US 1536306

I'll verify this patent against live sources before summarizing.

Let me check for any litigation or CAFC docket activity, and try to confirm the claim text.

Search scope and verification note

I searched for the specific number 1536306 in patent databases and for any litigation/docket record. Results below are grounded in the patent text supplied plus two independent live sources: Google Patents US1536306A and FreePatentsOnline 1536306.

Important parsing caution (no auto-correction applied): the identifier string "1536306" also appears in unrelated records — e.g., EP 1536306 A1, "Proximity authentication system" (Broadcom). That is a different document and is not the patent summarized here. Likewise, the numeral 1536306 appears in unrelated corporate/numbering lists. I have excluded those matches.

CAFC 2026 docket check: no results. I found no Federal Circuit (or any court) docket, and no USPTO PTAB proceeding, involving US 1,536,306. This is consistent with the record: the patent's anticipated expiration is May 5, 1942, and its legal status is "Expired – Lifetime." A 2026 appeal would require a live district-court or PTAB decision, which the record does not show. I state this as a negative finding from search, not as a certified docket clearance.

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Bibliographic summary — US 1,536,306

Abstract: The original 1925 printing has no formal abstract; pre-1930 US patents were not required to include one. The statement of purpose (which Google Patents surfaces in its "Definitions" field) reads: "the object of the invention is to attach blades to an impeller hub securely and to shape the blades in such a manner that they are reinforced by those portions which are used for the purpose of attachment." I flag this as a paraphrase-derived object statement, not an abstract as filed.

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Plain-language overview

Stated problem. Attaching impeller blades to a hub securely while also making the blades stiff enough to resist bending in service — with the insight that the very material used for attachment can double as a reinforcing rib.

Disclosed structure (referring to the drawings). A hub A carries a central flange B projecting radially and perpendicular to the hub axis. Several blades are mounted on the hub, each with a relatively flat outer portion C extending beyond flange B and terminating toward the hub in curved "wings" D that curve forwardly of flat portion C and serve to entrain and direct fluid inward toward the larger radial portion. Each blade extends laterally on both sides of flange B — i.e., a double-flow blade — and is cut away at E so it can be slipped onto the hub over flange B. Blades are preferably pressed from sheet steel. A groove F is pressed into the blade face running substantially from tip to inner edge; the rear wall of that groove is punched out from the inner edge out to the outer edge of flange B, leaving two attaching flanges G projecting rearwardly, through which rivets H pass into flange B. Beyond flange B, the pressed-out metal constitutes a rib G that stiffens the blade against bending. Additional flanges J on the rear of the blades near the hub base give further support against bending along a radial line, with recesses K in the hub accommodating bolts or rivets L. The assembled hub is mounted on shaft O for rotation between stationary shrouds P, with fluid discharged into diffuser R of the blower casing.

Key point of the disclosure: the attachment tabs and the stiffening rib are the same piece of metal — the rib terminates in the attachment flanges — so reinforcement comes "for free" from the attaching structure.

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Independent claims

There is one claim, and it is independent. The record shows the specification ending with "I claim:" followed by a single unnumbered claim, with no dependent claims. As printed (with scan artifacts preserved and readable corrections noted in brackets):

"A runner for a centrifugal blower including a hub havin[g] a base and a central flan[g]e extending radially therefrom and a doub[l]e flow impeller blade formed integrally and extending on opposite sides of the [flange] of the hub and having a rib pressed out on its back face beyond the hub flange to reinforce the blade, said rib terminating in flanges for attachment to the hub."

Plain-language scope of that claim — a centrifugal blower runner having:

1. a hub with a base and a central flange extending radially from it;
2. a double-flow impeller blade formed integrally and extending on both opposite sides of the hub flange;
3. a rib pressed out on the blade's back face, located beyond the hub flange, whose function is to reinforce the blade; and
4. that same rib terminating in flanges used to attach the blade to the hub — i.e., the reinforcement and the attachment means are structurally unified.

Uncertainty flag. Only one claim is present in the OCR record I could retrieve, and the claim is unnumbered. I could not open the original scanned PDF to confirm whether the printed patent carried a "1 Claim" statutory header or any claim numbering. The substance above is reliable; the formal claim count is high-confidence-but-not-document-verified.

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Related-art context (from the record)

Later patents citing US 1,536,306 include US 2,457,325 (axial flow fan), US 2,581,872 (propeller fan blade retaining construction), US 3,246,834 (blower housing), and Sunonwealth publications US 2003/0063976, US 6,568,907, and US 2009/0028710 (impeller structure / fan blade). Similar-document listings include US 4,028,005, "Impeller blade reinforcement" (1977), which is thematically closest to the pressed-rib reinforcement concept claimed here.

Sources: Google Patents US1536306A (full text supplied); FreePatentsOnline record 1536306 (confirming title, assignee, application no. US69089124A, filing 02/06/1924, publication 05/05/1925, assignee INGERSOLL RAND CO, class 415/98).

I'll search for litigation involving US patent 1536306.

Let me run additional targeted searches to confirm.

Let me do a few more targeted checks including litigation databases.

Litigation Search Results: US Patent 1,536,306

Bottom line: I found no litigation involving US Patent 1,536,306. No district court case, Federal Circuit appeal, ITC investigation, or PTAB proceeding (IPR/PGR/CBM) records this patent as a patent-in-suit or subject patent in any source I searched.

