Conveyor drive and bearing specs are where most quotes go thin. The belt gets a paragraph, the frame gets a drawing, and the drive gets a horsepower number and nothing else. Horsepower is the least useful number on that page. The service factor behind it, the ratio that sets belt speed, and the suffixes on a bearing part number are what decide whether it lives in a recycling plant or dies in a season.
Service Factor: The Multiplier That Sizes the Gearbox
A gear drive's service factor is a sizing multiplier, not an overload allowance. Take the power the application needs, multiply by the service factor, then pick a reducer rated for that larger number. A factor of 1.0 means the reducer is rated for exactly what you calculated and nothing more. Zero margin.
AGMA, the American Gear Manufacturers Association, publishes the application tables reducer manufacturers build their selection charts from, and conveyors get their own rows. Two things set the factor: how the belt is fed, and how many hours a day the drive runs.
| Conveyor, general purpose | Up to 3 hrs/day | 3 to 10 hrs/day | Over 10 hrs/day |
|---|---|---|---|
| Uniformly loaded or fed | Not listed | 1.00 | 1.25 |
| Not uniformly fed | 1.00 | 1.25 | 1.50 |
| Reciprocating or shaker | 1.25 | 1.50 | 1.75 |
Move one square right or one row down and the same machine needs a bigger gearbox. Run it past ten hours a day instead of three and the factor climbs a step. Feed it with a loader bucket or a walking floor instead of a metered stream and it climbs again, because that conveyor is not uniformly fed. A drive sized on the uniform row for a plant that dumps into a hopper is sized for a machine you do not own.
Where 1.4 Comes From
A second AGMA convention applies directly to the drives Remcon uses. ANSI/AGMA 6021-G89, the standard for shaft-mounted and screw conveyor drives, sorts applications into three classes with fixed service factors: Class I at 1.0, Class II at 1.4, Class III at 2.0.
- Class I (1.0) — steady load, ten hours a day or less, no heavy shock and light shock only on a limited basis.
- Class II (1.4) — over ten hours a day, steady or moderate shock load.
- Class III (2.0) — over ten hours a day with moderate shock, and heavy shock possible for up to ten hours a day.
So 1.4 is not a number somebody invented. It is the published Class II factor for shaft-mount drives, and a shock-loaded recycling conveyor running a full shift is Class II at minimum. Heavy shock, the kind a jam or a dropped slug delivers, puts it in Class III. The surge when a slug hits the belt is the load that matters, not the average.
Two Things People Get Wrong
A NEMA motor nameplate carries a service factor too, commonly 1.15, but that one is an overload tolerance: the motor can carry roughly 15 percent past nameplate horsepower, at the cost of life if it runs there. A gear service factor is a selection multiplier applied before you pick the gearbox. They do not add. Service factor also raises only a reducer's mechanical rating, not its thermal rating, so a drive can pass the mechanical selection and still cook its oil.
Ratio: Belt Speed and Starting Torque
Ratio does two jobs at once. It sets output speed, and therefore belt speed, since the belt travels one drive pulley circumference per pulley revolution. It also multiplies torque, handing the pulley more twist to break a loaded belt away from a standstill.
Those pull against each other and the application decides the balance. A manual sorting conveyor wants a slow belt so people can see and grab. A baler feed conveyor wants enough speed to keep the chamber fed. An optical sorter feed belt wants speed to spread and singulate the stream, covered in our guide on why optical sorters underperform on bad feed presentation. One ratio does not serve all three.
Starting torque is what gets skipped. A conveyor sitting loaded overnight breaks away against static friction, settled material, and a belt that has taken a set. Size for the running load alone and the drive starts fine empty and stalls loaded. A VFD tunes speed without swapping sheaves but does not create torque, and a standard TEFC motor loses cooling airflow as speed drops because its fan is on the shaft.
How Remcon Drives a Conveyor
Remcon has used shaft-mounted, v-belt-driven reducers since 1990, slider bed conveyors included. The reducer rides on the drive shaft, a separate motor turns it through v-belts and sheaves, and a torque arm takes the reaction. Ratio stays adjustable afterward, since the sheaves add reduction on top of the gearbox and a pair of sheaves is cheaper to change than a gearbox. A v-belt also works as a mechanical fuse: on a jam it can slip rather than pass the whole shock into the shaft and the gearcase.
