Machine Design #23: Selecting and Arranging a Chain Drive – Power, Link Count and Life

The roller chain is one of the oldest power-transmission mechanisms, yet it still appears very often in automatic machines, conveyors, lifting mechanisms and production equipment. The reason is fairly simple: a chain transmits large loads, does not slip like a friction belt, works over a relatively large center distance, and withstands oil, heat or dust environments much better than many belts.

However, choosing the right chain part number is only half the work. Many chain drives fail early not because of a lack of nominal load rating, but because the sprocket has too few teeth, the shafts are misaligned, the chain is over-tensioned, there is no elongation take-up mechanism, or the lubrication is in the wrong place.

This article focuses on the points a machine designer really has to decide: in which case to use a chain, which type to choose, how to calculate the tension and link count, how to arrange the slack, and what sign to take as the mark for replacing the chain.

The coefficients and limits in this article are reference design values. When finalizing a part number, prioritize the catalog of the correct maker, correct series, number of chain strands, lubrication method and actual environmental conditions.

1. How is the chain working inside?

Seen from outside, the chain is only wrapping around the sprocket and running in a closed loop. But the part that decides the life lies in the very small zone between the pin and the bush.

When a chain link enters or leaves the sprocket, the links must rotate relative to each other. The outer pin rotates and slides inside the bush hole of the inner link. Essentially, the pin–bush pair works nearly like a plain bearing under fluctuating load and boundary lubrication.

If the oil film is insufficient, the pin and bush contact metal directly. The consequences usually happen in this order:

the pin surface and bush hole wear;
the clearance between links increases;
the actual chain pitch gradually increases;
the total chain length increases, even though the chain plate is not stretched like rubber;
the chain begins to ride up on the sprocket teeth, makes noise, vibrates, and can eventually jump teeth or break.

This phenomenon is called wear elongation. So when evaluating chain life, you cannot only look at the breaking load. You need to consider at the same time:

the contact pressure at the pin–bush pair;
the joint velocity;
the impact load and the number of starts;
the ability of oil to reach the correct pin–bush gap;
dust, water, chemicals or temperature damaging the lubricant film.

The role of the chain plate and roller

The chain plate is the part that bears the main tensile force. It must withstand repeated load, impact load at start/stop and stress concentration around the pin hole. The material is usually carbon steel or heat-treated alloy steel to balance hardness, fatigue strength and toughness. The thickness, plate profile and quality of pin pressing directly affect the allowable tension.

The roller turns freely outside the bush. When it contacts the sprocket tooth, the roller converts most of the sliding contact into rolling contact, thereby reducing impact, reducing tooth wear and helping smoother engagement. With a chain without rollers, contact with the teeth is mainly sliding, so wear and noise are usually higher.

2. Pitch is the foundational dimension

The chain pitch p is the center distance between two adjacent pins. This is the basic dimension that decides:

the overall size of the chain;
the load-transmitting capacity;
the sprocket diameter;
the moving mass;
the vibration level from the polygon effect;
the cost and installation space.

For example, in a common roller-chain system:

RS40 has a pitch of about 12.7 mm;
RS80 has a pitch of 25.4 mm.

A large pitch increases the load-transmitting capacity but makes the chain heavier, the sprocket larger, and the noise at high speed noticeably higher. A small pitch benefits a compact machine and smoother running, but has lower torque and tension limits.

When choosing the pitch, you should not just ask "how much load". You need to weigh three factors together:

the power or tension to be transmitted;
the chain speed;
the allowable space for the sprocket and tensioning mechanism.

The basic dimensions of roller chains are usually based on JIS B 1801, ANSI or equivalent standards. However, you should not understand that every product with the same number is absolutely interchangeable. For special chains, stainless chains, oil-free chains, high-strength chains or special connecting links, you need to re-check the inner width, roller diameter, plate thickness, allowable load and joint-link type.

3. When should you use a chain instead of a belt or gears?

Criterion	Roller chain	V-belt	Timing belt	Gears
Does it slip	No slip like a friction belt	Can slip	No slip until it jumps teeth	No slip
Load and torque	Large, fairly good with impact	Small to medium	Medium	Very large
Center distance	Flexible, usable over a relatively large distance	Medium	Medium	Usually short
Noise	Higher due to metal contact	Low	Medium	Depends on accuracy grade and lubrication
Lubrication	Needed, except the oil-free type	None	None	Usually needed
Oil and heat resistance	Better than ordinary rubber belts	Limited	Limited by belt material	Good
Maintenance	Lubricate, check elongation, adjust slack	Adjust tension, replace belt	Adjust tension, check teeth	Manage oil and clearance
Initial cost	Medium	Low	Medium to high	High

A chain suits when you need to:

transmit a relatively large torque between two spaced shafts;
not allow cumulative slip like a V-belt;
work in an oil, heat or dusty environment;
arrange multiple sprockets on the same transmission loop;
use the chain strand itself as the pulling element of a conveyor or to carry attachments.