What I searched

• General web/patent search for "1536306" combined with litigation terms (lawsuit, plaintiff, defendant, infringement, docket)
• Searches targeting Ingersoll-Rand (the assignee) as plaintiff with terms "1,536,306" / blower / impeller
• Searches for the patent title "Radial impeller" in a litigation context
• Litigation-oriented sources surfaced in results (CourtListener, Unified Patents/PTAB materials, PACER Monitor, Docket Alarm, RPX Insight, FreePatentsOnline and Google Patents litigation tabs)

None returned a case in which US 1,536,306 was asserted or challenged.

Patent status context (per the patent record)

This is an 1925 patent that expired in 1942. It predates any modern electronic litigation docketing system, so even if a suit had been filed during its 17-year term, a docket record would likely not survive in PACER, CourtListener, or commercial litigation databases, which generally begin coverage in the 1990s–2000s. Practically, in view of expiration, no live litigation is possible.

Important caveats on search hits that are NOT this patent

My searches returned several items containing the string "1536306" that are different legal instruments. I flag them because they are easy to confuse:

• EP 1 536 306 A1 — "Proximity authentication system," published 2005-06-01 (Buer et al., Broadcom). This is a European application, not US 1,536,306. It appears in Google LLC v. Proxense LLC, IPR2024-00782 / IPR2024-00784, only as prior-art Exhibit 1005 — not as a patent-in-suit, and not the US patent you asked about.
• GB 1 536 306 A — "Electronic monitoring apparatus," British Steel Corp. A UK patent, unrelated.
• A Kansas PSC exam-pass list, a Brazilian municipal procurement notice ("Protocolo 1536306"), an Indian trademark (application 1536306), and an Italian corporate spin-off document — all coincidental matches on the same number string.

Also note: an Ingersoll-Rand infringement case did appear in results (Ingersoll-Rand Co. v. Black & Decker Mfg. Co., 192 F.2d 270 (4th Cir. 1952)), but that concerned the Pott impact-wrench patent, not US 1,536,306, and involved a different technology entirely. I am not attributing it to this patent.

Confidence

High confidence that no litigation is known or of record for US 1,536,306. Because this patent expired in 1942 and predates searchable litigation archives, I cannot rule out that some unrecorded dispute existed during its term; I have no evidence of one, and I am not inferring that one occurred.

Proceedings overview

Total AIA trial proceedings on file: 0 — no IPRs, no PGRs, no CBM reviews, no derivation proceedings, and no PTAB appeal of any kind involving US 1536306. The structured "PTAB proceedings on file" block from the USPTO Open Data Portal returns nothing, and targeted web searches (PTAB E2E / PTAB Decisions / Docket Alarm / CourtListener) surface no petition, institution decision, Final Written Decision, or settlement naming this patent. Bottom line for a defendant: the absence of PTAB activity is not a "hardened patent" signal here — it is a "this patent expired in 1942 and cannot be asserted" signal. US 1536306 issued 1925-05-05 on an application filed 1924-02-06 and, under the pre-1995 17-years-from-grant term (35 U.S.C. § 154), reached its anticipated expiration on 1942-05-05 — the legal status recorded on the face of the Google Patents record is "Expired – Lifetime." There is no enforceable claim to invalidate, which is precisely why no petitioner ever bothered.

(No proceedings to list)

There is no proceeding number, petitioner, panel, ground, institution decision, FWD, settlement, or CAFC appeal to report for US 1536306. Rather than fabricate an entry to fill this section, here is what I checked and what I found:

• USPTO ODP structured block: empty as to AIA trials — treated as canonical per the operating rules.
• Google Patents record (https://patents.google.com/patent/US1536306/en): shows only Journal-type events — filing 1924-02-06, grant 1925-05-05, expiration 1942-05-05. No reissue, no ex parte reexamination, no inter partes proceeding, no assignment-of-record change away from Ingersoll-Rand Co.
• Cited-by / family data: the six-to-seven "Cited By" references are all ordinary later patent citations (e.g., US2457325, US2581872, US3246834, US20090028710A1). None of them is a PTAB paper.
• Web searches for petition activity: no hits tie US 1536306 to any IPR/PGR/CBM number.

Why no AIA trial was even legally or practically available

Worth stating explicitly, because it explains the empty docket and forecloses a "maybe they're hiding something" theory:

• PGR is unavailable by statute — 35 U.S.C. § 321 applies only to patents whose claims have an effective filing date on or after 2013-03-16. This patent's effective filing date is 1924-02-06, and it is a pre-AIA patent under first-to-invent.
• CBM is unavailable — it required claims directed to a financial product or service (AIA § 18(d)(1)), which a sheet-steel centrifugal blower impeller is not; the CBM program also sunset on 2020-09-16.
• IPR (§ 311(a)) is nominally available against any patent regardless of filing date, and the Board has instituted IPRs on expired patents in rare circumstances (e.g., for pre-expiration damages windows). But with expiration in 1942, every act of alleged infringement would fall outside the six-year damages lookback of 35 U.S.C. § 286 — there is no damages window and no injunctive window, so there is no economic case to fund a petition.

Name-collision warning (this is the trap I actually found)

If someone runs a bare "1536306 IPR" search, they will surface two unrelated documents on different numbering authorities, and it would be an error to attribute either to this patent:

1. EP 1536306 A1 — Broadcom Corp., "Proximity authentication system," published 2005-06-01. This one does appear in PTAB records, but as an exhibit, not as the challenged patent: it is Ex. 1005 in Google LLC v. Proxense, LLC, IPR2024-00782 and IPR2024-00784 (petitions filed 2024-04-19), on a "Notice of Exhibit list" and a "Petitioner's Updated Exhibit List" (2024-08-30). The challenged patent in those proceedings is a Proxense patent, not US 1536306, and the petitioner is Google, not any predecessor of Ingersoll-Rand.
2. GB 1536306 A — British Steel Corp., "Electronic monitoring apparatus" (kurtosis-coefficient bearing-failure detector), filed 1975-03-12 in the UK. Unrelated authority, unrelated subject matter, no US proceedings.

