Slip Clutch: What is it, How it works, And How To Maintain It?

Slip Clutch: What is it, How it works, And How To Maintain It?

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Tractors are multipurpose machines designed to take care of almost all agriculture-related tasks. The modern production of machinery lets tractors has PTOs. PTOs and slip clutches go hand in hand. What is this slip clutch, and how does it work? Do these slip clutches need maintenance?

The slip clutch is a freewheel mechanism that protects the PTO and the implement gearbox. It helps to reduce the impact of extreme force experienced by a PTO and the implement. Slip clutches are simple to use and maintain.

As they say, “with great power comes great responsibility.” With tractors, great power brings greater danger to the machinery and the equipment. A slip clutch helps in reducing the costs from damages due to this immense power. You already know this if you have worked on a farm.

This article will help both beginners and experts know about the slip clutch in detail. I will discuss its operation and maintenance process. I will also mention some tips and tricks to make the most out of your slip clutch.

What is a slip clutch?

A slip clutch is a disc-like mechanism that consists of many layers. This mechanism is a synthesis input clutch flange, springs, bolts, pressure plate, and friction plates. The slip clutch is installed between the implement gearbox and the PTO shaft. 

This equipment acts as a security for the PTO shaft and the implement. Most implements have pre-installed slip clutches. If bought separately, the price can vary from few dollars to thousands.

The slip clutch has a compact shape, with all the moving parts confined inside a circular body. Each component has its value in the whole mechanical synthesis. To know more about slip clutches, check out this video from Tractor Mike.

Below are the details of each part:

Input clutch flange

Input clutch flange is connected to the PTO shaft using a metallic yoke. A male spline connects a yoke to the clutch. In some instances, with a stationary implement, the slip clutch is connected to the shaft without a yoke. 

Both the tightened ends ensure the safety of the shaft and the implement gearbox. If they remain loose, the PTO shaft might get out of control, making it extremely dangerous for the surroundings.

Power plate

The power plate introduces the power inside the stationary slip clutch. Power plate spins inside the covers of the clutch body. With optimal pressure and friction, the torque is controlled. Power plates are made of high carbon steel, which is sturdy and rust-proof.

Springs

Springs provide flexibility to the whole mechanism. Bolts pass through these springs and apply pressure on the springs. When the operation starts, these springs apply pressure on the drive plates to increase the friction inside the clutch.  

Bolts

The maximum length of the bolt is exposed on the PTO side. They pass through the springs to bind the whole mechanism. Only friction plates are left out, or you can say, contained without any holes.

Friction Plates

Friction plates are the most crucial part of the slip clutch. Their health determines the performance of the clutch and the safety of the machinery. The number of friction plates varies from 2 to 4, depending on the brand and model of the implement. Friction plates provide slippage and optimal friction to the whole operation.

The material used to make the plates is the same as that of semi-metallic brake pads in vehicles. These brake pads bear maximum damage and are not covered in the warranty. If the bolts are adjusted optimally, the life of these plates gets extended.

What is a slip clutch used for?

The slip clutch is used for the protection of equipment or the tractor PTO. It is used with a rotary mover(Bush Hog), a rotary tiller, a rotor cutter, and a post-hole digger. Bush hog, a rotary mover brand, sells their implement with a pre-installed slip clutch.

Application

Slip clutches are used with the tractor PTO shafts. The tractor uses two categories of employment, the passive and the ones with rotary or gear mechanisms. For example, a tiller and a harrow are passive implements. Both of these implements are pulled by the tractor. Downwards pressure is applied with the hydraulics system.

The implements like a rotary tiller or a bush hog require the PTO drive engagement to perform the rotary action for more effective operation. Tractor PTOs create high torque to deal with rough terrain or to change the landscape. The rotary blades clear the ground or break the soil or cut the small trees. But there might be some rocks and dead animals that can get stuck inside the rotor. 

For example, when a flex-wing or a bush hog is engaged with the PTO shaft. Their blades cut anything below the cover of the mover. Sometimes there are rocks or dead vermins on the ground. They get stuck inside the rotors as there is no way to detect them. This can be damaging for the gearbox. If the gearbox stays intact, the extra force can damage the PTO shaft or the PTO drive itself. 

To overcome these issues slip clutches are used. When the back-torque becomes more than the torque applied by the PTO, the slip clutch slips to adjust the torque. The friction plates inside the clutch act as the breaks to slow the motion down. 

How does a slip clutch work?

When engaged with the PTO drive, the slip clutch limits the torque passed on to the implement. This is done by the friction applied by the friction plates. These plates provide enough friction for the force to transmit through the clutch onto the gearbox of the implement. When in action, the PTO end of the slip clutch moves faster than the engaged end.

Can you adjust a slip clutch?

No matter what the torque from the PTO is, the torque of the implement end remains the same. If the user finds that the torque is low, they can adjust the bolts by tightening them. Do not tighten them too much, as it may reduce the life of the friction plates.  

How to adjust a slip clutch?

To adjust the slip clutch, use a permanent marker or a paintbrush and draw a straight line on the plates. This line will act as an indication of the alignment. Once engaged with the PTO, if the slip clutch is working, the line will break. This is the confirmation that the clutch has slipped, and it is okay to use the implement. 

In the scenario where the line is still intact, this means the clutch is not slipping, and the bolts are tighter than required. In this case, the blots are to be adjusted using a ruler or a stick provided by the manufacturer. The length of each bolt has to be the same. Measure the length of the bolt from the plate to the tip of the bolt.

How to maintain a slip clutch?

In agriculture, most of the equipment and machinery are used seasonally. This means it is only used in a particular season. Conventional farming depends on seasons. A machine used for sowing might not see a day of light until the same time next year. And standing machines degrade fast. Therefore maintenance is a constant process to keep the equipment safe.

Slip clutches require minimum maintenance throughout the year. But, like any other farm machinery, rust can damage the clutch parts if left in the open. Slip clutches are very compact and are usually kept with implements. 

Cracks in the springs

To maintain the slip clutches, open the bolts and remove the springs. Check for any cracks in the springs. These thick springs can bear heavy loads and enormous pressure. Sometimes even if they break, they remain intact outside the bolts. Therefore, it is advised to inspect each spring thoroughly. If you see a crack, order a new one from your manufacturer. 

Inspect the rusty bolts

When in the field, you never know when you might need to alter the operational condition of your machinery. So, check the blots and their threadings at least once a year. It is better to replace them in the shed rather than on the field. Again new bolts can be ordered from the suppliers. For rusted bolts, use sandpaper to clean them off.

Replace the friction plates

Friction plates are just like brake pads; they degrade with time. Although if used optimally, the wear and tear can be reduced immensely. But in some cases and on large farms, the life period of these plates can be comparatively shorter. 

These plates can be replaced after a careful inspection. To do so, dismantle the slip clutch and take out the friction plates. Check their thickness and any irregularities in the form. Order new friction plates if required. Replace the plates and perform a test run. 

Bonus tips and safety

  • Always keep extra bolts and springs as they can get instant and irreparable damage.
  • You do not need extra pair of friction plates, as they take time to degrade.
  • Always turn your PTO off before removing the slip clutch.
  • Do not use power tools to adjust the bolts. These bolts need to be adjusted minutely. The power tools might break their threads. 
  • Never use the water to clean the inside of a slip clutch.
  • To increase the life of friction plates, adjust the bolts for different jobs.
  • In the off-season, try to keep the equipment inside a shed away from the moisture.
  • One indication of the slip clutch not working is excessive heat and burning smell. If you experience this, then stop the machine immediately.
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