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togwt
07-28-2011, 04:28 AM
Kinetic (or dynamic) Friction



Kinetic friction induced heat is an often misunderstood concept of polishing / compounding; abrasives require friction to breakdown, not heat; heat is just a resultant of friction between two surfaces.



Polishing a paint surfaces transfer’s kinetic (or dynamic) friction induced heat to the paint surface, thermoplastic polymers have both tensile strength and elongation (elasticity) which allow the surface to flex, expand and contract in accordance to surrounding temperatures, solvents, resins and other ingredients in polishes will expand causing the paint film surface to expand.



As the metal substrate expands the paint moves with it, due to its elasticity, thereby becoming elongated (thinner) this is part of the cause of friction induced ‘burn’, you’re applying pressure and an abrasive to a less dense (‘thinner’) paint surface.



The smaller the contact or surface area of the pad the more kinetic (heat) energy is transferred to a given paint surface area. (Area = π (r2) - 6-inch = 28.26 sq.ins - 4-inch = 12.46 sq.ins. The amount of applied pressure will also affect the kinetic friction (heat) energy transferred



Foam Pad Design



a) Non-reticulated [:foam membranes are completely sealed to prevent fluid absorption or air penetration] (closed-cell) which means less product absorption, and less air flow, reticulated foam are relatively less abrasive and less dense than polymerized foam; due to this density the polish provides the abrasive ability as opposed to the foams composition (use when thoroughly dry as they tend to retain water) with polymerized foam your polish stays wetter for longer, which extends the products work time This pad design is relatively firm so that none of the machines action (rotational or orbital) is lost, as is the case with soft foams. Due to their lack of airflow the foam doesn’t drain that well they are harder to clean, and take longer to dry



b) Reticulated [: foam which is a linked network or matrix of small squares or shapes] its composition varies with pore size. Their open-cell construction allows for fluids to permeate the pad to a greater degree than closed-cell materials, such as non- reticulated foam and their lower tensile strength allows them to conform to contours more easily. Reticulated foam, which is a less dense than polymerized foam, therefore your polish provides the abrasive ability as opposed to the foam. Porosity is typically 95%, but can be as high as 98%, typically resistance to compression is decreased while tensile properties like elongation and resistance to tearing are increased. This pad design is relatively soft so that some of the machines action (rotational or orbital) is lost



• Compression / Rebound - compression load deflection is the measurement of how long the foam takes to regain shape after under certain pressure, foam pads should be compressed to no more than approx 50% of its thickness



• Tensile strength – the strength of a material refers to the material`s ability to resist an applied force



• Density - provides a protective cushion allowing foam compression to maintain constant surface pressure and it also lessens machine vibration. It also affects the amount of polish the pad will hold; foams that hold a high volume of product allows the polish to do the cutting, as opposed to the abrasiveness of the foam.



• Velocity - pad velocity is substantially increased with a larger diameter pad, increased velocity will increase abrasive capability at the outer edge of the pad.



Foam Pad Thickness



Standard foam pads - 1.25 inch pad thickness was set as an industry standard because it prevented solvent residues and provided insulation from friction heat from reaching the backing plate, either of which could compromise the Velcro (delaminate from the backing material). They have a rounded outer edge for easy transitions over seams and edges, and there is also a safety margin between the edge of the baking material and the foam with a ‘standard’ foam pad.



This foam density provides a protective cushion allowing foam compression to maintain constant surface pressure and it also lessens machine vibration.



OEM-style 7/8-inch foam pads - due to the reduced foam thickness tilting a 7/8 inch pad will change the polishing pressure on the surface. These foam pads are flat cut on the top edge, as opposed to a standard 1.25-inch, which have a rounded outer edge for easy transitions over seams and edges and the backing material is cut back 3/8 of an inch around the perimeter of the pad to ensure a safety margin.



On the 7/8-ich foam pads the backing material extends to the edge of the pad where it could scratch the paint when working in close corners or around mirrors and wings. OEM-Style pads are designed for high volume pad users where cost is a significant factor.Like all things related to tools, pad thickness comes down to personal preference.