Neither is a proceeding on US 1536306. I flag them because a due-diligence memo that conflates them would tell a defendant the wrong patent has been attacked and survived.

Strategic summary

Claim status. US 1536306 has exactly one claim as issued: "A runner for a centrifugal blower including a hub having a base and a central flange extending radially therefrom and a double flow impeller blade formed integrally and extending on opposite sides of the flange of the hub and having a rib pressed out on its back face beyond the hub flange to reinforce the blade, said rib terminating in flanges for attachment to the hub." That claim was never cancelled, never amended, never reexamined, and never construed by the PTAB — because no AIA trial ever existed. It is not "sustained" in any meaningful adversarial sense; it is simply expired and unenforceable. There is no "Untested vs. Sustained" split to map, and no surviving-claim list to give you, because there is no live claim.

Estoppel landscape. § 315(e)(2) estoppel is inapplicable — estoppel attaches only to a petitioner in an instituted IPR/PGR, and there has been none. Practically this is academic: a defendant does not need estoppel protection when the asserted right expired 83 years ago. If you are nonetheless facing a demand letter, your defense is not an invalidity theory — it is unenforceability by expiration and § 286's damages bar, plus standing to seek fees if the assertion was baseless.

Pattern signals. None of the usual signals exist: no repeat petitioner, no serial IPR filings, no PTAB appellate practice by the owner (Melach J. Nusim, assignor to Ingersoll-Rand Co., Jersey City, N.J.), no defensive aggregator such as Unified Patents in the chain, no CAFC docket. The absence of IPRs on a 100-year-old expired patent is not a signal about patent strength; it is a signal that no one has asserted it, because no one can.

Recommended next steps

1. If you received a demand letter or a complaint citing US 1536306 / patent number 1,536,306 — verify the number before doing anything expensive. Assertion of a patent that expired 1942-05-05 is not merely a weak case; it is a non-starter, and a demand built on it (or a demand that has mis-cited an unrelated number, such as the Broadcom EP 1536306 or a modern US patent) may support a Rule 11 / § 285 fee motion. There is no FWD to quote or link here, because none exists — do not let anyone hand you a "PTAB decision" purportedly about this patent without checking its authority prefix (US vs. EP vs. GB) and its challenged-patent number.
2. Confirm expiration from the primary record, not a secondary database: the Google Patents legal-status entry reads "Expired – Lifetime" with an anticipated expiration of 1942-05-05 (https://patents.google.com/patent/US1536306/en). For a pre-1995 patent, the 17-year-from-grant term under § 154 governs; there is no terminal disclaimer, PTA, or reissue in the file history that could extend it.
3. If the real target is a different patent, re-run the analysis on the correct number — a live IPR landscape, estoppel map, and FWD analysis would then be worth the effort. For a check on any PTAB paper or CAFC opinion you are later handed, verify it at USPTO PTAB E2E (https://ptacts.uspto.gov/ptabweb/) and, for appeals, CourtListener (https://www.courtlistener.com/) — I did not find any such paper for US 1536306 and do not represent that an exhaustive sealed/confidential sweep is possible, though for a 1924 patent with a 1942 expiry the residual uncertainty is negligible.
4. No litigation milestones to calendar. There are no institution deadlines, no statutory one-year FWD clocks, and no oral hearings pending, because there is no pending proceeding.

I'll reconstruct the assignment chain for US 1,536,306, starting with the USPTO Assignment Center and cross-references.

Let me probe the Assignment Center directly and cross-reference corporate/inventor history.

Ownership-chain reconstruction — US 1,536,306 ("Radial impeller")

Method note and a limitation, stated up front. The Assignment Center (https://assignmentcenter.uspto.gov/, mirrored at https://assignment.uspto.gov/patent/index.html) is an interactive, session-based search interface; I could not execute a live query against it in this run. My findings below are grounded in (a) the authoritative patent text supplied, which carries the assignment legend on its face, and (b) public/indexed search returns. I state explicitly where the record is silent rather than inferring a conveyance.

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Inventors

Pattern assessment — no adverse pattern. This is a career engineer-inventor of the assignee, not a departing founder:

• His Turbo-Blower Department posting at Phillipsburg is the same engineering unit that would have produced the subject blower, so the invention arose inside the operating company's R&D function.
• He is a repeat inventor for the same assignee in the same period: US 1,505,283, "Combined gas exhauster and tar extractor," issued 1924-08-19, also naming "MELACH J. NUSIM ... ASSIGNOR TO INGERSOLL-RAND COMPANY, OF JERSEY CITY, NEW JERSEY."
• There is no evidence of the inventor departing the original assignee within 12 months of the 1924-02-06 filing, and no fire-sale precursor pattern.

Minor evidentiary discrepancy: the two biographical sources give different Easton street addresses (416 Cattell St. vs. 541 Lafayette St.). Both are 1920s–30s publication dates and cannot be reconciled from available material; this is immaterial to ownership.

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Original assignee

Ingersoll-Rand Company, Jersey City, New Jersey, a corporation of New Jersey — named on the face of the patent and confirmed as both original and current assignee in the Google Patents and FreePatentsOnline records.

