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Equipment selection is crucial to the achievement of airless spraying of industrial coatings. No matter whichever market you serve, the machine must dependably deliver a select coating type at the right application rate under different operating conditions. If the equipment is not correctly suited for the job, quality concerns, and equipment failures often lead to budget overruns, schedule delays, and unhappy customers. 

The key to airless spraying is producing enough fluid pressure at the gun to atomize the substance into a pattern that provides consistent coverage. Many factors need to be considered when selecting airless spraying machines, including an available power supply, coating type, application demand, the distance between the pump and spray gun, operating environment, portability, and maintenance specifications.



Airless pumps can be powered by air, electric, or gas power sources. The selection of power is often determined by the operating conditions and availability of power sources. The key factors of each source are shown below.

Power Source Pros Cons


Air (Pneumatic)

  • Convenient for builders using air-compressor-driven blasting equipment
  • Safer in explosive environments
  • Capable of handling large tip sizes
  • Capable of operating multiple spray guns
  • Easily handles long spray hoses 
  • Noisier than other kinds
  • Can be inclined to icing in cold environments 
  • Requires a large-sized compressor



  • Quieter than other sources
  • Reduces energy costs
  • Less prone to icing
  • Does not demand a large compressor
  • Handles long spray hoses
  • Need 240V on-site as well as an electrician
  • Only works with smaller tip-sizes



  • Greater portability
  • Capable of high production rates 
  • Helpful in handling heavier, thicker coatings
  • All-in-one power source (does not require electricity or compressor)
  • Not allowed in hazardous environments
  • May need permits for fuel on Jobsite.




The coating model also plays a key role in spray equipment. Industrial coatings are typically epoxy, polyurea, or polyurethane-based, highly viscous materials. Higher pressure pumps allow pumping more viscous materials and optimizing pressures for less dense substances.

If solvents are used to lower viscosity, one key factor to consider is the length of time the material needs to be sprayable after being hand-mixed (hot potted). The proportion of solids in the coating is another key factor. As the solids percentage increases, the number of the solvent decreases, and pot life decreases.



The rate at which coating is to be sprayed, or application demand, is also a key factor in selecting spraying equipment. The pressure required to atomize the material often determines the appropriate pump. Tip size required for proper coverage, the number of guns, duty cycle, and pump flow rate also need to be analyzed.  

A combination of both pressure and flow of the pump determines the application rate. Many pumps have enough pressure to spray a coating, but they’re offered in different sizes (or flow rates). 

The flow rate that the pump is capable of achieving also needs to be considered. For example, a sprayer with a larger pump fluid section can handle more demanding applications because it cycles slower.




To properly atomize and apply coating material, the pump must overcome the pressure drop in the hose. As hose lengths increase, pressure drops increase, and additional pumping pressure is needed. 

The diameter of the spray hose also affects the pressure drop. By increasing the hose diameter, pressure drop can be reduced. Elevation of the application area can also affect the pressure drop. If the application area is higher than the sprayer, a larger pressure drop will occur through the hose. Coating suppliers and product data sheets can provide additional information on the pressure required.


Various operating environments demand different spraying equipment. Temperature and humidity are often key factors to consider. Air motors can experience icing issues, as ambient air is compressed and exhausted out of the pump at a colder temperature. A good motor design will mitigate icing and possible pressure loss. Some advanced sprayers feature thermally isolated poppets on the motors insulated from motor castings to virtually eliminate pilot valve freezing.

If sprayers are used in hazardous locations, pump type must be considered. Gas pumps are generally not allowed in these areas. If an electric pump is being used, agency approval is needed for operation in a hazardous location.



Portability is a different factor to consider. Most sprayers are typically available on carts and may be moved around a job site. Pump size can also affect portability. While larger pumps often help achieve higher application rates, the pump size should also be optimized to maximize portability. In industrial environments and smaller projects, if one person can maneuver a sprayer, a smaller unit at a lower cost may make sense.



A sprayer that’s easy to troubleshoot and maintain will make life easier – and jobs more profitable. The equipment dealer can advise on ease of maintenance, regular maintenance tasks, and anticipated lifespan of wear items for various sprayers. Some key maintenance questions to ask:

  • Are common items easily accessible, or is disassembly required? 
  • Are any special tools required, or can common tools handle most maintenance tasks?
  • How easy is it to remove the cover?
  • Is there a convenient place on the sprayer to store essential tools and parts? 
  • Are replacement parts reasonably priced and readily available?


