Selection Process
- 4 -
Ball Reverser®selection has three steps, determination
of (1) Load (2) Speed and (3) Life.
The axial load (P) on a Ball Reverser is the applied force
parallel to the screw. All side loads (Pr) should be taken
by the Guide System. Each has its own coefficient of fric-
tion (µ).
In all applications, the maximum inertia load (Pt) at
the turnaround must not exceed the maximum
allowable load (Pm), Figure 7.
Step 1 Determine Load
(A) Calculate P using the formula in either
Figure 4, 5, or 6.
(B) Calculate Pt, Figure 8 and compare to Pm Figure 7.
(C) Using the higher value of P or Pt, select the BR with
a higher Pm from Figure 7.
(D) Select Stroke, page 6.
Step 2 Determine Speed
(A) Calculate RPM from linear speed and lead.
(B) Compare the calculated RPM to the Limiting Speed
(LS) and select the appropriate BR size in Figure 7.
Step 3 Determine Life
(A) Calculate nut assembly and screw in L10 life.
(B) Compare lower number vs. application
requirements.
Example:
Given: Horizontal Application (Figure 4)
Stroke = 8.9 inches Pa = 30 lbs. Pr = 0 W = 20lbs.
GS = Ball Bushings (µ = .004)
Travel Rate = 600 inches/min a = .1g.
Life Required = 4 hours/day, 5 days/week, 100 weeks.
Step 1
(A) P = (0 + 20) 0.004 + (20 x 0.1 x 386) + 30 = 32.08 lbs.
386
(B)Pt = 32.08 + 7.6 x 20 (600)2 = 86.8 lbs.
1x106
(C)Pt = 86.8 lbs. < Pm 98 of the BR1800, therefore the
BR 1800 is acceptable.
(D)For stroke of 8.88 inches, select BR1818-1, i.e.
index "18".
Step 2
(A)600 inches/min. ÷x 1.00 inch Lead = 600 RPM
(B)The BR 1800 Limiting Speed is 800 RPM, therefore
the BR1800 is acceptable in this application.
Step 3
(A)NL = 16666 212 3= 8016 hours
600 32.08
SL = 16666 x 18 145 3= 2330 hours
600 86.8
(B)Therefore the life expectancy is 2,330 hours, which is
the lower of the two values and is above the 2,000
hours required.
Summary:
BR1800 meets Load, Speed and Life minimum. Stroke
index "18" is acceptable, 8.88 vs. 8.90 inches, therefore
the most suitable part number is BR1818-1 (MBR 1818-1
for metric mounting holes).
Other Considerations:
For certain applications, it is helpful to know the torque
required to drive the Load. In the above example the
torque required would be:
T = 86.8 x 1 = 30.67 lb-in.
2.83
Winding:
These applications have the maximum axial load for the
Ball Reverser occurring at the ends of the cable drum.
This is calculated as a function of the fleet angle (θ) and
cable tension (Tc) shown in Figure 6.
Example:
Given:
Drum Width: = 66 inches
Cable Tension: = 10,000 pounds
Cable Diameter: = .5 inch
X= 377 inches (Distance between Ball Reverser
center line and cable guide)
Y= 33 inches (1/2 the cable drum width)
Calculate:
Fleet Angle (θ) = ARCTAN y = 33 = .0875 = 5°
x 377
P = Tc (SIN θ) P = 10,000 (0.0872) P = 872 lbs.
When P has been calculated follow the normal steps for
selecting the appropriate size of Ball Reverser®. Figure
7 indicates that a BR2100 series is required because of
its rated capacity of 1,100 lbs. To determine the proper
stroke, subtract the cable diameter from the drum width.
If this stroke cannot be found, consult our Engineering
department. In this example, the appropriate “index” is
“44” with a stroke of 65.5 inches, (66 inches minus .5 =
65.5 inches). The correct part number is BR2144-1.
ASK ABOUT OUR OTHER LINEAR MOTION PRODUCTS.
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