Welding UHMWPE

If you come across a polyethylene (PE) material that is difficult to weld, fabricate or repair, it is probably Ultra High Molecular Weight PE. This formulation of polyethylene has a molecular weight about 10 times higher than High Molecular Weight PE (HMWPE). The higher molecular weight results in very high scrape resistance and impact strength.

Because of these properties, UHMWPE is found in a large variety of applications. It can be used as liner material for dump trucks, rail cars or silos and chutes, slide plates, bearings and bushings. It also works well in cold area applications.

UHMWPE seems to be used more and more today. While it has great properties, it also can be challenging to install large parts or linings. Mechanical fasteners can be used for installation but may eventually corrode and cause contamination. Because of UHMWPE’s low surface energy, it is difficult to achieve a good bond with adhesives and this is not an alternative in food applications.

So, what other options are there? With proper equipment and the proper technique, you can weld UHMWPE. The properties of the material will make it impossible to achieve the same weld strength as you would get with HDPE, but for many applications the strength is sufficient.

There are a variety of welding systems that can be used to weld UHMWPE. The most important factor is the control of the three welding parameters: temperature, pressure and time/speed. When choosing the right equipment for a particular application, consult the manufacturer to determine if their equipment meets your requirements. See the Welding Equipment & Supplies beginning on page 29 of this issue for 17 leading suppliers of a variety of welding equipment and accessories.

The most commonly used equipment includes:

Hot plate welding:

for sheets and pipes

Spin welding:

for round fittings and other round parts [up to 4” diameter]

Injection welding:

for repairs and fabrication

Hot Plate Welding

Hot plate sheet welders are typically used in high production environments due to the cost and size of the machinery. Large welds can be made fairly quickly and with good quality. Depending on the welding machine, various angles can be welded. Some equipment will handle sheet sizes of 8 or 10 feet in length. The width can be much more, depending on the shop set-up.

Hot plate welders for pipes are available for different diameters and PNs (pressure numbers) which refer to the OD/ID wall thickness. For large diameters and thick pipe welding, the set up for these welders would be in a shop or on a cart/trailer. You will also find smaller, portable units that are ideal for welding in trenches.

Spin Welding

This type of welding equipment is used to weld round parts. Through circular motion and pressure, the welder achieves friction and thus the weld temperature. In order to produce a quality spin weld you need to control the welding parameters. Spin welders are typically stationary and do not easily handle larger parts.

Injection Welding

This process produces high quality welds by reducing the oxidation and stress factor inside the weld. It uses a heated aluminum tip instead of hot gas to preheat the parent material.

Its small size and light weight make it possible to weld in a wide variety of set-ups from tight areas to in-shop or on-site repairs and fabrication.

It may be difficult to find UHMWPE welding rod. As an alternative you can use HMWPE rod. The anchored molecular chain construction of UHMWPE makes welding it a challenge. So proper preparation is key. The weld area must be clean and, depending on the weld design, the material may need to be beveled out to weld to the root.

The weld temperature should be 536°F or 280°C. This is the weld temperature for the HMWPE material as a higher temperature setting would damage the HMWPE welding rod molecule structure.

UHMWPE requires a higher weld temperature than the unit will be able to achieve. To overcome this, a small butane torch should be attached to the welder to pre-heat the UHMWPE parent material. The pre-heater has an open flame. This requires special handling in order to keep the equipment safe.

The distances of the flame to the tip and flame to the parent material are important. The flame needs to be pointed in front of the tip and leads the tip by 3/4” or 20 mm. When the flame comes in contact with the parent material, the welding process needs to start immediately to avoid damaging it. If this has not been done, the UHMWPE material will degrade and the weld quality will be affected.

In conclusion, whatever type of welding your shop is doing, proper training is essential to consistently producing quality welds. Plastic welding will be easier if you are trained in the proper techniques, understand the importance of the three welding parameters, know the application, know the material and know the welding system.

Written by Andy Bramer, Plastics Technologist for Drader Injectiweld, Inc. Mr. Bramer has been working since 1983 with a wide variety of plastic materials and equipment. His background includes three years apprenticeship training as a plastic fitter, two years school for Plastic Master Technician and supervisor for a plastic shop in Germany, where he also received his DVS plastic welding certificates.

For more information, contact him at 800-661- 4122 ext. 236 / 780-440-2231 ext. 236 or via E-mail at abramer@drader.com.