Conversely, a chain is not the best choice when the machine needs to be extremely quiet, clean, at very high speed or precisely positioned at the servo level.

Is a chain absolutely synchronous?

A chain drive is a forced-engagement mechanism: the roller meshes with the sprocket tooth, so continuous slip like a friction belt does not occur. The average speed ratio is determined by the number of teeth:

n₂ / n₁ = z₁ / z₂

Where:

n₁: the driving shaft speed;
n₂: the driven shaft speed;
z₁: the number of teeth on the driving sprocket;
z₂: the number of teeth on the driven sprocket.

For example, a driving sprocket with 10 teeth and a driven sprocket with 20 teeth: the average speed of the driven shaft is half that of the driving shaft.

However, you should not equate "no slip" with "absolutely precise positioning". A chain drive still has:

clearance between the pin and bush;
wear elongation;
instantaneous velocity fluctuation from the polygon effect;
the elasticity of the whole system;
installation error and sprocket runout.

So a chain suits maintaining the transmission ratio and mechanical synchronization under a large load, but for a fast indexing mechanism or positioning that needs high repeatability, a precise timing belt, a gearbox or a direct servo drive is usually easier to control.

4. Choose the right chain type by function

4.1. RS roller chain – the basic choice for transmission

RS chain is a reasonable starting point for most ordinary drives. The advantages are:

a wide size range;
easy to buy;
reasonable cost;
a good balance between tensile strength, fatigue strength, impact resistance and wear resistance;
many corresponding standard sprocket types.

The limitation of the standard steel type is that it rusts easily when it meets water and must be lubricated periodically. If the machine works in a wash-down, chemical, clean-room environment or where oil must not drip onto the product, you need to switch to a dedicated series rather than use a standard chain and improvise a fix later.

4.2. Double-pitch chain – reasonable for long, low-speed conveyors

A double-pitch chain has a pitch of about twice the base RS chain. Over the same length, the number of pins and bushes is reduced nearly by half, so:

the chain mass is reduced;
the number of parts is reduced;
the cost is lower;
the inertial load of the whole chain loop is reduced;
it is favorable for long, slow-running conveyors.

Two common roller types:

S roller: standard roller diameter;
R roller: a roller larger than the chain plate height, which can roll directly on a rail.

The R roller is especially useful when you want to reduce friction force over a long load section. However, you should not use double-pitch for high-speed drives just to reduce cost; a large pitch increases the polygon effect and engagement impact.

4.3. Oil-free chain

An oil-free chain uses a sintered bush containing oil. When the joint heats up and bears pressure, oil seeps out onto the pin–bush surface; when it stops, part of the oil returns to the porous hole by capillary action.

This type suits:

packaging machines;
printing;
food or pharmaceutical zones where oil contamination is not allowed;
positions hard to access for maintenance;
machines that need to reduce downtime for oiling.

But "oil-free" does not mean it can be used everywhere. You need to check carefully:

the allowable tension is usually lower than an equivalent lubricated steel chain;
the impact resistance;
the working temperature of the oil contained in the bush;
the effect of wash water, solvent or abrasive dust;
whether additional oil is allowed per the maker's guidance.

Many standard series work in about -10 °C to 150 °C; dedicated heat-resistant types can be higher, with some products up to about 230 °C. The final value must be taken from the catalog of the correct series.

4.4. Attachment chain for load-carrying mechanisms

For a conveyor, the chain not only transmits force but also carries fixtures, pusher bars, pallets or parts. Common attachments include:

Type	Symbol	Characteristic	Typical application
A attachment	A1/A2	A horizontal tab on one side	Mount slats, buckets, support plates
K attachment	K1/K2	Horizontal tabs on both sides	Mount a wide plate, fixture needing stability on both sides
SA attachment	SA1/SA2	A vertical tab on one side	Mount a pusher bar or part on a vertical face
SK attachment	SK1/SK2	Vertical tabs on both sides	Mount a pusher bar, guide or fixture on both sides
Extended pin	EP	A pin extended outward	Hang products, mount an auxiliary roller or cam follower
Hollow pin	HP	A hollow pin	Thread a cross bar connecting two chain strands
G attachment	G	A hole on the link plate	Thread a bar or mount an auxiliary mechanism

The numbers 1 and 2 usually indicate the number of holes on the attachment, for example A1 has one hole and A2 has two holes.

