What are Rubberised Track pads

Trackpads Track Pads for tensioners pushers vehicles

What are Track Pads? - An Introduction.

Track pads are also known as Tensioner Pads, Cable-Lay Pads, Pipe-Lay Pads, Chain Tensioner Pads, Track Covers, Trackpads, Tank Pads and Caterpillar Track Pads.

Put simply, they are rubber or polyurethane pads bonded to a backing plate during the moulding process.

For a case study on one of our trackpad projects, click here . We regularly make trackpads which range from 1kg – 15kg each.

What are Track Pads used for?

Caterpillar tracks are most commonly used on excavators, military tanks and other vehicles. They are also found on many types of machinery, especially in the subsea world.

When using Track Pads for vehicle-related applications, the pads are primarily used to prevent or reduce damage to the road surface. They also make the ride a little more comfortable.

Old and new M1 Abrams rubberised tank track pads

Old and new track pads on an M1 Abrams Tank (above) and pads on a Road Maintenance machine, below. (images sourced from Wikipedia)

Rubberised track pads on road maintenance sealing vehicle

When used for stationary machinery, Track Pads will normally be used on the 2-4 sets of caterpillar tracks within the machine designed to feed or retrieve pipes, cables or chains. Below is an example of a machine AVMR worked on with Hydraulic Alliance.

Pipe feeding conveyor track pads cables chains

This circa 250 tonne machine was designed to push a new water mains pipe 1 - 1.5km down the inside of an old pipe. This saved time, cost and resource when compared to digging a trench.

As the new pipe was relatively fragile, plastic deformation was a risk. If the pipe became oval in its profile threading it down the old pipework would have become much more challenging.

As a result, AVMR conducted friction testing and developed a rubber material which was fit for purpose and offered high coefficients of friction. This machine design had four sets of caterpillar tracks rather than two, as can be seen below, but for more many applications two sets of caterpillar tracks is sufficient.

AVMR.com Hydraulic Alliance partnership - pipe pushing machine for water mains pipes.

An individual caterpillar track from this machine can be seen below. Each set of tracks can clamp the pipe with different pressures; the aim is to grip the pipe sufficiently to maintain static friction, but not clamp enough to induce permanent deformation in the pipe.

AVMR.com & Hydraulic Alliance designed this pipe pushing and pulling machine.

What are important considerations when designing a Track Pad?

There are a few questions to consider when designing track pads, such as:

Application: What will the pads be doing and interfacing with (e.g. road, cables etc). If not a vehicle, do you have any understanding of the loads which the item being pushed / pulled by the machine can tolerate?
Environment: What will the environment be like where the pads are used e.g. Temperature, presence of abrasive materials or foreign objects, interaction with other fluids and gases incl. solvents, oils & chemicals.
Loading: what pull / push loads are anticipated and what clamping loads have been planned for? How important is an even distribution of load across the interface? Cables and pipes can be damaged if clamping forces exceed thresholds, or if the elastomer does not offer sufficient load distribution.
Resistance to both wear and tear: High abrasion and tear resistance can be easily achieved but often at the expense of friction. At first sight, this may seem like a balancing act, however other tools and options are available to help us achieve both.

Then there are the basic design questions such as the pad-machine interface, but AVMR prefer to understand the bulleted points first, as the basic design questions are often influenced by them. Note that in the pads on the above image there are no visible mounting holes. This was due to some key aspects of the design, which required a consistent rubber-pipe interface.

What can go wrong with Track Pads?

AVMR have not just manufactured tens of thousands of track pads, we have also tried to keep in touch with customers to understand the performance of our products, and that of other non-AVMR products. It is incredibly easy to make two identical looking products, which perform very differently. Often this comes down to considering the right factors upfront, as above.

The below points are areas we have heard customers, and potential customers, talk about, and are all based on experience:

Elastomer Selection:

Note, we have not said Rubber Selection. In some applications, albeit very few, Polyurethane might be a better option.

We have seen poor upfront decisions on polymer selection result in particularly short product life. Not all rubbers are the same, even though they might look the same. This applies to rubber type (e.g. natural, EPDM, Neo etc), base compound quality, reinforcing and non-reinforcing fillers.

Rubber Consistency:

Track pads have to 'work as a team', so we need similar properties across all of the pads. If material and production controls are not in place, two consecutive batches of the same compound can differ sufficiently to result in different modulii/modulus' which means that some pads take more of the load than others.

What under-cured rubber can look like. Porosity in the rubber is a clear sign of insufficient cure in the area.

Image taken at AVMR showing an inconsistent cure. This photo was taken while conducting product commissioning trials. Process changes then resulted in a consistent cure.

In addition, when trackpads are moulded, it is very easy to have different levels of cure both on the outside of the product and towards its core (see image above showing typical porosity of an inconsistently cured product). This adds to the potential variation in material properties on the product.

In a different application, we have seen modulus variations of +/-60% in competitor products. The potential for this amount of variation in a track pad could lead to, at best, accelerated wear rates or, at worst, increased clamping pressures being required and therefore damage to the product being carried.

The above picture was taken while AVMR were conducting rubber cure consistency checks within a new track pad product. Each of these pads weighed approximately 14Kg.

Bond Consistency:

There are a number of potential pitfalls when bonding elastomers, but larger items, like trackpads, are subject to increased risks. Elastomer de-lamination will result in a significant reduction to product life, so it is important to get this right.

Bonding agents can attempt to bond to the rubber while the rubber is still flowing over the substrate surface. Before the agent has the opportunity to bond properly, the rubber has moved on and broken the partially made bonds. The result, is areas of the product with low-to-no bond integrity.

For some applications, this issue might be considered as an acceptable risk, but not in this case. The rubber should be anchored to the backing plate consistently across the whole surface. Trackpads are normally subject to high lateral and compressive loads simultaneously, all of which are transmitted through the bonded area. A reduced bonded area increases stress in the surrounding areas which can also lead to reduced life expectancy of the product through internal abrasion, tearing and increased pressure on the remaining bond interface.

In the above image, AVMR are conducting one of our bond checks.

Insufficient Corrosion Resistance

Many Track Pad enquiries we receive rely purely on painted mild steel backing plates for corrosion resistance. This may be fine initially, however if the application is in an abrasive environment, or not handled carefully, the paint can chip off. When products are not regularly maintained (ie when paint is not reapplied) corrosion can start to creep in.

As most track pads are operated outside, in conditions that are often damp and sometimes very salty, that corrosion can grow. If the corrosion starts to creep under the bond of the product, de-lamination can start. This will accelerate as the weak point initiated then propagates.

Issues like this inevitably start on the leading edge of the product, which is typically in tension during normal operations. As the pad is used, any weaknesses are opened up therefore allowing corrosive material to wash further into the bonded area.

De-lamination of rubber on a track pad caused by incorrect corrosion resistance.

Early signs of delamination can be seen on this Track Pad along the leading edge. The root cause of this issue is insufficient corrosion protection on the mounting plate.