APPLICATION TECHNOLOGY This topcoat provides abrasion resistance by distributing
a lubricant through the film, providing good ‘slip’ properties. Additionally this lubricant alters the torque-tension relationship. This provides a lower friction coating and also makes the torque- tension performance more consistent.
Friction properties Coatings change the torque-tension properties of fasteners.
Materials like zinc metal, have a relatively high and unpredictable friction. In the case of zinc/zinc alloys, if fasteners are used without a friction control fluid, the increase in friction results in lower bolt tension for a given torque, resulting in a joint weakness.
Recycling A feature of all metal
coatings is their recyclability. Today, some 40% of iron, 30% of zinc and 25% of nickel comes from recycled metal. Therefore when a steel fastener has finished its service life, the metal used in its manufacture and protection may potentially be re-used.
Legislation The two primary directives that a coated
fastener has to comply with are ELV (End of Life Vehicle Directive) and RoHS (Restriction of the Use of Hazardous Substances). The former is based on the recycling of a car at the end of its life and the latter is concerned with the recycling of electronic components. For over 10 years now, the greater part of
Correct lubrication provides a lower friction coating and makes the relationship more predictable
Environmental compatibility and impact Finally any coating today must meet both industry specific and more general environmental requirement.
“ Coatings change the torque-tension proper ties of fasteners.”
the global automotive supply chain has been subject to the ELV Directive. For a coated fastener, the area key of concern was the restriction on the use of hexavalent chromium compounds, extensively used in passivation films until around mid part of the last decade. Since this time passivates based on ELV compliant trivalent chromium have been employed. Today’s high performance coatings use trivalent chromium passivates which exceed the white rust performance of the older hexavalent types and have exceptional resistance to thermal shock, critical when the component is used in areas subject to high temperatures (e.g. under hood of a car).
Summary Performance, robustness, friction properties and
environmental compatibility are the primary drivers for fastener coatings. Electroplated zinc and zinc alloy systems, long established as the primary sacrificial coating for steel, continues to evolve to meet these requirements. Increased performance is delivered by zinc-nickel, which
also meets the need for a robust coating both in assembly and application. By applying a specific lubricated topcoat, the torque- tension requirements are met. Finally by using metals which can be recycled and avoiding the use of hexavalent chromium, the current environmental criteria are satisfied.
www.macdermid.com
146 Fastener + Fixing Magazine • Issue 74 March 2012
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180