ENGRAVING PROCESSES

J. & F. Krüth GmbH utilizes a chemical etching process to make a photographic negative of the texture on a metal.

The equipment to be textured must be protected from acid damage by a coating. The area to be engraved remains uncoated but is spread with an acid-resistant film, which protects those areas of the texture not to be engraved from the acid, for example, the veins of a leather texturing.

The etching process is carried out using acids formulated specifically for the purpose, which are pumped through nozzles and sprayed onto the surface. The application time determines the depth. Many textures require more than one etching. The desired image is created by a combination of different etching operations and films.
v Among these there are also steps not requiring acid-resistant film, as the surface is line engraved. On that account, besides the depth of this kind of engraving, the overall engraving erosion must be relayed. The total engraving erosion is the distinctive characteristic which is given to the rear section of masked surfaces and the increase in wall-thickness. This should not be disregarded, since some engravings of 0.15 mm have an engraving erosion of between 0.3 and 0.4 mm.

Below, we have compiled for you the most important engraving prerequisites:

Engraving
Photochemically etched textures. Single and multiple etchings are possible. Leather, wood and erosion patterns, for example, can be reproduced, as well as a host of different fantasy patterns.

Steel
1.2738 TS HH, 1.2311, 1.2316 and 1.2711. Case-hardened steels such as 1.2162 and 1.2764. Through hardnesses such as 1.2767 or 1.2343. Other steels are etchable, too. Tool steel 1.2738 TS HH is currently the tempered steel with the best prospects for etching. Buderus recommends it! Other etchable metals are copper, brass, zinc, Zamak, beryllium copper and sheet aluminium in certain alloys. Cast aluminium generally develops cavities when etched. Upon request, J. & F. Krüth GmbH will gladly test your chosen material.

Engraving depths
Measured in microns (µ), engraving depths usually range between approximately 10 and 250 µ, measured by surface profile gauges. The stated margin number value is an average profile depth of 5 single measurements in every 2.5 mm.

Draft Angle
In conventional plastics and wall thicknesses of approximately 2 mm the necessary draft angle should be reckoned, as a rule of thumb, as 0.7° for every 10 µ deep. This is not the case when the material on the support shrinks.

Welded Joints
Very often welded joints are exposed with etching. The best preparation is to note the steel supplier’s stipulated specifications. Using 1.2738, this means that the equipment is to be heated to around 400° C, and afterwards to about 550° C and then slowly cooled in an oven. Material of a similar alloy must always be used for the welding electrode.

Gloss level – Susceptibility to scratching
These two characteristics are closely related. A very glossy surface, as a rule, is less susceptible to scratching than a matte surface. We can adjust the lustre on the equipment, as this piece shows. The gloss level, however, is dependent on a combination of many factors, such as the plastic type, the injection temperature, the equipment temperature and other parameters not under our control.

Hardening methods
Through hardening, tempering or surface hardening by heating has, as a rule, no effect on the etching. Where there are differently hardened parts in the one piece of equipment, there may be slight differences in the etched image and in the gloss. We strongly recommend that you avoid nitriding before engraving, as this may lead to uneven etching and gloss levels. Tenifer nitrided surfaces generally give poor results.

Coatings
There is a large number of different surface coatings. Essentially, a coating can only be applied after etching. Coatings can enhance the surface hardness, the gloss level, the slip during injection and removal of the moulding, as well as resistance to corrosion. (We provide a coating with Ni-On 100, which combines many of these features.)