• Primary line of business at filing: heavy industrial machinery — rock drills, reciprocating and centrifugal compressors, blowers, and pumps. The inventor's own department (Turbo-Blower, Phillipsburg NJ) was the blower/compressor business, so this was a core-product-line patent, not an off-strategy filing.
• Did they ship a product embodying the claims? Yes, on the evidence available. The specification is written around an assembled, installable machine: the hub-and-blade runner is mounted on shaft O between stationary shrouds P, discharging into diffuser R of a blower casing. That is a description of a production centrifugal blower architecture, and the assignee's Turbo-Blower Department was manufacturing exactly that class of equipment. This is the strongest available indicator of an operating-company-origin patent.
• Current status: Operating. The corporate lineage is layered and worth spelling out, because the name "Ingersoll-Rand" today belongs to a different legal entity than the 1925 assignee:
  • Pre-2020: legacy Ingersoll-Rand plc (Ireland-domiciled holding company for the historic New Jersey business).
  • 2020-03-01: Gardner Denver Holdings, Inc. completed its merger with Ingersoll-Rand's Industrial segment and took the name "Ingersoll Rand Inc." (NYSE: IR), HQ 800-A Beaty Street, Davidson, NC. The compressor/blower/vacuum product lines — including the Nash and Hoffman & Lamson blower brands — sit in this company's Industrial Technologies and Services segment.
  • Also 2020: the remainder of legacy Ingersoll-Rand was spun off as Trane Technologies plc (NYSE: TT), the HVAC/climate business.
  • Current scale: publicly traded, ~$6.9–8.0B revenue, ~15,000–21,000 employees, market cap roughly $31B (mid-2026 data).
• Not a bankruptcy case. No Chapter 7/11 proceeding is associated with either the 1925 assignee or either 2020 successor.

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Assignment timeline

The Assignment Center has no records for this patent, and I could not find any recorded post-issuance assignment in any indexed source. I say that plainly rather than reconstructing a chain that does not exist.

Three independent reasons this is the expected result, not a search failure:

1. Age of the instrument. The patent issued 1925-05-05 and its anticipated expiration was 1942-05-05. Any conveyance during its 17-year term predates electronic docketing by half a century.
2. The USPTO's reel/frame regime postdates this patent. Reel/frame microfilm indexing of assignments began in the 1950s. Pre-1955 conveyances were recorded in the older Liber/Page books, which are not part of the Assignment Center's searchable corpus. A 1924–1942 assignment for this patent, if it exists, would live in that liber system.
3. The only conveyance that matters is on the face of the patent. The printed heading reads "...MELACH J. NUSIM, OF EASTON, PENNSYLVANIA, ASSIGNOR TO INGERSOLL-RAND COMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY." That "ASSIGNOR TO" legend is itself proof of a pre-issue assignment executed on or about the 1924-02-06 filing date and recorded by the Office before grant. I could not retrieve the liber/page number, the exact execution date, or the correspondent of record, and I will not fabricate them.

Correspondent of record: not retrievable. No attorney or agent name is available for the 1924 recording. Consequently, signal #3 below cannot be evaluated at all — that is a data gap, not a negative finding.

Per the brief's instruction, I state this plainly. I continue below with the remaining sections only because the timeline diagram, signal table, and verdict are analytically required; they are correspondingly short.

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Timeline diagram

timeline
    title Ownership of US 1536306
    1924 : Nusim files application 690891
         : Assigns rights to Ingersoll-Rand
    1925 : Patent 1536306 issues
    1942 : Patent expires
    2020 : IR industrial unit merges with Gardner Denver

The 1942-to-2020 gap is intentional and is the substance of the finding: the patent was public domain for 78 years before any corporate transaction involving the assignee's corporate family occurred, and that 2020 transaction was a merger of companies, not a transfer of this (long-expired) patent.

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NPE / troll-pattern signals

Cross-check for consistency: this is fully consistent with the earlier-generated sections, which found no litigation, no PTAB proceeding, no CAFC docket, and a legal status of "Expired – Lifetime" with expiration 1942-05-05. No contradiction to flag.

Number-collision caution (carried forward, restated briefly): searches on the string "1536306" surface EP 1 536 306 A1 ("Proximity authentication system," Buer et al./Broadcom) — a different instrument, appearing in Google LLC v. Proxense LLC, IPR2024-00782/-00784, only as prior-art Exhibit 1005. That exhibit is a European publication, not a patent-in-suit, and emphatically not US 1,536,306. Also excluded: GB 1 536 306 A (British Steel), a Karnataka PSC exam list, a Brazilian procurement protocol, an Indian trademark application, and a Lite-On inventor ID. None of these are ownership events for this patent.

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Verdict

Insufficient data — in the specific sense the rubric defines: only the original assignment exists.

The chain consists of exactly one link, proven by the face-of-patent legend "MELACH J. NUSIM ... ASSIGNOR TO INGERSOLL-RAND COMPANY" executed on or about 1924-02-06, with no recorded post-issuance assignment retrievable from the Assignment Center or any indexed source. The substantive character, however, is unambiguous even on thin records: this is an operating-company-origin, internally generated, core-product patent that was held by its manufacturer until it expired 1942-05-05 — 78 years before the next corporate transaction in the assignee's family, which was a merger of companies rather than a conveyance of this patent. There is no basis in the record for any NPE characterization, and I decline to infer one from the age or era of the patent.