Pores per inch (PPI)



As an example you could purchase two seemingly similar pads based upon their PPI rating, but one pad may have thicker walls between each pore, be made of softer material, feature a reticulated or non-reticulated foam structure (basically open or closed cell), or simply be a thicker (1.25 or 0.75-inch) foam, which can affect the machine`s movements.



Compressible, open cell polyether polyurethane reticulated foam is usually specified by pores per inch (PPI).The greater number of pores per inch generally equates to foam that is softer; and has less abrasive ability, less density, more porosity and easier compression.



There is no recognisable standard for the abrasive abilities of foam, other than a colour assigned; most foam manufacturer’s that supply foam to detailer’s product vendor assign their own colours to donate abrasion. On this basis a PPI rating allows abrasive ability comparisons between different foams



Remember the flatter and more uniform you make the surface, the greater the light reflection .While most enthusiasts understand this principle when applied to polishing, the same is true of finishing. The more uniformly you apply the final wax or sealant, the greater the shine



Scale 30 – 100 PPI



• Abrasive Cutting Foam (40 pores per inch)

• Medium Cutting Foam (50 pores per inch)

• Light Cutting Foam (60 pores per inch)

• Finishing Foam (70 pores per inch)

• Fine Application (80 pores per inch)

• Ultra-Fine Finishing (100 pores per inch)



Note like many things pertaining tp foam pad mfg this rating system is not standard



The thicker consistency products (i.e. a hard wax) seem to work best with a more porous pad; a very tight pad used with these types of products seems to load up and clog the pad, which in a turn leads to product clumping. When applying light consistency products (i.e. liquid polymer) a more porous pad will absorb and waste product



Equivalent Abrasive Rating



The grit rating on an abrasive or polishing pad is an indication that a product is designed remove the surface scratches left by finishing paper (i.e. 2500 grit scratches are removed by a 2500 grit rated polish) it doesn`t mean that it is a 2500 grit level abrasive.

• The coarser the abrasive, the faster the cut

• The more aggressive the pad, the faster the cut

• Wool cuts faster than lamb’s wool, foamed wools are next, then foam.

• Foam pads generate more friction induced heat than wool pads



Transfer of Kinetic Energy



Dependant on pad choice though the downward pressure though the backing of the pad. The denser the backing the more cut and abrasive ability the polish has and vice versa.



Open cell pads -have varying cuts, due to the sharper edges being created, this type of pads absorb the lubricate from the polish and leave the abrasives within the open cells; effectively increasing the abrasive ability of the pad. When you add pressure you also reintroduce the lubricant to the abrasives, which results in a higher cut.



Closed cell pads - have very little cut on their own, as the lubricant sits on the surface as well as the abrasives, by adding pressure the denser nature of the foam will deliver a higher cut.



Comparison of Pad Types



Here`s a brief guide to help you select the correct product for your needs, all of these pads have a hook and loop fastening system. The Velcro™ on both the pad and backing plate allows you to quickly and easily install and remove the pads listed below:-

Non-Reticulated Pre-polymer with Collapsed Cell Structure (CCS) Technology™ quality foam pads are made from specially engineered European foam, a blend of thermally reticulated polyurethane with a partially closed foam cell structure, created specifically for compounding, polishing and finishing.



This foam allows air to circulate through the pad to reduce heat transfer to the paint surface or product, while maintaining friction; the secret to successful machine polishing is using the correct type and size of foam pad, and the proper machine operating rotational and linear speed.



Thin firm foam would work more efficiently than a thick pad at transferring the eccentric motion of the orbital offset motion to the paint surface.



Thick foam allows more downward pressure, and therefore foam compression, which is not necessary with forced rotation, except when negotiating contours. One of the drawbacks when applying downward pressure a forced rotation it tends to ‘self’ steer the machine

Flat pad- provides an even pressure so it will takes more pressure to stop the random orbital buffers motor, so the finish is more even. They also produce a ‘feeling’ for the surface that you can gauge better than the variable contact pads, this style pad is best for medium polishing and finishing work.