Each of the factors discussed in this article (power source, coating type, application demand, the distance between the pump and spray gun, operating environment, portability, and maintenance requirements) plays a key role in selecting an airless sprayer.) Also, here are some general items to consider when selecting equipment:

  • Make sure you have sufficient fluid pressure at the gun to provide consistent coverage. 
  • A dependable, high-quality sprayer may have a higher initial cost, but the successful completion of more jobs on time is possible if you consider all the right factors. 
  • Rugged sprayers can perform various environmental conditions and make the difference between a good day’s work and a day of frustrating delays.
  • Work with a qualified technical representative to make the right decision

Troubleshooting for a Graco Reactor 2 Integrated Elite E-XP2i ...
Plural-component spray equipment can be utilized for using spray polyurethane foam (SPF), polyurea, urethanes, and epoxies. If you supply spray used services, it is necessary to do every little thing you can to maintain your plural-component devices and sprayers in good condition whatsoever times to reduce downtime and upkeep costs. Follow these 5 standards to obtain one of the most out of your tools with every passing year.
1. Examine Your Power Supply Daily
Daily, examine the voltage on your device( s). Be sure to examine coolant and oil levels also. Beginning the engine up as well as allowing it run for around five minutes will help you identify any other concerns you might not notice once you leave the generator.
Power Supply | Pinnacle West
When beginning the engine, turn on the main circuit breaker and inspect the radiator as well as compressor colder for debris. If there is debris, utilize pressed air to cleanse the parts. Evaluate the engine, compressor, as well as radiator for leaks, as well as the fuel and also coolant tubes.

Make certain to inspect the hr meter for any kind of future service( s) that might be due. You can locate the service schedule for oil, fuel, and also air filter modifications in your tools manuals. This will certainly guarantee every little thing is functioning as effectively as possible, and also it decreases the danger of damage and also downtime down the line.

A couple of basic checks daily can save you a great deal of cash on repair work in the future, and also it virtually ensures much less stress and anxiety from economic losses due to being down on the work.

2. Care for Your Hoses
Delivering more to your bottom line - New Graco Series 2 E-XP2 ...Hoses are responsible for transporting plural-component products to where they need to go. As a result, maintaining them in superior condition is crucial. To prevent your plural-component chemicals from freezing in cold weather, always bring your pipes right into the rig and hang them correctly on a hose rack. Be sure to maintain them kept and also change scuff jackets as needed. An alternative to typical scuff is making use of shielded or non-insulated items. These form-fitting items are made with a thick nylon that make them immune to tearing and also other environmental factors, while making use of Velcro to maintain them in position and also kind to the hose pipe.

When changing in between open- as well as closed-cell products, ensure you purge your B side with water so you don't infect and also lock up your whole system and the pipes, which can be pricey to repair. While you are not spraying, or if you are placing your gear away for lasting storage, be sure to flush both the An and B sides with an authorized solvent. Refraining so can force you to squander a lot of time on the following task trying to get every little thing prepped as well as prepared to go. If you have any type of questions, consult your chemical supplier or a tools professional on flushing processes, and also, as constantly, make sure to adhere to appropriate safety and security method when taking care of the products.

3. Purchase Annual Electric Motor Maintenance
If a motor is not in good working condition, your equipment can refrain from doing a lot. Having it serviced a minimum of when annually will certainly make a massive influence on your procedures. An expert in the field can take a detailed consider your system as well as identify whether new parts or repair work is needed. Be sure to utilize a devices technician who is qualified to deal with your brand name of device in order to guarantee appropriate upkeep.

Preventive maintenance checklist for centrifugal pumpsFor power sources, make sure to take your unit to a qualified solution center of the producer to ensure that all service warranties are promoted. You can go to the internet site for the producer to discover service facilities, and also your initial documentation might detail the terms of your warranty. This is a far better choice than waiting till your spray tools fails.

4. Maintain Spare Parts handy
The best option to prevent longer downtimes, in case a component of your spray machine is not functioning, is to maintain extra components available. This is a simple and also budget friendly action to take, and also it is a much better alternative than getting what you believe to be the issue at the time of failure.

Your spray gun is the component in your spray system that is more than likely to have problems. Its internal components break from usage more quickly than any other component of the spray system. Taking care of your spray gun is a bit extra tedious, but it will certainly profit your work and also company. After every job, it's important to get rid of any excess chemical from within the gun to stop build-up and clogging. It's an excellent concept to break down the weapon every now and then and also soak all the pieces in a cleansing solvent, thus removing any debris as well as cleaning the components. When rebuilding the gun, make sure to grease all the O-rings to stop them from breaking down quicker.

If you are not keeping your spray gun daily after splashing, you can end up with a great deal of issues that can cause you downtime as well as economic loss, so you want to be sure to maintain usual spare components on your spray gear in case of gun failure. Buying a back-up weapon in case the parts required are out hand is likewise a perfect means to reduce downtime on a job and also minimize troubles-- particularly if you are not currently changing the components as needed when they are failing. Transfer pump parts are other excellent extra components to continue your spray rig to ensure your system is always running.

