Manual Chapters
The portfolio contains various product groups, organized by naming, delivery form, and labeling. The long term storage of the dip spin tanks is carried out according to regulations.
The term pretreatment refers to various processes to prepare the surface prior to applying the coating system. The quality of a coating system depends largely on the quality of the pretreatment of the surface. The better the pretreatment, the higher the quality of the applied coating system.
"Pretreatment is the key!"
Various methods of surface pretreatment are described below. These processes are intended for the treatment of uncoated metals and surfaces which have been plated with a metallic coating.
All coating materials must be prepared prior to use. Prior to opening the product container or applying the coating material to parts, the temperature of the coating material must be acclimated to the ambient temperature. If the temperature of the coating material has not been acclimated to the ambient temperature, there is a risk that condensation could form which will contaminate the zinc flake coating with moisture and damage it. During transportation and storage, the soild particles in the coating material will settle on the bottom of the delivery container. As a result, it is necessary to mix the contents of the container until all of the solid components are thoroughly integrated into solution prior to application.
Safety instructions for handling chemicals, potential hazards and protective measures must be observed in accordance with the product safety data sheets.
The design of the production facilities must be carried out in accordance with the applicable local regulations and in consultation with the plant constructors. In particular, the regulations on explosion protection must be observed.
The maximum mass of solvent to be introduced into curing ovens must be agreed upon with the equipment manufacturers. A high concentration of zinc-containing dusts in plants can lead to a metal fire or explosion. Cleaning intervals must be agreed upon with the system manufacturer.
Irrespective of the coating application method, temperature and dew-point are two process variables that will negatively impact the performance of the zinc flake coating materials. To ensure consistent quality, it is essential to properly control and maintain both of these variables within defined operating limits.
Irrespective of the coating application technique, the process step which immediately follows is the curing or drying process. Typically this process is performed by means of convection curing; however, induction and infrared curing can also be used for special applications.
In order to achieve the best possible coating system quality, there are a number of in-process inspections that must be performed before, during and after the coating application process.
| Coating Material | Part | Environment | |
|---|---|---|---|
| Pre-coating tests | Temperature, Viscosity, Solids content, Coating level | Cleanliness | Temperature, Relative humidity, Dew point |
| In-process tests | - | ||
| Post-coating tests | - | Wetting, layer weight (layer thickness), adhesion, coefficient of friction, corrosion protection | - |
The procedures for these in-process inspections are provided in the sub-sections which follow. For additional information, please see Section 10: Inspection Plans.
In-process maintenance intervals depend on the rate and volume of production, the respective environmental influences, and the type of parts to be coated. Due to these variables, this section should only be regarded as a general guideline that each coating applicator should adapt according to their specific conditions of use.
| Maintenance measures | Interval |
|---|---|
| Viscosity + temperature | Every 2 hours |
| Solids content | Once per working shift |
| Filters | Once per week |
| Cleaning the coating baskets | Define minimum requirements, then define cleaning intervals |
| Cleaning the coating racks | Define minimum requirements, then define cleaning intervals |
| Cleaning of all application components | Define minimum requirements, then define cleaning intervals |
| Furnace temperature, furnace profile | Once per month |
| Coating level | Define minimum requirements, monitor every 2 hours |
The following process equipment components are to be inspected at regular intervals, compared with reference samples (where applicable), and cleaned accordingly:
- Coating immersion tank (interior and sidewalls)
- Vibration tables and shaker systems
- Oven conveyor belts
- Sheet metal trays
- Spray application components (e.g. hoses, nozzles)
- Filters, racks, coating baskets, and all components in direct contact with the coating materials
The coating line should be cleaned once per working shift (e.g. every 8 hours) to remove any residual contaminants in the general vicinity of the production equipment (e.g. centrifuge). Removing debris and other potential contaminants near the coating line on a frequent basis will prevent small residues from sticking to parts or entering the fresh coating material.
As a function of the quality system, each applicator will document and maintain records for the coating processes and coating related functions performed at their facility. A few examples of the aspects of the coating process which are documented include the following: the quantities and properties of the parts received for coating, incoming and outgoing part inspections, the type of pre-treatment and coating system that are applied, and the coating line and production equipment utilized to apply the coating systems. As the process documentation will be customized by the coating applicator to suit their specific needs and operations, this section is provided for general guidance only and does not include information on all of the process related functions that are documented. For example, records for measuring instruments and other inspection tools are not discussed in this section.
During the coating application process, it is necessary to add new coating material or solvent to replace the materials which have been lost due to consumption or evaporation. As a result, the coating level must be checked on regular frequency. The quantity of the material that has been added, the type of material that has been added, and the lot number of the material that has been added should be recorded. In addition, the date and time of the material addition should also be recorded. Following the material addition, the measurements of coating viscosity and solids content should also be documented on the same form.
Identifying characteristics of the parts to be coated are documented on an application card (e.g. job card, work order, traveler tag) which remains with the parts throughout the entire process (i.e. from the time of part receipt to return shipment to the customer). The part specific characteristics usually listed on the application card include the following:
- Type of part/part geometry
- Weight/volume/bulk density of the parts
- Delivery condition (oily, heat-treated, etc.)
- Pretreatment
- Description and thickness of the coating system to be applied
In addition, the parameters that are to be used to apply the coating materials can also be listed on the application card or a separate coating process instruction. Examples of some of the process parameters which may be listed on the card are as follows:
- Coating viscosity
- Program number
- Load weight (or loading requirements)
- Basket or rack descriptions
- Curing requirements
Upon receipt at the coating applicator, the parts to be coated must be inspected to verify the description and quantities received are in agreement with (i.e. match) the terms of the work contract. In addition, the condition of the received parts must also be inspected to ensure they are in a suitable condition to be processed. The inspection should include an examination of part surface properties (e.g. excess oil, rust-free, scale) and presence of foreign materials (e.g. mixed parts, debris). If necessary, incoming inspection for specific part attributes such as ability to gauge may also be performed.
Upon return delivery to the customer, the coated parts must be inspected to ensure the requirements of the work contract have been fulfilled. Prior to shipping the coated parts to the customer, a series of tests will be performed to assess the quality of the coating system. Depending upon the specific requirements applicable to the parts, these tests may include assessments of corrosion resistance, ability to gauge, and coefficient of friction as well as several other coating system attributes which may be tested.
The specified characteristics, methods, and sample sizes listed in the control plans must be customized to the applied coating process and include a statistical evaluation and validation. All adjustments must be traceable.
In the event of complaints from the supply chain, Dörken will review the control plans and define corrective measures together with the responsible authority at the coating applicator.
The control plans, as well as further downloads of the application manual (to which reference is made here), can be found in the login area of our homepage: Login Area.
Examples of control plans:
- CPLAN Storage and varnish preparation
- CPLAN Incoming and outgoing goods
- CPLAN Pretreatment – degreasing
- CPLAN Pretreatment – blasting
- CPLAN Bath monitoring
- CPLAN Machine data
- CPLAN Curing