Verification links:

• USPTO Assignment Center: https://assignmentcenter.uspto.gov/
• Legacy Assignment Search interface: https://assignment.uspto.gov/patent/index.html
• Google Patents record (legal events, current assignee, expiration): https://patents.google.com/patent/US1536306/en
• FreePatentsOnline record (assignee, application no. US69089124A, class 415/98): https://www.freepatentsonline.com/1536306.html

Residual uncertainty I cannot close: whether a liber/page recording of the 1924 Nusim→Ingersoll-Rand assignment exists in the USPTO's pre-1955 books, and what correspondent filed it. Confirming that would require the USPTO's paper/liber assignment records or the original assignment document, neither of which is in the indexed corpus I could reach.

I'll verify the record for US 1,536,306 and identify its cited/relevant prior art before making any § 102 assertions.

The first pass returned mostly noise. Let me verify the actual citation record on the patent itself and check the pre-1924 documents.

Now let me pin down the pre-1924 documents in the "Similar Documents" set and search for the closest structural prior art.

Scope note and search limits

I ran live searches against patent-database mirrors of the USPTO record (Google Patents US1536306A and FreePatentsOnline 1536306). I did not have API access to USPTO PatentCenter/Public PAIR for this docket, and I hit my tool-call ceiling before I could open every candidate's original scan. Where I state a date or holding that I could only see in an OCR snippet or a secondary source, I flag it as unverified. I did not auto-correct any number: "1536306" here means US 1,536,306, not EP 1 536 306 A1 (Broadcom proximity authentication) or GB 1 536 306 A (British Steel) — both of which are different instruments that surface on the same string.

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Finding 1 — US 1,536,306 has no cited prior-art references of record (negative finding)

This is the single most important result, and it changes the shape of the assignment:

• The Google Patents record for US 1,536,306 contains no "Citations" / "Patent Citations" block. It contains only "Cited By" (documents citing it) and "Similar Documents" (algorithmic, not examiner-attributed).
• This is expected. The modern front page with a structured "References Cited" field was not introduced until the 1970s. In 1925, examiner-cited art lived only in the paper file wrapper, and the printed specification (which I have in full) recites no prior patents or publications anywhere in its text.
• Consequence: the set of documents "cited for 1536306" is empty. There are no backward citations to analyze for § 102. Anything I list below is either (a) a forward citation, which cannot be § 102 art, or (b) my own search-derived candidate art, which I mark as such.

I could not open the original scanned PDF to confirm a "1 Claim" header or any marginal citations; treat the absence of citations as high-confidence-but-not-scan-verified.

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Finding 2 — The forward citations ("Cited By"), and why none is § 102 prior art

Per the record, US 1,536,306 is cited by seven later documents. All of them post-date the Feb. 6, 1924 filing and the May 5, 1925 grant, so by definition none can anticipate the claim under § 102(a) or § 102(b). They are relevant only as evidence of the claim's technological lineage (and, potentially, as § 103 context — outside this task).

Verdict on all seven: no § 102 anticipation. All are later in time. #2 (blade-retaining construction) and #4 (blower housing) are the most thematically adjacent, and the Sunonwealth trio shows the claimed hub/blade architecture surviving into modern impeller design — but that is lineage, not prior art.

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Finding 3 — Candidate § 102 prior art (pre-Feb. 6, 1924), analyzed element-by-element

3.1 The governing standard and the element list

For a 1924-filed, 1925-granted patent the applicable statute is the pre-AIA § 102. Anticipation requires a single reference disclosing every element, arranged as claimed. (Legal-history caveat: under the statute then in force the public-use/on-sale bar was two years, the familiar one-year period dating from the 1939 amendment — I have not re-verified that amendment's text in this session, so treat the critical-date arithmetic as provisional.)

The sole claim (unnumbered; I will call it Claim 1) breaks into these elements:

• E1 runner for a centrifugal blower
• E2 hub having a base
• E3 central flange extending radially from the hub
• E4 a double-flow impeller blade
• E5 blade formed integrally
• E6 blade extending on opposite sides of the hub flange
• E7 rib pressed out on the blade's back face
• E8 rib located beyond the hub flange
• E9 rib reinforces the blade
• E10 rib terminating in flanges for attachment to the hub (the dual-function limitation)

Element E10 is the crux — reinforcement and attachment unified in one piece of metal.

3.2 The only two pre-1924 entries in the record's own "Similar Documents" list

Note: US 860,465 is the one pre-1924 "Similar Document" that is a centrifugal fan by title, and it is therefore the single most interesting candidate in the record. I was unable to open it before exhausting my searches. I am not asserting it does or does not anticipate; I am flagging it as the first document to pull in any follow-up.

3.3 US 632,740 — Parker, "Ventilating-fan" (verified from full text)

• Full citation: H. L. Parker, "Ventilating-fan," US Letters Patent No. 632,740; granted Sept. 12, 1899; filed Sept. 9, 1898; Serial No. 690,555; assignee Emerson Electric Manufacturing Co., St. Louis, MO.
• Description (verified): An axial propeller-type ventilating fan. A spider A with inclined arms a; blades B stamped of sheet metal and riveted to the arms; blade formed with a longitudinal bend; an auxiliary fin E / fin F at the rear of the blade to throw a solid column of air near the axis. The patent expressly states the "longitudinal bend extending nearly throughout the length of each blade strengthens said blades considerably to resist vibration," and that the "fins at the rear portion of the blade are by being bent stiffened to resist torsional strains." Four claims.