5. Follow Service and Upkeep Schedules
Many layers specialists can agree that, as a result of the nature of their business, regular maintenance on their spray gear is typically overlooked. Lengthy days and requiring timetables can leave specialists having little to no time at all to execute regular and also preventative maintenance on their devices. Preventive and also scheduled upkeep on all tools is key to maintaining the components of your spray system running longer and without failure.

310666H Xtreme Mix 185 Repair, Plural Component Proportioner, U.S. ...
Describe each equipment supplier's standards for maintenance schedules. Tools suppliers and service technicians can also give you with precautionary maintenance to assist keep your system up and running. You ought to always describe the producers' routines for upkeep, but the complying with sample timetable will certainly give you a suggestion of what to expect:


Daily: Examine oil levels, clean air/oil external radiator, tidy cooler filter, and clean air filter.

1,000 hours: See guidebook.Air DryerDaily: Inspect that auto drainpipe is discharging.Regular monthly: Clean particles from ambient air filter, tidy with soap and water, as well as permit to dry before reinstalling.Annual: Change separator filter component.Spray Foam MakerDaily: Examine pump lubrication degree. Fill up as needed with throat seal fluid.Weekly: Grease circulation valves with suitable oil. Tidy particles out of electrical cupboard vent holes.Spray GunDaily: Grease weapon with ideal grease, drill blending chamber, and examine shutoff displays.As needed: Tidy blending chamber nozzle by involving piston security lock, usage right size drill to clean nozzle, make use of stiff bristle brush to tidy air cap, as well as clean liquid manifold, impingement components, and/or passages.Fresh Air System500 hours: Change inline outlet filter and inlet filter.DesiccantDaily: Look for shade change from blue to pink and also replace as required.

By doing daily checks, by complying with manufacturers' timetables for servicing your source of power part and compressor, by caring for your hoses, as well as by maintaining spare parts accessible, you'll have the ability to keep your plural-component sprayer at its optimum efficiency. If you ever have concerns regarding the upkeep to be carried out weekly as well as yearly, connect to your tools provider, who can give you guidelines for each and every element.

Image result for How to Prevent Mold with Spray Foam Insulation

When you think of mold, does your mind ramble to that loaf of bread you left on the counter too long? It’s gross, but that type of image is relatively safe – tossing it in the trash quickly gets rid of your problem. Other types of mold and mildew lurking in your home are much harder to get rid of – not to mention they’re hazardous to you, your family, and your house. What are some signs that mold might be hiding in your home? Perhaps more importantly, how can you prevent rust from growing to begin with?

Signs of Mold in Your Home
Sometimes detecting mold in your home is as simple as taking a close look. Is there black or green spots on your walls? That’s mold, and it’s imperative that you deal with it quickly, before it spreads. But what if you don’t see it? If your home has a stubborn musty odor, that’s a pretty good sign that mold is hiding somewhere.

Some of the most common indicators of mold are actually in your own body. When the image is growing in your home, you’re sure to inhale some of it. Symptoms of mold inhalation often look like allergy symptoms: you may be coughing or sneezing. In many cases, you may begin to feel lightheaded or confused. If you’re experiencing symptoms, don’t disregard what your body is trying to tell you. Schedule a check-up for yourself, and one for your home too! Your doctor will be able to identify signs of mold inhalation, and a home professional will be able to locate mold.

What’s Causing Mold in My Home?
Mold is often a symptom of a more vital problem in your home: water damage. Sometimes, people know they’ve experienced recent water damage due to flooding or a burst pipe. Other times, it goes unnoticed. Whatever the case, moisture problems should be taken sincerely. A discolored ceiling may be simple to repaint, but if it’s hiding structural damage, you’re going to have a much more serious problem later on.

Mold has very few needs: it wants moisture, warm temperatures, and biodegradable material to munch on. This adds up to bad news for Florida residents, especially in the past few months. Hurricane Irma supplied the moisture, the Florida climate provides warm temperatures, and wooden housing materials offer the biodegradable mold food.

But what if your home hasn’t been flooded? The culprit might be your attic – more specifically, faulty or missing attic insulation. Many people think that insulation’s only job is to keep warm air inside, but that’s not the case. Homes in warm climates need insulation too. Proper insulation keeps fresh air in and moisture out. Gaps in insulation allow humid air to sneak in and take up residence.

Mold’s favorite partner in crime is your HVAC system. Pipes lead conditioned air into each room in your home. If the image is hiding in your walls or attic, mold spores can enter your HVAC system, spreading (and growing) all over your house. Suddenly your problem gets a lot bigger!

