Plastic plain bearings defies harsh conditions on ambulance tail lifts

Although the company’s core product is the loader crane, Palfinger is also very well known for its tail lifts. If, for example, a supermarket does not have a ramp for delivering goods, a lorry with a lift platform is necessary. The tailboard of the vehicle is pivoted into a horizontal position and then lowered or raised so that the cargo can be loaded or unloaded safely and as quickly as possible. Located at the back of the lorry, these tail lifts operate in harsh environmental conditions and can often receive rough treatment from the operator and insufficient maintenance – a culmination of reasons why Palfinger uses igus plastic plain bearings on its tail lifts.

With its manufacturing plant based in Hoykenkkamp near to Bremen, Germany, Palfinger makes 15,000 lift platforms each year for vehicles that can be driven anywhere in the world. “A tail lift is located just behind the lorry, which is a harsh and difficult environment – just about everything rusts here,” says Eike Rulfs, head of design and development at Palfinger, describing the application environment.

Here, road spray in wet conditions can cause issues for the moving parts. In wintery conditions, when road salt is added into the mix, the spray is even more corrosive. In these corrosive environments, lack of lubrication at the bearing points unsurprisingly leads to the failure of the lift platforms. If the function of a lift platform is not guaranteed, goods cannot, for example, be delivered to the supermarket. If the tail lift were on an ambulance, the patient cannot be safely taken away from the accident site.

There are 12 bearing points on each hoist of a lift platform. If metallic bearings are used here, it is absolutely necessary to lubricate them regularly. “Who is supposed to do this maintenance work?” asks construction manager Rulfs, “Where should a grease gun be stored?” Maintenance-free properties and corrosion-resistance were therefore the required criteria for the components in a new project.

In the UK, there is an added legal stipulation that every patient is brought into the ambulance by means of a lifting aid. The vehicles are box vans with twin wheels on the rear axle and a vehicle weight of five tons. For added protection from corrosion, Palfinger’s customer opted to replace the conventional steel bolts on the lift platform with stainless

“We were already acquainted with the Igus plain bearing products,” says Rulfs. “With the change to stainless steel bolts came a good opportunity to switch to the plastic plain bearings here too.”

The new material Iglidur Q290 from Igus was launched on the market at the right time for the construction of the lift platform of the ambulance. Like all plain bearing materials made of Igus high-performance plastics, it is optimised for friction and wear, and is also self-lubricating.

The compatibility of the plain bearings was very important to Palfinger – the bearings should fit into the existing housings of the structure; igus therefore created a custom bearing dimension - available exclusively to Palfinger.

Iglidur Q290 also has excellent friction and wear values on stainless steel shafts and therefore fits very well with the new Palfinger bolts. The material is well suited for forces up to 55 MPa and readily accepts edge loads. With metallic bearings, this would have led to problems.

Compared to metallic bearings, there is very little risk of damaging bearings and shaft with the flexible iglidur material. This doesn't happen even with a single-sided loading of the platform and the resulting edge loads, or when used for other purposes, for example, when a lorry with a tail lift is used as a snow plow.

“Being maintenance-free and corrosion resistant, as well as lower in price compared to metallic bearings, are not the only advantages of using igus bearings,” concludes Rulfs, “Our industry is so tightly calculated that it is also very valuable if whole work steps can be saved during assembly, when bearings can be pressed in easily and no longer have to be lubricated. All these combined benefits have endeared us to Igus bearings.”