Fixed or Floating Bearing Assignment

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About This MicroSim

A shaft grows as it warms. If both bearings clamp it axially, the growth becomes an axial load that shortens bearing life, so FanPedia (pp. 97-99) lets only one bearing locate the shaft: the fixed bearing. The floating bearing carries the shaft radially but lets its outer ring slide axially in the housing. This MicroSim applies the rules from Chapter 17 in their decision order:

1. At 301°F and above, every bearing type uses one fixed and one floating bearing. Go to step 3.
2. At 300°F and below, ball bearings use two fixed bearings (A), except on Arrangements 3SI, 7SI, 3DI and 7DI, where FanPedia's footnote says one fixed and one floating may be required (D, engineering review). Roller and split roller bearings use one fixed and one floating.
3. With a floating bearing, a horizontal mount puts the fixed bearing at the drive end (B) and a vertical mount puts the floating bearing at the drive end (C).

Each of ten illustrative scenario cards gives the fan type, arrangement, mounting orientation, bearing type and operating temperature. You choose one of four configurations: A, two fixed bearings; B, fixed at the drive end and floating at the non-drive end; C, floating at the drive end and fixed at the non-drive end; D, flag for engineering review. The cards come in a fixed order, with one attempt each. After you commit, the sim draws the shaft (horizontal or vertical, as the card says) with its sheave or coupling, impeller and two pillow blocks, labels the drive-end and non-drive-end bearings, marks each one fixed (clamped between locating rings) or floating (double arrow along the shaft), and names the rule step that decided the card.

Mastery is 8 of 10 cards correct on the first (and only) attempt. After card 10 the sim shows the score, whether mastery was reached, and each missed card with the rule step that decided it.

The shaft drawing is a schematic: a vertical fan is drawn with its drive end at the top, and the impeller sits between the bearings on Arrangement 3 family fans and outboard of them on Arrangements 1, 8 and 9.

How to Use

1. Read scenario card 1 and choose a configuration with the A, B, C or D button (or keys 1-4 or A-D). The full text of each option is listed on the card.
2. Press Commit (or Enter). The answer locks. "✓ Correct." or "✗ Not quite." appears with the reason, the correct configuration letter, and the rule step that decided it; the shaft drawing now shows which bearing is fixed and which floats.
3. Press Next card (or Enter) and repeat. "Cards correct: n of 10" keeps the running score.
4. After card 10, press See results. Read the missed cards, then press Start over to try all ten again. Notice that orientation only matters once a floating bearing is needed.

Keyboard: keys 1-4 or A-D choose a configuration; Enter commits, then goes to the next card. Tab reaches every button.

Data label: "Illustrative scenarios · Source: FanPedia pp. 91, 97–99", at the bottom left of the drawing.

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Lesson Plan

Learning Objective

The learner will apply the fixed-floating bearing rules to assign the correct bearing configuration to ten fan scenarios defined by mounting orientation, bearing type, operating temperature and arrangement, with at least 8 of 10 correct (Bloom: Apply, verb: apply).

Audience

Adult professional development: new application engineers, sales staff, representatives and facilities staff.

Duration

10-15 minutes

Prerequisites

• Drive end and non-drive end bearings (Chapter 17)
• Fixed and floating bearings (Chapters 16 and 17)
• Ball, roller and split roller bearing types (Chapters 16 and 17)
• Horizontal and vertical mounting, and the fixed-floating bearing rules (Chapter 17)

Activities

1. Scenario cards (6-8 min): Ask the four questions in order for each card (horizontal or vertical, ball or roller, above or below 300°F, straddle arrangement or not) before committing.
2. Review (2-3 min): On the results screen, read the rule step for every missed card and say which question you skipped.
3. Discussion (2-3 min): Cards 6 and 10 differ by one degree. Explain why that degree changes the answer.

Common Misconceptions Addressed

• Every fan needs a floating bearing: cards 1, 5 and 6 use two fixed ball bearings.
• The fixed bearing is always on the drive end: cards 4 and 9 are vertical and float at the drive end.
• Temperature does not matter for ball bearings: cards 6 (300°F, two fixed) and 10 (301°F, fixed and floating).
• The 300°F cutoff works the same way on straddle arrangements: card 8 (Arrangement 3SI, ball, 250°F) is an engineering review item.

Assessment

• The running line "Cards correct: n of 10" counts first-attempt answers (there is only one attempt). At the end the sim shows "First-attempt score: n of 10" and the mastery line; mastery is 8 of 10.
• Looking at the shaft drawing before committing is not evidence of mastery. Ask the learner why the floating bearing moves to the drive end on a vertical fan.

References

1. FanPedia: The Fan & Blower Encyclopedia - Twin City Fan's reference; pp. 97-99 (Fixed & Floating Bearings) give the placement and quantity rules and the 3SI, 7SI, 3DI and 7DI footnote, and p. 91 defines drive end and non-drive end bearings.
2. Rolling-element bearing - Wikipedia overview of ball and roller bearings and how they carry radial and axial loads.
3. Thermal expansion - why a warm shaft grows longer and needs one bearing free to slide.