Spray Foam Insulation to Prevent Mold
It isn’t enough to have insulation. You have to have the right kind for your home. While there are many different types of insulation, the best fit for Florida homes is closed cell spray foam insulation. Unlike other insulation materials, spray foam is water resistant, meaning it keeps that dangerous moisture where it belongs: outside. As a bonus, spray foam forms an airtight seal. Outside air and allergens will stay out of your home, and the fresh air that you pay to heat or cool will stay within, which can drastically cut your utility bills!

Take Matter Into Your Own Hands

Stop mold before it starts by keeping precipitation out of your home. Spray foam insulation is your biggest ally in the fight against humidity. Don’t wait until you have a predicament. Prevent mold by preparing your free spray foam consultation from Energy Monster.


It is best known for supporting our body for a large part of the day, in mattresses, upholstered furniture, and car seats. What is sometimes less known is that we enjoy the benefits of hundreds of polyurethane foam articles without even noticing. Its applications are virtually endless, ranging from small but essential items such as sponges in the kitchen, medical dressings to large filters and soundproofing systems that keep our environment clean and quiet.

Related image
Polyurethane is a leading member of the wide-ranging and highly diverse family of polymers or plastics. Polyurethane can be solid or can have an open cellular structure, in which case it is called foam… and foams can be flexible or rigid. ArmorThane, which has developed a website specifically dedicated to answering all questions on building insulation with polyurethane foam.

Learn more quickly about the many applications of polyurethane through the video below, developed by ISOPA, the European Diisocyanate and Polyols Producers Association. For more extensive information on all forms of polyurethanes, please visit ArmorThane, com if you would like to order some polyurethane...


The manufacturing of polyurethane foam is a process of great industrial importance in the automotive and furniture sector. The operation of demolding is the most delicate, since the foam sticks firmly to the walls of the mold onto which it has spread. In order to avoid the use of demolding agents, the proposal is to coat the inside of the molds with non-stick coatings. In this work, three types of different coatings were studied: fluoropolymers, ceramics, and elastomers. After carrying out different tests in the laboratory, two fluoropolymer coatings (PFA (perfluoroalkoxy) and PTFE (polytetrafluoroethylene)) were selected for a test at the industrial level and, after 1500 cycles of demolding, it was experimentally proven that the PFA coating is the most adequate for the use studied.

 non-stick coatings; polyurethane foam; aluminium molds; FEP; PFA; RTV silicone rubber; sol-gel

1. Introduction

The polyurethanes (PURs) include an extensive group of polymers with an enormous range of compositions and properties, with applications such as adhesives, elastomers, coatings, and foam [1,2]. The main areas of applied usage of polyurethane foam are those that require absorption and padding. Flexible uses of polyurethane foam include: cushions used in car seats and in furniture, floor coverings and carpets, mattresses, pillows, and household appliances, among others [3,4].
The production of polyurethane foam is accomplished by polycondensation of polyisocyanates with polyols [5,6]. The mixture of the aforementioned components in their respective adequate proportions, and after having been removed from the mold, generates a reaction that produces a gas and the formation of foam. Following this step, the molded piece and foam are removed and allowed to cool. The force of the demolding can reach high values [7]. At the time of demolding of the foam pieces, it is necessary that the mold surface manifests a low superficial energy [8] and has a favorable texture [9]. Furthermore, the creation of a mechanical barrier to avoid fixing [10], the prevention of spreading between the surfaces, and limitation of electrostatic attraction [11] are all required.
The polyurethane foam industry normally uses demolding agents in liquid form [12], which are applied to the mold surface in order to manufacture the polyurethane foam using the reaction technique [13]. These are usually aqueous dispersions with amine accelerators, foam stabilizers with siloxanes, polyethylene waxes, and polybutadienes. The reduction or elimination of the demolding agents is of interest to these industries because of the high consumption and cost of these products. The application of non-stick coatings could provide a substantial improvement to solving the problem.
Non-stick coatings are used in many applications of industrial molding. Studies have been made of applications with coatings of fluoropolymers, as described in [14,15,16], of sol-gel type, as shown in [17], and of silicon rubber, as in [18], among others. Studies have examined the behavior of PUR foam in aluminum molds with commercial coatings of polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and fluorinated ethylene propylene (FEP), as described in [19,20]. Nevertheless, the authors have not found previous works centered on the use of other non-stick coatings for PUR molds, such as ceramic coatings or RTV1 (silicone rubber)-type elastomer coatings.
The main aims of this study are to identify and evaluate different non-stick coatings applied to aluminium molds in order to manufacture PUR foam without the necessity of a demolding agent. The coatings studied were: TFI 851 E (PTFE), TF-76521 (PFA), TFI-3531 (FEP), TFC-51 N (sol-gel type), TS-RTV1 silicone rubber without cerium, and TS-RTV1 doped with cerium. These coatings could be especially useful for PUR foam release applications because they have characteristics such as: low surface energy, hydrophobicity, excellent anti-adhesion properties, high chemical resistance, good mechanical properties, and high temperature stability [21,22,23,24,25].
To study the behavior of the coatings, traditional techniques (roughness measurement, sliding angle measurement) were used. Also, a recently patented test of release force of PUR foam and a new method focused on the behavior of the coatings on the front of one of the foam components were employed [26]. Finally, industrial tests were performed to verify the results of laboratory. These tests are considered the second important contribution of the study.
The structure of this paper is as follows: Section 2 describes the equipment and material used; Section 3 shows the results, which are thereafter discussed in Section 4; finally, the conclusions are expressed in Section 5.

