Conveyor drive and bearing specs are where most quotes lack detail. A quote gives the belt a paragraph and the frame a drawing. The quote gives the drive a horsepower number and nothing else. Horsepower is the least useful number on that page. Three things decide whether the drive lasts in a recycling plant or fails in one season. The three things are the service factor behind the horsepower number, the ratio that sets belt speed, and the suffixes on a bearing part number.
Service Factor: The Multiplier That Sizes the Gearbox
A gear drive's service factor is a sizing multiplier, not an overload allowance. Start with the power that the application needs. Multiply this power by the service factor. Then pick a reducer rated for the larger number. If the factor is 1.0, the reducer is rated for exactly what you calculated and nothing more. There is zero margin.
AGMA, the American Gear Manufacturers Association, publishes the application tables. Reducer manufacturers build their selection charts from these tables. Conveyors have their own rows in the tables. 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 |
If you move one cell right or one row down in the table, the same conveyor needs a bigger gearbox. If you run the conveyor past ten hours a day instead of three, the factor goes up one step. If you feed the conveyor with a loader bucket or a walking floor instead of a metered stream, the factor goes up again. The reason is that the 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 is the standard for shaft-mounted and screw conveyor drives. The standard 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 that somebody invented. This number is the published Class II factor for shaft-mount drives. A shock-loaded recycling conveyor that runs a full shift is Class II at minimum. Heavy shock puts the conveyor in Class III. A jam or a dropped slug delivers this kind of shock. 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 also carries a service factor, commonly 1.15. That factor is an overload tolerance. The motor can carry roughly 15 percent past nameplate horsepower, but its life is shorter if it runs there. A gear service factor is a selection multiplier that you apply before you pick the gearbox. The two factors do not add. A service factor also raises only the mechanical rating of a reducer, not its thermal rating. So a drive can pass the mechanical selection and still overheat its oil.
Ratio: Belt Speed and Starting Torque
Ratio does two jobs at once. Ratio sets output speed, and therefore belt speed. The reason is that the belt travels one drive pulley circumference per pulley revolution. Ratio also multiplies torque. The pulley then has more torque to break a loaded belt away from a standstill.
The two jobs conflict. The application decides the balance. A manual sorting conveyor needs a slow belt so people can see and grab. A baler feed conveyor needs enough speed to keep the chamber fed. An optical sorter feed belt needs speed to spread and singulate the stream. Our guide on why optical sorters underperform on bad feed presentation covers this. One ratio does not serve all three.
Starting torque is the factor that is skipped. A conveyor that sits loaded overnight breaks away against static friction, settled material, and a belt that has taken a set. If you size the drive for the running load alone, the drive starts fine when empty and stalls when loaded. A variable frequency drive (VFD) adjusts speed without changing sheaves but does not create torque. A standard totally enclosed fan-cooled (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, including on slider bed conveyors. The reducer is mounted on the drive shaft. A separate motor turns it through v-belts and sheaves. A torque arm takes the reaction. The ratio stays adjustable afterward. The reason is that 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. If the conveyor jams, the v-belt 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 matters. Two bearings with the same first four digits and different suffixes look identical on the shelf. If you order by the first four digits, 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. The digit 6 means a single-row deep groove ball bearing. The second digit is the diameter series. The series sets how much steel surrounds 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 the code by 5. So 10 means 50 mm. A 6310 has a 50 mm bore, a 110 mm outside diameter, and a 27 mm width.
2RS: Two Rubber Contact Seals
RS is a rubber lip seal that touches the inner ring. The leading 2 means one seal on each side. That contact is the purpose of the seal. The seal keeps a wet, dusty recycling stream out of the raceway, and it keeps the factory grease in. The alternative on the same shelf is 2Z (also written ZZ). A 2Z bearing has two sheet-steel shields that stop close to the inner ring without touching it. Shields add almost no drag and suit clean, higher-speed service. Contact seals add a little drag, and they run a little slower. Contact seals 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
The C3 suffix is the field that people substitute without thinking, and it is also the field that makes bearings fail. Radial internal clearance is the play between the balls and the raceways before the bearing is mounted. C3 means greater than Normal clearance. C3 is not a precision grade, and it is not tighter. For a 50 mm bore, Normal is roughly 6 to 23 microns, and C3 is roughly 18 to 36 microns. A bearing does not keep the clearance it shipped with.