Element-by-element:

§ 102 verdict: no anticipation of Claim 1. Too many elements missing (E1–E6, E10). Its only instructional value is the idea that a formed feature of a sheet-metal blade can double as a stiffener — a concept that is old and, standing alone, cannot reach the claimed hub-flange/double-flow combination.

(Incidental caution: Parker's application Serial No. 690,555 is numerically adjacent to Nusim's Serial No. 690,891. These are different applications and must not be conflated — I am preserving both identifiers literally.)

3.4 Tentatively identified pre-1924 art (flagged as not fully verified)

These surfaced in searches but I could not confirm bibliographic data or content against the original documents. I present them as leads, expressly not as established § 102 art:

• US 902,533 (OCR snippet read as a rotary fan/pump patent referencing a pending application filed Nov. 25, 1907). The snippet shows multiblade elements carried in drum form between two circular heads, a head 10 integral with a conical end 11 mounted on a hub 12 on shaft 13, in a snail-shell casing 31, plus radial blades 25 that help draw fluid into the eye and act as spokes. Inventor, number, and grant date unverified. If accurate, it discloses (E1), possibly (E2), and drum-type blade mounting — but not E3/E4/E6/E7/E8/E10.
• US 1,022,846, Irving, granted Apr. 9, 1912, "double propeller blade" design licensed for Eck "Ming" fans. Source is a secondary design-history text, not the patent. Axial propeller art; no hub flange, no pressed rib terminating in attachment flanges. No anticipation.
• US 1,370,284, Carlson — a fan "particularly designed for a turbine blower" whose wide blades overlap adjacent the hub; quoted approvingly in a contemporaneous fan-patent opinion (CourtListener Harvard PDF, Upson-lineage litigation). Pre-1924 by number/era, but content taken from a court opinion's quotation, not the patent. Appears to be an axial/turbine-blower blade-overlap teaching, not a double-flow centrifugal runner. No anticipation on the face of the quotation.
• Art named in the same court opinion but not verified by me: US 525,928 (Thompson fan), US 1,725,344 (Dennis — three wide blades; issued 1929, i.e., post-1924 and thus unavailable), US 119,584 (De Man), and German patent No. 47,116 (Desgoffe). A foreign patent can be § 102 art only if it qualifies as a printed publication; I have no verification of its accessibility or date.
• Thematically closest document in the entire record, but post-dating and therefore not § 102 art: US 4,028,005, "Impeller blade reinforcement" (1977-06-07); also US 3,728,043, "Flexible blade fan with ribbed blades" (1973-04-17). These confirm the pressed-rib-on-blade concept matured after 1536306.

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Bottom line

1. US 1,536,306 cites no prior art. There is no examiner citation block in the record and no reference named in the specification. The literal request — "each patent citation for 1536306" — returns an empty set for § 102 purposes. I am reporting that rather than manufacturing citations.
2. The seven "Cited By" documents (US 2,457,325; US 2,581,872; US 3,123,284; US 3,246,834; US 2003/0063976; US 6,568,907; US 2009/0028710) all post-date the patent and therefore cannot anticipate under § 102 — none of them reads on Claim 1 as prior art.
3. Among pre-1924 art, the verified reference (Parker, US 632,740, 1899) fails on E1–E6 and E10 and therefore does not anticipate the sole claim. The strongest unexamined candidate is US 860,465, "Centrifugal fan" (1907-07-16), which I could not retrieve.
4. No identified reference anticipates the sole claim. The claim's apparent point of novelty — a pressed-out back-face rib that itself terminates in the attachment flanges securing the blade to a central radial hub flange on which a double-flow blade rides — is not met by any pre-1924 document I could verify. Absent a reference disclosing all of E1–E10 in a single disclosure, there is no § 102 anticipation.

What I could not verify, and would verify next: (a) the original scanned front page and file wrapper of US 1,536,306 for any paper-file citations; (b) the full text of US 860,465; (c) full bibliographic data for US 902,533; (d) whether the printed patent carried a "1 Claim" header.

I'll verify the dates and disclosures of the closest references listed in the page's Prior Art section before analyzing.

Let me verify a few more of the listed references and their dates.

Obviousness Analysis — US 1,536,306 ("Radial impeller") under 35 U.S.C. § 103

0. Two threshold flags before the analysis

0.1 Date contradiction. This task states "Current Date: April 26, 2026." The previously generated sections of this analysis state today's date is 2026-09-27, and the source fetch timestamp on the Google Patents page is 2026-09-27T18:18:13.988Z. The gap is immaterial to a § 103 analysis of a patent that expired in 1942, but per the no-auto-correction rule I am flagging it rather than harmonizing it.

0.2 The "Prior Art" section of this page is not a § 103 prior-art list. It is Google's machine-generated citation graph (a "Cited By" list and a "Similar Documents" list) plus a keyword index. Nothing in it has been filtered for antecedency. That is decisive here, and it is the single most important finding of this task: only two of the ~32 references listed pre-date the February 6, 1924 filing date.

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1. Governing law and the critical date

US 1,536,306 was filed 1924-02-06 and granted 1925-05-05, so it is a pre-AIA patent. Pre-AIA 35 U.S.C. § 102(a)/(b)/(e) and § 103 govern. Because the patent issued before the 1952 Act, the standard actually applied to it at the time was the judge-made "invention" requirement of R.S. 4886 (see Hotchkiss v. Greenwood, 52 U.S. (11 How.) 248 (1850); Cuno Eng'g Corp. v. Automatic Devices Corp., 314 U.S. 84 (1941)). Modern practice, however, would apply Graham v. John Deere Co., 383 U.S. 1 (1966), and KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007). I analyze under the modern standard below, and note in § 8 where the two diverge.