2. Materials and Methods

2.1. The Foam Mold

The diisocyanate of 4,4′ methylene diphenyl diisocyanate (MDI) and polyol used in the manufacturing of polyurethane foam was supplied by Grupo Copo Company (Vigo, Spain), which is a company that specializes in the development and manufacturing of alveolar polymers in the automobile field. The foam was obtained from mixing polyol formed with MDI with a weight relation of 100/57.7 (polyol/MDI). The foams were obtained in an enclosed mold, resulting in a density between 64 and 66 kg/m3.
The process of obtaining the foam was to pour a measured quantity in weight of polyol over a quantity of MDI and mix vigorously with a mixer (1000 rpm) for 10 s. Immediately afterwards, without pause, the dilution was poured into the molds in a uniform manner. The molds were preheated to a temperature of 50–60 °C, after which the poured combination of polyol and MDI was put in an oven at 60 °C for a period of 5–7 min. The foam formed and grew. The mold was sealed with lids.
To study the release force of the polyurethane foam, a rectangular mold was made with removable lids: one for the base and one for the top. Added to this was an intermediate plate with four window cutouts. These windows allowed rectangular samples to be taken, with one side being non-stick coated. The flat specimens came out in such a way that the uncoated side faced outward, without having been in contact with the foam which is formed inside the mold. The mold is shown in Figure 1.
Figure 1. Rectangular mold for the manufacturing of polyurethane (PUR) foam: (a) frame of the mold with four window plates to insert flat non-stick specimens; (b) piece of PUR foam obtained.
The walls of the molds are made from mechanized cast-aluminium EN AC 42100 and their internal dimensions are 197 × 165 × 48 mm3. The windows permit the insertion of flat specimens of 49 × 49 × 1.2 mm3 of aluminium EN AW 5754, one of whose sides is non-stick coated, thus leaving a surface of 45 × 45 mm2 in actual contact with the foam. This allows one to determine the release force of the foam on the coating after various cycles.
Twenty cycles were carried out. Each cycle of foam studied entailed the following: (a) the mounting of the frame; (b) formation of the PUR foam in the mold; (c) after 20 min of curing, release with dynamometric equipment and determination of the release force of the non-stick coated plates with PUR foam; (d) demolding of the PUR foam from the mold; and (e) cleaning of the mold and preparation for the next cycle. An axial force testing machine IMADA MX2 500 N with 100 N dynamometer (Imada Co., Ltd., Toyohashi, Japan) was used in the tests.

2.2. The Coatings

The coatings were selected for their toughness and applicability to industry, and due to previous experience using the applicator TECNIMACOR (Cordoba, Spain). Six coatings were studied with this method and four specimens were taken from each coating. The molds were made identically.
The coatings studied were (Figure 2):
  • TFI 851 E is a coating made with PTFE, whose recommended use is for multi-layered antiadherents applied to demolding in engineering, the food industry, and the metal-mechanical industry in general.
  • TF-76521 is a fluoropolymer based on PFA, among whose common uses are: trays and molds for bakery and related industries, and in solutions for engineering in general.
  • TFI-3531 is a fluoropolymer based on FEP, and among its uses are: molds for thermoforming, molds for thermofusion, hoppers for doughs in the food industry, etc.
  • TFC-51 N is a non-stick coating of the sol-gel type; it is used in kitchen utensils and renowned for its resistance to wear and toughness.
  • Finally, TS-RTV1 is a silicon rubber elastomeric coating that polymerizes in the air and is typically used in the bakery industry. Tests were carried out with the elastomers without doping and doped with nanoparticles, such as those proposed in the literature [27].
Figure 2. Tested coatings: (a) TFI-76521 (perfluoroalkoxy (PFA)); (b) TF-531 (fluorinated ethylene propylene (FEP)); (c) TFI-851E (polytetrafluoroethylene (PTFE)); (d) TS-RTV1 (silicone rubber); (e) RTV1 + Ce (silicone rubber +cerium); and (f) TFC-51N (sol-gel. Ceramic).
The coatings were characterized by means of determining their thickness and pencil hardness resistance. The layer thickness was measured by Leptoskop 2024 of Karl Deutsche measuring equipment (KARL DEUTSCH Prüf- und Messgerätebau GmbH + Co KG, Wuppertal, Germany), with a resolution of 0.1 µm under the ISO 2808 standard [28] and the scratch resistance test according to ISO 15184 [29]. For the determination of color, a RAL color normalized table (RAL gemeinnützige GmbH, Bonn, Germany) of 1625 colors was used [30].

