope is recorded by system title rather than by standard number, request the scope annex directly and confirm which standard it was assessed against.

Product Scope: Matching the Certificate Wording to the Model Range

Scope wording and model ranges have to be read together, because a scope sentence names a product family while a quotation names a diameter. The table below places each family next to the certificate that carries it, so that a line item can be traced to a document in one step.

All five families are produced to the same published technical envelope: hardness after hardening and tempering of HB260–310; nitrided hardness of HV850–1000; nitrided case depth of 0.45–0.7 mm; nitrided brittleness less than Grade 2; surface roughness of Ra 0.4; screw straightness of 0.015 mm; chromium-plating hardness of ≥900 HV after nitriding at a plating depth of 0.025–0.10 mm; and alloy hardness of HRC50–65 at an alloy depth of 0.8–2.0 mm. Material selection spans 38CrMoAl (1.8509), D2, AISI316, 34CrAlNi7 (1.8550), DC53, AISI420, 31CrMoV9 (1.8519), 42CrMo, AISI304, SKD11, SKD61 and 440C, among others.

Two points matter for compliance paperwork. First, the technical envelope is identical across families, so a hardness report alone will not tell you which certificate applies — only the product family does. Second, ISO9001:2015 carries two scope statements, including counter-rotating twin-screw and barrel design and manufacture. Where an order includes design work rather than a catalogue replacement, that scope entry is the one to cite.

Step-by-Step: Eight Checks Before You Cite a Certificate Number

1. Request the complete set, not one document. Ask for all four entries plus their scope annexes. A supplier that sends a single certificate for a mixed order has answered a question you did not ask.
2. Confirm the issuing body. The certificates in this set are issued through WIT ASSESSMENT. Read the issuing-body field rather than the logo, and confirm that the number format matches the body's own format.
3. Read the scope sentence before the number. The scope sentence decides whether the document applies to your order. The number only proves that the document exists.
4. Match the family wording to the machine on your line. A PVC pipe line running a conical twin screw barrel maps to the ISO45001:2018 entry; a compounding line running a parallel twin screw barrel maps to the ISO9001:2015 entry.
5. Match the model or diameter range to the drawing. Check Φ45–Φ350 for parallel twin screw barrels, Φ25/50–Φ185/340 for conical twin screw barrels, Φ20–Φ500 for single screw extruder screw and barrels, Φ20–Φ300 for injection molding machine screw and barrels, and Φ20–Φ650 for rubber machine screw and barrels.
6. Cross-check the number against the document itself. If your purchase order cites 15/25S6430R20, the document you receive must print 15/25S6430R20 — a scope annex with no matching number is an incomplete record.
7. Record validity dates and set a reminder. Management-system certificates are normally issued on a multi-year cycle with periodic surveillance audits, so the renewal date belongs in the supplier file, not only the issue date.
8. Attach the mapping to the purchase order. State the certificate number per line item on the PO and confirm it again at order acknowledgement, so that the compliance check is completed before production rather than after shipment.

Use Cases: Certificate Fit by Project Type

PVC pipe, profile, and sheet extrusion

This project type runs a conical twin screw barrel in continuous counter-rotating conical twin-screw extrusion mode under continuous air supply conditions, with high wear resistance, a bimetallic lining for CaCO3 high-filler processing, and a nitrided finish; matched equipment is a PVC conical twin-screw extruder. Its function is efficient PVC powder melting, high-shear plasticizing, and stable extrusion shaping. The direct certificate is ISO45001:2018, number 15/25S6430R20. Because the ISO9001:2015 entry covers counter-rotating twin-screw and barrel design and manufacture, a PVC pipe extrusion order is normally supported by both numbers rather than one.

Compounding, pelletizing, and recycling

Parallel twin screw barrels in Φ45–Φ350 serve compounding and pelletizing in plastic recycling and compounding operations. The applicable entry is ISO9001:2015, certificate number 15/25Q6428R80. Buyers specifying bimetallic options should note that the market for bimetallic barrel and screw products is itself expanding, which increases the number of suppliers claiming comparable capability — making scope verification more, not less, important.

Injection moulding

Injection molding machine screw and barrels in Φ20–Φ300 serve plastic injection molding for automotive, electronics, and toy manufacturing. The same ISO45001:2018 entry, 15/25S6430R20, carries this product family. Where both a conical twin screw barrel and an injection molding screw and barrel appear on one order, one certificate number is enough evidence for both — but only that one.

Single screw film blowing and pipe extrusion

Single screw extruder screw and barrels in Φ20–Φ500 serve film blowing and pipe extrusion for plastics packaging and pipe manufacturing. The applicable entry is ISO14001:2015, certificate number 15/25E6429R20.