Two things use up the clearance. The first is the press fit, which stretches the inner ring and closes the clearance. Published figures show that a 0.013 mm interference removes as much as 0.010 mm on its own. The second is heat. The inner ring sits on the shaft, runs hotter than the outer ring, and expands more.
If both effects act on a Normal-clearance bearing in a hot, tightly fitted position, the operating clearance can go negative. Negative clearance is preload. A preloaded bearing carries stress that it was never rated for and makes friction that it cannot shed. The bearing gets hotter, expands more, and preloads itself harder. This sequence is the runaway. It is how a bearing of exactly the right size fails early for a reason that nobody can see on the shelf. C3 is the allowance for exactly those two effects. For this reason, 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
The table below lists the suffixes that you see on a conveyor drive. Spellings vary by manufacturer. For example, SKF writes 2RS1 where a distributor writes 2RS. The meanings stay the same.
| Suffix | What it means | When it is the right choice |
|---|---|---|
| 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 limited 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. The bearing is sealed on both sides. It has 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 are more often supported by mounted pillow blocks. In a pillow block, the bearing is an insert locked onto the shaft. When you order replacement parts, copy every suffix off the part that you are replacing.
What to Ask on a Conveyor Quote
- Ask for the service factor, not only the horsepower. Horsepower with no service factor gives no information 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 increases past ten hours.
- Ask what the belt speed will be at the quoted ratio. Also ask whether the speed can be changed without a new gearbox.
- Ask for full bearing part numbers, including suffixes. If a quote says "sealed bearings" and nothing else, ask which seal and which clearance.
These questions belong with the rest of the list in our guide on how to buy a conveyor and which quotes to distrust. The questions also pair with how to read a conveyor belt spec. The belt, the drive, and the bearings are specified together, or they are specified wrong.
We build every conveyor to order at our Airway Heights, Washington shop. We never build from catalog stock. We specify the drive with the rest of the conveyor. Tell us the material, how it is fed, and how many hours a day it runs. Call (509) 244-9439. You can also request a quote.
Conveyor Drive and Bearing FAQ
What service factor should a conveyor gearmotor have?
ANSI/AGMA 6021-G89 sets three classes for shaft-mounted conveyor drives. The service factor is 1.0 for Class I, 1.4 for Class II, and 2.0 for Class III. 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 that runs a full shift is Class II at minimum. So 1.4 is a defensible minimum. Heavier shock duty indicates a factor of 2.0.
What does 6310-2RS-C3 mean on a bearing?
The 6310-2RS-C3 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. The 10 is the bore code. 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 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 microns. The extra clearance exists because a mounted bearing loses clearance in two ways. An interference fit stretches the inner ring. A hot inner ring expands more than a cooler outer ring. C3 is correct where press fits, heat, or both would otherwise reduce operating clearance to zero.
Can I substitute a Normal clearance bearing for a C3?
A Normal clearance bearing is not a safe substitute in a hot or tightly fitted position. An interference fit plus thermal growth can make the operating clearance of a Normal-clearance bearing negative. Negative clearance is preload. A preloaded bearing carries contact stress that it was never rated for and generates friction that it cannot shed. The bearing 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?
The seal choice depends on the environment. 2RS is two rubber contact seals whose lips touch the inner ring. The contact keeps wet, dusty, abrasive material out and the grease in. The cost is 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. The motor service factor and the gear drive service factor 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. However, continuous operation there shortens its life. An AGMA gear drive service factor is a sizing multiplier that is applied before the reducer is selected. The two factors do not add. One does not substitute for the other.