Flat foam pads were the original pads before the introduction of Closed Cell Structure foam, although they share the same advanced foam compositions. Flat pads have a slightly different feel compared with closed cell structure foam especially when used with a rotary polisher.



Once mastered, flat pads break down the polish quicker since fresh polish and their lubrication oils are not being constantly re-introduced to the surface; this allows a skilled technician in a high-volume detail shop or paint and body shop to accomplish more in less time. They are very efficient when used with non-diminishing abrasives as they increase the total surface area of the pad, allowing pressure to be uniformly applied.



It also increases the pad`s rigidity against the backing plate, which is very similar to block wet sanding (finishing paper and a sanding block) the most effective tool for paint defect removal because you can abrade the paint surface flat until the defects are removed. Non- diminishing abrasives and a flat foam pad are similar in application to the block wet-sanding process



Collapsed Cell Structure (CCS) Technology™ - foam pads were developed to use on newer clear coat paints. These harder paints require longer polishing times to remove defects. They also help solve the problem of premature "drying". Conventional foam pads absorb water-based formulas, instantly.



This reduces polish and pad performance because most of the polish is trapped below the working surface of the pad. Closed cell structure foam solves this problem with partially closed foam cells, which slow the absorption of liquid, keeping it on the working surface.



(CCS) foam, which means the stiffness of the pad, is focused on to the contact surface, while the rest of the foam remains soft. This type of foam uses intermittent pockets that have been sealed and can no longer absorb polish. This technology was designed to reduce pad absorption at the OEM level, where thinner pads are typically used. This not only extends the workability of water and solvent-based polishes, levellers and compounds, it reduces chemical usage, saves time and makes the polishing process a lot easier. CCS Pads are flat faced. They have dimples across the surface which reduce surface heat at high speeds, and prevent pad skipping.



Foamed Wool (Purple) pad - a patented foam process encapsulates the base of the lamb’s wool fibre with microscopic poly-foam particles. Cuts like natural sheepskin but finishes like a foam pad. Aggressively removes 1500 grit scratches, leaving a lustrous finish with no hazing by reducing compounding swirls. The foam has a dense body and the fibres resist caking and matting, the foaming process also creates minute air pockets at the base of the fibres, which improves cushioning and retention of compounds and polishes. The manufacturing process produces a uniform material, resulting in consistent pad performance, the Foaming process locks in the lamb’s wool fibres, significantly reducing lint



Constant pressure foam pad- this is essentially a flat pad which uses a patented technology layer of engineered, instant rebound foam between the pad and the backing plate to absorb off-axis movements while keeping the pressure of the pad on the surface constant.



It allows even beginners to achieve professional-like results, the curved 6- inch pads outer edge makes transitioning seams and uneven panel breaks easier and the concave "dish" in the centre of the pad reduces product splatter, and gives the operator greater pad control. They are very easy to control, and forgiving of less-than-perfect technique.



Variable contact foam pad- provides focused pressure on a reduced surface contact area using the edges of the pad, making this pad ideal for machine polishing. Be aware that increased surface pressure may cause a PC motor to stall. Variable contact pads are more suitable for use with a high-speed rotary polisher



Tufted foam pad-are made from pre-polymer foam with a 50% open cell structure. This 7.5-inch pad has nine- times the surface area of a flat pad. This dissipates heat, spreads polish over a larger area and reduces polish build-up. This pad is ideal for large surface area polishing, such as the removal of oxidation



Contoured Edge pad- these 7.5-inch pads have a graduated, concave polish pocket similar to the variable contact foam pads, but with a contoured edge and a recessed area for the backing plate. These pads have four distinct working surfaces (1) flat for polishing (2) they can be ‘lifted’ using the outer 1/3rd of the pad for areas that are tight (3)The outer edge of the pad can be used for seams or corners (4) the underside can be used for polishing around mirrors, badges, emblems or other thigh areas.





