in Vol. 4 - March Issue - Year 2003
A New Masking Solution: Environmentally Safe, UV Curable Masking Resins
Author Douglas B. Berowitz, Sales & Marketing Manager of Composition Materials Co. Inc.
UV curing system for small parts
Filling turbine cooling holes with Burn-Off Masking Resin
Burn-off Masking Resin used to keep cooling holes clear during Plasma Spray Application.
Peelable resin used for grit blasting application
Peelable resin used for plating application
Masking of components and surfaces is a necessary part of every surface finishing process. Whether for abrasive cleaning, acid stripping, shot peening, plasma spray, or plating, masks act as a self-sacrificing barrier for surface protection. The process of masking may seem simple enough, but a thorough analysis reveals that it can add significant costs to any operation. These costs may not be readily visible, as the masking material is typically not the major contributing element to cost. Rather, it is the masking process itself, specifically the labour that can be the major cost factor. The more intricate a component, the longer it takes to apply and remove traditional masks, such as tapes, waxes, and solvent-based lacquers. In addition, there are other hidden costs associated with using these masks. They can include scrap, component rework, production bottlenecks, workman’s compensation claims, and higher insurance premiums. When the cost of labor is factored in with the other hidden costs, it becomes apparent that simply using a lower priced masking material will not provide the desired cost savings that are required for greater competitiveness in the market.
When traditional paths cannot offer tangible savings opportunities, the door must be opened to new technology. Such technology is now available with UV Curable Masking Resins.
First introduced in the mid 1990’s, UV Curable Masking Resins have the potential to provide similar, if not greater, cost reductions in the current surface finishing industry. The ability to apply a UV maskant and cure it instantly facilitates uninterrupted component processing. For ease of use, UV Masking Resins offer several viscosity variations, from the consistency of water to non-flowing gels. This permits controlled coverage, including coating depth, in a single application. UV Curable Masking Resins are easily dispensed, both in manual and fully automated processing lines. Conventional, labour-intensive masking can be replaced with semi-automated or automated systems that provide controlled spraying, dipping, or precision placement of the UV curable, liquid masking resin. The superior adhesion and exceptional resiliency of UV Curable Masking Resins can also improve component quality by reducing post-processing rework and scrap, arising from deficiencies in traditional masking methods and products. The durability of UV Curable Masks makes it possible to mask only once for multiple surface processing operations, eliminating stripping and re-masking between processes. Simply stated, this increased efficiency leads to lower cost.
The UV masking resins are available in several viscosities and can be applied to components by spraying, dipping or brushing. The resins are grouped to offer three methods of removal: incineration, peeling, or solubility in water.
Types of UV Curable Resins:
Burn-Off Masking Resins
These grades typically offer the best surface adhesion and provide the greatest resistance to heat and aggressive chemical solutions such as acid/alkali baths. Some burn-off grades also offer a secondary heat curing capability for masking areas where UV light cannot penetrate. The heat curable grades can be used for core cavity sealing to protect from debris, plating baths, and laser burn-through during drilling operations. Surface curing with UV light may take 20-30 seconds under a flood lamp, while heat curing may require 30-45 minutes in a 300o F oven. Cure times can be slightly higher or lower based on the volume of maskant applied and size and configuration of the component.
The removal process for a burn-off grade mask requires the components to be baked in an air-enriched furnace between 900o F and 1400o F. Typically, the higher the temperature, the shorter the bake cycle. However, duration of the bake cycle must be qualified for each specific series of masked components. Variables such as volume of mask applied, location of the mask (surface or core cavity), and thermal conductivity of the component will factor into determining the appropriate cycle time. Complete burn-off can be achieved in as little as 15 minutes for thinly coated surfaces. For core cavities, cooling holes on turbine blades, or thick mask coatings, a bake cycle of one hour or slightly longer may be required.
Obviously, burn-off masks are limited to parts that can tolerate high heat, such as the “hot” components of a turbine engine. In many cases, an existing heat-treating operation may also be used to burn-off the mask. The burn-off process effectively incinerates the mask leaving no residue on the component surface. The composition of the UV Curable Mask allows it to completely combust and be exhausted from the furnace. And, the metallurgy of the heat-treated component remains unaffected by the UV Curable Masking Resin.
