Which materials are suitable for graining?

Material selection and heat treatment play a key role with regard to the later graining result. Even at the material procurement stage it is important to ensure that only steels are used that are suitable for graining. All relevant tool components (sliders, inserts, etc.) should be produced from the same material to avoid possible risks to the grain quality and gloss level.

Suitable materials include:

Code name	Material no.	Eschmann name
40 CrMnNiMo 8-6-4 --- ---	1.2738 EST Special alloy ---	ES Aktuell 1000 ES Aktuell 1200 *) Standard for master pattern
40 CrMnMo 7 ---	1.2311 EST Special alloy	ES Aktuell ES Multiform SL
X37 CrMoV 5-1 ---	1.2343 ESU *) limited Special alloy *) limited	ES Maximum 500 ES Primus SL

Use ESR (electroslag remelting) quality material in hot work steels. There may be a difference in the grain quality and/or gloss level (depending on the thermal conductivity, amongst other things) in comparison to conventionally hardened and tempered plastic mould steels due to case hardening and the alloy!

*) see “What is meant by gloss level?”

Can non-ferrous metals be etched?

Apart from alloyed steels, the most common non-ferrous metals (e.g. copper, aluminium, brass or zinc) and non-alloyed steel can also be etched. However, it is generally recommended to test the desired etching result in advance on a trial plate. For some of these materials a rougher etching base and/or a completely deviating grain quality, amongst other things, may be produced as a result of the chemical reaction of the acid with the base material.

Non-ferrous metals do not have 100 percent graining capability.

Can textures be welded?

Welding should generally be carried out by a specialist company and the graining capability of the welded areas needs to be guaranteed. A key factor in determining a structure's suitability for welding is that the weld metal has the same structure as the base material in terms of composition, hardness and strength. Accordingly, the welding method, material and necessary heat treatment must be selected on the basis of their later graining capability.

Welding requirements:

• Sufficient preliminary work (including sanding cracks in U-shaped moulds, etc.)
• Correct choice of welding electrode
• Suitable heat treatment to avoid increased hardness and stress cracks
• Damages caused by incorrect handling of
• See also: page 38 of the technical catalogue of Eschmann Stahl GmbH

ATTENTION! Deviations in the gloss level and grain depth on the finished product cannot be excluded even if welding is carried out by professionals!

What should be taken into consideration for draft angles?

The minimum draft angles for the ejection of the full grain depth are indicated for each structure.

The following rule of thumb applies:
A maximum grain depth of 0.02 mm can be ejected for each 1° of conicity.

Plastic properties (e.g. flame-retardant design, glass-fibre reinforced, etc.), material shrinkage, wall thicknesses and tool design and contour (e.g. cooling, sprue, sliders, etc.) and production parameters in injection moulding operations can influence this value. For example, in areas with expected core shrinkage, three times the standard conicity value for the ejection of the full grain depth may be necessary.

The following should be taken into consideration for a tool design compatible with a moulded part:

• the minimum draft angle for the structure (according to information provided by the graining company)
• material-related aspects (e.g. for PC-ABS, ABS, PP-compounds, etc.)
• tool-related aspects (e.g. core shrinkage, wall thickness changes, gas channels, etc.)

A reduction in the grain depth is possible and must be agreed in individual cases with the end user!

What is meant by scuffing?

Scuffing is a deformation of the plastic in the direction the item is ejected and is frequently referred to as "stress whitening". The causes for this may be wall thickness changes, high graining pressure, insufficient shrinkage of the item, material properties of the plastic used, etc. Although it is possible to optimise the scuffing over the grained surface by reducing the grain depth, this must be agreed in detail with the end user as this will change the grain impression.

Note:
The occurrence of scuffing cannot generally be excluded, even with adequate draft angles as well as reduced grain depth!

What does “texturing over tool split” mean?

Free-form areas on the sliders and/or insert split lines are often not permitted for items in which the graining is in the main visual area. Loose tool parts are grained in the assembly in such cases, i.e. over partitions.
It is important to ensure the following:

• Partitions must be aligned and free of burr before etching.
• Inserts/sliders must be aligned when fixed on the cavity (installation aids are to be provided by the customer or the (slider) in build, e.g. with large tools, is to be supported by a tool maker).
• All graining areas remain visible and accessible even when fixing loose parts.
• Sharp-edge partitions ("cutter edges/top") are avoided to prevent damage caused by the removal of material during etching, otherwise this will affect the running time.

The position and distribution of partitions should generally be agreed with the end user.

If loose parts are not suitable for graining in the assembly (e.g. due to restricted access, tendency towards burring, etc.), free-form areas can be agreed.

ATTENTION! Free-form areas should also be completely etched to avoid ejection problems and are not intended as split line protection. Partial etching is possible and should be agreed where necessary.

What is meant by gloss level?

"Gloss is a visual perception that occurs when viewing surfaces. The perception of glossiness is more pronounced, the more directionally the light is reflected."

The light is not only reflected in the main direction of reflection but also reflected diffusely in other directions with rough – and thus etched – surfaces. This reduces the reproduction accuracy of the surface: a reflected object is no longer depicted as a brilliant image, but as a blurred image. The more uniform the diffusion of light into the room, the lower the intensity of the directional component and the more matt the surface.

The gloss level is determined by:

• Surface roughness
• SPlastic reproduction accuracy
• Tool wall temperature
• Plastic and processing parameters
• Measuring angle (medium/matt gloss at 60° - 85° angle of reflection)
• Thermal conductivity of the steel used, etc.

The gloss level can be measured reliably on flat surfaces.
A specific gloss level for the item cannot be guaranteed.