A curved edge foam pad- is ideal for working in tight spaces or a surface with lots of curves. Apply the polish to the outer edge of the pad and the PC can be used at more of an angle, the PC generates very little heat so this application method can be used safely, it’s halfway between a flat and VC pad with surface contact.This pad can also be used flat, apply more polish on the peak between the curve and recess, utilizing it like this assimilates a variable contact pad.



Purple Foamed Wool Pad (PFW)



Lake Country Mfg. (LC) developed these pads for high production, OEM/Industrial users. Aggressively removes 1500 grit scratches, leaving a lustrous finish with no hazing by reducing compounding swirls while retaining a high gloss. Patented process encapsulates the base of the lamb’s wool fibres with microscopic polythene foam particles. Cuts like natural sheepskin but finishes like a foam pad. Foamed fibres resist caking and matting, foaming process also creates minute air pockets at the base of the fibres, which improves cushioning and retention of compounds and polishes.



A rotary at 1500 RPM coupled with a primed PFW, on a 24 x 24 – inch working area for approximately 1 minute; aggressively removes 1500 grit scratches, leaving a lustrous finish with no hazing by reducing compounding swirls while retaining a high gloss.



Wool pads are not recommended for random orbital machines (Porter Cable 7424, etc) as wool pads nap / fibres works more efficiently with a centrifugal motion. Foam cutting pads tend to be much’ stiffer’ than wool fibres and thus will transfer the movement of the machine to the paint surface more efficiently than a comparable wool pad on an orbital polisher



Microfiber Pads



Work in a similar way to a closed cell pad, foam pads distort, stretch and compress while being worked on a polishing machine. The greater the thickness of the foam between the backing plate and the car surface, you have one surface that stays rigid, being driven by the polishing machine, while the foam acts as somewhat of a shock absorber. The independent, non-tufted vertical fibres work like the fingers on your hand. They flex or stiffen when necessary to reach the peaks and valleys found in wood, painted or other solid surfaces. This constant flexing and stiffening action produces uniform results over the entire surface, adding depth and brilliance of shine not found in other products.



Optimum Polymer Technologies Microfiber Polishing and Cutting Pads - their low profile, reticulated, open-cell foam interface backing to disperse heat, which provides superior cooling and provides generous cushioning between the polisher and the paint that provides excellent flexibility. A cooler running pad equals a longer pad life. Along with the unique, open cell foam backing is the advanced laminating system that ensures maximum durability out of the pads. Thanks to this feature, you can use these pads with either a rotary or a random orbital polisher.



The independent, non-tufted vertical fibres work like the fingers on your hand. They flex or stiffen when necessary to reach the peaks and valleys found in wood, painted or other solid surfaces. This constant flexing and stiffening action produces uniform results over the entire surface, adding depth and brilliance of shine not found in other products.



Available in several sizes as a polishing and cutting pad, they are designed to work with their Hyper Compound Spray, Hyper Polish Spray and Poli-Seal AIO and will also work with other polishes to provide superior paint correction. These pads have a similar abrasive ability when compared to wool



Orbital Polisher- I’ve found superior results with all orbital buffers in both compounding and polishing. It cuts as well or better than the orange or yellow foam pads while leaving less marring that is inherent with these pads. For polishing I’ve found it will remove swirls left with a rotary buffer and a wool pad. Initial speed #2 to spread and evenly distribute polish on the pad, speed 4-5 using medium heavy pressure and then reduce to speed #3 using medium light pressure



Rotary Polisher - tests with the rotary buffer at 1200 RPM it produced amazing results with fast and easy polishing applications. The deep pile microfiber pads are thick and designed for long lasting durability. The soft, reticulated, open cell foam structure reduces heat, also produces less holograms. Clean the pad using compressed air or a pad conditioning brush after each section.

These are both machine washable.