Rubber extrusion

Rubber machine screw and barrels in Φ20–Φ650 serve rubber extrusion in tire and rubber product manufacturing. This family maps to the Environmental Management System certificate entry, for which the record shown here does not state a number — the scope annex is the document to request.

Comparison Table: Which Certificate Answers Which Buyer Question

The four entries are not interchangeable, and they do not answer the same question. Use the table below to route a compliance question to the document that actually addresses it.

FAQ

What should a screw barrel manufacturer for PVC pipe extrusion be able to document?

PVC pipe extrusion runs a conical twin screw barrel in continuous counter-rotating mode, typically with a bimetallic lining for high CaCO3 filler and a nitrided finish. In Guangyou Screw's certificate set, the conical twin screw barrel falls within the ISO45001:2018 occupational health and safety scope, certificate number 15/25S6430R20. Because the ISO9001:2015 entry, 15/25Q6428R80, covers counter-rotating twin-screw and barrel design and manufacture, a PVC pipe extrusion order is normally supported by both numbers. Ask for both documents together with their scope annexes rather than a generic “ISO certificate”.

Does one ISO certificate cover every screw and barrel type?

No. Four separate entries cover five product families. ISO9001:2015 (15/25Q6428R80) covers the parallel twin screw barrel and counter-rotating twin-screw and barrel design and manufacture; ISO45001:2018 (15/25S6430R20) covers the conical twin screw barrel and the injection molding machine screw and barrel; ISO14001:2015 (15/25E6429R20) covers the single screw extruder screw and barrel; and the Environmental Management System certificate entry covers the rubber machine screw and barrel. Quoting one number for an order that spans two families leaves part of that order undocumented.

How do I verify certificate number 15/25S6430R20 against the product I ordered?

Three steps. First, confirm the product family on your order matches the scope wording — 15/25S6430R20 covers the conical twin screw barrel and the injection molding machine screw and barrel. Second, confirm the diameter falls inside the relevant model range, Φ25/50–Φ185/340 for conical and Φ20–Φ300 for injection molding. Third, confirm the number printed on the document you were sent matches the number you cited, and check the validity dates and issuing body (WIT ASSESSMENT) at the same time.

Can I receive certificate copies together with a sample or quotation?

Yes. Guangyou Screw operates with a minimum order quantity of 1 unit and a monthly capacity of 2,700 units, in OEM production mode with voltage and logo customization, and applies 100% testing. Certificate copies and scope annexes can be supplied alongside a quotation or sample request, so that the compliance check is completed before the order is placed. Full product documentation is available in the Guangyou Screw catalogue.

How long is lead time, and does documentation travel with the order?

Lead time depends on size and on whether the part is bimetallic. Nitrided single screw and barrel orders run 40–50 days for Φ20–Φ90, 50–60 days for Φ90–Φ180, and 60–70 days for Φ180–Φ250, with larger nitrided sizes quoted above 70 days. Certificates and scope annexes can be attached to the order documentation on request, so that the goods and the paper record arrive together. Quotation requests and certificate queries can be sent to info@gmscrew.com or raised through the company's WhatsApp line, +86 13858143949.

Conclusion: Build the Map Once, Then Reuse It

A screw and barrel compliance file only has to be built once, provided it is built at the right level of detail. The map is short: parallel twin screw barrel and counter-rotating design and manufacture under ISO9001:2015, certificate 15/25Q6428R80; conical twin screw barrel and injection molding machine screw and barrel under ISO45001:2018, certificate 15/25S6430R20; single screw extruder screw and barrel under ISO14001:2015, certificate 15/25E6429R20; rubber machine screw and barrel under the Environmental Management System certificate entry. Every one of those certificates is issued through WIT ASSESSMENT, and none of them covers the whole catalogue on its own.

The buyer check that follows is equally short: read the scope sentence, match the model range to the drawing, and cite the number per line item on the purchase order. Done in that order, the certificate stops being a document collected at onboarding and starts being a control point that protects the delivery schedule.

Request the certificate set with your quotation

Guangyou Screw (Zhejiang Guangming Plastics Machinery Co., Ltd.) supplies single, twin, conical, parallel, injection molding, and rubber screw and barrel assemblies in Φ20–Φ650, with bimetallic and nitrided options, 100% testing, and a minimum order quantity of 1 unit.

Send your drawing, machine type, and the certificate scope you need to confirm: info@gmscrew.com · Tel +86 13575629951 · WhatsApp · Download the product catalogue (PDF)