Designing a conveyor system involves more than just bolting a motor to a frame. If you undersize the motor, it won't start under load due to breakaway torque . If you oversize it, you waste thousands on electricity and oversized VFDs. In this guide, we will walk through the engineering math required to size a conveyor motor and gearbox correctly, specifically focusing on the critical "Dynamic Tension" resulting from inertia. Table of Contents 1. The Physics: Effective Pull (Te) 2. Calculating Motor Power (Worked Example) 3. The Inertia Problem: VFD vs DOL 4. Gearbox Ratio Selection 5. Frequently Asked Questions Advertisement 1. The Physics: Effective Pull (Te) The first step in any sizing calculation is determining the Effective Pull ( T e ) . This is the sum of all forces resisting the motion of the belt. The Basic Formula: T e = F friction + F gravity + F material...
Figure 1: Standard Stud Needle Roller Cam Follower anatomy.
Needle Roller Cam Followers
Needle Roller Cam Followers feature a heavy outer ring cross-section and a full complement of needle rollers. They provide high dynamic and static load-carrying capability and anti-friction performance in a compact footprint. These components are essential as track rollers, cam followers, and in a wide array of linear motion systems.
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- Standard Stud: Threaded stud mounting for moderate loads. Available with crowned outer rings to mitigate misalignment.
- Heavy Stud: Enhanced stud strength for high-shock or heavy-duty loading applications.
- Yoke Type: Ideal for loads exceeding stud capabilities. Clevis mounting provides dual-side support via a high-strength pin.
- CamCentric®: Adjustable design for precision positioning; perfect for eliminating backlash.
- Crowned Outer Rings: Optimized for curved tracks or skewed travel directions to minimize thrusting.
Technical Comparison: Cam Followers vs. Standard Bearings
1. Structural Differences
Standard ball and roller bearings are typically mounted in rigid housings that support the entire circumference. Consequently, forces are transmitted directly into the housing without significant ring deformation.
In contrast, cam followers are supported at a single point. Individual roller forces generate bending moments on the outer ring around this contact point. This results in ring deformation, reversed bending stresses, and a concentrated load zone (see Fig. 2).
Figure 2: Load zone distribution and contact stress concentration.
2. Capacity and Load Limits
Service life evaluation for cam followers must account for rolling element capacity, outer ring deformation, track capacity, and stud bending stress. For best results, operating loads should not exceed 50% of the dynamic capacity.
2.1 Track Capacity
Track capacity is the load a track can withstand without plastic deformation. The standard baseline is HRc 40.
Figure 3: Understanding Hertzian stress distribution in point-contact loading.
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| Table 1: Track Capacity Modification Factors | ||
|---|---|---|
| Track Hardness [HRc] | Tensile Strength [psi] | Capacity Factor |
| 26 | 128,000 | 0.45 |
| 32 | 146,000 | 0.61 |
| 36 | 165,000 | 0.79 |
| 40 | 180,000 | 1.00 |
| 44 | 208,000 | 1.24 |
| 50 | 247,000 | 1.58 |
| 54 | 281,000 | 1.94 |
| 58 | 312,000 | 2.35 |
| 60 | 335,000 | 2.60 |
2.2 Stress Equations
Steel-on-Steel Contact Stress (RBC Standard):
σc max = 3237 ×
√
[psi]
F
leff × D
General Hertz Contact Stress (Roark):
σc max = 0.591 ×
√
F × E
D × w
2.3 Bending and Shear Stresses
Assuming a tight mount, the concentrated force F generates a bending moment Mb:
Mb = F × ( + )
B
2
1
32
Figure 4: Bending moment diagram for stud type cam follower.
2.4 Yoke Roller Pin Shear Stress:
Ï„shear =
2 × F
Ï€ × PD2
Source: RBC Bearings
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