When ordering an attachment chain, the drawing or order code must clearly show:

the attachment type;
the mounting side left/right or both;
the repeat pitch, for example every 2L, 4L, 6L;
the mounting direction and running direction;
the starting link of the attachment cycle;
the tolerance of the distance between the two chain strands if there is a cross bar.

If the attachment repeats on an even number of links, arranging it on the outer link usually makes assembly and joint management more convenient.

5. The sprocket decides more than the designer usually thinks

A chain drive must be seen as a system consisting of chain + sprocket + shaft + bearing + tensioning mechanism + lubrication. Choosing a good chain but using a sprocket with the wrong tooth count, worn teeth or plane misalignment still gives a very short life.

5.1. Pitch circle diameter

The pitch circle diameter of the sprocket can be calculated fairly accurately from geometry:

d = p / sin(180° / z)

Where:

d: the pitch circle diameter, mm;
p: the chain pitch, mm;
z: the number of teeth.

This formula is needed when converting the shaft torque into chain tension.

5.2. Number of teeth on the small sprocket

The fewer teeth the small sprocket has, the more the chain's path differs from a circle. The chain accelerates and decelerates cyclically each time a link enters engagement; this is the polygon effect. The consequences are:

increased vibration and knocking;
increased dynamic load;
faster pin–bush wear;
increased load on the shaft and bearing;
difficulty running smoothly at high speed.

Practical rules:

you should choose a small sprocket of 15 teeth or more;
if space allows, 17 teeth or more is usually better;
avoid going below 13 teeth, unless the speed is low and it has been checked against the catalog.

5.3. Number of teeth on the large sprocket and the transmission ratio

A large sprocket with too many teeth will be very sensitive to chain elongation. Even a small amount of elongation shifts the engagement point noticeably and increases the risk of tooth riding.

In ordinary design:

you should avoid a sprocket over about 120 teeth;
the single-stage transmission ratio should usually be kept around 1:7 or lower;
if a large reduction is needed, consider splitting into multiple stages or using a gearbox.

5.4. Tooth material and treatment

For a machine running many cycles, high load or with abrasive dust, you should use a sprocket with heat-treated teeth, for example induction hardening as a maker option. Teeth that are too soft will wear into a hook shape, making the chain hard to disengage and increasing the impact load.

You can choose:

a finished sprocket already machined with a bore, keyway and set screw;
a rough-bore sprocket for machining to a special shaft;
a taper-lock or quick-release hub sprocket when replacement for maintenance is needed.

When the teeth are clearly worn into a hook shape or the chain has run past the elongation limit, just replacing with a new chain on worn sprockets usually makes the new chain fail very fast. You need to inspect and replace as a set when necessary.

6. The chain-drive selection procedure

Step 1: Determine the working conditions

Before opening the catalog, you need to at least finalize:

the actual motor power or torque;
the driving shaft speed;
the transmission ratio;
the operating hours per day;
the number of starts/stops;
whether there is reversing;
whether the load is steady, mildly impacting or heavily impacting;
the temperature, water, oil, chemicals and dust;
whether there is a cleanliness requirement or no-oil requirement;
the mounting orientation: horizontal, inclined or vertical;
the expected center distance;
the guarding and maintenance-access requirements.

Step 2: Calculate the design power

The catalog usually gives the power-transmitting capacity under standard conditions. The actual load must be multiplied by the service factor Ks:

P_d = P × K_s

Where:

P: the actual transmitted power, kW;
P_d: the design power, kW;
K_s: the service factor by motor type and impact level.

Reference values:

Load nature	Example	Electric motor / turbine	Internal combustion engine
Steady load, almost no impact	Fan, pump, steady-load conveyor	1.0	1.2
Mild impact	Machine tool, compressor, uneven-load conveyor	1.3	1.4
Heavy impact	Press, crusher, construction equipment	1.5	1.7

For example, a 10 kW motor, heavy impact load and Ks = 1.5:

P_d = 10 × 1.5 = 15 kW

When looking up the table, you must choose a chain that meets at least 15 kW at the correct small-sprocket speed and the correct lubrication method.