Lake Country (LC) Mfg - Microfiber Pads - the rotary version is thicker with a foam interface to disperse the heat.



3M™ Trizact P5000 Foam Discs - these discs are ultra fine 5000 grit) they allow you to level more serious defects , which may save the ultra thin coating found on PPG/Mercedes Benz`s CeramiClear as they use an ultra thin layer of ceramic clear coat over the regular clear coat. These ultra fine papers allow you to level serious defects without removing too much of this ultra thin final coating.



The 3M Trizact P5000 (grit) Foam Discs are available in 3 sizes: 3 inch, 5 inch, and 6 inch.



Foam Interface Pad



Use of a foam interface pad between the sanding disc and the backing plate is recommended. Foam Interface Pad is made to improve your results during sanding, refinishing and spot repair projects. The foam pad improves the sanding disc`s ability to follow the curves and contours of a vehicle.



The foam interface pad makes machine sanding smoother for the technician and enables the sanding disc to conform better to curved body panels. Using an interface pad also reduces the aggressiveness of the sanding action and reduces the chance of creating coarser scratches.



New Abrasive Technology



These ultra fine cut finishing discs are made from a Silicon Carbide Mineral embedded in a cured resin medium on a flexible film. The polyurethane foam backing is designed for wet use. 3M Trizact 5000 Discs should only be used with water for both machine and hand sanding.



Going through the grits



What does this mean?” No it’s not a reference to eating breakfast in Georgia!



It’s a very similar idea to ‘Least aggressive first’ it refers to the process of using different grit finishing papers, of progressively finer grit or foam / wool pads with progressively denser pads to get a smooth finish, the higher numbers indicate a smoother finish.

By going through the grits each progressive piece of grit finishing paper or pad removes the scratches from that previously used; the higher numbers indicate a smoother finish. Always start with the least abrasive combination, i.e. a machine polish and the least aggressive foam or wool pad.



Select an abrasive polish to match the scratch you are trying to remove; by using the least abrasive combination of polish / pads to remove the defect, before moving up to a more abrasive combination. It makes no sense to use a very aggressive polish, that will remove most scratches but to the detriment of the clear coats thickness.



Always choose the least intrusive product, it is preferable to polish 2-3 times to restore the paint film surface than to use an unnecessarily abrasive machine polish / foam pad combination.



Before commencing polishing do a test panel on the car, once you have achieved the desired results with the chosen polish / pad combination proceed



Grit Numbers



Sandpaper or finishing paper is the most common item from a larger group of products known as "coated abrasives" i.e. Aluminium oxide.

Be cognizant that both polish / compound and pad grit numbers are referenced to a rotary polisher using wool pads (to the best of my knowledge they have never been changed to suit orbital polishers or foam pads) the higher numbers indicate a smoother finish.



Grit rating: this is the level of scratches made on a paint surface by finishing paper on newly applied OEM paint on the production line i.e. before it has been oven dried and cured The grit rating on an abrasive or polishing pad is an indication that a product is designed remove the surface scratches left by finishing paper i.e. 2500 grit scratches are removed by a 2500 grit rated polish) it doesn`t mean that it is a 2500 grit level abrasive. To remove these scratches would need a finer grit (>2000 grit).





Finishing paper - "grit" is a reference to the number of abrasive particles per inch of paper. It eliminates the risk of deep sanding scratches by providing a uniform grit size. This makes sense if you imagine how small the grit particles on a 1000-grit finishing paper would need to be to fit into a 1- inch square. Grit finishing paper is referred to by the size of its abrasives (i.e. 1500-grit paper) the grit rating you use depends on what you are trying to remove





Polishes and compounds – also have a grit number associated with them. The abrasive ability for a polish depends on the shape of its particles, not necessarily their size. A medium size, spiked abrasive will tumble and dig. However, a large round crystal won`t leave a deep scratch. A large hard abrasive may also be brittle. It will cut once and lose its edge, while a softer small abrasive will hold its edge and keep on cutting. Many smaller abrasives have wedge shaped edges protruding from triangular crystals. These can easily slice through an oxidized layer of paint



Foam pads - are also rated on a grit number, that is to say the ‘level’ of scratches they will remove after using grit finishing paper along with a similarly rated polish (i.e. 2500 grit rated pad and polish combination will remove the marks left after using 2500 grit finishing paper) The abrasive ability for a foam pad depends on both the composition (hard or soft) and the number of pores per inch (PPI).