2.3. Laboratory Tests

The surface roughness of the antiadherent was evaluated after each cycle of release. For measuring the surface roughness, a Mitutoyo SJ-201 measuring device (Mitutoyo Corporation, Sakado, Japan) was used and the parameters RaRz, and Rq were measured.
The sliding angle was measured as an indicator of the non-stick capacity of the coatings of the test plates after each foam cycle [31]. To determine this, a device was used equipped with a tilting plate, which was able to tilt to a degree of 10°/min and which also enabled a specific volume of water to be dropped onto the coated surfaces. The drops of water used to determine the angle measurement were demineralized and of 10°/min, and they were deposited by means of an adjustable volume pipe. A digital inclinometer was used to measure up to a precision of (0.05°). The inclinometer is magnetic and can be placed on the edge of the tilting plate. The detection of the overall sliding of the drop was done visually. For each surface to be analyzed, three drops were deposited and analyzed.
The equipment used to obtain measurements for release force was the model MX2 500 N manufactured by IMADA (Imada Co., Ltd, Toyohashi, Japan) with the incorporation of a dynamometer of 100 N. The tests were carried out with a speed–displacement of 100 mm/min. This is the speed of release for each cycle of foam. Four figures were obtained, one for each specimen, on the release force of each cycle of the foaming.
In order to determine the release force of the PUR foam on the specimens of aluminium with non-stick coating, bonded with cyanoacrylate glue was a steel sheet of 35 × 35 mm2 on the side that was not covered by the samples of Al–Mg. On this steel sheet, a magnetized part was fixed by incorporating it with a screwed nut with a cylindrical section, on which the hook was screwed to enable fixing it to the test bench with a dynamometer (Figure 3).
Figure 3. Setup to determine the release force in the coated specimens of 45 × 45 mm2.

2.4. Laboratory Tests with MDI

The influence of the coated surfaces after prolonged contact with MDI was studied. It is known that the MDI, one of the reagents of PUR foam, produces a penetrating effect on the coatings [19]. For this, a vial of 10 mL capacity was used, into which was poured 5 mL of MDI. Then, the vial was placed facedown with the mouth leaning on the coating, firmly held by sticky tape, and placed in an oven at 60 °C for variable times, from 24 to 120 h.
Once done, the roughness Ra and the release force of the PUR foam was determined. In addition, an analysis was made by means of a Quanta 400 model sweeping electronic microscope (Thermo Fisher Scientific, Hillsboro, OR, USA) of the surface conditions of the coatings, which were then mapped with the spectroscopy technique of energy dispersive of X-rays (EDX).

2.5. Tests in the Industry

Finally, a test was carried out in real surroundings with the two best-behaved coatings from the laboratory tests. The coatings were applied in molds supplied by the Copo Iberica S.A. Company (Vigo, Spain) at the TECNIMACOR facilities. The field tests were carried out at CETEC (Technological Centre of Grupo Copo).
The same stages and operations were performed as with any mold production (preparation, adjustments and carousel placing, adjustments to casting parameters, and system servicing).
The requirement is that the piece be taken out easily from the mold without any type of tearing of the polyurethane and without resistance to the demolding operation.
The mold was tested in a circular carousel of HR (high resilience) polyurethane foaming with an automated PUR injection system.

3. Results

3.1. The Coatings

The data on coatings (thickness, scratch resistance, and color) are shown in Table 1. They are in agreement with the characteristics expected, as described in [32] for fluoropolymers or in [33] for ceramic materials.
Table 1. Non-stick coatings on aluminum plates used in cycles of forming of PUR foam.

3.2. Laboratory Tests without MDI

The behavior of the different coatings in the laboratory tests was studied, thus determining the critical sliding angle, roughness, and release force after each foam cycle of the proposed specimens. Twenty consecutive cycles were carried out for each set of coated specimens. The results are shown in the illustrations accompanying Figure 4Figure 5Figure 6 and Figure 7.
Figure 4. Critical sliding angle (°) of the coatings studied. Initial state and after 20 cycles.
Figure 5. Roughness Ra (µm) of the coatings studied. Initial state and after 20 cycles.
Figure 6. Release force of PUR foam on a flat surface of 45 × 45 mm2 as a function of the foam cycles analyzed. Non-fluoropolymer coatings.
Figure 7. Release force of PUR foam on a flat surface of 45 × 45 mm2 as a function of the foam cycles analyzed. Fluoropolymer coatings.

