Cold welding polymer to the rescue

Transcription

1 Cold welding polymer to the rescue By Leif Andersen, Technical Product Manager Welding, WSS Most of us have experienced what we referred to as Plastic Steel at one time or another. It can be from trying to patch up a corroded or dented part on a car or stopping a leaking water pipe. These types of quick fix solutions have come a long way over the last couple of years and have been fully accepted into the production and maintenance industry. How do Cold Repair compounds work? Cold repair compounds are chemical reactions between Base (Resin) and Activator (Hardener) producing an extensive interlocking network. They will normally be polyester, polyurethane and epoxy materials and the Base/Resin will in most cases have a filler material added. A polymer is a molecule that is made by linking many small units (monomers) together to form a large molecule. The polymer can be made of a single species (homopolymers) or of several different monomers (copolymers). Polymers occur naturally (biopolymers) but are also made synthetically in large amounts. The term polymerisation describes the chemical reactions that produce polymers by repeated combination of monomers to make long or large molecules. The different types of reaction are numerous and several distinctly different ways of categorising the reactions are used. It is important to understand the difference between Thermoplastic and Thermosetting polymers. In Thermoplastic polymers (a), the molecules will during the chemical reaction link up and form long chains. By heating up them, the molecules separate and the material can be recycled. Thermosetting polymers (b) are different because they also create a cross linking process that make the finale cured product permanent and irreversible. In this article, we will only concern our self with thermosetting polymers. Polymer repairs can be emergency repairs, but sometime also permanent repairs are performed.

2 Where Cold Repair compounds should be used: Emergency Repairs If no energy source in the form of electricity for arc welding or oxyacetylene gas for gas welding or brazing are available Cold Repair Compounds represent the alternative. The energy is built into the product and is released when base and activator is mixed together. It is a fast solution because the curing time for some of the products is down to a few minutes. Uncomplicated in use and no rigging up time makes it perfect for emergency repairs Where Hot Work is not permitted Cold repair systems are cold curing processes. There is no risk of heat or sparks causing ignition. Maximum temperature during polymerisation can reach 70ºC (158ºF) Base materials chemistry is normally of no concern because the bonding is mostly mechanical and not chemical. Where base material is not weldable Certain materials are simply not weldable because of chemistry or because the material is so corroded that there is nothing to weld on. Sometime welding method/ Equipment/ consumable or operator knowledge is not available Where distortion is unacceptable Welding causes expansion and contraction resulting in distortion. If this is unacceptable, cold welding polymer can be the solution Where there is restricted space Polymer products can if necessary be injected trough small openings and holes

3 Where specific properties are required In many cases, polymer compounds have better wear properties than weld overlays. Specifically concerning wear and tear in fluid flow environments. Large surfaces that are worn are also much faster overlaid with polymer compounds than with weld bead overlays Where you need non-metal repairs Rubber, plastic and composite materials cannot be repaired by traditional welding methods. Polymer will very often represent the perfect solution for this type of materials Where not to use: At low temperatures When the ambient temperature is below 5ºC (40ºF) there will be no curing/ solidification. Polymerisation will not start if the temperature is below 0ºC (32ºF) Unsupported side impact Impact Impact Most polymer products will fail if unsupported side impact applications are at play Unsupported Supported

4 High temperatures Polymers are mostly made from organic materials. At service temperatures above 120ºC (248ºF) they will start to carbonise and fail in service. For elastomers (Rubber grade materials) the limit is around 90ºC (194ºF) There are in-organic polymers available but they might have other limitations How to prepare surfaces The bonding between the polymer compound and the base material we refer to as addition. It is partly mechanical (approx.80%) and partly chemical hydrogen bindings (approx.20%). It is therefore important to put a lot of attention into surface preparation. Oil, rust and other impurities represent a barrier that will prevent addition so important that surfaces are cleaned. Roughening of the same surface also increases the surface area and gives a better key. Create if possible a cross scoring pattern. Important that surface is roughened not polished. Rubber surfaces are particularly difficult to roughen. There are special tools for abrading of rubber. Increase surface area Oil impregnated casting Critical repairs as pump house repairs should be abrasive blasted to a minimum standard SA 2 ½. Profile microns. The blasting medium should be angular grit. Casting items have an open structure. They might have been salt or chemically impregnated. If this is the case, they should be heated to 80ºC (176ºF) by hot air over night to sweat out the contamination. Remove the contamination using a cleaner then re blast the surface Application of the products Application should be carried out as soon as possible after the surface preparation is completed, otherwise oxidation can take place. Do not apply product when relative humidity exceeds 85% nor when surface is less than 3ºC (37ºF) above dew point. In addition, as mentioned before the work site temperature must be 5ºC (40ºF) in order for the polymer chemical reaction to take place. There are a number of different polymer products available and they have different ways of activating the hardening process. Light-activated resins are one-part translucent polymers that cure and quickly harden when exposed to specific light spectrums. The required wavelength for cure is specific to the resin chemistry. Dentists have used visible-light activated resins as adhesives for decades. Light curing unit (LCU) is based on blue light-emitting diodes (LED). Some polyurethane materials simply become activated and start the curing process when in contact with water. However, the most common type of activating the curing process is by mixing Base and Activator together. In the following this last mentioned method is covered