Peelable Masking Resins
Perhaps the most versatile of UV Masking Resins, the peelable grades, provide good adhesion to most clean, metal surfaces, are resilient enough to withstand a variety of surface treatment processes, and can be removed through a simple peeling process. Cured in a few seconds with UV light, peelable masks have been successfully qualified for surface protection in processes such as grit blasting, shot peening, acid cleaning, plating and anodized coatings.The surface bond is very strong and durable, possessing sufficient adhesion to survive through multiple surface cleaning and processing operations, eliminating the need to strip and re-mask between processes. Peelable UV Masking Resins offer uniform adhesion from edge to edge, preventing processing media from creeping underneath.
Peelable UV Masks are removed by prying up an edge manually or with the help of a non-abrasive tool, then pulling. The elasticity of the material typically permits fast removal of the mask in one piece rather than in fractured segments. No residues remain on the surface after the mask is removed. The peeling process is made even easier by warming the cured masking resin to 120-150o F in a warm water bath or oven, or using a localized heating element. The peeled material, essentially a plastic resin, is non-hazardous and may be disposed of in accordance with local regulations for industrial scrap plastic.
Water Soluble Masking Resins
Water soluble UV Curable Masks provide excellent protection for “dry” finishing processes such as grit blasting, grinding, shot peening, and plasma spraying. They can be applied using the same methods as the peelable grades. But the truly significant feature of the water-soluble grades is their removal mechanism. Unlike the burn-off and peelable grades, which are urethane-based, the water soluble masks are formulated with water soluble polymers. As their name suggests, the water-soluble grades dissolve in liquid. The ideal removal method utilizes heated water (140o – 180o F) and a spray wash or agitated/ultrasonic bath. The mask completely dissolves in the water leaving no residue on the component surface.
In today’s environment, process cost reduction has taken on a greater meaning – survival. Competitive pressures in the market are forcing manufacturers to evaluate every aspect of their processes for cost reduction opportunities. However, age old operations such as masking, are taken for granted and not targeted for improvement.
Alternative masking methods such as UV Curable Masking Resins open the door to savings never before possible. Labour costs can be cut in half, scrap eliminated, and overall component processing time reduced by as much as 60-70%. In addition to cost cutting opportunities, UV Curable Masking Resins improve the quality of the environment in the workplace, removing health hazards and reducing risk of operator injury. Benefits of this nature can lead to improved employee morale, which contributes to higher productivity.
A very positive case has been built for today’s UV Curable Masking Resin Technology. Undoubtedly, more and more masking applications suitable for UV Curable Masks will be identified. The one constant that will continue to drive these applications will be cost reduction and improved productivity in the workplace.
At one Glance
UV Masking Resin Technology The technology for Ultraviolet (UV) Curable Masking Resins originated from UV Curable Aerobic Acrylic Adhesives and Coatings. Commercialized in the early 1980’s, Aerobic Acrylic Adhesives and Coatings have provided new efficiencies to manufacturers, resulting in millions of dollars in cost savings.
a) Increased Through-put: UV Curable Aerobic Acrylics take seconds to cure instead of hours. Curing bottlenecks are eliminated, resulting in significant productivity gains.
b) Worker and Environmentally Friendly: UV Curable Aerobic Acrylics do not contain solvents, eliminating special handling requirements and costly ventilation systems.
c) Minimal Capital Investment: UV Curable Aerobic Acrylic Adhesives and Coatings are cured with lamps that produce ultraviolet energy. Lamps of many styles are available at moderate cost. Investment in an average UV curing system is typically recovered in the first year of operation, or sooner.
d) Easily Integrated into Automated Production: UV Curable Aerobic Acrylics can be dispensed in a variety of ways including bead placement, dip and spray. UV curing lamps are easily placed into existing production lines, utilizing minimal space for curing.
Douglas B. Berkowitz
Sales & Marketing Manager
Composition Materials Co. Inc.
125 Old Gate Lane, Milford, CT 06460, USA
Toll Free (USA): 800 262 7763
Tel. +1.203.874 6500
Fax: +1.203.874 6505