3.3. Laboratory Tests with MDI

The lowest values of the release force of the PUR foam were obtained with the fluoropolymer coatings of FEP and PFA. For both, after contact with the MDI reagent, the roughness (Ra), the sliding angle, and the release force of the PUR foam (Table 2) were determined.
Table 2. Roughness Ra (µm), sliding angle (°), and release force of PUR foam (N) on of the FEP and PFA coatings studied. After 24 h and 120 h.
SEM (scanning electron microscope) images of the PFA and FEP coatings (Figure 8) were taken in their initial state and after 24 h and 120 h of contact with MDI.
Figure 8. Images obtained by SEM, after contact with 4,4´methylene diphenyl diisocyanate (MDI), of TF-3635 (FEP): (a) reception; (b) after 24 h; and (c) after 120 h, and of TF-76521 (PFA): (d) reception; (e) after 24 h; and (f) after 120 h.
Along with the morphology obtained by SEM, an EDX analysis was performed. Due to their chemical composition, the elements that allow identification of the coatings of FEP, PFA, and MDI are fluorine and nitrogen, respectively (Figure 9).
Figure 9. EDX mapping with fluorine (blue) and nitrogen (red) labeling in PFA specimens attacked with MDI for 120 h.

3.4. Tests in the Industry

Finally, field tests were taken with pieces of factory-produced PUR foam. The industrial test results are shown in Table 3.
Table 3. Results of the industrial test of pieces of PUR foam in a mold of aluminium with two tracks, so that in one, the FEP-type coating was applied, and in the other, PFA was applied.

4. Discussion

In the present work, the behavior of different coatings in the processes of demolding of PUR foam was studied; a total of six different coatings undergoing 20 demolding cycles were examined. After each cycle, each coating was characterized by means of the sliding angle, surface roughness, and release force. The coatings with the best behavior then underwent an additional laboratory test, with MDI in the molds, on an industrial scale.
In relation to the critical sliding angle (Figure 4), it is necessary to indicate:
  • The highest values were obtained with elastomer coatings of silicon rubber TS-RTV1 (20°–22°). These values are compatible with those found in the literature [34].
  • There seems to be no difference between the values of the non-stick application of silicon rubber with or without cerium. Previous studies reported lower values for RTV1 + Ce and better behavior in the case of contact with water or ice [24]. These phenomena were not identified for PUR foam.
  • The lowest values of the sliding angle were obtained with TF-5621 coatings of PFA base (11°–13°), TF-3531 with FEP base (12°–13°), and the sol-gel, ceramic, TFC-51 N (13°–14°).
Regarding the roughness of the coatings (Figure 5):
  • The lowest values were obtained with the TFC-51 N ceramic coating (0.3–0.5 µm). This is not related to low values for release force of PUR foam. Similar conclusions were reached in the case of foodstuff demolding (pancake) on metallic surfaces for sol-gel coatings [33].
  • The RTV1 coatings without cerium, those doped with cerium, and those of PTFE/TFI-851 E base obtained Ra values oscillating between 0.9 and 1.2 µm, the highest.
  • The coatings with resins rich in PFA and FEP gave intermediate values between 0.7 and 1.0 µm, the FEP type roughness values being slightly higher than the PFA ones. In the case of fluoropolymer coatings, the roughness appears to show the opposite effect to the sol-gel (ceramic) coatings. The lowest values for roughness, among others, coincided with lower values for release of PUR foam. This was studied in [35].
In relation to the release force (Figure 6 and Figure 7), in the 20 cycles carried out, it must be pointed out that:
  • The lowest results were obtained with the TF-3531 (FEP) and TF-76521 (PFA) coatings. The values obtained varied between 5 and 20 N. These results coincide with those observed by Figueiredo et al. [19] and Akinci and Cobanoglu [20].
  • The silicon rubber, the ceramic type, and PTFE re-coverings seem to show a more unstable behavior and obtained release force values varying between 20 and 50 N.
  • The results indicate that the critical sliding angle may be a good indicator for the selection of coating, since the lowest sliding angle coincides with the coating with less release force, as was also observed in [20].
From the results of thickness and pencil hardness (Table 1Figure 6 and Figure 7), it can be said that:
  • The coatings with better behavior presented similar thicknesses and surface hardness: PFA produced 55 ± 10 μm and an H–F hardness; FEP had 50 ± 5 μm and an F hardness.
  • There is no relationship between the thickness or hardness of the coating and the demolding behavior of the PUR foam. The harder coatings (TFC-51 N) or thicker coatings (TS-RTV1 or TS-RTV1 + Ce) that were tested had poor performances in the release force tests.
From the results obtained after the tests with MDI, the following points can be affirmed:
  • The images FEP and PFA coatings contacted with MDI show a significant change after exposure (Figure 8 and Figure 9). These results coincide with the literature in the case of PFA [19].
  • Initially, a compact fibrillar structure was observed in the control specimens (a) and (d), even without contact with MDI. After exposure and after 24 and 120 h, the surface acquired a grainy texture. It can be seen that the grains of the FEP coatings are bigger than those of PFA. Taking into account that the grains are produced with the MDI attack, (Figure 8), we can infer that the attack is more severe in the FEP coatings than those of PFA, just as observed by Figueiredo et al. [19].
  • Furthermore, the sliding angle increased significantly after the attack, although less so in the PFA than the FEP, as seen in [20], but not the release force, which was almost unalterable. This occurred in a similar way with both coatings.
After the industrial test, it can be pointed out that:
  • The expectations of the laboratory test were confirmed, and the best results were obtained with the TF-76521 (PFA) coating, which seems to allow the manufacturing of some 1500 pieces without using any type of demolding and practically without incidences.
  • For the TF 3531 (FEP) coating, some incidences began, initially slight, but then greater, after about 500 pieces. Both experimental results on an industrial scale confirm the idea proposed by Figueiredo et al. [19] and Akinci and Cobanoglu [20].
Finally, the follow affirmations can be stated after the present study:
  • The critical sliding angle can be a good indicator for the selection of a coating for molds for manufacturing of PUR pieces, since the lower sliding angle values are associated with lower release force values.
  • The topography generated by the FEP and PFA coatings seems to have a certain similarity with the hydrophobic effects associated with the “lotus leaf” phenomenon [36], creating structures that allow trapping a certain level of air in the rough surfaces [37]. Therefore, fluorinated coatings with Ra roughness levels in the range of 0.8–1 μm have a better response than coatings with less roughness. PTFE coatings are also highly fluorinated coatings with Ra values similar to FEP and PFA but, in this case, their porous structure seems to produce foam interlocking effects that significantly increase the release force of the PUR foam.
  • On the other hand, the study of the contact with isocyanate shows us that the isocyanate percolates through the hollows of the surface and wears out the upper part of it. Small areas of the surface where the MDI adheres begin to appear, eventually forming films of this compound that clog the polymer. This phenomenon is more intense in FEP coatings than in PFA coatings. This effect can also be responsible for the increase in the adhesion measured, because if the surface of a chemically very hydrophobic material is covered with another less hydrophobic one, the non-stick capacity must necessarily be lost.