Critical date for § 103 art: on or before 1924-02-06 (with the possibility of an earlier invention date via Rule 131-type swearing behind, nothing in the record suggests one).

PHOSITA (ca. 1924): a mechanical engineer or skilled sheet-metal draftsman with 2–4 years' experience in the design of centrifugal fans/blowers and stamped-metal parts — familiar with fan-wheel balancing, blade-vibration problems, riveted and spot-welded sheet-metal assemblies, and press-forming techniques (beads, swages, ribs, flanged edges).

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2. Which listed references are even available as § 103 art

Consequence: the thematically closest item on the page — US 4,028,005, "Impeller blade reinforcement" — is not prior art and may not be used in a § 103 combination. It is admissible only as background evidence that the pressed-rib approach persisted in the art. Similarly, US 3,728,043 ("Flexible blade fan with ribbed blades," 1973) is unusable. Any § 103 rejection built on these would be legally defective from the outset.

Note also that a US patent filed before 1924 but published after could qualify under pre-AIA § 102(e); nothing in the record suggests any listed reference has a pre-1924 effective filing date (US 1,649,161's earliest foreign filing appears to be Canada, Jan. 1926).

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3. Claim element breakdown

The single unnumbered claim (OCR-degraded; bracketed text is my reconstruction, not a correction of the record) resolves to four elements:

Preamble: "A runner for a centrifugal blower including…" — a structural article claim; the preamble is likely limiting as a structural environment.

Scope observations that increase obviousness exposure: the claim recites none of the specification's distinguishing detail — not the forwardly curved wings D, not the cut-away E, not groove F, not flanges J, not the hub recesses K/L, not "sheet steel," not any rib proportion, length, or shape. The claim is far broader than the disclosed embodiment, so it must stand or fall on L1–L4 alone.

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4. What the two qualifying references teach

4.1 US 632,740 (Parker, 1899) — grounded, strong

Retrieved text (https://patents.google.com/patent/[US632740A](/patent/US632740A)/en) shows Parker teaches, in the same field (fans) and on stamped sheet-metal blades:

• Riveted blade-to-hub attachment: "A indicates a spider having as many arms or flukes a as desired… to them blades B are secured by suitable rivets b or otherwise."
• Stamped sheet-metal blades: "Blades B… are preferably stamped of suitable metal."
• An integral, formed feature that both does an aerodynamic job and stiffens the blade: "the longitudinal bend extending nearly throughout the length of each blade strengthens said blades considerably to resist vibration," and "the fins at the rear portion of the blade are by being bent stiffened to resist torsional strains."
• A back-side formation: "I also provide an auxiliary fin at the back of each blade, so that almost as much air is delivered from a point near the axis of rotation…"

Parker thus discloses the conceptual core of L3 — stiffening a stamped fan blade by an integrally formed, back-side rib/fin — and the conventional fastening of such blades by rivets (relevant to L4). Parker's stated problem (blade vibration/noise) is the same problem family Nusim addresses ("reinforce the blade," "reinforcing and stiffening the blade against bending").

What Parker does not show: a hub with a radial central flange (L1); a blade straddling that flange on both sides (L2); and its stiffening fin is not used as the attachment structure (L4).

4.2 US 860,465 (1907) — cannot be characterized; flag

I was able to confirm only the bibliographic fact — grant 07/16/1907, title "Centrifugal fan" (Google Patents 1907 sitemap, https://www.google.com/patents/sitemap/en/Sitemap/Unknown_Category/1907_182.html). My attempts to retrieve its text returned adjacent 1907–1912 centrifugal-fan patents, not this document. I therefore do not know what US 860,465 discloses and will not ascribe content to it. On this record it can be used only as evidence that centrifugal-fan structure was a crowded, mature art by 1907.

4.3 Supplementary art found incidentally (outside the page's Prior Art section — flagged)

While searching, a genuinely pre-1924 centrifugal-fan reference surfaced: US 1,017,215 (R. A. Ilg, filed 1909-10-02, granted 1912-02-13), describing a drum-like centrifugal fan wheel with narrow elongated blades, and — materially for L2 — "the fan casing is provided with a suction opening on both sides, whereby one series of blades acts mainly upon air induced through the opening in one side… and the alternate series… through the opening of the opposite side." This is double-flow/double-inlet architecture, i.e., a blade array serving two inlet paths. I flag it expressly as not part of the page's Prior Art section, and its use would require verification of whether any single blade there actually straddles a central flange.

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5. Obviousness combinations

Combination A — 632,740 + 860,465 (both on the page, both pre-1924)

Teaches: L3 in substance (pressed/bent integral back-side stiffener on a stamped fan blade), plus the riveted-attachment expedient bearing on L4.
Motivation to combine (KSR): same field of endeavor (fans/blowers; the '306 patent and both references sit in the F04D fan art per the page's own classification F04D 29/28, 29/281); the same known problem (blade vibration/bending in a high-speed rotor) was expressly identified by Parker three decades earlier; and combining two references in a single crowded art requires no leap. KSR rationales (A) known technique to improve a similar device in the same way, and (B) predictable mechanical result.
Gap: the combination still does not supply L1 (central radial flange), L2 (integral double-flow blade on opposite sides of that flange), or L4 (rib terminating in attachment flanges). As a two-reference case on this record, it is insufficient for a prima facie case of obviousness as to those limitations.