Besides Ks, some catalogs also have factors by number of strands, temperature, speed, small-sprocket tooth count or lubrication type. You should not merge or omit these factors yourself.

Step 3: Calculate the chain speed

v = p × z × n / 60,000

Where:

v: the chain speed, m/s;
p: the chain pitch, mm;
z: the number of teeth on the sprocket under consideration;
n: the rotational speed, rpm.

The chain speed directly affects the engagement impact and the lubrication method. As the speed increases, just brushing grease on the outside is usually no longer enough; you may have to use drip, an oil bath or oil circulation per the maker's instructions.

Step 4: Check the tension

From the power and chain speed:

F_t = 1,000 × P / v

Where:

F_t: the tangential tension, N;
P: the transmitted power, kW;
v: the chain speed, m/s.

Or from the torque and pitch circle diameter:

F_t = 2,000 × T / d

Where:

T: the shaft torque, N·m;
d: the sprocket pitch circle diameter, mm.

Then you need to add or multiply in the effect of dynamic load, acceleration, the weight of the carried load, rail friction and the load from an inclined/vertical arrangement. A general check form can be written:

F_design = (F_work + F_acc + F_other) × K_s

The selection condition:

F_design ≤ F_allow

F_allow must be the allowable tension in the catalog, not the breaking load.

Step 5: Choose one strand or multiple strands

A double or triple-strand chain does not mean the load capacity increases exactly 2 or 3 times. Length deviation, shaft stiffness and load distribution between strands make the service factor lower than the theoretical sum. When using a multi-strand chain, you must apply the maker's multi-strand factor and check the stiffness of the shaft, hub and bearing.

Step 6: Check the safe load for lifting

For a chain used to hang, lift people, lift goods or hold a load with a risk of falling, you must not select only by the power-transmission table. You need to:

calculate the static load, dynamic load and impact load at stop;
consider the uneven load between branches;
apply the safety factor per law, standards and equipment requirements;
have an independent anti-fall mechanism when regulations require;
prioritize a dedicated lifting-chain series, not self-substitute with an ordinary transmission chain.

Some leaf-chain applications in forklifts or lifting equipment require a safety factor against the breaking load of about 5 or more, but the mandatory value depends on the standard and machine type. You must prioritize the legal regulations and the applicable standard at the place of use.

7. Calculating the link count and center distance

After choosing the chain pitch and the number of teeth of both sprockets, you need to calculate the link count L_p and the center distance C.

Conventions:

p: the chain pitch, mm;
C: the center distance, mm;
L_p: the total number of links measured in pitches;
z_L: the number of teeth on the large sprocket;
z_S: the number of teeth on the small sprocket.

7.1. From center distance to link count

L_p = (z_L + z_S)/2
      + 2C/p
      + [(z_L - z_S)² / (4π²)] × p/C

The result is usually a decimal number. You need to:

round up;
prefer adjusting to an even number of links;
use the finalized link count to calculate the exact center distance backwards.

Nominal chain length:

L = L_p × p

7.2. From link count to center distance

Let:

A = 2L_p - z_L - z_S

Approximate center distance:

C = p/8 × [A + √(A² - 0.81 × (z_L - z_S)²)]

The factor 0.81 is the approximate value of 8/π².

The calculated result should not be put straight onto the drawing without an adjustment mechanism. The chain will have an initial length tolerance and will continue to elongate from wear, so you need a take-up stroke or a sliding motor base.

A short example

Suppose:

chain pitch p = 12.7 mm;
small sprocket z_S = 17;
large sprocket z_L = 34;
expected center distance C = 500 mm.

Substitute into the first formula to calculate L_p, then round to an even number of links. Continue using the chosen link count in the backward formula to compute C, giving the actual layout dimension. This step avoids the errors of "the chain is not long enough" or "the adjustment base is already out of stroke right at installation".

8. Why should you design an even number of links?

The chain is made of alternating inner links and outer links. When the total number of links is even, the two ends can be connected by a standard joint link.

If the total number of links is odd, you usually have to use an offset link. The plate of an offset link is geometrically bent off-line, so it bears an additional bending moment; its load capacity and fatigue strength can be only about 60–80% of the standard chain, depending on the type and maker.

So the priority order should be:

slightly adjust the center distance;
change the number of sprocket teeth if the transmission ratio still allows;
change the position of the tensioning mechanism;
only use an offset link when there is no other option and the load has been reduced per the catalog.

Besides the strength issue, an even number of links also makes maintenance easier, the joint more common, and reduces the risk of wrong assembly in the field.