Reading a Bearing Part Number: 6310-2RS-C3
"6310-2RS-C3" is not decoration. Every field is load-bearing, and two bearings with the same first four digits and different suffixes look identical on the shelf. Order by the first four and you can put the wrong bearing in the position without ever seeing the mistake.
6310 — Type, Series, and Bore
The first digit is the bearing type, and 6 means a single-row deep groove ball bearing. The second digit is the diameter series, which sets how much steel wraps a given bore: a 63xx has a heavier cross-section and higher load rating than a 62xx of the same bore. The last two digits are the bore code. Codes 00, 01, 02, and 03 mean 10, 12, 15, and 17 mm; from 04 up, multiply by 5, so 10 means 50 mm. A 6310 is 50 mm bore, 110 mm outside diameter, 27 mm wide.
2RS — Two Rubber Contact Seals
RS is a rubber lip seal that touches the inner ring, and the leading 2 means one on each side. That contact is the point: it keeps a wet, dusty recycling stream out of the raceway and the factory grease in. The alternative on the same shelf is 2Z, also written ZZ, two sheet-steel shields that stop just short of the inner ring without touching. Shields add almost no drag and suit clean, higher-speed service. Contact seals drag a little and run a little slower, and they are the right answer anywhere there is glass dust, moisture, or fines in the air. Sealed bearings are normally lubricated for life, so seal choice and service life are one decision.
C3 — Greater Than Normal Internal Clearance
This is the field people substitute without thinking, and it is the one that kills bearings. Radial internal clearance is the play between the balls and the raceways before the bearing is mounted. C3 means greater than Normal clearance. It is not a precision grade and it is not tighter. For a 50 mm bore, Normal runs roughly 6 to 23 microns and C3 roughly 18 to 36. A bearing does not keep the clearance it shipped with.
Two things eat it. The press fit stretches the inner ring and closes the clearance, and published figures show a 0.013 mm interference removing as much as 0.010 mm on its own. Then heat: the inner ring sits on the shaft, runs hotter than the outer ring, and grows more.
Stack those on a Normal-clearance bearing in a hot, tightly fitted position and operating clearance can go negative. Negative clearance is preload. A preloaded bearing carries stress it was never rated for, makes friction it cannot shed, gets hotter, expands more, and preloads itself harder. That is the runaway, and it is how a bearing of exactly the right size fails early for a reason nobody can see on the shelf. C3 is the allowance for exactly those two effects, which is why it is the default in electric motors and most hot, tightly fitted industrial positions.
C3 is not universally better. In a light, cool, loosely fitted position the extra clearance spreads load over fewer balls. Match the suffix to the machine.
Bearing Suffix Decode Table
These are the suffixes you will meet on a conveyor drive. Spellings vary by manufacturer, so SKF writes 2RS1 where a distributor writes 2RS, but the meanings hold.
| Suffix | What it means | When it is the right call |
|---|---|---|
| Z | One sheet-steel shield, non-contacting | Clean, dry, higher-speed positions |
| 2Z / ZZ | Sheet-steel shields both sides | Clean service, protected both sides |
| RS | One rubber contact seal, lip touches the inner ring | Contamination on one side only |
| 2RS / 2RS1 | Rubber contact seals both sides | Wet, dusty, abrasive duty — the recycling default |
| RZ / 2RZ | Low-friction non-contact rubber seal | Moderate dirt where seal drag matters |
| RSH / 2RSH | Sheet-steel-reinforced contact seal (SKF designation) | Heavier-duty sealing than a plain RS |
| C2 | Internal clearance smaller than Normal | Light load, cool running, loose fits |
| CN (usually omitted) | Normal internal clearance, the baseline | Standard fits, standard temperatures |
| C3 | Internal clearance greater than Normal | Interference fits, hot inner ring, motors and drives |
| C4 | Greater clearance than C3 | Heavier interference or higher operating heat |
| C5 | Greater clearance than C4 | Extreme thermal or fit conditions |
| N | Snap ring groove in the outer ring | Axial location in a through-bore housing |
| NR | Snap ring groove plus the snap ring supplied | Same, with the ring included |
| K | Tapered bore, 1:12 taper | Mounting on a taper seat or adapter sleeve |
| E | Modified internal design, usually higher load rating | Where capacity is tight in the same envelope |
| J | Pressed sheet-steel cage | General-purpose standard cage |
| M | Machined brass cage | Shock load, higher temperature, higher speed |
| TN9 / TNG | Glass-fiber-reinforced polyamide cage | Quieter and lighter, temperature-limited |
| P5 / P6 | ISO precision class 5 or 6, tighter than standard | Precision shafting, not typical conveyor duty |
So 6310-2RS-C3 reads as a 50 mm bore deep groove ball bearing in the heavier 63 series, sealed both sides, with extra clearance for a press fit and a hot inner ring. A number like that usually comes from inside the drive; conveyor head and tail shafts more often ride in mounted pillow blocks, where the bearing is an insert locked onto the shaft. Copy every suffix off the part you are replacing when you order replacement parts.