Combination B — 632,740 + 860,465 + a double-inlet/double-width wheel reference

Add a pre-1924 reference showing a centrifugal wheel whose blades serve two inlets (candidate: US 1,017,215 (Ilg, 1912), flagged in § 4.3 as outside the page's list; a properly scoped search of the pre-1924 art would very likely produce better ones, e.g., double-width blower wheels integral with a center plate).
Motivation: double-width/double-inlet wheel construction was a known expedient for increasing capacity without increasing wheel diameter; mounting a formed blade symmetrically about a central radial flange (or center plate) is the natural way to obtain a symmetric double-flow blade from a single stamping and to give the riveted joint a shear-bearing surface. KSR rationales: (C) design incentive, (E) "obvious to try" a known mounting arrangement, (F) market/manufacturing pressure toward a single-stamped blade replacing paired blades.
Assessment: with such a third reference this becomes a strong prima facie case as to L1–L3.

Combination C — 632,740 + 860,465 + common knowledge of sheet-metal rib/bead stiffening + double-inlet practice

This is the broadest attack and the one most likely to succeed before a modern tribunal, but it is also the one with the most procedural risk: reliance on "common knowledge" to supply L4 (rib terminating in attachment flanges) without a documentary reference invites an In re Venner / "hindsight" objection. It is best framed not as a separate combination but as evidence that pressing or beading a stiffening rib into a sheet-metal part, and using an existing flange as a fastening foot, were "familiar elements" used for their "known functions" (KSR, 550 U.S. at 416).

Why a PHOSITA would make the final step to L4

Nusim's own specification frames the objective as "attach blades to an impeller hub securely" and "shape the blades in such a manner that they are reinforced by those portions which are used for the purpose of attachment." That statement is the statement of the problem, and where the problem is so stated, the solution's direction is telegraphed: once a rib is pressed out of a blade that must be riveted to a flange, running the rib's free end out into two lateral tabs that overlie the hub flange is a predictable mechanical expedient — it adds shear area to the joint at zero material cost, since the metal is already displaced rather than removed. Element G in the specification is generated as a by-product of punching out the rear wall of groove F. A PHOSITA optimizing for manufacturing cost would reach it without inventive effort. This is the A&P Tea Co. v. Supermarket Equipment Corp., 340 U.S. 147 (1950) "aggregation of old elements, each doing its own job" posture, and Lincoln Engineering Co. v. Stewart-Warner Corp., 303 U.S. 545 (1938) ("mere perfection of… does not rise to the dignity of invention").

Teaching away? Analysis

I find no teaching away and no criticality argument available:

• Nothing in Parker discourages forming a stiffening rib on a blade's back; Parker affirmatively praises it.
• Nusim's punching away of the groove's rear wall removes metal, yet the claim recites no minimum rib thickness, depth, or length, so there is no criticality to defend.
• No reference of record disparages a ribbed attachment foot, and no unpredictable result is claimed or disclosed.

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6. Anticipation (for completeness)

No reference of record anticipates the claim. US 632,740 alone lacks the radial hub flange (L1) and the double-flow blade straddling it (L2). None of the post-1924 references may be considered. § 102 is therefore not the operative ground; § 103 is.

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7. Secondary considerations

There is no objective evidence of record: no commercial-success evidence, no long-felt but unsolved need, no failure of others, no copying, no licensing, no praise. The prior sections of this analysis establish that no litigation exists for US 1,536,306 and that the patent expired 1942-05-05 (anticipated expiration per the page's legal-status field). The absence of litigation or commercial evidence cuts both ways — it is not evidence of non-obviousness, and I do not treat it as such; but it also means there is no nexus-tested rebuttal evidence available to rescue the claim if a prima facie case is made out.

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8. Historical-standard caveat

Under the Hotchkiss/Cuno "invention" standard contemporaneous with this grant, a court could have held that unifying the attachment tabs with the pressed rib amounted to more than "the skill of the calling." Inverse dicta run the other way as well: A&P Tea and Lincoln Engineering were decided under the same strict-invention era and invalidated exactly this kind of convenient regrouping of old mechanical elements. The modern KSR standard is materially more likely than the 1925-era standard to invalidate this claim.

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9. Bottom line

Analytical conclusion: On the record supplied by this page, the claim is not provably obvious — but the reason is a defect in the supplied prior-art list, not a strength in the patent. The real § 103 vulnerability is the claim's breadth: it recites only a flanged hub, an integral double-flow blade straddling that flange, a pressed back-face rib beyond the flange, and that rib ending in attachment flanges. US 632,740 already teaches the heart of the third element — an integrally formed back-side fin that stiffens a stamped sheet-metal fan blade while performing an aerodynamic function — and teaches riveting blades to a hub. The remaining distance is a pre-1924 double-inlet centrifugal wheel (for L1–L2) plus the well-known mechanical convention of using an already-formed portion of a part as its mounting foot (for L4).

Most significant unresolved verification item: US 860,465 — the second of only two qualifying references on this page — has not been read. Determining its disclosure (inventor, assignee, whether it shows a radial hub flange, a ribbed or beaded sheet-metal blade, or double-inlet construction) is the single highest-value next step for this analysis. Until then, my treatment of it as a field/skill indicator rather than a substantive reference is a deliberate limitation, not a finding.

Caveat on all claim mapping: every element quotation above derives from the OCR-degraded Google Patents text (e.g., "flan e," "doubde flow," "thefiange"), whose errors I have bracketed rather than silently corrected. If the printed patent's claim 1 contains language the OCR dropped, the element breakdown in § 3 would need to be re-run.