9. Slack: do not tension it like a V-belt

A chain needs a certain amount of slack to engage naturally and compensate for small deviations. Over-tensioning the chain does not make the system "tighter" but creates a continuous baseline load on:

the pin–bush;
the shaft;
the bearing;
the motor mounting structure;
the sprocket teeth.

A commonly used starting value is the sag at the middle of the slack branch equal to about 2–4% of the span length. For a vertical drive, frequent reversing or one with vibration, you should manage it more strictly, usually below about 2%, and also check the maker's guidance.

For example, a free span 500 mm long, the reference sag is about:

500 × 2% = 10 mm
500 × 4% = 20 mm

This is a reference range, not a general tolerance for every mechanism.

An over-tight chain

increased heat and pin wear;
the bearing fails fast;
the motor draws more current;
hard to install the joint link;
a squeal or knock at engagement.

An over-slack chain

the slack branch vibrates and hits the cover;
the chain easily slips off the guide;
large impact at start/reverse;
can ride the teeth or jump teeth;
the attachment is in the wrong relative position to the product-receiving mechanism.

The adjustment mechanism should be there from the drawing

a motor base with a slide slot and a push screw;
a bearing block with a take-up unit;
an idler or tensioner on the slack branch;
enough stroke to compensate for installation tolerance and wear elongation;
a reference mark or scale so both sides adjust evenly;
a firm locking mechanism after adjustment.

The idler should not press on the tight branch without a clear reason. When using a tension wheel, you need to check the reverse-bending radius, the number of teeth in engagement and the load on the bearing.

10. Aligning the shafts and sprockets

A correctly chosen chain can still fail fast if the two sprockets are not in the same plane or the two shafts are not parallel.

When alignment is off, the inner edge of the chain plate rubs the side of the tooth. Common signs:

one side of the chain plate is shiny or scratched;
the sprocket teeth wear unevenly on one side;
the chain runs in a wavy manner;
a periodic squeal;
increased heat at one bearing;
uneven pin and bush wear.

Commonly encountered reference values:

shaft non-parallelism within about ±1/300;
sprocket plane misalignment within about C/1000, or about 1 mm depending on size and the maker's guidance.

Good design should let the assembler be able to adjust, rather than just requiring a nice value on the drawing. Some practical ways:

machine the mounting datum face of the two bearing blocks together;
allow adjusting the hub position or a spacer;
provide a measuring surface to place a straightedge or laser alignment;
use a shaft shoulder and a stop ring with controllable dimensions;
avoid a non-re-machined welded structure in the area of precise bearing-block mounting.

After assembly, you should turn it by hand a few revolutions and check whether the chain shifts to one side before running the motor.

11. Lubricate in the right place

A common mistake is to only oil the roller surface because that is the visible part. The zone that needs oil most is the gap between the pin and bush, located on both sides of the link plate.

Practical principles:

feed oil onto the slack branch, right before the chain enters the sprocket;
bring oil to the gap between the inner plate and the outer plate so it seeps into the pin–bush;
clean off abrasive dust before adding new oil;
choose the viscosity by temperature and speed;
avoid using grease that is too thick, which only clings outside and cannot get into the joint;
do not let oil drip onto the product, sensor or a weld/glue zone.

Depending on speed and load, the method can be:

periodic manual oiling;
drip;
an oil bath or oil-slinger disk;
circulating oil pump.

If the position cannot be properly lubricated and the oil cannot be shielded, you should switch to an oil-free chain or change the transmission principle from the start.

12. Wear elongation is the main life indicator

A chain should not be used until it breaks. The reasonable replacement mark is when wear elongation makes the chain no longer engage the tooth pitch correctly.

Measurement formula:

Elongation (%) = (L_m - L_0) / L_0 × 100

Where:

L_m: the actual measured length of several chain pitches;
L_0 = N × p: the nominal length of N pitches.

You should measure over a span with as many pitches as possible within reach, pull the chain with a light force to remove the free clearance, and measure at several different positions of the chain loop. Do not measure just one link because the error is too large.

Reference limits by the number of teeth on the large sprocket:

Teeth on the large sprocket	Reference allowable elongation
60 teeth or fewer	1.5%
61–80 teeth	1.2%
81–100 teeth	1.0%
101–110 teeth	0.8%

Some systems may allow up to about 2%, but for a many-teeth sprocket, timing attachment or a mechanism prone to tooth jumping, the limit must be lower. Always take the final value from the catalog.