5 The measuring: Always measure out Base and Activator quantity is accurately and in line with instruction on the date sheet. If a critical application, use mixing ratio per weight. Measure out base and activator accurately Mix base and activator until streak free The Mixing: Mix Base and Activator until streak free. Any base or activator not mixed sufficiently will not solidify and weaken the final repair. Do the mixing on a clean flat plate spreading it out thinly. This will slow down the curing process. Make sure to familiarise yourself with the products pot life. This is the time you have available before product start solidifying. The pot life depend largely on the ambient temperature. The higher the temperature the shorter the pot life. Press first a thin layer of product onto the surface Do not heap on the product Applying: Do not heap the product on. This will lead to bad bonding. A good bonding is secured by pressing a thin layer of product on to the surface, working it down in cracks and openings. After the bonding is secured, add more product and build up to required height. If further strength is required to the repair, add reinforcement bandage. Wrap the bandage into the product in order to encapsulate it. The bandage will work the same way as adding steel reinforcement into a concrete constructions. If the repair require machining after curing, do not use reinforcement bandage.

6 The use of a doubler or overlap plates can also be useful if large section of an item to be repaired are missing. Surface preparation is also in this case absolutely necessary if a successful result is to be active This type of repairs often require metal grade type polymers where the fillers can be phosphor steel Leaking pipes represent a large application area for cold curing polymers. Very popular because of its simplicity is the knitted, fiberglass tape coated with special urethane resins that are water-activated to change from a wet adhesive tape to a hard urethane plastic in 30 minutes. Immerse the roll in water and wrap around the leaking pipe. After short time, the product solidify. Pipe after being cleaned and abraded Pipe after repair There are also special Aqua grade type of polymers that can be mixed and applied under water. They can be applied to fresh or salt-water environment. These materials are two-component epoxy products. High Temperature repair compounds are in-organic and is a ceramic and stainless filled one- part water based paste and temperature resistant up to 1093ºC (2000ºF) They require a very slow curing rates.

7 Ceramic Repairs Cavitation wear found in fluid flow environments are best repaired by ceramic fillers. After the cavitation has been filled with a compound and allowed to cure to initial setting (sticky on the surface) it is overpainted with a liner ceramic. This is done in order stop the fluid flow undermining the locally repaired cavitation. Surface overpainted Cavitation s filled with Pump housing base material Rubber repairs A synthetic rubber is any artificial elastomer. These are mainly polymers synthesised from petroleum byproducts. Two thirds of all rubbers in use are synthetic rubber, rest are natural rubber. Easy to use twin pack mixing & application system. A divider keep base and activator separated. When removed the products flows together and are hand mixed inside the plastic pouch.

8 Cold Welding Polymer system for use on-board In a repair situation always, consider weld repair as first option. If for reasons mentioned in first part of this article this is not possible, consider Polymer Cold Welding based on the mention limitations. Cold repair system kit-a Emergency and permanent repairs on pipes, all types of mechanical equipment and machine components on-board. Weight: 12.5 kg Product no (Product marked # in below product range list to be found in KIT-A) Cold repair product range Metal repairs Metalgrade Ready Stick# Set, 0,86 Kg Product no Leak Stop I Set, 0,16 Kg Product no Leak Stop II# Set, 0,23 Kg Product no Leak Stop III Set, 0,33 Kg Product no Ceramic repairs Metalgrade Express# Set, 0,58 Kg Product no Metalgrade Rebuild# Set, 1,10 Kg Product no Metalgrade Hi Temp# Set, 0,42 Kg Product no Aquagrade Rebuild# Set, 0,95 Kg Product no Rubber repairs Ceramigrade Rebuild# Set, 1,0 Kg Product no Ceramigrade Liner# Set, 0,92 Kg Product no Ceramigrade Abrashield Set, 5,4 Kg Product no Rubbergrade 6 Rebuild# Set, 0,59 Kg Product no Rubbergrade 6 Remould# Set, 0,59 Kg Product no