What to Ask on a Conveyor Quote
- Ask for the service factor, not just the horsepower. Horsepower with no service factor says nothing about margin.
- Say how the conveyor is fed. "Uniformly fed" and "a loader dumps a bucket in the hopper" are different rows on the AGMA chart.
- Say how many hours a day it runs. The required factor steps up past ten hours.
- Ask what the belt speed will be at the quoted ratio and whether it can be changed without a new gearbox.
- Ask for full bearing part numbers, suffixes included. If a quote says "sealed bearings" and nothing else, ask which seal and which clearance.
Those belong with the rest of the list in our guide on how to buy a conveyor and which quotes to distrust, and they pair with how to read a conveyor belt spec. Belt, drive, and bearings get specified together or they get specified wrong.
Remcon builds every conveyor to order at our Airway Heights, Washington shop, never out of catalog stock, and the drive gets specified with the rest of it. Tell us the material, how it gets fed, and how many hours a day it runs. Call (509) 244-9439 or request a quote.
Conveyor Drive and Bearing FAQ
What service factor should a conveyor gearmotor have?
For shaft-mounted conveyor drives, ANSI/AGMA 6021-G89 sets three classes: Class I at a service factor of 1.0, Class II at 1.4, and Class III at 2.0. Class I is steady load ten hours a day or less. Class II is over ten hours a day with steady or moderate shock. A shock-loaded recycling conveyor running a full shift is Class II at minimum, so 1.4 is a defensible floor, and heavier shock duty points to 2.0.
What does 6310-2RS-C3 mean on a bearing?
It is a single-row deep groove ball bearing with a 50 mm bore, 110 mm outside diameter, and 27 mm width. The 6 is the bearing type, the 3 is the diameter series, and the 10 is the bore code, where codes from 04 up are multiplied by 5. 2RS means rubber contact seals on both sides. C3 means radial internal clearance greater than Normal.
What does C3 clearance actually do?
C3 is radial internal clearance greater than Normal. For a 50 mm bore, Normal is roughly 6 to 23 microns and C3 is roughly 18 to 36. That extra clearance exists because a mounted bearing loses clearance two ways: an interference fit stretches the inner ring, and a hot inner ring expands more than a cooler outer ring. C3 is correct where press fits, heat, or both would otherwise drive operating clearance to zero.
Can I substitute a Normal clearance bearing for a C3?
Not safely in a hot or tightly fitted position. Interference fit plus thermal growth can drive a Normal-clearance bearing's operating clearance negative, which is preload. A preloaded bearing carries contact stress it was never rated for, generates friction it cannot shed, heats up, expands further, and preloads itself harder until it fails. The two bearings look identical on the shelf, so always match the clearance suffix on the part you are replacing.
Is 2RS or 2Z better for a conveyor bearing?
It depends on the environment. 2RS is two rubber contact seals whose lips touch the inner ring, which keeps wet, dusty, abrasive material out and the grease in at the cost of a little drag and a lower speed limit. 2Z is two sheet-steel shields that do not touch, so they add almost no friction but seal less well. For recycling and solid waste service, contact seals are the right answer.
Does a motor's 1.15 service factor give the gearbox margin?
No. They are different quantities. The NEMA service factor on a motor nameplate, commonly 1.15, is an overload tolerance: the motor can run about 15 percent past nameplate horsepower without immediate damage, though continuous operation there shortens its life. An AGMA gear drive service factor is a sizing multiplier applied before the reducer is selected. They do not add, and one does not substitute for the other.