C) Fractional Overrun to Closure (Defined in Class)

ME 314 HW5

Problem#1

A compression spring is made of 0.16 inch A227 wire wound in a mean coil diameter of 1.2 inches. The spring is specified to be preset (set removed) with ends squared and ground. The spring is required to exert a force of 60 lbs at 2.5 inches, and 100 lbs at a length of 2 inches. Determine:

a) The spring constant

b) Solid length

c) Fractional overrun to closure (defined in class)

d) Shear stress at solid length

e) Design margin (factor of safety) against set

f) Design margin against buckling Problem#2 – Reverse Engineer a Pen Spring

Find a click-on click off pen. You cannot get this information from others in class. Take the spring out. Measure the following. I have placed a caliper and a scale (only up to 300 grams – use a kitchen or grocery shop scale if necessary) in the cubical next to the department mailroom (EB 402). Work in inch-lbs units.

1. The free length of the spring

2. The wire diameter

3. The wire OD

4. The force it takes to start moving the spring (minimum force)

5. The force just before clicking on or off (maximum force)

6. The spring length at minimum force

7. The spring length at maximum force

1. Observe the end conditions

2. Assume the wire is made of the cheapest in the list given in the book

3. Assume the wire is not preset (or set-removed)

Determine the following

a) Solid length

b) Force at solid length

c) Spring constant

d) Clash allowance

e) Fractional overrun to closure (defined in class)

f) Shear stress in the wire at maximum force

g) Shear stress in the wire at solid force h) Design margin guarding against set (when fully closed) i) Design margin guarding against buckling at maximum load j) Weight of the spring k) (Rough guess). If bought at large quantities, what would each cost?