5. Conclusions

A study was carried out on the most important non-stick coatings, according to their typical use in engineering, to address adhesion problems in aluminium pieces. Coatings were selected that are representative of the most-used typologies: elastomers (silicone rubber), ceramics (sol-gel), and fluoropolymers.
A procedure was designed to manufacture PUR foam and to determine the adhesion force in aluminium specimens coated in different materials. A laboratory test was carried out identifying the coatings with the best behavior in the demolding of PUR foam. The idealness of these selected coatings was confirmed in field tests.
Ultimately, for the manufacturing of PUR foam, the aluminium molds—which contained non-stick coatings on their walls—have the following behavior:
  • The molds coated with RTV elastomer with and without cerium, and molds with PTFE coating, are not apt for PUR foam demolding. Although the values of maximum release force, roughness, and sliding angle remain relatively stable with an increasing number of cycles, the values of release force are high, around 2–2.5 times those of the FEP and PFA type. On an industrial scale, this will result in difficulty in demolding and incidences in production.
  • The molds coated in ceramic of the sol-gel type are unadvisable for the manufacturing of PUR foam because, although the sliding angle values obtained are average and of low roughness, the release force is high and undergoes a notable increase when the number of cycles increases, up to 3 times the values of FEP and PFA coatings.
  • The molds coated with PFA- and FEP-type fluoropolymers are the most apt for manufacturing PUR foam. They undergo no significant variation in sliding angle, roughness, and release force values. They possess the lowest values of release force and sliding angle, although their roughness values are relatively high.
  • Between the two fluoropolymer coatings with the better responses, it has been determined that FEP coatings suffer from an isocyanate (MDI) condition of a greater magnitude than PFA coatings.
  • In an industrial application, it was possible to manufacture around 1500 units of PUR foam in aluminium molds with a PFA-type coating, and around 500 units with FEP, without incidences. From then on, the coated molds needed demolding to some degree: in the case of PFA, 1 out of every 4 foamings; for FEP, 1 out of every 2.
  • The PFA fluoropolymer coatings allowed the obtaining of a significant amount of PUR foam pieces without any type of demolding. When the coating began to wear out, it was still useful, with a significant saving in demolding.

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