Process for manufacturing a fixing device

Abstract

The invention relates to a process for manufacturing a fixing device and a fixing device made by such a process. In particular, albeit not exclusively, the present invention relates a fixing device for application in fixing to concrete and like materials/substrates. The present invention therefore seeks to provide a fixing device for fixing to concrete, other like substrates which overcomes, or at least reduces some of the known problems of the prior art. The present invention also seeks to provide a fixing device which has enhanced corrosion resistance.

1 . A process for manufacturing a fixing device for fixing to concrete and like substrates, the process comprising:
 a) selecting a heat treatable steel for forming the fixing;   b) rolling the steel to form a fixing product;   c) applying a nitriding process so as to penetrate the surface of the steel, whereby to create a surface skin; and, d) applying a Sherardizing diffusion process so as to increase corrosion resistance.   
     
     
         2 . A process according to  claim 1 , wherein the steel has a low silicon content. 
     
     
         3 . A process according to  claim 1 , wherein the steel is 34CrMo4 steel. 
     
     
         4 . A process according to  claim 1 , wherein the steel is rolled in a cold-forming die comprising first and second die members; each die member being arranged with respect to the other die member such that grooves defined in a first die member are positioned such that, in use, the dies are reciprocated in parallel planes with respect to each other the steel is rolled whilst the die members are brought together in proximity, whereby the corresponding upstanding members in the steel mate with corresponding grooves in the second die member. 
     
     
         5 . A process according to  claim 1 , wherein the nitriding process comprises a gas nitriding process conducted at a temperature about 520° C., to provide a low distortion “thermochemical” heat treatment process. 
     
     
         6 . A process according to  claim 1 , wherein the nitriding process comprises a plasma nitriding process wherein intense electric fields are used to generate ionized molecules of the gas around the surface to be nitride, the reactivity of the nitriding media arising from the gas ionization. 
     
     
         7 . A process according to  claim 1 , wherein the Sherardizing diffusion process comprises the heating of the fixings are heated together with a zinc powder, with the powder size being in the range of 5-80 m, whereby zinc-alloy is formed in a diffusion process to markedly provide a significant increase in corrosion resistance. 
     
     
         8 . A process according to  claim 7 , wherein the Sherardizing diffusion take place in a rotating barrel. 
     
     
         9 . A process according to  claim 7 , wherein the Sherardizing process is performed in a non-oxidizing atmosphere. 
     
     
         10 . A process according to  claim 9 , wherein the non-oxidizing atmosphere comprises nitrogen. 
     
     
         11 . A process according to  claim 7 , wherein the Sherardizing diffusion process is performed over a sufficient period of time to ensure that from the surface, inward to the core, distinct regions are created. 
     
     
         12 . A process according to  claim 7 , wherein the process is performed at temperatures of between 340 and 500° C. for a period of between 30 minutes and 180 minutes. 
     
     
         13 . A process according to  claim 7 , wherein the diffusion process is performed at temperatures below 300° C., for a period of between 30 minutes and 360 minutes, where the zinc powder sublimates. 
     
     
         14 . A process according to  claim 7 , wherein the coating powder can comprise a number of additives, selected from a range including zinc, tin, iron, aluminium, magnesium, whereby to provide further beneficial properties, the powders being provided in a range of percentages from 0.1-5% of the overall powder weight, with the powder size being in the range of 5-80 μm. 
     
     
         15 . A process according to  claim 7 , wherein the coating powder comprises a clay material, such as kaolin (Al 2 O 3 •2SiO 2 ), with powder size of about 10 μm. 
     
     
         16 . A fixing device manufactured in accordance with  claim 1 .