Plastics Identification – How to Identify Plastics prior to welding

Plastics Identification – how to identify plastics prior to welding:

Plastic Welding & repair is relatively easy to carry out, and providing you follow a few fundamental steps, strong structural welds can be achieved. Due to the high replacement cost of damaged plastic components Welding & repair of these parts becomes a very wise choice.

Getting into Plastics Repair offers the repairer a number of significant advantages –

  1. Improved Customer Service – parts on order can take some time obtain, Having the necessary skills & equipment to carry out such repairs, helps to improve customer serivce as you can get the vehicle back to the customer, improving turnaround times.
  2. More work opportunties – A repairer with the necessary skills & equipment now has a service to offer to other repairers.
  3. More profits – ALL of the profits from the repair work come to you ! You can now stop sending half of your profits to the other repairer.

Plastics Identification:
You can only weld “like” materials. For example, Polypropylene (most car bumers) can only be welded with a Polypropylene welding rod. So it is very important to first identify the material to be welded. Today most plastics used in the manufature of modern vehicles are stamped with plastics identification codes, however, where this identification is not present, a welding test is required to ID the material to be welded. There are some 20 commonly found plastics and many more made up of two or more mixtures of materials, known as ‘plastic composite materials’. As only “like” materials can be welded, identifying the plastic correctly is vital. There are two ways to identify plastics – the first is known as a “Flame Test” and the second (our recommended option) is to use our “Rod Test Kit” (RTK).

Flame Test:
This involves taking a small slither of the parent material and using a pair of tweezers, ignite the material over a Bunsen flame. By observing the way in which the plastic slither burns, the flame colour and smoke formations from the part and whether is drips etc.

Flame Test Observations:

  1. Ignition – is the plastic hard to ignite?
  2. Once burning, is the flame self extingishing?
  3. Does it burn at all?
  4. Does it drip?
  5. What colour is the flame?
  6. Does the flame spit or is it stable?
  7. How does it smell? (sweet, rancid, burning wool, rubber)

This simple flame test can give you a pretty accurate indication of the plastic type, however there are a number of negative aspects to using such a test. The first is the fact that you are introducing a flame into your working environment. Also the flame observation no. 7 above (How does it smell?) involves you having to inhale fumes & odors created after burning and degrading of the material has taken place. We do not recommend this test as personally I will not inhale burning plastic of any kind.

So this leads me to the safest and most recommended ID test method, the Rod Test Kit (RTK).

Rod Test Kit (RTK) : We only recommend this method
This plastic ID test kit provides the welder with over 40 different materials for ID testing. It is by far the most easy and safe way to verify your plastic material type. The RTK rods have been specially selected for weldability and compatibility with a wide range of commonly found plastics in the Automotive Repair and Fabrication industries. RTK rods are UV stablized where applicable. The Techspan RTK contains the following thermoplastic materials: ABS, ABS Blend, ABS/PA, ABS/PBT, ABS/PC, ASA/PC, ASA/PBT, AES, ASA, HDPE(crate), HDPE(pipe), HIPS(Polystyrene), HMWPE, LLDPE(PE), MDPE(Pipe), MDPE(Rotational), PA(Nylon 6), PA66HS, PA/PPE-GTX, PBT, PC, PC/PBT, PC/PET, PET-G, PMMA(Acrylic), POM(Acetal), PP(Sheet), PP(Crate), PP(Homopolymer), PP/EPDM, PPE, PPE/PA, PPO(Noryl), PUR, PVC(Flexible), PVC(Rigid), C-PVC, RANCO(Random PP), TPR and UHMWPE.

Rod Test Kit procedure:

  1. Simply clean an area on the underside of the part to be tested. Ensure you remove any contamination (grease, oils, paints etc) before attempting his test.
  2. Select a rod from the RTK that appears and feels similar to the parent material.
  3. Attempt to weld (approx. 30mm) of the selected rod to the parent material, leaving a tail (30mm long) at 90 deg to the parent.
  4. Once complete, allow to cool. It is important to note that plastics will not hold full strength until completely cold.
  5. Attempt to remove the rod with a pair of pliers, pulling at 90 deg to the welded part. If the rod snaps off leaving the material on the parent, you know you have a match.
  6. Repeat the test with another rod selection until you find the correct match.

Buy the Rod Test Kit (RTK) online here.