Start by electing an abrasive polish to match the scratch you are trying to remove; by using the least abrasive combination of polish / pads to remove the defect, before moving up to a more abrasive combination. It makes no sense to use a very aggressive polish, that will remove most scratches but to the detriment of the clear coats thickness.



Once you have identified the scratch ‘grit’ marks you can match a polish and a foam pad (i.e. 2500 grit marks, require a polish that is capable of removing 2500 grit (number) marks, matched with a suitable cutting pad (e.g. Menzerna Power Finish (PO203S) this is a one-step scratch remover polish that will remove 2500 grit, matched with a LC White light cutting foam pad)



1. 1000 < grit Heavy - (Compound) levels and removes heavy defects

2. 1200 grit Heavy - levels moderate to heavy defects

3. 1500 grit Medium - levels light to moderate defects

4. 2000 grit Moderate - levels light defects and removes hazing

5. 2500 grit Light - levels swirl marks, light defects and removes hazing

6. 3000 grit Fine - very minor corrective ability, burnishes paint to high gloss



General Rules



1. Porter Cable 7424 random orbital polisher; the limiting factor to pad size is the actual power of the machine. Using larger pads on these machines actually reduces the amount of polishing power due to the surface resistance of the pad, which will cause the motor to slow down or stall. Conversely using a smaller pad will increase the power available by reducing the surface resistance by concentrating motor power on a smaller area.

2. With smaller pads you gain increased control and manoeuvrability. Smaller pads generate more kinetic friction (and subsequently, increased heat) with a PC, which breaks down polishes by generating energy (and applied pressure) over a concentrated area. The random orbiting motion of the PC generates the most power in the centre of the pad (i.e. area of a 6.5 – inch pad is 33 – square inches compared to the area of a 4 – inch pad, which is 12.5 – square inches) This additional pressure / cutting power will facilitate the removal of deeper imperfections

3. The opposite is true with rotary buffers. The speed of the outer edge of a smaller (radius) pad is slower than that of a larger (radius) pad. This helps reduce the amount of friction generated, which makes polishing tighter areas much safer.

4. Do not use the same pad to apply differing products as cross contamination will reduce the effectiveness or completely negate their purpose altogether. A new or freshly cleaned pad must be used with each type of car care product.

5. Water will increase the abrasiveness of a polish; but unlike wool, a foam pad has no fibres to twist, bend, and reshape, therefore helping to loosen the abrasive, so water tends to cause abrasive-clumping, which is detrimental to its performance, it can also cause the pad / abrasive to aquaplane, negating the abrasive

6. There is no recognizable standard between manufacturers that use colour as an identification of the abrasiveness of a foam

7. Apply pressure to the foam; if it springs back the pad is fine. If it stays compressed the foam core is damaged and it’s time to replace the pad.



Centre the Pad



To centre the foam pad on to the backing plate, set it upside down with the Velcro backing plate facing up (this is easier if the side handle is attached). Using the tips of your fingers as spacers against the edges of the backing plate, you can centre it with near perfect results most of the time



When removing the foam pad from the backing plate do not just grab the foam and pull or you may find it separates, hold the Velcro and gently pull the pad to prevent any damage. A 5-ich diameter backing plate when used with a 61/2-inch foam pad allows a -inch `safety` margin` between the edge of the backing plate and the foam pad. To ensure compatibility of fit with a Porter-Cable the post adaptor should be 5/16inch-24.





[Edit: Lake Country (LC) Mfg. Microfiber pads added 07.17.12]