Signs to stop and inspect immediately

having to adjust the take-up continuously over a short period;
the chain rides up on the tooth tips instead of sitting at the tooth roots;
the knocking increases fast;
a stiff link appears that does not flex freely;
rollers crack, jam or wear flat;
the chain plate is abraded on one side;
deep rust around the pins;
the joint link is loose, the clip is missing or installed the wrong way;
an attachment is bent or cracked around the hole.

13. Common design mistakes

Choosing the chain by motor power but ignoring impact load

A 5.5 kW motor does not mean choosing directly by the 5.5 kW line. A cam mechanism, press, clamping mechanism or a conveyor receiving products in cycles can create a peak load much higher than the average load.

Using a sprocket with too few teeth to save space

The machine still runs but vibrates, is noisy and wears fast. The cost saved on the sprocket is usually paid back in bearings, chain and downtime.

Not leaving take-up stroke for the chain

The newly installed chain is already near the end of the adjustment slot. After a short time, there is no more ability to compensate for elongation, and you have to cut links or modify the motor base.

Forcing an odd total link count

Using an offset link without reducing the load makes one link the weak point of the entire chain loop.

Oiling the roller but not the pin

The surface looks very "oil-wet" but the main friction zone is still dry.

Using a stainless chain for fear of rust but keeping the steel-chain load

Many stainless types have a lower allowable tension than a carbon-steel chain of the same size. You must re-select by the catalog, not swap the material one-for-one.

Two parallel load-carrying chain strands without controlling synchronization

Length deviation and misalignment make one strand bear most of the load. With a cross bar, you need to consider matched-and-tagged chain pairs or the maker's set-matching guidance.

No safety cover

The engagement point between the chain and sprocket is a very dangerous drawing-in pinch point. The drive must have suitable guarding, while still having an inspection door and a convenient lubrication point. A door opening into the danger zone should have an interlock when the risk assessment requires.

14. Chain-drive design checklist

Conditions and load

The power, torque, speed and transmission ratio are determined.
The load has been classified as steady, mildly impacting or heavily impacting.
The acceleration load, the load from weight and friction have been calculated.
The running hours, number of start/stop and reversing are determined.
The legal requirements have been checked if it is a lifting or load-hanging mechanism.

Chain and sprocket selection

The chain type suits water, heat, dust, chemicals and cleanliness requirements.
The design power has been multiplied by the correct service factor.
The design tension is smaller than the allowable tension in the catalog.
The small-sprocket tooth count is preferably 15, better from 17.
The large sprocket is not too large and the single-stage ratio is reasonable.
Whether the teeth need hardening has been determined.
A multi-strand chain has used the correct load-distribution factor.

Mechanical arrangement

The total number of chain links is even.
The offset link is avoided or the load has been reduced per the catalog.
The center distance has been recalculated after rounding the link count.
There is enough take-up stroke for installation and wear elongation.
The slack branch has space, a guide or a suitable tensioner.
The two shafts are parallel and the two sprockets are in the same plane.
The structure allows measuring and adjusting alignment in the field.

Lubrication and maintenance

Oil can reach the correct pin–bush gap.
There is an inspection door, an oiling point or an automatic oil system.
There is a way to prevent oil from dripping onto the product.
The chain elongation can be measured without dismantling the whole machine.
The elongation limit and inspection cycle are clearly specified.
There is a plan to check tooth wear, joint link and attachment.

Safety

The drawing-in point between the chain and sprocket is guarded.
The cover does not obstruct maintenance but cannot be opened arbitrarily while the machine runs.
The lifting mechanism has anti-fall or an independent safety measure when needed.
There is power lockout and an operating procedure before tensioning the chain or replacing the joint.

15. Conclusion

Whether a chain drive is durable is not decided by a single breaking-load number. The actual life is the result of the whole system:

choosing the right pitch and the right chain type;
using enough teeth to reduce the polygon effect;
calculating the power and tension with the actual load factor;
keeping an even number of links and avoiding an offset link;
leaving take-up stroke for elongation;
aligning the two shafts and two sprockets;
oiling the correct pin–bush pair;
replacing the chain by elongation, not waiting until it breaks.

In machine design, a chain is often chosen because it is "strong and easy to use". That very thought easily leads to underrating alignment, slack and lubrication. A good chain drive is not the most-tensioned drive or the one using the largest chain, but the drive that runs at the right load, has a clear oil path, can be adjusted after installation, and has a measurable maintenance mark.

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