Cardan Joints or Hooke joints?
The Cardan joint was invented by Gerolamo Cardano in the 15th century, or at least the gimbal mountings that a modern day Universal joint contains.
The Cardan joint gimbals are what we see today in the cross or bearings cross of a universal joint, the actual universal joints themselves were accredited to Robert Hooke in the 16th century.
Since then the universal joint was further refined by Clarence Spicer who is credited with the current day Spicer universal joint.
Regardless of who invented it, the technology has only marginally improved since its invention 500 or 400 years ago (depending on who you believe invented it https://en.wikipedia.org/wiki/Universal_joint
Bearing Cross or Block and Pin coupling
The principals of the cardan or universal joint are the same, a 4 point gimbal is the same base component, this allows for pivoting on both the X and Y plane allowing the 2 non aligned shafts it is connected to, to pivot.
The universal joint has developed from the block and pin design to now include needle bearings invented in 1949 by Dr Georg Schaeffler. The needle bearings helped overcome one of the main issues that block and pin universal joints face and that’s heat.
Speed and Angular misalignment creates heat that wears bearings
The heat is created in two ways, 1. By the speed of the rotation of the coupling, the faster it goes the more heat it creates. 2. The angle of use, universal joints must be used at small angles of misalignment otherwise either the block and pin will seize due to heat or the expensive needle bearings will need to be constantly replaced.
Constant Bearing greasing
The only real world way to dissipate the heat is using grease, the only problem is with the heat being created constantly the grease will dry out and need to be constantly replaced. In the case of agricultural couplers its greasing cycle is every 8 hours, so every few days!!.
Water ruins needle bearings in universal joints
Outside of heat and worn internal components are environmental factors, where is it being used, is it being used in a clean environment or the opposite a dirty one, is it being used with equipment that makes food or drugs?
These usage factors also add to the practicality of using these universal or cardan joints.
The design idea being around for 500 years means that something better must have been invented especially in these different environments. The mechanical engineers or machinery designers have had to work within the constrains of what Cardan or universal joints can do.
Reduced ROI on Universal joints
Slow machinery down, ensure a constant greasing cycle which makes life harder for the machinery owner/operator which also reduces the return on investment of the machinery, with the constant stopping of machinery to grease and also replace the worn bearings and blocks.
That is only the bearing cross, you need to add into this same maintenance schedule the yokes or hubs as they are sometimes called. The input and output yokes hold the bearing cross in place and they too have their own issues.
Broken or Cracked Yokes
Yokes are made usually from either cast iron or alloy steel (alloy steel if you want a yoke that doesn’t rust or needs to be used in a clean environment), these coupler connections have to be machined down to allow the bearing cross to be inserted into the “ears” of the yokes.
This machining now takes the yoke from being tough at one end (where the connection is made between machinery and power source like an engine or motor) to more delicate at the the other end.
This now means the yoke can crack or snap, either through excess torque or a sudden stoppage for example if the machinery jams. This means the yoke or yokes need to be replaced. A sudden stoppage can also mean with no safety device installed extensive machinery damage, far more than the cost of a replacement cardan joint.
So what do Twin Spring Couplings do differently verses a Cardan Joint?
The Twin Spring Coupling is as its name suggests made from dual torsion springs, this is different from any other spring couplings in that the twin spring design means its
- As flexible as a needle bearing universal joint/ cardan joint
- Has no bearing cross to grease, or replace
- Built in shear pins allows a safety mechanism to ensure excess torque or equipment stoppages don’t damage equipment.
- One piece design means no broken yokes to contend with
- Higher speeds
- Available in sizes ranging from 150ft lbs. up to 500ft lbs. static torque.
Outside of that it is also available in most of the same spline and shaft shapes and sizes that the standard Cardan joints are available in regardless of which industry they are used in, both Imperial and Metric sizes.
A longer lasting flexible universal joint alternative, high speed and torque
What’s different? They are a little longer than a standard Cardan joint but this is to allow their improved flexibility. That being said, making shaft lengths smaller to incorporate this new coupling over its 500 year old uncle is a small price to pay for all the benefits that comes with a no maintenance, one piece safety coupling with the flexibility of a universal joint with a far greater ROI and smaller maintenance schedule
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